Journal of Applied Physics
1089-7550
0021-8979
Mỹ
Cơ quản chủ quản: AIP PUBLISHING , American Institute of Physics
Lĩnh vực:
Physics and Astronomy (miscellaneous)
Phân tích ảnh hưởng
Thông tin về tạp chí
The Journal of Applied Physics (JAP) is an influential international journal publishing significant new experimental and theoretical results of applied physics research. Topics covered in JAP are diverse and reflect the most current applied physics research, including: Dielectrics, ferroelectrics, and multiferroics- Electrical discharges, plasmas, and plasma-surface interactions- Emerging, interdisciplinary, and other fields of applied physics- Magnetism, spintronics, and superconductivity- Organic-Inorganic systems, including organic electronics- Photonics, plasmonics, photovoltaics, lasers, optical materials, and phenomena- Physics of devices and sensors- Physics of materials, including electrical, thermal, mechanical and other properties- Physics of matter under extreme conditions- Physics of nanoscale and low-dimensional systems, including atomic and quantum phenomena- Physics of semiconductors- Soft matter, fluids, and biophysics- Thin films, interfaces, and surfaces
Các bài báo tiêu biểu
Raman and optical characterization of multilayer turbostratic graphene grown via chemical vapor deposition We synthesize large-area graphene via atmospheic-pressure (AP) chemical vapor deposition (CVD) on copper, and transfer to SiO2 wafers. In contrast to low-pressure CVD on copper, optical contrast and atomic force microscopy measurements show AP-CVD graphene contains significant multi-layer areas. Raman spectroscopy always shows a single Lorentzian 2D peak, however systematic differences are observed in the 2D peak energy, width, and intensity for single- and multi-layer regions. We conclude that graphene multi-layers grown by AP-CVD on Cu are rotationally disordered.
Tập 110 Số 1 - 2011
Low-Frequency Negative Resistance in Thin Anodic Oxide Films Negative resistance and large current densities have been observed in the direct-current—voltage characteristics of five metal-oxide-metal sandwiches prepared from evaporated metal films. The systems studied and their voltages for maximum current are: Al-SiO-Au, 3.1 V; Al-Al2O3-Au, 2.9 V; Ta-Ta2O5-Au, 2.2 V; Zr-ZrO2-Au, 2.1 V; and Ti-TiO2-Au, 1.7 V. For aluminum oxide, which has been most extensively studied, the voltage for maximum current is independent of film thickness for films between 150 and 1000 Å thick; the phenomenon is not field dependent. Peak-to-valley ratios of 30:1 and current densities of 10 A/cm2 are typical. Maximum current densities at peak voltage are 25 A/cm2; minimum current densities are 0.01 A/cm2. Switching time from peak current to valley current is <0.5 μsec but negative resistance is not found for 60-cycle voltages. Establishment of the dc characteristics and dependence on temperature and atmosphere are described. Electron emission from aluminum oxide sandwiches can occur at 2.5 V. Space-charge-limited currents in the insulator provide a possible mechanism for the current-voltage curves and large currents below the voltage for maximum current through the oxide films. The mechanism responsible for negative resistance is uncertain.
Tập 33 Số 9 - Trang 2669-2682 - 1962
The dc voltage dependence of semiconductor grain-boundary resistance A model is developed to describe the potential barriers which often occur at grain boundaries in polycrystalline semiconductors. The resistance of such materials is determined by thermionic emission over these barriers. The dc grain-boundary current density as a function of applied voltage is calculated using several forms for the density of defect states within the boundary region. In all cases, the currents are Ohmic at low voltages; they can attain a quasisaturated level at intermediate voltages, and they display a sharp bias dependence at high voltages. The details of the intermediate and high-voltage characteristics are found to depend strongly on the grain-doping density and on the density and energy distribution of defect states at the grain boundary. Contrary to previous assertions, we find that the large current-voltage nonlinearities found in real materials are most likely associated with defect-state densities that decrease above the zero-bias Fermi level. The results of the model are compared with previous experimental data on Si and Ge bicrystals and on polycrystalline ZnO varistors. Finally, a detailed method for determining the energy density of grain-boundary defect states from current-voltage data is developed.
Tập 50 Số 5 - Trang 3414-3422 - 1979
Instability of relativistic electron-beam–dielectric system as a mechanism for microwave generation The dispersion relation of relativistic rectilinear electron beam propagating along a guide magnetic field in a dielectric is investigated by cold fluid model. In such a system, due to anomalous Doppler effect, the instability occurs when the electron velocity exceeds the wave phase velocity. The growth rate and spatial growth rate are studied analytically and the nonlinear saturated efficiency is given analytically for the first time. Numerical results show that the saturated efficiency approaches about 10%–30%. The distinctive interaction mechanism is promising for the design of a new kind of compact high-power microwave generation devices.
Tập 102 Số 10 - 2007
Controlling fluorescence lifetime of rare-earth element in amorphous inorganic solids via very small compositional adjustments Fluorescence lifetime of hypersensitive 4f-4f transitions of rare-earth elements embedded in amorphous inorganic solids can be dramatically modified by compositional adjustment of the hosts tantamount to not more than 1 mol % without any elaborated thermal treatments. It is possible to modify a spontaneous emission rate of Dy3+:(F11∕26,H9∕26)→H15∕26 transition in chalcogenide Ge–As–S glasses through selective addition of low levels of Ga and CsBr. Along with the change of the spontaneous emission rate, multiphonon relaxation rate involved in the (F11∕26,H9∕26) state also significantly varies upon the minute compositional adjustment. The combination of these effects results in the measured lifetime of the fluorescing (F11∕26,H9∕26) level being greatly enhanced. Such behaviors are attributed to the hypersensitive nature associated with the H15∕26↔F11∕26 transition and preferential coordination of bromine in the nearest-neighboring shell of the Dy3+ ions, which is formed spontaneously during the vitrification process of the host materials. These experimental observations show the most extreme dependence of the fluorescence lifetime on small compositional changes reported compared to any other noncrystalline solid-state dielectric. As such coutilization of many hypersensitive transitions of rare-earth elements and those host materials used in this study may present a unique opportunity to control absorption and emission properties, especially fluorescence lifetimes, through a minute compositional adjustment.
Tập 98 Số 2 - 2005
Midinfrared emission properties of Pr3+-doped chalcogenide glasses at cryogenic temperature Low-temperature midinfrared emission properties of Pr3+-doped Ge30Ga2As6S62 and Ge28Ga5As12Se55 glasses (at. %) were investigated. Emissions centered at 3400 and 4700 nm were clearly observed from sulfide and selenide glasses, respectively, when the specimens were cooled to 20 K. The measured lifetime of the G41 level in sulfide glass increased from 320 μs at room temperature to 400 μs at 20 K. The intensity and quantum efficiency of the emission from the Pr3+:(3F3, 3F4) level in selenide glass also increased as the temperature decreased to 120 K. The enhancement resulted from a decrease in nonradiative multiphonon relaxation at low temperatures. The temperature dependence of the multiphonon relaxation rates indicated that the asymmetrical stretching vibration of GeS4 tetrahedra (375 cm−1) is primarily responsible for the multiphonon relaxation process in sulfide glass.
Tập 93 Số 11 - Trang 8970-8974 - 2003
Comparative study of energy transfers from Er3+ to Ce3+ in tellurite and sulfide glasses under 980 nm excitation We have demonstrated that the population feeding from the I11/24 level to the 1.5 μm fluorescence emitting I13/24 level of Er3+ ions in low phonon energy glass hosts can be enhanced by codoping with Ce3+ under optical pumping at 980 nm. The nonradiative energy transfer Er3+: 4I11/2; Ce3+: 2F5/2→Er3+: 4I13/2; Ce3+: 2F7/2, occurs in the form of phonon-assisted energy transfer, and therefore the feeding rates are faster in the tellurite glasses, which have a comparatively higher phonon energy than in the sulfide glasses. The cross-relaxation process for I13/24: 4I13/2→4I15/2: 4I9/2, which lowers the population density of the I13/24 manifold and causes a deleterious effect in the 1.5 μm fluorescence intensity, is more severe in the sulfide glasses. Population feeding rate from the I11/24 to the I13/24 level is significantly enhanced by way of cerium codoping into tellurite glasses, which promises an efficient 980 nm pumped broadband Er3+-doped fiber amplifier.
Tập 88 Số 7 - Trang 3832-3839 - 2000
Particle Size Dependence of Coercivity and Remanence of Single-Domain Particles The coercive force and remanence of essentially spherical iron and iron-cobalt alloy particles with diameters from 20 to 3000 Å have been measured at 4°, 76°, and 207°K and compared to the theoretically predicted behavior. The remanence shows a broad, plateau-like maximum while the coercive force has a rather sharp maximum. The maximum of the coercive force occurs at a much larger particle diameter than the maximum of the remanence. It is shown that these essential characteristics follow from the theory. Deviations from theory are seen in the smaller size range and can be accounted for by the distribution of particle sizes. A general treatment of the coercive force of mixtures of thermally stable, high coercive force particles with superparamagnetic and multidomain particles is given.
Tập 34 Số 3 - Trang 656-658 - 1963
341 nm emission from hydride vapor-phase epitaxy ultraviolet light-emitting diodes Hydride vapor-phase epitaxy (HVPE) was used to grow aluminum gallium nitride-based p–n diode structures on sapphire (0001) substrates. In the diode structure, an n-type AlGaN photon-emitting layer was sandwiched between n-type and p-type AlGaN cladding layers that contained higher AlN concentrations. These diode structures were processed and subsequently packaged into transistor outline cans. The light-emitting diodes (LEDs) were characterized using a state-of-the-art spectroradiometer. LED spectral emission occurred at a peak wavelength of 341 nm with a typical full width at half-maximum of approximately 14 nm. Pulsed injection currents of 110 mA resulted in greater than 2 mW of optical output power at a wavelength of 341 nm. This HVPE-grown LED’s pulsed optical power output level is comparable to reported results on similar sized metalorganic chemical vapor deposition grown ultraviolet LEDs with emission wavelengths near 340 nm.
Tập 95 Số 12 - Trang 8247-8251 - 2004
Effect of anionic surfactant concentration on the variable range hopping conduction in polypyrrole nanoparticles The mechanism of charge transport in polypyrrole (PPy) nanoparticles prepared with different concentrations (5 to 30 mM) of anionic surfactant (sodium dodecyl sulfate) is reported. Transmission electron microscopy technique confirms the formation of PPy nanoparticles of sizes ∼52 to 28 nm under surfactant directed approach. The room temperature electrical conductivity of the prepared nanoparticles found to increase from 3 to 22 S/cm with surfactant concentration. The temperature dependent activation energy rules out the possibility of band conduction mechanism in the prepared PPy nanoparticles and thus the synthesized nanoparticles are analyzed under variable range hopping (VRH) model for conduction mechanism. The PPy nanoparticles, reduced with liquid ammonia, hold 3D VRH conduction mechanism for the charge transport. However, in the doped samples, some deviation from 3D VRH conduction behavior at higher temperatures (>150 K) has been observed. This may be attributed to the presence of anionic surfactant in these samples. The doping of anionic surfactant causes rise in conducting islands, which may lead to the change in the shape/distribution of density of states governed by Gaussian or exponential type near Fermi level.
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