bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements of near forward scattered laser light in a large inertial confinement fusion plasma (invited)
Authors: Moody J. D. , MacGowan B. J. , Glenzer S. H. , Kirkwood R. K. , Kruer W. L. , Pollaine S. M. , Williams E. A. , Stone G. F. , Afeyan B. B. , Schmitt A. J.
Published: July 2002

We describe an instrument which measures the angular spread and spectrum of near forward scattered laser light from a probe beam in a long scalelength laser plasma. The instrument consists of a combination of time integrating and time resolving detectors which measure the scattered light amplitude over four orders of magnitude for a range of angles. These measurements allow us to study the beam spray resulting from various laser and plasma conditions and determine the density fluctuations associated with this beam spray.
A fiber-optic attenuator calibration system using high frequency substitution method
Authors: Singh Ranjit , Kawakami Tomoteru
Published: July 2002

A fiber-optic attenuator calibration system based on a high frequency substitution method has been developed using a 30 MHz precision piston attenuator equipped with a laser interferometer as a standard. The uncertainty of attenuation calibration for a typical 10 dB attenuator is 0.025 dB at two standard deviation levels. The resolution of the system is 0.001 dB and the dynamic range is 25 dB in a single step.
High-resolution x-ray spectromicroscopy with the Tokyo electron beam ion trap
Authors: Nakamura N. , Faenov A. Ya. , Pikuz T. A. , Nojikawa E. , Shiraishi H. , Currell F. J. , Ohtani S.
Published: July 2002

A high-resolution x-ray spectrometer with a spherically bent quartz crystal and an x-ray sensitive charge coupled device (CCD) have been applied to the observation of highly charged ions produced and trapped in the Tokyo electron beam ion trap (EBIT). The spectrometer made it possible to measure the spatial distribution and wavelength of the radiation at the same time. A simple, but lower energy resolution method was also used, by taking advantage of the intrinsic energy resolution of the CCD. The possibility to apply such techniques to diagnostics of an EBIT is discussed.
High-resolution CO-laser sideband spectrometer for molecular-beam optothermal spectroscopy in the 5–6.6 μm wavelength region
Authors: Merker U. , Engels P. , Madeja F. , Havenith M. , Urban W.
Published: July 2002

We have set up a new CO-laser sideband spectrometer for high-resolution molecular-beam optothermal spectroscopy in the mid infrared. By mixing CO-laser lines with tunable microwave radiation, a spectral coverage of about 50% is achieved. Using a microwave resonator, a typical output power of 3 mW is realized in the region of 5–6.6 μm (1500–2000 cm−1). The resolution in our molecular-beam apparatus with optothermal detection is 2.8 MHz (full width at half maximum). The new setup allowed the observation of the first high-resolution rotationally resolved spectrum of formic acid dimer (HCOOH)2.
Vertical variant of a double channel-cut crystal spectrometer for investigation of laser-generated plasmas
Authors: Renner O. , Patel P. K. , Wark J. S. , Krousky E. , Young P. E. , Lee R. W.
Published: July 2002

The theoretical design of multicrystal instruments which define a new class of spectrometers based on the vertical dispersion principle is reported together with experimental confirmation of design. Previous designs in the vertical-variant scheme—which have been fielded successfully in laser-produced plasma experiments—have operated with one or two crystal surfaces in a configuration that deflects the diffracted radiation back in the general direction of the source. The additional reflecting surfaces described here direct the radiation along a radial vector from the source to the detector, independent of the Bragg angle. Thus, the experimental setup is more flexible and greatly facilitates the coupling of the spectrometer to a charge-coupled device or streak camera. One of these instruments, a double channel-cut crystal spectrometer working in the vertical dispersion mode (DCCV), employs a total of four diffracting crystal surfaces. A compact design of the DCCV prototype is compatible with small bore reentrant diagnostic access tubes (e.g., the 6 in. manipulator) employed at several large-scale laser facilities. This high-dispersion spectrometer combines a high spectral resolution [R=13 500 with Si(111) crystals] with a one-dimensional spatial resolution of the order of 20 μm.
Six-circle diffractometer for surface diffraction using an in-vacuum x-ray detector
Authors: Albrecht M. , Antesberger H. , Moritz W. , Plöckl H. , Sieber M. , Wolf D.
Published: July 2002

We report on the design of a diffractometer, which offers improved capabilities for x-ray experiments in ultrahigh vacuum. Its main features are (i) the possibility to follow the evolution of diffraction spots in situ during adsorption or film deposition; (ii) the measurement of reflections at high exit angles, i.e., large perpendicular momentum transfer. This goal is achieved by placing a movable x-ray detector inside the vacuum chamber. (iii) Other surface analysis equipment, e.g., a low-energy electron diffraction or an electron energy analyzer can be moved in front of the sample and operated simultaneously with x-ray diffraction. (iv) A load lock system—currently in preparation—will allow the quick exchange of samples without breaking system vacuum. In addition, a new design of the chi circle used for sample alignment provides a compact, space-saving design of the diffractometer.
A compact electron energy analyzer for measuring field emission energy distributions
Authors: Bernhard John M. , Rouse Ambrosio A. , Sosa Edward D. , Gnade Bruce E. , Golden David E. , Chalamala Babu R.
Published: July 2002

A simple instrument to determine field emission tip work functions and shape functions from simultaneous current–voltage (I–V) characteristics and field emission energy distributions of field emitter tips and tip arrays is described. This instrument uses a cylindrical energy analyzer with a few correcting elements to simulate a hemispherical analyzer and provides a low cost and more compact alternative to a commercial hemispherical spectrometer. I–V curves and energy distributions may be automatically obtained as a function of time to study field emission tip degradation with usage and/or exposure to gases of interest.
Magnetoresistance in La2/3Ca1/3MnO3+δ : Dependence on magnetic history
Authors: von Helmolt R. , Wecker J. , Lorenz T. , Samwer K.
Published: July 2002

We investigated the magnetoresistance of La2/3Ca1/3MnO3+δ magnetic thin films. Under certain conditions, the magnetoresistance curves show a remarkable hysteresis and the resistance becomes dependent on the magnetic history. A relaxation behavior of the resistance has also been observed. Hysteresis and relaxation of the resistance are very similar to the phenomena of magnetoviscosity of the magnetic moment in spin glasses and the magnetic aftereffect in hard magnets.
Nucleation of homoepitaxial films grown with ion assistance on Pt(111)
Authors: Esch Stefanie , Bott Michael , Michely Thomas , Comsa George
Published: July 2002

The nucleation of Pt films grown by ion beam assisted deposition on Pt(111) has been studied by scanning tunneling microscopy. At temperatures T≥200 K, the simultaneous ion bombardment during vapor phase deposition leads to a substantial increase in the island number density caused by nucleation at ion impact induced adatom clusters. This increase is observed even in the higher temperature range where after ion bombardment alone the ion impact induced adatom clusters are no longer present.
Properties of a Si doped GaN/AlGaN single quantum well
Authors: Salvador A. , Liu G. , Kim W. , Aktas Ö. , Botchkarev A. , Morkoç H.
Published: July 2002

Quantization of band-to-band transition in a Si doped GaN/AlGaN quantum well was investigated. A good fit to the room-temperature photoluminescence (PL) spectrum of the GaN quantum well studied was obtained using values 0.3me and 0.19me for the heavy hole and conduction electron effective masses, respectively, and a 67:33 conduction to valence band offset.
Effects of Si thermal oxidation on B diffusion in Si and strained Si1−xGex layers
Authors: Kuo P. , Hoyt J. L. , Gibbons J. F. , Turner J. E. , Lefforge D.
Published: July 2002

Silicon thermal oxidation was used to characterize the interaction of Si interstitials with a Si1−xGex layer and with B in Si1−xGex. Diffusion of B in a Si marker layer, positioned under a Si1−xGex layer, was monitored as excess Si interstitials were injected into the bulk by the oxidation of the Si capping layer (T=850 °C, t=18 min). The Si1−xGex layer did not affect the oxidation-enhanced diffusion of B in the Si marker layer. Hence, Si1−xGex (x<0.30) does not appear to be a strong sink for Si interstitials. In addition, the enhancement from Si thermal oxidation (T=800 °C, t=60 min) of the measured B diffusivity in Si1−xGex is similar to that in Si. This indicates that, as in Si, the mechanism for B diffusion in Si1−xGex (x<0.18) primarily involves Si interstitials.
Current transport in amorphous silicon n/p junctions and their application as ‘‘tunnel’’ junctions in tandem solar cells
Authors: Hegedus Steven S. , Kampas Frank , Xi Jianping
Published: July 2002

Current transport in a-Si based n/p (‘‘tunnel’’) junctions is investigated using current-voltage- temperature and quantum efficiency measurements. Currents are nearly ohmic and temperature independent under typical solar cell operating conditions. Incorporating a thin a-Si(B) p+ layer between the n and p layers and replacing either a-Si layer with a microcrystalline layer improves the device by reducing the resistance and increasing the recombination. Light soaking improves the devices slightly. These results are consistent with a recently proposed recombination-tunneling model. Incorporating improved interconnect junctions in tandem solar cell devices improved the initial and stabilized performance.
Wet thermal oxidation of AlAsSb lattice matched to InP for optoelectronic applications
Authors: Blum O. , Geib K. M. , Hafich M. J. , Klem J. F. , Ashby C. I. H.
Published: July 2002

We demonstrate wet thermal oxidation of an AlAsSb layer lattice matched to an InP substrate. Oxidation in an InGaAs/AlAsSb/InGaAs structure proceeds in a lateral direction, producing an oxide layer embedded between two layers of InGaAs. Auger analysis and Raman spectroscopy indicate conversion of the AlAsSb into an aluminum oxide with an elemental antimony layer at the top oxide-InGaAs interface. Scanning electron microscope cross-sectional views of partially and fully oxidized samples are also presented.
Radiation effects of focused ion beam microfabrication on Ni disilicide thin films by in situ transmission electron microscopy
Authors: Tanaka Miyoko , Furuya Kazuo , Saito Tetsuya
Published: July 2002

Structural changes of epitaxial Ni disilicide thin films on Si(111) were investigated with an in situ transmission electron microscope (TEM) incorporated with a focused ion beam (FIB). Epitaxial growth of NiSi2 on a Si(111) TEM specimen was achieved by the combination of Ni deposition and subsequent annealing. Three different sized squares were microfabricated by 25 keV Ga+-FIB onto this specimen during TEM observation at room temperature. FIB lithography caused the exfoliation of Ni silicide film along the microfabricated lines and the defects adjacent to the beam incident area. The beam affected area outside of the microfabricated line was about 2–3 μm.
The growth and properties of epitaxial KNbO3 thin films and KNbO3/KTaO3 superlattices
Authors: Christen H.-M. , Boatner L. A. , Budai J. D. , Chisholm M. F. , Géa L. A. , Marrero P. J. , Norton D. P.
Published: July 2002

Potassium niobate (KNbO3) thin films and potassium niobate/tantalate (KNbO3/KTaO3) superlattices have been grown on KTaO3 (001) substrates by pulsed laser deposition. The thin-film structures were analyzed by Rutherford backscattering/ion-channeling techniques, x-ray θ–2θ and Φ scans, and both conventional and Z-contrast scanning transmission electron microscopy. Excellent film flatness and crystallinity are evidenced by these techniques. At room temperature, the KNbO3 films are characterized by an orthorhombic structure which differs from that of bulk KNbO3. The interfaces between the layers in the KNbO3/KTaO3 superlattice structures were found to be compositionally sharp on an atomic scale.
Surface tension effects in tunneling microscopy
Authors: Conroy J. F. T. , Janata Jiri
Published: July 2002

Induced electric charge lowers the surface tension of the substrate below the tunneling tip and creates a sharp surface tension gradient in its vicinity. For mercury as the substrate, the random waving is amplified by the gradient of the surface tension, resulting in observable mechanical ‘‘waving’’ of the surface that increases with the applied bias voltage. Its amplitude reaches a minimum at the potential of zero charge. In agreement with the Gibbs–Lippmann equation these effects are mitigated by the presence of adsorbed films but may lead to translocation of adsorbates by the biased tunneling tip.
Epicentral and near epicenter surface displacements on pulsed laser irradiated metallic surfaces
Authors: Spicer James B. , Hurley David H.
Published: July 2002

The elastic deformations associated with the pulsed laser, photothermal heating of an aluminum alloy surface have been measured within the irradiated region using a Michelson-type interferometer. The displacements within this region have been measured and have been compared to calculations based on temperature-rate dependent thermoelasticity theory. The quantitative agreement between calculation and experiment shows the contributions of the local thermal expansion and the propagating acoustic modes on the overall displacements at the epicenter and near the epicenter of the irradiated region. Nonlinear effects on the propagation of the near-field surface acoustic wave may be present.
Growth and characterization of II–VI blue light-emitting diodes using short period superlattices
Authors: Wu B. J. , Kuo L. H. , DePuydt J. M. , Haugen G. M. , Haase M. A. , Salamanca-Riba L.
Published: July 2002

We investigate the properties of II–VI short period superlattice (SPSL) blue light-emitting diodes grown by molecular beam epitaxy. The device consists of a ZnSe active layer, SPSL MgZnSSe cladding layers, and a ZnSeTe digital graded contact. The SPSL structure is made of alternating layers of MgSe, ZnSe, ZnS, and ZnSe. Highly ordered SPSL layer structures are successfully grown. Tweedlike contrast is observed in the pseudomorphic SPSL from our transmission electron microscopy analysis. The device shows high purity blue emission at 460 nm at room temperature with a 13 nm full width at half maximum. Operating at 14 A/cm2, the half-intensity lifetime is more than 13 h at room temperature with an external quantum efficiency of ∼0.1%.
The mechanism of texture formation during film growth: The roles of preferential sputtering and shadowing
Authors: Ying Feng , Smith Richard W. , Srolovitz David J.
Published: July 2002

Nonequilibrium molecular dynamics simulations have been employed to develop a mechanistic model for the development of an out-of-plane (fiber) texture in polycrystalline thin films. The depositing atoms preferentially sputter film atoms from grains with high surface energies. As the film grows, an atomic shadowing mechanism leads to the lateral growth of the grains with a height advantage—eventually leading to the occlusion of randomly oriented grains.
Nanoscale replication for scanning probe data storage
Authors: Terris B. D. , Mamin H. J. , Best M. E. , Logan J. A. , Rugar D. , Rishton S. A.
Published: July 2002

Recently, there have been significant advances in demonstrating the possible application of scanning probe techniques for high density data storage. While many obstacles have yet to be overcome, one of the more promising applications of such devices is for very high density read-only disk drives. Such an application requires the means to pattern and replicate nanometer scale features over macroscopic dimensions. We have developed a technique for both mastering and replicating data patterns for use in such a device at a density 100 times that of current read-only disks. The process consists of using electron beam lithography to write data features as small as 50 nm and a photopolymerization process to faithfully replicate the written marks.
Comparison of electrical and luminescence data for the A center in CdTe
Authors: Castaldini A. , Cavallini A. , Fraboni B. , Fernandez P. , Piqueras J.
Published: July 2002

We have investigated the electrical and optical properties of the deep levels responsible for the 1.4–1.5 eV luminescence band usually observed in II–VI compounds. We compared the energy levels found by cathodoluminescence and junction spectroscopy methods for semi-insulating (CdTe:Cl and Cd0.8Zn0.2Te) and semiconducting samples (undoped CdTe). The techniques utilized were deep level transient spectroscopy (DLTS) on semiconducting samples and photoinduced current transient spectroscopy and photo-DLTS on high resistivity materials. These last two techniques are complementary and allow the determination of the trap character (donor/acceptor). Three acceptor levels are seen in the electrical transient data at Ev+0.12, 0.14, and 0.16 eV with hole capture cross sections of 2×10−16, 1×10−16, and 4×10−17 cm2, respectively. The lowest level is seen only in Cl doped material corroborating the literature optical and electron spin resonance identification of a level at Ev+0.12 eV as being a VCd+ClTe donor–acceptor pair center. All three levels may be present in the 1.4 eV luminescence band.
High-frequency capacitance resonance of ZnO-based varistor ceramics
Authors: Ezhilvalavan S. , Kutty T. R. N.
Published: July 2002

Capacitance resonance of ZnO varistor ceramics can be shifted from gegahertz to a few megahertz frequency region with increasing amounts of specific secondary phases. The observed resonance is due to the total inductance of the varistor ceramics wherein the grain boundaries are shorted at high frequencies, which arises from the dynamic exchange of charge carriers at the grain interiors and the trap states that are formed at the depletion regions around the grain boundaries. This is applicable to ZnO/ZnO grain boundaries as also to ZnO/secondary phase boundaries. The capacitance-voltage studies show direct correlation between the magnitude of capacitance resonance and the nonlinearity coefficient in current-voltage relations.
Visible photoluminescence from pressure annealed intrinsic Czochralski-grown silicon
Authors: Karwasz G. P. , Misiuk A. , Ceschini M. , Pavesi L.
Published: July 2002

Visible luminescence from thermal treated intrinsic Czochralski-grown silicon is reported. Oxygen precipitates were formed in a nearly oversaturated silicon by a two-step thermal treatment with auxiliary use of high pressures. A wide photoluminescence band peaked at about 2.3 eV is observed in those samples for which the first treatment was performed at a relatively high temperature and which show a higher amount of oxygen precipitates and oxygen related defects. Scanning electron microscopy of the best performing samples show the presence of submicron conglomerates on the surface. We have tentatively attributed the luminescence emission to the defects in the suboxide SiOx phase formed in the oxygen precipitates.
Substitutional gold in Si1−xGex
Authors: Nikolajsen F. , Kringho/j P. , Larsen A. Nylandsted
Published: July 2002

It is demonstrated that relaxed Si1−xGex of 0≤x≤0.25 grown by molecular beam epitaxy, using the compositional grading technique, can be doped with gold by a high-temperature indiffusion process from a deposited gold layer. Substitutional gold in both p- and n-type alloy layers has been identified and characterized by deep level transient spectroscopy, and the donor and acceptor levels of neutral, substitutional gold in the SiGe alloys were studied as a function of the Ge content. The data suggest that both the donor and acceptor levels are pinned to the conduction band.
Spectroellipsometry for characterization of Zn1−xCdxSe multilayered structures on GaAs
Authors: Lee Joungchel , Collins R. W. , Heyd A. R. , Flack F. , Samarth N.
Published: July 2002

The dielectric functions of 0.5–1.5-μm-thick Zn1−xCdxSe (0≤x≤0.34) epilayers on (100) GaAs were measured by spectroellipsometry (SE) over the photon energy range 1.5≤E≤5.3 eV. These spectra were parameterized using the Sellmeier and Lorentz equations for photon energies below and above the fundamental gap region, respectively. We have demonstrated the usefulness of this parameterization in analyses of SE data collected on a ZnSe heterostructure and a Zn1−xCdxSe quantum well that provide accurate layer thicknesses and compositions.
Picosecond relaxation and thermal diffusion in amorphous silicon
Authors: Wright O. B. , Zammit U. , Marinelli M. , Gusev V. E.
Published: July 2002

We have studied the time-resolved reflectivity changes in the picosecond–nanosecond range induced by picosecond visible optical pulses in ion-implanted amorphous silicon-on-sapphire. Illumination from the front side of the thin film probes the picosecond carrier relaxation processes. Heat release from trapped carriers in the 100-ps range is shown to be significant. Illumination from the substrate side probes, in addition, the ultrafast diffusion of heat to the substrate. The derived thermal diffusivity is shown to correspond to a near-surface layer much thinner than the optical absorption depth.
High-temperature superconducting Josephson fluxon–antifluxon transistors
Authors: Berkowitz S. J. , Zhang Y. M. , Mallison W. H. , Char K. , Terzioglu E. , Beasley M. R.
Published: July 2002

We have realized the Josephson fluxon–antifluxon transistor (JFAT) in high temperature superconductivity using an asymmetric control line on top of either bicrystal junctions or Co-doped YBa2Cu3Ox superconductor–normal–superconductor (SNS) junctions. We have measured current gains as high as 6 for 30 μm-wide bicrystal JFATs (30 K) and as high as 3 for Co-doped SNS JFATs (50 K). An improvement in gain over the Josephson vortex flow transistor, due to improved coupling efficiency, is demonstrated. There is also a reduction of control line inductance that should lead to an improvement in gate speed.
X-ray generation enhancement from a laser-produced plasma with a porous silicon target
Authors: Nishikawa Tadashi , Nakano Hidetoshi , Ahn Hyeyoung , Uesugi Naoshi , Serikawa Tadashi
Published: July 2002

X-ray generation enhancement from a laser-produced plasma with a porous Si target is reported. For a porous surface formed on a Si wafer, the self-reflectivity of a femtosecond pulse becomes considerably small. The observed energy penetration depth is 25–30 μm, which is much larger than the skin depth of solid density matter. Using a porous Si target, the threshold of the pre-pulse intensity required for soft x-ray emission enhancement can be reduced. It also contributes to enhance the pre-pulse effect, and soft x-ray generation enhancement ranging from 1.6 to 6.5 times is observed depending on the pre-pulse intensity.
Thermal conductivity of Si–Ge superlattices
Authors: Lee S.-M. , Cahill David G. , Venkatasubramanian Rama
Published: July 2002

The thermal conductivity of Si–Ge superlattices with superlattice periods 30<L<300 Å, and a Si0.85Ge0.15 thin film alloy is measured using the 3ω method. The alloy film shows a conductivity comparable to bulk SiGe alloys while the superlattice samples have a thermal conductivity that is smaller than the alloy. For 30<L<70 Å, the thermal conductivity decreases with decreasing L; these data provide a lower limit to the interface thermal conductance G of epitaxial Si–Ge interfaces: G> 2 × 109 W m−2 K−1 at 200 K. Superlattices with relatively longer periods, L>130 Å, have smaller thermal conductivities than the short-period samples. This unexpected result is attributed to a strong disruption of the lattice vibrations by extended defects produced during lattice-mismatched growth.
Light-emitting electrochemical cells from a blend of p- and n-type luminescent conjugated polymers
Authors: Yang Yang , Pei Qibing
Published: July 2002

We demonstrate polymer light-emitting electrochemical cells (LECs) made of a blend of p- and n-type luminescent conjugated polymers. These two polymers, poly[9-(3,6,9-trioxadecyl)- carbazole-3,6-diyl] (TOD–PC, a p-type polymer) and poly[2,3-di(p-tolyl)–quinoxaline-5,8-diyl] (DT–PQX, a n-type polymer), are blue and blue–green emission polymers, respectively, both with high photoluminescent quantum efficiency. However, the photoluminescence of the polymer blend is completely quenched, due to the charge transfer between the two polymers. A new and faint orange–yellow photoluminescence emission, which has photonic energy consistent with the energy difference of the π band of TOD–PC and the π* and of DT–PQX, has been observed. LECs fabricated from this polymer blend show strong current injection and bright electroluminescence at this new emission color, which is believed to be due to the interpolymer radiative recombination of the electrons from the n-type polymer and holes from the p-type polymer. Such an independent p doping of TOD–PC and n doping of DT–PQX in the blend and interpolymer radiative recombination provide an interesting way of generating new emission colors in the LEC system.
Stoichiometry and thickness variation of YBa2Cu3O7−x in pulsed laser deposition with a shadow mask
Authors: Trajanovic Z. , Choopun S. , Sharma R. P. , Venkatesan T.
Published: July 2002

The deposition of particulate species, typically seen in pulsed laser deposition can be eliminated by the deployment of a line-of-sight shadow technique. Since the technique uses the discrimination between ballistic and diffusive species, it is important to understand the lateral stoichiometry and thickness dependence under various deposition conditions. We present in this study the dependence of the lateral thickness and stoichiometry of YBa2Cu3O7−x deposited by a shadow mask pulsed laser technique on the background oxygen pressure and the shadow mask position from the target. We determined Y atoms to be limiting the lateral stoichiometric uniformity. Due to its diffusive nature, shadowed pulsed laser deposition also allowed us to improve the thickness uniformity across the wafer.
Photoluminescence properties of cubic GaN grown on GaAs(100) substrates by metalorganic vapor phase epitaxy
Authors: Wu J. , Yaguchi H. , Onabe K. , Ito R. , Shiraki Y.
Published: July 2002

Photoluminescence (PL) measurements were performed on cubic GaN films grown on GaAs(100) substrates by metalorganic vapor phase epitaxy. The cubic GaN films show a high optical quality that enables us to study the PL spectra in detail. From temperature and excitation intensity dependence, the emission lines at 3.274 and at 3.178 eV were assigned to the excitonic transition and the donor–acceptor pair transition, respectively. We also observed two additional emission lines at 3.088 and 3.056 eV. An excitonic emission at 3.216 eV with full width half maximum value as small as 73 meV was observed at 300 K.
Characterization of the dominant midgap levels in Si-doped GaN by optical-isothermal capacitance transient spectroscopy
Authors: Hacke P. , Okushi H.
Published: July 2002

Optical-isothermal capacitance transient spectroscopy (O-ICTS) was used to characterize prominent midgap carrier traps in Si-doped n-type GaN grown by metalorganic vapor phase epitaxy. Strong carrier photoionization was observed from two deep levels to the conduction band. The first level photoionizes in the broad range from below 1.8 eV to over 2.3 eV. Seen in all n-type GaN, this level is believed to be defect related and involved in the commonly observed yellow luminescence. The second, more dominant O-ICTS peak develops with incident photon energy of ∼2.3 eV. This is a previously unreported, yet unidentified level of impurity nature. The two midgap states can be clearly distinguished by means of the time constant for photoionization of carriers from the deep levels.
Orientational holographic grating observed in liquid crystals sandwiched with photoconductive polymer films
Authors: Ono Hiroshi , Kawatsuki Nobuhiro
Published: July 2002

We presented a novel type of orientational photorefractive device, consisting of liquid crystals (LCs) sandwiched with photoconductive polymer films across the insulated polymer films. The photoexcited charges were generated in the photoconductive layers and eventually become trapped in the dark areas at the insulated polymer surfaces. The resulting space charge field reoriented the LC molecules and the holographic gratings were generated. The strong beam coupling effects were observed and the refractive index modulation Δn was estimated to be of the order of 3.6×10−3.
Two-color infrared detection using intersubband transitions in multiple step quantum wells with superlattice barriers
Authors: Mei Ting , Karunasiri G. , Chua S. J.
Published: July 2002

A dual-band multiple quantum well infrared photodetector has been fabricated for the near and mid-infrared detection. The structure consists of InGaAs/GaAs step quantum wells separated by AlGaAs/GaAs superlattice barriers. The step quantum wells are designed to have two bound states and a quasi-continuum above the superlattice barriers. The bound-to-bound and bound-to-continuum transitions are employed for the dual-band detection. The superlattice barriers are used to extract the photocurrent from the bound-to-bound transition with a relatively low external electric field, which keeps the dark current low. This work demonstrates the use of a new quantum well structure for the fabrication of multicolor quantum well infrared photodetectors.
Photocurrent from photocorrosion of aluminum electrode in porphyrin/Al Schottky-barrier cells
Authors: Murata Kazuhiko , Ito Shoji , Takahashi Kohshin , Hoffman Brian M.
Published: July 2002

Current–voltage characteristics under illumination of monochromatic light for metal-free tetrabenzporphyrin, metal-free triazatetrabenzporphyrin, and metal-free phthalocyanine in (indium–tin–oxide)/porphyrin/Al sandwich cells seem to show high-energy conversion efficiencies of 14%, 7.7%, and 5.5%, respectively. However, according to the simultaneous measurement of both short-circuit photocurrent and transmittance of the aluminum electrode with time, the transmittance of Al linearly increases as the photocurrent flows into the external circuit. It is concluded that all photocurrents in the above cells arise from photoaccelerated corrosion of aluminum electrode and do not originate from conversion of light energy to electrical energy.
Impact of low carbon concentrations on the electrical properties of highly boron doped SiGe layers
Authors: Osten H. J. , Lippert G. , Gaworzewski P. , Sorge R.
Published: July 2002

We present results on the effect of carbon coevaporation by molecular beam epitaxy on electrical properties of highly boron doped SiGe:C layers for C concentration of around 1020 cm−3. Such C concentrations are needed for substantial suppression of boron outdiffusion. The concentration of electrically active boron and the hole mobility are not affected by the addition of carbon. Carbon-related defects, typically observed for C concentrations below the bulk solid solubility limit (<1018 cm−3), do not significantly reduce the concentration of electrically active B in SiGe:C. However, carbon coevaporation affects carrier lifetimes. The generation lifetime is reduced by more than one order of magnitude in SiGe:C compared with analogous SiGe layers.
High net gain at 514 nm in a photorefractive polymer doped with a chalcone derivative
Authors: Mager L. , Melzer C. , Barzoukas M. , Fort A. , Méry S. , Nicoud J.-F.
Published: July 2002

We report on the photorefractive properties of a low Tg composite consisting of functionalized polysiloxane doped with a chalcone derivative. The high transparency of this doping molecule enabled the observation of high net gain at 514 nm. Orientational and Pockels contributions to the total refractive index variations were measured by frequency-dependent ellipsometry experiments. Finally, the field dependence of the gain coefficient is described using Kukhtarev’s model for the space charge field with an effective trap density as a single fitting parameter.
Infrared absorption in amorphous silicon from ab initio molecular dynamics
Authors: Debernardi Alberto , Bernasconi Marco , Cardona Manuel , Parrinello Michele
Published: July 2002

We present an ab initio calculation of the infrared vibrational spectrum of amorphous silicon. The electron polarization, which is the main ingredient to obtain the infrared spectra, is evaluated using the recent formulation in terms of Berry’s phase, while the time evolution of the system is studied using Car–Parrinello molecular dynamics. Our results are in quantitative agreement with experimental data and also with the results of empirical calculations based on a bond-dipole model.
Localized electron trapping and trap distributions in SiO2 gate oxides
Authors: Ludeke R. , Wen H. J.
Published: July 2002

Localized trap filling and trap creation in SiO2 were investigated by injecting electrons into metal-oxide-semiconductor structures with a scanning tunneling microscope. The resulting charging causes changes in the oxide potential that were studied as a function of an applied oxide field. The charge densities and charge distributions were obtained by modeling the field dependence of the potential arising from multiple sets of sheet charges in the oxide.
Magnetic properties and magnetic domain structures of NdFe10.5Mo1.5 and NdFe10.5Mo1.5Nx
Authors: Yang Jinbo , Mao Weihua , Cheng Benpei , Yang Yingchang , Xu Hai , Han Baoshan , Ge Senlin , Ku Wanjun
Published: July 2002

We succeed in preparing anisotropic magnetic powders with high performance based on the NdFe10.5Mo1.5Nx nitrides. The properties of these materials are favorable for permanent magnet application. The domain structures of the NdFe10.5Mo1.5 and NdFe10.5Mo1.5Nx were studied by using magnetic force microscopy. Upon nitrogenation, a domain structure transition from complex maze to simple stripe was found. This transition is due to the strongly uniaxial magnetocrystalline anisotropy induced by interstitial nitrogen atoms. Together with magnetic measurements, we have calculated the domain wall energy γ, exchange constant A, domain wall thickness δ, and critical single-domain particle size Dc of NdFe10.5Mo1.5 and NdFe10.5Mo1.5Nx.
Infrared spectroscopy of Er-containing amorphous silicon thin films
Authors: Zanatta A. R. , Nunes L. A. O.
Published: July 2002

Hydrogenated amorphous SiEr (a-SiEr:H) thin films were deposited by cosputtering. Oxygen and nitrogen were employed as impurity enhancers of Er3+ emission of light at 1540 nm, and photoluminescence, infrared absorption, and Raman spectroscopies were performed as a function of various annealing temperatures. As-deposited O-contaminated and N-doped a-SiEr:H samples exhibit Er3+ related photoluminescence, low intensity at room temperature, and maximum intensity after thermal annealing at ∼500 °C. In addition to the enhancement of the Er3+ emission of light, thermal annealing provokes the outdiffusion of hydrogen bonded to silicon atoms. The experimental data suggest that both hydrogen and thermal treatments improve the Er3+ related photoluminescence by decreasing the occurrence of nonradiative processes.
A universal damage induced technique for quantum well intermixing
Authors: Kowalski O. P. , Hamilton C. J. , McDougall S. D. , Marsh J. H. , Bryce A. C. , De La Rue R. M. , Vögele B. , Stanley C. R. , Button C. C. , Roberts J. S.
Published: July 2002

We report a novel technique for quantum well intermixing which is simple, reliable and low cost, and appears universally applicable to a wide range of material systems. The technique involves the deposition of a thin layer of sputtered SiO2 and a subsequent high temperature anneal. The deposition process appears to generate point defects at the sample surface, leading to an enhanced intermixing rate and a commensurate reduction in the required anneal temperature. Using appropriate masking it is possible to completely suppress the intermixing process, enabling large differential band gap shifts (over 100 meV) to be obtained across a single wafer.
Image storage based on biphotonic holography in azo/polymer system
Authors: Wu Pengfei , Wu Xiaochun , Wang Li , Xu Jiren , Zou Bingsuo , Gong Xiong , Huang Wei
Published: July 2002

Image storage has been investigated with the biphotonic holographic method in an azo/polymer film. Experimental results show that this biphotonic holographic storage has high spatial resolution and exhibits an image enhancement effect after blocking the noncoherent light. The mechanism of biphotonic holographic storage is attributed to the redistribution of cis form azo molecules induced by both coherent light and noncoherent light.
Spatially resolved tunneling spectroscopy of superconducting wires with artificial pinning centers
Authors: Levi Y. , Millo O. , Rizzo N. D. , Prober D. E. , Motowidlo L. R.
Published: July 2002

We used scanning tunneling microscopy and spectroscopy to study with nanometer resolution the spatial variation of superconductivity in the vicinity of the interface between normal and superconductor regions. The samples were novel superconducting wires consisting of ordered arrays of sub-micron diameter normal metal filaments, either Cu or Ni, embedded in a NbTi superconducting matrix. By taking topographic images simultaneously with current–voltage curves, we obtain information about the local quasi-particle density of states on both sides of the interface.
Electro-optic characteristics of a liquid crystal cell in a homogeneous-to-twisted planar mode
Authors: Lee S. H. , Kim H. Y. , Galabova H. G. , Allender D. W.
Published: July 2002

The electro-optic properties of a novel liquid crystal device associated with a homogeneous to twisted-planar (HTP) transition have been investigated. The cell plates are prepared in such a way that in the absence of an electric field the liquid crystal orientation is uniform throughout the cell, and thus between crossed polarizers the cell appears black (off state). When an electric field of a particular configuration is applied, a 90° twist is imposed, and the cell transmits light (on state). It was found that the HTP device exhibits wide viewing angle and excellent color characteristics. The dependence of the electro-optic effect on rubbing directions and cell gap has also been investigated.
Visible dual-wavelength light generation in optical superlattice Er:LiNbO3 through upconversion and quasi-phase-matched frequency doubling
Authors: Zheng Jian-jun , Lu Yan-qing , Luo Gui-peng , Ma Jing , Lu Ya-lin , Ming Nai-ben , He Jing-liang , Xu Zu-yan
Published: July 2002

Optical superlattice Er:LiNbO3 was fabricated by inducing a periodic ferroelectric domain structure into the crystal during the growing process. Because of the combination of the nonlinear optical properties of LiNbO3 and the spectral properties of Er3+, the crystal can simultaneously emit the second harmonic light through quasi-phase matching and the green light through upconversion at room temperature. Pumped by infrared diode lasers, violet-and-green and blue-and-green light generation was demonstrated in two samples. The detailed absorption spectrum and emission spectrum of upconversion were measured. The possible physical mechanism was discussed.
Electroluminescence of a novel terbium complex
Authors: Gao X. C. , Cao Hong , Huang Chunhui , Li Biaoguo , Umitani Shigeo
Published: July 2002

We describe efficient electroluminescence from a terbium complex, tris-(1-phenyl-3-methyl-4isobutyryl-5-pyrozolone)-bis(triphenyl phosphine oxide) terbium (PTT). The green-emitting material possesses much higher photoluminescence efficiency compared to the commonly used green light emitter, 8-hydroxyquinoline aluminum (ALQ). The rarely observed emission from the hole transport layer, N, N′-bis (3-methylphenyl)- N, N′-diphenyl-benzidine (TPD) of the device ITO/TPD/PTT/Al proves that PTT also is a good electron transporting material. The ITO/TPD/PTT/ALQ/Al device shows luminance up to 920 cd/m2 at a drive voltage of 18 V and a luminous efficiency of 0.51 lm/W at a current density of 0.70 mA/cm2, which are up to now the highest among devices using rare-earth complex materials as emitters.
Continuous-wave emission in the ultraviolet from diatomic excimers in a microdischarge
Authors: Frame J. W. , John P. C. , DeTemple T. A. , Eden J. G.
Published: July 2002

Emission on the I2 (D′→A′), XeI (B2Σ1/2+→X2Σ1/2+) and XeO (2 3Π→1 3Π) bands, peaking in the ultraviolet at 342, 253 and 238 nm, respectively, has been generated on a continuous basis in a microdischarge with a static gas fill. Discharges are produced in Kr/I2, Xe/I2, or Xe/O2 gas mixtures by cylindrical devices 400 μm in diameter and fabricated in silicon. Rare-gas–halide and –oxide microdischarge lamps are attractive ultraviolet or vacuum ultraviolet sources and XeI, in particular, appears to be a potential replacement for Hg resonance line radiation (253.7 nm).
Red–green–blue photopumped lasing from ZnCdMgSe/ZnCdSe quantum well laser structures grown on InP
Authors: Zeng L. , Yang B. X. , Cavus A. , Lin W. , Luo Y. Y. , Tamargo M. C. , Guo Y. , Chen Y. C.
Published: July 2002

Room-temperature optical pumped lasing emission in the red, green, and blue has been obtained from ZnCdMgSe/ZnCdSe quantum well (QW) laser structures grown on InP substrates. The structures are nearly identical, except for variations in the thickness and/or composition of the QW layer. No other single set of semiconductor materials has been demonstrated whose structures are pseudomorphic on one single substrate, and produces light emitters throughout the entire visible range. Our results demonstrate the potential for these materials as integrated full color display devices.
Electromechanical properties of sol-gel derived Ca-modified PbTiO3 films
Authors: Kholkin A. , Seifert A. , Setter N.
Published: July 2002

Piezoelectric coefficients and electric field-induced strains are investigated in Ca-modified PbTiO3 (PCT) films deposited by sol-gel technique. The microstructural evolution and related electromechanical properties are studied as a function of Ca content and porosity of the films. The porosity is tailored by changing the heating rate during the final crystallization anneal. It is found that piezoelectric properties of porous films heated at slow rates are superior to those of dense films crystallized using higher heating rates. This is explained as a result of the constraining effect of the substrate, which apparently reduces the piezoelectric and strain responses in dense films. Electromechanical properties are also improved with Ca addition due to the decrease of tetragonality and ease of 90° domain rotation. Charge piezoelectric coefficients in porous films are close to those of PCT ceramics of the same composition. These results, combined with the low dielectric constant, make PCT films an attractive material for microelectromechanical applications.
Ion-beam synthesis and structural characterization of ZnS nanocrystals in SiO2
Authors: Bonafos C. , Garrido B. , López M. , Romano-Rodriguez A. , González-Varona O. , Pérez-Rodrı́guez A. , Morante J. R.
Published: July 2002

In this letter, we report the ion-beam synthesis and the structural characterization of ZnS nanocrystals in SiO2. Both electron diffraction and x-ray diffraction measurements show the precipitation of ZnS nanocrystals having a wurtzite–2H structure and infrared spectroscopy confirms the presence of Zn–S bonding. Upon annealing, transmission electron microscopy observations show the Ostwald ripening of the precipitates coupled with a self-organization in two layers parallel to the free surface. This self-organization has been also detected by secondary ion mass spectroscopy, and its origin is discussed in terms of a pure Ostwald ripening process and/or a consequence of the implantation damage.
A deep level induced by gamma irradiation in Hg1−xCdxTe
Authors: Hu Xinwen , Fang Jiaxiong , Wang Qin , Zhao Jun , Lu Huiqing , Gong Haimei , Zhang Shengkun , Lu Fang
Published: July 2002

Admittance spectroscopy and deep-level transient spectroscopy measurements have been performed on n+-on-p Hg1−xCdxTe (x=0.595) planar photodiodes grown by improved zone melt method. After 1.0 Mrads gamma irradiation, a new trap center is observed at 0.19 eV above the valence band, while the well-known 0.15 eV trap level disappears. The trap densities for these two levels are almost the same. We attribute this phenomenon to the gamma irradiation, which produces a compound defect correlated with Hg vacancy.
Characteristics of high quality tantalum oxide films deposited by photoinduced chemical vapor deposition
Authors: Zhang Jun-Ying , Lim Boon , Boyd Ian W. , Dusastre Vincent
Published: July 2002

A method is presented for the photodeposition of tantalum oxide films from tantalum ethoxide and nitrous oxide using 172 nm radiation. The composition of the tantalum oxides deposited by this technique was determined by x-ray photoelectron spectroscopy while the optical and electrical properties were characterized using ellipsometry, capacitance–voltage, and current–voltage techniques. A leakage current density as low as 3.2×10−7 A cm−2 at a voltage of 10 V is obtained for the as-grown films. This is several orders of magnitude better than for any other Ta2O5 films deposited using either conventional or plasma-chemical vapor deposition techniques.
Energy selective optically pumped stimulated emission from InGaN/GaN multiple quantum wells
Authors: Schmidt T. J. , Cho Yong-Hoon , Gainer G. H. , Song J. J. , Keller S. , Mishra U. K. , DenBaars S. P.
Published: July 2002

Optically pumped stimulated emission (SE) from InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition has been systematically studied as a function of excitation photon energy (Eexc) to further understand the origin of SE in these structures. Optically pumped SE was observed for excitation photon energies well below that of the absorption edge of the MQWs, indicating the states responsible for the soft absorption edge in these structures can efficiently couple carriers with the gain region. “Mobility edge”-type behavior in the SE peak was observed as Eexc was varied. The effective mobility edge measured in these SE experiments lies ∼110 meV above the main spontaneous emission peak and ∼62 meV above the SE peak. Tuning the excitation energy below the mobility edge was found to be accompanied by a drastic increase in the SE threshold due to a decrease in the effective absorption cross section. The experimental results indicate that the SE peak observed here has the same microscopic origin as the spontaneous emission peak, i.e., radiative recombination of localized states.
Oxide thickness dependence of energy shifts in the Si 2p levels for the SiO2/Si structure, and its elimination by a palladium overlayer
Authors: Kobayashi Hikaru , Kubota Tomohiro , Kawa Hidefumi , Nakato Yoshihiro , Nishiyama Masayoshi
Published: July 2002

The energy difference between the oxide and substrate Si 2p peaks for silicon oxide/Si structures increases with the oxide thickness. The dependence of the energy shift on the oxide thickness almost disappears with the deposition of a thin palladium overlayer, because of the avoidance of the surface charging effect due to photoemission and because of the nearly constant energy shift resulting from extra atomic relaxation. The true chemical shift of silicon oxide layers thicker than 2 nm is determined to be ∼3.8 eV. For the thickness dependence of the oxide Si 2p energy, the extra atomic relaxation and charging effect are dominant for oxide layers thinner than ∼2 nm and thicker than ∼4 nm, respectively. In the intermediate thickness region, both the effects are important.