bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical study of the quasistatic capacitance of metal–insulator–semiconductor structures in amorphous semiconductors
Authors: Kleider J. P. , Mencaraglia D.
Published: July 2002

We present the theoretical analysis of the quasistatic capacitance of metal–insulator–semiconductor structures for the case of amorphous semiconductors. The contribution of the bulk of the semiconductor is emphasized. We show that the semiconductor bulk capacitance is simply given by the ratio, taken at the insulator/semiconductor interface, of the space-charge density to the electric field. From the explicit expressions of these quantities as a function of the surface potential, a numerical calculation of the capacitance versus bias curves is performed. This is used to discuss the ability of the capacitance to reproduce the underlying structures of the density of states (DOS) in the gap. We derive also approximate analytical expressions of this capacitance in the case of exponentially distributed band-tail states. Moreover, we show that it is possible to reconstruct the DOS of the amorphous semiconductor from the bias dependence of the semiconductor capacitance using simple approximate analytical expressions. In particular, the square of the bulk semiconductor capacitance can lead in most cases to a reasonable DOS reconstruction. Using the capacitance versus bias curves derived from the numerical simulation, the accuracy of the reconstruction is then checked on DOS examples consisting of two exponential band tails and a Gaussian deep defect density, which can be representative of typical amorphous semiconductors such as hydrogenated amorphous silicon (a-Si:H). We emphasize the influence on the deep gap states reconstruction of the bulk Fermi-level position, whether it is located in a DOS minimum or not. We also discuss the influence of the characteristic temperature in the case of an exponential band tail which should be met in the accumulation bias regime. As this was done in the crystalline case to develop the metal–oxide–semiconductor technology, the method proposed can be used as a characterization tool to investigate metastability phenomena and to optimize technological processes related to amorphous semiconductor field-effect devices.
Material properties of low pressure chemical vapor deposited silicon nitride for modeling and calibrating the simulation of advanced isolation structures
Authors: Smeys Peter I. L. , Griffin Peter B. , Saraswat Krishna C.
Published: July 2002

The increasing cost and complexity of semiconductor process development has lead to the widespread use of multidimensional semiconductor process simulators. The success of a program like SUPREM−IV is primarily due to the fact that it is based on physical models, rather than empirical equations. This is in contrast to the first generation of process simulators, which calculated impurity profiles and oxide thickness in one dimension based on semiempirical approaches. SUPREM−IV incorporates two-dimensional coupled stress-dependent oxidation and impurity diffusion, which allows the accurate simulations of state-of-the-art integrated processes, provided that accurate model parameter sets are available. In this article we present an improved calibration methodology for simulation of advanced isolation technologies using SUPREM−IV, based on the experimental determination of the material properties of silicon nitride. The proposed strategy is applicable not only to SUPREM−IV but to any numerical simulator that uses the stress-dependent oxidation models to calculate oxide growth. In order to simulate experimental isolation boundary shapes, the oxidation models in SUPREM−IV must be calibrated. This requires a set of five fitting parameters, i.e., the material viscosities and activation volumes for stress-dependent diffusion, reaction rate, and critical stress. These parameters form a quintuplet but are not unique.

Multiplying the viscosity values and dividing the activation volumes by a constant will yield exactly the same isolation structure boundary shape. The calculated stresses in the substrate however do not remain constant when different quintuplets are used. This has serious implications since isolation structures require the stress levels in the silicon substrate to remain well below the yield stress of silicon. If a nonoptimal parameter set is used, incorrect designs will result. Based on the experimental extraction of the silicon nitride viscosity by measuring the relative film thickness shrinkage rate as a function of temperature, a scaled parameter set has been derived. SUPREM−IV simulations predict identical boundary shapes but the simulated stress levels are different from the values obtained using the default parameter set. In order to validate the stress simulations, a comparison with experimental stress values measured by micro-Raman spectroscopy has been carried out. It has been found that the quintuplet based on the experimental nitride viscosity values yields the best agreement with the experimental stress data, supporting the accuracy of the new model parameter set.
Effect of an InGaP cap layer on annealing-induced conductivity degradation in heavily Si-doped n+GaAs epilayers
Authors: Watanabe Kazuo , Hyuga Fumiaki , Sugitani Suehiro , Nittono Takumi
Published: July 2002

Results are presented on the use of metalorganic chemical-vapor deposition (CVD)-grown InGaP lattice matched to GaAs as part of a capping scheme to protect an n+GaAs epilayer during high-temperature annealing. Such an epilayer structure is important for heterostructure metal-semiconductor field-effect transistors (HMESFETs). It is shown that a surface InGaP layer is more effective than undoped GaAs in preventing conductivity degradation and Si diffusion for an n+GaAs epilayer during high-temperature annealing under plasma-enhanced CVD SiO2 capped condition. In addition, the mechanism of the protective effect is discussed. The results point to the potential applicability of the InGaP for protecting n+GaAs channel epilayers under the gates of HMESFETs during annealing after ion implantation for source/drain ohmic contact or device isolation.
Two-dimensional approach for solving the inverse problem for deep level transient spectroscopy
Authors: Batovski Dobri , Hardalov Chavdar
Published: July 2002

A general method for processing deep level transient spectroscopy (DLTS) data is presented. It is shown that the theoretical model is a two-dimensional Fredholm equation of the first kind with a four-dimensional integral kernel. The method is based on the numerical solving of the inverse ill-posed problem of the theoretical model via regularization algorithms. Starting from a two-dimensional C(T,t) surface one can obtain the corresponding C0(E,σ) surface, i.e., the continuous distribution equivalent to the deep levels concentrations for a given sample in both energy and cross-section coordinates.
Study of tensile deformation in shocked Z-cut, α-quartz using time resolved Raman spectroscopy
Authors: Gallivan S. M. , Gupta Y. M.
Published: July 2002

An experimental method has been developed to use time resolved Raman spectroscopy as a microscopic probe of tensile deformation in shocked crystals. Tension is produced in the sample interior by the interaction of rarefaction waves generated in plate impact, uniaxial strain experiments. Optical fibers are used to transmit visible light from a pulsed laser to the sample and to transmit the scattered light to a recording system with 50 ns time resolution. The strain-induced shift of the 464 cm1, A1 line of α-quartz was measured. Results are presented for longitudinal stresses ranging from 54 kbar in tension to 60 kbar in compression. For each experiment, the 464 cm−1 line exhibited a shift toward higher frequency in compression, followed by a return to the ambient position upon unloading, followed by a comparable shift toward lower frequency in tension. This latter shift correlates to a marked increase in the intertetrahedral (Si–O–Si) bond angle of quartz with tension. Comparison with earlier work and the analysis presented here suggests that there is also significant distortion of the SiO4 tetrahedra and a mechanism for this distortion is proposed.
Texture-induced asymmetric reactions in TiN/Al–Cu/TiN
Authors: Hong Q. Z. , Jeng S. P. , Havemann R. H. , Tsai H. L. , Liu H. Y.
Published: July 2002

Thermally induced reactions in TiN/Al–Cu/TiN have been investigated. It is observed that the amount of the reactions is different at the two interfaces between Al–Cu and TiN. While there is minimal reaction between Al–Cu and the TiN overlayer, the reaction between Al–Cu and the TiN underlayer increases the sheet resistance of Al–Cu by as much as 15%. It is further shown that the asymmetric reactions are most likely caused by the different degree of (111) texture of TiN grown on amorphous SiO2 and textured, polycrystalline Al–Cu.
Enhanced radiative decay in disordered GaAs/Al0.3Ga0.7As superlattices
Authors: Ranganathan Radha , Edmondson K.
Published: July 2002

Characteristics of the photoluminescence (PL) from disordered and ordered GaAs/Al0.3Ga0.7As superlattices are compared. The disordered superlattices (DSL) are nonperiodic and the ordered superlattices are periodic. The PL emission is much stronger in the DSLs by a factor that depends on the PL excitation wavelength and excitation power. These observations are interpreted in terms of an enhanced radiative decay rate in the DSLs brought about by the breakdown of translational symmetry in these systems.
Mechanism for resonance in the interaction of tunneling particles with modulation quanta
Authors: Hagmann Mark J.
Published: July 2002

Numerical simulations of quantum tunneling with time-dependent barriers show that there is a resonance, with a marked increase in the tunneling current. For square barriers the resonance occurs when the tunneling particles absorb modulation quanta and the length of the barrier is a multiple of one-half de Broglie wavelengths. The resonance has a similar mechanism with triangular barriers. However, the relationship is more complex because the absorption and emission of modulation quanta takes place throughout the full length of the barrier, whereas this exchange only occurs at the ends of a square barrier.
Correlation between anisotropy and oxygen or substituted cation in high-temperature superconductors
Authors: Tang Hongxing , Zhu Jinsheng , Li Xiao-Guang , Zhang Yuheng
Published: July 2002

We analyze the effect of oxygen content and cation substitution on the anisotropy of high-Tc superconductors. On the basis of the Josephson coupled block model, the relationship between the anisotropy parameter γ and the oxygen doped (δ, equivalent to doped oxygen) or ion substituted (x, substituted ion) in Y-based systems is found to be γ=γ0/(1−x/xc), which gives a good explanation of the anisotropy variations of the superconducting samples YBa2Cu3O7−δ , Y1−xPrxBa2Cu3O7−δ, YBa2Cu3−xFexO7−δ, and YBa2Cu3−xZnxO7−δ; here xc is a fitting parameter. With the same phenomenological method, the x (or δ) dependence of γ of La2−xSrxCuO4−y can be described as γ=γ0/x. It can be seen that the coupling between superconducting layers is closely related to the doping states.
Microstructure and magnetic properties of CoCrPt/Cr films on ultrasmooth NiP/AlMg substrates
Authors: Tang Li , Laughlin David E. , Lambeth David N. , Doerner Mary F.
Published: July 2002

Investigation of the correlation between the microstructure and magnetic properties of Co68Cr20Pt12/Cr thin films which were sputter deposited under different conditions onto 95 mm ultrasmooth NiP/AlMg disk substrates (Ra∼2 Å) has been carried out. Grain morphology characteristics of the films and disk surface roughness were studied by transmission electron microscopy (TEM) and by atomic force microscopy. Tilted-specimen electron diffraction patterns were used to determine the crystallographic texture of the films. The low coercivity of the disks deposited at 100 °C preheated substrates is attributed to the randomly oriented grains of the CoCrPt/Cr layers. Enhancement of the coercivity of the disks deposited on 220 °C preheated substrates is thought to be mainly due to the (112̄0)CoCrPt/(002)Cr crystallographic texture and uniformly distributed grains which are equiaxed in shape. The strength of the (112̄0)CoCrPt/(002)Cr texture can be modified by the Ar gas pressure during the deposition of the Cr underlayer.
Infrared absorption of Ge epitaxial films on a GaAs substrate
Authors: Dubey M. , Jones K. A. , Han W. Y. , West L. C. , Roberts C. W. , Dunkel J. P. , Peticolas L. , Bean J. C.
Published: July 2002

Germanium films were deposited on GaAs (100) substrates with or without an epiready surface oxide at temperatures between room temperature (RT) and 500 °C using an ultrahigh-vacuum e-beam deposition system. The film at 100 °C on a substrate with a surface oxide had a flat absorption curve over the wave-number range investigated, 500–4000 cm−1, with an absorption of less than 10/cm at 1000 cm−1 (10 μm wavelength). Films deposited at RT and 50 °C on substrates with a surface oxide had comparable low absorption, but they contained an absorption peak at 830 cm−1 associated with the Ge—O bonds. Although all three films were amorphous, the films deposited at the lower temperatures were more porous. This enabled oxygen to percolate in from the atmosphere to form the Ge—O bonds. The films deposited at 150 °C and above on substrates with a surface oxide and at 100 °C with the surface oxide removed thermally in situ prior to deposition the Ge films, and the single crystal films deposited at 400 and 500 °C on oxide-free substrates, had strong absorption in the vicinity of the Ge/GaAs interface with the characteristic of two-dimensional free-carrier absorption.
Giant magneto-impedance effects in Metglas 2705M
Authors: Sommer R. L. , Chien C. L.
Published: July 2002

Giant magneto-impedance (GMI) results for Metglas 2705M have been studied in two measuring geometries in several field annealed samples. A rich variety of peak features in GMI, all within a small field range, have been observed. The various features in the GMI are discussed in terms of magnetic susceptibility and microstructural properties of the amorphous ribbon.
Effect of grain boundary ledge on the dislocation-free zone model of fracture: Transgranular microcrack nucleated from a grain boundary ledge
Authors: Shiue Sham-Tsong
Published: July 2002

The effect of grain boundary ledge on the dislocation-free zone model of fracture is investigated in the case of a transgranular microcrack nucleated from a grain boundary ledge. The dislocation distribution functions to simulate the crack and plastic zone, the numbers of dislocations in the crack and plastic zone, the stress field, and the stress intensity factor at the crack tip (or the energy barrier for the dislocation emission from the crack tip) are obtained. If the Burgers vector of dislocations comprising the grain boundary ledge has the same sign as that of plastic zone dislocations, the dislocation distributions to simulate the plastic zone, the number of dislocations in the plastic zone, the stress field in the dislocation-free zone, and the stress intensity factor at the crack tip increase with increasing number of grain boundary ledge dislocations, but increase with decreasing grain size. Both sides of the grain boundary ledge dislocations have different effects on the dislocation-free zone size, plastic zone size, and the applied stress to accumulate the plastic zone dislocations. The stress intensity factor at the crack tip increases with increasing dislocation-free zone size. When there is no dislocation-free zone in front of the crack tip, the stress intensity factor is zero regardless of whether the grain boundary ledge dislocations exist.
Magnetic and thermodynamic properties of Sr2LaFe3O9
Authors: Wang J. T. , Lin C. L. , Mihalisin T.
Published: July 2002

Measurements of the magnetization, specific heat, and 57Fe Mössbauer spectrum are presented for Sr2LaFe3O9. The temperature dependence of the specific heat and magnetization indicates that Sr2LaFe3O9 undergoes an antiferromagnetic transition at TN=203 K. The small entropy removal ΔS and small effective paramagnetic moment μeff suggest an itinerant character for the Fe moment in this compound. In low applied fields, the zero field cooled (ZFC) and field cooled (FC) magnetization below TN exhibit a hysteretic behavior indicating the existence of some ferromagnetic correlation. This behavior is suppressed by high applied fields. The 57Fe Mössbauer spectrum measured at 4.2 K for Sr2LaFe3O9 indicates two superimposed hyperfine fields of 260 and 450 kOe with area ratios of 1/3 and 2/3, respectively, consistent with previous measurements.
Magnetic imaging in the presence of external fields: Technique and applications (invited)
Authors: Gomez Romel D. , Burke Edward R. , Mayergoyz Isaak D.
Published: July 2002

Magnetic force microscopy (MFM) in the presence of an external magnetic field has been developed. This has led to further understanding of image formation in MFM as well as new insights concerning the interaction of magnetic recording media with an external field. Our results confirm that, at low applied fields, image formation results from the interaction of the component by the local surface field along the direction of the probe’s magnetization. By reorienting the probe’s magnetization by an appropriate application of an external field, it is possible to selectively image specific components of the local field. At higher applied fields, the probe becomes saturated and the changes in the images may be attributed to magnetization reversal of the sample. We have observed the transformations that occur at various stages of the dc erasure of thin-film recording media. This technique has also been applied to conventional magneto-optical media to study domain collapse caused by increasing temperature with an external bias field. The methods, results, and their analysis are presented.
Optical collimation and compression of a thermal atomic beam
Authors: Tsao C.-C. , Wang Y. , Weiner J. , Bagnato V. S.
Published: July 2002

We have performed an experiment to optically cool and compress a thermal beam of sodium atoms by employing a two-dimensional version of a magneto-optical trap. The beam compressor employs a tapered transverse magnetic field gradient formed by four pairs of permanent magnets. We measure the efficiency of collimation and compression as function of longitudinal velocity group.
Electric field effect on the diffusion modified AlGaAs/GaAs single quantum well
Authors: Panda Sudhira , Panda B. K. , Fung S. , Beling C. D.
Published: July 2002

The electron subband energies and wave functions in an interdiffusion-induced AlxGa1−xAs/GaAs/AlxGa1−xAs single quantum well are calculated in the presence of the dc electric field using the finite difference method. The mean lifetimes are obtained from the time-dependent probability of tunneling of the wave packet out of the well by the applied electric field. The effect of the applied electric field on the subband energies in the well is the same as in the as-grown square quantum well when the interdiffusion length is below 20 Å . In the well with higher diffusion length the barrier height reduces so that the wave function tunnels out of the well. The linear and nonlinear intersubband absorption coefficients and the change in the real part of the index of refraction are calculated with the applied electric field at 100 kV/cm and without the field in both the as-grown square well and the diffusion modified well with the interdiffusion length at 20 Å.
Simulation of a surface-reflection neutral stream source
Authors: Nichols Christopher A. , Manos Dennis M.
Published: July 2002

We have developed a computational model to optimize the design of a surface reflection neutralization source of hyperthermal neutrals for charge-free processing. For the deployment of this technique to production (≥8 in. wafers) processing, a system design study has been completed. A Monte Carlo model is used to determine the energy and angular distributions of reflected hyperthermal neutrals at the surface of a wafer, as well as flux uniformity. A simple form for the plasma profile is chosen to allow simulation of various profiles reported in the literature. Neutrals are launched from the reflector consistent with the relative plasma density at each position on the reflector with angular and energy distributions consistent with experimental observations. These neutrals are then followed through interactions with thermal background atoms and the plasma. Charge exchange, ionization, and elastic scattering processes are considered for argon as the main feedstock gas. The results show the trade off between a high density plasma for substantial wafer neutral flux and losses of the neutral stream due to ionization and charge exchange in the plasma stream.
Efficiency and thermal stability of Pt gettering in crystalline Si
Authors: Cacciato A. , Camalleri C. M. , Franco G. , Raineri V. , Coffa S.
Published: July 2002

We have investigated the efficiency and the thermal stability of Pt gettering at different sites in crystalline Si. In particular, we compared the gettering performances of heavily n-type doped regions formed by P diffusion, cavities formed after high-temperature annealings of He implanted Si, and damage induced by ion implantation of B, C, or Si. These sites were introduced on one side of wafers containing a uniform Pt concentration in the range 1×1013–5×1014 atoms/cm3. The uniform concentration of Pt was attained by means of Pt implantation followed by a high-temperature thermal process. The gettering efficiency of the different sites was monitored during thermal processes at 700 °C for times ranging from 1 to 48 h. Thermal stability of gettering was investigated with a subsequent thermal process in the temperature range 750–900 °C during which part of the gettered Pt is released in the bulk of the wafer. The kinetics of Pt gettering at the different sites is found to be similar since it is fully dominated by the kick-out diffusion mechanism of the metal impurity. The thermal stability is instead site-dependent and can be described in terms of an effective binding enthalpy of 1.9, 2.6, and 3.0 eV between Pt atoms and cavities, P-doped region, and ion-implantation damage, respectively. The physical meaning of the binding enthalpy is investigated and discussed.
Chemical interaction of Na with cleaved (011) surfaces of CuInSe2
Authors: Klein A. , Löher T. , Pettenkofer C. , Jaegermann W.
Published: July 2002

To study the beneficial effect of sodium-containing substrate material on the photovoltaic properties of thin-film CuInSe2 solar cells the chemical interaction of Na with CuInSe2 has been investigated by synchrotron excited photoelectron spectroscopy. A clean CuInSe2 (011) surface was prepared by cleaving an oriented single crystal in UHV. The cleaved surface exhibits an electron affinity of χ≊4.6 eV. The Se 3d level shows a surface core level shift of −0.4 eV. Na was sequentially deposited in UHV in small steps from a commercial dispenser source. Initially ionized Na adsorbs on the surface leading to a shift of the surface Fermi level by 0.3 eV closer to the conduction band. Removal of Cu from the surface is observed. For higher Na deposition a chemical reaction of Na with the CuInSe2 surface occurs leading to the formation of metallic indium and Na2Se.
Growth mechanism of YMnO3 film as a new candidate for nonvolatile memory devices
Authors: Fujimura Norifumi , Azuma Shu-ichiro , Aoki Nobuaki , Yoshimura Takeshi , Ito Taichiro
Published: July 2002

We have proposed ReMnO3 (Re: rare earth) thin films for nonvolatile memory devices. We examine the growth mechanism of YMnO3 films on (0001)ZnO:Al/(0001) sapphire substrate using rf magnetron sputtering and pulsed laser deposition methods with oxide compound target. We have succeeded in obtaining (0001) epitaxial YMnO3 films on (111) MgO and (0001)ZnO:Al/(0001) sapphire substrate, and polycrystalline films on (111)Pt/(111)MgO. For an optimal structure, the film needed much less oxygen from the gas phase compared to other oxide films. The composition (Y/Mn ratio) of the YMnO3 films changed drastically by varying the partial oxygen pressure in the sputtering gas. In addition the Y/Mn ratio slinfled with sputter time due to target surface modification, probably caused by Y segregation. An extremely small amount of oxygen is required to form the YMnO3 crystal. This was confirmed by pulsed laser deposition experiments.
Investigation of semiconducting YBaCuO thin films: A new room temperature bolometer
Authors: Shan P. C. , Çelik-Butler Z. , Butler D. P. , Jahanzeb A. , Travers C. M. , Kula W. , Sobolewski Roman
Published: July 2002

We explore the application of the semiconducting phases of YBaCuO thin films as a bolometer for uncooled infrared detection. For this study, four different structures were built with different types of buffer layers: YBaCuO on a Si substrate with and without a MgO buffer layer, and on an oxidized Si substrate with and without a MgO buffer layer. These films were all amorphous without a detectable long range order. For comparison, crystalline tetragonal YBa2Cu3O6.5 and YBa2Cu3O6.3 thin films on a LaAlO3 substrate were included into the study. All six films exhibited semiconducting resistance versus temperature characteristics. The bolometer figures of merit, responsivity, and detectivity were calculated from the measured temperature coefficient of resistance (TCR) and the inherent noise characteristics of the temperature sensing element. The room temperature TCRs for all four amorphous films were greater than 2.5% K−1. The highest TCR of 4.02% K−1 was observed on the amorphous YBaCuO thin film deposited on MgO/Si without a SiO2 layer. The TCR of the tetragonal films, on the other hand, remained 2% K−1 or less in the same temperature range. Noise measurements performed in the 1–100 Hz frequency range revealed a quadratic dependence on the bias current as would be expected from ohmic electrical characteristics. The Johnson and 1/f regions were clearly identified in the noise spectrum. From TCR and noise measurements, we estimated the amorphous semiconducting YBaCuO bolometers would have a responsivity as high as 3.8×105 V/W and a detectivity as high as 1.6×109 cm Hz1/2/W for 1 μA bias current and frame frequency of 30 Hz if integrated with a typical air-gap thermal isolation structure.
Er–Yb codoped CaF2 thin films grown by molecular beam epitaxy
Authors: Daran E. , Legros R. , Pernas P. , Fontaine C.
Published: July 2002

Yb:Er: codoped CaF2 monocrystalline films have been grown by molecular beam epitaxy (MBE) using YbF3, ErF3, and CaF2 evaporation on CaF2 substrates. Luminescence and excitation of luminescence at 25 K are measured in order to investigate the role of Yb3+ codoping and the effect of the growth conditions during the MBE process on the incorporation of active rare-earth species in CaF2. It is found, from a comparison with earlier work on singly doped thin films, that the energies of the levels of Er3+ ions are not modified by the double doping, whereas mixed complex centers are formed. Growth conditions are found to be important controlling factors for the incorporation of Yb3+ as a sensitizer, and, consequently, for the transfer efficiency. From excitation and absorption spectra it is shown that the lowest component of the Er:4I11/2 manifold has an energy higher than that of Yb:2F5/2 and the consequences are discussed.
Stoichiometry-dependent deep levels in p-type InP
Authors: Nishizawa Jun-ichi , Kim Kiyoon , Oyama Yutaka , Suto Ken
Published: July 2002

Photocapacitance measurement is applied to investigate the stoichiometry-dependent deep levels in p-type InP crystals doped with Zn prepared by 4 h annealing at 700 °C under controlled phosphorus vapor pressure. Photocapacitance results reveal three dominant deep levels. A dominant deep level at 1.05 eV above the valence band is detected commonly before and after annealing, and the change of level densities is shown as a function of the phosphorus vapor pressure. Another two deep levels are also detected after annealing at 0.74 eV above the valence band and at 0.51 eV below the conduction band. In view of the deviation from the stoichiometric composition of InP, possible origins of these levels and their optical transition mechanism are discussed.
High resolution x-ray diffraction studies of short-period CdTe/MnTe superlattices
Authors: de Naurois M. , Stangl J. , Faschinger W. , Bauer G. , Ferriera S.
Published: July 2002

We have investigated the elastic properties of epitaxial MnTe layers using triple axis high resolution x-ray diffraction and reciprocal space mapping. A series CdTe/MnTe superlattices (SLs) grown by molecular beam epitaxy and nearly strain compensated, were deposited on [001] Cd1−xZnxTe substrates. In order to obtain the MnTe content of these SLs without an a priori knowledge of the elastic properties of cubic MnTe, annealing experiments were performed to interdiffuse the individual layers into a mixed Cd1−xMnx Te alloy layer. For a precise analysis of the data, it was found to be important to determine the in-plane strain of the superlattice layers using reciprocal space maps around symmetric and asymmetric reciprocal lattice points. The value for the Poisson ratio of zinc-blende MnTe was determined to be ν=C11/2C12=0.77±0.15.
Monte Carlo study of the magnetic properties of Fe-rich Al–Fe disordered alloys
Authors: Restrepo J. , González J. M. , Pérez Alcázar G. A.
Published: July 2002

We present a simulational study of the magnetic properties of disordered Fe-rich Al–Fe alloys. Our study has been developed in the framework of a simple site-diluted Ising model with nearest-neighbor interactions and by using a Monte Carlo algorithm. From our results, it is concluded that, in agreement with previous experimental data, disordered Al–Fe alloys exhibit ferromagnetic behavior up to higher Al concentrations than the ordered ones.
Strong uniaxial magnetic anisotropy of nanostripes obtained by cutting thin epitaxial Fe layer using the atomic saw method
Authors: Ressier L. , Schuhl A. , Nguyen Van Dau F. , Postava K. , Goiran M. , Peyrade J. P. , Fert A. R.
Published: July 2002

We have applied the “atomic saw” method developed on semiconductor heterostructures to cut thin epitaxial Fe films deposited on (001) MgO substrate into Fe nanostripes. This method is based on dislocation slipping. We have controlled the slip along the (110) MgO planes and obtained Fe stripes along the [110] direction. We present the magnetic study of 2- and 5-nm-thick Fe films which have been cut by this method, with a deformation up to 8%. The surface of the deformed film, studied by atomic force microscopy, is characterized by regular steps, a few nm high, and from 50 nm to 2 μm wide, depending on the slipping plane density. Strong uniaxial magnetic anisotropy has been observed by magneto-optical measurements. Surprisingly, the easy magnetic axis is perpendicular to the nanostripes. Various possible mechanisms are discussed. However, it results probably in the relaxation of the elastic strain field at the Fe/MgO interface.
Magnetic force microscopy of Terfenol-D fracture surfaces
Authors: Lord D. G. , Holden A. P. , Grundy P. J.
Published: July 2002

Magnetic field gradient images are presented from the domain structure observed on {111}, {110}, and {112} fracture surfaces of float-zoned Terfenol-D (Tb0.3Dy0.7Fe1.95) using silicon cantilevers coated with CoCr tips. The influence of both dendrite boundaries and growth twin boundaries on both the symmetries and spacings of the image features is clearly revealed. The effects of magnetic fields, applied in the specimen plane, are also presented.
Effect of higher order magnetostatic forward volume wave modes on Bragg diffraction of laser light in a layered yttrium iron garnet film geometry
Authors: Peng Liang-Ping , Parekh J. P. , Tuan H. S.
Published: July 2002

The present article reports a theoretical study of the TM0⇥TE0 mode conversion of laser light through Bragg diffraction by higher order magnetostatic forward volume waves (MSFVWs) in a layered yttrium iron garnet (YIG) film geometry. It is found that this mode conversion can be significant, thereby somewhat mitigating the previously reported advantage of YIG film layering, i.e., layering affords a significant improvement in the bandwidth for magneto-optic coupling. Computations of the level of magneto-optic (MO) coupling caused by higher order MSFVWs excited by a microstrip transducer in a double YIG film layered structure are presented. The use of a triple YIG film layered geometry with lifted transducers for suppressing the unwanted effect of higher order MSFVW modes on the MO coupling is discussed.
Mossbauer investigation of some layered Fe(II)Cl compounds
Authors: Mostafa M. F. , Atallah A. S. , Emrick R.
Published: July 2002

Mossbauer effect studies (ME) for members of the alkylene-diammonium series, (CH2)n(NH3)2Fe(II)Cl4, where n=3, 4, 5, and 6 are presented. At 78 K the ME spectra reveal similar general features showing an 8 line well split hyperfine spectra; the effective magnetic field is in the range 18.5–20 T. Fitting the magnetization curves to the theoretical models showed that all compounds are best fitted to a 2d Ising system with β values in the range of 0.124–0.151, D=1.05–1.12, and TN=102.2–105.2 K for n=3 to n=6, respectively. Structural phase transitions have been found for the n=3 and 6 compounds at Ts=230 and 242 K, respectively. Electric permittivity of two members of the series is presented and related to the ME results.
Thermal anomalies and the insulator–metal (I–M) transition in Mn3+/Mn4+ perovskites
Authors: Hejtmánek J. , Jirák Z. , Krupička S. , Martin C. , Simon Ch. , Maignan A. , Raveau B. , Grivei E. , Issi J. P.
Published: July 2002

We report a comparative study of two ferromagnets—Pr0.7Sr0.1Ca0.2MnO3 and Pr0.85K0.15MnO3— which exhibit the same formal Mn valency, similar Tc and saturated moments at 5 K. While for former sample the magnetic transition is accompanied by the insulator–metal transition at T∼Tc , the insulator–metal (I–M) transition is not observed in the latter one despite the expectation based on the Goldschmidt’s tolerance factor. The first order character of the I–M transition in Pr0.7Sr0.1Ca0.2MnO3 is demonstrated by a discontinuity of the unit cell volume, step of the specific heat and huge enhancement of the thermal conductivity. The lack of these anomalies in Pr0.85K0.15MnO3 suggests that the properties of perovskite manganites are critically influenced by both a strong phonon–electron coupling arising from a Jahn–Teller splitting of eg orbitals of the Mn3+ ion and the local lattice effects due to size mismatch of the large cations.
New high performance magneto-optic media: Tb/Bi/FeCo and Tb/Pb/FeCo superlattices (invited)
Authors: Victora R. H. , Brucker C. F. , Hatwar T. K. , Hurst J. E. , Uryson B. , Karns D.
Published: July 2002

Tb/Bi/FeCo and Tb/Pb/FeCo superlattices are demonstrated to offer Kerr rotation and figure of merit (reflectivity times Kerr rotation) substantially exceeding that offered by conventional TbFeCo recording materials, particularly at blue wavelengths. Superlattices such as 4.4 Å Tb/2.0 Å Bi/5.0 Å Fe0.6Co0.4 exhibit squarenesses suitable for magneto-optical recording and figure of merits of 0.20, 0.18, and 0.14 at wavelengths of 780, 650, and 430 nm, respectively. Dynamic testing with 780 and 490 nm light demonstrates that the high figures of merit translate to carriers several dB above those produced by TbFeCo alloys. Furthermore, very high carrier-to-noise ratios such as 54 dB at a mark length of 0.75 μm (4 MHz) and 60 dB at long mark lengths (1 MHz) are obtained using 490 nm light and a bandwidth of 30 kHz.
Kerr effect study of the onset of magnetization in Fe films on GaAs(001)-2×4
Authors: Kneedler E. M. , Jonker B. T.
Published: July 2002

We have studied the magnetic behavior of epitaxial bcc Fe(001) films grown on molecular beam epitaxy-prepared GaAs(001)-2×4 substrates, with film thicknesses ranging up to ∼16 monolayers (ML) (∼23 Å). We present measurements of the thickness-dependent evolution of the magnetic properties of the Fe films as determined by in situ magneto-optical Kerr effect. Particular attention is given to the substrate-induced in-plane uniaxial magnetic anisotropy. We find that the onset of room-temperature ferromagnetism occurs between 4 and 8 ML, and that the anisotropy is dominated by a uniaxial in-plane component such that the two 〈110〉 axes are inequivalent for all coverages studied. Although the initial nucleation and growth results in 2D islands elongated along [1̄10], the in plane easy axis is perpendicular to this direction along [110], indicating that shape anisotropy does not play a significant role.
Raman scattering of InSb quantum dots grown on InP substrates
Authors: Armelles G. , Utzmeier T. , Postigo P. A. , Briones F. , Ferrer J. C. , Peiró P. , Cornet A.
Published: July 2002

In this paper we present the Raman scattering of self-assembled InSb dots grown on (001) oriented InP substrates. The samples were grown by pulsed molecular beam epitaxy mode. Two types of samples have been investigated. In one type the InSb dots were capped with 200 monolayers of InP; in the other type no capping was deposited after the InSb dot formation. We observe two peaks in the Raman spectra of the uncapped dot, while only one peak is observed in the Raman spectra of the capped dots. In the case of the uncapped dots the peaks are attributed to LO-like and TO-like vibration of completely relaxed InSb dots, in agreement with high resolution transmission electron microscopy photographs. The Raman spectra of the capped dot suggest a different strain state in the dot due to the capping layer.
Thermally assisted macroscopic quantum resonance on a single-crystal of Mn12-acetate
Authors: Lionti F. , Thomas L. , Ballou R. , Barbara B. , Sulpice A. , Sessoli R. , Gatteschi D.
Published: July 2002

Magnetization measurements have been performed on a single monocrystal of the molecule Mn12-acetate (Mn12Ac). Steps were observed in the hysteresis loop for values of the applied field at which level crossings of the collective spin states of each manganese clusters take place. At these fields, the magnetization relaxes at short time scales, being otherwise essentially blocked. This novel behavior is interpreted in terms of resonant quantum tunneling of the magnetization from thermally activated energy levels. Hysteresis loop measurements performed for different field orientations and alternating current (ac) susceptibility experiments confirm this picture.
Heterostructures in GaInP grown using a change in V/III ratio
Authors: Chun Y. S. , Murata H. , Lee S. H. , Ho I. H. , Hsu T. C. , Stringfellow G. B. , Inglefield C. E. , DeLong M. C. , Taylor P. C. , Kim J. H. , Seong T.-Y.
Published: July 2002

A natural monolayer {111} superlattice (the CuPt ordered structure) is formed spontaneously during organometallic vapor phase epitaxial (OMVPE) growth of Ga0.52In0.48P. The extent of this ordering process is found to be a strong function of the input partial pressure of the phosphorus precursor during growth due to the effect of this parameter on the surface reconstruction and step structure. Thus, heterostructures can be produced by simply changing the flow rate of the P precursor during growth. It is found, by examination of transmission electron microscope (TEM) and atomic force microscope (AFM) images, and the photoluminescence (PL) and PL excitation (PLE) spectra, that order/disorder (O/D) (really less ordered on more ordered) heterostructures formed by decreasing the partial pressure of the P precursor during the OMVPE growth cycle at a temperature of 620 °C are graded over several thousands of Å when PH3 is the precursor. The ordered structure from the lower layer persists into the upper layer. Similarly, D/O structures produced by increasing the PH3 flow rate yield PL spectra also indicative of a graded composition at the heterostructure. The grading is not reduced by a 1 h interruption in the growth cycle at the interface. Similar heterostructures produced at 670 °C using tertiarybutylphosphine (TBP) as the P precursor show a totally different behavior. Abrupt D/O and O/D heterostructures can be produced by abruptly changing the TBP flow rate during the growth cycle. PL and PLE studies show distinct peaks closely corresponding to those observed for the corresponding single layers. TEM dark field images also indicate that the interfaces in both for D/O and O/D heterostructures are abrupt. The cause of the difference in behavior for TBP and PH3 is not clear. It may be related to the difference in temperature.
Thermal expansion and microwave surface reactance of copper from the normal to anomalous skin effect region
Authors: Inagaki Shigemi , Ezura Eizi , Liu Jian-Fei , Nakanishi Hiroshi
Published: July 2002

The microwave surface reactance of copper was measured over the temperature range from 300 to 14 K using the TE011 mode of a cylindrical cavity. The result was that with decreasing temperature the ratio of the reactive-to-resistive component remained at around 1 from 300 to 75 K, and increased to 1.32 at 14 K, in contrast to the theoretical extreme anomalous limit, equal to or higher than ∛. The discrepancy between the measured and theoretical values may be attributed to the quality of the material and the surface finishing. In this experiment an accurate measurement of the resonant frequency is important. Associated with the frequency, we discuss two thermal-expansion measurement techniques: cavity dilatometry and capacitance dilatometry. Further, the usefulness of the present data for studying high-Tc films will be mentioned.
Sputtering power dependence of the magnetic properties of CoCrPt
Authors: Yumoto Seiji
Published: July 2002

The magnetic properties of CoCrPt films produced by sputtering at power levels of 0.1, 0.3, 0.5, and 1 kW are studied with special emphasis placed on the structural properties we previously obtained using several x-ray experimental methods [J. Appl. Phys. 77, 2321 (1995)]. In measurements on the saturated magnetic state, the saturation magnetization of the 0.1 kW film was found to be about 20% lower than those of the other films. This is ascribed to the segregated structure of this film (described in the above reference). The out-of-plane magnetic anisotropy decreases as the sputtering power decreases. Its magnitude is related to the hcp(002) intensity and its orientation is slightly tilted from the normal direction. The in-plane magnetic anisotropy, on the other hand, increases sharply as the sputtering power decreases to levels below 0.5 kW. This increase is a result of the small grain structure produced by the sputtering at very low power levels. In the unsaturated magnetic state, three magnetic properties were measured: field-induced magnetic anisotropy and two types of magnetic torque loss, that is, intrinsic torque loss and field-induced torque loss related to field-induced magnetic anisotropy. The field-induced magnetic anisotropy is a consequence of the quenched magnetic domain structure produced by applying a strong external magnetic field. This anisotropy for films sputtered at 0.3, 0.5, and 1 kW is unusual in that the magnetization switching field is larger than the anisotropy field. This is ascribed to the intrinsic spatial and amplitude dispersion of the magnetization. Taking the structural and magnetic properties of CoCrPt into consideration made it clear that wall displacement rather than rotation magnetization is the major factor responsible for both types of torque loss. The rotation magnetization also made a significant contribution to intrinsic torque loss, but a limited contribution to field-induced torque loss.
Magnetic properties of melt-spun Sm2+δFe15Ga2C2 permanent magnets
Authors: van Lier J. , Seeger M. , Kronmüller H.
Published: July 2002

The change in the magnetic properties of melt-spun Sm2+δFe15Ga2C2 permanent magnets with variation of the Sm content δ has been investigated in the range of −0.05⩽δ⩽0.20. A drastic increase in the coercive field μ0HC from 1.5 to 2.2 T at room temperature has been observed for δ⩾0.1. This can be understood as an influence of the Sm-rich nonmagnetic intergranular phase, occurring due to the Sm excess. Room temperature values of the maximum energy density up to (BH)max=64.2 kJ/m3 (δ=0.03) can be obtained. The samples with higher Sm contents exhibit larger values of the maximum energy density at elevated temperatures (T⩾450 K). For δ=0.13, a value of (BH)max=31.4 kJ/m3 has been observed at 500 K. The microstructural parameters αK and Neff describing the influence of the nonideal microstructure on the coercive field in the framework of the nucleation model were determined from the temperature dependence of the coercive field.
Electrical characterization of subbands in the HgCdTe surface layer
Authors: Gui Y. S. , Zheng G. Z. , Chu J. H. , Guo S. L. , Zhang X. C. , Tang D. Y. , Cai Yi
Published: July 2002

The subband dispersion relations have been computed as a function of the surface electron concentration in the accumulation layers of n-Hg1−xCdxTe photoconductive detectors, while the mobility and concentration for all kinds of carriers in the subband are determined from Shubnikov-de Haas (SdH) oscillation measurements and quantitative mobility spectrum analysis (QMSA). The results show that the QMSA can provide accurate electric parameters for all kinds of carriers in the subband without considering the complex energy band in the semiconductors, while the SdH oscillation can only offer qualitative data because the analysis is based on parabolic energy band approximation.
Effect of substitution of La by alkaline earth metal on the thermoelectric properties and the phase stability of γ-La3S4
Authors: Katsuyama S. , Tanaka Y. , Hashimoto H. , Majima K. , Nagai H.
Published: July 2002

The Seebeck coefficient, electrical resistivity, and thermal conductivity of La3−xAxS4 with the Th3P4-type structure (the γ-phase) for A=Ca, Ba, and x=0–0.8 have been measured as a function of alkaline earth metal content and temperature to determine the optimum dopant concentration and doping agent by calculating the corresponding figure of merit (Z). With an increase of x, the Seebeck coefficient and electrical resistivity increase, while the thermal conductivity decreases. The decrease of thermal conductivity is ascribed to the decrease of the electron concentration and the increase of the phonon scattering accompanying the substitution for La by an alkaline earth metal. As a result, La2.2Ca0.8S4 has a maximum value of Z of 2.3×10−4 °C−1 at 700 °C. We also have examined the long term stability of γ-La3−xAxS4. The substitution for La by alkaline earth metal of La3S4 stabilized the Th3P4-type structure at high temperature.
Photostimulated luminescence of AgI clusters in zeolite-Y
Authors: Chen Wei , Wang Zhanguo , Lin Zhaojun , Lin Lanying , Fang Keming , Xu Yan , Su Mianzeng , Lin Jianhua
Published: July 2002

AgI clusters in zeolite-Y (AgI/Y) were prepared by Ag+ exchange followed by reaction with NaI in solution. The formation of the clusters was determined by transmission electron microscopy and Auger electron spectroscopy. The clusters were uniform and even in size, 1.0–2.0 nm. The fluorescence spectrum of the clusters consists of two emission bands, which are attributed to AgI and Ag clusters, respectively. Photostimulated luminescence (PSL) is observed by stimulation at 675 or at 840 nm. The PSL spectrum of AgI/Y is consistent with the emission spectrum of Ag clusters and thus the PSL is considered to be caused by the charge transfer or carrier migration from the zeolite framework or from the AgI clusters to the Ag clusters. The appearance of PSL indicates that these materials may find application as a medium for erasable optical memory.