bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of interface quality on structural and optical properties of GaxIn1−xAs/AlyIn1−yAs superlattices lattice matched to (001) InP
Authors: Tapfer L. , Stolz W. , Ploog K.
Published: July 2002

The structural and optical properties of GaxIn1−xAs/AlyIn1−yAs superlattices grown lattice matched to InP by molecular-beam epitaxy have been studied by means of x-ray diffraction and infrared absorption spectroscopy. Our results demonstrate that the growth of a strain-free interface configuration is the most important condition to obtain narrow x-ray diffraction linewidths and sharp optical transition lines.
Characterization of waveguides formed by proton-exchange in MgO-doped and Nd:MgO-doped LiNbO3: A comparison with congruent material
Authors: Loni A. , Keys R. W. , De La Rue R. M.
Published: July 2002

Proton-exchanged waveguides fabricated in LiNbO3 doped with 4.5% MgO and 0.1–0.2 % Nd:4.5% MgO have been characterized by prism-coupling and infrared-absorption spectroscopy. Single and multimode doped waveguides have temporally stable effective mode indices, and the refractive-index profiles are identical to those observed for proton exchange in congruent LiNbO3. Effective diffusion coefficients for proton exchange in doped x and z-cut substrates have been estimated for waveguide-fabrication temperatures in the range 182–235 °C. While diffusion coefficients for MgO:LiNbO3 and Nd:MgO:LiNbO3 appear to be identical, waveguides formed in the doped substrates have substantially smaller diffusion coefficients compared to waveguides formed in congruent LiNbO3, the magnitudes being down by as much as 50% for x-cut waveguides and 37% for z-cut waveguides. These results should prove of value when using the proton-exchange technique to design waveguide lasers in Nd:MgO:LiNbO3.
Optical emission spectroscopy of rf discharge in SF6
Authors: Radovanov S. B. , Tomčik B. , Petrović Z. Lj. , Jelenković B. M.
Published: July 2002

In this paper we present experimental results obtained for a rf discharge in SF6 and for SF6 with Ar and/or N2. The data for power dependence of some emission lines usually used in actinometry are acquired and their applicability and excitation kinetics discussed. We also present the spatial (time averaged) variations of some emission lines. From such data the spatial dependence of the high-energy tail of the electron energy distribution function may be obtained.
Preparation of diamondlike carbon films by electron cyclotron resonance chemical vapor deposition
Authors: Nagai I. , Ishitani A. , Kuroda H. , Yoshikawa M. , Nagai N.
Published: July 2002

Diamondlike carbon films were prepared by electron cyclotron resonance chemical vapor deposition. Structures of the carbon films were characterized by Raman spectroscopy and Fourier-transform infrared spectroscopy. The relationship between the properties of films and growth conditions has been examined. High-energy ion species extracted from a discharge of methane in the electron cyclotron resonance cavity, which is positively-biased electrically against the earthed substrate, have an important role in the growth behavior of hard diamondlike carbon films.
Strain measurements in heteroepitaxial yttria-stabilized zirconia on Si by ion beam channeling
Authors: Fukumoto Hirofumi , Yamamoto Masateru , Osaka Yukio , Nishiyama Fumitaka
Published: July 2002

Yttria-stabilized zirconia (YSZ) films have been epitaxially grown on Si(100) substrates at 800 °C by vacuum evaporation. By post-annealing in dry O2 at 800 °C, SiO2 layer was formed at the YSZ/Si interface. Strain in heteroepitaxial cubic YSZ films has been measured by ion beam channeling. The strain was found to be tensile. This tensile strain is caused as the sample is cooled down after growth due to the difference in thermal expansion coefficients between YSZ and Si. The tensile strain is increased by annealing in dry O2, due to the SiO2 layer formed at the YSZ/Si interface. The tensile strain is also introduced in the near-interface region of Si substrate under SiO2.
The optimization of multipole magnetizing fixtures for high-energy magnets
Authors: Lee J. Kelly , Furlani E.
Published: July 2002

Modern high-energy magnetic materials such as samarium-cobalt and neodymium-iron-boron require very large magnetizing fields to achieve full saturation. In some cases the recommended magnetizing field is as high as 40 kOe. Such a field is readily achievable in a large solenoid, and unidirectional magnetization is easily accomplished. Many applications, such as motors and linear actuators, however, require multipole magnets. The problem of designing custom fixtures for multipole magnetization has often been considered more of an art than a science. This paper shows that by mathematically modeling the capacitor discharge magnetizer and the fixture the problem can be solved with reasonable predictability. Two different multipole fixture designs are presented along with the experimental results. The basic equations are presented and used to predict the magnetic-field intensity inside the fixtures. It is shown that optimum performance is achieved when the resistance of the fixture is equal to the parasitic resistance of the magnetizer. Finite-element analysis is also used as part of the design process. The experimental results have been achieved using a high-voltage, low-energy capacitor-discharge magnetizer and air core fixtures. The magnetization patterns that are produced are very sharp and well defined.
Electrical activity of aluminum implanted in silicon: An interface problem in high-power devices
Authors: Brüesch P. , Halder E. , Kluge P. , Rhyner J. , Roggwiller P. , Stockmeier Th. , Stucki F. , Wiesmann H. J.
Published: July 2002

Because of its high diffusivity in silicon, aluminum is best suited for deep diffusions often required in high-voltage-power semiconductor devices. The ion implantation technique allows the reproducible low dosage doping necessary, e.g., for the new concepts of junction termination systems. The most important drawback of using aluminum as a p-type dopant in silicon is its low electrical activity after the anneal. In order to obtain a deeper insight into the mechanisms responsible for the loss of the electrical activity, we have studied the states of aluminum implanted into silicon before and after annealing by means of spreading resistance, secondary-ion mass spectroscopy, transmission electron microscopy, and energy-dispersive x-ray techniques. The case study presented here [Czochralski grown (100) silicon, implanted dose 3×1015 cm−2, junction depth 6 μm] reveals that the major source for the loss of the electrical activity is out-diffusion, i.e., segregation into the native silicon oxide layer and/or evaporation into the vacuum. In addition, the activity is reduced by the formation of aluminum oxide precipitates. The results are discussed in the light of optical studies on the same materials performed previously as well as on the basis of a diffusion model which allows for out-diffusion. The large rate constant for out-diffusion indicates that the native oxide layer represents a highly reactive surface for aluminum. From the diffusion model it is possible to calculate an approximate electrical activity Ã(xj) as a function of junction depth xj, which qualitatively reproduces well the observed activity A(xj). This demonstrates that our case study is representative for a large number of samples which were implanted and annealed under widely different conditions. Some technical processes which could possibly enhance the electrical activity are discussed.
Tungsten-carbon multilayers for x-ray optics prepared by ArF excimer-laser-induced chemical vapor deposition
Authors: Mutoh Katsuhiko , Yamada Yuka , Iwabuchi Takashi , Miyata Takeo
Published: July 2002

The authors have studied the characteristics of tungsten (W) and carbon (C) thin films, and W/C multilayers prepared by ArF excimer-laser-induced chemical vapor deposition using tungsten hexafluoride and benzene gases. Amorphous W and C films with very smooth surfaces were obtained at substrate temperatures of 100–200 °C and 100–300 °C, respectively. In small-angle x-ray scattering measurements for the multilayers deposited at 200 °C, a first order of multilayer reflections were clearly observed. Furthermore, Auger electron spectroscopy showed that W and C layers in the multilayers were periodically deposited.
Secondary defect evolution in ion-implanted silicon
Authors: Gaiduk P. I. , Larsen A. Nylandsted
Published: July 2002

A possible correlation between the annealing of secondary defects in silicon with high P background and anomalous diffusion of As or Sb was investigated. The P background (9×1019–4×1020 cm−3) was formed by phosphorus implantation (80 keV (2–10)×1015 cm−2), followed by rapid thermal annealing. Dislocation loops and misfit dislocations of various densities were formed under these conditions. Subsequently, As or Sb was implanted, and finally the crystals were annealed by rapid thermal annealing. By a combination of Rutherford backscattering/channeling, transmission electron microscopy and Hall measurements, anomalous diffusion of Sb and As and reduction or complete annealing of the secondary defects were found in the presence of the high P background. The results are discussed in terms of interaction between impurities and dislocations or defect complexes.
Exploratory observations of random telegraphic signals and noise in homogeneous hydrogenated amorphous silicon
Authors: Choi W. K. , Owen A. E. , LeComber P. G. , Rose M. J.
Published: July 2002

Noise measurements on unhydrogenated and hydrogenated rf sputtered intrinsic amorphous silicon reported by D’Amico, Fortunato, and Van Vliet [Solid-State Electron. 28, 837 (1985)] have 1/f  and Lorentzian spectra, respectively. Similar noise measurements on glow-discharge deposited hydrogenated amorphous intrinsic silicon reported by Bathaei and Anderson [Philos. Mag. B 55, 87 (1987)] gave a 1/f m spectrum with 0.7<m<1. Even more recently Ley and Arce [Proc. MRS Symposium, San Diego (1989)] have reported random telegraph signals in a-Si:H/a-Si1−xNx:H double barrier structures. The associated noise was a Lorentzian noise spectrum. In this paper the first observation of random telegraph signals in notionally homogeneous heavily doped (p+) glow-discharged-deposited amorphous silicon is reported. It was found that the current passing through the sample fluctuates between two easily identifiable levels with the periods of fluctuations separated by a quiescent period. The occurrence of these fluctuations is unpredictable but the current noise spectrum obtained during quiescent periods is Lorentzian, probably indicative of a generation-recombination process. Noise measurements are not possible at higher biases (>105 V/cm) as the current fluctuates chaotically and this is also the prebreakdown regime of the sample.
The role of Ga antisite defect in the activation process of transmuted impurities in neutron-transmutation-doped semi-insulating GaAs
Authors: Satoh M. , Yokoyama K. , Kuriyama K.
Published: July 2002

In neutron-transmutation doping for undoped and In-doped GaAs irradiated with thermal and fast neutrons of 1.5×1018 and 7.0×1017 cm−2, we have found for the first time photoluminescence emissions around 860 and 935 nm at 77 K associated with the two difference levels of Ga antisite defect (GaAs). It is suggested that the annealing of GaAs defects plays an important role in the activation process of transmuted impurities as well as the annealing of As antisite defects forming midgap electron traps. The GaAs defects are annihilated in an annealing temperature range from 650 to 700 °C, accompanied by an abrupt decrease in resistivity.
Growth mechanism and morphology of semiconducting FeSi2 films
Authors: Dimitriadis Charalabos A. , Werner Jurgen H.
Published: July 2002

Semiconducting β-FeSi2 films grown on (100)-oriented Si and on (11̄02)-sapphire substrates are investigated by x-ray diffraction, Nomarski optical microscopy, stress, and surface roughness measurements. As a result of an exothermic, nucleation controlled reaction, we observe a characteristic ring-shaped surface pattern of the silicide. Surface roughness and stress in β-FeSi2 are less pronounced for films grown at lower temperatures and cooling rates. Sapphire substrates result in smoother surfaces than Si due to the match of the thermal expansion coefficient of sapphire to the silicides.
A model to calculate the temperature induced by a laser
Authors: Garrido C. , León B. , Pérez-Amor M.
Published: July 2002

Numerical models to calculate temperature distributions during laser chemical vapor deposition (LCVD) of spots and during the direct writing of lines are presented. The temperature variation of the thermal conductivities of the substrate and the deposit are taken into account in both models. Results are used to study the LCVD deposition of platinum spots and lines on pyrex glass substrates.
Calculated magnetic and electronic properties of Co/Pd superlattices
Authors: Victora R. H. , MacLaren J. M.
Published: July 2002

The electronic and magnetic properties of several Co/Pd superlattices are predicted using the layer Korringa-Kohn-Rostoker method. The superlattice polarizations, per Co atom, are found to exhibit a strong oscillatory dependence on Pd layer thickness; this result is in agreement with previous experimental observation. The effect is mostly caused by the induced Pd polarization which is found to depend strongly on superlattice and distance from the Co layer. Particularly surprising is the behavior of the Pd layer most distant from the Co: in Co/3Pd and Co/4Pd it has enhanced polarization relative to its neighboring Pd layers, in Co/5Pd the polarization is negative. In contrast, spin polarizations on Co atoms are predicted to attain a fairly uniform value of 2.00 electrons regardless of Pd thickness.
Atomic ordering in GaAsP
Authors: Chen G. S. , Jaw D. H. , Stringfellow G. B.
Published: July 2002

CuPt type ordering, which consists of a monolayer compositional modulation along one of the 4 〈111〉 directions in the lattice, was studied using transmission electron microscopy for GaAs1−xPx with values of x extending from 0.25 to 0.85. The samples were grown by organometallic vapor phase epitaxy on nominal (001) GaAs substrates that were misoriented by varying amounts in three directions. No CuPt type ordering was observed for GaAs1−xPx with x ≤0.35, while ordering was found to occur for 0.4≤x≤0.85. The direction of substrate misorientation has a major effect on the determination of which of the four possible CuPt variants are formed for 0.4≤x≤0.85. Two variants, with ordering on the (1̄11) and (11̄1) planes, appear for epilayers grown on substrates oriented exactly on the (001) plane and for substrates misoriented by 6° towards the [110] direction. Only one variant, with ordering on the (1̄11) plane, appears for epilayers grown on substrates misoriented by 6° towards [1̄10]. These ordering-induced spots observed in transmission electron diffraction (TED) patterns for GaAsP occur only for the [110] cross section. From TED studies of GaInP grown on similar substrates, we conclude that the CuPt variants in GaAsP are exactly the same as for GaInP. Further evidence supporting this conclusion was obtained by growing first a layer of GaInP followed by a layer of GaAsP. High-resolution dark field electron micrographs show domains of the same variants in both layers. A mechanism describing the formation of the specific ordered variant for both GaAsP and GaInP is proposed. From studies of ordering in a strain-layer superlattice, the strain due to lattice mismatch was found to play no significant role in the propagation of ordered domains. Microtwins, also generated due to lattice mismatch, can act as domain boundaries and prevent the propagation of the ordered domains.
Velocity ratio measurements of a gyrotron electron beam
Authors: Guss W. C. , Grimm T. L. , Kreischer K. E. , Polevoy J. T. , Temkin R. J.
Published: July 2002

A 140 GHz high-power gyrotron has recently been operated in a 14 T Bitter magnet to characterize emission as a function of magnetic field and beam current. The velocity ratio (or pitch angle) α=〈v⊥〉/〈v∥〉 of the beam electrons is a critical parameter for high-efficiency gyrotron operation and was measured using a capacitive probe located in the beam tunnel before the cavity. The observed velocity ratio decreased as the beam current increased while the beam voltage and magnetic fields were held fixed. This decrease in α partially explains the reduced gyrotron efficiency observed at high-beam currents. The velocity ratio exhibited saturation effects as a function of both the beam current and the control-anode voltage, at low cathode magnetic field values. Particle code results show a decrease in α as a function of beam current that is consistent in magnitude with the observed values.
Epitaxial growth of chloroaluminum and vanadyl phthalocyanine films on alkali halide single crystals by the molecular-beam-epitaxy technique
Authors: Hoshi Hajime , Maruyama Yusei
Published: July 2002

Epitaxial chloroaluminum and vanadyl phthalocyanine (AlPcCl and VOPc) films have been prepared on alkali halide (100) surfaces by the molecular-beam-epitaxy technique. Their structures have been studied by scanning electron microscopy and transmission electron microscopy. The films consist of densely packed crystallites and seem to be continuous. The predominant phase of AlPcCl/NaCl is newly found bidirectionally oriented tetragonal, NaCl(100)(√13×√13)R±11°-AlPcCl. The phase of AlPcCl/KCl and AlPcCl/KBr is bidirectionally oriented tetragonal, KCl(100)(√10×√10)R±27°-AlPcCl and KBr(100)(√10×√10)R±27°-AlPcCl, respectively. The predominant phase of AlPcCl/KI is unidirectionally oriented tetragonal, KI(100)(3×3)R45°-AlPcCl. The phase of VOPc/KCl is bidirectionally oriented tetragonal, KCl(100)(√10×√10)R±27°-VOPc, while that of VOPc/KBr is unidirectionally oriented tetragonal, KBr(100)(3×3)R45°-VOPc. The preferential epitaxial lattice orientation is discussed based on the degree of lattice matching between phthalocyanine and substrates.
Auger electron diffraction study of the growth of Fe(001) films on ZnSe(001)
Authors: Jonker B. T. , Prinz G. A.
Published: July 2002

The growth of Fe films on ZnSe(001) epilayers and bulk GaAs(001) substrates has been studied to determine the mode of film growth, the formation of the interface, and the structure of the overlayer at the 1–10 monolayer level. Auger electron diffraction (AED), x-ray photoelectron spectroscopy (XPS), and reflection high-energy electron diffraction data are obtained for incremental deposition of the Fe(001) overlayer. The coverage dependence of the AED forward scattering peaks reveals a predominantly layer-by-layer mode of film growth at 175 °C on ZnSe, while a more three-dimensional growth mode occurs on the oxide-desorbed GaAs(001) substrate. XPS studies of the semiconductor 3d levels indicate that the Fe/ZnSe interface is less reactive than the Fe/GaAs interface.
Lattice location of diffused Zn atoms in GaAs and InP single crystals
Authors: Chan L. Y. , Yu Kin Man , Ben-Tzur M. , Haller E. E. , Jaklevic J. M. , Walukiewicz W. , Hanson C. M.
Published: July 2002

We have investigated the saturation phenomenon of the free carrier concentration in p-type GaAs and InP single crystals doped by zinc diffusion. The free hole saturation occurs at 1020 cm−3 for GaAs, but the maximum concentration for InP appears at mid 1018 cm−3. The difference in the saturation hole concentrations for these materials is investigated by studying the incorporation and the lattice location of the impurity zinc, an acceptor when located on a group III atom site. Zinc is diffused into the III-V wafers in a sealed quartz ampoule. Particle-induced x-ray emission with ion-channeling techniques are employed to determine the exact lattice location of the zinc atoms. We have found that over 90% of all zinc atoms occupy Ga sites in the diffused GaAs samples, while for the InP case, the zinc substitutionality is dependent on the cooling rate of the sample after high-temperature diffusion. For the slowly cooled sample, a large fraction (∼90%) of the zinc atoms form random precipitates of Zn3P2 and elemental Zn. However, when rapidly cooled only 60% of the zinc forms such precipitates while the rest occupies specific sites in the InP. We analyze our results in terms of the amphoteric native defect model. We show that the difference in the electrical activity of the Zn atoms in GaAs and InP is a consequence of the different location of the Fermi level stabilization energy in these two materials.
Geometrical theory of critical thickness and relaxation in strained-layer growth
Authors: Dunstan D. J. , Young S. , Dixon R. H.
Published: July 2002

In the growth of pseudomorphic strained layers, the critical thickness is the thickness up to which relaxation does not occur and beyond which relaxation occurs by plastic deformation of the layer. Previous theories have concentrated on the strain energy and kinetics of dislocation formation. We present a purely geometrical argument which predicts critical thicknesses and also predicts how relaxation progresses with increasing thickness. We find that the critical thickness, in monolayers, is approximately the reciprocal of the strain. Some relaxation occurs abruptly at critical thickness, and further relaxation is hyperbolic with thickness. The model can also handle multilayer structures. If all the layers have the same sign of strain, the model predicts that relaxation will occur at the lowest interface. These results are found to be in good agreement with experimental observations of dislocations in epitaxial structures of InGaAs grown on GaAs.
Chemical, microstructural, and internal friction characterization of Al/Cu thin-film reactions
Authors: Su C. M. , Bohn H. G. , Robrock K.-H. , Schilling W.
Published: July 2002

Cu/Al bilayer reactions have been studied by Rutherford backscattering, Auger depth profiling, transmission electron microscopy (TEM), and internal friction. In the later stage of the solid-state reaction Al2Cu Θ phase growth occurs in a planar manner at the top of the Al film and additionally along the grain boundaries of the columnar Al grains. For the early stage of the reaction where only small amounts of Cu have diffused into the Al, internal friction proved to be the only experimental technique sensitive to Cu concentrations below 500 ppm. It was found that 300 ppm of Cu are already sufficient to shift the grain boundary relaxation peak observed by internal friction to higher temperatures compared to pure Al. This behavior reflects a rise in activation energy for grain boundary diffusion from 0.55 eV for Al to about 1 eV for the AlCu system. At higher Cu concentrations the grain boundary relaxation peak remains unaffected up to a Cu concentration of 5%, decreases for higher concentrations and is completely suppressed at 19%. This behavior is closely related to microstructural changes at the grain boundaries as observed by TEM.
Some features of power balance in normal glow discharge in CO2, N2, and their mixtures with He
Authors: Shun’ko E. V.
Published: July 2002

The results of the theoretical and experimental investigation of a power balance in a normal glow discharge in CO2, N2, and their mixtures with He are given. It is shown that power contributed to this discharge goes essentially to the excitation of the metastable oscillatory levels of the CO2 and N2 molecules and to their dissociation. It is ascertained that the relaxation of the excited levels occurs on the discharge tube walls, while the recombination takes place into the tube space by the triple collisions with the transition of bond energy to the Joule heat. The experimental data enable one to assert also that the shape of the electron distribution function in the discharge considered is invariant with respect to average electron energy into its range 0.3≤〈ε〉≤6 eV.
Binary Fe–Nd metastable phases in the solidification of Fe–Nd–B alloys
Authors: Landgraf F. J. G. , Missell F. P. , Knoch G. , Grieb B. , Henig E.-T.
Published: July 2002

It has been shown that a binary Fe–Nd metastable phase A1 is responsible for coercivity of ≂5 kOe in Fe80Nd5B as-cast alloys. It is rapidly transformed into Fe14Nd2B after a very short annealing at 600 °C and it is also present in alloys of magnet composition. Thus it may account for the lower coercivity of as-sintered magnets. Here we discuss how this phase can be formed in the solidification of Fe–Nd–B magnets. The microstructure and thermal events of DTA samples of constant 60 at. % Nd were used to construct a vertical section of the Fe–Nd–B ternary phase diagram. The solidification of alloys related to magnet compositions did not follow the path predicted by the known phase diagrams which leads to a ternary eutectic. Instead, they pass through a transition reaction, involving Fe4NdB4, liquid, Fe14Nd2B, and Nd, which may reach the binary Fe–Nd eutectic, giving rise to different metastable phases, depending on the cooling rate: A1, A′1 or Fe17Nd2. A new version of the liquidus projection of the Nd-rich corner of the ternary phase diagram is presented.
Atomic microstructure and electronic properties of a-SiNx:H deposited by radio frequency glow discharge
Authors: Maeda Keiji , Umezu Ikurou
Published: July 2002

a-SiNx:H films of various composition x were deposited by rf glow discharge (GD). The deposition rate was analyzed for three ranges of gas flow ratio R = [NH3]/[SiH4] depending on the deposition mechanism. Properties of these films were measured by means of x-ray photoelectron spectroscopy (XPS), infrared (IR) absorption, optical absorption, and the temperature dependence of electrical conductivity. The composition x was determined by XPS. For large values of R, x was found to be saturated at 1.7. The variation of H content was detected by IR absorption. The variation of coordinating atoms of Si with increasing x was deduced from the variation of XPS spectra of the Si 2p core-level and the shift of Si-H stretching vibration frequency in IR absorption. Based on the random bonding model and assuming bonding units to the central Si atom to be Si, N, and NH, probabilities of Si tetrahedra with various coordinating units were obtained. The results indicate that there are many Si—Si bonds for the stoichiometric x=1.33 and that the concentration of Si—Si bonds diminishes at around the saturation value x=1.7. These results seem to imply that the presence of Si—Si bonds to some extent is a prerequisite condition for film deposition by GD. Experimental results of optical absorption analyzed by Tauc relation revealed the presence of two kinds of x region whose properties are quite different.

For x<1.5, its optical absorption is similar to a-Si:H modified by the presence of N. With increasing x, the optical band gap EO increases and B coefficient in the Tauc plot decreases. At about x=1.5, Si—Si bonding effectively disappears and the optical absorption abruptly changes to that similar to β-Si3N4. Considering these results, the change of electronic band structure with x was deduced on the basis of the atomic structure obtained above and by the tight binding approximation. For x<1.5, the optical band gap is due to Si—Si bonding, the energy gap of which increases, and the linear band tail becomes broad with increasing x. From the observed temperature dependence of conductivity, variations of the activation energy and pre-exponential factor are obtained with x up to x=1.0. For the decrease of conductivity with x, the contribution from the pre-exponential factor is much larger than that from the activation energy. This result can be understood by a transport mechanism in the electronic band structure obtained above. Finally, it is concluded that the electronic properties of a-SiNx:H deposited by GD ran.
Si defect induced Au-Si diffusion size effects
Authors: Vaisleib A. V. , Goldiner M. G. , Keloglu O. Yu. , Kotov I. N.
Published: July 2002

Diffusion of gold into silicon crystal has been investigated, taking into account both the dissociative and the kickout mechanisms. Expressions for the determination of critical sample thicknesses and temperatures at which one transfer mechanism substitutes for the other have been derived. Fields of different Au-Si diffusion transfer regime realization are defined.
Glassy polarization in the ferroelectric tungsten bronze (Ba,Sr)Nb2O6
Authors: Bhalla A. S. , Guo R. , Cross L. E. , Burns G. , Dacol F. H. , Neurgaonkar R. R.
Published: July 2002

We report accurate temperature dependent measurements of optic indices of refraction, the birefringence, and the strain in the ferroelectric tungsten bronze crystals Ba0.25Sr0.75Nb2O6 and two compositions of (Ba2−xSrx)2(K1−yNay)2(NbO3)10. These results are compared to our previous results in Ba0.4Sr0.6Nb2O6. From the experimental data, it appears that far above the ferroelectric Tc, up to a temperature Td, these crystals possess a local, randomly oriented polarization, Pd, with similar Td values, irrespective of their chemical composition and Tc. Various aspects of our understanding of the polarization behavior and other effects in this ferroelectric system are discussed.
Charge accumulation and band edge in the double barrier tunneling structure
Authors: Fu Y. , Willander M.
Published: July 2002

Due to various scattering processes, the wave function coherence is broken during transport in the double barrier resonant tunneling structure (DBRTS). Based on this coherence breakdown, local states are assumed to exist in the well region in DBRTS and the Schrödinger equation is solved self-consistently together with the Poisson equation. The properties of the charge accumulation in local states are investigated and presented as possible mechanisms to explain three sets of recent experimental results: (a) the redshift and broadening of photoluminescence and photoluminescence excitation peaks, (b) the peak in the specific capacitance-voltage spectrum at the resonance, and (c) the appearance/disappearance of the shoulder peak adjacent to the resonance peak in I-V spectra without/with an external capacitor connected in parallel to the DBRTS.
Photothermal vibration for a membrane in water
Authors: Inaba Seiki , Hane Kazuhiro
Published: July 2002

Photothermal vibration was observed in water for a stainless-steel membrane with a cantilever structure. The resonance frequency obtained was low compared with that in air, and resonance sharpness Q was considerably smaller (Q=7) than that in air (Q=200). The frequency shift compared to the air resonance case was explained by sound radiation in water.
Effect of collisions on ion dynamics in electron-cyclotron-resonance plasmas
Authors: Hussein Makarem A. , Emmert G. A. , Hershkowitz N. , Claude Woods R.
Published: July 2002

A one-dimensional kinetic code is used to study the effect of ion-neutral (charge exchange and elastic scattering) and ion-ion collisions on plasma flow in the downstream region of an electron-cyclotron-resonance plasma etching system. Ions are assumed to leave the source region at the Bohm velocity. Argon, nitrogen, and CF4 plasmas are simulated, assuming that the dominant ion species are Ar+, N2+, and CF3+, respectively. Results show that charge exchange and elastic scattering collisions play a significant role in reducing the electrostatic potential variation in the downstream region. For neutral gas pressures above ∼1 mTorr, the potential drop in the downstream region is small, which means that most of the energy with which ions hit the substrate surface is gained while crossing the substrate sheath region. Although the effect of ion-ion collisions on the plasma potential profile and on the ion distribution function is weak, ion-ion collisions are responsible for transferring energy from the parallel to the perpendicular direction and hence increasing the perpendicular ion temperature.
Detailed model of the afterglow region of a microwave generated oxygen plasma
Authors: Chou Chin-Hao , Wei Ta-Chin , Phillips Jonathan
Published: July 2002

A one-dimensional mass continuity equation was used to model a low pressure, high radical concentration, nonisothermal oxygen afterglow reactor. This type of afterglow system has never been modeled despite its broad range of uses: low temperature passivation of polycrystalline silicon thin film transistors, chemical vapor deposition and etching, ceramic superconductor oxidation, growing silicon dioxide surfaces, and surface cleaning including the removal of photoresist films. It was shown that the model, with no adjustable parameters, yielded very good agreement with experimental measures of O-atom flux. The temperature profile and charged particle concentration profile used in the model were measured experimentally. The model was manipulated to study the influence of temperature profile, pressure, homogeneous and heterogeneous kinetics, O-atom generation, and flow rate on the afterglow plasma. Some results were surprising, such as the finding that the value and position of maximum O-atom concentration can be readily manipulated. The model was also used to assess the validity of a frequently used probe of O-atom flux.
Epitaxial Fe/Cu superlattices on Si(111)
Authors: Schreiner W. H. , Mosca D. H. , Teixeira S. R. , Mattoso N.
Published: July 2002

We report on the successful epitaxial growth of Fe/Cu superlattices on Si(111) wafers at room temperature. The superlattices were characterized with x-ray diffraction, conversion electron Mössbauer spectrometry, and selected area electron diffraction experiments. The epitaxial growth is crucially dependent on which element is deposited first on the bare Si(111).
Diffusion effects and nucleation of thin film boron nitride growth from borazine on the Si(100) surface
Authors: Gates S. M. , Chiang C.-M. , Beach D. B.
Published: July 2002

Time-of-flight (TOF) direct recoiling (DR) studies of borazine (B3N3H6) decomposition on the Si(100) surface between 100 and 850 °C are reported. The DR method with a grazing incidence angle directly detects the diffusion of light adsorbate elements into sites below the first Si layer, and this migration process is examined here as a function of temperature (T). Submonolayer coverages of coadsorbed B and N atoms (from B3N3H6) occupy subsurface sites after annealing above 550 °C. The B + N results are compared with the well-studied N atom (from NH3) case and limited data for boron from B10H14. The atomic composition of the initial growth surface during thermal chemical vapor deposition (CVD) of boron nitride (BN) from B3N3H6 is surveyed in situ as a function of T using DR in a B3N3H6 flux of 4×1016 molecules cm−2 s−1. Desorption of surface hydrogen plays a central role in controlling both the submonolayer diffusion effects and thermal CVD growth of BN.
Structural and magnetic properties of NdFe12−xMoxN1−δ compounds
Authors: Wang Y. Z. , Hu B. P. , Rao X. L. , Liu G. C. , Yin L. , Lai W. Y. , Gong W. , Hadjipanayis G. C.
Published: July 2002

A series of nitrides NdFe12−xMoxNi1−δ with x=1–2.5 and δ≤0.2 have been investigated. All nitrides are of the ThMn12 tetragonal structure with the unit cell volumes about 3% larger than their parent alloys. Curie temperatures are enhanced by nitrogenation about 160 K and increase linearly with decreasing content x of Mo. NdFe12−xMox exhibits a weak uniaxial anisotropy with a value of BA less than 0.6 T when x≥1.75. After nitrogenation, all nitrides have a strong uniaxial anisotropy. Values of the anisotropy field BA increase monotonically from 6.35 T for x=2.5 up to 9.5 T for x=1 as decreasing content x of Mo. Saturation magnetizations also increase monotonically with decreasing content x.
Molecular dynamics and quasidynamics simulations of low-energy particle bombardment effects during vapor-phase crystal growth: Production and annihilation of defects due to 50 eV Si incident on (2×1)-terminated Si(001)
Authors: Kitabatake M. , Greene J. E.
Published: July 2002

Molecular dynamics and quasidynamics simulations, utilizing the Tersoff many-body potential, were used to investigate projectile incorporation and defect production as well as lattice relaxation, diffusion, and annihilation of defects resulting from 50 eV Si irradiation of (2×1)-terminated Si(001). A unity trapping probability, in sites distributed between the epitaxial overlayer and the fourth lattice layer (l=4), was obtained for Si projectiles irradiating an array of high- and low-symmetry points in the primitive surface unit cell. Exchange epitaxy events were observed in which a lattice atom came to rest at an epitaxial (1×1) bridge site while the projectile stopped in a substitutional lattice site. In addition, several collision sequences resulted in the opening of additional dimers, up to four per irradiation event, thus providing (1×1) sites for migrating adatoms during ion-assisted crystal growth. The primary residual lattice defects produced were split and hexagonal interstitials, although tetragonal, bond-centered, and pentagonal interstitials were also produced in layers l=2 through l=14 with the average interstitial layer depth <l≳=2.3. Calculated interstitial migration activation energies Em decreased toward the surface with minimum energy paths generally involving tetragonal sites. Ion-irradiation-induced interstitials can thus be easily annealed out over time periods corresponding to the deposition of less than one monolayer under typical Si molecular-beam-epitaxy conditions. Fewer vacancies were produced, although they have a higher migration activation energy, and they were distributed over a shallower depth, l≤7. Complete annealing of ion-irradiation-induced vacancies requires interaction with deeper interstitials, moving toward the surface, and incident Si projectiles.
Theory of electron resonant tunneling of Si-based double-barrier structures
Authors: Chiang J. C. , Chang Yia-Chung
Published: July 2002

We present theoretical studies of resonant-tunneling characteristics of Si-based double-barrier structures within a tight-binding model. The model consists of four antibonding (sp3) orbitals per lattice site and is capable of describing the low-lying conduction bands accurately throughout the entire Brillouin zone. Current-voltage curves for some selected Si/Ge strained-layer double-barrier structures and lattice-matched Si/GaP double-barrier structures for different crystallographic orientations are calculated. Negative differential resistances are found for these structures.
A novel switchable glazing formed by electrically induced chains of suspensions
Authors: Tada Hiroaki , Saito Yasuhiro , Hirata Masahiro , Hyodo Masato , Kawahara Hideo
Published: July 2002

Chains of submicron size rodlike TiOxNy particles, formed along an electric field by the so-called electrorheological effect, were softly fixed in a silicone elastomer film interposed between a pair of indium–tin oxide glasses. It has been found that the transmittance of the device was remarkably changed by displacing one substrate relatively to the other. This transmittance variation was linear with the relative displacement between substrates. For a displacement of about 35 μm, a solar transmittance change of 40.7% was obtained, while it was below 6.9% for a cell containing TiO2 particles. The excellent optical properties of the cell using TiOxNy particles as switchable glazing was imputable to the large absorption coefficient of the particles over the wavelength of the solar spectrum (∼105 cm−1) and to a drastic variation in the cross-sectional area of the particle chain for the light when submitting the substrates to shear stress. This new type of the switchable glazing was referred to as ‘‘shear stress-type dipole particle chain in elastomer.’’
Free-carrier absorption of nondegenerate semiconductors in quantizing magnetic fields: Nonpolar optical phonon scattering
Authors: Wu Chhi-Chong , Lin Chau-Jy
Published: July 2002

The effect of nonpolar optical phonon scattering on the free-carrier absorption in n-type semiconductors such as germanium has been investigated quantum mechanically in quantizing magnetic fields. It is assumed that the energy band structure of electrons in semiconductors is nonparabolic and the dominant scattering mechanism for conduction electrons is of the nonpolar optical phonon scattering. When the radiation is polarized parallel to a dc magnetic field B, the absorption coefficient appears to be of a complex value due to the interaction between the radiation field and the optical phonon field in nondegenerate semiconductors. Results show that the real part of the absorption coefficient oscillates with the magnetic field in the high-field region, and imaginary part of the absorption coefficient appears with a few extremum points (peaks and dips) in high magnetic fields. These are different from those of the acoustic phonon scattering in III–V compound semiconductors such as InSb or GaAs, in which the absorption coefficient oscillates with the magnetic field in lower magnetic fields and then increases monotonically with the field.
X-ray scattering studies of FeSi2 films epitaxially grown on Si(111)
Authors: Gay J. M. , Stocker P. , Réthoré F.
Published: July 2002

A laboratory x-ray diffractometer for surface and thin-film studies is presented. Ex situ structural characterization of FeSi2 films epitaxially grown on Si(111) is reported. Both specular and nonspecular reflectivities are measured on β-FeSi2 films grown by solid-phase epitaxy and reactive deposition epitaxy techniques. A detailed comparison is performed of the electron density profile of the films normal to the surface, as well as of their surface roughness. In-plane diffraction is also measured at grazing incidence. For the β-FeSi2 sample investigated, the (110) epitaxy on Si(111) is clearly shown. For a film grown by molecular-beam-epitaxy codeposition at 550 °C, the existence of a new metastable phase which is in registry with silicon along the Si〈1̄ 10〉 direction and slightly out of registry, (3.0±1.0)% compressed along the Si〈112̄〉 direction, is reported.
Permeability resonances in permalloy stripes (abstract)
Authors: Smith Neil , Jagielinski Tomasz , Freeman Jay , Koeppe Peter
Published: July 2002

This work presents the experimental low field (Hac≊0.01 Oe) complex permeability spectra μ(f)=μ′(f)−jμ″(f) (between 1 and 200 MHz) of L=1-cm-long NiFe stripes as a function of stripe width W (10 μm to 1 cm), film thickness T (0.1 to 4 μm), and the history-dependent initial domain configuration. It will be demonstrated that occurrence of strong resonances in μ(f) is closely linked to the domain structure of the stripes, and in particular the linear density of the 180° transverse domain walls (observed by Bitter techniques) characteristic of a periodic flux-closed domain pattern. Square films (L=W=1 cm) of all measured thicknesses that have a low linear density (<30 walls/cm) of 180° domain walls show no observable resonances, and their spectra μ(f) are instead well described by classical eddy current predictions. In contrast, highly pronounced resonance peaks (μ″≳μdc≊2000) are observed in 0.1 μm≤T≤2 μm stripes that have been anhysteretically demagnetized with a longitudinal field, where the static domain structures have linear wall densities ≊1000 walls/cm. When demagnetized with a transverse field, alternative static domain configurations with roughly 1/5 the 180° wall density show substantial reduction in the amplitude of the resonance peaks. In contrast, the frequency location of the resonances is found to essentially be independent of both stripe width and wall density, but roughly scales inversely with film thickness: fres≊(20 MHz)(T/μm)−1 for the first, primary resonance peak. This phenomenon is believed to be linked to resonances in the internal motion of the 180° walls during low amplitude flux conduction, and has potential negative implications for the frequency limitations on the reproduce performance of NiFe thin-film inductive heads. Theoretical/phenomenological explanations of the measurement data will also be discussed.
Refinement on the theories of measurement for trap density from space-charge-limited current
Authors: Lu Lianggang
Published: July 2002

The theory of space-charge-limited current (SCLC) measurement for determining an arbitrary energy distribution of traps of insulators and semiconductors is put forward in this article. As a result, no restriction is given to the trap densities of the sample tested, which is caused by neglecting free carriers in the previous theories of SCLC measurement. It is shown by numerical computations that the relative errors near the band edges that usually differ by as much as several orders of magnitude is greatly improved. The refinement is also expected to be useful in the high-temperature region.
Critical Josephson current as a characterization tool for superconducting junction arrays
Authors: Leridon Brigitte , Maoli Roberto
Published: July 2002

Arrays of Nb/Al-Al2O3/Nb junctions used for heterodyne detection in radioastronomy were measured. Observing the current-voltage curve for different values of the external magnetic field, and interpreting the dc Josephson current, we were able to distinguish the behavior of each junction, and to estimate the inhomogeneities in areas, in critical currents, or in leakage currents among them. This provides an indication of possible cancellation of the Josephson current which is a source of additional noise and polarization instabilities (drop-back) in high-frequency superconductor-insulator-superconductor heterodyne receivers.
Thermoreflectance studies in Cd1−xFexTe thin films
Authors: Ariza-Calderón H. , Mendoza-Alvarez J. G. , Sánchez-Sinencio F. , Alvarez-Fregoso O. , Lastras-Martínez A. , Ramírez-Flores G.
Published: July 2002

Thermoreflectance spectroscopy (TR) has been used to analyze Cd1−xFexTe thin films grown by radio-frequency sputtering on glass substrates. Films with different Fe concentration x in the range 0.05≤x≤0.15 were grown under the same conditions of substrate temperature and Ar pressure. To follow the growth of the ternary CdFeTe compound, the evolution of the E0 point in the spectrum was monitored for different films. Compared to a CdTe film grown under the same conditions, the CdFeTe films show a shift in the spectrum of the E0 point to higher energies for x=0.05, 0.10, and 0.15. Besides, both CdTe and CdFeTe films show evidence of the presence of a band of localized states below the band gap, probably related to the growth mechanism. For an x value of 0.10, the TR spectrum shows a line shape related to the presence of an extra transition that we have interpreted as due to additional levels arising from the Fe 3d orbitals.
Reverse-bias annealing kinetics of Mg-H complexes in InP
Authors: Balasubramanian Sathya , Kumar Vikram , Balasubramanian N.
Published: July 2002

The reactivation kinetics of hydrogen-passivated Mg acceptors in InP have been studied by annealing experiments carried out with different reverse biases. It is shown using a new analysis that the actual dissociation energy of the Mg-H complexes can be estimated even without applying a sufficient reverse bias to overcome retrapping of H at the dopant site. The dissociation process follows a first-order kinetics and the dissociation frequency and activation energy were estimated at various depths ranging from the surface up to 0.5 μm using an empirical analysis of the experimental data. A bias-independent dissociation energy of 1.40±0.08 eV was obtained when estimated at the surface. An apparently higher dissociation energy results when calculated in the bulk. This overestimation is pronounced for low-bias anneals and is explained as a result of retrapping. The concentration profile data is consistent with the positively charged state of the diffusing H in p-InP.