bluuebunny/crossref_metadata_2025 huggingface dataset:
Recirculating gas flow, coaxial geometry CO2 laser
Authors: Guo Zhen , Gao Gui-zhen , Wen Jian-guo , Cai De-fang
Published: July 2002

A sealed-off transversely excited atmosphere CO2 laser with a gas internal coaxial circulation scheme is presented. Long-lived (106 shots) stable glow discharges at a pulse repetition frequency up to 33 Hz are demonstrated. The minimum clear ratio is found to be smaller than Dzakowic’s theoretical limit [G. S. Dzakowic and S. A. Wutzke, J. Appl. Phys. 44, 5061 (1973)].
Creep in superconductive composites with anisotropic pinning potentials
Authors: Sumption M. D. , Collings E. W.
Published: July 2002

A model which describes the creep of finite size superconductive samples with anisotropic U0’s and Jc’s has been completed. The 2D model developed assumes anisotropic values of these parameters are associated with two orthogonal directions. The effective creep rate is found to be intermediate between these two creep rates, and is significantly influenced by sample geometry. This model is applied to measurements of magnetization creep in the proximity effect coupled NbTi/Cu multifilamentary superconductive composites. Creep measurements as a function of field at T=4.2 K were made for untwisted samples of various lengths. With the aid of this model, pinning potentials for the proximity effected matrix from 5.3 to 10 meV are extracted for these samples. PE creep for longer, twisted samples was also measured. It is suspected that end effects influence creep in the twisted as well as the untwisted strands.
Below gap photoreflectance of semi-insulating GaAs
Authors: Röppischer H. , Stein N. , Behn U. , Novikov A. B.
Published: July 2002

Below-gap structures in photoreflectance spectra of semi-insulating GaAs were observed originating from electroabsorption of light reflected from the back surface. The peak amplitude of these structures was strongly temperature dependent within the range (78–290) K. The different lineshape at low temperature in comparison to that at room temperature suggested different physical mechanisms. This conclusion was proven experimentally using a two phase lock-in technique by which a fast (X) and slow (Y) component of the spectra could be separated. A fit procedure provides the pure back surface reflection effect for both components. The X mode dominating at low temperatures is attributed to electromodulation of the field-broadened excitonic absorption tail whereas the Y mode originates from the Franz–Keldysh electroabsorption.
Substrate temperature dependence of homoepitaxial growth of Si using mass selected ion beam deposition
Authors: Al-Bayati A. H. , Boyd K. J. , Marton D. , Todorov S. S. , Rabalais J. W. , Zhang Z. H. , Chu W. K.
Published: July 2002

Homoepitaxy of silicon at low temperature has been achieved using low-energy mass selected silicon ion beams. Reflection high-energy electron diffraction and Rutherford backscattering spectrometry have been utilized to assess the quality of silicon films deposited from 15 eV 28Si+ beams in the temperature range of 50–350 °C. Auger electron spectroscopy was used to monitor the contaminant levels on the surfaces. The films deposited at 350 °C are epitaxial and of a quality near that of the original substrate. The growth rate at 350 °C is ≊200 times faster than that for solid phase epitaxy. At 50 and 200 °C layer-by-layer epitaxial growth was inhibited and evidence for formation of three-dimensional islands in the early stage of growth followed by transition to an amorphous phase was observed. The transition to an amorphous phase occurred at lower film thickness (smaller ion dose) for lower temperatures. It is shown that small amounts of N+2 impurity in the 28Si+ beam, sufficient to add 1.4 at. % N to the silicon film, result in amorphous films, even at the highest temperature used, 350 °C. The effects of substrate temperature, contamination, and surface damage on the growth mechanism are discussed.
Thermal diffusivity measurement of near-pseudobinary HgCdTe solid and melt, Te-rich HgCdTe and HgZnTe melts, and pure Te solid and melt by the laser flash technique
Authors: Maleki Hossein , Holland Lawrence R.
Published: July 2002

The thermal diffusivities of mercury cadmium telluride, (Hg1−xCdx)1−yTey, and mercury zinc telluride, (Hg1−xZnx)1−yTey, with 0.55≤y≤1.0 and 0.0125≤x≤0.054 65, and of pure Te were measured from 350 to 850 °C by the laser flash technique. The diffusivity of near-pseudobinary Hg1−xCdxTe solids decreased more rapidly with temperature approaching the melting point than did pseudobinary solids previously reported: The solid diffusivity for x=0.028 17 and y=0.55 was 0.83 mm2/s at 371 °C, decreasing to 0.22 mm2/s at 614 °C. The diffusivity of Te-rich (Hg1−xCdx)1−yTey melt increased with x and with temperature: The melt diffusivity for x=0.039 36 and y=0.782 was 0.91 mm2/s at 485 °C, increasing to 4.93 mm2/s at 851 °C. For Te-rich (Hg1−xZnx)1−yTey melt with x=0.0125 and y=0.7944 there appeared to be a minimum diffusivity of about 2.6 mm2/s near 690 °C. The thermal diffusivity of pure Te solid was 0.97 mm2/s at 300 °C and decreases to 0.64 mm2/s at 439 °C. The melt diffusivity of pure Te was 1.52 mm2/s at 486 °C, increased to 3.48 mm2/s at 584 °C. Experimental data presented can be used to calculate the thermal conductivity needed for designing systems capable of growing a better quality single crystal of these materials.
Thermal emission of charges at Si3N4-GaAs interfaces plasma pretreated with H2, Ar, and Ar+H2
Authors: Wang Q. H. , Bowser M. I. , Swanson J. G.
Published: July 2002

Thermal emission of charges has been studied in Si3N4-GaAs structures which were prepared using direct plasma-enhanced chemical-vapor deposition. A comparison has been made of the effects of predeposition plasma treatments using hydrogen, argon, and a mixture of the two. Channel current transient spectroscopy was used in the temperature range 77–350 K. All of the samples exhibited electron emission from an interface-state continuum with energies that were consistent with the interface-state-band model proposed by Hasegawa. When argon and hydrogen were used together two extra processes were observed. One of these was due to an electron trap with an activation energy of 0.05 eV; this response was from states at the remote edge of the depletion region several thousand angstroms from the interface. The necessity for argon and hydrogen suggests that argon had created structural damage permitting the entry of hydrogen atoms to form electrically active complexes in the damaged region. The second process which had an activation energy of 0.05 eV resembled hole emission but, because hole injection was an unlikely process, this observation has been attributed to an interfacial polarization process exhibiting thermally activated relaxation. The corresponding dipole moment per unit area was 1.0×1011 C m. Since this mechanism also required the action of argon and hydrogen it was concluded that this was damage related, with electrical activity produced by the hydrogen atoms.
A model for surface damage in ion-irradiated solids
Authors: Averback R. S. , Ghaly Mai
Published: July 2002

A model for defect production near the surface of an ion-irradiated solid is developed based on the concept of local melting. The model shows that, as heat diffuses radially outward from the track of an ion, a cylinder of melt is created, and owing to the large volume change on melting, pressure is developed in the liquid. Unlike displacement cascades in the interior of the crystal, the pressure is relieved by the viscous flow of liquid through the surface. The results of the model are compared to results from molecular dynamics simulations and to experimental observations.
Surface segregation during Si/Gen/Si(100) interface formation
Authors: Lu Z. H. , Baribeau J.-M. , Lockwood D. J.
Published: July 2002

X-ray photoelectron spectroscopy was used to detect the segregated Ge in the Si cap layer of a Si/Gen/Si(100) heterostructure. Surface oxide peaks were used to identify unambiguously the surface segregated Ge atoms. A close to atomic layer-by-layer profile was obtained through room-temperature UV-ozone oxidation and selective chemical etching. The results show that there is always certain amounts of Ge distributed throughout the cap layer irrespective of the initial amount of Ge deposited. The total amount of segregated Ge from Gen/Si(100) was found to be about 2 monolayers. The Ge concentration is found to be higher on the cap layer surface than in the cap layer. Raman spectroscopy was also used to profile the Ge-Ge and Ge-Si vibrational lines, and the results confirm Ge segregation.
Field-effect induced electron channels in a Si/Si0.7Ge0.3 heterostructure
Authors: Holzmann M. , Többen D. , Abstreiter G. , Schäffler F.
Published: July 2002

Size effects in field-effect induced wires imposed upon a high-mobility Si/Si0.7Ge0.3 heterostructure were studied by magnetotransport. Spatial separation of the electron channels was accomplished by means of a periodically modulated Schottky gate. The magnetoresistance parallel to the wires shows a well-pronounced peak at magnetic fields <0.3 T at a gate bias ≤0 V. This maximum results from diffuse boundary scattering and proves the existence of spatially separated electron channels. From its position wire widths varying from 0.14 to 0.28 μm can be estimated.
Electron transport in Sb-doped metalorganic epitaxial GaAs grown at moderate As-rich conditions
Authors: Yakimova R. , Arnaudov B. , Evtimova S. , Paskova T.
Published: July 2002

The influence of antimony incorporation in GaAs metalorganic vapor phase epitaxial (MOVPE) layers has been investigated. The results obtained concern the behavior of the carrier concentration (n) and the mobility (μ) developed from Hall effect measurements. In order to achieve a reliable quantitative interpretation the samples studied have been grown at a moderate V/III ratio which ensures n-type conductivity and does not favor SbGa heteroantisite defect formation. Three regions of specific influence of Sb doping on the electrical parameters have been distinguished. For Sb mole fraction in the input gas phase (MFTMSb) ranging between 0 and 6×10−6, n slightly decreases, while the mobility sharply increases compared with undoped layers. This is discussed in terms of electrically active and neutral As vacancies. The quantitative consideration of the scattering mechanism offers the possibility of correcting the compensation ratio in the undoped GaAs samples determined by commonly used procedures. The n and μ dependences at higher Sb doping have been related to residual amphoteric impurity redistribution between Ga and As sublattices. In the heavily doped region the effect of the charged Ga vacancies has been involved. It has been shown that the Sb incorporation in the optimum concentration limits leads to an improvement of the electrical characteristics of MOVPE GaAs layers.
Proposal of interband tunneling structures with strained layers
Authors: Ru Guoping , Li Aizhen
Published: July 2002

A type of interband tunneling structure with strained layers is proposed. InxGa1−xSb/ InxAl1−xSb/InAs/InxAl1−xSb/InxGa1−xSb strained resonant interband tunneling structures are theoretically studied by calculating current-voltage characteristics using realistic band structure and making comparisons to analogous unstrained structures. The results show that the interband tunneling windows of strained structures can be expanded by the introduction of strain in the InAs quantum-well layer. With a wider interband tunneling window, the peak current density is enhanced due to the broader tunneling transmission spectrum and higher bias required for resonant interband tunneling. The peak current density is also examined as a function of InAs well width for different InAlSb barrier widths.
Novel methods for the fabrication of ferromagnetic nickel and nickel boride thin films
Authors: Zych D. , Patwa A. , Kher S. S. , Spencer J. T. , Kushneir J. , Goodby A. J. , Boag N. M. , Dowben P. A.
Published: July 2002

Metal-rich nickel boride thin films fabricated from boron-containing precursor compounds by a cluster deposition process are shown to be ferromagnetic. The metal-rich films fabricated by this approach exhibit hysteresis curves similar to those obtained for pure nickel foils. These films are a mixture of pure nickel and the Ni3B nickel boride phases. It is postulated that the hysteresis curves with smaller remnant magnetizations obtained from these films are a consequence of Ni3B inclusions within the films. Other novel organometallic source compounds for nickel chemical-vapor deposition are briefly reviewed.
Observations and implications of gap closure in plasma opening switch operation
Authors: Goyer John R. , Kortbawi David
Published: July 2002

Plasma opening switches are believed to develop voltage through opening and magnetically insulating a gap formed in plasma injected between two conducting electrodes. Data will be presented to show that a relatively simple assumption about the behavior of this gap suffices to describe the overall operation of the switch. Specifically, the observed increase, then decrease, of operational voltage as a function of conduction time can be accounted for by the switch gap linearly decreasing with conduction time, while the conducted current increases. In addition to presentation of data to demonstrate this collapse, analysis is performed to couple the gap history to the voltage predicted for the switch, and to optimize this latter quantity.
Near-surface defects created by 355 nm laser irradiation of rutile
Authors: Le Mercier T. , Quarton M. , Fontaine M.-F. , Hague C. F. , Mariot J.-M.
Published: July 2002

Sintered disks of TiO2 (rutile) have been exposed to the beam of a 355 nm laser. X-ray photoelectron spectroscopy studies show that the strong energy deposition at the surface is responsible for the formation of Ti3+ ions down to a depth of 0.4 μm. The presence of these ions produces a large decrease in the electrical resistivity from 109 Ω cm in nonirradiated TiO2 to 10 Ω cm after laser treatment. Temperature dependent resistance measurements indicate that the creation of Ti3+ ions leads to the formation of energy levels in the gap and to a hopping-driven conduction at room temperature.
Base and collector leakage currents of AlGaAs/GaAs heterojunction bipolar transistors
Authors: Liou J. J. , Huang C. I. , Bayraktaroglu B. , Williamson D. C. , Parab K. B.
Published: July 2002

Base and collector leakage currents are extremely important to AlGaAs/GaAs heterojunction bipolar transistor (HBT) dc characteristics, and a simple model to describe such currents is presented. This study suggests that these currents are originated from the electron and hole leakage through the dielectric-layer (e.g., polyimide, nitride, etc.) interface at the emitter-base and base-collector peripheries, as well as through the n+-subcollector/semi-insulating substrate interface. Five HBTs having similar intrinsic make-ups (i.e., doping concentration and layer thickness) but different extrinsic make-ups (i.e., finger pattern, perimeter, dielectric layer, etc.) are investigated, and with the aid of the model, the possible mechanisms contributing to their leakage behavior identified.
Triple electron scattering rates in a single mode quantum wire
Authors: Shadrin V. D.
Published: July 2002

In quantum limit when only lower subband in a quasi-one dimensional system such as the electron gas confined in the quantum wire is occupied by electrons, pair electron collisions do not cause momentum and energy exchange between electrons. In this case more complex scattering events will determine electron momentum, energy, and phase relaxation. We calculated electron-electron scattering rates associated with triple scattering events with participation of two electrons and one charged impurity. The electron temperature relaxation time in triple collisions is estimated. We show that this time can be comparable with momentum relaxation time.
A mean field description of the transition to the mixed state of superconducting microbridges with low vortex pinning forces
Authors: Bernstein P. , Hamet J. F. , Blanc-Guilhon B. , Flament S. , Dubuc C. , Bok J. , Zhang X. Q. , Contour J. P. , Ladan F. R.
Published: July 2002

We propose a mean field description of the phenomena occurring in superconducting thin film microbridges with low pinning forces when vortices are nucleated. This model allows for computation of the vortex velocity, the penetration depth, the critical current density, and the vortex nucleation field in a microbridge from its dimensions, its current voltage characteristics, and the coherence length of the microbridge material. Moreover the effect of an external magnetic field is shown to be strongly dependent on its spatial distribution. The model predictions are compared to experimental results obtained from TlBaCuO and YBaCuO vortex flux transistors and a long YBaCuO microbridge.
Effect of heat treatment on the phases of melt-spun NdFeB alloys
Authors: Cheng Zhao-hua , Mao Ming-xi , Yang Chun-li , Zhang Yi-de , Li Fa-shen , Shen Bao-gen , Zhang Jun-Xian , Sun Ji-jun
Published: July 2002

The phase composition of crystallized NdxFe81.5−xB18.5 (x=3, 4, 4.5, 6, 12, and 15) alloys annealed under optimal condition are investigated by means of zero-field spin-echo nuclear magnetic resonance (NMR) and Mössbauer effect (ME), together with x-ray diffraction (XRD). It is found that the phase composition depends on the Nd concentration. The samples with 12–16 at. %-Nd contain Nd2Fe14B magnetically hard phase and Nd1.1Fe4B4 paramagnetic phase. Their large coercive fields are due to the very fine size of Nd2Fe14B crystallite below the critical size of single domain particles, and some minor phases precipitated at grain boundaries, which have a pinning domain wall effect. The samples with a lower Nd concentration (x=3–6 at. %) consist of body-centered-tetragonal (bct)-Fe3B and a small amount of α-Fe, and no Nd2Fe14B and Nd1.1Fe4B4. Furthermore, the NMR results show that the spectra corresponding to bct-Fe3B in the samples annealed at 670 °C distort and broaden more seriously than that of pure bct-Fe3B in the Nd4Fe77.5B18.5 alloy annealed at 839 °C, and the difference of their spin-lattice and spin-spin relaxation time is very large, implying that B atoms have at a different nearest-neighbor environment. Thus, it is reasonable to assume that Nd atoms enter into bct-Fe3B and that such a compound has a large coercive field.
Electrical resistivity studies on antiferromagnetic Cu3Pt-Mn spin glass
Authors: Radha S. , Nigam A. K. , Chandra Girish
Published: July 2002

Results of electrical resistivity ρ(T) measurements on (Cu3Pt)100−xMnx alloys with 0.5, 1, 1.85, and 3 at. % Mn in the temperature range of 1.8–300 K are presented. For 0.5 and 1.0 at. % Mn alloys, ρ(T) shows a maximum at low temperature followed by a minimum at a higher temperature. For 1.85 and 3 at. % Mn alloys, both the minimum and maximum in resistivity are washed out. The observed behavior seems to result from the weak indirect Ruderman–Kittel–Kasuya–Yosida interaction responsible for spin glass behavior in these alloys.
Scaling of viscosities of glass forming alloys
Authors: Lee K. L. , Kui H. W.
Published: July 2002

The viscosity of molten Ni80P20 was measured from 1143 to 1253 K by the capillary flow method. It can be described very well by the Vogel–Fulcher equation. When the viscosity is expressed in a reduced temperature scale which is defined as T/Tg where Tg is its glass transition temperature, it follows the principle of corresponding states, the same as other easy glass forming systems.
Crystallinity and I-V characteristics of Ag thin films deposited on fractal substrates
Authors: Xu Yu-Qing , Wang Jing-Song , Ye Gao-Xiang , Zhang Qi-Rui
Published: July 2002

The crystallinity, surface morphology, and I-V characteristics of the Ag thin films deposited on fractal substrates by rf magnetron sputtering have been investigated. The poor crystallinity, fractal surface morphology, and abnormal nonlinear I-V behavior of the thin films have been observed. The crystallinity of the films deposited on the fractal substrates is improved by increasing the substrate temperature and the thickness of the thin films. The nonlinear I-V characteristics are influenced by the thickness of the thin films, substrate temperature, and measuring environment.
Influence of hydrogenation on inter- and intragranular critical currents in YBa2Cu3O7−δ
Authors: Ciszek M. , Klamut J. , Zaleski A. J. , Drulis H. , Klamut P. W. , Olejniczak J.
Published: July 2002

The influence of hydrogenation on the inter- and intragranular critical current density has been studied using an ac technique. With increasing hydrogen content, intergranular critical current density decreases drastically, whereas pinning inside the grains is increased.
Assessment of clustering induced internal strain in AlInAs on InP grown by molecular beam epitaxy
Authors: Hase A. , Künzel H. , Zahn D. R. T. , Richter W.
Published: July 2002

Low-temperature photoluminescence (PL) and Raman measurements were performed on AlInAs grown lattice matched to InP by molecular beam epitaxy at reduced growth temperature (Ts). The PL of layers grown at Ts above 500 °C is dominated by excitonic emission, whereas for lower Ts donor-acceptor related transitions prevail. Below a critical Ts of 450 °C a marked shift towards lower emission energies with a maximum shift near 400 °C is observed that is attributed to a modified band edge due to clustering. Comparable trends are detected by Raman spectroscopy. The observed reduction of the separation of the InAs- and AlAs-like longitudinal optical phonon modes (LOInAs and LOAlAs) demonstrates local internal strain to be present as a result of clustering. This effect reaches a maximum for Ts at 400 °C. A shift of the LOInAs solely accounts for this behavior. In addition strong asymmetric broadening of the LOAlAs-phonon line observed on low Ts material indicates an increasing reduction of the correlation length and suggests the structural disorder to be correlated with the AlAs sublattice. Taking into account the pressure dependence of the AlInAs energy gap and the frequency shift of the LOInAs phonon, the local internal strain equivalent pressure was calculated from the PL and Raman results, respectively, giving similar values of up to 5 kbar for material grown at 400 °C.
Suppression of AlSb oxidation with hydrocarbon passivation layer induced by MeV-He+ irradiation
Authors: Nakata Jyoji , Shibata Tomohiro , Nanishi Yasushi , Fujimoto Masatomo
Published: July 2002

A very thin hydrocarbon coating layer of at most a few monolayers induced by the electronic scattering of MeV-He+ ion-beam irradiation effectively and completely suppresses oxidation of the compound semiconductor AlSb, which is liable to be oxidized by mere exposure to air, because of the coating layer’s hydrophobic property. Of the many kinds of hydrocarbons, alkyl and phenyl groups are particularly effective for oxidation suppression. The AlSb oxidation mechanism and oxidation suppression mechanism are discussed.
Evaluation of anisotropic thermoelectricity of sintered Bi2Te3 on the basis of the orientation distribution of crystallites
Authors: Ohsugi I. J. , Kojima T. , Sakata M. , Yamanashi M. , Nishida I. A.
Published: July 2002

Anisotropic thermoelectric characteristics of a sintered Bi2Te3 system have been evaluated on the basis of the orientation distribution of crystallites. Uniaxially anisotropic resistivities, Hall coefficients, and thermal conductivities of sintered Bi2Te3 were expressed by linear combinations of those of single crystal. The combination coefficients are specified by an anisotropy parameter that may be estimated by the anisotropy in the observed resistivities. Two types of x-ray diffraction experiments were performed to confirm the validity of the estimate. The observed diffraction intensities were reasonably consistent with the orientation distribution predicted by the anisotropy parameter. Theoretical curves of resistivities, Hall coefficients, and thermal conductivities of the sintered material were calculated by using the orientation distribution which was specified by a parameter estimated by the observed resistivities. The theoretical curves were in reasonable agreement with the observed data.
Femtosecond relaxation of minority electrons in heavily carbon-doped GaAs
Authors: Davidson Andrew , Compton Richard C. , Wise Frank , Mars Dan , Miller Jeff
Published: July 2002

Relaxation of minority electrons in carbon-doped GaAs with hole concentrations as high as 6×1019 cm−3 is measured with femtosecond optical techniques. The relaxation of photoexcited electrons depends strongly on the doping level above 1019 cm−3. The dependence of the transient absorption and reflectivity on the hole concentration indicates that electrons relax rapidly by electron-hole scattering into low-energy states which are available as a result of band-gap renormalization and band tailing.
Temperature effects in the multiphoton photoemission of laser irradiated α-SiO2
Authors: Martin Philippe , Guizard Stéphane , Petite Guillaume
Published: July 2002

The effects of the sample temperature on laser induced electron emission of α-SiO2 is discussed. The sample was irradiated using the third harmonic of a Nd:YAG laser, with pulse durations of 30 ps, at intensities in the 109 W cm−2 range, leading to an electron emission due to multiphoton absorption. We measured both the total photocurrent and the photoelectron energy spectrum for temperatures ranging between room temperature and 250 °C. We observed a strong increase of the photocurrent, which is associated with the disappearance of the charging effect due to the holes left by the emission. We interpret this as a result of a thermally induced, trapping/detrapping, electron conductivity. This interpretation is based on the fact that hole conductivity is too small to account for our observations and that intrinsic electron conductivity does not show the correct temperature behavior. The increase of the photocurrent is, however, mainly due to an increase of the defect creation yield with the temperature. From these observations possible applications to the problem of low energy electron spectroscopy on insulating samples are discussed.
Electrical transport quantum effects in the In0.53Ga0.47As/In0.52Al0.48As heterostructure on silicon
Authors: Georgakilas A. , Christou A. , Zekentes K. , Mercy J. M. , Konczewicz L. K. , Vila A. , Cornet A.
Published: July 2002

Electrical transport in a modulation doped heterostructure of In0.53Ga0.47As/In0.52Al0.48As grown on Si by molecular beam epitaxy has been measured. Quantum Hall effect and Subnikov–De Haas oscillations were observed indicating the two-dimensional character of electron transport. A mobility of 20 000 cm2/V s was measured at 6 K for an electron sheet concentration of 1.7×1012 cm−2. Transmission electron microscopy observations indicated a significant surface roughness and high defect density of the InGaAs/InAlAs layers to be present due to the growth on silicon. In addition, fine-scale composition modulation present in the In0.53Ga0.47As/In0.52Al0.48As may further limit transport properties.
Gain enhancement in InAlAs/InGaAs heterojunction bipolar transistors using an emitter ledge
Authors: Kyono C. S. , Binari S. C. , Ikossi-Anastasiou K.
Published: July 2002

Improved gain was observed at low currents when a thin emitter ledge was incorporated into npn In0.52Al0.48As/In0.53Ga0.47As heterojunction bipolar transistors. A 40-nm-thick n-In0.52Al0.48As emitter ledge resulted in over four times higher gain at low biases due to reduced surface recombination.
Phase transition of new solid solution crystal Li0.7Na0.3NbO3
Authors: Kim J. B. , Kim J. N.
Published: July 2002

A ferro-antiferroelectric Li0.7Na0.3NbO3 solid solution crystal was grown from the melt by the Czochralski method. It has been found from the high temperature x-ray diffraction that the crystal is orthorhombic with a unit cell of dimensions a=5.374(9) Å, b=5.152(1) Å, and c=16.738(0) Å at 25 °C, and undergoes a structural phase transition from orthorhombic to tetragonal at 480 °C. It was confirmed from the observation of the D-E hysteresis loop and the pyroelectric measurements that the mixed crystal Li0.7Na0.3NbO3 undergoes a first order ferroelectric phase transition at 480 °C. In the dielectric measurements, the dielectric behavior in the vicinity of the phase transition temperature reveals a diffusive character and also a pronounced dielectric dispersion due to an ionic hopping observed over the wide temperature range near 298 °C.
Role of fluorine atoms on the thermal stability of the silicide/silicon structure
Authors: Tsui Bing-Yue , Chen Mao-Chieh
Published: July 2002

It has been known that thermal stability of the silicide/silicon system can be improved by fluorine incorporation. Two mechanisms have been proposed—the fluorine buffer model and the grain growth retardation model. This communication examines the validity of these two mechanisms. Fluorine ions are introduced into the PtSi/Si structure by implantation at various energies and to various dosages. If the fluorine ions are confined in the silicide layer, the grain growth is retarded, however, no improvement of the thermal stability can be obtained. On the other hand, if most of the implanted fluorine ions are located near the PtSi/Si interface, the grains of the fluorinated silicide film can grow to be larger than those of the unfluorinated silicide film without becoming discontinuous to the film. It is thus concluded that the fluorine accumulation at the interface, i.e., the fluorine buffer model, plays the dominant role on the thermal stability of the fluorinated PtSi/Si structure.
Optical properties of polyimide during ArF excimer laser ablation
Authors: Hahn D. W. , Pettit G. H. , Ediger M. N.
Published: July 2002

Reflectivity measurements of the backsurface of thin polyimide films indicate a transient decrease in reflectivity during ArF (193 nm) excimer laser ablation. The posterior surface reflectivity is decreased by 20%–40% over the range of incident laser fluences from 75 to 175 mJ/cm2, respectively. The results are discussed within the framework of a theoretical model of saturable absorption, and calculations are presented which are in good agreement with the experimental results. It is concluded that the observed decrease in reflectivity is the result of transient changes in the optical properties within the solid polymer material which occur during ultraviolet laser ablation.
Efficient Raman conversion of high repetition rate, 193 nm picosecond laser pulses
Authors: Tomov I. V. , Chen P. , Rentzepis P. M.
Published: July 2002

Efficient generation of Stokes lines has been obtained in H2, CH4, N2, and O2 by 10 ps, 300 Hz, 193 nm laser pulses. A 60% energy conversion efficiency was recorded for the first Stokes of H2 and 40% in CH4. For the pressure range 1–30 atm the conversion efficiency did not change with pump pulse repetition rate up to 300 Hz. The higher order Stokes observed were generated mainly by means of four wave mixing.
Free-electron laser intracavity light as a source of hard x-ray production by Compton backscattering
Authors: Dattoli G. , Gallardo Juan C. , Ottaviani P. L.
Published: July 2002

In this paper we consider the x-ray production by Compton backscattering of intracavity visible free-electron laser (FEL) radiation. We discuss the interplay between the build-up of the laser in the cavity and the backscattered signal including the effects of the e-beam degradation (energy spread) induced by the FEL interaction.
Property change of AgOx recordable compact disk with various dielectric films
Authors: Haratani S. , Tominaga J. , Dohi H. , Takayama S.
Published: July 2002

A recordable compact disk media with an inorganic material, AgOx, is reported. A scanning tunneling microscope image of a polycarbonate substrate of this media after recording was measured and the pit shapes of the image were evaluated. It was found that there existed a linear correlation between the pit shapes and the cross-talk value with a coefficient of 0.959, and the mechanism of the pit formation was proposed by the scanning tunneling microscope image. The optical and electrical property changes were investigated by use of different dielectric thin films, SiO2, SiN, LaSiON, and SiNO. A cross-talk value of a disk using a SiNO film was improved to mostly satisfy the compact disk standard. The property changes can be explained by the proposed pit formation model.
Local chemical composition of HgBaCaCuO high-temperature superconductors
Authors: Alméras P. , Dell’Orto T. , Coluzza C. , Almeida J. , Margaritondo G. , Xue Y. Y. , Meng R. L. , Chu C. W.
Published: July 2002

The microchemical composition and the electronic structure of the two superconductors HgBa2Ca2Cu3O8+δ (Hg-1223) and HgBa2Ca1Cu2O6+δ (Hg-1212) were analyzed with the technique of photoemission with high spatial resolution. This enabled primary spectral peaks to be separated from their satellites due to local charging induced by the primary photon beam. Each sample contains superconducting and impurity phases with inhomogeneous spatial distributions. The oxygenation-induced increase in the critical temperature is related to a increase in the Cu-O plane carrier concentration.
Predictions of the efficiencies of superconducting small antennas connected to lossy ground planes using a Sommerfeld integral technique
Authors: Cook G. G. , Khamas S. K. , Bowling D. R. , Overfelt P. L. , Hageman L.
Published: July 2002

Electrically small loops and monopoles are modeled over infinite lossy ground planes using a modification to the Sommerfeld approach, in order to assess the performance of YBCO antennas connected to typical metallic ground planes. Calculated results suggest that for antennas with low radiation resistances, significant efficiency improvements can be obtained with YBCO elements even if the ground planes remain lossy, and that little is to be gained by making the ground planes superconducting if the antenna elements remain lossy.
Self-multilayered structures of SiN films prepared by plasma-enhanced reactive sputtering
Authors: Sugimoto Iwao , Nakano Satoko , Kuwano Hiroki
Published: July 2002

Nanometer structures are fabricated with SiN films prepared by plasma-enhanced reactive sputtering using He and Ne Penning effects. These structures are characterized by microscopic and spectroscopic investigations. Films produced with He-N2 and with Ne-N2 gases consist of multilayered structures with columnar and equiaxed layers even though the sputtering conditions are kept constant. The equiaxed layers, which tend to be thin and stressed, are resistant to chemical etching using buffered hydrogen fluoride (BHF) because of the oxygen- and hydrogen-poor structures, whereas the columnar layers consisting of oxygen-rich components are thick and easily etched. The He-N2 film with thickness more than 2 μm basically consists of a simple two-layered structure: a thick columnar layer beneath an equiaxed thin top layer. BHF etching forms closely packed bundles of SiN fibers with mean thickness of 10 nm. The Ne-N2 film consists of a multilayered structure with many layers with thin equiaxed layers inserted between thick columnar layers. The multilayered structure is probably due to two different surface temperatures that were used for depositing alternate layers. The combination of these two complementary structures provides the useful characteristics of high chemical etching resistivity and low film stress.
Triply resonant enhancement of third-order nonlinear optical susceptibility in compositionally asymmetric coupled quantum wells
Authors: Lien Chenhsin , Huang Yimin , Wang Junfu
Published: July 2002

The third-order nonlinear optical susceptibility χ(3)(3ω) due to the intersubband transitions in the four-level AlInAs/GaInAs compositionally asymmetric coupled quantum well (CACQW) is investigated theoretically. The subband eigenenergy En of the CACQW structure could be designed to form an equally spaced energy-level ladder. Since the eigenenergy spacing could be designed to resonate with the pumping source, the third-order nonlinear optical susceptibility could be greatly enhanced through the triple resonance. Based on the theoretical calculations, a magnitude of ‖χ(3)(3ω)‖ as high as 2.2×105 (nm/V)2 can be achieved for the CACQW structure. This is a more than eight orders of magnitude enhancement as compared to that of the bulk value in GaAs. In addition to the design of CACQW structure, the triple resonance can also be achieved by biasing the CACQW under a proper electric field due to the large Stark effect of the CACQW structure.
Investigation of tensile-strained InGaAlP multiquantum-well active regions by photoluminescence measurements
Authors: Watanabe Minoru , Matsuura Hatsumi , Shimada Naohiro
Published: July 2002

The use of a tensile-strained multiquantum-well (MQW) active region in 630-nm-band InGaAlP MQW laser diodes is investigated through photoluminescence (PL) measurements. The critical conditions for lattice relaxation of strained MQW layers are also discussed. Emissions due to electron–heavy-hole recombination and electron–light-hole recombination are observed in the PL spectrum. A large energy difference (about 38 meV) is found between the two peaks, and radiative recombination is dominant in the MQW structure. These are thought to decrease the threshold current of tensile-strained MQW laser diodes. The MQW active region is thought to be extremely close to the critical conditions for lattice relaxation, but no adverse effects on optical properties are observed. It is concluded that such a tensile-strained MQW active region has advantages for use as the active region of 630-nm-band laser diodes.
Surface energies and morphologies of chemical-vapor-deposited diamond films
Authors: Zhang Yafei , Zhang Fangqing , Chen Guanghua
Published: July 2002

Using a model where a fraction of carbon dangling bonds on the growth surface are saturated by hydrogen, the surface energies of chemical-vapor-deposited diamond crystals during the preparation process have been calculated. The results show that the surface energies increase with the increasing substrate temperature, and the surface energy-temperature curves of the three most energetically favored crystal planes, (100), (110), and (111), intersect at a critical substrate temperature. Then, the changes of predominant facets in the surface morphology from {100} to {111} with the increasing substrate temperature can be interpreted. Furthermore, it is found that the surface energies of diamond are lower than that of graphite in the chemical-vapor-deposition process of diamond.
New critical-state model for magnetization of hard type-II superconductors
Authors: Johansen T. H. , Bratsberg H.
Published: July 2002

We propose a critical-state model based on the empirical fact that the critical current density Jc in high-Tc superconductors in some cases is found to decay to an essentially field independent level at large inductions B. The new critical current function, Jc(‖B‖), consists of a constant plus a field dependent term of the Kim model type. Analytical expressions for internal induction profiles and the entire shape of major magnetization loops, as well as the initial branch, are derived for the infinite slab geometry. As an illustration it is shown that the new model gives a precise overall description of a magnetization loop measured for melt processed YBa2Cu3Ox.
Heat transfer to liquids in nonuniform electric fields
Authors: Ryde Tuula , Nunge Richard J. , Arajs Sigurds
Published: July 2002

A numerical solution of the equations of change for heat transfer from a heated horizontal wire suspended in a liquid dielectric and subjected to a nonuniform electric field has been obtained. A key assumption made was that the electric field in the liquid was the same as that for an isothermal dielectric. The results support the experimental measurements reported earlier [T. Ryde, S. Arajs, and R. J. Nunge, J. Appl. Phys. 69, 606 (1991)] for hexane in which the electric Nusselt numbers were higher in ac fields than in corresponding dc fields.
Brillouin scattering from surface acoustic phonons in a ZnSe-ZnSe1−xSx strained-layer superlattice
Authors: Guan Z. P. , Fan X. W. , Xia H. , Jiang S. S. , Zhang X. K.
Published: July 2002

Brillouin scattering studies were performed on ZnSe-ZnSe1−xSx strained-layer superlattices with the composition x∼0.2. We have observed scattering from longitudinal guided modes (LGM) whose velocities are determined primarily by the C11 elastic constant. From the measured velocity of the first-order LGM of the quasitransverse acoustic mode and of the quasilongitudinal acoustic mode, the C11 and C44 elastic constants in ZnSe-ZnSe1−xSx superlattice film have been observed.
Energy deposition in thin films calculated using electron transport theory
Authors: Biewer Theodore , Rez Peter
Published: July 2002

In scanning electron microscopy and low voltage point-projection microscopy there is considerable interest in estimating beam damage which can be related to the energy deposited in the specimen. We derive an expression for the energy deposition using the electron transport equation and give results for beam energies of 1–10 kV incident on 100 and 200 nm carbon films. The elastic scattering was modeled using a Rutherford cross section and the inelastic scattering cross section was derived from the Bethe stopping power equation. For the 100-nm-thick amorphous carbon film 90% of the incident beam energy is deposited in the sample at 2 keV, but at 6 keV only 20% of the energy is deposited. The 200 nm sample exhibited a similar curve with 20% deposition occurring at 9 keV. Our calculations show the same variation with beam energy as reported experimental results.
Ultrasonic phase velocity and elastic modulus in isotopically enhanced manufactured diamonds
Authors: Hurley D. C. , Gilmore R. S. , Banholzer W. F.
Published: July 2002

We have performed ultrasonic pulse-echo experiments to measure the longitudinal and transverse acoustic velocities in nine single-crystal manufactured diamonds. The 13C concentration in the samples ranged from nearly 0% to 99%. Small (4%–5%) but distinct decreases in both the longitudinal and transverse 〈100〉 phase velocities with increasing 13C content were observed. Using these velocities and density data, values for the cubic elastic moduli c11 and c44 were determined. Within experimental uncertainty (typically <0.5%), c11 remained constant with 13C content. However, c44 was observed to decrease by 2% over the range 0%–99% 13C. Phase velocities in 〈111〉-oriented samples remained nearly constant with isotope content, implying a 2%–6% increase in 13C diamond’s effective elastic constants 1/3(c11+2c12+4c44) and 1/3(c11−c12+c44) over those of 12C diamond. Together with experimentally determined densities and crystalline orientations and the above results for c11 and c44, the 〈111〉 velocities were used to numerically invert the Christoffel equation for the elastic modulus c12. Surprisingly, c12 nearly doubled in the range 0% to 99% 13C, implying a 17% increase in the bulk modulus K=1/3(c11+2c12).
Mathematical modeling of high-power transferred arcs
Authors: Cao M. , Proulx P. , Boulos M. I. , Mostaghimi J.
Published: July 2002

The behavior of an argon arc in a transferred arc furnace with a cold cathode and anode has been investigated using an elliptic model with emphasis on a high-current, long arc (L=100–200 mm, I=500 A). Conservation equations for the laminar arc column are written assuming local thermodynamic equilibrium. The governing equations are solved by employing an efficient finite difference method. The anode is included in the calculation domain. Numerical calculations performed for a transferred argon arc show good agreement with temperature measurements obtained by emission spectroscopy. The results also indicate that, except in regions close to the anode, the arc behavior is parabolic.
Local crystal orientation in III-V semiconductors: Polarization selective Raman microprobe measurements
Authors: Irmer G.
Published: July 2002

The determination of local crystal orientation is of interest in understanding the dynamics of crystal growth processes. Examples are the investigation of grain and twin boundaries or microstructures in semiconductors. Raman microprobe measurements can be performed contactless, without destruction and with a local resolution of about 1 μm. The information contained in the scattering intensity of the LO and TO phonons in dependence on the polarization direction of the exciting laser beam is used to determine the complete orientation of zinc-blende-type III-V semiconductor crystals. Sample rotation is not necessary. The reliability of the Raman method is demonstrated investigating a twin lamella in HB-grown GaAs.
Erasure of photorefractive gratings in barium titanate
Authors: Li J. , Li X. H. , Lu F. Y. , Wang H. F. , Yuan S. Z. , Zhu Y. , Wu X.
Published: July 2002

An analytical solution of the light-induced decay of the photorefractive gratings from the charge transport equations with shallow and deep traps is presented. It is predicted that the light-induced decay curve is biexponential, and a superposition of the shallow- and deep-trap decays in the special case is suggested. The prediction is verified in the light-induced photorefractive grating erasure experiments. The erasing intensity dependence of photoconductivity of the BaTiO3 sample is also presented.
Semiconductor-metal graded-index composite thin films for infrared applications
Authors: Lamb James L. , Nagendra C. L.
Published: July 2002

Theoretical/experimental studies have been carried out on germanium:silver (Ge:Ag) graded-index composite thin films which demonstrate that graded coatings, consisting of varied concentrations of Ag with respect to the Ge film thickness, exhibit different optical properties ranging from selective infrared (IR) reflectance to broadband IR absorptance. The graded coatings have been produced by dc magnetron cosputtering of Ge and Ag and the spectral properties are found to be stable against temperature. The coatings have been applied to an infrared tunnel sensor (micro-Golay cell) to improve the device performance.
Remanent magnetization of layered and isotropic superconductors (abstract)
Authors: Bugoslavsky Yu. V. , Minakov A. A. , Vasyurin S. I.
Published: July 2002

There are contradicting data on the anisotropy of remanent magnetization of high-temperature superconductors. To clarify the mechanism of this anisotropy we performed a comparative study of thermoremanent (TRM) and isothermal remanent (IRM) magnetizations. We report on the results obtained on layered single crystals of LaCrSuO and RBaCuO (R=Y,Gd) families as well as on isotropic soft alloy Bi:Pb:Sn and nontextured ceramic YBaCuO samples. The experiments were done by means of a vibrating-sample magnetometer. The external magnetic field up to 8 kOe was applied to magnetize the samples at arbitrary directions. It was found that all the studied plate-like samples show the effect of ‘‘easy remanent magnetization axis:’’ the vectors of IRM and TRM tend to point along the normal of the plate at any magnetizing or cooling angle. In the case of TRM this effect can be well described considering the influence of the sample shape. This fact was proved by measurements on samples with substantially different aspect ratios. Thus, we argue that the anisotropy of TRM is not related to anisotropic flux trapping. The anisotropy of IRM is a more complex phenomenon, as it involves inhomogeneous flux distribution in the sample. Nevertheless, it was found that the dependence of IRM direction on the magnetizing angle is also governed mainly by the sample shape. The corrections to the effective demagnetization factors were calculated, which arise due to the flux distribution. The analysis of the absolute value of IRM on the magnetizing angle allows one to distinguish between the influence of the critical current anisotropy and the sample shape.