bluuebunny/crossref_metadata_2025 huggingface dataset:
n-type doping of the diluted magnetic semiconductor Zn1−xMnxSe
Authors: Abad H. , Jonker B. T. , Yu W. Y. , Stoltz S. , Petrou A.
Published: July 2002

We report on the intentional n-type doping of the diluted magnetic semiconductor Zn1−xMnxSe using ZnCl2 as the dopant source. Samples with varying Mn concentrations and carrier densities were grown by molecular beam epitaxy and characterized using Hall effect, x-ray diffraction, and photoluminescence measurements. Net carrier concentrations in excess of 1018 cm−3 are readily obtained for x≤0.08. Useful carrier densities can be achieved for Mn concentrations x≤0.15, above which the samples are highly insulating. The controlled doping of this alloy provides another material for use in the fabrication of wide gap semiconductor device structures.
Depth correlated lateral variations of layer thicknesses in GaAs-AlGaAs multiple quantum wells investigated by cathodoluminescence
Authors: Menniger J. , Kostial H. , Jahn U. , Hey R. , Grahn H. T.
Published: July 2002

Lateral variations of the exciton confinement energy Ecx have been investigated in a GaAs-AlGaAs multiple quantum well (MQW) structure using cathodoluminescence (CL) imaging in a scanning electron microscope. The MQW structure was grown by molecular beam epitaxy on a 2° misoriented GaAs substrate. The CL image of a defined MQW region does not change its lateral intensity distribution after removing different numbers of quantum wells by etching, indicating a correlated variation of Ecx between different quantum wells on a length scale of several μm. The variation of Ecx is connected to a mound like surface topography.
Resolution and intensity considerations of an ideal He atom time-of-flight spectrometer for measurements of surface phonon dispersion curves
Authors: Smilgies D.-M. , Toennies J. P.
Published: July 2002

Analytic expressions are derived to calculate the instrumental width of the phonon energy-loss peaks obtained in a helium atom inelastic scattering apparatus used in the measurement of surface phonon dispersion curves at single crystals. The formulas take into account all the kinematic effects arising from the velocity distribution of the incident beam, the angular resolution of the instrument, as well as the finite time resolution of the time-of-flight detection system. Implications for the optimal design parameters are discussed.
Negative magnetoresistance in parallel magnetic fields in InGaAs quantum wells with a δ-doped layer close to the quantum well
Authors: Herfort J. , Friedland K.-J. , Kostial H. , Hey R.
Published: July 2002

The magnetotransport properties in pseudomorphic GaAs/InGaAs/GaAs and AlGaAs/InGaAs/GaAs quantum wells with a Si δ-doped layer in the barrier close to the quantum well have been investigated. In the GaAs/InGaAs/GaAs system, a giant negative magnetoresistance is observed in the parallel magnetic field configuration. The effect is less pronounced if the doping is performed in the AlGaAs barrier. We attribute this giant negative magnetoresistance to the reduction of an additional impurity scattering process between two-dimensional states in the quantum well and inhomogeneously distributed donor states in the δ-doped layer. The experimental results in the GaAs/InGaAs/GaAs system are found to be in excellent agreement with a model that takes into account an oscillation between two-dimensional states and the δ-doped layer including an additional momentum in parallel magnetic fields.
New generation of oxide target for the deposition of ferroelectric thin films by sputtering
Authors: Descamps M. , Remiens D. , Chabal L. , Jaber B. , Thierry B.
Published: July 2002

PbTiO3 thin films have been prepared on Si/SiO2 substrates by radio frequency planar magnetron sputtering technique. The target used in this experiment consists of multilayers of PbO and TiO2 obtained by tape casting and cold pressing. The composition of the film is easily controlled by the thicknesses of the PbO and TiO2 layers and also by the surface erosion. Target design and preparation, growth parameters and annealing conditions have been optimized to obtain stoichiometric films in the tetragonal crystal structure without second phase.
Internal friction and its thermal evolution measured on very thin platinum films
Authors: Pelosin V. , Badawi K. F. , Branger V.
Published: July 2002

Internal friction has been measured between 300 and 800 K on thin platinum films using a vibrating reed device. The 575 and 1500 Å thick samples were deposited with ion assistance on silicon substrate. It has been shown that the damping level is considerably reduced by annealing between 650 and 800 K. Thanks to isothermal experiments, we have determined the activation enthalpy of the process involved in the present structural evolution. The calculated energies and complementary transmission electron microscopy micrographs let us assume that the observed mechanism is closely related to microstructural rearrangements located at grain boundaries.
Cation interdiffusion in InGaAsP/InGaAsP multiple quantum wells with constant P/As ratio
Authors: Hamoudi A. , Ougazzaden A. , Krauz Ph. , Rao E. V. K. , Juhel M. , Thibierge H.
Published: July 2002

On quaternary/quaternary multiple quantum wells, with constant P/As ratio and In-rich wells, we show the possibility of producing a blueshift of the heavy hole exciton line with interdiffusing only group III atoms, similarly to GaAs/GaAlAs and InGaAs/GaAs systems. This kind of structure, particularly suitable for group III diffusion study, has allowed us to obtain a quantitative value of the In–Ga interdiffusion coefficient at 850 °C: DIn–Ga≊4.72×10−16 cm2 s−1.
Spatial distribution of light-induced defects in hydrogenated amorphous silicon
Authors: Zhou Jiang-Huai , Kumeda Minoru , Shimizu Tatsuo
Published: July 2002

We have deduced the spatial distribution of defects in light-soaked hydrogenated amorphous silicon (a-Si:H) from the thickness dependence of the areal defect density using a large number of film thicknesses, ranging from 0.05 to 8.7 μm. The light soaking was done with strong white light generated by a Xe lamp with an infrared-cut filter and the defects were measured using electron spin resonance. The distribution of defects is found to be highly nonuniform and has an inverse power-law form Nv(x)=Ax−α, where Nv(x) is the defect density at depth x measured from the surface, and A and α (≊0.6) are constants and depend on the light-soaking time. Our results show unambiguously that the Staebler–Wronski effect is a bulk effect, however the regions close to the surface are affected much more by light soaking than the regions deep in the bulk of the sample.
Asymmetric YBa2Cu3O7−x dc SQUID: A three terminal device with current gain at 77 K
Authors: Koelle D. , Kleiner R. , Ludwig F. , Miklich A. H. , Dantsker E. , Clarke John
Published: July 2002

We have fabricated asymmetric, two-junction YBa2Cu3O7−x dc superconducting quantum interference devices (SQUIDs) on SrTiO3 bicrystal substrates and used them as three-terminal amplifiers by injecting signal currents directly into part of the superconducting loop. Using a second, readout SQUID to monitor changes in the critical current, we have achieved current gains up to 2.3 at 77 K. By coupling two SQUIDs together, we have increased the gain to 8.5 at 77 K. The experimental results are compared with numerical simulations, which are used to discuss potential increases in the gain.
On the wavefront distortion in holograms recorded in thermoplastic films
Authors: Carreño F. , Bernabeu E.
Published: July 2002

This letter analyzes the quality of reproduction of holograms recorded in thermoplastic media as a function of the variations in coating thickness of the different layers. The fidelity of reproduction is investigated by means of a phase sampling interferometric technique. It is found that the distortion depends on the processing parameters. A criterion for the optimization of the coating thickness of the layers is given.
Local phase detection probes in fluid/fluid two-phase flows
Authors: Cartellier A. , Achard J. L.
Published: July 2002

Phase detection is of primary importance for both the control and the characterization of fluid/fluid two-phase flows. Admitting that local probes ideally give access to the indicator function of one of the phases, various theoretical treatments of this information are reviewed. Optical, impedance, thermal and electrochemical techniques are then detailed, both for the associated theory of operation and the practical designs. A qualitative description of probe/interface interactions provides some insight into typical signal evolutions. From experiments performed in well-controlled conditions, the relation between signal and hydrodynamic phenomena can be partially quantified. Additional difficulties encountered in realistic situations are presented. Usual signal processing techniques are analyzed, as well as calibration procedures. The resulting accuracy of the sensors is then discussed on the basis of volume fraction measurements. Suggestions are given for future improvements.
Transverse Kerr magneto-optic measurements with a rotating analyzer ellipsometer
Authors: Minden H. T.
Published: July 2002

The use of a rotating analyzer ellipsometer is proposed to measure the spectral variation of the transverse Kerr magneto-optic effect. A low inductance coil is placed close to the sample in such a way that an alternating magnetic field is applied in the plane of the sample and perpendicular to the plane of incidence. First the quantities ψ and Δ are measured in the conventional way. For the magneto-optic effect the magnetization is varied at a high frequency. The analyzer and polarizer are fixed at specified angles while the magneto-optic signal is measured with a lock-in detector. The data are used to determine the real and imaginary parts of the magneto-optic coefficients and their relative sign. It is shown how to calculate from this measurement the value of the off-diagonal elements of the dielectric tensor.
Resonant-tunneling injection hot electron laser: An approach to picosecond gain-switching and pulse generation
Authors: Tolstikhin Valery I. , Willander Magnus
Published: July 2002

Recently, we proposed a three-terminal laser structure for fast gain-switching application using carrier heating, where hot electrons with well-defined and variable energy are injected into an active region via resonant tunneling. A picosecond pulse generation from this device has now been analyzed, including associated transport phenomena and structure design. By means of numerical modeling we demonstrate that a resonant-tunneling injection hot electron laser is capable of generating well-shaped optical pulses switched by varying the injected electron energy.
Stacking power MOSFETs for use in high speed instrumentation
Authors: Baker R. J. , Johnson B. P.
Published: July 2002

A reliable circuit configuration is described for stacking power metal–oxide semiconductor field effect transistors (MOSFETs). The resulting circuit has a hold off voltage N times larger than a single power MOSFET, where N is the number of power MOSFETs used. The capability to switch higher voltages and thus greater amounts of power, into a 50 Ω load, in approximately the same time as a single device is realized. Design considerations are presented for selecting a power MOSFET. Using the design method presented, a 1.4 kV pulse generator, into 50 Ω, with a 2 ns rise time and negligible jitter is designed.
Temperature dependence of the etch rate and selectivity of silicon nitride over silicon dioxide in remote plasma NF3/Cl2
Authors: Staffa J. , Hwang D. , Luther B. , Ruzyllo J. , Grant R.
Published: July 2002

The etch rates and selectivity of Si3N4 over SiO2 have been investigated by microwave discharging a mixture of NF3  and Cl2 and flowing the resultant fluorine and chlorine atoms and interhalogenous molecules simultaneously over a silicon wafer covered with low pressure chemical vapor deposition (LPCVD) Si3N4, and a wafer covered with thermally grown SiO2. The temperature dependence of the etch rates of Si3N4 and SiO2 in the NF3/Cl2 mixture was examined in the range from 25 to 500 °C, and the selectivity of the nitride etch over the oxide etch as well as nitride etch rate was found to increase with increasing temperature. It was also found that both etch rates and selectivities increase with NF3 flow rates within the range used in this study.
Possibility of depositing magnetic iron oxide films by excimer laser ablation of an organometallic polymer
Authors: Ouyang Meng , Hiraoka Hiroyuki
Published: July 2002

Magnetic iron oxide films were successfully deposited on heated fused-quartz substrates via the plume generated by the excimer laser ablation of poly(ferric methacrylate), an organometallic polymer, in an oxygen atmosphere. The investigation for the deposited films by means of x-ray photoelectron spectroscopy, Raman spectroscopy, x-ray diffraction, and scanning electron microscopy demonstrates that these films consist of iron-rich Fe3O4 and α-Fe2O3 phases that are made up of ball-like grains with nanometer-size structure. Magnetic hysteresis loop of the deposited film was also measured. The values of saturation magnetization, remanence magnetization, and coercivity are 35.6 emu/cm3, 6.13 emu/cm3, and 200 Oe, respectively.
Optimization of hemispherical electrostatic analyzer manufacturing with respect to resolution requirements
Authors: Vilppola J. H. , Keisala J. T. , Tanskanen P. J. , Huomo H.
Published: July 2002

Electrostatic analyzers with different geometries have been used extensively in space plasma investigations. When the energy resolution requirements are such that ΔE/E≊10% the instrument is rather simple to design and to manufacture. However, when an energy resolution of ≊1% is required, the manufacturing costs increase rapidly. For analyzers with an energy resolution of ≊10% the calibration can also be used to correct for manufacturing errors when they appear. In this paper, it has been shown that to reach an energy resolution ΔE/E=(1.6±0.2)% using a hemispherical electrostatic analyzer with outer and inner radii 101.25 and 98.75 mm respectively and plate thickness 0.4 mm, an accuracy of 25 μm in the alignment of one hemisphere with respect to the other is sufficient. It is also shown that the effect on the energy resolution of an indentation of the surface of one of the conductors can be neglected as long as its depth is less than ≊100 μm. Larger indentations can easily be detected in the manufacturing process. For each case considered, the maximum permitted loss of transmitted particles with respect to the transmission of an ideal instrument has been defined as 10%. Similarly, it has been specified that the deviations in the distributions of entrance angles of transmitted particles shall be less than 0.1°.
Step induced desorption of AsHx in atomic layer epitaxy on GaAs (001) vicinal substrates
Authors: Lee Jeong-Sik , Iwai Sohachi , Isshiki Hideo , Meguro Takashi , Sugano Takuo , Aoyagi Yoshinobu
Published: July 2002

We investigate the growth rate of GaAs homoepitaxy on (001) just and vicinal substrates as a function of substrate temperature, feeding rate of source gases, and H2 purge duration during the atomic layer epitaxy (ALE) process. The desorption of AsHx (x=0, 1, 2) on vicinal surfaces during ALE was confirmed to be the migration of adsorbed AsHx molecules on the surface and desorption at the steps.
Surface-related breakdown in silicon: Imaging of current filaments in long p+-n−-n+ structures
Authors: Hankla B. J. , Williams P. F. , Frecks G. A. , Peterkin F. E.
Published: July 2002

We present Schlieren images which show the existence and evolution of current filaments during the very early stages of surface-related breakdown inside 1 cm silicon p+-n−-n+ structures. These images confirm our previous finding that breakdown occurs in the silicon rather than in the ambient, and suggest that a streamerlike mechanism may be responsible.
Coulomb blockade and electrical field effect in nanoscale granular microbridges
Authors: Miura N. , Yoshikawa N. , Sugahara M.
Published: July 2002

Nanoscale microbridges made of NbN granular thin films were fabricated by the edge-defined process. The diameter of NbN grains is ∼8 nm, and the size of the microbridges is ∼50 nm in width and ∼200 nm in length. We have observed a clear Coulomb blockage at 4.2 K in current–voltage characteristics. In order to investigate electrical field effects, a gate electric field was applied to the microbridge. We observed periodic conductance modulations with the gate voltage period of 15–20 V, from which the gate-grain capacitance is estimated to be 0.01 aF. The experimental results agree with numerical simulation based on the model of a two-dimensional array of single-electron-tunneling junctions.
Position- and temperature-dependent optical properties of spark-processed silicon
Authors: Ludwig M. H. , Hummel R. E. , Augustin A. , Hack J. , Menniger J.
Published: July 2002

The structure of spark-processed silicon was examined in a comparative study of optical micrographs utilizing ultraviolet laser light and electron beams for excitation. Whereas the photoluminescence (PL) was found to be dominantly generated in granular structures near the surface, the cathodoluminescence (CL) mainly propagates from holes which were created during the preparation process. PL and CL spectra are not identical in their spectral distributions. Low temperature luminescence measurements for both excitation modes reveal a high degree of local disorder.
Low-temperature scanning tunneling microscope for use on artificially fabricated nanostructures
Authors: Wildöer J. W. G. , van Roy A. J. A. , van Kempen H. , Harmans C. J. P. M.
Published: July 2002

A scanning tunneling microscope (STM) has been developed, dedicated for use on artificially fabricated nanostructures at low temperatures. With this STM mesoscopic phenomena can be studied, combining the unique possibilities of scanning tunneling microscopy and artificially fabricated nanostructures for investigating the physics in this regime. The STM is vibration insensitive, has reliable coarse approach mechanisms in three dimensions, and operates at low temperatures. In order to be able to position the tip above the structure of interest, also a searching strategy has been developed. In this article we describe design and operation of the STM and demonstrate searching.
The phi meter: A simple, fuel-independent instrument for monitoring combustion equivalence ratio
Authors: Babrauskas Vytenis , Parker William J. , Mulholland George , Twilley William H.
Published: July 2002

An instrument has been developed to monitor the equivalence ratio in combustion systems. It is based on a novel oxygen consumption measuring method. The instrument does not require knowledge of the chemical composition of the process being monitored. Both gaseous and solid (soot) products of incomplete combustion are successfully handled. The device is relatively compact and can be developed for moderate cost and portable use.
Theoretical optical gain in InGaAsP/InP quantum well lasers: Evaluation of different envelope function schemes
Authors: Meney A. T. , Jones G.
Published: July 2002

The authors demonstrate that in 1.55 μm InGaAsP/InP quantum well lasers proper inclusion of the conduction-valence coupling is essential to obtain accurate gain characteristics. It is shown that the orbital character of the confined subbands, and the resulting optical matrix elements, play a dominant role.
Investigation of the interfacial order of nematic liquid crystal on photopolymer coated conducting glass substrates with a scanning tunneling microscope
Authors: Jain S. C. , Rajesh K. , Samanta S. B. , Narlikar A. V.
Published: July 2002

High resolution images of individual molecules of the liquid crystalline material adsorbed on a photopolymer treated transparent conducting (indium oxide coated) glass plate have been obtained with a scanning tunneling microscope (STM). The ultrathin layer of the photopolymer poly-vinyl-4-methoxy-cinnamate (PVMC) on the conducting glass plate was deposited by the bulk induced alignment technique reported earlier [S. C. Jain and H.-S. Kitzerow, Appl. Phys. Lett. 64, 2946 (1994)]. The liquid crystal molecules exhibit a positional order, in addition to a high degree of orientational order of the bulk nematic. This surface ordering of the nematic liquid crystal at the polymer interface is quite different from the ordering observed on graphite and molybdenum disulphide substrates. A small ensemble of molecules show antiparallel ordering of the cyano-phenyl-cyclo-hexane molecules in agreement with the calculations of Schadt et al. [Liq. Cryst. 5, 293 (1989)].
Carbonization-induced SiC micropipe formation in crystalline Si
Authors: Scholz R. , Gösele U. , Niemann E. , Leidich D.
Published: July 2002

The defect structure of Si substrates at their β-SiC/Si interfaces generated in a chemical vapor deposition (CVD) process by carbonization with C2H4 has been investigated in detail by transmission electron microscopy (TEM) using differently prepared cross section and planar specimens. A new category of defects of minute size and high area density has been found and identified as SiC micropipes formed by Si outdiffusion and simultaneous ingrowth of SiC. A model of self-adjusting micropipe formation is proposed.
Electrochemiluminescence from porous silicon in formic acid liquid-junction cells
Authors: Green Will H. , Lee Eric J. , Lauerhaas Jeffrey M. , Bitner Theodore W. , Sailor Michael J.
Published: July 2002

Visible light emission from porous silicon can be stimulated by applying a positive bias to a formic acid/sodium formate liquid junction cell. The emission lasts for 45 min at +2.75 V applied potential (<5 mA/cm2, power conversion efficiency ≳10−2%) and is reliably generated from n- or p-type porous silicon. An applied voltage as low as 1.3 V is capable of generating the red (720 nm) emission, indicating that current-induced chemical reactions aid in the generation of charge carriers. A mechanism involving oxidation of formic acid followed by electron injection from a CO2− radical is proposed. Infrared spectra of the porous silicon surface taken after anodization show formation of a stable silyl-ester species that is thought to be responsible for the increase in radiative recombination efficiency through passivation of surface defects.
History dependent domain structures in giant-magnetoresistive multilayers
Authors: Hardner H. T. , Weissman M. B. , Parkin S. S. P.
Published: July 2002

Resistance noise measurements of several types reveal the field history dependence of domain structure in sputtered Co/Cu multilayers. We find many smaller domains as the field is decreased from saturation towards zero, but as the field changes sign and is increased in the opposite direction we observe a smaller number of larger domains. Cycling the field without changing its sign preserves the smaller domains, strongly reducing the Barkhausen noise. Discrete fluctuations in resistance due to individual domains yield domain size estimates.
Electroabsorption enhancement in disordered, strained InGaAs/GaAs quantum well
Authors: Micallef Joseph , Li E. Herbert , Weiss Bernard L.
Published: July 2002

The results of modeling the application of an external electric field to disordered, strained InGaAs/GaAs single quantum well are presented. An error function profile is used to model the constituent atoms composition after interdiffusion. Results indicate that the exciton Stark shift in the disordered quantum well is greater than in the as-grown 10 nm wide In0.2Ga0.8As well, and that the change in electroabsorption near the fundamental exciton absorption peak is enhanced by 30% in the disordered quantum well for a 30 kV/cm electric field applied perpendicular to the well. These results may be used to achieve optical modulators with improved performance characteristics in strained quantum well structures.
Effects of turbulent fluctuations on density measurements with microwave reflectometry in tokamaksa)
Authors: Mazzucato E. , Nazikian R.
Published: July 2002

The short-scale turbulence of tokamak plasmas has deleterious effects on the measurement of plasma density with microwave reflectometry. Density fluctuations may lead to large amplitude and phase modulations of the reflected wave which can impair the measurement of the wave group delay, and hence the determination of the plasma density. The role played by different types of turbulent fluctuations and the limitations imposed on microwave reflectometry are discussed.
Signal gain due to a polarization coupling in an AlGaAs channel waveguide
Authors: Aitchison J. S. , Kang Jin U. , Stegeman G. I.
Published: July 2002

We experimentally demonstrate signal gain for picosecond signals due to an orthogonally polarized pump beam in an AlGaAs channel waveguide at a wavelength of 1.55 μm, below half the band gap. We show as much as 40% signal gain, or depletion, depending on the polarization states of the pump and the probe. The results are in good agreement with theory.
ECE imaging array diagnostic development of TEXT-U
Authors: Hsia R. P. , Geck W. R. , Cheng S. , Zhang W.-M. , Domier C. W. , Luhmann N. C.
Published: July 2002

Wide bandwidth, low cost, 20 channel monolithic, and hybrid Schottky diode mixer arrays are under development for electron cyclotron emission (ECE) diagnostics on TEXT-U. These arrays, designed to measure 2nd harmonic ECE emission between 90 and 140 GHz, will be used to form two-dimensional temperature profiles and two-dimensional images of thermal fluctuations. Fabrication and test results are presented, together with details regarding the actual implementation on TEXT-U.
Calibration and testing of a sixteen-beam grating-based division-of-amplitude photopolarimeter
Authors: Cui Y. , Azzam R. M. A.
Published: July 2002

Results for the calibration and testing of a 16-beam grating-based division-of-amplitude photopolarimeter, that take into account the effect of source polarization and imperfections of the polarization state generator, are presented. A model is developed to analyze the elements of the instrument matrix obtained from calibration. The experimental results are compared with the predictions of the model, and useful information is extracted about the optical elements of the system.
Ion plasma sputtering as a method of introducing solid material into an electron cyclotron resonance ion source
Authors: Harkewicz R. , Billquist P. J. , Greene J. P. , Nolen J. A. , Pardo R. C.
Published: July 2002

A direct ion plasma sputtering effect has been observed in an electron cyclotron resonance ion source and developed into a reliable and simple method for producing ion beams from some solid materials. We describe the ion sputtering technique used with the Argonne Tandem Linac Accelerator System Positive Ion Injector Electron Cyclotron Resonance ion source to produce, to date, stable beams of nickel, silver, tellurium, gold, lead, and bismuth and present the results obtained in test cases.
Characteristics of a two-component chemically-assisted ion-beam etching technique for dry-etching of high-speed multiple quantum well laser mirrors
Authors: Sah R. E. , Ralston J. D. , Weisser S. , Eisele K.
Published: July 2002

We have developed a two-component chemically-assisted ion-beam etching (CAIBE) technique for dry-etching of high-speed multiple quantum well (MQW) laser mirrors. This two-component process relaxes several constraints in the dry-etching of Al containing opto-electronic device structures with Cl2 alone. The strained 3×100 μm2 In0.35Ga0.65As/GaAs undoped and p-doped 4-QW ridge waveguide lasers containing GaAs/AlAs binary short-period superlattice cladding layers with cavities fabricated by this CAIBE technique demonstrate record direct modulation bandwidths of 24 GHz (Ibias=25 mA) and 33 GHz (Ibias=65 mA), respectively.
Direct observation of injected charges at insulator-electrode interfaces in strongly diverging fields
Authors: Ditchi T. , Bazin G. , Lewiner J. , Alquié C.
Published: July 2002

Various theoretical models have been proposed to explain the behavior of insulator-electrode interfaces in the case of strongly diverging electric fields. Until now, direct measurement of the charge transferred at these interfaces could not be performed. In this letter, we propose a novel structure which allows for such measurements. An application is presented in which charge transfer around 30 μm diameter wires embedded in an insulator is directly observed.
Carrier leakage in blue-green II–VI semiconductor lasers
Authors: Buijs Maarten , Shahzad Khalid , Flamholtz Sharon , Haberern Kevin , Gaines Jim
Published: July 2002

Carrier confinement in blue-green II–VI semiconductor lasers was investigated. For devices longer than 300 μm an energy barrier of 260–280 meV was found to confine the electrons, the carrier being mainly responsible for leakage, within the active region. Shorter devices show more leakage due to an increased importance of mirror losses which require higher threshold gain. Due to the low conductivity of the p-type cladding layer there is a sizable contribution of drift to the total leakage current.
Ground tilt seismic spectrum measured with a new high sensitivity rotational accelerometer
Authors: Luiten A. N. , Beccaria M. , Bernadini M. , Braccini S. , Bradaschia C. , Cella G. , Ciampa A. , Curci G. , Cuoco G. E. , D’Ambrosio E. , Dattilo V. , De Salvo R. , Del Fabbro R. , Di Virgilio A. , Feng G. , Ferrante I. , Fidecaro F. , Gaddi A. , Gennai A. , Giazotto A. , Holloway L. , La Penna P. , Losurdo G. , Malik S. , Mancini S. , Pan H. B. , Paoletti F. , Pasqualetti A. , Passuello D. , Poggiani R. , Raffaelli F. , Viceré A. , Zhang Z.
Published: July 2002

We describe a new rotational accelerometer exhibiting excellent rotational acceleration sensitivity of 2–3×10−9 rad s−2/√Hz for frequencies below 2 Hz and increasing as the square of frequency for frequencies higher than 2 Hz. The sensitivity to horizontal linear accelerations and static tilts is 60 dB less than its rotational sensitivity. The accelerometer has been used to characterize the seismic ground tilt spectrum. Measurements of the performance of the device and of the seismic rotational spectrum are presented.
Band alignment at the CdS/Cu2In4Se7 heterojunction interface
Authors: Nelson A. J. , Schwerdtfeger C. R. , O’Brien W. L.
Published: July 2002

Band offsets at the CdS/Cu2In4Se7 heterojunction interface were studied by synchrotron radiation soft x-ray photoemission spectroscopy. CdS overlayers were sequentially grown in steps, at room temperature, on the Cu2In4Se7 crystal. Photoemission measurements were acquired after each growth to determine the electronic structure at the heterojunction interface. Results of these measurements indicate that the valence-band offset ΔEvbm is 1.10(±0.20) eV and that the conduction-band offset ΔEcbm is 0.22(±0.20) eV for the CdS/Cu2In4Se7 heterojunction.
Secondary defect annihilation in ion beam processed SixGe1−x layers using titanium silicide
Authors: Kyllesbech Larsen K. , La Via F. , Lombardo S. , Raineri V. , Campisano S. U.
Published: July 2002

The secondary defect annihilation titanium silicidation in SixGe1−x layers, formed by high dose Ge implantation in (100) silicon, has been studied systematically as a function of the Ge fluence, implantation energy, and TiSi2 thickness. Rutherford backscattering spectrometry and transmission electron microscopy have been used to investigate the damaged SixGe1−x layer recovery and to monitor the germanium diffusion and reaction during the silicidation. For the highest fluence of 3×1016 Ge/cm2 (≊15 at. % Ge) it is found that nearly a complete annihilation of the secondary defects can be achieved after the first low-temperature silicidation step. After a second high-temperature silicidation step all residual defects have been removed. For fluences lower than 3×1016 Ge/cm2 a complete recovery is already obtained after the first silicidation step.
High temperature sound velocity measurement with piezoelectric transducers
Authors: Alves J. Maia , Vallêra A. M.
Published: July 2002

A technique for high temperature sound velocity measurement using piezoelectric transducers, that avoids the existence of the usual high temperature bond between the sample and the buffer, was developed. This bond is frequently responsible for a large attenuation and distortion of the sound field, with a consequent inaccuracy in the experimental results. This technique was successfully used by the authors to make good quality measurements of sound velocity in iron–silicon single crystals from room temperature to T≈1000 °C, unlike other authors who report strong attenuation in different regions of this temperature range for similar samples. The furnace, which is only 35 mm wide, allows work under magnetic field and a controlled atmosphere up to 1300 °C.
Direct observation of precipitates and self-organized nanostructures in molecular-beam epitaxy grown heavily doped GaAs:Si
Authors: Gwo S. , Miwa S. , Ohno H. , Fan J.-F. , Tokumoto H.
Published: July 2002

We report a cross-sectional scanning tunneling microscopy investigation of heavily Si doped [001]-oriented GaAs grown by molecular-beam epitaxy. At a very high doping level (6×1019 cm−3), Si-doping induced precipitates are directly observed in XSTM images of the as-grown epitaxial layers. Most of the precipitates are found to have a characteristic oval shape with the long axis (∼80 Å) along the growth direction. In contrast to the low diffusivity of randomly distributed Si dopants in the moderate doping regime, these precipitates are found to be highly mobile and spontaneously form ‘‘nanowires’’ during crystal growth.
Mechanisms for polycrystalline silicon defect passivation by hydrogenation in an electron cyclotron resonance plasma
Authors: Cielaszyk E. S. , Kirmse K. H. R. , Stewart R. A. , Wendt A. E.
Published: July 2002

An in-line mass spectrometer and Langmuir probes have been employed to examine mechanisms of plasma immersion hydrogen passivation of grain boundary defects in polycrystalline silicon thin film transistors. Relative fluxes of H+ and H+2 as well as total ion current density were measured at the substrate location in an electron cyclotron resonance hydrogen discharge. Measurements were made over a range of operating conditions over which passivation rates have been shown to vary dramatically. Data presented show a strong correlation of both H+ flux and ion bombardment energy with good transistor performance obtained at operating pressures below 1 mTorr. This suggests that discharge operating conditions that promote dissociation of H2 to form H and H+ (which may diffuse more rapidly through solid material than H2), as well as increased sheath voltages and therefore ion energy at the substrate, are important to obtaining acceptable process rates.
A multipurpose miniature piston-cylinder diamond-anvil cell for pressures beyond 100 GPa
Authors: Yu. Machavariani G. , Pasternak M. P. , Hearne G. R. , Rozenberg G. Kh.
Published: July 2002

A miniature piston-cylinder diamond-anvil cell (DAC) was constructed and tested for pressure operation at and beyond 100 GPa. Its advantages compared to other piston-cylinder DACs are its compactness (22-mm diam by 21-mm high), self-contained force generator, and simple way of operation. Tungsten carbide backing plates are used for supporting the anvils; one with a hemispherical shape allowing for parallelism alignment, and one with a flat circular shape allowing for lateral alignment of the anvils’ culets. The force is generated by six M3 Allen screws and is conveyed to the piston via force rings. Pressures to 130 GPa were achieved with beveled culets having 300-μm flats and Re gaskets. Design features, mode of operation, and performance are described. The latter has been demonstrated for the particular case of Mössbauer spectroscopy in La57FeO3.
Ultrafast gain-switching dynamics in 1.5 μm dynamical single-mode semiconductor lasers: 50–130 GHz high frequency self-pulsations
Authors: Wang Jian , Schweizer Heinz , Kovač Janez , Kaden Christiane , Zielinski E. , Klenk M. , Weinmann R.
Published: July 2002

In this letter generation of up to 130 GHz high frequency self-pulsation in ultrafast gain-switched InGaAs/InGaAsP dynamical single-mode lasers with monolithically integrated external cavities is reported. With various active cavity lengths and external cavity lengths, the dependence of the pulsation frequency on the length of the respective cavity is shown and analyzed in detail for a pulsation frequency range from 50 to 130 GHz. Theoretically, by treating the external cavity as a gain-switched laser amplifier and taking into account the coherent time-dependent amplification, shortening and reflection of an incident picosecond optical pulse in the gain-switched amplifier, we can well understand and simulate the observed high frequency self-pulsations.
Generation and tuning of second harmonic radiation produced by ultrashort dye laser pulses from a gold surface
Authors: Moustaïzis S. D. , Papadogiannis N. A. , Fotakis C. , Farkas Gy. , Tóth Cs.
Published: July 2002

Tunable second harmonic radiation has been generated on a gold surface by means of a dye laser system capable of emitting pulses of 450 fs and 4.5 ps duration. The intensity of harmonic radiation was maximum along the direction of the reflected incident laser beam, when the polarization direction of the incoming radiation was vertical to the target surface (p polarization). The efficiency for second harmonic generation was found to depend strongly on the pulse duration of the laser beam. The observed change of the harmonic generation efficiency as a function of the angle of incidence and the pulse duration of the laser beam suggests that, due to coherence effects, the actual overlapping spatial dimension of the interaction region between the laser pulse and the electron gas of the metallic surface plays an important role.
Suppression of self-pulsation for tens of gigahertz optical pulses from passively mode-locked semiconductor lasers
Authors: Yu J. , Bimberg D.
Published: July 2002

43 GHz repetition rate Fourier transform-limited light pulses of a width of 1.5 ps are achieved by passively mode-locking an ion-implanted semiconductor laser in a very short external cavity. A higher repetition rate is limited by strongly mixed self-pulsation. A numerical investigation of passive model-locking is carried out based on the solution of traveling wave rate equations of an external cavity semiconductor laser. We find that the gain nonlinearity factor can significantly influence the present range of the mixed self-pulsation. With the increase of the nonlinearity factor, the operation tends to pure passive mode-locking at a low injection current. In addition, the proper adjustment of the ratio of differential absorption to differential gain and the carrier lifetime in the absorber can reduce the necessary current for pure passive mode-locking.
Observation of a single photoluminescence peak from a single quantum dot
Authors: Nagamune Y. , Watabe H. , Nishioka M. , Arakawa Y.
Published: July 2002

We observed a very sharp photoluminescence peak from a single GaAs/AlGaAs quantum dot structure by using a microphotoluminescence measurement technique. The spectral linewidth was more suppressed by decreasing the excitation laser power, which is mainly due to reduction of the filling effect of quantized energy levels. The minimal spectral linewidth with low excitation laser power was 0.9 meV.
Compression mechanism of picosecond optical pulse in far infrared waveguide free electron laser
Authors: Hu Suxing , Fu Ensheng
Published: July 2002

We have investigated the compression mechanism of picosecond optical pulses in a far infrared waveguide free electron laser driven by a radio frequency linear accelerator. With a pertinent waveguide gap b and the required original phase velocity of the electron bunch, the longitudinal length of a picosecond optical pulse will be continuously shortened so that the pulse power increases quickly until saturation occurs. In order to continue the compression process, an optimal cavity detuning ΔLc is necessary.
UV-induced transmission frustration in optical fibers
Authors: Danailov M. B. , Apai P.
Published: July 2002

In this letter we report experimental observations of transient UV-induced frustration of the visible light transmission through Ge-doped single mode fibers. Fiber side exposure to single nanosecond UV pulses at 266 and 248 nm is found to cause an abrupt decrease in transmission immediately following the pulse and a transmission recovery in microsecond time scale. Transmission changes were monitored at several visible wavelengths and for different types of Ge-doped single mode fibers. The reported effect occurs independently of the growth and saturation of the permanent UV-induced absorption reported by other authors.
Properties of vapor phase epitaxial zinc selenide codoped with cadmium and chlorine
Authors: Bao K. , Healey P. D. , Gokhale M. , Ayers J. E. , Jain F. C.
Published: July 2002

Zinc selenide epitaxial layers have been grown by ultraviolet-assisted organometallic vapor phase epitaxy (OMVPE) with cadmium and chlorine codoping, using the sources DMSe, DMZn, DMCd, and HCl. Growth was carried out at 400 °C with ultraviolet irradiation at an intensity of 4 or 7.5 mW/cm2. Samples codoped with cadmium showed increased incorporation of chlorine donors relative to control samples having no cadmium codoping. This effect was more pronounced at the lower ultraviolet intensity. The growth rate for the doped films decreased with increasing mole fraction of hydrogen chloride. By the use of cadmium codoping, we have achieved the highest electron concentrations yet reported for hydrogen chloride doping of OMVPE-grown ZnSe. The best results obtained in this study were an electron concentration of 2.4×1018 cm−3 and a resistivity of 0.0141 Ω cm (300 K values). We have proposed a model based on the compensation of tetrahedral misfit to explain these results.
All-fiber-optic sensor for liquid level measurement
Authors: Ilev Ilko K. , Waynant Ronald W.
Published: July 2002

An experimental realization of a simple all-fiber-optic sensor for liquid level measurement is demonstrated. It is an intensity-modulated on–off switching sensor whose operating principle is based on the frustrated-total-internal-reflection effect caused by the refractive-index change of the surrounding medium. The basic optical element in the scheme is a sensing single fiber which serves simultaneously to transmit both the forward laser emission to the investigated medium and the useful signal backreflected from the fiber tip that is the sensing element. In order to achieve a maximum sensor sensitivity, we use a specially shaped fiber tip in two profile variants: angled and retroreflecting. The experimental investigations of the sensor properties and the results obtained at the pure-water level measurement confirm the sensor potential in liquid level determination with a high accuracy, exceeding 10 μm.
Fluorescence temperature sensing on rotating samples in the cryogenic range
Authors: Bresson F. , Devillers R.
Published: July 2002

A surface temperature measurement technique for rotating samples is proposed. It is based on the concept of fluorescence thermometry. The fluorescent and phosphorescent phenomena have been applied in thermometry for ambient and high-temperature measurement but not the cryogenic domain, which is explored using thermocouple- or platinum resistor-based thermometers. However, thermal behavior of Yb2+ ions in fluoride matrices seems to be interesting for thermometry in the range 20–120 K. We present here a remote sensing method which uses fluorescence behavior of Yb2+ ion-doped fluoride crystals. The fluorescence decay time of such crystals is related to its temperature. Since we developed a specific sol–gel process (OrMoSils) to make strongly adherent fluorescent layers, we applied the fluorescence thermometry method for rotating object surface temperature measurement. The main application is the monitoring of surface temperature of the ball bearing or turbopump axis in liquid propulsion rocket engines. Our method is presented and discussed, and we give some experimental results. An accurate calibration of the decay time of CaF2:Yb2+ versus temperature is also given.
Growth model for PbTiO3 thin films grown by surface-reaction enhanced metalorganic chemical vapor deposition
Authors: Yamashita Atsushi , Tatsumi Toru
Published: July 2002

PbTiO3 thin films were prepared by surface-reaction enhanced metalorganic chemical vapor deposition. The deposition rate was limited by supply of a Ti precursor. In contrast, the deposition rate and composition were kept constant for a certain range of Pb-source feeding, although the deposition rate of PbTiO3 was lower than that of TiO2. From these results, we proposed a growth model for PbTiO3: stoichiometric PbTiO3 film is grown by the Ti species arriving and reacting on the Pb-covered surface. The Ti sticking coefficient is rather small on such a surface. This model qualitatively explains the change in step coverage.
Synthesis of fullerenes from diamond
Authors: Yosida Yositaka
Published: July 2002

Synthesis of fullerenes using a standard dc arc evaporation of composite graphite anode containing 0–100 wt % of diamond is reported. The benzene soluble material-to-soot weight ratio W increases linearly with increasing diamond composition CD up to 45 wt %. At 50 wt %, W is 1.86 times as large as that for pure graphite. Above 50 wt %, W turns to decrease linearly. It is shown that diamond and graphite contribute independently to W. The graphite contribution to the linear behaviors is discussed in terms of kinetics of the transformation from planar sp2 network to quasitetragonal sp3 hybridization through quasiplanar sp2 hybridization during the dc arc. Furthermore, a new type of encapsulation compound, single crystals of diamond encapsulated in multiwalled carbon nanocages, is presented.
Neutral beams for the International Thermonuclear Experimental Reactor
Authors: Inoue T. , Di Pietro E. , Mondino P. L. , Bayetti P. , Hemsworth R. S. , Massmann P. , Fujiwara Y. , Hanada M. , Miyamoto K. , Okumura Y. , Watanabe K. , Krylov A. , Kulygin V. , Panasenkov A.
Published: July 2002

Receiving higher emphasis on the neutral beam (NB) off-axis current drive, the NB system is being highlighted for the steady state operation of the International Thermonuclear Experimental Reactor (ITER). To fulfill the physics requirement of heating and current drive, the NB system delivers ∼50 MW of D0 beams at 1 MeV into the ITER plasmas. The NB injector was designed so as to minimize the axial length, to avoid cost impact on the building. It was estimated by nuclear analyses that the insulation gas around the beam source would cause radiation induced conductivity, which would result in a power dissipation of >100 kW in the gas itself. As a result the present design utilizes vacuum insulation around the beam source. Since the vacuum pressure inside/outside the beam source ranges 10−1–10−2 Pa, both gas (glow) and vacuum arc discharges are taken into account in the design.
Growth of epitaxial Si1−xGex layers on Si(001) surface, by catalytical decomposition of disilane and germane: Photoemission studies
Authors: Chelly R. , Angot T. , Bolmont D. , Koulmann J. J.
Published: July 2002

Si1−xGex alloys grown by catalytical decomposition of a mixture of disilane and germane on Si(001) at 620 K and room temperature (RT) have been prepared and analyzed in situ with surface techniques such as x-ray and ultraviolet photoelectron spectroscopies (XPS and UPS), low energy electron diffraction (LEED), and x-ray photoelectron diffraction (XPD). A comparison is made with the case of an undecomposed gas mixture under the same experimental conditions. We show that films prepared at RT are amorphous. Films prepared at 620 K are well ordered and exhibit sharp 2×1 LEED patterns. Films grown at RT and subsequently annealed at as high as 820 K have a poorer crystalline quality.