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Journal of Applied Physics

Issue 2 • Date Jan 2003

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Displaying Results 1 - 25 of 86
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Nanoscale thermal transport

    Page(s): 793 - 818
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    Rapid progress in the synthesis and processing of materials with structure on nanometer length scales has created a demand for greater scientific understanding of thermal transport in nanoscale devices, individual nanostructures, and nanostructured materials. This review emphasizes developments in experiment, theory, and computation that have occurred in the past ten years and summarizes the present status of the field. Interfaces between materials become increasingly important on small length scales. The thermal conductance of many solid–solid interfaces have been studied experimentally but the range of observed interface properties is much smaller than predicted by simple theory. Classical molecular dynamics simulations are emerging as a powerful tool for calculations of thermal conductance and phonon scattering, and may provide for a lively interplay of experiment and theory in the near term. Fundamental issues remain concerning the correct definitions of temperature in nonequilibrium nanoscale systems. Modern Si microelectronics are now firmly in the nanoscale regime—experiments have demonstrated that the close proximity of interfaces and the extremely small volume of heat dissipation strongly modifies thermal transport, thereby aggravating problems of thermal management. Microelectronic devices are too large to yield to atomic-level simulation in the foreseeable future and, therefore, calculations of thermal transport must rely on solutions of the Boltzmann transport equation; microscopic phonon scattering rates needed for predictive models are, even for Si, poorly known. Low-dimensional nanostructures, such as carbon nanotubes, are predicted to have novel transport properties; the first quantitative experiments of the thermal conductivity of nanotubes have recently been achieved using microfabricated measurement systems. Nanoscale porosity decreases the permittivity of amorphous dielectrics but porosity also strongly decreases the thermal condu- ctivity. The promise of improved thermoelectric materials and problems of thermal management of optoelectronic devices have stimulated extensive studies of semiconductor superlattices; agreement between experiment and theory is generally poor. Advances in measurement methods, e.g., the 3ω method, time-domain thermoreflectance, sources of coherent phonons, microfabricated test structures, and the scanning thermal microscope, are enabling new capabilities for nanoscale thermal metrology. © 2003 American Institute of Physics. View full abstract»

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  • Design and evaluation of omnidirectional one-dimensional photonic crystals

    Page(s): 819 - 830
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    We have theoretically and experimentally studied a wide range of realistic fabrication parameters for the formation of omnidirectional photonic band gaps (PBGs) in one-dimensional photonic crystals (1D PCs). Photonic band structures in 1D PCs have been analyzed for the cases with and without a defect layer. It is shown that a defect state in the defect-mode PBG behaves like an electronic impurity level in the gap with a change in thickness (i.e., optical path) of the defect layer. Three types of 1D PC structures (Te/polystyrene, Si/SiO2, and ZnS/SiO2), which are designed for applications in the infrared region (especially for the wavelength of 1.55 μm) and in the visible region, are proposed and demonstrated their high reflectance (R) properties experimentally. For example, a six-pair Si/SiO2 1D PC fabricated with a structure parameter (period=388.5 nm, filling factor=0.406) exhibits a wide range omni-PBGs in the wavelength range of 1310–1742 nm. The measured R spectra are in very good agreement with calculated results. In particular, the R spectra of a ZnS/SiO2 1D PC in the wavelength range of 190–800 nm are almost the same as those calculated using complex refractive indices. We also propose conditions to obtain omni-PBGs and band structures for a high refractive-index ambient medium (n). © 2003 American Institute of Physics. View full abstract»

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  • Characteristics of single defect laser modes in a two-dimensional square lattice photonic crystal slab

    Page(s): 831 - 837
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    Square lattice photonic crystal single defect nanocavity structures are formed in free-standing slab InGaAsP materials emitting near 1.55 μm. Laser operations are achieved from two types of resonant modes, a degenerate dipole mode and a nondegenerate whispering-gallery-like mode. Each laser mode is identified by the measurement of mode shapes, quality factors, and polarization. The threshold absorbed pump power is estimated to be less than 0.2 mW for the whispering gallery mode. It is found, by rate equation analyses, that nonradiative surface recombination, which takes ≫60% of carrier recombination near threshold, is one of the main limiting factors for the low-threshold operation of photonic crystal single defect lasers. © 2003 American Institute of Physics. View full abstract»

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  • Influence of the thickness and doping of the emission layer on the performance of organic light-emitting diodes with PiN structure

    Page(s): 838 - 844
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    We have studied the behavior of various intrinsic emission zones on the characteristics of organic light-emitting diodes with a p-doped hole-transport layer and an n-doped electron-transport layer based on our previous work [J. S. Huang, M. Pfeiffer, A. Werner, J. Blochwitz, K. Leo, and S. Liu, Appl. Phys. Lett. 80, 139 (2002)]. This configuration is referred to as a PiN structure. Because the p- and n-doped regions occupy nearly 80% of the total thickness in our PiN device, the intrinsic region becomes a narrow layer between two doped regions. This intrinsic region includes the region where the radiative recombination occurs. Thus, the nature of this layer plays an important role in determining the actual device performance. Employing 8-tris-hydroxyquinoline aluminum as an emitter, we investigated the influence of the thickness of the emitter layer on the performance of the device. The optimum thickness of the emitter layer is found to be 20 nm. Combining the fluorescence dye doping method, we have optimized the PiN structure device. Two emitter systems have been used: Alq3 doped with two highly fluorescent laser dyes, Quinacridone or Coumarin 6, respectively. We have demonstrated the influence of the thickness and the doping of the emission zone on the characteristics of a doped emitter device with PiN structure, and obtained higher-efficiency PiN structure devices. The different properties of PiN devices corresponding to two different emitter dopants with different trapping effect are also discussed. © 2003 American Institute of Physics. View full abstract»

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  • Effect of finite relaxation time on modeling neutral transport in hydrogen plasma

    Page(s): 845 - 850
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    In low-temperature hydrogen plasma, the effect of neutral transport on the relative population of excited-level neutrals has been investigated. In particular, the validity of the quasi-steady-state approximation of collisional radiative model for a neutral transport simulation of detached divertor plasma is discussed. The relaxation times of the population density are compared with the residence time in detached plasma by solving the time-dependent zero-dimensional rate equations. It is shown that the relaxation times of the population density are comparable with the residence time (10-6–10-5s) for vibrationally excited hydrogen molecules, which means that the transport of vibrationally excited molecules strongly affects the spatial distributions of their densities and reaction rates for ion conversion and dissociative attachment. The one-dimensional Monte Carlo calculation results support these transport effects. It is important to follow the traces of each vibrationally excited molecule separately. © 2003 American Institute of Physics. View full abstract»

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  • High-current capillary discharge with prepulse ablative plasma

    Page(s): 851 - 854
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    Generation of axisymmetric stable, long plasma channels with temperatures of 8 eV and electron densities ∼1019cm-3 by a high-current evaporating-wall capillary discharge with prepulse ablative plasma is reported. Results of spectroscopic measurements of the temperature and electron density of plasma produced in a polyethylene capillary are presented. The discharge provides a convenient source of dense highly ionized plasmas for laser-plasma interaction studies. © 2003 American Institute of Physics. View full abstract»

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  • Nanoscale analysis on interfacial reactions in Al–Si–Cu alloys and Ti underlayer films

    Page(s): 855 - 858
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    Solid-phase reactions at the interface between sputtered Al–Si–Cu alloys and Ti films were investigated at the atomic scale by high-resolution transmission electron microscopy and energy dispersive x-ray spectroscopy (EDS) coupled with a field-emission (scanning) transmission electron microscope. The analysis results showed that the interface is composed of an amorphous-like Ti–Si layer, an intermediate-crystalline layer, and a Si-dissolved TiAl3 layer containing dissolved Si TiAl3 with a crystallographic relationship with the Al film. The nanometer-scaled interlayers effectively play a role as a barrier suppressing the interdiffusion reaction of Al and Ti during annealing treatment. Further, the quantitative composition of the interlayers was revealed by the analysis of the intensity profiles obtained from EDS elemental maps. © 2003 American Institute of Physics. View full abstract»

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  • Pulsed laser deposition of diamondlike carbon films on polycarbonate

    Page(s): 859 - 865
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    Diamondlike carbon films have been deposited on polycarbonate by pulsed laser deposition technique by irradiating highly oriented pyrolytic graphite with high-energy excimer laser pulses (248 nm wavelength, 20 ns duration, and up to 37 J/cm2 energy density). Irradiations were performed in different atmospheres: (1) moderate vacuum (10-2Pa), (2) nitrogen atmosphere (1 Pa), and (3) argon atmosphere (1 Pa). The structure of the deposited films was analyzed with Raman spectroscopy. In vacuum-deposited films, a transition from mainly disordered graphitic carbon to up to 80% ta-C occurs above a laser energy density threshold of 7 J/cm2. No such transition was observed in films deposited in nitrogen up to energy densities as high as 33 J/cm2. In argon atmosphere the transition is only observed at high-laser energy density, ≈23 J/cm2. The results are discussed in terms of combined ballistic and chemical effects affecting both plume dynamics and bonding configuration of the growing film. The Fourier transform infrared spectroscopy showed that films deposited in nitrogen atmosphere contain nitrogen and hydrogen, thus becoming unstable when exposed to air. The hardness of ta-C coated polycarbonate, as measured by nanoindentation technique, is about 8 GPa, while when disordered graphitic carbon was deposited on the substrates hardness does not exceed 5 GPa. Measurement of the internal stress in the deposited films suggests that atomic relaxation occurs for laser-pulse energies exceeding 10 J/cm2, with residual stress values of the order of 1 GPa in films deposited in vacuum. In these conditions, given the strong interfacial chemical bonds, the adhesion strength is very high. In films deposited in nitrogen atmosphere the internal stress is almost constant for pulse laser energy up to 20 J/cm2 while it slowly increas- es at higher energies. © 2003 American Institute of Physics. View full abstract»

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  • Ni/Si solid phase reaction studied by temperature-dependent current-voltage technique

    Page(s): 866 - 870
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    The temperature-dependent current–voltage (I–V–T) technique has been used to study the Ni/Si solid phase reaction by measuring the Schottky barrier height (SBH) inhomogeneity of Ni-silicide/Si Schottky diodes. The experimental results show the strong dependence of SBH inhomogeneity on the Ni/Si solid phase reaction. The SBH distribution of the diodes annealed at 500 and 600 °C can be described by a single-Gaussian function and the diode annealed at 500 °C is found to have the best homogeneity and the smallest leakage current. The SBH distribution of the diodes annealed at 400, 700, and 800 °C can be described by a double-Gaussian function in which the mean value of the second Gaussian function is substantially smaller than that of the dominant Gaussian function. The variation of SBH inhomogeneity, an interface property, is related to the phase evolution process in the Ni/Si solid phase reaction, and verified by reverse I–V measurements. Our results indicate that the I–V–T technique may be developed as a wafer-level testing tool to monitor the silicidation process in the complementary metal–oxide–semiconductor device fabrication. © 2003 American Institute of Physics. View full abstract»

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  • Vacancy and interstitial depth profiles in ion-implanted silicon

    Page(s): 871 - 877
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    An experimental method of studying shifts between concentration-versus-depth profiles of vacancy- and interstitial-type defects in ion-implanted silicon is demonstrated. The concept is based on deep level transient spectroscopy measurements utilizing the filling pulse variation technique. The vacancy profile, represented by the vacancy–oxygen center, and the interstitial profile, represented by the interstitial carbon–substitutional carbon pair, are obtained at the same sample temperature by varying the duration of the filling pulse. The effect of the capture in the Debye tail has been extensively studied and taken into account. Thus, the two profiles can be recorded with a high relative depth resolution. Using low doses, point defects have been introduced in lightly doped float zone n-type silicon by implantation with 6.8 MeV boron ions and 680 keV and 1.3 MeV protons at room temperature. The effect of the angle of ion incidence has also been investigated. For all implantation conditions the peak of the interstitial profile is displaced towards larger depths compared to that of the vacancy profile. The amplitude of this displacement increases as the width of the initial point defect distribution increases. This behavior is explained by a simple model where the preferential forward momentum of recoiling silicon atoms and the highly efficient direct recombination of primary point defects are taken into account. © 2003 American Institute of Physics. View full abstract»

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  • Surface modification of graphitic foam

    Page(s): 878 - 882
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    This article discusses surface-related issues and possible modification approaches in high-porosity graphitic foam. The microcellular solid is made of graphitic carbon walls, ligaments, and beams supporting a network of interconnected pores. This makes the exposed surface area very high and its understanding a necessity for most applications. Graphitic planes are seen to be stacked at various orientations with respect to exposed surfaces. Therefore, a simplified analytical model that assumes “random” graphitic planes forming a three-dimensional array of tetrahedral cells may be an appropriate approximation. The influence of oxidizing chemicals such as nitric acid and hydrogen peroxide on surface properties has been studied using electron microscopy, photoelectron spectroscopy, and water absorption tests. Bulk properties such as density measurements and mechanical tests have been performed in parallel. It is seen that exposure to nitric acid results in an increase in oxygen-containing functional groups on the surface, which may lead to increased infiltration of polar matrix fluids such as water and epoxy resins. This possibility is further supported by water absorption studies that show increased water infiltration in foam after nitric acid treatment. Electron microscopy and density studies indicate that some surface etching occurs with concentrated nitric acid exposure, but not significant enough to decrease density. Strength of the stand-alone foam is reduced for concentrated nitric acid treatment, but the elastic modulus is unaffected. The scientific significance of these results in terms of future surface modification of microcellular solids has been discussed. © 2003 American Institute of Physics. View full abstract»

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  • Electromigration model for the prediction of lifetime based on the failure unit statistics in aluminum metallization

    Page(s): 883 - 892
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    A failure model for electromigration based on the “failure unit model” was presented for the prediction of lifetime in metal lines.The failure unit model, which consists of failure units in parallel and series, can predict both the median time to failure (MTTF) and the deviation in the time to failure (DTTF) in Al metal lines. The model can describe them only qualitatively. In our model, both the probability function of the failure unit in single grain segments and polygrain segments are considered instead of in polygrain segments alone. Based on our model, we calculated MTTF, DTTF, and activation energy for different median grain sizes, grain size distributions, linewidths, line lengths, current densities, and temperatures. Comparisons between our results and published experimental data showed good agreements and our model could explain the previously unexplained phenomena. Our advanced failure unit model might be further applied to other electromigration characteristics of metal lines. © 2003 American Institute of Physics. View full abstract»

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  • Evolution of normal stress and surface roughness in buckled thin films

    Page(s): 893 - 897
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    In this work we investigate buckling of compressed elastic thin films, which are bonded onto a viscous layer of finite thickness. It is found that the normal stress exerted by the viscous layer on the elastic film evolves with time showing a minimum at early buckling stages, while it increases at later stages. The normal stress also shows a minimum as a function of applied compressive stress, which depends strongly on the viscosity of the underlying layer and strain values. Furthermore, with decreasing viscosity the film roughness amplitude also shows a minimum at early buckling stages. The effect of the viscosity becomes more pronounced with increasing strain in the film. Finally, decreasing elastic film thickness and/or increasing viscous layer thickness also enhance buckling roughness. © 2003 American Institute of Physics. View full abstract»

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  • Self-affine roughness effects on the contact area between elastic bodies

    Page(s): 898 - 902
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    We have calculated the real contact area between elastic bodies with self-affine rough surfaces, which are described in terms of analytical correlation models in Fourier space. It is found that the roughness has a strong influence on the real contact area A(λ) at lateral length scales λ which are comparable with the in-plane roughness correlation length ξ, and for significant applied loads σo beyond the linear regime (or A∝σo). The effect of the roughness exponent H can be rather complex, depending on the relative magnitude of the roughness correlation length ξ with respect to the lateral length scale λ where the contact area is considered. Finally, we also show that descriptions of the influence of the roughness that is only based on power law approximations of the self-affine roughness spectrum are rather insufficient, especially for large roughness exponents H (≫0.5). © 2003 American Institute of Physics. View full abstract»

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  • Formation of Au0.6Ge0.4 alloy induced by Au-ion irradiation of Au/Ge bilayer

    Page(s): 903 - 906
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    We report on the formation of a-axis oriented Au0.6Ge0.4 alloy on a Si(100) substrate on 120 MeV Au-ion irradiation of a Au/Ge bilayer and subsequent vacuum annealing at 360 °C. Irradiation-induced changes occurring across the Au/Ge interface were studied using Rutherford backscattering spectrometry. Phase identification was done by x-ray diffraction and the surface morphology of the samples was studied by scanning electron microscopy. Formation of oriented Au0.6Ge0.4 alloy was confirmed by transmission electron microscopy and discussed on the basis of swift heavy ion induced effects followed by thermal annealing. © 2003 American Institute of Physics. View full abstract»

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  • Self-diffusion of boron in TiB2

    Page(s): 907 - 911
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    Self-diffusion studies of boron in polycrystalline TiB2 were carried out as a function of temperature, using a specially designed experiment with stable 10B tracers, 11B-enriched TiB2 samples, and secondary ion mass spectrometry for depth profiling. The diffusivities were extracted from the isotope depth profiles in the range between 950 and 1600 °C. They obey an Arrhenius behavior with an activation enthalpy of about ΔH=2.2 eV and a preexponential factor of D0=4×10-12m2/s. Interpolation of the diffusivities to the melting point of 3225 °C reveals a very low value of about D(Tm)≈10-15m2/s, which reflects the covalent bonds present in the material. A possible explanation for the low values obtained for D0 and ΔH is the assumption of a diffusion mechanism via vacancies, where in addition to thermal vacancies a substantial concentration of structural vacancies are present. The possible influence of grain boundaries and of the anisotropic crystal structure on the results is discussed together with crystallographic diffusion paths. © 2003 American Institute of Physics. View full abstract»

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  • Thermal stability and electron irradiation effect on Zr-based amorphous alloys

    Page(s): 912 - 918
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    Specimens of Zr66.7Cu33.3, Zr65.0Al7.5Cu27.5, and Zr65.0Al7.5Ni10.0Cu17.5 amorphous alloys with different thermal stability were irradiated by high energy electrons at an accelerated voltage of 2000 and 1000 kV. Electron irradiation was performed at 298 and 103 K. Crystallization of three amorphous alloys was accelerated by this irradiation and nanocrystalline structures were obtained. The critical total dose required for crystallization of the amorphous phase by electron irradiation depends strongly on the irradiation temperature and stability of this amorphous phase. The phase stability and crystallization behavior of the amorphous phase are discussed based on the electron irradiation effect. © 2003 American Institute of Physics. View full abstract»

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  • Contact angle measurements for adhesion energy evaluation of silver and copper films on parylene-n and SiO2 substrates

    Page(s): 919 - 923
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    Copper and silver films are being considered for future multilevel interconnect systems. The reduction of feature size has also demanded the use of different low-dielectric materials (e.g., parylenes) in place of conventional silicon dioxide based layers. Adhesion of these materials with each other is a major hurdle in the reliable and durable performance of the devices. Contact angle measurements are used to measure adhesion energies of Cu and Ag layers on substrates of either SiO2 and Pa–n. Qualitative tape-test analysis indicates improved adhesion of these films with anneal and plasma treatment. Surface energy increase of parylene–n using oxygen plasma treatment is demonstrated using sessile water-drop method. The increase in adhesion for the Ag/Pa–n system is attributed to increased roughness and presence of carbonyl groups on the surface. The contact angle measurements are corrected to compensate for the effect of roughness. The adhesion energy for Ag/Pa–n system increases from 0.33 to 1.28 N/m with plasma treatment. Higher-surface energies of copper at room temperature attribute to higher-copper adhesion energy when compared to that of silver. © 2003 American Institute of Physics. View full abstract»

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  • Ultrathin Ag films on H:Si(111)-1×1 surfaces deposited at low temperatures

    Page(s): 924 - 929
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    The growth, structure, and electronic properties of thin Ag films on H-terminated Si(111) surfaces were investigated with Auger electron and photoelectron spectroscopy (and atomic force and secondary electron microscopy). The films were either evaporated at room temperature (RT) or deposited at low temperature (LT) and subsequently annealed to RT in the thickness range between 1 and 50 monolayers (0.2–12 nm). The LT preparation leads to large Ag islands on a wetting monolayer which form a continuous Ag film above a critical thickness of 30 monolayers. Ultraviolet photoelectron spectra and work function measurements reveal a (111) surface orientation of the Ag islands. In constrast, RT deposition results in Stranski-Krastanov growth of smaller and irregularly shaped islands which do not form a continuous layer even up to film thicknesses of 45 monolayers. © 2003 American Institute of Physics. View full abstract»

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  • Effects of annealing ambient on the formation of compensation defects in InP

    Page(s): 930 - 932
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    Positron annihilation lifetime (PAL) and photoinduced current transient spectroscopies (PICTS) have been employed to study the formation of compensation defects in undoped InP under different annealing processes with pure phosphorus (PP) ambience and iron phosphide (IP) ambience, respectively. The different annealing ambiences convert the as-grown n-type undoped InP into two types of semi-insulating (SI) states. The positron average lifetimes of as-grown InP, PP SI-InP, and IP SI-InP are found to be 246, 251, and 243 ps, respectively, which are all longer than the bulk lifetime of 240 ps, indicating the existence of vacancy-type positron-trapping defects. For as-grown InP, VInH4 complexes are the dominant defects. They dissociate into VInHn(0≤n≤3) acceptor vacancies under PP ambience annealing, compensating the residual shallow donors and turning the material semi-insulating. In forming IP SI-InP, diffusion of iron into VIn complexes under IP ambience annealing produces the substitutional compensation defect FeIn, causing a shorter positron average lifetime. The PICTS measurements show that a group of vacancy-type defects has been suppressed by iron diffusion during the annealing process, which is in good agreement with the PAL results. © 2003 American Institute of Physics. View full abstract»

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  • Infrared and Raman spectroscopy of [Pb(Zn1/3Nb2/3)O3]0.92–[PbTiO3]0.08 and [Pb(Mg1/3Nb2/3)O3]0.71–[PbTiO3]0.29 single crystals

    Page(s): 933 - 939
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    Far-infrared reflectivity spectra of [Pb(Zn1/3Nb2/3)O3]0.92–[PbTiO3]0.08 and [Pb(Mg1/3Nb2/3)O3]0.71–[PbTiO3]0.29 single crystals were investigated between 10 and 530 K, micro-Raman spectra were recorded between 300 and 800 K. No phonon softening was observed near either of the ferroelectric phase transitions. The low-frequency dielectric anomaly in the paraelectric phase is caused by contribution of dynamic polar nanoclusters with the main dispersion in the microwave range. Infrared and Raman spectra confirm the locally doubled unit cell (Zprim=2) in the paraelectric and ferroelectric phases due to the ordering in the perovskite B sites and occurrence of polar nanoclusters in the paraelectric phase. The lowest-frequency transverse optical (TO1) phonon mode active in the infrared spectra is underdamped in contrast to the recent result of inelastic neutron scattering, where no TO1 mode could be observed for the wave vectors q≤0.2 Å-1. This discrepancy was explained by different q vectors probed in infrared and neutron experiments. The infrared probe couples with very long-wavelength phonons (q≈10-5 Å-1) which see the homogeneous medium averaged over the nanoclusters, whereas the neutron probe couples with phonons whose wavelength is comparable to the nanocluster size (q≥10-2 Å-1). © 2003 American Institute of Physics. View full abstract»

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  • Elastic modulus of amorphous boron suboxide thin films studied by theoretical and experimental methods

    Page(s): 940 - 944
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    Boron suboxide BOx thin films have been deposited on Si (100) by reactive rf magnetron sputtering of B powders in an Ar/O2 atmosphere. Elastic recoil detection analysis and x-ray diffraction were used to study the influence of the O incorporation on the film composition and structure and relate them to mechanical properties, which were evaluated by nanoindentation. As x in BOx was increased from 0.08 to 0.18, the elastic modulus of the x-ray amorphous films decreased from 273 to 231 GPa, by 15%. This can be understood using classical molecular dynamics (MD) with a Buckingham-like interaction potential: The increase in the O concentration and corresponding formation of B–O bonds, shown to be longer than the B–B bonds, resulted in larger ionic contributions as well as a density reduction. This increased ionicity was responsible for the observed decrease in elastic modulus. As even more O was incorporated (x≫0.18), the H concentration increased, exceeding 0.3 at. %. This may cause the formation of boric acid (H3BO3) as a result of the chemical reaction with H2O upon atmosphere exposure. The presence of van der Waals and hydrogen bonding, associated with H3BO3 formation, provides a reasonable explanation for the extensive decrease in elastic modulus from 231 to 15 GPa, by 94%. The parameterization for the Buckingham-like interaction potential, introduced in this study, can be used for MD simulations of amorphous BOx systems without H3BO3. © 2003 American Institute of Ph- ysics. View full abstract»

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  • Development of microstructure in Cr and Cr/CoCrPt films made by pulsed laser deposition

    Page(s): 945 - 950
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    Cr films and Cr/CoCrPt bilayer films have been grown using ion-beam-assisted pulsed laser deposition (PLD). High mobility conditions such as a substrate temperature above 350 °C, a low deposition rate, and a high laser energy promote the formation of a {100} bcc crystallographic preferred orientation in the Cr layer, while a {110}-oriented film is formed under other conditions. The {100} orientation can be formed at lower temperatures if the film is bombarded by energetic Ar ions during growth. CoCrPt grows with the hcp-{112¯0} orientation on bcc-Cr {100} underlayers, which is the same epitaxial relationship that occurs in sputtered Cr/Co-alloy films used in hard disk recording media. PLD CoCrPt films also have magnetic properties broadly similar to those of sputtered films. The PLD film microstructure development is interpreted in terms of the preferential nucleation of {100}-oriented Cr crystals during the early stages of film growth. © 2003 American Institute of Physics. View full abstract»

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  • Forbidden transitions and the effective masses of electrons and holes in In1-xGaxAs/InP quantum wells with compressive strain

    Page(s): 951 - 956
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    Two types of forbidden transitions are identified in In1-xGaxAs/InP undoped quantum wells (QWs) with compressive strain by low-temperature (1.8 K) magneto-optical absorption. One of them is due to the interband transitions with different principal quantum numbers and is observable mainly in a low magnetic field and the other corresponds to P- and D-type exciton states and gets stronger as the magnetic field increases. By analyzing the forbidden transitions the in-plane effective masses of electrons (me,ρ*) and heavy holes (mh,ρ*) are simultaneously determined, together with the z-direction (growth-direction) ones (me,z*,mh,z*). The theoretically predicted relation among the electron effective masses [Sugawara etal, Phys. Rev. B 48, 8102 (1993)], me,Γ6≪me,ρ*≪me,z*, where me,Γ6 is the band-edge electron effective mass of bulk material, is therefore verified. The difference between the values of me,z* and me,ρ* is found to decrease as the strain in the QW drops. © 2003 American Institute of Physics. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory