bluuebunny/crossref_metadata_2025 huggingface dataset:
Causes of death in Canadians with haemophilia 1980–1995
Authors: Walker I. R. , Julian J. A. ,   ASSOCIATION OF HEMOPHILIA CLINIC DIRECTORS OF CANADA
Published: July 2002

The life expectancy of individuals with haemophilia was close to that of the general population in the early 1980s. Since then, life expectancy has decreased, due to transfusion‐transmitted virus infections. Deaths in individuals with haemophilia were investigated by analysing 2450 records from the Canadian Hemophilia Registry, for the years 1980–1995. Deaths were tabulated by age, year and cause, and compared with that of the Canadian male population by calculating standardized mortality ratios (SMRs). The median life expectancy at 1 year of age was calculated for various subpopulations and the impact of various population characteristics was assessed by survival regression modelling. There were 359 deaths and the annual number of deaths increased significantly after 1986. Risk factors were seropositivity to human immunodeficiency virus (relative risk 16.7, 95%CI 11.1–25.1), severe haemophilia (1.9, 1.3–2.7) and moderate haemophilia (1.8, 1.2–2.6). In HIV antibody negative individuals, the overall death rate was not increased (SMR 0.9, 95%CI 0.7–1.1) and only haemorrhage was significantly increased. In HIV antibody positive individuals, causes of death which were significantly increased were acquired immunodeficiency syndrome, liver failure, haemorrhage, lymphoma, liver cancer, nonspecific infections, and trauma or violence. Deaths due to the acquired immunodeficiency syndrome accounted for only 66% of the excess deaths in individuals who were HIV antibody positive. Life expectancy has markedly decreased since the onset of the HIV epidemic. The impact of HIV is underestimated by considering only deaths due to the acquired immunodeficiency syndrome; other HIV‐linked causes need also to be considered.
Modern pollen spectra from tropical South India and Sri Lanka: altitudinal distribution
Authors: Bonnefille R. , Anupama K. , Barboni D. , Pascal J. , Prasad S. , Sutra J. P.
Published: July 2002

We analysed the pollen content of 106 surface soil samples from evergreen and deciduous tropical forests distributed between 6° and 13° of latitude north in South India and Sri Lanka. The samples were collected along altitudinal gradients, ranging from 50 to 2420 m, in five regions that experience different rainfall regimes. Original pollen data from tropical vegetation subjected to seasonal monsoon rains are presented along altitude/temperature gradients. This paper includes a summarized description of the vegetation types mapped in the area.

The pollen results are presented in the form of quantitative pollen diagrams and correspondence analyses. They show clear distinct pollen assemblages and markers for all types of vegetation in deciduous and evergreen vegetation. Forests are well identified by percentages of Arboreal Pollen greater than 50%, despite the fact that Dipterocarpaceae and Lauraceae are hardly recorded by pollen.

The pollen distinction between low, medium and high elevation evergreen forests matches that established by ecologists. The botanical limits, respectively, placed at 900 m and 1500 m limits, correspond to the 20 °C and 15 °C‐values of mean temperature of the coldest month. They appear clearly identified in the modern pollen record. This justifies further use of pollen data in Biome modelling.
Occlusal force distribution on the dental arch during various levels of clenching
Authors: Kumagai H. , Suzuki T. , Hamada T. , Sondang P. , Fujitani M. , Nikawa H.
Published: July 2002

The purpose of this study was to explore the occlusal force distribution on the dental arch in the intercuspal position and to evaluate the relationship between the clenching strength and the occlusal force distribution. These variables were recorded using the Dental Prescale System in 16 healthy young adults. The number of tooth contacts, occlusal force and occlusal contact area increased linearly as clenching strength increased. The distribution of the occlusal force was greatest at the molar region followed by the premolar and anterior teeth region. The proportion of occlusal force (occlusal force at each region/total occlusal force) on molar regions increased as clenching strength increased. On the contrary, the proportion of occlusal force on the premolar and anterior teeth regions decreased as clenching strength increased. These findings suggest that control of occlusal force is important in diagnosis of the nature of occlusal contacts.
Mental health work observed: a comparison of the perceptions of psychiatrists and mental health nurses
Authors: Dallender J. , Nolan P.
Published: July 2002

This study explores mental health nurses’ and psychiatrists’ perceptions of their work. It was carried out in five mental health Trusts in the West Midlands, UK. Three groups were surveyed: psychiatrists, hospital‐based nurses and community mental health nurses (CMHNs). Results showed that CMHNs’ sources of job satisfaction and dissatisfaction were more similar to those of psychiatrists than to those of their hospital‐based counterparts. All three groups cited the intrinsic worthwhileness of their work, autonomy, the scope for creativity, the variety their job offered and their contact with clients as contributing to their overall job satisfaction. Hospital‐based nurses listed the support they received from colleagues as their second source of job satisfaction, whereas CMHNs and psychiatrists cited the provision of care to patients. Excessive administrative duties and the absence of or poor quality of management were perceived by all three groups as sources for dissatisfaction with their work. Hospital nurses cited job insecurity as a principal concern more frequently than CMHNs and psychiatrists. The paper concludes by discussing recommendations for changes to improve the nature of the work in mental health services and in the work environment. Changes must reflect the concerns of the different groups of mental health professionals.
Safety of the Canadian blood supply in 1980–85: using a paediatric cohort for risk assessment of human immunodeficiency virus (HIV) infection
Authors: King  , Corey  , Major  , Poon  , Child
Published: July 2002

The risk of HIV from transfusions in Canada in the period 1980–85 was estimated, using the information from a transfused paediatric cohort. Children who were transfused between January 1980 and November 1985 at a tertiary care paediatric hospital were contacted by letter. With this notification, HIV testing for recipients was recommended. HIV testing histories were obtained. The number tested for HIV was estimated from the questionnaire responses and from data matching with the HIV‐testing laboratory. Cases of HIV infection were identified through multiple sources. In this cohort, 11 028 children were transfused a mean of 21 units. Of the 10 220 living recipients, the estimated proportion tested for HIV was 86% to 91%. Thirty‐one cases of HIV infection were identified, representing 0.28% of the cohort but 0.34% of those expected to have been tested. The estimated HIV incidence per 1000 units transfused ranged from 0.028 [95% CI 0.0007, 0.155] in 1980 to 0.445 [95% CI 0.2592, 0.712] in 1985. This suggests that the risk of HIV from transfusions in Canada continued to rise until the implementation of HIV testing of donors in November 1985.
Freshwater organisms that build stromatolites: a synopsis of biocrystallization by prokaryotic and eukaryotic algae
Authors: FREYTET PIERRE , VERRECCHIA ERIC P.
Published: July 2002

In freshwater environments such as river and stream bottoms, rocks and submerged vegetation are covered with a biological felt (also called a periphyton, microbial mat, biofilm, etc.) that is susceptible to calcification. Compilation of an extensive bibliography and our own observations have allowed the identification of 44 species of Coccogonophyceae, 122 Hormogonophyceae, 2 Chrysophyceae, 35 Chlorophyceae, 3 Xanthophyceae, 2 diatoms, and 3 Rhodophyceae that grow on calcareous tufa and coat vegetation. Diverse genera include species that are also calcified but impossible to determine because they lack reproductive organs. Crystals have been described from 74 species in the literature and we have observed 53 others. They can be classified into 10 groups: (1) platelets on cell walls (Volvocales, analogues of coccolithophorids) (2) crystals in mucilage (Synechococcus, diatoms, Hydrurus) and calcified stalks (Oocardium) (3) sheaths containing crystals in the form of simple or three‐branched needles, dendritic crystals, and crystals with box‐work fabric (Geitleria, Scytonema) (4) sheaths containing calcite spherulites (5) stalks intersecting a large crystal (Cymbella) (6) micrite tubes (Phormidium, Schizothrix) (7) isolated rhombohedra (Zygnema, Scytonema), rhombohedra in clusters or chains (Nostoc parmelioides) (8) sparite platelets (Vaucheria) or isodiametric crystals (Scytonema, Chaetophora) (9) large crystals crosscut by many parallel filaments (Rivularia, Batrachospermum), and (10) fan‐like crystals (Phormidium). These crystals can be arranged in clusters or form regular laminations. They can transform into isodiametric sparite crystals to form fan‐like or radial palisadic structures. Knowledge of primary crystals and their diagenetic transformations is necessary to correctly interpret freshwater stromatolites. The latter always result from intense calcification and are a diagenetic transformation of a biological felt made of many prokaryotic and eukaryotic algal species, small invertebrates, and organic and mineral debris.
Malignant chondroid syringoma of the skin: Magnetic resonance imaging features
Authors: Nicolaou S , Dubec Jj , Munk Pl , O'Connell Jx , Lee Mj
Published: July 2002

Skin tumours are usually divided into melanoma and non‐melanoma types. Malignancies of the adnexal structures, of which sweat gland tumours are an example, are characterized under the non‐melanoma types. Sweat gland malignancies are rare tumours that are usually associated with a poor prognosis. Given the rarity of these tumours, MRI findings of such tumours have not been described previously in the literature. We present a case report of an unusual malignant tumour of sweat gland origin known as a malignant chondroid syringoma of the skin with described MRI features. The MRI features are non‐specific depicting intermediate signal intensity, changes on the proton density sequence and increased signal on the T2 and STIR‐weighted sequences. Although these imaging features are characteristic of most soft tissue masses MRI can, in most cases, accurately depict the anatomic extent and identify tissue of origin, depth of invasion and relation to adjacent structures, such as muscles and bones. Thus high‐resolution MRI of the skin in the future can be extremely helpful in characterizing and staging dermal neoplasms.
Study of the correlation between the vacA genotype of Helicobacter pylori, the VacA product and gastroduodenal disease
Authors: Youli Zhang , Houyu Liu , Kang Zhou , Caimei Ni , Meiyu Hu , Jianjun Jin
Published: July 2002

OBJECTIVE: To determine vacA genotypes and the vacuolating cytotoxin (VacA) activity of Helicobacter pylori strains isolated from patients with chronic gastritis (CG), peptic ulcers (PU) and gastric cancer (GC), and to investigate the relationship between the vacA genotypes of H. pylori, their product, VacA, and gastroduodenal diseases.

METHODS: Sixty‐two H. pylori strains were isolated from patients with CG (27 cases), PU (24 cases) and GC (11 cases) as diagnosed by either endoscopy or surgical pathology. The vacA genotypes of the H. pylori strains were tested by polymerase chain reaction (PCR). HeLa cell assays for VacA activity were carried out using a 20‐fold concentrated culture supernatant of H. pylori in vitro. Culture supernatants of H. pylori strain NCTC 11637 and culture supernatants without H. pylori were used as positive and negative controls, respectively.

RESULTS: All 62 H. pylori strains contained the vacA gene. The signal sequence and mid‐region gene of the 62 H. pylori strains were s1a and m2 types, respectively. Mosaicism in vacA alleles was type s1a/m2 exclusively. The total rate of VacA expression in vitro was 37.1%; the rates of VacA expression in H. pylori strains isolated from patients with CG, PU and GC were 33.33, 29.17 and 63.64%, respectively. The proportion of strains expressing VacA in patients with GC was higher than those in patients with CG and PU, but the difference in VacA expression rates in CG, PU and GC strains was not significant (P > 0.05).

CONCLUSIONS: The vacA genotype of H. pylori cannot be used to predict the clinical consequences of infection with that strain of H. pylori. Moreover, the VacA activity of H. pylori in vitro cannot be used to predict whether subjects infected with H. pylori will be more likely to develop CG, PU or GC. No correlation between vacA genotype and VacA expression was found in the present study.
The relevance of the glycaemic index to our understanding of dietary carbohydrates
Authors: Frost G. , Dornhorst A.
Published: July 2002

Aims To review the evidence for the importance of glycaemic index of dietary carbohydrate in disease prevention and control

Methods A critical appraisal of the literature published in English between and cited on Medline between January 1966 and October 1999.

Results Using basic, intervention and epidemiological studies from experienced teams, evidence that the glycaemic index of diet may influence outcome in terms of cardiovascular risk, risk of metabolic syndrome diseases and pregnancy was found

Conclusions Consideration of glycaemic indices in making dietary recommendations may be expected to produce additional health benefit.
A longitudinal study of cycloplegic refraction in a cohort of 350 Japanese schoolchildren. Anisometropia
Authors: Yamashita Tetsuhiro , Watanabe Shinobu , Ohba Norio
Published: July 2002

The intereye difference of cycloplegic refraction was determined in a cohort of 350 rural Japanese schoolchildren aged 6 to 11 years. The intereye spherical difference remained statistically unchanged throughout 5 years, with mean value ranging from 0.21 to 0.28 D, median from 0.15 to 0.20 D, and the 95th percentile from 0.58 to 0.85 D. The prevalence of 1.0 D or greater spherical anisometropia was up to 3.1%. Linear regression analyses of the longitudinal data from individual children revealed that 295 (84.3%) children had remained unchanged while 55 (15.7%) showed significant increase or decrease in the amount of anisometropia with increasing age. The intereye astigmatic difference was also statistically unchangeable, with mean value ranging from 0.28 to 0.36 D, median from 0.20 to 0.39 D, and the 95th percentile from 0.70 to 0.90 D. The prevalence of 1.0 D or greater astigmatic anisometropia was up to 4.3%. There was a significant correlation between the spherical and astigmatic anisometropia. The results show the current state of intereye refractive difference in Japanese schoolchildren, demonstrating that it remains unchanged and significant anisometropia is rare during school age.
Investigations on Transcript Sizes, Steady State mRNA Concentrations and Diurnal Expression of Genes Encoding Fucoxanthin Chlorophyll a/c Light Harvesting Polypeptides in the Centric Diatom Cyclotella cryptica
Authors: Oeltjen A. , Krumbein W. E. , Rhiel E.
Published: July 2002

Abstract: The transcript sizes of fcp genes of Cyclotella cryptica, belonging to different fcp gene clusters and encoding different fucoxanthin chlorophyll a/c light harvesting polypeptides (Fcps), were determined. Furthermore, the diurnal expression of the fcp1/fcp2/fcp3/fcp5 gene cluster and the steady state mRNA concentrations of all gene clusters were investigated in response to light quality and quantity. The mRNAs of the gene cluster consisting of fcp1/fcp2/fcp3/fcp5 are approx. 950 bases in length, whereas those of the fcp4 and the fcp6/fcp7/fcp12 clusters are approx. 1050 (fcp4), 880 (fcp6/fcp7) and 1150 (fcp12) bases in lengths. The transcript levels of the fcp1/fcp2/fcp3/fcp5 gene cluster increased with the onset of light, reached a maximum around noon and dropped in the afternoon. The steady state mRNA concentrations of the fcp1/fcp2/fcp3/fcp5 gene cluster and of the fcp4 gene cluster were higher, when Cyclotella cryptica was grown in low light, while the steady state mRNA concentration of the fcp6/fcp7/fcp12 gene cluster increased under high light growth conditions. The steady state mRNA concentrations of all gene clusters were highest when Cyclotella cryptica was grown in red light, intermediate in green light, and lowest in blue light.
Fractional quantum Hall effect in a high-mobility GaAs/AlxGa1−xAs multiple quantum well heterostructure
Authors: Shayegan M. , Wang J. K. , Santos M. , Sajoto T. , Goldberg B. B.
Published: July 2002

We report the realization of a high mobility [μ≂4.8×105 cm2/(V s)] selectively doped GaAs/AlxGa1−xAs multiple quantum well structure with low density (ns ≂1.7×1011 cm−2 for each of the 85 wells) grown by molecular beam epitaxy. The activation energy for the fractional quantum Hall state at the Landau-level filling factor ν=1/3 is Δ≂2 K, the highest value ever reported for any multiple quantum well structure. Such a structure is nearly ideal for studies of the thermal properties of the two-dimensional electron system in the fractional quantum Hall regime.
Magnetization and domain structure of cylinders and spheres in subsaturating fields
Authors: Bryant P. , Suhl H.
Published: July 2002

We explore the magnetization patterns and domain walls which may occur in ferromagnetic cylinders and spheres in a certain range of sizes, placed in a uniform external magnetic field below saturation. The solutions found are field-free inside the sample. The analysis is explicitly carried out for circular and elliptic cylinders and spheres, and may be extended to general ellipsoids.
Ion-implanted Zn diffusion and impurity-induced disordering of an AlGaAs superlattice
Authors: Zucker E. P. , Hashimoto A. , Fukunaga T. , Watanabe N.
Published: July 2002

The diffusion coefficient of ion-implanted Zn and the Al-Ga interdiffusion coefficient in an Al0.5Ga0.5As/GaAs superlattice (SL) are extracted from secondary-ion mass spectroscopy profiles for four diffusion times at 750 °C. The zinc diffusion coefficient goes as the square of the zinc concentration, implying local thermal equilibrium, and is over 200 times smaller than reported values for gaseous-source Zn diffusions at 650 °C in GaAs. The SL disordering rate increases with increasing zinc concentration and is attributed to the diffusion of positively charged column III interstitials (Ga+mI or Al+mI) with m between 2 and 3.
Rapid thermal oxidation of thin nitride/oxide stacked layer
Authors: Chang W. T. , Shih D. K. , Kwong D. L. , Zhou Y. , Lee S.
Published: July 2002

The effects of rapid thermal oxidation (RTO) on the chemical vapor deposited nitride/oxide layer for thin gate dielectrics were studied. Successful growth of a top oxide of ∼25 Å was confirmed using x-ray photoelectron spectroscopy and no punchthrough of the chemical vapor deposited nitride was observed for a nitride thickness of 60 Å. Changes in electrical properties after RTO were studied using current-voltage and charge-to-breakdown measurements. Results indicate that the top oxide reduces the leakage current under positive gate bias and increases the leakage current at high fields for negative gate bias. In addition, the charge to breakdown of the layer is increased after RTO.
Negative photoconductivity due to carrier drag in GaAs/AlGaAs quantum wells
Authors: Juen S. , Höpfel R. A. , Gossard A. C.
Published: July 2002

Negative photoconductivity caused by ‘‘carrier drag’’ is experimentally verified for the first time. In p-modulation-doped GaAs/AlGaAs quantum wells carrier drag, leading to ‘‘negative absolute mobility’’ of injected minority electrons, results in a decrease of the total in-plane current in the quantum wells. The temperature dependence of the measured differential photoconductivity quantitatively agrees with the expected behavior due to the effect of electron-hole scattering.
Dual-mode microwave/radio frequency plasma deposition of dielectric thin films
Authors: Martinu L. , Klemberg-Sapieha J. E. , Wertheimer M. R.
Published: July 2002

Thin films have been deposited in a ‘‘dual frequency mode’’ plasma, in which differing amounts of radio frequency (rf, 13.56 MHz) power were applied to the substrate, while sustaining the plasma with constant microwave (2.45 GHz) power. We report results pertaining to deposition of silicon oxide and organosilicon thin films. The rf-induced negative dc self-bias voltage is shown to affect plasma-chemical reactions, causing very significant changes in the deposition rate, film composition, and dielectric properties of the resulting materials. This provides a powerful new technique for producing ‘‘tailored’’ films, while preserving the important advantages of high deposition rates and low substrate temperatures.
Thermodynamics approach to catastrophic optical mirror damage of AlGaAs single quantum well lasers
Authors: Moser A. , Latta E.-E. , Webb D. J.
Published: July 2002

The time dependence of catastrophic optical damage (COD) was studied for the cw operation of AlGaAs single quantum well lasers with cleaved mirrors. An empirical rule is proposed, which yields the time for a COD failure in the form of a rate equation, containing a frequency factor and an activation energy. In this way COD is explained as a thermally activated process, depending on the mirror temperature.
Integrable parametric waveguide spectrometer—a nonlinear optical device capable of resolving modes of semiconductor lasers
Authors: Vakhshoori D. , Walker J. , Dijaili S. , Wang S. , Smith J. S.
Published: July 2002

In this letter we demonstrate a new kind of spectrometer capable of resolving the modes of a 1.3 μm quaternary laser diode. The device uses the nonlinear sum frequency generation of light in the semiconductor waveguide to map out the frequency spectrum of the input beam. This device was used to obtain the spectrum of a multimode Fabry–Perot 1.3 μm laser diode. Furthermore, the same device was used to observe the shift in the individual Fabry–Perot mode as well as the shift in the overall spectrum of the laser diode as a function of current. These observations indicate that the waveguide spectrometer can be useful for applications like implementing frequency division multiplexing communication systems by allowing the determination of absolute and relative frequencies of different channels in a compact fashion.
Temperature and field dependence of the switching behavior of induced molecular tilt near the smectic A–C* transition
Authors: Lee Sin-Doo , Patel J. S.
Published: July 2002

A fast electro-optic switching has been achieved in the smectic A phase of a electroclinic (EC) mixture, based on large EC coupling to the applied electric field. Near the transition from the smectic A to the chiral smectic C* phase, we have observed for the first time strong field dependence of the switching time, resulting from nonlinear behavior of the induced molecular tilt. As temperature increases, however, the switching time remains essentially constant. In addition, there is no temperature dependence at sufficiently high fields. A simple-mean field description is presented to account for the experimental results.
Direct determination of the ambipolar diffusion length in GaAs/AlGaAs heterostructures by cathodoluminescence
Authors: Zarem H. A. , Sercel P. C. , Lebens J. A. , Eng L. E. , Yariv A. , Vahala K. J.
Published: July 2002

A new technique for determining carrier diffusion lengths by cathodoluminescence measurements is presented. The technique is extremely accurate and can be applied to a variety of structures. Ambipolar diffusion lengths are determined for GaAs quantum well material, bulk GaAs, Al0.21Ga0.79As, and Al0.37Ga0.63As. A large increase in the diffusion length is found for Al0.37Ga0.63As and is attributed to an order of magnitude increase in lifetime.
Low-temperature reaction in tungsten layers deposited on Si(100) substrates
Authors: Cros A. , Pierrisnard R. , Pierre F. , Layet J. M. , Meyer F.
Published: July 2002

Tungsten layers have been evaporated with an electron gun under ultrahigh vacuum conditions on atomically clean Si(100) substrates. The metallic films deposited on substrates at room temperature are mostly in the body-centered-cubic α phase of tungsten. Upon annealing at 400 °C, the bulk of the layer stays unreacted but we have observed the appearance of cracks in the metallic film and the segregation of silicon atoms at the surface. These atoms are not in the form of crystalline WSi2.
Subpicosecond reflective electro-optic sampling of electron-hole vertical transport in surface-space-charge fields
Authors: Min Lixing , Miller R. J. Dwayne
Published: July 2002

A new method of electro-optic sampling field transients, using above-band-gap optical probes in reflection, is analyzed theoretically and experimentally demonstrated to be within a factor of 2 as sensitive as electro-optic sampling in transmission. The technique is ideally suited to the study of interfaces due to the surface selective nature of the evanescent field probe. Studies of the dynamics of photogenerated electron-hole pair separation in surface-space-charge fields at GaAs(100)/oxide interfaces show that the hole carrier transit time is faster than 500 fs. Using longitudinal electro-optic sampling beam geometries, this technique has an intrinsic resolution of 50 fs.
Integrated optic adiabatic polarization splitter on silicon
Authors: Shani Yosi , Henry Charles H. , Kistler R. C. , Kazarinov R. F. , Orlowsky K. J.
Published: July 2002

An adiabatic polarization splitter, fabricated with silica and silicon nitride films on a silicon substrate, is demonstrated. A rejection of the unwanted polarization (cross talk) of −20 to −34 dB was achieved with single filtering and −35 to −45 dB with double filtering. The device had a 1.5 dB insertion loss and a very small wavelength dependence.
Energy levels in quantum wires studied by tunneling and magnetotransport experiments
Authors: Hirler F. , Smoliner J. , Gornik E. , Weimann G. , Schlapp W.
Published: July 2002

We have studied the one-dimensional (1D) subband energies in quantum wires fabricated on GaAs-GaAlAs heterostructures. Magnetoresistance oscillations were used to investigate the influence of an applied gate voltage on the 1D subband energies for various geometrical widths of the fabricated quantum wires. For the first time, we measure directly the 1D subband energies by tunneling spectroscopy. As a result, both the confining potential and the influence of an additional magnetic field are well described by a simple harmonic oscillator model.
Metalorganic chemical vapor deposition growth of undoped GaAs with a low electron concentration on a Si substrate
Authors: Nozaki S. , Wu A. T. , Murray J. J. , George T. , Egawa T. , Umeno M.
Published: July 2002

We have successfully grown an undoped GaAs layer with a low electron concentration on Si by metalorganic chemical vapor desposition (MOCVD). The back and side edges of the Si substrate were covered with a Si3N4/SiO2 stacked layer to suppress Si incorporation into GaAs by the gas phase transport mechanism during the MOCVD growth. A 3-μm-thick undoped GaAs layer with an electron concentration of 3×1014 cm−3, as low as the electron concentration of a GaAs layer grown on a GaAs substrate, was grown on the Si substrate even at 750 °C.
Excimer-laser-induced crystallization of hydrogenated amorphous silicon
Authors: Winer K. , Anderson G. B. , Ready S. E. , Bachrach R. Z. , Johnson R. I. , Ponce F. A. , Boyce J. B.
Published: July 2002

The electronic transport properties and structural morphology of fast-pulse excimer-laser- crystallized hydrogenated amorphous silicon (a-Si:H) thin films have been measured. The room-temperature dark dc conductivities and Hall mobilities increase by several orders of magnitude at well-defined laser energy density thresholds which decrease as the impurity concentration in the films increases. The structural morphology of the films suggests an impurity-induced reduction of the a-Si:H melt temperature as the origin of this behavior.
Graded-index optical fibers of methyl methacrylate-vinyl benzoate copolymer with low loss and high bandwidth
Authors: Ohtsuka Yasuji , Nihei Eisuke , Koike Yasuhiro
Published: July 2002

The interfacial-gel copolymerization of 3/1, or 4/1 (wt/wt) methyl methacrylate-vinyl benzoate monomer mixture followed by heat drawing results in graded-index plastic optical fibers with attenuation loss of 212 and 134 dB/km at 652 nm, respectively, and with bandwidths of 170 and 260 MHz km, respectively, in comparison with 6 MHz km of the current step-index plastic optical fiber. Now, it has been confirmed experimentally that graded-index fibers are tremendously superior to step-index fibers for data-carrying capacity, while attenuation losses of both fibers are comparable.
Growth of epitaxial CoSi2 on (100)Si
Authors: Dass M. Lawrence A. , Fraser David B. , Wei Chih-Shih
Published: July 2002

A bilayer CoSi2/TiN has been grown on (100)Si, starting from a (100) p-type Si wafer deposited with thin layers of Ti followed by Co metal, through a two-stage annealing in a nitrogen environment and an intervening etch. In this process, Co and Ti switch places to form CoSi2 covered with TiN on Si. Cross-section transmission electron microscopy, and Rutherford backscattering/channeling spectrometry were used to characterize the bilayer sample. The CoSi2 was found to be single crystal, fully coherent, and epitaxial with (100)Si, whereas the TiN at the top of CoSi2 was polycrystalline. The stress in the CoSi2/TiN layer was found to be 1.9×1010 dynes/cm2. The planar (100) CoSi2/Si interface was interrupted with {111} ledges which are believed to be structural ledges present to maintain the coherency at the interface.
Differential gain of GaAs/AlGaAs quantum well and modulation-doped quantum well lasers
Authors: Takahashi T. , Nishioka M. , Arakawa Y.
Published: July 2002

The differential gain which is an important parameter for modulation dynamics in semiconductor lasers is evaluated experimentally by measuring the gain coefficient and the carrier lifetime in GaAs/AlGaAs double-heterostructure (DH) lasers, quantum well (QW) lasers, and p-modulation-doped quantum well (p-MDQW) lasers. The results indicate that the differential gain of the QW laser is 2.4 times as high as that of the DH laser, which is consistent with the theory. In addition, it is found that improvement of the differential gain using the p-MDQW structure is not so large as that expected by the theory. This result suggests that enhanced energy broadening due to the reduction of the equivalent dephasing time τeqin, which includes both the dephasing time τin due to the intraband relaxation and the band tailing effects, significantly affects the gain spectra in the p-MDQW lasers, which is confirmed by the measurement of the spontaneous emission spectra.
Low-rate plasma oxidation of Si in a dilute oxygen/helium plasma for low-temperature gate quality Si/SiO2 interfaces
Authors: Bright A. A. , Batey J. , Tierney E.
Published: July 2002

Low-rate plasma oxidation of Si, involving a small oxygen concentration in a low-power He plasma at low processing temperatures (∼350 °C), is shown capable of producing excellent interface properties, good uniformity, and low defect density. As an interfacial layer for plasma-enhanced chemical vapor deposited (PECVD) SiO2 films, the plasma oxide is key to achieving high quality composite (plasma oxide/PECVD) oxide structures, which essentially match the electrical quality of thermal oxides. Such low-temperature oxide films are suitable for critical device applications, such as the gate oxide in metal-oxide-semiconductor devices and the base passivation layer in advanced bipolar devices.
Electron wave diffraction by semiconductor gratings: Rigorous analysis and design parameters
Authors: Henderson Gregory N. , Glytsis Elias N. , Gaylord Thomas K.
Published: July 2002

An exact rigorous coupled-wave analysis has been developed to model ballistic electron wave diffraction by gratings with periodic effective mass and/or potential energy variations. Design expressions have been derived to calculate diffracted angles, to identify evanescent orders, and to identify the Bragg condition. Design expressions for Bragg regime (up to 100% diffraction efficiency in a single order) and Raman–Nath regime (high diffraction efficiency divided among multiple orders) diffraction are presented along with example Ga1−xAlxAs grating designs. Design procedures for ballistic electron switches, multiplexers, spectrometers, and electron waveguide couplers are described.
Self-aligned technology for tungsten-contacted InP-based etched mesa laser devices
Authors: Katz A. , Pearton S. J. , Geva M.
Published: July 2002

The characteristics of W metallization for use as self-aligned ohmic contacts and selective area etching and regrowth masks on InP-based laser structures are reported. rf-sputtered W films under either compressive or tensile stress were examined. Mesas for epitaxial regrowth were obtained by CF4/O2 dry etching of the previously deposited W film, followed either by HBr/H2O2/H2O wet chemical etching or CH4/H2/Ar electron cyclotron resonance plasma etching of ∼4 μm of InP. The W film preserved its inert metallurgical nature while heated under PH3/H2 ambient at 700 °C for 20 min, simulating the standard regrowth conditions. The W contacts on n-InP (n=5×1018 cm−3) substrates yielded stable, low contact resistivity (0.2 Ω cm) after rapid thermal processing at 600–700 °C.
Photorefractive crystal waveguide with periodically reversed c axis for enhanced two-wave mixing
Authors: Ito Fumihiko , Kitayama Ken-ichi
Published: July 2002

A photorefractive crystal waveguide with periodically reversed c axis (PCW-PX) is proposed for enhanced photorefractive two-wave mixing. In PCW-PXs, only the guided modes which have a particular propagation angle with respect to the waveguide axis are selectively coupled to the other guided modes. The mode-descriminative photorefractive coupling in two-wave mixing is experimentally verified in prepared BaTiO3 PCW-PXs.
Effects of carrier transport on high-speed quantum well lasers
Authors: Nagarajan Radhakrishnan , Fukushima Toru , Corzine Scott W. , Bowers John E.
Published: July 2002

We present a model for the dynamic response of quantum well lasers which shows that the carrier transport across the separate confinement heterostructure region and the barriers can be critical in determining the modulation bandwidth. We also show that, depending on the particular quantum well laser structure, a large part of the experimentally measured reduction in modulation bandwidth is due to transport factors.
Photoluminescence of hydrogenated SimGen superlattices
Authors: Arbet-Engels V. , Kallel M. A. , Wang K. L.
Published: July 2002

The effect of hydrogen passivation on the photoluminescence of Si-rich superlattices is investigated. The as-grown samples show many defect-related luminescence signals and several additional luminescence peaks believed to originate from the superlattice. The background luminescence along with the dislocation and defect lines are found to be passivated by the hydrogen atoms. The intensity of the superlattice peak increases after passivation and its phonon replica, initially submerged in the background and defect luminescence signals, is highlighted. After a subsequent temperature annealing in N2, the background luminescence is increased as hydrogen outdiffuses but the superlattice main peak decreases, perhaps due to the change of the carrier lifetime.
Photorefractivity in vanadium-doped ZnTe
Authors: Ziari Mehrdad , Steier William H. , Ranon Peter M. , Trivedi Sudhir , Klein Marvin B.
Published: July 2002

We report on the observation of photorefractivity in vanadium-doped zinc telluride in the 0.63–1.3-μm-wavelength range. Photorefractive two-beam coupling, along with photoluminescence and absorption spectroscopy, are used to characterize a vapor-phase transfer-grown crystal. At 0.63 μm, we measure a grating-formation time of 15 μs at an intensity of 4.7 W/cm2, which is comparable to GaAs at 1.06 μm, and is faster than photorefractive cubic and ferroelectric oxides.
Electro-optic, piezoelectric, and dielectric properties of zinc tris thiourea sulfate
Authors: Ramabadran Uma B. , Zelmon David E. , Kennedy Gretchen C.
Published: July 2002

Recently, it has been demonstrated that semiorganic materials have potential for very efficient nonlinear optical devices. Among many recently reported materials is zinc tris thiourea sulfate. We report measurements of the electro-optic, piezoelectric, and dielectric constants of this new material.
Scanning tunneling microscopy and spectroscopy of Si/SiGe(001) superlattices
Authors: Yu E. T. , Halbout J.-M. , Powell A. R. , Iyer S. S.
Published: July 2002

Cross-sectional scanning tunneling microscopy and spectroscopy were used to study a modulation-doped Si/Si0.76Ge0.24(001) superlattice. Contrast between the Si and Si0.76Ge0.24 layers has been observed in topographic images. Features such as band-edge discontinuities and band bending arising from doping have been detected in spectroscopic measurements at a series of points across the superlattice structure.
Josephson oscillations and noise temperatures in YBa2Cu3O7−x grain-boundary junctions
Authors: Divin Yu. Ya. , Mygind J. , Pedersen N. F. , Chaudhari P.
Published: July 2002

The ac Josephson effect was studied in YBa2Cu3O7−x grain-boundary junctions (GBJ) in the temperature range from 4 to 90 K. The temperature dependence of the linewidth of millimeter-wave Josephson oscillations was measured and it is shown that the derived effective noise temperatures may be as low as the physical temperature in the temperature range investigated. In the millimeter-wave range, linewidths as low as 380 MHz were found at liquid-nitrogen temperatures.
Dielectric function of solid C70 films
Authors: Ren Song-Lin , Wang Kai An , Zhou Ping , Wang Ying , Rao A. M. , Meier M. S. , Selegue J. P. , Eklund P. C.
Published: July 2002

Using variable-angle ellipsometry and normal incidence reflection/transmission optical techniques we have measured the dielectric function ε(ω) at room temperature for solid C70 films over the photon energy range 0.5≤E≤5.3 eV. The onset of absorption across the highest-occupied-molecular-orbit (HOMO)–lowest-unoccupied-molecular-orbit (LUMO) gap is measured to be 1.25 eV. Furthermore, structure in the interband absorption at 2.41, 3.10, 3.50, and 4.45 eV is observed. The refractive index at zero frequency is estimated to be n(0)=1.94 as compared to the value n(0)=1.90, which we obtained for solid C60 from our previous study.
Femtosecond multiphoton generation of the self-trapped exciton in α-SiO2
Authors: Joosen W. , Guizard S. , Martin P. , Petite G. , Agostini P. , Santos A. Dos , Grillon G. , Hulin D. , Migus A. , Antonetti A.
Published: July 2002

Nonlinear optical excitation of crystalline quartz with intense femtosecond UV pulses yields the 2.8 eV recombination luminescence of the self-trapped exciton. The relation between the excitation and emission intensities reveals two- and three-photon kinetics for photon energies of 4.4 and 4.0 eV at excitation densities below 1018 cm−3. These power laws are not sizably influenced by transient linear absorption, self-focusing, and filamentation.
Near band edge polarization dependence as a probe of structural symmetry in GaAs/AlGaAs quantum dot structures
Authors: Tanaka T. , Singh J. , Arakawa Y. , Bhattacharya P.
Published: July 2002

In order to obtain the polarization dependence of optical transitions in GaAs/AlGaAs quantum dot structures, a three-dimensional Schrödinger equation describing the heavy hole–light hole mixing via a k⋅p formalism is solved. The polarization dependence is investigated as a function of the symmetry of the quantum dot, indicating that the polarization dependence is very sensitive to the symmetry of the confining structure. We also examine how the optical properties of the quantum dot evolve towards those of a quantum wire by allowing one axis of the dot to increase.
Distributed feedback strained layer quantum well heterostructure 980 nm laser fabricated by two-step metalorganic chemical vapor deposition
Authors: Cockerill T. M. , Honig J. , Forbes D. V. , Coleman J. J.
Published: July 2002

Data are presented for single longitudinal mode, strained-layer AlGaAs-GaAs-InGaAs quantum well heterostructure distributed feedback lasers emitting near 980 nm. Device fabrication consists of conventional holographic photolithography and two-step metalorganic chemical vapor deposition growth. Regrowth over a GaAs grating layer and GaAs solid phase mass transport are discussed. The lasers are single mode up to twice Ith, have differential quantum efficiencies of 50%, and have threshold current densities of 600 A/cm2.
Frequency multiplication in actively mode-locked semiconductor lasers
Authors: Onodera N. , Lowery A. J. , Zhai L. , Ahmed Z. , Tucker R. S.
Published: July 2002

We report a method that enables an external-cavity semiconductor laser to be actively mode locked at multiples of the radio frequency (rf) drive frequency. The key to this method is the choice of the relationship between the external cavity resonance frequency and the rf drive frequency. The repetition rate of the output pulses is the lowest common multiple of the external cavity resonance frequency and the rf modulation frequency. The method has been demonstrated in a laser with a cavity resonance frequency of 1 GHz; 17 GHz pulse streams were generated using rf drive frequencies of 8.49 and 5.67 GHz.
Resonantly enhanced, frequency doubling of an 820 nm GaAlAs diode laser in a potassium lithium niobate crystal
Authors: Reid J. J. E.
Published: July 2002

A potassium lithium niobate crystal was used to double the resonantly enhanced emission of an 820 nm GaAlAs, single-mode diode laser. With a passive resonator enhancement factor of 73 and 11.5 mW of incident near-infrared power, 0.36 mW of second harmonic were produced in quasi-cw operation. The optical quality of the crystal is described and compared with that of KNbO3.
Oxygen desorption from molybdenum oxide by synchrotron radiation and its surface-cleaning applications
Authors: Nagase Masao , Utsumi Yuichi , Akawaza Housei , Urisu Tsuneo
Published: July 2002

The effects of synchrotron radiation (SR) irradiation on molybdenum oxide are studied. Removal of native molybdenum oxide by SR irradiation is observed by reflection high-energy electron diffraction and Auger-electron spectroscopy measurements. SR irradiation changes MoO3 thin films to MoO2. Indications are that SR-stimulated oxygen desorption is the cause. Those SR-irradiated molybdenum surfaces which are originally covered with native oxide are found to be highly reactive with disilane gas, while nonirradiated surfaces are not.
X-ray photoelectron spectroscopy study of GaAs surface exposed to a rf hydrogen plasma
Authors: Debiemme-Chouvy C. , Ballutaud D. , Pesant J. C. , Etcheberry A.
Published: July 2002

Using x-ray photoelectron spectroscopy analysis, it is shown that hydrogen plasma treatment of the gallium arsenide surface induces a modification of the superficial stoichiometry. The resulting surface composition presents a gallium enrichment and is the same whatever the initial composition. The departure from the stoichiometry increases with the plasma power. After the plasma treatment, the absence of arsenic oxidation and an abnormal gallium suboxidation state is observed. Moreover, these new gallium and arsenic oxidation states are stable when the sample is left in the air.
Unimportance of siloxene in the luminescence of porous silicon
Authors: Friedman S. L. , Marcus M. A. , Adler D. L. , Xie Y.-H. , Harris T. D. , Citrin P. H.
Published: July 2002

Near-edge- and extended-x-ray absorption fine structure measurements, as well as luminescence excitation and emission spectra, were obtained from samples of porous Si and siloxene. Combined, these data establish that, contrary to a recently proposed explanation, siloxene is not generally responsible for the observed room-temperature luminescence in porous Si.
Studies of dynamic magnetostriction by time-resolved scanning fiber interferometry
Authors: Freeman M. R. , Nunes G.
Published: July 2002

Measurements of the magnetostrictive response of nickel cylinders to sudden step changes in applied magnetic field are performed with a time-resolved scanning fiber interferometer. A crossover is observed, as a function of decreasing cylinder diameter, from eddy current- to longitudinal phonon-limited response times. Spatially resolved measurements reveal the nonuniform distortion of the face of the rod as the induced magnetization propagates in toward the center. The results demonstrate, here in the context of magnetics, the general promise of time-resolved scanning probe methods.
High performance dc SQUID magnetometers with single layer YBa2Cu3O7−x flux transformers
Authors: Koelle D. , Miklich A. H. , Dantsker E. , Ludwig F. , Nemeth D. T. , Clarke John , Ruby W. , Char K.
Published: July 2002

We have fabricated high-transition temperature superconducting magnetometers involving a flux transformer patterned in a single film of YBa2Cu3O7−x (YBCO) on a 50-mm-diam substrate. This transformer is inductively coupled to a loop that in turn is directly coupled to a dc superconducting quantum interference device, patterned in a single layer of YBCO deposited on a SrTiO3 bicrystal. At 77 K, the lowest magnetic field noise achieved is 31 fT Hz−1/2 at frequencies above 5 Hz, increasing to 39 fT Hz−1/2 at 1 Hz.
Fabrication of GaAs nanostructures with a scanning tunneling microscope
Authors: Snow E. S. , Campbell P. M. , Shanabrook B. V.
Published: July 2002

A method for fabricating GaAs nanostructures with a scanning tunneling microscope (STM) is presented. Utilizing a previously developed Si STM fabrication technique, the STM is used to pattern a thin (5 nm) epitaxial Si layer which is grown on GaAs. The patterned Si layer is used as a mask for wet etching the GaAs. This fabrication technique is quite general and should extend to other material systems provided a surface epitaxial Si layer can be grown.
Surface passivation of GaAs using ArF excimer laser in a H2S gas ambient
Authors: Yoshida N. , Chichibu S. , Akane T. , Totsuka M. , Uji H. , Matsumoto S. , Higuchi H.
Published: July 2002

A dry surface passivation of GaAs using the combination of H2S gas with an ArF excimer laser was examined. Native oxides at the surface were etched away by laser irradiation in vacuum. By subsequent laser irradiation in a H2S gas ambient, the surface was covered with sulfur atoms. The dry passivation technique in this study is comparable to the wet passivation process using (NH4)2Sx treatment in terms of the sulfur coverage ratio.
Josephson junctions, interconnects, and crossovers on chemically etched edges of YBa2Cu3O7−x
Authors: Faley M. I. , Poppe U. , Soltner H. , Jia C. L. , Siegel M. , Urban K.
Published: July 2002

A technique of ultraviolet photolithography of YBa2Cu3O7−x and PrBa2Cu3O7−x films combined with nonaqueous Br-ethanol chemical etching was developed. Josephson junctions, interconnects, and crossovers on the basis of chemically etched edges of c-axis oriented YBa2Cu3O7−x thin films were prepared and investigated. For the Josephson junctions with a PrBa2Cu3O7−x barrier, the IcRn product values of about 10 mV at 4.2 K and up to about 0.6 mV at 77 K were achieved. Shapiro steps were observed in the temperature range up to about 89 K. Critical current spreads of about ±10% were observed. At 77 K, the electrodes of crossovers carried more than 106 A/cm2. For a 160-nm-thick SrTiO3 intermediate layer in crossovers, a resistivity of more than 109 Ω cm was achieved at T≤100 K.