bluuebunny/crossref_metadata_2025 huggingface dataset:
Haemodynamic stability during moderate hypotensive anaesthesia for spinal surgery. A comparison between desflurane and isoflurane
Authors: Beaussier M. , Paugam C. , Deriaz H. , Mestari M. , Chandon M. , Sautet A. , Lienhart A.
Published: July 2002

Background: The aim of this study was to compare desflurane and isoflurane for spinal procedures requiring moderate levels of controlled arterial hypotension, when these agents were administered via a semi‐closed circuit at 1 l min−1 fresh gas flow.

Methods: After ethics committee approval and written informed consent, 20 ASA I or II patients were randomly allocated to receive either desflurane (n=10) or isoflurane (n=10), in O2/N2O (1:1) for maintenance of anaesthesia. Induction of anaesthesia, fentanyl dosing and volume loading were standardized. Blood pressure was invasively monitored and maintained within a target systolic blood pressure (SBP) range of 80 to 100 mmHg during the study period. Results were presented as medians and interquartiles, and non‐parametric statistical methods were used.

Results: Patient demographic data, SBP and heart rate prior to surgery, and duration of the procedure were similar between the two groups. During the study period, tighter arterial blood pressure control was maintained with desflurane as compared with isoflurane. SBP was 21.2% (9.5–41.7) of time outside the range 80–100 mmHg with isoflurane and 5.1% (0.6–10.3) with desflurane (P<0.01).

Conclusions: Desflurane, administered via a semi‐closed circuit at 1 l min−1 fresh gas flow, maintained better haemodynamic stability in spinal surgery requiring moderate arterial hypotension than isoflurane.
Antibacterial synergistic effect of chlorhexidine and hydrogen peroxide against Streptococcus sobrinus, Streptococcus faecalis and Staphylococcus aureus
Authors: Steinberg D. , Heling I. , Daniel I. , Ginsburg I.
Published: July 2002

Chlorhexidine (CHX) and Hydrogen peroxide (HP) are potent antibacterial agents that are used in controlling dental plaque. However, both agents bear undesired side‐effects. We have tested the hypothesis that an antibacterial synergistic effect can occur between the two agents against Streptococcus sobrinus, Streptococcus faecalis and Staphylococcus aureus. We have found that at several combinations of HP and CHX an antibacterial synergistic effect does occur, while at other combinations a non‐significant synergism was noticed. No antagonism between the two agents was found in our experimental system. It can be postulated that the mechanism of this synergistic effect is via alteration of the bacterial cell‐surface by CHX thereby allowing for an increased amount of HP to penetrate and to react with the intercellular organelles of the bacteria. These results suggest that CHX and HP can be of use in controlling the dental plaque in the oral cavity.
Chronic Daily Headache in the Posttrauma Syndrome: Relation to Extent of Head Injury
Authors: Couch James R. , Bearss Candace
Published: July 2002

Objective.—To evaluate the occurrence of continued intermittent headache and chronic daily headache in patients with head injury and the relationship between severity of the headache problem and intensity of the head injury.

Background.—In the majority of patients with posttraumatic headache, the condition is self‐limited, but a minority of patients may develop persistent headaches. The features of posttraumatic headache may vary, but the most distressing type is the chronic daily headache. This study evaluates occurrence of chronic daily headache in relation to the intensity of head injury.

Methods.—All patients with head injury who were seen by the senior author (J.R.C.) in the Southern Illinois University Medical School (SIUMS) Neurology Clinic between 1980 and 1991 were identified from the SIUMS headache registry. Data on headache status before and after head injury was obtained, and patients with more than one headache per week before head injury were excluded. Each patient's headache status at the time of the clinic visit was classified as chronic daily headache (headache occurring at least 5 of 7 days for 6 months), intermittent migraine, or no headache. Head injury severity was graded by duration of loss of consciousness or amnesia as minimal (less than 5 minutes), mild (5 to 60 minutes), moderate (1 to 24 hours), or severe (more than 24 hours).

Results.—There was an inverse relation between extent of head injury and occurrence of chronic daily headache. For minimal head injury (n = 54), 80% had chronic daily headache, and 11% had no headache, while for moderate/severe head injury (n = 23), only 27% had chronic daily headache, and 68% had no headache (P<.001, χ2).

Conclusion.—This study suggests that the risk of developing posttraumatic chronic daily headache is greater for less severe head injury compared with moderate/severe head injury. The reason for this relation is unclear.
Medical Care for Nursing Home Residents: Differences by Dementia Status
Authors: Burton Lynda C. , German Pearl S. , Gruber‐Baldini Ann L. , Hebel J. Richard , Zimmerman Sheryl , Magaziner Jay , For The Epidemiology of Dementia in Nursing Homes Research G
Published: July 2002

OBJECTIVE: To understand the use of medical services by nursing home residents.

DESIGN: Descriptive, longitudinal study comparing medical service use of residents by dementia status and describing the use of medical services following detection of fever or infection.

SETTING: Fifty‐nine randomly selected nursing homes in Maryland from 1992 to 1995.

PARTICIPANTS: 2153 residents admitted to one of 59 randomly selected nursing homes.

MEASUREMENT: A panel of psychiatrists and neurologists ascertained dementia based on review of medical records, interview data with significant others and nursing staff, and results of a cognitive exam. Medical service use was abstracted from medical records.

BACKGROUND: Understanding the use of medical services by nursing home residents as distinct from services provided by the nursing home is important, particularly as new medical care models are tested. This study compares the medical service use of residents by dementia status and describes the use of medical services following detection of fever or infection.

RESULTS: Residents with dementia compared with those without dementia had lower annual rates of physician visits (10.2 vs 12.7, P < .001) and hospitalizations (0.9 vs 1.2, P < .001), virtually the same rate of emergency department visits, and similar lengths of stay in the hospital. Subsequent to infection, a lower proportion of residents with dementia had either a physician visit, an emergency department visit, or a hospital admission compared with residents without dementia (27.2% vs 32.2%, P < .001). In 87% of infections, an antibiotic was used, implying meaningful contact with a physician. Residents with dementia compared with those without dementia had fewer physician visits subsequent to fevers (20.6% vs 29.9%, P < .001) and infections (21.8% vs 27.5%, P < .001).

CONCLUSIONS: The association of less medical service use by individuals with dementia compared with those without dementia may reflect differences in health status or implicit end‐of‐life decision‐making and a proclivity toward less‐aggressive treatment for these individuals.
The Differential Influence of Distinct Clusters of Psychiatric Symptoms, as Assessed by the General Health Questionnaire, on Cause of Death in Older Persons Living in a Rural Community of Japan
Authors: Yasuda Nobufumi , Mino Yoshio , Koda Shigeki , Ohara Hiroshi
Published: July 2002

OBJECTIVES: To examine the influence of distinct clusters of psychiatric symptoms on subsequent cause‐specific mortality in older persons living in the community.

DESIGN: A prospective cohort study over 7.5 years.

SETTING: Otsuki‐town, Kochi prefecture, Japan.

PARTICIPANTS: Nine hundred eighty community‐dwelling persons, aged 65 to 84 in 1991.

MEASUREMENTS: Psychiatric symptoms at baseline were measured using the 30‐item version of the General Health Questionnaire (GHQ‐30). A factor analysis was performed on the responses of all 980 subjects. The relationships between subscale scores on the identified factors and causes of deaths occurring over 7.5 years in 817 respondents with no physical disability at baseline were assessed using a proportional hazards model adjusted for age, gender, chronic conditions under treatment, regular physical activity, and availability of close or casual neighbors.

RESULTS: The factor analysis identified three clusters of psychiatric symptoms: depression, apathy/anergia, and anxiety. In the proportional hazards model, which included three GHQ subscales depicting these factors simultaneously, the depression subscale was associated with increased mortality from cerebrovascular disease (multivariate adjusted hazard ratio per unit increase in the standard score on the depression subscale = 2.04, 95% confidence interval (CI) = 1.17–3.55), and the apathy/anergia subscale was associated with increased mortality from noncancer and noncardiovascular causes (multivariate adjusted hazard ratio per unit increase in the standard score on the apathy/anergia subscale = 1.71, 95% CI = 1.25–2.34). The anxiety subscale was not associated with any cause of death.

CONCLUSION: Depressive symptoms and symptoms indicating apathy/anergia have differential influences on subsequent causes of death in older persons living in the community. Identification of specific psychiatric symptom clusters may contribute to the prevention of deaths from specific causes in older populations.
Severe Dementia and Adverse Outcomes of Nursing Home‐Acquired Pneumonia: Evidence for Mediation by Functional and Pathophysiological Decline
Authors: Van Der Steen Jenny T. , Ooms Marcel E. , Mehr David R. , Van Der Wal Gerrit , Ribbe Miel W.
Published: July 2002

OBJECTIVES:

To assess whether the severity of dementia is related to unfavorable outcomes of nursing home‐acquired pneumonia and how this relationship is mediated.

DESIGN:

Prospective cohort study.

SETTING:

Psychogeriatric wards of 61 nursing homes in the Netherlands.

MEASUREMENTS:

Dementia severity and the possible mediators swallowing disturbance, aspiration, insufficient food intake, weight loss, and dehydration were measured and related to the following outcomes: death (rate), cure rate, and increase in discomfort at the onset of pneumonia.

PARTICIPANTS:

Demented patients (n = 374) treated with antibiotics for pneumonia.

RESULTS:

Dementia severity was independently related to death rate within the first week after pneumonia (hazard rate ratio = 3.0 for the most severely demented quartile versus the least demented quartile, 95% confidence interval (CI) = 1.1–8.3) and to 3‐month mortality (odds ratio (OR) = 2.5, 95% CI = 1.1–5.4). The latter relation was in part mediated by aspiration and weight loss (OR dementia severity adjusted for these mediators declined from 2.5 to 1.9, 95% CI = 0.8–4.3). Dementia severity was not related to cure rate within 2 weeks nor to an increase in discomfort after 3 days compared with before the pneumonia.

CONCLUSION:

The functional and pathophysiological consequences of progressive dementia account in part for increased 3‐month mortality after pneumonia. Mid‐term mortality is expected to be high only in the most severely demented patients and in less severely demented patients who aspirated or who lost weight. Implications for end‐of‐life decision‐making and effectiveness of preventive and curative interventions are discussed. J Am Geriatr Soc 50:439–448, 2002.
Serum Albumin Concentration and Clinical Assessments of Nutritional Status in Hospitalized Older People: Different Sides of Different Coins?
Authors: Covinsky Kenneth E. , Covinsky Michael H. , Palmer Robert M. , Sehgal Ashwini R.
Published: July 2002

OBJECTIVES:

Malnutrition is common in hospitalized older people, and some have advocated routine nutritional screening. Serum albumin and clinically based measures such as the Subjective Global Assessment (SGA) are two potential methods of assessing nutritional status in hospitalized older people. Although both measures are strongly associated with prognosis, it is not clear whether they measure similar or different clinical constructs. Our goal was to assess the degree of clinical concordance between these measures.

DESIGN:

Cross‐sectional study.

SETTING:

The inpatient medical service of a university teaching hospital.

PARTICIPANTS:

Three hundred eleven older (aged ≥70) patients.

MEASUREMENTS:

We independently measured serum albumin and performed the SGA on 311 older medical patients (aged ≥70) shortly after hospital admission. The SGA classified patients as well nourished, moderately malnourished (generally 5% weight loss with mild examination findings), or severely malnourished (generally>10% weight loss with marked findings) based on findings from a directed history and examination. We compared the distribution of clinical rating in patients with differing albumin levels and examined diagnostic test characteristics of albumin as a predictor of malnutrition as diagnosed on clinical examination.

RESULTS:

The mean age of subjects was 79.9; 64% were women, 42% were African American. Discordance between albumin and the SGA was common. For example, 38% of patients with albumin levels of 4.0 g/dL or higher were at least moderately malnourished on the SGA, whereas 28% of patients with albumin levels lower than 3.0 g/dL were rated as well nourished. No choice of albumin level was associated with simultaneously acceptable sensitivity and specificity as a predictor of SGA ratings. The area under the receiver operating characteristic curve for albumin level as a predictor of SGA rating was 0.58, suggesting that the ability of either measure to predict the other measure is only marginally better than chance.

CONCLUSIONS:

Albumin levels and clinical assessments, two possible measures of nutritional status in hospitalized older people, are often discordant. To some extent, this reflects limitations in both measures as markers of nutritional status. However, it also demonstrates that, in this population, albumin and clinical assessments of nutritional status reflect fundamentally different clinical processes. J Am Geriatr Soc 50:631–637, 2002.
Isolation and Characterisation of Pitef1 Encoding the Translation Elongation Factor EF‐1α of the Root Endophyte Piriformospora indica
Authors: Bütehorn B. , Rhody D. , Franken P.
Published: July 2002

Abstract: Piriformospora indica (Hymenomycetes, Basidiomycota) is a newly described endophyte which interacts with the roots of a great variety of plants, showing a positive effect on biomass production. In order to obtain a tool for molecular studies on P. indica, Pitef1 encoding the translation elongation factor EF‐1α in P. indica has been cloned and analysed. Comparison of the genomic and cDNA sequence revealed the presence of seven introns in the coding part of the gene and at least one in the 5′untranslated region. Pitef1 is only present as one copy in the genome, as determined by Southern blot analysis. Interaction with roots of Zea mays in a time course experiment was analysed in relation to hyphal development and RNA accumulation, showing high expression of this gene. The Pitef1 promoter should therefore be a good tool to construct vectors for the development of a transformation system for P. indica. The gene Pitef1 might, in addition, be useful for estimating the amount of active mycelium during in planta development and for the calibration of RNA accumulation analyses of differentially expressed fungal genes.
Impurity-induced layer disordering of In0.53Ga0.47As/In0.52Al0.48As heterostructures
Authors: Baird R. J. , Potter T. J. , Lai R. , Kothiyal G. P. , Bhattacharya P. K.
Published: July 2002

Impurity-induced layer disordering of In0.53 Ga0.47 As/In0.52 Al0.48 As heterostructures grown by molecular beam epitaxy has been observed by Auger electron spectroscopy depth profiling. We find that Si+ ion implantation to concentrations greater than 2×1019 atoms cm−3 enhances the intermixing of Ga and Al in these heterostructures at an annealing temperature of 1075 K. However, the relatively high temperature which is required to activate the interdiffusion of Ga and Al in the region of high Si concentration is sufficient to induce In diffusion in regions of lower Si concentration. Zinc diffusion is found to completely intermix the Ga and Al in the heterolayers at temperatures as low as 825 K, which is below the temperature at which significant In diffusion occurs in undoped regions.
Cyclotron resonance measurements of electron effective mass in strained AlGaAs/InGaAs/GaAs pseudomorphic structures
Authors: Liu C. T. , Lin S. Y. , Tsui D. C. , Lee H. , Ackley D.
Published: July 2002

Electron effective mass in the InxGa1−xAs conduction channel of strained AlGaAs/InGaAs/GaAs pseudomorphic structures is measured using far-infrared cyclotron resonance techniques at 4.2 K. The measured cyclotron mass is heavier than the conduction-band-edge mass in bulk InxGa1−xAs. This result is explained by the large two-dimensional electron density realized in the structure, and the lattice strain that exists in the InxGa1−xAs layer.
Selective laser pyrolysis of metalorganics as a method of forming patterned thin-film superconductors
Authors: Mantese J. V. , Catalan A. B. , Mance A. M. , Hamdi A. H. , Micheli A. L. , Sell J. A. , Meyer M. S.
Published: July 2002

Fine line superconductors of Y-Ba-Cu-O were formed on 〈100〉 SrTiO3 by the completely nonvacuum techniques of metalorganic deposition and selective laser pyrolysis. Lines 35 μm wide were written, using an Ar laser, in metal neodecanoates prior to pyrolysis. Regions of the metalorganics not exposed to laser pyrolysis were developed away using a xylene wash. Complete pyrolysis of the metal neodecanoates and rapid thermal annealing produced lines having superconducting onsets above 90 K and zero resistance at 69 K.
Growth of superconducting Bi2Sr2CaCu2O8+x films on alumina, silicon, and fused quartz
Authors: Hung L. S. , Agostinelli J. A. , Paz-Pujalt G. R. , Mir J. M.
Published: July 2002

Interactions between superconducting Bi2Sr2CaCu2O8+x films and substrates were investigated by ion backscattering, x-ray diffraction, and four-point probe resistivity measurements. During annealing at temperatures above- 800 °C, Bi2Sr2CaCu2 oxide films rapidly reacted with alumina, Si, Si covered with SiO2, and quartz, resulting in catastrophic failure. Zr-based barrier layers were used to minimize film-substrate interactions. When a single ZrO2 layer was interposed between the superconducting oxide film and the underlying substrate, the Bi2Sr2CaCu2 oxide films showed a large-grained polycrystalline microstructure and exhibited the orthorhombic structure. Films on sapphire showed transitions to the superconducting state beginning near 100 K with zero resistance achieved at 70 K. Films on Si and thermally grown SiO2 showed a similar drop in resistance around 95 K, whereas the transition was broad and the zero resistance state was not reached. For films on quartz, high thermal stress caused cracking of the superconducting oxide film. Best results were achieved using a barrier composed of a Zr-Si-O mixed layer underneath ZrO2. In this case, the films grown on Si and quartz were uniform and showed the onset to superconductivity at 95 K, attaining zero resistance at 70 K.
Neutral E′ centers in microwave downstream plasma-enhanced chemical-vapor-deposited silicon dioxide
Authors: Warren W. L. , Lenahan P. M. , Robinson B. , Stathis J. H.
Published: July 2002

We have utilized electron spin resonance and capacitance versus voltage measurements to study E′ centers generated by the photoemission of electrons into silicon dioxide films prepared by plasma-enhanced chemical vapor deposition (PECVD). The oxides were deposited on crystalline silicon substrates downstream from a microwave discharge. The E′ center is an unpaired electron in a nonbonding sp3 hybrid orbital on a silicon bonded to three oxygen atoms. In conventional thermal SiO2 films on silicon, E′ centers are the dominant deep hole traps. However, the E′ centers generated in the PECVD oxides are generated by electron injection into the oxide and are almost certainly electrically neutral. Our results unequivocally demonstrate fundamental differences in the point defects in thermally grown SiO2 on silicon and PECVD oxides.
Synthesis of heteroepitaxial Si/CoSi2/Si structures by Co implantation into Si
Authors: van Ommen A. H. , Ottenheim J. J. M. , Theunissen A. M. L. , Mouwen A. G.
Published: July 2002

Heteroepitaxial Si/CoSi2/Si structures have been formed in both (100) and (111)Si by high-dose implantation of Co. During the implantation, Co is incorporated in the Si lattice as CoSi2 with the same orientation as the Si substrate. Upon annealing the implanted Co distribution is transformed into an epitaxial Si/CoSi2/Si layered structure. Sputtering of Si during the implantation of Co was studied using an implanted Si3N4 marker layer. The Si/CoSi2/Si/Si3N4/Si multilayer structure that is formed in this way demonstrates the potential of the ion beam synthesis technique.
Preparation and patterning of YBaCuO thin films obtained by sequential deposition of CuOx/Y2O3/BaF2
Authors: Hess Nir , Tessler Leandro R. , Dai Uri , Deutscher Guy
Published: July 2002

Superconducting thin films of YBaCuO were prepared by stacking layers of CuOx , Y2O3, and BaF2 onto substrates held at room temperature. The CuOx layer was obtained by oxidizing in air a previously deposited metallic Cu film. After deposition of the subsequent layers, the films were annealed at 880 °C in flowing oxygen. Samples 1 μm thick on sapphire showed an onset at Tonsetc =85 K and zero resistance at T0c =70 K; on yttria-stabilized zirconia (YSZ), Tonsetc =90 K and T0c =80 K. Patterned films are easily obtained by applying conventional photolithographic methods to the Cu film.
Observation of the second energy level of the EL2 defect in GaAs by the infrared absorption technique
Authors: Manasreh M. O. , Mitchel W. C. , Fischer D. W.
Published: July 2002

The second energy level of the EL2 defect (EL2+/++ ) is observed by using the infrared absorption technique and monochromatic light irradiation in undoped and lightly alloyed unannealed bulk GaAs. The EL2+/++ spectrum exhibits a complex structure and it does not exist in annealed samples. The EL2+/++ →EL20/+ and EL20/+ →EL2+/++ transitions were obtained by illuminating the samples with 0.7≤hν≤0.95 eV and 1.3≤hν≤1.5 eV, respectively. The transformation EL2+/++ ↔EL20/+ can be achieved in less than 10 s and can be repeatedly switched back and forth between the two states.
Mechanism of subpicosecond electrical pulse generation by asymmetric excitation
Authors: Sano E. , Shibata T.
Published: July 2002

Using full-wave analysis, the motion of the electric field in a coplanar transmission line (two parallel lines) fabricated on nondamaged silicon-on-sapphire when a part of the gap between the two lines is excited by ultrashort optical pulse is demonstrated and the mechanism for the electrical pulse generation is discussed.
Annealing in a PbO atmosphere for high T
c superconductivity of Bi-Sr-Ca-Cu-O films
Authors: Takano Akihiro , Yoshimoto Mamoru , Koinuma Hideomi , Nagata Hirotoshi
Published: July 2002

(Bi-Sr-O)/(Ca-Cu-O) multilayered films were prepared by a plasma-controlled sputtering method and annealed under various conditions to induce the superconductivity in the films. The annealing in the presence of PbO vapor at 860 °C was effective to convert the unleaded insulating multilayered films to superconductors with onset and zero-resistivity temperatures of 113 and 103 K, respectively. Auger electron spectroscopy verified the incorporation of Pb in the films.
Antiphase-domain-free GaAs grown on pseudomorphic Si (100) surfaces by molecular beam epitaxy
Authors: Adomi K. , Strite S. , Morkoç H.
Published: July 2002

GaAs has been grown on pseudomorphic Si (100) surfaces and (100) surfaces misoriented 4° toward [011] and [001] in order to study the quality of the GaAs on Si interface in the absence of misfit dislocations. We obtain completely two-dimensional single-domain GaAs epitaxy after only 80 Å of deposition as observed by in situ high-energy electron diffraction. Transmission electron microscopy verifies that the GaAs grown on pseudomorphic Si is free of antiphase domains and other notable defects.
Blue and green cw upconversion lasing in Er:YLiF4
Authors: Hebert T. , Wannemacher R. , Lenth W. , Macfarlane R. M.
Published: July 2002

Two new laser transitions are reported for the Er3+ ion in YLiF4: in the blue at 469.7 nm and in the green at 560.6 nm. These are pumped with red and near-infrared laser radiation using nonlinear excitation processes in which more than one upconversion step occurs, yet the threshold pump powers are as low as 10 mW. Single longitudinal mode cw operation was observed at temperatures below 40 K. This is the first report of a blue laser using the Er3+ ion, and the first report of an infrared-pumped blue laser.
Real-time hologram construction and reconstruction using a high-resolution spatial light modulator
Authors: Fukushima Seiji , Kurokawa Takashi , Ohno Masayoshi
Published: July 2002

Real-time construction and reconstruction of Fresnel holograms is demonstrated using an optically-addressable ferroelectric liquid-crystal spatial light modulator with a resolution up to 175 line pairs/mm. A bright holographic image is read out due to the optical separation between the write and read sides by a dielectric mirror.
Microstructure of erbium-implanted Si
Authors: Eaglesham D. J. , Michel J. , Fitzgerald E. A. , Jacobson D. C. , Poate J. M. , Benton J. L. , Polman A. , Xie Y.-H. , Kimerling L. C.
Published: July 2002

A study is presented of the relation between microstructure and 1.54 μm photoluminescence (PL) in high-energy ion-implantated Er in Si as a function of implant dose, energy, and temperature and subsequent anneal. Transmission electron microscopy (TEM) of material implanted at 500 keV and ≳100 °C and annealed at 900 °C to activate the Er PL suggests the solubility of Er in Si to be ≊1.3±0.4× 1018 cm−3 at 900 °C. Precipitates take the form of platelets (probably ErSi2) ≊100–300 Å in diameter and ≊10 Å thick. The 1.54 μm PL saturates at ≊5× 1017 cm−3, before the apparent solubility limit. Layers in which the Si is fully amorphized and subsequently regrown by solid phase epitaxy during an anneal show increased Er incorporation in the crystalline Si but segregation at the amorphous-crystalline interface. In buried amorphous layers regrown from top and bottom, segregation leads to a line of high Er concentration near the center of the layer: Regrowth from a single interface leads to a segregation pileup of Er at the interface until the precipitation threshhold is reached.
Effect of the dislocation density on minority-carrier lifetime in molecular beam epitaxial HgCdTe
Authors: Shin S. H. , Arias J. M. , Zandian M. , Pasko J. G. , DeWames R. E.
Published: July 2002

The photoconductive minority-carrier lifetime has been measured as a function of temperature and etch-pit density in n-type HgCdTe grown by molecular beam epitaxy with a composition range x=0.22–0.23 to determine the limiting recombination mechanisms, particularly those related to dislocation density. In the extrinsic region at temperatures T<77 K, the minority-carrier lifetime is limited by Shockley–Read recombination. Strong correlation between minority-carrier lifetime and dislocation density is observed.
Growth of highly strained InAs/InP heterostructures by metalorganic chemical vapor deposition using tertiarybutylarsine
Authors: Tran C. A. , Masut R. A. , Cova P. , Brebner J. L.
Published: July 2002

InAs/InP highly strained quantum well, multiquantum well, and superlattice structures with abrupt interfaces have been grown using tertiarybutylarsine. The diffraction of x-ray wave fields in these heterostructures has been used to examine the structural properties of quantum wells with a thickness of a few monolayers. The high resolution five-crystal x-ray diffraction patterns of single and multiple quantum wells exhibit a modulation of the interferences fringes which strongly depends on the structural parameters of these layers. A computer simulation of the x-ray experimental Bragg diffraction pattern using dynamical theory shows good agreement between the measured and simulated spectra.
Hole confinement effects on multiple Si δ doping in GaAs
Authors: Shibli S. M. , Scolfaro L. M. R. , Leite J. R. , Mendonça C. A. C. , Plentz F. , Meneses E. A.
Published: July 2002

The observation of quantum-confined optical transitions in multiple δ doping in GaAs, grown by molecular beam epitaxy, is reported. Doping efficiency and carrier confinement are investigated by Hall and photoluminescence measurements. Hall measurement results for multiple δ-doped samples show a dramatic enhancement of carrier concentrations compared to the uniform doping case. From photoluminescence spectra we observed that the cutoff energy is significantly affected by the spacing between the dopant sheets. The strong localization of confined photoexcited holes in the spacing layers of these structures plays a fundamental role in the interpretation of the optical data.
Continuous-wave photoluminescence excitation spectra of multiple narrow-stepped quantum wells: Evidence for saturation of interface traps
Authors: Ding Y. J. , Guo C. L. , Li S. , Khurgin J. B. , Law K.-K. , Merz J. L.
Published: July 2002

Continuous-wave photoluminescence excitation spectra of multiple narrow-stepped quantum wells at room temperature have been measured for the first time. It has been observed that photoluminescence intensity increases stronger than proportionally to the square of the laser intensity. This phenomenon can be attributed to the radiative recombination between free carriers in parallel with the dominant nonradiative recombination on the saturable interface traps. Intensity-dependent trapping efficiency and ratio between electron and hole nonradiative decay times, and the ratio between trapping and nonradiative recombination rates have been derived from the experiment.
Epitaxial growth of BaTiO3 thin films by organometallic chemical vapor deposition
Authors: Wills L. A. , Wessels B. W. , Richeson D. S. , Marks T. J.
Published: July 2002

Epitaxial BaTiO3 thin films were grown in situ on (100) LaAlO3 by low-pressure organometallic chemical vapor deposition using the precursors Ba (hexafluoroacetylacetonate)2 (tetraglyme) and titanium tetraisopropoxide. The phase composition and epitaxial quality were sensitive to the reactant partial pressures and growth temperature. Deposition at 800 °C yielded [100]-oriented BaTiO3 films. In-plane epitaxy was confirmed for the BaTiO3 films by x-ray diffraction.
High-power 630–640 nm GaInP/GaAlInP laser diodes
Authors: Ou S. S. , Yang J. J. , Fu R. J. , Hwang C. J.
Published: July 2002

High-power visible laser diodes operating at 630–640 nm have been demonstrated. The devices have a GaInP/GaAlInP single quantum well, graded-index separate confinement heterojunction. For 100 μm broad stripe uncoated lasers, threshold current densities of 1.06 KA/cm2 and pulsed output powers as high as 1.5 W/facet (total 3 W) at room temperature were achieved by optimizing the device cavity length. By coating rear facets with high-reflectivity coatings, threshold current densities were reduced to 750 A/cm2, and output powers of 1.95 W were obtained. Unusual differential quantum efficiency versus cavity length characteristics were observed and are attributed to carriers spillover from the spacer/waveguide regions into the cladding layers.
Ordering induced splitting of light-hole and heavy-hole bands in GaInP grown by organometallic vapor-phase epitaxy
Authors: ’t Hooft G. W. , Riviere C. J. B. , Krijn M. P. C. M. , Liedenbaum C. T. H. F. , Valster A.
Published: July 2002

The origin of the polarization of the photoluminescence in ordered InGaP is investigated. The ordering induced lowering of the cubic crystal symmetry is caused by a superlattice and/or strain effects in two of the four 〈111〉 crystal directions resulting in a splitting of the heavy-hole and light-hole valence bands. Using simple arguments from k⋅p theory, the difference in photon energy as well as the intensity ratio of the luminescence in the two polarization directions along the cleavage facets is explained as a function of temperature.
Auger recombination in modulated photoreflectance characterization of silicon wafers
Authors: Forget B. C. , Fournier D. , Gusev V. E.
Published: July 2002

We have used photoreflectance signal as a function of modulation frequency to characterize electronic transport properties in silicon wafers. Due to the high densities of free carriers generated in such an experiment, we propose a theoretical model which takes into account Auger recombination. This nonlinear recombination process is usually neglected in the interpretation of photothermal phenomena. Our experimental results, in good accordance with theoretical prediction, show that this nonlinear recombination process not only cannot be neglected, but can be the dominant recombination process for certain experimental configurations, particularly for modulation frequencies up to 100 kHz and pump power ranging from 1.5 kW/cm2 to 9 kW/cm2.
Time-resolved measurements of carrier recombination in experimental semiconductor-doped glasses: Confirmation of the role of Auger recombination
Authors: Ghanassi M. , Schanne-Klein M. C. , Hache F. , Ekimov A. I. , Ricard D. , Flytzanis C.
Published: July 2002

Using three different time-resolved techniques: degenerate four wave mixing, nonlinear absorption, and luminescence, we show that, for our CdSxSe1−x-doped glasses, under high excitation conditions, Auger recombination is the dominant recombination process. This explains the broad range of luminescence lifetimes previously reported. After photodarkening, we also observe a reduction in the nonradiative lifetime.
Enhancement of photoluminescence intensity of GaAs with cubic GaS chemical vapor deposited using a structurally designed single-source precursor
Authors: MacInnes Andrew N. , Power Michael B. , Barron Andrew R. , Jenkins Phillip P. , Hepp Aloysius F.
Published: July 2002

A two order-of-magnitude enhancement of photoluminescence intensity relative to untreated GaAs has been observed for GaAs surfaces coated with chemical vapor-deposited GaS. The increase in photoluminescence intensity can be viewed as an effective reduction in surface recombination velocity and/or band bending. The gallium cluster [(t-Bu)GaS]4 was used as a single-source precursor for the deposition of GaS thin films. The cubane core of the structurally characterized precursor is retained in the deposited film producing a cubic phase. Furthermore, a near-epitaxial growth is observed for the GaS passivating layer. Films were characterized by transmission electron microscopy, x-ray powder diffraction, and x-ray photoelectron and Rutherford backscattering spectroscopies.
Aluminum nitride/silicon carbide multilayer heterostructure produced by plasma-assisted, gas-source molecular beam epitaxy
Authors: Rowland L. B. , Kern R. S. , Tanaka S. , Davis Robert F.
Published: July 2002

Pseudomorphic structures containing β(3C)-SiC and 2H-AlN have been grown on vicinal α(6H)-SiC(0001) at 1050 °C by plasma-assisted, gas-source molecular beam epitaxy. Reflection-high energy electron diffraction and cross-sectional high-resolution transmission electron microscopy showed all layers to be monocrystalline. The AlN layers were uniform in thickness. Defects in these layers initiated at steps on the 6H-SiC film. The 3C-SiC layers contained a high density of stacking faults and microtwins caused primarily by the interfacial stresses generated by the mismatch in lattice parameters between AlN and β-SiC coupled with the very low stacking fault energy of SiC. This is the first report of the deposition of single crystal SiC/AlN/SiC thin film heterostructures on any substrate as well as the first report of the epitaxial growth of single crystal layers of binary materials with three different crystal structures.
Potential dependent etching of Si(111) surfaces in NH4F solutions studied by scanning tunneling microscopy
Authors: Houbertz R. , Memmert U. , Behm R. J.
Published: July 2002

The initial phases of anodic Si(111) etching in 40% NH4F solution at potentials between −0.97 VAg/AgCl (open circuit potential) and +0.5 VAg/AgCl were investigated by scanning tunneling microscopy. Pores of several hundred angström width and 10–30 Å depth, increasing with more anodic potentials, signal the beginning formation of a porous surface. The observation of atomic steps proves the crystallinity of the new surface and the absence of an amorphous deposit layer under these conditions.
Photoconductive sampling probe with 2.3-ps temporal resolution and 4-μV sensitivity
Authors: Kim Joungho , Williamson Steven , Nees John , Wakana Shin-ichi , Whitaker John
Published: July 2002

We report on a novel probe technology which is applied to the measurement of high-speed guided electrical signals. The probe consists of a high-impedance gate fabricated using an interdigitated electrode structure on semi-insulating, low-temperature-grown GaAs, and its operation is based on the optoelectronic technique of photoconductive sampling. The probe has a dynamic range of ≳106, permitting the linear measurement of short-duration signals with amplitudes ranging from microvolts up to several volts. Its resistance is 100 MΩ, and its capacitance is less than 0.1 fF, making this probe attractive for noninvasive, external circuit testing of ultrahigh-speed devices and circuits.
Absolute magnetic penetration depth of thin-film niobium measured by fluxoid quantization
Authors: Cunningham C. E. , Park G. S. , Cabrera B. , Huber M. E.
Published: July 2002

The absolute magnetic penetration depth of a superconducting niobium film is measured using fluxoid quantization. Laser pulses drive part of a thin, planar niobium loop normal, changing its quantum fluxoid state. We determine the total inductance of the loop by measuring the coupling of the fluxoid to a superconducting quantum interference device at various loop temperatures. We fit the temperature dependence of the inductance data to the Bardeen–Cooper–Schrieffer (BCS) theory to determine the magnetic and kinetic inductances. The kinetic inductance is directly related to the penetration depth through the geometry of the loop, and the measured penetration depth agrees well with the BCS theory.
Power modulation technique for noncontact high-temperature calorimetry
Authors: Wunderlich R. K. , Fecht H.-J. , Willnecker R.
Published: July 2002

A new noncontact calorimetric method has been developed based on inductive heating of a metallic spherical bulk sample by a power-modulated radio-frequency field under ultrahigh vacuum conditions. From the pyrometrically measured temperature response the specimen’s external (due to radiative heat loss) and internal relaxation time (due to thermal conductivity) are found to differ by more than two orders of magnitude allowing the specific heat as well as thermal conductivity of the sample to be determined as a function of temperature. The agreement between the measured and predicted temperature response for solid Nb demonstrates the applicability and accuracy of the method which is particularly useful for metastable or chemically reactive samples at high temperature.
Repetitive excitation of charge oscillations in semiconductor heterostructures
Authors: Brener I. , Planken P. C. M. , Nuss M. C. , Pfeiffer L. , Leaird D. E. , Weiner A. M.
Published: July 2002

We create forced excitonic charge oscillations in semiconductor heterostructures by excitation with periodic optical pulse sequences. The far-infrared radiation that accompanies the charge oscillations shows temporal interference patterns for pulse sequences with different optical phase profiles, providing evidence for phase induced population transfers between exciton levels in a semiconductor.
Layer-by-layer growth of GaAs studied by glancing angle scattering of fast ions
Authors: Fujii Yoshikazu , Narumi Kazumasa , Kimura Kenji , Mannami Michi-hiko , Hashimoto Toyoyuki , Ogawa Kiyoshi , Ohtani Fumihiko , Yoshida Tamio , Asari Masatoshi
Published: July 2002

Angular distribution of scattered ions at glancing angle incidence of 3 keV He ions on a (001) surface of GaAs is studied during its molecular beam epitaxial growth. We report observation of intensity oscillations of the scattered ions from the growing surface. The period of the oscillations corresponds to the growth time of one monomolecular layer. The oscillations of the intensity is due to the oscillatory change in surface step density during layer-by-layer growth of the surface. This observation is in agreement with the intensity oscillations of reflection high-energy electron diffraction (RHEED) from epitaxially growing surface of GaAs.
Effect of electron temperature on negative hydrogen ion production in a low-pressure Ar discharge plasma with methane
Authors: Iizuka S. , Koizumi T. , Takada T. , Sato N.
Published: July 2002

Production of negative hydrogen ions (H−) is continuously controlled in a low-pressure Ar discharge plasma with methane by using a pin-hollow cathode. The electron temperature is changed by varying the pin length. An enhanced production of negative hydrogen ions is observed with a decrease in the electron temperature.
High-speed optical sampling measurement of electrical wave form using a scanning tunneling microscope
Authors: Takeuchi Koichiro , Kasahara Yukio
Published: July 2002

The optical sampling measurement of a high-speed electrical wave form using a scanning tunneling microscope (STM) is demonstrated. An optical pulse train from a laser diode (LD) is used to turn on and off a photoconductive switch on a STM probe to measure a signal from a Schottky barrier diode (SBD) in a sampling procedure. A time resolution less than 300 ps has been achieved. This novel method has the potential to create a breakthrough in ultra-high-speed wave form measurement through this unique combination of optical sampling and STM technology.
Silicon-induced local interface dipole in Al/GaAs(001) Schottky diodes
Authors: Cantile M. , Sorba L. , Yildirim S. , Faraci P. , Biasiol G. , Franciosi A. , Miller T. J. , Nathan M. I.
Published: July 2002

Al/Si/GaAs(001) diode structures grown by molecular beam epitaxy were examined as a function of the thickness of the Si interface layer and the intensity of the As or Al flux employed during Si deposition. We found that Schottky barriers as low as 0.3–0.4 eV (in the presence of a sufficiently high As flux) or as high as 1.0–1.1 eV (in the presence of a sufficiently high Al flux) can be established on n-type GaAs at Si coverages in the submonolayer to monolayer range. We therefore associate the tunability of the barrier height with a Si-induced local interface dipole.
Measurement of the velocity of current filaments in optically triggered, high gain GaAs switches
Authors: Loubriel G. M. , Zutavern F. J. , Hjalmarson H. P. , Gallegos R. R. , Helgeson W. D. , O’Malley M. W.
Published: July 2002

Pictures are presented of the time evolution of current filaments during optically triggered, high gain switching in GaAs. Two filaments are triggered with two laser diode arrays and the time delay between them is varied. When the filament that is triggered first crosses the switch the voltage drops and the other filament ceases to grow. By varying the delay between the lasers, the tip velocity is measured to be 2±1×109 cm/s, 100 times larger than the peak drift velocity of carriers in GaAs. This observation supports switching models that rely on carrier generation at the tip of the filament.
Photoluminescence from nanocrystallites embedded in hydrogenated amorphous silicon films prepared by plasma enhanced chemical vapor deposition
Authors: Liu Xiang-na , Wu Xiao-wei , Bao Xi-mao , He Yu-liang
Published: July 2002

We report in this letter the observation of visible photoluminescence (PL) at room temperature from nanocrystallites embedded in hydrogenated amorphous silicon films, which are prepared in a plasma enhanced chemical vapor deposition system by using strong hydrogen-diluted silane as the reactant gas source, without any post-processing. The PL is attributed to the radiative recombination process of carriers in the nanocrystallites, and the quantum size effect is responsible for the emission above the band gap of bulk crystal Si. The critical deposition parameters of this type of film are identified.
Influence of inductance induced noise in an YBa2Cu3O7 dc-SQUID at high operation temperatures
Authors: Nilsson P. Å. , Claeson T. , Hansen J. B. , Kühle A.
Published: July 2002

The voltage modulation depth of a high Tc dc-SQUID was measured at temperatures close to Tc and compared to a model by Enpuku et al. where the flux noise from the SQUID inductance is taken into account. The device was an YBa2Cu3O7 dc-SQUID made on a bicrystal substrate of SrTiO3. The design was of the Ketchen square-washer type with an inductance of 67 pH. Measurements were made in a temperature interval from 75 to 87 K, where the voltage modulation depth changed from 4.5 to 1.4 μV in close agreement with the model.
Infrared to visible energy upconversion in Er3+-doped oxide glass
Authors: Reddy B. R. , Venkateswarlu P.
Published: July 2002

Intense green emission was observed at room temperature from the 4S3/2 level of Er3+ doped in a multielement oxide glass when its 4I9/2 level was resonantly excited with a near-infrared laser beam of 797 nm. Our studies indicate that energy transfer and excited state absorption are responsible for the generation of upconverted green emission from the sample. The upconversion efficiency is found to be 0.14%.
Resonant Raman scattering and spectral ellipsometry on InAs/GaSb superlattices with different interfaces
Authors: Behr D. , Wagner J. , Schmitz J. , Herres N. , Ralston J. D. , Koidl P. , Ramsteiner M. , Schrottke L. , Jungk G.
Published: July 2002

We have used Raman spectroscopy and spectral ellipsometry to investigate InAs/GaSb short-period superlattices (SLs), grown by molecular-beam epitaxy, with either InSb- or GaAs-like interfaces. Room-temperature ellipsometric measurements show spectral features in the dielectric function due to the E1 and E1+Δ1 interband transitions of GaSb and InAs. For SLs with small InAs layer thicknesses (4 ML InAs/10 ML GaSb) the critical point energies are found to depend on the type of interfacial bonding, with an energy shift of up to 50 meV observed between SLs with GaAs- and InSb-like interfaces. Resonant Raman measurements show a pronounced enhancement in scattering efficiency for the superlattice phonons and, in particular, for the interface modes for incident photon energies matching the critical point energies of the SL.
Interpretation of the luminescence quenching in chemically etched porous silicon by the desorption of SiH3 species
Authors: Hadj Zoubir N. , Vergnat M. , Delatour T. , Burneau A. , de Donato Ph.
Published: July 2002

The effect of thermal annealing on chemically etched porous silicon was studied by combined photoluminescence, infrared spectrometry, and thermal-desorption spectrometry experiments. The results show that the release of SiH3 and SiF3 entities is a first step in the photoluminescence degradation in porous silicon. These entities desorb before molecular hydrogen.