bluuebunny/crossref_metadata_2025 huggingface dataset:
Last but not least: nestling growth and survival in asynchronously hatching crimson rosellas
Authors: Krebs Elizabeth A.
Published: July 2002

1. Many species of altricial birds hatch their young asynchronously within broods. Although there are many potential benefits to parents, hatching asynchrony reduces the growth and often the survival of last‐hatched nestlings. The consequences of hatching asynchrony on the growth, size at fledging and survival of male and female nestlings of an Australian parrot, the crimson rosella (Platycercus elegans) were examined.

2. Crimson rosella broods hatched over 1·5–7 days, creating mass hierarchies where first‐hatched chicks were up to seven times larger than last‐hatched chicks. Hatching asynchrony and mass hierarchies increased over the breeding season, but were not strongly correlated with brood size.

3. Male chicks grew faster and were larger at fledging than females. Growth rates did not differ between hatching ranks. Chicks of all ranks were of equal sizes at fledging, but last‐hatched male chicks had lower fledging mass in pairwise analyses. Female mass at fledging did not decrease with hatching rank. Chick growth rates and size or mass at fledging were not related to hatching asynchrony, mass or size hierarchies in broods, brood size, laying date or year in mixed‐model analyses.

4. Last‐hatched chicks had the same post‐fledging survival as other chicks, however, they were more likely to die during the nestling period. Increased mortality of last‐hatched nestlings occurred only at hatching and chicks had equal mortality rates over the remainder of the nestling period. Early brood reduction was not associated with brood size or hatching asynchrony but increased over the breeding season, and in broods with high hatching success.

5. Hatching asynchrony in rosellas, unlike in most previous studies, did not lead to poor growth and subsequent survival of last‐hatched chicks. This suggests that the costs of hatching asynchrony are low in this species and that selective feeding by parents may increase the growth and survival of last‐hatched chicks.

6. Reduced growth and survival of later hatched chicks is not an inevitable consequence of asynchronous hatching; however, the costs to parents of overcoming competitive interactions between chicks may be higher than the benefits in most species.
The effects of wildfire on ground‐active spiders in deciduous forests on the Swiss southern slope of the Alps
Authors: Moretti Marco , Conedera Marco , Duelli Peter , Edwards Peter J.
Published: July 2002

The influence of fire upon biodiversity has been investigated in many ecosystems under a wide range of environmental conditions. However, there is no information on how fire affects faunal biodiversity in deciduous forest ecosystems prone to winter fires, such as those on the southern slopes of the Alps.

The main aim of this study was to analyse the effects of single and repeated fires on the structure and species diversity of spider communities in chestnut forests in southern Switzerland. A second objective was to interpret the ecological response of forest‐floor habitats to wildfires, using epigeic spiders as bioindicators.

One‐hundred and thirty‐three spider species were found in pitfall trap samples collected between April and September in burnt and control sites in chestnut coppices. Species richness and community composition were influenced by fire frequency and the time elapsed since the last fire. About 19% of the species were trapped exclusively in sites that had been repeatedly burnt, while 11% occurred only in unburnt coppice. Post‐fire development of the spider community was chiefly from individuals that survived in situ. We found no characteristic pioneer species in any of the burnt sites. There were indirect effects of fire on the spider community, through interactions between species arising from the changing environmental conditions following a fire.

After a single fire, changes in community composition were only observable during the first 2 years. At sites that had experienced repeated fires, there was a more persistent influence on community composition. These sites were characterized by an increase in species richness and species diversity. The presence of a wide ecological range of species in ‘repeated fire’ sites was probably due to the mosaic structure of the environment and the wide range of microclimate conditions at the soil surface, with a predominance of xeric conditions.

The spider communities of chestnut forests were resilient to disturbance by fire. Both the formerly intensive management of these forests (until the 1950s) and a history of frequent fires that goes back to the Neolithic period have played an important part in the development of the spider community in these forests.
Is the range size of migratory birds constrained by their migratory program?
Authors: Bensch Staffan
Published: July 2002

Aim Intuitively, species in which the individuals migrate long distances between summer and winter quarters should be more likely to disperse and colonize new breeding areas than resident species. However, it has repeatedly been noted that many bird species with large ranges are residents. This paradox was tested on land birds breeding in the boreal forest of the Palaearctic, the largest uninterrupted stretch of habitat on earth.

Methods The longitudinal distribution of two land bird communities on each side of the Eurasian continent, in Scandinavia and eastern Siberia, were used to test whether migratory birds indeed have a lower colonization success than resident birds.

Results The migratory species are significantly less likely than resident species to have a range including both regions. The pattern held true even after controlling for latitudinal effects and local abundance, and was also observed at the level of genus and family.

Main conclusions The relatively low colonization success of migratory species into new breeding areas may be because these new areas require novel migratory programs (migratory distance, direction and timing) in order for the birds to reach suitable wintering grounds.
The effect of unsteady winds on sediment transport on the stoss slope of a transverse dune, Silver Peak, NV, USA
Authors: Neuman C. Mckenna , Lancaster N. , Nickling W. G.
Published: July 2002

Rapid (10 s) measurements of sediment transport and wind speed on the stoss slope of a transverse dune indicate that the majority of sand transported is associated with fluctuations in wind speed with a periodicity of 5–20 min duration. Increases in the sediment transport rate towards the dune crest are associated with a small degree of flow acceleration. The increase in wind speed is sufficient, however, to greatly increase values of the intermittency index (γ), so that the duration of saltation is extended in crestal regions of the dune. The pattern of sediment transport on the stoss slope and, therefore, the locus of areas of erosion and deposition change with the regional wind speed. Erosion of the crest occurs during wind speed events just above transport threshold, whereas periods of higher magnitude winds result in deposition of sand upwind of the crest, thereby increasing dune height. Although short‐term temporal and spatial relations between sand transport and wind speed on the stoss slope are well understood, it is not clear how these relations affect dune morphology over longer periods of time.
Clinical manifestations of Bacillus cereus meningitis in newborn infants
Authors: Tokieda K , Morikawa Y , Maeyama K , Mori K , Ikeda K
Published: July 2002

Abstract:
Bacillus cereus (B. cereus) meningitis sometimes occurs in patients with risk factors, which are associated with central nervous system (CNS) anomalies, surgical or anaesthetic access to CNS. We observed two cases of B. cereus meningitis in neonates without such risk factors. The clinical courses of both neonates were fulminant, and routine antibiotic therapy failed. Intracranial haemorrhage was evident at autopsy. According to the previous neonatal case reports and our experience, we found that six of seven neonates were premature babies admitted to the neonatal intensive care unit, five died within a week of onset of the disease, and six had intracranial haemorrhage. We speculate that B. cereus meningitis may occur in neonates, even without any of the risk factors previously described in adult case reports, and that the clinical manifestations of the meningitis might be chjpccterized by the high incidence of intracranial haemorrhage and poor mortality.
Genes for jaundice
Authors: Hardikar W
Published: July 2002

Abstract: The inheritable causes of jaundice comprise a large group of conditions of varying frequency, from Gilbert’s syndrome which is relatively common, to the very rare Crigler–Najjar syndrome. Although these conditions have been well chjpccterized clinically and in some cases biochemically, the underlying molecular defects were unknown because of a lack of knowledge about the process of bile secretion by hepatocytes. The recent cloning of several transporters for bile acids and other organic anions has enabled a greater understanding of this process and allowed correlation of the malfunction of these genes with specific disease processes. This new knowledge will provide for precision in diagnosis, allow antenatal testing and provide opportunities for gene therapy for some of the more serious disorders.
Geomorphology of Australian estuaries: Review and prospect
Authors: Kench Paul S.
Published: July 2002

Over the past 30 years there has been a wealth of research examining the geomorphology of Australian estuaries. This paper reviews the major regional controls on estuarine geomorphic development and discusses the focus of research efforts to understand estuarine evolution, configuration and processes controlling geomorphic development and change. The presence and position of estuaries along the Australian coastline is controlled by large‐scale climate‐led changes in sea‐level, the antecedent structure of the coast and tectonic activity. The configuration of Australia’s estuaries is controlled by a number of environmental factors identified by Jennings & Bird (1967) including climate, oceanographic regime, sediment availability, structure and mineralogy, and tectonics. Interaction of these factors produce a range of estuarine configurations around the Australian continent from wave‐dominated, microtidal, bar‐built estuaries in the south to low energy macrotidal estuaries in the north which have produced extensive low‐lying coastal plains. The principle focus of geomorphologists during the past 30 years has been understanding the medium to long‐term development of estuaries in response to fluctuating sea‐level over the past 125 000 years. Classifications and models of estuarine development and associated biological community response to estuary development have been identified based on lateral and vertical sedimentary sequences. Results have provided essential information on the physical resources and characteristics of estuarine systems including the distribution of sediment facies that host a variety of different ecological communities. There has been a paucity of research examining contemporary processes controlling geomorphic change in Australia’s estuaries. A morphodynamic approach to the study of estuaries is advocated that evaluates morphology‐process responses as estuaries evolve. This approach requires increased research efforts to identify regional differences in estuarine geomorphic development, hydrodynamic processes and sedimentation. It is also advocated that studies examine how the morphodynamic behaviour of estuaries over thousands of years has influenced estuary ecology. Such studies will provide a more complete understanding of the factors influencing the morphology and ecology of contemporary estuaries.
Perinatal mortality in Type 2 diabetes mellitus
Authors: Cundy T. , Gamble G. , Townend K. , Henley P. G. , MacPherson P. , Roberts A. B.
Published: July 2002

Aims In many parts of the world the number of pregnancies in women with Type 2 diabetes mellitus (DM) now exceeds that in women with Type 1 DM, but there are few data published on perinatal mortality in Type 2 DM. This study reports observational data on perinatal mortality in Type 2 DM from a population with a high background rate of this disorder.

Methods Over a 12‐year period (1985–1997) at the Diabetes Clinic at National Women’s Hospital, Auckland, there were 434 pregnancies in women with Type 2 DM (256 known and 178 diagnosed with gestational diabetes mellitus (GDM), but confirmed to have Type 2 DM early post‐partum), 160 pregnancies in women with Type 1 DM and 932 in women with GDM. Perinatal mortality was classified as either intermediate fetal death (20–28 weeks’ gestation), late fetal death (28 weeks’ gestation to term) or early neonatal death (up to 1 month post‐partum).

Results The perinatal mortality in Type 2 DM was 46.1/1000, significantly higher than the rates for the general population (12.5), Type 1 DM (12.5) and GDM (8.9) (P < 0.0001). Congenital malformations accounted for only 10% of the perinatal mortality. There was a seven‐fold increase in the rate of late fetal death and 2.5‐fold increase in the rates of intermediate fetal and late neonatal death. Subjects with Type 2 DM were significantly older and more obese than subjects with Type 1 DM, and presented later to the diabetes service.

Conclusions Perinatal mortality in Type 2 DM is significantly increased, mainly owing to an excess of late fetal death. Maternal factors such as obesity may be important contributors to the high perinatal mortality. Women diagnosed with GDM who have unrecognized Type 2 DM are also at high risk, but perinatal mortality is low in women with milder degrees of glucose intolerance in pregnancy.
Self‐monitoring in Type 2 diabetes mellitus: a meta‐analysis
Authors: Coster S. , Gulliford M. C. , Seed P. T. , Powrie J. K. , Swaminathan R.
Published: July 2002

SUMMARY

Aims  Self‐monitoring of blood or urine glucose is widely used by subjects with Type 2 diabetes mellitus. This study evaluated the effectiveness of the technique at improving blood glucose control through a systematic review and meta‐analysis.

Methods  Randomized controlled trials were identified that compared the effects of blood or urine glucose monitoring with no self‐monitoring, or blood glucose self‐monitoring with urine glucose self‐monitoring, on glycated haemoglobin as primary outcome in Type 2 diabetes.

Results   Eight reports were identified. These were rated for quality and data were abstracted. The mean (sd) quality score was 15.0 (1.69) on a scale ranging from 0 to 28. No study had sufficient power to detect differences in glycated haemoglobin (GHb) of less than 0.5%. One study was excluded because it was a cluster randomized trial of a complex intervention and one because fructosamine was used as the outcome measure. A meta‐analysis was performed using data from four studies that compared blood or urine monitoring with no regular monitoring. The estimated reduction in GHb from monitoring was −0.25% (95% confidence interval −0.61 to 0.10%). Three studies that compared blood glucose monitoring with urine glucose monitoring were also combined. The estimated reduction in GHb from monitoring blood glucose rather than urine glucose was −0.03% (−0.52 to 0.47%).

Conclusions  The results do not provide evidence for clinical effectiveness of an item of care with appreciable costs. Further work is needed to evaluate self‐monitoring so that resources for diabetes care can be used more efficiently.
Butalbital in the Treatment of Headache: History, Pharmacology, and Efficacy
Authors: Silberstein Stephen D. , McCrory Douglas C.
Published: July 2002

Analgesics containing butalbital compounded with aspirin, acetaminophen, and/or caffeine are widely used for the treatment of migraine and tension‐type headache. The butalbital‐containing compounds are efficacious in placebo‐controlled trials among patients with episodic tension‐type headaches. Despite their frequent clinical use for migraine, they have not been studied in placebo‐controlled trials among patients with migraine. Barbiturates can produce intoxication, hangover, tolerance, dependence, and toxicity. Butalbital can result in intoxication that is clinically indistinguishable from that produced by alcohol. Butalbital‐containing analgesics can produce drug‐induced headache in addition to tolerance and dependence. Higher doses can produce withdrawal syndromes after discontinuation. Butalbital‐containing analgesics may be effective as backup medications or when other medications are ineffective or cannot be used. Because of concerns about overuse, medication‐overuse headache, and withdrawal, their use should be limited and carefully monitored.
Rapid thermal annealing of YBaCuO films on Si and SiO2 substrates
Authors: Aslam M. , Soltis R. E. , Logothetis E. M. , Ager R. , Mikkor M. , Win W. , Chen J. T. , Wenger L. E.
Published: July 2002

A very rapid thermal annealing technique has been employed on sputter-deposited YBaCuO films. After an O2 anneal (with or without a N2 preanneal) at temperatures as high as 920 °C for 8–12 s, films on (100)Si and on SiO2 /Si substrates exhibited superconductivity onsets above 95 K and zero resistance in the range 40–66 K.
Analytic comparison of the sensitivities of bulk-wave, surface-wave, and flexural plate-wave ultrasonic gravimetric sensors
Authors: Wenzel S. W. , White R. M.
Published: July 2002

We show that, for small added masses, the sensitivities of bulk-mode, surface-mode, and flexural plate-mode gravimetric ultrasonic sensors are respectively 2/ρλ, ≊1/ρλ, and 1/2ρd, where ρ is the density of the sensor substrate material, λ is the wavelength, and d is the plate thickness of the flexural-mode sensor.
Millimeter wave surface resistance of epitaxially grown YBa2Cu3O7−x thin films
Authors: Klein N. , Müller G. , Piel H. , Roas B. , Schultz L. , Klein U. , Peiniger M.
Published: July 2002

We have measured the surface resistance of two c-axis oriented YBa2Cu3O7−x thin-film samples in a copper host cavity at 86.7 GHz between 4.2 and 300 K. High quality films of 0.6 and 0.4 μm thickness have been grown epitaxially on SrTiO3 by pulsed excimer laser ablation. Their millimeter wave absorption drops sharply at a transition temperature of 86 and 88 K to a corresponding surface resistance at 77 K of 18 mΩ and less than 8 mΩ, respectively. These values exceed the best results on polycrystalline samples and come close to the expectation from classical superconductors. Therefore, applications of high Tc superconductors up to THz frequencies can be envisaged now.
Growth of 200 Å superconducting Bi-Sr-Ca-Cu oxide thin films
Authors: Yeh J.-J. , Hong M.
Published: July 2002

Preferentially ĉ-axis oriented superconducting Bi-Sr-Ca-Cu oxide films as thin as 200 Å have been successfully grown on MgO(100) substrates. Even though such thin films are only 6–7 unit cells thick, they still exhibit bulk superconducting properties. These films typically exhibit a superconducting transition temperature at 80 K and a critical current density of 105 A/cm2 at 50 K as determined by transport measurements. The ability to grow even thinner films is controlled by the exact film stoichiometry and the smoothness of the substrate surface.
Centrifugal mass separation in rotating plasmas produced by a coaxial plasma gun
Authors: Ikehata T. , Suzuki M. , Tanabe T. , Mase H.
Published: July 2002

Rotating Cu/Zn plasmas produced by a coaxial plasma gun have been applied to plasma centrifuge. A separation factor of up to 10 is measured over a radius of 4 cm when a current of 13 kA and an axial magnetic field of 2.5 kG are applied. Plasma parameters are: rotation frequency ω=1.1×106 rad/s, density n∼1015 cm−3, and ion temperature Ti=10 eV. The separation factor of 2 is attained even in the plasma core where the density is higher than one-half of the peak value. This is attributed to the fact that a strong centrifugal force forms a hollow density profile which gives the density peak at a radius of 2 cm.
Relationship between trapped holes, positive ions, and interface states in irradiated Si-SiO2 structures
Authors: Kenkare P. U. , Lyon S. A.
Published: July 2002

We show that trapped holes at the Si-SiO2 interface account for all of the interface states generated by gate-positive irradiation of metal-oxide-silicon structures. The field-induced conversion of trapped holes to interface states is found to be the rate-limiting step in interface state buildup. Interface-state generation by hole trapping at the Si-SiO2 interface also plays a role for gate-negative irradiation. However, our experiments demonstrate an additional avenue for interface-state formation under these conditions. Holes created in the SiO2 layer are swept to the Al-SiO2 interface where they release positive ions. The transport of these ions to the Si-SiO2 interface under gate-positive field results in new interface states. Our data do not support models involving liberation of protons in the bulk of the SiO2 layer by hole transport through the oxide.
Kinetics of silicon epitaxy using SiH4 in a rapid thermal chemical vapor deposition reactor
Authors: Liehr M. , Greenlief C. M. , Kasi S. R. , Offenberg M.
Published: July 2002

The equilibrium hydrogen surface coverage on Si(100) during silicon epitaxy using SiH4 has been measured in a rapid thermal chemical vapor deposition reactor. The hydrogen coverage could be ‘‘frozen out’’ completely on the surface by a rapid cool-down and pump-down of the reactor up to temperatures of ≂575 °C; at temperatures above 575 °C only partial ‘‘freeze-out’’ is achieved. Surface hydrogen was titrated in situ using the reactor as a thermal desorption spectrometer. Epitaxial silicon films were grown in the temperature range 450–700 °C and the film growth kinetics was correlated with the equilibrium hydrogen coverage. The growth mechanism changes from the low-temperature regime, where the surface is hydrogen covered, to the high-temperature regime, where the surface is essentially clean.
High-speed rotation of magnets on high T
c superconducting bearings
Authors: Moon F. C. , Chang P.-Z.
Published: July 2002

Levitation and rotation of cylindrical rare-earth magnets on yttrium-barium-copper-oxide superconducting bearings has been sustained at speeds of up to 120 000 rpm with a surface speed of 40 m/s. The decay of the free rotation rate has been measured at both atmospheric pressure and a partial vacuum to 2.6 μm Hg. The decay measurements in vacuum indicate that the flux drag torques are constant and independent of speed. The magnetic shear stress on the rotor magnet is estimated to be 150 dyn/cm2. It is believed that drag torques on rotating magnets are related to asymmetry in the flux density pattern of the magnet.
Anomalous superperiodicity in scanning tunneling microscope images of graphite
Authors: Kuwabara M. , Clarke D. R. , Smith D. A.
Published: July 2002

An anomalously large periodicity has been observed in scanning tunneling microscope images of a (00.1) graphite sample. The unusual contrast has hexagonal symmetry, a periodicity of 7.7±0.2 nm and is superimposed on the usual a=0.246 nm atomic spacing of graphite. Current-voltage curves recorded in the scanning tunneling spectroscopy mode from the region showing the superperiodicity exhibit slightly more metallic behavior than those from neighboring normal regions. One possible explanation for the observed periodicity is that it is a rotational moiré pattern resulting from the overlap between a misoriented layer of graphite and the underlying graphite single crystal.
Grain refinement induced by a critical crystal growth velocity in undercooled melts
Authors: Willnecker R. , Herlach D. M. , Feuerbacher B.
Published: July 2002

Containerless undercooling by electromagnetic levitation has been used to measure both growth velocity and grain size as a function of undercooling in Cu70Ni30 and Cu69Ni30B1 alloys. At a critical undercooling ΔT* the temperature dependence of the growth velocity changes discontinuously. This is accompanied by a sudden drop of grain size in the solidified product by more than two orders of magnitude. The comparative investigations show that it is not a critical undercooling that initiates the grain refinement process, but rather a critical crystal growth velocity, which approximately equals the diffusive speed.
Indium doping of n-type HgCdTe layers grown by organometallic vapor phase epitaxy
Authors: Ghandhi S. K. , Taskar N. R. , Parat K. K. , Bhat I. B.
Published: July 2002

n-type doping of mercury cadmium telluride was achieved using trimethylindium as the dopant source. The layers, grown by the alloy growth technique, were doped to ∼5×1018 cm−3. The donor concentration in these layers was found to exhibit a linear dependence on the dopant partial pressure over the carrier concentration range from 5×1016 to 3×1018 cm−3. Reasonably high electron mobility values were observed in these indium-doped layers. Typically, layers with a Cd fraction x=0.23, doped to 3.5×1016 cm−3, exhibited a mobility value of 7.5×104 cm2/V s at 40 K. High electron mobility values, measured over the entire doping regime, suggest a high electrical activity of indium in these layers. The optically measured band edge in these indium-doped layers was observed to shift to higher energy with increasing doping. The band-edge energy values measured in 1×1017 and 3×1018 cm−3 doped layers correspond to x=0.23 and x=0.3, respectively. This increase can be due to an increase in the Cd fraction, or to a Burstein–Moss shift of the band edge with doping.
Evidence for the passivation effect in (NH4)2Sx-treated GaAs observed by slow positrons
Authors: Lee Jong-Lam , Wei Long , Tanigawa Shoichiro , Oigawa Haruhiro , Nannichi Yasuo
Published: July 2002

We applied slow positrons to the as-etched GaAs and/or the (NH4)2Sx-treated GaAs. The results show that a thin oxide film is easily formed on the surface of as-etched GaAs as soon as the etched surface is exposed to air for several minutes before the measurement. On the other hand, the monolayer of chemisorbed sulfur atoms in the (NH4)2 Sx-treated GaAs is effective in protecting the clean surface from the adsorption of oxygen atoms. The mean diffusion length of positrons is not affected by the conditions of the surface treatment. This implies that the centers for the trapping of a positron are not created below the free surface by those treatments.
Large stable photoinduced refractive index change in a nonlinear optical polyester polymer with disperse red side groups
Authors: Shi Yongqiang , Steier William H. , Yu Luping , Chen Mai , Dalton Larry R.
Published: July 2002

The photoinduced refractive index change of polyester with disperse red side groups was studied at several different wavelengths. This material exhibits a large photoinduced index change (0.3 at 633 nm) and in addition when poled has a sizable second-order nonlinear optical effect. This index change was monitored over 1000 h and long-term stability was demonstrated. Based on these results, a method using only photomasks to define channel waveguides and other patterns in such polymers was suggested and experimentally demonstrated. This photoinduced index change may have wide applications in integrated optical systems when these or other similar polymers are involved.
Periodic lattice distortions as a result of lattice mismatch in epitaxial films of two-dimensional materials
Authors: Parkinson B. A. , Ohuchi F. S. , Ueno K. , Koma A.
Published: July 2002

Epilayers of transition metal dichalcogenides (TMDs) with two-dimensional structures can be grown with molecular beam epitaxy onto other TMDs substrates without regard to lattice matching. Although there is no strong bonding between the epilayer and the substrate, the van der Waals interaction between the two hexagonally closest packed lattices results in a periodic distortion which, due to electronic effects, is prominently imaged with the scanning tunneling microscope.
Measurement of energy penetration depth of subpicosecond laser energy into solid density matter
Authors: Zigler A. , Burkhalter P. G. , Nagel D. J. , Rosen M. D. , Boyer K. , Gibson G. , Luk T. S. , McPherson A. , Rhodes C. K.
Published: July 2002

The energy penetration depth characteristic of the interaction of intense subpicosecond (∼600 fs) ultraviolet (248 nm) laser radiation with solid density material has been experimentally determined. This was accomplished by using a series of ultraviolet transmitting targets consisting of a fused silica (SiO2) substrate coated with an 80–600 nm layer of MgF2. The measurement of He-like and H-like Si and Mg lines, as a function of MgF2 thickness, enabled the determination of the energy penetration depth. It was found that this depth falls in the range of 250–300 nm for a laser intensity of ∼3×1016 W/cm2. Based on numerical simulations, it is estimated that solid density material to a depth of ∼250 nm is heated to an electron temperature of ∼500 eV.
Correlation of spectral output and below-threshold gain profile modulation in 1.3 μm semiconductor diode lasers
Authors: Hayward Joseph E. , Cassidy Daniel T.
Published: July 2002

A residue which is characteristic of internal scattering is extracted from the below threshold spectra of 1.3 μm semiconductor diode lasers by fitting a smooth function to the measured gain profile. The residue is found to be correlated with the above threshold spectral output. This suggests that the amount of scattering in the active region is an important quantity in determining the spectral output of semiconductor diode lasers.
New approach to grow pseudomorphic structures over the critical thickness
Authors: Lo Y. H.
Published: July 2002

We propose to grow pseudomorphic and heteroepitaxial structures on thin, free-standing substrates. From the theoretical analysis, pseudomorphic layers of arbitrary thickness can be grown on a substrate thinner than the critical thickness. Even if the substrate is twice as thick as the critical thickness, very high-quality heteroepitaxy can still be achieved with all the threading dislocations gettered by the thin substrate. The conclusions derived from the theoretical models can be applied to most of the pseudomorphic and heteroepitaxial material systems of current interest.
Epitaxial growth of aluminum nitride on Si(111) by reactive sputtering
Authors: Meng W. J. , Heremans J. , Cheng Y. T.
Published: July 2002

We have studied growth of aluminum nitride (AlN) on Si(111) by ultra-high vacuum (UHV) reactive dc-magnetron sputtering under a mixture of Ar and N2 gases. As-grown films have been examined by x-ray diffraction, Auger electron spectroscopy (AES), and transmission electron microscopy (TEM). Results of x-ray diffraction show texturing with AlN [0001]//Si[111]. Complementary TEM examinations observe epitaxy of AlN on Si(111), with AlN[112̄0]//Si[22̄0]. The AlN/Si interface is sharp and flat. The lowest substrate temperature required to achieve epitaxy Tepi has been determined to be ∼600 °C. A dislocation density in AlN film grown at 700 °C has been estimated to be ∼3×1011/cm2.
Electron resonant tunneling in Si/SiGe double barrier diodes
Authors: Ismail K. , Meyerson B. S. , Wang P. J.
Published: July 2002

We report upon the fabrication and characterization of the first n-type resonant tunneling diodes in the SiGe materials system. The devices fabricated were Si/SiGe/Si/SiGe/Si double-barrier diodes, employing strain-relieved SiGe as the barrier layers surrounding pseudomorphic tensile strained Si. These devices were prepared using ultrahigh vacuum chemical vapor deposition. Negative differential conductance is observed at room temperature in these devices with a peak-to-valley ratio of 1.2. The corresponding value at 77 K is 1.5.
Effects of HF cleaning and subsequent heating on the electrical properties of silicon (100) surfaces
Authors: Huang L. J. , Lau W. M.
Published: July 2002

Changes in surface-band bending of both boron-doped and phosphorus-doped silicon (100) samples by exposure (40 s) to hydrofluoric acid (HF) with varying HF concentrations were studied by x-ray photoelectron spectroscopy. Effects of subsequent thermal annealing was investigated by in situ heating in vacuum. Hydrogen termination of the dangling bonds on silicon was found to be an effective means to reduce surface gap states on silicon. Near-flatband surfaces were observed on both n- and p-Si by the HF exposure when the doping concentration was not less than 1×1016/cm3, and when the HF concentration was not higher than 5%. A higher HF concentration promoted hydrogen diffusion and the formation of an H-B species in p-Si. As such, band bending increased on p-Si. However, the deactivation of boron could be recovered by annealing for less than 1 h at a temperature as low a 120 °C.
Displacement threshold energy for type IIa diamond
Authors: Koike J. , Parkin D. M. , Mitchell T. E.
Published: July 2002

A type IIa natural diamond was irradiated at room temperature with energetic electrons. The threshold energy for displacement of atoms from their lattice sites was determined for three principal crystallographic directions by observing the formation of defect clusters during irradiation in a transmission electron microscope. The displacement-threshold energies were found to be 37.5±1.2 eV for the electron incident in the [100] direction, 45.0±1.3 eV in the [111] direction, and 47.6±1.3 eV in the [110] direction.
Normal incidence infrared detector using p-type SiGe/Si multiple quantum wells
Authors: Park J. S. , Karunasiri R. P. G. , Wang K. L.
Published: July 2002

The photoresponse of p-type SiGe/Si multiple quantum well infrared detectors is measured as a function of incidence beam polarization. With the infrared (IR) beam polarized in the growth direction, a photoresponse peak is observed at near 8.6 μm with a full width at half maximum (FWHM) of about 80 meV. On the other hand, with the beam polarized parallel to the growth plane (normal incidence), a peak is observed at near 7.2 μm with nearly the same FWHM. The photoresponse at peak positions is about 0.3 A/W for both cases. With an unpolarized beam, the peak photoresponse of about 0.6 A/W is observed for the present unoptimized structure. The results of the detection of normal incidence IR suggest possible applications of SiGe/Si multiple quantum wells for normal incidence IR detection.
2×n surface structure of SiGe layers deposited on Si(100)
Authors: Butz R. , Kampers S.
Published: July 2002

The surface structure of SiGe layers deposited on Si(100) has been studied by surface analysis techniques. The 2×1 surface reconstruction is changed into a 2×n (n≳8) structure observed in low energy electron diffraction. Scanning tunneling microscopy pictures reveal that after (n−1) subsequent dimers one dimer is missing. The density of missing dimers depends on the Ge content and on the layer thickness. Auger electron spectra show a strong Ge segregation. The evaluation of the intensities of low energy electron diffraction can explain the structure by a small expansion of the topmost SiGe layer enriched by Ge.
Epitaxial growth of (001) Al on (111) Si by vapor deposition
Authors: Thangaraj N. , Westmacott K. H. , Dahmen U.
Published: July 2002

Heteroepitaxial growth of (001) Al thin films on Si (111) single crystal substrates by vapor deposition was studied by means of x-ray diffraction, Rutherford backscattering spectrometry, and transmission electron microscopy techniques. It was observed that the films deposited at room temperature exhibit random (111) texture, while the films deposited at 280 °C show perfect epitaxial alignment of (001) Al planes with (111) Si planes. In the interface plane 〈110〉 close packed directions in both the film and the substrate are parallel and hence Al grows with three orientation variants in a unique mazed tricrystal arrangement.
A comparative study of GaN epilayers grown on sapphire and SiC substrates by plasma-assisted molecular-beam epitaxy
Authors: Lin M. E. , Sverdlov B. , Zhou G. L. , Morkoç H.
Published: July 2002

We report structural, electrical, and optical data for GaN samples grown on both 6H-SiC and sapphire substrates. A two-stage substrate preparation procedure was employed for removing oxygen from 6H-SiC and c-plane sapphire substrates without the need for elaborate high-temperature thermal degassing. Both sapphire and SiC substrates were treated with hydrogen plasma to reduce the surface contamination as evidenced by the observation of sharp (1×1) reconstruction RHEED (reflected high-energy electrons diffraction) patterns. Thin AlN buffer layers were employed and the crystalline quality of GaN films was studied by temperature-dependent Hall measurements, photoluminescence, and x-ray diffraction. Layers with room-temperature mobilities as high as 580 cm2/V s on SiC substrates were obtained.
Sol-gel glass waveguides prepared at low temperature
Authors: Sorek Y. , Reisfeld R. , Finkelstein I. , Ruschin S.
Published: July 2002

Planar waveguides of TiO2-organically modified silanes deposited on glass substrates were prepared by the sol-gel method, either in a pure form or doped by red perylimide laser dye, and their optical properties characterized. The refractive index increases and film thickness decreases as TiO2 contents rise. Waveguiding in the pure film and the trapped luminescence in the doped films were measured. Typically three guided modes were observed.
Open air deposition of SiO2 film from a cold plasma torch of tetramethoxysilane-H2-Ar system
Authors: Inomata Kiyoto , Ha Hyunkwon , Chaudhary Khaliq A. , Koinuma Hideomi
Published: July 2002

A rf plasma beam was generated in the stream of atmospheric pressure argon to be exhausted from a cylindrical nozzle into air. The temperature measurements indicate a nonequilibrium low temperature nature of this plasma. By using this cold plasma torch, films were deposited on the substrates placed in air at growth rates higher than 100 Å/s by feeding tetramethoxysilane into the plasma. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy revealed that the films were essentially SiO2 and their structures and properties could be improved by admixing hydrogen in the plasma. The SiO2 films deposited at a rate of 120 Å/s from Si(OCH3)4-H2-Ar plasma had surfaces as smooth and hard as Corning 7059 glass.
Hydrogen induced donor-type Si/SiO2 interface states
Authors: de Nijs J. M. M. , Druijf K. G. , Afanas’ev V. V. , van der Drift E. , Balk P.
Published: July 2002

Study of donor-type Si/SiO2 interfaces states shows that these centers anneal at room temperature when neutral but are stable when charged positively. Moreover, the anneal process is accompanied by the release of H. We propose that the donor states are related to H attached to interfacial network sites, most likely O atoms, constituting electrically active complexes. When positively charged, H is strongly bonded; when neutral H is only weakly attached. In the latter case it can escape and dimerize so that the states disappear. Similar complexes tying down H in a positively charged state would constitute small cross-section hole traps in the bulk of the oxide.
Ablation of polymer films by a femtosecond high-peak-power Ti:sapphire laser at 798 nm
Authors: Kumagai Hiroshi , Midorikawa Katsumi , Toyoda Koichi , Nakamura Shinki , Okamoto Takuya , Obara Minoru
Published: July 2002

Femtosecond infrared pulses from an ultrashort high-peak-power Ti:sapphire laser were successfully utilized for ablation of polymer films such as polytetrafluoroethylene, tetrafluoro- ethylene-hexafluoropropylene copolymer, and polyimide. Good agreement between experimental data and calculations from a model suggested that simultaneous absorption of three photons for polyimide and five photons for tetrafluoroethylene-hexafluoropropylene copolymer predominated over the other absorptive channels and that such a multiphoton absorption was induced efficiently.
Electron drift mobility of oxadiazole derivatives doped in polycarbonate
Authors: Tokuhisa Hiroaki , Era Masanao , Tsutsui Tetsuo , Saito Shogo
Published: July 2002

Charge drift mobilities of five oxadiazole derivatives doped in polycarbonate (PC) were evaluated with the time-of-flight technique. It is demonstrated that oxadiazoles incline to having electron-transport characteristics. In particular, an oxadiazole with naphthyl substituent (BND) was found to possess high potential of electron transport; the electron drift mobility of 50 wt % BND doped PC was 2.2×10−5 cm2 V−1 s−1 at an electric field of 7.5×105 V cm−1 at room temperature. In addition, incorporating strong electron-releasing substituents into oxadiazoles was demonstrated to add hole transport characteristics to oxadiazoles.
Near-field optical microscopy in liquids
Authors: Muramatsu Hiroshi , Chiba Norio , Homma Katsunori , Nakajima Kunio , Ataka Tatsuaki , Ohta Satoko , Kusumi Akihiro , Fujihira Masamichi
Published: July 2002

The scanning near-field optical microscopy imaging of specimens in liquid and of cultured cells in aqueous solutions is reported. A scanning near-field optical/atomic-force microscope (SNOM-AFM) was developed, in which the scanning of an optical-fiber probe cantilever over the specimen was controlled by noncontact mode AFM (dynamic mode AFM). This imaging mode reduces damage to the probe and soft specimens. The resonant frequency of the probe cantilever decreased 20% to ≊14 kHz and the Q factor decreased by a factor of 8 to ≊30 in water, compared with these values in air, which was sufficient to perform SNOM-AFM imaging in liquid.
Thermal diffusivity measurement of thin films by means of an ac calorimetric method
Authors: Hatta Ichiro , Sasuga Yasunaga , Kato Ryozo , Maesono Akikazu
Published: July 2002

A new method to measure thermal diffusivity of a thin sample was developed using a light-irradiated ac calorimetric technique. The experimental conditions and the fundamental equations for the measurement are discussed. In principle, this method can be applied no matter how thin a sample may be. This method was tested for samples of nickel, silicon, stainless steel, and alumina in the range from 50 to 300 μm in thickness. The measured thermal diffusivities coincide satisfactorily with the values reported for bulk materials. It is concluded that this method is useful in the measurement for thin materials with a variety of thermal diffusivities, and the sample mounting is easy in comparison with other methods.
Inductive energy transfer circuit proof of principle experiment
Authors: Zucker O. , Long J. , Lindner K. , Giorgi D. , Navapanich T.
Published: July 2002

For the conventional method of direct transfer of energy between a storage inductor and an uncoupled load inductor, the maximum energy which can be transferred to the load inductor is 25% of the initial stored energy. The Meatgrinder, a novel inductive energy storage and transfer circuit, has been shown to approach 100% energy transfer efficiency. A low-current-level experiment has been performed which has verified the predicted behavior of the inductive transfer circuit and demonstrated an energy transfer efficiency of 47.5%. In order to address the issue of the circuit operation at a higher current level, a second experiment was conducted. The peak current reached was 3.9 kA and the results verified that the current multiplication and energy transfer of the circuit does scale with current.
New normalization procedure for modulation spectroscopy
Authors: Shen H. , Parayanthal P. , Liu Y. F. , Pollak Fred H.
Published: July 2002

We report a new type of normalization procedure for modulation spectroscopy experiments in order to obtain the relative change in the reflectance (transmittance) spectrum ΔR/R(ΔT/T). Our new technique utilizes a servomechanism driven variable neutral density filter which keeps the dc component of the signal from the detector constant by varying the intensity of the light striking the sample. This method is particularly useful for photoreflectance measurements which can have background problems due to scattered pump light and/or photoluminescence. Advantages for other modulation spectroscopies, particularly in the region of the fundamental band gap of semiconductors, also will be discussed.
ac method for measuring low-frequency resistance fluctuation spectra
Authors: Scofield John H.
Published: July 2002

An ac technique is described for measuring low-frequency resistance fluctuation spectra with improved sensitivity over dc methods achieved by avoiding preamplifier 1/f noise. The technique, easily implemented with decade resistors and a lock-in amplifier, allows the current noise of low-resistance (r<10 kΩ) specimens to be measured to frequencies below 1 mHz. Use of a center-tapped, four-probe specimen geometry allows discrimination between specimen and contact noise and eliminates noise due to bath temperature variations. The technique is demonstrated in use to determine the dependence of the 1/f noise of Cr films on film area. Measurements with simultaneous direct and alternating currents provide means to study the noise of nonlinear devices and frequency-dependent conductors.
Thermal contact of joints between different kinds of metals at low temperatures
Authors: Mamiya T. , Yano H. , Uchiyama T. , Inoue S. , Miura Y.
Published: July 2002

It was found from electrical measurements at 4.2 K that good thermal contact between different kinds of metals can be obtained much more effectively by fastening two pieces with a screw of a large diameter rather than by welding. The thermal conduction of a threaded joint between silver and platinum has been achieved equal to that of copper-to-copper joints.
Improved hot-wire procedure for thermophysical measurements under pressure
Authors: Håkansson B. , Andersson P. , Bäckström G.
Published: July 2002

A new and simplified version of the circuitry for the transient hot-wire method is presented. The circuitry provides a wide range of currents allowing probe wires of various diameters to be used in order to match the thermal properties of the specimen to be investigated. The analysis of the temperature increase during the heat pulse is based on the exact solution for a heated wire immersed in a medium. Data are corrected for varying power. The method was tested by computer simulations and by measurements of the thermal conductivity (λ) and the heat capacity per unit volume (ρcp ) of glycerol at room temperature and atmospheric pressure, and for CsCl and NaCl at room temperature and at pressures up to 2 GPa. The results on glycerol and CsCl are in excellent agreement with previous works. The inaccuracy in λ and ρcp is estimated as 1%–2% and 3%–5%, respectively, but the standard deviation of the measurements is as low as 0.2% for λ and 1% for ρcp. The improved procedure makes it possible to detect systematic errors caused by reflection of the heat pulse from the walls of the high-pressure cell. This error, which reveals itself by a curvature of the residual, defined as the difference between fitted function and data, was demonstrated in the case of NaCl. A theoretical estimate of the influence of perturbations due to reflection was also carried out and it was found that the error mainly affects the value of ρcp.