bluuebunny/crossref_metadata_2025 huggingface dataset:
Si(100) etching by translational energy controlled atomic chlorine beams
Authors: Teraoka Yuden , Nishiyama Iwao
Published: July 2002

Si(100) etching was investigated using a translational energy controlled atomic chlorine beam. The results were compared with translational-energy-induced molecular beam etching and conventional gas etching. The etch rate was enhanced by increasing the translational energy of the chlorine atoms up to 0.98 eV. The reaction yield of the atomic beam etching was several hundred times greater than that of translational-energy-induced molecular beam etching. The activation energy of the atomic beam etching at a 0.28 eV translational energy was determined to be 0.76±0.16 eV from an Arrhenius plot. It decreased to 0.62±0.09 eV when the translational energy was increased to 0.98 eV. These values were smaller than those for translational-energy-induced molecular beam etching (1.2±0.3 eV) and conventional gas etching (2.7±0.3 eV).
Photoluminescence studies of broadband excitation mechanisms for Dy3+ emission in Dy:As12Ge33Se55 glass
Authors: Turnbull D. A. , Gu S. Q. , Bishop S. G.
Published: July 2002

Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy of Dy2S3-doped As12Ge33Se55 glasses demonstrate that the broad, below-gap PLE mechanism observed previously for rare-earth emissions in Er- and Pr-doped chalcogenide glasses is a general or universal feature of rare-earth-doped chalcogenide glasses, provided the transition energies of the rare earths are in the correct energy range. The PL spectrum excited in the 815 nm Dy3+ absorption band shows the 1150, 1340, and 1700 nm sequence of Dy3+ transitions expected for Dy-doped chalcogenide glasses. The PLE spectra of the 1340 (6F11/2,6H9/2→6H15/2) and 1700 nm (6H11/2→6H15/2) Dy3+ emissions exhibit broad excitation bands from ∼500 to 1000 nm, upon which the sharp intra F-band absorptions of Dy3+ are superimposed. These broad PLE bands are characterized by an exponentially decreasing slope with decreasing energy in the spectral range below the Urbach edge which is associated with the below-gap, defect- and impurity-induced exponential tails observed in the below-gap absorption spectra of chalcogenide glasses. At high energy, the exponentially rising Urbach absorption edge of the host glass, which leads to competing nonradiative decay mechanisms, eventually dominates the absorption spectrum and imposes an exponentially decreasing slope on the PLE spectra. These features of the broadband PLE have been observed in the PLE spectra of the Er-, Pr- and Dy-doped chalcogenide glasses we have studied. There is a difference in the relative strengths of the broad PLE bands, with the broadband for the 1340 nm PL band being a factor of 3 stronger than that for the 1700 nm PL emission. In addition, there is a shift in the peak energy of the different PLE spectra. Qualitatively speaking, the higher the energy of the luminescence transition, the higher the energy of the corresponding broad PLE peak. Proposed mechanisms for the broadband PLE of rare-earth emissions in chalcogenide glasses are discussed in the context of models for the below-gap, defect- and impurity-induced exponential absorption tails, including the possible role of lattice relaxation associated with charge transfer transitions and the involvement of transition metal impurities.
Binding of cobalt and iron to cavities in silicon
Authors: Myers S. M. , Petersen G. A. , Seager C. H.
Published: July 2002

The chemisorption binding of Co and Fe to cavity walls in Si was quantitatively characterized in the temperature range 973–1273 K in order to evaluate the efficacy of cavities for impurity gettering. The cavities were formed by He ion implantation and annealing. Then, with the solution concentration of Co or Fe being held at the solid solubility through prior formation of excess metal-silicide phase, the equilibrium number of metal atoms bound to the cavities was measured. Using this information in conjunction with published solubilities, a binding free energy relative to interstitial solution was extracted. The binding free energies for cavity-wall chemisorption of Co and Fe were found to be less than those for precipitation of the respective silicide phases, a reversal of the ordering previously observed by us for Cu and Au. Nevertheless, model calculations indicate that the chemisorption mechanism is important together with silicide precipitation for cavity gettering of all four elements. The results of this work, taken with the known thermal stability and the anticipated device-side compatibility of cavities, suggest that these sinks will prove attractive for gettering.
Temperature dependence of the refractive index of direct band gap semiconductors near the absorption threshold: Application to GaAs
Authors: Tanguy Christian
Published: July 2002

Using a semiempirical model of the dielectric constant taking excitonic effects correctly into account, we calculate dn/dT for direct band gap semiconductors by separating the contribution of the excitonic enhancement near the band gap energy Eg from a background term described by the high frequency dielectric constant ε∞. Comparison of the model with experimental data suggests that dEg/dT≊−4.5×10−4 eV K−1 and dε∞/dT≊1.32×10−4 K−1 for GaAs at room temperature, a significant shift from the currently accepted values of these parameters.
A ferroelectric-superconducting photodetector
Authors: Lin H. , Wu N. J. , Geiger F. , Xie K. , Ignatiev A.
Published: July 2002

A ferroelectric-superconducting photodetector has been developed and characterized. An atomically ordered PbZrTiO3 (PZT) ferroelectric gate was grown over a c-oriented YBa2Cu3O7−x (YBCO) high Tc superconductor substrate by excimer laser deposition. Irradiation of the PZT gate with photons near the ferroelectric gap energy resulted in a measurable change of the drain-source photocurrent with the device at a temperature near Tc of the YBCO. The critical temperature of the YBCO base was shifted up to 4 K when the PZT gate was irradiated with photon flux of wavelength from 300 to 500 nm. A responsivity of 360 A/W was measured and an upper bound on response time to optical irradiation of 100 ns was determined.
GaAs multilayer p+-i homojunction far-infrared detectors
Authors: Perera A. G. U. , Yuan H. X. , Gamage S. K. , Shen W. Z. , Francombe M. H. , Liu H. C. , Buchanan M. , Schaff W. J.
Published: July 2002

A molecular beam epitaxy grown wavelength tunable GaAs p+-i homojunction interfacial work-function internal photoemission far-infrared detector is developed. The multilayer (p+-i-p+-i-…) detector structures consist of 2, 5, and 10 emitter layers. Experimental results are explained in terms of the number of emitter layers and the doping concentrations of the emitter layer. A detector with 10 multilayers and an emitter layer doping concentration (Ne) of 3×1018 cm−3 shows a current responsivity of 2 A/W, an effective quantum efficiency of 9.2% (at 26.3 μm) with a cutoff wavelength of 85 μ and the noise equivalent power of 2.18×10−12 W/Hz at 4.2 K.
Magnetoresistance oscillations induced by periodically arranged micromagnets (invited)
Authors: Ye P. D. , Weiss D. , Gerhardts R. R. , Nickel H.
Published: July 2002

Probing magnetic fields can be done, e.g., by employing the well established Hall effect. Alternatively, we make use of the ballistic motion of electrons in high mobility two-dimensional electron systems (2DES) to probe electrically the stray field of periodically arranged micomagnets. We investigate the magnetoresistance of the 2DES underneath arrays of magnetic strips and magnetic dots having periods between 500 nm and 1 μm. The periodic stray field gives rise to pronounced oscillations of the resistivity as a function of a homogeneous (weak) magnetic field. The magnetization orientation of the dots and strips can be aligned in different directions with respect to the current flow through the device. The observed magnetoresistance depends characteristically on the magnetization direction and can be understood in terms of the stray field pattern probed by the electrons.
Electrostatic discharge sensitivity of giant magnetoresistive recording heads
Authors: Wallash Albert J. , Kim Young K.
Published: July 2002

In this article electrostatic discharge (ESD) damage to giant magnetoresistive (GMR) recording heads is studied for the first time. The ESD failure threshold was measured using an extremely short duration (1 ns) metal contact ESD transient. The failure energy required to melt the GMR recording head was 2.3 nJ, about half of the 5 nJ of energy needed to melt a conventional anisotropic magnetoresistive (AMR) head design. Scanning electron microscope scans of ESD damaged AMR and GMR heads show localized melting of the sensors. It is concluded that recording heads with GMR sensors, planned for use in the near future, will have significantly lower ESD failure thresholds than AMR recording heads in use today. Finally, scaling arguments show that an AMR head design with the same reduced cross-sectional area of the GMR head has a comparable ESD failure threshold.
Heteroepitaxial growth of highly oriented diamond on cubic silicon carbide
Authors: Kawarada H. , Wild C. , Herres N. , Locher R. , Koidl P. , Nagasawa H.
Published: July 2002

We have deposited epitaxial diamond films with very low angular spread on epitaxial β-phase silicon carbide layers on silicon (001) substrates. From x-ray rocking curve measurements, half-widths of the angular spread of the crystal orientation as low as 0.6° have been determined, which is the smallest value ever reported in heteroepitaxial diamond films and appears to be smaller than those of the β-phase silicon carbide underlayers. The film surface exhibits a roughness of about 100 nm with very few discernible boundaries due to misorientation. The optimization of the bias-enhanced nucleation process and the control of selective growth are the main factors for the improvement of the crystallinity.
Leakage currents in amorphous Ta2O5 thin films
Authors: Chiu Fu-Chien , Wang Jenn-Jyh , Lee Joseph Ya-min , Wu Shich Chuan
Published: July 2002

Tantalum oxide (Ta2O5) is an important material for future dynamic random access memory application owing to its high dielectric constant. This work examines the structural and electrical properties of Ta2O5 thin films deposited by plasma-enhanced chemical vapor deposition using a penta ethoxy tantalum Ta(OC2H5)5 liquid source. The x-ray diffraction patterns indicate that the as-deposited thin films are amorphous and become polycrystalline after rapid thermal annealing above 650 °C. The level of carbon contamination is below that which can be detected by Auger electron spectroscopy measurement. Electrical measurements performed on amorphous Ta2O5 using a Au/Ta2O5/Pt/Ti/Si metal-tantalum oxide-metal structure exhibit a low leakage current, reasonable breakdown field (5.4 MV/cm), and high dielectric constant (23–25). The leakage current is 2×10−8 A/cm2 at 1 MV/cm. In addition, the leakage current mechanism of amorphous Ta2O5 capacitors is investigated by plotting the ln(J) vs E1/2 curves at a low electric field (<2 MV/cm) and plotting ln(J/E) vs E1/2 curves at a high electric field (>2 MV/cm). The dominant conduction mechanism is due to Schottky emission at low electrical field and Poole–Frenkel emission at high electrical field. According to our results, the Ta2O5 thin films annealed in N2 or O2 at 800 °C exhibit a much higher leakage current than amorphous Ta2O5 , possibly due to the out-diffusion of Ti during high temperature annealing.
Electrodeposited CdTe—optical properties
Authors: Rakhshani A. E.
Published: July 2002

For the measurement of optical constants, the electrodeposited films of CdTe were lifted off their opaque substrates and transferred onto glass slides using a transparent liquid adhesive. This technique proved to give results more reliable than those obtained on samples in which CdTe is deposited on CdS-coated conducting glass. The measured optical dispersion in the photon energy range of E<1.5 eV is in excellent agreement with that for the single crystal. The optical absorption coefficient was determined in the E<3.5 eV range and was compared with that for the single crystal. The results revealed two direct allowed transitions at 1.50 eV [Γ8 valence band(VB)→Γ6 conduction band(CB)] and 2.43 eV [Γ7(VB)→Γ6(CB)] and three indirect allowed transitions at 1.27 eV [L4,5(VB)→Γd], 1.83 eV [L6(VB)→Γd], and 2.84 eV [Γ8(VB)→L6(CB)]. The 1.27 and the 1.83 eV transitions, which have not been reported previously and were not detected in single-crystal data, are attributed to the transitions to a grain-boundary-related defect energy band Γd, 0.65 eV above Γ8 (VB). The indirect transitions at 1.83 and 2.84 eV are assisted by phonons having energies of 80 and 84 meV, respectively.
Structure of Co layers in Co/Cu multilayers at the first antiferromagnetic maximum studied by nuclear magnetic resonance
Authors: Jȩdryka E. , Wójcik M. , Nadolski S. , Kubinski D. J. , Holloway H. , Panissod P.
Published: July 2002

Using Co59 nuclear magnetic resonance, a structural study has been performed on a series of Co/Cu multilayers with Cu thickness of 9 Å (corresponding to the first maximum of antiferromagnetic coupling) and Co thickness varying between 10 and 50 Å. The structure of the Co layer is fcc for small Co thicknesses. With increasing Co thickness, a rapid increase of hcp Co content is observed, particularly for samples between 10 and 30 Å Co. The equivalent thickness of the deposited Co involved in the mixed interface planes is estimated to be a total of about 5 Å for both interfaces of the Co layer. The interface maintains a relatively sharp concentration profile similar to that observed in samples at the second maximum of antiferromagnetic coupling. However, a certain degree of topological disorder in the interface is introduced by the onset of hcp stacking.
Investigation of carrier removal in electron irradiated silicon diodes
Authors: Taylor S. J. , Yamaguchi M. , Matsuda S. , Hisamatsu T. , Kawasaki O.
Published: July 2002

We present a detailed study of n+\p\p+ silicon diodes irradiated with fluences of 1 MeV electrons high enough to cause device failure due to majority carrier removal. Capacitance–voltage (C–V) measurements were used to monitor the change in the carrier concentration of the base of the device as a function of radiation fluence. These were compared to the defect spectra in the same region obtained by deep level transient spectroscopy, and to the current–voltage characteristics of the device, both before and after annealing. We observed the expected deep levels with activation energies of 0.18 and 0.36 eV, but the C–V results imply that other trap levels must play a more important role in the carrier removal process.
Precipitation of Al2Cu in blanket Al-Cu films
Authors: Marcus Matthew A. , Bower J. Eric
Published: July 2002

We have used x-ray absorption spectroscopy to study the formation and dissolution of θ-Al2Cu precipitates in blanket Al-Cu films. In one series of experiments, we examined films deposited at different temperatures and average Cu concentrations. For a given temperature, there is a Cu concentration above which precipitates form. This effective solvus agrees with the equilibrium solvus at high temperatures, but exceeds the equilibrium values at low deposition temperatures. The formation of precipitates correlates with a pileup of Cu in the part of the film which was deposited first. This pileup is explained by a model involving precipitate growth at grain boundaries and grain growth during deposition. We also measured the kinetics of precipitation formation and dissolution in Al−0.5 w/o Cu. In the range 200–270 °C, the precipitation kinetics show an activation energy of 0.54 eV, which is lower than that for grain-boundary diffusion of Cu in Al. Precipitate dissolution over the range 300–400 °C shows an activation energy of 1.37 eV, consistent with lattice diffusion. These results may be useful in designing heat treatments which will minimize the occurrence of precipitates in integrated-circuit interconnects when process corrosion could be a problem, yet leave the material with precipitates before use, when electromigration becomes an issue.
Synthesis and magnetic properties of Ni–Al2O3 thin films
Authors: Kraus Gerald T. , Lu Yung-Cheng , Trancik Jessika E. , Mitro Diana M. , Giannelis Emmanuel P. , Thompson Michael O. , Sass Stephen L.
Published: July 2002

Ni–Al 2 O 3 nanocomposite thin films have been produced on sapphire, silicon, and silica substrates by a combination of sol-gel processing and partial reduction reactions. Transmission electron microscopy shows Ni particles, ∼20 nm in diameter, embedded in slightly larger diameter alumina grains. X-ray diffraction lattice parameter measurements suggest that the Ni is in a state of nonhydrostatic strain. Magneto-optical Kerr effect measurements indicate that the Ni particles in the films on the silicon and silica substrates support perpendicular magnetization. The saturation Kerr rotation increases linearly with film thickness to values above pure Ni and independent of reflectivity, indicating that the material is behaving as a Faraday rotator. The enhanced magnetic properties of the composite films are related to the nonhydrostatic strain developed in the Ni particles during fabrication. It is argued that the strains originate from the coefficient of thermal expansion mismatch between the film and substrate, and likely the volume shrinkage associated with the reduction reaction.
In situ transmission electron microscopy study of plastic deformation and stress-induced voiding in Al–Cu interconnects
Authors: Jawarani D. , Kawasaki H. , Yeo I.-S. , Rabenberg L. , Stark J. P. , Ho P. S.
Published: July 2002

Plastic deformation in submicron wide Al-1 wt %Cu interconnects was studied in situ using a straining device in the transmission electron microscope. Dislocation motion occurred readily in unpassivated lines but was nonexistent in passivated lines due to the presence of stiff oxide sidewalls. Instead heterogeneous void nucleation occurred on straining to a critical limit. The void morphology was always near hemispherical and the nucleation always took place at the line edges. Further stretching of the lines led to a rupture of the sidewalls away from the lines, resulting in immediate dislocation motion. Void nucleation, cross slip, and operation of dislocation sources at line edges were all recorded on video. It was noted that dislocations almost parallel to the plane of the lines are rarely observed and furthermore, their movement is sluggish. Based on the dislocation configuration observed in these lines, a generalized geometrical model was arrived at in order to determine the significance of grain orientation on yield stress of passivated lines with columnar, bamboo grains. Frequent occurrence of twinning within the grains indicated that plastic deformation was indeed restricted in confined metal lines.
Local structures of isovalent and heterovalent dilute impurities in Si crystal probed by fluorescence x-ray absorption fine structure
Authors: Wei Shiqiang , Oyanagi Hiroyuki , Kawanami Hitoshi , Sakamoto Kunihiro , Sakamoto Tsunenori , Tamura Kazuhisa , Saini Naurang L. , Uosaki Kohei
Published: July 2002

Local structures of dilute isovalent and heterovalent impurity atoms in Si crystal (Si:X, X=Ga, Ge, As) have been studied by fluorescence x-ray absorption fine structure. The distortion of local lattice around the impurity atoms was evaluated from the Si–X bond length determined by extended x-ray absorption fine structure. The results demonstrate that the local lattice deformation is strongly dependent on the electronic configuration of impurity atoms, i.e., we find an anomalous expansion (0.09±0.01 Å) along the [111] direction for donor (As) atoms but much smaller magnitude (0.03±0.01 Å) for isovalent (Ge) atoms and acceptor (Ga) atoms. The results suggest that the local lattice distortions are strongly affected by the Coulomb interactions between the localized charge, which piles up to screen the ion core and the bond charge, and the ion-core repulsion. Absence of anomaly in case of negatively charged Ga atoms suggests that the former mechanism is a dominant factor for anomalous lattice expansion.
Dielectric and transport properties of magnetic insulators irradiated with GeV heavy ions
Authors: Costantini J. M. , Salvetat J. P. , Brisard F.
Published: July 2002

The dielectric and ac/dc transport properties of single crystals of yttrium iron garnet (Y3Fe5O12 and Y3Fe5O12:Si), and barium hexaferrite (BaFe12O19 and BaFe12O1 9:Co,Ti) were investigated after irradiations with Xe and Pb ions in the GeV range. In the virgin n-type samples (Y3Fe5O12:Si and BaFe12O19:Co,Ti), the strong dielectric relaxation below 100 kHz is found to correspond to a space-charge polarization at the blocking metal/insulator contacts yielding a nonohmic dc conductivity. The relaxation frequency decreases with increasing amorphization yield in relation to the decrease of the insulators bulk dc conductivity which becomes ohmic in the amorphous phases. The ac conductivity data of both crystalline and amorphous Y3Fe5O12:Si above 100 kHz and for 100 K<T<300 K exhibit two contributions: (i) that of carrier transport in a disordered or inhomogeneous medium varying as νs, with s≃0.8, (ii) and that of a two-site polaron hopping process of charge transfer between Fe2+ and Fe3+ with an activation energy of 0.29 eV for T>180 K. The dc conductivity data of crystalline Y3Fe5O12:Si for 80 K<T<300 K are discussed on the basis of a small polaron hopping conduction mechanism between Fe2+ and Fe3+ with an activation energy around 0.28 eV for T>125 K, in agreement with the activation energy around 0.28 eV of the space-charge dielectric relaxation frequency for T>180 K. All amorphous phases data are consistent with the picture of hopping conduction between gap states in a disordered medium with (i) an νs dependence for the ac conductivity above a critical frequency proportional to the dc conductivity, (ii) and an exp(−T−1/4) law for the dc conductivity.
Crystallographic transformations of rapidly quenched Sm10Fe90−xTix and magnetic properties of their nitrides
Authors: Xiao Q. F. , Zhang Z. D. , Zhao T. , Liu W. , Sui Y. C. , Zhao X. G. , Geng D. Y.
Published: July 2002

Sm 10 Fe 90−x Ti x alloys (x=0, 1, 3, 4, 5, 6, 8, 10) were prepared by rapid quenching and sequent annealing. Structural transformations from amorphous, metastable-to-equilibrium phases, and magnetic properties of their nitrides were systematically investigated. A CaCu5-type metastable phase was formed for 0⩽x⩽10 as the crystallization of the amorphous alloys occurred below 700 °C. The CaCu5-type structure is transformed into a TbCu7-type one with increased annealing temperature (above 700 °C). These alloys have different structures including Th2Zn17 type for 0⩽x⩽3, TbCu7 type for 3<x<6, and ThMn12 type for 6⩽x⩽10, at high annealing temperatures (above 950 °C). Nitrogenation was carried out at 460 °C for 6 h. The best hard magnetic properties are obtained after nitriding for x=3. It gives Hc=17.6i kOe, 4πMr=7.7 kG, and (BH)max=6.8 MGOe for the TbCu7-type phase and Hc=8.6i kOe, 4πMr=8.4 kG, and (BH)max=10.2 MGOe for the CaCu5-type one. Although the coercivity of the CaCu5-type phase is lower than that of the TbCu7-type one, enhanced remanence of the former has been observed.
Effect of reflectivity at the interface of oxide layer on transverse mode control in oxide confined vertical-cavity surface-emitting lasers
Authors: Huang Yong-Zhen
Published: July 2002

The transverse mode control in oxide confined vertical-cavity surface-emitting lasers is discussed by modeling the dielectric aperture as a uniform waveguide and an extra reflectivity at the oxide layer. The phase of the extra reflectivity and the refractive index step can be adjusted to change the mode threshold gain. We calculate the lateral refractive index step from the mode wavelength difference between aperture and perimeter modes, and compare it with that obtained from the weighted average index. The mode reflectivity in terms of the lateral optical confinement factor at the oxide layer is considered in calculating the threshold gain for transverse modes. The numerical results show that higher transverse modes can be suppressed by adjusting the position of a thin AlAs-oxide layer inside a three-quarter-wave layer in the distributed Bragg reflector.
Planar spatial correlations, anisotropy, and specific surface area of stationary random porous media
Authors: Berryman James G.
Published: July 2002

An earlier result of the author showed that an anisotropic spatial correlation function of a random porous medium could be used to compute the specific surface area when it is stationary as well as anisotropic by first performing a three-dimensional radial average and then taking the first derivative with respect to lag at the origin. This result generalized the earlier result for isotropic porous media of Debye et al. [J. Appl. Phys. 28, 679 (1957)]. The present article provides more detailed information about the use of spatial correlation functions for anisotropic porous media and in particular shows that, for stationary anisotropic media, the specific surface area can be related to the derivative of the two-dimensional radial average of the correlation function measured from cross sections taken through the anisotropic medium. The main concept is first illustrated using a simple pedagogical example for an anisotropic distribution of spherical voids. Then, a general derivation of formulas relating the derivative of the planar correlation functions to surface integrals is presented. When the surface normal is uniformly distributed (as is the case for any distribution of spherical voids), our formulas can be used to relate a specific surface area to easily measurable quantities from any single cross section. When the surface normal is not distributed uniformly (as would be the case for an oriented distribution of ellipsoidal voids), our results show how to obtain valid estimates of specific surface area by averaging measurements on three orthogonal cross sections. One important general observation for porous media is that the surface area from nearly flat cracks may be underestimated from measurements on orthogonal cross sections if any of the cross sections happen to lie in the plane of the cracks. This result is illustrated by taking the very small aspect ratio (penny-shaped crack) limit of an oblate spheroid, but holds for other types of flat surfaces as well.
Effects of Ga and As desorption on the chemical beam epitaxy growth of (001) GaAs as measured by reflection high energy electron diffraction
Authors: Junno B. , Miller M. S. , Jeppesen S. , Samuelson L.
Published: July 2002

We have studied the balance between growth and desorption at a (001) GaAs surface in a chemical beam epitaxy chamber using reflection high energy electron diffraction. We found the growth rate to be proportional to the flux of our precursors tertiarybutylarsine and triethylgallium (TEG). The growth rates and desorption rates were found to be nearly constant in large temperature regions. The surface cracking of TEG limited the growth rate for low temperatures, and the desorption of Ga and As limited the high temperature growth rates. For high temperatures we show that through the application of the law of mass action the heat of evaporation for Ga can be determined to be 4.2±0.2 eV. This is very close to the values measured in molecular beam epitaxy. We thus conclude that the high temperature behavior is not determined by precursor desorption or chemistry and that the hydrogen and other chemical reaction products do not appreciably alter the GaAs phase diagram at chemical beam epitaxy growth conditions.
Magnetic force microscopy using nonoptical piezoelectric quartz tuning fork detection design with applications to magnetic recording studies
Authors: Todorovic M. , Schultz S.
Published: July 2002

We have developed a novel form of magnetic force microscopy that uses a commercial piezoelectric quartz tuning fork to detect magnetic forces and force gradients. Such a detection system is extremely simple and inexpensive, compared to conventional optical methods of cantilever vibration detection. The setup is, in addition, characterized by small size, which makes it attractive for studies done in constrained spaces. The instrument is first described, then theoretical comparison of signal to noise ratio and resolution is made with the conventional optical detection techniques of cantilever vibration, and finally, first images of thin film media commercial hard disk magnetic bit transitions, point response of magnetoresistive elements, and field gradients above the write gap of a commercial hard disk head are presented.
Processing effects on the magnetostrictive and physical properties of SmFe2/metal composites
Authors: Pinkerton F. E. , Capehart T. W. , Herbst J. F. , Brewer E. G. , Murphy C. B.
Published: July 2002

Hot pressed SmFe2/Fe and SmFe2/Al composites combine the large magnetostriction of SmFe2 with the mechanical robustness of the Fe or Al matrix. Here we report the dependence of the magnetostriction, density, and mechanical hardness on processing parameters, specifically on the SmFe2 volume fill fraction and the consolidation temperature. The magnetostriction increases monotonically with increasing SmFe2 content, but both the density and hardness decrease; low fill fraction composites are within 10% of theoretical density and have hardnesses of 40–85 Rockwell B, whereas hot pressed SmFe2 powder alone has high porosity (exceeding 30%) and is too soft to register on the Rockwell B hardness scale. The best combination of properties lies in the range of 40%–60% SmFe2. Similar competition between magnetostriction and physical properties is observed as a function of the temperature used to consolidate the samples. The magnetostriction falls slowly as the hot press temperature increases, probably as a result of chemical reaction between the SmFe2 phase and the matrix metal. On the other hand, higher temperature improves the consolidation, resulting in higher density and hardness. These results demonstrate that the magnetostrictive and physical properties of SmFe2 composites can be tailored by adjusting the fill fraction and processing temperature.
Magnetic moment and hyperfine field on Fe sites in RFe6Sn6 compounds
Authors: Rao Xiao-lei , Cullen J. , Skumryev V. , Coey J. M. D.
Published: July 2002

Electronic structure and hyperfine fields are calculated for antiferromagnetic YFe6Sn6 using the linear muffin-tin orbital method. The results show that Fe atoms have a strong ferromagnetic character with a full majority-spin band. The Fe moment is 2.2 μB while the Fermi contact term contributes a hyperfine field of 20 T at the natural lattice parameters. The hyperfine field is close to the experimental value of 22 T measured at low temperature. The calculation shows that the core s electrons contribute 24 T to the hyperfine field, but the 4s electron contributes 4 T in the opposite direction. Calculations using different unit cell volumes reveal that only the core electron contributions to the hyperfine field are proportional to the Fe magnetic moment with a conversion factor of 11.8 T/μB; the 4s contribution is not. The large local Fe moment and small hyperfine field are similar to those found in Fe2P and FeO.
Anomalous low-field magnetization in La2/3Ca1/3MnO3 near the critical point: Stable clusters?
Authors: Amaral V. S. , Araújo J. P. , Pogorelov Yu. G. , Sousa J. B. , Tavares P. B. , Vieira J. M. , Lopes dos Santos J. M. B. , Lourenço A. A. C. S. , Algarabel P. A.
Published: July 2002

The magnetic behavior of bulk La2/3Ca1/3MnO3 (TC=267 K) at low fields in the paramagnetic phase was studied. Near TC(T−TC<30 K) we find a sequence of steplike features in the effective Curie constant C(T)=M(T−TC)/H at well defined temperatures and intermediate plateaus, accompanied by temperature hysteresis. On approaching TC, the C values at each plateau follow a geometrical progression, with the effective spin S doubled at each step. The first plateau gives S=5.5, corresponding to a cluster of three Mn3+ ions sharing one extra hole. This suggests that close to TC short range magnetic order at low fields develops hierarchically through a series of most stable cluster states.
A kinetic Monte–Carlo study of the effective diffusivity of the silicon self-interstitial in the presence of carbon and boron
Authors: Johnson M. D. , Caturla M.-J. , Díaz de la Rubia T.
Published: July 2002

The effect of carbon on self-interstitial diffusion in Si is studied by means of a kinetic Monte–Carlo simulation. It is found that modest levels of carbon (≳1017 cm−3) significantly reduce the effective interstitial diffusivity. From fitting self-interstitial profiles, migration energies and prefactors of the effective diffusivity have been determined for a variety of background carbon levels. In addition, we re-examine recent experiments performed in samples with significant levels of carbon, which attempt to measure the effective diffusivity by monitoring the spreading of boron marker layers. We show that the presence of boron in delta-doped markers significantly alters the measured self-interstitial diffusivity.
Electrical characterization of MeV heavy-ion-induced damage in silicon: Evidence for defect migration and clustering
Authors: Giri P. K. , Mohapatra Y. N.
Published: July 2002

We have studied electrical activity of defects created by high-dose MeV heavy-ion implantation in n-silicon. Heavy damage induced by Ar+ and Au+ ions is embedded within depletion layers of Schottky diodes. The defects are characterized using capacitance–voltage (C–V), current–voltage (I–V), deep-level transient spectroscopy (DLTS) and time analyzed transient spectroscopy techniques. Large concentration of defects in the depletion layer of as-implanted device lead to unusual features in C–V and I–V characteristics. The damage layer is found to extend several microns beyond the ion range or the damage profile predicted by standard Monte Carlo simulation packages. The dominance of a single trap in the damaged region is established from hysteresis effect in C–V, space-charge-limited conduction in forward I–V and DLTS spectrum. With annealing in the temperature range of 400–600 °C, the observed changes in the defect profile indicate that the effective electrical interface between damaged and undamaged layer moves progressively towards the surface. From transient spectroscopic analysis the major defect is found to be a midgap trap whose energy is sensitive to the degree of disorder in the damaged layer. The experimental features in C–V characteristics have been simulated using model charge profiles taking into account crossing of the Fermi level with the midgap trap within the depletion layer. The simulations suggest the presence of a compensated region and a sharp negatively charged defect profile at a distance much larger than that expected from ion range. Our results constitute experimental evidence, in qualitative agreement with recent predictions of molecular dynamics simulations, of defect migration and clustering of interstitial related defects even at room temperature in the case of high-dose irradiation.
Characterization of breakdown phenomena in light emitting silicon n+p diodes
Authors: Snyman Lukas W. , Aharoni Herzl , du Plessis Monuko
Published: July 2002

A 10 kV, 10−10 A focused electron beam was used to map localized charge multiplication, and localized avalanche breakdown sites in the depletion region of light emitting silicon n+p junctions. It was observed that the localized avalanche breakdown sites led to the formation of large densities of extremely small current filaments in the junction. The dimension of each filament was well into the submicron range (100–150 nm in diameter) and the densities of the filaments varied laterally across the junction between 4×108 and 4×1010 cm−2. Accurate and high resolution maps of the current filaments could be obtained. The formation of the individual current filaments (microavalanche sites) at a submicron level are apparently related to localized defect and materials effects. The distribution of the current filaments at the micron level relates to the strength and distribution of electric field at the junction interface. Direct evidence has been obtained that the nonuniformities in the light emission patterns on a larger scale (10–100) microns are controlled by dopant striations on the lower doped p-side of the diode junction.
Optically pumped mid-infrared vibrational hydrogen chloride laser
Authors: Miller Harold C. , McCord John , Hager Gordon D. , Davis Steven J. , Kessler William J. , Oakes David B.
Published: July 2002

The results of an experimental investigation of an optically pumped vibrational laser in HCl are reported. Two different excitation sources were used: a Nd:yttrium–aluminum–garnet laser pumped optical parametric oscillator and a Raman shifted alexandrite laser. Overtone pumping on the (2,0) and (3,0) bands was employed to produce laser oscillation on the (3,2) and (2,1) bands near 3.8 μm. We also developed a model for the optically pumped laser and compare predictions of the model to the observed behavior of the laser. The photon efficiency of the HCl laser was found to be approximately 60%, consistent with model predictions and with previous optically pumped hydrogen halide lasers.
Electrical isolation of n-type GaAs layers by proton bombardment: Effects of the irradiation temperature
Authors: de Souza J. P. , Danilov I. , Boudinov H.
Published: July 2002

The electrical isolation in n-type GaAs layers produced by proton irradiation at temperatures from −100 to 300 °C was investigated. The threshold dose for the isolation (Dth) was found almost identical for irradiation at temperatures from −100 to 220 °C. At 300 °C, a dose of ≅1.3 times higher is required for the isolation threshold. In samples irradiated to a dose of Dth at −100 °C or nominal room temperature, the isolation is maintained up to a temperature of ≈250 °C. In those samples irradiated at 300 °C it persists up to ≈350 °C. For doses of 3Dth or above, the stability of the isolation is limited to temperatures of 450–650 °C, irrespective of the irradiation temperature (Ti). For practical applications where doses in excess to 5Dth are usually employed, the irradiation temperature (from −100 to 300 °C) has only a minor effect on the formation and thermal stability of the electrical isolation.
Characterization of sputtered amorphous platinum dioxide films
Authors: Maya L. , Riester L. , Thundat T. , Yust C. S.
Published: July 2002

Amorphous platinum dioxide, a-PtO2, films are formed commonly during reactive sputtering of platinum at relatively high power density levels and high oxygen partial pressures. The structure of a-PtO2 is intermediate between the crystalline alpha and beta phases of this compound and either phase may form upon annealing or by lowering the power density during sputtering. Amorphous platinum dioxide is a semiconductor, and its resistivity depends on deposition parameters. Films of a-PtO2 are dense, chemically resistant, smooth, reflective, and have a hardness similar to titanium nitride. The films may be reduced in hydrogen at room temperature or in carbon monoxide at 200 °C to produce metallic platinum with crystallite sizes in the range of 5–10 nm. Any of these properties may be exploited to produce films that could be used in the development of sensors, optical materials, and in microelectronics.
Laser plasma interaction at an early stage of laser ablation
Authors: Lu Y. F. , Hong M. H. , Low T. S.
Published: July 2002

Laser scattering and its interaction with plasma during KrF excimer laser ablation of silicon are investigated by ultrafast phototube detection. There are two peaks in an optical signal with the first peak attributed to laser scattering and the second one to plasma generation. For laser fluence above 5.8 J/cm2, the second peak rises earlier to overlap with the first one. The optical signal is fitted by a pulse distribution for the scattered laser light and a drifted Maxwell–Boltzmann distribution with a center-of-mass velocity for the plasma. Peak amplitude and its arrival time, full width at half maximum (FWHM), starting time, and termination time of the profiles are studied for different laser fluences and detection angles. Laser pulse is scattered from both the substrate and the plasma with the latter part as a dominant factor during the laser ablation. Peak amplitude of the scattered laser signal increases but its FWHM decreases with the laser fluence. Angular distribution of the peak amplitude can be fitted with cosn θ(n=4) while the detection angle has no obvious influence on the FWHM. In addition, FWHM and peak amplitude of plasma signal increase with the laser fluence. However, starting time and peak arrival time of plasma signal reduce with the laser fluence. The time interval between plasma starting and scattered laser pulse termination is proposed as a quantitative parameter to characterize laser plasma interaction. Threshold fluence for the interaction is estimated to be 3.5 J/cm2. For laser fluence above 12.6 J/cm2, the plasma and scattered laser pulse distributions tend to saturate.
Magnetostriction in spin valves
Authors: Baril Lydia , Gurney Bruce , Wilhoit Dennis , Speriosu V.
Published: July 2002

We report an accurate method for the measurement of the saturation magnetostriction λs of thin conducting ferromagnetic films using spin valve structures. We describe an alternative to the cantilever beam method, called the bending method, which utilizes the inverse magnetostrictive effect. Typical soft ferromagnetic films exhibit hysteretic magnetization loops, which make the measurements of the magnetoelastic energy (hence λs) imprecise or erroneous. We show how to resolve the hysteresis problem by application of a transverse field. We also demonstrate the quantitative connection between the cantilever and bending method in a comparative study of films spanning a large magnetostriction range. The sensitivity of measurement of magnetostriction using the bending method is better than 1×10−7.
Barkhausen noise in soft amorphous magnetic materials under applied stress
Authors: Durin Gianfranco , Zapperi Stefano
Published: July 2002

We report experimental measurements of Barkhausen noise on a Fe64Co21B15 amorphous alloy under tensile stress. We interpret the scaling behavior of the noise distributions in terms of the depinning transition of the domain walls. We show that stress induced anisotropy enhances the effect of short-range elastic interactions that dominate over long-range dipolar interactions. The universality class is thus different from the one usually observed in Barkhausen noise measurements and is characterized by the exponents τ≃1.3 and α≃1.5, for the decay of the distributions of jump sizes and durations.
Effect of the boron:rare-earth ratio on metastable phase formation in Nd2Fe14B-based nanocomposites
Authors: Lewis L. H. , Panchanathan V.
Published: July 2002

Magnetic nanocomposite alloys developed from amorphous precursors by annealing often exhibit metastable transition phases that ultimately control the kinetics of the nucleation and growth of the desired RE2Fe14B-type phase. It is thus important to understand the effect of starting composition on the formation of the metastable transition phases found in the nanocomposite system. The relationships between composition and the nature of metastable phase formation in the low-boron content melt-spun nanocomposite alloy Nd2[Co0.06(Fe1−xCrx)0.94]23.2B1.48 (0⩽x<0.09) were studied and compared with results of other authors. The crystallization sequence undertaken by the quenched samples during annealing was followed by differential thermal analysis and x-ray diffraction. Differences in the nominal starting boron:RE compositional ratio of the alloy may produce significant changes in the nature and stability of the metastable phases present in the system. In general, a high compositional ratio (B:RE≈1–4) promotes the initial formation of Fe3B and complex boron-rich intermetallic phases such as the cubic Nd2Fe23B3, the hexagonal NdFe12B6 and the cubic Y3Fe62B14-type phases in the quenched material, while a low compositional ratio (B:RE<0.5) is favors the formation of α-Fe and a 2-17-type phase. It is suggested that the focus of further studies done to optimize the performance of these nanocomposite alloys should be on the effect that alloying additions have upon the metastable phases, and not on the final equilibrium phases.
Primary beam energy dependence of properties in ion beam sputtered spin–valve films
Authors: Hegde Hari , Wang Jinsong , Hayes Alan , Kanarov Viktor , Yevtukov R. , Devasahayam Adrian J. , Gambino Richard J. , Mao Ming , Miller Mark
Published: July 2002

Spin–valve films with the structure Ta/NiFe/FeCo/Cu(18–30 Å)/FeCo/FeMn–70 Å/Ta were deposited using a Veeco ion beam deposition (IBD) system, model IBD-350. The physical properties of these spin–valve films as a function of primary ion beam energy have been studied in a primary ion beam energy range of 600–1500 eV. Xe was used as the working gas. The optimal ion beam energy range for the best spin-valve performance has been found to be around 600 eV. Giant magnetoresistance (GMR) values of ΔR/R∼8% have been measured for the spin–valve films deposited in this energy range. A strong dependence on beam energy of magnetic properties for these spin–valve films has been observed in the energy range from 600 to 1500 eV. ΔR/R for spin–valve films with a Cu layer thickness of 22 Å decreases from 7.5% at 600 eV monotonically to 6.1% at 1500 eV with increasing ion beam energy. Interlayer coupling field increases from 20 Oe at 600 eV to 37 Oe at 1500 eV. Further reduction in the interlayer coupling field to 13 Oe and an increase in ΔR/R to 8% have been achieved by depositing the free layer at 1000 eV and the rest of the layers at 600 eV. These are consistent with the improvement in crystallographic orientation and crystallinity of these spin–valve films.
In situ scanning tunneling microscopy characterization of step bunching on miscut Si(111) surfaces in fluoride solutions
Authors: Hoffmann Peter M. , Vermeir Inge E. , Natarajan Arun , Searson Peter C.
Published: July 2002

The immersion of Si surfaces in fluoride solutions results in the formation of a hydrogen passivated surface. The resulting surface morphology is dependent on the solution composition and the crystallographic orientation of the surface. Etching of miscut Si(111) in fluoride solutions can lead to the formation of mesa-like features. In this article we show that these features are due to the formation of step bunches during the etching process. The density of these features is dependent on the etch rate, the applied potential, and the fluoride ion concentration of the etching solution.
Luminescence from dislocations in silicon-germanium layer grown on silicon substrate
Authors: Lee Hosun , Choi Suk-Ho
Published: July 2002

We have studied the temperature and power dependence of the photoluminescence spectra which arose from the dislocations at the hetero-interface of very thin and partially strained Si0.6Ge0.4 alloys grown on silicon substrates. The temperature dependence of the integrated intensities of the Si D lines was compared to the literature. We attribute the absence of the SiGe D lines to the combined effect of the small conduction band offset and the large capture probability of the carriers by the dislocations in the underlying Si substrate.
Central-cell corrections for Si and S in GaAs in a strong magnetic field
Authors: Heron R. J. , Lewis R. A. , Simmonds P. E. , Starrett R. P. , Skougarevsky A. V. , Clark R. G. , Stanley C. R.
Published: July 2002

The central-cell correction has been determined experimentally for the two donor impurities S and Si in GaAs. Data have been obtained for magnetic fields to 39 T, corresponding to γ≈6. The observed behavior is in good agreement with theory. The analysis permits accurate evaluation of zero-field central-cell corrections, yielding 0.110 and 0.059 meV for S and Si, respectively.