bluuebunny/crossref_metadata_2025 huggingface dataset:
Linear IgA disease
Authors: Fracs Justine R Smith Mbbs , Fracp Ann Kupa Mbbs , Frcs Douglas J Coster Mbbs
Published: July 2002

Purpose: A case of linear IgA disease is reported to alert ophthalmologists and physicians to this unusual cause of chronic cicatrizing conjunctivitis.

Methods: Clinical records of a patient suffering from linear IgA disease were reviewed.

Results: A 65‐year‐old woman with a complicated medical history experienced rapidly progressive chronic cicatrizing conjunctivitis leading to corneal perforation. Undiagnosed gingivitis and palatal ulceration had been present for 5 years prior to the onset of ocular symptoms and vitamin C deficiency had followed the consequent dietary restrictions. A diagnosis of linear IgA disease was made on conjunctival biopsy, which demonstrated linear deposits of IgA along the epithelial basement membrane. The perforation was managed successfully with a conjunctival pediculate flap. Control of the inflammation was achieved with systemic prednisolone and cyclophosphamide but at the expense of serious systemic side‐effects.

Conclusions: Linear IgA disease causes progressive conjunctival cicatrization in many affected individuals. Although dapsone generally controls the inflammation, heavier systemic immunosuppression was required in this case. Involvement of skin or other mucosal surfaces may become symptomatic before the conjunctivitis, and physicians must be educated to refer patients for ophthalmological review on diagnosis. Conversely, ophthalmologists encountering ocular linear IgA disease should be aware of the possibility of other mucosal involvement requiring physician intervention.
Chemo‐embolization of hepatic tumours
Authors: Al‐Bassam Sulaiman H , Munk Peter L , Sallomi David F , Morris D Christopher , Lee Mark J , Chung Stephen W , Connell Douglas G
Published: July 2002

Over the past decade, increasing use of chemo‐embolization with chemotherapeutic agents emulsified in oil has been made in the treatment of both primary and metastatic liver tumours. These lesions are often not amenable to surgical resection and are not responsive to systemic chemotherapy. Chemo‐embolization provides an additional therapeutic option which, in some instances, can provide significant benefit. This pictorial review discusses the technique of chemo‐embolization, as well as aspects of patient selection, complications, and tumour response.
Clostridium septicum septicaemia with myonecrosis
Authors: Salanitri GC , Tauro PG
Published: July 2002

A case of fatal spontaneous gas gangrene due to Clostridium septicum septicaemia associated with an occult rectal malignancy is presented. This condition has a rapid progression and a high mortality even with prompt treatment. It is important that the radiologist considers this diagnosis in an appropriate clinical setting to allow rapid instigation of appropriate therapy.
Expression of apoptotic regulatory molecules in renal cell carcinoma: Elevated expression of Fas ligand
Authors: Olive Colleen , Cheung Catherine , Nicol David , Falk Michael C
Published: July 2002

Renal cell carcinoma (RCC) is the most common renal neoplasm. Despite being infiltrated by tumour infiltrating lymphocytes (TIL), these TIL are unable to control tumour growth in vivo, suggesting that the cytotoxic capacity of TIL against RCC is impaired, or that the tumour cells are resistant to killing and therefore escape detection by the immune system. It is postulated that the expression of apoptotic regulatory molecules in RCC favours tumour cell survival. The present study has therefore determined the expression of Fas (APO‐1/CD95), Fas ligand (Fas L) and bcl‐2 in these tumours. The expression of Fas, Fas L and bcl‐2 mRNA transcripts was determined in RCC, normal kidney and peripheral blood by semiquantitative reverse transcriptase polymerase chain reaction (RT‐PCR), following RNA extraction and cDNA synthesis from tissues and cell samples. Transcript levels were measured by densitometry after Southern blot hybridization of PCR products with internal radio‐labelled oligonucleotide probes; a densitometry score was assigned to each hybridizing DNA band and expressed as a ratio of the glyceraldehyde‐3‐phosphate dehydrogenase content. In peripheral blood, the expression of Fas L and bcl‐2 transcripts was similar between patients and normal healthy individuals; however, Fas transcript expression was significantly down‐regulated in the patients’ versus normal peripheral blood (P = 0.026). Most interestingly, significantly up‐regulated Fas L expression was observed in RCC compared to normal kidney (P = 0.041). In contrast, bcl‐2 transcripts were well represented in normal kidney but markedly decreased in RCC (P = 0.021). The expression of Fas transcripts in normal kidney and RCC was variable. These data demonstrate elevated expression of Fas L transcripts in RCC, but the functional relevance of this remains to be investigated.
Allelic variation in the vacA gene of Helicobacter pylori isolated from Chinese patients
Authors: Xuhuai Ji , Burroni Daniela , Guoming Xu , Pagliaccia Cristina , Reyrat Jean‐Marc , Zhenxing Tu , Hua Ding , Yiqi Du , Rappuoli Rino , Telford John L
Published: July 2002

OBJECTIVE: To characterize the vacA alleles present in Chinese Helicobacter pylori strains and to compare the allelic variation in the vacA gene of Chinese strains with that of Western strains.

METHODS: Twenty‐two single colonies of H. pylori isolated from five biopsy specimens with different gastric disorders were characterized for the expression of VacA protein and for evaluating the cytotoxic activity in HeLa cells. Five representative strains were selected and the vacA gene was amplified by PCR and subjected to automatic DNA sequencing using a primer walking strategy.

RESULTS: Four strains expressed the VacA protein. Only one of the five strains induced vacuole degeneration in HeLa cells. All five vacA genes coded for identical signal peptides of the sla allele and had similar sequences encoding a 37 kDa subunit and outer membrane exporter. One of the five strains expressed a VacA protein with a middle region of the m1 allele and the others of the m2 allele. The four m2 allele strains had little vacuolating activity in HeLa cells. Phylogenetic analysis indicated that the homology of the Chinese vacA genes was 97.6–99.2% compared with 91.3–92.0% in the Western strains.

CONCLUSIONS: There are allelic variations in the vacA gene between Chinese and Western H. pylori. Chinese H. pylori strains form a phylogenetically independent cluster separated from Western isolates. The m2‐type strains seem to be more prevalent in China. Cytotoxicity in HeLa cells appear to associate with the middle region but not the signal sequence.
Localization and quantitative study of hepatic oval cells in patients with chronic liver diseases: A pathological analysis of 29 liver specimens
Authors: Dekai Qiu , Xiong Ma , Yanshen Peng , Xiaoyu Chen , Yao Shi
Published: July 2002

OBJECTIVE: To observe the morphological characteristics of oval cells in human chronic liver disease and to determine the relationship between the number of oval cells and the grading and staging of liver fibrosis.

METHODS: Oval cells in paraffin‐embedded sections of three normal control livers and 29 chronically diseased livers were detected by using histoimmunochemistry. Cells were counted and scored if they satisfied the morphological criteria for oval cells and showed cytoplasmic staining.

RESULTS: Oval cells were not observed in normal livers. In chronic liver disease, oval cells were characterized by the presence of an ovoid nucleus, a small‐sized cell and scanty cytoplasm, and were located predominantly in the periportal region and fibrous septa. The number of oval cells increased significantly (F = 22.60, P < 0.01) as the staging of fibrosis increased (7 ± 3, 12 ± 3, 25 ± 7, 33 ± 9, and 44 ± 10 in stages 0–4, respectively). There were significant differences between all stages (P < 0.05) except those in stages 0 and 1, and 1 and 2. The number of oval cells was significantly related to the staging of liver fibrosis (r = 0.88, P < 0.01).

CONCLUSION: Oval cells are frequently detected in chronically diseased livers. Their presence is related to the staging of fibrosis.
Occupational urothelial tumours: a regional case study
Authors: Sorahan  , Hamilton  , Wallace  , Bathers  , Gardiner  , Harrington
Published: July 2002

Objective

 To investigate the role of occupational exposures in the risk of developing urothelial cancer.

Materials and methods

 Occupational histories, obtained using a self‐administered questionnaire, for 803 patients with urothelial cancer (first diagnosed 1991–93) were compared with similar information for 2135 matched controls. Relative risks (RRs) were estimated using conditional logistic regression. Comparisons were also made with historical regional employment information available from the 1971 census.

Results

 There were many statistically significant positive associations for urothelial cancer risks and ever being employed in specified occupations (with or without statistical adjustment for smoking status in 1991). Smoking‐adjusted RRs of >2.0 were obtained for seven occupations; manufacture of fire lighters/ patent fuels (RR 4.30, 95% confidence interval 0.78–23.79), rodent extermination (3.71, 1.20–11.48), manufacture of dyestuffs (2.61, 0.98–7.00), leather work (2.51, 1.44–4.35), cable manufacturing industry (2.46, 1.20–5.04), textile printing and dyeing (2.32, 0.98–5.45), and sewage works (2.19, 1.16–4.11). Analyses of the occupations followed in 1971 (thus allowing for 20‐year latency) indicated an elevated RR for workers in the plastics industry (5.22, 1.57–17.36).

Conclusions

 The historical legacy of exposure to aromatic amines in the rubber, cable‐making, dyestuffs and other industries remains. An important proportion of patients presenting with urothelial tumours are likely to have had occupational exposure to urothelial carcinogens. A review of occupational exposures in the contemporaneous plastic, textile and leather industries is warranted.
‘Sausage toe’: a reliable sign of underlying osteomyelitis
Authors: Rajbhandari S. M. , Sutton M. , Davies C. , Tesfaye S. , Ward J. D.
Published: July 2002

Aims To follow‐up patients with a ‘sausage’ deformity of the toe associated with local neuropathic ulceration to confirm the diagnosis of underlying osteomyelitis. This was based on our observation that some diabetic patients with suspected pedal osteomyelitis with a local neuropathic ulcer have a ‘sausage’ deformity of a toe.

Methods Over a period of 2 years, 14 patients with foot ulcers, who were observed to have the ‘sausage’ deformity of a toe in the diabetic foot clinic were followed up and investigated.

Results Underlying osteomyelitis was confirmed in six on the very first X‐ray examination. A further seven had osteomyelitis diagnosed on bone scanning. Both the X‐ray and the bone scan were equivocal in one patient, whose ulcer only healed after an 8‐week course of antibiotics. Antibiotic therapy was successful in 11 patients and three patients required amputation of the affected toe. Following successful treatment, there was full resolution of the ‘sausage toe’ in the majority.

Conclusions The appearance of a ‘sausage toe’ should alert the physician of the possibility of underlying osteomyelitis in diabetic foot, so that prompt treatment can be commenced with antibiotics.
Normal pericardial fluid in the fetus: color and spectral Doppler analysis
Authors: Yoo S.‐J. , Min J.‐Y. , Lee Y.‐H.
Published: July 2002

Objectives

To estimate the incidence of sonographic identification of pericardial fluid in normal fetuses and to evaluate the flow pattern of pericardial fluid by using color and spectral Doppler techniques.

Methods

We evaluated 27 normal fetuses for the presence of pericardial fluid by using gray‐scale two‐dimensional and M‐mode ultrasound, and color and spectral Doppler techniques.

Results

Pericardial fluid was detected in 52% of cases by two‐dimensional and M‐mode ultrasound and in 81% of cases by color Doppler. The pericardial fluid moved towards the ventricles during systole and towards the atria during diastole. In 9 of 22 fetuses with pericardial fluid identified by color Doppler, spectral waveforms were obtained. The waveforms confirmed the bidirectional flow pattern identified at color Doppler. In six cases there was monophasic systolic and biphasic diastolic flow. In the remaining three cases, the flow was monophasic during both systole and diastole.

Conclusions

Pericardial fluid can be identified with color Doppler in the majority of normal fetuses. It characteristically shows bidirectional flow as it moves with ventricular systole and diastole. Spectral waveforms can be obtained from the pericardial fluid. The presence of pericardial fluid per se should not be considered as abnormal. Color‐coded pericardial fluid should not be mistaken for coronary artery blood flow. Copyright © 2001 International Society of Ultrasound in Obstetrics and Gynecology
AUTOMIC FAILURE AND NORMAL PRESSURE HYDROCEPHALUS IN A PATIENT WITH CHRONIC DEMYELINATING INFLAMMATORY NEUROPATHY
Authors: Laurà M. , Mazzeo A. , Sinicropi S. , Di Leo R. , Girlanda P.
Published: July 2002

A 75‐year‐old man with HCV hepatitis developed at the age of 70 presented with rest and action tremor localized at both hands and progressive cognitive impairment with memory loss. Four years later he begun to complain of progressive fatigue, occasional falls, numbness at the extremities and orthostatic hypotension. One month after admission, he rapidly worsened with inability to walk, mainly because of autonomic failure. Neurological examination revealed gait disturbances, including a wide base of support and short stride, slurred speech, reduction of upward gaze, rest and action tremor at both hands, intrinsic hand muscle and anterior tibialis muscle wasting and weakness on both sides, absent deep tendon reflexes, loss of vibration sense at lower limbs, and bilateral pes cavus. Routine laboratory studies, autoantibodies, thyroid function, neoplastic markers and immunoelectrophoresis were normal. Cryoglobulins were absent, whereas CSF protein content was increased (142 mg/dl). Autonomic nervous system investigation detected severe orthostatic hypotension. Nerve conduction studies showed absent sensory potentials and a marked reduction of compound motor action potential amplitudes and of motor conduction velocities. A sural nerve biopsy revealed remarkable onion bulb‐like changes, endoneurial and perivascular infiltrations of inflammatory cells. Psychometric tests showed mild cognitive impairment. Brain MRI was consistent with normotensive hydrocephalus. The findings indicated the presence of chronic inflammatory demyelinating polyneuropathy, autonomic nervous system involvement and normal pressure hydrocephalus. A condition of multiple system atrophy (MSA) might be taken into account, even if somatic peripheral nerve involvement may rarely occur in MSA. Moreover the normal pressure hydrocephalus could be due to the high protein content in CSF (Fukatsu R et al., 1997).
Anomalous diffusion of fluorine in silicon
Authors: Jeng S.-P. , Ma T.-P. , Canteri R. , Anderle M. , Rubloff G. W.
Published: July 2002

The diffusion of ion implanted F in Si has been studied by the use of secondary ion mass spectroscopy and thermal desorption spectroscopy. In the dose range studied (below amorphization threshold), F exhibits an anomalous out-diffusion behavior which is characterized by the depletion of F in Si substrate at temperatures ≥550 °C with complete suppression of diffusion deeper into the bulk of Si. F species which migrate to the surface react with native oxide and Si to form volatile Si oxyfluoride and Si fluoride, which then evaporate from the surface. There is clear evidence that the formation of Si oxyfluoride correlates strongly with the thermally activated anomalous migration of F. While the driving force for the anomalous F migration has not yet been identified, it appears that the electric field is not a dominant mechanism.
GaN/AlN digital alloy short-period superlattices by switched atomic layer metalorganic chemical vapor deposition
Authors: Asif Khan M. , Kuznia J. N. , Olson D. T. , George T. , Pike W. T.
Published: July 2002

In this letter we report the fabrication of GaN/AlN short-period superlattices using switched atomic layer epitaxy. Superlattice structures with GaN well thicknesses ranging from 2.6 to 20.8 Å (with AlN barrier thicknesses of 2.5, 7.5, and 15 Å) were deposited over basal plane sapphire and characterized for their structure, crystallinity, and optical properties. Cross-sectional transmission electron micrographs indicate GaN/AlN interfaces and the superlattice surfaces are atomically smooth. The structures exhibit strong room temperature photoluminescence and a sharp absorption edge indicating a high optical quality.
Metastable SiGeC formation by solid phase epitaxy
Authors: Strane J. W. , Stein H. J. , Lee S. R. , Doyle B. L. , Picraux S. T. , Mayer J. W.
Published: July 2002

We report the synthesis and detailed structural characterization of SiGeC metastable alloys formed by solid phase epitaxial regrowth. Epitaxial layers with 0.7 and 1.4 at. % C are formed by 700 °C regrowth of multiple energy carbon implants into preamorphized Si0.86Ge0.14 layers on Si substrates. Transmission electron microscopy and Rutherford backscattering spectrometry show heteroepitaxial regrowth of Si1−x−yGexCy layers into the metastable diamond cubic phase. Fourier transform infrared spectroscopy verifies that the carbon occupies substitutional lattice sites. Double crystal x-ray diffraction measurements of Si1−x−yGexCy and Si1−yCy reference layers quantify the C-induced tensile strain component. This strain compensates for the compressive strain in the SiGe layers, and indicates a change in lattice constant per atomic fraction C in agreement with Vegard’s law.
Metal ion dependent luminescence effects in metal tris-quinolate organic heterojunction light emitting devices
Authors: Burrows P. E. , Sapochak L. S. , McCarty D. M. , Forrest S. R. , Thompson M. E.
Published: July 2002

We present a systematic analysis of the relationship between the photoluminescence (PL), light emitting device electroluminescence (EL), and conducting properties of a series of metalquinolates, Mq3, where M is a metal (Al, Ga, In, or Sc), and q3 is tris-(8-hydroxyquinoline). We compare the solution and thin film PL quantum yields and spectra of each quinolate with the EL quantum efficiencies of organic heterojunction light emitting diodes using the compound as the emitter layer. Our results indicate that, contrary to previous reports, the relative PL yield is not a good indicator of the EL quantum efficiency of a particular material. Specifically, we find that while the PL of Alq3 films is four times that of Gaq3, light emitting devices made from these two materials have comparable electroluminescence quantum efficiencies and long-term stabilities. Furthermore, the Gaq3 devices have an approximately 50% higher power efficiency than Alq3 structures, suggesting that Gaq3 is a superior emitter material for display applications.
Shimming a superconducting nuclear-magnetic-resonance imaging magnet with steel
Authors: Hoult D. I. , Lee D.
Published: July 2002

Using a recently published paper as a basis, the magnetic field produced by steel bars inserted in a superconducting NMR imaging magnet is analyzed in a spherically harmonic basis set. A description is then given of how such bars were used to improve the homogeneity of the field within the magnet’s imaging volume from 1.2 parts per thousand to about 10 ppm. The poor homogeneity was caused by the magnet’s being placed in a steel-laden environment, a situation normally shunned by investigators, and it is the author’s contention that the results obtained abrogate the main objection to NMR equipment’s being installed in an ordinary hospital building. To facilitate the latter, the equations developed may also be used to estimate, prior to installation, the effects of the proposed environment on field homogeneity.
Atom-probe investigation of III–V semiconductors: Comparison of voltage-pulse and laser-pulse modes
Authors: Hashizume Tomihiro , Hasegawa Y. , Kobayashi A. , Sakurai T.
Published: July 2002

Pulse-field evaporation of III–V compound semiconductors was investigated employing our high-performance time-of-flight atom probe, which accommodates the demand for precise knowledge of both mass (focusing type) and energy deficits (straight type) of field-evaporated ion species. We show that laser-pulse mode can yield correct compositions only if an appropriate dc holding field range is used, which is 0.35 to 0.65 for the GaAs presently studied.
Micro-size polyacrylamide gel electrophoresis system
Authors: Hinson W. G. , Pipkin J. L. , Anson J. F. , Casciano D. A. , Burns E. R.
Published: July 2002

The development and characterization of a micro-size two-dimensional polyacrylamide gel electrophoresis system is described. Some of the techniques which have evolved with use of the system are also discussed. This apparatus has unique features which provide advantages over other small scale units. Up to ten first- and second-dimension gels can be processed simultaneously with excellent resolution of protein regions. Consistent reproducibility is possible from protein samples as small as 400 ng and individual protein regions as small as 1 pg can be visualized by silver staining of the two-dimensional gels. Similar sensitivities are achieved in autoradiographs of 3H-labeled proteins extracted from the nuclei of cultured cells. The application of this system in conjunction with flow cytometric examination of nuclear DNA and electrostatic cell sorting of specific cell nuclei to provide homogeneous sample populations, allows subtle variations in isotope incorporation in proteins to be detected; whereas many times in generalized tissue samples these changes are masked. Also, these techniques elucidate the effects of external stimuli (chemicals, drugs, or environment) on protein synthesis and phosphorylation for analyses and comparison. Fabrication drawings are available upon request.
Twin-wire resistance probe rotameter
Authors: Liu C. Y. , Ng K. L. , Poo A. N.
Published: July 2002

The principle of the twin-wire resistance probe rotameter is developed in this article. The main feature of the design is a low-cost flowmeter with an electrical output capability. From performance tests conducted on both a simulated rotameter and an actual rotameter constructed based on the principle described, good agreement was observed between experimental and analytical results. It was found that the output voltage from this flowmeter depends mainly upon the material and the size of the float used, and the angle of the taper of the surface of the meter.
Measuring ambient ozone with high sensitivity and bandwidth
Authors: Pearson Richard
Published: July 2002

An ozone (O3) analyzer for use in eddy-correlation measurements is described which has an unfiltered bandwidth of at least 20 Hz and sensitivity of at least 0.1 ppbv at 12-Hz bandwidth. Based on chemiluminescence with nitric oxide, it is designed primarily for use on meteorological aircraft, but it also works well for tower measurements. It is significant that the detecting mechanism responds linearly to time-dependent inputs, which is a definite advantage for applications involving measurements of eddy fluxes and spectra of O3. The unit is highly specific, the only known interference being a slight quenching of the chemiluminescence by water vapor. The unit does not respond to cloud liquid water or to precipitation, and excellent performance has been obtained in the presence of these two conditions. The entire package weighs 110 kg and requires 360 W at 110 V ac (60 or 400 Hz), and 1200 W at 28 V dc.
Performance of the high-resolution SX700/II monochromator
Authors: Domke M. , Mandel T. , Puschmann A. , Xue C. , Shirley D. A. , Kaindl G. , Petersen H. , Kuske P.
Published: July 2002

This article reports on the high-resolution performance of the grazing-incidence plane grating monochromator SX700/II, installed at BESSY by the Freie Universität Berlin, in the photon energy range from about 40 to 900 eV. The high resolving power up to 10 000 achieved with this monochromator is based on improving the figure error of the ellipsoidal focusing mirror, on reducing the vertical dimension of the beam source, and on employing a 5-μm exit slit. We report on high-resolution gas-phase studies in the double-excitation region of He, as well as at core-excitation thresholds of Ne, Ar, Kr, and Xe in the photon-energy range from ≂45 eV to ≂900 eV. In addition, high-resolution core-excitation spectra at the K thresholds of C, N, and O are presented for gas-phase CO, N2, and O2. In all cases, high-n Rydberg states and/or vibrational sidebands of the electronic excitations were resolved. The various contributions to the present instrumental linewidths are discussed as well as the prospects for further improvements in resolution with this monochromator.
Giant room-temperature magnetoresistance in the FeRh alloy
Authors: Algarabel P. A. , Ibarra M. R. , Marquina C. , del Moral A. , Galibert J. , Iqbal M. , Askenazy S.
Published: July 2002

The magnetoresistance of the FeRh alloy has been measured in the temperature range 200–300 K using high pulsed magnetic fields up to 36 T. This compound shows a first-order magnetic transition from the antiferromagnetic (AF) low-temperature state to the ferromagnetic (F) high-temperature state at TAF–F=405 K. The F state is very close in energy to the AF state and can be reached by applying a magnetic field. The measurements made within the AF state show that the AF–F transition is accompanied by a giant magnetoresistance effect (ΔR/R≊50%).
Humidity control device for a semiclosed environment
Authors: Spadafore Steven W. , Pierce Joanna , Sul E. Yong-Soo , Musselman Ronald L.
Published: July 2002

A portable device that easily maintains a desired humidity at room temperature ranging from 50% to 95% in a small, closed environment is described. This device permits extended x-ray and spectroscopic analysis of crystals that require a humidified environment by passing a stream of air over heated water. An electronic controller coupled with a humidity sensor provides feedback and control.
Flow cytometry signal processing and data acquisition with a personal computer using an RTI-800 multifunction A/D I/O board
Authors: Bakker Schut Tom C. , Florians Alex , van der Werf Kees O. , de Grooth Bart G.
Published: July 2002

The design and implementation of a data management system, consisting of a real-time data processing and a PC-based acquisition system, for measurement of flow cytometric data is described. The data processing system makes use of an erasable programmable logic device for implementation of dedicated control logic. The signal processing system is used for measuring the peak heights of 8 analog signals and simultaneous digital measurement of the time of flight. Four window discriminators are used for data selection and sorting applications. The data acquisition system is based on an MS-DOS PC with a slightly modified commerical A/D I/O board, which we used to measure 8 analog signals (12 bit A/D converted) and 32 bit digital information per event. Using an IBM compatible personal computer with an 8 MHz AT bus, the total system is capable of measuring about 10 000 events per second.
Review of plane grating focusing for soft x-ray monochromators
Authors: Petersen H. , Jung C. , Hellwig C. , Peatman W. B. , Gudat W.
Published: July 2002

During the last 10 years various types of soft x-ray monochromators have been developed, which are optically based on the plane grating focusing condition introduced in 1980. These instruments as well as those using the original 1980 optical configuration are reviewed and compared to the other type of high performance soft x-ray grating monochromator, the Rowland circle based spherical grating monochromator (SGM). Performance data of a plane grating monochromator (HE-PGM-3), which was recently commissioned at BESSY and which offers a broad spectral range (40–2000 eV) and very high spectral resolution (up to E/ΔE∼10 000) are given in more detail. The performance of grating and crystal monochromators is compared in the 1–2 keV photon energy range.
Nanostructure fabrication using laser field enhancement in the near field of a scanning tunneling microscope tip
Authors: Jersch J. , Dickmann K.
Published: July 2002

The scanning tunneling microscope (STM) has been combined with laser excitation and was used for modification of metal surfaces in air. This technique enables processing of structures with a lateral resolution of approximately 10 nm. The form of the created features ranges from craters and ditches to hillocks. The process has been demonstrated on gold and gold/palladium substrates by utilization of tungsten, silver, and platin/iridium tips. Using pure silver tips or silver-coated tungsten tips, a transfer of tip atoms to the substrate occurred. In the case of uncoated tungsten tips, we observed substrate evaporation and surface grain reorganization at low laser intensities, respectively. No distortion of the employed tips during the structuring process was observed. Several future oriented applications are conceivable, such as, for example, high density data storage and fresnel optics for x rays.
Hardness and fracture toughness of bulk single crystal gallium nitride
Authors: Drory M. D. , Ager J. W. , Suski T. , Grzegory I. , Porowski S.
Published: July 2002

Basic mechanical properties of single crystal gallium nitride are measured. A Vickers (diamond) indentation method was used to determine the hardness and fracture toughness under an applied load of 2N. The average hardness was measured as 12±2 GPa and the average fracture toughness was measured as 0.79±0.10 MPa√m. These values are consistent with the properties of brittle ceramic materials and about twice the values for GaAs. A methodology for examining fracture problems in GaN is discussed.
Optical system for rapid materials characterization with the transient grating technique: Application to nondestructive evaluation of thin films used in microelectronics
Authors: Rogers John A. , Fuchs Martin , Banet Matthew J. , Hanselman John B. , Logan Randy , Nelson Keith A.
Published: July 2002

This letter describes a noncontact, automated means for nondestructively measuring the physical (elastic, thermal, electronic, optical) properties of bulk samples, surfaces, supported or unsupported thin films, and multilayer assemblies. The method, which is based on the transient grating technique, uses specially constructed beam-shaping optics to manipulate excitation and probe laser beams for initiating and detecting motions in a sample. We illustrate the approach by determining the thicknesses and mechanical properties of metal films commonly used in microelectronics.
Extension of colossal magnetoresistance properties to small A site cations by chromium doping in Ln0.5Ca0.5MnO3 manganites
Authors: Barnabé A. , Maignan A. , Hervieu M. , Damay F. , Martin C. , Raveau B.
Published: July 2002

The Mn site substitutions of charge ordered (CO) manganites Ln0.5Ca0.5MnO3 (Ln=La–Tb) have been investigated. Among the different studied doping elements, chromium is shown to be the most efficient one to induce a metal insulator (MI) transition in the CO undoped insulators. A new Tm(〈rA〉) magnetic diagram, where 〈rA〉 is the A site cationic average radius, is established for the oxides Ln0.5Ca0.5Mn1−xCrxO3, which demonstrates that 〈rA〉 is not a rhedibitory parameter for the occurrence of colossal magnetoresistance (CMR) properties. The average size limit 〈rA〉L≈1.19 Å below which the MI transition is suppressed in the undoped CO compounds is indeed lowered to 〈rA〉L≈1.14 Å in the Cr-doped materials. The electron microscopy study of these Cr doped oxides shows that this spectacular effect corresponds with the disappearance of the structural transition associated with CO.
Minority-carrier lifetime and efficiency of Cu(In,Ga)Se2 solar cells
Authors: Ohnesorge B. , Weigand R. , Bacher G. , Forchel A. , Riedl W. , Karg F. H.
Published: July 2002

Room-temperature recombination dynamics has been investigated in a large set of different Cu(In,Ga)Se2 absorber films and compared to the electrical device characteristics of the respective solar cell modules. For a given cell preparation process, a characteristic relation between the low-injection minority-carrier lifetime of the absorber layers and the conversion efficiency of the solar cells is observed: Long lifetimes correlate with high open circuit voltages and conversion efficiencies, while no significant influence of the lifetime on the short circuit current is found.
Laser action from two-dimensional distributed feedback in photonic crystals
Authors: Meier M. , Mekis A. , Dodabalapur A. , Timko A. , Slusher R. E. , Joannopoulos J. D. , Nalamasu O.
Published: July 2002

We report an analysis of the operation of a new type of laser resonator with two-dimensional distributed feedback from a photonic crystal. The gain medium consists of a 2-(4-biphenylyl)-5(4-tert-butylphenyl)-1,3,4-oxadiazole host doped with Coumarin 490 and DCM and is deposited on lithographically patterned Si/SiO2 structures. Bragg reflections caused by the grating diminish the group velocity of photons along some directions of crystallographic symmetry to zero, and the resulting feedback gives rise to laser oscillations. Dispersion relations for photons were calculated analytically and are used to interpret the laser emission spectra.
Thickness-dependent magnetotransport in ultrathin manganite films
Authors: Sun J. Z. , Abraham D. W. , Rao R. A. , Eom C. B.
Published: July 2002

To understand the near-interface magnetism in manganites, ultrathin films of La0.67Sr0.33MnO3 were grown epitaxially on single-crystal (001) LaAlO3 and (110) NdGaO3 substrates. The temperature and magnetic field-dependent film resistance is used to probe the film’s structural and magnetic properties. A surface and/or interface related dead layer is inferred from the thickness-dependent resistance and magnetoresistance. The total thickness of the dead layer is estimated to be ∼30 Å for films on NdGaO3 and ∼50 Å for films on LaAlO3.
Model for crystallization kinetics: Deviations from Kolmogorov–Johnson–Mehl–Avrami kinetics
Authors: Castro Mario , Domı́nguez-Adame Francisco , Sánchez Angel , Rodrı́guez Tomás
Published: July 2002

We propose a simple and versatile model to understand the deviations from the well-known Kolmogorov–Johnson–Mehl–Avrami kinetics theory found in metal recrystallization and amorphous semiconductor crystallization. We analyze the kinetics of the transformation and the grain-size distribution of the product material, finding a good overall agreement between our model and available experimental data. The information so obtained could help to relate the mentioned experimental deviations due to preexisting anisotropy along some regions, to a certain degree of crystallinity of the amorphous phases during deposition, or more generally, to impurities or roughness of the substrate.
Optically and thermally detected deep levels in n-type Schottky and p+-n GaN diodes
Authors: Hierro A. , Kwon D. , Ringel S. A. , Hansen M. , Speck J. S. , Mishra U. K. , DenBaars S. P.
Published: July 2002

N-Schottky and p+–n GaN junctions are currently used for different technologies. A comparison of the deep levels found throughout the entire band gap of n-GaN grown by metal-organic chemical vapor deposition under both configurations is presented. Both deep level optical spectroscopy and deep level transient spectroscopy measurements are used allowing the observation of both majority and minority carrier traps. Deep levels at Ec−Et=0.58–0.62, 1.35, 2.57–2.64, and 3.22 eV are observed for both diode configurations, with concentrations in the ∼1014–1016 cm−3 range. The 0.58–0.62 eV level appears correlated with residual Mg impurities in the n side of the p+–n diode measured by secondary-ion-mass spectroscopy, while the 1.35 eV level concentration increases by a factor of ∼4 for the Schottky junction possibly correlating with the carbon profile. The 2.57–2.64 eV level is a minority carrier hole trap in n-GaN, likely related to the yellow photoluminescence band, and is detected both optically from the conduction band (2.64 eV) and thermally from the valence band (0.87 eV).
Direct potential fit analysis of the X 1Σg+ state of Rb2: Nothing else will do!
Authors: Seto Jenning Y. , Le Roy Robert J. , Vergès Jean , Amiot Claude
Published: July 2002

High resolution A-X emission data involving vibrational levels of the ground X 1Σg+ electronic state up to v″=113, spanning 99.8% of the potential well, have been acquired for three isotopomers of Rb2. While a good fit (σ̄f=1.03) to the 12 148 transition frequencies (with uncertainties ±0.001 cm−1) is obtained from an unconstrained combined-isotopomer Dunham-type analysis, it requires a large number (62) of expansion parameters, and the resulting empirical centrifugal distortion constants (CDCs) are unreliable for extrapolation to higher-J. Moreover, Dunham expansion fits using constrained theoretical values of the first six CDCs (up to Ov) fail to properly represent the data, as even higher-order CDCs are required. However, a direct fit of these data to an analytical “modified Lennard-Jones” potential energy function involving only 16 fitted parameters yields essentially the same quality of fit as did the unconstrained Dunham fit, and should be reliable for extrapolation to arbitrarily high J. This potential form incorporates the proper R−6 asymptotic behavior of the potential, and is constrained to have the theoretically predicted C6 dispersion coefficient. Although the dataset involves the three isotopomers 85,85Rb2, 85,87Rb2, and 87,87Rb2, none of the present analyses was able to determine any Born–Oppenheimer breakdown effects.
High precision ac susceptometer for measuring the temperature and magnetic field dependence of the penetration depth in superconductor single crystals
Authors: Bidinosti C. P. , Hardy W. N.
Published: July 2002

An ac susceptometer has been developed for very sensitive measurement of the magnetic moment of small samples as a function of temperature and applied dc field. The system was designed specifically for measurements on small single crystals of the high Tc superconductor YBa2Cu3O7−δ in the Meissner state. The natural platelet geometry of these crystals allows results to be easily transcribed into changes in the material’s magnetic field penetration depth, Δλ, an important quantity in the exploration of the underlying physics of its superconductivity. The resolution of the technique is of the order of one tenth of an angstrom for a sample of area ∼2 mm2.
X-ray diffraction analysis of the defect structure in epitaxial GaN
Authors: Heinke H. , Kirchner V. , Einfeldt S. , Hommel D.
Published: July 2002

High-resolution x-ray diffraction has been used to analyze the type and density of threading dislocations in (001)-oriented GaN epitaxial layers. For this, (00l) and (hkl) Bragg reflections with h or k nonzero were studied, the latter one measured in skew symmetric diffraction geometry. The defect analysis was applied to a variety of GaN layers grown by molecular-beam epitaxy under very different conditions. The outcome is a fundamental correlation between the densities of edge- and screw-type dislocations.
Reactions of O2+ with OH-isoprene adduct isomers: Exothermicity, product ions, and rate constants
Authors: Zhang Renyi , Lei Wenfang
Published: July 2002

The ion-molecule reaction C5H8OH+O2+→C5H8OH++O2 has been investigated in order to develop detection scheme for the OH-isoprene adduct radicals using the chemical ionization mass spectrometry (CIMS) method. Ab initio molecular orbital calculations have been employed to determine the structures and energies of the product ions from the charge transfer reactions of O2+ with the OH-isoprene adduct radicals. Geometry optimizations of the OH-isoprene adduct cations were performed with density function theory (DFT)-B3LYP calculations and the energies were computed with the single-point calculation using the coupled-cluster theory with single and double excitations including perturbative corrections for the triple excitations [CCSD(T)]. At the CCSD(T)/6-311G** level of theory with corrected zero-point-energy (ZPE), the ionization potentials of the four OH-isoprene adduct isomers with OH additions to C1- to C4-positions (isomers I to IV) are 6.9, 5.6, 6.0, and 7.1 eV, respectively. The ion-molecule collision rate constants between O2+ and the OH-isoprene adduct radicals were estimated using the average-dipole-orientation (ADO) theory, along with our calculated the permanent dipole moment and polarizability for the OH-isoprene adduct isomers. We also report direct measurements of the ion-molecule reaction rate constant using the CIMS method, which are in good agreement with the predicted values using the ADO theory.
Evidence of a dihydrogen bond in gas phase: Phenol–borane-dimethylamine complex
Authors: Naresh Patwari G. , Ebata Takayuki , Mikami Naohiko
Published: July 2002

We report here the formation of a gas phase complex bound by a dihydrogen bond between phenol and borane-dimethylamine in supersonic jets. Laser induced fluorescence excitation, fluorescence detected infrared, and IR–UV hole-burning spectroscopies were carried out to characterize the complex. Quantum chemical calculations were used to derive the structure of the complex, providing excellent agreement with the spectroscopic data. To the best of our knowledge, we for the first time established experimentally the formation of a dihydrogen bonded complex in the gas phase.
Temperature dependence of the electron–phonon scattering time of charge carriers in
p
-Si/SiGe heterojunctions
Authors: Andrievskiı̆ V. V. , Berkutov I. B. , Komnik Yu. F. , Mironov O. A. , Whall T. E.
Published: July 2002

Si/Si 0.64 Ge 0.36 heterojunctions with p-type conductivity exhibit an electron overheating effect. An analysis of the damping of the amplitudes of the Shubnikov–de Haas oscillations upon a change in temperature and applied electric field yields the temperature dependence of the electron–phonon relaxation time: teph=10−8T−2 s.
Self-consistent solutions to the intersubband rate equations in quantum cascade lasers: Analysis of a GaAs/AlxGa1−xAs device
Authors: Donovan K. , Harrison P. , Kelsall R. W.
Published: July 2002

The carrier transition rates and subband populations for a GaAs/AlGaAs quantum cascade laser operating in the mid-infrared frequency range are calculated by solving the rate equations describing the electron densities in each subband self-consistently. These calculations are repeated for a range of temperatures from 20 to 300 K. The lifetime of the upper laser level found by this self-consistent method is then used to calculate the gain for this range of temperatures. At a temperature of 77 K, the gain of the laser is found to be 34 cm−1/(kA/cm−2), when only electron–longitudinal-optical phonon transitions are considered in the calculation. The calculated gain decreases to 19.6 cm−1/(kA/cm−2) when electron–electron transition rates are included, thus showing their importance in physical models of these devices. Further analysis shows that thermionic emission could be occurring in real devices.
The calculation of C13 chemical shielding tensors in ionic compounds utilizing point charge arrays obtained from Ewald lattice sums
Authors: Stueber Dirk , Guenneau Flavien N. , Grant David M.
Published: July 2002

An embedded ion method is proposed for accurately calculating the C13 chemical shift tensors in ionic compounds. The method models an ionic crystal by embedding an ion of interest inside an array of point charges. The potential, produced by an infinite ionic lattice, at the location of the ion of interest can be simulated accurately utilizing a point charge array obtained by the Ewald summation method. The Ewald summation method, as implemented in the computer program EWALD, in conjunction with the quantum-mechanics program GAUSSIAN 98 is used to generate a self-consistent point charge array that simulates the Ewald potential in a defined region at the center of the array. Subsequently, the chemical shift tensor calculation is performed using GAUSSIAN 98 on the ion of interest positioned in the region inside the point charge array in which the Ewald potential is established. The embedded ion method was tested on potassium methyl-trithiocarbonate (KS2CSCH3) whose crystal lattice is composed of potassium cations and molecular S2CSCH3− anions. The principal values of the C13 chemical shift tensors in KS2CSCH3 were measured in a stationary cross polarization nuclear magnetic resonance experiment. It is shown that the correlation between experimental and calculated principal values improves significantly when the C–H bond distances are optimized from their x-ray values. It is further demonstrated that a substantial improvement in the correlation is obtained when the chemical shielding tensor calculation is performed on an S2CSCH3− anion embedded inside a point charge array obtained by the Ewald summation method. The embedded ion method was completed applying the B3P86/cc-pVTZ, B3LYP/cc-pVTZ, and MP2/cc-pVDZ quantum-mechanical computations and the various results are compared and analyzed.
Electron cyclotron emission imaging diagnostic of Te profiles and fluctuations
Authors: Deng B. H. , Domier C. W. , Luhmann N. C. , Brower D. L. , Donné A. J. H. , Oyevaar T. , van de Pol M. J.
Published: July 2002

A novel high resolution, two-dimensional (2-D) plasma diagnostic technique, electron cyclotron emission imaging, is reviewed. Its high spatial and temporal resolution is illustrated from the measurement of small-scale structure in Te profiles. Its 2-D measurement capability has been utilized to “visualize” plasma turbulence structures in the Rijnhuizen Tokamak Project (RTP) [Hogeweij et al., Phys. Scr. 51, 627 (1995)]. Comprehensive experimental results of Te fluctuations in RTP are presented. Possible correlation between the characteristics of the measured Te fluctuations and ηi mode theory predictions are indicated, which calls for further theoretical and experimental investigation. Future diagnostic developments are also discussed.
Interface states at the anodized Al2O3-metal interface
Authors: Hickmott T. W.
Published: July 2002

The capacitance of Al–Al2O3-metal capacitors with Al2O3 of different thicknesses, formed by anodizing evaporated Al films in ethylene glycol-based or H2O-based electrolytes to different voltages, has been measured between 10 kHz and 1 MHz for ten metal electrodes. The linear dependence of inverse capacitance on anodizing voltage, and thus on Al2O3 thickness, shows that there is an interface capacitance in series with the bulk capacitance due to the dielectric properties of anodized Al2O3. The interface capacitance, CI, is not a characteristic of the Al2O3-metal combination; it depends on the vacuum deposition conditions for the metal electrodes. CI is associated with interface states at the Al2O3-metal interface, not with field penetration into metal electrodes.
Temperature dependence of optical transitions in AlGaAs
Authors: Lourenço S. A. , Dias I. F. L. , Duarte J. L. , Laureto E. , Meneses E. A. , Leite J. R. , Mazzaro I.
Published: July 2002

AlGaAs structures with different aluminum concentration (x=0.0, 0.17, 0.30, and 0.40) were characterized by photoluminescence and photoreflectance techniques. The temperature dependence of optical transitions in the temperature ranging from 2 to 300 K were investigated. Y. P. Varshni [Physica (Utrecht) 34, 194 (1967)], L. Viña et al. [Phys. Rev. B 30, 1979 (1984)], and R. Pässler [Phys. Status Solidi B 200, 155 (1997)] models were used to fit the experimental points. The Pässler model gave the best adjustment to the experimental points. The tree models showed that the empirical parameters obtained through the adjustment of the experimental data in the three different models are aluminum composition dependent in the ternary alloy.