bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in risk factors of preterm delivery in France between 1981 and 1995
Authors: Foix‐L’Hélias L. , Blondel B.
Published: July 2002

Because of the important changes in medical care and the social context of pregnancy, the relevance of well‐established risk factors of preterm delivery (< 37 weeks) needs to be re‐assessed. The objective of this study was to determine whether the associations between maternal characteristics and preterm delivery in France in 1995 were similar to those in 1981. We used two national representative samples of births, 5577 newborns in 1981 and 13 318 in 1995. Univariable and multivariable analyses were applied to identify variables associated with increased risk of preterm delivery. Some risk factors were similar in 1981 and 1995, including age > 34 years and previous adverse obstetric history. Other factors that were observed in 1981 but which were not linked to preterm delivery in 1995 included the mothers being very young, single or foreign. However, parity and previous induced abortion were associated with preterm delivery in 1995, but not in 1981. These results show that the definition of high‐risk groups used in prevention programmes should be brought up to date regularly.
Arachnoiditis associated with arachnoid cyst formation and cord tethering following myelography: Magnetic resonance features
Authors: Shah Jeshil , Patkar Deepak , Parmar Hemant , Prasad Srinivasa , Varma Ravi
Published: July 2002

The reported incidence of clinically significant arachnoiditis following oil‐based contrast media myelography is approximately 1%. The incidence of arachnoiditis in the dorsal spine is even more rare. Acquired arachnoid cyst formation can occur with arachnoiditis of various aetiologies. A case is presented of a patient with chronic backache, radiculopathy, weakness and muscle wasting, who had undergone myelography with oil‐based contrast media about 28 years ago. There was no history of spinal surgery, spinal canal stenosis, disc disease or trauma, all of which are known to increase the risk of arachnoiditis. Magnetic resonance imaging features are presented in this case of arachnoiditis with arachnoid cyst formation, and cord tethering.
High impact of nephropathy on five‐year mortality rates among patients with Type 2 diabetes mellitus from a multi‐ethnic population in New Zealand
Authors: Simmons D. , Schaumkel J. , Cecil A. , Scott D. J. , Kenealy T.
Published: July 2002

Aims Type 2 diabetes mellitus and its complications are common among Polynesians in New Zealand. This study investigated the mortality from diabetes among indigenous Maori and recent migrants from the South Pacific.

Methods Death certificates and other reports were collected to enumerate those who had died in an across‐community cohort study of 765 diabetic patients aged 40–79 years in 1991. Five year mortality status was ascertained in 99.7% and death certificates were obtained from 129 (88%) of the 146 who had died. Diabetes was missed from 36% of death certificates.

Results Compared to Europeans with Type 2 diabetes, Maori with Type 2 diabetes were 2.66 (1.63–4.35) fold as likely to die from diabetes‐related conditions, including a 13.1 (3.7–46.4) fold greater risk of death from nephropathy. Pacific Islands Polynesians with Type 2 diabetes had a similar mortality to Europeans with Type 2 diabetes (hazards ratio 1.06 (0.68–1.65)). After 6 years, 10.7 (2.2–19.3)% more Maori had died than Pacific Islands Polynesians.

Conclusions Maori with Type 2 diabetes are dying from diabetic compli‐cations, particularly nephropathy, at an alarming rate. The magnitude of the difference between Maori and Pacific Islands Polynesians suggests environmental rather than inherited factors are involved and these need further investigation.
Management of the Central Nasal Support Complex in Naso-orbital Ethmoid Fractures
Authors: Vora Neil M. , Fedok Fred G.
Published: July 2002

Central nasal support structures are frequently injured in patients with naso-orbital ethmoid fractures. Diagnosis of these injuries can be difficult and, to optimally manage them, a thorough understanding of the complex anatomy is essential. The goal of surgical repair is to reestablish the aesthetics and function to this region without complication. Appropriate imaging and classification of the central nasal support injury and classification of the naso-orbital ethmoid fractures must be accomplished prior to formulating a successful treatment plan. This article reviews the anatomy, patient assessment, imaging, and classification systems. Currently accepted management of specific injuries are outlined.
Laser-assisted chemical etching of copper
Authors: Ritsko J. J. , Ho F. , Hurst J.
Published: July 2002

Copper films several microns thick can be rapidly etched (0.1–0.5 μm/s) in a chlorine atmosphere using 308 nm pulsed excimer laser radiation. Etch rates exhibit a practical threshold of ∼0.1 J/cm2 and saturate above 0.3 J/cm2. The etching mechanism involves reaction of copper and chlorine in the time between the laser pulses to form a nonstoichiometric chloride which is thermally ablated by the laser. Photochemical effects appear to be unimportant. The etch rate increases roughly as the square root of the laser pulse rate, suggesting that reactive diffusion is a limiting factor. As the substrate temperature increases, the etch rate rises, then falls, indicating the competition of processes such as adsorption, desorption, and reaction of chlorine molecules on copper chloride surfaces. A simple model based on chemical kinetics suggests that the copper-chlorine reaction at pressures above 0.1 Torr is controlled by a physisorbed intermediate state.
Cathodoluminescence study of substrate offset effects on interface step structures of quantum wells
Authors: Wada K. , Kozen A. , Hasumi Y. , Temmyo J.
Published: July 2002

The interface structures of single quantum wells grown on vicinal (100) substrates with a controlled offset 0.2° are studied by cathodoluminescence microscopy. Bright and dark stripe patterns are periodically observed in monochromatic images of the single quantum wells and the stripes replicate stair-like stepped interfaces. It is further shown that the observed terrace width is several times larger than the average interstep distance of monolayer steps calculated from the offset angle and that the step height is not one monolayer. Based on the results, a new interface structure model has been proposed that takes the offset angle into account. Finally, it is shown that employing growth interruption during epitaxial growth as an interface smoothing technique has limitations.
Direct formation of conductor films by laser sublimating of ceramics
Authors: Morita Noboru , Watanabe Takehiro , Yoshida Yoshitaro
Published: July 2002

A new method for direct formation of conductor lines onto ceramic substrates is presented. This method involves the selective forming of aluminum thin films by decomposing aluminum nitride (AlN) ceramics in argon (Ar) gas atmosphere with a Q-switched yttrium aluminum garnet (YAG) laser. The aluminum films can also be employed as a catalyst in electroless plating. With nickel (Ni) electroless plating solution, Ni conductor lines with a specific resistance about 1×10−7 Ω m were directly and selectively formed on the aluminum layer.
High coercivity in rapidly quenched Sm(Fe, T)12-type magnets
Authors: Singleton E. W. , Strzeszewski J. , Hadjipanayis G. C.
Published: July 2002

The magnetic and structural properties of melt-spun Sm(FeT)12 alloys where T=Ti,V,Al,Cu,Ga,Si and with some containing small amounts of B and C have been studied. The samples are magnetically soft in the as-quenched state. High coercive fields are developed upon heating the samples at temperatures ranging from 750 to 1050 °C. The tetragonal ThMn12-type structure was found in all the alloys after annealing. The highest coercivities have been obtained on a Sm10Fe80Ti7.5B2.5 sample with Hc ≂7.7 kOe. These coercivities are much higher than those obtained previously and make these alloys good candidates for permanent magnet development.
Observation of multiple silicon dangling bond configurations in silicon nitride
Authors: Jousse D. , Kanicki J. , Stathis J. H.
Published: July 2002

We show that silicon dangling bonds with different nearest-neighbor configurations and energy levels can be resolved by electron spin resonance (ESR) in silicon nitride. Using an in situ bias technique on large-area metal-nitride-silicon structures, we demonstrate that the ESR line in Si-rich nitride consists of an inhomogeneous distribution of discrete components at different g values. We show that trapping of holes occurs at a site with a g value of 2.0052 corresponding to a pure Si environment, while electron trapping occurs at a site with a g value of 2.0028, corresponding to a pure N environment.
Tunneling acoustic microscope
Authors: Takata Keiji , Hasegawa Tsuyoshi , Hosaka Sumio , Hosoki Shigeyuki , Komoda Tsutomu
Published: July 2002

A new type of microscope, which is based upon both a scanning tunneling microscope (STM) and a technique for detecting acoustic waves, is described. An acoustic wave generated in a STM’s sample, by vibration of its tip, is detected by a piezoelectric transducer coupled to the sample. The amplitude of the acoustic wave corresponds to the strength of the force interaction between the tip and the sample, and is sensitive to tip-sample spacing. We have been successful in keeping the spacing constant by using a new feedback loop that holds this amplitude constant without tunneling. This method enhances the features of the STM without reducing its functions and enables simultaneous use of both force interactions and tunneling current to investigate the properties of samples. Topographies taken by the new feedback system and tunneling current images are shown.
Elastic constants of sodalite Na4Al3Si3O12Cl
Authors: Li Zhuang , Nevitt M. V. , Ghose Subrata
Published: July 2002

The elastic stiffness constants of sodalite Na4Al3Si3O12Cl (cubic, a=8.882 Å;Z=2), a framework-type aluminosilicate with cubo-octahedral cages, have been determined by an ultrasonic method. The measured values are C11,88.52(71); C12,38.70(50); and C44,36.46(33) GPa. Because of its structural flexibility, the bulk modulus KS(55.30 GPa) and shear modulus μ (31.30 GPa) values in sodalite are considerably smaller than those in densely packed cubic silicate structures such as spinel and garnet.
Control of ballistic electrons in macroscopic two-dimensional electron systems
Authors: Spector J. , Stormer H. L. , Baldwin K. W. , Pfeiffer L. N. , West K. W.
Published: July 2002

We introduce three basic components for the manipulation of quasi-classical ballistic electrons in very high mobility two-dimensional electron systems and evaluate their effectiveness using the transverse electron focusing technique. We present an electron absorber or electron randomizer, demonstrate electron focusing in an area of tunable electron density, and present a simplified version of an injector/collector for ballistic carriers in two dimensions.
Grain boundary mediated amorphization in silicon during ion irradiation
Authors: Atwater Harry A. , Brown Walter L.
Published: July 2002

Amorphous Si is nucleated heterogeneously at grain boundaries during irradiation of polycrystalline Si thin films by 1.5 MeV Xe+ ions for temperatures of 150–225 °C. Moreover, the heterogeneous nucleation kinetics of amorphous Si are strongly dependent on grain boundary structure. Following formation at grain boundaries, the amorphous Si layer grows at a rate comparable to that previously observed at a pre-existing planar amorphous-crystal interface. As amorphization proceeds, a decrease in average grain size and a marked change in the grain size distribution results. We suggest a simple atomistic model for amorphous phase formation in Si in which the nucleation kinetics are dependent on the point defect-grain boundary interactions.
Relationship between etch pit densities and oxygen concentrations on CdTe
Authors: Yokota Katsuhiro , Yoshikawa Toshiharu , Inano Sigeru , Morioka Takeshi , Katayama Saichi
Published: July 2002

The density of etch pits and the concentration of O in melt-grown CdTe increased as the residual gas pressure in ampoules during preparation increased. The etch pit density increased proportionally to the integral strength of an infrared TeO2 absorption band, which presents the oxygen concentration.
Infrared absorption spectra in bulk Fe-doped InP
Authors: Fornari R. , Kumar J.
Published: July 2002

We have observed that the absorption spectra in bulk Fe-doped indium phosphide differ considerably from those recorded on undoped and n-type samples. In the former case it was seen that the absorption edge presents a tail whose shape depends on the concentration of iron atoms incorporated into the matrix. Based on this phenomenon, we present a new nondestructive method which can be successfully employed to measure the iron concentration in semi-insulating InP.
Vertical-cavity surface-emitting InGaAs/GaAs lasers with planar lateral definition
Authors: Orenstein M. , Lehmen A. C. Von , Chang-Hasnain C. , Stoffel N. G. , Harbison J. P. , Florez L. T. , Clausen E. , Jewell J. E.
Published: July 2002

A planarity preserving method for the definition of vertical-cavity surface-emitting lasers (VC-SEL) is described. A strained-layer InGaAs quantum well VC-SEL structure was grown and lasers were laterally defined using a tailored deep proton implantation process. In these lasers we obtained low threshold current densities of 1000 A/cm2 and efficient cw operation. This method facilitates large-scale integration of VC-SEL devices.
Selective deposition of aluminum from selectively excited metalorganic source by the rf plasma
Authors: Masu Kazuya , Tsubouchi Kazuo , Shigeeda Nobuyuki , Matano Tatsuya , Mikoshiba Nobuo
Published: July 2002

A selective method of depositing aluminum onto silicon was developed using trimethylaluminum and hydrogen as source gases. Trimethylaluminum was selectively decomposed into excited species through the well controlled radio frequency (13.56 MHz) excited hydrogen plasma of 0.03–0.06 W/cm3. Excited species were reacted on the silicon surface to produce aluminum without carbon incorporation at 230–260 °C. The thermally oxidized silicon dioxide line and space pattern and contact windows were successfully filled with selectively deposited 3000-Å-thick aluminum.
Surface preparation for the heteroepitactic growth of ceramic thin films
Authors: Norton M. Grant , Summerfelt Scott R. , Carter C. Barry
Published: July 2002

The morphology, composition, and crystallographic orientation of the substrate influence the nucleation and growth of deposited thin films. A method for the preparation of controlled, characteristic surfaces is reported. The surfaces are suitable for the heteroepitactic growth of thin films. When used in the formation of electron-transparent thin foils, the substrates can be used to investigate the very early stages of film growth using transmission electron microscopy. The substrate preparation involves the cleaning and subsequent annealing to generate a surface consisting of a series of steps. The step terraces are formed on the energetically stable surface, and controlled nucleation and growth of films at step edges is found. The substrate materials prepared using this technique include (001) MgO, (001) SrTiO3, and (001) LaAlO3.
Probe calibration in magnetic force microscopy
Authors: Göddenhenrich T. , Lemke H. , Mück M. , Hartmann U. , Heiden C.
Published: July 2002

Quantitative image interpretation in magnetic force microscopy requires information about the geometric and magnetic configuration of the employed microprobe. If the magnetic microfield of a given sample is known in detail, a calibration of the probe is possible. Using the well-defined current-induced microfield of a nanolithographically structured conducting pattern, calibration measurements combined with model calculations provide an insight into the effective domain configuration of magnetic force microscopy probes.
Friction reduction and zero wear for 52100 bearing steel by high-dose implantation of carbon
Authors: Kobs K. , Dimigen H. , Denissen C. J. M. , Gerritsen E. , Politiek J. , van Ijzendoorn L. J. , Oechsner R. , Kluge A. , Ryssel H.
Published: July 2002

Ion implantation of carbon in the AISI 52100 bearing steel yields a distinct reduction in friction and wear. This improvement is strongly dependent on the implanted fluence. The coefficient of friction decreases from 0.6 to 0.2 for doses >1×1018 cm−2 (energy 100 keV) and a wear reduction to nearly ‘‘zero wear’’ was obtainable even under severe wear conditions. The counterpart (unimplanted AISI 52100 steel ball) shows a similar behavior, which demonstrates that the tribological system is totally changed. Mössbauer spectroscopy and x-ray diffraction revealed that hexagonal ε-carbide is formed on implantation. On the other hand, Rutherford backscattering spectrometry shows that for high doses a large fraction of the implanted carbon is not contained in this carbide.
Clean grain boundaries and weak links in high T
c superconducting YBa2Cu3O7−x thin films
Authors: Shin D. H. , Silcox J. , Russek S. E. , Lathrop D. K. , Moeckly B. , Buhrman R. A.
Published: July 2002

It is demonstrated that polycrystalline thin films of high Tc superconducting YBa2Cu3O7−x can be grown with clean grain boundaries, i.e., without a boundary layer of segregation or different phase. In clean stoichiometric samples, angular misorientations of grains may be the origin of weak link behavior. High-resolution scanning transmission electron microscope images of films grown on ZrO2 and MgO by reactive evaporation, reactive sputtering, and laser ablation show atomic lattice images of clean grain boundaries. X-ray microanalysis with a 10 Å spatial resolution also indicates no composition deviation at the grain boundaries. Grain sizes and epitaxial relations of samples prepared by different methods are characterized.
Thermal dissociation energy of the Si-H complex in n-type GaAs
Authors: Roos G. , Johnson N. M. , Herring C. , Harris J. S.
Published: July 2002

The thermal dissociation kinetics of the hydrogen-donor complex in n-type GaAs:Si were determined from bias-temperature anneals on hydrogenated Schottky-barrier diodes. The anneal kinetics are approximately first order and yield a thermal dissociation energy for the Si-H complex of 1.2±0.1 eV. Depth redistribution of the Si-H complexes both within the depletion layer of biased diodes and in the field-free region of unbiased diodes suggests that hydrogen in n-type GaAs can migrate as a negatively charged species.
Low-field spin-valve magnetoresistance in Fe-Cu-Co sandwiches
Authors: Chaiken A. , Lubitz P. , Krebs J. J. , Prinz G. A. , Harford M. Z.
Published: July 2002

Fe-Cu-Co sandwiches have been grown on glass and silicon substrates using electron beam evaporation. Because the typical coercive field of a thin Co film is higher than that of a typical Fe film, the magnetization curves of these sandwiches show clearly the separate, sequential reversal of the Fe and Co moments as a function of applied field. In the applied field region where the moments of the two magnetic layers are antialigned, the spin-valve magnetoresistance shows a peak of over 3% in amplitude at room temperature.
Charge redistribution in the multiple levels of the DX center
Authors: Su Z. , Farmer J. W.
Published: July 2002

The multiple DX levels are studied by using the rate-window scan method of deep level transient spectroscopy. It is found that the electron concentrations in the individual DX levels do not always increase monotonically with filling time, showing a charge redistribution effect. This charge redistribution in the DX levels indicates that the DX center is negatively charged and that each defect site is able to generate multiple states in different levels. The charge redistribution effect unambiguously rules out all existing small lattice relaxation models, while it is understood within the broken-bond negative U model.
Photoemission spectroscopy of GaAs:As photodiodes
Authors: McInturff D. T. , Woodall J. M. , Warren A. C. , Braslau N. , Pettit G. D. , Kirchner P. D. , Melloch M. R.
Published: July 2002

We report on photoemission measurements of molecular-beam-epitaxy-grown GaAs p-i-n structures, in which the optically active insulating GaAs layer contains As precipitates (GaAs:As). GaAs:As is formed by low-temperature growth of GaAs at 225 °C, followed by an anneal at 600 °C. Layers grown in this way have been reported to be sensitive to subband-gap light. The measured barrier height of 0.7 eV, extracted from a well-behaved Fowler plot, indicates that the mechanism for photodetection involves arsenic clusters embedded in GaAs acting as internal Schottky barriers.
Relaxation by the modified Frank–Read mechanism in compositionally uniform thin films
Authors: LeGoues F. K. , Eberl K. , Iyer S. S.
Published: July 2002

Relaxation of compositionally graded SiGe films during growth has recently been shown to occur through the multiplication of dislocations by the so-called modified Frank–Read mechanism. Here, we show that the same mechanism is observed, during ex situ annealing of highly metastable, compositionally uniform layers. However, unlike graded layers, threading dislocations penetrate the upper layers of the film after relaxation. We explain the occurrence of the modified Frank–Read mechanism in ungraded layers by the lack of dislocation nucleation sites. The threading dislocations result from the fact that, in compositionally uniform layers, all dislocations tend to be located at (or very near) the plane of the interface, generating numerous pinning sites.
Extremely high frequency pulse magnetic resonance by picosecond magneto-optic sampling
Authors: Freeman M. R. , Brady M. J. , Smyth J.
Published: July 2002

An exceptionally broadband method for pulse magnetic resonance detection is described which enables measurements over a broad range of applied magnetic fields and affords excellent coupling to microscopic specimens. Employing a picosecond magneto-optic sampling technique with high temporal and spatial resolution, the precessing magnetization of a spin system is directly observed as a function of time following a photoconductively triggered spin tipping pulse. Free induction decays from 200 MHz to 200 GHz have been measured using a single device, for which the frequency limit in principle is of order 1 THz. Examples are presented for ferromagnetic resonance in yttrium iron garnet films at room temperature.
Intervalence band absorption in strained and unstrained InGaAs multiple quantum well structures
Authors: Fuchs G. , Hörer J. , Hangleiter A. , Härle V. , Scholz F. , Glew R. W. , Goldstein L.
Published: July 2002

We report the direct determination of absorption losses in unstrained InGaAs/InGaAsP and InGaAs/InGaAlAs and strained InGaAs/InGaAsP layer multiple quantum well (MQW) laser structures. In the case of the unstrained structures we find a strong dependence of the absorption on carrier density indicating the presence of an intrinsic optical loss mechanism, the intervalence band absorption (IVBA). In the strained layer InGaAs/InGaAsP structures, IVBA is completely switched off. Our results explain the superiority of strained layer InGaAs MQW lasers.
Facet modulation selective epitaxy−a technique for quantum-well wire doublet fabrication
Authors: Tsai Charles S. , Lebens John A. , Ahn Channing C. , Nouhi Akbar , Vahala Kerry J.
Published: July 2002

The technique of facet modulation selective epitaxy and its application to quantum-well wire doublet fabrication are described. Successful fabrication of wire doublets in the AlxGa1−xAs material system is achieved. The smallest wire fabricated has a crescent cross section less than 140 Å thick and less than 1400 Å wide. Backscattered electron images, transmission electron micrographs, cathodoluminescence spectra, and spectrally resolved cathodoluminescence images of the wire doublets are presented.
Demonstration of broadband tunability in a semiconductor laser using sampled gratings
Authors: Jayaraman V. , Cohen D. A. , Coldren L. A.
Published: July 2002

We propose and demonstrate a new monolithic laser structure in which the fractional tuning range Δλ/λ can be more than an order of magnitude larger than the fractional index change Δμ/μ in one section. The key idea involves using grating mirrors with grating elements removed in a periodic fashion. These ‘‘sampled gratings’’ have reflection spectra with periodic maxima. By using two such mirrors with identical grating pitch but mismatched sampling periods, it is possible to tune among the various reflectivity maxima. Our initial experimental results show 29.3 nm of tuning in an InGaAsP laser.
Spin dependent recombination in Pt-doped silicon p-n junctions
Authors: Christmann P. , Wetzel C. , Meyer B. K. , Asenov A. , Endrös A.
Published: July 2002

Electrically detected magnetic resonance experiments showing spin dependent recombination in commercial p-n diodes are presented. The observed anisotropy in the g values along with the marked shift from the free electron g-value point to a metal-vacancy complex. Deep level transient spectroscopy reveals the presence of the Pt acceptor level (0/−) at Ec−0.23 eV and the donor level (+/0) at Ev+0.32 eV in the same device. Calculations of the recombination rates support that spin dependent recombination occurs at the Pt (+/0) donor level.
Characteristics of high performance YBa2Cu3O7 step-edge junctions
Authors: Luine J. , Bulman J. , Burch J. , Daly K. , Lee A. , Pettiette-Hall C. , Schwarzbek S. , Miller D.
Published: July 2002

Step-edge Josephson junctions are engineered grain boundary junctions fabricated using standard lithographic and film deposition techniques. We report a systematic study of 180 YBa2Cu3O7 step-edge junctions and identify a fabrication technique which results in a 90% yield of working junctions with critical current spreads from 30% to 50% (1σ/Ic-ave)over the entire substrate. Technically useful critical current values at 65 K can be obtained by adjusting YBa2Cu3O7 film thickness. IcRn values, approximately independent of film thickness, are ∼1 mV at 4.2 K and ∼0.1 mV at 65 K. Most junctions exhibit ideal electrical behavior in accordance with the RSJ model.
Dark and photoconductivity behavior of C60 thin films sandwiched with metal electrodes
Authors: Yonehara Hisatomo , Pac Chyongjin
Published: July 2002

Sandwich cells of C60 thin film with a front Al electrode reveal considerable rectifying effects and large photocurrents (quantum yields ≤54%) under air. The action spectra closely follow the optical absorption spectrum of the film. The relationship between photocurrent (Jph) and incident light intensity (Pin) changes from Jph∝(Pin)0.95±0.05 at Pin<3×10−7 W/cm2 to Jph∝(Pin)0.53±0.03 at higher Pin, suggesting that the photocurrent is controlled by the interaction of excitons with impurity sites at surface and near-surface of C60 in the absence and presence of bimolecular recombination depending on light intensity.
Room-temperature exciton absorption engineering in II-VI quantum wells
Authors: Pelekanos N. T. , Haas H. , Magnea N. , Mariette H. , Wasiela A.
Published: July 2002

We observe large room-temperature exciton absorption in the wavelength region around 0.8 μm in CdTe-based quantum wells. This comes as a result of a room-temperature exciton engineering concept particularly suitable for II-VI quantum wells where, by appropriate quantum-well confinement, the exciton binding energy approaches and exceeds the LO phonon energy. This condition results in a drastic reduction of the exciton-LO phonon coupling. As a consequence, the temperature-induced exciton broadening, due to scattering events with LO phonons, is reduced and large excitonic absorption is observed at room temperature.
Interaction of hydrogen and deuterium with copper in GaAs
Authors: Hofmann G. , Madok J. , Haegel N. M. , Roos G. , Johnson N. M. , Haller E. E.
Published: July 2002

We have investigated hydrogen and deuterium passivation of two copper-related deep levels at EV+0.13 eV and EV+0.40 eV in GaAs with deep level transient spectroscopy (DLTS). The DLTS signals of the two copper-related acceptor levels disappear after exposing the samples to a remote hydrogen or deuterium plasma at 300 °C for 1/2 h. Both copper-related levels can be reactivated by thermal annealing. The copper-related donor–accepter pair luminescence at 1.36 eV is correlated with the DLTS signal of the copper-related acceptor level at EV+0.13 eV.
Magnetic properties and giant magnetoresistance of granular permalloy in silver
Authors: Jiang J. Samuel , Xiao John Q. , Chien C. L.
Published: July 2002

We report the first results of magnetic properties and giant magnetoresistance of granular permalloy in a metallic matrix. These new materials have resistivities comparable to those of the ferromagnetic alloys currently used in magnetoresistive devices, but yield significantly larger magnetoresistance effects that are nearly isotropic.
High-brightness InGaAlP green light-emitting diodes
Authors: Sugawara H. , Itaya K. , Nozaki H. , Hatakoshi G.
Published: July 2002

Candela class InGaAlP surface-emission green light-emitting diodes (LEDs) have been successfully fabricated. The growth of InGaAlP on an intentionally misoriented substrate improved emission properties, as confirmed by a quantitative estimation of the diffusion length in the active material. A Bragg reflector using InGaAlP was realized for the first time. A new device structure, including this Bragg reflector, drastically improved the light extraction efficiency. An external quantum efficiency of 0.7% at 573 nm green light was obtained, corresponding to a luminous intensity of 2 cd.
Formation of a C49 TiGe2 phase during annealing a coevaporated Ti0.33Ge0.67 alloy
Authors: Hong Q. Z. , Barmak K. , d’Heurle F. M.
Published: July 2002

The coevaporated, amorphous Ti0.33Ge0.67 alloy crystallizes at 315 °C into a metastable C49 structure, which transforms to the equilibrium C54 structure at higher temperatures around 535 °C. This result differs from that obtained from binary reactions between Ti and Ge where the C49 phase is not observed. The electron diffraction pattern for the C49 phase exhibits extra spots as predicted by Bourret et al. for a large period polytype [A. Bourret, F. M. d’Heurle, F. K. LeGoues, and A. Charai, J. Appl. Phys. 67, 241 (1990)]. Additional evidence for the formation of the C49 TiGe2 is found by annealing a Ti0.33Ge0.67/Ti0.33Si0.67 bilayer. The bilayer crystallizes into a solid solution of C49 TiGe2-TiSi2 before transforming to a C54 solid solution at lower temperatures than pure C49 TiSi2.
Photoluminescence characterization of Er-implanted Al2O3 films
Authors: van den Hoven G. N. , Snoeks E. , Polman A. , van Uffelen J. W. M. , Oei Y. S. , Smit M. K.
Published: July 2002

Al2O3 films on oxidized Si substrates were implanted with 800 keV Er ions to peak concentrations ranging from 0.01 to 1 at. %. The samples show relatively broad photoluminescence spectra centered at λ=1.533 μm, corresponding to intra-4f transitions in Er3+. At an Er peak concentration of 0.23 at. %, post-implantation thermal annealing up to 950 °C increases the photoluminescence intensity by a factor 40. This is a result of defect annealing, which increases the luminescence lifetime from 1 to 7 ms, as well as an increase in the Er3+ active fraction. High Er concentrations are achieved with only moderate concentration quenching effects.
Gas-source molecular beam epitaxial growth, characterization, and light-emitting diode application of InxGa1−xP on GaP(100)
Authors: Chin T. P. , Chang J. C. P. , Kavanagh K. L. , Tu C. W. , Kirchner P. D. , Woodall J. M.
Published: July 2002

Highly lattice-mismatched InxGa1−xP (x≤0.38) layers were grown on GaP substrates by gas-source molecular beam epitaxy. A relatively thin, compositionally linear-graded buffer layer was used to reduce the number of threading dislocations. Studies by double-crystal x-ray diffraction and transmission electron microscopy show this buffer layer to be 97% strain-relaxed along both 〈110〉 directions with dislocations well confined within the graded buffer and the substrate. Threading dislocation densities in the top layers were less than 1×107 cm−2. Room-temperature photoluminescence, ranging from 560 to 600 nm, is achieved. Heterojunction p-i-n diodes emitting at 560 nm at 300 K exhibit good rectifying and reverse breakdown characteristics.
General expression for the electrically detected magnetic resonance signal from semiconductors
Authors: Xiong Z. , Miller D. J.
Published: July 2002

A general expression is obtained for the electrically detected magnetic resonance (EDMR) signal from semiconductors based on the electron-hole pair model. The expression is applicable for all values of the trapping, dissociation, and recombination rates of the levels involved. Measurements of the EDMR signal as a function of microwave power are used to obtain values for the dissociation and recombination rates for a center in a Si diode.
Roughness at the interface of thin InP/InAs quantum wells
Authors: Brasil M. J. S. P. , Nahory R. E. , Tamargo M. C. , Schwarz S. A.
Published: July 2002

We investigated the interface roughness of InP/As quantum wells using photoluminescence and secondary ion mass spectroscopy. Typical photoluminescence spectra consist of multiple lines. The energies of the observed peaks have a remarkable behavior; namely, both the peak energies and the separations between peaks change from sample to sample. We discuss the interpretation of the observed emission lines in connection with questions such as interface roughness, island formation and lateral confinement. We also discuss the strong influence of parameters such as the growth temperature and the substrate orientation on the interface roughness.
Low-temperature modifications in the defect structure of amorphous silicon probed by in situ Raman spectroscopy
Authors: Battaglia A. , Coffa S. , Priolo F. , Compagnini G. , Baratta G. A.
Published: July 2002

The modifications occurring in the defect structure of ion implanted amorphous silicon below room temperature have been probed by Raman spectroscopy. Amorphous silicon layers were irradiated at 77 K by 3 keV He+ ions and analyzed in situ by Raman spectroscopy. This low-temperature ion irradiation produces a shift in the transversal optical (TO) peak position from 471 to 463 cm−1 and a broadening in its halfwidth from 43 to 50 cm−1. Moreover after an annealing at 300 K the vibrational properties come back to their initial state. It is speculated that the modifications induced by low-temperature ion irradiation are associated with the production and annihilation of highly mobile defects.
Giant magnetoresistance in electrodeposited superlattices
Authors: Alper M. , Attenborough K. , Hart R. , Lane S. J. , Lashmore D. S. , Younes C. , Schwarzacher W.
Published: July 2002

We have observed ‘‘giant magnetoresistance’’ in short-period Cu/Co-Ni-Cu alloy superlattices electrodeposited from a single electrolyte under potentiostatic control. The superlattices were grown on polycrystalline Cu substrates which were removed before transport measurements were made. Room-temperature magnetoresistances of over 15% in applied magnetic fields of up to 8 kOe were observed in superlattices having Cu layer thicknesses of less than 10 Å.
GaAs heteroepitaxy on an epitaxial Si surface with a low-temperature process
Authors: Mori Hidefumi , Tachikawa Masami , Sugo Mitsuru , Itoh Yoshio
Published: July 2002

This letter reports the growth of an anti-phase-free GaAs layer on a (100) epitaxial Si substrate offset by 0.5° without high-temperature treatment prior to growth. Atomic force microscopy shows that the epitaxial Si surface has regular steps prior to growth. The average terrace width is 25.6 nm, and the step height is calculated to be 0.22 nm from the terrace width and offset angle, which approximately corresponds to a double atomic layer height of (100) Si of 0.27 nm. This single domain structure of the epitaxial Si surface gives the heteroepitaxial GaAs a high crystalline quality. Secondary ion mass spectrometry profiles show an abrupt GaAs-Si interface. Laser diodes on epitaxial Si substrates show room-temperature cw operation which confirms device applicability.
Autocorrelation function analysis of phase formation in the initial stage of interfacial reactions of molybdenum thin films on (111)Si
Authors: Liang J. M. , Chen L. J.
Published: July 2002

Autocorrelation function (ACF) analysis has been applied to the high resolution transmission electron microscope images of amorphous interlayers formed in the interfacial reactions of ultrahigh vacuum deposited molybdenum thin films on (111)Si. Mo3Si was identified to be the first nucleated crystalline phase which is correlated to the stable structure of the amorphous Mo-Si alloy. Both Mo3Si and Mo5Si3 were found to form simultaneously under certain annealing conditions. The results demonstrate the usefulness of the ACF analysis of atomic images in amorphous interlayers formed in the initial stage of reactions in metal thin films on silicon.
Characterization of Si/Si1−xGex/Si quantum wells by cathodoluminescence imaging and spectroscopy
Authors: Higgs V. , Lightowlers E. C. , Xiao X. , Sturm J. C.
Published: July 2002

Cathodoluminescence (CL) imaging and spectroscopy have been used to characterize fully strained SiGe quantum wells grown on Si. At T≊5 K, the CL spectra contain only band edge luminescence features. Monochromatic imaging with the no-phonon line attributed to the bound excitons in the quantum well, has shown that the distribution of the luminescence from the wells is not uniform. The thinnest well (33 Å) contained a low density of nonradiative (luminescence reduction up to 100%) spots 40–100 μm in size. The thickest well (500 Å) contained similar nonradiative spots and also dark line features oriented along the 〈110〉 directions. These dark line features are areas of nonradiative recombination (up to 70%) and have been identified by transmission electron microscopy as misfit dislocations.
Characteristics of 5-eV absorption band in sputter deposited GeO2-SiO2 thin glass films
Authors: Nishii Junji , Yamanaka Hiroshi , Hosono Hideo , Kawazoe Hiroshi
Published: July 2002

Thin films (4.6 μm thick) of 5 GeO2-95 SiO2 and 55 GeO2-45 SiO2 (mol %) glasses were prepared by rf sputtering method in an Ar-O2 atmosphere. An intense absorption band at around 5 eV was distinctly observed in both films after the as-deposited films were annealed at 350 °C for 30 min in a vacuum. A part of this 5-eV band was gradually decreased by UV irradiation. Saturated absorptivity changes (−Δα∞) of the UV bleached component, which is considered to be the origin of Hill gratings [K. O. Hill, Y. Fujii, and B. S. Kawasaki, Appl. Phys. Lett. 32, 647 (1978)] and second-harmonic generation in SiO2 glass fibers doped with GeO2, after a prolonged irradiation were 50 cm−1 for 5 GeO2-95 SiO2 films and 400 cm−1 for 55 GeO2-45 SiO2 films. These values are greater by one or two orders of magnitude than those (∼2 cm−1) of bulk germanosilicate glasses prepared by the vapor axial deposition method.
Band lineup at an organic-inorganic semiconductor heterointerface: perylenetetracarboxylic dianhydride/GaAs(100)
Authors: Hirose Y. , Chen W. , Haskal E. I. , Forrest S. R. , Kahn A.
Published: July 2002

We present a photoemission study of the electronic properties of an interface between the organic semiconductor; 3, 4, 9,10 perylenetetracarboxylic dianhydride (PTCDA) and n-type GaAs(100). We examine the evolution of the interface electron distribution as a function of PTCDA overlayer thickness. The highest occupied molecular orbital level of PTCDA is measured at 0.7±0.1 eV below the GaAs valence band maximum. The PTCDA ionization potential is measured at 6.4±0.15 eV. The discrepancy between the band alignment deduced from photoemission and transport measurement suggests that interface states or polarization effects play a role in determining the transport properties of the organic-inorganic heterojunction diodes.
Interstitial traps and diffusion in epitaxial silicon films
Authors: Cowern N. E. B.
Published: July 2002

Oxidation-enhanced diffusion in molecular beam epitaxially grown epitaxial silicon films decreases rapidly with depth due to trapping of injected interstitials at microscopic defects. Apparently inconsistent data on trapping kinetics, recently reported in the literature, are resolved by analyzing the time evolution of the interstitial distribution CI(x,t). The analysis enables characterization of trap size and trap concentration in the parts-per-billion range.
Epitaxial growth of metal-phthalocyanines on selenium-terminated GaAs(111) surfaces
Authors: Yamamoto Hideki , Tada Hirokazu , Kawaguchi Takafumi , Koma Atsushi
Published: July 2002

Epitaxial films of chloro-aluminum- and vanadyl-phthalocyanines (AlPcCl and VOPc) have been prepared on GaAs(111)B surfaces by effective passivation of the surface dangling bonds with Se atoms. AlPcCl molecules are found to form commensurate centered rectangular lattices on the substrate with an intermolecular distance of 1.44 nm by means of reflection high energy electron diffraction. VOPc molecules, on the other hand, form incommensurate square lattices in which they are arranged along the 〈101̄〉 axes of the substrate with an intermolecular distance of 1.37 nm. The lattice matching condition between the grown films and the substrate determines the molecular arrangements.
Effects of NH3 nitridation on oxides grown in pure N2O ambient
Authors: Bhat M. , Yoon G. W. , Kim J. , Kwong D. L. , Arendt M. , White J. M.
Published: July 2002

Effects of NH3 nitridation on the chemical and electrical properties of N2O oxides have been studied. Compared with NH3-nitrided SiO2, NH3 nitridation does not degrade the electrical properties of N2O oxides, thus resulting in superior impurity diffusion barrier properties, while preserving excellent interface immunity to hot-carrier injection and much lower charge trapping. Correlation studies between the chemical and electrical properties of NH3-nitrided N2O and NH3-nitrided SiO2 have been done to explain these results.
Optical gain of optically pumped Al0.1Ga0.9N/GaN double heterostructure at room temperature
Authors: Kim S. T. , Amano H. , Akasaki I. , Koide N.
Published: July 2002

In this letter, we report the measurement of the gain of an optically pumped Al0.1Ga0.9N/GaN double heterostructure (DH) which was prepared on a sapphire substrate by metalorganic vapor phase epitaxy using an AlN buffer layer. At room temperature, the optical gain of stimulated emission from Al0.1Ga0.9N/GaN DH was measured to be 160 cm−1 at pumping power density of 200 kW/cm2.
Blue light generation by resonator-enhanced frequency doubling of an extended-cavity diode laser
Authors: Kozlovsky W. J. , Risk W. P. , Lenth W. , Kim B. G. , Bona G. L. , Jaeckel H. , Webb D. J.
Published: July 2002

Frequency doubling of diode laser radiation was achieved by operating an AR-coated diode laser in an extended laser cavity which contained a monolithic potassium niobate frequency doubling resonator as an intracavity element. Extended cavity operation ensured that the diode laser would oscillate only at frequencies that were resonant with the intracavity resonator. A diffraction grating was used to ensure single mode oscillation at the wavelength needed for noncritically phase-matched second harmonic generation. At 100 mA of injection current to the GaAlAs diode laser, 14 mW of 429 nm light were produced.
Polycrystalline silicon thin film transistors deposited at low substrate temperature by remote plasma chemical vapor deposition using SiF4/H2
Authors: Woo Jae Ik , Lim Hong Joo , Jang Jin
Published: July 2002

Polycrystalline silicon was deposited on Corning 7059 glass by remote plasma chemical vapor deposition using SiF2/H2. Raman spectroscopy indicated a crystalline fraction of 85% in films deposited at a substrate temperature of 350 °C. Thin film transistors made of this material exhibited a field effect mobility of 7.5 cm2/V s and a threshold voltage of 6.1 V.
Atomic structure and luminescence excitation of GaAs/(AlAs)n(GaAs)m quantum wires with the scanning tunneling microscope
Authors: Pfister M. , Johnson M. B. , Alvarado S. F. , Salemink H. W. M. , Marti U. , Martin D. , Morier-Genoud F. , Reinhart F. K.
Published: July 2002

We report on the imaging of a molecular beam epitaxially grown GaAs/(AlAs)n(GaAs)m quantum well-wire array by means of cross-sectional scanning tunneling microscopy (XSTM) and scanning tunneling-induced luminescence (STL). XSTM provides atomically resolved cross-sectional images of sets of quantum well wires with chemical sensitivity within the group III species and electrical sensitivity to single dopant atoms. This permits the precise observation of growth mechanisms and the identification of defects responsible for inhomogeneities in the growth morphology, as well as the determination of dopant incorporation throughout the structure. STL permits the relative quantum efficiency of individual quantum wires to be quantified.
Transmission electron microscopy study of fluorine and boron implanted and annealed GaAs/AlGaAs
Authors: Ooi B. S. , Bryce A. C. , Marsh J. H. , Martin J.
Published: July 2002

The residual damage in fluorine and boron ion implanted GaAs/AlGaAs has been studied using transmission electron microscopy both before and after rapid thermal processing. The results showed no extended defects in as-implanted materials. A dense network of interstitial dislocation loops has been observed in boron implanted samples after annealing. Most of these dislocation defects were located in GaAs layers rather than in AlGaAs layers. Only a small number of dislocation loops were found in the fluorine implanted and annealed material. Compared to boron, fluorine is a better candidate for neutral impurity induced disordering applications.
Superconductivity and gaint negative magnetoresistance in YBa2Cu3O7/La0.67Ba0.33MnO3 superlattices
Authors: Jakob G. , Moshchalkov V. V. , Bruynseraede Y.
Published: July 2002

It is shown that the recently discovered giant negative magnetoresistance (GMR) effects in ferromagnetic La1−xMxMnO3 (M=Ca,Sr,Ba) are compatible with the existence of high Tc superconductivity in c-axis oriented YBa2Cu3O7/La0.67Ba0.33MnO3 superlattices. From magnetoresistivity measurements we deduce that above Tc the giant GMR persists up to room temperature. Below Tc the superlattices show a quasi-two-dimensional superconductivity of the YBa2Cu3O7 layers coexisting with magnetism in the La0.67Ba0.33MnO3 layers.
Conduction band discontinuities in Ga0.5In0.5P-AlxGa0.5−xIn0.5P heterojunctions measured by internal photoemission
Authors: Yow H. K. , Houston P. A. , Hopkinson M.
Published: July 2002

The conduction band discontinuities in Ga0.5In0.5P-AlxGa0.5−xIn0.5P heterojunctions, lattice matched to GaAs and grown by molecular beam epitaxy, were measured by internal photoemission techniques at room temperature over the whole compositional range. The discontinuity is found to vary linearly in x as (0.59x)eV for x≤0.30 and as (−0.18x+0.23)eV for x≳0.30, whereas the inferred valence band discontinuity (band-gap difference minus the conduction band discontinuity) varies as (0.61x)eV. The direct–indirect gap crossover composition in AlxGa0.5−xIn0.5P is found to be close to x≊0.3.
Metallization of poly(4-methyl-1-pentene) microcellular foam
Authors: Perry W. Lee , Dye Robert C. , Apen Paul G. , Foreman Larry , Peterson Eric
Published: July 2002

Low density microcellular foam from poly(4-methyl-1-pentene) (PMP) has been metallized by laser-induced chemical vapor deposition (LICVD). KrF excimer laser radiation (248 nm) was used to photolytically decompose molybdenum hexacarbonyl with and without a buffer gas. Metal oxycarbide deposits 100 μm in diameter were formed. The microstructure of the PMP foam was unaltered. The deposition was confirmed to be 100 μm using scanning electron microscopy and energy dispersive x-ray spectroscopy. X-ray fluorescence was used to determine that approximately 80 ng of material was deposited.