bluuebunny/crossref_metadata_2025 huggingface dataset:
Separation of Pure and Immunoreactive Virus‐Like Particles Using Gel Filtration Chromatography Following Immobilized Metal Ion Affinity Chromatography
Authors: Cheng Yu‐Shen , Lee Meng‐Shiou , Lai Su‐Yuan , Doong Shyue‐Ru , Wang Min‐Ying
Published: July 2002

A purification process was developed to obtain highly pure rVP2H particles, formed by a structural protein (VP2) of the infectious bursal disease virus (IBDV) with six additional histidine residues at its C‐terminus. The ultimate goal was the development of an efficient subunit vaccine against IBDV infection. The particles within the infected High‐Five (Hi‐5) cell lysates were partially purified by employing immobilized metal ion (Ni2+) affinity chromatography (IMAC). The initial step could recover approximately 85% of immunoreactive rVP2H proteins but failed to separate the rVP2H particles from the free rVP2H proteins or its degraded products. To separate the particulate form from the free form of rVP2H, an additional step was added, which used either gel filtration chromatography or CsCl density gradient ultracentrifugation. Both were able to produce extremely pure rVP2H particles with a buoyant density close to 1.27 g/cm3. However, the former method can process a larger sample volume than does the latter. By integrating IMAC and gel filtration chromatography, 1 mg of extremely pure rVP2H particles was routinely obtained from a 500 mL Hi‐5 cell culture broth. The separation of the particulate form from the free form of rVP2H proteins exposes their respective immunogenicity to induce the virus‐neutralizing antibodies and the ability to protect chickens from IBDV infection. Additionally, the abundant quantities of pure rVP2H particles coupled with their uniform dimensions facilitates an understanding of higher order structure of the immunogenic particles and can therefore result in improved vaccines against the virus.
Correction of mucopolysaccharidosis type IIIb fibroblasts by lentiviral vector-mediated gene transfer
Authors: VILLANI Guglielmo R.D. , FOLLENZI Antonia , VANACORE Borghina , di DOMENICO Carmela , NALDINI Luigi , di NATALE Paola
Published: July 2002

Mucopolysaccharidosis type IIIB (MPS IIIB; or Sanfilippo syndrome type B) is a lysosomal disease, due to glycosaminoglycan storage caused by mutations on the α-N-acetylglucosaminidase (NAGLU) gene. The disease is characterized by neurological dysfunction but relatively mild somatic manifestations. No effective treatment is available for affected patients. In the present study, we evaluated the role of a lentiviral vector as the transducing agent of NAGLU cDNA in MPS IIIB fibroblasts. The vector expressed high transduction efficiency and high levels of enzymic activity, 20-fold above normal levels, persisting for at least 2 months. PCR experiments confirmed the integration of the viral vector into the target genome. The NAGLU activity restored by virus infection was sufficient to normalize glycosaminoglycan accumulation, which is directly responsible for the disease phenotype. Metabolic labelling experiments on transduced fibroblasts exhibited, in the medium and in cellular lysates, polypeptide forms of 84 and 80kDa respectively related to the precursor and mature forms of the enzyme. The enzyme secreted by transduced MPS IIIB fibroblasts was endocytosed in deficient cells by the mannose 6-phosphate system. Thus we show that lentiviral vectors may provide a therapeutic approach for the treatment of MPS IIIB disease.
Mu-class glutathione transferase from Xenopus laevis: molecular cloning, expression and site-directed mutagenesis
Authors: De LUCA Antonella , FAVALORO Bartolo , ANGELUCCI Stefania , SACCHETTA Paolo , Di ILIO Carmine
Published: July 2002

A cDNA encoding a Mu-class glutathione transferase (XlGSTM1-1) has been isolated from a Xenopus laevis liver library, and its nucleotide sequence has been determined. XlGSTM1-1 is composed of 219 amino acid residues with a calculated molecular mass of 25359Da. Unlike many mammalian Mu-class GSTs, XlGSTM1-1 has a narrow spectrum of substrate specificity and it is also less effective in conjugating 1-chloro-2,4-dinitrobenzene. A notable structural feature of XlGSTM1-1 is the presence of the Cys-139 residue in place of the Glu-139, as well as the absence of the Cys-114 residue, present in other Mu-class GSTs, which is replaced by Ala. Site-directed mutagenesis experiments indicate that Cys-139 is not involved in the catalytic mechanism of XlGSTM1-1 but may be in part responsible for its structural instability, and experiments in vivo confirmed the role of this residue in stability. Evidence indicating that Arg-107 is essential for the 1-chloro-2,4-dinitrobenzene conjugation capacity of XlGSTM1-1 is also presented.
Interleukin 4 therapy for patients with chronic lymphocytic leukaemia: a phase I/II study
Authors: Lundin J. , Kimby E. , Bergmann L. , Karakas T. , Mellstedt H. , Österborg A.
Published: July 2002

Interleukin 4 (IL‐4) is a pleiotropic type II cytokine which has been shown to have a direct killing effect on lymphoma and B‐cell chronic lymphocytic leukaemia (B‐CLL) cellsin vitro. The clinical effects and toxicity of IL‐4 treatment in patients with B‐CLL were evaluated. Fourteen patients with B‐CLL who were in partial remission after chemotherapy received one, two or three 8‐week cycles of escalating doses (2, 4 or 6 µg/kg/d s.c.) of IL‐4 for 3 d/week. Clinical response was analysed after each treatment cycle and toxicity was monitored continuously. Ten patients (71%) had progressive disease (PD) during IL‐4 treatment. This was mainly attributable to an increase (two‐ to fourfold) of the blood lymphocyte count during IL‐4 therapy. After cessation of IL‐4 treatment, the lymphocytosis decreased spontaneously in 8 out of 12 evaluable patients. Splenomegaly remained unchanged in 7/7 patients, whereas enlarged lymph nodes were reduced by > 50% in 1/13 patients and by 25–50% in 4/13 patients. None of the patients achieved an objective tumour regression (complete or partial remission). A temporary increase (16–60%) of the platelet count was observed during IL‐4 treatment. The platelet count decreased in 8/11 patients after the end of IL‐4 therapy. World Health Organization (WHO) grade I/II fever, arthralgia and fatigue was observed in one‐third of the patients and was more commonly seen with the highest dose (6 µg/kg/d). One patient developed pulmonary oedema and WHO grade III neutropenia was recorded in three patients. IL‐4 was well tolerated by most patients in an outpatient setting. The anti‐tumour activity observed in previousin vitrostudies was not verified by the presentin vivotrial which showed that IL‐4 may instead increase the number of CLL cells in blood, indicating that IL‐4 may have induced a stimulatory or antiapoptotic effect on the CLL cells in blood. These results may have important implications for the development of immunotherapy of CLL. In addition, the potential platelet‐stimulatory effect of IL‐4 warrants further studies.
Nucleotide‐binding domain 1 of cystic fibrosis transmembrane conductance regulator
Authors: Duffieux Francis , Annereau Jean‐Philippe , Boucher Julien , Miclet Emeric , Pamlard Olivier , Schneider Michael , Stoven Véronique , Lallemand Jean‐Yves
Published: July 2002

Cystic fibrosis is caused by mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). This protein belongs to the large ATP‐binding cassette (ABC) family of transporters. Most patients with cystic fibrosis bear a mutation in the nucleotide‐binding domain 1 (NBD1) of CFTR, which plays a key role in the activation of the channel function of CFTR. Determination of the three dimensional structure of NBD1 is essential to better understand its structure–function relationship, and relate it to the biological features of CFTR. In this paper, we report the first preparation of recombinant His‐tagged NBD1, as a soluble, stable and isolated domain. The method avoids the use of renaturing processes or fusion constructs. ATPase activity assays show that the recombinant domain is functional. Using tryptophan intrinsic fluorescence, we point out that the local conformation, in the region of the most frequent mutation ΔF508, could differ from that of the nucleotide‐binding subunit of histidine permease, the only available ABC structure. We have undertaken three dimensional structure determination of NBD1, and the first two dimensional 15N‐1H NMR spectra demonstrate that the domain is folded. The method should be applicable to the structural studies of NBD2 or of other NBDs from different ABC proteins of major biological interest, such as multidrug resistance protein 1 or multidrug resistance associated protein 1.
The value of family screening for patients with cystine stone disease in northern Jordan
Authors: Bani Hani  , Matani  , Smadi
Published: July 2002

Objective

 To assess the prevalence of cystinuria and cystine stone disease among families of patients with cystine stones, and to determine their distribution by age, sex and associated morbidity.

Subjects and methods

 The study comprised 180 relatives (87 males and 93 females, mean age 43 years) descended from two brothers over four generations who live in two areas in northern Jordan. Data were collected using a questionnaire and home visits, by urinary cystine testing and radiology to detect stone, and assessing hypertension and renal impairment.

Results

 Of the 180 subjects, 104 (58%) had a positive reaction for cystine in urine; 33 (32%) of these were younger than 15 years. Twenty members (11%) of the families had evidence of renal cystine stone disease. Hypertension and renal impairment were detected in a significant proportion of individuals with cystine stone disease.

Conclusion

 Cystinuria is a major risk factor for cystine stone formation. Family screening is valuable in detecting the cystinuric population and in assessing individuals with stones. Early recognition, treatment and counselling result in better management and prevention. The establishment of a cystine study group in our region is essential.
Community‐Acquired Pneumonia in Older Veterans: Does the Pneumonia Prognosis Index Help?
Authors: Mody Lona , Sun Rongjun , Bradley Suzanne
Published: July 2002

OBJECTIVES:

Mortality rates from pneumonia increase steadily with age. Recently, a disease severity model (the Pneumonia Prognosis Index (PPI)) has been developed to predict mortality from community‐acquired pneumonia (CAP). PPI ranks severity of pneumonia from 1 to 5, with 5 being most severe. This retrospective study utilizes the PPI to address the prognosis of CAP in older adults.

DESIGN:

Retrospective review of medical charts.

SETTING:

Department of Veterans Affairs Medical Center.

PARTICIPANTS:

All adults aged 60 and older admitted to a Veterans Affairs Medical Center with CAP between January 1 and December 31, 1998.

MEASUREMENTS:

PPI was calculated using subjects' demographics, comorbidities, presenting symptoms, and laboratory measurements.

RESULTS:

Eighty‐two patients aged 60 and older were admitted with 101 episodes of CAP. The mean age ± standard deviation was 72 ± 9. Seventy‐four episodes were admitted from the emergency room, 20 from another hospital, seven from nursing homes, and five from outpatient clinics. Mean length of stay was 7.1 ± 6 days. Comorbid conditions included coronary artery disease, diabetes mellitus, congestive heart failure, neoplasm, stroke, and renal failure. Most episodes fell into higher PPI classes, with 20% in Class 3, 46% in Class 4, and 32% in Class 5. PPI score was significantly related to length of stay (P < .001), intensity of care (P < .0001), and presence of complications (P < .001). Mortality was 14% at 30 days: 0.5% in Class 3, 10.8% in Class 4, and 25% in Class 5.

CONCLUSION:

The PPI was effective in identifying older adults with CAP who were at risk of a poor outcome, but the practical utility of this index remains to be determined. Further prospective studies are required to elucidate the importance of comorbidities, severity at presentation, and premorbid functional status on clinical and functional outcomes of CAP in older adults. J Am Geriatr Soc 50:434–438, 2002.
Second-harmonic generation at 421 nm using injection-locked GaAlAs laser array and KNbO3
Authors: Chun M. K. , Goldberg L. , Weller J. F.
Published: July 2002

Significant improvement in frequency doubling efficiency of a cw output of a GaAlAs laser diode is described. Up to 0.72 mW of 421 nm power was generated by illuminating a KNbO3 crystal with a 270 mW diffraction-limited beam generated by an externally injection-locked laser diode array, operating in a single-mode and single-far-field lobe.
Coherence length in quantum interference devices having periodic potential
Authors: Tsubaki Kotaro , Tokura Yasuhiro
Published: July 2002

A measurement of coherence length in the quantum interference device using drain current oscillation is proposed. The coherence length for a quantum interference device, called the washboard transistor, is measured by the proposed method. The merit of this method is that the quantitative value of the coherence length is measured using only quantum interference phenomena.
Diffusion coefficient of a pair of nitrogen atoms in float-zone silicon
Authors: Itoh Taizoh , Abe Takao
Published: July 2002

Outdiffusion profiles of nitrogen in silicon were measured by secondary ion mass spectrometry to determine its diffusion coefficient in a temperature range of 800–1200 °C. The total amount of the nitrogen outdiffusion agrees with the change in infrared absorption by heat treatment. The experimental results give the diffusion coefficient of nitrogen as D=2.7×103 exp(−2.8eV/kT)cm2/s. This value is five orders of magnitude larger compared with the reported expression of 0.87 exp(−3.29eV/kT)cm2/s. Nitrogen–nitrogen-pair-like molecule in crystals corresponds to the former value and substitutional nitrogen atom to the latter one. These two types of nitrogen in silicon may allow us to clarify the various effects of nitrogen such as strengthening of crystals and suppression of swirls and D-defect generation.
Spectroscopic and ion probe measurements of KrF laser ablated Y-Ba-Cu-O bulk samples
Authors: Dyer P. E. , Greenough R. D. , Issa A. , Key P. H.
Published: July 2002

The KrF laser ablation of Y-Ba-Cu-O bulk samples has been studied using visible UV spectroscopy and ion probes. Principal luminescent species, expansion velocities, and the extent of ionization in the ablation plume have been determined in this way, providing information on the interaction of relevance to ablation as a film deposition source.
Oxygen-nitrogen complexes in silicon formed by annealing in nitrogen
Authors: Hara Akito , Fukuda Tetsuo , Miyabo Toru , Hirai Iesada
Published: July 2002

Oxygen-nitrogen complexes with the shallow donor characteristic represented by the effective mass theory were formed in Czochralski silicon (CZ Si) annealed in a nitrogen atmosphere. By fitting the depth profile of this defect to a diffusion equation, we estimated the nitrogen diffusion coefficient to be about 2×10−6 cm2/s at 1270 °C. This value is 105 times larger than that indicated by previously reported data.
GaAs/AlGaAs multiquantum well infrared detector arrays using etched gratings
Authors: Hasnain G. , Levine B. F. , Bethea C. G. , Logan R. A. , Walker J. , Malik R. J.
Published: July 2002

Efficient coupling of long-wavelength infrared (LWIR) radiation to a two-dimensional (2-D) array of GaAs/AlGaAs multiple quantum well detectors is achieved by illumination through chemically etched diffraction gratings. Gratings were fabricated on the back surface of the GaAs substrate as well as selectively on the top contact of the detector mesas. Both top and bottom illumination schemes were employed. In all cases, high coupling efficiency (>90%) of the gratings was observed as measured by comparing the responsivity to that of an identical detector illuminated through an angle-polished facet. The results demonstrate the feasibility of high-sensitivity GaAs LWIR imagers.
Soft and hard ionization thresholds in Si and GaAs
Authors: Sano Nobuyuki , Aoki Takahiro , Yoshii Akira
Published: July 2002

We introduce a new simple model of ionization probabilities in semiconductors, which clarifies the origin of softness and hardness of the ionization thresholds observed in Si and GaAs, respectively. It is shown that the ionization probability is, in principle, hard in both materials in the sense that the electrons rapidly ionize when they approach the threshold energies, and that the softness is mainly introduced from the fact that the threshold energies strongly depend upon the wave vectors of the initiating electrons.
Preferential propagation of pores during the formation of porous silicon: A transmission electron microscopy study
Authors: Chuang S.-F. , Collins S. D. , Smith R. L.
Published: July 2002

A transmission electron microscopy study of porous silicon reveals that pores selectively propagate in the 〈100〉 crystallographic directions on both n- and p-type silicon, independent of dopant concentration or anodization conditions.
Interband tunneling in single-barrier InAs/AlSb/GaSb heterostructures
Authors: Beresford R. , Luo L. F. , Longenbach K. F. , Wang W. I.
Published: July 2002

Negative differential resistance due to interband tunneling has been observed at room temperatures for the first time in polytype heterostructures of InAs/AlSb/GaSb. The peak-to-valley ratio is about 1.7:1 (5.5:1 at 77 K) for an AlSb barrier width of 2.5 nm. The peak current density is studied as a function of barrier width and compared to calculations based on the two-band model.
Hydrogen-accelerated thermal donor formation in Czochralski silicon
Authors: Stein H. J. , Hahn S. K.
Published: July 2002

Acceleration of thermal donor formation at 400 °C in Czochralski Si by a hydrogen plasma has been observed using low-temperature infrared absorption and spreading resistance probe measurements. The accelerated formation in as-grown Si is attributed to hydrogen diffusion and catalyzed conversion of electrically inactive nuclei to thermal donors. When the nuclei concentration is small such as in rapid thermal annealed Si, hydrogen interaction at SiO bonds is suggested as the rate-limiting step in thermal donor formation.
Tunable diode laser frequency modulation spectroscopy through an optical fiber: High-sensitivity detection of water vapor
Authors: Carlisle Clinton B. , Cooper David E.
Published: July 2002

Frequency modulation spectroscopy through a single-mode optical fiber has been demonstrated for monitoring H2O vapor at 7665 cm−1. Using a 2.5 mW distributed feedback laser and 100 m of optical fiber, a minimum detectable absorption of 5×10−7 was achieved. To obtain this sensitivity limit, very large spurious signals and technical noise were suppressed using a dual-channel detection scheme.
Ordering in semiconductor alloys
Authors: Bernard J. E. , Dandrea R. G. , Ferreira L. G. , Froyen S. , Wei S.-H. , Zunger A.
Published: July 2002

A thermodynamic first-principles theory of stability, including charge transfer, elastic forces, and atomic relaxations reveals the physical origins of stable and metastable ordering in bulk and epitaxial semiconductor alloys and superlattices.
Thermoelectric effect spectroscopy of deep levels—application to semi-insulating GaAs
Authors: Šantić B. , Desnica U. V.
Published: July 2002

A new method, thermoelectric effect spectroscopy, is proposed for the analysis of deep levels in semi-insulating materials. Besides the information on energy position and relative concentrations of traps, the main advantage of the method is its ability to determine the trap sign, i.e., the method is capable to resolve electron traps from hole traps. The proposed method is very simple for application. It is also shown how in combination with other techniques it can give a complete picture about trap-filling dynamics during low-temperature transient phenomena caused by illumination. The applicability and validity of the method are demonstrated on GaAs in which both electrons and hole traps are found.
Proposal of novel electron wave coupled devices
Authors: Tsukada N. , Wieck A. D. , Ploog K.
Published: July 2002

We propose a novel structure for electron wave devices that utilizes the mutual coupling effect between electron wave guides. The structure consists of two parallel electron wave guides with a coupling region controlled by a gate voltage. Using simple theoretical calculations, we estimate the switching time and the coupling length required for electron transfer to be 2 ps and 0.28 μm, respectively.
Preparation of bulk metallic glass Pd40Ni40P20 under high pressure
Authors: Xu Yingfan , Huang Xinming , Wang Wenkui
Published: July 2002

The bulk metallic glass Pd40Ni40P20 was prepared from the cast alloy in a belt apparatus under high pressure. The absence of crystallization in the bulk metallic glass was confirmed by x-ray diffraction and differential thermal analysis. The microstructure of the glass was examined by scanning electron microscopy and optical microscopy.
Power and magnetic field-induced microwave absorption in Tl-based high T
c superconducting films
Authors: Portis A. M. , Cooke D. W. , Gray E. R. , Arendt P. N. , Bohn C. L. , Delayen J. R. , Roche C. T. , Hein M. , Klein N. , Müller G. , Orbach S. , Piel H.
Published: July 2002

The increase in the microwave surface resistance Rs of high Tc superconductors at elevated microwave power levels is reported for both oriented and unoriented Tl-based films as a function of rf magnetic field at 820 MHz and 18 GHz. The application of dc magnetic fields produces qualitatively similar increases in Rs and in the surface reactance Xs. The increase in Rs with dc field is shown to arise from simple decoupling of grains by intergranular magnetic flux. The increase in Rs with microwave power, on the other hand, is a consequence of hysteretic intergranular processes.
Reduction in sidewall recombination velocity by selective disordering in GaAs/AlGaAs quantum well mesa structures
Authors: Hamao N. , Sugimoto M. , Kohmoto S. , Yokoyama H.
Published: July 2002

Sidewall recombination in SiO2-capped GaAs/AlGaAs multiple quantum well mesa structures is investigated using a time-resolved photoluminescence technique. Nonradiative recombination lifetimes in annealed samples are improved significantly compared with those in samples which are not annealed. This effect contributes to a reduction in sidewall recombination velocity due to disordering of quantum wells at the sidewall by cap annealing. Numerical analysis is used to fit the experimentally observed sample size dependence of the nonradiative lifetimes to calculated curves. This shows that the effective sidewall recombination velocity is reduced from 8×106 to 4×104 cm/s.
Study of the composition of thin dielectrics grown on Si in a pure N2O ambient
Authors: Chu T. Y. , Ting W. , Ahn J. H. , Lin S. , Kwong D. L.
Published: July 2002

The composition of ultrathin oxides grown on both [100] and [111]Si substrates in pure N2O in a conventional furnace has been studied using Auger electron spectroscopy (AES) analysis, chemical etching, and electrical measurements. Results show a peak nitrogen concentration at the Si-SiO2 interface which decreases from the Si-SiO2 interface to the oxide surface. This nitrogen distribution is responsible for superior electrical properties of metal-oxide-semiconductor (MOS) devices with these films as gate dielectrics.
Characterization of Y-Ba-Cu-O thin films and yttria-stabilized zirconia intermediate layers on metal alloys grown by pulsed laser deposition
Authors: Reade R. P. , Mao X. L. , Russo R. E.
Published: July 2002

The use of an intermediate layer is necessary for the growth of YBaCuO thin films on polycrystalline metallic alloys for tape conductor applications. A pulsed laser deposition process to grow controlled-orientation yttria-stabilized zirconia (YSZ) films as intermediate layers on Haynes Alloy No. 230 was developed and characterized. YBaCuO films deposited on these YSZ-coated substrates are primarily c-axis oriented and superconducting as deposited. The best YBaCuO films grow on (001) oriented YSZ intermediate layers and have Tc (R=0) = 86.0 K and Jc ∼ 3×103 A/cm2 at 77 K.
Fabrication and properties of polycrystalline-SiC/Si structures for Si heterojunction devices
Authors: Chaudhry M. I. , Wright R. L.
Published: July 2002

Polycrystalline-SiC/Si heterojunctions are fabricated by growing n-type polycrystalline SiC films on p-type Si substrates using a low-temperature chemical vapor deposition technique. The heterojunctions show rectification with low leakage currents. The typical value of the ideality factor is 1.2. This study indicates that polycrystalline SiC is a promising material for fabricating Si heterojunction devices.
Long-range, minority-carrier transport in high quality ‘‘surface-free’’ GaAs/AlGaAs double heterostructures
Authors: Gilliland G. D. , Wolford D. J. , Kuech T. F. , Bradley J. A.
Published: July 2002

Using a novel time-resolved optical photoluminescence imaging technique, analogous to the electrical Haynes–Shockley experiment, we have measured room-temperature minority-carrier transport in a series of ‘‘surface-free’’ GaAs/Al0.3Ga0.7As double heterostructures. These measurements are only possible in ‘‘surface-free’’ samples in which the band-to-band radiative recombination lifetimes are long−here up to 2.5 μs. We find minority-carrier transport to be ‘‘diffusive,’’ with diffusion lengths of up to ∼140 μm. We also find transport in thick (≳1 μm) structures to be mediated by hole-dominated ambipolar diffusion, whereas for thinner structures a transition from ambipolar to free-electron-dominated diffusion is observed. These results demonstrate that our heterostructures become effectively modulation doped for GaAs thicknesses ≲1 μm.
Measurement of thermal diffusivity of polycrystalline diamond film by the converging thermal wave technique
Authors: Lu Grant , Swann Walter T.
Published: July 2002

The in-plane thermal diffusivity of a polycrystalline diamond film has been measured to be 7.05 cm2/s with the converging thermal wave technique. This technique is shown to be simple, accurate, rapid to perform, and is independent of sample thickness and shape. Both high and low thermal diffusivity materials can be characterized with the technique.
Method to obtain uniform bookshelf textures in smectic C* liquid crystals
Authors: Jákli A. , Saupe A.
Published: July 2002

A new method is described to obtain homogeneous bookshelf textures in thin films of ferroelectric smectic C* material with short pitch and high Ps. The surfaces were coated with silane to obtain a homeotropic texture. The sample was realigned to a homogeneous bookshelf texture under simultaneous application of an electric field and shearing. The texture is stable and gives a very good contrast (∼80) under permanent drive condition.
Characterization of photoluminescent porous Si by small-angle scattering of x rays
Authors: Vezin V. , Goudeau P. , Naudon A. , Halimaoui A. , Bomchil G.
Published: July 2002

A microstructural study of high-porosity porous silicon layers formed on lightly P-doped wafers has been performed by x-ray small-angle scattering (SAXS) using the powerful and parallel beam of the synchrotron radiation. When the porosity of the sample is increased from 55% to 85% there is a continuous modification in the shape of the scattering profiles. The silicon skeleton mass fractal dimension decreases continuously. For porosity around 85%, the value for which the sample starts to display a strong photoluminescence at room temperature, there is a large increase in the pore size. The scattering profiles are characteristic of an isotropic three-dimensional structure.
Relationship between nonlinear resistivity and the varistor forming mechanism in ZnO ceramics
Authors: Raghu N. , Kutty T. R. N.
Published: July 2002

The use of a number of perovskite phases M″ M′O3−x, as the only forming additive in ZnO ceramics, produces a high nonlinearity index, α(up to 45), where M′ is a multivalent transition-metal ion and M″ is an alkaline earth or a rare-earth ion. From this study, the formation parameters crucial to high nonlinearity, such as nonstoichiometry in the as-received ZnO powder, low x values of the additives and fast cooling rate after the sintering, are explainable on the basis of a depletion layer formation at the presintering stage. This is because of the surface states arising out of the chemisorbed oxygen. The depletion layer is retained during sintering as a result of the higher valence state of M′ ions, preferentially present at the grain-boundary regions. The fast cooling freezes in the high-temperature concentration of donor-type defects, thereby decreasing the depletion layer width.
X-ray photoelectron spectroscopy of initial stages of nucleation and growth of diamond thin films during plasma assisted chemical vapor deposition
Authors: Waite M. M. , Shah S. I.
Published: July 2002

We have carried out x-ray photoelectron spectroscopy on diamond thin films deposited by microwave assisted chemical vapor deposition technique using a H2-CH4 plasma. Films grown for different lengths of time, from 1 min to several hours, were analyzed for the surface composition in the C 1s and Si 2p regions. The results indicate the presence of SiC in the initial stage of nucleation due to the carbon interaction with the Si substrate. Graphite starts to form in early stages of nucleation as the substrate becomes supersaturated with carbon. A diamond peak starts to appear after the incubation period and a simultaneous decrease in the carbide and graphite peak intensities was observed. Graphite is preferentially etched during the growth but SiC remains as an impurity even after several hours of deposition.
Off-axis laser deposition of YBa2Cu3O7−δ thin films
Authors: Holzapfel B. , Roas B. , Schultz L. , Bauer P. , Saemann-Ischenko G.
Published: July 2002

We report on YBa2Cu3O7−δ thin-film preparation by a new laser deposition geometry, the so-called off-axis laser deposition. Combined with radiation-based substrate heating, this results in c-axis oriented, epitaxial YBa2Cu3O7−δ thin films with critical current densities above 106 A/cm2 at 77 K and zero field and an exceptionally good surface quality, with complete absence of the otherwise observed laser droplets. As proved by atomic force microscopy, the surface roughness is <80 Å over an area of at least 10×10 μm2. Using this off-axis geometry it is possible to coat both sides of a substrate simultaneously, providing a one-step process in double-sided thin-film deposition. Both YBa2Cu3O7−δ films on the substrate show identical superconducting properties.
Investigation of the growth mechanism of diamond (111) facets using high resolution electron energy loss spectroscopy
Authors: Sun Biwu , Zhang Xiaopin , Zhang Qinzhe , Lin Zhangda
Published: July 2002

Diamond (111) facets deposited at 0.2% CH4 by remote feed with hot filament chemical vapor deposition (HFCVD) method have been investigated using high resolution electron energy loss spectroscopy (HREELS). The grown diamond (111) facets are terminated by CH radicals. With the help of atomic deuterium reaction with (111) facets, it is found that (111) facets consist of (111) faces and {110} steps, and atomic deuterium first replaces the hydrogen atoms adsorbed on (111) faces. After the continuous growth of grown diamond (111) facets at 0.2% CH4 of local feed for 30 min, CH3 vibrational modes on (111) facets have been detected. It is suggested that both C2H2 and CH3/CH4 contribute to the growth of diamond (111) surface, the C2H2 species to the growth along [011̄] direction, and CH3 radicals to the formation of kernels.
X-ray and Raman scattering characterization of Ge/Si buried layers
Authors: Headrick R. L. , Baribeau J.-M. , Lockwood D. J. , Jackman T. E. , Bedzyk M. J.
Published: July 2002

Germanium buried layers in (001) oriented silicon with thicknesses of 2–12 monolayers have been studied with synchrotron x-ray diffraction, x-ray reflectivity, and Raman scattering spectroscopy of visible light. Relaxation, strain, and intermixing have been observed via diffraction and intermixing is inferred from vibrational frequency shifts.
Epitaxial Si films on Ge(100) grown via H/Cl exchange
Authors: Gates S. M. , Koleske D. D. , Heath J. R. , Copel M.
Published: July 2002

Thin Si films have been grown isothermally on Ge(100) substrates using alternating exposures of Si2H6 and Si2Cl6, maintaining chlorine and hydrogen surface termination. At 465 °C, film growth rate is roughly 2 monolayer per cycle (one cycle equals 1 Si2H6 and 1 Si2Cl6 exposure). At 475 °C a uniform epitaxial film is obtained, while islanding is observed at higher T. This process is thermally activated and is not strictly self-limiting, but has certain desirable characteristics of atomic layer epitaxy growth.
InGaAs/GaAs strained quantum wire lasers grown by organometallic chemical vapor deposition on nonplanar substrates
Authors: Walther M. , Kapon E. , Caneau C. , Hwang D. M. , Schiavone L. M.
Published: July 2002

The structure and device characteristics of InGaAs/GaAs strained quantum wire (QWR) lasers grown by organometallic chemical vapor deposition on 0.25-μm pitch periodic corrugations are reported. The crescent-shaped InGaAs wires, 14–17 nm thick and 70–80 nm in full width, are formed in situ due to surface diffusion of In and Ga species to the bottom of the grating grooves. Room-temperature pulsed operation has been achieved with threshold current densities of 1.9 kA/cm2 for 1.1 mm long lasers with uncoated facets. For laser stripes aligned perpendicular to the wires, the lasing wavelength remains almost constant at 920 nm for temperatures 80<T<150 K due to second-order Bragg reflection from the QWR array. The possibility of achieving gain-coupled distributed feedback using the periodic gain modulation in these devices is discussed.
Low temperature silicon epitaxy in an ultrahigh vacuum rapid thermal chemical vapor deposition reactor using disilane
Authors: Sanganeria Mahesh K. , Violette Katherine E. , Öztürk Mehmet C.
Published: July 2002

Epitaxial silicon films have been deposited by a new technique which combines an ultrahigh vacuum (UHV) environment with rapid thermal chemical vapor deposition (RTCVD). The technique is referred to as UHV/RTCVD. Using Si2H6, B2H6, and H2 as process gases, low temperature (T≤800 °C) and high throughput (growth rate ≳0.25 μm/min) processing have been achieved in the 90 mTorr (1 Pa=133.32 Torr) total pressure regime. Epitaxial growth was achieved on hydrogen passivated silicon surfaces without using a high temperature in situ clean. Effect of the growth temperature on the generation lifetime of the films grown on 4–11 Ω cm (100) silicon substrates was studied at three different temperatures of 700, 750, and 800 °C using the Zerbst technique. The epitaxial films were in situ doped with boron to a doping level of 1–2×1016 cm−3. Generation lifetimes, as high as 400 μs, were measured with no strong dependence on the growth temperature. Chemical purity of the films was studied using secondary ion mass spectroscopy, which indicated low oxygen and carbon levels on the order of 1017 cm −3.
Sequential-ion-implantation synthesis of ternary metal silicides
Authors: Tan Zhengquan , Namavar F. , Heald S. M. , Budnick J. I.
Published: July 2002

By implanting two different metals in sequence into Si(100), we find that new ternary silicides can by synthesized with simple binary silicide structures. The synthesis of CoSi2-type (Co,Fe)Si2, and CoSi-type (Co,Fe)Si and (Fe,Ni)Si is demonstrated. The structure is largely determined by the first implanted metal and the total dose of the two metals, allowing one to design the structure of the ternary silicide. The two implanted species occupy equivalent positions in the same structure and the metal composition may be continuously varied in a given structure. This opens new possibilities for the synthesis of ternary and multinary compounds and alloys.
Preparation of oriented PbTiO3 thin films using a spin-on sol-gel process
Authors: Carper Mark D. , Phulé Pradeep P.
Published: July 2002

A novel sol-gel process for the preparation of grain-oriented thin films of PbTiO3 is reported. Using a moisture tolerant molecularly modified titanium isopropoxide and hydrated lead acetate PbTiO3 films with both c- and a-axis orientations could be prepared on platinized silicon substrates at 550 °C. The average grain size of films prepared at 600 °C was ≊0.1 μm. The a-axis orientation increased with further heat treatment at temperatures between 600 and 700 °C. The relative changes in the thin film orientation may be due to thin films stresses caused by thermal expansion mismatch existing during cooling through the Curie transition temperature.
Photoluminescence in ZnSe-based quantum well wire structures
Authors: Ding J. , Nurmikko A. V. , Grillo D. C. , He Li , Han J. , Gunshor R. L.
Published: July 2002

We have fabricated quantum well wire structures by using electron beam lithography and reactive ion etching techniques on (Zn,Cd)Se/Zn(S,Se) multiple quantum well structures. Photoluminescence efficiencies have been studied as a function of the wire width (down to about 400 Å), and temperature. The results indicate that the sidewall surfaces exposed during the dry etching play an important role in providing nonradiative centers for the optically injected carriers, strongly diminishing the radiative efficiencies in the smallest structures.
Time-modulated electron cyclotron resonance plasma discharge for controlling generation of reactive species
Authors: Samukawa Seiji , Furuoya Shuichi
Published: July 2002

This study examines modulated electron cyclotron resonance (ECR) plasma discharge occurring within a few tens of μs. It can control the generation of reactive species in plasmas. Reactive species are measured by an actinometric optical emission spectroscopy in the pulsed plasma. Good correlation is found between the density ratio of CF2 radicals and F atoms in the CHF3 plasma, and the combination of the pulse duration and pulse intervals. These characteristics are explained by the dependence of reactive species generation in ECR plasma on a time within a few tens of μs. This method provides for controlling the polymerization during SiO2 etching.
Investigation of the recombination activity of misfit dislocations in Si/SiGe epilayers by cathodoluminescence imaging and the electron beam induced current technique
Authors: Higgs V. , Kittler M.
Published: July 2002

Misfit dislocations in as-grown and Ni-contaminated Si/SiGe epilayers have been characterized by cathodoluminescence (CL) spectroscopy, cathodoluminescence imaging, and the electron beam induced current technique (EBIC). Dislocations in the as-grown layers had no radiative recombination (D bands) and no detectable room temperature EBIC contrast. Following Ni contamination the D bands were observed and the EBIC contrast increased. CL dark line contrast is observed by monochromatic imaging of the Si substrate luminescence. The CL dark line contrast was observed from all the dislocations, whether contaminated or as grown. The CL dark line contrast and EBIC contrast show a 1:1 correspondence of the nonradiative recombination at the misfit dislocation and also a semiquantitative agreement with the variation in measured contrast of the individual dislocations.
Low-temperature silicon homoepitaxy by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition
Authors: Tae Heung-Sik , Hwang Seok-Hee , Park Sang-June , Yoon Euijoon , Whang Ki-Woong
Published: July 2002

High quality silicon homoepitaxial layers are successfully grown at 560 °C by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition (UHV-ECRCVD) using a SiH4/H2 plasma. The effects of substrate dc bias on the in situ hydrogen plasma clean and the subsequent silicon epitaxial growth are examined by the reflection high-energy electron diffraction (RHEED), secondary ion mass spectroscopy (SIMS), and cross-section transmission electron microscopy (XTEM). It is observed that the substrate dc bias plays a significant role in obtaining a damage-free, clean Si substrate prior to epitaxial growth. Severe damage in the Si surface is observed by XTEM, though RHEED shows a streaky pattern, when the substrate is electrically floating, but the damage can be suppressed with +10 V dc bias to the substrate. Substrate dc bias during plasma deposition drastically changes the crystal structure from polycrystalline at −50 V to high quality epitaxial silicon at substrate biases greater than +50 V. Precise control of the ion energy during in situ cleaning and plasma deposition is very important in low-temperature Si epitaxy by UHV-ECRCVD and it is possible by proper control of the substrate dc bias.
Activation characteristics of a long wavelength infrared hot-electron transistor
Authors: Lee C. Y. , Tidrow M. Z. , Choi K. K. , Chang W. H. , Eastman L. F. , Towner F. J. , Ahearn J. S.
Published: July 2002

The origin of current reduction in an infrared hot-electron transistor is examined by studying the thermal activation energy of the emitter and the collector dark current as a function of emitter bias Ve. For the emitter, the activation energy Eae is found to be determined by the thermionic emission (TE) process at a small Ve. At higher Ve, Eae decreases linearly with Ve due to the increase of the thermally assisted tunneling (TAT) current enhanced by dopant migration. For the collector, the activation energy Eac is significantly higher than Eae at low biases, indicating that the collector accepts higher energy electrons injected from the emitter. For the device under study, at Ve=0.5 V, the value of Eac is the same as that of the emitter at low biases. This result shows that, up to this bias, the collector dark current consists of only the TE current but not the TAT current, thus greatly improving the detector performance.
Synthesis of epitaxial Pt on (100)Si using TiN buffer layer by pulsed laser deposition
Authors: Tiwari P. , Wu X. D. , Foltyn S. R. , Jia Q. X. , Campbell I. H. , Arendt P. A. , Muenchausen R. E. , Peterson D. E. , Mitchell T. E. , Narayan J.
Published: July 2002

High-quality epitaxial Pt films were deposited by pulsed laser deposition on (100)Si using TiN as a buffer layer. The films were (100) oriented normal to the substrate surface with a high degree of in-plane orientation with respect to the major axes of the substrate and buffer layer. An ion beam minimum channeling yield of 39% was obtained for the Pt films, indicating high crystallinity. High-resolution transmission electron microscopy results showed that interfaces between substrate/film and film/film were quite smooth and no perceptible interdiffusion was observed. The epitaxial TiN layer effectively acts as a barrier to impede metal-substrate reaction and helps in good adhesion of the Pt films on (100)Si. This structure is suitable for epitaxial growth of oxide films on Si with an underlying conductive electrode.
Ultrafast-lifetime quantum wells with sharp exciton spectra
Authors: Lahiri I. , Nolte D. D. , Harmon E. S. , Melloch M. R. , Woodall J. M.
Published: July 2002

Sharp quantum-confined excitons in semi-insulating low-temperature-growth AlAs/GaAs quantum wells with 15 ps carrier lifetimes are demonstrated. High-quality well-barrier interfaces can be grown at low substrate temperatures and annealed up to temperatures of 700 °C, beyond which interface mixing broadens the exciton transitions. Electroabsorption from the quantum-confined Stark effect in as-grown modulators approaches 10 000 cm−1, which is comparable to traditional high-temperature growth quantum wells. The low-temperature growth quantum well structures eliminate the need for postgrowth processing, such as ion implantation for photorefractive quantum wells, ultrafast saturable absorption, or electro-optic sampling applications.
Blue-violet light emitting gallium nitride p-n junctions grown by electron cyclotron resonance-assisted molecular beam epitaxy
Authors: Molnar R. J. , Singh R. , Moustakas T. D.
Published: July 2002

Blue-violet gallium nitride (GaN) light emitting p-n junctions were grown by the method of electron cyclotron resonance-assisted molecular beam epitaxy. This method has been modified to minimize plasma induced defects. Contrary to similar devices grown by metalorganic chemical vapor deposition, these devices do not require any postgrowth annealing to activate the Mg acceptors in the p layer. These devices turn-on at approximately 3 V and have a spectral emission peaking at 430 nm.
Dynamics of a band-edge transition in GaN grown by molecular beam epitaxy
Authors: Smith M. , Chen G. D. , Lin J. Y. , Jiang H. X. , Salvador A. , Sverdlov B. N. , Botchkarev A. , Morkoç H.
Published: July 2002

Time-resolved photoluminescence spectroscopy has been used to probe the dynamics of optical transitions in GaN epitaxial layers grown by molecular beam epitaxy. In particular, systematic measurements on a band-edge transition at about 3.42 eV have been carried out. Recombination lifetimes of this transition have been measured at different emission energies. Our results clearly show that the time-resolved photoluminescence can provide immense value in the understanding of the dynamic processes of optical transitions in GaN.
Far-infrared laser diagnostic on ELMO Bumpy Torus and extreme far-forward laser scattering on the Impurity Study Experiment
Authors: Casson W. H. , Hutchinson D. P. , Ma C. H. , Staats P. A. , Wilgen J. B.
Published: July 2002

A far-infrared (FIR) laser scattering diagnostic has been installed on the ELMO Bumpy Torus (EBT) experiment, and tests conducted on the system using a TPX Bragg cell show that the system is fully functional. Scattering experiments to date have shown only small detectable signal levels during normal operation and during ion cyclotron heating (ICH) fast-wave and slow-wave propagation experiments. On the Impurity Study Experiment (ISX), the output signal from the rf amplifiers of the FIR interferometer has been spectrum analyzed and shows frequency-shifted sidebands that correspond to extreme far-forward scattering of the laser beam as it passes through the plasma. Although the scattered signal cannot be resolved spatially, the scattered intensity provides information about density fluctuation levels and MHD activity during different modes of operation. Agreement has been found with measurements made by the x-ray diagnostic and the heavy-ion beam probe.
Absolute calibration of a ten-channel grating polychromator for electron temperature measurements on Princeton large torus
Authors: Cavallo A. , Cutler R.
Published: July 2002

It has been possible to calibrate absolutely the ten-channel grating polychromator installed on PLT (Princeton large torus). Radiation from a blackbody source (eccosorb at liquid-nitrogen temperature) was chopped at 275 Hz and the signal detected using a lock-in amplifier with an integration time constant set at 125 s. A cascade of six grating filters was used to eliminate higher-order radiation from the input to the instrument. Each channel could be calibrated in approximately 2 h; under these conditions the rms calibration signal to noise for a typical channel is about 60.
Visible spectroscopy surveys of the OHTE plasma (abstract)
Authors: Jackson G. L. , Register D. F.
Published: July 2002

A Jarrell-Ash 0.27-m triple grating spectrometer with a high-speed intensified diode array detector has been used to perform time-resolved surveys of the visible emission (2200-7000 Å) from the OHTE plasma. Using a 512 diode array, spectra are obtained every 516 μs during the shot. The spectral width of the scan is 150, 300, or 1200 Å depending on the grating selected. Surveys at up to 500 kA for OHTE plasmas indicate a complete absence of metal emission lines with the graphite bead vacuum liner. In the 5200-Å region, a clear iindow has been identified for optical bremsstrahlung measurements. Other details of the spectra will be discussed.