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  • Articles  (45,947)
  • American Institute of Physics (AIP)  (45,947)
  • Applied Physics Letters  (24,553)
  • Journal of Applied Physics  (21,394)
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  • Articles  (45,947)
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  • 1
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    Disentangling energetic and charge-carrier dynamic influences on the open-circuit voltage in bulk-heterojunction solar-cells (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-12-09
    Description: A combination of transient and static techniques has been applied to bulk-heterojunction solar-cells to gain insight into the influence of charge-carrier dynamics and of energy level shifts in the vicinity of the cathode on the open-circuit voltage. Devices with a different thermal-annealing history but with similar active layer-morphology were compared. P3HT:PC 60 BM bulk heterojunction solar-cells with a standard ITO/PEDOT:PSS/active-layer/Al were investigated. We show that the open-circuit voltage increase that occurs when a sample is annealed before or after cathode deposition is due roughly one third to a shift between the energetics of the photoactive blend adjacent to the cathode and that in the bulk of the photoactive layer and roughly two thirds to a significant increase in the charge-carrier lifetime for this type of solar-cell.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Band alignment of MAPb(I1–xBrx)3 thin films by vacuum deposition (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-12-09
    Description: In this work, the mixed bromide iodide lead perovskites CH 3 NH 3 Pb(I 1– x Br x ) 3 (0 ≤  x  ≤ 0.67) thin films were prepared by co-evaporation of CH 3 NH 3 I, PbI 2 , and PbBr 2 . The electronic properties of CH 3 NH 3 Pb(I 1– x Br x ) 3 thin films were investigated by X-ray and ultraviolet photoelectron spectroscopy in-situ . The results of core level binding energy show that there is no chemical shift of the C1s, N1s, Br3d5, and I3d5 when the Br composition changes, while there is an approximately linear chemical shift of Pb4f7 to higher binding energy as the Br composition increases. The density functional theory calculation reveals that there is more charge transfer from Pb to Br than I, which results in the chemical shift of Pb4f states. On the other hand, the valence band maximum increases as the Br composition increases, while the work function shows no obvious change, because the conduction band is dominated by Pb 6 p orbitals while the valence band is dominated by halide p orbitals. Our work demonstrates the adjustability of the energy level alignment of MAPb(I 1– x Br x ) 3 by the Br composition.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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  • 3
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    Structural properties of Co2TiSi films on GaAs(001) (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-12-09
    Description: Co 2 TiSi films were grown by molecular beam epitaxy on GaAs(001) and analyzed using reflection high-energy electron diffraction, and electron microscopy. In addition, X-ray diffraction was combined with lattice parameter calculations by density functional theory comparing the L 2 1 and B 2 structures and considering the influence of non-stoichiometry. Columnar growth is found and attributed to inhomogeneous epitaxial strain from non-random alloying. In films with thicknesses up to 13 nm, these columns may be the origin of perpendicular magnetization with the easy axis perpendicular to the sample surface. We found L 2 1 and B 2 ordered regions, however the [Co]/[Ti]-ratio is changing in dependence of the position in the film. The resulting columnar structure is leading to anisotropic B 2-ordering with the best order parallel to the axes of the columns.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
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  • 4
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    Pressure and temperature dependence of the laser-induced plasma plume dynamics (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-12-09
    Description: The influence of different background gases and substrate heating on the plasma plume dynamics from silver ablation is investigated by species selected time and space resolved imaging. The results provide a time-resolved understanding on how those process parameters affect the expansion: from a free expansion in vacuum with velocities exceeding 20 000 m/s to a very slow expansion in Ar at 1 × 10 −1 mbar with arrival velocities of 280 m/s. In addition, we observe a rebound of the ablated material on the substrate holder leading to a re-coating of the ablated target. At 1 × 10 −1 mbar, it seems that the expansion of the plasma plume displaces a considerable portion of the background gas and traps it against the frontal area of the substrate holder. This leads to a transient high local pressure just above the substrate. In the case of Ar, the rebound is enhanced due to inelastic scattering, whereas for an O 2 background, an area of high reactivity/emission in addition to the rebound is created. Imaging of selected species shows that the light emission in this area is mainly due to excited Ag and metal oxygen species. There is a clear influence of substrate heating on the plasma expansion due to the background gas density gradients, reducing the stopping ability of the background gas and already detectable 2 cm away from the substrate. Both rebound and excitation effects are reduced in intensity due to the substrate heating.
    Print ISSN: 0021-8979
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  • 5
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    Optical and electronic properties of conductive ternary nitrides with rare- or alkaline-earth elements (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-12-09
    Description: Conductive nitrides, such as TiN, are key engineering materials for electronics, photonics, and plasmonics; one of the essential issues for such applications is the ability of tuning the conduction electron density, the resistivity, and the electron scattering. While enhancing the conduction electron density and blueshifting the intraband absorption towards the UV were easily achieved previously, reducing the conduction electron density and redshifting the intraband absorption into the infrared are still an open issue. The latter is achieved in this work by alloying TiN by rare earth (RE = Sc, Y, La) or alkaline earth (AE = Mg, Ca) atoms in Ti substitutional positions. The produced Ti x RE 1−x N and Ti x AE 1−x N thin film samples were grown by a hybrid arc evaporation/sputtering process, and most of them are stable in the B1 cubic structure. Their optical properties were studied in an extensive spectral range by spectroscopic ellipsometry. The ellipsometric spectra were analyzed and quantified by the Drude-Lorentz model, which provided the conduction electron density, the electron mean free path, and the resistivity. The observed interband transitions are firmly assigned, and the optical and electrical properties of Ti x RE 1−x N and Ti x AE 1−x N are quantitatively correlated with their composition and crystal structure.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
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  • 6
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    Bragg superlattices formed in growing chemically vapor deposited diamond (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-12-09
    Description: A Bragg superlattice is created in the process of the diamond growth from a gaseous phase via the nanoscale boron modulation doping method. To maximize the Bragg superlattice reflection coefficient at the violet edge of the visible range, the thicknesses of either of two layers in its period were made close to the quarter-wavelength of radiation in this spectral domain. The vacuum wavelength dependence of the transition coefficient of electromagnetic radiation in the optical and near infrared range through this superlattice is measured. The most pronounced Bragg features are lying at the violet edge of the optical range, where the contrast of the diamond dielectric permittivity due to modulation doping is much smaller than in the red and infrared domain. Its accordance with simulation results based on secondary ion mass spectroscopy data on the thicknesses and boron atom concentrations for doped layers is demonstrated.
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    Electronic ISSN: 1089-7550
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  • 7
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    The stress statistics of the first pop-in or discrete plastic event in crystal plasticity (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-12-09
    Description: The stress at which the first discrete plastic event occurs is investigated using extreme value statistics. It is found that the average of this critical stress is inversely related to the deforming volume, via an exponentially truncated power-law. This is demonstrated for the first pop–in event observed in experimental nano-indentation data as a function of the indenter volume, and for the first discrete plastic event seen in a dislocation dynamics simulation. When the underlying master distribution of critical stresses is assumed to be a power-law, it becomes possible to extract the density of discrete plastic events available to the crystal, and to understand the exponential truncation as a break-down of the asymptotic Weibull limit.
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    Electronic ISSN: 1089-7550
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  • 8
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    Infrared laser ablation of polymeric nanocomposites: A study of surface structure and plume formation (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-12-09
    Description: The behavior of carbon nanotube composites subjected to laser pulse heating with a 1070 nm variable pulse duration laser has been studied. Previous work has shown that carbon nanotube composites form a protective network on the surface of a composite, which reduces heat input to the underlying polymer and slows mass loss. In this work, we have studied the interaction between the incident laser and the plume formed above the composite. We have correlated these interactions with features observed in the time-resolved mass loss data and confirmed them with observations using high-speed video of the laser irradiations. Beam interactions were studied as a function of laser irradiance and nanotube content. It is shown that beam-plume interactions occur for the carbon nanotube composites and that the interactions occur at shorter pulse durations for increased nanotube content and laser irradiance. When we eliminate beam-plume interaction through alteration of the sample orientation relative to the incident beam, we are able to elucidate the individual contributions of the carbon nanotube surface network and the plume to the observed decrease in mass loss after laser irradiation. We examine the plume content using microscopy and Raman spectroscopy and show that greater beam absorption occurs when there is a higher graphitic content in the plume.
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  • 9
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    Performance degradation of superlattice MOSFETs due to scattering in the contacts (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-12-09
    Description: Ideal, completely coherent quantum transport calculations had predicted that superlattice MOSFETs (SL-MOSFET) may offer steep subthreshold swing performance below 60 mV/dec to around 39 mV/dec. However, the high carrier density in the superlattice source suggests that scattering may significantly degrade the ideal device performance. Such effects of electron scattering and decoherence in the contacts of SL-MOSFETs are examined through a multi-scale quantum transport model developed in NEMO5. This model couples the NEGF-based quantum ballistic transport in the channel to a quantum mechanical density of states dominated reservoir, which is thermalized through strong scattering with local quasi-Fermi levels determined by drift-diffusion transport. The simulations show that scattering increases the electron transmission in the nominally forbidden minigap, therefore, degrading the subthreshold swing ( S.S. ) and the ON/OFF DC current ratio. This degradation varies with both the scattering rate and the length of the scattering dominated regions. Different SL-MOSFET designs are explored to mitigate the effects of such deleterious scattering. Specifically, shortening the spacer region between the superlattice and the channel from 3.5 nm to 0 nm improves the simulated S.S. from 51 mV/dec. to 40 mV/dec.
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  • 10
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    Cherenkov terahertz surface plasmon excitation by an electron beam over an ultrathin metal film (2016)
    American Institute of Physics (AIP)
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    Publication Date: 2016-12-09
    Description: The mechanism of Cherenkov excitation of terahertz (THz) surface plasma wave (SPW), by a relativistic electron beam propagating over an ultrathin metal film deposited on glass, is investigated. The SPW field falls off exponentially in vacuum as well as glass, while the surface plasmon resonant frequency is lowered by the reduction of film thickness. The SPW field causes density bunching of the beam leading to current modulation and generation of THz radiation via the Cherenkov interaction. The frequency of the THz decreases with the energy of the beam, whereas the growth rate increases.
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