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Journal of Applied Physics

Issue 8 • Date Apr 2000

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Displaying Results 1 - 25 of 68
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Local vibrational modes of impurities in semiconductors

    Page(s): 3593 - 3617
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    Omnipresent impurities such as carbon, oxygen, silicon, and hydrogen play important roles, both detrimental and beneficial, in the fabrication of solid-state devices. The electronic and vibrational properties of semiconductors are significantly altered by the presence of impurities. Atoms that are less massive than the host atoms, typically, show local vibrational modes (LVMs). Unlike lattice phonons, LVMs are localized in both the real and frequency domains, giving rise to sharp peaks in infrared-absorption and Raman-scattering spectra. The isotopic composition of the impurity and the surrounding atoms results in well-defined shifts in the vibrational frequencies. In Ge, GaAs, and CdTe, the host–isotope disorder leads to complex vibrational spectra that can be simulated by empirical, quasimolecular models. External parameters such as temperature and pressure (uniaxial and hydrostatic) have been tuned over a wide range to yield information about symmetry and impurity–host interactions. In this article, issues relating to LVMs in semiconductors are reviewed, with an emphasis on infrared and Raman spectroscopy. Experimental and theoretical studies of LVMs in semiconductors are described for several representative examples. © 2000 American Institute of Physics. View full abstract»

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  • The modeling of excimer laser particle removal from hydrophilic silicon surfaces

    Page(s): 3618 - 3627
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    We summarize experimental results on the successful removal of submicron-sized polystyrene latex, carboxylate-modified latex, SiO2, and Al2O3 particles from hydrophilic silicon surfaces by excimer laser, using both dry and steam cleaning; the cleaning and damage thresholds have also been determined for these particles. Adhesion and removal models for an ideal sphere particle, that include van der Waals forces, hydrogen bonding, and thermoelastic effects, theoretically explain the laser cleaning results. Two models of the removal force due to the explosive evaporation of liquid film have been calculated and compared. The effects of both asperities on the particle surface and particle aggregation have also been considered. The results of the calculations show that even those surface asperities which are small compared with the particle dimension can cause a large reduction in both adhesion and thermoelastic removal forces. The theoretical predictions are consistent with the experimental observations. © 2000 American Institute of Physics. View full abstract»

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  • Spatial behavior of energy relaxation of electrons in capacitively coupled discharges: Comparison between Ar and SiH4

    Page(s): 3628 - 3636
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    The electron energy relaxation in space has been investigated for electropositive Ar and electronegative SiH4 discharges by a 1D Particle-in-cell/Monte Carlo code. The ionization rate has been studied since this rate is strongly influenced by the energy relaxation mechanism. The ionization rate in the two kinds of discharges at a low pressure (30 mTorr), a low power (8 W), and a low frequency (13.56 MHz) is regarded as the reference case. The effects of pressure, power, and frequency on the ionization rate have been observed and compared between the two types of discharges. With the pressure increasing from 30 to 400 mTorr, in the case of the argon discharge the ionization peak moves from the plasma bulk (nonlocal behavior of the electron energy distribution function) towards the momentary cathodic presheath (local behavior). In addition to a similar variation of the ionization rate, in the silane discharge an ionization peak occurs near the momentary anodic presheath, and at the high pressure the ionization in the plasma bulk is still considerable. The power can only influence the ionization rate quantitatively. The effect of frequency on the ionization rate is similar for both kinds of discharges. With increasing frequency the ionization rate tends to a somewhat local character, i.e., the ionization appears closer to the momentary cathode. This is attributed to the fact that at the high frequency a bulk electric field in the bulk is found clearly out of phase with the sheath fields, and the energetic electrons are pushed towards the cathode earlier in space. Meanwhile, in the silane discharge the distinctive ionization, which is strongly present at the anodic presheath and in the plasma bulk at low frequency, almost disappears. © 2000 American Institute of Physics. View full abstract»

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  • Energy influx from an rf plasma to a substrate during plasma processing

    Page(s): 3637 - 3645
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    The energy influx delivered by an rf plasma to a metal substrate has been studied by a calorimetric method with a thermal probe. By changing the substrate voltage, the influence of the kinetic energy of the charge carriers to the thermal power could be determined. The measured energy influx for an argon plasma can be explained mainly by ions, electrons, and their recombination. In the case of an oxygen plasma, where the energy influx is under comparable conditions about 50% higher, also other transfer mechanisms such as surface-aided atom association and relaxation of rovibrational states have to be taken into consideration. © 2000 American Institute of Physics. View full abstract»

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  • Calculation of ion energy distributions from radio frequency plasmas using a simplified kinetic approach

    Page(s): 3646 - 3653
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    Using an elementary kinetic approach, a procedure is described for calculating ion energy distributions (IEDs) from radio frequency (rf) plasmas. The calculated distributions, which are in the form of histograms, are used to fit experimental argon and CF3+ IEDs measured in a Gaseous Electronics Conference rf reactor modified to operate in a pulsed inductively coupled mode. Given the average plasma potential profile and its time dependence, the calculation incorporates a number of parameters used in more comprehensive treatments of the problem to determine the shape of the IED. The reverse calculation that determines the average potential profile, given an experimental IED, cannot be uniquely done, but some insights may be gained in some cases if a sufficient number of plasma related parameters are known, e.g., the shape and amplitude of the rf modulation. The results of the calculation indicate that argon ions forming the IEDs during the bright (H) mode come nearly exclusively from a presheath region that extends far into the interior of the plasma. The calculations also suggest that the CF3+ ions forming the IEDs observed during the dim (E) mode may preferentially come from near the “edge” of the bulk plasma. Possible significances of this difference are noted. © 2000 American Institute of Physics. View full abstract»

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  • Polarization beam smoothing for inertial confinement fusion

    Page(s): 3654 - 3662
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    For both direct and indirect drive approaches to inertial confinement fusion (ICF) it is imperative to obtain the best possible drive beam uniformity. The approach chosen for the National Ignition Facility uses a random-phase plate to generate a speckle pattern with a precisely controlled envelope on target. A number of temporal smoothing techniques can then be employed to utilize bandwidth to rapidly change the speckle pattern, and thus average out the small-scale speckle structure. One technique which generally can supplement other smoothing methods is polarization smoothing (PS): the illumination of the target with two distinct and orthogonally polarized speckle patterns. Since these two polarizations do not interfere, the intensity patterns add incoherently, and the rms nonuniformity can be reduced by a factor of . A number of PS schemes are described and compared on the basis of the aggregate rms and the spatial spectrum of the focused illumination distribution. The  rms nonuniformity reduction of PS is present on an instantaneous basis and is, therefore, of particular interest for the suppression of laser plasma instabilities, which have a very rapid response time. When combining PS and temporal methods, such as smoothing by spectral dispersion (SSD), PS can reduce the rms of the temporally smoothed illumination by an additional factor of . However, it has generally been thought that in order to achieve this reduction of , the increased divergence of the beam from PS must exceed the divergence of SSD. It is also shown here that, over the time scales of interest to direct or indirect drive ICF, under some conditions PS can reduce the smoothed illumination rms by nearly  even when the PS divergence is much smaller than that of SSD. © 2000 American Institute of Physics. View full abstract»

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  • Lattice relaxation and metastability of the EL2 defect in semi-insulating GaAs and low temperature GaAs

    Page(s): 3663 - 3668
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    Using the two-dimensional reciprocal space mapping, we have clearly established the relative positions of the arsenic atom (EL2 defect) corresponding to its stable and metastable configurations. It is shown that lowering only the temperature of the sample, before transition, induces transformation of the lattice. Characteristic temperature (120–140 K) below which such transformation takes place is the same as for thermal recovery of the defect. It is suggested that this temperature related lattice relaxation might promote a further transition to the metastable state. Full reciprocal space maps of the x-ray diffracted intensity are shown for the whole substrate-layer system. © 2000 American Institute of Physics. View full abstract»

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  • Evidence for the effect of carbon on oxygen precipitation in Czochralski silicon crystal

    Page(s): 3669 - 3673
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    This article reports some new experimental evidence for the effect of carbon on oxygen precipitation in a high carbon content Czochralski silicon (H[C] Cz-Si) crystal. The oxygen precipitation occurring at an intermediate temperature of 950 °C has been especially investigated. In such case, the carbon atoms slightly participate in oxygen precipitation with 1200 °C preannealing, while the carbon atoms actively participate in oxygen precipitation with low temperature preannealing. The experiments show that the 1230 cm-1 absorption band in the Fourier transmission infrared spectrum definitely originates from the oxygen precipitates involving insignificant carbon reduction; on the other hand, the oxygen precipitates involving significant carbon reduction are surely irrelevant to the 1230 cm-1 absorption band. According to the correlation of the change in oxygen and carbon concentrations during oxygen precipitation, it is plausible that there is a critical precipitate size which distinguishes the carbon behavior in oxygen precipitation, that is, the carbon atoms actively participate in oxygen precipitation when the precipitates are smaller than the critical size; whereas, the carbon atoms are only slightly involved in oxygen precipitation when the precipitates are larger than the critical size. © 2000 American Institute of Physics. View full abstract»

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  • Defects in neutron transmutation doped silicon studied by positron annihilation lifetime measurements

    Page(s): 3674 - 3677
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    Neutron transmutation doping of n-type silicon was obtained by irradiating the samples with thermal neutrons in order to create P atoms. Positron lifetime measurements were carried out and the evolution of the induced defects was studied by thermal annealing of the samples. The annealing out of the divacancy was seen between 200 and 350 °C. Around 700 °C large vacancy clusters (containing about eight vacancies) are formed. All the defects are annealed above 800 °C. © 2000 American Institute of Physics. View full abstract»

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  • Longitudinal and lateral stress measurements in shock-loaded gabbro and granite

    Page(s): 3678 - 3682
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    Plate impact experiments have been performed on two igneous rocks of different grain size. Shock stresses have been measured using embedded manganin stress gauges, up to ∼12 GPa. In the coarser grained material data was obtained by impacting rock flyer plates onto previously characterized targets. Results are compared and contrasted to the existing data for other geological materials. In the finer-grained material lateral stress was also measured. In combination with the longitudinal stresses, these results have been used to obtain the materials shear strength under shock loading conditions. Results suggest that the material is deforming in an inelastic manner. © 2000 American Institute of Physics. View full abstract»

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  • CuInSe2 phase formation during Cu2Se/In2Se3 interdiffusion reaction

    Page(s): 3683 - 3690
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    Diffusion couples based upon Cu2Se/In2Se3 pairings have been examined in order to identify the kinetics of intermediate phase development and the associated phase equilibria. For the diffusion couples annealed at 550 °C for 1.5 h, all phases included in the Cu2Se–In2Se3 pseudobinary phase diagram section developed including the CuInSe2 (CIS) phase. Also, the In6Se7 phase formed for annealing times in excess of 1.5 h at 550 °C, indicating a modification of the diffusion pathway outside the pseudobinary phase diagram section. The growth of the CIS phase formed by reactive diffusion follows parabolic kinetics (x2=kt) with the k value of 3.3×10-8cm2/s. CIS phase precipitates with a dendritic morphology are also produced within the Cu2Se side of the diffusion couple far from the initial interface, indicating that In is the fast component during interdiffusion. Based upon electron diffraction analysis and simulation of electron diffraction patterns, the dendritic shaped CIS precipitate structure was uniquely determined to be the metastable zinc blende type rather than the stable chalcopyrite-type structure. The structure and orientation relationship between the metastable CIS phase and the Cu2Se matrix satisfy the conditions- established for the development of a solid state dendritic morphology. © 2000 American Institute of Physics. View full abstract»

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  • A study of effect of cyanine dyes on ionic conductivity of AgBr grains

    Page(s): 3691 - 3695
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    (1) On adsorption to cubic AgBr grains, both a 9-methyl-thiacarbocyanine (dye 1) and a 5,5-dichloro-9-ethyl-thiacarbocyanine (dye 2), increased the conductivity of the grains with interstitial silver ions as carriers, repelling silver ions at the surface kink sites into interstitial positions. (2) On adsorption to octahedral AgBr grains, both dyes 1 and 2 increased the conductivity of the grains with mobile silver ions on the surface as carriers, whereas neither dyes 1 nor 2 increased the conductivity of the grains with interstitial silver ions as carriers. It is considered that the dye molecules repelled silver ions at surface sites, not into interstitial positions, but into surface sites where silver ions are mobile. (3) Dye 1 was preferably adsorbed to (100) faces on the surface of tetradecahedral AgBr grains, increasing the conductivity of the grains with interstitial silver ions as carriers, and was then adsorbed to the (111) faces after the saturation of the (100) faces by the dye, giving little influence on the ionic conductivity. On the contrary, dye 2 was preferably adsorbed to the (111) faces, giving little influence on the conductivity, and was then adsorbed to the (100) faces after the saturation of the (111) faces by the dye, increasing the conductivity. This result provided a method to examine the kind of faces on the surface of silver halide grains. (4) The observation of preferential adsorption on different crystal faces was successfully used to prove the presence of (100) faces on the side surfaces of a twinned tabular grain. © 2000 American Institute of Physics. View full abstract»

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  • Effects of donor concentration on transient enhanced diffusion of boron in silicon

    Page(s): 3696 - 3699
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    The effects of substrate donor concentration on transient enhanced diffusion (TED) of boron implanted into silicon wafers predoped with arsenic or phosphorus have been investigated by using secondary ion mass spectroscopy and theoretical simulations. Boron ions have been implanted at low energy (10–20 keV) and successively annealed in the temperature range 700–1000 °C. No detectable boron TED (TED≪10×) has been observed in samples uniformly predoped with P at the concentration of 1.2×1020 cm-3. The B TED is strongly reduced even in the samples predoped with As. However, for the highest As concentration (1.3×1020 cm-3) an exponential high diffusivity tail has been detected in the B profiles at all the examined annealing temperatures. This anomalous effect has been attributed to the interstitials produced by an As clustering reaction occurring during the low temperature annealing. The main effects responsible for the vanishing of the B TED, i.e., ionization of the interstitials (Fermi level effect), competitive behavior of P in the interaction with the interstitials, and donor-acceptor pairing have been examined and discussed. © 2000 American Institute of Physics. View full abstract»

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  • Low-temperature formation of Si(001) 2×1 surfaces from wet chemical cleaning in NH4F solution

    Page(s): 3700 - 3706
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    In situ reflection high-energy electron diffraction and thermal desorption spectroscopy were used to investigate the surface structure and chemistry of Si(001) surfaces after wet chemical etching in dilute HF and ammonium fluoride (NH4F) solutions. The HF-etched surfaces were found to be rough and terminated by mono-, di-, and tri-hydride species, in good agreement with previous vibrational spectroscopy measurements. The surface roughness observed after HF treatment appears to arise from surface defects such as adstructures and kinks left on the surface after the removal of the oxide layers. The Si(001) etching processes in NH4F solution were found to be highly anisotropic, and the etching time in the solution was found to be the key parameter which determined the chemistry and the morphology of the surface. We show that for a limited etching time (∼1 min), a flat and bulk-like dihydride-terminated Si(001) surface could be formed and this surface was found to transform, upon annealing in ultrahigh vacuum, into a well-developed 2×1 reconstruction at a temperature as low as ∼400 °C. Our results also suggested that (111) microfacets were formed on Si(001) surfaces only after a prolonged etching in NH4F solution and they remained stable up to an annealing temperature of ∼650 °C. © 2000 American Institute of Physics. View full abstract»

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  • Dependence of crystallinity on oxygen pressure and growth mode of La0.3Sr1.7AlTaO6 thin films on different substrates

    Page(s): 3707 - 3710
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    The influence of oxygen pressure on epitaxial quality of La0.3Sr1.7AlTaO6 (LSAT) films deposited by laser ablation on SrTiO3(100), LaAlO3(100), and MgO(100) substrates has been investigated. X-ray diffraction shows only (00l) peaks in the oxygen pressure range from 10-3 to 500 mTorr. However, the crystallinity of LSAT films is found to be sensitive to oxygen pressure and dependent on substrates. LSAT films on SrTiO3 have the narrowest full width at half maximum (FWHM) of 0.05° at 300 mTorr. The films on LaAlO3 exhibit a FWHM of 0.3° at 50–100 mTorr. On MgO substrate, significant improvement of crystallinity is achieved at 200–300 mTorr, but rocking curves give an FWHM of 0.70°–1.00° due to the large lattice mismatch between LSAT and MgO. Atomic force microscopy analyses demonstrate smooth LSAT surfaces without identified grains. Reflection high-energy electron diffraction studies suggest a two-dimensional growth mode for LSAT films on SrTiO3 and LaAlO3 and a three-dimensional growth mode for LSAT films on MgO. Cross-sectional high-resolution electron micrographs indicate that LSAT films on SrTiO3 and LaAlO3 have defect-free epitaxial structure and atomically flat interfaces. An 80 Å thick intermediate layer with partially disordering is observed between LSAT films and MgO substrates. © 2000 American Institute of Physics. View full abstract»

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  • Strain and photoluminescence characterization of cubic (In,Ga)N films grown on GaAs(001) substrates

    Page(s): 3711 - 3714
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    Cubic InxGa1-xN films were successfully grown on GaAs(001) substrates by metalorganic chemical-vapor deposition. The values of x content ranging from 0.10 to 0.24 obtained at different growth conditions were measured by double-crystal x-ray diffraction (XRD). The perpendicular and parallel elastic strain of the In0.2Ga0.8N layer, Є=0.4% and Є||=-0.4% for GaN and Є=0.37% and Є||=-0.37% for InGaN, respectively, were derived using the XRD measurements. The inhomogeneous strain and the average grain size of the In0.2Ga0.8N/GaN films were also studied by XRD. Photoluminescence spectra were used to measure the optical characterization of the InxGa1-xN thin films with different In composition, and the near-band-edge emission dependence of cubic InxGa1-xN on the x value is nearly linear with In content x≤0.24. © 2000 American Institute of Physics. View full abstract»

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  • Thermal stability and breakdown strength of carbon-doped SiO2:F films prepared by plasma-enhanced chemical vapor deposition method

    Page(s): 3715 - 3722
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    Carbon-doped SiO2:F films were deposited by changing the CH4 flow rate, [CH4], using a plasma-enhanced chemical vapor deposition technique from SiH4/O2/CF4/CH4 mixtures. The thermal stability for the films deposited with a fixed temperature of 300 °C was investigated through the changes in the dielectric constant S), IR spectra and stress with annealing temperature, TA, from 400 to 800 °C. The breakdown strength for films as-deposited were also measured. The addition of carbon to SiO2:F films resulted in the films with low ЄS (up to 3.0) and high water resistivity. Addition of high [CH4] in the films resulted in stable ЄS for TA=500 °C or less. The CH4 addition initially decreased the breakdown strength but then increases again. Under the application of sum rule to the analysis of the vibrational absorption, it was suggested that the decrease in ЄS with [CH4] results from the decrease in the effective dynamic charge of Si–O dipoles along with the direct contribution of Si–F bonds incorporated to SiO2. The dec- rease in Si–F and Si–O peak frequencies based on the analysis of the charge transfer model suggested an increase in the Si–F and Si–O bond length, in addition to a decrease in the Si–O–Si bond angle. © 2000 American Institute of Physics. View full abstract»

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  • The field-induced cholesteric-nematic phase transition and its dependence on layer thickness, boundary conditions, and temperature

    Page(s): 3723 - 3729
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    Chiral-nematic liquid-crystal layers which have a short pitch, homeotropic boundary conditions, and bistable properties are investigated with respect to the temperature dependence of their field-induced cholesteric-nematic phase transition. Hereto the threshold field needed for the transition is studied as a function of the layer thickness. This is done for various temperatures. The threshold field hardly depends on the layer thickness. Moreover, it sharply rises below -5 °C. Both the value of the threshold field and its temperature dependence can be fully described in terms of liquid-crystal bulk material parameters, the conditions at the homeotropic boundary layer used do not play a role. From the threshold field data the twist elastic constant is determined as a function of temperature. This temperature dependence is compared to the temperature dependence as determined from the square of the long range order parameter calculated from temperature dependent refractive index data. A good correlation is found between both data sets of the twist elastic constant. © 2000 American Institute of Physics. View full abstract»

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  • Surfactant controlled growth of GaInP by organometallic vapor phase epitaxy

    Page(s): 3730 - 3735
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    The effect of the surfactant Sb has been studied for GaInP semiconductor alloys grown by organometallic vapor phase epitaxy. Dramatic changes in the optical and electrical properties of GaInP with CuPt ordering have been observed. A small concentration of triethylantimony (TESb) in the vapor is found to cause Sb to accumulate at the surface. In situ surface photoabsorption analysis indicates that Sb changes the surface bonding by replacing the [1¯10] P dimers that are responsible for the formation of the CuPt structure during growth with [1¯10] Sb dimers. As a result, the degree of order for the GaInP layers is decreased, as shown by transmission electron diffraction studies. The 20 K photoluminescence spectra show a 131 meV peak energy increase for GaInP layers grown on vicinal substrates when a small amount of Sb [Sb/P(v)=4×10-4] is added to the system during growth. The use of surfactants to control specific properties of materials is expected to be a powerful tool for producing complex structures. In this article, the growth of heterostructures by modulating the Sb concentration in the vapor is demonstrated. © 2000 American Institute of Physics. View full abstract»

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  • Structure and interface-controlled growth kinetics of ZnAl2O4 formed at the (112¯0) ZnO/(011¯2) Al2O3 interface

    Page(s): 3736 - 3743
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    The solid state reaction between metalorganic chemical vapor deposition grown epitaxial ZnO films and the R-plane sapphire substrate after annealing at 1000 °C for various times in an O2/N2 atmosphere was studied in detail. Multiple epitaxial relationships between the reaction product (ZnAl2O4) and the reactants were observed, as determined by cross-sectional transmission electron microscopy. In the dominant epitaxial relationship (A1), the (22¯0) plane of ZnAl2O4 was parallel to the (1¯101) plane of Al2O3. A twin (A2) of orientation A1, i.e. (22¯0) ZnAl2O4//(101¯1) Al2O3, and a closely related orientation (B) wherein the (22¯0) ZnAl2O4 plane is parallel to the (1¯21¯0) ZnO plane (which is equivalent to a clockwise rotation about the [1¯1¯2] ZnAl2O4 or [0001] ZnO zone axis relative to A2), were also obse- rved. Enhanced growth was observed at grain boundaries. It was necessary to measure the spinel growth rate from grains with the same orientation far away from grain boundaries because the growth rate was observed to be influenced by the orientation of the grains in addition to the enhanced growth at grain boundaries. The growth rate was observed to follow a linear rate law during early stages (for grains with orientation A1), suggesting an interface-controlled reaction. The structures of the ZnO/Al2O3, ZnO/ZnAl2O4 and ZnAl2O4/Al2O3 interfaces were studied for grains with this orientation (A1). The 13.7% lattice mismatch between ZnO and ZnAl2O4 was relieved by a series of misfit dislocations spaced five to six (11¯00) ZnO planes apart. Due to the small lattice misfit (2.1%) at the ZnAl2O4/Al2O3 interface, very few misfit dislocations were present. This interface was faceted and the sapphire surface had a series of single steps. It is expected that the reaction at the ZnAl2O4/ZnO interface is the rate-controlling step due to the necessity for a dislocation climb (of a large number of misfit dislocations) for movement of this interface. View full abstract»

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  • Strain and shape analysis of multilayer surface gratings by coplanar and by grazing-incidence x-ray diffraction

    Page(s): 3744 - 3758
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    The surface shape and the spatial distribution of strain in GaInAs/InP multilayer gratings is experimentally determined by combining high-resolution x-ray diffraction and grazing-incidence diffraction. Dramatic deformations of the diffraction patterns in the measured reciprocal space maps of such gratings indicate a strongly nonuniform character of lattice distortions in the layers, caused by elastic strain relaxation. By coupling x-ray diffraction theory and elasticity theory within one single evaluation formalism, an experimental strain and shape analysis could be performed which was not yet available in this form by other methods. The different components of the strain tensor are determined by recording diffraction patterns around different reciprocal lattice points. We study how the strain relaxation of the multilayer grating evolves towards the free surface, and how the local strain distribution is modulated due to the compositional profile of the layered setup. Furthermore, the article describes in detail the effects of the grating shape, the multilayer morphology, and the lattice strain field on the diffraction patterns of multilayered gratings. © 2000 American Institute of Physics. View full abstract»

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  • Effect of coating thickness on thermal stresses in tungsten-coated optical fibers

    Page(s): 3759 - 3762
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    This study investigates the effect of coating thickness on the thermal stresses in tungsten-coated optical fibers. Theoretical results indicate that the maximum normal stress in the tungsten coating decreases with increasing coating thickness. However, the maximum shear stress at the interface of the glass fiber and tungsten coating increases. Eight samples of tungsten-coated optical fibers with coating thicknesses of 58, 75, 101, 128, 158, 383, 557, and 1013 nm, respectively, are immersed in liquid nitrogen for one day. Experimental results show that thermal stresses will either break or delaminate the tungsten coating. The crack density decreases with increased coating thickness, while the delaminated area of tungsten coating increases. The theoretical results can explain the break and delamination of the tungsten coating in the optical fiber. To minimize the break and delamination of the tungsten coatings in the optical fibers, the optimal thickness of the tungsten coating is about 158 nm. © 2000 American Institute of Physics. View full abstract»

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  • Surface superstructure on fullerenes annealed at elevated temperatures

    Page(s): 3763 - 3767
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    Scanning tunneling microscopy images of fullerenes annealed at elevated temperatures are investigated. Three types of ringlike superstructures of (×)R30° of graphite, the circular type, the U type, and the semicircular type, are observed on the curved surface of the fullerenes annealed in the temperature range from 2073 to 2673 K. A new modified interference model, in which both the α and β site atoms contribute to the tunneling current caused by the curved surface, is proposed. The model well simulates the three types of the ringlike superstructure of graphite and the continuous change from the triangular structure of graphite to the ringlike superstructure of graphite. © 2000 American Institute of Physics. View full abstract»

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  • Observations of reaction zones at chromium/oxide glass interfaces

    Page(s): 3768 - 3776
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    Cr is often used in thin metallic film structures on oxide glasses since it exhibits good adhesion. The most likely explanation of the basic adhesion mechanism is the formation of a graded metal oxide layer at the interface. In general, details of the interface properties are needed to get a complete understanding of phenomena such as adhesion. We report here observations of interface structures using spatially resolved electron energy loss spectrometry with a small probe (2 Å) scanning transmission electron microscope. Two interfaces, evaporated Cr/alkaline earth boroaluminosilicate glass and sputtered Cr/barium boroaluminosilicate glass, are examined. As expected from the classical adhesion theory, very thin partially oxidized intermediate layers are seen in both samples. However, a 5 nm Cr diffusion layer is also found in the evaporated Cr/glass system (without heat treatment), but it appears absent in the sputtered Cr glass system (with heat treatment). This difference suggests that the mechanisms of the adhesion of Cr to oxide glass are dependent on interface history. © 2000 American Institute of Physics. View full abstract»

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

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P. James Viccaro
Argonne National Laboratory