ALBERT

Beschreibung: Barnacles are one of the most prominent hardfouling organisms in the marine environment. They are able to adhere efficiently to nearly every surface underwater including artificial ones like ship hulls and maritime installations. This overgrowing can lead to huge economical costs. Previous studies have shown that specific microstructure types including micropillars can reduce the initial settlement of barnacles. However, it is not clear how adult barnacles are influenced by microstructured surfaces and whether microstructures can even decrease the resulting adhesion strength of them under natural conditions. Therefore, the aim of this study was to systematically investigate the influence of height, diameter, aspect ratio and flexibility of fibrillar microstructures made from polydimethylsiloxane (PDMS) on initial settlement of barnacles as well as the permanent attachment of adult ones. Micropillars with three different heights (50 µm, 100 µm, 200 µm) and two different diameters (25 µm, 50 µm) were exposed to the Baltic Sea for 12 weeks. On a weekly basis, all barnacles (Balanus [= Amphibalanus] improvisus) were tracked individually to calculate the release-to-settlement ratio and to capture the average attachment duration prior to detachment. The results have shown that with increasing height, both initial settlement and fouling density development were reduced. An increase of diameter showed a similar relationship but at a much smaller scale. All tested microstructures decreased the detachment rates of barnacles from the surface compared to a flat PDMS control. However, they appear to complicate the development of a strong adhesive joint in the young adult phase. Some grade of flexibility in the microstructures appeared to increase the fouling retention. The results shed light in the interaction between adult barnacle adhesion and microstructures and may help in the development of new antifouling technologies.

Beschreibung: DLC:Si and DLC:N (diamond-like carbons doped with Si or N) functional layers in different configurations are deposited on polyurethane (PU) for bioengineering applications using CCP (capacitively coupled plasma) discharge generated in the PE CVD (plasma-enhanced chemical vapor deposition) system. Scanning electron microscopy (SEM) observations show that the obtained single and multilayers are continuous and well adherent to the substrates, but they differ in surface morphologies. DLC:Si layers form granular-like outer surfaces, while DLC:N ones a mosaic structure of plain areas. Topography analyses by atomic force microscopy (AFM) and optical profilometry reveal that Si-doped layers are characterized by significantly higher surface roughness (Ra ca. 5 nm) in comparison to N-doped layers (Ra ca. 0.3 nm) and also higher values of profile roughness parameter Rz (up to 32 μm vs. about 13 μm). Energy-dispersive X-ray spectroscopy (EDS) analysis indicates the homogenous chemical composition of the layers. DLC:N layers, are characterized by significantly higher polar component of surface free energy (up to ca. 5.0 mJ/m2). DLC:Si layers exhibit higher values of diiodomethane contact angle (up to ca. 90°) compared with DLC:N layers (up to ca. 55°). The attenuated total reflectance Fourier transform infrared spectroscopic measurements (ATR-FTIR) of the layers reveal that the addition of silicon to the DLC structure increases the content of terminal CHn bonds (n = 1, 2, 3) as well as beneficial Si–H and Si–CHn bonds, which significantly reduce the internal stresses in the layers. Both DLC:Si and DLC:N layers exhibit no cytotoxic effects using the human osteoblast-like cell line and human keratinocytes.

Beschreibung: Ba x Sr 1− x Fe 12 O 19 /Fe 3 O 4 /polyacrylic acid/polythiophene (Ba x Sr 1− x Fe 12 O 19 /Fe 3 O 4 /PAA/PTh) nanocomposites with multi-core–shell structure were successfully synthesized by four steps. The samples were characterized by FTIR, X-ray diffraction (XRD), transmission electron microscope (TEM), vibrating sample magnetometer, and radar absorbing material reflectivity far-field radar cross-section method, respectively. XRD and TEM results indicated that the obtained nanoparticles have multi-core–shell morphology. The magnetic properties and microwave absorption analyses reveal that there are interphase interactions at the interface of Ba x Sr 1− x Fe 12 O 19 , Fe 3 O 4 , PAA, and PTh, which can affect the magnetic properties and microwave absorption properties of the samples. The microwave-absorbing properties of nanocomposites were investigated at 8–14 GHz. A typical layer absorber exhibited an excellent microwave absorption with a −26 dB maximum absorption at 14 GHz. Compared with core material, the coercivity and saturation magnetization of multi-core–shell nanocomposites decrease obviously, but the microwave absorption properties of nanocomposites are improved greatly. The results show that these composite could be used as advancing absorption and shielding materials due to their favorable microwave-absorbing properties.

Beschreibung: This paper presents a simplified model of a terminal mobile where a monopole antenna is associated with three different metamaterials: artificial magnetic conductor (AMC), electromagnetic band gap and resistive high-impedance surface (RHIS). The objective is to evaluate what is the metamaterial which is the best solution to reduce exposure. The exposure has been evaluated using a simplified phantom model. Results show that both AMC and RHIS reduce the exposure preserving the antenna performances. A reduction of 23 % of specific absorption rate 10 g has been obtained when the monopole is associated with an optimized RHIS structure. Antenna with and without metamaterials has been realized. The experimental results confirm the performances given by simulation in terms of impedance matching and radiation.

Beschreibung: Systematic numerical study of near-infrared radiation formed during filamentation in air revealed the formation of robust light bullet first registered in the experiment (Chen et al. in Appl Phys B 91:219, 2008 ). The near-infrared light bullet propagates along the filament axis with the divergence 〈1 mrad and the quasi-constant duration of ~30 fs. The central wavelength of the bullet gradually increases from 860 to 900 nm during the propagation. The results of our numerical simulation are in agreement with the experiments (Chen et al. in Appl Phys B 91:219,  2008 ; Uryupina et al. in Appl Phys B 110:123, 2013 ).

Beschreibung: The annealing effects of c -plane sapphire (α-Al 2 O 3 ) substrate with a vicinal-cut angle of α  = 0.25° toward the a -plane \(\left( {11\overline{2} 0} \right)\) on the quality of epitaxial ZnO films grown by metal organic chemical vapor deposition were studied. The atomic steps formed on sapphire substrate surface by annealing at high temperature were analyzed by atomic force microscopy (AFM). The annealing effects of sapphire substrate on the microstructural and optical properties of the ZnO films were examined by high-resolution X-ray diffraction, scanning electron microscopy, AFM and photoluminescence spectroscopy. Experimental results indicate that the film quality is strongly affected by annealing treatment of the sapphire substrate. X-ray diffraction study revealed that ZnO films deposited on c -plane sapphire substrate annealed at T  ≥ 1050 °C exhibit a wurtzite phase and have a c -axis orientation. The decrease in FWHM for (0004) and \(\left( {10\overline{1} 4} \right)\) ZnO peak confirms the improvement of the crystalline quality of ZnO thin film as increasing annealing substrate temperature. Sapphire annealing at 1100 °C for 3 h under oxygen prior to ZnO film growth is the best to achieve ZnO film with good structural and optical quality.

Beschreibung: Flame flatness is one of the most critical factors in evaluating the performance of a flat-flame burner. In this paper, the flame flatness of a flat-flame burner is validated using a resolution-doubled one-dimensional wavelength modulation spectroscopy tomography (1D-WMST) technique that only uses one view of multiple parallel laser beams. When the interval of two neighboring parallel laser beams is Δ r , a designed novel geometry of the parallel laser beams realizes a doubled tomographic resolution of Δ r /2. Using the proposed technique, the distributions of temperature and H 2 O mole fraction in an axisymmetric premixed flame are simultaneously reconstructed and hence the flame flatness of a flat-flame burner can be validated. The flatness factor is quantitatively described by the similarity between the reconstructed and expected distributions of H 2 O mole fraction. For flat and non-flat flames, the experimental results agree well with the CFD simulation results, denoting that the resolution-doubled 1D-WMST technique provides a noninvasive, reliable and low cost way to validate the flame flatness of the flat-flame burner.

Beschreibung: We report on the optical performances of laccaic acid dye in solution at different concentrations and dye–poly(methyl methacrylate) composite thin films. The linear spectral characteristics including optical constants, i.e. refractive index ( n ) and extinction coefficient ( k ), were carried out in a comprehensive way through absorbance, fluorescence and ellipsometric studies. The nonlinear optical parameters such as nonlinear absorption coefficient β eff (or β 2 ), the imaginary third-order susceptibility (Im[ χ (3) ]) and the imaginary part of second-order hyperpolarizability ( γ ) of the samples were evaluated using the open-aperture Z-scan technique with a laser pulse duration of 10 ns at 532 nm wavelength. The corresponding numerical values of these parameters were of 10 −10 , 10 −11 and 10 −32 order, respectively. Two-photon absorption was revealed to be the main driving physical mechanism in the nonlinear response. This suggests that laccaic acid dye can be a potential candidate for NLO materials application.

Beschreibung: We demonstrate a sensor based on tunable diode laser absorption spectroscopy for the detection of hydrogen fluoride (HF) gas at ambient pressure. Absorption from the HF R(1) ro-vibrational peak at ν̃  = 4038.962 cm −1 (2.476 µm) in the fundamental (Δ ν  = 1) band is measured. A quantitative spectral fit based on HITRAN data is used to account for overlapping spectral peaks of HF and water vapor, with an rms residual noise of 5 × 10 −4 absorbance units. The sensor is optimized for the detection of transient variations in HF concentration. We measure noise-equivalent concentrations for HF of 38 parts-per-trillion by volume (ppt) for 1-s integration times and 2.3 ppt for 10-min integration times.

Beschreibung: We report on the absorption profile of the monoclinic holmium-doped \(\hbox {KY}(\hbox {WO}_4)_2\) crystal near the optic axis for the maximal absorption wavelength at 1960 nm. The full angular distribution of the absorption coefficient at the vicinity of such optical singularity has been experimentally and numerically investigated. Furthermore, laser experiments along the optic axis have been carried out. So-called conical refraction laser and classical Gaussian laser operation are compared near the optic axis, taking into account the complex absorption profile.

Beschreibung: We demonstrate a novel and compact fiber-probe pressure sensor based on a micro-Fabry–Perot interferometer (FPI). The device is fabricated by splicing both ends of a short-section simplified hollow-core photonic crystal fiber (SHC-PCF) with single-mode fibers. Then, a microchannel is drilled by a femtosecond laser micromachining in the SHC-PCF to allow air to diffuse in. The pressure sensing mechanism is based on the dependence of the air refractive index on pressure. We use both theory and experiment to investigate the sensing characteristics. A micro-FPI with a length of 272 μm demonstrates a pressure sensitivity of 4.071 nm/MPa at 1580 nm and a low-temperature sensitivity of 1.1 pm/°C at atmospheric pressure. We further study the temperature cross sensitivity of the sensor under different pressures. The sensor also shows strong stability and good reversibility, and may be potentially used in pressure sensing applications.

Beschreibung: We study the thermo-optic Goos–Hänchen (TOGH) effect in a prism–waveguide coupling structure with silicon-on-insulator waveguide. Stationary-phase method is utilized to calculate the TOGH shift. When the waveguide is regarded as a two-dimensional planar waveguide, a nonlinear relation between GH shift and temperature is obtained. Based on the noticeable TOGH effect, a sensitive temperature modulator or sensor can be realized. As the waveguide width is limited, the proposed structure can be regarded as a three-dimensional rectangular waveguide. We explore the GH shift and TOGH effect for different modes propagating in rectangular waveguide which show different linear relations between GH shift and temperature, which can be used to design mode-selective device based on TO effect.

Beschreibung: Determination of phosphorus and boron concentrations in Czochralski-grown silicon wafer-thick samples has been examined by means of low-temperature high-resolution far-infrared transmission measurements with p -polarized light incident at Brewster angle. The measurements were taken at about 8.7 K with a spectral resolution of 0.5 cm −1 under halogen light illumination. Linear correlations are clearly obtained between the absorption coefficients of several phosphorus and boron transitions and their concentrations, which are approximately in the range of 7.7 × 10 13 –1.6 × 10 15  atoms cm −3 for phosphorus and of 2.5 × 10 14 –7.6 × 10 14  atoms cm −3 for boron. The correlations are obtained regardless of the surface processing conditions of the samples. These are because interference fringes due to internal multiple reflections in wafer-thick silicon samples are almost suppressed using this incidence. The detection limit of phosphorus is about 1.2 × 10 13  atoms cm −3 and that of boron is about 4.2 × 10 13  atoms cm −3 . P -polarized Brewster angle incidence has made it possible to determine phosphorus and boron concentrations in wafer-thick samples.

Beschreibung: Nanocrystalline CeO 2 /C 3 N 4 was synthesized via a one-step solution combustion method using urea as fuel for the first time. The effects of the molar ratio of urea to cerium chloride on the photocatalytic activity of the synthesized samples were investigated. The synthesized nanocrystalline CeO 2 /C 3 N 4 shows small size and large surface exposure area. Photocatalytic degradation of methylene blue demonstrates that the synthesized nanocrystalline CeO 2 /C 3 N 4 possesses enhanced photocatalytic activity. It is proposed that the enhanced photocatalytic activity might be related to the favorable morphology and structure, and the effective charge separation between C 3 N 4 and CeO 2 in the photocatalytic process.

Beschreibung: Vertical MBE- and MOCVD-grown \({n}^{+}/{n}\hbox {-GaAs}/\hbox {Al}_{0.25}\hbox {Ga}_{0.75}\hbox {As}\) structures used for microwave electronics have been studied with continuous wave and time-correlated single photon counting dynamic photoluminescence technique. The photoluminescence spectra and light emission lifetimes are used to explain the recombination mechanisms of the excited carriers. This paper presents results showing the differences in recombination characteristics of \({n}^{+}\hbox {-Al}_{0.25}\hbox {Ga}_{0.75}\hbox {As}\) layers grown using MBE process compared with MOCVD process. One of these differences is that the PL spectrum of the MOCVD-grown layer is shifted towards the forbidden energy gap region, as well as the characteristic recombination time is longer than for the MBE-grown sample. This peculiarity can be attributed to the formation of the localised band tails in the \({n}^{+}\hbox {-Al}_{0.25}\hbox {Ga}_{0.75}\hbox {As}\) MOCVD-grown sample. The proposed analytical model explains the differences in microwave detection properties of the samples grown by MBE and MOCVD processes.

Beschreibung: Hybrid nanocomposites of II–VI semiconductor nanoparticles are gaining great interest in nonlinear optoelectronic devices. Present work includes the characterization of CdSe polymer nanocomposite prepared by chemical in situ technique. From X-ray diffraction, the hexagonal wurtzite structure of nanoparticles has been confirmed with spherical morphology from transmission electron microscopy. Ag–CdSe hybrid polymer nanocomposite has been prepared chemically at different Ag concentrations. The presence of Ag in hybrid nanocomposite has been confirmed with energy-dispersive X-ray spectroscopy. The effect of varying Ag concentration on the linear and nonlinear optical properties of the nanocomposites has been studied. In linear optical parameters, the linear absorption coefficient, refractive index, extinction coefficient and optical conductivity have been calculated. The third-order nonlinear optical properties have been observed with open- and closed-aperture Z-scan technique. The large nonlinear refractive index ~10 −5  cm 2 /W with self-focusing behaviour is due to the combined effect of quantum confinement and thermo-optical effects. The enhanced nonlinearity with increasing Ag content is due to the surface plasmon resonance, which enhances the local electric field near the nanoparticle surface. Thus, Ag–CdSe hybrid polymer nanocomposite has favourable nonlinear optical properties for various optoelectronic applications.

Beschreibung: The effect of doping palladium (Pd) at the Cu site of CaCu 3 Ti 4 O 12 powders (CCPTO) synthesized by sol–gel technique on electrical properties was studied. XRD analysis revealed the formation of CCTO and CCPTO ceramics with some minor quantities of impurities. SEM micrographs revealed that the grain size decreased with Pd doping. TEM micrographs of CCPTO powder showed the formation of irregular-shaped particles of ~40 nm. The dielectric constant and dielectric loss showed a significant enhancement with Pd doping. A significant decrease in grain-boundary resistance with Pd doping was ascertained by impedance spectroscopy study.

Beschreibung: This work focuses on the composition and microstructure of the lead white pigment employed in a set of paintworks, using a combination of µ-XRD and 2D scanning XRF, directly applied on five drapery studies attributed to Leonardo da Vinci (1452–1519) and conserved in the Département des Arts Graphiques , Musée du Louvre and in the Musée des Beaux - Arts de Rennes . Trace elements present in the composition as well as in the lead white highlights were imaged by 2D scanning XRF. Mineral phases were determined in a fully noninvasive way using a special µ-XRD diffractometer. Phase proportions were estimated by Rietveld refinement. The analytical results obtained will contribute to differentiate lead white qualities and to highlight the artist’s technique.

Beschreibung: We report on an experimental study of vacuum-induced suppression and enhancement of four-wave mixing (FWM) signal in a composite atom–cavity system. By scanning the additional dressing field, the suppression ratio of the FWM signal can reach 90 % compared with 40 % without cavity. We attribute the enhanced suppression and enhancement to the atom–cavity coupling arising from a vacuum-induced Raman process, which amplifies the dressing effect from the additional field. Also, the dressing asymmetry of the atom–cavity coupling is discussed and used to estimate the nonlinearity of atomic medium in the cavity. The suppression and enhancement can be interpreted by a dressed-state picture and agree with theoretical calculations. The investigation may find applications in optical switch and quantum memory controlled by cavity.

Beschreibung: By simultaneously using a multi-walled carbon nanotube (MWCNT) and a monolayer graphene saturable absorber (SA) in the cavity, a laser-diode-pumped dual-loss-modulated passively Q-switched Tm:LuAG laser at 2 μm is demonstrated for the first time. In comparison with the singly passively Q-switched laser with MWCNT or monolayer graphene SA, the doubly passively Q-switched laser with both MWCNT and monolayer graphene SA can generate shorter pulse width and higher peak power. A maximum pulse width compression ratio of 2.8 and a highest peak power enhancement factor of 4 were obtained at the incident pump power of 5.8 W, respectively. The experimental results show that the dual-loss modulation is an efficient method to compress the pulse widths and improve the peak powers of the Q-switched lasers at 2 μm.

Beschreibung: Photoexcitation dynamics in a three-step photoionization of atomic uranium has been investigated using time-resolved two-color three-photon and delayed three-color three-photon photoionization signals. Investigations are carried out in an atomic beam of uranium coupled to a high-resolution time-of-flight mass spectrometer using three tunable pulsed dye lasers. Dependence of both the signals on the second-step laser photon fluence is studied. Excited-level-to-excited-level photoexcitation cross section and photoionization cross section from the second excited level are simultaneously determined by analyzing the two-color three-photon and three-color three-photon photoionization signals using population rate equation model. Using this methodology, photoexcitation and photoionization cross sections at seven values of the second-step laser wavelength have been measured. From the measured values of the photoexcitation cross sections, we have obtained excited-level-to-excited-level transition probabilities and compared these with the values reported in the literature.

Beschreibung: Easel paintings on canvas are subjected to alteration mechanisms triggered or accelerated by moisture. For the study of the spatial distribution and kinetics of such interactions, a moisture exposure chamber was designed and built to perform neutron radiography experiments. Multilayered sized and primed canvas samples were prepared for time-resolved experiments in the ICON cold neutron beamline. The first results show that the set-up gives a good contrast and sufficient resolution to visualise the water uptake in the layers of canvas, size and priming. The results allow, for the first time, real-time visualisation of the interaction of water vapour with such layered systems. This offers important new opportunities for relevant, spatially and time-resolved material behaviour studies and opens the way towards numerical modelling of the process. These first results show that cellulose fibres and glue sizing have a much stronger water uptake than the chalk–glue ground. Additionally, it shows that the uptake rate is not uniform throughout the thickness of the sized canvas. With prolonged moisture exposure, a higher amount of water is accumulating at the lower edge of the canvas weave suggesting a decrease in permeability in the sized canvas with increased water content.

Beschreibung: Titanium dioxide thin films were coated on soda-lime glass substrates using spray pyrolysis method with a thickness of 152 ± 10 nm. The films were irradiated with hydrogen ions at room temperature at various beam energies and fluences. Optimized incident beam energy and beam fluence were obtained to improve photocatalytic and hydrophilicity properties of TiO 2 thin films by narrowing the band gap. Samples were characterized by scanning electron microscopy to study the surface morphology and by UV–Vis absorption spectroscopy to measure the band gap. The optical band gap of H-doped anatase TiO 2 thin films irradiated with hydrogen beam with energies of 2 and 4 keV and a fluence of 10 15 ions/cm 2 was narrowed from 3.34 eV (before irradiation) to 3.04 and 2.92 eV (after irradiation), respectively. The irradiated sample with energy of 4 keV with a fluence of 10 15 ions/cm 2 has the best improvement. This is attributed to the contraction of the band gap and to the increase in surface active site. Furthermore, it was observed that photocatalytic and hydrophilicity properties of this sample were improved, as well.

Beschreibung: A theoretical analysis of the photorefractive sensitivity of Ti:PPLN ridge waveguides in comparison with conventional Ti:PPLN channel waveguides is presented. In particular, intensity-dependent photorefraction, effective indices, waveguide modes and power-dependent SHG in Ti:PPLN ridge and channel waveguides are modeled for a wide range of parameters. Results predict a much better damage resistance of Ti:PPLN waveguides with ridge geometry in comparison with conventional indiffused channels. This superiority of ridge waveguides is attributed to their higher effective refractive index contrast and more tightly confined guided modes. The theoretical predictions are supported by experimental results for second harmonic generation (SHG) at room temperature and for light-induced detuning characteristics of the phase-matching wavelength.

Beschreibung: In this paper, nanocrystalline ZnO film with porous structure was successfully prepared on alumina substrate by the technology of screen printing and the subsequent heat treatment. The fundamental characteristics of the as-prepared sample were examined through XRD, FE-SEM, EDX and PL spectra measurements. Meanwhile, photoelectric responses of it were tested under UV and white light irradiation, respectively. Different photocurrent curves were obtained. Under UV light, the photocurrent with comparatively high amplitude of each cycle could mostly recover upon the light off. While for white light, the photocurrent with low amplitude just partially recovered when the light was turned off. This phenomenon indicated that, after the white light off, a large number of free electrons still remained within the materials. To calculate the amount of the remained free electrons, three photocurrent parameters, which are related to the density of free electrons in ZnO, were defined for the first time. Furthermore, the explanations for the different photoelectric responses of ZnO based on the double Schottky barrier model were also proposed.

Beschreibung: The evolution of the microstructure and texture of Cu-2.7Be alloys during hot rolling was investigated and related to the mechanical properties of the resulting sheets. Hot cross-rolling is shown to be an effective way to refine the hard and brittle secondary-phase particles in Cu-2.7Be alloys. The Cu- and brass-type textures increase and decrease in prevalence, respectively, during the rolling process. The yield strengths along the first and second rolling directions, and 45° to the former, are all enhanced because the corresponding Schmid factors decrease as the sheets are rolled thinner. The ductility anisotropy of the as-rolled sheets is related to the distribution and shape of the secondary-phase particles therein.

Beschreibung: Novel In 2 O 3 /BiVO 4 heterojunction composite photocatalysts with tunable In 2 O 3 content were prepared using a mild hydrothermal method. The structure, composition, and optical properties of the In 2 O 3 /BiVO 4 composites were determined by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–Vis diffuse reflectance spectroscopy, Brunauer–Emmett–Teller surface analysis, and X-ray photoelectron spectroscopy. Furthermore, photocatalytic activities of the as-prepared composites were investigated by studying the degradation of methylene blue (MB) solutions under simulated visible light irradiation ( λ  〉 420 nm). It was found that the 50 % proportion of In 2 O 3 in the In 2 O 3 /BiVO 4 composite exhibited the highest photocatalytic performance, leading to 91 % decomposition of MB within 240 min of irradiation.

Beschreibung: Photovoltaic Cu 2 ZnSnS 4 (CZTS) thin films have been deposited on the glass substrate by a simple and low-cost spray pyrolysis technique without sulfurization treatment in a toxic atmosphere. The influence of the substrate temperatures on the structural, compositional, morphological, optical and electrical properties of the CZTS films was investigated. The formation of kesterite structure in the films was confirmed using X-ray diffraction measurements. The improved crystallinity of the CZTS with a (112) orientation was observed with increasing the substrate temperature. The band gap of all films was found to be in the range from 1.44 to 1.56 eV which is close to the ideal band gap for the highest theoretical conversion efficiency of solar cell. AFM analysis revealed a smooth, compact and crack-free morphology. The electrical studies showed that all these samples had a p-type conductivity, and the free hole density and mobility increased with increasing the substrate temperature.

Beschreibung: The various Co 2 MnSi films, from chemical ordered L 2 1 state to completely disordered amorphous state, were prepared on glass substrates with different deposition/annealing temperatures. The influence of deposition/annealing temperature on the crystallographic defects and atomic disorders, and further on the magnetic and transport properties of the Co 2 MnSi films were investigated in detail. The decrease in crystallinity leads to the structure disorder, spin disorder and further the reduction of magnetization as well as the increase of residual resistivity. The dominant source in anomalous Hall effect for the polycrystalline samples is the skew scattering, while the skew scattering coefficient a becomes larger with the increasing deposition temperature, due to the increase of skew scattering center introduced by the increasing structure disorder.

Beschreibung: The luminescence of a nitrogen-vacancy (NV) center in a nanodiamond (ND) is of great interest because of its features, especially in the field of nanophotonics. When an NV center in an ND is located in the vicinity of the surface, the emission is often disturbed by any surface defects, resulting in non-radiative recombination. In this work, we performed dressed photon–phonon (DPP) etching of the NDs, and found that the size of the NDs decreased, while the cathodoluminescence (CL) intensity increased. We assume that this increase in the CL intensity originates from the removal of the surface protrusions and/or defects by DPP etching.

Beschreibung: This paper has investigated the dynamic behavior of a cylindrically shaped DNA nanoparticle during its displacement on a rough substrate by an atomic force microscope. Due to the cylindrical geometry of the DNA nanoparticle, two multi-asperity models have been considered for the adhesion between nanoparticle and rough substrate. The two selected models for the contact between smooth and rough surfaces have been further developed for cylindrical geometries. One of these models is analytical and based on uniform asperities and the other one is based on random asperities. Also, in each of these models, the real area of contact between particle and rough substrate has been calculated based on the number of asperities in contact. Then, a 3D dynamic model for the manipulation of cylindrical nanoparticle on rough substrate has been developed and simulated. The maximum difference between the results obtained from the two multi-asperity models is 〈5 %, indicating a good agreement between the two models. The comparison of critical forces indicates that the critical force necessary for moving a particle is smaller for rough substrates than for smooth substrates and larger compared to the critical force obtained from the Rabinovich model, which is single-asperity model. Finally, the surface roughness parameters were estimated from the topographic images, and the manipulation process was simulated for these substrates by developing the relevant equations. The obtained results indicated that the critical force for a substrate with a higher root-mean-square roughness is smaller and particles can be moved easier on such a substrate.

Beschreibung: Electropulsing treatment is a practical method to arrest crack propagation. The microstructure characterization and research on the forming mechanism are difficult due to the small affected area (0.01–1 mm 2 ), high-temperature gradient (10 2  K/mm) and change rate (10 4 –10 7  K/s). In this paper, the 1045 steel plate with a preexisting crack subjected to high-voltage pulses was investigated. The surface morphologies and microstructure around the crack tip were observed using optical microscopy and scanning electron microscopy. Experimental results showed that the material around the tip melted, splashed and blunted under electropulsing treatment. The microstructure around the molten hole was divided into four distinct regions. An electro-thermal coupled model considering material ejection, cavity formation, current oscillation and temperature-dependent material properties was proposed to investigate the dynamic formation process of molten hole and gradient microstructure. The uneven temperature distribution, high cooling rate and insufficient carbon diffusion led to the formation of gradient microstructure.

Beschreibung: Nanostructured metallic backside reflectors (BSRs) are crucial for enhanced optical absorption in thin-film amorphous silicon solar cells. The structural fabrication based on rapid aluminum (Al) anodization has a potential for roll-to-roll processes, which are promising for low-cost and large-scale fabrication of BSRs. In this regard, the short fabrication time via appropriate choice of acid, acid concentration, temperature, and time-dependent voltage control is very important. In addition, we first demonstrate the trimming of structural height by using conventional Al anodization, so the best pore size of BSRs with the same structural height can be determined. According to integrated external quantum efficiency (IEQE) calculations, the nanostructured BSR with 430-nm pore size shows 51.6 % IEQE improvement compared with the value of the flat BSR. Moreover, it is interesting that the absorption spectra of a -Si:H on nanostructured Al BSRs with and without the 100-nm Ag coating are highly similar even if the optical properties of Al and Ag are different.

Beschreibung: Two-color laser-induced incandescence (LII) measurements are carried out in diffusion flames and at the exhaust of a homemade soot generator, both fueled with ethylene and methane. Two-color prompt LII signals, their ratio and the corresponding temperature have been analyzed as a function of laser fluence. In particular, the effect of fuel, soot load and gas/particle initial temperature on LII measurements have been investigated. LII spectral measurements have also been performed in all conditions for validation. The results suggest that the incandescence is sensitive to both optical and non-optical physical properties of the particles. Moreover, soot volume fraction measurements are dependent on the laser fluence used, indicating that the soot temperature influences the refractive index absorption function. Such issues can be overcome by working at high laser fluences, where the saturation curves are independent from the experimental conditions if the soot absorption function near soot sublimation threshold is known.

Beschreibung: The nature of charge transport mechanism in poly(3,4-ethylenedioxythiophene) nanofiber bundles has been studied as a function of temperature, magnetic field and AC electric field. High-resolution transmission electron micrographs show the formation of nanofibers with an average diameter of 14 nm. X-ray diffraction analysis depicts the enhancement of polymer chains ordering with increasing dopant concentration. Analysis of the temperature dependence of resistivity reveals a three-dimensional variable range hopping electrical conduction mechanism in the synthesized nanofibers system. A large positive magnetoresistance has been observed at low temperature, which shows a decreasing trend with increasing temperature as well as dopant concentration. The high value of positive magnetoresistance at low temperature has been explained by the wave function shrinkage model. The decrease in frequency exponent s with increasing temperature suggests that the AC conduction takes place through correlated barrier hopping mechanism.

Beschreibung: The Roman invasion introduces new alloys and metallurgical practices in Iberian Peninsula. The southwestern end of this region has many evidences of connections with the Roman World, but there are no studies about the manufacture and use of copper-based artefacts during this period. Therefore, a set of about 20 ornaments, tools and small attachments recovered at the Roman sites of Monte Molião and Cidade das Rosas was studied by an analytical approach combining micro-EDXRF, optical microscopy, SEM–EDS and Vickers microhardness testing. The artefact composition shows a good correlation with function, namely pure copper for nails and rivets, low-tin bronze (2–6 wt% Sn) for basic tools, high-tin bronze (14 wt% Sn) for fibulae and high-lead bronze (19 wt% Pb) for a decorated jug handle. The manufacture also depends on function because most artefacts were subjected to thermomechanical processing, except the ornaments that would not benefit from post-casting work. Brass and gunmetal were only present in the site with a later chronology. A metallurgy visibly ruled by economical, aesthetical and technological concerns reinforces the evidences about the total integration of Southwestern Iberian Peninsula in the Roman World, but further studies will be essential to determine the evolution of copper-based alloys in Lusitania under Roman influence.

Beschreibung: Rapid thermal annealing effects on the electrical, structural and surface morphological properties of a fabricated Ti/p-GaN Schottky diode (SD) have been investigated. The AFM results showed that the surface morphology of the Ti/p-GaN SD is reasonably smooth at different annealing temperatures. The estimated Schottky barrier height (SBH) of the as-deposited and 200 °C annealed Ti/p-GaN SDs is found to be 0.88 eV ( I – V )/1.02 eV ( C – V ) and 0.91 eV ( I – V )/1.11 eV ( C – V ). Results showed that the SBH increases to 0.98 eV ( I – V )/1.26 eV ( C – V ) upon annealing at 300 °C for 1 min in N 2 ambient. However, the SBH slightly decreases to 0.94 eV ( I – V )/1.17 eV ( C – V ) after annealing at 400 °C. Using Norde method and Cheung’s functions, the series resistance, SBH and ideality factor of the Ti/p-GaN SD are estimated and discussed at various annealing temperatures. Also, the difference between the SBHs calculated by I – V and C – V methods are discussed. Further, the interface state density N ss of the Ti/p-GaN SD is calculated and it is found to be decreases upon annealing at 300 °C and then slightly increases after annealing at 400 °C. Experimental electrical results are also correlated with the interfacial microstructure of the Ti/p-GaN SD. The SIMS and XRD results revealed that the increase or decrease in the SBHs of the Ti/p-GaN SD upon annealing could be attributed to the formation of Ti–N and Ga–Ti interfacial phases at the interface.

Beschreibung: Artificial intelligence models have the capacity to eliminate the need for expensive experimental investigation in various areas of manufacturing processes, including the material science. This study investigates the applicability of adaptive neuro-fuzzy inference system (ANFIS) approach for modeling the performance parameters of thermal expansion coefficient (TEC) of perovskite oxide for solid oxide fuel cell cathode. Oxides (Ln = La, Nd, Sm and M = Fe, Ni, Mn) have been prepared and characterized to study the influence of the different cations on TEC. Experimental results have shown TEC decreases favorably with substitution of Nd 3+ and Mn 3+ ions in the lattice. Structural parameters of compounds have been determined by X-ray diffraction, and field emission scanning electron microscopy has been used for the morphological study. Comparison results indicated that the ANFIS technique could be employed successfully in modeling thermal expansion coefficient of perovskite oxide for solid oxide fuel cell cathode, and considerable savings in terms of cost and time could be obtained by using ANFIS technique.

Beschreibung: The depth-to-width aspect ratio of pattern engineering by surface plasmons is limited for its field intensity exponential attenuation property. We here report a method to enhance patterns’ aspect ratio with a mask–photoresist–dielectric–metal four-layer metallic waveguide structure. The parameters, index and thickness, of the dielectric layer are discussed and analyzed to illustrate their affection to the patterns’ resolution and aspect ratio. A small thickness of dielectric with its index higher than photoresist will enhance the resolution and aspect ratio of pattern by these proposed structures. Numerical simulation results show that 40 nm half-pitch and 100 nm depth patterns could be performed by a chromium mask with period of 160 nm at the wavelength of 365 nm.

Beschreibung: The welding of transparent materials with ultrashort laser pulse at high repetition rates has attracted much attention due to its potential applications in fields such as optics, microfluidics, optofluidics and precision machinery. One demanding issue is the stable and reliable welding of different materials without the utilization of an intermediate layer or an optical contact. In this work, we maximized the size of the molten volume in order to generate a large pool of molten material which is able to fill an existing gap between the samples. To this end, we used bursts of ultrashort laser pulses with an individual pulse energy of up to \(10\,\upmu \hbox {J}\) . The laser-induced welding seams exhibit a base area with a size of up to \(450\,\upmu \hbox {m}\,\times 160\,\upmu \hbox {m}\) . Using these large modifications, we are able to overcome the requirement of an optical contact and weld even gaps with a height of about \(3\,\upmu \hbox {m}\) . Bulging of the sample surface and ejection of molten material in the gap between the two samples allow to bridge the gap and enable successful welding. We also determined the breaking strength of laser-welded fused silica samples without an optical contact by a three-point bending test. The determined value of up to 73 MPa is equivalent to 85 % of stability of the pristine bulk material.

Beschreibung: The welded joints of dissimilar materials have been widely used in automotive, ship and space industries. The joint quality is often evaluated by weld seam geometry, microstructures and mechanical properties. To obtain the desired weld seam geometry and improve the quality of welded joints, this paper proposes a process modeling and parameter optimization method to obtain the weld seam with minimum width and desired depth of penetration for laser butt welding of dissimilar materials. During the process, Taguchi experiments are conducted on the laser welding of the low carbon steel (Q235) and stainless steel (SUS301L-HT). The experimental results are used to develop the radial basis function neural network model, and the process parameters are optimized by genetic algorithm. The proposed method is validated by a confirmation experiment. Simultaneously, the microstructures and mechanical properties of the weld seam generated from optimal process parameters are further studied by optical microscopy and tensile strength test. Compared with the unoptimized weld seam, the welding defects are eliminated in the optimized weld seam and the mechanical properties are improved. The results show that the proposed method is effective and reliable for improving the quality of welded joints in practical production.

Beschreibung: Heating of conductive materials by electric current is used in many technological processes. Application of electric pulses to metallic glasses induces their fast crystallization, which is an interesting and complex phenomenon. In this work, crystallization of the Fe 83 B 17 amorphous alloy induced by pulses of electric current produced has been studied using X-ray diffraction and transmission electron microscopy. Ribbons of the alloy were directly subjected to single pulses of electric current 250 µs long formed by a capacitor discharge. As the value of \(\smallint I^{2} {\text{d}}t\) was increased from 0.33 to 2.00 A 2  s, different crystallization stages could be observed. The crystallization began through the formation of the nuclei of α-Fe. At high values of \(\smallint I^{2} {\text{d}}t\) , α-Fe and tetragonal and orthorhombic Fe 3 B and Fe 23 B 6 were detected in the crystallized ribbons with crystallites of about 50 nm. Thermal annealing of the ribbons at 600 °C for 2 min resulted in the formation of α-Fe and tetragonal Fe 3 B. It was concluded that pulses of electric current produced by a capacitor discharge induced transformation of the Fe 83 B 17 amorphous phase into metastable crystalline products.

Beschreibung: Iron dendritic micropines are synthesized by a hydrogen reduction, where the hematite dendritic micropines prepared by a hydrothermal method are used as starting materials. The as-obtained dendritic iron exhibits enhanced coercivity and remanent magnetization at room temperature and high complex permittivity at 2–18 GHz due to the peculiar shape anisotropy and good crystallinity. The negative imaginary permeability is observed at 14.5–18.0 GHz, suggesting it has a potential as a left-handed material. The paraffin-based composites containing 30 wt% dendritic irons show large permittivity resulting from the charge polarization and the conductivity and have a minimal reflection loss (RL) of −37.4 dB at 7.4 GHz when the thickness ( d ) is 2.0 mm. The RL values less than −20 dB are obtained in the frequency range of 5.5–12.9 GHz when d increases from 0.9 to 3.0 mm.