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Journal of Applied Physics

Issue 3 • Date Aug 1999

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Displaying Results 1 - 25 of 105
  • Issue Cover

    Page(s): c1
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    Freely Available from IEEE
  • Issue Table of Contents

    Page(s): toc1
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  • Transmission properties at microwave frequencies of two-dimensional metallic lattices

    Page(s): 1177 - 1180
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    The transmission properties of different metallic photonic lattices (square and rectangular) have been experimentally studied. A numerical algorithm based on time domain finite differences has been used for simulating these photonic structures. The introduction of defects in the two-dimensional metallic lattice modifies its transmission spectrum. If metal rods are eliminated from (or added to) the lattice, extremely narrow peaks are observed at some particular frequencies below (or above) the band pass edge. © 1999 American Institute of Physics. View full abstract»

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  • Sensitized near-infrared luminescence from polydentate triphenylene-functionalized Nd3+, Yb3+, and Er3+ complexes

    Page(s): 1181 - 1185
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    Hexa-deutero dimethylsulfoxide (DMSO-d6) solutions of terphenyl-based Nd3+, Yb3+, and Er3+ complexes functionalized with a triphenylene antenna chromophore exhibit room temperature near-infrared luminescence at wavelengths of interest for the optical telecommunication network (∼1330 and ∼1550 nm). The sensitizing process takes place through the triplet state of triphenylene as can be concluded from the oxygen dependence of the sensitized luminescence. A significant fraction of the excited triphenylene triplet state is quenched by oxygen, instead of contributing to the population of the luminescent state of the lanthanide ion. The luminescence lifetimes of the triphenylene-functionalized lanthanide complexes ((2)Ln) are in the range of microseconds with a lifetime of 18.6 μs for (2)Yb, 3.4 μs for (2)Er, and 2.5 μs for (2)Nd in DMSO-d6. These luminescence lifetimes seem almost completely dominated by the vibrational quenching by the organic groups in the polydentate ligand and solvent molecules, which leads to low overall luminescence quantum yields. © 1999 American Institute of Physics. View full abstract»

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  • Multiple phase gratings in pure, Yb- and P-doped Pb5Ge3O11 after different thermal treatments

    Page(s): 1186 - 1190
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    Multiple phase gratings are written in pure, Yb- and P-doped Pb5Ge3O11 crystals: a fast grating and a slow grating with substantially different response times compensate each other. Doping and thermal treatments have strong influences on the behavior of both gratings. Reduction treatments of Yb-doped samples lead to a significant decrease of the response time of the slow grating, while that of the fast grating is diminished by more than two orders of magnitude. P doping significantly increases the response time of the fast grating. Possible origins of both gratings are discussed. © 1999 American Institute of Physics. View full abstract»

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  • Analysis and modeling of Nd:Ti:LiNbO3 Fabry-Pérot channel waveguide lasers

    Page(s): 1191 - 1195
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    Based on the bidirectional fast Fourier transform beam propagation method (FFT-BPM), a self-consistent Nd:Ti:LiNbO3 Fabry-Pérot waveguide laser model has been developed. By using the bidirectional FFT-BPM and the attenuation effect of pumping and resultant lasers within the waveguide cavity, the interference effect and physical behaviors of the population inversion longitudinal and transversal spatial effects were observed. The resultant laser power is saturated if the waveguide is longer than a critical length, which is a function of the pumping power. Moreover, the resultant laser power density is a nonuniform function along the longitudinal dimension within the waveguide cavity. © 1999 American Institute of Physics. View full abstract»

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  • Spectroscopic measurement of packaging-induced strains in quantum-well laser diodes

    Page(s): 1196 - 1201
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    Packaging-induced strain is studied in high-power semiconductor lasers by a noninvasive optical technique. Fourier-transform photocurrent measurements with intentionally strained laser array devices for 808 nm emission reveal spectral shifts of optical transitions within the active region. These shifts by up to 10 meV serve as a measure for the strain status within the active layer of the devices and are compared with model calculations. For different packaging architectures we quantify the strain portion which is transmitted to the optically active region of the semiconductor device. © 1999 American Institute of Physics. View full abstract»

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  • Analytical model of the relaxation of a collisionless ion matrix sheath

    Page(s): 1202 - 1207
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    The temporal evolution of a collisionless ion matrix sheath in front of an electrode biased to a pulsed high negative voltage is investigated analytically and numerically. In the relaxation process a matrix extraction phase and a subsequent sheath expansion phase can be distinguished. For the matrix extraction phase we present an analytical model that is based on special solutions of the ion fluid equations and that is free of artificial assumptions. The model results in an explicit formula for the ion current to the electrode. The results are compared with numerical solutions of the ion fluid equations and show excellent agreement. By a simple parameter ansatz the model is extended to describe the sheath expansion phase. © 1999 American Institute of Physics. View full abstract»

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  • Evaluation of self-bias potential distribution on a powered electrode of supermagnetron plasma apparatus

    Page(s): 1208 - 1212
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    The distribution of self-bias potential (Vdc) on a powered electrode of a supermagnetron plasma system, where both electrodes are supplied phase-shifted radio frequency (rf) currents, was measured using five electrical probes buried in the electrode. For comparison, the same was measured for a conventional magnetron plasma system. Measurements were carried out with an Ar discharge at the pressure region of 4–50 mTorr. The data obtained with the supermagnetron and the conventional magnetron plasm systems were used to map the Vdc distribution on the powered electrodes of each plasma source. When the phase difference between rf currents applied to the two parallel electrodes of supermagnetron plasma system were changed, a drastic change of the Vdc is observed. The uniformity of the Vdc distribution is greatly improved when the phase difference between rf currents is varied from 0° to about 180°. The further increase of phase difference between two rf currents causes a decrease of the uniformity of the Vdc distribution. The uniformity of the Vdc obtained on the electrode of supermagnetron plasma source with 180° phase-shifted currents is observed to be superior to that of the conventional magnetron plasma source. © 1999 American Institute of Physics. View full abstract»

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  • Langmuir probe in low temperature, magnetized plasmas: Theory and experimental verification

    Page(s): 1213 - 1220
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    Langmuir probe theory, adapted to magnetized, partially ionized, low temperature processing plasmas with radial diffusion dominated by electron-neutral collisions, was verified in electron cyclotron resonance (ECR) plasmas. Plasma parameters such as plasma potential, electron temperature, plasma density, and the ratio of electron saturation current to ion saturation current (Ie*/Ii*) were measured by single-sided planar probe in various ECR plasmas (H2, He, N2, O2, Ar, and CF4). The neutral pressure was varied between 0.5 and 8.5 mTorr and the microwave power between 170 and 1250 W with good matching conditions; the reflected power was kept at less than 3% of the input power. The measured ratios of Ie*/Ii*, and other plasma parameters were consistent with the probe theory for pressures greater than 2.0 mTorr for various plasmas of Ar, He, H2, and N2. These results indicate that the electron-neutral collisional probe theory works well for magnetized ECR plasmas (magnetic flux densities of 0.8–1.0 kG). © 1999 American Institute of Physics. View full abstract»

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  • The effect of as-implanted damage on the microstructure of threading dislocations in MeV implanted silicon

    Page(s): 1221 - 1225
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    The dose dependence of as-implanted damage and the density of threading dislocations formed after MeV implants into Si is measured. The role of the damage and amorphization in the evolution of dislocation microstructure is assessed. As-implanted damage is analyzed by Rutherford backscattering spectroscopy and channeling. Defect etching is used to delineate threading dislocations in near-surface regions of annealed (900 °C, 30 min) samples. For a variety of implants with 1.1 μm projected range (600 keV B, 1 MeV P, and 2 MeV As) we observe a sharp onset for formation of threading dislocations with a peak in dislocation density at a dose of about 1×1014 cm-2, this dose depends on the ion mass. With a further increase in dose, the dislocation density decreases. This decrease, however, is drastically different for the different ions: sharp (4–5 orders of magnitude) reduction for P and As implants and slow decline for B implant. The sharp decrease in the density of threading dislocations at higher doses is correlated with the onset of amorphization observed by channeling for P and As implants. Our data for low-temperature implants provide conclusive proof that a reduction in the dislocation density for P and As implants is a result of amorphization. © 1999 American Institute of Physics. View full abstract»

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  • A neutron powder diffraction study of the system La2(Co1-xFex)16Ti for x=0.0, 0.2, and 0.4

    Page(s): 1226 - 1229
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    The nuclear and magnetic structures of La2(Co1-xFex)16Ti have been studied by neutron powder diffraction for the compositions x=0.0,0.2,0.4. The compound crystallizes with the symmetry of space group R3¯m. Site occupancy results show significant departures from a purely statistical distribution, with the Ti atoms located in sites which interact weakly with La, and with the Co atoms occupying preferentially the sites with strong La interaction. These results are consistent with the enthalpies of formation of equiatomic alloys of rare earth and 3d elements. The spin ordering at all compositions and temperatures is ferromagnetic. At room temperature the moments are aligned along the c axis for the compositions x=0.0 and x=0.2, and form an angle of about 57° with c for x=0.4. This tilt angle is a function of temperature and the moment is aligned along c at 11 K, moving gradually towards the a,b plane as the temperature increases. © 1999 American Institute of Physics. View full abstract»

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  • Structural changes in InP/Si solar cells following irradiation with protons to very high fluences

    Page(s): 1230 - 1235
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    Precisely how the short circuit current (JSC) is produced in a proton irradiated n+p InP/Si solar cell at very high fluence levels has been determined from combined measurements of the cell structure using electrochemical capacitance–voltage profiling and detailed analysis of the spectral quantum efficiency. Type conversion in the base region of the cell is shown to occur before an anomalous peak in the degradation curve for JSC is reached at high damage levels. The short circuit current, and hence the cell efficiency, ultimately collapse because the high absorption coefficient of InP eventually prevents the generation of electron–hole pairs close enough to the effective cell junction from being collected. © 1999 American Institute of Physics. View full abstract»

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  • A universal relation for the stress dependence of activation energy for slip in body-centered cubic crystals

    Page(s): 1236 - 1244
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    By analyzing experimental data in the literature, the activation energy H for slip in body-centered cubic metals is found to approximately obey the simple relation H≈0.1 μb3(1-t)2, where t is the applied stress normalized by the zero-temperature Peierls stress, μ is the <111> shear modulus, and b the 1/2<111> Burgers vector. Such universal relation is explained by analyzing the activation processes of kink-pair generation and expansion along threefold screw dislocations using the generalized Peierls–Nabarro model [A. H. W. Ngan, J. Mech. Phys. Solids 45, 903 (1997)]. The model also predicts qualitatively the general form of the orientation dependence of Peierls stress at zero temperature. © 1999 American Institute of Physics. View full abstract»

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  • Comparative study of analytical methods for Hugoniot curves of porous materials

    Page(s): 1245 - 1254
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    This study compares five methods to compute Hugoniots for porous materials, with experimental data for porous copper. The methods compare well when porosities are low. Three methods model shock velocity versus particle velocity data over a range of porosities with reasonable accuracy. P–v data are much more discriminatory and only two methods reproduce experimental data at high porosities with some degree of accuracy. Comparisons are made by plotting analytical results on curves fitted through experimental data points. Above certain porosities Hugoniot curves display anomalous behavior where (dP/dv)≫0. A new method is presented which contains only two parameters {KT, and [(∂KT/∂P)]T} and which models both normal and anomalous Hugoniots curves. © 1999 American Institute of Physics. View full abstract»

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  • An analytic model for the prediction of incoherent shaped charge jets

    Page(s): 1255 - 1265
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    It is now a well recognized fact that the jet from a shaped charge can be overdriven in the sense that the fastest moving particles are not produced as a cohesive mass of material. Rather, the tip material may be produced as a number of discrete particles which possess different nonzero radial components of velocity and hence spread out from the axis of symmetry of the charge. Such a jet is classed as incoherent and when this incoherency occurs the jet’s target penetration capability is invariably degraded. This physical phenomenon is the subject matter of this article. Several experimental results using common shaped charge materials are presented first. An analytic model which predicts the jet speed at the transition point between a coherent and incoherent state is then described. This model is based on the assumption that a stagnant core with circular boundaries exists in the flow region. Further, the flow field is assumed to be compressible with circular streamlines. The Murnaghan equation of state is used to relate the pressure and density in the flow region where the jet is produced. It is postulated that the transition between a coherent and incoherent state occurs when the circular flow becomes wholly supersonic. The critical Mach number for coherency is shown to be approximated to high accuracy by a simple formula depending on the collapse angle of the flow and the incoming flow speed. Excellent agreement between the model predictions and the experimental data is demonstrated. View full abstract»

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  • Kinetic analysis of interfacial diffusion accompanied by intermetallic compound formation

    Page(s): 1266 - 1272
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    In interfacial reactions, a short-circuit diffusion along grain boundaries or interfaces can be accompanied by intermetallic compound formation. The compound penetrates the grain boundaries or the interfaces. This is a generic reliability issue for layered thin film structures because it causes a decrease in adhesion strength of the thin films. We have modified Fisher’s grain boundary diffusion model to include this reactive kinetic process, and an analytical solution was obtained. A t1/4 dependence of penetration is found, the same as Fisher’s model. The important kinetic parameters in the solutions are a diffusion coefficient along the short-circuit path, an intrinsic interdiffusion coefficient in the compound, and a partition coefficient. A comparison between the calculated and measured data from the lateral penetration of eutectic SnPb solder along the interface between electroless Ni and oxysilicon nitride dielectric, accompanied by Ni3Sn4 compound formation, is given. © 1999 American Institute of Physics. View full abstract»

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  • On the decay of end effects in conduction phenomena: A sandwich strip with imperfect interfaces of low or high conductivity

    Page(s): 1273 - 1279
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    The rate of decay of end effects in steady state heat conduction in a symmetric sandwich strip with anisotropic constituents and imperfect interfaces between the layers is studied. Two kinds of imperfect interfaces are considered: an imperfect interface which models a thin interphase of low conductivity and an imperfect interface which models a thin interphase of high conductivity. In the former case, the normal component of the heat flux is continuous at the interface, whereas the temperature field undergoes a discontinuity which is proportional to the normal component of the heat flux. In the latter case, the temperature field is continuous at the interface and the normal component of the heat flux exhibits a discontinuity proportional to a surface differential operator of the temperature, called the surface Laplacian. The characteristic rate of decay of end effects is given by the smallest real and positive root of a transcendental equation. This rate decreases as the discontinuity in the temperature or the heat flux across the interface increases, in either kind of the imperfect interface. Exact duality relations are shown to exist between the decay rate of end effects in strips with imperfect interfaces of low conductivity, and that in strips with imperfect interfaces of high conductivity. © 1999 American Institute of Physics. View full abstract»

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  • Analysis of failure mechanisms in electrically stressed Au nanowires

    Page(s): 1280 - 1286
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    An analysis of polycrystalline Au thin film interconnects of widths ranging from 850 to 25 nm, and lengths ranging from 1.0 μm to 20 nm which have been electrically stressed to the point of failure is presented. For the longer wires (widths 60–850 nm), the failure current density is typically found to be 1012A m-2, essentially independent of the wire width, and then rapidly approaching zero for thinner wires. For the wider wires, failure occurs at the end towards the negative electrode; for narrow wires, failure tends to occur towards the center of the wire, as observed using scanning electron microscopy and atomic force microscopy. The mean time to failure for fixed current density is seen to decrease with decreasing wire width. The failure current density for a given wire width increases as the length decreases. An analysis of the temperature profile based on calculations of a simple model is presented which shows that this width-dependent behavior of narrow lines is not anticipated from the assumption of a homogeneous line subject to thermally-assisted electromigration alone. © 1999 American Institute of Physics. View full abstract»

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  • Growth of undulating Si0.5Ge0.5 layers for photodetectors at λ=1.55 μm

    Page(s): 1287 - 1291
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    Si0.5Ge0.5/Si multiquantum-well structures are grown using a production-compatible ultrahigh vacuum chemical vapor deposition system. The structures are designed in order to obtain dislocation-free undulating strained layers used as the absorbing layers in photodetector structures. The Si/SiGe/Si stack on a silicon-on-insulator wafer is used as the waveguiding layer. Transmission electron microscopy and photoluminescence are used to characterize the undulating layers. A photoluminescence emission corresponding to the band edge “no phonon” transition is measured at a wavelength beyond 1.55 μm. Preliminary data from metal–semiconductor–metal photodetectors fabricated with this material show a responsivity of approximately 0.1 A/W at the telecommunication wavelength of λ=1.55 μm. © 1999 American Institute of Physics. View full abstract»

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  • Evolution of mosaic structure in Si0.7Ge0.3 epilayers grown on Si(001) substrates

    Page(s): 1292 - 1297
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    In this article, we report a study of mosaic structures in partially relaxed Si0.7Ge0.3 epilayers grown on Si(001) substrates by x-ray double- and triple-axis diffractometry. The samples have different layer thicknesses and hence different degrees of strain relaxation. Our results show that, at early stages of strain relaxation, the films contain mosaic regions laterally separated by perfect regions. This is because the mosaic structure caused by a misfit dislocation is effectively localized in a lateral range of the layer thickness. Therefore, far from the dislocations, the film is virtually a perfect crystal. With the increase in the degree of strain relaxation, and consequently in the dislocation density, the mosaic regions of the layer expand while the perfect regions shrink and finally vanish completely. Moreover, our results indicate that the conventional method of estimating dislocation density from the x-ray rocking curve width fails in our case. © 1999 American Institute of Physics. View full abstract»

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  • Measurement of aluminum concentration in the Ga1-xAlxSb/GaSb epitaxial system

    Page(s): 1298 - 1305
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    The composition of several Ga1-xAlxSb epitaxial layers of different thicknesses grown by molecular beam epitaxy on GaSb with x ranging between 0.1 and 0.8, has been obtained independently by high resolution x-ray diffraction, Rutherford backscattering spectrometry, and reflection high-energy electron diffraction. From the comparison between the results obtained by the different experimental methods, it has been possible to point out that the lattice constant of the layer increases nonlinearly with the Al content. A comparison with theoretical models has been done. A phenomenological equation has been derived for a correct analysis of the x-ray results. © 1999 American Institute of Physics. View full abstract»

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  • Homoepitaxial growth and hydrogen incorporation on the chemical vapor deposited (111) diamond

    Page(s): 1306 - 1310
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    A systematic study of the effect of growth conditions (temperature, microwave power, and pressure) on the hydrogen incorporation and growth rate of (111) homoepitaxial diamond synthesized by microwave plasma assisted chemical vapor deposition is carried out by secondary ion mass spectrometry. Significant quantities of hydrogen incorporation in the (111) homoepitaxial diamond are detected for the growth conditions employed. Hydrogen concentration and growth rate are found to increase with an increase in the substrate temperatures. The increase of microwave power decreases the hydrogen incorporation and increases the growth rate. The effect of pressure rise is similar to that of microwave power. However, the effect of pressure rise over 50 Torr on hydrogen incorporation and growth rate is small. The decrease of hydrogen incorporation can be explained by the suppression of defects in the growing film by atomic hydrogen in the gas phase. © 1999 American Institute of Physics. View full abstract»

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  • Mechanism of bump formation on glass substrates during laser texturing

    Page(s): 1311 - 1316
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    A quantitative model is proposed to elucidate and predict the dome-shaped surface topography resulting from CO2 laser heating of glass substrates. In the analysis, a permanent structural change in glass is induced by a higher glass transition temperature due to the faster cooling process, with a final topography being determined by the temperature history resulting from the absorbed laser energy. The analysis is validated by experiment, which focuses on the energies which trigger the permanent deformation and induce a dome-shaped topography. The dimensions (maximum height and base area) of the bump show a logarithmic dependence on energy as expected from the theory. Using the constants determined from the experimental data and our analysis, bump profiles over a range of laser fluences are predicted. These two constants provide the information for determining the new glass transition temperature and the threshold energy needed to form a permanent bump. The result also suggests that the topography is mostly determined from the conditions at the end of the laser pulse. The effects of thermally induced stress on the model, and the physics of bump formation in chemically strengthened glass are addressed. © 1999 American Institute of Physics. View full abstract»

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  • A crystalline hydrogenated carbon film obtained by plasma enhanced chemical vapor deposition

    Page(s): 1317 - 1321
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    A hydrogenated carbon film in a crystalline form has been prepared on Si (001) using a radio frequency plasma enhanced chemical vapor deposition process. The crystalline film is metastable and has polymer-like features with a mass density of about 1.20 g/cm3 and an optical band gap of about 2.75 eV. The stability of the structure and properties of the film was studied by thermal annealing at successively higher temperatures in the air. Upon heating, the film showed a two-step structure change which resulted in a two-step change in the film properties. The relationship between the properties and the bonded hydrogen in the film was also discussed. © 1999 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