bluuebunny/crossref_metadata_2025 huggingface dataset:
Methicillin-resistant Staphylococcus aureus infection in vascular patients
Authors: Nasim A , Thompson M M , Naylor A R , Bell P R F , London N J M
Published: July 2002

Background

The increasing prevalence of methicillin-resistant Staphylococcus aureus (MRSA) is a major threat in arterial surgery and poses a considerable therapeutic challenge. The aim of this study was to assess the prevalence of MRSA infection in patients treated in the vascular unit.

Methods

A retrospective case-note review was undertaken to identify the nature of the infection and the outcome.

Results

During 1993–1998, a total of 115 patients (4 per cent of the total) were positive for MRSA. Of these, 67 were colonized and 48 were infected by MRSA. The number of MRSA infections increased yearly (1 per cent in 1994 to 5 per cent in 1998). Of the 48 patients infected by MRSA, one had wound infection following brachial embolectomy which eventually resolved. Two patients had undergone carotid endarterectomy necessitating removal of an infected Dacron patch, one of whom developed a hemiparesis. Eleven patients had undergone elective abdominal aortic aneurysm (AAA) repair (five developed pneumonia, two septicaemia, two wound infection, one a false aneurysm at the site of insertion of an endovascular stent, and one developed crossover graft infection after endovascular AAA repair and died). Five patients had undergone ruptured AAA repair (two developed pneumonia, one wound infection and two developed graft infection and died). Four patients undergoing reconstruction for aortic occlusive disease developed MRSA infection, two of whom died. Twenty-five patients with MRSA infection had undergone lower limb procedures. Five of these had graft infection leading to amputation in three and death in two. One patient developed primary arterial infection following embolectomy resulting in arterial rupture.

Conclusion

These results suggest that the prevalence of MRSA infection in vascular patients is increasing. Infection of aortic grafts appears to be uniformly fatal and lower limb graft infection is associated with a high rate of limb loss.
Prospective audit of carotid endarterectomy in Scotland
Authors: Bradbury A W , Cooper G , Dennis M , Engeset J , Holdsworth R , Pell J , Quin R , Ruckley C V , Slack R , Stonebridge P A , Welch G
Published: July 2002

Background

Carotid endarterectomy (CEA) is a proven means of stroke prevention provided it is performed in appropriate patients, soon after the index ischaemic event and with low perioperative morbidity and mortality rates. This study investigated how well these conditions are being met in Scotland.

Methods

This was a prospective study of all 485 CEAs performed in National Health Service hospitals between 1 September 1997 and 31 September 1998. Data collection was by four independent research nurses.

Results

The median patient age was 67 (interquartile range 61–73) years; 461 patients (95 per cent) were operated on for focal symptoms, 389 of whom had a stenosis of 70 per cent or more. Some 36 per cent of patients were seen by the operating surgeon within 2 weeks of referral and 35 per cent were operated on within 1 month thereafter. The perioperative combined major stroke and death rate was 3 per cent. Operations were performed by 30 surgeons in 13 hospitals. The number of CEAs per surgeon ranged from one to 49, with ten surgeons undertaking fewer than ten operations. The number of CEAs per hospital ranged from four to 99 with only three surgeons undertaking more than 50 operations. The number of CEAs per hospital ranged from four to 99 with three hospitals undertaking 50 or more operations in the study period.

Conclusion

Despite the ‘diffuse’ nature of vascular surgical services necessitated by the demography and geography of Scotland, CEA is currently being performed with a perioperative major stroke and death rate substantially lower than that reported from randomized controlled trials. However, the overall effectiveness of surgery might be improved by reducing the delays to surgery.
Natural history of atherosclerotic renal artery stenosis
Authors: Crinnon J N , Stansby G P , Wolfe J H N
Published: July 2002

Background

Atherosclerotic renal artery stenosis (ARAS) may result in hypertension and progressive renal failure culminating in dialysis. However, the natural history of ARAS is unclear, and the necessity and timing of intervention is not established. The effect of ARAS on renal function and the control of blood pressure has been investigated.

Methods

Forty-eight patients (median age 73 years) with haemodynamically significant stenosis (more than 50 per cent diameter narrowing) of one or both renal arteries were enrolled in a multicentre prospective study. The patients were divided into three groups: 50–69 per cent unilateral stenosis (n = 17; group 1), 70–99 per cent unilateral stenosis (n = 16; group 2) and bilateral disease (n = 15; group 3). Baseline measurements of serum creatinine, kidney length and diastolic blood pressure were recorded and these were repeated at every 6 months. Any intervention to revascularize the kidney was recorded. Follow-up was for at least 2 years.

Results

Results at 2 years are shown.

The mortality rate in all groups was significant. All patients in group 1 and 2 were managed conservatively whereas the majority with bilateral disease underwent angioplasty (n = 8) or surgery (n = 3). Despite intervention one patient became dialysis dependent and the creatinine level deteriorated in the remaining patients. In patients with unilateral disease there was no significant change in renal function or blood pressure. Furthermore, renal size (baseline: 102 (96–107) mm; follow-up 100 (96–108) mm) and the number of antihypertensive drugs per patient remained similar.

Conclusion

In patients with unilateral stenosis the effect on renal function and blood pressure seems to be benign and intervention is seldom indicated. Revascularization in patients with bilateral disease does not improve the dismal mortality rate and whether it reduces the requirement for haemodialysis remains unproven.
Raised levels of plasma big endothelin 1 in patients with colorectal cancer
Authors: Simpson R A , Dickinson T , Porter K E , London N J M , Hemingway D M
Published: July 2002

Background

The aim was to assess the role of plasma Big Endothelin (ET) 1 levels as a marker of disease presence and stage in colorectal adenocarcinoma.

Methods

Big ET-1 was measured in the plasma of 37 patients with colorectal cancer. Preoperative systemic plasma levels of Big ET-1 in patients with cancer were compared with levels in 20 age- and sex-matched controls. Portal plasma samples were collected at operation in addition to peripheral venous samples. Immunohistochemical staining for Big ET-1 was performed on a selection of primary tumour specimens and liver metastases.

Results

Median (range) preoperative systemic plasma levels of Big ET-1 were significantly higher in patients with cancer than in controls (1·0 (0·3–9·7) versus 0·2 (0·0–6·0) fmol/ml; P = 0·0001). Intraoperative portal plasma levels of Big ET-1 were significantly higher in patients with Dukes' ‘D’ disease than in patients with Dukes' A, B and C disease (2·1 (1·4–10·0) versus 1·2 (0·3–6·6) fmol/ml; P = 0·01). Similarly, systemic plasma levels were significantly higher in patients with Dukes' ‘D’ disease than in those with localized disease (1·9 (1·2–9·7) versus 1·2 (0·2–8·3) fmol/ml; P = 0·01). The presence of microvascular invasion in the tumour specimens was associated with a significantly raised portal plasma level of Big ET-1 (1·6 (1·5–2·1) versus 1·1 (0·8–1·3) fmol/ml; P = 0·04). Immunohistochemistry localized Big ET-1 to the cancer epithelial cells.

Conclusion

The plasma level of Big ET-1 is significantly raised in patients with colorectal cancer. Patients with liver metastases have significantly higher levels than those with localized disease.
Interleukin 10-deficient colitis: new similarities to human inflammatory bowel disease
Authors: Kennedy R J , Hoper M , Deodhar K , Erwin P J , Kirk S J , Gardiner K R
Published: July 2002

Background

Interleukin (IL) 10 is a potent anti-inflammatory cytokine. Disruption of the IL-10 gene in C57/Black6 mice results in enterocolitis in the presence of intestinal bacteria. This study investigated gut mucosal barrier function sequentially during the development of colitis in this model.

Methods

Animals were bred in specific pathogen-free conditions and transferred to conventional housing at 4 weeks. Mice were evaluated at 6, 8, 10, 12, 14 and 15 weeks of age. Barrier function was assessed by measuring intestinal permeability and antibody response to systemic endotoxaemia (antibody to the core glycolipid region of lipopolysaccharide; EndoCAb). Colons were harvested and a histological injury score (HIS) was calculated.

Results

The HIS increased progressively until 12 weeks, with an associated increase in intestinal permeability, and immunoglobulin (Ig) M and IgG EndoCAb. The HIS correlated positively with both intestinal permeability and IgM and IgG EndoCAb. Intestinal permeability showed a positive correlation with EndoCAb.

Conclusion

IL-10 knockout mice develop colitis with an associated disturbance in gut mucosal barrier function, as measured by increased permeability and endotoxaemia. The colitis found in the IL-10 knockout mouse shares these histological, physiological and biochemical features with human inflammatory bowel disease and is therefore suitable for therapeutic trials. A measure of endotoxaemia correlated directly with intestinal permeability in this model.
Detection of thyroid stimulating (TSAB)‐ and thyrotropin stimulation blocking (TSBAB) antibodies with CHO cell lines expressing different TSH‐receptor numbers
Authors: Wallaschofski H. , Paschke R.
Published: July 2002

BACKGROUND

With the aim of assaying TSH‐receptor antibodies (TSHR AB) and to distinguish different TSHR AB activities, several in vitro bioassays for the determination of TSHR AB have been developed. The bioassay using the CHO cell line expressing the hTSH‐receptor (hTSHR) is the most sensitive and least cumbersome assay system. However, up to now, the CHO cell bioassay has been performed with cells expressing much higher TSHR numbers than normal thyroid epithelial cells and with variable assay conditions.

DESIGN AND PATIENTS

To determine the optimal CHO cell bioassay conditions we therefore systematically investigated the influence of different assay parameters on the sensitivity of the CHO cell bioassay for the detection of TSHR antibodies in 197 patients with Graves' disease treated with antithyroid drugs and tried to define optimal assay conditions.

RESULTS

Compared to JP09 cells (90 000 hTSHR/cell), JP26 cells (2000 hTSHR/cell) exhibited a higher stimulation index (maximal bTSH‐stimulated cAMP production/cAMP production stimulated by pooled normal serum without bTSH) which is most likely due to the lower number of hTSHR expressed per JP26 cell compared to JP09 cells. Due to their low nonspecific stimulation by normal sera, 40 000 JP26 cells per well of a 96 well plate was found to be the optimal cell number. Moreover, a serum dilution of 1/10 yielded the highest stimulation results of bTSH and thyroid stimulating antibodies (TSAB). Applying these optimal conditions for the determination of TSH‐receptor antibodies only 10 of 34 TSBAB positive serum samples detected with JP26 cells were detectable with the JP09 cell line. In 197 patients with Graves' disease treated with antithyroid drugs 111 (56%) were TSAB positive. 34 (40%) of 86 TSAB negative patients were positive for thyrotropin stimulation blocking antibodies (TSBAB).

CONCLUSION

Improvement of CHO bioassay conditions for the determination of TSH receptor antibodies leads to increased bioassay sensitivity which is most pronounced for the detection of TSBAB. Whether this increased sensitivity for the determination of TSBAB is of prognostic significance for detecting possible sequential changes in the individual TSHR AB profile of patients with Graves' disease, remains to be determined by further follow up studies.
Possible roles of extracellular matrix and cytoskeleton in leech body wall muscles
Authors: De Eguileor M. , Grimaldi A. , Boselli A. , Tettamanti G. , Lurati S. , Valvassori R. , Lanzavecchia G.
Published: July 2002

Round circomyarian fibres of leeches are peculiar helical muscles. The fibres are characterized by a lack of junctions, being separated by a thick extracellular matrix, and by scarce end‐plates. Even so, the fibres grouped in units show the same degree of contraction. Biochemical, immunocytochemical and ultrastructural studies were performed in order: (a) to demonstrate the presence in the extracellular matrix of fibronectin, collagen type IV and laminin and in the cytoskeleton of desmin and α‐actinin; (b) to show the possible link of extracellular matrix with the scaffold of intermediate filaments; (c) to evaluate how the extracellular matrix can play a role in the transduction of a signal during contraction–relaxation–superelongation phases.
The effects of moisture on the dielectric relaxation of urethane dimethacrylate polymer and composites
Authors: Mohsen N. M. , Craig R. G. , Filisko F. E.
Published: July 2002

Dielectric characterization evaluated the influence of sorbed moisture on urethane dimethacrylate (UDMA) polymer matrix and unsilanated and silanated zirconia‐silica (ZS)‐filled UDMA composites. The moisture content (MC) of samples tested ranged from 0 to 7·32% with maximum values for UDMA, silanated and unsilanated ZS‐filled UDMA were 3·72, 6·0 and 7·32%, respectively. Dielectric spectra were measured from 0·053 to 100 kHz and from −180 to 180 ¯C. Small MC stiffened the polymers, which was shown by a shift of β‐peaks to higher temperatures, a decrease in the half width of bands and an increase in the change of activation energies. Higher MC resulted in water plasticizing the polymer by shifting the β‐peaks to lower temperatures. Maximum water sorption restricted the motion of the polymer chains and the b‐peaks shifted to higher temperatures. Further, increasing MC shifted the a‐relaxation to lower temperatures in both UDMA and composites. However, in composites with unsilanated ZS, a new relaxation occurred at high temperatures and low frequencies which was attributed to Maxwell–Wagner–Sillars (MWS) polarization. Thus, in UDMA, water occurs as fragments that form non‐freezing clusters. However, in unsilanated ZS–UDMA composites, bulk water can exist at the polymer–filler interface and form disordered structures of ice at low temperatures which can evaporate at high temperatures. Silanated ZS–UDMA composites function similarly to UDMA at low MC but are more plasticized at high temperatures.
From the Secretary's Desk
Authors: Grant Don
Published: July 2002

Since my first report, some key issues have developed and naturally a number of others have appeared on the horizon. The College Executive Committee (CEC) recently met in Dunedin to coincide with the New Zealand National Conference.
Body composition in adults with Type 1 diabetes at onset and during the first year of insulin therapy
Authors: Rosenfalck A. M. , Almdal T. , Hilsted J. , Madsbad S.
Published: July 2002

Aims To describe body composition in patients with Type 1 diabetes at diagnosis and during the first year after initiation of insulin therapy.

Research design and methods In 10 (eight male and two female) newly onset Type 1 patients, age 31.5 ± 3.2 years (27–37 years) (sd and range), body mass index (BMI) 20.8 ± 1.6 (19.2–23.4) kg/m2, body composition was estimated by means of dual‐energy X‐ray absorptiometry (DXA) whole body scanning supplemented by estimation of total body water (TBW) (isotope dilution technique with 3H2O) at diagnosis and after 1, 3, 6 and 12 months of insulin therapy.

Results During the first year after onset of diabetes body weight (BW) increased 4.3 ± 2.9 (0.1–8.3) kg (P = 0.0012) distributed as a 13.3% (1.6 kg) increase in total fat mass (FM) and 4.9% (2.5 kg) increase in lean body soft tissue mass (LBM). The self‐reported weight loss at onset was 6.3 ± 2.5 kg (1.5–10.0 kg). Compared with two reference populations the Metropolitan Life Insurance Co. and a healthy age and sex‐matched local DXA scanned group the initial body composition data demonstrated BW 6.2 kg below ideal weight and a significant reduction of the FM (25% or –0.87 sd), whereas LBM was within the expected range.

Conclusions During the first year after onset of Type 1 diabetes the mean increase in BW is 6.5% with a 13.3% increase in FM and a 4.9% increase in LBM. Self‐reported data on premorbid BW suggest an approximately 10% reduction in BW at onset of Type 1 diabetes. Compared with a healthy reference population initial body composition data demonstrate a 25% reduction of the FM, whereas only a minor and non‐significant reduction in the LBM is encountered. These data indicate that uncontrolled diabetes is rather a fat catabolic state than, as previously believed, a protein catabolic state.
A Comparison of Two Methods for Identifying Frail Medicare‐Aged Persons
Authors: Brody Kathleen K. , Johnson Richard E. , Ried L. Douglas , Carder Paula C. , Perrin Nancy
Published: July 2002

This article compares the efficacy of two screening methods to identify frail Medicare‐aged persons using self‐report questionnaire data: a clinical judgment method developed by nurse and social worker professionals in a community‐based long‐term care department and an empirical research method previously developed by the Center for Health Research using computer formulas and stepwise logistic regression coefficients. A sub‐aim was to see whether the empirical method proved robust over time by measuring aggregate utilization and mortality in frail and nonfrail cohorts, which would increase the interest of physicians, managed care organizations, and other agencies providing service to Medicare beneficiaries.
Seasonal Changes in Diel CO2 Exchange of Three Central European Moss Species: a One‐Year Field Study
Authors: Zotz G. , Rottenberger S.
Published: July 2002

Abstract: Diel courses of net CO2 gas exchange, water relation parameters and microclimatic conditions of three bryophyte species (Grimmia pulvinata, Schistidium apocarpum, Tortula ruralis) were studied in the Botanical Garden Würzburg (Franconia, Germany) over the course of one year. At the exposed study site, i.e., the upper surface of an anthropogenic limestone wall, photosynthetic active radiation (PFD) was hardly limiting for carbon gain, while plant water relations were of much greater importance: the time of metabolic activity correlated rather closely with the diurnal carbon budget. Carbon gain was highly seasonal in all three species, with the highest diel carbon budgets (NP24h) being observed in autumn, while near zero NP24h were typical for summer. Annual carbon gain differed considerably between the three species, and Tortula ruralis was by far the most productive. The estimates of annual productivity derived from gas exchange measurements in Grimmia pulvinata were compared with direct measurements of growth: the results of these different approaches yielded quite similar values.
Band-gap profiling for improving the efficiency of amorphous silicon alloy solar cells
Authors: Guha S. , Yang J. , Pawlikiewicz A. , Glatfelter T. , Ross R. , Ovshinsky S. R.
Published: July 2002

We have developed an amorphous silicon alloy based solar cell with a novel structure in which the optical gap of the intrinsic layer changes in a substantial portion of the bulk. Computer simulation studies show that for a given short circuit current, it is possible with this structure to obtain higher open circuit voltage and fill factor than in a conventional cell design. Experimental cell structures have been made and confirm the theoretical prediction. The new cell design shows a considerable improvement in efficiency. Incorporation of this structure in the bottom cell of a triple device has resulted in the achievement of 13.7% efficiency under global AM1.5 illumination.
100 GHz traveling-wave electro-optic phase modulator
Authors: Nees J. , Williamson S. , Mourou G.
Published: July 2002

Dramatic bandwidth enhancement has been achieved in a GaAs traveling-wave electro-optic phase modulator by the addition of a GaAs superstrate to suppress both velocity mismatch and electrical dispersion.
Third-harmonic generation of an alexandrite laser in β-BaB2O4
Authors: Imai Shinichi , Yamada Toshitaka , Fujimori Yasutomo , Ishikawa Ken
Published: July 2002

We report the first cascading third-harmonic generation by light from an alexandrite laser in β-BaB2O4. Ultraviolet (UV) light was generated by mixing the fundamental laser light with the second-harmonic light. The calculated effective nonlinear constant for type I mixing is nearly three times larger than that for type II. Using type I mixing we demonstrated UV light generation in the wavelength region 244–259 nm with 24% mixing efficiency at maximum.
Enhanced electron spin polarization in photoemission from thin GaAs
Authors: Maruyama T. , Prepost R. , Garwin E. L. , Sinclair C. K. , Dunham B. , Kalem S.
Published: July 2002

The polarization of photoemitted electrons from thin GaAs layers grown by molecular beam epitaxy has been measured. Polarization as high as 49% was observed for a 0.2-μm-thick GaAs sample at excitation photon wavelengths longer than 750 nm. The maximum polarization is dependent on the thickness of the GaAs layer, decreasing to about 41% for a 0.9-μm-thick GaAs sample.
Photoluminescence measurements for GaAs grown on Si(100) and Si(111) by molecular beam epitaxy
Authors: Sobiesierski Z. , Woolf D. A. , Westwood D. I. , Williams R. H.
Published: July 2002

Photoluminescence measurements have been used to characterize Si-doped GaAs layers, ranging in thickness from 1.1–8.1 μm, grown on Si(111) and misorientated Si(100) substrates by molecular beam epitaxy. 4.2 K PL spectra for GaAs/Si (100) show a strain-induced splitting between the heavy and light hole valence bands which corresponds to a biaxial tensile stress of 2.8± 0.15 kbar acting on the GaAs layer. Similar measurements for GaAs/Si(111) indicate that the GaAs layer is subject to a biaxial tensile stress of 3.9±0.15 kbar at 4.2 K. Furthermore, the intensity and line shape of luminescence features for GaAs/Si(111) for the first time indicate a crystalline quality comparable with the best GaAs/Si(100) material.
Terahertz surface impedance of thin YBa2Cu3O7 superconducting films
Authors: Nuss Martin C. , Goossen Keith W. , Mankiewich Paul M. , O’Malley Megan L.
Published: July 2002

Using coherent terahertz time-domain spectroscopy, we measure the surface impedance of 500-Å-thick unpatterned superconducting YBa2Cu3O7 films in the normal and the superconducting state. Both real and imaginary parts of the surface impedance are measured simultaneously from the amplitude and phase changes of the terahertz bandwidth pulses transmitted through the superconducting films.
Selective removal of a Si0.7Ge0.3 layer from Si(100)
Authors: Krist A. H. , Godbey D. J. , Green N. P.
Published: July 2002

The selective removal of epitaxial Si0.7Ge0.3 from {100} silicon using an aqueous based etch is reported. An etch consisting of HNO3:H2O:HF(0.5%), 40:20:5 at 22 °C, removes Si0.7Ge0.3 at a rate of 207 Å/min, and removes {100} Si at a rate of 16 Å/min. This corresponds to a selectivity of 1321 where the selectivity is defined as the ratio of the Si0.7Ge0.3 to {100} Si etch rates. This etch leaves the surface smooth and free from pitting or trenching as observed by optical microscopy. The results obtained are consistent with a germanium enhanced oxidation mechanism of the Si0.7Ge0.3 alloy during semiconductor removal.
Diffusion of vanadium in silicon
Authors: Sadoh T. , Nakashima H.
Published: July 2002

The diffusion profiles of vanadium in silicon have been investigated. In the temperature range 950–1200 °C an in-depth profile measurement by deep level transient spectroscopy was used, and in the temperature range 600–800 °C an annealing experiment which employed a technique for profiling the concentration of deep levels within a depletion region was used. From the two kinds of concentration-profile measurements, the diffusion coefficient of interstitial vanadium in silicon was determined, and it is represented by the expression DV= 9.0×10−3 exp(−1.55/kT) cm2 s−1.
Second-harmonic generation of blue light in LiNbO3 crystal with periodic ferroelectric domain structures
Authors: Lu Ya-lin , Mao Lun , Cheng Shi-de , Ming Nai-ben , Lu Yu-tian
Published: July 2002

A LiNbO3 crystal with periodic laminar ferroelectric domain structures (460 domains) was used to generate 430 and 435 nm radiation by quasi-phase-matched frequency doubling at room temperature. Blue light output of 0.2 μJ energy was measured for input energy 5 μJ of fundamental wave in pulse operation.
Intensity and phase noise in microcavity surface-emitting semiconductor lasers
Authors: Agrawal Govind P. , Gray George R.
Published: July 2002

The noise characteristics of vertical-cavity surface-emitting (VCSE) lasers are studied by using the Langevin rate equations modified suitably to include the enhanced spontaneous emission occurring in such microcavity lasers. The intensity and frequency noise spectra show the effects induced by suppression of relaxation oscillations. However, such a suppression depends on the output power as well as on transverse dimensions of the VCSE laser. The laser linewidth increases considerably as a result of enhanced spontaneous emission.
Preparation of oriented silicon carbide films by laser ablation of ceramic silicon carbide targets
Authors: Rimai L. , Ager R. , Logothetis E. M. , Weber W. H. , Hangas J.
Published: July 2002

Stoichiometric films of SiC, 60–150 nm thick, were deposited on [001] and [111] Si wafers by laser ablation of ceramic stoichiometric SiC targets. Films grown at substrate temperatures above 1050 °C show orientation epitaxial to the Si substrate along the film normal. Depending on the deposition conditions, the oriented crystallite dimension along this direction ranges from 20 nm up to the film thickness. The crystallite dimensions in the film plane range from 20 to 70 nm. Raman spectra indicate that the films often contain material other than crystalline SiC. Some of that is in the form of small (3–5 nm) graphitic inclusions.
The bulk modulus of C60 molecules and crystals: A molecular mechanics approach
Authors: Ruoff Rodney S. , Ruoff Arthur L.
Published: July 2002

In this letter, the bulk modulus of an individual C60 molecule is calculated in terms of the C,C bond force constant. A range of values for the bulk modulus is obtained with literature values for the force constant. The values obtained all exceed the bulk modulus (441 GPa) of diamond. With a C,C bond force constant equal to that between adjacent carbon atoms in graphite, 7.08 mdyn/Å, a bulk modulus of 903 GPa is obtained. On the basis of a simple composite model it is calculated that single closest-packed C60 crystals of C60 will have a bulk modulus of roughly 668 GPa under hydrostatic pressures. The calculated bulk modulus for a single C60 ‘‘buckyball’’ therefore suggests the possibility that a C60 crystal could be the most incompressible material known, at a pressure above about 50 GPa.
Numerical studies of quantum conduction through a junction of wide-narrow geometry
Authors: Nonoyama S. , Ishibashi K. , Aoyagi Y. , Namba S.
Published: July 2002

The conductance of the wide-narrow geometry in the ballistic transport regime has been calculated by numerical scattering matrix methods. The oscillations of the conductance as a function of the width of the wide region relative to that of the narrow region was found. The period of oscillation corresponds to twice the width, where a new subband is generated as the width of the wide region is increased. The amplitude of the oscillation decreases with an increase in the width of the wide region. The effects of contact potential at a junction are also discussed.
Time dependence of recombination-enhanced impurity diffusion in GaAs
Authors: Uematsu Masashi , Wada Kazumi
Published: July 2002

The time dependence of recombination-enhanced impurity diffusion (REID) has been investigated. The decrease in the peak current density of tunnel diodes was simulated based on the analysis in terms of the kinetics of the decay of the recombination center. The present results suggest that in the REID the energy released on minority-carrier injection at the recombination center enhances the annihilation of the recombination center, in which a group III point defect that enhances the Be diffusion is emitted.
Temperature-dependence of the growth orientation of atomic layer growth MgO
Authors: Huang Ron , Kitai Adrian H.
Published: July 2002

High-quality MgO thin films deposited on Si(111) substrates by atomic layer growth (ALG) are formed by a hydrolysis surface reaction of Mg(C2H5)2 and H2O. The growth orientation of MgO changes from (111) to (100), when the temperature of the silicon substrate changes from 600 to 900 °C. The growth orientation difference of MgO grown by ALG is rationalized in terms of the surface diffusion coefficients on MgO.
Observation of dislocation stresses in InP using polarization-resolved photoluminescence
Authors: Colbourne Paul D. , Cassidy Daniel T.
Published: July 2002

Localized stresses have been observed on the surface of InP wafers using spatially resolved and polarization-resolved photoluminescence. These stresses have been identified as the stress fields around individual dislocations based on the match in shape and magnitude between calculated and observed stress patterns. This technique provides an accurate, nondestructive method of detecting and characterizing dislocations in InP and other luminescent semiconductors.
Effect of photoexcitation on the surface band bending in δ-doped GaAs:Si/Al0.33Ga0.67As double heterostructures
Authors: Richards D. , Wagner J. , Fischer A. , Ploog K.
Published: July 2002

Photoluminescence spectroscopy in combination with electric-field-induced Raman scattering have been used to study the effect of photoexcitation on the surface electric field due to surface trap states in δ-doped GaAs:Si/Al0.33Ga0.67As double heterostructures. Upon variation of the optical power density over four orders of magnitude a continuous reduction of the surface electric field is found for increasing cw illumination. This is evident from a decrease of the electric-field-induced Raman signal and from a high-energy shift of the photoluminescence due to recombination of electrons at the δ-doping layer with photogenerated holes localized at the topmost heterointerface. For the highest power densities of ≂103 W/cm2 the electric field at that interface becomes almost zero indicating that band bending due to surface trap states is essentially removed.
Thermal imaging using the atomic force microscope
Authors: Majumdar A. , Carrejo J. P. , Lai J.
Published: July 2002

We have developed a new and simple technique for thermal imaging with submicrometer spatial resolution using the atomic force microscope. The method is particularly unique for simultaneously obtaining thermal and topographical images of biased electronic devices and interconnects where there could be different materials and potential variations on a scan surface. Application to a biased metal-semiconductor field-effect transistor showed the heating under the gate and a hot spot between the gate and drain where the electric field is known to be the highest. Thermal images of a biased polycrystalline Al-Cu via structure showed the grain boundaries to be hotter than within the grain. With the development of electronic devices and structures in the submicrometer range, this technique can become very useful as a tool for thermal characterization and property measurement.
Efficient, single-axial mode oscillation of a beta barium borate optical parametric oscillator pumped by an excimer laser
Authors: Robertson Gordon , Henderson Angus , Dunn Malcolm H.
Published: July 2002

Intracavity etalons have been used to obtain single axial mode oscillation of a beta barium borate optical parametric oscillator pumped at 308 nm by a XeCl excimer laser. Two high finesse etalons were sufficient to select a single axial mode of the resonant signal wave over a tuning range 400–560 nm with the increase in oscillation threshold due to etalon insertion being kept below 1.5 times. Addition of a grating enabled single axial mode oscillation to be maintained out to degeneracy (616 nm).
Simulation of the shielding of dust particles in low pressure glow discharges
Authors: Choi Seung J. , Kushner Mark J.
Published: July 2002

The dynamics of the shielding of particulates (‘‘dust’’) in low pressure glow discharges have been investigated with a pseudoparticle-in-cell simulation for electrons and ions in the vicinity of a dust particle. The potential of the dust particle, and the orbital nature of ions around the dust particle, depend on the collisionality of the ions. Collisions of orbiting ions effectively increase the ion flux collected by the particle, thereby increasing its potential to more positive values. Electron and ion momentum transfer and collection cross sections for scattering from the dust particle are presented.
Erbium laser ablation: The effect of dynamic optical properties
Authors: Cummings Joseph P. , Walsh Joseph T.
Published: July 2002

Ablation characteristics of Q-switched Er:YAG (λ=2.94 μm) and Er:YSGG (λ=2.79 μm) lasers have been compared. For equivalent fluences per pulse, the Er:YAG laser radiation cuts deeper craters into a tissue phantom than the Er:YSGG laser radiation. The Er:YAG laser irradiation created lower plume velocities than Er:YSGG laser irradiation. The data have been interpreted in terms of a dynamically changing absorption coefficient model and suggest that, in contradistinction to low-intensity water absorption spectra, the effective absorption coefficient during ablation is greater at 2.79 than at 2.94 μm.
Femtosecond ellipsometric study of nonequilibrium carrier dynamics in Ge and epitaxial Si1−xGex
Authors: Choo H. R. , Hu X. F. , Downer M. C. , Kesan V. P.
Published: July 2002

The time-resolved, above-gap optical response of optically thick Si1−xGex alloys to carrier injection by a femtosecond pump pulse is measured across the entire compositional range (0≤x≤1) using a novel femtosecond ellipsometric technique which clearly distinguishes the real and imaginary parts of the time-varying dielectric function ε1(t)+iε2(t). The results are modeled microscopically in terms of the Drude contribution from a diffusing hot electron-hole plasma, augmented by transient-induced absorption from hot-carrier-induced band renormalization. Further corrections from thermal band-gap shrinkage, intervalley scattering, and transient interband absorption saturation are also discussed.
Influence of deposition pressure on the output characteristics of low pressure chemical vapor deposited polycrystalline silicon thin-film transistors
Authors: Dimitriadis C. A. , Coxon P. A. , Economou N. A.
Published: July 2002

The influence of the deposition pressure on the output characteristics of low pressure chemical vapor deposited polycrystalline silicon thin-film transistors is investigated. The polysilicon films are deposited at pressures 40, 10, and 0.5 mTorr. For channel lengths L greater than 10 μm, the device has the conventional output characteristics dominated by the grain boundaries. In short-channel devices (L<10 μm), the experimental results show the presence of the ‘‘kink’’ effect and a reduction of the threshold voltage at high drain biases. When the deposition pressure of the polysilicon layer decreases, despite the increase of the grain size, the kink effect becomes more pronounced due to the enhanced diffusion of dopants from the source and drain contacts along the grain boundaries. The enhanced dopant diffusion reduces the effective channel length resulting in higher channel electric fields and increased kink effect.
Surface Fermi level pinning in epitaxial InSb studied by electric-field-induced Raman scattering
Authors: Wagner J. , Alvarez A.-L. , Schmitz J. , Ralston J. D. , Koidl P.
Published: July 2002

Electric-field-induced Raman scattering by longitudinal optical (LO) phonons has been used to study the surface Fermi level position in InSb layers grown by molecular beam epitaxy on (100) GaAs. From the analysis of a variety of layers it is found that the LO phonon scattering intensity, relative to that of intrinsic two-LO phonon scattering, decreases with increasing optical power density in n-type samples, but remains constant in p-type and undoped layers, which are residual p type. The power dependence of the relative LO phonon intensity for n-type doping is shown to be caused by a surface electric field, the strength of which is reduced upon increasing illumination due to screening by photogenerated carriers. As this effect is only found in n-type layers, we conclude that the surface Fermi level is pinned at the valence band thus giving rise to a sizeable surface electric field in n-type but not in p-type material.
Molecular beam epitaxial growth of CdZnS using elemental sources
Authors: Wu B. J. , Cheng H. , Guha S. , Haase M. A. , De Puydt J. M. , Meis-Haugen G. , Qiu J.
Published: July 2002

We report on the first molecular beam epitaxial (MBE) growth of CdZnS on (100) GaAs substrates using elemental Zn, Cd, and S sources. Single crystal cubic CdZnS layers lattice matched to GaAs have been successfully prepared. The competition in incorporation between Cd and Zn under different sulfur flux conditions is investigated. Under appropriate growth conditions, the Cd1−xZnxS composition is directly related only to the ratio of the group II beam equivalent pressures. The background sulfur in the MBE growth chamber is found to etch the freshly thermally cleaned GaAs substrates and generate high density of pits on the surfaces. Methods to prevent the sulfur etching are also discussed.
Phonon limited intersubband lifetimes and linewidths in a two-dimensional electron gas
Authors: Faist Jerome , Sirtori Carlo , Capasso Federico , Pfeiffer Loren , West Ken W.
Published: July 2002

Using an excited-state induced absorption spectroscopy technique, we have measured the lifetime of a state separated from the ground state by less than the optical phonon energy in a modulation-doped structure. A lifetime of τ=(300±100) ps is found in agreement with the prediction for the emission of an acoustic phonon. Moreover, we report the first direct evidence of a lifetime-broadened intersubband absorption line with a full width at half-maximum of 2.66 meV for a transition energy of E13=136 meV.
Ultrafast dynamics in field-enhanced saturable absorbers
Authors: Karin J. R. , Helkey R. J. , Derickson D. J. , Nagarajan R. , Allin D. S. , Bowers J. E. , Thornton R. L.
Published: July 2002

Absorption recovery dynamics of GaAs/AlGaAs field-enhanced waveguide saturable absorbers are studied by pump-probe differential transmission measurements. We compare the response of bulk and single quantum well absorbers at different reverse bias levels and pump powers, and find an ultrafast transient in the response, followed by a slower rise before the final recovery. The absorption fully recovers after a few picoseconds, which is an important result for mode-locked lasers.
Simple scaling law for positron stopping in multilayered systems
Authors: Aers G. C.
Published: July 2002

Using a simple model to take into account the backscattering effects of interfaces we have developed a scheme which removes the necessity for time-consuming Monte Carlo calculations in the generation of positron stopping profiles in multilayer systems. This scheme uses tabulated mean depth and backscattering fraction data for positrons in the materials constituting the multilayer and represents a computation time saving of several orders of magnitude. This makes detailed multilayer defect profiling with positrons a practical possibility.
Giant magnetic field dependent impedance of amorphous FeCoSiB wire
Authors: Beach R. S. , Berkowitz A. E.
Published: July 2002

The impedance of an amorphous Fe4.3Co68.2Si12.5B15 wire (100 μm diameter) exhibits an extraordinarily large frequency dependent resistance in addition to the previously reported frequency dependent wire reactance. The frequency response of both the resistance and reactance is almost entirely suppressed by an axial magnetic field HA<150 Oe, resulting in a typical magnetoresistance for frequencies f<1 MHz of the order of the dc wire resistance. The magnetoresistance at f=1 MHz is ΔR/Rsat=370%. As the bulk of the magnetic response occurs for HA<5 Oe, this system shows great technological promise. We give a quantitative analysis of the phenomenon, which is rooted in classical electrodynamics.
Pulsed laser deposition of silicon carbide at room temperature
Authors: Capano M. A. , Walck S. D. , Murray P. T. , Dempsey D. , Grant J. T.
Published: July 2002

The objective of this letter is to report on the successful deposition of SiC by pulsed laser deposition at room temperature. Deposition of SiC films is accomplished by ablating a 6H-SiC target, using the 248 nm radiation from a KrF* excimer laser. X-ray photoelectron spectroscopy data conclusively show that the films are silicon carbide. The Si 2p peaks are observed from a film at 100.3 eV, from a 6H-SiC standard at 100.3 eV, and from a Si standard at 99.7 eV. Similar scans of the C 1s peak reveal a shift in binding energy from 284.7 eV for a graphite standard, to 283.3 eV for a deposited film, and 283.4 eV for the SiC standard. Further, the integrated areas and shapes of the peaks from the film and the SiC standard are equivalent. Transmission electron microscopy reveals a film microstructure which is largely amorphous, but which contains a significant volume fraction of SiC crystallites. Analysis of the electron diffraction patterns indicates that the crystallites are β-SiC. The relationship between the film microstructure and the energy contained within the laser-generated plume is also considered.
Raman scattering and x-ray diffraction investigations of highly textured (Pb1−xLax)TiO3 thin films
Authors: Feng Z. C. , Kwak B. S. , Erbil A. , Boatner L. A.
Published: July 2002

Highly textured lead lanthanum titanate (PLT) thin films grown on Si(100) substrates by the metalorganic chemical vapor deposition technique are characterized using x-ray diffraction (XRD), Raman spectroscopy, and energy-dispersive x-ray analysis. The texturing consisted of an alignment of the {100} crystallographic axes of the film perpendicular to the Si substrate. The tetragonality of the films was found to decrease as the lanthanum concentration increased. Raman spectra exhibited features characteristic of bulk PLT, including the observation of the soft mode. Variations of the phonon modes for PLT have been investigated as a function of La concentration and sample temperature.
Novel YBa2Cu3O7−x and YBa2Cu3O7−x/Y4Ba3O9 multilayer films by bias-masked ‘‘on-axis’’ magnetron sputtering
Authors: Xu Jun-Hao , Zheng Guo-Guang , Grishin A. M. , Moon B. M. , Rao K. V. , Moreland John
Published: July 2002

In situ YBa2Cu3O7−x (YBCO) films have been fabricated on SrTiO3 (001) and LaAlO3 (001) substrates by on-axis biased-radio-frequency magnetron sputtering in Ar-10% O2 at total pressures as low as 3 Pa (3×10−2 mbar) and a deposition rate 210 nm/h. Negative oxygen ion-resputtering has been considerably reduced by introducing a biased copper mask between the substrate and target. The surface morphology and physical properties of the films are greatly improved on applying a positive dc substrate bias with respect to the grounded deposition chamber. We have obtained superconducting YBCO films with transport critical current as high as 106 A/cm2 at 77 K and low normal-state resistivity by this approach. Scanning tunneling microscopy analyses of the films with the best superconducting properties reveal a spiral growth mechanism. However, films deposited by negative dc bias under identical sputtering conditions are insulating. From x-ray θ-2θ and rocking curve measurements, we identify the insulating films to be c-axis oriented Y4Ba3O9 (YBO) films. Furthermore, YBCO films could be grown on the YBO layers without any degradation of TC and c-axis orientation. This novel bias sputtering feature gives us a unique opportunity to produce superconductor/insulator, YBCO/YBO, multilayers from a single YBCO target.
Damage and lattice strain in ion-irradiated AlAs
Authors: Partyka P. , Averback R. S. , Forbes D. V. , Coleman J. J. , Ehrhart P. , Jäger W.
Published: July 2002

Radiation-induced damage and strain in AlAs were investigated by measurements of the lattice parameter using x-ray diffraction. Irradiations employed MeV C, Ar, and Au ion beams at 25 or 80 K. The out-of-plane lattice parameter increased with fluence at low doses, saturated, and then decreased to nearly its original value. The in-plane lattice parameter did not change, throughout. These results were independent of the irradiation particle when scaled by damage energy. Selected samples were examined by high-resolution and conventional transmission electron microscopy. Recovery of the lattice parameter during subsequent thermal annealing was also investigated.
p-type CdSe grown by molecular beam epitaxy using a nitrogen plasma source
Authors: Ohtsuka Takeo , Kawamata Junji , Zhu Ziqiang , Yao Takafumi
Published: July 2002

We report the growth of p-type CdSe having zinc blende structure with the hole concentration of 1×1017 cm−3 by molecular beam epitaxy using a nitrogen plasma source. The electrical and optical properties of CdSe:N epilayers are characterized by Hall and photoluminescence (PL) measurements. PL spectra from p-type CdSe:N epilayers at 14 K show dominant emission associated with a neutral donor-bound excitation at 1.745 eV and two kinds of donor-acceptor pair emission bands with zero phonon energies of 1.724 and 1.695 eV. An Au/p-CdSe:N electrode is examined as ohmic contact for p-ZnSe in terms of current-voltage characteristic. It is shown that the Au p-CdSe electrode works as an ohmic contact for p-ZnSe.
Electronic microrefrigerator based on a normal-insulator-superconductor tunnel junction
Authors: Nahum M. , Eiles T. M. , Martinis John M.
Published: July 2002

We present measurements on a novel electronic microrefrigerator that can cool conduction electrons significantly below the lattice temperature. A normal-insulator-superconductor tunnel junction is used to extract electrons from the normal metal electrode whose energy is higher than the Fermi energy. Electrons with an average energy equal to the Fermi energy are returned to the metal by a superconducting contact. Consequently, the high-energy thermal excitations are removed from the normal metal, thus cooling the electrons. For lattice temperatures higher than 100 mK the data can be explained by a simple theory incorporating the BCS density of states in the superconducting electrode and the coupling between electrons and phonons. At lower temperatures our measurement suggests that the electron energies in the normal electrode depart strongly from an equilibrium distribution.
Thermal annealing of buried Al barrier layers to passivate the surface of copper films
Authors: Ding P. J. , Wang W. , Lanford W. A. , Hymes S. , Murarka S. P.
Published: July 2002

Annealed metallic bilayers consisting of Cu/Al/SiO2 are studied from the perspective of providing both surface passivation and diffusion barrier/adhesion promoter function for advanced copper based metallization. Upon annealing this bilayer film at 400 °C or higher, enough Al dissolves into the Cu to provide substantial oxidation resistance at the copper surface. The resistivity of these annealed films is approximately 4.5 μΩ cm. Compared to films of pure copper, these bilayer films are much more adherent to SiO2 and much more stable (both morphology and diffusion) on SiO2.