bluuebunny/crossref_metadata_2025 huggingface dataset:
Carrier mobilities in graded InxGa1−xAs/Al0.2Ga0.8As quantum wells for high electron mobility transistors
Authors: Strauß U. , Bernklau D. , Riechert H. , Finkbeiner S.
Published: July 2002

We investigate modulation-doped InxGa1−xAs/AlyGa1−yAs quantum wells grown by molecular beam epitaxy with respect to carrier mobility and its dependence on In content, In distribution, populations of electron subbands, and local positions of electron wave functions. We find that the room-temperature electron mobilities are dominated by the In contents at the maxima of the electron wave functions rather than by the average In contents. At 77 K the mobilities are most strongly influenced by the distance between doping layers and the maxima of the electron wave functions. As a practical result of this study, we present a quantum well structure for high electron mobility transistors with a carrier mobility as high as 8100 cm2/V s at 295 K for an electron density of 2.5×1012 cm−2.
Microstructural evolution during epitaxial growth of Ag on vicinal InP(100) surfaces
Authors: Krishnamurthy M. , Drucker J. S.
Published: July 2002

The initial stages of epitaxial growth of Ag on InP(100) have been studied using in situ and ex situ electron microscopy. Vicinal InP substrates were cleaned by heating to about 400 °C in ultrahigh vacuum. Silver was deposited at substrate temperatures between 350 and 500 °C. The microstructural evolution was monitored for coverage between 0.5 and 8 monolayers using in situ high spatial resolution secondary electron microscopy and ex situ plan-view transmission electron microscopy (TEM). At sub-monolayer coverage, uniform, faceted islands of Ag are formed with edges aligned along InP 〈110〉 directions. Continued deposition leads to growth of preexisting islands followed by coalescence. During coalescence, a reduction in the island height, an increase in island-substrate interfacial area, and a disappearance of faceting are observed. At high coverage, during high temperature (450 °C) growth, the formation of faceted pits are observed. For higher temperatures (500 °C) and at low coverage, islands transform from square to rectangular shapes. Plan-view TEM indicates that the smallest Ag islands (∼5 nm) are not coherent with the substrate and that there are two distinct epitaxial relationships between the Ag islands and the InP substrate. For high-temperature growth, the (110)Ag plane is parallel to InP(100) substrate and there is evidence for chemical reaction and presence of In on the surface. For lower temperature depositions (350–400 °C), the (100)Ag is parallel to (100) InP.
Charge state control of hydrogenation in silicon
Authors: Seager C. H. , Anderson R. A.
Published: July 2002

We demonstrate that periodic exposure to zero bias during in situ hydrogenation of reverse-biased p-type Schottky barrier structures has dramatic effects on H penetration. H influx can be slowed or even stopped by such protocols. By contrast, similar pulsing techniques produce almost no changes of penetration in n-type barriers during hydrogenation; this latter observation is in sharp contrast to the expectations that charge conversion from H+ to H− would reverse the drift of H species. We suggest that these effects are caused by the charge conversion of relatively immobile H-related defects. In the p-type barriers this results in a weakening or reversal of the near surface electric field, effectively stopping the drift of H+ into the bulk.
Characterization of rodlike structures in Si–Ge–GaP alloys
Authors: Srikant V. , Jesser W. A. , Rosi F. D.
Published: July 2002

High-temperature microstructure of Si–Ge alloys containing 10–15 mole % GaP were studied. Quenching the 80/20 Si–Ge alloy (80 at. % Si) from above 1125 °C and the 50/50 Si–Ge alloy (50 at. % Si) from above 1025 °C resulted in a duplex microstructure. The two-phase regions consisted of a regular array of rodlike structures (GaP) in a Si–Ge matrix whereas the monophase regions were pure Si–Ge. These rodlike structures were found to lie along the [001] direction and result in {002} spots in a [100] electron diffraction pattern. The ‘‘rods’’ were about 35 and 45 nm in diameter in the case of the 80/20 and 50/50 alloy, respectively. These structures are not stable on annealing and do not form when the solidification rate is decreased.
Exchange coupling between ferromagnetic fcc Ni81Fe19 and antiferromagnetic bcc CrMnPt films
Authors: Soeya Susumu , Hoshiya Hiroyuki , Fuyama Moriaki , Tadokoro Shigeru
Published: July 2002

We studied an antiferromagnetic CrMnPtx [(Cr:Mn≂1:1) in atomic percent] film for an exchange-biased layer, focusing especially on the relationships between the exchange coupling properties of the CrMnPtx (top)/Ni81Fe19(bottom) films and the character of its CrMnPtx film. The best Pt content to obtain a large exchange coupling of the CrMnPtx film was 5.0–8.0 at. %. Typically, the exchange coupled 50 nm CrMnPt5−8/40 nm Ni81Fe19 films exhibited a relatively large exchange coupling field of ∼22 Oe and a high blocking temperature of ∼380 °C. Besides, the CrMnPt5−8 film deposited on the Ni81Fe19 film had a considerably high resistivity of ∼300–350 μΩ cm. These large exchange coupling and high resistivity values were obtained only when the α-phase with a disordered bcc structure was stabilized in the CrMnPtx film by the underlying fcc Ni81Fe19 film. The Pt within the CrMnPtx film might localize the Mn magnetic moment. As to why the CrMnPtx film having the Pt content of 5.0–8.0 at. % could give the Ni81Fe19 film a large exchange coupling, this was attributed to the nearest neighbor Mn–Mn atomic distance within the CrMnPt5−8 film being the same as the distance at which the Mn–Mn exchange interaction showed the maximum negative value. Furthermore, the decrease in size of the exchange coupling field and lowered blocking temperature for tCrMnPt<30 nm (tCrMnPt: CrMnPtx film thickness) were thought to originate from a decrease of antiferromagnetic CrMnPtx anisotropy with decreasing tCrMnPt.
Interdiffusion of lateral composition modulated (GaP)2/(InP)2 short-period superlattices with different encapsulants
Authors: Malin J. I. , Chen A. C. , Bonkowski J. E. , Baker J. E. , Cheng K. Y. , Hsieh K. C.
Published: July 2002

The interdiffusion of lateral composition modulated (GaP)2/(InP) 2 short-period superlattices (SPSs) is reported. The lateral composition modulation is achieved by the strain induced lateral layer ordering (SILO) process. A blueshift in the interband transition is observed by photoluminescence spectroscopy for capless and SiO 2 encapsulated annealed SPSs (800 °C, 5.5 h), while the intensity and wavelength of Si3N4 encapsulated annealed SPSs are only slightly perturbed. From transmission electron microscopy, capless annealed SPSs (800 °C, 5.5 h) retain their lateral composition modulation, however, the (001/2) satellite reflections disappear. For long anneal times (48 h), the interband transition corresponds to that of a In0.50Ga 0.50P alloy, suggesting the lateral composition modulation disappears. The observed lateral interdiffusion coefficient exceeds the vertical by a factor of ∼30, suggesting SPS interdiffusion is enhanced by native point defects.
Development of an analytical model for the laser machining of ceramic and glass-ceramic materials
Authors: Engin Doruk , Kirby Kevin W.
Published: July 2002

A laser machining model for ceramics and glass ceramics is developed from the analytical treatment of a one-dimensional vaporization problem with a distributed heat source. Analytical solutions are derived for evolution of the material system from an arbitrary initial state to a quasisteady state. The developed solutions are used to predict the behavior of high-intensity Nd:YAG laser pulses (up to 107 W/cm2, ms duration) on a typical ceramic or glass ceramic material. Predictions include the critical intensity required for vaporization of material Ic, the material removal ΔM, and thickness of the affected residual surface layer S after a single laser pulse of given shape and intensity. Predictions are compared with the numerical calculations from a commercially available software package.
Temperature distributions and their evolution in non-planar energy beam microprocessing: A fast algorithm
Authors: Arnold N.
Published: July 2002

We present a fast algorithm for calculations of the temperature distributions induced by the energy beam in the three-dimensional deposits of arbitrary shape. It combines analytical approximations, numerical fast Fourier transform, and the multigrid technique. The accuracy of the method is demonstrated with problems that can be solved analytically. The behavior of the center temperature in laser-deposited spots and stripes of different shapes and sizes is studied. The results can explain explosive growth in laser-induced deposition and instabilities in laser direct writing, and provide a tool for a quantitative analysis of energy beam microprocessing.
Effect of stray capacitances on single electron tunneling in a turnstile
Authors: Kang Young Bong , Hu G. Y. , O’Connell R. F. , Ryu Jai Yon
Published: July 2002

Based on the exact solution for the potential profile of the 2N turnstile with equal junction capacitances C, equal stray capacitances C0, and a coupling capacitance Cc, we obtain explicit expressions for the Gibbs free energy as well as the corresponding charging energy and the barrier height. In particular, we analyze the effects of the stray capacitances on the turnstile operation. In the C0=0 case, our results for the turnstile operation reduce to those of D. V. Averin, A. A. Odintsov, S. V. Vyshenskii [J. Appl. Phys. 73, 1297 (1993)]. In general, when C0/C is increased, the operable region of the turnstile decreases. Thus, in order to have a high quality turnstile, it is necessary to keep the stray capacitances small.
Ablation and blow-off characteristics at 248 nm of Al, Sn and Ti targets used for thin film pulsed laser deposition
Authors: Timm R. , Willmott P. R. , Huber J. R.
Published: July 2002

Laser ablation characteristics in vacuum using excimer radiation at 248 nm and pulse durations of 17 ns for Al, Sn and Ti are presented. Ablation yields are measured as a function of input laser energy and target refreshment rate using gravimetric techniques. The laser ablation thresholds for Al, Sn, and Ti are found to be 3.15, 0.89, and 2.35 J⋅cm−2, respectively. Ablation is inefficient, the majority of the laser input energy being shielded from the surface by the phenomenon of laser supported absorption, which results in heating of the nascent plasma. As the plasma becomes superheated during impingement of the laser pulse, energy is partially re-emitted in the form of black-body radiation. Mean kinetic energies of the ablation plasma species are determined by time resolved mass spectroscopy to be of the order of 5–50 eV. Target roughness and thin film morphology have been investigated using atomic force microscopy and scanning electron microscopy. Target roughness increases due to exfoliation and explosive boiling as the material is successively irradiated at a given point. Beyond a certain roughness, laser droplets are formed which propagate with the ablation plasma onto the growing film. Guidelines are presented for the rate of refreshment of exposed target material required to minimize incorporation of macroscopic material in the growing film.
Observation of 〈100〉 misfit dislocations in In0.06Ga0.94As/GaAs heterostructure by synchrotron radiation topography
Authors: Zeng W. , Jiang S. S. , Ferrari C. , Gennari S. , Salviati G.
Published: July 2002

〈100〉 oriented misfit dislocations in In0.06Ga0.94As/GaAs heterostructures with relatively low misfit f (f=0.0043) have been observed by synchrotron radiation topography. InGaAs samples consist of 2500, 4000, and 6500 Å thick In0.06Ga0.94As layers grown by molecular beam epitaxy at 580 °C. All the topographs were taken by synchrotron radiation double crystal topography. The panchromatic cathodoluminescence complementary technique in the scanning electron microscope was also applied. Misfit dislocations lying along both 〈100〉 and 〈110〉 directions have been observed. The dislocations parallel to 〈100〉 directions have much lower density and extension in length than those aligned along the 〈110〉 directions. The climb mechanism of the generation of dislocations, probably due to the high density of point defects during the high temperature growth, is discussed.
1/f noise in magnetic Ni80Fe20 single layers and Ni80Fe20/Cu multilayers
Authors: Gijs M. A. M. , Giesbers J. B. , van Est J. W. , Briaire J. , Vandamme L. K. J. , Beliën P.
Published: July 2002

We have investigated the room temperature 1/f noise of microstructured soft magnetic Ni80Fe20 films, showing the anisotropic magnetoresistance effect, and of Ni80Fe20/Cu magnetic multilayers, showing the giant magnetoresistance effect. We find that the 1/f noise in magnetic multilayers is considerably enhanced with respect to the noise of the single domain layer, which sets a limit on the usability of giant magnetoresistance materials for low-frequency applications.
Electrical properties of a new polymer/photoresist composite
Authors: Bruschi Paolo , Nannini Andrea
Published: July 2002

A new technique for growing thin films of conducting polymer with arbitrary geometry on substrates compatible with the microelectronic technologies is proposed. The new procedure utilizes commercial photoresist patterns properly modified in a way to make them suitable for the oxidation of a large class of monomers. The technique was tested with pyrrole, obtaining thin films of a composite material (resist/polypyrrole) with high conductivity. The new material was optically, morphologically, and electrically characterized. Four probe resistors and Wheatstone microbridges were built in order to measure the resistance as a function of temperature and the resistance fluctuation spectral density, respectively. Analysis of the results on the basis of conduction models of disordered media is presented. The time stability of the electrical parameters was also investigated.
Si, Be, and C ion implantation in GaAs0.93P0.07
Authors: Lee J. W. , Lee K. N. , Pearton S. J. , Abernathy C. R. , Hobson W. S. , Han H. , Zolper J. C.
Published: July 2002

The activation efficiencies of implanted Si, Be, and C in GaAs0.93P0.07 have been measured in the annealing range 650–950 °C. Be provides much higher sheet hole densities than C, even when the latter is coimplanted with Ar to enhance the electrical activity. The maximum activation efficiency of Be is ∼60% at a dose of 5×1014 cm2 whereas that of C is an order of magnitude lower. Si produces donor activation percentages up to ∼20% under optimized annealing conditions. Capless proximity annealing is adequate for surface preservation up to ∼950 °C, as measured by scanning electron microscopy and atomic force microscopy. Photoluminescence measurements provide evidence that nonradiative, damage-related point defects remain in the GaAsP even after annealing of 950 °C.
Transport properties of hydrogenated p-GaInAs doped with carbon
Authors: Theys B. , Bourgeois F. , Chevallier J. , Svob L. , Miloche M. , Driad R. , Benchimol J. L.
Published: July 2002

Highly carbon-doped Ga0.47In0.53As layers grown by chemical beam epitaxy have been exposed to a deuterium plasma. Deuterium diffusion profiles reflect very strong C–D interactions. Concerning electronic transport properties, from p-type when as-grown, these GaInAs samples turn to n-type after plasma exposure. Annealings of deuterated layers have also been performed. They show that temperatures as high as 450 °C must be reached before p-type conductivity is fully restored in the material.
Semiconductivity in YBa2−xSrxCu3Oy
Authors: Uluǧ A. , Uluǧ B. , Şener E.
Published: July 2002

Structural and electrical properties of YBa2−xSrxCu3Oy prepared under ambient oxygen pressure were systematically investigated for 0≤x≤2.0. Samples with high Sr contents, x≥1.7, showed semiconductive properties with an activation energy of ∼150 meV at high temperature, T≥80 K. At low temperatures, T≤80 K, activation energy dropped to ∼3.00 and ∼0.85 meV for x=1.7–1.8 and x=1.9–2.0, respectively. It is argued that YSr2Cu3Oy is likely to have a tetragonal structure and that the disorder introduced by Sr substitution affects electrical conduction, which involves charge hopping between the CuO chains at high Sr contents.
Analysis of ac temperature wave during the measurement of thermal diffusivity of two-layered platelike samples
Authors: Yamane Tsuneyuki , Katayama Shin-ichiro , Todoki Minoru
Published: July 2002

A theoretical consideration of two-dimensional ac temperature waves in a two-layered platelike sample for application to thermal diffusivity measurement parallel to a sample surface using an ac calorimetric method is presented. The analysis is based on the Fourier-transformed Green’s function technique. It is concluded that this thermal system deviates from an apparent one-layered system of which the thermal diffusivity parallel to a sample surface is calculated based on steady state heat flow under the following conditions: (a) the frequency of the supplied ac thermal energy is high, (b) the difference between the thermal diffusivities of the layers is large, and (c) the layer with higher thermal diffusivity is thin. This deviation is due to the inhomogeneous ac temperature distribution normal to the sample surface. If experimental conditions are the reverse of conditions (a)–(c), an ac calorimetric method can be used to measure the thermal diffusivity of thin samples on substrates.
The behavior of small bubbles generated by electrical current impulses over a wide range of applied pressures
Authors: McCluskey F. M. J. , Denat A.
Published: July 2002

Very small bubbles are generated in chemically different insulating liquids in a repeatable and controlled way. A constant dc voltage is applied between a sharp point and a plane electrode. Above a threshold voltage, the current is ‘‘impulsional.’’ The origin of each impulse is an electron avalanche while the consequence is the formation of a small bubble at the point electrode. The relationship between the injected electrical energy and the maximum bubble size is examined. Depending on the liquid used, and therefore the level of energy injected, different behaviors were observed. In particular, results for very low energy injections were explained by mechanical rather than thermal processes. The nonequilibrium plasma formed following an electron avalanche, brings about the emission of a pressure transient, behind which there is an ‘‘afterflow’’ of matter. The liquid travelling outwards from this point source causes the liquid to break down mechanically, thus forming an almost empty cavity, which disappears on collapse. In the case of high energy injection, energy is lost to local heating of the liquid.
Deep levels in uniformly Si doped GaAs/AlxGa1−xAs quantum wells and superlattices
Authors: Jia Y. B. , Han Z. Y. , Grimmeiss H. G. , Dobaczewski L.
Published: July 2002

Uniformly Si doped GaAs/Al0.33Ga0.67As multilayer structures have been studied by deep level transient spectroscopy (DLTS) and photocapacitance measurements. DLTS spectra showed five peaks which are related to defects in the GaAs layers. The concentration of these defects decreased with increasing layer thickness. An additional peak, which has been observed with forward bias filling pulses, is suggested to be related to defects near the surface, most probably due to defect accumulation in multilayers. Their emission and capture properties as well as photoionization cross sections have been studied. Evidence is provided that the emission and filling processes of these deep levels are modified due to the energy quantization in the conduction band and the carrier transport through the quantum structures. No DX center related DLTS peaks or other features like persistent photoconductivity effects have been observed in any of our samples.
Thermal reactions of Pd/AlxGa1−xAs contacts
Authors: Chuang H. F. , Lee C. P. , Tsang J. S. , Fan J. C.
Published: July 2002

Pd/AlxGa1−xAs Schottky contacts and their thermal reactions are studied by capacitance–voltage measurements, current–voltage measurements, and x-ray diffraction. The thickness of AlxGa1−xAs consumed by the Pd/AlxGa1−xAs reaction during annealing was calculated. For annealing temperatures below 300 °C the Schottky characteristics of the diodes were good but the electrical junction moves into AlxGa1−xAs after annealing. The amount of junction movement was calculated directly from our measurements. The diffusion coefficients of Pd in AlxGa1−xAs and the activation energy were estimated. The activation energy was found to be larger for higher Al concentration. PdAl, PdAs2, PdGa5, and Pd5Ga2 were detected in the compounds formed by the Pd/AlxGa1−xAs reaction after annealing.
Thermodynamic effects in the ion-beam mixing of Fe-Al and Mo-Cr multilayers
Authors: Knystautas Émile J. , Lo Russo Sergio , Kelly Roger , Miotello Antonio
Published: July 2002

Ion-beam mixing of Fe-Al and Mo-Cr multilayers was studied by alternately sputtering with 5 keV Ar+ and then analyzing with Auger electron spectroscopy. The target temperature was variously room temperature, 450, 525, or 600 K. The two systems were chosen on the basis of having heats of mixing (ΔHm) which were opposite in sign, namely H1:1m=−0.25 eV for solid Fe-Al and ΔH1:1m=+0.075 eV for solid Mo-Cr. (ΔH1:1m applies to a 1:1 composition.) With Fe-Al a well-defined peak broadening was observed as the profiling temperature increased, while with Mo-Cr there was a slight narrowing of the peaks with increasing temperature. The results were analyzed in terms of numerical solutions of a diffusion equation which contained terms appropriate not only to ballistic motion but also to the motion of bombardment-induced residual defects. The latter were assumed to be in part ‘‘chemically guided,’’ as quantified with the parameter ‘‘qp’’ (qp∼∝ΔHm). A major difference between Fe-Al and Mo-Cr was found. The peak changes with Fe-Al scaled with what we have termed the effective diffusion coefficient Deff=Dt(1−qp/4). Here Dt is the total diffusion coefficient, i.e., it describes the total diffusivity for all mixing processes. With Mo-Cr, on the other hand, the peak changes scaled approximately with 1/qp. The mixing behavior of Fe-Al, with negative ΔHm, could thus be said to be mainly kinetic (with Deff playing a major role), while that of Mo-Cr, with positive ΔHm, is more nearly thermodynamic (with qp playing a major role).
Magnetization imaging at high spatial resolution using transmission electron microscopy
Authors: Daykin A. C. , Jakubovics J. P.
Published: July 2002

A new method of imaging has been developed for mapping the distribution of magnetic induction in thin films in a conventional transmission electron microscope. The method produces differential phase contrast images at high spatial resolution without using expensive additional equipment. The capabilities of our method are demonstrated by the measurement of domain wall width in a NdFeB alloy specimen, and by the determination of the two-dimensional magnetic induction distribution in a Co/Cr/Co trilayer.
Antiphase locking in a two-dimensional Josephson junction array
Authors: Basler M. , Krech W. , Platov K. Yu.
Published: July 2002

We consider theoretically phase locking in a simple two-dimensional Josephson junction array consisting of two loops coupled via a joint line transverse to the bias current. Ring inductances are supposed to be small, and special emphasis is taken on the influence of external flux. It is shown that in the stable oscillation regime both cells oscillate with a phase shift equal to π (i.e., antiphase). This result may explain the low radiation output obtained so far in two-dimensional Josephson junction arrays experimentally.
Improvement of the stability of hydrogenated amorphous silicon films by intermittent illumination treatment at elevated temperature
Authors: Sheng Shuran , Kong Guanglin , Liao Xianbo
Published: July 2002

The intermittent illumination treatment by white light at elevated temperature is proved to be a convenient and efficient method for the improvement of the stability of hydrogenated amorphous silicon (a-Si:H) films. The effect of the treatment on electrical properties, light-induced degradation, and gap states of undoped a-Si:H films has been investigated in detail. With the increase of cycling number, the dark- as well as photo-conductivities in annealed state and light-soaked state approach each other, presenting an unique irreversible effect. The stabilization and ordering processes by the present treatment can not be achieved merely by annealing under the same conditions. It is shown that the treatment proposed here results in a shift to higher values of the energy barriers between defects and their precursors, and hence an improved stability of a-Si:H films.
Growth of high quality Al0.22Ga0.78As layers on Si substrates by metalorganic chemical vapor deposition
Authors: Baskar K. , Soga T. , Jimbo T. , Umeno M.
Published: July 2002

High quality epitaxial layers of Al0.22Ga0.78As have been grown on Si substrates by adopting thermal cycle annealing. The quality of the Al0.22Ga0.78As has been assessed by photoluminescence, deep-level transient spectroscopy, and double-crystal x-ray diffraction studies. The emergence of a new luminescence emission (1.718 eV), high concentrations of shallow levels, passivation of a deep level (0.43 eV), and dislocation reduction in the high-temperature thermal cycle annealed samples have been explained by a silicon diffusion mechanism and the formation of complex point defects. Deep-level emission at 0.64 eV has been attributed to disordering in the epitaxial layers.
Indented barrier resonant tunneling rectifiers
Authors: Di Ventra M. , Papp G. , Coluzza C. , Baldereschi A. , Schulz P. A.
Published: July 2002

This article concerns a novel negative-conductance device consisting of a series of N laterally indented barriers which exhibits resonant tunneling under one bias polarity and simple tunneling under the opposite one, thus acting as a rectifier. Electrons undergo resonant tunneling when the bias creates a band profile with N triangular wells which can each contain a resonant state. From 1 to N the addition of each indentation can be used to increase the current density and the rectification ratio, calculated at the current-peak bias at resonance, provided that at a given bias all the states in the triangular wells align each other with the emitter Fermi energy in order to form a resonance along the structure.
Microwave plasma characteristics during bias-enhanced nucleation of diamond: An optical emission spectroscopic study
Authors: Whitfield Michael D. , Jackman Richard B. , Rodway Don , Savage James A. , Foord John S.
Published: July 2002

A negative bias applied to a nondiamond substrate at the initiation of microwave plasma-enhanced chemical-vapor deposition of thin-film diamond can lead to diamond nucleation, high crystalline density, and an improved level of crystallographic alignment. In this work, optical emission spectroscopy has been used to study changes in the chemical species within the plasma that occur as a result the applied bias to a tungsten substrate. The ratio of C2 to CH species detected changes considerably as does the atomic hydrogen intensity as the bias is applied. Both effects appear to be greatest near the substrate surface. The results are discussed in terms of possible origins for the bias-enhanced nucleation process.
Shock-induced transformations of carbyne
Authors: Borodina T. I. , Fortov V. E. , Lash A. A. , Zhuk A. Z. , Babaev V. G. , Guseva M. B.
Published: July 2002

The influence of the shock wave loading on films of amorphous carbyne was explored. Chemically synthesized films were deposited on copper disks of 1 mm thickness. X-ray and transmission electron microscopy examination of 10 and 150 μm carbyne films recovered after shock loading at pressures of 18, 26, and 36 GPa were carried out. It was detected that 10 μm films partially transformed to carbyne crystals with a size of about 1 μm. Thick films of carbyne transformed to a mixture of an amorphous carbon phase and nanocrystalline cubic diamond.
Butterfly curves and critical modes for second-order spin-wave instability processes in yttrium iron garnet films
Authors: Kabos P. , Patton C. E. , Wiese G. , Sullins A. D. , Wright E. S. , Chen L.
Published: July 2002

Combined Brillouin light-scattering (BLS) and microwave pumping techniques were used to measure the second-order spin-wave instability threshold microwave field amplitudes and characterize the critical modes for ferromagnetic resonance (FMR) saturation in 4.15 μm-thick yttrium iron garnet films at 8.47 GHz with the static magnetic field in-plane. To the best of our knowledge, this work represents the first BLS measurements for second-order FMR saturation processes in ferrite materials. Several new results were obtained: (1) A new type of butterfly curve for second-order processes. (2) Strong scattering from modes at low wave numbers in the 104 rad/cm range. (3) An observed in-plane propagation direction for these low wave number modes at 90° to the in-plane static field direction. These results differ significantly from the behavior expected from the bulk sample instability theories of Suhl and Schlömann, which predict critical modes at wave numbers and propagation directions in the 105–106 rad/cm and 0° ranges, respectively, and a sharp cusplike response centered at FMR. These results indicate that significant modifications of the bulk theory, which take into account the real modes supported by the film, are needed to realistically model second-order instability processes in films.
Thermal stability of sulfur-treated InP investigated by photoluminescence
Authors: Han I. K. , Woo D. H. , Kim H. J. , Kim E. K. , Lee J. I. , Kim S. H. , Kang K. N. , Lim H. , Park H. L.
Published: July 2002

The effect of sulfur (S) treatments on InP is investigated by low-temperature photoluminescence (PL) measurements. For both n- and p-InP, the PL intensity is observed to increase about four times in magnitude if the scattering by the S overlayer is relatively small. Some PL bands are observed to disappear after S treatments and then reappear if the S-treated surface is heat treated at 220 °C in a vacuum of 10−3 Torr. By observing their dependence on the excitation power density, the doping level of the samples, and measurement temperature, these PL bands are ascribed to the optical transitions via surface states. Our results thus indicate that the S-treated InP surface may not be stable at a subsequent processing temperature of about 250 °C.
Effective interband g factors in diluted magnetic semiconductor Cd1−xFexTe
Authors: Wang Xuezhong , Chen Chenjia , Liu Anwen , Wang Rongming , Ma Kejun
Published: July 2002

The effective interband g factors γΓ and γL at the Γ and L points of the Brillouin zone for Cd1−xFexTe with x=0.01 and 0.04 have been determined in the temperature range of 70–300 K from Faraday rotation measurements. The results show that the dominant contribution to γΓ is due to the sp–d exchange interaction between Fe2+ ions and free carriers, while the intrinsic contribution is dominant for γL. The exchange interaction integral N0(β−α) at the Γ point has also been obtained.
Mechanical stress power measurements during high-power laser ablation
Authors: Shannon Mark A. , Rubinsky Boris , Russo Richard E.
Published: July 2002

Laser-induced stresses have been studied extensively to understand macroscopic phenomenon during high-power laser ablation of solids. Recently, a norm of stress times the rate of change in stress, similar to mechanical stress power, was monitored acoustically in the target and ambient medium during high-power laser-material interactions, and compared with stress measurements. This study investigates the relationship between stress and the stress powerlike measurements (P*), and their dependence on laser energy, intensity, and spot size. The importance of different components of stress on the measurements is also considered. Results from ablation of aluminum targets by a 30 ns uv excimer laser are presented that show changes in P* with laser energy coupling, and the dependence of P* on laser intensity and stress components. Potential issues are raised for further study of stress power as a diagnostic tool of laser-material interactions and as a fundamental mechanism of laser-energy coupling.
Picosecond spectral hole burning in ZnCdTe layers
Authors: Benhmida M. , Netiksis V. , Robino M. , Grun J.-B. , Petrauskas M. , Hönerlage B.
Published: July 2002

The spectral and temporal behavior of absorption bleaching due to band- and state-filling processes in Cd1−xZnxTe polycrystalline layers with a nominal composition x=0.17 are investigated. The absorption bleaching due to band-filling effects has a decay time in the range of 35 and 90 ps which depends on the photon energies of the pump and test beams. It is attributed to the relaxation of quasi-Fermi levels through the bottom (top) of the conduction (valence) band and corresponds to the lifetime of nonequilibrium charge carriers. The absorption bleaching due to state-filling processes corresponds to the nonthermal part of the energy distribution of free carriers and therefore depends on the photon energy of the pump beam. A hole burning is found which peaks near the photon energy of the pump laser and which follows the temporal shape of the laser pulses (20 ps). The asymmetry of the hole-burning spectrum is attributed to the energy dependence of the density of states which is important for electron–electron scattering processes.
Faraday effect of GaS3/2–GeS2–LaS3/2-based glasses containing various rare-earth ions
Authors: Qiu Jianrong , Qiu J. B. , Higuchi H. , Kawamoto Y. , Hirao K.
Published: July 2002

Sulfide glasses of 50GaS3/2⋅20GeS2⋅20LaS3/2⋅10LnSn/2 (Ln=rare earth ions, n=2 for Eu and 3 for other ions) compositions have been prepared. The wavelength dispersions in the Faraday effect of the glasses have been examined. Glasses containing LaS3/2 and YS3/2 have positive Verdet constants in the wavelength region from 550 to 850 nm, and the magnitude of the Verdet constants decreases with increasing wavelength. On the other hand, the Verdet constants of glasses containing Eu2+ and Ce3+ are negative, and the absolute magnitude of the Verdet constants decreases with increasing wavelength. The effective transition wavelengths of glasses containing various paramagnetic rare-earth ions have been calculated based on the Van Vleck and Hebb theory. Factors determining the Verdet constants of these glasses are discussed.
Influence of free carrier concentration on absorption and third-order susceptibilities of n-type ZnSe crystals
Authors: Sahraoui B. , Chevalier R. , Phu X. Nguyen , Rivoire G. , Bala W.
Published: July 2002

This study analyzes the dependence of third-order susceptibilities at 532 nm of n-type ZnSe crystals in relation to free carrier concentration and annealing temperatures. The nonlinear optical absorption and the efficiency of degenerate four-wave mixing of ZnSe are investigated. We find that the magnitude of the nonlinear absorption decreases with the electron concentration and annealing temperature increase, while the nonlinear refractive index increases slightly.
A high-voltage triggered pseudospark discharge experiment
Authors: Ramaswamy K. , Destler W. W. , Rodgers J.
Published: July 2002

The design and execution of a pulsed high-voltage (350–400 keV) triggered pseudospark discharge experiment is reported. Experimental studies were carried out to obtain an optimal design for stable and reliable pseudospark operation in a high-voltage regime (≳350 kV). Experiments were performed to determine the most suitable fill gas for electron-beam formation. The pseudospark discharge is initiated by a trigger mechanism involving a flashover between the trigger electrode and hollow cathode housing. Experimental results characterizing the electron-beam energy using the range-energy method are reported. Source size imaging was carried out using an x-ray pinhole camera and a novel technique using Mylar as a witness plate. It was experimentally determined that strong pinching occurred later in time and was associated with the lower-energy electrons.
The theory of thermodynamic-acoustoelastic stress gauge
Authors: Kim Kwang Yul , Sachse Wolfgang
Published: July 2002

Combining the thermodynamics at finite deformation with the acoustoelasticity of a specimen, which is initially stressed in three principal directions and subsequently subjected to finite uniaxial loading, we present the methods of constructing an absolute stress (or force) gauge that may be used to determine residual stresses and serve as an alternative to dead weight for calibration of load cells. Formulas for the effective Young’s modulus and Poisson’s ratio, both evaluated at a current stress level, are derived in terms of thermodynamic elastic coefficients and stresses, which are generally equal to the initial stresses plus applied stresses. It is shown that the effective adiabatic Young’s modulus and Poisson’s ratio can be obtained from relevant wave speeds measured in various directions. The true principal stress under uniaxial loading can be calculated, if one measures directly the dimensional changes in three principal directions and relevant wave speeds in various directions and makes use of the adiabatic-isothermal conversion of the Young’s modulus and Poisson’s ratio. If the applied stress is measured the initial or residual stress can be calculated. One the other hand, if the initial stresses are zero and the applied stress is unknown, one can calculate the applied stress, which may be used to calibrate a load cell in a wide range of forces exceeding 1000 tons.
Study of effect of SiH4 gas heating during growth of hydrogenated microcrystalline silicon on SiO2 by plasma-enhanced chemical-vapor deposition
Authors: Arai Takeshi , Shirai Hajime
Published: July 2002

The effect of SiH4 source gas heating on the properties of hydrogenated microcrystalline silicon film grown by plasma-enhanced chemical-vapor deposition was investigated to improve the crystallinity and inhomogeneities at the early stage of growth on an amorphous substrate such as glass. Optimization of the deposition conditions for μc-Si:H film structure and characteristics was carried out for a film around 1000 Å thickness and as a function of the cathode heating temperature Tc. The grazing incidence x-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy, and UV-visible spectroscopic ellipsometry results showed that the SiH4 gas heating significantly improved the crystallinity and inhomogeneities from the early stage of Si thin film growth at Tc≳550 °C and Ts of 180 °C condition. The role and effect of the cathode heating in the μc-Si:H growth is discussed.
Very low-roughness diamond film deposition using a surface-wave- sustained plasma
Authors: Borges C. F. M. , Airoldi V. T. , Corat E. J. , Moisan M. , Schelz S. , Guay D.
Published: July 2002

We have investigated the operating parameters controlling the average roughness Ra of diamond films obtained through chemical-vapor deposition using microwave-sustained plasmas. The plasma was provided by a surface-wave discharge in the form of a convex hemisphere facing the substrate and the films were deposited on Si(100) substrates. The procedure leading to fine grain, low-roughness diamond films called for high microwave power density absorbed in the plasma and very small grain size powder for substrate pretreatment in an ultrasonic bath, using hexane as the suspension liquid. Pretreating then with ≤ 0.25 μm diamond grit and operating, for example, with a microwave power density of 25 W/cm3 (1.2 kW total absorbed power) and 0.75% CH4 in a CH4–H2 mixture, we got Ra = 6 nm for a 1-μm-thick film with an average crystallite size of 50 nm. The corresponding nucleation density was remarkably high, at 7.5×1010 cm−2; diamond film isoquality was good and adhesion to the substrate strong.
Thermal stability of hydrogen and sulfur atoms in a-SiSx:H films
Authors: Itoh Takashi , Nitta Shoji , Wang S. L. , Taylor P. C.
Published: July 2002

The thermal stability of hydrogen and sulfur atoms in a-SiSx:H films is studied using gas effusion spectra and electron spectroscopy for chemical analysis. Two evolution peaks of hydrogen are found above 400 °C in gas effusion spectra of a-SiSx:H films. Sulfur atoms are evolved only above 550 °C. The stability of sulfur and the relationship of dangling bonds to sulfur effusion are discussed.
Microstructure modifications induced by bonded hydrogen in N-rich SiNx:H films
Authors: Paloura E. C. , Lioutas Ch. , Vouroutzis N. , Arnoldbik W. M. , Habraken F. H. P. M. , Kuo Y.
Published: July 2002

The effect of bonded hydrogen in the atomic microstructure of nitrogen-rich SiNx:H films is investigated using extended x-ray-absorption fine-structure spectroscopy (EXAFS). The hydrogen concentration in the examined films, as measured by elastic recoil detection analysis, takes values in the range 25–33 at. %. It is shown that hydrogen, which is mostly bonded to N, alters the film microstructure, as that is determined by the nearest-neighbor distances and coordination numbers. The measured N–Si nearest-neighbor distance is modified by the presence of N—H bonds and it is shorter than that corresponding to Si3N4 by 3%. This bond length reduction is attributed to the higher electronegativity of hydrogen than that of the replaced Si atoms. In addition, the coordination number N in the nearest-neighbor shell, consisting of Si atoms, is reduced to 2 from the expected coordination of 3 in Si3N4. Furthermore, EXAFS detects the presence of partially reacted Si (a-Si:N) phase, embedded in the SiN matrix, the concentration of which depends on the deposition conditions (rf power and gas flow ratio). The existence of the a-Si:N phase is confirmed by plane-view transmission electron microscopy measurements.
Effect of ion bombardment on the long-range chemical order in FePd films
Authors: Sürgers C. , Kay E. , Wang S. X.
Published: July 2002

Fe1−xPdx films of nearly equiatomic composition (0.47≤x≤0.56) have been prepared by ion-beam sputtering at substrate temperatures TS=350 °C. During growth the films were bombarded by Xe+ ions with energies EXe=0–100 eV and an ion-to-atom arrival ratio of R=0.3. Films were characterized by x-ray diffraction and the wavelength dependent magneto-optic Kerr effect. Without bombardment, the films are partly chemically ordered with a long-range order parameter S≊0.7. For energies EXe up to 50 eV the chemical order survives to a high degree and only moderate modifications in the structural data and Kerr spectra are observed, whereas for EXe=100 eV the chemical order is completely destroyed. In contrast, the epitaxial quality seems to be unaffected by the bombardment for EXe≤50 eV. This shows that low-energy ion bombardment during growth only leads to a randomization of the Fe and Pd atoms on the lattice sites without causing significant structural damage.
Metal/polymer interface adhesion by partially ionized beam deposition
Authors: Wu P. K. , Dabral S. , Yang G.-R. , Gittleman B. , Li C. , McDonald J. F. , Lu T.-M.
Published: July 2002

It is shown that a peel strength of larger than 70 g/mm adhesion can be achieved between Cu and Parylene-N surfaces using the partially ionized beam (PIB) deposition technique while the conventional deposition techniques such as thermal evaporation, e-beam evaporation, and sputtering give no measurable adhesion. With the PIB process, neither an adhesion enhancement layer nor substrate pretreatment is required. In the PIB deposition, up to 5% of self-ions and 3 kV substrate bias were used during deposition. Secondary-ion-mass spectroscopy revealed a Cu–Parylene-N intermixed layer located at the Cu/Parylene-N interface. It is proposed that the mechanical interlocking provided by the graded interface region may play a role for the observed adhesion enhancement.
Plasma deposition and characterization of photoluminescent fluorinated nanocrystalline silicon films
Authors: Cicala G. , Capezzuto P. , Bruno G. , Schiavulli L. , Perna G. , Capozzi V.
Published: July 2002

Fluorinated nanocrystalline silicon films, nc-Si:H,F, have been deposited from SiF4–SiH4–H2 mixtures by means of the plasma enhanced chemical vapor deposition technique. The presence of fluorine atoms, which are effective etchant species, promotes selective etching giving nanocrystalline films. These materials, with grain size of 100–200 Å, show a room temperature photoluminescence centered at 1.62 eV. Also, the widening of the optical energy gap (Eg=2.12 eV) is mainly due to the presence of nanocrystals rather than to the H content of 4.5 at. %.
Fabrication of ZnSe/ZnS quantum wires using high index GaP substrates
Authors: Tomasini P. , Arai K. , Wu Y. H. , Yao T.
Published: July 2002

ZnSe/ZnS quantum wires and quantum dots were grown on unpatterned substrates by molecular beam epitaxy. Several substrate orientations were compared. These structures exhibited a strong luminescence. A linear crystallographic dependence of the photoluminescence peak energy was observed when comparing structures grown in the same experimental conditions. All samples exhibited also strong zero-dimensional–one-dimensional confinement signatures. An empirical analysis is provided illuminating the issue involved by the redshift.
Si-doped and undoped Ga1−xInxSb grown by molecular-beam epitaxy on GaAs substrates
Authors: Roslund J. H. , Swenson G. , Andersson T. G.
Published: July 2002

Growth by molecular-beam epitaxy and characterization of Si-doped and unintentionally doped Ga1−xInxSb layers in the full compositional range on GaAs substrates are reported. The grown samples were characterized by reflection high-energy electron diffraction, x-ray diffraction, Hall-effect measurements, and secondary-ion-mass spectroscopy. The unintentionally doped layers had carrier concentrations below 6×1016 cm−3 with a maximum at x≊ 0.5, where the conduction switched from p to n type. Silicon doping in the 1017 cm−3 range provided acceptors up to x≊0.85 for a growth temperature of 430 °C. For higher x values conduction was mixed and the Hall-effect data suggest that an inversion layer of electrons could be present on the surface.
Kink effect on subthreshold current conduction mechanism for n-channel metal-oxide-silicon devices
Authors: Chen S. S. , Lin S. C. , Kuo J. B.
Published: July 2002

An analysis of the subthreshold current conduction mechanism for partially depleted silicon–on–insulator n-channel metal–oxide–silicon devices considering kink effect is reported. For a device with a low leakage current, the kink effect dominates the subthreshold region. Based on the analytical model, for a thicker gate oxide, or for a more heavily doped thin film, the gate voltage at the onset of kink effect in the subthreshold region is higher.
Nonequilibrium thermal noise in GaAs/GaAlAs superlattice miniband
Authors: Dutisseuil E. , Sibille A. , Palmier J. F. , Thierry-Mieg V. , de Murcia M. , Richard E.
Published: July 2002

We present the first measurement of non-equilibrium thermal noise (i.e. hot electron diffusion noise) related to vertical transport in superlattice minibands. Bias dependence of the longitudinal diffusion coefficient has been extracted from experimental data and compared with two models. We show that this coefficient is a clearly decreasing function of the applied electric field, in agreement with theoretical models. This result highlights the potential superiority of superlattices in millimeter wave devices as regards noise.
Asymmetric secondary electron emission flux in ferroelectric KTiOPO4 crystal
Authors: Rosenman G. , Skliar A. , Lareah Y. , Angert N. , Tseitlin M. , Roth M. , Oron M. , Katz M.
Published: July 2002

It is shown that secondary electron emission current from ferroelectric domains with opposite directions of spontaneous polarization in ferroelectric KTiOPO4 crystals (KTP) is substantially asymmetric. The effect originates from asymmetry of elementary electron processes in noncentrosymmetric crystals. A nondestructive method of ferroelectric domain observation by secondary electron emission microscopy in KTP crystals is developed, which enables observation of a domain grating in periodically poled KTP frequency doubler.