bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical and experimental analysis of the switching mechanism in heterostructure hot-electron diodes
Authors: Higman T. K. , Higman J. M. , Emanuel M. A. , Hess K. , Coleman J. J.
Published: July 2002

We report a theoretical analysis of the switching mechanism in the heterostructure hot-electron diode which confirms our earlier qualitative description. In addition, we present new experimental data on improved multilayer structures grown by metalorganic chemical vapor deposition which show the same negative differential resistance as reported previously. We show that these experimental data are in overall agreement with the theoretical results.
A spectroscopic ellipsometry study of the growth and microstructure of glow-discharge amorphous and microcrystalline silicon films
Authors: Kumar Satyendra , Pandya D. K. , Chopra K. L.
Published: July 2002

Spectroscopic ellipsometry (SE) has been used to study the surface, microstructure, and optical properties of glow-discharge deposited amorphous and microcrystalline silicon films. The SE data has been analyzed using multilayer models, effective medium approximation, and linear regression analysis. The studies have shown that with increasing rf power and silane dilution, a gradual transition from good (dense) a-Si:H to a spongy material with a large density deficit, and then to a microcrystalline material is obtained. A quantitative analysis of the microstructure of a-Si:H films with growth parameters has been carried out. Combined with infrared and x-ray diffraction measurements, the results have been explained in terms of a nucleation and growth model.
On the flow equation in device simulation
Authors: Price Peter J.
Published: July 2002

The nonlocal effect of an inhomogeneous electric field on the carrier drift velocity is considered with particular reference to n-Si. A field-dependent phenomenological length constant, giving the first-order effect of the field gradient, is discussed in terms of the Boltzmann equation. It is also shown how this constant may be calculated from the actual effect of a small ‘‘step’’ in an otherwise homogeneous field, by a formula which extends a previously given formula for this case.
Accounting for the crossover phenomenon in the response of longitudinal and transverse piezoresistance gauges in shock wave experiments
Authors: Rosenberg Z. , Brar N. S.
Published: July 2002

The response of a transverse piezoresistance gauge under plane shock wave loading is different than that of a longitudinal piezoresistance gauge. For a given combination of gauge and embedding matrix the response of the transverse gauge can be higher than that of the longitudinal gauge in a certain range of shock stresses, and lower at a different stress range. This ‘‘crossover phenomenon’’ defines a certain stress level (σ*), for which the response of the two gauges is equal. In this paper we analyze this crossover of the gauge’s responses analytically. The analysis accounts for the crossover stress in terms of the yield strength of gauge material and the deviatoric stresses in the embedding matrix. We show that when the yield strength of the gauge is higher than that of the matrix, there is no crossover of the gauge’s response. Experimental results are presented to support the analysis.
Density measurements of Hg(63P0,1,2) in a discharge using saturated laser absorption and hook methods
Authors: Bigio Laurence
Published: July 2002

Two laser-based techniques are used to derive radial density distributions and absolute densities for the three 63PJ excited states of mercury in the positive column of a low-pressure Hg-Ar dc discharge. In the saturated laser absorption (SLA) method, a pulsed dye laser, traversing the discharge axially, is scanned through one of the 63PJ→73S1 transitions. At high laser powers the power absorbed from the beam on resonance approaches a constant saturated value directly proportional to the number density of Hg atoms in the 63PJ state selected. On-axis absolute density estimates and radial distribution results are presented for the three states at several discharge conditions. The hook method, a well-known interferometric technique, more accurately establishes the absolute densities on axis, and several off-axis measurements are compared with SLA results.
Annealing of Sb+-ion-implanted Si
Authors: Holland O. W. , Fathy D.
Published: July 2002

The behavior of Sb+-implanted Si(100) during rapid thermal annealing was studied at different annealing temperatures and implantation doses. The range of dose was chosen so that the concentration of implanted Sb spanned the limit of solid solubility in Si. It is shown that the behavior of the Sb in excess of solubility limits is dependent on both the heating cycle and the implantation dose. Under certain conditions the excess Sb migrates to the surface where it forms a thin continuous film. However, under different conditions Sb precipitates and remains in the bulk. In the latter case, an anomalous loss of Sb from substitutional solid solution occurs. The mechanisms responsible for the precipitation behavior and its effect on dopant activation are discussed. Transmission electron microscopy and Rutherford backscattering were used to characterize the samples.
The optical dispersion parameters in WO3 thin films
Authors: Toyoda Taro
Published: July 2002

In WO3 thin films the optical dispersion parameters (single-oscillator energy E0 and dispersion energy Ed developed by Wemple and DiDomenico [Phys. Rev. B 3, 1338 (1971)]) have been analyzed in the sample thickness range 100–1000 nm using the experimental results by Davazoglou and Donnadieu [Thin Solid Films 147, 131 (1987)]. The single-oscillator energy E0 exhibits no thickness dependence in three different oxidation modes (mode 1: annealed at 600 °C in air; mode 2: annealed at 500 °C in air; mode 3: annealed at 500 °C in oxygen). The dispersion energy Ed exhibits a large thickness dependence for all modes, which shows the difference in the sample preparations.
High coercivity Nd-Fe-B magnets with lower dysprosium content
Authors: Kim A. S.
Published: July 2002

The elements Dy and Al play very important roles in the magnetic properties of Nd-Fe-B base compounds. The proper combination of Dy and Al may provide a significant improvement in the magnetic properties. With this in mind, close examinations have been made of the magnetic properties of several (Nd,Dy)-(Fe,Al)-B alloys. As a result, (Nd,Dy)-(Fe,Al)-B alloys containing equal atomic amounts of Dy and Al have been found to provide superior permanent magnetic properties. When compared to Nd-Dy-Fe-B or Nd-Fe-Al-B alloy of equivalent Dy or Al content, they have a much higher Hci . The reduction in Br associated with the addition is markedly less. The Hci of the alloys increases linearly with Dy content at a rate of about 7.5 kOe/at. % Dy, when the alloys contain equal atomic amounts of Dy and Al; or, approximately 1.4× the rate of (Nd,Dy)-Fe-B alloys. When Al is present, much less Dy is required to reach a given coercivity level. Thus, a magnet with high (BH)max and Hci can be more economically produced with Nd-Dy-Fe-Al-B alloys. The small Al additions, as described above, result in higher coercivities and lower irreversible losses at elevated temperatures without increasing temperature coefficients, and thus extend the application temperature range.
Characterization of p-type GaAs heavily doped with carbon grown by metalorganic molecular-beam epitaxy
Authors: Saito Koki , Tokumitsu Eisuke , Akatsuka Takeshi , Miyauchi Motoya , Yamada Takumi , Konagai Makoto , Takahashi Kiyoshi
Published: July 2002

p-type GaAs with doping levels of up to 5.8×1020 cm−3 has been grown by metalorganic molecular-beam epitaxy (MOMBE) using carbon (C) as a dopant. The mobility and minority-carrier diffusion length of the C-doped MOMBE layers were comparable to those of Be-doped MBE layers. The diffusion coefficient of C at 900 °C was estimated to be 6×10−15 cm2 /s which is about two orders of magnitude less than that of Be (1×10−12 cm2 /s). In addition, the lattice constant of C-doped GaAs was found to be 5.6533 Å which completely matches that of the substrate, while the lattice constant of Be-doped GaAs decreases to 5.6467 Å at a doping level of 2×1020 cm−3 as reported by Lievin et al. [Inst. Phys. Conf. Ser. No. 79, 595 (1985)].
Preparation of Pb(Zr,Ti)O3 thin films by sol gel processing: Electrical, optical, and electro-optic properties
Authors: Yi Guanghua , Wu Zheng , Sayer Michael
Published: July 2002

Crack-free transparent ferroelectric polycrystalline Pb(Zr,Ti)O3 thin films were prepared by spin-coating solutions of complex alkoxides. The preparation of stock solution, firing, and annealing of films was described. The coating of the intermediate layer of Al2O3 increased the adhesion between Pb(Zr,Ti)O3 thin films and glass substrates. The crystalline phases of films with varying Zr/Ti ratios were investigated. The dielectric constants were about 260. The remanent polarization and coercive field were 6.6 μC/cm2 and 26.7 kV/cm, respectively. The refractive index of the perovskite Pb(Zr,Ti)O3 films was 2.6 at 6328 Å, and the absorption edge was at 3400 Å. The quadratic and linear electro-optic effects were measured with respect to the Zr/Ti ratio from 40/60 to 60/40 for films grown on glass substrates. The quadratic and linear electro-optic coefficients were about 1×10−18 m2 /V2 and 2.4×10−11 m/V at 6328 Å, respectively.
Characterization of the Mn acceptor level in GaAs
Authors: Montelius L. , Nilsson S. , Samuelson L. , Janzén E. , Ahlström M.
Published: July 2002

We report on deep-level transient spectroscopy investigations of the Mn acceptor level in GaAs, including measurements of the emission and capture of holes and of the capture of electrons. A comparison is made between electron capture rates obtained from space-charge techniques and from photoluminescence decay measurements.
On epilayer tilt in ZnSe/Ge heterostructures prepared by molecular-beam epitaxy
Authors: Kleiman J. , Park R. M. , Mar H. A.
Published: July 2002

ZnSe/Ge heterostructures prepared by molecular-beam epitaxy were characterized by ‘‘full-rotation’’ double-crystal rocking curve x-ray analyses with particular emphasis placed on the measurement of tilt between the (400) planes of ZnSe and Ge. It was found that the value of the tilt angle between such planes depends on both the epilayer thickness and the orientation of the substrate plane. A simple model is proposed in the paper of tilt formation and its development. Steps on the substrate surface are shown to be responsible for a redistribution of the bond lengths between the atoms of the substrate and the epilayer in the interface region leading to the formation of tilt between the planes in the epilayer and the substrate. Particular types of stress in the epilayer are shown to affect the final value of the tilt. It was also found that the structural and optical properties of ZnSe/Ge layers appear to be optimized for Ge substrate surface orientations around 2° off (100)→[110].
Thickness-dependent formation of Gd-silicide compounds
Authors: Molnár G. , Geröcs I. , Petö G. , Zsoldos E. , Jároli E. , Gyulai J.
Published: July 2002

Gd-silicide phases were investigated by x-ray diffraction. The results showed that not only one phase exists in a Gd thin-film and silicon substrate reactions. The first phase formed was hexagonal GdSi≊1.7, the second orthorhombic GdSi2. The ratio of the two phases depends on temperature of the heat treatment, and at a given temperature and time of annealing, a dependence of the thickness of the evaporated Gd layer was found. At ∼100-nm Gd thickness the dominant phase was orthorhombic GdSi2, at ∼250 nm hexagonal GdSi≊1.7. In the 300–1000-nm interval orthorhombic GdSi2 was the main component again. Rutherford backscattering analysis showed that the phases were found mixed within the layer. This thickness-dependent formation could be described with a simple model proposed by Gösele and Tu [J. Appl. Phys. 53, 3252 (1982)].
Effect of oxygen on magnetic properties of Nd-Fe-B magnets
Authors: Kim A. S.
Published: July 2002

Oxygen plays a very important role in the magnetic properties of R-Fe-B-type alloys. As the oxygen content increases in Nd-Fe-B and Nd-Dy-Fe-Al-B alloys, the alloys gradually lose their magnetic and thermomagnetic properties: the Hci decreases and both the temperature coefficient of Hci and the irreversible temperature loss increase. The degradation of thermomagnetic properties may be accounted for by depletion of the Nd-rich phase in the grain boundaries through Nd oxidation. High coercivity magnets, relatively stable with respect to temperature, can be produced by minimizing the oxygen content in R-Fe-B alloys.
Geminate recombination in photorefractive crystals
Authors: Twarowski Allen
Published: July 2002

Even though the Kukhtarev model [Sov. Tech. Phys. Lett. 2, 438 (1976); Sov. Phys. Solid State 16, 2414 (1975); Ferroelectrics 22, 949 (1979); Sov. J. Quantum Electron. 8, 231 (1978); Opt. Commun. 23, 338 (1977)] successfully describes many aspects of the photorefractive effect, the physics of photocarrier generation has not been explicitly accounted for in discussions of this model. In this paper, Onsager’s model [Phys. Rev. 54, 554 (1938)] for initial recombination of charge pairs is used to describe the photogeneration process and a quantum yield which is a function of both electric field and temperature is introduced into the Kukhtarev model. While the steady-state value of grating strength is only weakly affected by these considerations, the rate of grating formation and decay may show a much greater sensitivity to the physics of photocarrier production in low dielectric materials.
Energy deposition of keV electrons in light elements
Authors: Valkealahti S. , Schou J. , Nieminen R. M.
Published: July 2002

The Monte Carlo simulation method has been used to investigate the spatial distribution of deposited energy for 1–10 keV electrons incident on solid hydrogen, nitrogen, neon, silicon, aluminum, and argon. In the simulation, elastic scattering cross sections are calculated exactly using the single-atom crystalline potentials. Inelastic energy loss processes for hydrogen are based on the ionization cross section from Green and Sawada [J. Atmos. Terr. Phys. 34, 1719 (1972)] and the gas-phase stopping power from Parks et al. [Nucl. Fus. 17, 539 (1977)]. For the heavier materials a modification of Gryziński’s [Phys. Rev. A 138, 305 (1965); 138, 322 (1965); 138, 336 (1965)] semiempirical expression for each core and valence electron excitation is used. The energy-deposition distribution of keV electrons and the ionization distribution of weakly bound electrons are practically equal, whereas the penetration depth distribution extends deeper into the material than the energy-deposition distribution. The energy-deposition distributions of keV electrons for light materials, except for hydrogen, can be represented quite well by a universal distribution. In addition, accurate Gaussian approximations for the different materials in the entire energy region from 1 to 10 keV have been evaluated. Parameters such as the mean penetration depth and the mean energy-deposition depth are included as well.
Impurity diffusion enhancement of interdiffusion in an InGaPAs-GaAs heterostructure
Authors: Lee K. H. , Park H.-H. , Stevenson D. A.
Published: July 2002

The influence of concurrent diffusion of Zn and Si on the interdiffusion on the cation and anion sublattices was studied in InxGa1−xPyAs1−y-GaAs heterostructures (with x and y≊0.05). The heterostructures are grown by liquid phase epitaxy and the diffusion sources are equilibrium ternary tie triangle sources. The extent of interdiffusion on both group III and V atoms is observed by depth profiling In and P, respectively, with secondary ion-mass spectrometry. The Zn diffusion selectively enhances the cation (In-Ga) interdiffusion, whereas Si diffusion enhances both cation and anion interdiffusion to the same extent. A kick-out mechanism is proposed to explain the selective enhancement of the cation interdiffusion induced by Zn, and a single vacancy mechanism is proposed for the interdiffusion due to Si. Based on those observations, we propose that the impurity diffusion mechanism is a major factor in determining the degree of enhancement.
Residual strains in heteroepitaxial III-V semiconductor films on Si(100) substrates
Authors: Sugo Mitsuru , Uchida Naoto , Yamamoto Akio , Nishioka Takashi , Yamaguchi Masafumi
Published: July 2002

A systematic study has been made of residual strains in heteroepitaxial GaP, GaAs, and InP layers on Si(100) grown by organometallic vapor phase epitaxy. For GaP films, the strain parallel to the interface changes from compressive to tensile for film thicknesses between 0.7 and ∼1.5 μm, showing that the dominant force for strains changes from a lattice mismatch to a discrepancy of the thermal expansion coefficient between GaP and Si. All GaAs and InP films examined (1–5 μm thick) have a tensile strain almost independent of the thickness. The magnitudes of the residual strains are in the order εGaAS>εGaP>εInP. The low strain in GaP films is due to the compensation of thermally induced tensile strain by a compressive strain, which is induced during the accommodation of lattice mismatch at the growth temperature. For GaAs and InP films, it is concluded that a fraction of the thermally induced tensile strain is accommodated during the cooling process by a reconfiguration of misfit dislocations at the interface. The level of residual strain in InP films, which is the lowest, is suggested to be due to the misfit dislocation rearrangement which can occur at a relatively low temperature (∼250 °C) in this material, as well as the low growth temperature and the small thermal expansion coefficient difference between InP and Si(100).
A numerical simulation method for the laser-induced temperature distribution
Authors: Rantala Tapio T. , Levoska Juhani
Published: July 2002

A numerical simulation approach for the evaluation of temperature distribution in a substrate during the laser processing is developed. The explicit finite-difference solution of the heat (diffusion) equation is chosen as the starting point in order to simply retain general nonlinearity, physical transparency, and flexibility of the procedure. The method is tested with a simulation of silicon substrate irradiated by cw argon laser, and the results are compared with those from experiments and exact analytical results, where available. Deficiences due to the omission of the nonlinearity, i.e., the temperature dependency of the material properties, in the results of approximative analytical approaches are discussed.
Laser performance of LiSrAlF6:Cr3+
Authors: Payne Stephen A. , Chase L. L. , Smith L. K. , Kway Wayne L. , Newkirk Herbert W.
Published: July 2002

We have lased the new material, LiSrAlF6:Cr3+ (Cr3+:LiSAF). The single crystals were grown by the horizontal zone melting technique. The spectroscopic properties of Cr3+:LiSAF are similar to those of other low-field Cr3+-doped systems, although the emission cross section is strongly π polarized and is also somewhat larger than has been measured for other fluoride hosts. The free-running lasing wavelength of Cr3+:LiSAF is 825 nm, and the tuning range extends from at least 780 to 920 nm. Using Kr laser pumping, we obtained slope efficiencies of 36% and 14% by utilizing output couplings of 4.8% and 0.8%, respectively. On the basis of these results, the extrapolated maximum efficiency of 53% is determined, to be compared to the quantum defect-limited value of 78%. It is concluded that a moderate level of excited state absorption (ESA) loss is responsible for the reduced efficiency of the Cr3+:LiSAF system. This contrasts with the related results previously obtained for LiCaAlF6:Cr3+, where it was concluded that the effects of ESA were negligible [IEEE J. Quantum Electron. QE-24, 2243 (1988)].
Spin coating: One-dimensional model
Authors: Bornside D. E. , Macosko C. W. , Scriven L. E.
Published: July 2002

The model of the spin-coating process presented here accounts for variations of concentration, viscosity, and diffusivity across the thickness of the spin-coated film. The flow of the liquid is governed by a balance between centrifugal driving force and viscous resisting force. Radial variations in film thickness and concentration are neglected. The Galerkin/finite-element method is employed to solve the equation set. Film thinning slows initially due to decreasing film thickness and ceases finally due to dramatically increasing viscosity of the coating liquid as solvents evaporate. The formation of a region of extremely low solvent concentration and correspondingly high viscosity and low binary diffusivity at the free surface, i.e., a solid ‘‘skin,’’ is predicted. Coating defects can occur if convective flow has not completely ceased when this skin forms. Skin formation can be eliminated or delayed by partially saturating the overlying gas with solvent or by using mixed solvents (having both high and low volatilities) in the coating liquid. The temperature variation in the film during coating varies negligibly from the ambient.
Magnetic susceptibility and resistivity of R(Co,A)2 where R=Y,Sc and A=Al, Si
Authors: Michels D. , Timlin J. , Mihalisin T.
Published: July 2002

Weak itinerant ferromagnetism appears in the Laves-phase compounds RCo2 (R=Y, Lu, Sc) as Al is substituted for Co, with a simultaneous increase in lattice constant. The Lu system has the maximum Tc (145 K) and a Co moment (0.65μB approximately 6 times those of the Y and Sc systems. This is unexpected since it is intermediate in lattice constant among these three systems. To investigate this the alloys (Y0.7Sc0.3)(Co,Al)2 were formed, which are comparable in lattice constant to Lu(Co,Al)2. In addition the alloys Y(Co,Si)2 and Sc (Co,Si)2 were made where substitution of Si for Co depletes the Co 3d band just as with Al substitution, but with about one-tenth the change in lattice constant. Magnetic-susceptibility and electrical-resistivity data for T=2–300 K are presented and discussed.
Crystallographic and magnetic behaviors of the R-Fe-C compounds
Authors: Xing Feng , Ho Wen-wang
Published: July 2002

Structural and magnetic properties of the ternary R14Fe78C8 compounds, where R=Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Lu, were systematically investigated. By means of properly annealing treatment, the tetragonal structure isotropic to the Nd2Fe14B phase could be well formed in the above compounds. The lattice constants and Curie temperatures were determined and correspondingly compared to those obtained in borides. The magnetizations at 1.5 K and room temperature were measured. The anisotropy behaviors of R14Fe78C8 were studied in detail, and we found that there was some evident difference in both carbides and borides.
Complex impedance measurements of capacitor structures on silicon with copper phthalocyanine dielectric
Authors: Nowroozi-Esfahani Rasoul , Maclay G. Jordan
Published: July 2002

Measurements were made of the capacitance and the conductance of several capacitor structures with a copper phthalocyanine (CuPc) dielectric at different voltages and in the frequency range of 102–106 Hz. A thermally evaporated CuPc film about 1300 Å thick was fabricated in a parallel-plate capacitor between gold and aluminum electrodes (Al‖CuPc‖Au). Two distributions of relaxation times are observed in this frequency range. At low frequencies voltage-dependent polarization (possibly interfacial polarization) appears to be the dominant mechanism of current conduction. At high frequencies a relatively voltage-independent hopping within and/or between molecules appears to be dominant. The CuPc remains polarized for a long time. Measurements were also made of the capacitance-voltage (C-V) characteristic of a Al‖CuPc‖SiO2‖Si capacitor at 104, 105, and 106 Hz for different scanning rates. The basic features of the device’s C-V characteristics are discussed.
Assessment of interface state density in silicon metal-oxide-semiconductor transistors at room, liquid-nitrogen, and liquid-helium temperatures
Authors: Hafez I. M. , Ghibaudo G. , Balestra F.
Published: July 2002

The interface state density of silicon metal-oxide-semiconductor (MOS) transistors operated at room, liquid-nitrogen, and liquid-helium temperatures is investigated using the conventional subthreshold slope technique. The magnitude of the interface state density found of the order of 1013–1014/eV cm2 at liquid-helium temperature, suggests that such states correspond to the localized states situated in the band tails below the mobility edge of the two-dimensional subband. Moreover, the interface state densities found by the subthreshold slope have been confirmed using the dynamic transconductance technique.
Theory of magnetoresistance in concentrated ferromagnetic alloys (invited)
Authors: Berger L.
Published: July 2002

Existing values of the magnetoresistance (ρ∥−ρ⊥)/ρ0 for crystalline Ni1−xFex, Ni1−xCox, Ni1−xMnx, Fe1−xCrx, and Fe1−x-Vx alloys depend on x in a way which disagrees with the traditional Smit theory, based on the Born approximation. The reasons are related to the variation of the 3d wave-function amplitude between chemically different atoms and, in turn, to a variation of s-d scattering intensity. Experimental atomic moments indicate that this 3d amplitude variation is large. The variation is related to the fact that d-d scattering is strong and resonant. We predict large deviations from Nordheim’s rule ρ↓∝ x(1−x) where ρ↓ is the spin-down resistivity, similar to the deviations found experimentally. Correspondingly, (ρ∥−ρ⊥)/ρ0 is much larger for x≂0 than for x≂1.
Investigation of the exchange mechanism in NiFe-TbCo bilayers
Authors: Cain William C. , Kryder Mark H.
Published: July 2002

The origin of the interfacial exchange coupling that exists in NiFe-TbCo bilayer thin films has been investigated through high resolution Kerr microscopy and VSM studies. Based on these experimental observations, a new model of the exchange mechanism for in-plane, ferromagnetic-perpendicular ferrimagnetic materials is developed. It is proposed that the local anisotropy in the TbCo layer varies from in-plane at the interface to perpendicular at the top surface. The relative magnitude of the exchange effect calculated with average TbCo Ku values, agrees with experimental data. The predicted dependence of the exchange field on NiFe and TbCo layer thickness also fit the experimental data.
Magnetism and structural chemistry of RECo13−xGax alloys (RE=La,Ce,Pr,Nd, and mischmetal MM)
Authors: Weitzer F. , Hiebl K. , Grin Yu. N. , Rogl P. , Noël H.
Published: July 2002

Alloys with the composition RECo13−xGax (x≤4.4) have been prepared by arc melting and subsequent annealing for 120 h at 800 °C in evacuated, Mo-lined silica capsules. The Ce,Pr compounds were found to decompose at 900 °C, and no compound formation was observed for the Gd,Sm members in the investigated temperature range from 600 to 900 °C. For the LaCo13−xGax system an extended homogeneity region was observed crystallizing with the cubic NaZn13 type for concentrations x<2.5. For concentrations x>2.5 x-ray powder diffraction analysis for all the rare earth members proved isotypism with a tetragonal NaZn13 -derivative structure, whose crystal symmetry and atom sites were consistent with the Ce2Ni17Si9 type of structure. From magnetization experiments in the range from 5 to 1300 K a generally hard-magnetic behavior was observed for all the RE alloys with tetragonal symmetry and ferromagnetic ordering occurs below Tc<650 K. Curie temperatures in the LaCo13−xGax system monotonically drop from Tc=1290 K for cubic LaCo13 to Tc=145 K for tetragonal LaCo8.7Ga4.3. For the Ce compound ferrimagnetic behavior is suggested. Assuming trivalent rare earth ions, effective paramagnetic moments of the Co atoms decrease as a function of x from 5.9 μB at x=3.1 to ∼3 μB at x=4.3.
Interdiffusion and short-range order in amorphous Ta-Si multilayer structures
Authors: Meyerheim H. L. , Lengeler B. , Göbel H. E.
Published: July 2002

Sequential sputter deposition of amorphous 4-nm-thick Ta and 7-nm-thick Si layers leads to the formation of a periodic multilayer that can be regarded as a synthetic one-dimensional crystal. A simple kinematical diffraction model is presented to discuss x-ray diffraction patterns obtained from the multilayer structure during annealing. Post-deposition annealing up to temperatures above 530 °C, where the lattice structure disappears, leads to Si diffusion into the Ta layers forming a nonstoichiometric Ta-Si phase. The high diffusion rate of Si in Ta leads to a homogeneous distribution of Si in the Ta (silicide) regimes. As shown by cross-sectional transmission electron microscopy, the interfaces remain sharp during the interdiffusion process. This makes the observation of low-angle Bragg reflections up to the 12th order possible. The local atomic structure around the Ta atoms was analyzed by measuring the extended x-ray-absorption fine structure above the Ta LIII edge at different probing depth conditions. During annealing the local Ta environment was found to be TaSi2 like, even if only a small portion of the Si has diffused into the Ta layers, and the silicide formation is far from stoichiometry. The formation of a Ta suboxide was detected in the surface region of the top Ta layer.
Control of the chemical reactivity of a silicon single-crystal surface using the chemical modification technique
Authors: Takahagi T. , Ishitani A. , Kuroda H. , Nagasawa Y. , Ito H. , Wakao S.
Published: July 2002

A technique is developed to control the chemical reactivity of a silicon single-crystal surface through chemical modification with atomic hydrogen. The reactivity of the reconstructed single-crystal surface prepared by high-temperature treatment in an ultrahigh vacuum is significantly decreased by capping the dangling bonds of top-layer silicon atoms with hydrogen atoms. The Si—H bonds on the hydrogenated surface are found to be much more stable against oxidation than the Si—Si back bonds. The hydrogen-passivated silicon surface is reactivated by electron beam irradiation. An ultrathin oxide layer pattern can be prepared using preferential oxidation of the area reactivated by a focused electron beam.
The gas source molecular beam epitaxial growth of AlxGa1−xP on (100) GaP
Authors: Baillargeon J. N. , Cheng K. Y. , Hsieh K. C. , Stillman G. E.
Published: July 2002

The growth of AlxGa1−xP for Al mole fractions between 0 and 1 has been achieved on (100) GaP substrates using gas source molecular beam epitaxy with elemental Ga and Al, and P2 cracked from PH3 as the source materials. The observed reflection high energy electron diffraction pattern of the GaP surface indicates that an exponential increase in the incident P2 flux is required to maintain good morphology beyond 690 °C. This temperature was found to correspond closely to the congruent vaporization temperature of Ga from the growth surface. The addition of Al on the surface was found to substantially increase the Ga congruent vaporization temperature from the GaP surface. The growth rates for AlxGa1−xP as a function of growth temperature between 600 and 750 °C were determined by transmission electron microscopy. Using elemental Si as an n-type dopant, free electron concentrations as high as 1.65×1019 cm−3 in GaP and 1.5×1019 cm−3 in Al0.28Ga0.72P were achieved.
Two-photon volume information storage in doped polymer systems
Authors: Parthenopoulos D. A. , Rentzepis P. M.
Published: July 2002

Volume information writing and reading is demonstrated for two photochromic materials doped in polymer systems that may be utilized in a 3D optical memory. Writing and reading in volume is achieved by means of two-photon processes and a means of erasing by two-photon processes is discussed. Some of the advantages and problems associated with the two-photon 3D memory device are discussed.
Thermal evolution of X/C multilayers (with X=W, Ni, or SiWSi): A systematic study
Authors: Dupuis V. , Ravet M. F. , Tête C. , Piecuch M. , Lepêtre Y. , Rivoira R. , Ziegler E.
Published: July 2002

The thermal behavior of X/C multilayers (nanometer-thick layers made of tungsten, nickel, or SiWSi alternating with carbide or pure carbon) was studied. Two types of annealing were performed: the pulsed laser annealing in air and the classical thermal annealing in a vacuum furnace. Depending on the composition and the structure of the layered materials, thermal stability or diffusion mechanisms were observed and further analyzed by small-angle x-ray scattering, transmission electron microscopy, and Auger electron spectroscopy. The results show that the period expansion and the reflectivity evolution, that were observed in some cases after treatment, are caused both by structural changes into the layers and by exchange of matter between layers. These changes always induce a partial graphitization of the amorphous carbon and, in the case of W/C multilayers, the formation of a W2C compound.
Electrical properties of Au/Nb-doped-SrTiO3 contact
Authors: Hasegawa Haruhiro , Nishino Toshikazu
Published: July 2002

Current-voltage measurements for Au/Nb-doped-SrTiO3 contacts have been performed over a temperature range from 4.2 to 277 K. The forward characteristics above 46 K are well described by the Schottky diode model. The temperature dependence of the parameter E{=[∂log I/∂(qV)]−1} and the saturation current IS show that a thermionic-field emission is dominant in the carrier transport mechanism across contacts above 101 K. It is found that the parameter E is too large compared with an estimated value from the Schottky diode model using a permittivity obtained from the inverse characteristics of capacitance-voltage measurements. We discuss the barrier properties and suggest the possibility of imperfect ionization of the impurity Nb at the surface of the SrTiO3:Nb substrate.
Galvanomagnetic voltages in the vicinity of a domain wall in ferromagnetic thin films
Authors: Berger L.
Published: July 2002

Ferromagnetic Ni-Fe films of thickness <85 nm contain Néel or crosstie walls, with wall thickness as large as 6 μm. Because of the anisotropic magnetoresistance Δρ/ρ0≂2% in Ni-Fe, the electrical resistivity is slightly larger inside a wall than in the adjacent domains, for currents normal to the wall. This should result in a detectable increase dV of the ohmic voltage between two miniature potential probes when a wall is located between them. For reasonable values of the dc current density, our calculations predict dV≂9 μV per wall. When the current is parallel to Néel walls, there should be a local decrease of the resistivity inside each wall, manifested as a decrease of the average sample resistance. This effect seems to provide an explanation for the upward resistance jumps observed in Ni-Fe magnetoresistive reading heads when Néel walls disappear. Also, because of the planar Hall effect, a voltage V should appear between two potential probes when one probe is located at the wall center.
Three-dimensional transient mass transfer model for laser chemical vapor deposition of titanium on stationary finite slabs
Authors: Kar A. , Azer M. N. , Mazumder J.
Published: July 2002

A mathematical model for mass transfer inside a laser chemical vapor deposition (LCVD) chamber is presented for pure titanium deposition from titanium tetrabromide on a stainless-steel (SS 304) substrate. A set of five three-dimensional, transient, and nonlinear partial differential equations is solved to account for the diffusion of various species inside the LCVD chamber and the thermal decomposition of titanium tetrabromide, titanium dibromide, and titanium monobromide at the surface of the substrate in order to determine the thickness of the titanium film deposited on the substrate. The model is used for studying the effects of various parameters on the deposition and shape of titanium films. The parameters which were varied are as follows: laser power, activation energy, total pressure inside the LCVD chamber, and partial pressure of titanium tetrabromide. Under certain conditions, the deposited titanium film is found to have a volcanic profile.
Compositional homogeneity of metalorganic chemical vapor deposition grown III-V compound semiconductor epilayers
Authors: Mackenzie R. A. D. , Liddle J. A. , Grovenor C. R. M.
Published: July 2002

The compositional homogeneity of epitaxially grown layers of GaInAs, AlInAs, and GaAlInAs on InP substrates has been investigated using pulsed laser atom probe techniques. All the material characterized was shown by transmission electron microscopy to have a fine-scale contrast variation, however only some of the samples were found, using atom probe techniques, to show distinct deviations from compositional uniformity. The average composition measured from each of the layers was that of the lattice-matched composition intended during growth, however the composition varied locally, on a scale of typically 10–20 nm, from the mean composition by up to 5 at. %.
Reversal mechanisms and domain structures in thin-film recording media (invited)
Authors: Zhu Jian-Gang , Bertram H. Neal
Published: July 2002

Magnetization reversal in longitudinal and perpendicular thin films is studied via computer simulation. Collective micromagnetic processes and the formation of magnetization patterns driven by magnetostatic interactions and intergranular exchange coupling is analyzed. In longitudinal thin films, it is found that a reversal starts by formation of magnetization vortices. The collective formation of vortices yields elongated reverse regions along the direction of the applied field. Intergranular exchange coupling enhances these magnetization structures and results in large-size domains. Reversal of a typical perpendicular film (CoCr) consists of discrete nucleation processes. Each individual process is characterized by a planar chain nucleation mode. These collective micromagnetic processes cause film magnetic properties to be significantly different from those of a simple assembly of noninteracting grains. Medium noise in perpendicular films occurs mainly away from transitions in distinct contrast to longitudinal films in which the noise is concentrated at transition centers. Intergranular exchange coupling increases the medium noise in all films.
Magnetic properties of epitaxial Co/Pd superlattices
Authors: Engel Brad N. , England Craig D. , Van Leeuwen Robert , Nakada Masafumi , Falco Charles M.
Published: July 2002

A series of Co/Pd superlattices with constant Pd layer thickness of dPd = 11 Å were grown on single-crystal GaAs(110) substrates by molecular beam epitaxy (MBE). A buffer layer of 500 Å of Pd provided an atomically smooth, fcc(111) single-crystal starting surface for the superlattice deposition. The resulting superlattices maintain this crystal symmetry and smoothness throughout their epitaxial growth. Details of the structural characterization of these samples are given elsewhere in these proceedings. The magnetic properties of these films have been measured by vibrating sample magnetometry. A perpendicular easy axis is found for all seven of the superlattices presented (dCo = 2, 4, 8, 10, 12, 17, and 20 Å). An unusually high coercive field of Hc = 6.6 kOe is observed for dCo = 2 Å, and decreases monotonically with increasing dCo. The saturation magnetization agrees well with a model composed of bulk Co layers with an additional contribution from polarized Pd. The uniaxial magnetic anisotropy energy can be described by both an interface term and a large volume term favoring a perpendicular easy axis for dCo < 23 Å. Comparisons with a series of polycrystalline multilayers simultaneously deposited on Si substrates reveal significant differences in the magnetic behavior.
Galvanomagnetic properties of epitaxial MnAl films on GaAs
Authors: Leadbeater M. L. , Allen S. J. , DeRosa F. , Harbison J. P. , Sands T. , Ramesh R. , Florez L. T. , Keramidas V. G.
Published: July 2002

Single-crystal films of τ-MnAl are grown by molecular-beam epitaxy on GaAs substrates. The extraordinary Hall effect shows a large hysteresis loop, and the magnetization is found to have a substantial component perpendicular to the plane of the film.
Effects of iron substitution on the magnetic anisotropy of YCo4B
Authors: Dung T. T. , Thuy N. P. , Hong N. M. , Hien T. D. , Franse J. J. M.
Published: July 2002

The effects of iron substitution on the magnetization, the magnetic anisotropy, the spin-reorientation temperature, and the Curie temperature of Y(Co1−xFex)4B have been studied on the cobalt-rich side for x values below 0.4. Temperature-induced spin-reorientation phenomena may be observed in compounds with x values below 0.02 by inspecting the low-field magnetization curves of bulk polycrystalline samples and by observing the change in the easy direction in field-oriented powdered samples. The spin-reorientation temperature shifts from 145 K for YCo4B to higher values with increasing x and the phenomenon disappears for values larger than 0.03. By analyzing the magnetization curves of field-oriented powder samples, the magnetic anisotropy has been evaluated. The value for the first anisotropy constant K1 at 4.2 K decreases in a nonlinear way with increasing x values and reaches a minimum around x=0.3.
Theory of polar-optical-phonon scattering in a semiconductor quantum wire
Authors: Ahn Doyeol
Published: July 2002

The scattering rates of electrons due to the interaction with the polar-optical phonons in a quasi-one-dimensional semiconductor quantum wire are studied theoretically using a simple cylindrical wire model. Many-body effects on the electron-phonon interaction are included by calculating the leading-order polaronic self-energy. Analytical formulas for the scattering rates are derived using the simple model where the envelope function is assumed to be constant inside a cylindrical wire and zero outside. The most prominent feature of the many-body effects is that the phonon absorption process is enhanced while the emission process is suppressed for the low-energy electrons with increasing electron density as compared with those of the single-particle model. Polar scattering rates are reduced for the one-dimensional electron gas in a quantum wire by an order of magnitude as compared with those of the two-dimensional electron gas.
Rapid-phase transitions of GeTe-Sb2Te3 pseudobinary amorphous thin films for an optical disk memory
Authors: Yamada Noboru , Ohno Eiji , Nishiuchi Kenichi , Akahira Nobuo , Takao Masatoshi
Published: July 2002

Amorphous films having a component of the stoichiometric GeTe-Sb2Te3 pseudobinary alloy system, GeSb2Te4 or Ge2Sb2Te5 representatively, were found to have featuring characteristics for optical memory material presenting a large optical change and enabling high-speed one-beam data rewriting. The material films being sandwiched by heat-conductive ZnS layers can be crystallized (low power) or reamorphized (high power) by laser irradiation of very short duration, less than 50 ns. The cooling speed of the sandwiched film is extremely high: more than 1010 deg/s, which permits the molten material to convert to the amorphous state spontaneously; whereas, a low-power pulse irradiation of the same duration changed the exposed portion into the crystalline state. The optical constant changes between the amorphous state and the crystalline state of them were measured to be large: from 4.7+i1.3 to 6.9+i2.6 and from 5.0+i1.3 to 6.5+i3.5, respectively. The crystallized portion was known to have a GeTe-like fcc structure by an analytical experiment using transmission electron microscopy, differential scanning calorimetry, and x-ray and electron diffraction methods. The high crystallization speed is ascribed to (1) the pseudobinary system which can form crystalline compositions without any phase separation, (2) the high symmetry of the fcc structure which is the nearest to the random amorphous structure, (3) the high-energy difference between the amorphous state and the fcc crystal state.
The distribution of fluctuation measurements within the random-phase model
Authors: Carlson A. W.
Published: July 2002

A variety of diagnostics measure fluctuating quantities at a small number of locations. A common method to estimate the wave-number spectrum S(k) at a given frequency is to make many measurements of the ‘‘local’’ wave number kl, which is the phase difference between two locations divided by their separation. The random-phase model allows the synthesis of a typical signal from a given S(k). We apply local wave-number analysis to such synthetic signals and show that, in the limit of small separation, the power-weighted mean of kl accurately reflects the mean of S(k), and the width of the distribution is exactly ■ times smaller than the width of S(k). We also show that no information on the shape of S(k) exists in the measurements. Finally, we generalize these results to finite separations, finite measurement volumes, and any number of locations.
Hole transport in liquid-crystalline media. I. Effect of matrices on hole drift mobilities of 1,2-trans-bis (9H-carbazol-9-yl)-cyclobutane doped in polymer liquid crystals
Authors: Ikeda Tomiki , Mochizuki Hiroyuki , Hayashi Yuko , Sisido Masahiko , Sasakawa Tomoyoshi
Published: July 2002

Hole drift mobilities have been measured in films of solid solution of trans-1,2-bis(9H-carbazol-9-yl) cyclobutane (DCZB) in various host polymers; polymer liquid crystals (PLCs) and amorphous polymers. The hole drift mobilities were found to depend on the host polymers and be higher in PLCs. The larger mobilities of the DCZB/PLC mixtures have been attributed to the orientational effect of carrier molecules in the host PLCs.
Investigations of Rh-based multilayers for soft x-ray applications by high-resolution electron microscopy
Authors: Li Z. G. , Smith David J. , Tsen S.-C. Y. , Boher P. , Houdy Ph.
Published: July 2002

A series of rhodium-based multilayer structures has been developed for soft x-ray applications by using ‘‘trilayer’’ structures and low density boron carbide spacing material. The microstructure of the multilayers was investigated by high-resolution electron microscopy and compared with those of tungsten- and nickel-based multilayers. Rh crystals having fcc structure but with different preferred orientations were identified in Rh-based layers. It was confirmed that the major limitation on the performance of the multilayer materials was the crystallization of the metal layers. High reflectivity and selectivity for x-ray mirrors was obtained in the case of W/Rh/C multilayers due to significant improvement in their microstructure, especially the interface roughness.
Cyclotron-phonon resonance in quasi-two-dimensional semiconducting structures
Authors: Bhat J. S. , Kubakaddi S. S. , Mulimani B. G.
Published: July 2002

A theory of phonon-assisted cyclotron resonance in quasi-two-dimensional semiconductor quantum-well structures is given. Using perturbation technique, expressions for absorption coefficients are obtained when the electrons are scattered by acoustic, nonpolar, and polar optical phonons. Extra peaks in the absorption spectrum due to transitions between Landau levels accompanied by emission and absorption of phonons are predicted. Numerical results for the frequency, magnetic field, and temperature dependence are given for parameters characteristic of GaAs.
Valence-band states of ion-bombarded polystyrene
Authors: Terrasi A. , Foti G. , Hwu Y. , Margaritondo G.
Published: July 2002

Ion-bombarded polystyrene with a 0.5-keV Ar+ beam has been investigated by means of photoelectron spectroscopy performed with synchrotron radiation. After a dose of 1015 ions/cm2 the evolution of the valence band of the bombarded sample towards an amorphous carbonlike configuration is reported. From the analysis of valence-band spectra we estimated the out-diffusion of hydrogen and showed that its electronic states remain well identified and stable until the hydrogen presence is about 35% with respect to the pristine sample. Finally, comparison with mass spectroscopy measurements on deuterated polystyrene has been performed to determine hydrogen evolution during the ion irradiation.