Single crystalline BaTiO_3 thin films synthesized using ion implantation induced layer transfer

Layer transfer of BaTiO3 thin films onto silicon-based substrates has been investigated. Hydrogen and helium ions were co-implanted to facilitate ion-implantation-induced layer transfer of films from BaTiO3 single crystals. From thermodynamic equilibrium calculations, we suggest that the dominant species during cavity nucleation and growth are H2, H+, H2O, Ba2+ and Ba–OH, and that the addition of hydrogen to the Ba–Ti–O system can effectively suppress volatile oxide formation during layer transfer and subsequent annealing. After ion implantation, BaTiO3 layers contain microstructural defects and hydrogen precipitates in the lattice, but after layer transfer, the single crystal is found to be stoichiometric. Using direct wafer bonding and layer splitting, single crystal BaTiO3 thin films were transferred onto amorphous Si3N4 and Pt substrates. Micro-Raman spectroscopy indicated that the density of defects generated by ion implantation in BaTiO3 can be significantly reduced during post-transfer annealing, returning the transferred layer to its single crystal state. Characterization using piezoresponse force microscopy shows that the layer transferred thin films are ferroelectric, with domain structures and piezoresponse characteristics similar to that of bulk crystals

Microstructure and properties of single crystal BaTiO3 thin films synthesized by ion implantation-induced layer transfer

Single crystal BaTiO3 thin films have been transferred onto Pt-coated and Si3N4-coated substrates by the ion implantation-induced layer transfer method using H+ and He+ ion coimplantation and subsequent annealing. The transferred BaTiO3 films are single crystalline with root mean square roughness of 17 nm. Polarized optical and piezoresponse force microscopy (PFM) indicate that the BaTiO3 film domain structure closely resembles that of bulk tetragonal BaTiO3 and atomic force microscopy shows a 90degrees a-c domain structure with a tetragonal angle of 0.5degrees-0.6degrees. Micro-Raman spectroscopy indicates that the local mode intensity is degraded in implanted BaTiO3 but recovers during anneals above the Curie temperature. The piezoelectric coefficient, d(33), is estimated from PFM to be 80-100 pm/V and the coercive electric field (E-c) is 12-20 kV/cm, comparable to those in single crystal BaTiO3

Surface evolution during crystalline silicon film growth by low-temperature hot-wire chemical vapor deposition on silicon substrates

We investigate the low-temperature growth of crystalline thin silicon films: epitaxial, twinned, and polycrystalline, by hot-wire chemical vapor deposition (HWCVD). Using Raman spectroscopy, spectroscopic ellipsometry, and atomic force microscopy, we find the relationship between surface roughness evolution and (i) the substrate temperature (230–350 °C) and (ii) the hydrogen dilution ratio (H2/SiH4=0–480). The absolute silicon film thickness for fully crystalline films is found to be the most important parameter in determining surface roughness, hydrogen being the second most important. Higher hydrogen dilution increases the surface roughness as expected. However, surface roughness increases with increasing substrate-temperature, in contrast to previous studies of crystalline Si growth. We suggest that the temperature-dependent roughness evolution is due to the role of hydrogen during the HWCVD process, which in this high hydrogen dilution regime allows for epitaxial growth on the rms roughest films through a kinetic growth regime of shadow-dominated etch and desorption and redeposition of growth species

A comparison of the impact of extensive and intensive reading approaches on the reading attitudes of secondary EFL learners

Extensive reading (ER) which encourages second or foreign (L2) learners to engage in a great deal of reading, has long been recognized as an efficient approach in L2 reading pedagogy. While many attempts have been made to understand the effect of ER on the cognitive domains of L2 learners, there has been insufficient investigation into how ER influences their affective domains. Particularly, reading attitudes, one of the key elements of affective factors involved in L2 reading, have received little attention. This classroom-based intervention study investigated the impact of ER on English as a foreign language (EFL) learners’ attitudes toward English reading compared to the influence of the traditional intensive reading (IR) approach. In addition, this study explored whether the impact of the ER approach on EFL learners’ reading attitudes is different depending on L2 proficiency. The study included two intact classes of EFL secondary learners (N = 72) who received either ER or IR instructional treatments for a 12-week period. For the results, ANCOVA showed that the ER approach fostered positive reading attitudes significantly more than the IR approach. In addition, the analysis indicated that the participants’ proficiency levels did not have a significant effect upon changes in their reading attitudes. That is, regardless of proficiency level, the ER approach demonstrated a significantly positive effect on participants’ reading attitudes in comparison with the IR approach

Nanomechanical characterization of cavity growth and rupture in hydrogen-implanted single-crystal BaTiO3

A thermodynamic model of cavity nucleation and growth in ion-implanted single-crystal BaTiO3 layer is proposed, and cavity formation is related to the measured mechanical properties to better understand hydrogen implantation-induced layer transfer processes for ferroelectric thin films. The critical radius for cavity nucleation was determined experimentally from blistering experiments performed under isochronal anneal conditions and was calculated using continuum mechanical models for deformation and fracture, together with thermodynamic models. Based on thermodynamic modeling, we suggest that cavities grow toward the cracking criteria at a critical blister size whereupon gas is emitted from ruptured cavities. The main driving force for layer splitting is the reduction of the overall elastic energy stored in the implanted region during the cavity nucleation and growth as the gaseous H2 entrapped within the cavities is released. Nanoindentation measurements reveal locally the mechanical property changes within the vicinity of a single cavity. Using the measured mechanical properties at the single-cavity level, we developed three-dimensional strain and stress profiles using finite element method

New Gauge Invariant Formulation of the Chern-Simons Gauge Theory: Classical and Quantal Analysis

Recently proposed new gauge invariant formulation of the Chern-Simons gauge theory is considered in detail. This formulation is consistent with the gauge fixed formulation. Furthermore it is found that the canonical (Noether) Poincar\'e generators are not gauge invariant even on the constraints surface and do not satisfy the Poincar\'e algebra contrast to usual case. It is the improved generators, constructed from the symmetric energy-momentum tensor, which are (manifestly) gauge invariant and obey the quantum as well as classical Poincar\'e algebra. The physical states are constructed and it is found in the Schr\"odinger picture that unusual gauge invariant longitudinal mode of the gauge field is crucial for constructing the physical wavefunctional which is genuine to (pure) Chern-Simons theory. In matching to the gauge fixed formulation, we consider three typical gauges, Coulomb, axial and Weyl gauges as explicit examples. Furthermore, recent several confusions about the effect of Dirac's dressing function and the gauge fixings are clarified. The analysis according to old gauge independent formulation a' la Dirac is summarized in an appendix.Comment: No figures, 44 page

EXAMINING THE RELATIONSHIP BETWEEN TRAVELERS\u27 DECISION-MAKING STYLES AND TRIP PLANNING

Decision-making styles have been used to explain a variety of consumer behaviors. The goal of the study presented in this paper was to apply the decision-making style instrument to the context of advance trip planning. The results suggest that an intuitive decision-making style influences the extent of trip planning while a spontaneous style influences the length of the advance planning period; however, the relationships found were not very strong. Also, no significant relationships were found for dependent decision-making style, lack of innovativeness and sensation seeking. The findings indicate that decision-making styles are less influential with respect to advance trip planning than expected. The limitations of the study and implications for further research are discussed

Astrometric Detection of Double Gravitational Microlensing Events

If a gravitational microlensing event is caused by a widely separated binary lens and the source approaches both lens components, the source flux is successively magnified by the individual lenses: double microlensing events. If events are observed astrometrically, double lensing events are expected to occur with an increased frequency due to the long range astrometric effect of the companion. We find that although the trajectory of the source star image centroid shifts of an astrometric double lensing event has a distorted shape from both of the elliptical ones induced by the individual single lens components, event duplication can be readily identified by the characteristic loop in the trajectory formed during the source's passage close to the companion. We determine and compare the probabilities of detecting double lensing events from both photometric and astrometric lensing observations by deriving analytic expressions for the relations between binary lensing parameters to become double lensing events. From this determination, we find that for a given set of the binary separation and the mass ratio the astrometric probability is roughly an order higher than the photometric probability. Therefore, we predict that a significant fraction of events that will be followed up by using future high precision interferometeric instruments will be identified as double lensing events.Comment: total 6 pages, including 4 figures and no table, ApJ, submitte

The UNAM-KIAS Catalog of Isolated Galaxies

A new catalog of isolated galaxies from The Sloan Digital Sky Survey (DR5) is presented. 1520 isolated galaxies were found in 1.4 steradians of sky. The selection criteria in this so called UNAM-KIAS catalog was implemented from a variation on the criteria developed by Karachentseva 1973 including full redshift information. Through an image processing pipeline that takes advantage from the high resolution (~ 0.4 ''/pix) and high dynamic range of the SDSS images, a uniform g band morphological classification for all these galaxies is presented. We identify 80% (SaSm) spirals (50% later than Sbc types) on one hand, and a scarce population of early-type E(6.5%) and S0(8%) galaxies amounting to 14.5% on the other hand. This magnitude-limited catalog is ~ 80% complete at 16.5, 15.6, 15.0, 14.6 and 14.4 magnitudes in the ugriz bands respectively. Some representative physical properties including SDSS magnitudes and color distributions, color-color diagrams, absolute magnitude-color, and concentration-color diagrams as a function of morphological type are presented. The UNAM-KIAS Morphological Atlas is also released along with this paper. For each galaxy of type later than Sa, a mosaic is presented that includes: (1) a g-band logarithmic image, (2) a g band filtered-enhanced image where a Gaussian kernel of various sizes was applied and (3) an RGB color image from the SDSS database. For E/S0/Sa galaxies, in addition to the images in (1), (2) and (3), plots of r band surface brightness and geometric profiles (ellipticity, Position Angle PA and A4/B4 coefficients of the Fourier series expansions of deviations of a pure ellipse) are provided...Comment: 40 pages, 17 figures and 3 table