Epitaxial growth of CoSi2 on Si(001) by reactive deposition epitaxy: Island growth and coalescence

Epitaxial CoSi₂ layers, which are phase pure but contain {111} twins, are grown on Si(001) at 700 °C by reactive deposition epitaxy. Transmission electron microscopy analyses show that the initial formation of CoSi₂(001) follows the Volmer-Weber mode characterized by the independent nucleation and growth of three-dimensional islands whose evolution we follow as a function of deposited Co thickness t_Co in order to understand the origin of the observed twin density. We find that there are two families of island shapes: inverse pyramids and platelets. The rectangular-based pyramidal islands extend along orthogonal 〈110〉 directions, bounded by four {111} CoSi₂/Si interfaces, and grow with a cube-on-cube orientation with respect to the substrate: (001)_CoSi2||(001)_Si and [100]_CoSi2||[100]_Si. Platelet-shaped CoSi₂ islands are bounded across their long 〈110〉 directions by {111} twin planes (i.e. {111}(001)_CoSi2||{111}_Si) and their narrow 〈110〉 directions by {511}_CoSi2||{111}_Si interfaces. The top and bottom surfaces are {22¯1}, with {22¯1}_CoSi2||(001)_Si, and {1¯1¯1}, with {1¯1¯1}_CoSi2||{11¯1}_Si, respectively. The early stages of film growth (t_Co ≤ 13 Å) are dominated by the twinned platelets due to a combination of higher nucleation rates resulting from a larger number of favorable adsorption sites in the Si(001)2 × 1 surface unit cell and rapid elongation of the platelets along preferred 〈110〉 directions. However, at t_Co ≥ 13 Å island coalescence becomes significant as orthogonal platelets intersect and block elongation along fast growth directions. In this regime, where both twinned and untwinned island number densities have saturated, further island growth becomes dominated by the untwinned islands. A continuous epitaxial CoSi₂(001) layer, with a twin density of 2.8 × 10¹⁰ cm^− 2, is obtained at t_Co = 50 Å.     

Exploratory search of academic publication and citation data using interactive tag cloud visualizations

The number of authors from different countries have recently increased in ecology papers, but the international collaboration among ecologists does not occur in an idiosyncratic way. In this paper, we quantified the level of international collaboration in ecology papers and the influence of geographic distance and socioeconomic factors on collaboration between countries. We obtained all papers from Thomson-ISI, classified as subject ecology between years 2000 and 2014 (total of 62,667 papers with international collaboration in 179 countries). The gravity model (binomial negative model) indicated that the level of international collaboration is moderate spatially structured, decreasing as the geographical distance among countries increase. Moreover, the geographic distance and socioeconomic factors explained 10% of the scientific collaboration among countries (Pseudo R ² = 0.10). Highly collaborative countries were found in similar trade blocs, with similar Human Development Index, similar scientific structure (i.e., number of citation per documents) and tended to be geographically close. Thus, international collaboration will continue increasing, and young ecologists will experience international collaboration, even with distant countries (both geographical and socioeconomic).     

Surface-based analysis methods for high-resolution functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) has become a popular technique for studies of human brain activity. Typically, fMRI is performed with >3-mm sampling, so that the imaging data can be regarded as two-dimensional samples that average through the 1.5-4-mm thickness of cerebral cortex. The increasing use of higher spatial resolutions, <1.5-mm sampling, complicates the analysis of fMRI, as one must now consider activity variations within the depth of the brain tissue. We present a set of surface-based methods to exploit the use of high-resolution fMRI for depth analysis. These methods utilize white-matter segmentations coupled with deformable-surface algorithms to create a smooth surface representation at the gray-white interface and pial membrane. These surfaces provide vertex positions and normals for depth calculations, enabling averaging schemes that can increase contrast-to-noise ratio, as well as permitting the direct analysis of depth profiles of functional activity in the human brain.     

Molecular plating of actinides on thin backings

Actinide targets on thick and thin backings are needed for experiments at heavy-ion accelerators. One of the efficient ways to prepare such targets is by molecular plating. Although many laboratories have successfully prepared targets on thick backings by this technique, it is quite difficult to make targets on thin backings (100 μg/cm² up to 1 mg/cm²). In recent years, we have plated targets on thin Ni and carbon backings, for example ²³⁴U targets on a 200 μg/cm² Ni backing. The Ni foils, evaporated on a copper substrate, are available commercially. We used these foils to plate ²³⁴U and afterwards we removed the copper by dissolving it in a mixture of ammoniacal trichloroacetic acid. In this way 400 μg/cm^{2 234}U targets were prepared on a 200 μg/cm² Ni backing. A 100 μg/cm^{2 243}Am target was prepared by plating onto a 75 μg/cm² carbon film left on its glass substrate for later floating. We found that a plating cell made from Teflon was difficult to use because it scratched the C film producing a liquid leak at the joint of the column and the C film. This sealing surface needs to be extremely smooth to avoid leakage. A column made of Delrin™ was then tried and did not produce any scratch on the carbon film surface. This column was used to prepare 100 μg/cm^{2 243}Am targets. Details of the technique will be presented.     

Challenges in researching racially sensitive topics in HMOs.

When research designed to close the disparities gap is conducted in real-world health care settings, unique sensitivities may arise, particularly when race is the focus of interventions. Researchers encountered this issue in the course of a randomized trial investigating the influence of ethnic identity (EI) among African American (AA) study participants. The study was conducted by the research programs at three health maintenance organizations (HMOs) and the University of Michigan Center for Health Communications Research, as described in this issue of the journal (Resnicow et al., 2009). This commentary describes the research partnership’s concerns for the racially sensitive nature of the study and the precautions undertaken to mitigate them. The research study’s experiences may be informative and insightful for health plans and research centers invested in health disparities research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A sociotherapeutic guide: Wherefore art thou?

R. M. Lipgar's (see record 1999-08068-006) compelling analysis of the therapeutic community underscores the usefulness of this still-underused treatment method. This relative neglect springs, in part, from the inconsistency between the method and the overall mission of many treatment facilities, the lack of information regarding the parameters that might need to be adjusted to optimize this approach for any particular setting, and the reliance on cognitive-behavioral methods that tend to ignore group process. Additional empirical work, including outcome studies, is needed to define the potential usefulness of sociotherapeutic methods. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Time reversal in polarized neutron decay: the emiT experiment

The standard electro-weak model predicts negligible violation of time-reversal invariance in light quark processes. We report on an experimental test of time-reversal invariance in the beta decay of polarized neutrons as a search for physics beyond the standard model. The emiT collaboration has measured the time-reversal-violating triple-correlation in neutron beta decay between the neutron spin, electron momentum, and neutrino momentum often referred to as the D coefficient. The first run of the experiment produced 14 million events which are currently being analyzed. However, a second run with improved detectors should provide greater statistical precision and reduced systematic uncertainties.     

Performance of the prototype LANL solid deuterium ultra-cold neutron source

A prototype of a solid deuterium (SD₂) source of Ultra-Cold Neutrons (UCN) is currently being tested at LANSCE. The source is contained within an assembly consisting of a 4 K polyethylene moderator surrounded by a 77 K beryllium flux trap in which is embedded a spallation target. Time-of-flight measurements have been made of the cold neutron spectrum emerging directly from the flux trap assembly. A comparison is presented of these measurements with results of Monte Carlo (LAHET/MCNP) calculations of the cold neutron fluxes produced in the prototype assembly by a beam of 800 MeV protons incident on the tungsten target. A UCN detector was coupled to the assembly through a guide system with a critical velocity of 8 m/s (⁵⁸Ni). The rates and time-of-flight data from this detector are compared with calculated values. Measurements of UCN production as a function of SD₂ volume (thickness) are compared with predicted values. The dependence of UCN production on SD₂ temperature and proton beam intensity are also presented.     

Trajectories of perceived adult and peer discrimination among Black, Latino, and Asian American adolescents: Patterns and psychological correlates.

This article presents results from a 3-year longitudinal study of the growth patterns and correlates of perceived discrimination by adults and by peers among Black, Latino, and Asian American high school students. Results revealed a linear increase over time in levels of perceived discrimination by adults, whereas perceptions of discrimination by peers remained stable over time. Asian American and non-Puerto Rican Latino adolescents (primarily Dominican) reported higher levels of peer and/or adult discrimination than did Puerto Rican youth, whereas Black adolescents reported a steeper increase over time in levels of perceived discrimination by peers and by adults than did Puerto Rican adolescents. Peer and adult discrimination was significantly associated with decreased self-esteem and increased depressive symptoms over time. Ethnic identity and ethnicity were found to moderate the relationships between perceived discrimination and changes in psychological well-being over time. Results underscore the need to include perceptions of discrimination when studying the development and well-being of ethnic minority adolescents. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

CrO2/Ag/YBCO Interface Study with a Flip-Chip Configuration

Transport across a CrC₂/Ag/YBCO interface was studied using a flip-chip configuration. The results were interpreted in the Andreev reflection scenario. It is shown that the surface spin-polarization of CrO₂ film, even after exposing to air, remained close to 100% to the T _c of YBa₂Cu₃O_{7− x} , a temperature limited by this method.