bluuebunny/crossref_metadata_2025 huggingface dataset:
Indium vacancy in as-grown InP: A positron annihilation study
Authors: Bretagnon T. , Dannefaer S. , Kerr D.
Published: July 2002

The positron lifetime technique has been used to investigate grown-in defects in various types of indium phosphide. A neutral monovacancy-type defect has been detected independently of the nature (Zn,Fe,Si,S) and concentration of the dopants. The defect is stable at least up to 800 °C, and is suggested to be a trapped indium vacancy.
Investigation of the defect structure of thin single-crystalline CoSi2 (B) films on Si(111) by transmission electron microscopy
Authors: Bulle-Lieuwma C. W. T. , Vandenhoudt D. E. W. , Henz J. , Onda N. , von Känel H.
Published: July 2002

Thin epitaxial single-crystalline B-type CoSi2 films (twin-oriented) have been grown in ultrahigh vacuum by stoichiometric codeposition of Co and Si on slightly misoriented (0.1°–0.3°) Si(111) substrates. The microstructure as well as the nature of interfacial defects has been investigated in detail by transmission electron microscopy. The defect structure is found to depend closely on the initial deposition parameters, annealing temperature, and the topography of the Si substrate. It will be shown that even during the early stages of layer growth, loss of coherence is obtained and lattice strain already starts to occur with the introduction of misfit dislocations with Burgers vector b=a/2〈110〉 inclined to the interface or with Burgers vector b=a/6〈112〉 parallel to it. It is demonstrated that ultrathin CoSi2 films with thickness of about 1 nm grown on slightly misoriented substrates with parallel surface steps, exhibit quite different defect structures at annealing temperatures between 300 °C and 550 °C. Control of the dislocation density has been obtained by applying a two-step growth procedure. CoSi2 layers grown to a thickness <hc (4–5 nm) exhibit line defects with Burgers vector b=a/6〈112〉 associated with interfacial misorientation-related steps. Above this thickness additional dislocations in the three equivalent directions are formed, indicating biaxial strain relaxation. In addition, calculations of the critical thickness hc of biaxial strain relaxation based on thermodynamic equilibrium theory are presented. It is shown that the observed critical thickness hc is in qualitative agreement with theoretical predictions.
Polycrystalline silicon recrystallized with excimer laser irradiation and impurity doping using ion doping method
Authors: Miyata Yutaka , Furuta Mamoru , Yoshioka Tatsuo , Kawamura Tetsuya
Published: July 2002

Polycrystalline silicon (poly-Si) thin films having large grain size have been obtained by XeCl excimer laser annealing of a-Si deposited by plasma enhanced chemical vapor deposition on SiNx. The grain size of poly-Si reaches to about 300 nm with excimer laser irradiation around 500 mJ/cm2. For excimer laser irradiation from 500 to 600 mJ/cm2, instead of further enlargement of grains, amorphous regions appear and increase in the grains. Most of the Si layer becomes an amorphous state at pulse energy density over 600 mJ/cm2. On the other hand, impurity implantation to a-Si layers using non-mass-separated ion doping equipment and a subsequent activation step with excimer laser irradiation enable us to obtain recrystallized poly-Si layers having low resistivity. By using ion doping and excimer laser annealing, we have obtained excellent n-channel thin film transistors, the field effect mobility in excess of 40 cm2/V s and the ON/OFF current ratio of more than 106, respectively.
Barkhausen noise in the re-entrant system Ni1−xMnx: A study of the power spectra
Authors: Sommer R. L. , Schmidt J. E. , Gomes A. A.
Published: July 2002

In this article, the power spectra of the Barkhausen noise of Ni1−xMnx is presented. The measurements were made in the ferromagnetic phase at several temperatures and manganese concentrations in order to map the effects of the degree of disorder and of the temperature on domain wall dynamics. Measurements in standard ferromagnetic materials were also made to compare the dynamics in both cases.
Calorimetric and photoacoustic investigation of KNO3 phase transitions
Authors: Westphal M. J. , Wood J. W. , Redin R. D. , Ashworth T.
Published: July 2002

Results of a thermodynamic study of the phase transitions of powdered KNO3 at two impurity concentrations (99.999% pure and 99.9% pure) are reported. Transition onset and peak temperatures have been measured between 350 and 420 K using both heat flow and photoacoustic calorimetry. The transition temperatures and characteristics observed with both techniques show excellent agreement. Specific-heat values calculated from scanning and stepped temperature heat-flow data, utilizing both positive and negative temperature increments, compare well with previously reported values. Enthalpies for the II-I, I-III, and III-II phase transitions were measured as 5.065, 2.603, and 2.084 kJ/mol, respectively, for 99.999% pure KNO3 powder using heat-flow calorimetry. The transition enthalpies and temperatures measured for 99.9% pure powder were slightly lower for all three transitions. Entropy changes for the II-I, I-III, and III-II transitions were 12.53, 6.61, and 5.30 J/mol K, respectively. Enthalpy, entropy, and Gibbs free-energy curves are presented with emphasis on the temperature range over which the ferroelectric phase transition occurs. The experimental data and calculated thermodynamic functions indicate that the ferroelectric phase III in bulk KNO3 is a metastable state at atmospheric pressure, which was not observed to exist below 350 K contrary to previous reports.
Metastable impact ionization of traps model for lock-on in GaAs photoconductive switches
Authors: Partain Larry , Day Derek , Powell Ron
Published: July 2002

A model for lock-on in GaAs photoconductive switches is proposed based on avalanche breakdown from impact ionization of deep EL2 traps. Compared to band-to-band impact ionization, the model predicts an order-of-magnitude reduction in the threshold electric field from the combination of three effects: (i) The EL2 trap is located in the middle of the gap and requires half the band-gap energy to access a band edge; (ii) avalanching a single carrier type from the trap requires approximately half the energy that is split between electron-hole pairs in band-to-band transitions; (iii) thermally assisted tunneling and Poole–Frenkel barrier lowering account for the remaining threshold reduction. Light triggering is provided by optical ‘‘bleaching’’ of EL2 and related traps into metastable states. This causes an increase in the mean free path for optical phonon emission and a decrease the threshold electric-field strength for avalanche. Model approximations, that retain order-of-magnitude level accuracy, give a calculated current rise time of 138 ps compared to a 200 ps measured value, a lock-on delay time of 1.1 ns compared to a measured value of ∼1 ns, and an optical threshold energy value of 10 mJ compared to a 2.1 mJ experimental value. Calculated thermal recovery rates from lock-on of ∼1 μs are consistent with experimental repetition rates of up to 1 kHz that require recovery in less than 1 ms.
Low jitter operation of a plasma opening switch
Authors: Goyer J. R. , Kortbawi D. , Childers F. K. , Sincerny P. S.
Published: July 2002

Low throughput jitter is crucial to the construction of modular pulsed power systems. Recently, the causes of throughput jitter in plasma opening switches have been identified and reduced in a pulsed power system using these switches as the last stage of pulse compression. The results of these changes to the system are presented and discussed. It is found that low jitter operation can be obtained and is consistent with current theoretical understanding of switch operation based upon measured reproducibility of the plasma sources used.
Charged particle flow in plasma-filled pinched-electron-beam diodes
Authors: Swanekamp S. B. , Stephanakis S. J. , Grossmann J. M. , Weber B. V. , Kellogg J. C. , Ottinger P. F. , Cooperstein G.
Published: July 2002

Plasma-filled pinched-electron-beam diode experiments have been performed on the Gamble II (1.5 MV, 800 kA, 60 ns) pulsed power generator at Naval Research Laboratory. These plasma-filled diode (PFD) experiments show three phases of behavior: a low impedance phase followed by a phase of rapidly increasing impedance that culminates in a relatively constant vacuum impedance phase. The duration of the low impedance phase as well as the final operating impedance depends on the prefill plasma density. The charged particle flow in the PFD is studied with one-dimensional (1-D) and two-dimensional (2-D) simulation models. These simulation models show the formation of growing sheaths at both electrodes during the low impedance phase. The end of the low impedance phase in the simulations coincides with the two sheaths meeting in the center of the anode-cathode (A-K) gap. Based on these observations, an analytic model was developed that treats the low impedance phase as symmetric bipolar sheaths. The analytical model adequately predicts the duration of the low impedance phase predicted by the 1-D simulation model. Differences between the bipolar model and the experiments or 2-D simulations can be explained in terms of magnetized sheaths which enhance the ion current over the bipolar level and cause the sheath to grow faster than the bipolar model. During the rapidly increasing impedance phase, the simulations show that the cathode sheath quickly expands to completely fill the A-K gap. At this time, charged particle flow in the simulation models are consistent with the vacuum gap spacing. Experimentally, the higher density, longer conduction time, PFD shots exhibited a significantly lower final impedances than predicted by 2-D simulations. This difference is probably caused by expanding electrode surface plasmas produced by the interaction of the plasma source with one or both electrode surfaces.
Simulation and analysis of silicon electro-optic modulators utilizing the carrier-dispersion effect and impact-ionization mechanism
Authors: Huang H. C. , Lo T. C.
Published: July 2002

A new type of Si guided-wave electro-optic modulator is proposed and analyzed. The modulator makes use of the impact-ionization mechanism for carrier generation, and the carrier-dispersion effect for electro-optic conversion. Both electrical and wave propagation properties of the modulator were examined by a two-dimensional device simulator and a three-dimensional waveguide simulator, respectively. Numerical estimates of phase modulation due to refractive-index change and intensity modulation due to optical absorption and radiation loss were obtained. One of important features of the prospected modulator is speed. The simulated turn-on and turn-off time of the modulator was less than 1 ns. GHz modulation is, therefore, possible for this class of modulators with device structure and doping profiles optimized for fiber coupling.
Acoustic propagation in anisotropic periodically multilayered media: A method to solve numerical instabilities
Authors: Potel Catherine , de Belleval Jean-François
Published: July 2002

Acoustic propagation through thick composites has become a subject of intensive study due to their application to nondestructive evaluation. The anisotropic multilayered media are now usually studied by the propagator matrix formalism. Though this formalism is very convenient, it leads to numerical instabilities for thick composites at high frequencies. These numerical instabilities come from the combination of very high exponential terms which reduces the dynamics of the calculation. A very interesting case is the one of anisotropic periodically multilayered media. The method developed in this paper uses Floquet waves which correspond to the modes of an infinite periodically multilayered medium. They are linear combinations of the real waves propagating in each layer of the medium. The Floquet wave numbers are the eigenvalues of the propagation matrix of one period of the medium. The anisotropic periodically multilayered medium can then be considered as a dummy medium in which the Floquet waves propagate. High exponential terms can be avoided through a judicious choice of reference of the Floquet waves’ amplitudes. This method enabled us to calculate reflection coefficients up until 40 MHz, of thick composites of carbone/epoxy placed in water. Furthermore, it has permitted us to not have a limitation for a single layer of any given material, at any given frequency.
Investigation of Pr-Fe-B magnets with high performance (abstract)
Authors: Lian F. Z. , Pourarian F. , Simizu S. , Sankar S. G. , Wallance W. E.
Published: July 2002

Pr-Fe-B magnets with high performance based on 2:14:1 structure were investigated. The effect of fabricating processes on the oxygen content and on the magnetic properties was studied. The coercivity iHc decreases, but the Br and (BH)max of the magnets increase with the decrease of the Pr content. The decrease in the α-Fe content of the alloys annealed at 1000 °C for more than 360 h results in the enhancement of the magnetic properties of the magnets. Under the optimum conditions, the magnetic properties for Pr14Fe79.5B6.5 magnets are found to be iHc=656 kA/m, Br=1.42 T, (BH)max=374 kJ/m3. The microstructures of the magnets were investigated. The effect of the secondary phases in the grain boundary on the coercivity of the magnets was studied.
Pyroelectrical investigation of charged and poled nonlinear optical polymers
Authors: Bauer Siegfried
Published: July 2002

A compact and easy-to-use experimental set-up for pyroelectric investigations of poled nonlinear optical (NLO) polymers is reported. The arrangement allows for the investigation of the NLO dipole relaxation under isothermal or nonisothermal (e.g., linear heating of the polymer) conditions. Furthermore, polarization patterns in the plane of a polymer film and polarization profiles in its thickness direction can be measured in the same experimental set-up. In waveguide structures, it is possible to determine the thicknesses of an active guiding layer and of the claddings, if their thermal parameters are known. The isothermal pyroelectric relaxation data are discussed within the framework of phenomenological relaxation functions. It is found that they cannot be fitted with the stretched exponential function, a result which is in agreement with broadband dielectric-relaxation measurements. Pyroelectric experiments are the only method for investigations of all these problems in one and the same easy-to-use set-up.
Single-electron memory
Authors: Nakazato K. , Blaikie R. J. , Ahmed H.
Published: July 2002

A single-electron memory cell, in which one bit of information is represented by the excess or shortfall of a precise number of electrons, is described. An experimental memory circuit was fabricated using side-gated constrictions in δ-doped GaAs, and the basic operation was confirmed from 30 mK up to liquid-helium temperature of 4.2 K. This memory can store information for longer than several hours. The intrinsic single-electron memory characteristics in a regime where cotunneling is neglected are investigated, and the overall characteristics are explained by a semiclassical model.
Structural characterization of II-VI separate confinement heterostructure lasers with Zn1−xMgxSySe1−y cladding layers
Authors: Petruzzello J. , Gaines J. , van der Sluis P.
Published: July 2002

We have investigated the structural characteristics of II-VI separate confinement heterostructure lasers grown on GaAs substrates and containing Zn1−xMgxSySe1−y quaternary cladding layers, ZnSe or ZnSySe1−y guiding layers and Zn1−zCdzSe quantum well active layers. The study was performed with a combination of transmission electron microscopy and high resolution x-ray diffraction techniques. We found that the quaternary cladding layers remain pseudomorphic to the GaAs substrate although they can be lattice mismatched up to 0.1%. When the 0.5-μm-thick optical guiding layer contains ZnSe, there is partial relaxation of the laser structure by misfit dislocations at the lower cladding-guiding layer interface and the threading dislocation density in the Zn1−zCdzSe quantum well active region is about 107 cm−2. However, when lattice matched (to GaAs)ZnSySe1−y is used as the guiding layer the entire laser structure is pseudomorphic and the threading dislocation density is <106 cm−2. The combination of low defect density and enhanced carrier and optical confinement by using Zn1−xMgxSySe1−y quaternary cladding layers has produced significant improvement in the room temperature threshold current (500 A/cm2) and maximum operating temperature (394 K).
Correlation of the structural and optical properties of luminescent, highly oxidized porous silicon
Authors: Cullis A. G. , Canham L. T. , Williams G. M. , Smith P. W. , Dosser O. D.
Published: July 2002

The light-emitting properties of rapid thermally oxidized porous Si are studied by both photoluminescence and cathodoluminescence methods. The structure of the material is examined by transmission electron microscopy, while its oxygen content is determined by x-ray microanalysis. These investigations show that crystalline Si nanostructures remain in the heavily oxidized porous material and account for its ∼750 nm red photo- and cathodoluminescence. The work demonstrates that the previously speculated possible importance of either Si-based amorphous phases or the interesting material, siloxene, in this regard is unrealistic. Furthermore, it is shown that the luminescence properties of silicon oxides are of paramount importance in interpreting the many additional (shorter wavelength) emission bands observed.
Effect of time-of-flight bunching on efficiency of light-ion-beam inertial-confinement-fusion transport schemes
Authors: Ottinger P. F. , Rose D. V. , Olson C. L.
Published: July 2002

The Laboratory Microfusion Facility (LMF) has been proposed for the study of high-gain, high-yield inertial-confinement-fusion targets. The light-ion LMF approach uses a multimodular system with applied-B extraction diodes as ion sources. A number of ion-beam transport and focusing schemes are being considered to deliver the beams from the diodes to the target. These include ballistic transport with solenoidal lens focusing, z-discharge channel transport, and wire-guided transport. The energy transport efficiency ηt has been defined and calculated as a function of various system parameters so that point designs can be developed for each scheme. The analysis takes into account target requirements and realistic constraints on diode operation, beam transport, and packing. The effect on ηt of voltage ramping for time-of-flight beam bunching during transport is considered here. Although only 5 mrad microdivergence calculations are presented here, results for bunching factors of ≤3 show that transport efficiencies of ≳50% can be obtained for all three systems within a range of system parameters which seem achievable (i.e., for diode microdivergence within 5–10 mrad, for diode radius within 10–15 cm, and for diode-ion-current density within 2–10 kA/cm2). In particular, the point design for the baseline LMF system using ballistic transport with solenoidal lens focusing and a bunching factor of 2 was calculated to have ηt=84%. Other factors affecting the overall system efficiency, but not included in the analysis, are also identified and estimated.
An array of dislocations in a strained epitaxial layer. II. Work hardening
Authors: Zhang Tong-Yi , Hack J. E. , Guido L. J.
Published: July 2002

The sequential generation of dislocations in a strained epitaxial layer is considered. It is found that an additional work component results from dislocation-dislocation interactions after some dislocations are generated and located in the interface between the epitaxial layer and the substrate. The interaction energies induced by a single dislocation and a dislocation array are derived. It is found that, in general, when the distance between a fresh dislocation and the nearest pre-existing dislocation is comparable to the layer thickness, the additional work component achieves the level of the self energy of an isolated dislocation. The additional work increases sharply with decreasing distance between the fresh and pre-existing dislocations. If the spacing between the dislocations exceeds approximately 20 times the layer thickness, the additional work becomes insignificant. These results are consistent with experimental observations.
Complex magnetization processes of exchange coupled trilayers
Authors: Wüchner S. , Voiron J. , Givord D. , Boursier D. , Préjean J. J.
Published: July 2002

The magnetization processes of two series of sandwiches of compositions Sm-Co/Co/Sm-Co′ and Sm-Co/Gd-Co/Sm-Co′ prepared by dc bias sputtering are presented. The layers of Sm-Co and Sm-Co′ have different compositions each with a different coercive field. The central layer consists of a soft magnetic material with a thickness varying from 500 to 5000 Å. In these systems, it is possible to stabilize a magnetic configuration with the magnetic moments of the external layers having opposite directions. Due to the magnetic coupling between the layers associated with the strong exchange interactions between cobalt atoms throughout the whole sample, a large planar Bloch wall is formed in the central layer. The width of this wall depends on the intrinsic properties of this central layer, but the magnetization processes vary with the relative magnitude of the wall width to the thickness of this layer. For a large thickness of the central layer, the Bloch wall is very mobile under applied field leading to a very large susceptibility.
Current-noise-power spectra of amorphous silicon thin-film transistors
Authors: Boudry J. M. , Antonuk L. E.
Published: July 2002

Current-noise-power spectra of thin-film transistors (TFTs) fabricated from hydrogenated amorphous silicon were measured. TFTs with aspect ratios ranging from 1:1 to 16:1 were examined in both the conducting and nonconducting modes. In the conducting mode, the noise levels could be predicted to within an order of magnitude by theories developed for crystalline metal-oxide field-effect transistors. In the nonconducting mode, the noise was found to scale with the TFT leakage current in a power-law fashion.
Hydrogen release kinetics during reactive magnetron sputter deposition of a-Si:H: An isotope labeling study
Authors: Abelson J. R. , Mandrell L. , Doyle J. R.
Published: July 2002

The release of molecular hydrogen from the growing surface of hydrogenated amorphous silicon films is determined using an isotope labelling technique. The results demonstrate that surface-bonded H atoms are readily abstracted by atomic hydrogen arriving from the gas phase. The films are deposited by dc reactive magnetron sputtering of a silicon target in an argon-hydrogen atmosphere. To achieve isotope labeling, we first deposit a deuterated amorphous silicon film, then commence growth of hydrogenated amorphous silicon and measure the transient release of HD and D2 from the growing surface using mass spectrometry. Release occurs when the supply of reactive hydrogen in the growth flux exceeds the incorporation rate into the film, and is observed under all experimental conditions. The net rate of H incorporation is known from ex situ measurements of film growth rate and hydrogen content. We combine the H release and incorporation data in a mass balance argument to determine the H-surface kinetics. Under conditions which produce electronically useful films, (i) 0.5–1.0 hydrogen atoms react with the growing surface per incorporated silicon atom, (ii) the near surface of the growing film contains 1–3×1015/cm2 of excess hydrogen, (iii) the dominant hydrogen release mechanism is by direct abstraction to form H2 molecules, and (iv) the kinetics of H release and incorporation can be described by constant rate coefficients. These data are supported by studies of H interactions with single-crystal silicon and amorphous carbon surfaces.
Thermoelectric devices using semiconductor quantum wells
Authors: Mahan G. D. , Lyon H. B.
Published: July 2002

The efficiency of thermoelectric devices are analyzed for a superlattice of semiconductor quantum wells. It is assumed that the quantum wells are the thermoelectric active elements, and the layers between conduct only heat. It is shown that the efficiency of the device depends on the property of both layers.
Spin reorientation transition in Ni films on Cu(100)
Authors: Wu S. Z. , Mankey G. J. , Huang F. , Willis R. F.
Published: July 2002

The magnetic anisotropy of Ni films grown on single-crystal Cu(100) was studied in situ using the surface magneto-optic Kerr effect. The easy axis of magnetization lies in the plane of the film for ultrathin films and it is perpendicular to the film above a switching thickness. This behavior is attributed to a specific contribution to the magnetocrystalline anisotropy energy induced by a change in the film microstructure above a critical thickness. In the Ni/Cu(100) system, the magnetoelastic interface anisotropy favors perpendicular magnetization which becomes comparable to the shape anisotropy at the switching thickness. We compare the switching thickness and magnetization of films grown using different processing conditions.
Time dependence effects in disordered systems
Authors: O’Grady K. , El-Hilo M. , Chantrell R. W.
Published: July 2002

In this paper the time variation of the thermoremanent magnetization (TRM) is examined. From a simple theory based on the relaxation of magnetic moments over the associated energy barrier we explain the various forms for the time variation of thermoremanent magnetization. For a narrow distribution of energy barriers the variation of TRM with ln(t) is predicted to be concave downwards when the relaxation takes place over barriers less than the average barrier. For barriers greater than the average barrier the variation of TRM vs ln(t) is predicted to be concave upwards. In the region where the relaxation takes place over barriers close to the average barrier the variation is initially concave downward and then concave upward.
In-plane magnetized YIG substrates self-biased by SmCo based sputtered film coatings
Authors: Cadieu F. J. , Hegde H. , Schloemann E. , Van Hook H. J.
Published: July 2002

Highly anisotropic SmCo based films with the TbCu7-type structure have been sputter deposited directly onto YIG substrates. The SmCo crystallites have the c axes approximately randomly splayed about the substrate plane such that the easy direction of magnetization of the SmCo film is in the film plane. The in-plane static energy product of the SmCo film layers was about 16 MG Oe. In-plane vibrating sample magnetometer hysteresis loops of the SmCo film and YIG substrate exhibit a composite form with the YIG field reversal shifted into the first quadrant by the looping field from the SmCo film layer. Approximately 4×4 mm2 pieces of YIG substrate have been measured to determine the YIG bias field and field required for reverse saturation of the YIG as a function of the SmCo based film layer thickness to YIG substrate thickness. It is observed that for SmCo to YIG thickness ratios greater than 0.22, the looping field from the SmCo film layer is sufficient to saturate the YIG magnetization in the reverse direction. SmCo film thicknesses in the range from 80 to 120 μm have been used in these studies. Special boundary layers have been used to promote thick film adhesion to the YIG substrates.
Theoretical predictions of interface anisotropy in the presence of interdiffusion (invited)
Authors: MacLaren J. M. , Victora R. H.
Published: July 2002

The first ab initio electronic structure calculations of the magnetocrystalline anisotropy of superlattices with imperfect interfaces are presented. Specifically the possibility of an interdiffusion between the layers at the interface in Co/Pd and Co/Pt superlattices is considered. The electronic structure calculations use the local spin-density formalism as implemented with the layer Korringa–Kohn–Rostoker method. Interdiffusion at the interface is modeled in two distinct ways. In the first approach a diffuse interface is represented by ordered arrangement of substitutions, while in the second approach interdiffusion is assumed to produce a substitutionally disordered random alloy on the layers at the interface, which is solved using the coherent potential approximation. The calculated interface anisotropies for superlattices with perfect and imperfect interfaces are, on average, modeled accurately by a simple Néel-type model. This model always predicts a reduction in magnetic anisotropy resulting from the presence of defects.
Dependence of damage and strain on the temperature of Si irradiation in epitaxial Ge0.10Si0.90 films on Si(100)
Authors: Lie D. Y. C. , Song J. H. , Vantomme A. , Eisen F. , Nicolet M.-A. , Theodore N. D. , Carns T. K. , Wang K. L.
Published: July 2002

Damage and strain produced in a 370-nm-thick strained epitaxial Ge0.10Si0.90 film on Si(100) by irradiation with 320 keV 28Si+ ions at fixed temperatures ranging from 40 to 150 °C and for doses from 1 to 30×1014/cm2 have been measured by MeV 4He channeling spectrometry, transmission electron microscopy, and high-resolution x-ray diffractometry. The ion energy was chosen so that the maximum damage created by irradiation occurs very near the GeSi-Si interface. For all temperatures, the retained damage and the perpendicular strain induced by the irradiation are significantly greater in the GeSi epilayer than in the Si substrate. For all doses the retained damage and the induced perpendicular strain become small above 100 °C. Both rise nonlinearly with increasing ion dose. They are related to each other differently in GeSi than in bulk Si or Ge irradiated at room temperature. Postirradiation furnace annealing can remove a large portion of the induced damage and strain for nonamorphized samples. Amorphized samples regrow by solid-phase epitaxy after annealing at 550 °C for 30 min; the regrown GeSi is, however, highly defective and elastically relaxed. A consequence of this defectiveness is that irradiation-induced amorphization in metastable GeSi is undesirable for applications where good crystalline quality is required. Ion implantation above room temperature can prevent amorphization.
Characterization of a radio-frequency discharge used for downstream plasma oxidation of Si
Authors: Cook J. G. , LeBrun L. , Zhongming Li , Ogryzlo E. A.
Published: July 2002

Recently it has been shown that high-quality SiO2 films can be grown on (100) Si downstream of a radio-frequency rf He/O2 discharge using a two-step process: plasma oxidation followed by remote plasma-enhanced chemical-vapor deposition [T. Yasuda, Y. Ma, S. Habermehl, and G. Lucovksy, J. Vac. Sci. Technol. B 10, 1844 (1992)]. The plasma oxidation is examined. For such a discharge the spatial distribution of atomic oxygen, the species held to be the oxidant, is calculated and it is found to be quite uniform for pressures below 0.5 Torr, with He:O2 ratios of 10:1, and glass walls. The distribution is nonuniform for clean stainless-steel chamber walls. By emission spectroscopy the downstream extension of the discharge is found to be appreciable, and sensitive to rf power, gas pressure, and the location of ground electrodes. It is concluded that the role of ion bombardment in plasma oxidation by this process should be further investigated.
Simulation of the angular distribution of resonance radiation from a positive column discharge
Authors: Doughty D. A.
Published: July 2002

A Monte Carlo simulation of radiation transport is used to determine the angular distribution of resonance radiation emanating from a positive column discharge. With the specification of the oscillator strength, absorption/emission profile, gas density, spatial distribution of radiating atoms, and boundary geometry, the angular distribution of photons arriving at the wall of the discharge is obtained. The ratio of the integral of the angular distribution to that for a diffuse, Lambertian surface is on the order of one-half for the parameter space studied here. When combined with a measurement of the absolute intensity at one angle, this distribution provides a means of determining the radiant emittance of the source when measurement of the actual distribution is problematic.
X-ray scattering from nonideal multilayer structures: Calculations in the kinematical approximation
Authors: Bruson A. , Toussaint J. C.
Published: July 2002

In the kinematical approximation, a two-dimensional model is described for X-ray scattering from multilayered films that includes discrete thickness fluctuations and interfacial correlated roughness. In this work, the influence of the thickness fluctuations and of the roughness that is introduced as small perturbations at the interfaces is studied on both specular and nonspecular reflectances. For specular direction, the kinematical calculations are compared with those calculated using the full optical Fresnel theory. It is shown that whenever the reflectance is low, both computations are in good agreement. Finally, the model is applied tentatively to fit the experimental specular and nonspecular spectra performed on Fe/Si multilayered samples.
Determination of interface properties between a depleted heteroepitaxial layer and a substrate from capacitance measurements
Authors: Goren D. , Nemirovsky Y.
Published: July 2002

A method for the determination of interface properties between a depleted heteroepitaxial layer and a substrate is presented. The method is based on the measurement of the zero bias capacitance of a metal gate that forms a Schottky contact with the depleted epilayer. The interface charge density can be extracted regardless of the exact values of the energy band discontinuities. A microscopic electrostatic analysis of the interface is presented which takes into account the effects of interface charges and interface dipoles. Experimental results are presented for the case of ZnTe epilayers grown by metal organic chemical vapor deposition on CdTe substrates.
Positron annihilation spectroscopy applied to porous silicon films
Authors: Knights A. P. , Kowalski G. , Saleh A. S. , Towner A. , Patel M. I. , Rice-Evans P. C. , Moore M. , Gledhill G. A. , Nossarzewska-Orlowska E. , Brzozowski A.
Published: July 2002

A monoenergetic slow positron beam has been used for the first time to profile porous silicon films. High values of the Doppler-broadened line shape parameters are observed, which correspond to positron annihilation within the porous layers and these are attributed to the decay of para-positronium. After allowing for the reduced density of the porous film, fitted values of thickness were deduced which were in reasonable agreement with values obtained from ellipsometry measurements. Low values of the Doppler parameters observed for the two samples with the thinnest films are attributed to oxide residing at the interface of the porous and bulk silicon regions. Etching the samples in a solution of 48% hydrogen fluoride reduced the porous film thickness significantly, suggesting that a considerable amount of the film consists of SiO2. A four-component convolution analysis routine is used to analyze the individual 511 keV annihilation peaks, the result of which confirms the formation of positronium within the porous layer. Positron annihilation is shown to be a promising method for the nondestructive investigation of thin porous films.
Experimental observations and analysis of CO2 laser-induced microcracking of glass
Authors: Allcock G. , Dyer P. E. , Elliner G. , Snelling H. V.
Published: July 2002

Transversely excited atmospheric pressure CO2 and modulated continuous-wave CO2 laser marking of soda-lime and borosilicate glasses has been investigated as a function of laser fluence and pulse duration. Marks are formed by a combination of surface crazing and material removal, the latter occurring predominantly through particles that are fractured from the surface. Various possible fracture mechanisms are analyzed and residual surface stress following rapid laser heating is identified as the most likely cause of microcracking. Scanning electron microscope studies show that relatively large fragments are produced, with a characteristic thickness that is dependent on the laser pulse duration, but that they predominantly remain locked in the surface. Gas phase products evolved during the interaction have also been subject to evaluation using spectroscopy of the luminous plume and fast photography techniques.
Interlayer exchange coupling in epitaxial Fe/Cr/Fe/Ag/GaAs(100) structures
Authors: Hicken R. J. , Daboo C. , Gester M. , Ives A. J. R. , Gray S. J. , Bland J. A. C.
Published: July 2002

The interlayer exchange coupling has been investigated in epitaxial Fe(20 Å)/Cr/Fe(20 Å)/Ag/GaAs(100) structures that contain a wedge-shaped (0–40 Å) Cr layer. Longitudinal and polar magneto-optical Kerr-effect (MOKE) and Brillouin light-scattering measurements have been combined to determine values for the relevant anisotropy constants and both the bilinear and biquadratic coupling strengths. The phase and period of the oscillations in the interlayer coupling are found to agree well with those reported by other researchers while the total coupling strength is found to be reduced. This reduction is presumably due to the presence of structural imperfections in our samples, and our results may therefore be of use in testing some of the recently proposed extrinsic biquadratic coupling mechanisms. Specifically, we find that for the Cr thicknesses studied the biquadratic coupling strength in our samples varies as d−1.4Cr where dCr is the thickness of the Cr layer. We also present results that show how the ultrathin Cr limit may be investigated. We show that the coercivity of the easy axis MOKE loops is sensitive to submonolayer coverages of Cr and that polar MOKE is sensitive to the strong ferromagnetic coupling found in the 0–4 Å Cr thickness range.
Time resolved study of a reactive low pressure plasma: Determination of basic data on electron-fluorine collisions
Authors: Elyaakoubi Mustapha , Ranson Pierre
Published: July 2002

Time resolved spectroscopy and electron concentration measurements were performed on an Ar–He–F2 mixture excited by an external rf antenna creating a plasma with features of a plasma source generated by a Helicon reactor commonly used in materials processing. The low pressure range and the simplified chemistry allow an appropriate modelling of some processes and lead to the determination of some fundamental data concerning atomic and molecular fluorine. We give a F2 direct dissociation coefficient by electron impact of about 2.0×10−9 cm3 s−1 for an electron temperature of 5 eV. Excitation rate coefficients of some fluorine levels (3p 2P3/2, 3p 4D7/2, and 3p′ 2F7/2) are given as well as rate coefficients of line emissions following F2 dissociation by electron impact.
Determination of recombinative lifetime and surface recombination velocities from wavelength dependence of photocurrent in insulator-semiconductor structures
Authors: Mostarshed Shahriar , Darling Robert B.
Published: July 2002

A method is described for extracting bulk minority carrier lifetimes and surface recombination velocities from insulator-semiconductor structures. Recombination in the bulk and at the two surfaces of the wafer are distinguished by using the wavelength dependence of the penetration depth of the incident light flux. Pulse modulated light from various wavelength light-emitting diodes is used to create excess minority carrier holes which are collected in the depletion region of an inverted surface. The spectral dependence of the resulting photocurrents can then be used to determine the surface recombination velocities and the bulk lifetime. A model is described which provides relationships between the bulk minority carrier lifetime, the surface recombination velocities, the absorption coefficient of the incident light, and the resulting capacitive current. The experimental values of lifetime and surface recombination velocity are combined to obtain an effective lifetime which is in good agreement with a combined lifetime obtained from the photoconductive decay technique.
Transient effects of ionizing and displacive radiation on the dielectric properties of ceramics
Authors: Goulding R. H. , Zinkle S. J. , Rasmussen D. A. , Stoller R. E.
Published: July 2002

A resonant cavity technique was used to measure the dielectric constant and loss tangent of ceramic insulators at a frequency near 100 MHz during pulsed fission reactor irradiation near room temperature. Tests were performed on single crystal and several different grades of polycrystalline Al2O3, MgAl2O4, AlN, and Si3N4. Lead shielding experiments were performed for some of the irradiations in order to examine the importance of gamma ray versus neutron irradiation effects. With the exception of AlN, the dielectric constant of all of the ceramics decreased slightly (<0.2% change) during the pulsed fission reactor irradiation. The dielectric constant of AlN was observed to slightly increase during irradiation. Significant transient increases in the loss tangent to values as high as 6×10−3 occurred during pulsed reactor irradiation with peak ionizing and displacements per atom (dpa) radiation fields of 4.2×104 Gy/s and 2.4×10−6 dpa/s, respectively. The loss tangent measured during irradiation for the different ceramics did not show any correlation with the preirradiation or postirradiation values. Analysis of the results indicates that the transient increases in loss tangent are due to radiation induced increases in the electrical conductivity. The loss tangent increases were proportional to the ionizing dose rate in all materials except for AlN, which exhibited a dose rate exponent of ∼1.6.
Surface profile dependence of surface plasmon band gaps on metallic gratings
Authors: Kitson S. C. , Barnes W. L. , Bradberry G. W. , Sambles J. R.
Published: July 2002

When surface plasmon polaritons propagate on a corrugated surface, an energy gap opens up in the dispersion of the surface mode. We present the results of an experimental technique that directly images this gap. The technique is used to measure the width and the central frequency of the gap as a function of the grating profile. The experimental results agree well with the predictions of a recently published analytic model. In particular the results confirm that the central frequency of the gap drops as the grating amplitude increases. This is a previously unconfirmed prediction, over which there has been some debate. We also demonstrate that it is possible to observe gaps that are an order of magnitude wider than those reported elsewhere.
Iron precipitation at oxygen related bulk defects in Czochralski silicon
Authors: Wijaranakula W.
Published: July 2002

Behavior of iron atoms in silicon during a simulated integrated circuit device fabrication process was examined. The results from the electron microscopic and deep-level transient spectroscopic analysis indicate that iron at concentrations below the solubility limit precipitates at a bulk stacking fault containing an oxide precipitate. Based upon the defect morphology and the eutectoid temperature of the α-FeSi2 phase, it is suggested that iron precipitation occurs during the cooling down period after a high-temperature treatment. The result shows that iron may react with oxygen atoms in the oxide precipitate via a Fe2O3 phase transformation which in turn causes a change in the precipitate morphology. In this study, it is suggested that iron precipitation at the bulk defects is fundamentally different from that of other transition metals such as nickel and copper where the precipitation occurs either along the Frank partial dislocations of the bulk stacking fault or at the punch-out dislocation loops originating at the oxide precipitate interface.
Quantitative characterization of additional ferromagnetic phase in melt-quenched and sintered Nd–Fe–B-based magnets
Authors: Lewis L. H. , Welch D. O. , Pourarian F.
Published: July 2002

Quantitative evidence of a ferromagnetic Fe-rich minor phase present in both melt-quenched/die-upset and sintered magnets based on the Nd2Fe14B composition is presented. Full hysteresis loops were obtained at elevated temperatures (650 K≤T≤800 K) and were subsequently decomposed to obtain the saturation magnetization Ms of the minor phase as well as the paramagnetic slope of the 2-14-1 major phase as a function of temperature. Assuming a composition of pure iron, the calculated volume % of the impurity phase in the die-upset magnets is consistent with that obtained from previous observations of the widths and geometry of the intergranular phase found in the same magnets. The magnetization of the ferromagnetic impurity phase in the melt-quenched magnets decreases more rapidly than that of pure iron; extrapolation indicates a Curie temperature in the range 925 K≤T≤975 K. The paramagnetic susceptibility of the Nd2Fe14B main phases exhibits Curie–Weiss behavior with the same paramagnetic Curie temperature for both sintered and die-upset samples. The Curie constants differ, however, probably due to the different degrees of crystallographic alignment.
Influence of the negative thermal-expansion coefficient on the luminescence properties of (CdMnMg)Te
Authors: Schenk H. , Wolf M. , Mackh G. , Zehnder U. , Ossau W. , Waag A. , Landwehr G.
Published: July 2002

In zinc-blende II–VI alloys the thermal-expansion coefficient for low temperatures is negative and becomes positive at higher temperatures. We investigated the luminescence properties of molecular-beam-epitaxy-grown (CdMnMg)Te layers in the temperature range from 2 up to 200 K and show that the anomalous temperature dependence of the lattice constant is reflected in the luminescence properties of the excitonic recombination and the internal transition of manganese (ITM). The temperature behavior of the ITM energy is nonmonotonic and the existence of a minimum in the photon energy (at the temperature TMn) can be correlated to the change of sign of the thermal-expansion coefficient. The decay constants of the ITM begins to decrease drastically at TMn, too. Considering a lattice constant dependent energy transfer rate to the infrared emitting state (1.2 eV) of the manganese ion the variation of the lifetimes can also be explained by the temperature dependence of the lattice constant. Furthermore, we have measured the ITM in bulk layers and observed a different dependence of the ITM properties on the temperature, demonstrating the influence of the growing conditions on the microscopic surrounding of the manganese ions.
Thermal and optical characterization of the calcium phosphate biomaterial hydroxyapatite
Authors: Bento A. C. , Almond D. P. , Brown S. R. , Turner I. G.
Published: July 2002

Thermal wave interferometry (TWI) has been used to measure the thermophysical properties of hydroxyapatite (HA) coatings, prepared by the plasma-spraying process on titanium alloy substrates. The properties measured were thermal diffusivity, thermal conductivity, thermal effusivity, and volumetric heat capacity and the optical absorption coefficient. The thermal conductivity obtained was found to be of similar magnitude to that of human tooth enamel. The results presented confirm the usefulness of TWI as a nondestructive technique for the characterization of plasma-sprayed HA coatings.
Comment on ‘‘Multiband coupling effects on electron quantum well intersubband transitions’’ [J. Appl. Phys. 77, 747 (1995)]
Authors: Lew Yan Voon L. C. , Willatzen M. , Cardona M. , Ram-Mohan L. R.
Published: July 2002

A multiband k⋅p theory was recently proposed [L. H. Peng and C. G. Fonstad, J. Appl. Phys. 77, 747 (1995)] in order to discuss the influence of band mixing on the selection rules for intersubband and interband optical transitions in quantum wells. We point out here that the analysis presented is incorrect.