bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of treatment with prostaglandin E1 and N‐acetylcysteine on pediatric liver transplant recipients: A single‐center study
Authors: Bucuvalas John C. , Ryckman Frederick C. , Krug Susan , Alonso Maria P. , Balistreri William F. , Kotagal Uma
Published: July 2002

Abstract: Prostaglandin E1 (PGE1) and N‐acetylcysteine (NAC) have been used as single agents to decrease reperfusion injury and improve outcome after solid‐organ transplantation (Tx). We hypothesized that combined treatment with NAC and PGE1 would be safe and reduce reperfusion injury. We therefore carried out a pilot study to assess the safety of this drug combination and gain information regarding the efficacy of treating pediatric liver transplant recipients with NAC and PGE1. The pilot study took the form of an open‐label study incorporating 25 pediatric liver transplant recipients (12 children in the treatment group and 13 children as controls). NAC (70 mg/kg) was given intravenously over 1 h following reperfusion and then every 12 h for 6 days. PGE1 (0.4 mg/kg/h) was given as a continuous intravenous infusion for 6 days, starting after the first NAC dose. The primary outcome was the safety of combined treatment with NAC and PGE1. Patient survival, graft survival, allograft rejection within the first 90 days after Tx, peak post‐transplant serum alanine aminotransferase (ALT) concentration, post‐transplant length of hospitalization, and post‐operative complications were secondary outcomes. Post‐operative complications occured at similar rates in both control and treated groups. No complications or adverse events occured in the treated group as a result of study drugs. The 3‐month patient survival rate was 100% for both groups. For the group treated with NAC and PGE1, peak serum ALT was lower and median length of stay was shorter but the differences did not reach statistical significance. The proportion of patients with allograft rejection was not significantly different between the two groups. However, rejection was more severe in the control group than in the treated group. In summary, infusions of NAC and PGE1 were safely administered to pediatric liver transplant recipients. However, a randomized controlled study is needed to determine the efficacy of treatment with NAC and PGE1.
Effect of drought on sorbitol and sucrose metabolism in sinks and sources of peach
Authors: Lo Bianco Riccardo , Rieger Mark , Sung Shi‐Jean S.
Published: July 2002

In peach (Prunus persica[L.] Batsch.), sorbitol and sucrose are the two main forms of photosynthetic and translocated carbon and may have different functions depending on the organ of utilization and its developmental stage. The role and interaction of sorbitol and sucrose metabolism was studied in mature leaves (source) and shoot tips (sinks) of ‘Nemaguard’ peach under drought stress. Plants were irrigated daily at rates of 100, 67, and 33% of evapotranspiration (ET). The relative elongation rate (RER) of growing shoots was measured daily. In mature leaves, water potential (Ψw), osmotic potential (Ψs), sorbitol‐6‐phosphate dehydrogenase (S6PDH, EC 1.1.1.200), and sucrose‐phosphate synthase (SPS, EC 2.4.1.14) activities were measured weekly. Measurements of Ψs, sorbitol dehydrogenase (SDH, 1.1.1.14), sucrose synthase (SS, EC 2.4.1.13), acid invertase (AI, EC 3.2.1.26), and neutral invertase (NI, EC 3.2.1.27) activities were taken weekly in shoot tips. Drought stress reduced RER and Ψwof plants in proportion to water supply. Osmotic adjustment was detected by the second week of treatment in mature leaves and by the third week in shoot tips. Both SDH and S6PDH activities were reduced by drought stress within 4 days of treatment and positively correlated with overall Ψwlevels. However, only SDH activity was correlated with Ψs. Among the sucrose enzymes, only SS was affected by drought, being reduced after 3 weeks. Sorbitol accumulation in both mature leaves and shoot tips of stressed plants was observed starting from the second week of treatment and reached up to 80% of total solutes involved in osmotic adjustment. Sucrose content was up to 8‐fold lower than sorbitol content and accumulated only occasionally. We conclude that a loss of SDH activity in sinks leads to osmotic adjustment via sorbitol accumulation in peach. We propose an adaptive role of sorbitol metabolism versus a maintenance role of sucrose metabolism in peach under drought stress.
Nifedipine or hydralazine as a first‐line agent to control hypertension in severe preeclampsia
Authors: AALI BIBI SHAHNAZ , NEJAD SAMIRA SHAHABI
Published: July 2002

Background. Pre‐eclampsia is one of the most serious and common complications of pregnancy. Nifedipine, a calcium channel blocker, and the vasodilator hydralazine have both been used as antihypertensive agents in this condition. The aim of this study was to determine which of these two agents is the most appropriate antihypertensive in the management of severe pre‐eclampsia.

Methods. One hundred and twenty‐six pre‐eclamptic patients with a gestational age of more than 20 weeks were randomized to receive either 8 mg nifedipine sublingually or 5–10 mg intravenous hydralazine. Women with a history of heart failure and women receiving antihypertensive treatment during the course of the current pregnancy were excluded. For each patient the following data were recorded; the number of drug administrations, the time needed to control blood pressure, mean urinary output, the time interval between effective control and a new hypertensive crisis after each drug administration and relevant adverse effects in mother or fetus.

Results. Effective control of blood pressure was achieved in both treatment arms. Data analysis indicated significantly fewer drug administrations in the nifedipine arm of the study. The time interval before a new hypertensive crisis following initial effective control of blood pressure was significantly longer in the nifedipine group when compared with hydralazine. Effective control of blood pressure was achieved more rapidly in multiparous patients receiving nifedipine (p=0.026). Mean urinary output before and after delivery was greater in the nifedipine arm of the study. There were no significant differences between the two groups in other variables. In addition, in neither group were there any serious adverse effects in mother or fetus.

Conclusion. Nifedipine is safe and more effective than hydralazine in controlling blood pressure in severe pre‐eclampsia. It has the added advantage of being cheaper and more widely available than the latter and is easily administered.
Different Plasmodium falciparum Recombinant MSP119 Antigens Differ in Their Capacities to Stimulate In Vitro Peripheral Blood T Lymphocytes in Individuals from Various Endemic Areas
Authors: GARRAUD O. , DIOUF A. , NGUER C. M. , DIEYE A. , LONGACRE S. , KASLOW D. C. , HOLDER A. A. , TALL A. , MOLEZ J. ‐F. , PERRAUT R. , MERCEREAU‐PUIJALON O.
Published: July 2002

This study reports on T‐cell proliferative responses to the 19‐kDa C‐terminal domain of the Plasmodium falciparum merozoite surface protein (MSP119). Three different recombinant proteins were used: an Escherichia coli product expressing the first EGF‐like domain and Saccharomyces cerevisiae and baculovirus/insect‐cell‐produced proteins containing both EGF‐like domains, the latter protein being produced with or without N‐glycosylation. Cell donors were P. falciparum‐immune adults with no recent history of clinical malaria and recruited from three Senegalese settings with different epidemiological parasite transmission. Each mononuclear‐blood‐cell preparation was stimulated with a range of concentrations of the three proteins. Most subjects’ mononuclear cells were reactive to at least one protein, but significant differences in lymphoproliferation were seen between the settings and within individual cultures depending on the protein source and concentration. Importantly, lymphoproliferation indices correlated inversely with the intensity of P. falciparum malaria transmission. When purified T lymphocytes were cultured in the presence of MSP119 plus autologous monocytes, B lymphocytes or a proposed CD1+ dendritic‐cell population as costimulatory cells, significant differences were observed depending on the individual's previous exposure to parasites. This study shows that the stimulation of lymphocyte proliferation in vitro with MSP119 depends on several factors, including epidemiological conditions and protein preparations.
Characteristics and Outcomes of Serious Traumatic Injury in Older Adults
Authors: Richmond Therese S. , Kauder Donald , Strumpf Neville , Meredith Tammy
Published: July 2002

OBJECTIVES: To describe the seriously injured older adult; characterize and compare the differences in injury characteristics and outcomes in three subgroups of seriously injured older adults: aged 65 to 74, 75 to 84, and 85 and older; and identify risk factors for death, complications, and discharge placement at hospital discharge.

DESIGN: A retrospective secondary analysis of a statewide trauma data set from 1988 through 1997.

SETTING: Data submitted from all designated trauma centers in Pennsylvania.

PARTICIPANTS: The data set yielded 38,707 patients with a mean age of 77.5 years with serious injury (mean number of injuries = 3.6, mean number of body systems involved = 2).

MEASUREMENTS: Key outcomes were mortality, complications, and discharge placement. Abbreviated Injury Score categorized injuries and Injury Severity Score (ISS) quantified anatomic severity of injury.

RESULTS: Mortality was 10%. Mean length of stay was 11.5 days. Just over half (52.2%) of survivors were discharged home; 25.4% were discharged to a skilled nursing facility. Injury severity, total number of injuries, complications, and increasing age were predictors of mortality (P < .01). The presence of preexisting comorbid medical conditions increased the odds of experiencing a complication over threefold. Increasing age, total number of injuries, injury to extremities or abdominal contents, injuries due to falls, and lower functional level predicted discharge to a skilled nursing facility (P < .01).

CONCLUSIONS: Traumatic injuries affect older adults of all ages and are typically multisystem and life threatening. The standard ISS does not fully capture the potential for mortality in older adults and does not predict discharge placement. The majority of older adults survive multisystem injury. Our findings indicate the need to examine outcomes beyond mortality and to make the identification and management of comorbid conditions a priority. A geriatric consultation service could be an important addition to the interdisciplinary trauma team.
High‐Velocity Resistance Training Increases Skeletal Muscle Peak Power in Older Women
Authors: Fielding Roger A. , LeBrasseur Nathan K. , Cuoco Anthony , Bean Jonathan , Mizer Kelly , Singh Maria A. Fiatarone
Published: July 2002

OBJECTIVES: Peak power declines more precipitously than strength with advancing age and is a reliable measure of impairment and a strong predictor of functional performance. We tested the hypothesis that a high‐velocity resistance‐training program (HI) would increase muscle power more than a traditional low‐velocity resistance‐training program (LO).
2.6 μm InGaAs photodiodes
Authors: Martinelli Ramon U. , Zamerowski Thomas J. , Longeway Paul A.
Published: July 2002

We have developed In0.82Ga0.18As p-n homojunction photodiodes that have a long-wavelength threshold at about 2.65 μm. A compositionally graded InxGa1−xAs layer accommodates the 2% lattice mismatch between the InP substrate and the In0.82Ga0.18As active layers of the device. At −2 V reverse bias the room-temperature dark current is 3.5 μA (32 mA/cm2), and the quantum efficiency is 70–75% over the wavelength interval of 2.1–2.6 μm.
Soft-magnetic properties and structure of Fe/CoNbZr multilayers
Authors: Dirne F. W. A. , den Broeder F. J. A. , Tolboom J. A. M. , de Wit H. J. , Witmer C. H. M.
Published: July 2002

The magnetic and structural properties of ion beam sputtered Fe/CoNbZr multilayers were studied as a function of the CoNbZr and Fe layer thickness. Good soft-magnetic properties (coercivity <40 A/m and permeability >1000) are obtained only when the Fe grains are small, which is the case for multilayers with Fe layer thicknesses below 10 nm and CoNbZr layer thicknesses above 4 nm. Thick CoNbZr layers (>4 nm) are amorphous and repeated nucleation of Fe grains is observed. When the CoNbZr layers are too thin (<3 nm) they are crystalline and do not interrupt the Fe grain growth. The resulting columnar growth of Fe throughout the total film thickness leads then to a drastic decrease of permeability and increase of coercivity.
Visible BaB2O4 optical parametric oscillator pumped at 355 nm by a single-axial-mode pulsed source
Authors: Fan Y. X. , Eckardt R. C. , Byer R. L. , Nolting J. , Wallenstein R.
Published: July 2002

A visible BaB2O4 optical parametric oscillator (OPO) pumped by a single-axial-mode 355-nm source has been demonstrated. An average output power of 140 mW with a signal wave conversion efficiency of 13% and an idler conversion efficiency of 11% for a total conversion efficiency of 24% has been achieved. The oscillator has continuously tuned from 412 nm to 2.55 μm limited by the infrared transmission range of the crystal. Through injection seeding we obtained single-axial-mode OPO operation with a corresponding OPO linewidth of less than 3 GHz.
Passivation of paramagnetic Si-SiO2 interface states with molecular hydrogen
Authors: Brower K. L.
Published: July 2002

Dry thermal oxides were grown on (111) silicon substrates at 850 °C. The Pb centers associated with this (111) Si-SiO2 interface were observed with electron paramagnetic resonance to be stable under subsequent annealing in vacuum up to at least 850 °C. The rate of passivation of Pb centers with H2 was observed to be proportional to the concentration of H2 in the oxide and the density of Pb centers. The forward reaction rate constant kf is temperature dependent and obeys the Arrhenius relationship having an activation energy Ef of 1.66±0.06 eV and a pre-exponential factor k0f of 1.94 (+2./−1.)×10−6 cm3 /s for temperatures at least between 230 and 260 °C. The linear H2 pressure dependence in the rate of passivation and the magnitude of k0f are reasonably consistent with a model in which the H2 molecule reacts directly with Pb centers during its diffusional motion among the interstices of the SiO2 network and the reaction site at Pb centers.
Heteroepitaxy of GaAs on Si and Ge using alternating, low-energy ion beams
Authors: Haynes T. E. , Zuhr R. A. , Pennycook S. J. , Appleton B. R.
Published: July 2002

Crystalline GaAs films have been grown epitaxially on silicon and germanium substrates at 400 °C by direct deposition of alternating 69Ga and 75As layers from electromagnetically switched low-energy ion beams. Positive gallium and arsenic ions were extracted simultaneously from a single ion source and mass analyzed prior to deceleration to a controlled deposition energy of 30 or 40 eV. Atomic layers of gallium and arsenic were deposited alternately by switching the analyzing magnetic field repeatedly to select either the 69Ga+ or 75As+ species. The structure and composition of the resulting layers have been characterized by cross-section transmission electron microscopy and ion channeling/backscattering spectrometry. The best crystal quality was obtained for a GaAs layer deposited on Ge using a 30 eV beam. This layer gave an ion channeling minimum yield of ≊6%. These results demonstrate the feasibility of growing isotopically pure, single-crystal compound semiconductor layers at relatively low temperatures by deposition from alternating, fully ionized, low-energy beams.
High efficiency single quantum well graded-index separate-confinement heterostructure lasers fabricated with MeV oxygen ion implantation
Authors: Xiong Fulin , Tombrello T. A. , Wang H. , Chen T. R. , Chen H. Z. , Morkoç H. , Yariv A.
Published: July 2002

Single quantum well AlGaAs/GaAs graded-index separate-confinement heterostructure lasers have been fabricated using MeV oxygen ion implantation plus optimized subsequent thermal annealing. A high differential quantum efficiency of 85% has been obtained in a 360-μm-long and 10-μm-wide stripe geometry device. The results have also demonstrated that excellent electrical isolation (breakdown voltage of over 30 V) and low threshold currents (22 mA) can be obtained with MeV oxygen ion isolation. It is suggested that oxygen ion implantation induced selective carrier compensation and compositional disordering in the quantum well region as well as radiation-induced lattice disordering in AlxGa1−xAs/GaAs may be mostly responsible for the buried layer modification in this fabrication process.
Time-resolved emission spectroscopy of the high T
c superconductor YBa2Cu3O7−x under laser ablation
Authors: Yoo K. M. , Alfano R. R. , Guo Xiaoming , Sarachik M. P. , Isaacs L. L.
Published: July 2002

Time-resolved luminescence spectroscopy is described for high Tc YBa2Cu3O7−x under 8 ps/530 nm laser ablation. The emission spectrum covered most of the visible spectrum and showed emission lines from ions. The emission profiles in time consist of fast (≊25 ps) and slow (≊1 ns) decay components.
Effect of carrier confinement on the laser-induced etching of GaAs/AlGaAs heterostructures
Authors: Ruberto M. N. , Willner A. E. , Podlesnik D. V. , Osgood R. M.
Published: July 2002

Laser-induced photochemical etching was used to etch GaAs/AlGaAs multilayered material. In this carrier-driven process, the confinement of photogenerated holes to the alternating GaAs layers resulted in the controlled lateral etching of buried GaAs layers. An application of this etching technique to forming microcleaved laser facets is described.
Impact ionization rates in an InGaAs/InAlAs superlattice
Authors: Kagawa Toshiaki , Kawamura Yuichi , Asai Hiromitsu , Naganuma Mitsuru , Mikami Osamu
Published: July 2002

An In0.53Ga0.47As/In0.52Al0.48As superlattice avalanche photodiode is fabricated by molecular beam epitaxy, and ionization rates are measured. The electron ionization rate is enhanced by a factor of 20 over hole ionization rate. This is the first time that such a remarkable increase has been observed for a superlattice. The increase is attributed to the large conduction-band offset.
I
n s
i
t
u growth rate measurements during molecular beam epitaxy using an optical pyrometer
Authors: SpringThorpe A. J. , Humphreys T. P. , Majeed A. , Moore W. T.
Published: July 2002

An optical pyrometer has been used to measure apparent temperature oscillations during the growth of GaAs/GaAlAs heterostructures by molecular beam epitaxy. The oscillations are due to an optical interference effect in the epitaxial layers and the period can be related to both growth rate and alloy composition. Measurements can be carried out on rotating substrates throughout the deposition cycle of complex device structures, and provide a convenient means of monitoring the uniformity of the deposition process.
Effect of particle-induced displacements on the critical temperature of YBa2Cu3O7−δ
Authors: Summers G. P. , Burke E. A. , Chrisey D. B. , Nastasi M. , Tesmer J. R.
Published: July 2002

The particle-induced depression of the superconducting critical temperature Tc of YBa2Cu3O7−δ is shown to be directly proportional, over seven orders of magnitude, to the nonionizing energy deposited in the lattice by primary knock-on atoms displaced by incident electrons, protons, and heavy ions. It is concluded that ΔTc is proportional only to the average number of defects produced and can therefore be predicted for any particle, energy, and fluence from a calculation of the nonionizing energy loss.
Radio frequency surface resistance of large-area Bi-Sr-Ca-Cu-O thick films on Ag plates
Authors: Bohn C. L. , Delayen J. R. , Balachandran U. , Lanagan M. T.
Published: July 2002

Films nominally 80 μm thick of Bi-Sr-Ca-Cu-O on silver substrates with surface areas from 1.25 to 182 cm2 were fabricated using two different processing procedures. Their rf surface resistances were measured as functions of temperature in the frequency range 2.65–29.2 GHz at low rf field amplitudes using cylindrical resonant cavities. The critical temperatures of the films were in the range 81–83 K. At X-band frequencies, the surface resistances matched that of room-temperature copper. The results were comparable to recent data on small pellets of bulk Bi-Sr-Ca-Cu-O.
Effects of surface hydrogen on the air oxidation at room temperature of HF-treated Si (100) surfaces
Authors: Hirashita N. , Kinoshita M. , Aikawa I. , Ajioka T.
Published: July 2002

Thermally stimulated desorption and x-ray photoelectron spectroscopy were used to study the air oxidation at room temperature of HF-treated Si(100) surfaces. The desorption results indicated an appreciable density of hydrogen at the surface. Air oxidation experiments with predesorbing surface hydrogen were carried out and an obtained linear relationship between the amount of H2 desorption and oxidation indicated that the oxidation was allowed by H2 desorption. The surface hydrogen was also found to be stable in air at room temperature and to contribute to a retardation in air oxidation of the surface.
Oriented cubic nucleations and local epitaxy during diamond growth on silicon {100} substrates
Authors: Jeng David G. , Tuan H. S. , Salat Robert F. , Fricano Glenn J.
Published: July 2002

Clusters of uniform-sized oriented cubic nucleations (OCNs) about 1–2 μm and local epitaxy crystals (LECs) of 120×150 μm2 on silicon {100} have been obtained by pretreating the substrate in situ followed by a typical diamond growth process with a microwave plasma-assisted chemical vapor deposition approach. The observations made under the scanning electron microscope reveal that the OCNs are not only oriented to one another, but also to the highly faceted LECs at an angle 45° off of the silicon substrate cleavage plane. The x-ray diffraction data show {400} dominant diamond.
Pick-up coil as a tool of measuring spin-lattice relaxation under electron spin resonance condition at high magnetic fields
Authors: Strutz T. , Witowski A. M. , de Bekker R. E. M. , Wyder P.
Published: July 2002

A new method of measuring the spin-lattice relaxation time in solids under far-infrared electron spin resonance condition is presented. The method is illustrated on Cd1−xMnxTe mixed crystals where the magnetization is due to the Mn2+ spins. The temperature dependence of the spin-lattice relaxation time is studied for a composition of x=0.005.
Effects of Peierls barrier and epithreading dislocation orientation on the critical thickness in heteroepitaxial structures
Authors: Chidambarrao D. , Srinivasan G. R. , Cunningham B. , Murthy C. S.
Published: July 2002

We have extended the mechanical equilibrium theory of J. W. Matthews and A. E. Blakeslee [J. Cryst. Growth 27, 118 (1974)] (MB) for determining the critical thickness in semiconducting heteroepitaxial films by including the effect of the Peierls barrier. The new formulation allows an evaluation of the dependence of critical thickness on the orientation of epithreading dislocation, and a comparison of theoretical predictions with measurements indicates that a knowledge of the epithreading dislocation orientation is necessary in predicting critical thicknesses in heteroepitaxial structures. In this formulation, the effect of the Peierls barrier is to bring the theoretical critical thicknesses closer to experimental values as compared to the predictions of the MB theory.
Low noise YBa2Cu3O7−δ grain boundary junction dc SQUIDs
Authors: Gross R. , Chaudhari P. , Kawasaki M. , Ketchen M. B. , Gupta A.
Published: July 2002

We have fabricated YBa2Cu3O7−δ grain boundary junction dc superconducting quantum interference devices (SQUIDs) with a square washer geometry design. The SQUIDs were formed in c-axis oriented epitaxial films with a single grain boundary of predetermined nature. These SQUIDs show perfectly periodic voltage-flux characteristics without hysteresis from 4.2 to 87 K. At 77 K intrinsic energy sensitivities of 1.5×10−30 and 3.0×10−30 J/Hz at 10 kHz were obtained for 60 and 110 pH SQUIDs, respectively. The intrinsic energy sensitivity limited by 1/f noise at 10 Hz was 1.2×10−28 and 5.5×10−28 J/Hz. The SQUID voltage noise was found to be almost identical to the voltage noise from one of its junctions. The flux focusing effect of the washer geometry was also measured.
Effect of interface quality on the electrical properties of p-Si/SiGe two-dimensional hole gas systems
Authors: Mishima T. , Fredriksz C. W. , van de Walle G. F. A. , Gravesteijn D. J. , van den Heuvel R. A. , van Gorkum A. A.
Published: July 2002

Electrical properties have been examined for single Si/Si0.8Ge0.2 p-type modulation-doped heterostructures which have been grown by molecular beam epitaxy. It is shown that the two-dimensional hole gas in a normal modulation-doped heterostructure (doped layer on the surface side) has a higher mobility than in an inverted structure (doped layer on the substrate side). Secondary-ion mass spectrometry analysis indicates that the lower mobility in the inverted structure is due to surface segregation of boron. Hole mobilities as high as 6000 cm2/V s at 2 K and 3800 cm2/V s at 6 K have been obtained which are the highest values reported so far for Si/SiGe heterostructures.
Internal photoemission and energy-band offsets in GaAs-GaInP p-I-N heterojunction photodiodes
Authors: Haase M. A. , Hafich M. J. , Robinson G. Y.
Published: July 2002

Internal photoemission has been observed in GaAs-Ga0.52In0.48P p-I-N heterojunction photodiodes grown by gas source molecular beam epitaxy. Threshold energies associated with this photocurrent mechanism have been accurately measured. Simple analysis provides a precise determination of the energy-band discontinuities in this heterostructure material system. The results indicate a conduction-band discontinuity of ΔEc=108±6 meV at room temperature.
Bistable behavior of a vibrating tip near a solid surface
Authors: Gleyzes P. , Kuo P. K. , Boccara A. C.
Published: July 2002

Experiments using a vibrating tip close to a solid surface have shown a bistable behavior of the motion. These measurements have been interpreted in terms of perturbed harmonic oscillators both numerically and analytically.
Plasma etching damage in GaAs studied by resonant Raman scattering
Authors: Pletschen W. , Wagner J. , Kaufel G. , Köhler K.
Published: July 2002

We have used resonant Raman scattering by longitudinal optical (LO) phonons to study the effect of reactive ion etching (RIE) in a CHF3 plasma on n-type GaAs. Interference effects between dipole allowed and electric-field-induced forbidden LO phonon scattering have been exploited to distinguish between impurity-induced and electric-field-induced forbidden scattering. This allowed us to analyze both RIE-induced near-surface damage and resulting changes in the space-charge electric field as a function of the self-bias voltage applied in RIE. For bias voltages beyond 200 V a well-defined increase in defect concentration and consequently a reduction in crystalline perfection was observed. The surface electric field averaged over the probing depth of the Raman experiment shows an initial decrease followed by an increase with increasing bias voltage.
Oxygen precipitation in silicon: The role of strain and self-interstitials
Authors: Taylor W. J. , Tan T. Y. , Gösele U. M.
Published: July 2002

Formation of SiO2 precipitates in silicon is associated with a large volume expansion. This leads to the generation of strain and a self-interstitial (I) supersaturation in the Si matrix, which in turn influence both the precipitate nucleation and growth processes. We have obtained an explicit expression correlating the strain to the self-interstitial supersaturation. For nucleation, we obtained an expression of the critical nucleus size containing the contribution of both factors. For growing precipitates, we have found a high I supersaturation at the SiO2-Si interface. This leads to a precipitate growth rate lower than that of the oxygen diffusion limited case. However, the extent of this growth rate lowering is not large, and the precipitate growth can still be regarded as being limited by oxygen diffusion within the accuracy range of most experiments.
Effect of midgap states in intrinsic hydrogenated amorphous silicon on sub-band-gap photoconductivity
Authors: Lee S. , Gunes M. , Wronski C. R. , Maley N. , Bennett M.
Published: July 2002

Photoconductivities, generated by photon energies less than the optical gap, in intrinsic hydrogenated amorphous silicon were measured over a wide range of carrier generation rates. Detailed numerical analysis of the corresponding sub-band-gap absorption was used to model the nature, densities, and distribution of midgap states. These derived gap state parameters are consistent with the electron lifetimes and their dependence on the generation rates. The analysis shows how the spectral response of the sub-band-gap photoconductivity (absorption) depends not only on the densities of midgap states but also on their location relative to the band edges. The position of these defect states can be obtained from sub-band-gap photoconductivity measurements providing that the corresponding occupation by electrons is taken into account.
Integrated distributed feedback laser and optical amplifier
Authors: Dutta N. K. , Lopata J. , Logan R. , Tanbun-Ek T.
Published: July 2002

The fabrication and performance characteristics of an integrated distributed feedback (DFB) laser and optical amplifier structure are described. The structure utilizes semi-insulating Fe-doped InP layers for current confinement to the active region, electrical isolation between the two sections, and for lateral index guiding. The amplified output has a slope of 1 mW/mA of laser current with the amplifier biased at 150 mA, which is a factor of 5 larger than that for a typical laser. The laser emits near 1.55 μm, and the spectral width under modulation of the amplified output is considerably smaller than that for a DFB laser for the same on/off ratio.
Impact ionization in Ga1−xAlxSb
Authors: Gouskov L. , Orsal B. , Pérotin M. , Karim M. , Sabir A. , Coudray P. , Kibeya S. , Luquet H.
Published: July 2002

We have measured impact ionization rates in Ga1−xAlxSb at x=0 and 0.08. For these Al contents, the ratio values of the spin-orbit splitting energy Δ to the energy gap Eg are, respectively, greater and lower than unity. We have determined that the ratio of the ionization coefficients kp/kn is greater than unity for both compositions and that it is much lower (kp/kn≊2) than the value (≳10) determined on our layers for x=0.04. Multiplication noise measurements confirm these results. The comparison to other published data show that the ionization in these antimonide compounds is not yet elucidated.
Formation of deep complexes in ZnSe during ohmic contact annealing
Authors: Heuken M. , Söllner J. , Guimarães F. E. G. , Marquardt K. , Heime K.
Published: July 2002

The formation of ohmic contacts to n-ZnSe grown by metalorganic vapor-phase epitaxy (MOVPE) on GaAs was investigated by current-voltage and photoluminescence (PL) measurements. Annealing of the contacts even at temperatures as low as 300 °C causes the formation of deep complexes with PL emissions at 2.25–2.35 and 1.97 eV. These centers degrade the electrical and optical properties of the ZnSe epitaxial layers. The effects of strain and Ga outdiffusion on ohmic contact properties was investigated in ZnSe layers of various thicknesses. Due to a gallium-doped ZnSe transition layer at the substrate heterointerface ohmic contacts are easily formed only on thin layers.
Structural and electro-optic properties of laser ablated Bi4Ti3O12 thin films on SrTiO3(100) and SrTiO3(110)
Authors: Jo W. , Yi G-C. , Noh T. W. , Ko D-K. , Cho Y. S. , Kwun S-I.
Published: July 2002

Bi4Ti3O12 thin films have been grown by laser ablation on SrTiO3(100) and SrTiO3(110) substrates. Substrate surface orientation is found to be an important growth parameter which determines crystal axis orientation, grain growth behavior, and electro-optic properties of the Bi4Ti3O12 thin films. The films grown on SrTiO3(110) shows a ferroelectric phase transition near 720 °C and a large quadratic electro-optic effect with the effective coefficient 1.1×10−16 m2/V 2.
Measurement of Schottky barrier energy on InGaP and InGaAlP films lattice matched to GaAs
Authors: Nanda A. , Hafich M. J. , Vogt T. J. , Woods L. M. , Patrizi G. A. , Robinson G. Y.
Published: July 2002

The Schottky barrier energies for both n-type and p-type materials have been measured for the wide band-gap alloys InGaP and InGaAlP when lattice matched to GaAs. A gold metallization was used and the barrier energy was measured on chemically etched surfaces using conventional current-voltage and photoemission techniques. In the range of alloy composition investigated, the sum of the n-type and p-type barriers was found not to equal the value of the energy gap determined from optical measurements. For InxGa1−x−yAlyP lattice matched to GaAs, the n-type Schottky barrier energy was found to decrease, while the p-type barrier increased, with increasing Al content y.
Formation of As precipitates in GaAs by ion implantation and thermal annealing
Authors: Claverie A. , Namavar Fereydoon , Liliental-Weber Z.
Published: July 2002

We show that it is possible to regrow an amorphous GaAs layer created by high dose As implantation at room temperature. If implantation parameters are carefully selected, As precipitates may be formed in the regrown layer with structural characteristics the same as those observed in semi-insulating GaAs grown by molecular beam epitaxy at low temperature. Transmission electron microscopy has been used to study the structure of these precipitates in connection with the structural defects which are seen in the layer. This process appears promising for the formation of low cost semi-insulating GaAs layers.
Negative and positive ions from CF4 and CF4/O2 rf discharges in etching Si
Authors: Lin Yun , Overzet Lawrence J.
Published: July 2002

The mass spectra of positive ions and negative ions from CF4 and CF4/O2 rf discharges with and without an etching silicon wafer are presented. The positive ion spectra are largely consistent with those obtained by prior investigations and do not exhibit large changes with the addition of silicon to the discharge. Only one silicon containing positive ion was found, SiF3+ at 85 amu. The negative ion spectra changes considerably with the addition of silicon to the discharge indicating that many of the silicon etching products tend to form negative ions rather than positive ions (or neutral species). In particular, the signal from SiF5− at 123 amu is very large, even larger than the signal of F− at 19 amu when silicon is present. (SiOF3−, SiOF4−, and Si2O2F5− can also have large signal intensities.) While atomic and molecular fluorine are difficult to detect in the positive ion spectra, they are both easily found as negative ions. Some of the relationships between the negative ion signals are consistent with the reactions proposed by C. J. Mogab, A. C. Adams, and D. L. Flamm, J. Appl. Phys. 49, 3796 (1978) and G. Smolinsky and D. L. Flamm, J. Appl. Phys. 50, 4982 (1979).
Capillary-based x-ray collector/collimator for diffraction applications
Authors: Kovantsev V. E. , Pant J. , Pantojas V. , Nazaryan N. , Hayes T. M. , Persans P. D.
Published: July 2002

We describe and characterize a new x-ray optical system in which x rays are steered using multiple reflections within hollow glass capillary tubes. The prototype beam-shaping collector/collimator evaluated for diffraction with CuKα x rays in this letter has throughput of 6% and increases the useful x-ray flux by more than a factor of 4 above that of slit collimation with comparable divergence.
Low threshold buried heterostructure vertical cavity surface emitting laser
Authors: Chang-Hasnain C. J. , Wu Y. A. , Li G. S. , Hasnain G. , Choquete K. D. , Caneau C. , Florez L. T.
Published: July 2002

We report the first low threshold, buried heterostructure (BH) vertical cavity surface emitting laser (VCSEL) using organometallic chemical vapor deposition regrowth. Very low threshold current of 0.8 mA and threshold current density of 490 A/cm2 are achieved with 8 and 32 μm diam BH VCSELs, respectively. Both 8 and 16 μm diam BH VCSELs emit a single TEM00 fundamental mode for current levels many times thresholds. Most single-mode emissions are linearly polarized with a predetermined direction in the [01̄1] crystal orientation.
Tunneling spectroscopy of midgap states induced by arsenic precipitates in low-temperature-grown GaAs
Authors: Feenstra R. M. , Vaterlaus A. , Woodall J. M. , Pettit G. D.
Published: July 2002

The scanning tunneling microscope is used to study arsenic precipitates in low-temperature-grown and annealed GaAs. Tunneling spectroscopy reveals a distribution of states throughout the band gap, arising from the precipitates, with the density of midgap states increasing as the precipitate size increases. The Fermi level is found to be pinned at EV+0.65 eV for 600 °C annealed material. For 800 °C annealed material the Fermi level is located at EV+1.05 eV in regions far from precipitates, and additional depletion regions are observed near the precipitates.
Electrical conductivity studies of diamond films prepared by electron cyclotron resonance microwave plasma
Authors: Jin S. , Moustakas T. D.
Published: July 2002

The electrical conductivity of diamond films, having different surface morphologies, was measured in the temperature range from 200 to 800 °C. The films were prepared by the electron cyclotron resonance plasma-assisted CVD method (ECR-PACVD) using CO/H2/O2 . We found that films with (111) surface morphology have electrical conductivity activation energies of between 0.3 and 0.4 eV, consistent with boron ionization energy in diamond. On the other hand, films with (100) morphology have an activation energy of 1.5 eV, consistent with the ionization energy of substitutional nitrogen. Due to their high solubility, boron and nitrogen are the most common impurities in natural and synthetic diamond. These data suggest that electrically active boron and nitrogen incorporation is correlated with the film growth along (111) and (100) directions, respectively.
Behavior of an ideal injecting contact on a trap-free polymer
Authors: Abkowitz M. , Facci J. S. , Stolka M.
Published: July 2002

Solution coatable insulators capable of unipolar photoinjected carrier transport with negligible loss of transiting charge to deep traps are required for the fabrication of organic electrophotographic receptors. Molecularly designed polymeric insulators with these characteristics can now be routinely synthesized. Such trap-free polymer films provide a unique venue for the study of contact and interface behavior. A test for distinguishing ohmic from emission limited contact behavior which exploits the availability of these polymers is described. The test involves direct comparison of dark injection transients excited by application of a voltage step to the contact under investigation, with small signal time-of-flight transients photoexcited by laser pulse irradiation through a semitransparent blocking contact on the opposite face of the same specimen film.
Determination of band gap narrowing and hole density for heavily C-doped GaAs by photoluminescence spectroscopy
Authors: Lu Z. H. , Hanna M. C. , Majerfeld A.
Published: July 2002

The energy band gap narrowing effect in heavily C-doped GaAs was investigated using photoluminescence spectroscopy. The band gap was determined over the hole density range 1017–4×1020 cm−3 at 10 and 300 K. The band gap data at low temperatures confirm the available theoretical calculations up to 1020 cm−3. An unexpected temperature dependence of the observed band gap at high doping levels is discussed on the basis of carrier-phonon interactions. We present an analysis of the band gap narrowing effect that can be used for nondestructive measurement of hole densities in the range 1017–4×1020 cm−3.
Photoreflectance study of surface Fermi level in molecular beam epitaxial grown InAlAs heterostructures
Authors: Hwang J. S. , Tyan S. L. , Chou W. Y. , Lee M. L. , Weyburne David , Hang Z. , Lin H. H. , Lee T. L.
Published: July 2002

We have studied the band gaps and the surface Fermi level positions of a series of In1−xAlxAs surface-intrinsic-n+ structures at room temperature by photoreflectance. Experiments demonstrated that over aluminum concentrations of 0.42–0.57, the surface Fermi level is not pinned at midgap, as commonly believed, but instead varies, respectively, from 0.50±0.01 to 0.81±0.01 eV below the conduction band edge.
Diffuse x-ray scattering from p+ porous silicon by triple axis diffractometry
Authors: Koppensteiner E. , Schuh A. , Bauer G. , Holy V. , Bellet D. , Dolino G.
Published: July 2002

Strain and microstructure of porous silicon on (001) wafers with different porosity were investigated by triple axis x-ray diffractometry using an instrumental resolution of 12 arcsec. The Bragg diffraction peaks arising from the porous Si contain information both on the mean strain (1.29–2.95×10−3) and on strain gradients (0.70–1.42×10−3) in these samples. In specimens with a porosity of 60% the pores are shown to be elongated over about 200 nm along the [001] direction, and over 50 nm in directions parallel to the growth plane. It is demonstrated that the correlation function for the pores has an extension along the [001] direction which is about a factor of 4 larger than along the [010] direction. From measurements of the intensity distribution of diffuse x-ray scattering a crystallographical damage in the silicon skeleton can be excluded. Regions of the porous layer near the interface to air are shown to be tensilely strained both along and perpendicular to the substrate normal.
Low temperature magnetic force microscope utilizing a piezoresistive cantilever
Authors: Yuan C. W. , Batalla E. , Zacher M. , de Lozanne A. L. , Kirk M. D. , Tortonese M.
Published: July 2002

We have developed a low temperature magnetic force microscope capable of operation down to 6 K in vacuum by using piezoresistive cantilevers. We use the non-contact frequency modulation technique to detect the magnetic force gradient between an iron-coated tip and the sample. We demonstrate the operation of this new instrument by obtaining images of magnetic domains in VHS tape at room temperature, 77 and 6 K. This microscope is ideally suited for the characterization of thin films of high temperature superconductors.
140-GHz metal-semiconductor-metal photodetectors on silicon-on-insulator substrate with a scaled active layer
Authors: Liu M. Y. , Chen E. , Chou S. Y.
Published: July 2002

Metal-semiconductor-metal photodetectors with 100-nm finger spacing and width on a silicon-on-insulator substrate that has a scaled active layer were fabricated and characterized using electro-optic sampling. The unique device structure cuts off carriers generated deep inside the semiconductor substrate, resulting in a measured response time of 3.2 ps and a bandwidth of 140 GHz. Furthermore, the detector structure makes the detector’s speed independent of the light penetration depth and thus the light wavelength. Good metal-semiconductor Schottky contact and low detector dark current have been achieved.
Atomic layer epitaxy of ZnS:Tb thin film electroluminescent devices
Authors: Kong W. , Fogarty J. , Solanki R.
Published: July 2002

Fabrication of green light emitting ZnS:Tb thin film electroluminescent devices using atomic layer epitaxy is described. In this investigation, particular emphasis is placed on the effect of Tb doping profiles and concentrations on the emission characteristics. It is shown that rapid thermal anneal of these devices has a significant effect on their emission lifetimes.
Temperature dependence of photoluminescence linewidth in modulation-doped pseudomorphic high electron mobility transistor AlxGa1−xAs/InyGa1−yAs/GaAs structures
Authors: Yu P. W. , Jogai B. , Rogers T. J. , Martin P. A. , Ballingall J. M.
Published: July 2002

We report the temperature dependent characteristics of photoluminescence linewidth in terms of two-dimensional electron gas sheet concentration for modulation δ-doped AlxGa1−xAs/InyGa1−yAs/GaAs structures. The electron concentration is obtained using a self-consistent solution of the coupled k⋅P Hamiltonian–Poisson equation. We find that only the full width at half maximum of the n=2 electron-subband-to-n=1 hole subband transition is useful for characterizing high electron density at T=2–300 K. The importance of hole localization for correlating the electron density with photoluminescence linewidth is discussed.
Two photon absorption of di-alkyl-amino-nitro-stilbene side chain polymer
Authors: Cha M. , Torruellas W. E. , Stegeman G. I. , Horsthuis W. H. G. , Möhlmann G. R. , Meth J.
Published: July 2002

The two photon absorption spectrum has been measured in the 780–1600 nm range for a di-alkyl-amino-nitro-stilbene side-chain polymer. A single two photon peak centered at 920 nm is observed with a peak two photon coefficient of 5.5 cm/GW. Bleaching via two photon absorption at this wavelength is investigated by measuring a refractive index change after an intensive exposure.
Is there an elastic anomaly for a (001) monolayer of InAs embedded in GaAs?
Authors: Bernard James E. , Zunger Alex
Published: July 2002

When a coherently grown (001)-oriented layer of InAs is embedded in a GaAs host, the coherency strain induces a perpendicular distortion of the embedded layer, predicted by continuum elasticity theory to be ε⊥=7.3%. Brandt, Ploog, Bierwolf, and Hohenstein, [Phys. Rev. Lett. 68, 1339 (1992)] have described a high-resolution electron microscopic analysis of such buried layers that appears to reveal a breakdown of continuum elasticity theory in the limit of monolayer films. In particular, they found for a single monolayer of InAs a lattice distortion that corresponds to ε⊥=12.5%. Here we report on an investigation into whether a first-principles local-density total energy minimization shows such an elastic anomaly in the monolayer limit. We find that it does not.
Semi-insulating 6H–SiC grown by physical vapor transport
Authors: Hobgood H. McD. , Glass R. C. , Augustine G. , Hopkins R. H. , Jenny J. , Skowronski M. , Mitchel W. C. , Roth M.
Published: July 2002

Semi-insulating 6H–SiC crystals have been achieved by using controlled doping with deep-level vanadium impurities. High resistivity undoped and semi-insulating vanadium-doped single-crystals with diameters up to 50 mm were grown by physical vapor transport using an induction-heated, cold-wall system in which high purity graphite materials constituted the hot zone of the furnace. Undoped crystals were p-type due to the presence of residual acceptor impurities, mainly boron, and exhibited resistivities ranging up to 3000 Ω cm. The semi-insulating behavior of the vanadium-doped crystals is attributed to compensation of residual acceptors by the deep-level vanadium V4+(3d1) donor located near the middle of the band gap.
Surface strains in epitaxial systems
Authors: Gray L. J. , Chisholm M. F. , Kaplan Theodore
Published: July 2002

The stress state of heteroepitaxial film systems is examined using a boundary integral method together with boundary conditions that allow deflections at the substrate/film interface. It is found that for geometries that deviate from planar structures significant variations in surface strain and film energy arise. These calculations explain recent important experimental results for Ge growth on Si, including observations for Ge islands on Si that show the surface lattice constant can exceed the bulk Ge value, and observations that the preferred region for growth on terraced films is not necessarily at the steps.