bluuebunny/crossref_metadata_2025 huggingface dataset:
Film growth studies with intrinsic stress measurement: Polycrystalline and epitaxial Ag, Cu, and Au films on mica(001)
Authors: Winau D. , Koch R. , Führmann A. , Rieder K. H.
Published: July 2002

Growth and microstructure of thin Ag, Cu, and Au films ultrahigh vacuum deposited onto single-crystalline mica(001) have been studied in situ by intrinsic stress measurements (ISM) and low-energy electron diffraction. Depending on the respective substrate temperature, three different modes of Vollmer–Weber (VW) growth can be clearly distinguished by ISM: (i) VW-type nucleation and subsequent columnar grain growth at low temperatures (110 K) where grain-boundary relaxation is the prevailing stress contribution, (ii) polycrystalline VW mode in a medium temperature range that is characterized by VW-type nucleation and grain growth in the continuous film and dominated by the capillarity stress, and (iii) epitaxial VW growth mode at temperatures above 470 K for Ag and 600 K for Cu and Au; here a novel stress mechanism due to the formation of ‘‘single-crystalline grain boundaries’’ appears during the network stage.
Bipolar-charge-transporting organic photoconductors
Authors: Yamaguchi Yasuhiro , Fujiyama Takahiro , Yokoyama Masaaki
Published: July 2002

A new class of bipolar-charge-transporting molecularly-doped polymers has been developed. The materials are ternary solid solutions comprised of 3,5-dimethyl-3′,5′-di-tert-butyl-4,4′-diphenoquinone (MBDQ), N,N,N′,N′-tetrakis (m-methylphenyl)-1, 3-diaminobenzene (PDA), and poly(4,4′-cyclohexylidenediphenyl carbonate) (PC-Z). No charge-transfer complexation occurs between the MBDQ and PDA. As a result the MBDQ and PDA function independently as electron and hole transport manifolds, respectively. Both electrons and holes can be injected into these materials from titanylphthalocyanine (TiOPc). In addition, it has been observed that the presence of MBDQ and PDA enhances the charge separation efficiency of the TiOPc.
Magnetic properties and crystal structure of Ti/Ni superlattices (abstract)
Authors: Haftek E. , Tan M. , Waknis A. , Barnard J. A.
Published: July 2002

A series of periodic multilayer Ti/Ni thin films of the form (xTi/yNi)n were grown at room temperature by alternate deposition of elemental Ti and Ni onto glass substrates using dc-magnetron sputtering. The thicknesses of the individual Ti and Ni layers are given by x and y, respectively, and the total number of bilayer units is n. For this set of experiments, x was fixed at 2.8 nm while y was systematically varied from 2.4 to 154 nm. The product ny was held constant for all samples so that each film contained the same quantity of Ni. The growth rates of Ti and Ni were 0.14 and 0.32 nm/s, respectively. The multilayers were tested in the as-deposited state for magnetic properties using a vibrating sample magnetometer. These superlattices showed a variety of magnetic characteristics which were dependent on the thickness of the Ni layers. The coercivity of the multilayers declined with Ni layer thickness from a maximum of 80 Oe to a minimum of 7 Oe. A systematic reduction in saturation magnetization (Ms) with Ni layer thickness was also observed (for multilayers with y<38 nm). In order to determine if the reduction in Ms could be attributed to a specific structural feature, a systematic study using transmission electron microscopy (imaging and electron diffraction) was made of the individual Ti/Ni and Ni/Ti bilayer units which comprise the superlattices. The bilayer units were grown under the same sputtering conditions used for the multilayers. Evidence was found for substantial strain (+4%) in the Ni layers and for the formation of Ni-Ti compounds presumably nucleated at the interfaces (the extra electron diffraction rings most closely match Ni3Ti).
Statistical properties of sputtering from individual atomic collision cascades in solids
Authors: Hou M. , Eckstein W.
Published: July 2002

The correlation between sputtering and several features of individual cascades is investigated with the trim.sp program. A comparison with other simulation models indicates that the sputtering statistics is not deeply influenced by the target model. Also, the distributions of sputtering related quantities were found quite similar when resulting from cascades generated by particles which are implanted or backscattered, although the number and the distribution of displacements produced can be well distinguished. A partition of the individual cascades is made based on the sputtering frequency. The sputtering energy distributions are found similar in all classes. These features illustrate the similarity between the statistics of sputtering from individual and statistical cascades. The situation is different as the relation between the number of sputtered atoms and the surface deposited energy is concerned. The same number of sputtered atoms is associated with a broad distribution of deposited energies. Their profile is dependent on the number of sputtered atoms, and the sputtering frequency is not always linearly dependent on either the mean or the mode of the surface-deposited energy distribution. Finally, a surface-deposited energy threshold is emphasized for sputtering, which correlates to the anisotropy of the momentum flux distribution in the vicinity of the surface.
Ultrasonic excitation and propagation in an acoustic superlattice
Authors: Zhu Yong-yuan , Ming Nai-ben
Published: July 2002

The ultrasonic excitation and propagation in an acoustic superlattice made of a LiNbO3 crystal is studied. Some interesting phenomena are predicted theoretically. The resonance is determined by the periodicity of the acoustic superlattice (ASL). The acoustic power emitted by the ASL into the transmission medium is directly proportional to N2 (N is the number of domains of the ASL). In view of these two features, the ASL may have potential applications in acoustic devices operating at frequencies of several hundred megahertz to several gigahertz. Another interesting phenomenon is the existence of a satellitelike resonance, whose frequency is related to the total thickness of the ASL. Using the ASL, resonators and transducers have been fabricated with operating frequencies in the range of 500–1000 MHz. Satellitelike resonances have been observed. Transducers with a very low insertion loss at 555 MHz and a 5.8% 3 dB bandwidth have been fabricated. The experiments basically confirm the theoretical predictions.
Theoretical study on the static performance of piezoelectric ceramic-polymer composites with 1-3 connectivity
Authors: Cao Wenwu , Zhang Q. M. , Cross L. E.
Published: July 2002

Inhomogeneous displacement profiles have been derived for a single-rod composite and a single-tube 1-3 ceramic-polymer composite under both uniaxial and hydrostatic stress. The effective piezoelectric constants for the composites have been derived in terms of the ceramic content, the piezoelectric and elastic constants of each component, and the aspect ratio of the ceramic rod. The stress concentration inside both phases is derived from the calculated inhomogeneous displacement profiles. It is found that only a finite portion of the polymer in the vicinity of the ceramic-polymer interface actually contributes to the stress transfer, and the induced additional stress on the ceramic also has a higher magnitude near the interface. The theoretical results quantitatively predict the performance of a given 1-3 structure, and can be used to optimize the design parameters, such as ceramic content, aspect ratio of the ceramic rods, rod geometry and rod arrangement, resin hardness, etc., for 1-3 structures designed for specific purposes.
Identification of a nonradiative recombination center in GaAs
Authors: Michler P. , Hangleiter A. , Dieter R. , Scholz F.
Published: July 2002

We report on the identification of the CuGa acceptor level as a recombination center in GaAs. Using time-resolved photoluminescence (PL) we have studied the recombination of excess charge carriers in metalorganic vapor-phase epitaxy GaAs/AlGaAs double heterostructures. The recombination in one particular set of samples was clearly nonradiative and the trap level derived from our measurements coincides with that of CuGa as seen in the PL spectra. The temperature dependence of the capture coefficients is consistent with a multiphonon process and allows for the determination of the coupling strength for electron and hole capture.
Magnetic-field-induced intermittency in spin-wave experiments
Authors: de Aguiar Flavio M. , Azevedo Antonio , Rezende Sergio M.
Published: July 2002

Chaotic behavior in spin-wave systems is usually observed with the variation of the driving parameter, namely, the incident microwave power. A variety of interesting phenomena can occur if one keeps the power fixed beyond the auto-oscillation threshold and varies another available parameter. We demonstrate this with X-band subsidiary-resonance experiments in an yttrium iron garnet (YIG) sphere with varying dc magnetic field. Besides period-doubling bifurcations, intermittent temporal bursting resulting from the collision of neighbouring period-I and chaotic attractors has been observed. These phenomena are qualitatively investigated in the light of the theory of crisis in dissipative systems due to Grebogi, Ott, Romeiras, and Yorke. In addition, for fixed magnetic field and varying microwave power, we observe that transient periods prior to auto-oscillation have a power-law dependence on the driving parameter, similarly to crisis-induced phenomena at higher power levels.
Iron doped bulk semi-insulating GaAs
Authors: Gray M. L. , Peterson L. , Tang R-S. , Saban S. B. , Blakemore J. S.
Published: July 2002

As an acceptor dopant with a solid:liquid distribution coefficient ks<1, iron is an example of an impurity which can be used in modest amounts to ensure that an adequate fraction of EL2 midgap defects are ionized along the length of a melt-grown GaAs crystal, as desired for semi-insulating behavior. The results of such deliberate doping with iron (when NFe is in the mid-1015 cm−3 range) are reported for crystals grown by both the liquid encapsulated Czochralski and the vertical gradient freeze methods. Except in the very tail region of such crystals (when NFe≳NEL2 and high resistivity p-type behavior results), GaAs with this modest iron modification to the compensation balance behaves with quite ordinary semi-insulating properties. The iron acceptors are then all ionized, and are optically ‘‘invisible.’’
Nondestructive diagnostic method using ac surface photovoltage for detecting metallic contaminants in silicon wafers
Authors: Shimizu Hirofumi , Munakata Chusuke
Published: July 2002

Effects of residual metal impurities after RCA (Radio Corporation of America) standard cleaning (alkaline and acid rinses) on the generation of ac surface photovoltages (SPVs) are investigated using n-type silicon wafers. Aluminum (Al) and iron (Fe) in the native oxide induce a negative charge, causing high ac SPVs in n-type wafers. The ac SPV dependency on the concentration of Al and Fe is determined. Nickel and zinc, however, have little effect on the generation of ac SPVs. In commonly employed cleaning processes, Al is the major impurity in the native oxide, and thus the ac SPV technique is applicable to nondestructive diagnostics for quality control in cleaning processes.
Micromechanics of coupled electroelastic composites: Effective thermal expansion and pyroelectric coefficients
Authors: Dunn Martin L.
Published: July 2002

The effective thermal-expansion and pyroelectric coefficients of two-phase coupled electroelastic composite materials are obtained by coupling various micromechanics theories with exact relations connecting their effective thermal and electroelastic moduli. Results are obtained for composites reinforced by ellipsoidal piezoelectric inhomogeneities and thus are applicable to a wide range of microstructural geometry including lamina, spherical particle, and continuous fiber reinforcement. The analytical framework is developed in a matrix formulation in which the electroelastic moduli are conveniently represented by a 9×9 matrix and the thermal-expansion and pyroelectric coefficients by a 9×1 column vector. Numerical results are presented for some typical composite microstructures which show the interesting behavior of these materials.
Oxidation processes in undoped GaAs and in Si-doped GaAs
Authors: Rim A. , Beserman R.
Published: July 2002

Samples of undoped GaAs- and Si-doped GaAs were oxidized at different oxidation temperatures, for different durations. Three different experimental techniques that complete each other were used: Raman scattering, Auger electron spectroscopy, and the ellipsometry technique. The growth of crystalline arsenic layer takes place after oxidation during 10 h, 45 min, and 5 min at temperatures of 400, 500, and 600 °C, respectively. The oxide layer is formed as a result of three competing processes: diffusion in accordance with Fick’s law, diffusion with larger diffusion coefficient through the oxide layer, and stopping of diffusion by the crystalline arsenic layer that grows at the GaAs/oxide interface. The effect of Si doping on the oxidation process of GaAs is to impede the crystallization of the arsenic layer, to diminish the diffusion coefficient in the course of the initial stages of the reaction between the oxygen and GaAs, and to cause a small rise in the activation energy.
Modeling of self-electro-optic-effect devices
Authors: Mares P. J. , Chuang S. L.
Published: July 2002

A detailed comparison is presented between a comprehensive theoretical model, which uses the linewidth as the only fitted parameter, and a consistent set of experimental data for (i) the electro-optical properties of quantum-well (QW) modulators and (ii) the input power versus output power characteristics of interband self-electro-optic-effect devices (SEEDs). The model, which is founded on basic principles, includes excitonic effects and employs the depletion approximation to relate the applied bias to the electric field and to phenomenologically approximate the internal quantum efficiency. It is shown that this model is able to emulate and predict the behavior of QW modulators and SEEDs very well.
Photosignal enhancement in Al-GaAs diodes due to surface plasmons and guided wave modes
Authors: Tamm I. R. , Dawson P. , Pate M. A. , Grey R. , Hill G.
Published: July 2002

Light of wavelength 632.8 nm and p-polarization is incident on a prism–air gap (varied from 0.7 to 7 μm)–Al-GaAs arrangement. Both the photosignal generated by the Schottky diode and the reflectance are measured as a function of the internal angle of incidence in the prism. There is significant, well-defined enhancement of the photosignal, up to a factor of ∼7.5, associated with two different types of enhanced absorption modes. For air gaps <1.5 μm there is photosignal enhancement due to an enhanced absorption feature (reflectance dip) that occurs at an angle of incidence just above critical angle in the prism; this feature corresponds to the excitation of a surface plasmon polariton at the Al-air interface. For air gaps ≳1 μm there are between one and ten photoresponse peaks at input angles less than the critical angle. The corresponding enhanced absorption features are due to leaky guided wave modes set up in the air gap.
Quantitative time-resolved observations of ground-state zinc atoms, methyl radicals, and excited CH radicals resulting from the 193 nm photodissociation of dimethylzinc
Authors: Elias Joseph A. , Wisoff Peter J. , Wilson William L.
Published: July 2002

The ArF laser photodissociation dynamics of dimethylzinc at 193 nm have been studied, and their implications for the growth of ZnSe thin films are discussed. A broadband, vacuum ultraviolet argon plasma emission has been used to acquire time-resolved absorption profiles from ground-state Zn atoms and methyl radicals. Time-resolved fluorescence from excited CH radicals has also been studied. The results indicate that the Zn concentration remains constant from 100 ns to 2 ms after the dissociating ArF pulse, indicating that this system is a good source for free Zn atoms. The CH3 radicals are formed immediately after the dissociation pulse and recombine within several hundred microseconds to form ethane. There was no indication of monomethylzinc (MMZn) formation, and the detected CH radical is likely to combine with H2 to form CH3 within several microseconds. This implies that the major sources for carbon contamination in the growth process (CH3, MMZn, CH) are unlikely to reach the growth surface.
In situ technique for measuring Ga segregation and interface roughness at GaAs/AlGaAs interfaces
Authors: Braun W. , Ploog K. H.
Published: July 2002

We describe a method, based on electron diffraction, for measuring the Ga segregation and roughness at GaAs/AlGaAs interfaces. By monitoring the phase of reflection high energy electron diffraction intensity oscillations, we can deduce changes of alloy composition in real time. In particular, we can relate the phase to the extent of As coverage and thereby explain the ‘‘forbidden range’’ for growth of GaAlAs. We have determined that segregation only occurs at the normal (AlAs on GaAs) interface and have detected Ga persisting on a nominal AlAs surface even after 20 monolayers.
Takeoff angle-dependent x-ray fluorescence of layered materials using a glancing incident x-ray beam
Authors: Tsuji Kouichi , Hirokawa Kichinosuke
Published: July 2002

We had previously shown that takeoff angle-dependent x-ray fluorescence (TADXRF) is a useful method for the characterization of thin films. Here we have calculated takeoff angle-dependence of fluorescent x rays at glancing incidence for multilayer materials. The experimental results of TADXRF for Au/Ni/SiO2 agree well with the calculated curves, suggesting that the calculation process is correct. As a result, the thickness, density, and the refractive index of layers can be estimated.
Schottky and ohmic contacts of Pd on p-type GaAs distinguished with hydrogen
Authors: Nie H.-Y. , Nannichi Y.
Published: July 2002

Contacts of Pd on p-type GaAs with a native oxide layer between them reveal ohmiclike behavior in air or vacuum at room temperature. This behavior is similar to that of contacts annealed at 450 °C for 5 min. To relate the interface electrical properties of the two contacts to their interfacial structures, we propose to measure current-voltage (I-V) and capacitance-voltage (C-V) characteristics in a hydrogen ambient. We show that these two contacts can be distinguished with atomic hydrogen. This method was confirmed with I-V and C-V measurements at low temperatures.
Analysis of the structure of multi-component carbon films by resonant Raman scattering
Authors: Marcus B. , Fayette L. , Mermoux M. , Abello L. , Lucazeau G.
Published: July 2002

Diamond and carbonaceous films grown in a microwave assisted plasma reactor have been characterized by x-ray diffraction, scanning electron microscopy, and Raman spectroscopy. This study is mainly focused on the identification of the different carbonaceous compounds which can coexist with the diamond depending on the synthesis parameters. Selective etching reactions and the excitation wavelength dependence of Raman cross sections of the different carbon species reveal that the broad and poorly structured Raman spectra in the 1100–1700 cm−1 region contain six components that arise from three different carbonaceous species: (i) one species is graphitic and is identified from the components at about 1350 and 1590 cm−1 which are resonantly enhanced as compared to the other components when the excitation energy is lowered from 3 to 2 eV. (ii) The second species is associated with the two broad bands at 1350 and 1550 cm−1 and is attributed to amorphous diamond-like carbon (a-C:H); both bands are resonantly enhanced by excitation energies in the range from 2.41 to 3.53 eV. These bands do not shift with exciting energy. (iii) The third species is associated with a band centered at about 1470 cm−1 and a weak band at 1150 cm−1. This 1470 cm−1 band overlaps with the 1550 cm−1 band of the diamond-like component, resulting in an apparent frequency down-shift when the incident photon energy decreases below the resonant enhancement range of the 1550 cm−1 band. Possible models for the structure of the third species are discussed.
Magnetic properties and magnetostriction in grain-oriented (TbxDy1−x)(Fe1−yMny)1.95 compounds
Authors: Kobayashi T. , Sasaki I. , Funayama T. , Sahashi M.
Published: July 2002

The magnetic properties and magnetostriction in grain-oriented (TbxDy1−x)(Fe1−yMny)1.95 compounds with 0.3≤x≤0.5, 0≤y≤0.2 prepared by the Bridgman method have been investigated. It is confirmed that the Mn substitution not only lowers the spin reorientation temperature but also enhances λ〈100〉. This large λ〈100〉 is contradictory to the single-ion model. For Tb0.5Dy0.5 (Fe0.9Mn0.1)1.95 compound, no spin reorientation, which induces the sharp drop in the magnetostriction is seen in the temperature range from 77 to 400 K. In addition, by choosing the appropriate compressive stress, the quite excellent thermal stability and the large magnetostriction of 2000 ppm in the low applied field can be realized in the Tb0.5Dy0.5 (Fe0.9Mn0.1)1.95 compound. These features make Tb0.5Dy0.5 (Fe0.9Mn0.1)1.95 a promising material applicable to the various giant magnetostrictive actuators.
Magnetoresistance in (Fe–Co)/Ag films
Authors: Tsoukatos A. , Dimitrov D. V. , Murthy A. S. , Hadjipanayis G. C.
Published: July 2002

The structural and magnetotransport properties of (FeyCo1−y)100−xAgx films were studied as a function of composition. Giant magnetoresistance (GMR) values were measured in these granular films, with the best GMR obtained for the composition (Fe0.33Co0.67)27Ag73, with values of 29% at 30 K and 11.7% at 300 K. XRD and TEM results have shown a fcc crystal structure with a relatively homogeneous microstructure. Magnetic data for the samples with the best GMR indicate a superparamagnetic behavior. The narrow peak in thermomagnetic data and low blocking temperature suggest a small and uniform size distribution of magnetic granules. A summary of the electrical transport properties is presented, in relation to the structural, microstructural, and magnetic properties.
Anomalous perpendicular magnetoanisotropy in Mn4N films on Si(100)
Authors: Ching K. M. , Chang W. D. , Chin T. S. , Duh J. G. , Ku H. C.
Published: July 2002

Ferrimagnetic Mn4N films were deposited on Si (100) substrate by dc reactive magnetron sputtering from sintered Mn target. Highly (002) textured Mn4N ordered phase is formed in situ at studied substrate temperatures of 150–250 °C without further annealing. Anomalous perpendicular magnetoanisotropy exists in these face-centered cubic films with larger coercivity measured perpendicular to the film (2000–3000 Oe) than that parallel (1100–1300 Oe), as is the remanence. Coercivity in either direction decreases, while the saturation flux density (from 240 to 610 G) increases with increasing substrate temperature. The anomalous perpendicular magnetoanisotropy is attributed to (1) the stress-induced anisotropy due to in-plane tensile stress coupled with a reverse magnetostriction, and (2) the shape anisotropy due to columnar grain structure.
Optimization of ion-beam induced charge microscopy for the analysis of integrated circuits
Authors: Breese M. B. H. , Saint A. , Sexton F. W. , Horn K. M. , Schöne H. , Doyle B. L. , Laird J. S. , Legge G. J. F.
Published: July 2002

The conditions necessary for obtaining both the maximum topographical image contrast and the maximum insensitivity to ion induced damage using ion-beam induced charge microscopy are presented and interpreted in terms of existing energy loss and damage theory. Ion-beam induced charge images and pulse-height spectra which are measured from a Sandia SA3002 memory device using MeV H+, H+2, and 4He+ ions with a range of incident energies are used to characterize these optimum experimental conditions. It is shown that ions which are stopped within the device depletion layers generate charge pulses which are much less sensitive to ion induced damage than longer range ions which are stopped in the device substrate.
Magnetic properties of Sm2Fe17−xSix and Sm2Fe17−xSixC compounds
Authors: Shen Bao-gen , Liang Bing , Wang Fang-wei , Cheng Zhao-hua , Gong Hua-yang , Zhang Shao-ying , Zhang Jun-xian
Published: July 2002

Iron-rich intermetallic compounds Sm2Fe17−xSix and Sm2Fe17−xSixC (x=0, 1, 2, and 3) were studied. The as-prepared compounds are single phase with the rhombohedral Th2Zn17-type structure except for Sm2Fe17C and Sm2Fe16SiC which contain some amounts of α-Fe. The unit cell volumes and saturation magnetization at room temperature are found to decrease linearly with increasing Si concentration x. The Curie temperature Tc is found first to increase and then to decrease with increasing Si content. X-ray diffraction measurements on magnetically aligned powder samples show that the easy magnetization direction of the Sm2Fe17−xSix samples with x≤2 is planar while that of the sample with x=3 is conical. The Sm2Fe17−xSixC samples with x≤3 exhibit an easy c-axis anisotropy at room temperature. The anisotropy field is 83 kOe for x=0 and it rises to 110 kOe at x=1, and then drops with increasing Si concentration to 55 kOe at x=3.
Interface properties of (NH4)2Sx-treated In0.5Ga0.5P Schottky contacts
Authors: Kwon S. D. , Kim C. H. , Kwon Ho Ki , Choe Byung-Doo , Lim H.
Published: July 2002

The effects of (NH4)2Sx solution treatment on the interface properties of metal-In0.5Ga0.5P Schottky contacts have been investigated by capacitance-voltage measurements and deep-level transient spectroscopy measurements. The (NH4)2Sx-treated samples show Schottky barrier heights that are more sensitive to the metal work functions. It is also found that (NH4)2Sx treatment of In0.5Ga0.5P can passivate the phosphorus-vacancy-related interface deep traps of Schottky contacts as well as suppress the generation of interface deep traps due to heat treatment.
Extended x-ray-absorption fine-structure study of InAs/InP and GaAs/InP strained heterostructures
Authors: Proietti M. G. , Turchini S. , Martelli F. , Garcia J. , Prosperi T.
Published: July 2002

Extended x-ray-absorption fine-structure measurements have been performed at the As K edge of GaAs/InP and InAs/InP strained single heterostructures grown by molecular-beam epitaxy. The results show a substantial conservation of the bond length in the strained epitaxial layers with respect to the corresponding bulk materials. The measures point out the formation of a thick InAsP (or InGaAsP) layer at the GaAs/InP interface.
Optical parametric amplification in the magnetoplasma in semiconductors
Authors: Iida Takashi , Mizushima Yoshihiko
Published: July 2002

A nonlinear parametric interaction is found in the magnetoplasma in a semiconductor. The spatial asymmetry is produced by the magnetic field in the Voigt configuration, where the Lorentz force acts on the drifting electrons. The nonpolar semiconductor can be used as the nonlinear optical element. The optical parametric conversion and the second-harmonic generation are discussed. The device operates in the infrared range. The efficiencies are found to be much larger than in conventional nonlinear optical crystals.
Theory of optical interband transitions in strained Si1−yCy grown pseudomorphically on Si (001)
Authors: Zollner Stefan
Published: July 2002

Recently W. Kissinger, M. Weidner, H. J. Osten, and M. Eichler [Appl. Phys. Lett. 65, 3356 (1994)] reported ellipsometry and electroreflectance measurements on the E0, E1, and E2 critical point energies in strained Si1−yCy alloys grown pseudomorphically on Si (001) using molecular-beam epitaxy. We present a theory explaining these energies using established deformation-potential theory and interpret the results and their implications for the band structure of these alloys.
Effective medium calculation of the anisotropic elastic modulii of composites with oriented ellipsoidal inclusions
Authors: Chui S. T. , Hsu W. Y. , Tian D.
Published: July 2002

We calculate the anisotropic elastic coefficient of composites of oriented ellipsoids in the effective medium approximation. The theoretical prediction is compared with experimental results for the longitudinal and transverse Young’s modulus of injection molded polymer blends of an amorphous thermoplastic polyester and an ethylene-propylene-diene rubber at different compositions. The different ‘‘percolation limits’’ experimentally observed are reproduced.
Photoluminescence study of band-gap alignment of intermixed InAsP/InGaAsP superlattices
Authors: Francis C. , Boucaud P. , Julien F. H. , Emery J. Y. , Goldstein L.
Published: July 2002

The band-gap alignment of InAs1−xPx/In0.53Ga0.47As1−yPy strained heterostructures fabricated by selective As–P interdiffusion in an as-grown InP/In0.53Ga0.47As superlattice has been investigated using low-temperature photoluminescence. Interdiffusion is performed using thermal anneals with phosphorous gas ambient. By analyzing both the energy and the integrated intensity of the superlattice photoluminescence along with their dependences on excitation intensity, it is demonstrated that the superlattice band alignment is of type I for x≳0.58 and y<0.21, whereas it switches to type II for x<0.58 and y≳0.21. Simulations show that in contrast to the type-I situation the band discontinuity mainly occurs in the conduction band for the type-II superlattice. The transition from type-I to type-II band alignment is attributed to composition changes and strain development at the heterointerfaces.
Low-temperature growth of giant magnetoresistance spin valves
Authors: Egelhoff W. F. , Chen P. J. , Misra R. D. K. , Ha T. , Kadmon Y. , Powell C. J. , Stiles M. D. , McMichael R. D. , Lin C.-L. , Sivertsen J. M. , Judy J. H.
Published: July 2002

We have investigated the dependence of the giant magnetoresistance (GMR) effect, the coercivity, the coupling field, and the resistivity on film deposition at low-substrate temperatures (150 K) in spin valve multilayers of the general type: FeMn/Ni80Fe20/Co/Cu/Co/Ni80Fe20/glass. Low substrate temperatures tend to suppress both thermally activated surface diffusion of deposited atoms and interdiffusion at interfaces, which often occur during thin-film deposition at room temperature. We find significant increases in the GMR, significant reductions in the magnetic coupling across the Cu layer, slight reductions in the coercivity of the unpinned film, and slight reductions in the resistivity depending on which parts of the multilayer are deposited at low temperature. When the entire film is deposited at 150 K we obtain a GMR of 8.8% at a coercivity of less than 0.5 mT (5 Oe).
Comparative evaluation of absorption coefficients of KCl:Eu2+ and CaF2:Eu2+ using a spectrophotometer and an integrating sphere
Authors: Sardar Dhiraj K. , Levy Louis B.
Published: July 2002

The absorption coefficients of two crystalline solid-state materials, KCl:Eu2+ and CaF2:Eu2+, are measured by the conventional method using a spectrophotometer. The Kubelka–Munk theory and diffusion approximation are also applied to determine the scattering and absorption coefficients of these samples from the measurements of diffuse transmission and reflection using an integrating sphere. The absorption coefficients obtained from these two different techniques are compared and their discrepancies are discussed in detail.
Magnetic properties of iron nanoparticles grown in a glass matrix
Authors: Roy S. , Roy B. , Chakravorty D.
Published: July 2002

Iron particles of diameters in the range 5.5–8.5 nm have been synthesized within a suitably chosen oxide glass by subjecting the latter to a 3Na+⇄Fe3+ exchange reaction followed by reduction treatment in hydrogen. Magnetic measurements have been carried out over the temperature range 20–300 K. The coercive force increases as the iron particle size is decreased. The maximum value of coercive force corresponding to 0 K (Hc0)∼548 Oe is obtained for a specimen having diameter of 6.5 nm. The magnetocrystalline anisotropy constant in the case of nanosized iron particles is estimated to be one order of magnitude higher than that of bulk iron.
Low-temperature photoluminescence of sulfur- and magnesium-doped InGaP epilayers grown by liquid-phase epitaxy
Authors: Jiang Gwo-Cherng
Published: July 2002

Sulfur- (n type) and magnesium- (p type) doped InGaP layers grown by liquid-phase epitaxy are investigated by low-temperature photoluminescence (PL) measurements in the energy range between 1.55 and 2.25 eV (800–550 nm). The PL spectrum of nominally undoped InGaP epilayer shows four different peaks. Besides a bound exciton recombination peak, three longitudinal optical-phonon replicas with one superimposed donor–acceptor emission are identified based upon their dependence of emission energies on temperature and excitation intensity. For heavily sulfur-doped epilayers, the transition peak from the conduction-band filling level shifts toward higher energy with increasing electron concentration. However, the near-band-edge emission peak shifts toward lower energy with increasing hole concentration due to band-gap shrinkage in magnesium-doped epilayers. A near-band-edge radiative emission mechanism is also proposed to explain the observed phenomena.
Poling temperature dependence of optical second-harmonic intensity of MgO–ZnO–TeO2 glasses
Authors: Tanaka Katsuhisa , Narazaki Aiko , Hirao Kazuyuki , Soga Naohiro
Published: July 2002

Poling temperature variation of optical second-harmonic intensity induced by electrical poling has been examined for 30ZnO⋅70TeO2, 5MgO⋅25ZnO⋅70TeO2, and 10MgO⋅20ZnO⋅70TeO2 glasses. The Maker fringe pattern of these glasses indicates that the orientation of electric dipoles presumably due to TeO4 trigonal bipyramids and TeO3 trigonal pyramids is not restricted within the glass surface but extends into the inside of bulk glass. The poling temperature dependence of second-harmonic intensity manifests a maximum in all the glasses. There exists a tendency that the poling temperature which corresponds to the maximum of second-harmonic intensity is higher in the glass with higher glass transition temperature. This fact suggests that the orientation of tellurite structural units occurs as a result of the structural relaxation of tellurite network at around the glass transition temperature.
Photoluminescence and electrical properties of Sn-doped CuGaSe2 single crystals
Authors: Schön J. H. , Baumgartner F. P. , Arushanov E. , Riazi-Nejad H. , Kloc Ch. , Bucher E.
Published: July 2002

Hall-effect and photoluminescence measurements have been carried out on Sn-doped CuGaSe2 single crystals. The doping was performed either during chemical vapor transport growth with iodine or by a diffusion step at temperatures between 200 and 400 °C. Room temperature resistivity can be varied in the range between 10−2 and 106 Ω cm. Hall-effect data can be explained using a model containing two acceptor levels, one of which is very shallow, and a donor level. Due to doping the concentration of the first acceptor, whose activation energy is 59 meV, is decreased and the donor concentration is increased, but no n-type conductivity was observed. The photoluminescence spectra can be explained by an acceptor level of 50 meV, two donor levels of 80 and 110 meV, respectively, and a deep state of 400 meV. VCu, VSe, VSe complexes, and Sn on cation lattice sites are suggested as origins of these states.
Comparison between disaccommodation and ferromagnetic resonance measurements in polycrystalline yttrium–iron–garnet samples
Authors: Torres L. , Zazo M. , Iñiguez J. , de Francisco C. , Muñoz J. M. , Hernandez P.
Published: July 2002

Polycrystalline yttrium–iron–garnet (YIG) samples were sintered in air at temperatures ranging from 1350 to 1450 °C. Ferromagnetic resonance measurements have been accomplished at 11 GHz from 77 to 350 K. The different contributions to the linewidth have been analyzed. These results are compared with previous measurements of magnetic disaccommodation in the same samples. A qualitative relationship between both kind of measurements for polycrystalline YIG samples by means of an induced anisotropy formalism is provided.
Evidence of crystalline diamond in thin films prepared by laser ablation of hard fullerene-based carbon
Authors: Kozlov M. E. , Fons P. , Durand H.-A. , Nozaki K. , Tokumoto M. , Yase K. , Minami N.
Published: July 2002

Thin carbon films have been prepared by ArF excimer laser ablation of hard fullerene-based carbon in vacuum. The target material was obtained from pressure–temperature treatment of C60 fullerene. Micro-Raman, electron energy loss, and electron diffraction measurements of deposited films reveal distinct evidence of a small microcrystalline diamond fraction. This appears to be the observation of crystalline diamond produced by laser ablation of a nondiamond target.
Description of magnetic anisotropy and spin–reorientation transitions in NdFe12−xMox and NdFe12−xMoxN (x=1.0, 2.0, 3.0)
Authors: Guslienko K. Yu. , Sinnecker E. H. C. P. , Grössinger R.
Published: July 2002

NdFe12−xMox and NdFe12−xMoxN (x=1,2,3) were investigated by studying the anisotropy field and the temperature or field-induced spin–reorientation transitions. The temperature dependence of the magnetic anisotropy field was determined by means of the singular-point-detection technique for polycrystalline aligned samples. A theoretical explanation of the magnetic anisotropy and the magnetic phase transitions is given. The temperature dependencies of the rare-earth anisotropy constants were calculated using the single-ion model within linear theory. Fitting the experimental data, a set of crystal-field and exchange-field parameters for Nd3+ ions was deduced. A first-order spin–reorientation transition from uniaxial to conical phase and a type-2 first-order magnetization process in the perpendicular field are calculated for NdFe11Mo. A canted magnetic structure and a type-1 first-order magnetization process in the axial field are predicted for NdFe12−xMoxN. A change of rare-earth anisotropy after nitrogenation was explained by a bonding charge and a superposition model. The calculated temperature dependence of the anisotropy fields in NdFe12−xMoxN is in good agreement with the experimental data over a wide temperature range.
Effects of ambient gas pressure on (1−x) SrTiO3-xBaTiO3 films prepared by pulsed laser deposition
Authors: Tseng Tzu-Feng , Yeh Ming-Hua , Liu Kuo-Shung , Lin I-Nan
Published: July 2002

Ambient gas pressure in pulsed laser deposition process has been observed to significantly modify the lattice parameters of (Sr1−xBax)TiO3 thin films. The lattice parameters a0 of the films deposited under low ambient pressure regime (P≤0.01 mbar) were larger than those found on the films grown under high ambient pressure regime (P≥0.1 mbar), regardless of the thin film composition (i.e., x value), substrate materials (Pt/Si or Si), or ambient gas species (O2 or N2). It is proposed from these observations that the large lattice parameters a0 of the films grown under low-pressure environment result from higher concentration of vacancies, which, in turn, are induced by the bombardment of energetic species ejected by laser beams.
Local activation energy and shape factor of current-voltage curve as investigation tools for semiconductor barrier structures
Authors: Popescu Corneliu , Apetz Rolf , Vescan Lili
Published: July 2002

Modeling of the I(V,T) dependence in thin film semiconductor structures suggests that experimental data, on temperature and voltage dependent activation energy and shape factor of the current, give significant information on the recombination process within the structure. Grounds are thus laid for further investigation on quantum well effects within such structures.
Direct simulation Monte Carlo study of H/H2 and H/H2/CO mixtures for diamond chemical vapor deposition
Authors: Sinkovits Robert S. , DeVore C. Richard
Published: July 2002

One-dimensional direct simulation Monte Carlo calculations have been carried out on H/H2 and H/H2/CO mixtures under operating conditions typical of diffusion-dominated diamond chemical vapor deposition processes. Mechanisms have been included in the model for the adsorption and recombination of hydrogen atoms on the diamond surface and the dissociation of molecular hydrogen at the interior of the reactor. Hydrogen atom fluxes and recombinative and conductive heat fluxes to the diamond surface are calculated as a function of pressure, gas composition, hydrogen dissociation and surface reaction probabilities, reactor temperature, and distance between the activating source and substrate. The numerical calculations are shown to be in excellent agreement with analytical results in the limiting regimes of free-streaming particles at low pressures and continuum hydrodynamics at high pressures.
Magnetic interaction between iron-oxide clusters precipitated in silicate glasses
Authors: Hayashi Miyuki , Susa Masahiro , Noda Shinichi , Nagata Kazuhiro
Published: July 2002

Annealing of 20CaO⋅20SiO2⋅7Fe2O3⋅6FeO glasses at 973 K in vacuo produced clusters of a nonstoichiometric solid solution between Fe3O4 and γ-Fe2O3. The growth of clusters proceeded by diffusion of iron ions and the predominant diffusant was Fe3+ ions. The phase of the clusters approached γ-Fe2O3 as the annealing time increased. Mössbauer spectroscopy revealed that these clusters had magnetic moments and showed superparamagnetism above the blocking temperature. It has been shown that the dipole interaction between two nearest clusters is smaller by a factor of 1/7 than the magnetocrystalline anisotropy energy. This indicates that the direction of the magnetic moment is predominantly determined by the magnetocrystalline anisotropy below the blocking temperature.
Unambiguous determination of crystal-lattice strains in epitaxially grown SiGe/Si multilayers
Authors: Nikulin A. Yu. , Zaumseil P. , Petrashen’ P. V.
Published: July 2002

A new method for unambiguous reconstruction of crystal-lattice strains in epitaxially grown layers from high-resolution x-ray diffraction data is proposed. The technique uses x-ray diffracted intensity profiles collected for two different radiation wavelengths. We enhance the theory for the previously developed algorithm for model-independent determination of crystal-lattice strain profiles in single crystals with epitaxially grown top-surface layers. The method relies on the retrieval of the scattered x-ray wave phase from its intensity profile via a logarithmic Hilbert transform. This phase-retrieval technique is always associated with the problem of complex polynomial root finding. A practical procedure for the mapping of complex polynomial roots is proposed to distinguish true and virtual zeros. This allows the phase of the diffracted x-ray wave to be retrieved unambiguously. The method was applied to determine physical dimensions and concentration composition of a Si/Si1−xGex/Si alloy multilayer structure typical for SiGe heterobipolar transistor device.
Segregation and surface transport of impurities: New mechanisms affecting the surface morphology of laser treated metals
Authors: Balandin V. Yu. , Gernert U. , Nink T. , Bostanjoglo O.
Published: July 2002

Melts were produced in as-grown and cleaned gold films by focused nanosecond laser pulses, with fluences too low to cause a measurable ablation. Their dynamics and solidification were followed with time-resolving transmission electron microscopy and analyzed by computer simulations. The liquids perform an oscillating flow on the time scale of 100 ns and solidify with an impurity-dependent large-scale distribution of material superimposed by nonresonant ripples. This behavior could be reproduced by simulations if impurity-dependent thermocapillarity and a new mechanism of distribution of surface active impurities were incorporated into the usual equations of energy, momentum, and mass conservation, i.e., periodically varying segregation at the crystallization front and transport by a mobile surface layer. The liquid is inferred to consist effectively of a fast-moving (⩽60 m/s) surface layer that accumulates most surface active atoms and slow (⩽1 m/s) bulk material.
Torsional resonances in magnetoelastic bimorphs
Authors: Peuzin J. C. , Mackay K.
Published: July 2002

In this paper, we show that torsional as well as flexion modes can be excited rather naturally in a magnetoelastic bimorph. This behavior is in contrast with that of usual piezoelectric bimorphs in which only flexion modes can be excited. We describe experimental results on the torsional resonances of bimorphs composed of a glass substrate and a highly magnetostrictive thin film of (TbDy)(FeCo)2 and show how basic linear piezomagnetic constants may be extracted from the resonance data. Finally, we discuss some possible applications of torsional resonance in magnetoelastic bimorphs.
Density of magnetic poles in amorphous ferromagnetic wires: An example of weak chaos
Authors: Velázquez J. , García C. , Vázquez M. , Hernando A.
Published: July 2002

While a single piece of Fe-base amorphous wire is well known to exhibit square hysteresis loop, it is experimentally shown here that when placing a set of n quasi-identical amorphous Fe-base wire its hysteresis loop consists of n large Barkhausen jumps separated by (n−1) horizontal stretches. This kind of loop is interpreted as arising from the magnetic interaction among wires. Each wire is considered to have a particular density of magnetic poles at the ends creating an additional field at its neighborhood. Such a density arises from the closure domain structure at the ends which is slightly modified after each reversal. These magnetic interactions are analyzed and proven to induce a weak chaotic behavior for the switching field of each single wire.
Preferential site distribution of dilute Pt and Ta in CoCr-based films: An extended x-ray absorption fine structure study
Authors: Kemner K. M. , Harris V. G. , Elam W. T. , Feng Y. C. , Laughlin D. E. , Woicik J. C. , Lodder J. C.
Published: July 2002

Extended x-ray absorption fine structure (EXAFS) measurements of Co78Cr22, Co86Cr12Ta2, and Co86Cr12Pt2 films were made to investigate the local structure and chemistry around Ta and Pt atoms to determine their site distributions in these alloys. Comparisons between the measured data and data collected from experimental standards and calculated using theoretical EXAFS simulation codes indicate that the Ta atoms are preferentially distributed to the Cr-enriched regions of the CoCr media, and the Pt atoms have an effect on the local environment of the Co atoms. Both Ta and Pt introduce a large amount of local structural disorder to the local environments in which they reside. The presence of Ta atoms in the Cr-enriched regions further reduces the magnetization of these regions, which enhances the magnetic isolation of the Co regions from each other. This helps improve the noise characteristics of the films. The portion of the Pt atoms residing in the Co-enriched regions increases the magnetic anisotropy of the films, thereby increasing their coercivity.
Characteristics of stacking faults in AlN thin films
Authors: Dovidenko K. , Oktyabrsky S. , Narayan J.
Published: July 2002

We have investigated growth characteristics and atomic structure of defects in AlN thin films grown by the metalorganic chemical vapor deposition technique on the (101̄2) r plane of α-Al2O3. The AlN films were single crystal and exhibited the following epitaxial relationship: (112̄0)AlN∥(101̄2)sap with the in-plane alignment of [0001]AlN∥[1̄011]sap. Using high-resolution electron microscopy and multislice image simulation, the predominant defects in AlN thin films grown on the r plane of α-Al2O3 were found to be low-energy intrinsic stacking faults of type I1 lying in the basal plane. This fault, with a 1/6[202̄3] resultant displacement vector, can be formed by removing one (0002) plane and then shearing the remaining half-crystal by displacement of 1/3[101̄0]. The faults appear as a single face-centered-cubic stack ABC inserted into the normal …ABAB… hexagonal sequence. We discuss the possible role of these defects in optical properties of semiconductor devices.