bluuebunny/crossref_metadata_2025 huggingface dataset:
A Potential Outcomes Approach to Developmental Toxicity Analyses
Authors: Elliott Michael R. , Joffe Marshall M. , Chen Zhen
Published: January 2006

Summary Estimating the effects of a toxin on fetal development in animal models such as mice can be problematic, because the number of pups that develop and survive until birth may simultaneously affect developmental outcomes such as birth weight and be affected by the introduction of a toxin into the fetal environment. Also, comparing pups that survived until birth at a high dose of the toxin with pups that survived at low doses may underestimate the effect of the toxin, because the lower dose means include the less healthy pups that would not survive if exposed to a higher level of toxin. We consider this problem in a potential outcomes framework that defines the effect of the dose on the outcome as the difference between what the outcome would have been for a pup had the dam in which the pup develops been exposed to dose level Z=z* rather than dose level Z=z. To disentangle the direct effect of dose from the effect of litter size, we focus on effects defined within principal strata that are a function of the survival status of the pups at each of the possible dose levels. A unique contribution to the potential outcomes literature is that we allow the outcome for a subject to be dependent on the principal stratum to which other subjects within a cluster belong.
The Performance of Random Coefficient Regression in Accounting for Residual Confounding
Authors: Gustafson Paul , Greenland Sander
Published: January 2006

Summary Greenland (2000, Biometrics56, 915–921) describes the use of random coefficient regression to adjust for residual confounding in a particular setting. We examine this setting further, giving theoretical and empirical results concerning the frequentist and Bayesian performance of random coefficient regression. Particularly, we compare estimators based on this adjustment for residual confounding to estimators based on the assumption of no residual confounding. This devolves to comparing an estimator from a nonidentified but more realistic model to an estimator from a less realistic but identified model. The approach described by Gustafson (2005, Statistical Science20, 111–140) is used to quantify the performance of a Bayesian estimator arising from a nonidentified model. From both theoretical calculations and simulations we find support for the idea that superior performance can be obtained by replacing unrealistic identifying constraints with priors that allow modest departures from those constraints. In terms of point‐estimator bias this superiority arises when the extent of residual confounding is substantial, but the advantage is much broader in terms of interval estimation. The benefit from modeling residual confounding is maintained when the prior distributions employed only roughly correspond to reality, for the standard identifying constraints are equivalent to priors that typically correspond much worse.
Intermarriages Between Western Women and Palestinian Men: Multidirectional Adaptation Processes
Authors: Roer‐Strier Dorit , Ben Ezra Dina
Published: January 2006

This article addresses cultural adaptation of Western‐Palestinian intermarried couples. Using in‐depth interviews, information was gathered from 16 participants, 7 Western women and 9 Palestinian men, living in Palestinian cities in the West Bank. Adaptation strategies are typified by the extent to which each spouse embraces the partner's culture. The data suggest that intermarriage engenders a multidirectional adaptation process. Patriarchy and East‐West power relations affect mainly the women, having to face marginalization on the basis of their gender and their foreignness. The men undergo a double process of cultural adaptation: to the Western culture and to their native culture after their return. Both the husbands’ extended family and the Israeli‐Palestinian conflict were found to affect both partners’ adaptation.
Parent‐Adolescent Involvement: The Relative Influence of Parent Gender and Residence
Authors: Hawkins Daniel N. , Amato Paul R. , King Valarie
Published: January 2006

The 1995 wave of the Add Health study is used to investigate the relative influence of parent gender and residence on patterns of parental involvement with adolescents. Adolescent reports (N =17,330) of shared activities, shared communication, and relationship quality with both biological parents are utilized. A multidimensional scaling analysis reveals that parent gender explains most of the variance in parent‐adolescent involvement, with residential status playing a secondary yet a fundamental role in accounting for these patterns. Resident mothers who do not live with adolescents’ biological fathers engage in the broadest range of activities with their children. Unpartnered resident fathers display patterns of parenting that are as similar to mothers as they are to other fathers.
Leaf chlorophyll concentration relates to transpiration efficiency in peanut
Authors: Sheshshayee M.S. , Bindumadhava H. , Rachaputi N.R. , Prasad T.G. , Udayakumar M. , Wright G.C. , Nigam S.N.
Published: January 2006

Two pot experiments were conducted in two different seasons at the University of Agricultural Science, Bangalore, India, to study (a) the relationship between chlorophyll concentration (by measuring the leaf light‐transmittance characteristics using a SPAD metre) and transpiration efficiency (TE) and (b) the effect of leaf N on chlorophyll and TE relationship in peanut. In Experiment (Expt) I, six peanut genotypes with wide genetic variation for the specific leaf area (SLA) were used. In Expt II, three non‐nodulating isogenic lines were used to study the effect of N levels on leaf chlorophyll concentration–TE relationship without potential confounding effects in biological nitrogen fixation. Leaf N was manipulated by applying N fertiliser in Expt II. Chlorophyll concentration, TE (g dry matter kg−1 of H2O transpired, measured using gravimetric method), specific leaf nitrogen (g N m−2, SLN), SLA (cm2 g−1), carbon isotope composition (Δ13C) were determined in the leaves sampled during the treatment period (35–55 days after sowing) in the two experiments. Results showed that the leaf chlorophyll concentration expressed as soil plant analytical development (SPAD) chlorophyll metre reading (SCMR) varied significantly among genotypes in Expt I and as a result of N application in Expt II. Changes in leaf N levels were strongly associated with changes in SCMR, TE and Δ13C. In both the experiments, a significant positive relationship between SCMR and TE with similar slopes but differing intercepts was noticed. However, correction of TE for seasonal differences in vapour pressure deficit (VPD) between the two experiments resulted in a single and stronger relationship between SCMR and TE. There was a significant inverse relationship between SCMR and Δ13C, suggesting a close linkage between chlorophyll concentration and Δ13C in peanut. This study provides the first evidence for a significant positive relationship between TE and leaf chlorophyll concentration in peanut. The study also describes the effect of growing environment on the relationships among SLA, SLN and SCMR.
In vitro rapid regeneration of plantlets from nodal explants of Mucuna pruriens– a valuable medicinal plant
Authors: Faisal M. , Siddique I. , Anis M.
Published: January 2006

A rapid and efficient protocol for the large‐scale propagation of a potential medicinal plant, Mucuna pruriens, through in vitro culture of nodal segment explants obtained from 15‐day‐old aseptic seedlings is described. Of the three different cytokinins, 6‐benzyladenine (BA), kinetin (Kin) and 2‐isopentenyl adenine (2‐iP) evaluated as supplements to Murashige and Skoog (MS) medium, BA at an optimal concentration of 5.0 μM was effective in inducing multiple shoots. Strength of the basal media also influenced the efficiency of shoot regeneration. The frequency of shoot regeneration tended to increase when the salt concentration in the basal media was reduced. Highest number of multiple shoots (23.3) and maximum average length (5.6 cm) were standardised on half‐strength MS medium supplemented with 5.0 μM BA along with 0.5 μM α‐naphthalene acetic acid (NAA) at pH 5.8. Rooting was best induced in shoots excised from proliferated shoot cultures on MS medium augmented with an optimal concentration of 1.0 μM indole‐3‐butyric acid (IBA). The in vitro‐raised plantlets with well‐developed shoots and roots were successfully established in earthen pots containing garden soil and were grown in greenhouse with 90% survival rate. The results of this study provide the first report on in vitro plant regeneration of M. pruriens.
The faintest accretors
Authors: King A. R. , Wijnands R.
Published: January 2006

Recent X-ray observations have detected a class of very faint X-ray transients in the Galaxy which probably reveal a previously unrecognized type of accretion on to neutron stars or black holes. We show that these systems cannot have descended from binaries with stellar-mass components of normal composition. Accretion of hydrogen-depleted matter on to stellar-mass black holes can account for individual systems, but requires that these transients should be observed to repeat within a few years, and does not explain why the class is distinctly faint.

Two other explanations appear to be quite natural. One invokes accretion by neutron stars or stellar-mass black holes from companions that were already brown dwarfs or planets when the systems formed, i.e. which did not descend from low-mass stars. The other possibility is that these systems are the endpoints of primordial (zero-metallicity) binaries in which the primary was extremely massive, and collapsed to a black hole of mass ≳1000 M⊙. The (primordial) companion must by now have reached an extremely low mass (≲0.01 M⊙) and be transferring mass at a very low rate to the black hole. This picture avoids the main difficulty encountered by models invoking intermediate-mass black hole formation at non-primordial metallicities, and is a natural consequence of some current ideas about Population III star formation.
Cosmic rays, lithium abundance and excess entropy in galaxy clusters
Authors: Nath Biman B. , Madau Piero , Silk Joseph
Published: January 2006

We consider the production of 6Li in spallation reactions by cosmic rays in order to explain the observed abundance in halo metal-poor stars. We show that heating of ambient gas by cosmic rays is an inevitable consequence of this process, and estimate the energy input required to reproduce the observed abundance of 6Li/H ∼ 10−11 to be of the order of a few hundred eV per particle. We draw attention to the possibility that this could explain the excess entropy in gas in galaxy groups and clusters. The evolution of 6Li and the accompanying heating of gas are calculated for structures collapsing at the present epoch with injection of cosmic rays at high redshift. We determine the energy required to explain the abundance of 6Li at z∼ 2 corresponding to the formation epoch of halo metal-poor stars, and also an increased entropy level of ∼300 keV cm2 necessary to explain X-ray observations of clusters. The energy budget for this process is consistent with the expected energy output of radio-loud active galactic nuclei, and the diffusion length-scale of cosmic ray protons responsible for heating is comparable to the size of regions with excess entropy. We also discuss the constraints imposed by the extragalactic gamma-ray background.
Discovery of a nearby M9 dwarf
Authors: Phan-Bao N. , Bessell M. S. , Martín E. L. , Simon G. , Guibert J. , Forveille T. , Delfosse X. , Crifo F. , Epchtein N. , Wood P. , Tajahmady F.
Published: January 2006

We report the discovery of a new M9.0 dwarf at only 8.2 pc, which we identified in our search for nearby ultracool dwarf (I−J≥ 3.0, later than M8.0) in the DENIS data base. We measure a very high proper motion of 2.5 arcsec yr−1. The PC3 index measured from its low-resolution spectrum gives a spectrophotometric distance of 8.2 pc. This makes it the third closest M9.0 dwarf.
Ca2+‐activated K+ channels in human melanoma cells are up‐regulated by hypoxia involving hypoxia‐inducible factor‐1α and the von Hippel‐Lindau protein
Authors: Tajima Nobuyoshi , Schönherr Kristina , Niedling Susanna , Kaatz Martin , Kanno Hiroshi , Schönherr Roland , Heinemann Stefan H.
Published: January 2006

Under chronic hypoxia, tumour cells undergo adaptive changes involving hypoxia‐inducible factors (HIFs). Here we report that ion currents mediated by Ca2+‐activated K+ (KCa) channels in human melanoma IGR1 cells are increased by chronic hypoxia (3% O2), as well as by hypoxia mimetics. This increase involves the HIF system as confirmed by overexpression of HIF‐1α or the von Hippel‐Lindau tumour suppressor gene. Under normoxic conditions the KCa channels in IGR1 cells showed pharmacological characteristics of intermediate conductance KCa subtype IK channels, whereas the subtype SK2 channels were up‐regulated under hypoxia, shown with pharmacological tools and with mRNA analysis. Hypoxia increased cell proliferation, but the KCa channel blockers apamin and charybdotoxin slowed down cell growth, particularly under hypoxic conditions. Similar results were obtained for the cell line IGR39 and for acutely isolated cells from a biopsy of a melanoma metastasis. Thus, up‐regulation of KCa channels may be a novel mechanism by which HIFs can contribute to the malignant phenotype of human tumour cells.
Generation of a physiological sympathetic motor rhythm in the rat following spinal application of 5‐HT
Authors: Marina Nephtali , Taheri Melody , Gilbey Michael P.
Published: January 2006

When applied in vitro to various CNS structures 5‐HT and/or NMDA have been observed to generate rhythmic nervous activity. In contrast, reports of similar in vivo actions are relatively rare. Here we describe a physiological sympathetic motor rhythm regulating the thermoregulatory circulation of the rat tail (T‐rhythm; 0.40–1.20 Hz) that can be elicited following intrathecal (i.t.) application of 5‐HT to an in situ‘isolated’ spinal cord preparation (anaesthetized rats spinalized at T10–T11 and cauda equina cut). i.t. injections were delivered to L1 as sympathetic neuronal activity to the tail (SNAT) arises from preganglionic neurones at T11–L2. SNAT was abolished after spinal transection (n= 18) and it did not return spontaneously. The administration of 5‐HT (250 nmol) generated rhythmic sympathetic discharges (n= 6). The mean frequency of the T‐like rhythm during the highest level of activity was 0.88 ± 0.04 Hz which was not significantly different from the T‐rhythm frequency observed in intact animals (0.77 ± 0.02 Hz; P > 0.05 n= 16). In contrast, NMDA (1 μmol) generated an irregular tonic activity, but it failed to generate a T‐like rhythm (n= 9), even though the mean levels of activity were not significantly different to those produced by 5‐HT. However, 5‐HT (250 nmol) applied after NMDA generated a T‐like rhythm (0.95 ± 0.11 Hz, n= 6). Our observations support the idea that 5‐HT released from rostral ventromedial medullary neurones, known to innervate sympathetic preganglionic neurones, can induce sympathetic rhythmic activity.
Glycine receptors in a population of adult mammalian cones
Authors: Balse E. , Tessier L.‐H. , Forster V. , Roux M. J. , Sahel J. A. , Picaud S.
Published: January 2006

Glycinergic interplexiform cells provide a feedback signal from the inner retina to the outer retina. To determine if cones receive such a signal, glycine was applied on cultured porcine cone photoreceptors recorded with the patch clamp technique. A minor population of cone photoreceptors was found to generate large currents in response to puff application of glycine. These currents reversed close to the calculated equilibrium potential for chloride ions. These glycine‐elicited currents were sensitive to strychnine but not to picrotoxin consistent with the expression of α–β‐heteromeric glycine receptors. Glycine receptors were also activated by taurine and β‐alanine. The glycine receptor antibody mAb4a labelled a minority of the cone photoreceptors identified by an antibody specific for cone arrestin. Finally, expression of the β subunit of the glycine receptor was demonstrated by single cell RT‐PCR in a similar proportion (∼13%) of cone photoreceptors freshly isolated by lectin‐panning. The identity of cone photoreceptors was assessed by their specific expression of the cone arrestin mRNA. The population of cone photoreceptors expressing the glycine receptor was not correlated to a specific colour‐sensitive subtype as demonstrated by single cell RT‐PCR experiments using primers for S opsin, cone arrestin and glycine receptor β subunit. This glycine receptor expression in a minority of cones defines a new cone population suggesting an unexpected role for glycine in the visual information processing in the outer retina.
Three methionine residues located within the regulator of conductance for K+ (RCK) domains confer oxidative sensitivity to large‐conductance Ca2+‐activated K+ channels
Authors: Santarelli Lindsey Ciali , Wassef Ramez , Heinemann Stefan H. , Hoshi Toshinori
Published: January 2006

Methionine‐directed oxidation of the human Slo1 potassium channel (hSlo1) shifts the half‐activation voltage by −30 mV and markedly slows channel deactivation at low concentrations of intracellular Ca2+ ([Ca2+]i). We demonstrate here that the contemporaneous mutation of M536, M712 and M739 to leucine renders the channel functionally insensitive to methionine oxidation caused by the oxidant chloramine‐T (Ch‐T) without altering other functional characteristics. Coexpression with the auxiliary β1 subunit fails to restore the full oxidative sensitivity to this triple mutant channel. The Ch‐T effect is mediated specifically by M536, M712 and M739 because even small changes in this residue combination interfere with the ability to remove the oxidant sensitivity following mutation. Replacement of M712 or M739, but not M536, with the hydrophilic residue glutamate largely mimics oxidation of the channel and essentially removes the Ch‐T sensitivity, suggesting that M712 and M739 may be part of a hydrophobic pocket disrupted by oxidation of non‐polar methionine to the more hydrophilic methionine sulfoxide. The increase in wild‐type hSlo1 open probability caused by methionine oxidation disappears at high [Ca2+]i and biophysical modelling of the Ch‐T effect on steady‐state activation implicates a decrease in the allosteric coupling between Ca2+ binding and the pore. The dramatic increase in open probability at low [Ca2+]i especially within the physiological voltage range suggests that oxidation of M536, M712 or M739 may enhance the Slo1 BK activity during conditions of oxidative stress, such as those associated with ischaemia‐reperfusion and neurodegenerative disease, or in response to metabolic cues.
Angiotensin II: a major regulator of subcutaneous adipose tissue blood flow in humans
Authors: Goossens G. H. , McQuaid S. E. , Dennis A. L. , Van Baak M. A. , Blaak E. E. , Frayn K. N. , Saris W. H. M. , Karpe F.
Published: January 2006

We investigated the functional roles of circulating and locally produced angiotensin II (Ang II) in fasting and postprandial adipose tissue blood flow (ATBF) regulation and examined the interaction between Ang II and nitric oxide (NO) in ATBF regulation. Local effects of the pharmacological agents (or contralateral saline) on ATBF, measured with 133Xe wash‐out, were assessed using the recently developed microinfusion technique. Fasting and postprandial (75 g glucose challenge) ATBF regulation was investigated in nine lean healthy subjects (age, 29 ± 3 years; BMI, 23.4 ± 0.7 kg m−2) using local Ang II stimulation, Ang II type 1 (AT1) receptor blockade, and angiotensin‐converting enzyme (ACE) inhibition. Furthermore, NO synthase (NOS) blockade alone and in combination with AT1 receptor blockade was used to examine the interaction between Ang II and NO. Ang II induced a dose‐dependent decrease in ATBF (10−9m: −16%, P= 0.04; 10−7m: −33%, P < 0.01; 10−5m: −53%P < 0.01). Fasting ATBF was not affected by ACE inhibition, but was increased by ∼55% (P < 0.01) by AT1 receptor blockade. NOS blockade induced a ∼30% (P= 0.001) decrease in fasting ATBF. Combined AT1 receptor and NOS blockade increased ATBF by ∼40% (P= 0.003). ACE inhibition and AT1 receptor blockade did not affect the postprandial increase in ATBF. We therefore conclude that circulating Ang II is a major regulator of fasting ATBF, and a major proportion of the Ang II‐induced decrease in ATBF is NO independent. Locally produced Ang II does not appear to regulate ATBF. Ang II appears to have no major effect on the postprandial enhancement of ATBF.
Human skeletal muscle intracellular oxygenation: the impact of ambient oxygen availability
Authors: Richardson Russell S. , Duteil Sandrine , Wary Claire , Wray D. Walter , Hoff Jan , Carlier Pierre G.
Published: January 2006

Intracellular oxygen (O2) availability and the impact of ambient hypoxia have far reaching ramifications in terms of cell signalling and homeostasis; however, in vivo cellular oxygenation has been an elusive variable to assess. Within skeletal muscle the extent to which myoglobin desaturates (deoxy‐Mb) and the extent of this desaturation in relation to O2 availability provide an endogenous probe for intracellular O2 partial pressure (P). By combining proton nuclear magnetic resonance spectroscopy (1H NMRS) at a high field strength (4 T), assessing a large muscle volume in a highly efficient coil, and extended signal averaging (30 min) we assessed the level of skeletal muscle deoxy‐Mb in 10 healthy men (30 ± 4 years) at rest in both normoxia and hypoxia (10% O2). In normoxia there was an average deoxy‐Mb signal of 9 ± 1%, which, when converted to P using an O2/Mb half‐saturation (P50) of 3.2 mmHg, revealed an P of 34 ± 6 mmHg. In ambient hypoxia the deoxy‐Mb signal rose to 13 ± 3% (P= 23 ± 6 mmHg). However, intersubject variation in the defence of arterial oxygenation (S) in hypoxia (S range: 86–67%) revealed a significant relationship between the changes in S and P(r2= 0.5). These data are the first to document resting intracellular oxygenation in human skeletal muscle, highlighting the relatively high P values that contrast markedly with those previously recorded during exercise (∼2–5 mmHg). Additionally, the impact of ambient hypoxia on P and the relationship between changes in S and P stress the importance of the O2 cascade from air to cell that ultimately effects O2 availability and O2 sensing at the cellular level.
Carbonic anhydrase gene expression in CA II‐deficient (Car2−/−) and CA IX‐deficient (Car9−/−) mice
Authors: Pan Peiwen , Leppilampi Mari , Pastorekova Silvia , Pastorek Jaromir , Waheed Abdul , Sly William S. , Parkkila Seppo
Published: January 2006

Using real‐time PCR and immunohistochemistry, we have examined the expression of carbonic anhydrase isozymes (CA) I, II, III, IV, IX, XII, XIII and XIV in the brain, kidney, stomach and colon of the wild‐type, CA II‐deficient (Car2−/−), and CA IX deficient (Car9−/−) mice. The expression of Car4, Car12, Car13 and Car14 mRNAs did not show any significant deviations between the three groups of mice, whereas both groups of CA deficient mice showed decreased expression levels of Car1 in the colon and Car3 in the kidney. The Car2 mRNA level was greatly reduced but not completely abolished in all four tissues from the Car2−/− mice in which no CA II protein was expressed. Sequencing the Car2 cDNA isolated from C57BL6 Car2−/− mice revealed two nucleotide differences from the wild‐type C57BL6 mice. One is a silent polymorphism found in Car2 mRNA from wild‐type DBA mice, which is the strain that provided the original mutagenized chromosome. The second change is a mutation that causes prematurely terminated translation at codon 155 (Gln155X). Car9 mRNA and CA IX protein expression levels were up‐regulated about 2.5‐ and 3.6‐fold, respectively, in the stomach of the Car2−/− mice. These results suggest that the loss of function of cytosolic CA II in the stomach of Car2−/− mice leads to up‐regulation of an extracellular CA, namely CA IX, which is expressed on the cell surface of the gastric epithelium.
Free molecular background flow in a vacuum chamber equipped with two-sided pumps
Authors: Cai Chunpei , Boyd Iain D. , Sun Quanhua
Published: January 2006

Spacecraft propulsion systems, such as Hall thrusters, are designed and tested in large vacuum chambers. The pumping capacity of modern facilities makes it possible to maintain pressures as low as 10−3–10−4Pa. One fundamental concern for the vacuum chamber is the facility effects on the chamber performance. In this study, several free molecular models are developed to analyze the rarefied background flow inside a vacuum chamber equipped with two-sided vacuum pumps. These models lead to various sets of analytical results including velocity distribution functions for the background flow and formulas to compute the vacuum pump sticking coefficient. These results can be used to evaluate the performance of vacuum chambers and to aid constructing proper background flows for particle simulations of these systems. The results indicate that the background flow conditions can have a significant nonzero mean velocity and cannot be considered to be described by a Maxwellian velocity distribution. The models are applied to analyze the rarefied background flow in a specific vacuum chamber. Calculations of the sticking coefficient for flow of xenon in the vacuum chamber yield values close to 0.40 for cryogenic pumps. Several modifications of the background flow treatment for particle simulations are proposed with the aid of these analytical results.
Control of plasma flux composition incident on TiN films during reactive magnetron sputtering and the effect on film microstructure
Authors: Muratore C. , Walton S. G. , Leonhardt D. , Fernsler R. F.
Published: January 2006

A hybrid plasma enhanced physical vapor deposition (PEPVD) system consisting of an unbalanced dc magnetron and a pulsed electron beam-produced plasma was used to deposit reactively sputtered titanium nitride thin films. The system allowed for control of the magnitudes of the ion and neutral flux, in addition to the type of nitrogen ions (atomic or molecular) that comprised the flux. For all deposition experiments, the magnitude of the ion flux incident on the substrate was held constant, but the composition of the total flux was varied. X-ray diffraction and atomic force microscopy showed that crystallographic texture and surface morphology of the films were affected by the plasma flux composition during growth.
Plasma etching of HfO2 at elevated temperatures in chlorine-based chemistry
Authors: Hélot M. , Chevolleau T. , Vallier L. , Joubert O. , Blanquet E. , Pisch A. , Mangiagalli P. , Lill T.
Published: January 2006

Plasma etching of HfO2 at an elevated temperature is investigated in chlorine-based plasmas. Thermodynamic studies are performed in order to determine the most appropriate plasma chemistry. The theoretical calculations show that chlorocarbon gas chemistries (such as CCl4 or Cl2–CO) can result in the chemical etching of HfO2 in the 425–625K temperature range by forming volatile effluents such as HfCl4 and CO2. The etching of HfO2 is first studied on blanket wafers in a high density Cl2–CO plasma under low ion energy bombardment conditions (no bias power). Etch rates are presented and discussed with respect to the plasma parameters. The evolution of the etch rate as function of temperature follows an Arrhenius law indicating that the etching comes from chemical reactions. The etch rate of HfO2 is about 110Å∕min at a temperature of 525K with a selectivity towards SiO2 of 15. x-ray photoelectron spectroscopy analyses (XPS) reveal that neither carbon nor chlorine is detected on the HfO2 surface, whereas a chlorine-rich carbon layer is formed on top of the SiO2 surface leading to the selectivity between HfO2 and SiO2. A drift of the HfO2 etch process is observed according to the chamber walls conditioning due to chlorine-rich carbon coatings formed on the chamber walls in a Cl2–CO plasma. To get a very reproducible HfO2 etch process, the best conditioning strategy consists in cleaning the chamber walls with an O2 plasma between each wafer. The etching of HfO2 is also performed on patterned wafers using a conventional polysilicon gate. The first result show a slight HfO2 foot at the bottom of the gate and the presence of hafnium oxide-based residues in the active areas.
Effectiveness of dilute H2 plasmas in removing boron from Si after etching of HfO2 films in BCl3 plasmas
Authors: Wang C. , Donnelly V. M.
Published: January 2006

B Cl 3 -containing plasmas are used to etch HfO2, a high dielectric constant (“high-k”) material. We have investigated several plasmas for their effectiveness in cleaning boron from the underlying Si surface after BCl3 plasma etching of HfO2, while removing a minimum amount of Si. X-ray photoelectron spectroscopy with vacuum sample transfer was used for surface analysis. B cleaning was optimum in dilute H2 plasmas (in Ar) compared to pure H2 plasmas. Dilute H2 plasmas slowed B cleaning process to a controllable time. In a 1% H2–Ar plasma, 20s was required to clean ∼90% B from the surface after a 60s overetch of HfO2 in BCl3 plasmas. The Si substrate was etched <3nm during this cleaning period, which was considerably suppressed comparing pure H2 plasma cleaning. Dilute I2 plasmas (in Ar) can also clean B from the Si surfaces in a short time (10s) but more Si substrate was etched compared to H2–Ar plasmas. BCl3–H2 plasmas deposited a thick B-containing layer on the Si surface instead of combining etching and cleaning into one step.
Ion-surface interactions on c-Si(001) at the radiofrequency-powered electrode in low-pressure plasmas: Ex situ spectroscopic ellipsometry and Monte Carlo simulation study
Authors: Amassian A. , Desjardins P. , Martinu L.
Published: January 2006

We use variable-angle spectroscopic ellipsometry (VASE) to investigate oxide and interface formation during plasma-oxidation of monocrystalline Si(001) at the radiofrequency (rf) powered electrode of a plasma-enhanced chemical vapor deposition reactor. HF-etched c-Si(001) wafers were exposed to an oxygen plasma under conditions similar to those used in optical coatings deposition in order to ascertain the effects of plasma-bulk interactions, and to gauge to what depth O2+ and O+ ions interact with and alter the structure and composition of the target in the presence of negative self-bias, VB. From VASE analyses, modifications are best described using a two-layer model: A top layer consisting of SiO2 and a defective interfacial layer (DL) composed of a mixture of c-Si, a-Si, and SiO2. The saturation value of the modification depth (oxide and DL thickness) increases from 3.4±0.4to9.6±0.4nm, for VB ranging from −60to−600V, respectively, and scales with Emax1∕2, where Emax is the maximum energy of ions from an rf discharge. These results are in agreement with nuclear ion-bulk interactions leading to atomic displacements and defect accumulation. The interfacial layer broadens with increasing ∣VB∣ while the fraction of a-Si detected increases from ∼1% up to ∼55% over the investigated VB range, indicative of ballistic and thus depth-dependent oxygen transport to the SiO2–Si interface. Monte Carlo simulations in the binary collision approximation predict significant surface recession due to sputtering, therefore resulting in an apparent self-limiting oxidation mechanism. The surface layers reach their steady-state thicknesses within the first 2min of plasma exposure and subsequently move into the bulk of the c-Si substrate as a result of oxide sputtering and oxygen transport.
Optical depth profiling of strontium titanate and electro-optic lanthanum-modified lead zirconium titanate multilayer structures for active waveguide applications
Authors: Amassian A. , Gaidi M. , Chaker M. , Martinu L.
Published: January 2006

Transparent polycrystalline strontium titanate (STO) and lanthanum-modified lead zirconium titanate (PLZT) thin films were deposited, respectively, on Si and on indium-doped tin oxide (ITO) coated glass by pulsed laser deposition (PLD). PLZT films are shown to exhibit electro-optic properties close to the bulk material when deposited on ITO in specific process conditions. The refractive index depth profile was determined by using a combination of variable angle spectroscopic ellipsometry and spectrophotometry, and the multisample analysis approach. PLZT films deposited at high O2 pressure, PO2, and annealed at 700°C were found to be more porous and inhomogeneous than low PO2 films. The optical properties of STO films strongly depend on PO2 as well: low PO2 depositions lead to denser film growth with homogeneous, bulk-like refractive index profile, while high PO2 depositions lead to porous and highly inhomogeneous films, exhibiting band-gap variation and formation of a 60-nm-thick interdiffusion layer on Si. We use an optical depth-profiling procedure to investigate the formation of three-layer air/PLZT/STO/ITO/glass stacks, where the PLZT and STO optical properties are optimized by controlling PO2 during STO deposition, in order to form a cladding layer for potential active waveguide applications.
Electrical properties of indium-tin oxide films deposited on nonheated substrates using a planar-magnetron sputtering system and a facing-targets sputtering system
Authors: Iwase Hideo , Hoshi Youichi , Kameyama Makoto
Published: January 2006

Distribution of the electrical properties of indium-tin oxide (ITO) film prepared by both a planar-magnetron sputtering system (PMSS) and a facing-targets sputtering system (FTSS) at room temperature were investigated. It was found that the outstanding non-uniformities of the electrical properties in noncrystalline ITO films are mainly due to the variation of the oxygen stoichiometry dependent on film positions on substrate surfaces. Furthermore, ITO film with uniform distribution of electrical properties was obtainable using FTSS.
SiC formation by C60 molecules as a precursor: A synchrotron-radiation photoemission study of the carbonization process
Authors: Cheng C.-P. , Pi T.-W. , Ouyang C.-P. , Wen J.-F.
Published: January 2006

Formation of SiC upon annealing an atomically clean Si(001)-2×1 surface covered with half a monolayer of C60 molecules has been investigated by a synchrotron-radiation photoemission. C60 molecules are chemisorbed at room temperature on the silicon surface via Si–C60 hybridization to form covalent bonds. During annealing of the film at 700°C, Si atoms in the first layer below the surface move upward to bond with C60 molecules, enhancing the formation of SixC60 and resulting in weakened C–C bonds within C60 molecules. Upon further annealing to 750°C, most C60 molecules decompose and formation of the SiC film begins. Total decomposition of C60 molecules occurs at 800°C, and only a SiC film is then found.
Study of annealed Co thin films deposited by ion beam sputtering
Authors: Sharma A. , Brajpuriya R. , Tripathi S. , Chaudhari S. M.
Published: January 2006

This paper presents structural, magnetic and transport property measurements carried out on as deposited as well as annealed Co (400Å) thin films. The magnetization measurements carried out using a magneto-optical Kerr effect (MOKE) technique show large increases in coercivity and saturation field values with annealing of the samples at higher temperatures. However, corresponding resistivity measurements show a gradual decrease in resistivity and drops to minimum at 500°C. Observed magnetization and resistivity behavior is mainly attributed to (i) change in crystal structure from hcp to fcc; (ii) increase in grain size; and (iii) stress relaxation due to the annealing treatment as revealed by x-ray diffraction measurements.
Ge interactions on HfO2 surfaces and kinetically driven patterning of Ge nanocrystals on HfO2
Authors: Stanley Scott K. , Joshi Sachin V. , Banerjee Sanjay K. , Ekerdt John G.
Published: January 2006

Germanium interactions are studied on HfO2 surfaces, which are prepared through physical vapor deposition (PVD) and by atomic layer deposition. X-ray photoelectron spectroscopy and temperature-programed desorption are used to follow the reactions of germanium on HfO2. Germanium chemical vapor deposition at 870 K on HfO2 produces a GeOx adhesion layer, followed by growth of semiconducting Ge0. PVD of 0.7 ML Ge (accomplished by thermally cracking GeH4 over a hot filament) also produces an initial GeOx layer, which is stable up to 800 K. PVD above 2.0 ML deposits semiconducting Ge0. Temperature programed desorption experiments of ∼1.0ML Ge from HfO2 at 400–1100 K show GeH4 desorption below 600 K and GeO desorption above 850 K. These results are compared to Ge on SiO2 where GeO desorption is seen at 550 K. Exploiting the different reactivity of Ge on HfO2 and SiO2 allows a kinetically driven patterning scheme for high-density Ge nanoparticle growth on HfO2 surfaces that is demonstrated.
Rapid thermal oxidation of Ge-rich Si1−xGex heterolayers
Authors: Bera M. K. , Chakraborty S. , Das R. , Dalapati G. K. , Chattopadhyay S. , Samanta S. K. , Yoo W. J. , Chakraborty A. K. , Butenko Y. , Šiller L. , Hunt M. R. C. , Saha S. , Maiti C. K.
Published: January 2006

Rapid thermal oxidation (RTO) of the Ge-rich (x=0.7)Si1−xGex heterolayer is reported. In particular, the structural modifications of SiGe films during oxidation process and the dependence of the oxidation kinetics on Ge content, oxidation temperature, and oxide thickness have been studied. The segregation mechanism of Ge at the oxide∕SiGe interface is discussed. Interface properties of the RTO-grown oxides studied using high-frequency capacitance-voltage (C-V) characteristics of metal-oxide-semiconductor capacitors are also reported.
Ultrasensitive leak detection during ultrahigh vacuum evacuation by quadrupole mass spectrometer
Authors: Chen Xu , Huang Tianbin , Wang Ligong , Jin Qiji , Cha Liangzhen
Published: January 2006

One must do ultrasensitive leak detection during ultrahigh-vacuum (UHV) evacuation, especially just before the device is sealed off from the vacuum system, to guarantee the longevity of the sealed high-vacuum or even UHV devices with small volume. A quadrupole mass spectrometer (QMS) with an UHV evacuation system can be used under accumulation mode to do the testing. Possible accumulate modes, as well as their advantages and shortcomings, are studied experimentally and discussed in this paper. We found that the opening action of the metal valve during accumulation mode always severely affects the height of the peak indicated by QMS and causes considerable errors. If we determine the leak rate by the peak area instead of the peak height, the situation is much improved. This method has proven quite useful in ensuring the tightness quality for complex sealed UHV devices with small volumes. Ultrasensitive leak detection has been carried out for such real evacuating devices, and a leak rate of 2×10−14Pa∙m3∕s was detected, which is far lower than its dynamic mode and the detection limit of the current advanced commercial leak detectors.
How deposition parameters control growth dynamics of nc-Si deposited by hot-wire chemical vapor deposition
Authors: Moutinho H. R. , To B. , Jiang C.-S. , Xu Y. , Nelson B. P. , Teplin C. W. , Jones K. M. , Perkins J. , Al-Jassim M. M.
Published: January 2006

We studied the growth of silicon films deposited by hot-wire chemical vapor deposition under different values of filament current, substrate temperature, and hydrogen dilution ratio. The physical and electrical properties of the films were studied by Raman spectroscopy, x-ray diffraction, atomic force microscopy, conductive-atomic force microscopy, and transmission electron microscopy. There is an interdependence of the growth parameters, and films grown with different parameters can have similar structures. We discuss why this interdependence occurs and how it influences the properties of the deposited films, as well as the deposition rate. In general, the films have a complex structure, with a mixture of amorphous, (220)-oriented crystalline and nanocrystalline phases present in most cases. The amount of each phase can be controlled by the variation of one or more of the growth parameters at a time.
In situ Fourier transform infrared characterization of the plasma chemistry in varying pulsed cycles of a 1,3-butadiene discharge in an inductively coupled gaseous electronics conference cell
Authors: Jindal A. K. , Prengler A. J. , Overzet L. J. , Goeckner M. J.
Published: January 2006

In situ Fourier transform infrared spectroscopy is used to characterize the plasma chemistry of pulsed 1,3-butadiene (H2CCHCHCH2) discharges subject to varying percentages of the duty cycle in a gaseous electronics conference cell. Variations in densities associated with the major observed spectral bands are closely examined as a function of duty cycle. The possible dissociation mechanisms responsible for all observed vibrations are investigated. For example, the data show that about 44% of CH2 stretching vibrations during continuous wave biasing are due to free CH2 daughter species, while only bound CH2 are observed during pulsing of the discharge. This indicates that only the π bond of the CC bond is cleaved during pulsed mode operation, with the σ being cleaved during cw biasing.
Effects of N2, O2, and Ar plasma treatments on the removal of crystallized HfO2 film
Authors: Chen Jinghao , Yoo Won Jong , Chan Daniel S. H.
Published: January 2006

The effects of plasma treatment using Ar, N2, and O2 on the removal of crystallized HfO2 films in a dilute HF solution were studied. The resulting damage in source and drain regions, and recess in isolation regions were also investigated. It was found that plasma nitridation with an ion energy of several hundred electron volts can lower the wet etch resistance of crystallized HfO2 films up to 70Å thick through the generation of Hf–N bonds. However, thermal nitridation did not introduce sufficient nitrogen into bulk crystallized HfO2 films to lower wet etch resistance. Plasma nitridation without bias power introduced nitrogen to the crystallized HfO2 in the region only within 10Å of the surface. The enhancement of the etch rate of crystallized HfO2 in dilute HF and the amount of recess in the active and isolation regions using N2, O2, and Ar plasma treatment have been evaluated. Results show that N2 plasma treatment is the most effective in enhancing the removal rate of crystallized HfO2 in dilute HF and minimizing recess on substrate among the plasmas studied.
Influence of excitonic singlet-triplet splitting on the photoluminescence of Si∕SiO2 multiple quantum wells fabricated by remote plasma-enhanced chemical-vapor deposition
Authors: Rölver R. , Först M. , Winkler O. , Spangenberg B. , Kurz H.
Published: January 2006

Excitonic effects in the photoluminescence (PL) of Si∕SiO2 multiple quantum wells are investigated. The structures were fabricated by remote plasma-enhanced chemical-vapor deposition and subsequent rapid thermal annealing which leads to the formation of nanocrystalline Si well layers. In addition to distinct confinement features, the energy splitting between excitonic singlet and triplet states is derived as a function of the Si layer thickness. Anomalous temperature dependence and sublinear dependence of the PL intensity on optical excitation power are observed. These effects result from the interplay between the occupation of dark triplet states and thermal activation of excitons into optically active singlet states.
Conduction anisotropy in porous thin films with chevron microstructures
Authors: Vick D. , Brett M. J.
Published: January 2006

Electrical conductivity measurements were performed on structurally anisotropic thin films deposited using the glancing angle deposition apparatus [K. Robbie and M. J. Brett, J. Vac. Sci. Technol. A 15, 1460 (1997); K. Robbie, J. Sit, and M. J. Brett, J. Vac. Sci. Technol. B 16, 1115 (1998); K. Robbie and M. J. Brett, US Patent No. 5,866,204 (2 February 1999)]. The films were comprised of bilayers of titanium over silica, engineered as a chevron morphology. Samples were evaporated at various incident vapor deposition angles α, in order to investigate the effects of morphology and voiding on the behavior of conductivity. A rapid decline in the conductivity, accompanied by an increase in conduction anisotropy in the plane of the substrate, was observed with increasing α. A random walk model was developed to model the transport properties of the films, and applied to microstructures predicted by a three-dimensional ballistic thin film simulator. In order to generate reasonable agreement between the modeling and measurement, it was necessary to incorporate the effect of native oxide formation on the exposed surfaces of the titanium layer.
Characterization of low dielectric constant plasma polymer films deposited by plasma-enhanced chemical vapor deposition using decamethyl-cyclopentasiloxane and cyclohexane as the precursors
Authors: Yang Jaeyoung , Lee Sungwoo , Park Hyoungsun , Jung Donggeun , Chae Heeyeop
Published: January 2006

We investigated the properties of plasma polymer films deposited by plasma-enhanced chemical vapor deposition using a mixture of decamethyl-cyclopentasiloxane (C10H30O5Si5) and cyclohexane (C6H12) as the precursors, which we refer to as plasma polymerized decamethyl-cyclopentasiloxane: cyclohexane (PPDMCPSO:CHex) films. The relative dielectric constants, k, of the plasma polymer films were correlated with the Fourier transform infrared absorption peaks of the C–Hx, Si–CH3, and Si–O related groups. As the amount of the CHx species in the as-deposited plasma polymer films increased, the k value and the leakage current density of the thin films decreased. The subsequent annealing of the PPDMCPSO:CHex film at 400°C for 1h further reduced the k value to as low as k=2.05. This annealed PPDMCPSO:CHex thin film showed a leakage current density of the order of 4×10−7A∕cm2 at 1MV∕cm and a breakdown field of 6.5MV∕cm. Through the bias-temperature stress test, it was estimated that the PPDMCPSO:CHex film with a k value of 2.05 would retain its insulating properties for ten years at 167°C under an electrical field of 1MV∕cm, when it is presented as a layer adjacent to Cu∕TaN(10nm).
Effect of assistant rf field on phase composition of iron nitride film prepared by magnetron sputtering process
Authors: Li W. L. , Zheng F. , Fei W. D.
Published: January 2006

Fe–N thin films were fabricated using a direct current magnetron sputtering process assisted by a radio-frequency (rf) field. The effect of the rf field on the phase composition of the films was investigated. The results indicate that with the assistance of the rf field, various kinds of iron nitrides can be obtained in the films, including α′-Fe–N, α″-Fe16N2, ξ-Fe2N, ε-Fe3N, and γ″-FeN with ZnS structure. It was found that the rf field greatly benefits the formation of iron nitrides in the Fe–N films.
Effects of Al content on grain growth of solid solution (Ti,Al)N films
Authors: Liu Z.-J. , Shen Y. G.
Published: January 2006

Substitutional solid solution (Ti1−xAlx)N films with different Al contents (0⩽x⩽0.41) were deposited onto unheated Si(100) substrates by reactive unbalanced close-field magnetron sputtering in an Ar–N2 gas mixture. The effect of Al atomic concentration on the sizes of crystal grains during deposition was investigated. X-ray diffraction analysis revealed that the incorporated Al atoms had an obvious impact on the grain growth of (Ti1−xAlx)N films and the average crystal grain size showed an exponential decay with Al atomic concentration. A phenomenological model was proposed to analyze this solute-drag effect occurring during film deposition. It was found that the presence of solute drag in normal grain growth resulted in a low kinetic growth exponent, and the exponential decay in average grain size with solute atomic concentration could be reproduced in our calculations.
The Theory of Plastic Flow in the Rotation Viscometer
Authors: Reiner Markus
Published: January 2006

The theory of plastic flow is based on the fundamental law proposed by Bingham, which is as follows: dvdr = μ(F − f) (1) where dvdr is the velocity gradient G, μ the mobility, F the shearing force, and f the yield value.