bluuebunny/crossref_metadata_2025 huggingface dataset:
The effectiveness of manual and rotary techniques in the cleaning of root canals: a scanning electron microscopy study
Authors: Ahlquist M. , Henningsson O. , Hultenby K. , Ohlin J.
Published: July 2002

Aim

The purpose of this scanning electron microscope (SEM) study was to compare the cleanliness of the root canal walls following either a manual or a rotary technique of canal instrumentation. The hypothesis was that a rotary technique would produce a cleaner root canal.

Methodology

Manual filing was performed on 10 extracted teeth using stainless steel S‐files (Sjödings, Sendoline, Sweden). Powered instrumentation was carried out on a further 10 extracted teeth, using ProFile® rotary nickel–titanium files in a handpiece (250 r.p.m.) according to the manufacturer’s instructions. A solution of 0.5% sodium hypochlorite was used for irrigation. The roots were cut longitudinally and the canal walls were examined for debris and smear layer at the apical, middle and coronal level.

Results

Significantly less debris was found in the apical region using the manual filing technique (P < 0.05); no significant differences could be found at the other levels. Overall, significantly less debris was found on the root canal walls using the manual technique when the data from the three levels were compared (P = < 0.05).

Conclusions

The manual technique employed in this study produced cleaner root canal walls than the rotary ProFile® technique.
Sleep and behaviour disturbance in Prader–Willi syndrome: a questionnaire study
Authors: Richdale A. L. , Cotton S. , Hibbit K.
Published: July 2002

The present authors describe sleep problems, including sleep apnoea and excessive daytime sleepiness (EDS), in subjects with Prader–Willi syndrome (PWS). The present paper reports a questionnaire study regarding sleep and behaviour in a group of 29 subjects with PWS, compared with an age‐ and gender‐matched control group. Those with PWS suffered from sleep problems more frequently than the control subjects. Problems included EDS, snoring and early waking. Sleep problems in PWS were not associated with body mass index or weight. Excessive daytime sleepiness was a distinctive feature of the group with PWS, and behavioural disturbance in PWS children and adolescents was associated with EDS. Excessive daytime sleepiness seems to be characteristic of PWS, and may be related to problems with the sleep–wake cycle and hypothalamic dysfunction.
Insulin aspart vs. human insulin in the management of long‐term blood glucose control in Type 1 diabetes mellitus: a randomized controlled trial
Authors: Home P. D. , Lindholm A. , Riis A. ,   for the European Insulin Aspart Study Group
Published: July 2002

SUMMARY

Aims  To compare the efficacy of insulin aspart, a rapid‐acting insulin analogue, with that of unmodified human insulin on long‐term blood glucose control in Type 1 diabetes mellitus.

Methods  Prospective, multi‐centre, randomized, open‐labelled, parallel‐group trial lasting 6 months in 88 centres in eight European countries and including 1070 adult subjects with Type 1 diabetes. Study patients were randomized 2:1 to insulin aspart or unmodified human insulin before main meals, with NPH‐insulin as basal insulin. Main outcome measures were blood glucose control as assessed by HbA1c, eight‐point self‐monitored blood glucose profiles, insulin dose, quality of life, hypoglycaemia, and adverse events.

Results  After 6 months, insulin aspart was superior to human insulin with respect to HbA1c with a baseline‐adjusted difference in HbA1c of 0.12 (95% confidence interval 0.03–0.22) %Hb, P < 0.02. Eight‐point blood glucose profiles showed lower post‐prandial glucose levels (mean baseline‐adjusted −0.6 to −1.2 mmol/l, P < 0.01) after all main meals, but higher pre‐prandial glucose levels before breakfast and dinner (0.7–0.8 mmol/l, P < 0.01) with insulin aspart. Satisfaction with treatment was significantly better in patients treated with insulin aspart (WHO Diabetes Treatment Satisfaction Questionnaire (DTSQ) baseline‐adjusted difference 2.3 (1.2–3.3) points, P < 0.001). The relative risk of experiencing a major hypoglycaemic episode with insulin aspart compared to human insulin was 0.83 (0.59–1.18, NS). Major night hypoglycaemic events requiring parenteral treatment were less with insulin aspart (1.3 vs. 3.4% of patients, P < 0.05), as were late post‐prandial (4–6 h) events (1.8 vs. 5.0% of patients, P < 0.005).

Conclusions  These results show small but useful advantage for the rapid‐acting insulin analogue insulin aspart as a tool to improve long‐term blood glucose control, hypoglycaemia, and quality of life, in people with Type 1 diabetes mellitus.
GaAs-on-InP heteroepitaxial waveguides grown by molecular beam epitaxy
Authors: Lo Y. H. , Deri R. J. , Harbison J. , Skromme B. J. , Seto M. , Hwang D. M. , Lee T. P.
Published: July 2002

The GaAs-on-InP heteroepitaxial waveguides are demonstrated for the first time using molecular beam epitaxy. A propagation loss of 9.3 dB/cm was obtained for waveguides grown on a 3° off (100) InP substrate. Compared to the 16 dB/cm loss for waveguides on (100) InP substrates, the waveguides on misoriented InP substrates exhibited a significantly lower loss. Based on photoluminescence studies, we attribute the propagation loss in both samples mainly to optical absorption by crystal defects. Defect densities of 4×1017 cm−3 and 2×1017 cm−3 are estimated for material on (100) and 3° off (100) substrates, respectively. Such heteroepitaxial waveguides may have applications in long-wavelength photonic integrated circuits.
Reduced moisture-induced degradation of YBaCuO superconducting films by silver and high deposition temperatures
Authors: Chang Chin-An
Published: July 2002

Moisture-induced degradation of the YBaCuO superconducting films is studied using layer structures deposited at low temperatures with and without a silver covering layer, and using films deposited at high temperatures with a silver barrier layer. For the former, Ag/Cu/BaO/Y2O3/YSZ and Cu/BaO/Y2O3/YSZ are compared, where YSZ stands for yttria-stabilized zirconia substrate. Superconducting films with zero resistance between 80 and 87 K are obtained, depending on the annealing temperatures. Upon removing the samples from liquid nitrogen and warming in flowing nitrogen, a large rise in film resistivity is observed for the structures without silver, resulting in reduced temperatures for zero resistance and reduced critical current density at 77 K. Much less degradation is observed, however, with the samples containing a silver layer. For the samples deposited at high temperatures, no degradation is observed from similar moisture exposures.
Picosecond nonlinear polarization switching with a fiber filter
Authors: Trillo S. , Wabnitz S. , Finlayson N. , Banyai W. C. , Seaton C. T. , Stegeman G. I. , Stolen R. H.
Published: July 2002

We report ultrafast all-optical switching between two orthogonal linear polarizations in a periodically twisted, birefringent fiber filter.
YBaCuO superconducting films on SiO2 substrates formed from Cu/BaO/Y2O3/Ag layer structures
Authors: Chang Chin-An , Tsuei C. C. , McGuire T. R. , Yee D. S. , Boresh J. P. , Lilienthal H. R. , Farrell C. E.
Published: July 2002

Cu/BaO/Y2O3/Ag layer structures were deposited on SiO2 substrates at 600 °C and post-annealed in oxygen at different temperatures. Superconducting oxides with a thickness of 5000 Å were formed at 800 °C, with an onset of 92 K and a zero resistance at 70 K. The films contain mainly the YBa2Cu3O7 phase, with the 103 and 020 diffraction peaks being the major ones observed. The high deposition temperature used is shown to help the formation of the YBa2Cu3O7 phase, leading to the observed superconductivity using SiO2 substrates.
Superconducting Bi-Sr-Ca-Cu-O films by magnetron sputtering of single Bi2O3-SrF2-CaF2-CuO targets
Authors: Levinson M. , Shah S. S. P. , Naito N.
Published: July 2002

Superconducting Bi-Sr-Ca-Cu-O films have been fabricated by rf magnetron sputtering using single mixed Bi2O3-SrF2-CaF2-CuO targets. Uniform, reproducible films were formed on SrTiO3 substrates with zero resistance as high as 78 K. Grain morphology and orientation were affected by annealing temperature and the F content of the films. The final films showed excellent environmental and mechanical stability.
Fine structure of EL2 defect absorption in GaAs
Authors: Kuszko W. , Jeżewski M. , Baranowski J. M. , Kaminska M.
Published: July 2002

High-resolution measurements of the zero phonon line (ZPL) of the EL2 intracenter absorption were performed. Several samples, both Czochralski and Bridgman grown, have been examined. The shape and position of the ZPL were virtually identical for all the samples. No splitting of the ZPL was detected.
Heteroepitaxial growth of Ge films on Si substrates by molecular beam epitaxy
Authors: Zhou G. L. , Chen K. M. , Jiang W. D. , Sheng C. , Zhang X. J. , Wang Xun
Published: July 2002

A new approach of growing thick Ge layers on Si substrates by molecular beam epitaxy is presented. A 30–80 Å thick Ge overlayer is first deposited on the Si(100) substrate at room temperature. By thermally annealing the sample to 300 or 500 °C for 10 min, the Ge atoms cluster into randomly distributed islands which would play a role in releasing the mismatch stress at the interface. The Ge film of 10 000 Å thickness epitaxially grown on this surface at 550 °C shows a better crystalline quality than that grown by a conventional method. A full width at half maximum of 262 s for the Ge (400) x-ray diffraction peak has been achieved.
X-ray topography of the coherency breakdown in GexSi1−x/Si(100)
Authors: Eaglesham D. J. , Kvam E. P. , Maher D. M. , Humphreys C. J. , Green G. S. , Tanner B. K. , Bean J. C.
Published: July 2002

An x-ray topography study is presented of the coherency breakdown in GexSi1−x/Si(100) strained epilayers. Finite dislocation densities (in excess of 103 cm−2) are observed at compositions in the range 12–13 at. % Ge for an epilayer thickness of h≊180 nm. Above 13 at. % Ge the dislocation density starts to change rapidly and this composition is identified as critical for h≊180 nm, a thickness which is almost a factor of 4 lower than the accepted ‘‘critical’’ thickness for this lattice mismatch. The result suggests that in low-mismatched GexSi1−x alloys the dislocation density will increase continuously at the ‘‘critical’’ thickness, as opposed to exhibiting a sharp onset. The implications of these results to the various models of the critical thickness transition are discussed.
Intensity dependence of picosecond nonlinear response time of polydiacetylene
Authors: Yang Lina , Dorsinville R. , Ho P. P. , Zou W. K. , Yang N. L. , Alfano R. R.
Published: July 2002

The relaxation time of the transient degenerate four-wave mixing grating in 4-butoxycarbonylmethylurethane polydiacetylene in polymethylmethacrylate matrix films has been found to be laser energy fluence dependent. This phenomenon is attributed to a transient reversible light-induced structure change in polydiacetylene films, involving a cooperative effect originating from side-chain intramolecular hydrogen bonding.
Thermal and electric field induced defects in InP metal-insulator-semiconductor structures
Authors: Tin C. C. , Barnes P. A. , Neely W. C.
Published: July 2002

The presence of deep levels in several samples of InP metal-insulator-semiconductor (MIS) structures was studied using the deep level transient spectroscopy technique. The InP MIS structures were fabricated using three different methods of oxide formation, two of which are chemical oxides and the third is plasma-grown oxide. Defect levels ranging from (Ec−0.22) to (Ec−0.6) eV were observed in the samples. However, the levels at about (Ec−0.22) and (Ec−0.35) eV were detected only after increasing the reverse-bias voltage to −2 V at a temperature of about 390 K. This phenomenon occurred in all the samples studied, irrespective of the method of oxidation. The appearance of the peaks corresponding to the shallower traps is irreversible and may explain the performance instability commonly encountered in InP MIS-based devices.
High photoconductive gain in lateral InAsSb strained-layer superlattice infrared detectors
Authors: Kurtz S. R. , Biefeld R. M. , Dawson L. R. , Fritz I. J. , Zipperian T. E.
Published: July 2002

Both large photoconductive gain and long wavelength photoresponse were observed in lateral photodetectors constructed from type II, InAsSb, strained-layer superlattices. In a novel, four-layer superlattice, gain values as large as 90 are reported with a long wavelength cutoff of 8.7 μm at 77 K. The gain is sensitive to the structure and composition of the superlattice, and the sweepout of minority carriers is eliminated with the appropriate contacts.
AlGaAs/GaAs multiple quantum well reflection modulators grown on Si substrates
Authors: Dobbelaere W. , Huang D. , Ünlü M. S. , Morkoç H.
Published: July 2002

We report for the first time large excitonic absorption at room temperature in AlGaAs/GaAs multiple quantum well structures grown on Si substrates in a p-i-n configuration, using photocurrent measurements. We demonstrate an optical reflection modulator which is based on the quantum-confined Stark effect and exciton broadening with a reverse bias voltage applied across the p-i-n structure. A 7.7% change in the reflectivity of the device with 6 V reverse bias voltage was observed. These results demonstrate clearly that optical device quality AlGaAs/GaAs is obtainable directly on Si substrates which has great implications with regard to the monolithic integration of optical III-V and electronic Si technology.
Ion beam induced oxidation of silicon
Authors: Holmén G. , Jacobsson Harald
Published: July 2002

A new physical phenomenon causing oxidation of silicon has been observed. The phenomenon is controlled by the impact of an energetic ion beam on a clean silicon target exposed to low-pressure oxygen. An oxide layer of 50–100 Å can be formed at room temperature by properly choosing the oxidation conditions. The growth was studied in situ by measuring the ion-induced secondary electron yield. A strong dependence on oxygen pressure and target temperature was observed. By studying the oxide with x-ray photoelectron spectroscopy, it was concluded that the film formed is stoichiometric SiO2 . A discussion on possible growth mechanisms is carried out in terms of ion energy deposition.
Minority-carrier lifetime of magnetic field applied Czochralski silicon wafers
Authors: Higuchi T. , Gaylord E. , Rozgonyi G. A. , Shimura F.
Published: July 2002

The dependence of minority-carrier lifetimes and diffusion length on starting silicon materials grown by the magnetic field applied Czochralski (MCZ), conventional Czochralski(CZ), and float-zone (FZ) methods has been investigated with a capacitance-time relaxation technique. MCZ silicon yields longer minority-carrier lifetimes and diffusion length than those of both CZ and FZ silicon materials. The generation lifetime of MCZ silicon increases, while the recombination lifetime decreases, with the initial oxygen concentration. These characteristics are correlated with grown-in defects and gettering by oxygen-related defects.
Atmosphere-sensitive 225 K feature in internal friction of YBa2Cu3O7−δ
Authors: Staines M. P. , Tallon J. L. , Robinson W. H. , Flower N. E.
Published: July 2002

The Young’s modulus and internal friction of YBa2 Cu3 O7−δ were measured from 280 to 80 K at 40 kHz using an ultrasonic composite oscillator technique. Three internal friction peaks intrinsic to the polycrystalline material which were observed at 105, 125, and 225 K disappeared when the sample was deoxygenated. Other structure in the internal friction between 220 and 280 K is ascribed to water vapor. The 225 K peak is reversibly eliminated on exposure to moist air. This is suggestive of internal friction at crystal surfaces or grain boundaries.
Effect of the post-deposition processing ambient on the preparation of superconducting YBa2Cu3O7−x coevaporated thin films using a BaF2 source
Authors: Chan Siu-Wai , Bagley B. G. , Greene L. H. , Giroud M. , Feldmann W. L. , Jenkin K. R. , Wilkins B. J.
Published: July 2002

We have investigated the effect of the post-deposition processing ambient on the preparation of YBa2Cu3O7−x thin films from a BaF2 source. The role of H2O vapor during the high-temperature anneal is understood through a thermodynamic analysis of the fluorine removal reaction. The role of a HF getter (e.g., SiO2) is understood through the same type of analysis. We have demonstrated that a zero resistance transition temperature at 77 K can be obtained for an annealing temperature as low as 690 °C for films deposited on SrTiO3 substrates by increasing the PH2O and decreasing PHF during the high-temperature soak cycle.
Chemical vapor deposition of YBa2Cu3O7 using metalorganic chelate precursors
Authors: Panson A. J. , Charles R. G. , Schmidt D. N. , Szedon J. R. , Machiko G. J. , Braginski A. I.
Published: July 2002

Superconducting films of YBa2 Cu3 O7 were prepared using metalorganic chelate precursors at ambient pressure. Ba and Y were transported using fluoride-substituted β-diketonates, while a β-keto-imide chelate was used for Cu. Deposition at 500 °C on Al2 O3 and SrTiO3 substrates by reaction with O2 saturated with room temperature water vapor formed crystalline mixtures of BaF2 , YF3 , and CuO. Superconducting YBa2 Cu3 O7 formed after annealing in Ar/H2O at 835 °C followed by O2 at 900 and 400 °C with a slow cooling in O2 to below 200 °C. A 2.3 μm film on a (100) SrTiO3 substrate had an onset Tc of 90 K with zero resistance at 70 K. The film showed a mixture of c- and a-axis orientation. A similar film on (11̄02) Al2O3 showed zero resistance at 65 K.
Infrared characterization of UV laser-induced silicon oxide films
Authors: Slaoui A. , Fogarassy E. , White C. W. , Siffert P.
Published: July 2002

Oxygen incorporation and subsequent oxidation of ion-implanted silicon have been performed using repetitive pulsed excimer laser irradiation working in the liquid phase regime. The kinetics of the oxidation and the characterization of the grown SiO2 were investigated by infrared spectroscopy. The origin of the broadening of the Si-O stretching band of these oxides grown from the liquid phase is discussed.
Comparison of water degradation of YBaCuO superconducting films made from different structures
Authors: Chang Chin-An , Tsai Julie A.
Published: July 2002

Immersion of YBaCuO superconducting films in water has shown a large difference in degradation between structures with and without silver. For the structures containing silver layers and depositing at a high temperature, superconducting films with zero resistance at 87 K remain superconductive at 77 K after 5 h immersion in water, with an increase in room-temperature film resistance by a factor of 4; the contact resistance remains low after 60 h of immersion, allowing the measurement at low temperatures. For the structures containing no silver and depositing at room temperature, the contact resistance rapidly increases with immersion times, making the measurement at 77 K difficult after 5 min of immersion. Changes in the sharpness of the superconductive transition, and structures of the films due to the water immersion are also compared.
Low-energy ion-enhanced deposition of SiO2 in rf magnetron plasmas
Authors: I Lin , Ting L. W.
Published: July 2002

A novel low-temperature (<50 °C) deposition process of a thin SiO2 film in a low-energy ‘‘rf hollow oval magnetron’’ system was studied. O2 is directly mixed with SiH4 and Ar for deposition under the low pressure (≲10 mTorr). The high electron density (1011 cm−3 ) and the high flux low energy (30 eV) ion bombardment greatly enhance the gas phase and surface processes. Uniform and dense thin films with smooth surface and good adhesion have been obtained. The film stoichiometry (from Si to SiO2), the index of refraction, and the film growth rate (from 1 to 35 Å/s) can be controlled by adjusting the SiH4 /O2 flow rates and their ratio.
Hydrogen concentration profiles in as-deposited and annealed phosphorus-doped silicon dioxide films
Authors: Xie Joseph Z. , Murarka Shyam P. , Guo Xin S. , Lanford William A.
Published: July 2002

Hydrogen concentration depth profiles in as-deposited and annealed phosphorus-doped silicon dioxide films were measured using the nuclear reaction profiling technique with 6.4 MeV 15N ion beam. The H2/Ar annealing of 450 °C for 60 min in furnace and the rapid thermal annealing at 1000 °C for 60 s in O2 or H2/Ar were carried out. It is found that hydrogen concentration is in the range of 1021–1022 per cm3 in as-deposited films. Annealing at high temperatures, even in a hydrogen containing medium, lowers the hydrogen concentration in all films. The hydrogen concentration gradually increased with time when the films were left in the room environment. The electrical properties of the oxide are found to be related to the presence of hydrogen. The observed correlation between the flatband voltage and the hydrogen concentration is presented and discussed.
Correlation of grain boundary defect structure with boundary orientation in Ba2YCu3O7−x
Authors: Nakahara S. , Fisanick G. J. , Yan M. F. , van Dover R. B. , Boone T.
Published: July 2002

Correlations between observed defect structures and the orientation of planes involved in grain boundary formation in single phase, nearly ideal density Ba2YCu3O7−x are presented. Three types of grain boundary structures are observed: (1) coherent boundaries with only a low-energy network of dislocations at the interface, which are associated with boundaries not involving a basal plane face, (2) semicoherent boundaries surrounded by a 50–1500 Å wide band of dislocation loops on the c-axis side of the basal-plane-faced boundary, and (3) incoherent boundaries where severe local strain has produced substantial plastic deformation and generation of small voids, again associated with basal-plane-faced boundaries. These results are interpreted using a model for local stress based on the known highly anisotropic thermal contraction of the material during cooling from sintering temperatures.
Planar weak-link devices from YBaCuO and BiSrCaCuO films
Authors: Gergis I. S. , Titus J. A. , Kobrin P. H. , Harker A. B.
Published: July 2002

Weak-link devices were fabricated from polycrystalline thin films of YBaCuO and BiSrCaCuO. Two distinct types of weak links have been found in these devices. The first type, found in all of the YBaCuO and most of the BiSrCaCuO devices, has relatively low dynamic resistances and critical currents with nearly linear temperature dependences. The second type of weak links, found in some BiSrCaCuO films, has much larger dynamic resistances and critical current temperature dependences similar to that of a tunnel junction. Superconductivity quantum interference devices (SQUID’s) fabricated from BiSrCaCuO showed a periodic response to applied fields that is consistent with the magnitude of the flux enclosed by the SQUID loop. Significant hysteresis was found in the SQUID response, apparently indicating flux penetration into the films at relatively low fields.
Optical characterization of surface and interface oxygen content in YBa2Cu3Ox
Authors: Kelly M. K. , Chan Siu-Wai , Jenkin K. , Aspnes D. E. , Barboux P. , Tarascon J.-M.
Published: July 2002

Because YBa2Cu3Ox exists over a range of oxygen content and low oxygen material is nonsuperconducting, it is important to be able to measure and control this parameter for application purposes. We present an optical technique for determining oxygen loss at surfaces and interfaces, where processing and contacts with other materials may affect composition and where usual techniques are insensitive. Using a strong absorption feature at 4.1 eV which appears at low oxygen composition, we find that overlayers of Al and In remove oxygen from YBa2Cu3Ox, but Ag, Au, and room-temperature exposure to moderate vacuum do not.
High T
c superconducting film as a fast nonlinear switch for noise discrimination in digital circuits
Authors: Frenkel A. , Venkatesan T. , Lin Chinlon , Wu X. D. , Hegde M. S. , Inam A. , Dutta B.
Published: July 2002

Measurements of fast nonlinear switching of a high Tc superconducting thin film at 70 K between the dissipative state (induced by an electrical current) and superconducting state are reported. System rise and fall times are measured to be about 1 ns and are limited by the parasitic components of the electrical circuitry. A novel scheme for noise discrimination in digital circuits using this switching has been proposed and experimentally demonstrated for speeds exceeding 200 Mb/s. This method allows significant reduction of amplitude noise and improvement of signal-to-noise ratio in digital circuits.
Growth of epitaxial YbBa2Cu3O7 superconductor by liquid-gas-solidification processing
Authors: Chen H. S. , Liou S. H. , Kortan A. R. , Kimerling L. C.
Published: July 2002

Superconductive films of YbBa2Cu3O7 have been epitaxially grown on SrTiO3 substrate by a novel liquid-gas-solidification process. A layer of metallic YbBa2Cu3 melt was coated on the substrate and in situ oxidized. The oxide films grown on the SrTiO3 (100) substrate are epitaxially oriented in structure with the c axis normal to the plane film. Values of Tc (R=0) of 82 K with a transition width of 1 K have been achieved. The critical current density Jc is typically 105 A/cm2 at 50 K and 104 A/cm2 at 77 K.
Highly oriented superconducting thin films derived from the sol-gel process
Authors: Kramer S. A. , Kordas G. , McMillan J. , Hilton G. C. , Van Harligen D. J.
Published: July 2002

Highly oriented YBa2Cu3O6+x superconducting thin films have been developed via sol-gel processing. Film deposition involved spin coating a ‘‘partially hydrolyzed’’ metal-alkoxide stock solution onto single-crystal [100] SrTiO3 substrates. Although scanning electron microscopy revealed the film consisted of oriented polycrystallites, from the broad statistical x-ray diffraction data the 1000 Å film ‘‘appeared’’ to be single crystal with moderate mosaic spread (i.e., full width at half-maximum was 0.3° in θ at a 2θ of 55°). No twinning of the crystal was found in any of the three orthogonal directions (2θ, φ, χ). The onset temperature Tc for the film was 55 K while the critical current density Jc was found to be 102 A/cm2.
Ion-implanted planar waveguides in barium sodium niobate
Authors: Zhang L. , Chandler P. J. , Townsend P. D.
Published: July 2002

Planar optical waveguides have been formed in Y-cut barium sodium niobate by He+ ion implantation.Refractive index profiles have been determined for n0 and ne using our dark-mode-spacing reflectivity calculation at 0.633 and 0.488 μm. The profiles are similar to those reported for LiNbO3 with optical barriers having −Δn∼5.5% for n0 and ∼3.5% for ne (at a dose of 3×1016 cm−2), and with an anomalous index increase in the guiding region for ne. The sharp modes suggest losses of a few dB/cm, and guide stability up to 500 °C has been determined.
Gating of germanium surfaces using pseudomorphic silicon interlayers
Authors: Vitkavage D. J. , Fountain G. G. , Rudder R. A. , Hattangady S. V. , Markunas R. J.
Published: July 2002

A novel insulator structure for gating of germanium surfaces has been developed. The structure consists of a very thin (on the order of 10 Å) pseudomorphic silicon layer deposited on the germanium surface prior to deposition of a silicon dioxide insulating layer. Both the silicon and silicon dioxide layers were deposited at low temperature by remote plasma-enhanced chemical vapor deposition. Low interface state densities and surface inversion have been obtained for both n- and p-type germanium substrates. X-ray photoelectron spectroscopy and ion scattering spectroscopy analysis indicate that the thin pseudomorphic silicon layer provides complete silicon coverage of the germanium surface. The silicon layer protects the germanium surface from undesirable oxidation during the silicon dioxide deposition. The electrical properties of germanium metal-insulator-semiconductor structures which incorporated the silicon interlayer were much improved compared to structures in which the silicon dioxide was deposited directly on the germanium.
Tl2O3 vapor process of making Tl-Ba-Ca-Cu-O superconductors
Authors: Sheng Z. Z. , Sheng L. , Su H. M. , Hermann A. M.
Published: July 2002

A new process for making Tl-Ba-Ca-Cu-O superconductors which is based on reactions between solid precursor Ba-Ca-Cu-oxides and vapor Tl2O3 has been developed. The Tl2O3 vapor process allows Tl-Ba-Ca-Cu-O superconductors to be easily made in the forms of complex bulk components, wires and fibers, and thick and thin films, and minimizes problems caused by toxicity and volatility of Tl starting compounds.
Monolayer abruptness in highly strained InAsxP1−x/InP quantum well interfaces
Authors: Schneider R. P. , Wessels B. W.
Published: July 2002

InAsxP1−x/InP strained quantum well structures have been prepared by atmospheric-pressure organometallic vapor phase epitaxy (OMVPE). Structures with compositions of x=0.40–0.67 and quantum well thicknesses of 0.8–16 nm were evaluated using photoluminescence spectroscopy. Strain in the pseudomorphic wells ranged from 1.3 to 2.1%. Doublets and multiplets are observed in the photoluminescence spectra and are attributed to luminescence from regions in the wells differing in thickness by a single monolayer, with atomically smooth interfaces over areas greater in lateral extent than the exciton diameter. Typical full widths at half maximum of the photoluminescence from the thinnest wells are 8–14 meV, comparable to the best reported values for thin lattice-matched quantum wells prepared from the InGaAs(P)/InP system using OMVPE.
High-power and high-speed semi-insulating blocked V-grooved inner-stripe lasers at 1.3 μm wavelength fabricated on p-InP substrates
Authors: Horikawa H. , Wada H. , Matsui Y. , Yamada T. , Ogawa Y. , Kawai Y.
Published: July 2002

A maximum cw power of 90 mW at 25 °C was obtained for a GaInAsP/InP laser with a semi-insulating InP current blocking layer grown by metalorganic vapor phase epitaxy on a p-type InP substrate, a 700-μm-long cavity, and an antireflection coating on the front facet. The 3 dB bandwidth was in excess of 6 GHz with a low parasitic capacitance of 15 pF despite the long cavity. The semi-insulating layer with the resistivity of 5×107 Ω cm was formed by doping only Fe. The current blocking characteristics of the blocking layer with the same configuration as the lasers were examined under various temperatures.
Maker fringes in biaxial crystals and the nonlinear optical coefficients of thiosemicarbazide cadmium chloride monohydrate
Authors: Dou S. X. , Jiang M. H. , Shao Z. S. , Tao X. T.
Published: July 2002

Precise theoretical results of Maker fringes in biaxial crystals are presented which include such necessary corrections as absorption, finite beamwidth effects, and multiple reflections. Their applications to the new nonlinear optical material, organometallic complex crystal thiosemicarbazide cadmium chloride monohydrate (TSCCC, point group Cs-m), and the corresponding experimental values of its six independent nonlinear optical coefficients are given.
Intersubband absorption in strained InxGa1−xAs/Al0.4Ga0.6As (0≤x≤0.15) multiquantum wells
Authors: Zhou X. , Bhattacharya P. K. , Hugo G. , Hong S. C. , Gulari E.
Published: July 2002

We report, for the first time, temperature-dependent intersubband absorption data in doped pseudomorphic InxGa1−xAs/Al0.4Ga0.6As (0≤x≤0.15) multiquantum wells. In this composition range the absorption resonance varies in the range 6–7 μm for 50 Å wells, which agrees extremely well with theoretical calculations.
Reduction of transient-enhanced diffusion of boron in silicon by implantation through oxide
Authors: Fan D. , Jaccodine R. J.
Published: July 2002

Transient-enhanced diffusion of boron is studied by comparing through-oxide and direct boron implants. Some of the directly implanted wafers are differentially anodized and etched to depths equal to the thicknesses of the thermal oxides. Spreading resistance profiles after annealing reveal that transient-enhanced diffusion of boron can be prevented by implantation through oxide. The result indicates that the presence of recoiled oxygen in the through-oxide implanted silicon can be important in reducing dopant-enhanced diffusion.
Influence of the As:Ga flux ratio on growth rate, interface quality, and impurity incorporation in AlGaAs/GaAs quantum wells grown by molecular beam epitaxy
Authors: Köhrbrück R. , Munnix S. , Bimberg D. , Larkins E. C. , Harris J. S.
Published: July 2002

The influence of group V:III flux ratio on the molecular beam epitaxy growth process of AlGaAs/GaAs quantum wells is studied by means of photoluminescence, using a careful line shape analysis. Upon enlarged group V flux, a sublinear increase of the growth rate and a reduction of shallow impurity incorporation is found, with, however, an increase of deep trap concentration, attributed to EL2.
Effects of indium doping on crystalline qualities of GaAs on Si by molecular beam epitaxy
Authors: Ohbu I. , Ishino M. , Mozume T.
Published: July 2002

The effects of In doping on crystalline qualities are demonstrated in the heteroepitaxy of GaAs on Si grown by molecular beam epitaxy. The etch pit density of the GaAs layers doped with In at 8×1017 cm−3 decreased by a factor of 7 compared with undoped GaAs layers. Dark regions observed in electron beam induced current images became small by In doping. The improvement of the crystalline qualities was also verified by Raman spectroscopy.
High quality ZnTe-ZnSe strained-layer superlattice with buffer layer prepared by hot wall epitaxy
Authors: Wu Y. H. , Yang H. , Ishida A. , Fujiyasu H. , Nakashima S. , Tahara K.
Published: July 2002

High quality ZnTe-ZnSe strained-layer superlattices grown on GaAs (001) substrates have been obtained by the hot wall epitaxy technique through introducing ZnTe and ZnSe buffers. Raman scattering from folded longitudinal acoustic phonons was observed. High-angle satellite reflection peaks due to Cu Kα1 and Kα2 radiations were clearly resolved in the x-ray diffraction patterns, and these patterns can be almost interpreted by a simple step model. The effect of the buffer layer on the strain of the superlattice is evaluated from the results of Raman scattering and x-ray diffraction measurements.
Homoepitaxial growth of ZnSe on dry-etched substrates
Authors: Ohkawa K. , Karasawa T. , Yoshida A. , Hirao T. , Mitsuyu T.
Published: July 2002

High quality ZnSe layers have been grown by molecular beam epitaxy on dry-etched ZnSe substrates. Surface damage caused by cutting and polishing of the ZnSe substrate was removed by dry etching using BCl3 gas to 10 μm depth. The dry-etched ZnSe substrates exhibited smooth surface morphology and showed excitonic emissions stronger than that from as-polished substrates in photoluminescence (PL) measurements at 11 K. The low-temperature PL spectra obtained from homoepitaxial ZnSe layers grown on the substrates dry etched at the optimum condition showed a strong free-exciton emission at 2.804 eV and a dominant donor-bound exciton emission at 2.798 eV. Since each excitonic emission shows a single peak, the homoepitaxial layers appear to be free from strain.
Ultrahigh Be doping of Ga0.47In0.53As by low-temperature molecular beam epitaxy
Authors: Hamm R. A. , Panish M. B. , Nottenburg R. N. , Chen Y. K. , Humphrey D. A.
Published: July 2002

Layers of Ga0.47In0.53As grown on InP by a beam epitaxy method have been doped with Be to p=5×1020 cm−3 by growth at substrate temperatures as low as 365 °C. The maximum doping level is strongly growth temperature dependent. Heterostructure bipolar transistors with base doping p=1×1020 cm−3, current gain β=54, and unity current gain cutoff frequency fT=140 GHz are illustrated.
Thermomagnetic writing in thin Co/Pt layered structures
Authors: Greidanus F. J. A. M. , Zeper W. B. , den Broeder F. J. A. , Godlieb W. F. , Carcia P. F.
Published: July 2002

In this letter we demonstrate thermomagnetic writing in a Co/Pt thin-film layered structure or multilayer: 25×(4.1 Å Co+19 Å Pt). This film exhibits perpendicular magnetic anisotropy, 100% remanence, and a coercive field of 76 kA/m at room temperature. The coercive field is a strong function of temperature and decreases to zero at 250 °C. In this layered film regular domains can be written with low applied fields (below 50 kA/m) and the writing threshold is about 4 mW. Their good magnetic and magneto-optical properties together with their high corrosion resistance make these layers promising candidates for magneto-optical recording.
Laser-assisted metalorganic chemical vapor deposition of zinc selenide epitaxial films
Authors: Shinn G. B. , Gillespie P. M. , Wilson W. L. , Duncan W. M.
Published: July 2002

Laser-assisted metalorganic chemical vapor deposition has been used to grow epitaxial zinc selenide at temperatures as low as 200 °C. The metalorganic sources, dimethylzinc (DMZ) and diethylselenide (DESe), were photodissociated with radiation from a 193 nm ArF excimer laser passing parallel to a (100) GaAs substrate. A two-stage purge scheme prevented deposition on the windows while minimizing disturbances of the gas flow in the growth region. The temperature dependence for both thermal and laser-assisted film growth rates was examined. The reactor pressure was maintained at 100 Torr with a 10:1 DESe to DMZ ratio and 0.12 Torr partial pressure of DMZ. The laser was operated at a repetition rate of 20 Hz with pulse energies of 50 mJ. The laser-assisted growth rate of ZnSe remained approximately constant at 1 μm/h over the temperature range 200–400 °C. At higher temperatures the thermally driven process begins to become important. Photoluminescence analysis indicates that the material grown at 400 °C by the laser-assisted process is of better quality than films grown by either method at other temperatures.
Influence of band-gap shrinkage on the carrier-induced refractive index change in InGaAsP
Authors: Botteldooren D. , Baets R.
Published: July 2002

The refractive index change induced by depletion of highly doped n-type InGaAsP materials is calculated. A new, numerically simple and accurate model for the high carrier density band-gap shrinkage is introduced. In contrast to the results of earlier calculations, our results show that the refractive index change depends only weakly on the difference between the optical wavelength used and the band-gap wavelength.
Temperature engineered growth of low-threshold quantum well lasers by metalorganic chemical vapor deposition
Authors: Dzurko K. M. , Menu E. P. , Beyler C. A. , Osinski J. S. , Dapkus P. D.
Published: July 2002

A new technique is demonstrated for the formation of narrow active regions in quantum well lasers. In temperature engineered growth (TEG), the substrate temperature is varied during the growth of epitaxial layers by metalorganic chemical vapor deposition (MOCVD) on nonplanar substrates, allowing two-dimensional control of device features. Buried heterostructure designs with submicron active region stripe widths are obtained without the need for fine process control of lateral dimensions. The contact area above the active region is coplanar with the surrounding surface and wide enough to allow easy contacting and heat sinking. Carrier confinement is accomplished by lateral thickness variation of the quantum well active region resulting in a local strip of minimum band gap. Lasers grown in this manner exhibit cw threshold currents as low as 3.8 mA (3.4 mA pulsed), having an as-grown active region width of 0.5 μm. The near-field optical profile indicates stable, single transverse mode operation and minimal current leakage in these devices.
High coercivities in as-cast Pr-Fe-B and Nd-Fe-B alloys with impurity additions
Authors: Hadjipanayis G. C. , Zhang Maocai , Gao Chuan
Published: July 2002

High coercivities have been obtained in as-cast R-Fe-B(M) alloys with impurity additions M such as Al, Cu, Pb, and Ag. The coercivities are obtained after a homogenization heat treatment at a temperature in the range of 900–1000 °C which leads to a special microstructure consisting of R2Fe14 B grains surrounded by an R-M-rich phase. The coercivity is attributed to localized domain wall pinning at around the grain boundaries.
Low-temperature laser photochemical vapor deposition of GaAs
Authors: York P. K. , Eden J. G. , Coleman J. J. , Fernández G. E. , Beernink K. J.
Published: July 2002

The growth of epitaxial GaAs at temperatures below 500 °C by ultraviolet laser-assisted metalorganic chemical vapor deposition has been investigated. Experiments were conducted at 248 nm (KrF excimer laser) and 351 nm (XeF) in normal incidence with laser fluences maintained below 13 mJ/cm2. While the growth rate was enhanced by 5–15% at 450 °C upon irradiating the substrate with 248 nm photons, no measurable effect was observed at 351 nm. This strong wavelength dependence at low fluence demonstrates that the film growth enhancement mechanism is photochemical in nature.
Effect of atmosphere on the formation of low T
c and high T
c phases in Bi-Pb-Sr-Ca-Cu-O superconductors
Authors: Hwang Nong M. , Bahng Gun W. , Moon Han G. , Park Jong C.
Published: July 2002

Two kinds of sintering atmosphere, N2 and air, were used to study the effect of atmosphere on the formation of the low Tc phase and the high Tc phase. The annealing temperatures were 810 °C in N2 and 850 °C in air. The resistivity measurements and the x-ray diffraction analysis showed that while the fraction of the high Tc phase continued to increase with sintering times in air, it did not increase in any appreciable amount even after 264 h of sintering in N2 atmosphere. Compared with air, N2 atmosphere enhanced the formation of the low Tc phase and inhibited the formation of the high Tc phase.
Growth-induced magnetic and optic anisotropy in bismuth-substituted iron garnet films
Authors: Lenz H. , Hansen P. , Tolksdorf W.
Published: July 2002

The growth-induced uniaxial magnetic anisotropy constant Kgu and the growth-induced birefringence Δng of (111) oriented epitaxial iron garnet films of composition R3−xBixFe5−yAlyO12 with R=Y, Gd, Sm have been investigated as a function of supercooling temperature ΔTs. The uniaxial anisotropy constant Kgu increases linearly with increasing ΔTs (0≤ΔTs≤100 K) in agreement with results reported for other bismuth-substituted rare-earth iron garnets. Δng turns out to be a linear function of Kgu and ΔTs. Δng is independent of the rare-earth species R in contrast to Kgu. The optical anisotropy arises primarily from the iron ions on the octahedral and tetrahedral sites as could be shown by the strong influence of diamagnetic dilution of the iron sublattices in the garnet crystal.
Intersubband population inversion in quantum wire structures
Authors: Briggs S. , Jovanovic D. , Leburton J. P.
Published: July 2002

When the spacing between subbands in a quantum wire is equal to the optic phonon energy a situation occurs under longitudinal field conditions where the upper subband population is enhanced with respect to the lower subband. We focus our investigation on the case where a third, intermediate subband is located slightly below the upper subband. We use a Monte Carlo simulation and obtain a population inversion between the upper and intermediate subbands. Intersubband optical transitions with the possibility of far-infrared stimulated emission seem to be significant.
Nonaqueous chemical depth profiling of YBa2Cu3O7−x
Authors: Vasquez R. P. , Foote M. C. , Hunt B. D.
Published: July 2002

A nonaqueous solution of Br in absolute ethanol (EtOH) has recently been reported [R. P. Vasquez, B. D. Hunt, and M. C. Foote, Appl. Phys. Lett. 53, 2692 (1988)] to be effective at removing nonsuperconducting surface species from YBa2 Cu3 O7−x films, leaving the surface close to the ideal stoichiometry. This same etchant is shown here to be an effective bulk etchant in chemical depth profiling through 1-μm-thick films. The Cu remains in the 2+oxidation state and the stoichiometry, as determined by x-ray photoelectron spectroscopy, is close to ideal and nearly constant throughout the profile, indicating the absence of any large preferential etching effects. The reaction of YBa2 Cu3 O7−x films with HF/EtOH, HCl/ EtOH, and I/EtOH solutions is also reported.
Anisotropic critical current density in superconducting Bi2Sr2CaCu2O8 crystals
Authors: Martin S. , Fiory A. T. , Fleming R. M. , Espinosa G. P. , Cooper A. S.
Published: July 2002

Critical current densities and resistivities were measured in a single crystal of the high Tc superconductor Bi2Sr2CaCu2O8 within the ab basal plane (∥) and along the c direction (⊥). A large anisotropy in critical current density is found, Jc∥/Jc⊥≊103, in quantitative agreement with the large normal-state resistivity anisotropy near Tc. The data provide strong evidence for a two-dimensional layered structure of metallic planes separated by semi-insulating barriers.
As-deposited Y-Ba-Cu-O superconducting films on silicon at 400 °C
Authors: Witanachchi S. , Patel S. , Kwok H. S. , Shaw D. T.
Published: July 2002

Y-Ba-Cu-O thin films have been grown on silicon at a substrate temperature of 400 °C by plasma-assisted laser deposition technique. These films were superconducting in an as-deposited state. Films deposited directly on silicon and films with a MgO buffer layer differed in their superconducting properties. Films with a MgO layer showed higher critical temperatures (70 K) and higher critical currents (3×103 A/cm2 at 31 K) than films deposited directly on Si. Depth profiling by Auger and x-ray photoelectron spectroscopy has been employed to study the diffusion and structural variation near the interface.
Mobility-lifetime products in CuGaSe2
Authors: Balberg I. , Albin D. , Noufi R.
Published: July 2002

We report the first accurate determination of mobility-lifetime products, μτ, in thin films of a Cu-ternary chalcopyrite by photoconductivity and ambipolar diffusion length measurements. We found that for Cu-deficient, nearly intrinsic CuGaSe2 at an illumination of about 0.25 AM1 the hole’s μτ is 6×10−6 cm2/V while the electron’s μτ is 2.6×10−9 cm2/V. The lifetime dependence on the light intensity was found to be characterized by the exponent γ−1=−0.44.
Sub-100-nm p+-n shallow junctions fabricated by group III dual ion implantation and rapid thermal annealing
Authors: Lin C-M. , Steckl A. J. , Chow T. P.
Published: July 2002

The fabrication of p+-n junctions with depth less than 100 nm using dual ion implantation of group III species (69Ga, 115In, 11B, 49BF2) in various combinations is reported. We have investigated both the single use of heavy group III (Ga and In) ions for creating shallow junctions and the dual implant approach where Ga or In was first used for preamorphization (and doping) followed by a B or BF2 implant. The optimum cases for sub-100-nm shallow junction formation among the group III combinations evaluated are Ga/B dual ion implantation followed by low-temperature (550–600 °C) rapid thermal annealing (RTA) for 15–30 s and In/B(B or BF2) dual ion implantation with higher temperature (900–1000 °C) RTA for 10 s. Junction depths of 60–100 nm and sheet resistances of 150–300 Ω/⧠ were obtained. Shallow junction diodes fabricated by this dual ion implant technology exhibit low leakage current densities of 8–30 nA/cm2 and good ideality factors of 1.01–1.05.