bluuebunny/crossref_metadata_2025 huggingface dataset:
Reversible optical storage utilizing pulsed, photoinduced, electric-field-assisted reorientation of azobenzenes
Authors: Hill R. A. , Dreher S. , Knoesen A. , Yankelevich D. R.
Published: July 2002

We demonstrate a method of permanent optical recording of digital data which exploits a fast photoisomerization of nonlinear molecules, followed by a slow permanent alignment within a polymer. Write and erase cycles are initiated by rapidly photoisomerizing azobenzene molecules into an intermediate state with a larger mobility. The molecules align or randomly orient within the polymer depending on the presence or absence of an electric field. During orientation, relaxation to a stable isomer occurs and the alignment becomes permanent. The recorded information can then be nondestructively read by second-harmonic generation. Nanosecond optical exposures were used, demonstrating that extremely fast recording rates are possible.
Negative submillimeter absorption in tunnel-coupled quantum wells under resonant infrared excitation
Authors: Vasko F. T. , Soldatenko Yu. N.
Published: July 2002

We have studied the redistribution of the electrons between the tunnel-coupled ground levels in double quantum wells (DQWs), caused by the resonant infrared (IR) excitation on the next level and relaxation of the photoexcited electrons due to spontaneous emission of the optical phonons. The condition for the inversion of the electron populations in the tunnel-coupled pair of ground states is presented as a function of the DQWs parameters. Negative absorption coefficient of the submillimeter radiation under intensive (2–4 kW/cm2) IR pumping and commonly realized parameters of DQWs is of order 20–50 cm−1.
High deposition rate amorphous silicon-based multijunction solar cell
Authors: Guha S. , Xu X. , Yang J. , Banerjee A.
Published: July 2002

We have investigated and optimized the deposition conditions for growth of amorphous silicon (a-Si:H) and silicon-germanium (a-SiGe:H) alloys at high rates using microwave glow discharge. The optimum substrate temperature is found to be higher and deposition pressure lower than the case for materials deposited at low rates using radio-frequency glow discharge. Using the optimized conditions, we report an active-area efficiency of 11.44% for a double-junction, dual-gap a-Si:H alloy solar cell in which the bottom cell incorporates a-SiGe:H alloy deposited at 100 Å/s.
Soft x-ray W/Be multilayer and its application to a diffraction grating Yuichi,Utsumi
Authors: Takahashi Jun-ichi , Urisu Tsuneo , Maezawa Hideki
Published: July 2002

Tungsten/beryllium multilayers were coated onto lamellar diffraction gratings using a neutral atom beam sputtering technique. Boundary roughness of the multilayer was estimated to be 6.0 Å as a standard deviation. Diffraction efficiency of the multilayer-coated grating was measured using monochromatized synchrotron radiation.
Use of high direct current bias to separate electrode from bulk impedance
Authors: Cohen Y. , Davidovich A. , Riess I.
Published: July 2002

It is shown that the electrode impedance can be separated from the bulk impedance in semiconductors and electrochemical cells using high dc biases. This is true both for two-point dc resistance measurements and for two-point ac impedance measurements. Experimental evidence on semiconductor thin films is presented. The dc biases required may be high, in the 50 V range, and can then be applied mainly to high resistance samples, in particular to thin films.
Measuring the specific heat of solids using a CO2 laser calorimeter
Authors: Scatena David J. , Herrit Gary L. , Reedy Herman E.
Published: July 2002

A method has been devised to measure the specific heat of solid materials, especially those used as optical components for the infrared part of the spectrum, using a CO2 laser vacuum calorimeter. The CO2 laser vacuum calorimeter is a device that can precisely determine the absorptivity, at 10.6 μm, of an optic that has been coated to reflect the laser beam. A sample to be tested is fabricated in the shape of a simple optical element, and a high-reflecting thin-film coating is applied. Witness samples of known specific heat are first tested to determine the percent absorption of the coating. The sample of unknown specific heat is then tested by irradiation by the CO2 laser in vacuum to find the specific heat of the substrate. The method was tested using samples fabricated of ZnSe, GaAs, Ge, and CdTe. Specific heat values calculated using this method were within 10% of commonly reported values. The accuracy of this method is ±15%. Because the mirror coating is highly reflective, substrate materials that are not normally capable of withstanding 10.6 μm radiation can also be tested. This test can be extended to include any solid material that can be formed into the proper geometrical shape.
Four-frame gated Wolter x-ray microscope
Authors: Ellis R. J. , Trebes J. E. , Phillion D. W. , Kilkenny J. D. , Glendinning S. G. , Wiedwald J. D. , Levesque R. A.
Published: July 2002

A four-frame gated x-ray microscope has been developed for the study of inertial confinement fusion. Four x-ray images were obtained by introducing flat, grazing incidence mirrors into the converging annular ray bundle of a previously developed Wolter x-ray microscope system. Gated microchannel plate detectors and associated drive electronics were developed which can record a sequence of gated images of less than 100 ps duration, with an interframe timing accuracy of ±50 ps. The resulting diagnostic can record one time-resolved image and four gated images simultaneously. The system is described, and images of an imploding capsule are presented which demonstrate the unique capabilities of the instrument.
Microscope at the Brewster angle: Direct observation of first-order phase transitions in monolayers
Authors: Hénon S. , Meunier J.
Published: July 2002

A microscope employing the characteristics of the reflection at the Brewster angle has been built for the study of first-order phase transitions in monolayers and the growth of two-dimensional domains without adding fluorescent impurities. It takes about 2.4 s to constitute an image.
Transient plane source techniques for thermal conductivity and thermal diffusivity measurements of solid materials
Authors: Gustafsson Silas E.
Published: July 2002

The general theory of the transient plane source (TPS) technique is outlined in some details with approximations for the two experimental arrangements that may be referred to as ‘‘hot square’’ and ‘‘hot disk.’’ Experimental arrangements and measurements on two materials, Cecorite 130P and Corning 9606 Pyroceram, using a hot disk configuration, are reported and assessed.
Physics and technology of electrohydrodynamic ion emitters in the USSR
Authors: Dudnikov V. G. , Shabalin A. L.
Published: July 2002

A review of an investigation in the physics and technology of electrohydrodynamic (liquid metal) ion emitters, developed in the USSR, is presented. The EHD emission of high brightness ion beams from melted dielectric and EHD emission of negative ions are discussed. The dynamics of spontaneous and forced oscillation with a quasidiscrete spectrum in the frequency range of up to 108 Hz, transient processes in emission, emission stability at low and high current, and physical models for the emission surface size calculation has been studied. The evolution of the momentum distribution function is analyzed. Some examples of the utilization of the designed EHD sources for submicron ion beam production, for micromachining and microdiagnostics, and for high voltage accelerators are discussed too.
Epitaxial heterostructures YBa2Cu3O7−δ/KTaO3 for microwave applications
Authors: Boikov Yu. A. , Ivanov Z. G. , Vasiliev A. L. , Pronin I. , Olsson E. , Claeson T.
Published: July 2002

Combinations of high TC superconducting and ferroelectric films may give rise to tunable, high-Q microwave components. c-axis oriented YBa2Cu3O7−δ films were grown by laser ablation on (001) and vicinically cut KTaO3 substrates and studied by x-ray diffraction and electron microscopy. Competitive superconducting properties were registered. YBa2Cu3O7−δ/KTaO3/YBa2Cu3O7−δ trilayers were deposited on silicon-on-sapphire buffered by CeO2/Y-ZrO2. The dielectric permittivity of KTO3 at 15–100 K decreased considerably when the layer was polarized by a dc voltage. A loss factor tan δ=0.007 was measured at 100 kHz and T=50–100 K.
Properties of laser-sputtered Ti/Be multilayers
Authors: Renner O. , Kopecký M. , Krouský E. , Schäfers F. , Müller B. R. , Chkhalo N. I.
Published: July 2002

Characteristics of Ti/Be multilayers deposited by laser sputtering were investigated by grazing incidence x-ray reflection. The reflectivity of mirrors was explained using exponential variation of dielectric function, the validity of scattering model was confirmed by synchrotron radiation reflectivity measurements at 1200 eV. The observed quasi-Bragg peaks were interpreted in terms of nonspecular scattering from interfacial roughness.
High-speed gated x-ray imaging for ICF target experiments (invited)
Authors: Bradley D. K. , Bell P. M. , Kilkenny J. D. , Hanks R. , Landen O. , Jaanimagi P. A. , McKenty P. W. , Verdon C. P.
Published: July 2002

We describe the use of gated microchannel-plate detectors as high-speed framing cameras in laser-driven inertial-confinement-fusion experiments. Using an array of pinholes to image the target, detectors capable of generating up to 16 individual frames with ∼90 ps resolution on a single laser shot are now in routine use. The detectors have been used to study the development of intentionally applied perturbations in laser-driven targets. In off-line tests new detectors have demonstrated time resolutions better than 40 ps.
Photoluminescence studies of single submonolayer InAs structures grown on GaAs (001) matrix
Authors: Li Wei , Wang Zhanguo , Liang Jiben , Xu Bo , Zhu Zhanping , Yuan Zhiliang , Li Jian
Published: July 2002

Optical properties of single submonolayer InAs structures grown on GaAs (001) matrix are systematically investigated by means of photoluminescence and time-resolved photoluminescence. It is shown that the formation of InAs dots with 1 ML height leads to localization of excitons under certain submonolayer InAs coverages, which play a key role in the highly improved luminescence efficiency of the submonolayer InAs/GaAs structures.
Island growth, strain, and interdiffusion in InAs1−xPx/InP heterostructures
Authors: Tweet D. J. , Matsuhata H. , Shioda R. , Oyanagi H. , Kamei H.
Published: July 2002

Using x-ray diffraction and transmission electron microscopy we have found that InAs1−xPx films deposited on InP(001) substrates with organometallic vapor phase epitaxy grow in an unusual island growth mode characterized by large strain-dependent interdiffusion. Initially, strong intermixing occurs, producing pseudomorphic islands of intermediate composition. These grow only until some point in the relaxation process, possibly a critical value of the strain, after which islands of the intended composition begin to appear. Furthermore, both types of islands are found to penetrate deeply into the substrate.
Torsion balances, torsion pendulums, and related devices
Authors: Gillies G. T. , Ritter R. C.
Published: July 2002

The torsion pendulum is not only a mainstay instrument in the world of precision measurement and gravitational physics, but is important in electrical science, biophysics, petrology, metallurgy, and various other fields of endeavor. Whether used in the ‘‘static’’ (deflection) mode, the ‘‘dynamic’’ (oscillating) mode, or in some more complex configuration, instrumentation of this kind enables one to isolate and measure weak effects that would otherwise be difficult if not impossible to observe against the background gravitational field of the earth. In this review, we present a brief history of fiber-suspended apparatus and assess the fundamental limits of performance of the dumbbell pendulum. We then inventory the different versions of such systems presently used by gravitational physicists and discuss the various interrogation techniques used to monitor the movement of the suspended test mass. Next, we tabulate some of the applications for torsion instruments outside of gravitational physics, and close with a few comments on the direction of research in this area.
Accurate, sensitive, and fully automatic method to measure sound velocity and attenuation
Authors: Tardajos Gloria , Gonzalez Gaitano Gustavo , Montero de Espinosa Francisco R.
Published: July 2002

An automatic high-precision ultrasonic system with the corresponding ultrasonic cell is described to measure simultaneously the speed of sound and the attenuation as a function of frequency. The technique is based on the pulse-echo method and is designed to detect small structural changes in liquids, when an external variable is changed. The precision of the technique is limited by the stability of the temperature, which was kept constant within ±0.5 mK. The method, which permits one to obtain the absolute value of the velocity as well as the attenuation with respect to the solvent, is fully automated for the whole variation of the external variable, which added to its fast response permits easy use in dynamic processes.
Time dependence of ferroelectric coercive field after domain inversion for lithium-tantalate crystal
Authors: Chao Shiuh , Davis William , Tuschel David D. , Nichols Ronald , Gupta Mool , Cheng Hsing C.
Published: July 2002

We found the ferroelectric coercive field of LiTaO3, both in forward and reverse direction, vary with time after the domain is inverted. The coercive field drops when the domain is inverted, then gradually recovers. This phenomenon is light sensitive. The existence of a net time-varying internal electric field after domain inversion is hypothesized. The internal field is composed of the depolarization field, which is due to the spontaneous electric dipole moments, and an opposite direction time-varying space-charge field which is due to the redistribution of free-carriers transport under the influence of the depolarization field. Electro-optical effect caused by the internal electric field has been observed by means of an in situ optical monitoring technique for the domain inversion process. The in situ optical monitoring technique is based on using the LiTaO3 thin-plate crystal as a low finesse Fabry–Perot interferometer.
A new offset technique for suppression of spurious signals in photoreflectance spectra
Authors: Yan D. , Qiang H. , Pollak Fred H.
Published: July 2002

A new technique to suppress the unwanted, spurious signals often encountered in photoreflectance spectra from semiconductors and semiconductor microstructures is described here. This approach utilizes a properly phase-shifted signal from the reference source that is applied to the lock-in amplifier’s differential input. This paper demonstrates that this new approach is superior to existing methods of background minimization and is simpler to implement. It is particularly effective when the spurious signal is much larger than the underlying desired trace.
Development and characterization of a pair of 30–40 ps x-ray framing cameras
Authors: Bradley D. K. , Bell P. M. , Landen O. L. , Kilkenny J. D. , Oertel J.
Published: July 2002

We have constructed two slightly different high-speed framing cameras for use on NOVA and the OMEGA Upgrade. Both units are based on the gating of a microchannel plate, with one detector having a pore length to diameter ratio half that of the other. We will discuss the factors limiting the temporal resolution of each detector and will compare the results of modeling with gate width measurements taken using a short-pulse laser. We will also compare time-resolved x-ray images recorded using one of these devices with data from an older (∼90 ps resolution) detector.
A 250-GHz microwave interferometer for divertor experiments on DIII-D
Authors: James R. A. , Nilson D. G. , Stever R. D. , Hill D. N. , Casper T. A.
Published: July 2002

A new 250-GHz, two-frequency microwave interferometer system has been developed to diagnose divertor plasmas on DIII-D. This diagnostic will measure the line-averaged density across both the inner and outer, lower divertor legs. With a cutoff density of over 7×1014 cm−3, temporal measurements of edge localized modes (ELMs) and plasma detachment are expected. The outer-leg system will use a double-pass method while the inner-leg system will be single pass. Two special three-dimensional (3D) carbon composite tiles are used, one to protect the microwave antennas mounted directly under the strike point and the other as the outer-leg reflecting surface. Performance, design constraints, and the thermal-mechanical design of the 3D carbon composite tiles are discussed.
Electron temperature in low-dimensional wires using thermal noise measurements
Authors: Kurdak Ç. , Tsui D. C. , Parihar S. , Lyon S. A. , Shayegan M.
Published: July 2002

We have studied electric field heating of low-dimensional electrons in GaAs/AlGaAs heterostructures at 4.2 K using thermal noise measurements. For the two-dimensional (2D) wire, the increase in electron temperature, ΔTe, extracted from noise measurements is in agreement with previous measurements of ΔTe and is explained by emission of acoustic and optical phonons. Measurements are extended to quasi-one-dimensional (Q1D) wires which are shorter than the 2D wires. In these Q1D wires, we find that for small ΔTe, power dissipation is more effective than in the 2D wires, due to additional energy relaxation through the contacts. This effect is most pronounced in the highest mobility wire where the energy relaxation length is the longest.
The flexible x-ray imager
Authors: Budil K. S. , Perry T. S. , Bell P. M. , Hares J. D. , Miller P. L. , Peyser T. A. , Wallace R. , Louis H. , Smith D. E.
Published: July 2002

A new gated x-ray framing camera has been developed at the Lawrence Livermore National Laboratory for use at the Nova laser facility. This diagnostic, the flexible x-ray imager, has been designed as a modular unit that can be rapidly reconfigured to change the spectral response, magnification, sensitivity, and spatial and temporal resolutions of the instrument. The electrical gate pulse width may be varied from 200 ps to 2 ns depending upon whether the experimental emphasis is on temporal resolution or sensitivity. The long integration times are particularly useful in experiments where motional blurring occurs over even longer time scales. A detailed description of the instrument and its varied uses is presented.
Review of high brightness ion sources for microlithography (invited)
Authors: Dudnikov V. G.
Published: July 2002

The state of the art of high brightness ion beam production for microlithography and trends of research and development in this field of activity is reviewed. High brightness and low-energy spread are crucial to the success of ion-beam lithography. Features of field emission liquid metal, melted dielectric, and cryogenic gaseous ion sources for fine focused beam production are discussed. Growth of energy spread and the drop in brightness by intrabeam interaction of ions are estimated. Limitation of positive ion-beam characteristics in plasma sources such as duoplasmatron, multicusp, rf, and microwave discharges sources are examined. Features of negative ion formation in surface plasma sources with cesium catalysis are discussed. Possibilities for ions cooling down to 1 eV in high-density beams are estimated. High-precision beam diagnostics will be discussed.
Fluence dependence of nonlinear optical response of cadmium texaphyrin
Authors: Si Jinhai , Wang Yougui , Zhao Jiang , Ye Piexian , Wang Duoyuan , Sun Wenfang , Dong Shiming
Published: July 2002

Third-order nonlinear optical response of a cadmium texaphyrin solution at 532 nm was measured using time-resolved degenerate four-wave mixing with picosecond pulses. The molecules of cadmium texaphyrin exhibit a large optical nonlinearity, which arises from the excited-state population. The dynamics of the nonlinear optical response show an evident fluence dependence. The temporal response is characterized by three components, a slower, a faster, and a fastest, which are attributed to populations of the first triplet excited state, the first singlet excited state, and the higher singlet excited state, respectively.
The multichannel triple-laser interferometer/polarimeter system at RTP
Authors: Rommers J. H. , Donné A. J. H. , Karelse F. A. , Howard J.
Published: July 2002

A 19-channel combined interferometer and polarimeter system has recently become operational at the Rijnhuizen Tokamak Project (a=0.164 m, R=0.72 m, Btor⩽2.5 T, Ip⩽150 kA, plasma pulse duration ⩽500 ms), in order to determine the poloidal magnetic field and plasma density distribution simultaneously. The method is based on the separate propagation of two counter-rotating, circularly polarized probing waves, and enables high temporal resolution measurements of both the interferometric and the polarimetric phase change using only one detector per line of sight. In this article a thorough discussion of the (polarization-related) optical, electronic, and computational aspects of the system will be presented.
High-efficiency energy up-conversion at GaAs-GaInP2 interfaces
Authors: Driessen F. A. J. M.
Published: July 2002

Luminescence far above the excitation energy is observed at GaAs- GaInP2 interfaces. The intensity of this up-converted signal varies superlinearly with excitation density. Up-converted photoluminescence excitation spectroscopy shows that the signal disappears if the excitation energy is tuned below the GaAs band gap. It is concluded that cold Auger processes and the presence of metastable states in the  GaInP2, induced by residual CuPt ordering, cause this nonlinear effect at these type I interfaces.
A miniature capacitance dilatometer for thermal expansion and magnetostriction
Authors: Rotter M. , Müller H. , Gratz E. , Doerr M. , Loewenhaupt M.
Published: July 2002

A very small capacitive sensor for measuring thermal expansion and magnetostriction of small and irregular shaped samples has been developed. A capacitive method with tilted plates is used. The tilted plate capacitance formula is used for the calculation of the capacitor gap, the calibration is performed by measuring the signal of a standard material. The active length of the sample can be less than 1 mm. The absolute resolution is about 1 Å. All mechanical connections of the dilatometer are carried out by tiny Cu–Be springs, enabling the small force on the sample to be adjusted (50–500 mN) and no additional sample fixing is necessary. The cell has been tested in the temperature range 0.3–200 K and in static magnetic fields up to 15 T. The zero signal of the dilatometer has been determined by measuring a silver sample. The correct operation and reproducibility has been verified by measuring the thermal expansion of Cu. The thermal expansion and magnetostriction of a DyCu2 single crystal has been determined. The advantage of this method compared to specific heat measurements is that a large temperature range can be covered with one equipment. This high static and dynamic range of sample length, temperature, and magnetic field suggests a number of possible applications, like the investigation of crystal field effects on the magnetoelastic properties of single crystals or structural phase transitions.
Silicon-anode detector with integrated electronics for microchannel-plate imaging detectors
Authors: Vickers J. S. , Chakrabarti S.
Published: July 2002

We describe a silicon anode with integrated electronics for use in photon-counting microchannel-plate (MCP) imaging detectors. Very-large-scale integrated techniques using a 2 μm complementary metal–oxide–semiconductor (CMOS) process allow a passive-anode region, which collects charge from the MCPs, to be surrounded by an active event-processing region. The anode region is made from a rectangular array of pads that are formed using the metal interconnect layers of the CMOS process. Individual pads are electrically connected to form isolated arrays of rows and columns; each row terminates at a well of one charge-coupled device (CCD) register, and each column terminates at a well of a second orthogonal CCD register. The distribution of charge within each register is used to encode the charge-cloud coordinates. A two-dimensional prototype anode was constructed with 128×80 pixels spaced at 50 μm intervals; the anode readout rate is 31 250 Hz. Subpixel centroiding techniques can be employed to reduce the number of pixels that must be read for a given resolution. We envision a rugged, compact, low-power, and low-mass single-substrate imaging anode with a direct (x,y) digital interface. The design offers large array formats with inherent pixel linearity, orthogonality, and stability. An identified upgrade path promises orders-of-magnitude increases in speed (up to 106 photons s−1) and dynamic range, while maintaining large pixel count (>4000×4000) and MCP pore-limited resolution (<8 μm).
Calibration of rectangular atomic force microscope cantilevers
Authors: Sader John E. , Chon James W. M. , Mulvaney Paul
Published: July 2002

A method to determine the spring constant of a rectangular atomic force microscope cantilever is proposed that relies solely on the measurement of the resonant frequency and quality factor of the cantilever in fluid (typically air), and knowledge of its plan view dimensions. This method gives very good accuracy and improves upon the previous formulation by Sader et al. [Rev. Sci. Instrum. 66, 3789 (1995)] which, unlike the present method, requires knowledge of both the cantilever density and thickness.
Fast bolometric measurements on the TCV tokamak
Authors: Furno I. , Weisen H. , Mlynar J. , Pitts R. A. , Llobet X. , Marmillod Ph. , Pochon G. P.
Published: July 2002

The design and first results are presented from a bolometric diagnostic with high temporal resolution recently installed on the TCV tokamak. The system consists of two pinhole cameras viewing the plasma from above and below at the same toroidal location. Each camera is equipped with an AXUV-16ELO linear array of 16 p–n junction photodiodes, characterized by a flat spectral sensitivity from ultraviolet to x-ray energies, a high temporal response (<0.5 μs), and insensitivity to low-energy neutral particles emitted by the plasma. This high temporal resolution allows the study of transient phenomena such as fast magnetohydrodynamic (MHD) activity hitherto inaccessible with standard bolometry. In the case of purely electromagnetic radiation, good agreement has been found when comparing results from the new diagnostic with those from a standard metal foil bolometer system. This comparison has also revealed that the contribution of neutrals to the foil bolometer measurements can be extremely important under certain operating conditions, precluding the application of tomographic techniques for reconstruction of the radiation distribution.
Preparation of a La0.5Sr0.5CoO3/PbZr0.56Ti0.44O3/La0.5 Sr0.5CoO3 multilayer structure on SrTiO3(100) and LaAlO3(100) substrates using the sol-gel method
Authors: Wang Fan , Uusimäki Antti , Leppävuori Seppo
Published: July 2002

A sol-gel spin-coating procedure was established to prepare La0.5Sr0.5CoO3/ PbZr0.56Ti0.44O3/La0.5Sr0.5CoO3 multilayer structure on SrTiO3(100) and LaAlO3(100) substrates. The films were characterized by means of x-ray diffraction, scanning electron microscopy, and electrical measurements. The results showed the advantages of the sol-gel processing in compositional control as well as in oriented growth of films. A high remnant polarization was obtained in the films prepared with this procedure.
Viscosity measurements based on experimental investigations of composite cantilever beam eigenfrequencies in viscous media
Authors: Bergaud Christian , Nicu Liviu
Published: July 2002

Experimental investigations have been conducted to study the multimode dynamic response of composite cantilever beams in various viscous media and to determine their viscosity. Theoretical eigenfrequencies are computed using the analytical model proposed by Sader [J. Appl. Phys. 84, 64 (1998)] based on the analysis of the hydrodynamic function of cantilever beams. A good agreement is found between theory and experiment for the first two resonant frequencies of composite beams operated in air and in water. The same experimental approach is used to determine the viscosity of ultrapure ethanol. Thus, it is established that Sader’s model represents an accurate alternative for the determination of liquid viscosity in small volumes (about 50 μl) which might be of great importance for microfluidics applications. Finally, the limits of the method are underlined by monitoring the dynamic response of cantilever beams in silicon oil.
High-quality p - type Hg1−xCdxTe prepared by metalorganic chemical vapor deposition
Authors: Bevan M. J. , Chen M. C. , Shih H. D.
Published: July 2002

An arsenic source, tris-dimethylaminoarsine (TDMAAs), was used as a p-type dopant for Hg1−xCdxTe prepared by metalorganic chemical vapor deposition (MOCVD). The Hg1−xCdxTe layers were grown using the interdiffused multilayer process (IMP) at 360 °C with dimethylcadmium, di-isopropyltelluride and elemental mercury. Hole concentrations at 77 K in the range of 2×10+16–7×10+17 cm−3 were obtained in Hg1−xCdxTe with x=0.2–0.35, and ∼30%–50% of the arsenic was electrically active based on the data from secondary ion mass spectrometry (SIMS) measurements. These MOCVD Hg1−xCdxTe layers show minority carrier lifetimes at 77 K in the range of 3 ns–4 μs, which compare favorably with those from the best arsenic-doped Hg1−xCdxTe films prepared by liquid phase epitaxy.
Towards realization of a delta-BSF solar cell: Infrared improvements
Authors: Kuznicki Z. T. , Grob J.-J. , Wu L.
Published: July 2002

Our previous modeling and simulation demonstrated that a considerable increase in Si single-crystal back surface field (BSF) solar cell performance is possible by modifications to give a so-called delta-BSF device. In our first measurements a widened absorption (up to λ≤3200 nm) and infrared photoconductivity (where the upper wavelength limit λ≤1900 nm was imposed by the emitting lamp) have been observed.
Ultraviolet subnanosecond pulse train generation from an all-solid-state Ce:LiCAF laser
Authors: Sarukura Nobuhiko , Liu Zhenlin , Segawa Yusaburo , Semashko Vadim V. , Naumov Alexander K. , Korableva Stella L. , Abdulsabirov Ravil Yu. , Dubinskii Mark A.
Published: July 2002

We have directly and passively generated a 290-nm, 600-ps pulse train from a Ce:LiCAF laser pumped by the fourth harmonic of a conventional 10-ns Q-switched Nd:YAG laser. This simple, all-solid-state, short-pulse laser has been realized by employing a recently studied, self-injection-seeding pulse-train generation scheme using Ce:LiCAF, a tunable ultraviolet laser medium.
Ordering phenomena in InAs strained layer morphological transformation on GaAs (100) surface
Authors: Cirlin G. E. , Guryanov G. M. , Golubok A. O. , Tipissev S. Ya. , Ledentsov N. N. , Kop’ev P. S. , Grundmann M. , Bimberg D.
Published: July 2002

Initial stage of InAs pseudomorphic layer transformation (1–3 ML) on GaAs (100) singular surface may result for sequential submonolayer molecular beam epitaxy in formation of a pseudoperiodic array of InAs ‘‘wires’’ along the [001] direction. Complex parquet structures having similar anisotropy are formed on misoriented surface (3° towards [0–11] direction). Increase in growth interruption time after each growth cycle for 2 ML InAs deposited on singular surface results in decomposition of the wires into dots arranged in a 2D square lattice. Intentional substrate misorientation stabilizes the initial ordering effect along [001] and does not change the direction of anisotropy.
Electric field controllable Josephson junctions of high quality in high-T
c superconductors
Authors: Mayer B. , Mannhart J. , Hilgenkamp H.
Published: July 2002

Three-terminal Josephson junctions, the third terminal of which can be used to control the electronic properties of the device, are the key to a number of exciting device applications of high-Tc superconductors. To this end a novel device structure has been developed, which consists of an inverted metal-insulator-superconductor field-effect transistor into which a bicrystal grain boundary junction is embedded. These devices are excellent Josephson junctions as exemplified by their current–voltage characteristics and the magnetic field dependencies of the critical currents. The critical current of the junctions can be changed by 8% per volt applied to the gate electrode, the gate currents being negligible. Because they are sensitive to electric as well as magnetic fields, the junctions can be controlled by two independent inputs.
Novel process for the production of large, stable photosensitivity in glass films
Authors: Simmons-Potter Kelly , Potter Barrett G. , McIntyre Dale C. , Grandon Paul D.
Published: July 2002

Germanosilicate glasses exhibit a significant photosensitive response which has been linked to the presence of oxygen-deficient germanium point defects in the glass structure. Based on this correlation, a process which produces highly photosensitive thin films without the use of hydrogen exposures, has been developed. This process, applicable to a wide range of desired xGeO2:bf>(1−x)SiO2 film composition, uses reactive atmosphere sputtering and allows extensive control of the degree of oxidation of the films during synthesis to produce dramatic demonstrations of photosensitivity. In preliminary tests, our films demonstrated ultraviolet-induced refractive index perturbations (Δn) of up to −4×10−3 in the visible and −0.4×10−3 at 1.5 μm. Since no hydrogen exposure was necessary, this process yielded stable films which retained their predisposition for large photosensitivity for over one year of storage.
Initial stages in the growth of carbon films produced in an Ar–CH4–H2 microwave discharge: Composition and surface layers morphology
Authors: Thomas L. , Jauberteau I. , Jauberteau J. L. , Cinelli M. J. , Aubreton J. , Catherinot A.
Published: July 2002

X-ray photoelectron spectroscopy and atomic force microscopy are employed in the characterization of the first stages in the growth of carbon layers on a (001) Si substrate which is not scratched with diamond powder before placing it in an Ar–2%CH4–H2 plasma discharge. Results show that the first layers could be formed in SiC grains where the carbon diamond particles nucleate. The high nucleation density of 1.109–5.109 nuclei. cm−2 and the low aggregates density lead to a smooth surface.
ZnSe-based birefringent waveguide as Pockels retarder in the blue-green spectral range
Authors: Babucke H. , Thiele P. , Prasse T. , Rabe M. , Henneberger F.
Published: July 2002

Electro-refractive modulation in the blue-green spectral range is demonstrated in strained, MBE-grown ZnSe waveguides with cladding layers of ZnMnSe on n-GaAs substrates. Utilizing the Pockels effect in Schottky-contacted structures with built-in birefringence, a contrast ratio better than 80:1 at 2.485 eV is achieved. The rise time of (4.7±0.5) ns is RC limited.
Evidence of quantum lateral confinement in side-gated resonant tunnelling diodes formed by patterned substrate regrowth
Authors: Quierin M. A. , Grimshaw M. P. , Ritchie D. A. , Burroughes J. H. , Leadbeater M. L. , Pepper M.
Published: July 2002

MBE regrowth on patterned np-GaAs wafers has been used to fabricate GaAs/AlGaAs double barrier resonant tunnel diodes with a side-gate in the plane of the quantum well. The physical diameters vary from 1 to 20 μm. For a nominally 1 μm diameter diode the peak current is reduced by more than 95% at a side-gate voltage of −2 V at 1.5 K, which we estimate corresponds to an active tunnel region diameter of 75 nm ± 10 nm. At high gate biases additional structure appears in the conductance data. Differential I-V measurements show a linear dependence of the spacing of subsidiary peaks on gate bias indicating lateral quantum confinement.
Auger suppression in CdHgTe heterostructure diodes grown by molecular beam epitaxy using silver as acceptor dopant
Authors: Skauli T. , Steen H. , Colin T. , Helgesen P. , Lo/vold S. , Elliott C. T. , Gordon N. T. , Phillips T. J. , White A. M.
Published: July 2002

Negative differential resistance due to Auger suppression is demonstrated in CdHgTe diodes grown by molecular beam epitaxy (MBE) using silver as acceptor dopant. These devices require growth of relatively complicated heterostructures, and control of n- and p-type doping over a large range. For this reason, the use of silver as an acceptor in CdHgTe devices grown by MBE has been reexamined. The results show that the diffusion of silver at the growth temperature does not necessarily preclude the use of silver doping in devices. For concentrations up to high 1017 cm−3, silver appears to be fully electrically active.
Photoinduced conductivity changes in polycrystalline diamond films
Authors: Gonon P. , Prawer S. , Jamieson D.
Published: July 2002

We report that the dark electrical properties of polycrystalline chemical vapor deposition diamond films are modified after exposure to UV light. UV illumination gives rise to an increase in the dark conductivity and to a change in the I–V characteristic from Iα exp (aV) for the as-grown material to IαV2 following UV irradiation. Thermally stimulated currents corresponding to an activation energy of about 1.9 eV are observed after UV illumination. The effects of UV irradiation can be totally reversed by thermal annealing and partially reversed by exposing the samples to white light.
Deep level defects in Mg-doped, p-type GaN grown by metalorganic chemical vapor deposition
Authors: Götz W. , Johnson N. M. , Bour D. P.
Published: July 2002

Deep level defects in Mg-doped, p-type GaN were characterized by deep level transient spectroscopy (DLTS) and photoemission capacitance transient spectroscopy (ODLTS). The measurements were conducted on n+-p junction diodes grown by metalorganic chemical vapor deposition. DLTS revealed discrete deep levels in the lower half of the band gap with activation energies for hole emission of 0.21, 0.39, and 0.41 eV. While DLTS is able to detect deep levels only in the proximity of the valance band edge in p-type, wide band-gap semiconductors, ODLTS enables detection of deep levels throughout the band gap of GaN. The ODLTS spectrum of Mg-doped, p-type GaN is dominated by a deep level with an optical threshold energy for photoionization of ∼1.8 eV. This deep level, which appears to be energetically located near midgap is present in the highest concentration (∼2.4×1015 cm−3) among the deep levels detected in our GaN material. None of the detected deep levels is present in sufficient concentration to significantly compensate the shallow acceptor dopant in our Mg-doped, p-type GaN.
Source of Ge centers in AlGaAs grown by organometallic vapor phase epitaxy and the effect of impurity getters
Authors: Lee Wei-I
Published: July 2002

A long term and comprehensive study has been performed to identify the origin of the Ge center in AlGaAs grown by organometallic vapor phase epitaxy. With a series of deductive investigations, AsH3 gas has been undoubtedly identified as the source of the Ge contamination. Depending on the AsH3 quality, one to two orders of magnitude of difference in Ge trap densities has been observed. Long-term observations indicate fairly constant Ge content throughout most of the AsH3 tank lifetime. Different impurity getters were attempted to remove the Ge contaminant. While most getters can eliminate the oxygen-related defects in AlGaAs, no getters were able to remove the Ge DX center.
Removal of hydrogen from the base of carbon-doped In0.49Ga0.51P/GaAs heterojunction bipolar transistors by ex situ annealing and the effects on device characteristics
Authors: Hartmann Q. J. , Hwangbo H. , Yung A. , Ahmari D. A. , Fresina M. T. , Baker J. E. , Stillman G. E.
Published: July 2002

The effects of ex situ high temperature annealing (T≳500 °C) on the hole and hydrogen concentration of the base and on the dc device characteristics of InGaP/GaAs heterojunction bipolar transistors grown by low-pressure metalorganic chemical vapor deposition have been studied. Using rapid thermal annealing, hydrogen can be completely annealed out of the base, activating the carbon acceptors. Due to the low diffusivity of carbon, the high temperatures necessary to remove most of the hydrogen do not degrade the device characteristics. Using this simple technique to eliminate hydrogen from the base prior to device fabrication should improve the reliability of GaAs-based transistors with a carbon-doped base. Results also indicate that unlike carbon-doped In0.53Ga0.47As, hydrogen does not significantly affect the minority carrier characteristics of carbon-doped GaAs.
Characterization of photoinduced birefringence change in optical fiber rocking filters
Authors: Psaila D. C. , Ouellette F. , Martijn de Sterke C.
Published: July 2002

We investigate the effects of UV exposure on the growth of optical fiber rocking filters written in hydrogen-loaded germanosilicate elliptical core fibers. We find that with increasing exposure, the rocking angle (induced birefringence) increases rapidly then begins to decrease, eventually erasing completely. With further exposure, the rocking angle is seen to increase again, reaching values of 3.5°. This corresponds to a photoinduced birefringence almost four times larger than previously recorded in optical fiber rocking filters. Furthermore, we show that at high UV fluences, the direction of rotation of the birefringent axes is opposite to that at low fluences.
Efficiency enhancement by a tapered dielectric grating in a Cherenkov laser
Authors: Shiozawa T. , Nishimura T.
Published: July 2002

A method for enhancing the efficiency of energy transfer from a relativistic electron beam to an electromagnetic wave in a Cherenkov laser is proposed. In a two-dimensional Cherenkov laser composed of a planar relativistic electron beam and a parallel plate waveguide loaded with a dielectric grating, either one of the grating parameters, or the slot width and the groove depth, is tapered or gradually decreased in accordance with the decrease in the drift velocity of the electron beam. The numerical simulation demonstrates that sufficient efficiency enhancement can be achieved by a tapered dielectric grating.
Migration of a Si microcluster due to the electron wind on a Si(001) surface
Authors: Doi Takahisa , Ichikawa Masakazu , Hosoki Shigeyuki , Ninomiya Ken
Published: July 2002

At a high temperature of about 1500 K, the migration of a Si microcluster was observed on a Si(001) surface by using an electron microscope. This cluster always existed together with an attendant region. This region melted first during heating because of its lower crystallinity compared to the Si substrate. The Si atoms in this melted zone were struck by electrons moving towards the anode and were pushed by the electron wind in the same direction as the electrons. The Si microcluster floating in the melted zone also migrated toward the anode side about ten times as fast as the Si electromigration atoms moving in the opposite direction.
Mechanisms of band-edge emission in Mg-doped p-type GaN
Authors: Smith M. , Chen G. D. , Lin J. Y. , Jiang H. X. , Salvador A. , Sverdlov B. N. , Botchkarev A. , Morkoc H. , Goldenberg B.
Published: July 2002

Time-resolved photoluminescence has been employed to study the mechanisms of band-edge emissions in Mg-doped p-type GaN. Two emission lines at about 290 and 550 meV below the band gap (Eg) have been observed. Their recombination lifetimes, dependencies on excitation intensity, and decay kinetics have demonstrated that the line at 290 meV below Eg is due to the conduction band-to-impurity transition involving shallow Mg impurities, while the line at 550 meV below Eg is due to the conduction band-to-impurity transition involving doping related deep-level centers (or complexes).
Direct writing of GaAs optical waveguides by laser-assisted chemical vapor deposition
Authors: Boutros K. S. , Roberts J. C. , Bedair S. M.
Published: July 2002

We demonstrate the direct writing of GaAs waveguide structures by selective area deposition using laser-assisted chemical vapor deposition (LCVD). The multimode waveguides have a Gaussian shape and a very smooth surface, and they exhibit losses as low as 5.4 dB/cm. The LCVD technique offers the capability of selective growth of independent device structures, and hence the capability of monolithic integration of these devices for optoelectronic applications.
Operation voltage reduction in ZnSe-based light-emitting diodes due to the use of n-type AlGaAs and CdZnSe buffer regions
Authors: Rennie J. , Nishikawa Y. , Saito S. , Onomura M. , Hatakoshi G.
Published: July 2002

On proposing the existence of a significant barrier between n-type GaAs and n-type ZnSe, in ZnSe-based devices, we examined various offset reduction buffers, in standard light-emitting diode structures, to assess their ability to reduce the excess voltages applied across this interface during operation. The main buffers investigated were CdZnSe and AlGaAs. The AlGaAs buffer was seen to have the largest effect, reducing the operation voltage from 17 V (GaAs buffer only sample) to 6.5 V at a current density of 1 A/cm2. Our results clearly indicate the utility of such buffer regions in reducing the operation voltages of these devices.
Studies on damage removing efficiency of B11+ and BF+2 implanted Si0.84Ge0.16 epilayers by rapid thermal annealing
Authors: Chen L. P. , Chou T. C. , Chien C. H. , Chang C. Y.
Published: July 2002

High quality metastable pseudomorphic Si1−xGex epilayers were grown by ultrahigh vacuum chemical vapor deposition using Si2H6 and GeH4. These epilayers were implanted with 40 keV B11+ and 100 keV BF+2 ions at a dose of 1×1015 ions/cm2 and then annealed by rapid thermal annealing (RTA) processes at temperatures of 600, 650, 700, and 750 °C for 30 s duration. Double-crystal x-ray diffractometry was used to evaluate the level of the implant-induced damage and the damage removing efficiency of both ion implanted samples at different RTA conditions. The results show that the RTA process is more effective at removing damage from B11+ implanted samples than from those implanted with BF+2.
Transverse mode dynamics in vertical cavity surface emitting lasers excited by fast electrical pulses
Authors: Buccafusca O. , Chilla J. L. A. , Rocca J. J. , Feld S. , Wilmsen C. , Morozov V. , Leibenguth R.
Published: July 2002

We report measurements of the transient multimode dynamics of vertical cavity surface emitting lasers excited by short (100–200 ps rise times, 1 ns duration) electrical pulses. Fast changes on the spatial distribution of the output power and strong mode competition are observed. Numerical simulations show that the observed dynamics are due to the partial overlap of the different transverse modes through spatial hole burning.
Influence of aging on the performance of solid source molecular beam epitaxy grown GaInP/AlGaInP quantum well lasers
Authors: Tappura K. , Aarik J. , Nurmi T. , Pessa M.
Published: July 2002

We have studied the influence of aging on the performance of GaInP/AlGaInP quantum well lasers grown by all solid source molecular beam epitaxy. A remarkable improvement in the laser characteristics was observed during the first 20–30 h of continuous wave operation at a constant current corresponding to the initial output power of 100 mW. After such an aging process the threshold current density was typically decreased 30% from its original value. The comparison of the experimentally and theoretically determined gain-current curves revealed the improved laser performance to be caused by the reduction of the nonradiative recombination rate.
Cutting off the diffraction: A numerical solution in scanning near-field optical microscopy
Authors: Xiao Mufei
Published: July 2002

In scanning near-field optical microscopy, the derived image is often obscured by diffraction effects. To reduce these, we subtract two images taken at different probe heights above the surface and obtain an enhanced image with the diffraction effects largely removed. We present the modelling and explore its foundation.