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1 Jul 1993

Volume 74, Issue 1, pp. 1-768

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Theoretical analysis of the static deflection of plates for atomic force microscope applications

John Elie Sader and Lee White

J. Appl. Phys. 74, 1 (1993); http://dx.doi.org/10.1063/1.354137 (9 pages) | Cited 83 times

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The analysis of the static deflection of cantilever plates is of fundamental importance in application to the atomic force microscope (AFM). In this paper we present a detailed theoretical study of the deflection of such cantilevers. This shall incorporate the presentation of approximate analytical methods applicable in the analysis of arbitrary cantilevers, and a discussion of their limitations and accuracies. Furthermore, we present results of a detailed finite element analysis for a current AFM cantilever, which will be of value to the users of the AFM.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Theory of microwave effects on bubble dosimeters

J. R. Swandic

J. Appl. Phys. 74, 10 (1993); http://dx.doi.org/10.1063/1.354141 (5 pages)

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Bubble dosimeters measure a neutron flux by its effect upon microscopic droplets of superheated liquid encased in a polymer gel. It has been observed that a microwave field can also induce bubble formation in some of the droplets. This article considers the theory of this phenomenon as an effect of a microwave‐induced temperature increase. Although the droplets are superheated, their confinement by a smooth gel surface and lack of impurities such as dust particles allow only homogeneous nucleation to occur. At room temperature the thermal fluctuations that give rise to critical size bubbles are very rare; the dosimeter thus has a long shelf life and a low spontaneous noise level. In the presence of a microwave field, the gel and droplets absorb energy and can be heated by 1–2 K for moderate powers; a high‐power microwave field is needed to produce an observable nucleation rate. The electromagnetic properties of the dosimeter determine the internal field and the microwave absorption. Then the microwave heating and thermal properties of the dosimeter lead to an elevated steady‐state temperature for the droplets. Finally, the nucleation rate is obtained from classical homogeneous nucleation theory, while the number of bubbles formed in an ensemble of droplets is found by a simple statistical argument. Although a special case is considered and several approximations are invoked, the qualitative results show this effect could lead to spurious neutron readings only for intense microwave fields or for an ambient temperature close to the nucleation temperature. For microwave bubble dosimetry, some nonthermal mechanism would be much more useful.
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28.41.Te Protection systems, safety, radiation monitoring, accidents, and dismantling
87.53.Bn Dosimetry/exposure assessment
78.70.Gq Microwave and radio-frequency interactions

Optically pumped laser action in double‐heterostructure HgCdTe grown by metalorganic chemical vapor deposition on a CdTe substrate

A. Ravid, G. Cinader, and A. Zussman

J. Appl. Phys. 74, 15 (1993); http://dx.doi.org/10.1063/1.354133 (5 pages) | Cited 13 times

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Photopumped laser action in a HgCdTe double‐heterostructure grown by metalorganic chemical vapor deposition on a CdTe substrate containing (311)‐ and (211)‐oriented grains was studied. The (311)‐oriented device exhibited laser action around λ=4 μm with a threshold power increasing exponentially from 56 mW at T=12 K to 2.8 W at the highest lasing temperature of 90 K. The (211)‐oriented laser device emitted around 2.5 μm. The threshold power of the (211) device was much higher than that of the (311) one (1.5 W at 12 K) and increased with temperature at a lower rate to 4.8 W at the highest lasing temperature of 110 K. Front illumination photoluminescence from both active and cladding layers of the (311)‐oriented heterostructure was studied as a function of temperature.
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78.45.+h Stimulated emission
42.55.Px Semiconductor lasers; laser diodes
78.55.Et II-VI semiconductors

Epitaxial waveguides of aluminum garnet

D. M. Gualtieri and R. C. Morris

J. Appl. Phys. 74, 20 (1993); http://dx.doi.org/10.1063/1.354147 (4 pages) | Cited 2 times

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Waveguides of high refractive index aluminum garnets have been epitaxially grown on 〈111〉‐oriented crystal wafers of yttrium aluminum garnet (Y3Al5O12, YAG) and clad with epitaxial YAG. Epitaxy was by the liquid phase solution growth technique from supercooled mixtures of lead oxide and boron oxide, as is common for the epitaxy of iron garnets. One composition which is particularly suited for waveguides is Tb1.78Lu1.22Al5O12, which has a refractive index at 632.8 nm of about 1.854, as compared with 1.828 for YAG, and has no absorption bands in the visible and near IR spectra. Since aluminum garnets have melting points above 1900 °C, such waveguides should find application in high temperature optical sensors.
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42.79.Gn Optical waveguides and couplers
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
78.66.Nk Insulators

Evidence of refractive index change by Ti indiffusion into LiNbO3 substrate as a result of multipulse free‐running ruby laser irradiation

Maria Dinescu, N. Chitica, Clementina Timus, I. N. Mihailescu, A. Andrei, Gabriella Maiello, L. Schirone, A. Ferrari, and M. Bertolotti

J. Appl. Phys. 74, 24 (1993); http://dx.doi.org/10.1063/1.354154 (7 pages) | Cited 1 time

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It is shown that the multipulse free‐running ruby laser irradiation of z‐cut LiNbO3 single‐crystalline samples with 400 Å‐thick Ti deposits results, under certain conditions, in an efficient Ti indiffusion with minimum perturbation. Implanted zones exhibit optical characteristics appropriate for the preparation of optical devices.
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42.70.-a Optical materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Transient ballistic and diffusive phonon heat transport in thin films

A. A. Joshi and A. Majumdar

J. Appl. Phys. 74, 31 (1993); http://dx.doi.org/10.1063/1.354111 (9 pages) | Cited 129 times

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Ballistic and diffusive phonon transport under small time and spatial scales are important in fast‐switching electronic devices and pulsed‐laser processing of materials. The Fourier law represents only diffusive transport and yields an infinite speed for heat waves. Although the hyperbolic heat equation involves a finite heat wave speed, it cannot model ballistic phonon transport in short spatial scales, which under steady state follows the Casimir limit of phonon radiation. An equation of phonon radiative transfer (EPRT) is developed which shows the correct limiting behavior for both purely ballistic and diffusive transport. The solution of the EPRT for diamond thin films not only produces wall temperature jumps under ballistic transport but shows markedly different transient response from that of the Fourier law and the hyperbolic heat equation even for predominantly diffusive transport. For sudden temperature rise at one film boundary, the results show that the Fourier law and the hyperbolic heat equation can significantly over‐ or underpredict the boundary heat flux at time scales smaller than the phonon relaxation times.
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68.60.Bs Mechanical and acoustical properties
05.70.Ce Thermodynamic functions and equations of state
63.20.-e Phonons in crystal lattices

Transient flow of a Maxwell fluid on a rotating disk

C. F. Chan Man Fong, D. De Kee, and B. Marcos

J. Appl. Phys. 74, 40 (1993); http://dx.doi.org/10.1063/1.354125 (5 pages) | Cited 9 times

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The unsteady flow of a thin layer of a Maxwell fluid is being considered. The radial speed and the thickness of the film are obtained analytically and numerically. The results obtained by both methods are in agreement.
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47.32.-y Vortex dynamics; rotating fluids
83.50.-v Deformation and flow
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Dynamics of the detonation products of lead azide: III. Laser‐induced hole burning and flow visualization

Y. Tzuk, B. Barmashenko, I. Bar, and S. Rosenwaks

J. Appl. Phys. 74, 45 (1993); http://dx.doi.org/10.1063/1.355253 (8 pages) | Cited 3 times

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The cloud of products formed following the detonation of lead azide (LA) contains solid particles. Utilizing a pulsed beam of a neodymium: yttrium aluminum garnet (Nd:YAG) laser, the particles are evaporated and hole burning through the opaque cloud is demonstrated. The characteristics of the hole and of the expanding cloud are monitored in real time by a HeNe beam, high‐speed framing photography and emission of excited Pb atoms. The hole is carried with the cloud and propagates at a constant velocity of 0.5–2.8 km/s, depending on the time and location of burning and given by d(h)/t(h), where d(h) is the distance from the LA sample to the center of the Nd:YAG beam and t(h) is the time from detonation to hole burning. The reduction in the number and size of the particles is monitored by scanning electron microscopy of the deposits formed on a substrate following the detonation. The propagation of the Nd:YAG laser pulse through the cloud is numerically modeled and provides an estimate of the increase in the temperature and the decrease of the size of the particles as a result of the interaction with the laser beam.  
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47.40.-x Compressible flows; shock waves
32.30.-r Atomic spectra

Vacuum ultraviolet spectroscopy study of excimer‐laser‐generated plasmas

G. Mehlman, D. B. Chrisey, P. G. Burkhalter, J. S. Horwitz, and D. A. Newman

J. Appl. Phys. 74, 53 (1993); http://dx.doi.org/10.1063/1.355267 (9 pages) | Cited 14 times

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The dispersed emission in the vacuum ultraviolet (VUV) (1200–3000 Å) from the plasma generated by the interaction of a KrF excimer laser with an Al and a YBa2Cu3O7 target has been measured. Emission spectra were collected as a function of distance above the target surface and as a function of laser fluence. The qualitative features of the plasmas from the two different targets were similar. The character of the emission spectra changed from a pseudocontinuous emission at the target surface to discrete emission from singly, doubly ionized species as well as neutrals at distances greater than ∼1.5 mm. The spatial variation indicated two regions: a high‐density sheath along the target where the core emission is close to blackbody; and beyond, a plasma with large opacity emitting a UV spectrum of intensity decreasing fast with distance. Estimates of the plasma temperature and density were between 2 and 4 eV and ∼1018/cm3, respectively.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
81.15.Fg Pulsed laser ablation deposition

Mass and energy analysis of gaseous species in NF3 plasma during silicon reactive ion etching

M. Konuma and E. Bauser

J. Appl. Phys. 74, 62 (1993); http://dx.doi.org/10.1063/1.355250 (6 pages) | Cited 17 times

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Neutral molecules and positive ions, extracted directly from the reaction zone during reactive ion etching of silicon in NF3 plasma, have been identified by quadrupole mass spectrometry. The main etching end products are SiF4 molecules and SiF+3 ions. Reactive species that contribute to the etching are atomic F radicals and F+2 molecular ions. Most of the positive ions in the plasma hold NF+2 ions and this facilitates etching of negatively biased Si by bombardment. Likewise, the kinetic energy of ions that impinge on an electrically grounded surface can be measured by using a cylindrical mirror analyzer. Within a certain range of plasma parameters there are no obvious differences in kinetic energies among the observed ions in the plasma. Under a constant NF3 pressure of 6.7 Pa, the characteristic mean ion energy of 4 eV at an rf power of 10 W increases to 20 eV by increasing the rf power to 90 W.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.70.Nc Particle measurements
81.65.-b Surface treatments
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

A steady‐state model for a low‐pressure Cs‐Ba diode

Christopher S. Murray, Mohamed S. El‐Genk, Bernard Wernsman, and Vladimir Z. Kaibyshev

J. Appl. Phys. 74, 68 (1993); http://dx.doi.org/10.1063/1.355232 (9 pages) | Cited 3 times

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A steady‐state model of a low‐pressure Cs‐Ba discharge is developed. It calculates the plasma density, electron temperature, Cs atom densities, and output voltage, assuming uniform conditions across the discharge gap and neglecting radiation losses. The model predictions are in good agreement with experimental data for a low‐pressure Cs discharge. Comparing the model to experimental data from a Cs‐Ba diode reinforce the validity of the system of equations and also confirms the assumption that barium has practically no effect on the current transport characteristics. The calculated I‐V curves for the Cs‐Ba diode match well with the experimental data below the emission current; however, above the emission current the calculated currents are much lower. This difference occurs when the model incorporates normal Schottky emission instead of anomalous Schottky. The effect of the latter is determined from estimates of the effective changes in the emitter work function for agreement between the model and experiments at high discharge currents. For such currents, results suggest that changing the Cs pressure strongly affects the anomalous Schottky emission, while changes in the Ba pressure seem to have a negligible effect.
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52.75.-d Plasma devices
52.80.-s Electric discharges

Carbon incorporation in GaAs and AlxGa1−xAs layers grown by molecular‐beam epitaxy

C. Giannini, C. Gerardi, L. Tapfer, A. Fischer, and K. H. Ploog

J. Appl. Phys. 74, 77 (1993); http://dx.doi.org/10.1063/1.355200 (5 pages) | Cited 6 times

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GaAs:C and AlxGa1−xAs:C films, grown by solid‐source molecular‐beam epitaxy with doping levels beyond 1019 cm−3, have been studied by high‐resolution double‐crystal x‐ray diffraction, Hall‐effect measurements, and secondary‐ion‐mass spectroscopy (SIMS). Comparison between x‐ray diffraction and Hall‐effect data indicate that carbon is preferentially incorporated as acceptor on As lattice sites both in the GaAs:C and in the AlxGa1−xAs:C films. It was found that the higher the AlAs mole fraction the higher is the concentration of carbon incorporated on As sites (CAs). Moreover, SIMS results showed that the total amount of carbon in the host lattices largely exceeds CAs. Our findings are explained by supposing that carbon atoms are incorporated on As sites and on interstitial sites. Furthermore, it is shown that the carbon interstitial concentration can be reduced growing at higher arsenic flux and higher substrate temperature in GaAs:C as well as in AlxGa1−xAs:C layers.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
61.72.uj III-V and II-VI semiconductors

An investigation of as‐implanted material formed by high dose 40 keV oxygen implantation into silicon at 550 °C

Y. Li, J. A. Kilner, R. J. Chater, A. Nejim, P. L. F. Hemment, and T. J. Tate

J. Appl. Phys. 74, 82 (1993); http://dx.doi.org/10.1063/1.355201 (4 pages) | Cited 41 times

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Device grade 〈100〉 single crystal silicon wafers have been implanted with 40 keV oxygen ions (16O+) over the dose range of 1×1017–8×1017/cm2 at a temperature of 550±10 °C. Transmission electron microscopy, ion channeling, and secondary ion mass spectroscopy studies show that during implantation the critical dose required to form a buried oxygen‐rich amorphous (SiOx, x<2) layer is lower than 1×1017 O+/cm2. As the dose increases from 1×1017 to 4×1017/cm2 the thickness of the buried SiOx layer increases and there is a corresponding decrease in the thickness of the single crystal silicon top layer, with the oxygen concentration and residual radiation damage playing important roles in determining its position and thickness. A dose of 5×1017/cm2 results in a continuous surface amorphous layer, with a buried SiO2 sublayer being formed in the region corresponding to the implanted oxygen peak. With further increasing dose, the buried SiO2 sublayer grows primarily towards the surface. The results for the sample implanted at a dose of 1×1017/cm2 show that surface defects can be attributed to agglomeration of interstitial silicon atoms created by the internal oxidation process.
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61.72.uf Ge and Si
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Effects of rapid quenching on the impurity site location in Zn‐diffused InP

Kin Man Yu, W. Walukiewicz, L. Y. Chan, R. Leon, E. E. Haller, J. M. Jaklevic, and C. M. Hanson

J. Appl. Phys. 74, 86 (1993); http://dx.doi.org/10.1063/1.355202 (5 pages) | Cited 11 times

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The lattice locations of Zn atoms in heavily Zn‐doped InP single crystal have been investigated by ion channeling techniques. The InP samples were rapidly quenched in diffusion pump oil after high‐temperature Zn diffusion. Ion channeling experiments performed along various major crystal axes suggest that a large fraction (20%–30%) of the Zn atoms are in the tetrahedral interstitial position in the InP lattice. It has been found that although the maximum hole concentration is not significantly affected by the cooling rate, there is a substantial increase in the incorporation of Zn on substitutional and tetrahedral interstitial lattice locations in the rapidly cooled samples as compared to the slowly cooled samples. The consequences of these results for understanding the mechanisms leading to the saturation of the free‐hole concentration in compound semiconductors are discussed.
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61.72.uj III-V and II-VI semiconductors
66.30.Lw Diffusion of other defects
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Nanoscale study of the as‐grown hydrogenated amorphous silicon surface

G. C. Stutzin, R. M. Ostrom, Alan Gallagher, and D. M. Tanenbaum

J. Appl. Phys. 74, 91 (1993); http://dx.doi.org/10.1063/1.355203 (10 pages) | Cited 10 times

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A scanning tunneling microscope has been used to study the topography of the as‐grown surface of device‐quality, intrinsic, hydrogenated amorphous silicon deposited by rf discharge from silane. The substrates were atomically flat, oxide‐free, single‐crystal silicon or gallium arsenide. No evidence for island formation or nanoscale irregularities was seen in studies of 100‐Å‐thick films on either silicon or gallium arsenide. The topography of 1000‐ and 4000‐Å‐thick films has much variation; many regions can be characterized as ‘‘rolling hills,’’ but atomically flat areas have also been observed nearby. Generally, it appears that surface diffusion plays a role in smoothing the film topography. In most regions, the observed slopes were 10% or less from horizontal, but some steep‐sided valleys, indicating incipient voids, were observed. The effect of the finite size of the scanning tunneling microscope probe tip is considered; this has an effect on the observed images in some cases.
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61.43.Dq Amorphous semiconductors, metals, and alloys
68.55.-a Thin film structure and morphology
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Examination of the multilevel diffraction model for interface roughness characterization by scanning tunneling microscopy

H.‐N. Yang, A. Chan, and G.‐C. Wang

J. Appl. Phys. 74, 101 (1993); http://dx.doi.org/10.1063/1.354139 (6 pages) | Cited 11 times

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Scanning tunneling microscopy (STM) has been used to investigate rough Au:Pd thin films. The Au:Pd surface is best described by the self‐affine scaling model, with the roughness exponent α=0.79±0.06 and the interface width w=15.0±0.5 Å measured directly from the STM images. We further show how α and w may be extracted from diffraction techniques by utilizing the multilevel diffraction theory, using the STM images as a model self‐affine surface.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.55.-a Thin film structure and morphology

Multilayer x‐ray mirrors: Interfacial roughness, scattering, and image quality

Eberhard Spiller, Daniel Stearns, and Michael Krumrey

J. Appl. Phys. 74, 107 (1993); http://dx.doi.org/10.1063/1.354140 (12 pages) | Cited 69 times

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Scattering of the multilayer coatings used for our normal incidence soft x‐ray telescope at λ=63.5 Å has been measured at λ=1.54 Å and grazing angles of incidence and at soft x rays near normal incidence. Furthermore, the edge of the moon is used as a known test target to estimate the amount of scattering in the arcsec range from images obtained on the date of the solar eclipse on July 11, 1991. The internal surfaces of the coating are inspected by high‐resolution electron microscopy. A theoretical model describing the evolution and replication of roughness from layer to layer throughout the structure, which is in agreement with all experimental data is presented. We find that practically all roughness caused by the growth of the multilayer structure occurs at spatial frequencies which are too high to produce scattering. The substrate roughness is replicated at lower spatial frequencies which might produce scattering within the field of view of an instrument. However, roughness in this range is below the 0.5 Å level again resulting in insignificant amounts of scatter.
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61.05.C- X-ray diffraction and scattering
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
95.85.Nv X-ray
78.66.-w Optical properties of specific thin films

Electrical activation of bismuth implanted into silicon by rapid thermal annealing and kinetics of defects

J. P. de Souza and P. F. P. Fichtner

J. Appl. Phys. 74, 119 (1993); http://dx.doi.org/10.1063/1.354142 (4 pages) | Cited 8 times

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The rapid thermal annealing (RTA) of Si implanted with Bi+, to a dose of 5.0×1014 cm−2 at the energy of 150 keV, was investigated using sheet resistivity, Hall measurements, and channeling analysis. Approximately 95% of the Bi dose is found substitutional and 90% is electrically active after annealing is performed at 600 °C for times longer than 1 min. The electrical activation yield of Bi after RTA at temperatures ≥700 °C is observed to decrease when increasing the temperature and time of the annealing process. The data taken from electrical measurements and angular scan across the 〈100〉 axis are evidence that the electrically inactive concentration of the Bi correlates with the concentration of Bi atoms located slightly displaced from the crystal rows.
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61.72.uf Ge and Si
61.72.Cc Kinetics of defect formation and annealing
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Photoluminescence properties of N‐implanted Al0.30Ga0.70As0.62P0.38 alloy grown on GaAs0.61P0.39 substrates

Chyuan‐Wei Chen and Meng‐Chyi Wu

J. Appl. Phys. 74, 123 (1993); http://dx.doi.org/10.1063/1.354143 (6 pages)

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Luminescence data are presented on nitrogen‐implanted Al0.30Ga0.70As0.62P0.38 epitaxial layers, which are grown on GaAs0.61P0.39 substrates by liquid‐phase epitaxy, with different annealing temperatures by the rapid thermal annealing technique. Except for the four emission peaks observed from undoped AlGaAsP layers, involving near‐band‐to‐band, donor‐to‐valence‐band, conduction‐band‐to‐acceptor, and donor‐acceptor‐pair transitions, we also observe the recombinations from the NΓ, N′Γ, and Nx states associated with the nitrogen isoelectronic impurity in the N‐implanted AlGaAsP layer. The existence of such states has been predicted by a theory of the N trap that includes both the long‐ and short‐range characters of isoelectronic impurity potential in III‐V alloys. The states NΓ and N′Γ are observed to lie below the Γ conduction‐band minimum by 24 and 16 meV, respectively. The Nx state is associated with indirect emission and is below the Γ conduction‐band minimum by 34 meV. This is a report on the luminescence study of N‐implanted AlGaAsP alloy.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors

Solid phase crystallization of thin films of Si prepared by plasma‐enhanced chemical vapor deposition

Y. Masaki, P. G. LeComber, and A. G. Fitzgerald

J. Appl. Phys. 74, 129 (1993); http://dx.doi.org/10.1063/1.354144 (6 pages) | Cited 54 times

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Solid phase crystallization of thin films of undoped amorphous Si prepared by plasma enhanced chemical vapor deposition has been studied by transmission electron microscopy (TEM). From the TEM images, the thermodynamic parameters for the amorphous and crystalline phases were extracted. These parameters were compared with those previously reported for evaporated, chemical vapor deposited, and self‐implanted amorphous Si. We conclude that the thermodynamic parameters are very similar for different amorphous Si films, although the initial structure of the films is comparatively different from one to another. To explain this, the existence of an intermediate amorphous state is assumed and discussed.
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61.43.Dq Amorphous semiconductors, metals, and alloys
68.55.-a Thin film structure and morphology
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Ion‐beam induced compaction in glassy carbon

D. McCulloch, A. Hoffman, and S. Prawer

J. Appl. Phys. 74, 135 (1993); http://dx.doi.org/10.1063/1.354145 (4 pages) | Cited 18 times

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Cross‐sectional transmission electron microscopy has been used to investigate the implanted layer in glassy carbon irradiated with 50 keV C ions to a dose of 5×1016 ions/cm2. It was found that in addition to the formation of an amorphous surface layer approximately 100 nm deep, the ion‐beam modified layer was compacted from the unirradiated density of 1.5 to 2.4±0.2 g/cm3. Ion implantation was also found to increase the refractive index of glassy carbon from 1.8±0.1 to 2.4±0.1 which is also consistent with the proposition that an increase in the density of the implanted layer has occurred. The formation of a dense, amorphous carbon surface layer could explain the observed increase in wear resistance of glassy carbon following ion implantation.
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61.80.Jh Ion radiation effects
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
81.40.Pq Friction, lubrication, and wear

Birefringence images of screw dislocations viewed end on in cubic crystals containing a long‐range stress field

Chuan‐Zhen Ge, Hai‐Wen Wang, and Nai‐Ben Ming

J. Appl. Phys. 74, 139 (1993); http://dx.doi.org/10.1063/1.354146 (7 pages) | Cited 7 times

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The expression for the intensity distribution and computer‐simulated images of screw dislocations with Burgers vector α〈111〉 or α/2〈111〉 viewed end on in cubic crystals subjected to a long‐range uniaxial stress has been obtained by considering the anisotropy of both elastic and photoelastic properties of the material. The computer‐simulated images of end‐on screw dislocations show twofold symmetry with a pair of dark and bright petals which result from the effect of a long‐range stress superimposed on that of the screw dislocations. The computer‐simulated images are in good agreement with the experimental images observed in Ba(NO3)2 and Gd3Ga5O12 crystals. The principal stress of the long‐range uniaxial stress field around the screw dislocation in the crystal wafer has been estimated, based on this theory.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Investigations of semiconductor superlattices by depth‐sensitive x‐ray methods

H. Rhan, U. Pietsch, S. Rugel, H. Metzger, and J. Peisl

J. Appl. Phys. 74, 146 (1993); http://dx.doi.org/10.1063/1.354130 (7 pages) | Cited 18 times

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Focusing on the structure determination of a GaInAs/InP superlattice (SL), the potential of grazing incidence diffraction (GID) to resolve structure parameters on a microscopic scale is compared to x‐ray reflectivity and conventional x‐ray diffraction (XRD) measurements. Usually, information on the density profile perpendicular to the surface is obtained by x‐ray reflectivity and on lattice mismatch by XRD. Since the penetration depth of x rays is much larger than the total thickness of the SL these methods measure parameters averaged over the whole structure. Furthermore, the depth sensitivity of both methods is small in the case of extremly high thickness ratios of the sublayers within the SL period. These disadvantages can be overcome using GID geometry for which the information depth can be reduced by keeping the angle of incidence αi and exit αf of the x‐ray beam with respect to the surface in the range close to the critical angle of total external reflection αC. This enables a depth‐selective structure determination. As an example measurements and computer simulations corresponding to the three different methods of a lattice‐matched (GaIn)As/InP SL are presented. The periodic length of the present SL and the thickness of the top layer was determined by all three methods to monolayer accuracy.
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61.05.C- X-ray diffraction and scattering
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

The yield point of In‐doped GaAs between 500 and 900 °C

Hans Siethoff, Hans Georg Brion, and Johannes Völkl

J. Appl. Phys. 74, 153 (1993); http://dx.doi.org/10.1063/1.354131 (6 pages) | Cited 3 times

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In‐doped (5×1019/cm3) GaAs single crystals with 〈123〉 orientation are compressed at different strain rates and temperatures between 500 and 900 °C. Two different regimes are observed. At high strain rates and temperatures below 700 °C, the strain‐rate dependence of the lower yield stress is characterized by a power law with a stress exponent of 3.7, while its temperature dependence obeys an Arrhenius law with an activation energy of 0.93 eV. The latter value is smaller than that found for undoped GaAs, but the stress exponent is practically unchanged. This regime is interpreted in terms of a kink mechanism; the rate‐controlling process is assumed to be governed by a strong interaction of In atoms with α dislocations. The regime occurring at low strain rates and temperatures above 700 °C is characterized by strong hardening and a weak temperature and strain‐rate dependence of the lower yield stress. This behavior is ascribed to a direct alloying effect. Different types of interaction between dislocations and impurities are discussed. The knowledge of the strain‐rate dependence of the lower yield stress, besides its temperature dependence, is a prerequisite for the interpretation of the measurements.
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62.20.F- Deformation and plasticity
61.72.Yx Interaction between different crystal defects; gettering effect

Determining elastic behavior of composites by the boundary element method

J. W. Eischen and S. Torquato

J. Appl. Phys. 74, 159 (1993); http://dx.doi.org/10.1063/1.354132 (12 pages) | Cited 43 times

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The boundary element method is applied to determine the effective elastic moduli of continuum models of composite materials. In this paper, we specialize to the idealized model of hexagonal arrays of infinitely long, aligned cylinders in a matrix (a model of a fiber‐reinforced material) or a thin‐plate composite consisting of hexagonal arrays of disks in a matrix. Thus, one need only consider two‐dimensional elasticity, i.e., either plane‐strain or plane‐stress elasticity. This paper examines a variety of cases in which the inclusions are either stiffer or weaker than the matrix for a wide range of inclusion volume fractions ϕ2. Our comprehensive set of simulation data for the elastic moduli are tabulated. Using the boundary element method, a key microstructural parameter η2 that arises in rigorous three‐point bounds on the effective shear modulus is also computed. Our numerical simulations of the elastic moduli for the hexagonal array are compared to rigorous two‐point and three‐point bounds on the respective effective properties. In the extreme instances of either superrigid particles or voids, we compare analytical relations for the elastic moduli near dilute and close packing limits to our simulation results.
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62.20.D- Elasticity
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