bluuebunny/crossref_metadata_2025 huggingface dataset:
The National Institute of Standards and Technology Cold Neutron Research Facility and magnetic neutron scattering (invited)
Authors: Rhyne J. J. , Majkrzak C. F.
Published: July 2002

The National Institute of Standards and Technology has under development a major Cold Neutron Research Facility which, upon completion, will make available approximately 15 new neutron-scattering instruments located on neutron guides on the reactor cold source. This facility, which includes the National Science Foundation Center for High Resolution Neutron Scattering, will be operated as a user facility, which is open via a proposal system to all scientists. This paper briefly reviews the types of cold neutron instruments that have particular relevance to magnetic problems. A discussion is given of neutron scattering from magnetic systems with examples of problems appropriate for the enhanced energy and wave-vector resolution of cold-source instruments. Included is a review of new experimental results and techniques that will be available, including reflectometry and grazing-angle diffraction, as well as more conventional techniques such as triple-axis inelastic scattering, small-angle scattering, and time-of-flight spectroscopy.
Magnetic and structural properties of high-coercivity Pr2Fe14B:Pr cosputtered films
Authors: Aylesworth K. D. , Sellmyer D. J. , Hadjipanayis G. C.
Published: July 2002

The results of structural and magnetic measurements on a series of films produced by cosputtering Pr21Fe72B7 and Pr are reported. The materials were deposited serially, 10–200 Å at a time, onto 700 °C Ta substrates attached to a computer-controlled stepping motor. The structure of the resulting films was examined by large- and small-angle x-ray diffraction, scanning electron microscopy, and by microprobe analysis. Magnetic measurements were made at temperatures from 4.2 to 300 K, in fields up to 80 kOe in a vibrating sample magnetometer. The films appear to consist of 1-μm grains of Pr2Fe14B with their c axes oriented perpendicular to the film plane, surrounded by a Pr-rich phase. The maximum room-temperature coercivity discovered so far is almost 20 kOe, which is close to the values reported for bulk Pr2Fe14B magnets.
Finite-size effects in the magnetic hysteresis behavior of Nd-Fe films
Authors: Tsoukatos A. , Hadjipanayis G. C.
Published: July 2002

The magnetic hysteresis properties of Nd-Fe films have been examined in films with different composition and thickness. All the films show a similar behavior; the coercivity is rather small at room temperature but it increases rapidly upon cooling to cryogenic temperatures. At these temperatures the coercivity is found to increase initially with the film thickness and then saturate at higher thickness. The maximum value of coercivity is much lower than that of melt-spun ribbons with similar composition. The coercivity has been attributed to domain wall pinning by small regions having a short-range order embedded in a Nd-Fe amorphous matrix.
Thermal and magnetic properties of Bi2CuO4 (abstract)
Authors: Sapina F. , Sanchis M. J. , Ibañez R. , Beltrán-Porter D. , Carvajal J. Rodríguez , Rillo C. , Burriel R. , Lera F. , Navarro R.
Published: July 2002

Since the discovery of the high-Tc superconductors, there is a great interest in the magnetic properties of copper oxides due to the possibility of a magnetic origin of the pairing mechanism. With this perspective, we decide to reinvestigate the structure and the magnetic properties of Bi2CuO4, a compound we use successfully as precursor of the Bi-Sr-Ca-Cu high-Tc superconductors. A neutron powder diffraction experiment allowed us to resolve the ambiguity in the structure, and revealed the existence of a magnetic phase transition to a 3D antiferromagnetic ordered state below 50 K. The nuclear structure can be described as formed by stacks of CuO4 units in the c-axis direction, linked in the stacks and with units in other stacks by BiO2 chains, so each stack is connected with four stacks. The space group was confirmed to be P4/ncc. The magnetic space group is P4/n′cc. There is a ferromagnetic ordering of the magnetic moments on Cu atoms along the stacks, and an antiferromagnetic ordering between the stacks. We present an interpretation of the magnetic properties of this compound, at the light of our previous results, and a discussion of a calorimetric experiment.
Critical behavior in alloys with random magnetic anisotropy
Authors: Lee K. M. , O’Shea M. J.
Published: July 2002

We have studied the critical behavior in amorphous Tb65Co35. Scaling analyses were done over a number of reduced temperature (t=‖T−Tc‖/Tc) ranges to ascertain that the critical regime had been reached. The magnetization follows linear (ferromagnetic) scaling at high fields (1–55 kOe) and nonlinear (spin-glass) scaling at low fields (<1 kOe). The critical exponents for ferromagnetic scaling and for spin-glass scaling are not a function of reduced temperature range.
Simulation of induction machine operation using a step-by-step finite-element method
Authors: Vassent E. , Meunier G. , Foggia A. , Sabonnadiere J. C.
Published: July 2002

In order to model the operation of an induction machine when space harmonics are neglected, the magnetodynamic model with the equivalent ac magnetization plot can be used. But when we want to simulate an induction machine with an open isthmus, for instance, the space harmonics cannot be neglected and a step-by-step method is a solution to modeling its action. In this paper, we develop a means of modeling an induction machine with a nonlinear step-by-step method. The motion of the rotor is taken into account through the displacement of its mesh. The basis of the method is that after each step of the simulation we rebuild only the air gap portion of the mesh. Applied to an industrial four-pole squirrel cage induction machine with an open isthmus, this method provides accurate values of the torque on the whole range of velocity. We have compared the curves obtained by this method with those by the magnetodynamic model for many different types of induction machines. Our method shows the effects of space harmonics on torque more accurately. The curves of torque at different velocities give us a lot of information on effects of harmonics.
High-field EPR in TEA(TCNQ)2 (abstract)
Authors: Janssen P. , Mordijck A. , Kesters L.
Published: July 2002

Electron paramagnetic resonance plays an important role in the study of low-dimensional materials. However, different effects can have nearly equal g values. In that case, the corresponding resonance lines are hard to resolve. The problem can be overcome by the use of much higher frequencies and correspondingly higher fields. We have studied the transmission of far infrared radiation through a single-crystalline sample of TEA(TCNQ)2 as a function of temperature and applied magnetic field. The radiation, in the wavelength range 100–2600 μm, was obtained using an optically pumped FIR laser. The magnetic field, up to 14 T, was oriented along the crystallographic c axis of the sample. Several minima were observed in the transmission. The interpretation given by Flandrois et al.1 can be used to explain the general features. However, there is some additional structure around the EPR lines. This can probably be explained in terms of interference effects.
The calculation of spin-Hamiltonian parameters via the cluster approach: New results for some quasi-one-dimensional magnetic materials (abstract)
Authors: Kirk Martin L. , Hatfield William E.
Published: July 2002

The cluster approach to magnetic susceptibility (CAMS) has been used to determine the spin-Hamiltonian parameters for the quasi-one-dimensional next-nearest-neighbor chain compounds Cu(HzH)Cl3(J1=−4.84, J2=−5.66), Cu(amp)Cl2 (J1=−3.79, J2=−3.24), and Cu(Me3en)Br2 (J1=−3.45, J2=−3.06). We will explain the magnetic behavior of these compounds in terms of various structural parameters. Specifically, the discussion will focus on the possibility of predicting the magnitude and nature of the exchange coupling based on the geometry of the bridge, as well as the onset of phase transitions based on the extended structures.
Mössbauer and magnetic-susceptibility studies on MmNi4.15Fe0.85 and its hydride
Authors: Oliver F. W. , Hammond E. C. , Bang-Zheng L. , Meng-Zhao L. , Seehra M. S.
Published: July 2002

Results are reported on MmNi5−xFex (x=0.85) (Mm=mischmetal) and its hydride from magnetic susceptibility (χ), Mössbauer, and scanning-electron-microscopy studies. The magnitude of χ, the shape of the χ-vs-T curve (50–300 K), and the magnitude of Tc (≂200 K) are all close to the values reported for LaNi4Fe. The magnetic properties are significantly changed by the hydriding process. χ (at 100 Oe) above Tc is increased by 100%, whereas at 77 K, χ is lowered by 25%, although Tc is unaffected. The Mössbauer spectra above Tc yield a paramagnetic doublet (isomer shift −0.13±0.01 mm s−1); however, as the temperature decreases, the doublet disappears at 125 K. Hydriding causes only a very small change in the isomer shift.
On the local magnetic moments of transition-metal Mössbauer impurities in ferromagnetic rare earths
Authors: Leal C. E. , Troper A.
Published: July 2002

Using isomer shift and hyperfine data of transition-metal Mössbauer impurities 193Ir and 57Fe diluted in the ferromagnetic rare-earth hosts Gd, Tb, and Dy, the formation of local moments at these impurities based on a two-band (s-d) model in the framework of an extended Ruderman-Kittel-Kasuya-Yosida picture is theoretically discussed. The experimental data of Mössbauer isomer shifts and hyperfine fields at the nobel probe 197Au placed in Gd, Tb, and Dy are also briefly discussed, based on an extended Daniel–Friedel model. The results exhibit a good agreement with the available experimental measurements.
Investigations of microstructure of thin TbFeCo films by high-resolution electron microscopy (abstract)
Authors: Li Z. G. , Smith David J. , Marinero E. E.
Published: July 2002

High-resolution electron microscopy has been applied to the study of the microstructure of TbFeCo alloys. Recently, we reported on the presence of microcrystals (2.5–7.5 nm) in sputter-deposited TbFeCo alloys,1 but their possible role in influencing the magnetic properties of these alloys is not yet clear. We have conducted further studies on structures consisting of SiN(8.0 nm)/TbFeCo(20 nm)/SiN(12.5 nm)/Si. Observations were made both in top view and cross section using standard techniques such as bright- and dark-field diffraction contrast imaging, as well as high resolution. We have confirmed the presence of nanocrystals in our plan-view observations. In addition, we conducted annealing experiments (ex situ) and recorded changes in magnetic properties such as coercivity. We find after about 36 h annealing time at 200 °C that the crystals grow from ∼3 nm to about 20 nm. The Hc change was measured to be −35%, but it is noted that most of the change occurred within the first 100 s (−25%). We will conduct further measurements to investigate whether the nanocrystallites are related in any way to the magnetic anisotropy of these alloys.
The transition ‘‘back’’ from two to three dimensions
Authors: Stubi R. , Leslie-Pelecky D. L. , Cowen J. A.
Published: July 2002

The return from ‘‘quasi-two-dimensional’’ to three-dimensional behavior of the spin-glass (SG) CuMn(13.5%) is studied in multilayer samples using pure Cu as an interlayer material. We measure how the quasi-static spin-freezing temperature Tf increases as the interlayer thickness Wil is decreased from 30 nm (2D) to 1 nm (3D), keeping the SG layer constant at WSG=4 nm. Alternative interpretations of this behavior have been used in terms of a simple mean-field RKKY model, the phenomenological scaling theory, and the Fisher and Huse droplet model of SG.
Magnetism in random fractals
Authors: Perreau M. , Levy J. C. S.
Published: July 2002

The structural and magnetical properties of a class of random fractals constructed in the same way as the Cantor set and the Sierpinski carpet and gasket, but with a random choice of the conserved subsegments (or subsquares or subtriangles) conserved at each step of segmentation, are studied by means of the transfer matrix formalism. New percolation properties of these structures are shown. This process is generalized in any Euclidean space. In three dimensions, two percolation thresholds appear corresponding respectively to a percolation through the lattice from a face to the opposite face and from an edge to the opposite edge. The magnetic properties of the generalized random Cantor set are investigated. The calculation of the magnetization shows the same critical behavior as for a system of disconnected spins.
Noncollinear phase of TbDy alloys
Authors: Foster J. J. , Cullen J. R.
Published: July 2002

TbxDy1−x is probably the simplest example of a magnetic system with competing anisotropy. Tb and Dy are both low-temperature easy-plane ferromagnets with well-characterized anisotropy energies, such that Tb moments prefer the b axis in the hcp structure, while Dy moments prefer the a axis. It has been predicted, by a two-subnetwork approximation, that the low-temperature phase of the alloys with x between 0.86 and 0.76 exhibits a nonsymmetry direction of magnetization, a noncollinear spin structure, and 12th-order anisotropy. However, the two-subnetwork approximation is suspect when used to describe magnetic structure in alloys near phase boundaries, such as those between the ferromagnetic and the noncollinear phase. Using a probability distribution for site occupation, we have calculated the fluctuations of the spin orientation and the spin-spin correlation function as a function of composition in the noncollinear phase. The mean-square fluctuation in spin orientation is proportional to (xb−x)1/2, where xb is the critical concentration which separates the b axis ferromagnet from the noncollinear magnet. The average orientation also varies as (xb−x)1/2. Therefore, the simple two-subnetwork model is not valid near the phase boundaries. In fact, we find that the fluctuations from the average site occupation increase the range of stability of the noncollinear phase.
Antiferromagnetic states in CopMg1−pO (abstract)
Authors: Giebultowicz T. M. , Rhyne J. J. , Seehra M. S. , Feng Z. , Minor W.
Published: July 2002

CopMg1−pO offers an excellent prototypical example for the study of antiferromagnetism in diluted fcc lattices. The system retains the same crystallographic structure (NaCl type) over the entire 0≤p≤1 range. The Co2+ ions form a randomly diluted fcc spin lattice with predominantly next-nearest-neighbor antiferromagnetic (AF) exchange coupling. No significant changes in J are expected with magnetic dilution, since the lattice parameter changes only slightly (∼1%) between p=1 and p=0. The χ(p,T) data1 for the system reveal a distinct crossover effect at p≊0.45. A similar behavior of the χ(p,T) curve was observed in an isostructural system EupSr1−pTe, and was interpreted as an AF→SG (SG=spin glass) transition.2 Recently, we have reported low-T neutron-diffraction data3 from CopMg1−pO samples with various p, showing a breakdown of the type-II AF long-range order (LRO) in the system at p≊0.47. In this paper we present the results of measurements of the temperature dependence of magnetic peak intensities and widths which provide a further evidence for a sharp LRO-SRO (short-range order) phase boundary in the system. However, neutron-diffraction data alone cannot answer the question of whether the SRO phase is a SG state. In order to obtain a closer understanding of the LRO-SRO transition in type-II antiferromagnets, we have carried out Monte Carlo simulations on diluted fcc spin arrays. Since CopMg1−pO is an Ising-like system (due to significant crystal-field anisotropy), and some other materials of current interest (e.g., EupSr1−pTe) are Heisenberg systems, we discuss this question in context of simulation data obtained from both Heisenberg and Ising spin arrays.
Temperature dependence of the electron-spin-resonance linewidth of copper (II) trimers
Authors: Zaspel C. E.
Published: July 2002

The temperature dependence of the electron-paramagnetic-resonance linewidth is calculated for a one-dimensional system of copper (II) trimers. The second moment of the resonance line is calculated from the following effective spin Hamiltonian H=Hs +Ha +Hh +H′s , where Hs is the intratrimer isotropic exchange interaction, Ha is the intratrimer anisotropic exchange interaction, Hd is the dipole–dipole interaction, and H′s is the intertrimer anisotropic exchange interaction. With the assumption that Hs is the dominant term in the Hamiltonian, the second moment has an approximate (T)1/2 temperature dependence. This is compared with experimental data for the copper trimer chain (4-picolinium) 2Cu3 Cl8.
Magnetic properties of the three-sites alternating bimetallic chains Cu3[M(cdta)]2(OH2)8(NO3)2⋅7H2O (M=Cu,Ni) (abstract)
Authors: Sapina F. , Escrivá E. , Beltrán D. , Fuertes A. , Drillon M. , Tejada J.
Published: July 2002

Progressing in the study of magnetic interacting bimetallic systems, we present here an analysis of the magnetic behavior of the compounds Cu3[M(cdta)]2(OH2)8(NO3)2⋅7H2O(cdta is trans-1,2-diamine-NNN′N′-tetra-acetate; M=Cu, Ni; in short, [Cu3M2]). These compounds show a novel and exotic structural arrangement. There are three different coordination positions for the metals: an octahedral-cdta-chelating one (Oc), which can be occupied by Cu or Ni cations, and two more, mainly hydrated, but involving oxygen atoms from the carboxylate groups of the cdta. The first of them shows square–pyramidal and the second one square-planar topology, SP and SC, respectively, and both are always occupied by copper cations. The connectivity among these units, leading to the chains, is warranted by the cdta-oxygen atoms, and can be described by the sequence -[Oc-(SP)2-Oc-SC]. The XmT-vs-T product for the [Cu3Cu2] compound shows a significant decrease when cooling down, which shows the presence of antiferromagnetic interactions. In the case of the [Cu3Ni2] compound, it also decreases when cooling down, but reaches a minimum at T=15 K, increases reaching a maximum at T=7 K, and then goes down suddenly. These behaviors will be discussed and magnetostructural correlations will be stablished.
Theoretical and experimental investigation of the magnetic x-ray dichroism of early 5d impurity atoms dissolved in ferromagnetic Fe
Authors: Ebert H. , Wienke R. , Schütz G. , Zeller R.
Published: July 2002

Polarization-dependent x-ray absorption is now going to be established as a new probe to study the magnetic and electronic structure of multicomponent systems. New experimental results are presented for early 5d impurity atoms dissolved in ferromagnetic Fe. The observed spectra clearly reflect the antiferromagnetic coupling of the local spin magnetic moment of the early 5d impurity atoms to the magnetization of the Fe host. From the data it is concluded that the change to a ferromagnetic coupling occurs at a higher atomic number in the 5d transition-metal series than deduced earlier from neutron scattering measurements. This conclusion is supported by first-principle calculations for the absorption spectra, which are based on the spin-polarized relativistic Korringa–Kohn–Rostoker–Green function method of band-structure calculation. The theoretical approach presented here, which has recently been applied to calculate the spectra of some late 5d impurities in Fe, results in a very satisfying agreement with experiment and allows a detailed, parameter-free discussion of the observed spectra.
Effect of sense current on Barkhausen noise in magnetoresistive recording heads
Authors: Brug J. A. , Anthony T. C. , Gill H. S.
Published: July 2002

The currents in the contact leads of a magnetoresistive (MR) head produce fields that influence the behavior of the underlying MR element. In the conventional lead configuration the current enters and leaves the MR element on the same side of the MR element. In the region where the conductor overlaps the MR element a field is produced that has a component that is along the easy axis of the MR element. The direction of this longitudinal field is in opposite directions on either side of the track and this destabilizes the MR element. Barkhausen noise results from the multidomain states that are produced. If instead the leads are configured to be on either side of the element the longitudinal fields are in the same direction and a single-domain state is stabilized. Results are presented that demonstrate the dependence of the hysteresis on the current. Kerr microscope measurements are shown that illustrate the behavior of the magnetization in the elements.
Density-of-states determination of amorphous silicon from space-charge-limited photocurrents
Authors: Kakinuma H. , Mouri M. , Sakamoto M. , Sawai H.
Published: July 2002

The density-of-states around midgap g(E) of undoped amorphous silicon (a-Si:H) has been determined by measuring the space-charge-limited photocurrent (SCLPC) of a-Si:H Schottky diodes under blue light (λ=450 nm) illumination. In this novel technique, a single type of photogenerated carrier is utilized as the source of space charge to dispense with highly doped layers required in the conventional space-charge-limited current (SCLC) technique. Conditions for the uniform formation of space charge are discussed and checked by the satisfaction of a scaling law for samples with different thicknesses. The g(E) deduced from the SCLPC is found to be similar to that from the SCLC technique.
Hydrogen neutralization and reactivation of chalcogen double-donor centers in silicon
Authors: Roos G. , Pensl G. , Johnson N. M. , Holm C.
Published: July 2002

Hydrogen passivation of chalcogen impurities (S, Se, and Te) in n- and p-type silicon was studied by deep-level transient spectroscopy (DLTS). After exposure to monatomic hydrogen from a remote microwave plasma, the chalcogen-related double-donor defects were completely neutralized near the exposed surface of the silicon samples (at 150 °C). Vacuum anneals of hydrogenated specimens revealed that the two donor levels of each chalcogen complex recover simultaneously. Reactivation of the double donors was quantitatively examined with DLTS measurements of hydrogenated specimens after isothermal anneals. The activation energies for reactivation of the neutralized chalcogen-impurity complexes are as follows: For isolated substitutional sulfur, selenium, and tellurium, the energies are 1.61±0.21 eV, 1.39±0.17 eV, 1.39±0.18 eV, respectively, and for the pure pairs of sulfur and selenium, they are 1.56±0.2 eV and 1.41±0.18 eV, respectively. The experimental results are discussed with regard to available calculations for hydrogen passivation of the sulfur impurity in silicon.
Response to ‘‘Comment on ‘Native acceptor levels in Ga-rich GaAs’ ’’ [J. Appl. Phys. 6
5, 596 (1989)]
Authors: Lagowski J. , Bugajski M.
Published: July 2002

Considering all aspects of the comment and the most recent deep level transient spectroscopy (DLTS) and Raman scattering results, we conclude that the 68-meV single aceptor center does exist in Ga-rich, p-type GaAs at concentrations exceeding that of the 78-meV center. Discussion in the comment which misconstrues our results is pointed out and a rebuttal is given to the unfounded objections against DLTS data.
A study of the dynamics of magnetic disaccommodation in amorphous ferromagnets. I. Experimental results
Authors: Allia P. , Beatrice C. , Vinai F.
Published: July 2002

Systematic room-temperature measurements of the aftereffect of the ac magnetic permeability have been performed on a Fe81B13.5 Si3.5C2 amorphous ribbon in order to get detailed information about the nature of the atomic ordering processes responsible for the magnetic relaxation. The magnetic aftereffect related to 180° domain-wall motion has been measured by means of a specific technique allowing periodic domain-wall displacements to be induced between two fixed, neighboring equilibrium positions by applying a square-wave field of proper amplitude and frequency. In this way, the average direction of the magnetization vector is cyclically modified in all points where the studied directional ordering processes may occur. As a consequence, the kinetics of ordering is modified in a characteristic way, giving rise to relevant variations in the intensity of the magnetic aftereffect measured between fixed times (t1=2×10−3 s and t2=10−1 s), and in the value of the magnetic induction at the time t2. All measurements have been performed at constant applied field. The degree of reliability of this experimental technique has been analyzed in detail. The magnetic aftereffect, ΔB=B(t1)−B(t2), and the magnetic induction B(t2) have been measured as functions of the number of domain-wall cycles, and after removing the square-wave field for a variable time t*. The results of many independent measurements are reported and discussed.
A study of the dynamics of magnetic disaccommodation in amorphous ferromagnets. II. Theoretical considerations
Authors: Allia P. , Beatrice C. , Vinai F.
Published: July 2002

The results obtained in part I are interpreted in terms of the viscosity field arising from independent processes of directional ordering for magnetic defects dispersed in the amorphous structure and interacting with the magnetization vector. A specific model is developed in order to take into account the changes in the ordering kinetics induced by the periodic magnetization rotations described in part I. This model, however, requires that the magnetic induction remain constant during the whole measurement; as a consequence, the model’s predictions cannot be directly compared with the experimental results, obtained instead at constant applied field. This difficulty is overcome by deriving a general relationship between the magnetic-induction decay and the viscosity field kinetics for an arbitrary number of half-periods of the square-wave field. The agreement of our theory with the experimental results turns out to be quite satisfactory. As consequence, the ordering processes responsible for the magnetic aftereffect in amorphous ferromagnets may be described as essentially uncorrelated.
Small signal ac analysis of a silicon doping superlattice under reverse bias
Authors: Teo K. H. , McMullin J. N. , Landheer D. , Denhoff M. W.
Published: July 2002

A simple linear electrical circuit model is developed to study the ac characteristics of a doping superlattice with selective contacts. Small signal ac measurements at different frequencies were carried out on silicon doping superlattices under reverse bias. Parameters such as capacitance, doping profile, ac conductance, and leakage resistance of a doping superlattice calculated from the model are shown to agree well with the experiment.
Penetration of electric fields into open conducting cavities
Authors: Boridy Elie
Published: July 2002

Penetration of an applied quasistatic electric field inside an open, conducting, spherical shield is analyzed. The shield is either empty or can be loaded with a concentric spherical conductor, and its opening is assumed to be circular. The electric potential and field multipole expansions are determined and, in the case of a hollow cavity, closed analytical expressions are provided. When the cavity is loaded, convergence of the multipole expansions is improved by a preconditioning technique which isolates the field singularity at the sharp edge of the aperture, and makes its analytical treatment possible. Numerical results for the electric field complement the theoretical analysis.
A comprehensive analysis of surface-acoustic-wave reflections. II. Second-order effects
Authors: Robinson H. , Hahn Y. , Gau J. N.
Published: July 2002

Three methods of evaluating the second-order contributions to the mechanical velocity shift and reflection coefficient for isotropic groove gratings are presented. The second-order terms contain the effect of evanescent and bulk modes generated through the interaction of a surface acoustic wave with a periodic overlay. All three methods will be shown to be numerically equivalent when calculated self-consistently, verifying the validity of all three within their respective limitations. The extension of these methods to arbitrary anisotropic substrates and overlays is discussed.
Study of the substrate bias in plasma depositions using an electron cyclotron resonance plasma
Authors: Shirai K. , Gonda S.
Published: July 2002

A variety of effects of substrate bias upon an electron cyclotron resonance plasma deposition have been studied, taking the deposition of amorphous boron carbide films as an example. First, the impact energy of ions incident on substrates was studied through the variation of the sheath potentials formed on insulating and conducting substrates. For this purpose, the plasma potential (Vp) was measured by the bias current-voltage (Ib-Vb) analysis, and the floating potential (Vf) was measured by the Langmuir probe method. These analyses show that the plasma potential is sufficiently influenced by the substrate bias for positive biases even if the area of the bias electrode is small. The energy of ions incident on conducting substrates is not effectively changed by imposing a positive bias. This effect can be explained in terms of the global balance of the electron and ion currents. This consideration leads to the criterion for the area of bias electrode at which the substrate bias perturbs the plasma potential. Next, the effects of the substrate bias upon the deposition processes and properties of the deposited films were studied through the variations of the deposition rates and the infrared absorption due to the atomic vibrations in the films. The deposition rates vary with the substrate bias according to the variation of sheath potentials: Vp−Vf for insulating substrates and Vp−Vb for conducting substrates. As the substrate bias increases negatively, the deposition rate on conducting substrates increases. This increase is hardly explained by the direct contribution of ions to the deposition. The comparison with other relevant discharge phenomena leads to the importance of the secondary electrons emitted from the substrate surface caused by the ion bombardment. The secondary electrons increase the densities of condensable neutral radicals in the vicinity of the substrate in a way similar to dc discharges.
The influence of indium doping on the [1̄10] indentation cracks in (100) n-type gallium arsenide
Authors: Lee S. W. , Ahn J. H. , Danyluk S. , Elliot A. G.
Published: July 2002

Microhardness indentation was used to determine the hardness and the microcrack anisotropy in In-doped gallium arsenide as a function of the doping level, indentation load and temperature. The hardness decreased with temperature from 600 kg/mm2 at room temperature to 50 kg/mm2 at 400 °C. There was no apparent influence of indium doping on the microhardness up to the maximum doping level, 0.41 at. %. However, the [110] and [1̄10] radial cracks emanating from the intersection of the Vickers diamond indentation diagonals varied significantly with temperature (in the range of room temperature to 250 °C) and doping level (up to a maximum of 0.41 at. %). Both crack orientations exhibited a maximum of the crack length at approximately 150 °C. The maximum in the crack length decreased and the spread of the crack lengths with temperature broadened out as the doping increased; the longest crack was 80×10−6 m for the undoped sample and 60×10−6 m for the sample doped to 0.41 at. %.The radial crack lengths varied with load as K=PCn, where n=0.65 at all temperatures except 200 °C, in which case n=0.77. This larger value of n has been associated with a transition in deformation mode at 1N. Scanning electron microscopy of the indentations showed that the [1̄10] cracks were discontinuous, suggesting that healing of these cracks may have occurred.
Energetics of molecular-beam epitaxy models
Authors: Krishnamurthy Srinivasan , Berding M. A. , Sher A. , Chen A.-B.
Published: July 2002

A Green’s function method is used to calculate the removal energies of constituent atoms from various unreconstructed semiconductor surfaces. An efficient difference equation approach within the second-neighbor tight-binding model is used. For a compound AB, binding energies for the A and B atoms on the (111), (1̄1̄1̄), (100), and (110) surfaces are calculated. Energy to remove an atom from the nearly full surface, Ec (where the removed atom leaves behind a surface vacancy), and from the nearly empty surface, Ed (where the removed atom was isolated on the surface), is obtained. Results are presented for Si, GaAs, CdTe, and HgTe. The surface sublimation energies are shown to depend on surface coverage and do not exhibit a simple linear relationship to the number of bonds broken, as is often assumed in modeling growth by molecular-beam epitaxy (MBE). Although the anion and cation extraction energies depend on surface coverage and orientation, when averaged over a double layer, they always sum to the bulk cohesive energy. Moreover, Ec−Ed can be positive, implying effective attractive in-plane surface interactions, or negative, implying effective repulsive interactions. Ec−Ed tends to be positive for covalent and narrow-gap semiconductors, and negative for wide-gap and more ionic semiconductors. Surface sublimation energies are important input parameters for the modeling of MBE growth; their importance is demonstrated using a simple thermodynamic growth model and results are shown to explain anomalies found in MBE growth of HgCdTe.
Characterization of pseudomorphic InGaAs channel modulation-doped field-effect-transistor structures grown by molecular-beam epitaxy
Authors: Kopf R. F. , Kuo J. M. , Kovalchick J. , Pearton S. J. , Jones E. D. , Ourmazd A.
Published: July 2002

This paper compares Hall-effect measurements combined with rapid thermal annealing (RTA) and low-temperature photoluminescence (4-K PL) as characterization techniques for the optimization of the growth of pseudomorphic InGaAs channel modulation-doped field-effect-transistor structures. The Hall-effect measurements with the RTA were used to determine the optimized growth temperature. 4-K PL was used to determine the quality of the InGaAs quantum well and the In mole fraction.
Structure analysis of Tb-Fe amorphous films using extended x-ray absorption fine structure
Authors: Takayama Shinji , Susa Kenzo , Ohta Norio
Published: July 2002

Extended x-ray absorption fine structure analysis was employed to obtain insight into the influence of structural change on the magnetic and magneto-optical properties of Tb-Fe amorphous films. Films made by bias sputtering show a 20% lower density and a lower apparent coordination number of Fe atoms around an Fe atom than those made by nonbias sputtering. However, their interatomic distances are unaffected by the sputtering methods. After samples made by nonbias sputtering have been annealed, the atomic distances of Fe-Fe and Tb-Fe tend to increase and decrease, respectively, while the apparent coordination number, N*, and the structural disorder parameter, σ, increase and decrease, respectively, in association with a large deterioration in magnetic and magneto-optical properties. On the other hand, in the case of bias-sputtering films, samples annealed at 200 °C show a large decrease in magnetic anisotropy, Ku, but no significant change in individual atomic distances and apparent coordination number. However, the disorder parameter, σ, increases slightly on annealing at 200 °C.
Pressure dependence of hydrogen uptake kinetics in thin metal films
Authors: Richards Peter M.
Published: July 2002

The characteristic equilibration rate for hydrogen uptake in a metal film is shown to go through a maximum at a pressure well below that for hydride formation. This is brought about by non-negligible change of bulk hydrogen site occupancy with pressure once the surface chemisorption sites have been saturated. The rate will increase again after going through a minimum if there is significant hydrogen in impurity sites which can saturate or if there is dissociation at weakly bound subsurface or alternate surface sites. In the latter case the degree and form of nonmonotonicity is strongly dependent on the sticking coefficient of the weak sites, and thus can provide information about their nature. Appreciable hydrogen at impurity sites or in grain boundaries can greatly limit the equilibration rate and lower the pressure beyond which it decreases. Results are in qualitative agreement with recent data on Pd-SiO2 films in metal-oxide-semiconductor devices. Quantitative agreement with the long-time behavior is possible if the polycrystalline films had a large amount of hydrogen in grain boundaries.
Reverse current and external quantum efficiency of zinc diffused 1.3-μm GaAlAsSb photodiodes
Authors: Mebarki M. , Belatoui T. , Joullie A. , Orsal B. , Alabedra R.
Published: July 2002

Zinc-diffused p+n photodiodes were prepared from 1.3-μm GaAlAsSb solid solution grown on GaSb (111) substrate by liquid-phase epitaxy. The reverse dark current was measured in the 77–300 K temperature domain. It has been found dominated by a defect tunneling component in a wide voltage range. The study of spectral photoresponse shows external quantum efficiency (without AR coating) as high as 57% at 1.3 μm.
Color modulator based on polymer dispersed liquid-crystal shutters
Authors: Pirš J. , Olenik M. , Marin B. , Žumer S. , Doane J. W.
Published: July 2002

A low-loss, high-intensity color modulator based on the dichroic-mirror-induced separation of the light into three color channels, modulated by polymer dispersed liquid-crystal shutters, is described. The maximum contrast obtained with the light-scattering-based shutter is estimated and compared with experimental values. The quality of color reproduction of the modulator is presented in a standard 2D CIE diagram while the luminance is included in the 3D version with an incandescent lamp used as the light source. The white color is reconstructed by the modulator with an efficiency of 50%.
The influence of bias power levels on mark length variability in rare earth–transition metal optical data storage media
Authors: Bartholomeusz Brian J. , Genova David J. , Hatwar Tukaram K.
Published: July 2002

Measured length variations of laser written marks in rare earth–transition metal (RE-TM) optical data storage media were found to be a strong function of test conditions. In particular, the mark length standard deviation was found to be inversely proportional to the difference between the threshold and bias power levels. Differences in mark length variabilities of various RE-TM compositions written with the same bias power were found to be attributable to their differing marking thresholds.
Cathodoluminescence of diamondlike films deposited by glow discharge
Authors: Alvarez F. , Koropecki R. R. , Fajardo F.
Published: July 2002

The room-temperature cathodoluminescence of diamondlike films produced by glow discharge is reported. The material was deposited onto dc biased substrates maintained at relatively low temperature (<100 °C). Two visible peaks around 2.3 eV (green) and 2.7 eV (blue-violet) were identified which are commonly found in natural and synthetic diamond, indicating the presence of crystalline particles in the films. Moreover, x-ray diffraction spectra of the samples before cathodoluminescence studies are identical to the ones reported for natural powder diamond.
Electron-beam-induced pattern etching of AlGaAs using an ultrathin GaAs oxide as a resist
Authors: Taneya M. , Sugimoto Y. , Hidaka H. , Akita K.
Published: July 2002

Electron-beam (EB)-induced pattern etching of AlxGa1−xAs (0≤x≤0.7) is described. An ultra-thin GaAs oxide at the surface of a GaAs/AlGaAs heterostructure wafer is used as a resist film. The GaAs oxide resist can be selectively removed by EB irradiation in a Cl2 ambient, which results in pattern etching of GaAs/AlGaAs. The etch rate of AlGaAs is examined as functions of substrate temperature, AlAs mole fraction, and EB flux. The results indicate that pattern etching is realized in the AlAs mole fraction range of 0≤x≤0.7
Perpendicular magnetic anisotropy of Fe/SiO2 multilayer film
Authors: Senda Masakatsu , Nagai Yasuhiro
Published: July 2002

This paper investigates the conditions which lead to soft-magnetic properties of Fe/SiO2 multilayer film from the viewpoint of perpendicular magnetic anisotropy. For very thin Fe layers, perpendicular magnetization is explained by considering interface anisotropy. On the other hand, perpendicular magnetization, which is thought to relate to Fe columnar crystal structure, is observed when the Fe layer is thick. It is interpreted that the minimum coercivity, at an Fe layer thickness of 7 nm, is realized where the sum of the perpendicular anisotropies becomes minimum and the magnetization orients almost completely in the plane.
Calcium gallioaluminate glasses
Authors: Shelby James E. , Slilaty Rita M.
Published: July 2002

Calcium gallioaluminate glasses containing either 63 or 67 mol % CaO and varying ratios of Ga2O3 to Al2O3 have been formed. The glass transformation temperature of these glasses decreases as gallia replaces alumina, whereas the thermal expansion coefficient, refractive index, density, and infrared cutoff wavelength increase. A slight mixed cation effect appears in the compositional dependence of the glass transformation temperature. These results will be discussed in terms of the structures of these glasses.
I
n s
i
t
u measurements of hydrogen motion and bonding in silicon
Authors: Seager C. H. , Anderson R. A. , Brice D. K.
Published: July 2002

Hydrogenation of both n- and p-type metal/thin oxide/silicon diodes has been studied using high frequency capacitance profiling. In situ observations of donor and acceptor passivation were made while H ions were implanted through thin gate metallizations at various energies and fluxes. TRIM code simulations of the implantation process as well as studies of the energy, dose, and flux dependence of capacitance data lead us to conclude that irradiation of 400 Å Al gated diodes with 800–1400 eV H ions rapidly establishes a time-independent near-surface H concentration which is proportional to both the ion flux and the implantation depth, and inversely proportional to the hydrogen diffusivity. While direct measurement of ion transits at a variety of electric fields establish that a unique mobility can be assigned to positive H ions, modeling of low and high field data in both n- and p-type samples is consistent with the notion that the positive charge state is occupied only 1/10 of the time. The time dependence of hydrogen penetration for both n- and p-type diodes indicates that hydrogen is, in addition to being trapped at unpassivated shallow donors or acceptors, becoming immobilized at other sites in silicon. The density of these secondary trapping sites correlates well with the shallow dopant population, suggesting that additional hydrogen may become trapped near already-passivated dopant atoms.
Low-temperature dynamic depth profile measurements of implanted deuterium in nickel: Precipitation of nickel deuteride
Authors: Petitpierre O. , Möller W. , Scherzer B. M. U.
Published: July 2002

Measurements of the retention of deuterium in polycrystalline nickel were obtained at 193 and 223 K through elastic-recoil detection using a 2.6-MeV 4He beam. The depth profiles so obtained show striking differences with their counterparts measured at higher temperatures. Although the profiles are homogeneous at implanted fluences lower than 3×1018 D+ cm−2, they present a large peak centered slightly deeper than the implantation range at higher fluences. Additional features develop as one further implants. The large peak is associated with the buildup of nickel deuteride. A one-dimensional computer model is developed which partly reproduces the features of the measured depth profiles.
On the dynamics of a laser-produced Be plasma and its implication for a Be/Ne photopumped x-ray laser scheme
Authors: Filbert P. C. , Kohler D. A.
Published: July 2002

A photoresonant-pumped x-ray laser scheme using Be and Ne is considered. In this scheme the Be iv 2p-1s transition at 75.93 Å is used to pump the Ne vii 2s-4p level at 75.77 Å. The wavelength mismatch can be decreased by either a bulk Doppler shift of the Be plasma produced by hydrodynamic expansion which requires a velocity of 6×107 cm/s, or by opacity broadening of the Be iv pump line, or by a combination of both. To investigate the viability of this particular scheme, preliminary studies were made of the Be plasma by focusing 14 to 24-J, 3-ns pulses of 1054-nm laser light onto a planar Be target. Using a time-of-flight technique, it is found that the velocity needed to Doppler shift the Be iv pump line into resonance with the Ne vii 2s-4p transition does not develop until at least 10 ns after the peak of the driving laser pulse. Spatially resolved time-integrated spectral measurements indicate that by this time the Be iv emissions have greatly decreased in intensity and this suggests that the needed bulk Doppler shift is difficult to achieve while still maintaining sufficient pump power. However, the observed opacity broadening of the Be iv pump line (0.7 Å FWHM) is found to be sufficient to create significant spectral overlap between the nearly resonant lines to allow photopumping to occur. It is also observed that the temporal duration of the opacity-broadened Be iv emission is roughly 5 ns (FWHM), which is significantly longer than the 3-ns driving laser pulse, and this fact can limit the efficiency of this particular x-ray laser approach.
Theory of lasers with intracavity optical mixing
Authors: Souma H. , Horie C.
Published: July 2002

Rate equation analysis is presented to describe intracavity frequency conversions in laser systems consisting of two laser cavities combined with a nonlinear optical material. The optimum coupling conditions for sum or difference frequency generations and second harmonic generation are derived, and the existence of forbidden ranges in nonlinear coupling coefficients is discussed. For the practical application, effects due to beam walk-off and acceptance angle are considered.
Alkali induced oxidation of silicon; a secondary ion mass spectrometry study
Authors: Ferron Julio
Published: July 2002

The process of alkali-induced oxidation of silicon has been studied by means of secondary ion mass spectrometry and Auger electron spectroscopy. We found that the oxide films obtained through this process show a very low level of alkali contamination. We have also found that the desorption of the alkali metal is characterized by two thermally activated processes.
Comment on ‘‘Determination of minority-carrier lifetime and surface recombination velocity by optical-beam-induced-current measurements at different light wavelengths’’ [J. Appl. Phys. 6
6, 3060 (1989)]
Authors: Donolato C.
Published: July 2002

It is shown that a recent analysis by Flohr and Helbig [J. Appl. Phys. 66, 3060 (1989)] of beam-induced current has already appeared in the literature, and can be simplified by using the results of von Roos and Luke [J. Appl. Phys. 54, 3938 (1983)].
Study of voltage fluctuations in a low-current electric arc
Authors: Vacquié S. , Rahhaoui B. , Rahal A. M.
Published: July 2002

The diffusion of metal vapors emitted by the copper anode of an electric arc in nitrogen (I=20 A) is correlated to the voltage variations measured between the anode and a stabilizing disk used as a probe. It is shown that the voltage fluctuations are due to modifications brought about on the electrical conductivity by the metal vapors. The amplitude and the duration of the voltage variations depend on the diffusion velocity of the copper vapors and on the initial density of the vapors emitted by the electrode.