bluuebunny/crossref_metadata_2025 huggingface dataset:
High transconductance heterostructure field-effect transistors based on AlGaN/GaN
Authors: Chen Q. , Asif  Khan M. , Yang J. W. , Sun C. J. , Shur M. S. , Park H.
Published: July 2002

We report on the fabrication and characterization of Al0.15Ga0.85N/GaN heterostructure field-effect transistors (HFETs) with transconductance as high as 120 mS/mm and saturated current density of 0.35 A/mm for a device with a gate length and width of 1 and 100 μm. This represents one of the best results for such device. A comparison of the maximum transconductance of devices on wafers with different channel conductance is presented to analyze the factors limiting the performance. Our data indicates the series resistance between the source and drain to be the limiting factor for the maximum dc transconductance.
Radiation enhanced diffusion of low energy ion-induced damage
Authors: Chen Ching-Hui , Green Debora L. , Hu Evelyn L. , Ibbetson James P. , Petroff Pierre M.
Published: July 2002

We have investigated the influence of concurrent above-band-gap laser illumination on the damage profile of GaAs/AlGaAs heterostructures subject to low energy (sub-keV) Ar+ ion bombardment. A dramatic change in damage profile was observed for these samples, compared with those that were not laser illuminated, and the degradation increases with the illuminated power intensity. Below-band-gap illumination results in a minimal increase in damage profile. Such results indicate the possibility of radiation-enhanced diffusion of defects, and may explain the observed high defect diffusivity at room temperature.
Thin film growth of semiconducting Mg2Si by codeposition
Authors: Vantomme André , Mahan John E. , Langouche Guido , Becker James P. , Van Bael Margriet , Temst Kristiaan , Van Haesendonck Chris
Published: July 2002

Ultrahigh vacuum evaporation of magnesium onto a hot silicon substrate (⩾200 °C), with the intention of forming a Mg2Si thin film by reaction, does not result in any accumulation of magnesium or its silicide. On the other hand, codeposition of magnesium with silicon at 200 °C, using a magnesium-rich flux ratio, gives a stoichiometric Mg2Si film which can be grown several hundreds of nm thick. The number of magnesium atoms which condense is equal to twice the number of silicon atoms which were deposited; all the silicon condenses while the excess magnesium in the flux desorbs. The Mg2Si layers thus obtained are polycrystalline with a (111) texture. From the surface roughness analysis, a self-affine growth mode with a roughness exponent equal to 1 is deduced.
Selective-area GaAs growth using nitrogen passivation and scanning-tunneling-microscopy modification on a nanometer scale
Authors: Kasu Makoto , Makimoto Toshiki , Kobayashi Naoki
Published: July 2002

A technique for the selective-area growth of GaAs on a nanometer scale is described. The technique comprises nitrogen (N)-passivation mask formation, scanning-tunneling-microscopy (STM) pattern modification, and metalorganic molecular-beam epitaxy. GaAs (001) surfaces are passivated with N radicals dissociated from N2 molecules and are modified by STM on a nanometer scale. GaAs nanostructures are then grown on the modified areas using trimethylgallium and tertiarybutylarsine. Uniform 6-nm-high and 50×50-nm2 dots were formed on 50×50-nm2 STM-modified areas. The advantage of the technique is that size-controlled nanostructures can be fabricated in specific positions and these nanostructures are free from contamination because all processes are performed in a vacuum.
The role of atomic hydrogen and its influence on the enhancement of secondary electron emission from C(001) surfaces
Authors: Humphreys T. P. , Thomas R. E. , Malta D. P. , Posthill J. B. , Mantini M. J. , Rudder R. A. , Hudson G. C. , Markunas R. J. , Pettenkofer C.
Published: July 2002

The role of chemisorbed hydrogen in the enhancement of low-energy electron emission from natural type IIb C(001) diamond surfaces has been investigated. A hydrogen induced low-energy emission peak, whose intensity was found to be a linear function of surface coverage, was observed. The direct observation of emission from vacuum level states in the photoemission spectra has determined a negative electron affinity of ∼0.4 eV for the hydrogenated C(001)-1×1 surface. Constant initial states photoemission has unambiguously identified the electron emission process with the escape of electrons from bulk electron states at the conduction-band minimum.
Fabrication and electrical properties of sol-gel derived BaTiO3 films with metallic LaNiO3 electrode
Authors: Li Aidong , Ge Chuanzhen , Lü Peng , Wu Di , Xiong Sibei , Ming Naiben
Published: July 2002

Metallic LaNiO3 (LNO) films were prepared on LaAlO3 (LAO) by metalorganic decomposition (MOD) and their application as the bottom electrode in sol-gel derived BaTiO3 (BTO) thin film was studied by means of x-ray diffraction, Raman spectroscopy, and scanning electron microscopy. BTO film on LNO-coated LAO exhibited preferred (100) orientation and smooth surface with fine grains (∼50 nm). Electrical measurements on BTO film capacitor showed good ferroelectric hysteresis, lower loss tangent and good insulating properties. These results indicated the BTO/LNO heterostructure fabricated by sol-gel and MOD technique to be a promising combination for microelectronic device applications.
Direct formation of nanocrystalline silicon by electron cyclotron resonance chemical vapor deposition
Authors: Choi Won Chel , Kim Eun Kyu , Min Suk-Ki , Park Chong-Yun , Kim Joon Hyung , Seong Tae-Yeon
Published: July 2002

We have confirmed the direct formation of nanosized crystalline silicon during the deposition of amorphous silicon layers by electron cyclotron resonance chemical vapor deposition (ECRCVD) on silicon and silicon–dioxide substrates. Two photoluminescence (PL) peaks at 680 and 838 nm were observed at room temperature from the samples. From cross-sectional high-resolution transmission electron microscopy (HRTEM) measurements, it was confirmed that nanosize silicon crystallites of 3–5 nm in diameter were randomly distributed throughout the amorphous silicon layer. Theoretical calculations using quantum size effects gave an average crystalline size of 4 nm which was consistent with the PL peak energy at 680 nm obtained from the sample. Also, the size of the crystallites could be controlled by the change of the substrate temperature during the deposition process.
Resonant tunneling through a self-assembled Si quantum dot
Authors: Fukuda M. , Nakagawa K. , Miyazaki S. , Hirose M.
Published: July 2002

Nanometer-scale Si quantum dots have been spontaneously fabricated on SiO2 by controlling the early stages of low-pressure chemical vapor deposition from pure silane. The tunneling current through Au/1 nm-SiO2/a single Si quantum dot/1 nm-SiO2/n+-Si(100) double-barrier structures has exhibited the clear current bump or negative conductance at 300 K with a peak current to valley ratio as high as 10.
Self-oscillating mode for frequency modulation noncontact atomic force microscopy
Authors: Giessibl Franz J. , Tortonese Marco
Published: July 2002

Frequency modulation atomic force microscopy (FM-AFM) has made imaging of surfaces in ultrahigh vacuum with atomic resolution possible. Here, we demonstrate a new approach which simplifies the implementation of FM-AFM considerably and enhances force sensitivity by directly exciting the cantilever with the thermal effects involved in the deflection measurement process. This approach reduces the mechanically oscillating mass by 6 to 8 orders of magnitude as compared to conventional FM-AFM, because external actuators and oscillating cantilever mounts are not needed. Avoiding external actuators allows the use of cantilevers with very high oscillation frequencies, which results in improved force sensitivity. Further, the implementation and operation of this new technique is significantly simplified, because external actuator, bandpass filter, and phase shifter are eliminated.
Observation of a Coulomb staircase in electron transport through a molecularly linked chain of gold colloidal particles
Authors: Sato T. , Ahmed H.
Published: July 2002

Submonolayer gold colloidal particles were deposited by using aminosilane [3-(2-aminoethylamino)propyltrimethoxysilane] as an adhesion agent on the substrate. It was observed that these submonolayer particles transform themselves into short chains of a few gold colloidal particles after a subsequent dithiol (1,6-hexanedithiol) treatment and an additional gold colloidal particle deposition. These chains bridged a gap that was formed between source and drain metal electrodes defined by electron beam lithography; thus realizing a quasi one dimensional current path between the source and drain. The device exhibited a clear Coulomb staircase at both 4.2 and 77 K.
Biaxially aligned buffer layers of cerium oxide, yttria stabilized zirconia, and their bilayers
Authors: Gnanarajan S. , Katsaros A. , Savvides N.
Published: July 2002

Biaxially aligned cerium oxide (CeO2) and yttria stabilized zirconia (YSZ) films were deposited on Ni-based metal (Hastelloy C276) substrates held at room temperature using ion beam assisted (IBAD) magnetron deposition with the ion beam directed at 55° to the normal of the film plane. In addition, we achieved, room-temperature epitaxial growth of CeO2 by bias sputtering to form biaxially aligned CeO2/YSZ bilayers. The crystalline structure and in-plane orientation of films was investigated by x-ray diffraction techniques. Both the IBAD CeO2 and YSZ films, and the CeO2/YSZ bilayers have a (111) pole in the ion beam direction.
Dispersion properties of aluminum nitride as measured by an optical waveguide technique
Authors: Tang Xiao , Yuan Yifang , Wongchotigul Kobchat , Spencer Michael G.
Published: July 2002

An aluminum nitride thin film on sapphire substrate was prepared by metal–organic chemical-vapor deposition for optical waveguide study. A rutile prism coupler was employed to display the waveguide modes (N lines) with wavelengths of 632.8, 532.1, 514.5, and 488.0 nm. The refractive index and thickness of the waveguide material were obtained by prism–coupler measurement. The parameters in the dispersion equation were determined by curve fitting. The attenuation in the waveguide was evaluated by scattering loss measurements using a fiber probe. The attenuation coefficient α is in the range of 1.5–2.1 cm−1 (5.4–7.6 dB cm−1), depending on the surface roughness of the sample and different orders of waveguide modes.
Size distribution of Ge islands grown on Si(001)
Authors: Goryll M. , Vescan L. , Schmidt K. , Mesters S. , Lüth H. , Szot K.
Published: July 2002

Atomic force microscopy analyses were performed on Ge islands on Si(001) grown by low pressure chemical vapor deposition in the temperature range from 525 to 700 °C. A comparison with theoretical models describing the growth of coherently strained and plastically relaxed islands is given to describe the observations. The mean diameter of coherently strained islands is found to be 170 nm over a wide range of temperature, whereas plastically relaxed islands grow up to diameters >500 nm. The aspect ratio turns out to be independent of the presence of dislocations. For the sample grown at 700 °C three size regimes could be observed, whereas the sample grown at the lowest temperature exhibits no island formation. At 550 °C islands with an average diameter of 33 nm and a low aspect ratio were observed; these could prove to be interesting in applications using quantum confinement effects.
Evolution of the Coulomb gap in tunnel-coupled quantum dots
Authors: Crouch C. H. , Livermore C. , Westervelt R. M. , Campman K. L. , Gossard A. C.
Published: July 2002

We report differential conductance measurements through a double quantum dot with adjustable interdot tunneling rate. The Coulomb gap of the double dot decreases continuously as the interdot tunnel conductance Gint is increased, from the gap of two isolated dots (when Gint∼0) to the gap of a single large dot of twice the total capacitance (when Gint=2e2/h). Excited electronic states in differential conductance measurements on single dots show a spectrum which is essentially independent of the number of electrons in the dot, but is not uniform.
Zero-dimensional excitonic confinement in locally strained Zn1−xCdxSe quantum wells
Authors: Nikitin V. , Crowell P. A. , Gupta J. A. , Awschalom D. D. , Flack F. , Samarth N.
Published: July 2002

We report on the observation of zero-dimensional (0D) excitonic confinement in locally strained Zn1−xCdxSe quantum wells. Strain fields from self-organized CdSe quantum dots are used to locally modulate the band structure of a nearby quantum well in a heterostructure, resulting in confinement in all three dimensions. The 0D nature of excitonic confinement is verified by the observation of sharp lines in photoluminescence (PL) spectra. The temperature dependence of the PL lifetime is markedly different than that of the CdSe quantum dots. High-resolution spectra show that the PL lines from the localized states are split into linearly polarized doublets.
In situ real-time analysis of alloy film composition and segregation dynamics with parallel detection reflection electron energy loss spectroscopy
Authors: Ahn C. C. , Yoshino H. , Tambo T. , Wong S. S. , He G. , Taylor M. E. , Atwater H. A.
Published: July 2002

Real-time measurements of GexSi1−x/Si(001) composition and segregation dynamics in Sn/Si(001) in molecular beam epitaxy are demonstrated using parallel detection reflection electron energy loss spectroscopy. Parallel detection enables quantitative acquisition of low-loss spectra in a time of <500 μs and surface composition determination in GexSi1−x/Si(001) via Ge L2,3 core loss analysis to a precision of approximately 2% in time of order 1 s. Segregation and trapping kinetics of monolayer thickness Sn films during Si epitaxy on Sn-covered Si(100) has also been studied using the Sn M4,5 core loss.
On the semiconducting state and structural properties of YH3 from first principles theory
Authors: Ahuja R. , Johansson B. , Wills J. M. , Eriksson O.
Published: July 2002

With the use of first principles theory we confirm the semiconducting ground state of the technologically interesting YH3 compound. Thus, unlike previously published theories, we demonstrate that density functional theory in the local density approximation reproduces the existence of a band gap. We also show that the HoD3 structure is the stable structure at ambient conditions, in agreement with experiment. In addition, we predict that moderate applied pressure will drive YH3 into the cubic structure.
Prebreakdown and breakdown effects in AlGaN/GaN heterostructure field effect transistors
Authors: Gradinaru G. , Khan M. Asif , Kao N. C. , Sudarshan T. S. , Chen Q. , Yang J.
Published: July 2002

Prebreakdown and breakdown effects under high electric fields in AlGaN/GaN heterojunction field effect transistors were studied. In the subthreshold regime, at large drain-to-source voltages (>80 V), along with the gate leakage current, a significant source current was measured. For a wide range of gate-to-source bias voltages in OFF and ON regimes, the breakdown voltage was limited by a rapid buildup of the source current, rather than a process dominated by gate leakage.
Dielectric property of (TiO2)x−(Ta2O5)1−x thin films
Authors: Gan J.-Y. , Chang Y. C. , Wu T. B.
Published: July 2002

( TiO 2 ) x −( Ta 2 O 5 ) 1−x thin films were prepared with radio-frequency magnetron sputtering deposition in this study. The dielectric constant measured from these films appears to critically depend on the amount of TiO2 incorporated into the film and post-anneal condition. The composition dependence was found similar to that reported on (TiO2)x−(Ta2O5)1−x bulk. The highest value of dielectric constant is about 55 for a TiO2 content of 8% and annealing at 800 °C. Compared to pure Ta2O5 thin films, significant enhancement in dielectric constant is obtained by adding small quantity of TiO2.
Large magnetoresistance in La0.7Sr0.3MnO3/SrTiO3/La0.7Sr0.3MnO3 ramp-edge junctions
Authors: Kwon C. , Jia Q. X. , Fan Y. , Hundley M. F. , Reagor D. W. , Coulter J. Y. , Peterson D. E.
Published: July 2002

We report on the fabrication of ferromagnet–insulator–ferromagnet junction devices using a ramp-edge geometry based on (La0.7Sr0.3)MnO3 ferromagnetic electrodes and a SrTiO3 insulator. The maximum junction magnetoresistance (JMR) as large as 23% is observed below 300 Oe at low temperatures (T<100 K). Our ramp-edge junctions exhibit JMR of 6% at 200 K with a field less than 100 Oe. The device performance at room temperature is believed to be limited by both the nearly equivalent coercive fields in the electrodes and the magnetization process, rather than by the insulating barrier.
Lateral electron confinement in narrow deep etched wires
Authors: Perez Florent , Zanier Sylvie , Hameau Sophie , Jusserand Bernard , Guldner Yves , Cavanna Antonella , Ferlazzo-Manin Laurence , Etienne Bernard
Published: July 2002

Narrow, dry, deep-etched GaAs/GaAlAs quantum wires with modulation doping are investigated by electronic Raman scattering (RS) and far-infrared magnetotransmission (FIR). Laterally-confined plasmon and magnetoplasmon dispersions and intensities lead to the determination of the confinement potential and the free and trapped electron densities. Free electrons are observed down to a critical width wc, significantly smaller under strong illumination (RS, wc=50 nm) than in dark conditions (FIR, wc=130 nm). The induced changes of the external confining potential and lateral electron distribution are analyzed in terms of a semiclassical electrostatic approach.
Surface anisotropy of polyimide film irradiated with linearly polarized ultraviolet light
Authors: Sakamoto K. , Usami K. , Watanabe M. , Arafune R. , Ushioda S.
Published: July 2002

Using polarized infrared (IR) absorption, we have investigated the surface anisotropy of a poly [4, 4′-oxydiphenylene-pyromellitimide] (PMDA-ODA) film that arises from anisotropic decomposition of the polyimide chain during irradiation with linearly polarized ultraviolet (LPUV) light. To monitor the surface anisotropy, we designed the sample structure so that the polyimide films decomposed uniformly over the entire film thickness. The surface anisotropy has a maximum at an irradiation energy of 105 J/cm2. For PMDA-ODA, the maximum surface anisotropy is significantly smaller than the surface anisotropy generated by rubbing. By analyzing the irradiation energy dependence of an IR absorption band, we found that the decomposition rate of the polyimide chain oriented parallel to the polarization direction of the LPUV light is greater only by ∼23% than that oriented perpendicular to it. This is the reason for the small surface anisotropy induced by the LPUV light irradiation.
Two-dimensional ordering of self-assembled Ge islands on vicinal Si(001) surfaces with regular ripples
Authors: Zhu Jian-hong , Brunner K. , Abstreiter G.
Published: July 2002

Two-dimensional ordering is achieved in a single layer of self-assembled Ge islands fabricated by molecular beam epitaxy on vicinal Si(001) surfaces with regular ripples caused by step bunching. The ripples with a typical period of about 120 nm lead to the long-range lineup of the Ge islands along their directions, while the strong repulsive interaction between the dense Ge islands determines their relative arrangement on different step bunches of a ripple. The ordering pattern can be tuned by the Ge coverage and the direction of the ripples. The ordering also helps to improve the size homogeneity of the Ge islands.
Optical properties and device applications of (InGa)As self-assembled quantum dots grown on (311)B GaAs substrates
Authors: Polimeni A. , Henini M. , Patanè A. , Eaves L. , Main P. C. , Hill G.
Published: July 2002

We have studied the optical properties of (InGa)As self-assembled quantum dots grown on (311)B-oriented GaAs substrates. The luminescence linewidth is considerably narrower than that of similar samples grown on (100). The difference is explained in terms of the in-plane coupling of dots which is more significant in (311)B. In order to assess the device potential of (311)B (InGa)As dots, we have studied the properties of edge emitting lasers by extending the well-known technology for (100) to the (311)B devices.
Interfacial reactions of Pd/Si0.76Ge0.24 by pulsed KrF laser annealing
Authors: Chen Da-Ren , Luo Jian-Shing , Lin Wen-Tai , Chang C. Y. , Shih P. S.
Published: July 2002

The interfacial reactions of Pd/Si0.76Ge0.24 were studied by pulsed KrF laser annealing as a function of energy density and pulse number. At an energy density of 0.1–0.4 J/cm2, a continuous germanosilicide layer composed of a low-temperature phase, Pd2(Si1−xGex), and a high-temperature phase, Pd(Si1−xGex), was formed. In contrast to vacuum annealing, Ge segregation out of the germanosilicide layer and the strain relaxation of the residual Si0.76Ge0.24 film could be effectively suppressed by pulsed KrF laser annealing at 0.1 J/cm2. Multiple pulse annealing at 0.1 J/cm2 could further homogenize the Pd concentration of the germanosilicide layer and promote the growth of Pd(Si1−xGex). Concurrently, the smoothness of the germanosilicide layer was substantially improved in comparison with those grown by vacuum annealing at temperatures above 200 °C. The studies also revealed that for multiple pulse annealing at 0.1 J/cm2 with a low repetition rate, 1 Hz, the evolution of phase formation and Pd diffusion could be proceeded by each individual laser pulse.
{311} defects in silicon: The source of the loops
Authors: Li Jinghong , Jones Kevin S.
Published: July 2002

The annealing kinetics of extended defects in Si+-implanted Si have been investigated by in situ annealing plan-view transmission electron microscopy (TEM) samples in a TEM. A 〈100〉 Czochralski-grown silicon wafer was implanted with 100 keV Si+ at the subamorphizing dose of 2×1014 cm−2. Following implantation, the effect of annealing of 800 °C was studied by in situ annealing. After 5 min of annealing at 800 °C, a dense collection of both {311} defects (3×1011/cm2) and small subthreshold dislocation loops (1×1011/cm2) were observed. Upon subsequent annealing, the {311} defect density decreased rapidly and the loop density increased. The evolution of approximately 500 {311} defects could be followed as a function of annealing time. The unfaulting of a {311} defect was observed to be the source of every subthreshold loop observed to from (about 150 loops in the monitored region). After the initial 5 min anneal at 800 °C, the probability of a {311} unfaulting into a loop was about 50%. Based on these observations, it is concluded that unfaulting of the {311} defects is the source of the subthreshold dislocation loops in nonamorphized ion-implanted silicon. 70% of the loops formed were determined to have a Burgers vector of a/3〈111〉, while 30% were perfect with a Burgers vector of a/2〈110〉.
Direct electronic transport through an ensemble of InAs self-assembled quantum dots
Authors: Jung S. K. , Hwang S. W. , Choi B. H. , Kim S. I. , Park J. H. , Kim Yong , Kim E. K. , Min S.-K.
Published: July 2002

Electronic transport properties through an ensemble of InAs self-assembled quantum dots are reported. A metal–semiconductor–metal diode with self-assembled quantum dots has been fabricated. Clear staircases are observed in the current–voltage characteristics measured from the diode, and several peak structures are identified in the differential conductance. These conductance peaks are interpreted as due to resonant tunneling through the energy states of the self-assembled quantum dots.
Radiative and nonradiative recombination processes in ultraviolet light-emitting diode composed of an In0.02Ga0.98N active layer
Authors: Narukawa Yukio , Saijou Shin , Kawakami Yoichi , Fujita Shigeo , Mukai Takashi , Nakamura Shuji
Published: July 2002

Radiative and nonradiative recombination processes have been studied in ultraviolet In0.02Ga0.98N light-emitting diodes (LEDs), by employing photoinduced voltage, electroreflectance, and time-resolved photoluminescence spectroscopy. It was found that excitons in the In0.02Ga0.98N active layer are weakly localized at low temperature, and delocalized above about 70 K, showing a three-dimensional feature in the temperature dependence of the radiative lifetime. The external quantum efficiency (ηext) of this LED is about ten times higher than the LED whose active layer is composed of GaN. Improvement of the ηext value by the addition of a small amount of In to the active layer is attributed to the suppression of the density of the nonradiative recombination center (NRC), as well as possibly to where the origin of the NRC is changed.
Clustering of ultra-low-energy implanted boron in silicon during postimplantation annealing
Authors: Schroer E. , Privitera V. , Priolo F. , Napolitani E. , Carnera A.
Published: July 2002

We report on the clustering behavior of ultra-low-energy (500 eV) implanted boron in silicon during the postimplantation activation annealing. The broadening of the boron concentration profile is found to be composed of a diffusing and a nondiffusing contribution. The nondiffusing part is attributed to clustered boron. The concentration of boron in clusters is found to be dependent on the annealing temperature and the annealing time. The amount of boron in clusters decreases with increasing annealing time. A dissolution time constant with an average activation energy of 2.3 eV is determined from this behavior.
Selective epitaxial growth of organic molecules on patterned alkali halide substrates
Authors: Shimada Toshihiro , Sakurada Takafumi , Koma Atsushi
Published: July 2002

Selective epitaxial growth of organic materials is found and analyzed. It is observed during the molecular beam epitaxy of organic molecules and charge transfer complexes on ionic surfaces. The selectivity comes from lattice matching condition on critical nuclei formation in contrast to compound semiconductors for which covalent chemical bonding plays essential roles. It can be utilized to fabricate micropatterns of crystalline organic materials accompanied by lithography processes of alkali halides using NH3 plasma. Feasibility of building three-dimensional microstructures has also been shown, which is readily applicable to make photonic crystals from optically functional organic materials.
Visible photoluminescence from self-assembled InAs quantum dots embedded in AlAs cladding layers
Authors: Lee U. H. , Lee D. , Lee H. G. , Noh S. K. , Leem J. Y. , Lee H. J.
Published: July 2002

Photoluminescence (PL) from InAs self-assembled quantum dots (QD) embedded in the AlAs matrix was strong and clean around 700 nm. PL efficiency remained quite high at room temperature compared to other QD systems embedded in GaAs cladding layers. Transmission electron microscope pictures from the structure showed a clear formation of relatively small and coherently strained InAs QD. The observed blueshift with accompanying broadening of PL spectra with the increase of excitation power is interpreted in terms of local carrier tunneling in a dense QD system. The PL peak redshift with the increase of temperature was very large, as much as 228 meV. The anomalous shift is interpreted as due to activation-energy differences between dots of different sizes.
Raman scattering from a self-organized Ge dot superlattice
Authors: Liu J. L. , Tang Y. S. , Wang K. L. , Radetic T. , Gronsky R.
Published: July 2002

We present a Raman scattering study of a self-organized Ge dot superlattice. The structure, which consists of 20 periods of Ge quantum dots sandwiched by 6 nm Si spacers, is grown on a Si (100) substrate by solid source molecular beam epitaxy. Cross-sectional transmission electron microscopy is used to characterize the structural properties of these Ge dots. Raman spectrum shows a downward shift of the Ge–Ge mode, which is attributed to the phonon confinement in the Ge dots. From polarization dependent Raman spectra, strong inter-sub-level transition in the Ge quantum dots is observed. From a simple calculation, the observed peak at 1890 cm−1 in the polarized spectrum is attributed to the transition between the first two heavy hole states of the Ge quantum dots.
Laser-assisted transfer of silicon by explosive hydrogen release
Authors: Toet D. , Thompson Michael O. , Smith P. M. , Sigmon T. W.
Published: July 2002

We present a technique for the transfer of silicon thin films. This transfer is effected by irradiating a hydrogenated amorphous silicon film deposited on a quartz substrate with an excimer laser pulse. The resulting release and accumulation of hydrogen at the film/substrate interface generates pressures sufficient to propel the silicon onto an adjacent glass receptor wafer. Transient optical transmission measurements indicate that the amorphous film is melted by the laser pulse and breaks into droplets during ejection. For fluences above 400 mJ/cm2, the transferred films adhere well to the receptors and can be smoothed using a second laser irradiation.
Magnetization vortices and anomalous switching in patterned NiFeCo submicron arrays
Authors: Shi Jing , Tehrani S. , Zhu T. , Zheng Y. F. , Zhu J.-G.
Published: July 2002

Switching characteristics of 20-nm-thick NiFeCo submicron arrays are systematically studied by means of magnetometry, magnetic force microscopy, and micromagnetic simulation based on solution of the Landau–Lifshitz–Gilbert equation. A switching anomaly found in these structures could not be described by the magnetization coherent rotation model. Both experimental data and simulation results indicate that trapped magnetization vortices are responsible for the switching anomaly.
Amorphous lanthanide-doped TiOx dielectric films
Authors: van Dover R. B.
Published: July 2002

Addition of Nd, Tb, or Dy to amorphous Ti–O thin films is found to improve the dielectric properties of the films. Specifically, substitution of 10–30 at. % of the dopant for Ti is found to dramatically decrease the leakage current, increase the breakdown voltage, and yet retain the relatively high dielectric constant ε=50–110 in films 35 nm thick. The high-specific-capacitance a-Ti1−yMyOx films thus produced are suitable for incorporation into future Si integrated circuit technology, e.g., for storage capacitors in semiconductor memory circuits.
Optical photonic crystals fabricated from colloidal systems
Authors: Subramania G. , Constant K. , Biswas R. , Sigalas M. M. , Ho K.-M.
Published: July 2002

Photonic crystals of close-packed arrays of air spheres in a dielectric background of titania have been fabricated with a ceramic technique. Unlike previous methods, ordering of the spheres and the formation of the titania network are performed simultaneously. The photonic crystals exhibit a reflectance peak and a uniform color at the position of the first stop band. The wavelength of the reflectance peak scales very well with the sphere size.
Growth and characterization of SrBi2Nb2O9 thin films by pulsed-laser ablation
Authors: Bhattacharyya S. , Bharadwaja S. S. N. , Krupanidhi S. B.
Published: July 2002

Polycrystalline films of SrBi2Nb2O9 were grown using pulsed-laser ablation. The ferroelectric properties were achieved by low-temperature deposition followed by a subsequent annealing process. The lower switching voltage was obtained by lowering the thickness, which did not affect the insulating nature of the films. The hysteresis results showed an excellent square-shaped loop with results (Pr=6 μC/cm2, Ec=100 kV/cm) in good agreement with earlier reports. The films also exhibited a dielectric constant of 250 and a dissipation factor of 0.02. The transport studies indicated an ohmic behavior, while higher voltages induced a bulk space charge.
Use of x-ray microbeams for cross-section depth profiling of MeV ion-implantation-induced defect clusters in Si
Authors: Yoon Mirang , Larson B. C. , Tischler J. Z. , Haynes T. E. , Chung J.-S. , Ice G. E. , Zschack P.
Published: July 2002

We have used submicron-resolution synchrotron x-ray beams to study the size, type, and depth distribution of ion-implantation-induced defect clusters in Si. A 0.65 μm resolution x-ray beam, generated using Fresnel zone plate focusing optics, was used to study (001)-oriented Si implanted at 300 °C with 10 MeV Si ions. Diffuse scattering measurements were made near the (220) Bragg reflection, as a function of depth on a (110) cross-sectioned sample, with a 0.65 μm depth resolution. The microbeam focusing optics and the depth-resolved scattering measurements are discussed, and an analysis of the intensity and lineshape of the diffuse scattering is presented in terms of existing models of vacancy and interstitial clusters in Si.
Formation of silicon–oxide layers at the interface between tantalum oxide and silicon substrate
Authors: Ono Haruhiko , Koyanagi Ken-ichi
Published: July 2002

Silicon–oxide layers formed at the tantalum–oxide/silicon interface were investigated by using Fourier transform infrared spectroscopy (FTIR). The samples were annealed in oxygen atmosphere, in nitrogen atmosphere, and in vacuum. It has been found that the formation of the interfacial silicon–oxide layers depends neither on the tantalum–oxide thickness nor on the annealing atmosphere, but on the annealing temperature. The silicon–oxide layer is formed even by annealing in vacuum. It is concluded that the silicon–oxide layer is formed not by a diffusion of the oxygen from the annealing atmosphere, but by a reaction between the tantalum–oxide film and the Si substrate. FTIR analysis and transmission electron microscopy of the interfacial layer show that the silicon–oxide layer has a bonding configuration different from a pure silicon dioxide.
Pressure stabilization and piezoelectric properties of polycrystalline perovskite PbZn1/3Nb2/3O3–PbTiO3
Authors: Koo T. Y. , Lee S. , Cheong S-W.
Published: July 2002

By using high-pressure heat treatment, we synthesized the single perovskite phase of polycrystalline (1−x)PbZn1/3Nb2/3O3–xPbTiO3 which was reported to show giant piezoelectricity in crystal forms. Piezoelectric constant of the polycrystalline materials at room temperature was found to become maximum at the rhombohedral side (x=8%) of morphotropic phase boundary. Microscopic strain under the electric field (E) along different crystallographic directions was identified by observing the x-ray Bragg peak shift of polycrystalline samples with E.
Exchange-biased La2/3Ca1/3(Sr1/3)MnO3 ultrathin films
Authors: Nikolaev K. R. , Krivorotov I. N. , Cooley W. K. , Bhattacharya A. , Dahlberg E. Dan , Goldman A. M.
Published: July 2002

Exchange-induced unidirectional anisotropy in trilayers consisting of a thin conductive ferromagnetic layer of La2/3Ca1/3(Sr1/3)MnO3 sandwiched between two antiferromagnetic layers of La1/3Ca2/3MnO3 has been demonstrated through studies of magnetization, magnetoresistance, and in-plane anisotropy of magnetoresistance. The structures were grown by ozone-assisted molecular beam epitaxy and were characterized by a number of techniques. The possibility for the development of exchange-biased magnetic tunnel junctions using these nonclassic double-exchange ferromagnets is discussed.
Scanning tunneling microscope light emission spectroscopy with picosecond time resolution
Authors: Uehara Y. , Yagami A. , Ito K. J. , Ushioda S.
Published: July 2002

Scanning tunneling microscope (STM) light emission spectroscopy with picosecond time resolution has been developed and applied to the measurement of time-resolved spectra of STM light emission from an evaporated Au film. The spectra consist of two components in the time-energy domain. The first component is excited by the picosecond tunneling current pulses that are generated by picosecond laser irradiation at the STM tip-sample gap. The second component arises from the plane-wave surface plasmon polaritons that are excited at the Au surface by the laser and made radiative by the presence of the STM tip that breaks the translational symmetry of the surface.
Temperature-independent switching rates for a random telegraph signal in a silicon metal–oxide–semiconductor field-effect transistor at low temperatures
Authors: Scofield John H. , Borland Nick , Fleetwood D. M.
Published: July 2002

We have observed discrete random telegraph signals (RTSs) in the drain voltages of three, nominally 1.25 μm×1.25 μm, enhancement-mode p-channel metal–oxide–semiconductor transistors operated in strong inversion in their linear regimes with constant drain-current and gate-voltage bias, for temperatures ranging from 4.2 to 300 K. The switching rates for all RTSs observed above 30 K were thermally activated. The switching rate for the only RTS observed below 30 K was thermally activated above 30 K but temperature independent below 10 K. This response is consistent with a crossover from thermal activation to tunneling at low temperatures. Implications are discussed for models of change exchange between the Si and the near-interfacial SiO2.
Implanted argon atoms as sensing probes of residual stress in ultrathin films
Authors: Lu W. , Komvopoulos K.
Published: July 2002

A technique for evaluating residual stresses in ultrathin films is presented and its effectiveness is demonstrated in light of residual stress measurements obtained for amorphous carbon (a-C) films of thickness 10–70 nm deposited on Si(100) substrates by radio-frequency sputtering. In this technique, small amounts of Ar atoms implanted within the near-surface region of the films are used as stress-sensing probes. The method is based on the effect of the film residual stress on the binding energy shift of the 2p electrons of implanted (or incorporated) Ar atoms determined from x-ray photoelectron spectroscopy. The basic requirements of this technique are discussed and its potential to determine residual stresses in ultrathin films is illustrated in light of comparisons with results obtained with a conventional stress measurement technique and annealing experiments performed with a-C films. The residual stress in the as-deposited a-C films, sensed by the incorporated Ar atoms, is confirmed by stress measurements based on the change of the sample curvature. In addition, the residual stress in a-C films leading to debonding after annealing, predicted by the present method, is shown to be in good agreement with that calculated from a blistering model for thin films under equibiaxial compression.
Spectroscopic investigations of a dielectric-surface-discharge plasma source
Authors: Arad R. , Tsigutkin K. , Ralchenko Yu. V. , Maron Y.
Published: July 2002

Spectroscopic investigations of the properties of a plasma produced by a flashboard plasma source, commonly used in pulsed plasma experiments, are presented. The plasma is used to prefill a planar 0.4 μs conduction time plasma opening switch (POS). A novel gas-doping technique and a secondary surface flashover plasma source are used to locally dope the plasma with gaseous and solid materials, respectively, allowing for spatially resolved measurements. The electron density, temperature, and plasma composition are determined from spectral line intensities and line profiles. Detailed collisional-radiative modeling is used to analyze the observed line intensities. The propagation velocity and divergence angle of various ions are determined from time-of-flight measurements and Doppler broadening of spectral lines, respectively. This allows for distinguishing the secondary plasma ejected from the POS electrodes from the plasma of the flashboard source.
Toward control of surface reactions with a scanning tunneling microscope. Structure and dynamics of benzene desorption from a silicon surface
Authors: Alavi Saman , Rousseau Roger , Seideman Tamar
Published: July 2002

A theoretical study of tip-induced desorption of benzene from a Si(100) surface is presented. The energetically forbidden process is triggered by inelastic resonance tunneling mediated by a cationic state of the substrate–adsorbate complex. Potential energy surfaces for the neutral and ionic states are computed within a cluster model. Quantum mechanical time-dependent wave packet calculations are used to explore the desorption dynamics. Extension of the scheme to study the response of different classes of organic adsorbates to tunneling current and to control of other surface reactions with a scanning tunneling microscope is discussed.
A combined crossed beam and ab initio investigation on the reaction of carbon species with C4H6 isomers. I. The 1,3-butadiene molecule, H2CCHCHCH2(X1A′)
Authors: Hahndorf I. , Lee H. Y. , Mebel A. M. , Lin S. H. , Lee Y. T. , Kaiser R. I.
Published: July 2002

The reaction between ground state carbon atoms, C(3Pj), and 1,3-butadiene, H2CCHCHCH2, was studied at three averaged collision energies between 19.3 and 38.8 kJmol−1 using the crossed molecular beam technique. Our experimental data combined with electronic structure calculations show that the carbon atom adds barrierlessly to the π-orbital of the butadiene molecule via a loose, reactantlike transition state located at the centrifugal barrier. This process forms vinylcyclopropylidene which rotates in a plane almost perpendicular to the total angular momentum vector J around its C-axis. The initial collision complex undergoes ring opening to a long-lived vinyl-substituted triplet allene molecule. This complex shows three reaction pathways. Two distinct H atom loss channels form 1- and 3-vinylpropargyl radicals, HCCCHC2H3(X2A″) and H2CCCC2H3(X2A″), through tight exit transition states located about 20 kJmol−1 above the products; the branching ratio of 1- versus 3-vinylpropargyl radical is about 8:1. A minor channel of less than 10% is the formation of a vinyl, C2H3(X2A′), and propargyl radical C3H3(X2B2). The unambiguous identification of two C5H5 chain isomers under single collision has important implications to combustion processes and interstellar chemistry. Here, in denser media such as fuel flames and in circumstellar shells of carbon stars, the linear structures can undergo a collision-induced ring closure followed by a hydrogen migration to cyclic C5H5 isomers such as the cyclopentadienyl radical—a postulated intermediate in the formation of polycyclic aromatic hydrocarbons (PAHs). © 2000 American Institute of Physics.
Secondary emission of dielectrics used in plasma display panels
Authors: Auday G. , Guillot Ph. , Galy J.
Published: July 2002

This experimental study concerns the secondary emission coefficient γ for two dielectrics (MgO and enamel) used in plasma display panels. Different pure rare gases were considered at pressures varying from 5 to 50 Torr. Here, we present the variations of coefficient γ as a function of the reduced field E/p. They were obtained by introducing the breakdown voltages measured experimentally on a sample of plasma panel, into the self-sustained equation. Concerning a 0.5 μm thick MgO layer, results are shown for five gases (helium, neon, argon, krypton, and xenon) whereas for a 25 μm thick enamel layer, they are presented for neon and xenon.
Determination of first and second magnetic anisotropy constants of magnetic recording media
Authors: Endo Yasushi , Kitakami Osamu , Okamoto Satoshi , Shimada Yutaka
Published: July 2002

We propose a simple method to evaluate the first and second magnetic anisotropy constants of high-density magnetic recording media with their easy axis in the film plane. By measuring the magnetization curve along the film normal, uniaxial anisotropy constants K1 and K2 can be determined simultaneously. The present method has been applied to (11⋅0) oriented CoCrPtTa hard disk media. The measured anisotropy constants are presented along with their temperature dependence. We also point out serious shortcomings of the currently used evaluation methods, such as the rotational hysteresis method and the singular point detection technique, which usually overestimate the magnetic anisotropy constant.
High-concentration ozone generator for oxidation of silicon operating at atmospheric pressure
Authors: Koike Kunihiko , Fukuda Tatsuo , Ichimura Shingo , Kurokawa Akira
Published: July 2002

A high-concentration ozone generator operating at atmospheric pressure was developed to produce ozone for use in fabrication of ultrathin silicon oxide films. A technique for adsorption onto silica gel, in which ozone has adsorption priority over oxygen, was adopted to obtain concentrated ozone. An ozone–oxygen mixture gas generated by a commercial ozonizer is fed in turn to three parallel adsorption columns that are kept at −60 °C. After the adsorption process, the ozone-enriched gas is desorbed by a slow warming of the columns from −60 to 0 °C and is stored in a storage vessel. Finally, the condensed ozone, at concentrations up to 30 vol % can be supplied continuously to a silicon oxidation chamber at atmospheric pressure and a constant flow rate. Moreover, highly concentrated ozone above 70 vol % can be produced in a batch process by using an additional purification procedure prior to the desorption. We confirmed that even with 25 vol % ozone gas, SiO2 film as thick as 6.3 nm grew on a Si substrate at 600 °C and 15 Torr in a 30 min exposure, while under the same experimental conditions only a 3.1 nm thick SiO2 film could be formed on the same substrate with pure oxygen.
A possible nature of “breathing” plasmas
Authors: Tokar M. Z. , Peterson B. J. , Nakamura Y. , Takeiri Y. , Noda N.
Published: July 2002

A model for “breathing” plasmas observed in the large helical device [Y. Takeiri et al., Plasma Phys. Controlled Fusion 42, 147 (2000)] is proposed. It takes into account the synergism of radiation losses from both low-Z (carbon, oxygen) and high-Z (iron) impurities in the plasma power balance.
Stimulated Brillouin and Raman scattering from a randomized laser beam in large inhomogeneous collisional plasmas. I. Experiment
Authors: Fuchs J. , Labaune C. , Depierreux S. , Tikhonchuk V. T. , Baldis H. A.
Published: July 2002

Experiments have been conducted at the LULI (Laboratoire pour l’Utilisation des Lasers Intenses) multibeam laser facility to study in detail stimulated Brillouin (SBS) and Raman (SRS) scattering from an intense (mean average intensity up to 1014 W/cm2) long (600 ps full width at half-maximum) laser beam interacting with thin exploded plastic foils. The plasmas are well characterized and the vacuum laser intensity distribution is well known due to using either random phase plates or polarization smoothing. Direct and simultaneous Thomson scattering measurements of the associated plasma waves allow us to obtain detailed information about the SBS and SRS temporal evolution and spatial localization. These data are being used to benchmark a statistical model of SBS and SRS from self-focused speckles. The results of this comparison will be presented in a companion paper. The analysis shows that both SBS and SRS are originated from self-focused speckles and reveals that plasma heating has an important effect on speckle self-focusing.
Instability of a broadband Langmuir wave spectrum in a dusty plasma
Authors: Farid T. , Shukla P. K. , Mirza A. M. , Stenflo L.
Published: July 2002

The nonlinear interaction between broadband Langmuir waves and electrostatic dust–acoustic perturbations in a uniform collisional dusty plasma is considered, taking into account the combined effects of the Langmuir wave ponderomotive force and the electron Joule heating nonlinearity. This coupling is governed by a Liouville equation for a Langmuir wave packet and an equation for a dust–acoustic perturbation that is driven by the ponderomotive and thermal forces of the random phase Langmuir waves. The mode coupling equations are then Fourier decomposed to derive the nonlinear dispersion relation. The latter is analyzed numerically for a Gaussian Langmuir wave spectrum, by taking parameters that are relevant for low-temperature dusty plasma discharges. It is found that a broadband spectrum of Langmuir waves is subjected to a rapidly growing modulational instability in a dusty plasma.