bluuebunny/crossref_metadata_2025 huggingface dataset:
Observation of a two-component electron population in a hollow cathode discharge
Authors: Hershcovitch A. I. , Kovarik V. J. , Prelec K.
Published: July 2002

A retarding potential technique has been employed to select electrons for extraction from a hollow cathode discharge. In ‘‘normal’’ operating pressures, the electron distribution function is Gaussian like with a superthermal tail. At low operating pressures, the electron distribution function has an additional distinct component of electrons with a very low thermal spread of 0.13 eV and an energy corresponding to the cathode potential.
Ion production from LiF-coated field emitter tips
Authors: Pregenzer A. L. , Bieg K. W. , Olson R. E. , Panitz J. A.
Published: July 2002

Ion emission has been obtained from a LiF-coated tungsten field-emitter tip. Ion formation is thought to be caused by the high electric field experienced by the LiF. At the time of emission the electric field at the surface of the LiF is calculated to be on the order of 100 MV/cm. Inside the LiF the field is on the order of 10 MV/cm. These fields exceed the value needed to produce bulk dielectric breakdown in LiF. The surface field is of sufficient magnitude to produce ion emission by field evaporation from the crystal surface. Even prior to dielectric breakdown, precursor processes can lead to ion formation. Electric-field-stress fragmentation of the LiF layer is thought to occur, followed by ionization of the fragments.
Longitudinal spin fluctuations in nickel
Authors: Böni P. , Martínez J. L. , Tranquada J. M.
Published: July 2002

The longitudinal and transverse spin fluctuations in Ni have been measured below Tc by means of polarized neutron scattering in the momentum range 0.06<q<0.18 Å−1. In transverse scans spin-wave peaks at Eq=Dq2 appear as expected from early measurements performed with unpolarized neutrons. The longitudinal magnetic scattering χL(q,E), on the other hand, is quasielastic without any signature of inelastic peaks near Eq. The q and T dependencies of χL(q,E) resemble the paramagnetic scattering above TC, i.e., the linewidth is roughly proportional to q2.5 and the integrated intensity I(q) is proportional to (q2+κ2z)−1.
Magnetic-phase diagram of a Mn0.9Co0.1P single-crystal. Irreversible behavior in a magnetic field
Authors: Becerra C. C. , Zieba A. , Oliveira N. F. , Jellvag H. F.
Published: July 2002

The magnetic-phase diagram of a Mn0.9Co0.1P single crystal was studied by ac susceptibility with a magnetic field (H) applied along its orthorhombic b axis. This system orders ferromagnetically at 197.5 K and below 37 K it shows a helimagnetic structure in H=0. The H-T phase diagram above 37 K is similar to the one found in pure MnP, including the presence of a Lifshitz multicritical point (HL =11.0 kOe, TL =99±1 K) at the confluence of the paramagnetic, ferromagnetic, and modulated fanlike phase. It was found that: (1) the hysteresis at the first-order transitions between the ordered phases is much larger than in MnP; (2) hysteretic behavior is observed inside the whole region of the phase diagram corresponding to the fanlike phase; (3) the second-order fan-para transition fades at low temperatures and an irreversible behavior is observed with the irreversibility field sharply increasing at lower temperatures. The last feature is in marked contrast with what is observed in pure MnP, where the second-order fan-para transition is very sharp and the transition field tends to a constant value at low temperatures.
Transfer matrix studies of d≥3 Ising models
Authors: Novotny M. A.
Published: July 2002

A novel numerical transfer matrix approach to obtain the critical behavior of Ising models in dimensions higher than two is described. The approach augments the physical transfer matrices with other matrices which do not necessarily have a straightforward physical interpretation. These additional matrices have approximately the same form as the physical transfer matrices, and for high dimensions may provide the only way of performing finite size scaling using transfer matrix calculations. Results are presented for the Ising model in three, four, and five dimensions.
Pulse height spectrum analysis of Barkhausen emissions in the frequency range 15–250 kHz (abstract)
Authors: Jiles D. C. , Hariharan S.
Published: July 2002

This paper reports the development and application of a new device for pulse height analysis of Barkhausen emissions which has been incorporated as an additional feature within existing magnetic multiparameter instrumentation described recently.1 We have used this to measure the magnetic properties and Barkhausen spectrum of a specimen of a medieval Damascus steel sword with a carbon content of 1.0 wt. %. This material has particularly interesting mechanical properties, however, the method of producing the steel has now been lost. Our interest was to see whether the magnetic properties of the material were exceptional. In fact, this was found not to be so, with a coercivity of 21 Oe (1680 A/m) and a hysteresis loss of 121 ergs/cm3 (12.1 kJ/m3), which were comparable with those observed in other steels with similar carbon content. The pulse height analyzer has been incorporated into the existing system and provides a spectrum of number of events against pulse amplitude. The greatest Barkhausen activity in the Damascus steel was found at the top of the frequency range measured, that is, between 200 and 250 kHz, with a maximum count rate of between 100 and 150×103/s at a pulse amplitude of 3.1×10−8 Wb/s. At lower frequencies the peak in activity occurred at slightly greater pulse amplitudes of up to 5.1×10−8 Wb/s. The present system enables pulse height analysis of Barkhausen emissions to be measured over a freuqency band of interest during simultaneous measurement of other magnetic properties such as magnetization and magnetostriction. Such analysis is complementary to the usual count rate information, which has been reported previously.2
Spin-wave spectrum for barium ferrite (abstract)
Authors: Marshall S. P. , Sokoloff J. B.
Published: July 2002

In order to determine whether barium ferrite will be suitable for microwave and millimeter wave device applications, it is essential to calculate the intrinsic ferrimagnetic resonance linewidth for perfect single crystals of this compound. The two mechanisms believed to be responsible for the intrinsic linewidth of barium ferrite, the Kasuya–LeCraw1 two-magnon one-phonon process and the two-magnon scattering caused by the time fluctuations of 2b site (trigonal symmetry site) ions,2 require knowledge of the magnon dispersion relations throughout the Brillouin zone, and not just near the zone center. We describe the calculations of the spin-wave spectrum for barium ferrite, which is a highly complex exchange-coupled hexagonal ferrimagnetic compound, using a method similar to that used by Harris for YIG.3 The exchange integrals are calculated by fitting the Weiss molecular field approximation to the sublattice magnetizations while including single-ion anisotropy. The value for the space-averaged stiffness constant as calculated from the acoustic mode of the spin-wave spectrum is 2.5×10−9 Oe cm4.
Micromagnetics of Co-based media: Experiment and model (invited)
Authors: McFadyen I. R. , Beardsley I. A.
Published: July 2002

The micromagnetics of Co86Cr14 thin-film longitudinal recording media has been investigated using Lorentz transmission electron microscopy, in the Fresnel and differential phase contrast (DPC) modes. The media studied were 350-Å-thick Co86Cr14 on a 200-Å Cr layer, both of which were rf sputtered onto Si3N4 membranes for ease of observation in the TEM. Different magnetization states were investigated by imaging the sample at various points in the remanent hysteresis loop. This allowed direct comparison between experimental conditions and a micromagnetic computer model which assumes the media to be an array of single-domain particles, interacting via magnetostatics and moderate integranular exchange [J.-G. Zhu and H. N. Bertram, J. Appl. Phys. 63, 3248 (1988)]. The DPC imaging technique allows vector maps and two-dimensional histograms of the integrated in-plane magnetic induction to be obtained at each magnetization state for comparison with the computer model. The scale and displacement of magnetization vortices and ripple between different states was also investigated. Both experiment and model show increasing dispersion with increasing reversal field and motion of magnetization vortices. Comparison, using the model, of individual magnetization states in an applied field and at remanence indicate a strong influence of stray fields from the media on the DPC image contrast.
A simple domain model of flux reversal in ferrites
Authors: Avery R. K. , DeFord J. F. , Kamin G. , Turner W. C. , Zentler J. M.
Published: July 2002

To design ferrite core accelerator cells and pulse power sources for use in linear induction accelerators, it is necessary to know how the ferrite behaves when its magnetization reverses in times of the order of 100 ns. To meet this need, a simple model has been developed to describe fast flux reversal in soft ferrite cores. The core material is represented by an effective spherical grain whose size, shape, and orientation of crystal axes are assumed to represent averages over many grains. The magnetization mechanism considered is the collapse of an effective spherical domain within the effective grain. A magnetization equation is derived for the field needed to drive the collapsing domain wall against the viscous force of spin relaxation damping. This equation is compared with experimental data taken on small cores of TDK PE11BL which were reset by a dc field and reversed in about 150 ns. The model fits the data well over a large part of the flux reversal for a wide range of dB/dt. The values of the parameters found from fitting the data are related to the magnetic properties. Alternative domain configurations which have been investigated are also mentioned.
Logarithmic corrections and antiferromagnetic chains (abstract)
Authors: Affleck I. , Bonner J. C.
Published: July 2002

There has recently been considerable interest in the numerical calculation of critical exponents for quantum spin chains with general spin s, stimulated by a remarkable prediction by Haldane and conformally invariant field theoretic calculations. In several instances numerical calculations have differed considerably from theoretical predictions, with misleading results. These discrepancies have generally been attributed to the presence of marginal operators resulting in logarithmic corrections which slow numerical convergence. Such phenomena seem to be ubiquitous in the area of quantum spin chains. However, until recently, no calculation was available for estimating quantitatively the expected shifts in exponent values obtained by numerical means. The purpose of this work is to call attention to such a calculation1 for the integrable Takhtajan–Babujian family of quantum spin chains, and make specific comparisons with a variety of spin chain exponents obtained numerically.2,3 Agreement with the analytic formulas is extremely good in all cases. This is an indication that finite-size scaling is a powerful tool for extracting critical exponents even in models with logarithmic corrections, provided that these corrections are taken into account in lowest order using the method of Ref. 1.
Nonlinear dynamics of magnetoexchange modes in YIG films (abstract)
Authors: McMichael R. D. , Wigen P. E.
Published: July 2002

The nonlinear dynamics of magnetoexchange modes in two films of yttrium iron garnet (YIG) with similar low-power spectra, but different mode densities have been investigated at perpendicular resonance. In this configuration, the resonances are not degenerate with a large number of short wavelength spin-wave modes as in bulk samples, and the density of modes near the resonances can be varied by adjusting the sample dimensions. Domains of auto-oscillation in applied field–pumping field parameter space appear to arise as fingers from each mode in the low-power spectrum. Differences between the behavior of the two samples are attributed to excitation of hidden modes from a degenerate exchange branch, exited through a process analogous to a second-order Suhl instability. A model of this system is proposed in which nonlinear interactions between modes are solely due to the shape demagnetization field. The resulting equations of motion have been integrated numerically using parameters determined from low-power FMR and from knowledge of the sample shape. Including only the modes from the main branch of the magnetoexchange spectrum that couple directly to a uniform pumping field, these calculations predict the frequency of auto-oscillation of the first finger to within 15% and predict the power at onset to within 1 dB. Hidden modes from the main branch may play an important role in the dynamics of the other fingers. We believe this to be the most accurate prediction of an auto-oscillation frequency in a magnetic system yet published.
Photon/polariton modes in a magnetic/nonmagnetic layered structure with magnetization antiparallel to each other (abstract)
Authors: How H. , Vittoria C.
Published: July 2002

We have calculated the photon/polariton spectrum of the surface and bulk waves in a magnetic/nonmagnetic layered structure where the magnetization in subsequent magnetic layers is antiparallel to each other. The magnetic layers are magnetized to saturation by a uniaxial anisotropy field parallel to the layer surfaces and the wave propagation direction is assumed to be perpendicular to the anisotropy axis (the Voigt configuration). Similar to electronic energy bands in solids the dispersion relations of the bulk modes form dispersion bands in a 1D superlattice of the layered structure. Surface modes form dispersion curves in between the bulk bands. The results are compared with those associated with the case where the magnetization of the layered structure is aligned parallel to each other by an external magnetic field.1,2 Polariton/photon modes are excited for both magnetization configurations. However, under ordinary conditions we find both forward and backward wave propagation dispersions of the surface waves only for the antiparallel magnetization case. A new type of surface propagating waves is also found whose appearance is unique to the Kittel, rather than the Voigt configuration.
Microscopic calculation of dynamical correlations in two-dimensional quantum antiferromagnets at low temperature (abstract)
Authors: Becher T. , Reiter G.
Published: July 2002

We calculate the spin-spin relaxation function for a two-dimensional quantum antiferromagnet at low temperature from first principles. The calculation justifies the picture of the system as a weakly interacting Bose gas of spin waves. The long wavelength behavior at T=0 is qualitatively consistent with hydrodynamic predictions based upon the existence of long-range order, although the spin-wave velocity contains nontrivial dynamical shifts that cannot be calculated from thermodynamic parameters.
Crystal structure and short-range and long-range order in CuSb2O6 (abstract)
Authors: Nakua A. , Greedan J. E. , Reimers J. N. , Yun H. , Stager C. V.
Published: July 2002

CuSb2O6 crystallizes in a monoclinically distorted trirutile structure. Atomic positions were determined by profile refinement of neutron powder diffraction data. An important feature of the structure is the presence of nearly square planar Cu2+ layers. The Cu-O-Cu superexchange pathways are such that short-range interactions are approximately one-dimensional. Evidence for short-range order is found from a susceptibility maximum at 60 K. Long-range order occurs near 25 K and an additional, first-order transition occurs at 8 K.
Three-dimensional micromagnetic simulations on the connection machine
Authors: Giles R. C. , Kotiuga P. R. , Humphrey F. B.
Published: July 2002

We are using the connection machine to perform three-dimensional micromagnetic simulations of films with interesting topological structures such as vertical Bloch lines. A critical element of the computations is the calculation of the demagnetizing field. We have extended the Fourier method of Mansuripur and Giles to three-dimensional films and implemented it on the connection machine. We discuss the algorithm and its parallel implementation.
Hyperfine specific heat in quasicrystalline AlMnSi
Authors: Wang K. , Garoche P. , Coqblin B.
Published: July 2002

The specific heat of the quasicrystalline Al73.2Mn21Si5.8 icosahedral phase has been measured using an ac method under a magnetic field up to 7 T, and a nuclear hyperfine contribution in 1/T2 has been observed below 1 K. Its magnitude increases with the magnetic field, and this effect is interpreted in terms of the Kondo effect with a Kondo temperature typically of order 20 K. The observed low Kondo temperature can be understood as due to a decrease of the sp density of states resulting from the icosahedral symmetry of this alloy.
CoPtB(O) alloy films as new perpendicular recording media
Authors: Hayashi K. , Hayakawa M. , Ohmori H. , Okabe A. , Aso K.
Published: July 2002

In search of new hard magnetic materials with high saturation magnetization and large coercivity, a comprehensive study was made on numerous Co- and CoPt-base crystalline alloys by means of sputtering techniques. It revealed that a newly found CoPtB(O) alloy system possessed excellent hard magnetic properties with remarkably large perpendicular coercivity and high saturation magnetization. This new alloy film, deposited onto room temperature substrates, shows the magnetic properties of 4πMs=12 kG, H⊥c=4000 Oe, and perpendicular anisotropy field Hk=22 kOe. These values are superior to those of prevailing materials such as CoCr perpendicular and CoPt or CoNi longitudinal recording media. The typical composition is Co69Pt20B6O5 (at. %), and oxygen plays a momentous role on the coercivity in this alloy film. As a magnetic recording medium, a write/read experiment of this film shows that the readout signal has a +9 dB peak-to-peak amplitude compared with that of metal particle tape at 1 μm wavelength and has +10 dB compared with that of a CoCr perpendicular medium at 0.5 μm wavelength.
Observation of transitions to spin-slip structures and splitting of the Néel temperature of holmium in magnetic fields
Authors: Willis Frank , Ali Naushad , Steinitz M. O. , Kahrizi Mojtaba , Tindall D. A.
Published: July 2002

We present the results of magnetization measurements on single-crystal holmium using a SQUID magnetometer in the temperature range from 4 to 140 K in magnetic fields up to 5.5 T. In low fields (0.01 T) the magnetization versus temperature data show a spiral to conical transition at Tc=16 K and the Néel temperature at 132 K. In addition, we observe new anomalies in the temperature dependence of the magnetization along the a, b, and c axes at 20, 24, 42, and 98 K. These new anomalies appear at the same temperatures as observed by Bates et al. [J. Phys. C 21, 4125 (1988); 21, 4113 (1988)] in ultrasonic velocity measurements on holmium. These anomalies could be accounted for within the frame work of the ‘‘spin-slip’’ model of Gibbs and co-workers. In the c axis magnetization we observe a splitting of the Néel temperature in magnetic fields greater than 0.5 T. The H-T phase diagrams of the magnetic phases of holmium for fields in three directions (along the a, b, and c axes) are presented.
Charge emission from silicon and germanium surfaces irradiated with KrF excimer laser pulses
Authors: Bialkowski M. M. , Hurst G. S. , Parks J. E. , Lowndes D. H. , Jellison G. E.
Published: July 2002

The authors report time-resolved measurements of the emission of positive and negative charge from Si and Ge surfaces irradiated with 248-nm KrF excimer laser pulses. With pulse energies both below and above the melting threshold, the time evolution of the emission currents is complex and strikingly different for Si and Ge. The positive ion emission signal from Ge persists only for the duration of the laser pulse (<60 ns), but in sharp contrast, the signal from Si continues for several microseconds. A tentative suggestion is made that the positive ions encounter a Knudsen layer created just above the surface of the Si target. More refined experiments, coupled with a theoretical effort, are proposed.
Theoretical and experimental studies of phototriggered discharges in argon and neon
Authors: Brunet H. , Lacour B. , Rocca Serra J. , Legentil M. , Mizzi S. , Pasquiers S. , Puech V.
Published: July 2002

Characteristics of phototriggered discharges in pure argon and neon have been experimentally and theoretically investigated at pressures between 0.5 and 5 bars and reduced electric fields E/N in the range 5 to 50 Td. Emphasis is laid on the breakdown delay time, defined as the time lag between the application of a very short preionization pulse and the occurrence of the discharge. The model, developed in the frame of the local field approximation, gives breakdown delay time values in excellent agreement with the experimental results. However, in pure neon, the experiments have revealed a large influence of very small amounts of easily ionizable impurities. The calculations point out that the discharge behavior is mainly determined by the electron multiplication rate due to direct ionization of ground state atoms. Other ionizing processes, such as two-step ionization or Penning effects, or the electrical parameters of the circuit (inductance, capacitance, and intensity of the preionization) have only a secondary effect on the breakdown delay time.
Microstructural control of diamond thin films by microlithographic patterning
Authors: DeNatale J. F. , Flintoff J. F. , Harker A. B.
Published: July 2002

Microlithographic patterning has been used to elucidate the mechanisms controlling diamond film nucleation and grain growth. The approach is capable of establishing a degree of control over diamond nucleation on the substrate, which can be used to improve film uniformity and enhance fine grained microstructure. The observed microstructures in the patterned films are consistent with an intrinsic growth mechanism based upon defect-initiated renucleation.
Disorder in vitreous SiO2: The effect of thermal annealing on structural properties
Authors: Lange P. , Schnakenberg U. , Ullerich S. , Schliwinski H.-J.
Published: July 2002

SiO2-passivation layers formed by thermal oxidation and various chemical vapor deposition (CVD) processes have been investigated by infrared spectroscopy and wet chemical etching studies in ammonium hydroxide water solutions. In order to obtain effects of thermal annealing on the dislocation structure of deposited oxides, these layers have been subjected to an annealing step. Disorder and water-related features in infrared spectra, as compared to activation energies and etch rates received from the etching experiments, show mainly two effects: the annealing of deposited films is accompanied by bond strain relaxation through viscous flow and decreased porosity without a measurable decrease in thickness. Within the infrared study, further evidence was obtained for disorder-induced mechanical mode coupling in oxides with a dislocation structure. In addition, the infrared spectroscopic and etching results for thermally grown oxides are very similar to those for annealed CVD oxides. Such a similarity was also obtained for unmodified CVD oxides processed at two very different temperatures.
Quantitative Auger sputter depth profiling of very thin nitrided oxide
Authors: Barla K. , Nicolas D. , Pantel R. , Vuillermoz B. , Straboni A. , Caratini Y.
Published: July 2002

Plasma nitridation of thin oxides has been investigated at a temperature of 950 °C for 10 min–6 h and within an rf power of between 400 and 1100 W. The nitrogen composition in these films has been characterized in sputter depth Auger experiments. The sensitivity of this technique has been widely improved by the use of the sequential layer sputtering model. This model allows the actual nitrogen distribution in the film to be determined by taking into account the sputtering effect and by the escape depth of oxygen and nitrogen electrons. The results are observed to be independent of the oxide thickness in the range of 10–60 nm. Rapid thermal nitridation of 16-nm-thick oxides at 950 °C for 300 s and at 1150 °C for 15–300 s has also been studied by this method. Comparison of the results obtained using both techniques is made with a view to microelectronic applications.
Pressure studies of resonant DX centers: Thermal emission from metastable Si and S donors in GaAs
Authors: Piotrzkowski R. , Suski T. , Wiśniewski P. , Ploog K. , Knecht J.
Published: July 2002

The analysis of the process of establishing a thermal equilibrium in a GaAs sample, in which the metastable state was created by high pressure freeze-out, makes possible a determination of the energy barrier for emission from resonant DX centers. We have found that Si and S centers exhibit qualitatively different pressure behavior. This result casts doubt on some models describing DX center.
Phase-locking in series arrays of Josephson junctions shunted by a complex load
Authors: Meyer H.-G. , Krech W.
Published: July 2002

The phase-locking in a large series array of Josephson junctions with a finite McCumber parameter shunted by a complex load is studied in the frame of the Stewart–McCumber model. Both the coherent and the incoherent mode are discussed. The influence of weakly time-dependent perturbations on the stability of the phase-locking as well as the optimum operating region are derived in a simple analytical way. The coherent oscillations are nearly sinusoidal and most stable for a bias current something greater than twice the junction critical current and a McCumber parameter of about 0.5; the corresponding oscillation frequency is about twice the junction characteristic frequency. Because of the finite McCumber parameter a complex load is required for the maximum power output given by an eighth of the sum of the single junction characteristic powers. In presence of thermal noise the array shows a second-order phase transition where the coherent mode can be considered as the higher-order phase. The critical temperature is proportional to the junction critical current.
Application of a semi-empirical sputtering model to secondary electron emission
Authors: Schwarz S. A.
Published: July 2002

A semi-empirical sputtering model is demonstrated to provide a good description of electron-induced secondary electron emission. A simple formula for the yield of secondary electrons as a function of primary energy, incident angle, and material parameters is obtained. In comparison to the most commonly employed semi-empirical model, the present model provides a superior fit to the universal energy dependence curve, a better description of energy and mass effects at off-normal incidence, and additional insights into factors affecting the magnitude of the yield. The bulk and surface contributions to the yield magnitude are separately deduced from experimental data in the literature. Trends in these contributions are assessed for metals and insulators.
Thermally stable ohmic contacts to n-type GaAs. VII. Addition of Ge or Si to NiInW ohmic contacts
Authors: Murakami Masanori , Price W. H. , Norcott M. , Hallali P.-E.
Published: July 2002

The effects of Si or Ge addition to NiInW ohmic contacts on their electrical behavior were studied, where the samples were prepared by evaporating Ni(Si) or Ni(Ge) pellets with In and W and annealed by a rapid thermal annealing method. An addition of Si affected the contact resistances of NiInW contacts: the resistances decreased with increasing the Si concentrations in the Ni(Si) pellets and the lowest value of ∼0.1 Ω mm was obtained in the contact prepared with the Ni-5 at. % Si pellets after annealing at temperatures around 800 °C. The contact resistances did not deteriorate during isothermal annealing at 400 °C for more than 100 h, far exceeding process requirements for self-aligned GaAs metal-semiconductor field-effect-transistor devices. In addition, the contacts were compatible with TiAlCu interconnects which have been widely used in the current Si process. Furthermore, the addition of Si to the NiInW contacts eliminated an annealing step for activation of implanted dopants and low resistance (∼0.2 Ω mm) contacts were fabricated for the first time by a ‘‘one-step’’ anneal. In contrast, an addition of Ge to the NiInW contacts did not significantly reduce the contact resistances.
KrF laser-induced ablation and patterning of Y–Ba–Cu–O films
Authors: Heitz J. , Wang X. Z. , Schwab P. , Bäuerle D. , Schultz L.
Published: July 2002

The ablation and patterning of Y–Ba–Cu–O films on (100) SrTiO3 and (100) MgO substrates by KrF excimer-laser light projection was investigated. Three different regimes of laser-material interactions were observed. Transition temperatures and critical current densities in laser-fabricated strip lines were investigated.
Effect of ion implantation dose on the interdiffusion of GaAs-AlGaAs interfaces
Authors: Kahen K. B. , Peterson D. L. , Rajeswaran G.
Published: July 2002

Experimental results of enhanced interdiffusion of GaAs-AlGaAs interfaces are reported. These are obtained by implanting Ar ions at doses ranging from 2×1013 to 5×1014 cm−2 into heterostructure samples followed by rapid thermal annealing at 950 °C for 30 s. The degree of intermixing decreases from the surface up to the projected ion range and is a function of the implantation dose. It is postulated that this variation results from the coalescence of some of the excess vacancies into extended defects, which are then unavailable to assist in the enhanced interdiffusion process. By assuming that the concentration of mobile vacancies at any depth is proportional to the ion’s electronic energy loss and inversely proportional to the ion’s nuclear energy loss, the calculated intermixing results are shown to be in good agreement with the experimental data.
Depth selective Mössbauer spectroscopic study of Fe3O4 epitaxial films
Authors: Fujii T. , Takano M. , Katano R. , Bando Y. , Isozumi Y.
Published: July 2002

Several (111) oriented 56Fe3O4 films containing a 5-Å-thick 57Fe3O4 probe layer at or below the surface were grown epitaxially on the α-Al2O3 (0001) surface by a reactive vapor deposition method. Conversion electron Mössbauer spectroscopy was applied at 6, 78, and 300 K by using a recently developed helium-filled proportional counter. The well-crystallized surface has been found to be surprisingly stable even in air as characterized by the Mössbauer parameters that are almost the same as for the bulk. Moreover, the Verwey transition was detected clearly even in the 5-Å-thick surface layer. However, the ferrous components seem to have changed their Mössbauer parameters probably because of their sensitivity to any crystalline field modifications in the surface. Generally speaking, the quality of epitaxial Fe3O4 films is very high: Any unusual surface state, if present, is confined in a shallow depth of ≤ 5 Å.
Au/Pt/Ti contacts to p-In0.53Ga0.47As and n-InP layers formed by a single metallization common step and rapid thermal processing
Authors: Katz A. , Weir B. E. , Dautremont-Smith W. C.
Published: July 2002

We have demonstrated the viability of depositing a thick Au bonding pad on top of Pt/Ti contacts on both p-InGaAs and n-InP within a single evaporation prior to heat treatment. This eliminates the usual post-sinter Au plating process. In particular, Au (500 nm)/Pt (60 nm)/Ti (50 nm) common contacts to Zn-doped 5×1018 cm−3 p-In0.53Ga0.47As and S-doped 1×1018 cm−3 n-InP were formed within a single pumpdown electron-gun evaporation and subsequently a single sintering process by means of rapid thermal processing. The lowest resistivity of these ohmic contacts were found to be 0.11 and 0.13 Ω mm (5.5×10−7 and 8×10−6 Ω cm2) for the p and n contacts, respectively. These values were achieved as a result of heating at 450 °C for 30 sec. This heat treatment caused a limited reaction at the Au-Pt and Pt-Ti interfaces, which did not lead to any significant intermixing of the Ti and Au. Thus, no significant indiffusion of the Au thorough the Pt barrier was observed and contact degradation did not occur. The stress of the as-deposited trilayer structure on InP was found to be 3×108 dyne cm2 tensile and increased to about 2×109 dyn cm2 as a result of the rapid thermal processing at 450 °C
Anomalous current-voltage behavior in titanium-silicided shallow source/drain junctions
Authors: Lin Jengping , Banerjee Sanjay , Lee Jack , Teng Clarence
Published: July 2002

The anomalous behavior of forward and reverse bias current versus applied voltage in titanium-silicided shallow source/drain junctions has been studied. The reverse leakage current characteristics in p+/n shallow junctions (Xj=130 nm) show that the current increases rapidly with titanium thickness and exponentially depends on the reverse bias voltage, while the activation energy of leakage current extracted from the temperature dependence of the current decreases with increasing reverse bias voltage. Forward current in a silicided junction is characterized at low temperatures for the first time. The ideality factor of the forward current increases as temperature decreases and has values higher than 2 at very low temperatures. This behavior cannot be explained by the field-independent Shockley-Hall-Read generation-recombination mechanism. A new mechanism involving the Frenkel–Poole barrier lowering of a trap potential is proposed.
Circular interdigital transducers
Authors: Barbaid S. , Duclos J. , Leduc M.
Published: July 2002

The purpose of this article is to establish the focusing properties of a new kind of transducer consisting of circular electrodes deposited on an isotropic substrate and covered by a thin piezoelectric layer. We first express the electromechanical equations of the device and determine its boundary conditions. Then, using the effective dielectric function and an appropriate approximation of the charge density, we obtain various functions (electric potential, displacements) giving a physical description of each medium. Last, we present the numerical results of our study, namely those concerning the displacements and proving the focusing capabilities of our device.
Boron contamination and antimony segregation at the interface of directly bonded silicon wafers
Authors: Widdershoven F. P. , Haisma J. , Naus J. P. M.
Published: July 2002

The characterization of the interface between directly bonded n-type silicon wafers by capacitance-voltage (C-V) profiling, secondary-ion mass spectrometry (SIMS), and transmission electron microscopy (TEM) is reported. At the interface a boron diffusion peak is found that can be explained by initial boron contamination of the wafer surfaces before bonding. Furthermore, the presence of an amorphous SiO0.54 layer at the bonding interface is revealed by TEM and SIMS. Antimony is shown to diffuse through this layer and to segregate at the interface. Diffusion and segregation phenomena are simulated with the process simulation package suprem-3 and C-V profiling is simulated with the device simulation package curry. Features in the C-V profiling results are explained in terms of the observed boron contamination. The behavior of the resistivity near the interface of directly bonded silicon wafers, reported in literature, is also explained by boron contamination.
Radiation-induced charge trapping in implanted buried oxides
Authors: Brady Frederick T. , Li Sheng S. , Krull Wade A.
Published: July 2002

We investigate the response of buried oxide layers formed by oxygen implantation to total dose x-ray irradiation. The characterization is based on C-V measurements of the buried oxide capacitor and on back-channel transistor measurements. Reduced charge trapping is found for material implanted with a lower oxygen dose, annealed at higher temperatures, and annealed for longer times. Also, total-dose irradiation was found to generate few interface traps. A particularly interesting result is that an increase in the concentration of shallow donors with x-ray dose was observed for certain samples. This increase in the donor concentration was observed only in the top Si film.
Field analysis of the Cerenkov doubling of infrared coherent radiation utilizing an organic crystal core bounded by a glass capillary
Authors: Hayata K. , Yanagawa K. , Koshiba M.
Published: July 2002

We present a mode field analysis of the second-harmonic electromagnetic wave that radiates from a nonlinear core bounded by a dielectric cladding. With this analysis the ultimate performance of the organic crystal-cored single-mode optical fiber waveguide as a guided-wave frequency doubler is evaluated through the solution of nonlinear parametric equations derived from Maxwell’s equations under some assumptions. As a phase-matching scheme we consider a Cerenkov approach because of advantages in actual device applications, in which the phase matching is achievable between the fundamental guided LP01 mode and the second-harmonic radiation (leaky) mode. Calculated results for organic cores made of benzil, 4-(N, N-dimethyl-amino)-3-acetamidonitrobenzen, 2-methyl-4-nitroaniline, and 4′-nitrobenzilidene-3-acetoamino-4-metxianiline provide useful data for designing an efficient fiber-optic wavelength converter utilizing nonlinear parametric processes. A detailed comparison is made between results for infinite and finite cladding thicknesses.
Growth of (100) Al/Fe and Fe/Al/Fe layers using the technique of metal-metal epitaxy on silicon
Authors: Chang Chin-An
Published: July 2002

(100)-oriented Al films, 1000 Å thick, have been grown on a (100) Fe layer near room temperature with the technique of metal-metal epitaxy on silicon. The technique uses a (100) Cu layer deposited epitaxially on (100) Si as the seed, followed by sequential epitaxy of Pd and Fe, before the deposition of Al. Further deposition of Fe on the grown (100) Al film retains the (100) epitaxial relation, resulting in a (100)-oriented Fe/Al/Fe/Pd/Cu/Si structure. The mutual epitaxy of Al and Fe in the (100) orientation thus enables the growth of (100)-oriented Al-Fe periodic structures using such a technique. Attempts at growing (100) Al films directly on several other seed layers, including Cu, Pd, and Au, have all failed.
Epitaxial growth of ZnS grown at low temperatures by atmospheric pressure metalorganic vapor phase epitaxy
Authors: Yodo Tokuo , Ueda Kazuhiro , Morio Kenji , Yamashita Ken , Tanaka Shuhei
Published: July 2002

Single crystalline epitaxial layers of undoped ZnS have been grown at 250–300 °C on (100)-oriented GaAs substrates by atmospheric pressure metalorganic vapor phase epitaxy using dimethylzinc (DMZ) and hydrogen sulfide as source materials. The premature reaction typically encountered with this source combination can be eliminated completely as well as in the case of ZnSe epitaxial growth using DMZ and hydrogen selenide, even at atmospheric pressure, by controlling the source gas velocity and the mole ratio. ZnS heteroepitaxial layers (heteroepilayers) with excellent mirrorlike surface morphologies, which were grown at 250 °C for the source gas mole (VI/II) ratio below 10, were obtained. The VI/II ratio dependence of the ZnS heteroepilayers is very different from that of ZnSe heteroepilayers, whose surface morphologies are mirrorlike at a VI/II ratio above 10. Also the surface morphologies of the ZnS heteroepilayers gradually begin to degrade as the growth temperature increases above 250 °C. Moreover, below 220 °C, the crystalline quality abruptly changes to polycrystal, as with bad hazy morphology, which is similar to that seen in ZnSe heteroepilayers grown below 210 °C. It is shown that it is necessary to grow ZnS layers epitaxially at least higher than 220 °C.
Synchrotron-radiation-induced decomposition of thin native oxide films on Si(100)
Authors: Niwano Michio , Katakura Hitoshi , Takakuwa Yuji , Miyamoto Nobuo
Published: July 2002

Thin native oxide films on Si(100) have been previously shown to be decomposed by exposing the film surface to synchrotron radiation (SR) in the vacuum-ultraviolet region. In this study, photoemission and photon-stimulated desorption (PSD) experiments are performed to investigate the synchrotron-radiation-induced decomposition of a native oxide film on Si(100). For mass analysis of the PSD ions, the time-of-flight method is utilized. Si 2p core-level and valence-band photoemission spectra demonstrate that the native-oxide decomposition preferentially takes place on the thin parts of the native oxide film which are terminated with Si—OH and Si—H bonds. It is shown that the native-oxide decomposition is accompanied by desorption of H+ and O+ ions. The H+ PDS ion yield decreases exponentially with increasing the exposure time of SR, whereas the O+ PSD one first increases with the exposure time, and subsequently decreases with the exposure time after the H+ PSD ion yield substantially drops. The behavior of the O+ PSD ion yield is explained in terms of the photon-induced Si—O bond breaking reaction promoted by removing surface hydrogen atoms through the H+ PSD process in which a Si—H bond and the O—H bond in a Si—OH bond are ruptured.
Phase matched noncollinear second harmonic generation in 2-methyl-4-nitroaniline single-crystal film waveguide
Authors: Sugihara O. , Kai S. , Uwatoko K. , Kinoshita T. , Sasaki K.
Published: July 2002

Phase matched noncollinear second harmonic generations (SHGs) are observed in 2-methyl-4-nitroaniline (MNA) single-crystal film waveguides. The phase matching condition is obtained by the cross point of the mode dispersion curves for the MNA waveguide. Theoretical analysis of the SHG conversion efficiency shows that the maximum efficiency is given by the conversion between the fundamental 1st mode and the SH 3rd mode. The experimental efficiency at this conversion is obtained to be 0.10% in the waveguide.
Structural, electrical, and optical properties of CuGaSe2 rf sputtered thin films
Authors: Mártil I. , Santamaria J. , Diaz G. Gonzalez , Quesada F. Sanchez
Published: July 2002

Thin films of CuGaSe2 have been produced by rf sputtering. Compositional, structural, electrical, and optical properties are strongly influenced by growth temperature. At substrate temperatures lower than 300 °C amorphous or poorly crystalline Se-excess films are obtained, showing high resistivity (≊103 Ω cm) and optical transitions at 1.62, 1.80, and 2.4 eV (values lower than the single-crystal counterparts). At the higher growth temperatures, polycrystalline films are obtained (average grain size 0.7 μm) with lower values of resistivity (1 Ω cm), and optical transitions at 1.68, 1.90, and 2.55 eV (very close to the single-crystal values). A hopping conduction mechanism has been detected at the lower measuring temperature (T<150 K), and a grain boundary limited conduction process at the higher measurements temperature (T>150 K). Structural and compositional characteristics are used to explain the behavior observed in the electrical and optical properties.
Photoreflectance of sulfur-annealed copper indium disulfide
Authors: Hsu T. M. , Lee J. S. , Hwang H. L.
Published: July 2002

The temperature dependence of the energy gaps for sulfur-annealed copper indium disulfide has been studied by photoreflectance in the temperature range of 10–300 K. The sulfur-annealed sample has been found to have larger transition energies, smaller positive temperature coefficients of energy gaps, and larger spin-orbit splitting energy than the as-grown sample. This can be explained by the reduction of d-level contributions in the upper valence band probably caused by the variation of lattice distance due to native defects.
Biaxial and uniaxial stress in gallium arsenide on silicon: A linear polarized photoluminescence study
Authors: Shen H. , Dutta M. , Eckart D. W. , Jones K. A. , Vernon S. M. , Dixon T. M.
Published: July 2002

We have observed anisotropic behavior of the polarization of low-temperature photoluminescence from thick gallium arsenide grown on silicon substrates. The identification of the observed transitions was obtained from analysis of the selection rules, the temperature dependence of the feature intensities, and the transition energies. We find that the low-temperature doublet peaks are due to the emissions from two regions of material experiencing two different kinds of stress, one being biaxial and the other uniaxial. The anisotropy is due to the preferential direction created by parallel microcracks.
Studies of zinc diffusion in gallium arsenide by rapid thermal processing
Authors: Rajeswaran G. , Kahen K. B. , Lawrence D. J.
Published: July 2002

Rapid thermal annealing has been used to diffuse Zn into GaAs from a thin film zinc silicate source prepared by atmospheric pressure chemical vapor deposition. For a diffusion temperature of 650 °C, comparisons were made with conventional, open-tube furnace annealing and the diffusivities were found to be similar, in contrast to previous experimental work. In the temperature range 650–750 °C, sharp zinc diffusion profiles are observed. Above 750 °C, kinks are seen in the diffusion profiles. These kinks are also observed when semi-insulating substrates are used instead of silicon doped n+ -substrates. Previously, we have introduced a zinc diffusion model based on the pairing of interstitial Zn with all acceptor species present during diffusion. The dominant species are found to be substitutional Zn and the gallium vacancy, where the concentration of the latter is a function of the background doping concentration. The results of this model are shown to agree with all of our experimental evidence and are also consistent with our experimental observation of two distinct activation energies for zinc diffusion into n+ -doped GaAs substrates, 1.1 eV and 2.6 eV for temperatures above and below ∼790 °C, respectively.
Interface influence on the high-field conduction phenomena of a thin dielectric liquid layer
Authors: Brosseau Christian
Published: July 2002

We report experimental work on the ac conduction phenomena of a thin dielectric liquid (capacitor impregnant) layer at high-electric field for several interfacial situations. The features revealed by these experiments show a strong dependence of the liquid electric losses (at frequency 50 Hz) and according to that, the liquid is in contact with a metallic or a polymer interface. An attempt is made to comment these measurements in terms of the existing theories of ionic conduction in nonpolar liquids: it turns out that charge-carrier injection in the neighborhood of the interface is the dominant contribution of the high-field liquid conductivity. A theoretical evaluation based on a unipolar injection model is given in agreement with the experimental results obtained in the different configurations.
Strain relaxation and its effect on radiation-induced interface traps in thin rapid thermally grown high-temperature oxides
Authors: Schwalke U. , Kerber M. , Mazure C. , Breithaupt B.
Published: July 2002

The radiation response of metal-oxide-semiconductor capacitors containing thin (50–150 Å) high-temperature (1200 °C) oxides grown by rapid thermal oxidation (RTO) and conventionally furnace-grown (800 °C) oxides are investigated by means of capacitance-voltage techniques. The results indicate that the Si/SiO2 interface is largely controlled by the oxide growth process. The prominent interface-trap state at Emg+0.2 eV, which characterizes furnace grown oxides is strongly suppressed in high-temperature RTO oxides. The improved radiation hardness is attributed to strain relaxation by viscous oxide flow which occurs during oxidation at 1200 °C.
Improved AlGaAs/GaAs double-barrier resonant tunneling structures using two-dimensional source electrons
Authors: Wu J. S. , Lee C. P. , Chang C. Y. , Chang K. H. , Liu D. G. , Liou D. C.
Published: July 2002

We report the enhancement of peak-to-valley current ratios (PVCRs) of double-barrier resonant tunneling structures (DBRTSs) based on the AlGaAs/GaAs material system. The PVCRs as high as 25.4 and 18 have been obtained at 77 K for superlattice and alloy barrier structures with 0.2-μm undoped electrodes, respectively. These are the largest PVCRs to date for AlGaAs/GaAs DBRTSs. The large band bending across the undoped electrodes causes size quantization of the accumulation layer, resulting in better resonant tunneling characteristics.