ALBERT

Description: In this paper, we have designed, fabricated and characterized silicon nitride grating couplers with high efficiency at 1490 nm. The devices are fabricated using deep UV photolithography with resolution requirement of ∼500 nm. The grating coupler fabricated yields a peak coupling efficiency of −5.1 dB. The 1-dB bandwidth of the grating coupler is 60 nm.

Description: We report on the defect-dominated light emission and ultraviolet (UV) photoconductivity characteristics of ZnO nanorods (NRs) fabricated using a facile, cost-effective, and catalyst-free thermal decomposition route under varying reaction temperatures. The morphological and structural studies reveal the formation of homogeneous quality nanorods in large scale at the highest reaction temperature of 600  ∘ C. The luminescence feature of the nanorods is dominated by the defect related emission over the typical band edge emission. The variation of band-edge and native defect-related emission response of the samples has been correlated to the morphology and microstructure. In photoconductivity studies, the I – V characteristics of the ZnO NRs prepared at different reaction temperatures in dark and under UV illumination ( λ =365 nm) follow the power law, i.e., IαV r . An enhanced ultraviolet photodetection has been observed in the nanorods fabricated at the highest reaction temperature of 600  ∘ C. The sample prepared at highest reaction temperature of 600  ∘ C exhibits UV photosensitivity value (photo-to-dark current ratio) of around 1.18×10 3 , which is much higher in magnitude compared to that of the samples prepared at lower reaction temperatures. The enhanced photoconductivity may be assigned to the development of uniformity and homogeneity of the nanorods. Further development of such ZnO nanostructures can form the basis of promising prototype luminescent and UV photodetecting devices.

Description: Characteristics of metal–oxide–high- k –oxide–silicon (MOHOS) memories with oxygen-rich or oxygen-deficient GdO as charge storage layer annealed by NH 3 or N 2 are investigated. Transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction are used to analyze the cross-sectional quality, composition and crystallinity, respectively, of the stacked gate dielectric with a structure of Al/Al 2 O 3 /GdO/SiO 2 /Si. The MOHOS capacitor with oxygen-rich GdO annealed in NH 3 exhibits a good trade-off among its memory properties: large memory window (4.8 V at ±12 V, 1 s), high programming speed (2.6 V at ±12 V/100 μs), good endurance and retention properties (window degradation of 5 % after 10 5 program/erase cycles and charge loss of 18.6 % at 85 °C after 10 years, respectively) due to passivation of oxygen vacancies, generation of deep-level traps in the grain boundaries of the GdO layer and suppression of the interlayer between GdO and SiO 2 by the NH 3 annealing.

Description: Tin targets immersed in ethanol and distilled water were ablated using a UV pulsed laser. The ablated products were investigated with transmission and scanning electron microscopy, X-ray photoelectron spectroscopy, and energy dispersive spectroscopy. For ablation in both liquids, the size distribution of the produced particles was bimodal, with particles having diameters of ∼10 nm and ∼1 μm. Formation mechanisms that caused the bimodal distribution are suggested. Ablation in ethanol resulted in nanoparticles that were found to be single crystals of tin coated with tin hydroxide (Sn(OH) 2 ) while ablation in water yielded nanoparticles that were polycrystalline tin dioxide (SnO 2 ) throughout.

Description: Thin aluminum oxide layers deposited on silicon by thermal atomic layer deposition can be used to reduce the electronic recombination losses by passivating the silicon surfaces. To activate the full passivation ability of such layers, a post-deposition annealing step at moderate temperatures (≈400  ∘ C, duration≈30 min) is required. Such an annealing step is commonly done in an oven in air, nitrogen, or forming gas atmosphere. In this work, we investigate the ability to reduce the duration of the annealing step by heating the silicon wafer with a microwave source. The annealing time is significantly reduced to durations below 1 min while achieving effective minority carrier lifetimes similar or higher to that of conventionally oven-annealed samples.

Description: A theoretical study is presented on the on/off current ratio limits for a ballistic coaxially-gated carbon nanotube field effect transistor (CNTFET) with highly doped source/drain regions. Based on changes in gate insulator dielectric constant and thickness, the current ratio has been estimated at different ambient temperatures. Decreasing the gate insulator thickness after a certain value around 3 nm causes the current ratio to degrade drastically. Although the higher dielectric constant values have a fair effect on current ratio, this effect could be suppressed when the device with a low gate insulator thickness works at a low ambient temperature. The simulation results also show that the temperature drastically degrades the current ratio value; whereas in a certain range of ambient temperature, tuning the values of gate insulator thickness and dielectric constant could be very helpful. In this way, the optimum values of gate insulator thickness and dielectric constant are identified to offer the highest on/off current ratio of the device.

Description: Pyramid-like spikes in a single crystal superalloy were investigated upon irradiation with picosecond (ps) laser pulses (200 ps, 800 nm, 1 kHz) under different laser fluences and pulse numbers. Both sides and grooves of pyramid-like spikes were covered with ripples, which had a period of ∼760 nm. The pyramid-like spike separation increased obviously with increasing laser fluence. Microstructural investigations indicate that the pyramid-like spikes were initiated with subsequent pulses from a smooth surface with corrugations and ripples. The coexistence of capillary waves for spikes and capillary waves for ripples in the melted material can be used to explain the formation of the pyramid-like spikes.

Description: This paper is to explore the effects of the liquid structure transition (LST) on the solidification kinetics of Sn-30 wt% Sb alloy by the Newton thermal analysis (NTA) method and the solidified microstructure analysis. Influence of the cooling rate on solidification behavior and microstructure was also concerned. With a self-designed sand mold, the cooling curves of five points were collected automatically in the process of solidification by a HYDRA. In the case of the liquid structure transition and a faster cooling rate, the modification melt treatment will lead to a higher undercooling of nucleation and an increased solidification latent heat in central part of solidifying castings, then the eventual grain size was evidently refined.

Description: In the paper we report on picosecond-laser bulk microstructuring and stimulated Raman scattering (SRS) in type IIa single-crystal diamond in the course of multipulse irradiation at λ =532 nm wavelength using an advanced ps-laser system equipped with additional setups for on-line video imaging and photoluminescence spectra measurements. The effect of crystal orientation (relative to the incident laser beam) on (i) optical breakdown thresholds, (ii) character of bulk modifications, and (iii) generation of stimulated Raman scattering in diamond during irradiation with picosecond pulses of different durations ( τ 1 =10 ps and τ 2 =44 ps) is studied. It is shown that the processes of laser-induced breakdown in the bulk of diamond (at the backside of the crystals) and bulk microstructure growth are governed by the dielectric breakdown mechanism. It is found that generation of high-order stimulated Raman scattering in diamond crystals has a considerable effect on the threshold of laser-induced breakdown and bulk microstructuring. Conditions of the efficient SRS lasing are determined, depending on the pulse duration and the direction ([100] and [110]) of the laser beam incidence. A method of local temperature measurements in the bulk of diamond based on the Stokes-to-anti-Stokes intensity ratio in the recorded SRS spectra is proposed, its applicability to determine a “pre-breakdown” temperature of diamond during multipulse ps-laser irradiation is discussed.

Description: Copper oxide (CuO) is a p-type semiconductor with a band gap of 1.2 eV, which is well known in high-temperature superconductor and antiferromagnetic (AFM) materials through Cu–O–Cu super-exchange interaction. In this paper, we report the strong anisotropic ferromagnetism (FM) in aligned CuO nanorod arrays synthesized by a microwave-assisted hydrothermal method. The transmission electron microscopy (TEM) image shows that the CuO nanorod consists of a large number of smaller nanorods with almost the same growth direction. The X-ray diffraction (XRD) pattern indicates that the CuO nanorods are well crystallized with highly preferred orientation of the [020] direction. These CuO nanorod arrays show room-temperature ferromagnetism, with strong magnetic anisotropy when the magnetic field is applied perpendicular or parallel to the rod axis. This phenomenon of room-temperature ferromagnetism in those aligned CuO nanorods might originate from uncompensated surface spins and shape anisotropy of the nanorods.

Description: (TiVCrZrY)N coatings were deposited onto Si substrate by the radio-frequency (RF) magnetron sputtering of a TiVCrZrY alloy target in an N 2 /Ar atmosphere. The crystal, microstructural, mechanical, and electrical properties at different N 2 -to-total (N 2 +Ar) flow-rate ratio ( R N ) values were investigated. The coating produced in pure Ar had an equiaxed structure with a hexagonal-close-packed phase. With increased R N , the crystallinity and grain size markedly decreased. The microstructure of (TiVCrZrY)N coatings transformed from V-shaped columnar with a rough-domed surface into fine fibrous with a smooth surface. The amorphous transition layer above the substrate was also significantly thickened. The hardness of (TiVCrZrY)N decreased from 20.9 GPa to 18.9 GPa, and the electrical resistivity increased from 398.2 μΩ⋅cm to 21870 μΩ⋅cm.

Description: The blue InGaN light-emitting diodes (LEDs), employing a lattice-compensated p-AlGaN/InGaN superlattice (SL) interlayer to link the last quantum barrier and electron blocking layer (EBL), are proposed and investigated numerically. The simulation results indicate that the newly designed LEDs have better hole injection efficiency, lower electron leakage, and smaller electrostatic fields in the active region over the conventional LEDs mainly attributed to the mitigated polarization-induced downward band bending. Furthermore, the markedly improved output power and efficiency droop are also suggested when the conventional LEDs corresponding to experiment data are replaced by the newly designed LEDs.

Description: In this paper, we investigate the resonance magnetoelectric (ME) effect in the middle supported multilayer composites consisting of high-permeability Fe-based nanocrystalline soft magnetic alloy Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 (FeCuNbSiB), Nickel (Ni), and piezoelectric Pb(Zr 1− x Ti x )O 3 (PZT). The coupling effect between positive magnetostrictive FeCuNbSiB and negative magnetostrictive Ni results in the build-in magnetic bias due to their different magnetic permeability and coercivity. As a result, a giant resonance ME voltage coefficient ( α ME, r ) at zero DC magnetic bias field ( H dc ) and multi-peaks of α ME, r for FeCuNbSiB/Ni/PZT/Ni/FeCuNbSiB composite are observed. The experimental results show that the giant zero-biased α ME, r strongly depends on the thickness of FeCuNbSiB ribbon. The maximum zero-biased α ME, r is up to 86 V/cm Oe for FeCuNbSiB/Ni/PZT/Ni/FeCuNbSiB with four-layer FeCuNbSiB ribbons, which is ∼500 times higher than that of the previously reported NKNLS-NZF/Ni/NKNLS-NZF trilayer composite. Compared with the peak α ME, r and the optimum H dc of Ni/PZT/Ni composite, the largest peak α ME, r of FeCuNbSiB/Ni/PZT/Ni/FeCuNbSiB composite with four-layer FeCuNbSiB ribbons increases ∼185 %, and the optimum H dc decreases ∼300 Oe, respectively. Based on the nonlinear magnetostrictive constitutive relation and the magnetoelectric equivalent circuit, a theoretical model of α ME, r versus H dc is built under free boundary conditions. Calculated zero-biased α ME, r and α ME, r versus H dc are in good agreement with the experimental data. This laminate composite shows promising applications for high-sensitivity power-free magnetic field sensors, zero-biased ME transducers and small-size energy harvesters.

Description: In this paper, we report on in-situ atomic force microscopy (AFM) studies of topographical changes in azobenzene-containing photosensitive polymer films that are irradiated with light interference patterns. We have developed an experimental setup consisting of an AFM combined with two-beam interferometry that permits us to switch between different polarization states of the two interfering beams while scanning the illuminated area of the polymer film, acquiring corresponding changes in topography in-situ . This way, we are able to analyze how the change in topography is related to the variation of the electrical field vector within the interference pattern. It is for the first time that with a rather simple experimental approach a rigorous assignment can be achieved. By performing in-situ measurements we found that for a certain polarization combination of two interfering beams [namely for the SP (↕, ↔) polarization pattern] the topography forms surface relief grating with only half the period of the interference patterns. Exploiting this phenomenon we are able to fabricate surface relief structures with characteristic features measuring only 140 nm, by using far field optics with a wavelength of 491 nm. We believe that this relatively simple method could be extremely valuable to, for instance, produce structural features below the diffraction limit at high-throughput, and this could significantly contribute to the search of new fabrication strategies in electronics and photonics industry.

Description: Traditional glass micromachining using laser processing in air would produce many kinds of defects, such as bulges, debris, micro-cracks and scorches. In this article, a poly-dimethylsiloxane (PDMS) protection processing has been presented to reduce the temperature gradient and heat-affected zone (HAZ) to achieve crack-free Pyrex glass machining. A good quality of etched surface which is a clear and much-reduced bulge without crack and scorch is achieved using CO 2 laser micromachining at 150 μm thick PDMS protection layer and the laser powers of 10–15 W and scanning speeds of 228–342 mm/s for five passes. The PDMS cover layer benefits feature size and bulge height reduction. The alpha-step measured profile shows that the much reduced bulge height around the rims of channel was about 1.2 μm at 150 μm thick PDMS about 13 times smaller than that in air. The ANSYS software was used to analyze the temperature distribution and thermal stress field of glass micromachining in air without and with PDMS cover layer. The smaller temperature gradient observed in PDMS protection processing has the smaller HAZ and diminishes the crack formation during the laser processing.

Description: To reduce the cost of the emitter diffusion process, there has been increasing interest to substitute the standard process of batch POCl 3 emitter diffusion used in the silicon solar-cell manufacturing industry with in-line diffusion processes such as the spray-on and screen-printing process. For this reason, it is essential to study and compare the processes of different diffusion methods from the point of view of the crystalline quality of the final wafers. X-ray transmission topography was employed to characterize the possible precipitates and other microdefects generated in Czochralski-grown silicon (Cz Si) during the emitter diffusion process carried out by screen-printing, spray-on and the standard process, in which the emitter was provided by a liquid (POCl 3 ) source. The results indicate that the phosphorus diffusion process influences the crystalline quality of the wafers and the efficiency of the external gettering process that takes place during phosphorus diffusion depends on the diffusion method employed.

Description: We propose the use of a La 2 O 3 (LO) film as the capping layer for improvement of a semiconductor/insulator interface in a solution-processed indium–tin–oxide (ITO) ferroelectric-gate thin-film transistor (FGT) device. It is demonstrated that the LO layer acts as a good barrier film not only for preventing the interdiffusion between the ITO semiconductor and lead–zirconium-titanate (PZT) insulator layers, but also for stabilizing the PZT surface structure. The fabricated FGT device exhibited high I on / I off , large M w , high μ FE and improved retention time of about 10 9 , 3.5 V, 7.94 cm 2  V −1  s −1 and 1 day, respectively, which are comparable to or better than those obtained with FGTs fabricated by means of conventional vacuum processes. We also point out that the key origin of the interface improvement is likely due to the incorporation of La into the PZT system, forming a La surface-modified PZT system which is more stable than the pure PZT in terms of Pb volatility and formation of oxygen vacancies.

Description: The results of ferroelectric properties studies of KNN doped with La and Ti and sintered at temperatures in the interval of 1100 °C–1190 °C are presented in this work. The doping was achieved by the substitution of La for ions in A sites and Ti for ions in the B sites. Values of 94 % of the theoretical density were accomplished. The effect of the sintering temperature and the inclusion of the La and Ti cations in the KNN structure is evident through the shift in the ferroelectric-paraelectric transition temperature of ∼110 °C with respect to that of pure KNN (420 °C). Microstructure and ferroelectric analyses were carried out using Piezoresponse Force Microscopy (PFM) and hysteresis loops with interesting results, Δ P r =9 (μC/cm 2 ) and P r / P max =0.41, even when the saturation of the materials is not reached.

Description: We have developed a high-performance laser energy meter based on anisotropic Seebeck effect in a strongly correlated electronic (SCE) thin film. SCE thin films, typically represented by high-temperature superconductor (HTS) cuprate and colossal magnetoresistance (CMR) manganite thin films, demonstrate tremendous anisotropic Seebeck effect. In this study, a La 2/3 Ca 1/3 MnO 3 thin film grown on a tilted LaAlO 3 substrate is tested with the fundamental, the second, the third, and the fourth harmonics (1064, 532, 355, 266 nm, respectively) of a Q-switched Nd:YAG laser over a wide range of temperatures from room temperature to 16 K. The peak-value of the laser-induced thermoelectric voltage signal shows a good linear relationship with the laser energy per pulse in the measured wavelength and temperature ranges. The combined advantages over other commercial laser detectors such as nanosecond-order response and spectrally broad and flat response over a wide range of temperatures, in situ real-time measurement, and energy savings, make the device an ideal candidate for next-generation laser detectors and laser power/energy meters.

Description: Co-doped ZnO epilayer films were grown by pulsed laser deposition (PLD) on vicinal cut silicon and sapphire substrates. Changes in deposition time were observed as a moderate effect on the quality of the films, and the influence of the thickness on thermoelectric signals from Zn 0.9 Co 0.1 O thin films were discussed. The effect of one of the main deposition parameters, the deposition time, on the crystallinity and electron mobility properties of the Zn 0.9 Co 0.1 O thin films grown on sapphire was investigated by means of X-ray diffraction (XRD) and laser-induced voltage (LIV) effect. It shown that the XRD rocking curve full-width half-maximun (FWHM) decreased as time increasing, and the LIV signals were observed along the tilting angle of the substrate orientation when the pulsed KrF excimer laser of 248 nm were irradiated on the films. When the films illuminated in pulse lasers, the highest signals occurred in the films with best crystalline quality, and the signals were higher in the films grown on sapphire than those on silicon substrates. It suggested that the electrical resistivity and electron mobility have close relations with not only the crystallinity but also with the interface of the thin films.

Description: Nanostructure formation on bulk noble metals (copper, gold and silver) by a femtosecond laser was studied aiming at the production of low-reflectivity surfaces. The target surface was irradiated with the beam of a 775 nm wavelength and 150 fs pulse duration Ti:sapphire laser. The fluence was in the 16–2000 mJ/cm 2 range, while the average pulse number was varied between 10 and 1000 depending on the scanning speed of the sample stage. The reflectivity of the treated surfaces was measured with a visible–near-infrared microspectrometer in the 450–800 nm range, while the morphology was studied with a scanning electron microscope. A strong correlation was found between the decreasing reflectivity and the nanostructure formation on the irradiated surface; however, the morphology of silver significantly differed from those of copper and gold. For the two latter metals a dense coral-like structure was found probably as a result of cluster condensation in the ablation plume followed by diffusion-limited aggregation. In the case of silver the surface was covered by nanodroplets, which formation was probably influenced by the ‘spitting’ caused by ambient oxygen absorption in the molten silver followed by its fast release during the resolidification.

Description: The automation in fabrication of CFRP (carbon-fiber-reinforced plastics) parts demands efficient and low-cost machining technologies. In conventional cutting technologies, tool-wear and low process speeds are some of the reasons for high costs. Thus, the use of lasers is an attractive option for cutting CF-preforms. A typical effect degrading the quality in laser cutting CF-preform is a bulged cutting edge. This effect is assumed to be caused by interaction of the fibers with the ablated material, which leaves the kerf at high velocity. Hence, a method for measuring the momentum and the velocity of the vapor is presented in this article. To measure the momentum of the ablated material, the CF-preform is mounted on a precision scale while cutting it with a laser. The direction of the momentum was determined by measuring the momentum parallel and orthogonal to the CF-preform surface. A change of the direction of the momentum with different cutting-speeds is assessed at constant laser-power. Averaged velocities of the ablation products of up to 300 m/s were determined by measuring the ablated mass and the momentum.

Description: We report a design method of surface plasmon polaritons sharp bends based on transformation optics. Plasmonic waveguide bends with different angles, which possess little radiation loss, are proposed. Transformation media can be simply achieved with homogeneous and nonmagnetic materials, which can be constructed by altering two different dielectric films. Electromagnetic simulations by a finite-element method on detailed examples have been performed to validate the designs.

Description: This article presents the results on the growth and characterization of BaSnF 4 thin films on glass substrates prepared by pulsed laser deposition technique. The structural results of BaSnF 4 thin film carried out by glancing angle X-ray diffraction technique indicates the formation of the film with similar structure (tetragonal, P 4 /nmm) to the bulk target material. The absorption coefficient and band gap of the film is determined by suitable analysis of the transmittance spectra. The transport properties of the thin films are studied using impedance spectroscopy in the temperature range of 323–573 K. The frequency-dependent imaginary part of impedance plot shows that the conductivity relaxation is non-Debye in nature. The scaling behavior of the imaginary part of impedance at various frequencies indicates temperature-independent relaxation behavior.

Description: UV irradiation of materials consisting of a polymer matrix that possesses precursors of noble metals followed by annealing results in creation of metal nanoparticles within the irradiated domains. Such photoinduced nanocomposites are promising for photonics applications due to the strong alteration of their optical properties compared to initial nonirradiated materials. We report our results on the synthesis and investigation of two kinds of these materials: Photoinduced Au nanocomposites based on PMMA matrices, including bulk materials prepared by means of the polymerization technique; photoinduced Ag nanocomposites with an organic–inorganic hybrid matrix based on TiO 2 gels. The experimental data on evolution of absorption spectra of these materials due to laser irradiation at different wavelengths are presented. The linear and nonlinear refractive index changes in these materials owing to light-induced nanonstructuring are investigated.

Description: The study of pollution performance on a wind turbine blade due to lightning is important, as it can cause major damage to wind turbine blades. In the present work, optical emission spectroscopy (OES) technique is used to understand the influence of pollutant deposited on a wind turbine blade in an off-shore environment. A methodical experimental study was carried out by adopting IEC 60507 standards, and it was observed that the lightning discharge propagates at the interface between the pollutant and the glass fiber reinforced plastic (Material used in manufacturing of wind turbine blades). In addition, as a diagnostic condition monitoring technique, laser-induced breakdown spectroscopy (LIBS) is proposed and demonstrated to rank the severity of pollutant on the wind turbine blades from a remote area. Optical emission spectra observed during surface discharge process induced by lightning impulse voltage is in agreement with the spectra observed during LIBS.

Description: We developed a method that accurately determines an unknown position of the high-intensity laser-pulse-material interaction site on the front side of a plate. It is based on interferometric measurements of a normal displacement at known positions on the plate’s rear side. The displacement is caused by reflections of various pulsed-laser-induced mechanical waves. We have superseded the long-established time-of-flight approach with the improved, triple-echo method. To accurately locate the origin of the laser-induced ultrasound on the plate with a known thickness, we only need to detect the arrivals of the first three consecutive mode unconverted waves. Our method works without knowing the propagation velocities of various ultrasonic waves and additionally solves some time-related drawbacks of the conventional time-of-flight approach. The relative uncertainty of the measured source-receiver separations obtained with the presented method is less than 0.01.

Description: Laser dry etching by a laser driven direct writing apparatus has been extensively used for the micro- and nano-patterning on the solid surface. The purpose of this study is to pattern the PEDOT:PSS thin film coated on the soda-lime glass substrates by a nano-second pulsed ultraviolet laser processing system. The patterned PEDOT:PSS film structure provides the electrical isolation and prevents the electrical contact from each region for capacitive touch screens. The surface morphology, geometric dimension, and edge quality of ablated area after the variety of laser patternings were measured by a 3D confocal laser scanning microscope. After the single pulse laser irradiation, the ablation threshold of the PEDOT:PSS film conducted by the nano-second pulsed UV laser was determined to be 0.135±0.003 J/cm 2 . The single pulse laser interacted region and the ablated line depth increased with increasing the laser fluence. Moreover, the inner line width of ablated PEDOT:PSS films along the patterned line path increased with increasing the laser fluence but the shoulder width increased with decreasing fluence, respectively. The clean, smooth, and straight ablated edges were accomplished after the electrode patterning with the laser fluence of 1.7 J/cm 2 and 90 % overlapping rate.

Description: Selectiveness of the laser processing is the top-most important for applications of the processing technology in thin-film electronics, including photovoltaics. Coupling of laser energy in multilayered thin-film structures, depending on photo-physical properties of the layers and laser wavelength was investigated experimentally and theoretically. Energy coupling within thin films highly depends on the film structure. The finite element and two-temperature models were applied to simulate the energy and temperature distributions inside the stack of different layers of a thin-film solar cell during a picosecond laser irradiation. Reaction of the films to the laser irradiation was conditioned by optical properties of the layers at the wavelength of laser radiation. Simulation results are consistent with the experimental data achieved in laser scribing of copper-indium-gallium diselenide (CIGS) solar cells on a flexible polymer substrate using picosecond-pulsed lasers. Selection of the right laser wavelength (1064 nm or 1572 nm) enabled keeping the energy coupling in a well-defined volume at the interlayer interface. High absorption at inner interface of the layers triggered localized temperature increase. Transient stress caused by the rapid temperature rise facilitating peeling of the films rather than evaporation. Ultra-short pulses ensured high energy input rate into absorbing material permitting peeling of the layers with no influence on the remaining material.

Description: An integrated microchemical–petrographic approach is here proposed to discriminate the provenance of archaeological pottery artefacts from distinct production centres. Our study focuses on a statistically significant sampling ( n =186) of volcanic temper-bearing potteries representative of the manufacturing and dispersion among the islands of the Aeolian Archipelago during the Bronze Age. The widespread establishment of new settlements and the abundant recovery of Aeolian-made ceramic in southern Italy attest for the increased vitality of the Archipelago during the Capo Graziano culture (Early Bronze Age–Middle Bronze Age 2; 2300–1430 BC). Potteries from three of the main known ancient communities (Lipari, Filicudi and Stromboli) have been studied integrating old collections and newly excavated material. Volcanic tempers have been first investigated through multivariate analyses of relative abundances of mineral and rock clasts along with petrographic characters. In addition, we performed in-situ mineral chemistry microanalyses by Electron Microprobe and Laser Ablation—Inductively Coupled Plasma Mass Spectrometry to assess major and trace element composition of the most common mineral phases. Four Temper Compositional Reference Units have been recognised based on compositional trends. Two units (AI and AX) are unequivocally distinct by their peculiar trace element enrichment and petrographic composition; they mostly contain samples from the sites of Lipari and Stromboli, respectively. Units AIV and AVIII, restricted to the sites of Filicudi and Stromboli, show distinct petrographic characters but overlapped geochemical fingerprints.

Description: Dissemination of Della Robbia glazed terracotta in the Marche (Italy) region started from the third decade of the 16th century. Numerous altarpieces, some of which no longer exist, document this artistic production. The protagonists of this diffusion phase were two of Andrea Della Robbia’s sons, Marco (Fra Mattia) and Francesco (Fra Ambrogio). This paper shows the results of the scientific investigations carried out on constitutive materials of different altarpieces located in South Marche belonging to the Fra Mattia’s production: the Coronation of Virgin between Saints Rocco, Sebastian, Peter martyr and Antonio abbot , dated back to 1527–1530, located in the collegiate church of S. Maria Assunta in Montecassiano; the Annunciation , dated back to 1520, placed in the church of S. Maria del Soccorso in Arcevia; the fragmentary Crowned Madonna and saints altarpiece, probably realized after 1531, today preserved in Civic Museum of Ripatransone. The first altarpiece was made in Montecassiano using two different assembling or production techniques: the external part of the lunette and the pillar strips are made of glazed polychrome terracotta, while the altar step and the internal part are an interesting and uncommon example of polychrome painted terracotta. The provenance of the glazed Arcevia altarpiece is not clear yet: some historians hypothesize a local manufacture of Fra Mattia and some others a Roman or Florentine production. The remaining parts of Ripatransone altarpiece are partially glazed and partially not coated perhaps because they were unfinished and not yet painted. Clay body samples collected from the above mentioned altarpieces were investigated using different analytical techniques (OM, XRD, XRF, PIXE) to point out differences in chemical and mineralogical composition and to determine if the altarpieces were made by using local raw clay materials or other clays from Tuscany or Campania as in the Della Robbia previous production. A comparison has also been made with literature data on the Della Robbia terracotta masterpieces. From the chemical point of view, the clay bodies show a good compositional homogeneity and result calcium and iron-rich according with the raw local materials. The presence of gehlenite, pyroxenes, and hematite and the incomplete decomposition of clay minerals indicate that firing for all different terracotta parts occurred in a thermal range between 800 and 950 °C, mostly in oxidizing conditions.

Description: Optical and biomedical properties of diamond-like carbon (DLC) films of various sp 2 , sp 3 bonds were studied. The layers were prepared by pulsed laser deposition (PLD) for laser energy densities from 4 J cm −2 to 14 J cm −2 . The percentage of sp 2 and sp 3 bonds was calculated using X-ray photoelectron spectroscopy (XPS). In dependence on density the films contained up to 70 % of sp 3 bonds. Optical properties were measured using spectroscopic ellipsometry in region from 250 nm to 1000 nm ( n =2.6–2.7; k =0.07–0.25) and by transmission measurement (from 200 nm to 1100 nm). The adhesion and growth of human fibroblasts and keratinocytes of DLC films were tested in vitro.

Description: Bubbles generated in water by focusing femtosecond and picosecond laser pulses in the presence of 100 nm gold nanoparticles have been investigated in the fluence range usually used for efficient cell transfection (100–200 mJ/cm 2 ). Since resulting bubbles are at the nanoscale, direct observation using optical microscopy is not possible. An optical in-situ method has been developed to monitor the time-resolved variation in the extinction cross-section of an irradiated nanoparticle solution sample. This method is used to measure the bubbles lifetime and deduce their average diameter. We show that bubbles generated with femtosecond pulses (40–500 fs) last two times longer and are larger in average than those generated with picosecond pulses (0.5–5 ps). Controlling those bubble properties is necessary for optimizing off-resonance plasmonic enhanced ultrafast laser cell transfection.

Description: To determine experimental conditions suitable for isotope analysis, we studied the plume dynamics of uranium. A uranium oxide sample was ablated by 2nd harmonic radiation from a Nd:YAG laser at a fluence of 0.5 J/cm 2 . The temporal evolution of the ablation plume was investigated in vacuum and helium environments. In vacuum, the flow velocity perpendicular to the sample surface was determined to be 2.7 km/s for neutral atoms and 4.0 km/s for singly charged atoms. These velocities are about 20 % lower than those of cerium measured under similar conditions. From the evolution of the plume in helium, we found that an observation time of 3–5 μs and an observation height of about 2.5 mm are most suited for obtaining higher sensitivity. Observation times less than 3 μs were unsuitable for precise isotope analysis since the spectral modifications arising from the Doppler splitting effect are different between the two uranium isotopes. Using the established conditions, we evaluated the calibration curve linearity, limit of detection, and precision for three samples having different abundances of  235 U.

Description: Nondiffracting Bessel beams have been recently applied to single shot ultrafast laser processing of high aspect ratio nanochannels. We review the principles and benefits of nondiffracting Bessel beams for material processing, and we compare experimental results with numerical simulations. We show how the stationarity of nonlinear propagation of ultrafast laser pulses allows high aspect ratio material processing.

Description: Electrical conductivity, Hall effect and magnetoresistance of In 2 O 3 :Sn thin films deposited on a glass substrates at different temperatures and oxygen pressures, have been investigated in the temperature range 4.2–300 K. The observed temperature dependences of resistivity for films deposited at 230 °C as well as at nominally room temperatures were typical for metallic transport of electrons except temperature dependence of resistivity of the In 2 O 3 :Sn film deposited in the oxygen deficient atmosphere. The electrical measurements were accompanied by AFM and SEM studies of structural properties, as well as by XPS analysis. It is established that changes of morphology and crystallinity of ITO films modify the low-temperature behavior of resistivity, which still remains typical for metallic transport. This is not the case for the oxygen deficient ITO layer. XPS analysis shows that grown in situ oxygen deficient ITO films have enhanced DOS between the Fermi level and the valence band edge. The extra localized states behave as acceptors leading to a compensation of n -type ITO. That can explain lower n -type conductivity in this material crossing over to a Mott-type hopping at low temperatures. Results for the low temperature measurements of stoichiometric ITO layers indicate that they do not show any trace of metal-to-insulator transition even at 4.2 K. We conclude that, although ITO is considered as a highly doped wide-band gap semiconductor, its low-temperature properties are very different from those of conventional highly doped semiconductors.

Description: Ion implantation was used to locally modify the surface of silica glass to create periodic plasmonic microstructures with Cu nanoparticles. Nanoparticles were synthesized by Cu-ion irradiation of the silica glass at the ion energy of 40 keV, dose of 5×10 16  ions/cm 2 and current density of 5 μA/cm 2 . This procedure involves low-energy ion implantation into the glass through a mask placed at the surface. Formation of nanoparticles was observed by optical spectroscopy and atomic force microscopy. The presented results clearly demonstrate how the low-energy ions can be used for the fabrication of photonic microstructures on dielectric surfaces in a single-step process.

Description: Au/Nb:SrTiO 3 /Ti structures were fabricated by depositing Au and Ti electrodes on a single crystal 0.5 wt% Nb:SrTiO 3 (NSTO) using rf-magnetron sputtering technique. Resistive switching properties at different temperature were investigated. The Ti/NSTO interface was ohmic contact, which indicated that the resistive switching behavior was attributed to Au/NSTO interface. The resistive switching behavior happened only at the temperature above 180 K, which was possibly caused by the increase of Schottky barrier height with the increase of temperature. The structure showed a semiconductor behavior at high-resistance state (HRS) and a metallic behavior at low-resistance state (LRS). The switching conduction mechanism of Au/NSTO/Ti device is primarily described as space-charge-limited conduction (SCLC) according to the electrical transport properties measurement.

Description: The ZnO nanowire (NW) array/TiO 2 nanoparticle (NP) composite photoelectrode with controllable NW aspect ratio has been grown from aqueous solutions for the fabrication of dye-sensitized solar cells (DSSCs), which combines the advantages of the rapid electron transport in ZnO NW array and the high surface area of TiO 2 NPs. The results indicate that the composite photoelectrode achieves higher overall photoelectrical conversion efficiency ( η ) than the ZnO NW alone. As a result, DSSCs based on the ZnO NW array/TiO 2 NP composite photoelectrodes get the enhanced photoelectrical conversion efficiency, and the highest η is also achieved by rational tuning the aspect ratio of ZnO NWs. With the proper aspect ratio (ca. 6) of ZnO NW, the ZnO NW array/TiO 2 NP composite DSSC exhibits the highest conversion efficiency (5.5 %). It is elucidated by the dye adsorption amount and interfacial electron transport of DSSCs with the ZnO NW array/TiO 2 NP composite photoelectrode, which is quantitatively characterized using the UV-Vis absorption spectra and electrochemical impedance spectra. It is evident that the DSSC with the proper aspect ratio of ZnO NW displays the high dye adsorption amount and fastest interfacial electron transfer.

Description: We report the photoluminescence eigenmodes of the ZnO semiconductor microcavity on a Ag/Si substrate at room temperature. The experiment results show that the photoluminescence modes do not depend on the excitation intensity. The eigenmode in the microcavity is considered to be the perpendicular Fabry–Perot modes, where the effect of the strong coupling between plasmon and exciton is observed with the reducing of the effective refractive index from original 2.0 to 1.67 at the wavelength of 585 nm. Meanwhile, there is also a coupling between the plasmon and the exciton-polariton in the band-edge region, and the effective refractive index 1.92 is in good agreement between the experimental and the theoretical results.

Description: Variations in the switching threshold voltage of memristive devices present significant challenges for their integration into large-scale circuits. In this paper, we propose to address this problem by adding a device exhibiting S-type (N-type) negative differential resistance (NDR) in series (parallel) with memristive devices. The main effect comes from the transition between low- and high-conductivity branches of the NDR device, which leads to a redistribution of the voltage drop inside the device stack, and, as a result, the effective lowering of variations in the switching threshold. The idea is checked experimentally using a TiO 2− x memristive device connected in parallel with a tunnel GaAs diode.

Description: The detailed chemical analysis of fossils has the potential to reveal great insight to the composition, preservation and biochemistry of ancient life. Such analyses would ideally identify, quantify, and spatially resolve the chemical composition of preserved bone and soft tissue structures, but also the embedding matrix. Mapping the chemistry of a fossil in situ can place constraints on mass transfer between the enclosing matrix and the preserved organism(s), and therefore aid in distinguishing taphonomic processes from original chemical zonation remnant within the fossils themselves. Conventional analytical methods, such as scanning electron microscopy (SEM) and pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) have serious limitations in this case, primarily, an inability to provide large (i.e., decimeter) scale chemical maps. Additionally, vacuum chamber size and the need for destructive sampling preclude analysis of large and precious fossil specimens. However, the recent development of Synchrotron Rapid Scanning X-ray Fluorescence (SRS-XRF) at the Stanford Synchrotron Radiation Lightsource (SSRL) allows the non-destructive chemical analysis and imaging of major, minor, and trace element concentrations of large paleontological and archeological specimens in rapid scanning times. Here we present elemental maps of a fossil reptile produced using the new SRS-XRF method. Our results unequivocally show that preserved biological structures are not simply impressions or carbonized remains, but possess a remnant of the original organismal biochemistry. We show that SRS-XRF is a powerful new tool for the study of paleontological and archaeological samples.

Description: Here for the first time we describe the use of high resolution nanoprobe X-ray fluorescence (XRF) mapping for the analysis of artists’ paints, hierarchically complex materials typically composed of binder, pigments, fillers, and other additives. The work undertaken at the nanoprobe sought to obtain highly spatially resolved, highly sensitive mapping of metal impurities (Pb, Cd, Fe, and other metals) in submicron particles of zinc oxide pigments used in early 20th century artists’ tube paints and enamel paints, with particular emphasis on Ripolin, a popular brand of French house paint used extensively by Pablo Picasso and some of his contemporaries. Analysis revealed that the Zn oxide particles only contain a little Fe, proving that the highest quality Zn oxide pigment, free of Pb and Cd, was used for Ripolin house paints as well as artists’ paints. Nanoprobe XRF mapping also demonstrated that artists’ tube paints generally have more abundant fillers and additional whites (based on Pb, Ti, Ca) than Ripolin paints, which contain mostly pure zinc oxide. The chemical characterization of paints at the nanoscale opens the path to a better understanding of their fabrication and chemical reactivity.

Description: We fabricated sulfur-doped black silicon by metal-assist chemical etching (MCE) and ion implanting. The morphologies of silicon nanowire (SiNW) arrays and the concentration of sulfur in black silicon were analyzed by scanning electron microscope (SEM). Sulfur-doped black silicon shows higher absorption in entire 0.3–2.5 μm wavelength range as compared to undoped SiNW arrays and flat silicon. The changes in the absorption spectra of black silicon with different etching durations and annealing temperature are also shown. Upon annealing, the absorption decreases significantly in 2–2.5 μm wavelength region. The novel results clearly indicate that sulfur implanting could produce below band gap absorption in the silicon substrate.

Description: The wettability of solid surface is a very important property of materials, which depends on both surface chemical composition and the geometry of the solid surface. We herein report a simple and inexpensive method to fabricate superhydrophobic surfaces with the use of mullite whisks (MWs) for the first time. Binary micro-/nano-structural surfaces were created by the incorporation of hydrophilic needlelike MWs with poly( γ -methacryloxypropyltrimethoxysilane) to exhibit hydrophobic behavior, which further showed superhydrophobicity with water contact angle of 152.4±2 ∘ after modified with stearic acid. The wettability variation from hydrophilicity to hydrophobicity and superhydrophobicity during the assembly process are discussed based on the scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, and contact-angle system. The superhydrophobicity of the surface could be attributed to the hierarchical microstructure of the rough surface induced by MWs and low surface energy of stearic acid.

Description: Luminescent properties of ZnO nanorods covered with Ag nanoparticles are examined. Nanorods were synthesized on AAO templates using Atomic Layer Deposition (ALD) technique. Two types of the samples were prepared with different arrangement of ZnO nanorods and doping conditions. Nanorods of the second type were codoped with Al, to stimulate defect-related emissions. The ZnO material fills heterogeneously the interior of the AAO nanopores and has hexagonal, wurtzite structure. Both types of structures exhibit a broad defect-related emission at about 440 nm, most probably related to recombination at zinc interstitial (Zn i ) defects. This emission in samples with a random distribution of ZnO:Al nanorods and finer Ag nanoparticles is enhanced by factor of ∼2.5 upon Ag deposition. The so-obtained material is interesting from the point of view of its application in blue range emitting diodes.

Description: The separation mechanism of opaque and transparent model micro-particles, graphite and polystyrene copolymer spheres, respectively, from polymethyl methacrylate (PMMA) substrates were investigated employing a ns-pulse laser radiating at 532 nm. The particles transparent in the visible wavelength range could be removed from PMMA efficiently in a very narrow fluence range between 1 and 2 J/cm 2 according to a simple 1D thermal expansion model. Above this fluence region, with single pulses, the transparent microspheres caused local ablation of the PMMA substrate in the optical microlens nearfield. This process led to removal of the particles themselves due to the expansion of the ablation plasma. The irregularly shaped graphite particles shaded the underlying substrate from the incoming radiation so that no optical nearfield damage mechanism could be observed. Therefore, a substantial cleaning window between 0.5 and more than 16 J/cm 2 was provided. The graphite data suggest an ablation mechanism of the particulates themselves due to a high optical absorption coefficient.

Description: The solid-state reaction in Pt(15 nm)/Fe(15 nm) and Pt(15 nm)/Ag(10 nm)/Fe(15 nm) thin films after post-annealing at 593 K and 613 K for different annealing times has been studied. The structural properties of these samples were investigated by various methods including depth profiling with secondary neutral mass spectrometry, transmission electron microscopy, and X-ray diffraction. It is shown that after annealing at the above temperatures where the bulk diffusion processes are still frozen, homogeneous reaction layers of FePt and FePt with about 10 at.% Ag, respectively, have been formed. Corresponding depth profiles of the element concentrations revealed strong evidence that the formation mechanism is based on a grain boundary diffusion induced solid-state reaction in which the reaction interfaces sweep perpendicularly to the original grain boundary. Interestingly, X-ray diffraction indicated that in both thin-film systems after the solid-state reaction the ordered L1 0 FePt phase, which is the requested phase for future magnetic data storage applications, is also present.

Description: Multiferroic bismuth ferrite (BiFeO 3 ) has attracted considerable attention due to applications related to the bulk photovoltaic effect in which the direction of polarization determines the direction of the photocurrent. Epitaxial thin films are produced by means of techniques that usually require high temperature processes. The hydrothermal method can be seen as an alternative route to obtain highly textured thin films in quantities compatible with batch processing; nevertheless, the structural, dielectric and electric properties are generally affected by the presence of hydrogen and other reaction by-products. In this work, functional and highly textured BiFeO 3 films were successfully produced on metallic SrTiO 3 :Nb (0.5 wt.%) (100) substrates via hydrothermal synthesis. X-ray diffraction (XRD) and Atomic Force Microscopy (AFM) were used to analyze the structural properties of the films. Piezoresponse Force Microscopy (PFM) and Photoconductive Atomic Force Microscopy (Pc-AFM) were used to determine their functional properties. We show the polarization switching and confirm the presence of the bulk photovoltaic effect for the first time in hydrothermally synthesized BiFeO 3 .

Description: Bilayer magnetostrictive-piezoelectric structures have certain advantages compared to bulk composites and this allows us to consider them as perspective materials for the development of devices based on the magnetoelectric effect. The theory of magnetoelectric effect in bilayer magnetostrictive-piezoelectric structure is presented taking into account the thickness dependence amplitude of the mechanical oscillations for the structures in form of rectangular plate. The equation for frequency dependence of the ME effect in the region on the electromechanical resonance was obtained, using motion equation, elastodynamics and electrostatic equations for the magnetostrictive, piezoelectric phases and taking into account the boundary conditions on the interface. The cases of longitudinal and transverse orientations of the electric and magnetic fields were considered. It is shown that the thickness dependence of the ME voltage coefficient has the maximum. The dependence between frequency and the thickness ratio of the layers is presented for both the theory and experiment.

Description: A reddish-orange phosphor, Ca 3 WO 6 :Sm 3+ , was synthesized by the convenient solid-state reaction method and characterized by X-ray diffraction (XRD). Photoluminescence properties and concentration quenching of Ca 3 WO 6 :Sm 3+ phosphor have been discussed in the excitation and emission spectra. Ca 3 WO 6 :Sm 3+ phosphor is able to generate a strong excitation peak, which matches the emission wavelength from near-UV LEDs. Energy transfer from Sm 3+ to Eu 3+ in Ca 3 WO 6 host is observed and investigated in detail. The chromaticity coordinates of Ca 3 WO 6 :Sm 3+ can be regulated to approach the NTSC standard values of red phosphor by codoping Eu 3+ ions. The photoluminescence properties suggest that novel Ca 3 WO 6 :Sm 3+ , Eu 3+ phosphor might have a potential application for near-UV LEDs.

Description: In this paper, we propose a new optical detection scheme for nanopore-based DNA sequencing with high resolution towards eventual base identification. We use ultraviolet light for excitation of a fluorescent probe attached to DNA and a nanopore in the silicon membrane that has a significantly large refractive index and an extinction coefficient at ultraviolet wavelengths. In this study, numerical electromagnetic simulation revealed that the z -polarization component (perpendicular to the membrane plane) of the electric field was dominant near the nanopore and generated a large electric field gradient at the nanopore exit, typically with a decay length of 2 nm for a nanopore with diameter of 7 nm. The large extinction coefficient contributed to reduction in background noise coming from fluorophore-labeled DNA strands that remain behind the membrane (the cis side of the membrane). We observed a high signal-to-noise ratio of single DNA translocation events under the application of an electric field.

Description: Relatively oxygen-free mesoporous cubic ZnS particles were synthesised via a facile solvo-hydrothermal route using a water–acetonitrile combination. Boosted UV emission at 349 nm is observed from the ZnS prepared by the solvo-hydrothermal route. The increased intensity of this UV emission is attributed to activation of whispering gallery modes of almost elliptical microstructures made of porous nanostructures.

Description: Rare earth (Eu 2+ ) ion doped halosilicate Ca 10 Si 6 O 21 Cl 2 was prepared by a solid state reaction method. The X-ray powder diffraction patterns, the scanning electron micrographs, the photoluminescence excitation and emission spectra, and the thermal stability were measured. The luminescence properties were investigated by dynamic excitation of a pulsed UV laser. Two typical Eu 2+ emission centers were suggested from two different Ca 2+ cation sites in the lattice. With increasing Eu 2+ -doping concentration, energy transfer between the two Eu 2+ centers can happen. The emission mechanism is discussed by analyzing the excitation and emission spectra, the concentration-dependent luminescence intensity, and the lifetimes. The colors of Ca 10 Si 6 O 21 Cl 2 :Eu 2+ change from bluish green to yellowish green by increasing the Eu 2+ -doping concentration. The luminescence stability with temperature was evaluated by the activation energy for thermal quenching.

Description: Three kinds of new comb-shape nanostructures of ZnO have been grown on single silicon substrates without catalyst-assisted thermal evaporation of Zn and active carbon powders. The morphology and structure of the prepared nanorods are determined on the basis of field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and x-ray diffraction (XRD). The growth mechanism of the ZnO nanocombs can be explained on the basis of the vapor–solid (VS) processes. In nanocombs 1 and nanocombs 2, the comb teeth grow along [0001] and the comb stem grows along [ $01\overline{1}0$ ], while in nanocombs 3, nanoteeth grow along [ $01\overline{1}0$ ] and stem grows along [0001]. The photoluminescence and field-emission properties of ZnO nanocombs 1–3 have been investigated. The turn-on electric field of ZnO nanocombs 1–3, which is defined as the field required to producing a current density of 10 μA/cm 2 , is 9, 7.7 and 7.1 V/μm, respectively. The field-emission performance relies not only on the tip’s radius of curvature and field enhancement factor, but also on the factor evaluating the degree of the screening effect.

Description: The authors present a nano-plasmonic disk resonator with a gap structure using the multi-mode interference effect coupling. The coupling intensity of the multi-mode interference effect coupling is 1.5 times greater than that of the conventional side coupling. The multi-mode interference effect is adopted as the coupling between the input bus waveguide and the nano-plasmonic disk resonator. The thickness of the dielectric layer, the width of the bus waveguide, and the length of the coupling portion are designed by theoretical calculations.

Description: We report single-step growth of spatially localized ZnO nanowires of controlled diameter to enable improved performance of piezoelectric devices such as nanogenerators. This study is the first to demonstrate the combination of electrodeposition with zinc nitrate and sodium citrate in the growth solution. Electrodeposition through a thermally-grown silicon oxide mask results in localization, while the growth voltage and solution chemistry are tuned to control the nanowire geometry. We observe a competition between lateral (relative to the (0001) axis) citrate-related morphology and voltage-driven vertical growth which enables this control. High aspect ratios result with either pure nitrate or nitrate-citrate mixtures if large voltages are used, but low growth voltages permit the growth of large diameter nanowires in solution with citrate. Measurements of the current density suggest a two-step growth process. An oxide mask blocks the electrodeposition, and suppresses nucleation of thermally driven growth, permitting single-step lithography on low cost p-type silicon substrates.

Description: The Si nanowire array (SiNWA) was achieved by metal-assisted etching. The effect of alkali-treating of SiNWA on the photovoltaic performance of solar cells was investigated. We found that the post-chemical treatment of SiNWA on solar cells could reduce (i) the surface reflection and (ii) the thickness of “dead layer” so that the short-wavelength spectral response is enhanced. As a result, a solar-spectrum-averaged reflectance of less than 3 % has been reached, a 3-fold enhancement on the spectral response of post-treated SiNWA cell at the wavelength of 400 nm has been observed, together resulting in a remarkable improvement of 45 % in the conversion efficiency.

Description: In this work we report the results of investigation of silver (Ag) nanoparticles prepared on a silica substrate by laser ablation. Our attention was focused on the mean diameter, size distribution and optical absorption properties of nanoparticles prepared in vacuum by using different laser wavelengths. The fundamental wavelength and the second, third, and fourth harmonics of a nanosecond Nd:YAG laser were used for nanoparticles fabrication. The corresponding values of the laser fluence for each wavelength were: 0.6 J/cm 2 at 266 nm, 0.8 J/cm 2 at 355 nm, 2.8 J/cm 2 at 532 nm, and 2 J/cm 2 at 1064 nm. The Ag nanoparticles produced have mean diameters in the range from 2 nm to 12 nm as the nanoparticles’ size decreases with the decrease of the wavelength used. The presence of the Ag nanoparticles was also evidenced by the appearance of a strong optical absorption band in the measured UV-VIS spectra associated with surface plasmon resonance (SPR). A redshift and widening of the absorption peak were observed as the laser wavelength was increased. Some additional investigations were performed in order to clarify the structure of the Ag nanoparticles.

Description: Nano-size phosphor particles of Y 2.97 Ce 0.03 (Al 1− x Gd x ) 5 O 12 were fabricated by ablating commercial micron-size powders in deionized water. We show that these colloidal phosphor nanoparticles suspended in deionized water can be used as a liquid sensor for all-optical, non-contact measurements of temperature with nanosecond time resolution. The nanophosphors can be used as temperature-sensing reporters in many applications where real-time measurements of temperature are necessary to understand physical processes, such as the mechanisms of temperature–time profiles in laser ablation.

Description: The use of laser beams as excitation sources for the characterization of semiconductor nanowires (NWs) is largely extended. Raman spectroscopy and photoluminescence (PL) are currently applied to the study of NWs. However, NWs are systems with poor thermal conductivity and poor heat dissipation, which result in unintentional heating under the excitation with a focused laser beam with microscopic size, as those usually used in microRaman and microPL experiments. On the other hand, the NWs have subwavelength diameter, which changes the optical absorption with respect to the absorption in bulk materials. Furthermore, the NW diameter is smaller than the laser beam spot, which means that the optical power absorbed by the NW depends on its position inside the laser beam spot. A detailed analysis of the interaction between a microscopic focused laser beam and semiconductor NWs is necessary for the understanding of the experiments involving laser beam excitation of NWs. We present in this work a numerical analysis of the thermal transport in Si NWs, where the heat source is the laser energy locally absorbed by the NW. This analysis takes account of the optical absorption, the thermal conductivity, the dimensions, diameter and length of the NWs, and the immersion medium. Both free standing and heat-sunk NWs are considered. Also, the temperature distribution in ensembles of NWs is discussed. This analysis intends to constitute a tool for the understanding of the thermal phenomena induced by laser beams in semiconductor NWs.

Description: We show that hole patterns and sponge-like layers at irradiated Ge surfaces originate from the same driving force, namely the kinetics of ion beam induced defects in the amorphous Ge surface layer. Ge hole patterns reported earlier for irradiation with low energy (5 keV) Ga + ions were reproduced for low energy Bi + but also for Ge + self-irradiation, which proves that the dominating driving force for morphology evolution cannot originate from the implanted impurities. At higher ion energies the well-known formation of sponge-like Ge surface layers after heavy ion irradiation was found for Bi + irradiation and Ge + self-irradiation, also. The transition from smooth surfaces via hole patterns to sponge-like morphologies with increasing ion energies was studied in detail. A model based on the kinetics of ion beam induced defects was developed and implemented in 3D kinetic Monte Carlo simulations, which reproduce the transition from hole patterns to sponge-like layers with increasing ion energy.

Description: 1 keV argon ion beam was employed to remove the oxide film of pure aluminum before diffusion bonding. A sound joint of pure aluminum was obtained by ion activation-assisted diffusion bonding at the low temperature of 350 ∘ C $350~{}^{\circ}\mathrm{C}$ , while the high-quality joining of pure aluminum was infeasible by conventional diffusion bonding at the temperature lower than 500 ∘ C $500~{}^{\circ}\mathrm{C}$ . The residual oxide film ratios of joints decreased with the increase of ion cleaning time. When the specimens were cleaned for 120 min, the joint with the maximum tensile strength of 62.3 MPa and the elongation of 14.1 % was obtained. The argon ion beam etching surface treatment provides a new route for the low-temperature diffusion bonding. The reliable diffusion bonded joint of pure aluminum indicates that low-temperature diffusion bonding is feasible for bulk materials, especially for materials with the outstanding plasticity.

Description: The structural, electronic and optical properties of Si n C n ( n =12,16,20,30,35 and 60) nanocages were studied using different approximations of density functional theory, i.e. local density approximation (LDA), generalized gradient approximation (GGA) and density functional theory based tight binding approximation (DFTB). The highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO) energy gaps were calculated for all nanocages. Time-dependent density functional theory (TD-DFT) was also applied for estimating of the optical excitation and exciton binding energies of the nanocages and the results compared with pure DFT calculations.

Description: Van de Pauw Hall measurement is an effective method to characterize the properties of semiconductors, such as bulk concentration, mobility, and resistivity, all of which are used to describe the purity level in the semiconductors. However, the performance of the ohmic contacts has a direct impact on the reliability and accuracy of the results obtained from the Van de Pauw Hall measurement. In the present work, the influences of different annealing techniques on the performance of the InSn ohmic contacts have been investigated using a High Purity Germanium (HPGe) crystal sample. The results show that the preferred annealing condition is at 400 °C for 1 hour, which has provided a significant improvement of the InSn contact quality and microscopic homogenization of the impurities in the HPGe crystal. The carrier concentration, charge mobility, and resistivity of the sample annealed at 400 °C for 1 hour are 5.772×10 10 /cm 3 , 1.883×10 4 × cm 2 /Vs, and 5.795×10 3 ×Ω cm at 77 K, respectively.

Description: To assess the potential uses of germanium as a nonlinear material in the mid IR we have measured the surface-damage threshold of germanium optical windows using femtosecond pulses at a wavelength of 3.9 μm. By working with a wavelength corresponding to a photon energy of less than half the band-gap energy, free-carrier generation due to one- and two-photon absorption was eliminated. The laser pulses had an energy of 5.5 μJ, a duration of 255 fs, and were focused to a waist size of approximately 100 μm. The multi-shot damage threshold of the germanium windows was estimated to be approximately 94 GW/cm 2 . The data should be of immediate benefit to industrial laser researchers and applications engineers working in the mid-IR region.

Description: We present a new method of synthesizing ZnO/TiO 2 core–shell nanowire (NW) arrays for the fabrication of dye-sensitized solar cells (DSSCs). Vertically aligned ZnO NW arrays were obtained on Si substrates, and modified by a TiO 2 shell in order to solve the recombination problems via a cost-effective spin-coating method. The structure of the ZnO/TiO 2 composite NW arrays was characterized. The experimental results indicate that the TiO 2 shell enhances the performance of the DSSCs, through improving the stability of the ZnO NWs and decreasing the recombination of photogenerated electrons on the NW surface. The highest overall conversion efficiency of the cell reaches about 3.0 %.

Description: In this work, first multi-wall carbon nanotubes (MWCNTs) with outer diameter about 20–30 nm are synthesized by a CVD method; they have been purified and functionalized with a two-step process. The approach consists of thermal oxidation and subsequent chemical oxidation. Then, monosize FePt nanoparticles along carbon nanotubes surface are synthesized by a Polyol process. The synthesized FePt nanoparticles are about 2.5 nm in size and they have superparamagnetic behavior with fcc structure. The CNTs surfaces as a substrate prevent the coalescence of particles during thermal annealing. Annealing at the temperature higher than 600  ∘ C for 2 h under a reducing atmosphere (90 % Ar + 10 % H 2 ) leads to phase transition from fcc to fct-L1 0 structure. So, the magnetic behavior changes from the superparamagnetic to the ferromagnetic. Furthermore, after the phase transition, the FePt nanoparticles have finite size with an average of about 3.5 nm and the coercivity of particles reaches 5.1 kOe.

Description: In this paper, a systematic study has been performed for the etching of negative photoresist SU-8 2005 using inductively coupled plasma. The etching rate, vertical profile, surface and sidewall roughness of the waveguide were investigated as a function of the chamber pressure, the bias power, the antenna power, the ratio of flow rate of Ar to O 2 , and the etching time. The etching parameters were studied in detail and optimized to minimize the surface roughness in etched areas. Ridge MZI waveguides with SU-8 2005 were fabricated under the optimized etching conditions, resulting in smooth and almost vertical patterns. The waveguides showed single-mode propagation at 1550 nm wavelength and low propagation loss of less than 1.565 dB/cm, which was similar to the waveguides fabricated by the wet-etching technique.

Description: Polymeric negative differential resistive (NDR) switching was explored based on the sandwiched structure of indium titanium oxide (ITO) coated polyethyleneterepthalate(PET)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)/silver(Ag) through electrohydrodynamic atomization (EHDA) printing technique. The NDR switching in the fabricated device with the structure of ITO/PEDOT:PSS/Ag was analyzed through semiconductor device analyzer under polarity dependent bipolar sweeping voltage of less than ± 5 V ${\pm} 5~\mathrm{ V}$ . Effect of the current compliance (CC) in the NDR switching of the fabricated switch has been demonstrated. Multiple resistive switching sweeps were taken to scrutinize the robustness of the fabricated device over 100 cycles. The non-volatility of the as-fabricated device was checked against different time stresses over 2500 s. The switching mechanism is proposed to be due to the transition between PEDOT + and PEDOT 0 chains. The current conduction mechanism involved in the PEDOT:PSS based NDR switches is attributed to the ohmic conduction at lower voltages, while space charge limited conduction and NDR effects were prominent due to the injection of carriers at higher voltages.

Description: In the present investigation, the axial buckling and post-buckling configurations of single-walled carbon nanotubes (SWCNTs) are studied including the thermal environment effect. For this purpose, Eringen’s nonlocal elasticity continuum theory is implemented into the classical Euler–Bernoulli beam theory to represent the SWCNTs as a nonlocal elastic beam model. A closed-form analytical solution is carried out to analyze the static response of SWCNTs in their post-buckling state in which the axial buckling load is assumed to be beyond the critical axial buckling load. Common sets of boundary conditions, named simply supported–simply supported (SS–SS), clamped–clamped (C–C), and clamped–simply supported (C–SS), are considered in the investigation. Selected numerical results are given to represent the variation of the carbon nanotube’s mid-span deflection with the applied axial load corresponding to various nonlocal parameters, length-to-diameter aspect ratios, temperature changes, and end supports. Moreover, a comparison between the post-buckling behaviors of SWCNTs at low- and high-temperature environments is presented. It is found that the size effect leads to a decrease of the axial buckling load especially for SWCNTs with C–C boundary conditions. Also, it is revealed that the value of the temperature change plays different roles in the post-buckling response of SWCNTs at low- and high-temperature environments.

Description: Strain-driven influences on the structural and optoelectronic properties of self-assembled InAs/GaAs multilayer quantum dot (MQD) heterostructures prompted our research into the growth of thermally stable MQD samples that were functional in an emission range technically favorable for communication lasers and intermediate band gap solar cells. We also studied parameter optimization by varying growth rate, capping layer thickness, seed quantum dot (QD) monolayer coverage, and post-growth annealing. A capping combination of InAlGaAs and i-GaAs was used. This combination helps in strain compensation, favors growth of multiple QD layers, functions as a strain-driven phase separation alloy, and helps increase QD stability. Photoluminescence results showed MQD sample emissions in the technologically significant range of 1.1–1.3 μm. Post-growth annealing at high temperatures led to inter-diffusion of the constituent QD materials, generation of low minimum energy states, and greater carrier involvement in intermediate band gap structures, thereby showing that annealing is a suitable method for post-growth manipulation. For one MQD sample, the annealing temperature was found to affect structural and optoelectronic properties as well as the presence of intermediate energy states. Heterostructure stability at annealing temperatures up to 750  ∘ C was found for the other samples. Transmission electron microscopy and photoluminescence results supported these findings.

Description: The modulation effect of microstructures on photoluminescence (PL) properties of silicon nanoclusters (Si NCs) in silicon-rich oxide (SRO) matrix prepared by electron-beam evaporation (EBE) and magnetron sputtering (MS) is investigated. A loose and porous microstructure is obtained from the SRO film prepared by EBE, while compact microstructure is acquired from that prepared by MS. The Si NCs with high density and good quality are formed in the SRO film prepared by EBE, and preferable PL performance of Si NCs is achieved in the EBE film with loose and porous microstructure. In contrast, the density and quality of Si NCs in the compact SRO film are suppressed and the PL properties are deteriorated due to the volumetric mismatching during the precipitation procedure of Si NCs. Optimization of the microstructures in SRO films should be made to reduce the volumetric mismatching and improve the PL properties of Si NCs.

Description: GaN nanoparticles were prepared on sapphire (0001) substrates with ZnO sacrificial layers by self assembly of Ga 2 O 3 films in their reaction with NH 3 . ZnO sacrificial layers with different thicknesses and Ga 2 O 3 films were deposited on sapphire substrates in turn by a radio frequency (RF) magnetron sputtering system. Nitridation of the Ga 2 O 3 films was then carried out in a quartz tube furnace. The effect of ZnO sacrificial layer thickness on the structure and optical properties of nanoparticles prepared by RF magnetron sputtering were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and photoluminescence (PL). GaN nanoparticles with ZnO sacrificial layers of different thicknesses possess hexagonal wurtzite crystal structure and have a preferred orientation with c axis perpendicular to the sapphire substrates. XRD, SEM, and AFM results reveal that the better-crystallinity, uniform, and well-dispersed GaN nanoparticles (∼30 nm) without agglomeration were obtained with a ZnO sacrificial layer 300-nm thick. The PL result reveals that the optical properties of the GaN nanoparticles are improved with a ZnO sacrificial layer 300-nm thick. Therefore, we suggest that a ZnO sacrificial layer 300-nm thick is the most suitable condition for obtaining better-quality GaN nanoparticles with good luminescence performance. Moreover, the mechanism of the formation of GaN nanoparticles with ZnO sacrificial layers is also discussed.

Description: Design and prototyping of a low profile, compact square loop microstrip line fed miniature patch antenna on 1.9 mm thick ceramic-polytetrafluoroethylene (PTFE) high dielectric composite material substrate is presented in this paper. The measured −10 dB return loss bandwidths of the antenna are 300 MHz (0.75–1.05 GHz) and 800 MHz (2.4–3.2 GHz) with 3.4 dBi, 8.86 dBi and 7.42 dBi at 900 MHz, 2.5 GHz and 3.0 GHz, respectively. The measured symmetric and almost stable radiation pattern makes the proposed antenna suitable for RFID, GSM, ZIGBEE, WBAN, LR-WPAN etc. integrated mobile devices.

Description: Artificial multiferroic superlattices (SL), consisting of BiFeO 3 (16 nm)/Bi 0.5 Na 0.5 TiO 3 (5 nm) (BFO/BNT SL), were grown on (001) SrTiO 3 single crystal by pulsed laser deposition method. The cross-sectional, surface morphology, and crystallographic structure of BFO/BNT SL and BFO single layer were investigated. It was found that the electrical, ferroelectric, and magnetic properties of BFO/BNT SL exhibit a remarkably enhancement compared with BFO single layer. The influence of BNT buffering layer, lattice strain, and interfaces interplay of the SL structure are supposed to benefit their ferroelectric and ferromagnetic properties. Our works suggested the BFO/BNT SL with an improved multiferroic characteristics have a promising application for the future informational storage devices.

Description: An approach for laser marking surfaces using a liquid–crystal-based spatial light modulator (LC-SLM) for beam patterning and manipulation is presented, designed to avoid the speckle interference problem which is a typical drawback of current SLM-based laser marking processes. In our approach, the LC-SLM is used to generate complex two-dimensional micropatterns (e.g., 20 × 20 datamatrices) with overall dimensions of 〈 320 by 320 μm. The micropatterns are generated in a series of 16 steps, using a Fresnel zone lens (FZL) combined with a computer-generated hologram (CGH); for each step the whole kinoform (FZL + CGH) is spatially shifted off-axis by a different amount of pixels to build-up the required pattern. In comparison with other SLM-based laser marking approaches already reported in the literature, our method not only eliminates (or at least significantly reduces) unwanted speckle interference but also reduces the laser power required for marking.

Description: In this paper we report the synthesis of highly luminescent ZnS and Mn-doped ZnS nanoparticles with uniform particle size distribution by liquid phase pulsed laser ablation. The formation of nanosized ZnS crystallites was confirmed by high-resolution transmission electron microscopy (HRTEM) images. The optical properties of these nanoparticles were studied by room temperature photoluminescence (PL) spectra. The PL emission from the ZnS nanoparticles shows a sharp peak in the UV region (334 nm) corresponding to the band edge and a broad peak in the visible region which can be attributed to the sulphur vacancies, cation vacancies and surface states in the nanocrystals. The yellow emission from the Mn-doped ZnS nanoparticles can be attributed to the radiative transition between 4 T 1 and 6 A 1 levels within the 3d 5 orbital of Mn 2+ .

Description: We present here for the first time the rigorous solution of the boundary diffraction problem of microwave scattering by a multilayered 2D cylinder. The cylinder layers may be made of isotropic, uniaxial anisotropic, electrically and (or) magnetically gyrotropic materials. The number and thickness of the layers may have arbitrary values in our solution. We calculated scattering diagrams (a radial component of real part of the Poynting vector) inside and outside of cylinder using the solution. Here we present scattering diagrams from a three-layered cylinder made of SiC and metamaterial or saturate magnetized ferrite. Diagrams were computed for wave incidence angles θ = π /2, π /3, π /6 inside of metamaterial/ferrite layer at a distance of 1 mm and outside of cylinder at a distance of 2.5 mm from the cylinder axis.

Description: In heterostructured metal–semiconductor system, plasmonic metal nanostructures can cooperate with semiconductors to enhance the solar light harness and energy conversion. In this study, we report on the plasmonically photocatalytic system constructed by in situ growth of semiconductor on metal nanostructures with high performance and stability. A facile and rapid microwave-assisted route was first explored to synthesize Ag nanocrystals, and subsequently converting them to Ag–AgCl nanohybrids was realized by in situ chemical transformation strategy at room temperature. These Ag–AgCl nanohybrids were characterized by X-ray diffraction, scanning electronic microscopy, and UV–vis absorption spectroscopy. The resulting Ag–AgCl nanohybrids showed remarkable photocatalytic activity and excellent durability for the degradation of organic pollutants under visible light irradiation. This finding provides a new way to improve photocatalytic efficiency through controllable chemical transformation.

Description: The aim of this paper is to study the laser-induced backside wet cleaning techniques for glass substrates. Two kinds of laser cleaning techniques are proposed in this study. The first involves applying an Nd:YAG laser to the backside of the substrate which is submerged in water. A metal plate is placed below the glass substrate. Most of the laser energy will be absorbed by the metal plate. The metal then vaporizes the water and generates a turbulent bubble flow. The bubble flow removes the alumina particles from the surface of the glass substrate. The second involves using a CO 2 laser to generate turbulent bubble flow to remove the particles. Both methods were successfully demonstrated for the removal of submicron particles of 0.5 μm in size. The phenomena of bubble generation and diffusion are presented in the paper. Because the laser is applied to the backside of the substrate, the damage due to the laser heat can be significantly reduced. The quality and efficient of the backside processing is better than those of the front side processing. The proposed techniques have great potential to provide an improved solution for glass cleaning.

Description: Computational modeling tools such as molecular dynamics (MD), ab initio, finite element modeling or continuum mechanics models have been extensively applied to study the properties of carbon nanotubes (CNTs) based on given input variables such as temperature, geometry and defects. Artificial intelligence techniques can be used to further complement the application of numerical methods in characterizing the properties of CNTs. In this paper, we have introduced the application of multi-gene genetic programming (MGGP) and support vector regression to formulate the mathematical relationship between the compressive strength of CNTs and input variables such as temperature and diameter. The predictions of compressive strength of CNTs made by these models are compared to those generated using MD simulations. The results indicate that MGGP method can be deployed as a powerful method for predicting the compressive strength of the carbon nanotubes.

Description: In this paper we review recent highlights of our research on the interaction of ultrafast laser pulses with surfaces with the aim of analyzing the fundamental mechanisms during micro/nanoprocessing of the irradiated surfaces and investigate the perspectives and applications arising from the irradiation of novel complex and functional materials with simple as well as temporally modulated femtosecond laser pulses. Our results on the irradiation of Si and ZnO surfaces show that the crater size and the ripple formation can be controlled by irradiation with properly temporally shaped laser pulses. Together with simulations of the dynamics of the phase changes of the material’s surface we show the potential for understanding and tailoring the engineering of smart optical materials at the micro- and nanoscale intended for novel optoelectronic applications and devices.

Description: Chiapas amber is a natural occurring fossil resin structurally composed of long macromolecule chains with semicrystalline phases associated with both fossil and polymerization process. The most conspicuous characteristic of this fossil polymer is that it preserves ancient organic inclusions. In the present work, PIXE/RBS spectrometry (particle-induced X-ray emission/Rutherford backscattering) were combined with complementary K-edge XANES spectroscopy (X-ray absorption near-edge structure) to identify the amount of sulfur in Chiapas amber. Initially, the amber samples were examined using infrared reflected photomicrography. Amber is transparent to infrared light and so embedded plants and animals are easily visible, showing them in extraordinary detail, as if they were immersed in a water-like solution. The PIXE/RBS data show that the proportion of sulfur in amber is significantly higher than that found in recently formed resins, consistent with the biogeochemical process that transforms the resin into amber during long-term burial in geological deposits. The sulfur K-edge XANES spectra from amber confirm the sulfur abundance and reveal sulfur species in the reduced and intermediate oxidation states in amber. Almost no oxidized sulfur was found, whereas the recent resins show mostly oxidized sulfur fractions. This indicates that labile oxidized sulfur decays during fossilization and resin maturation must occur under conditions of oxygen depletion. The implications of the presence of sulfur in amber for organic preservation is also discussed here. Sulfur compounds work as a polymer additive that promotes intense resin solidification. This restricts the early oxidant-specific biodegradation of the embedded biomatter and, over geological time, provides greater stability against chemical changes.

Description: Submicron-sized NiAl 2+ X O 4 fragments and nanocondensates of Ni-doped γ-Al 2 O 3 , Al-doped NiO and β-Ni(OH) 2 were synthesized simultaneously by pulsed laser ablation of NiAl 2 O 4 powder in water and characterized using X-ray/electron diffraction and optical spectroscopy. The NiAl 2+ X O 4 is Al-enriched spinel with dislocations and subgrains. The Ni-doped γ-Al 2 O 3 spinel has paracrystalline distribution (i.e., with fair constant longitudinal spacing, but variable relative lateral translations) of defect clusters and intimate intergrowth of θ -Al 2 O 3 and 2x( $ \overline{1} $ 3 $ \overline{1} $ ) commensurate superstructure. The Al-doped NiO has perfect cubo-octahedron shape and as small as 5 nm in size. The β-Ni(OH) 2 and 1-D turbostratic hydroxide lamellae occurred as a matrix of these oxide nanoparticles. The colloidal suspension containing the composite phases has a minimum band gap of 5.3 eV for potential photocatalytic applications.

Description: Red long-lasting phosphor Y 2 O 2 S:Eu 3+ , Zn 2+ , Ti 4+ nanotubes were prepared by hydrothermal method. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence and thermoluminescence spectra (TL) were used to characterize the long-lasting phosphor. XRD investigation revealed that the product synthesised under 750 °C for 6 h was a pure phase of Y 2 O 2 S. SEM observation showed that the sulfuretted phosphor inherited the tube-like shape from the precursor. Under 325 nm UV excitation, the result indicated the strongest red-emission lines at 627 nm, corresponded to the transition from 5 D 0 to 7 F 2 level of Eu 3+ ion. Both the afterglow decay curves and TL curves revealed that the phosphor had efficient luminescent and excellent long-lasting properties.

Description: We have performed a non-equilibrium quantum transport calculations for a two-terminal mesoscopic system including a magnetic quantum dot. Using the non-equilibrium Green’s function technique, we have obtained electric current and charge distribution in the temperature range from 1 to 10 K as a function of magnetic field. Results indicate that the density of carriers essentially can be controlled by temperature and bias voltage.

Description: A rutile TiO 2 (α-TiO 2 ) and hexagonal wurtzite ZnO nanocomposite was directly and synchronously synthesized via arc discharge method submerged in de-ionized water. In correlation with the detailed characterization of the morphology, and crystalline structure of the prepared ZnO–TiO 2 nanocomposites, the UV–visible and photoluminescence properties were studied. X-ray diffraction and transmission electron microscopy investigations revealed the co-existence of α-TiO 2 and hexagonal wurtzite ZnO phases with the ZnO and α-TiO 2 nanoparticles are in nanorod and nanospheres morphologies, respectively. The diameters of the synthesized nanocomposite particles are in the range of 5–70 nm. Interestingly, the as-prepared ZnO–TiO 2 nanocomposite shows better photocatalytic activity for photodegradation of the methylene blue dye than both of pure ZnO and TiO 2 nanocatalyts. This work would explore feasible routes to synthesize efficient metal or/and metal oxide nanocomposites for degrading organic pollutants, gas sensing or other related applications.

Description: A direct electronics printing technique through atomized spraying for patterning room-temperature liquid metal droplets on desired substrate surfaces is proposed and experimentally demonstrated for the first time. This method is highly flexible and capable of fabricating electronic components on various target objects, with either flat or rough surfaces, made of different materials, or having different orientations from 2D to 3D geometrical configurations. With a pre-designed mask, the liquid metal ink can be directly deposited on the substrate to form various specific patterns which lead to the rapid prototyping of electronic devices. Further, extended printing strategies were also suggested to illustrate the adaptability of the method. For example, it can be used for making transparent conductive film with an optical transmittance of 47 % and a sheet resistance of 5.167Ω/□ due to natural porous structure. Different from the former direct writing technology where large surface tension and poor adhesion between the liquid metal and the substrate often impede the flexible printing process, the liquid metal here no longer needs to be pre-oxidized to guarantee its applicability on target substrates. One critical mechanism was that the atomized liquid metal microdroplets can be quickly oxidized in the air due to its large specific surface area, resulting in a significant increase of the adhesion capacity and thus firm deposition of the ink to the substrate. This study paved a generalized way for pervasively and directly printing electronics on various substrates which are expected to be significant in a wide spectrum of electrical engineering areas.

Description: Dopamine was encapsulated into nanoporous amorphous TiO 2 matrix by sol–gel method under atmospheric conditions. A second sample was obtained by the addition of the crown-ether 15C5 in this previous sample. Thin films were spin-coated on glass wafers. No heat treatment was employed in both films. All films were characterized using infrared spectroscopy, high resolution transmission electronic microscopy, X-ray diffraction, optical absorption and scanning electronic microscopy. Despite the films prepared with 15C5 were no calcined, a partial crystallization was identified. Anatase and rutile nanoparticles with sizes of 4–5 nm were obtained. Photoconductivity technique was used to determine the charge transport mechanism on these films. Experimental data were fitted with straight lines at darkness and under illumination wavelengths at 320, 400, and 515 nm. It indicates an ohmic behavior. Photovoltaic and photoconductivity parameters were determined from the current density vs. the applied-electrical-field results. Amorphous film has bigger photovoltaic and photoconductive parameters than the partially crystalline film. Results observed in the present investigation prove that the nanoporous TiO 2 matrix can protect the dopamine inhibiting its chemical instability. This fact modifies the optical, physical and electrical properties of the film, and is intensified when 15C5 is added.

Description: This paper reports the synthesis and characterization of nanocrystalline tin oxide (SnO 2 ) powders by a simple method using a chitosan–polymer complex solution. To obtain SnO 2 nanocrystalline powders, the precursor was calcined at 500–600 °C in air for 2 h. The phase composition of calcined samples was studied by X-ray diffraction (XRD). The XRD results confirmed the formation of a SnO 2 phase with tetragonal structure. The particle sizes of the powder were found to be 22–23 nm as evaluated by the XRD line broadening method. TEM investigation revealed that the SnO 2 samples consist of crystalline particles of 19–21 nm. The corresponding selected area electron diffraction analysis further confirmed the formation of the tetragonal structure of SnO 2 without any impurity phases. The optical properties of the samples were explored by Fourier transform infrared spectroscopy, optical absorption and Raman studies. The estimated band gaps of the samples were in the range of 3.44–3.73 eV.

Description: Mg- and Si-doped GaN layers deposited by metalorganic chemical vapor deposition method were irradiated with femtosecond pulse duration laser of three different wavelengths 1,030, 515 and 343 nm. Both single and multiple shot laser induced damage thresholds of doped GaN layers were evaluated and discussed. The scanning electron microscopy employed with electron beam induced current and energy dispersive X-ray techniques were used to study laser damage morphology. It was observed that ablated area and laser-induced damage increased with irradiation fluence. The mechanism of damage generation by Gaussian beam profile laser was considered.

Description: Polarization effects are studied within nitride light-emitting diodes (LEDs) manufactured on standard polar and semipolar substrates. A new theoretical approach, somewhat different than standard ones, is proposed to this end. It is well known that when regular polar GaN substrates are used, strong piezoelectric and spontaneous polarizations create built-in electric fields leading to the quantum-confined Stark effects (QCSEs). These effects may be completely avoided in nonpolar crystallographic orientations, but then there are problems with manufacturing InGaN layers of relatively high Indium contents necessary for the green emission. Hence, a procedure leading to partly overcoming these polarization problems in semi-polar LEDs emitting green radiation is proposed. The (11 2 2) crystallographic substrate orientation (inclination angle of 58 ∘ to c plane) seems to be the most promising because it is characterized by low Miller–Bravais indices leading to high-quality and high Indium content smooth growth planes. Besides, it makes possible an increased Indium incorporation efficiency and it is efficient in suppressing QCSE. The In 0.3 Ga 0.7 N/GaN QW LED grown on the semipolar (11 2 2) substrate has been found as currently the optimal LED structure emitting green radiation.

Description: Photothermal deflection spectroscopy is used in order to investigate near- and sub-band gap absorption of Si-doped GaSb epilayers deposited by MBE on a semi-insulating GaAs substrate. The optical absorption spectra show an extra absorption on the transparency region below the bandgap due to free-carrier absorption. However, for energies above the gap, we notice a linear behavior of the square root of the absorption coefficient versus the heating beam energy, which is attributed to phonon-assisted absorption. From interpolation of the phonon absorption to low energies we have determined the free-carrier absorption that is found to follow the Drude law.

Description: TiO 2 thin films of different thickness were prepared by the Electron Beam Evaporation (EBE) method on crystal silicon. A variable angle spectroscopic ellipsometer (VASE) was used to determine the optical constants and thickness of the investigated films in the spectral range from 300 to 800 nm at incident angles of 60°, 70°, and 75°, respectively. The whole spectra have been fitted by Forouhi–Bloomer (FB) model, whose best-fit parameters reveal that both electron lifetime and band gap of TiO 2 thin film have positive correlation to the film thickness. The refractive indices of TiO 2 thin film increase monotonically with an increase in film thickness in the investigated spectral range. The refractive index spectra of TiO 2 thin films have maxima at around 320 nm and the maxima exhibit a marginally blue-shift from 327.9 to 310.0 nm with an increase in film thickness. The evolution of structural disorder in the TiO 2 thin film growth can be used to explain these phenomena.

Description: Alkaline earth metal hydroxide nanoparticles dispersions have demonstrated to be efficient for the preservation of cellulose-based artifacts, providing a stable neutral environment and, if in excess, turning into mild alkaline species. New formulations tailored for specific conservation issues have been recently obtained via a solvothermal reaction, starting from bulk metal, and short chain alcohols. Using this synthetic procedure, stable, and high concentrated calcium hydroxide nanoparticles dispersions can be obtained. The characterization of nanoparticles was carried out by dynamic light scattering, transmission electron microscopy and X-ray powder diffraction and showed that the dispersed systems are particularly suitable for the application on porous substrates. In a direct application of this technology, acidic paper and canvas samples were artificially aged after deacidification using calcium hydroxide nanoparticles dispersed in short chain alcohols. Cellulose viscosimetric polymerization degree (DPv), cellulose pyrolysis temperature, and samples’ pH were evaluated upon the aging and in terms of protective action arising from the applied treatment. In particular, determinations of DPv clearly showed that the degradation of acidic paper and canvas samples proceeds at higher rates with respect to deacidified samples. These evidences were also confirmed by the thermogravimetric analysis of samples, in which the benefits due to the deacidification treatments are measured in terms of pyrolysis temperature of cellulose. These new formulations of nanoparticles dispersions expand the palette of available tools for the conservation of cellulose-based works of art, such as easel paintings, and manuscripts, potentially opening the way for the intervention on parchment and leather, whose preservation is a particularly challenging task.

Description: It is shown that in polar InGaN QWs emitting in the blue-green spectral region a Stokes shift between spontaneous emission (SE) and optical transition observed in contactless electroreflectance (CER) spectrum (absorption-like technique) can be observed even at room temperature, despite the fact that the SE is not associated with localized states. Time resolved photoluminescence measurements clearly confirm that the SE is strongly localized at low temperatures whereas at room temperature the carrier localization disappears and the SE can be attributed to the fundamental transition in this QW. The Stokes shift is observed in this QW system because of the large built-in electric field, i.e., the CER transition is a superposition of all optical transitions with non-zero electron-hole overlap integrals and, therefore, the energy of this transition does not correspond to the fundamental transition of InGaN QW. Lasing from this QW has been observed at the wavelength of 475 nm, whereas the SE was observed at 500 nm. The 25 nm shift between the lasing and SE is observed because of a screening of the built-in electric field by photogenerated carriers. However, our analysis shows that the built-in electric field inside the InGaN QW region is not fully screened under the lasing conditions.

Description: BaTiO 3 thin films were deposited by pulsed laser deposition on Pt–Si at different laser pulse repetition frequencies. X-ray diffraction spectra show that preferred oriented films can be grown by adjusting the pulse repetition frequency. Enhanced dielectric and ferroelectric properties obtained in films deposited at 1 Hz is attributed to preferred orientation, low strain and homogeneous grain distribution. The films deposited at 1 Hz show an impressive remanent polarization of 21.4 μC/cm 2 with a coercive field of 70.0 kV/cm. The shift in Curie temperature, which stems from changing the laser pulse repetition frequency, is associated with the strain state in the film.

Description: Nanopatterned sapphire substrates were fabricated by annealing of patterned Al thin films. Square-patterned Al thin films with the diagonal length of 600 nm, period of 1 um and height of ∼200 nm were obtained by the Laser Interference Lithography and Reactive Ion Etching. Patterned Al thin films were subsequently subjected to dual stage annealing due to the melting temperature of Al thin films (660  ∘ C). The first comprised a low temperature oxidation anneal. The hillocks formation on Al thin films was minimized with an oxidation annealing at 450  ∘ C for 24 h. The little change in the morphology of patterned Al thin films was observed at 450  ∘ C for 24 h. This was followed by a high temperature annealing to induce growth of the underlying sapphire single crystal to consume the oxide layer. The SEM results show the patterns were retained on sapphire substrates after high temperature annealing at less than 1200  ∘ C. The XRD and Raman results reveal that the orientation of island patterns by dual stage annealing of patterned Al thin films for 24 h at 450  ∘ C, and 1 h at 1000  ∘ C, was the same as that of the sapphire (0001) substrates.