Ion yields and erosion rates for Si1−xGex(0x1) ultralow energy O2+ secondary ion mass spectrometry in the energy range of 0.25–1 keV

We report the SIMS parameters required for the quantitative analysis of Si1−xGex across the range of 0 ≤ x ≤ 1 when using low energy O2+ primary ions at normal incidence. These include the silicon and germanium secondary ion yield [i.e., the measured ion signal (ions/s)] and erosion rate [i.e., the speed at which the material sputters (nm/min)] as a function of x. We show that the ratio Rx of erosion rates, Si1−xGex/Si, at a given x is almost independent of beam energy, implying that the properties of the altered layer are dominated by the interaction of oxygen with silicon. Rx shows an exponential dependence on x. Unsurprisingly, the silicon and germanium secondary ion yields are found to depart somewhat from proportionality to (1−x) and x, respectively, although an approximate linear relationship could be used for quantification across around 30% of the range of x (i.e., a reference material containing Ge fraction x would give reasonably accurate quantification across the range of ±0.15x). Direct comparison of the useful (ion) yields [i.e., the ratio of ion yield to the total number of atoms sputtered for a particular species (ions/atom)] and the sputter yields [i.e., the total number of atoms sputtered per incident primary ion (atoms/ions)] reveals a moderate matrix effect where the former decrease monotonically with increasing x except at the lowest beam energy investigated (250 eV). Here, the useful yield of Ge is found to be invariant with x. At 250 eV, the germanium ion and sputter yields are proportional to x for all x

Conducting Measurement Invariance Tests with Ordinal Data: A Guide for Social Work Researchers

Objective: The validity of measures across groups is a major concern for social work researchers and practitioners. Many social workers use scales, or sets of questionnaire items, with ordinal response options. However, a review of social work literature indicates the appropriate treatment of ordinal data in measurement invariance tests is rare; only 3 of 57 articles published in 26 social work journals over the past 12 years used proper testing procedures. This article synthesizes information from the literature and provides recommendations for appropriate measurement invariance procedures with ordinal data. Method: We use data from the Cebu Longitudinal Health and Nutrition Survey to demonstrate applications of invariance testing with ordinal data. Using a robust weighted least squares estimator and polychoric correlation matrix, we examine invariance of a 10-item Perceived Stress Scale (PSS) across 2 young adult groups defined by health status. We describe 2 competing approaches: a 4-step approach, in which factor loadings and thresholds are tested and constrained separately; and a 3-step approach, in which loadings and thresholds are tested and constrained in tandem. Results: Both approaches lead to the same conclusion that the 2 dimensions of the PSS are noninvariant across health status. In the absence of invariance, mean scores on the PSS factors cannot be validly compared across groups, nor should latent variables be used in the hypothesis testing across the 2 groups. Readers are directed to online resources. Conclusions: Careful examination of social work scales is likely to reveal fit or noninvariance problems across some groups. Use of appropriate methods for invariance testing will reduce misuse of measures in practice and improve the rigor and quality of social work publications

The FAA: A Tombstone Agency? Putting the Nickname to the Test

The purpose of this research was to investigate Federal Aviation Administration (FAA) activity before and after six catastrophic airline accidents to examine the alleged reactive policysetting reputation of the FAA. Actions reviewed were regulatory, inspection, and enforcement activities. The study revealed that change in agency activity does occur following an accident. The location of the event appears to influence the direction of change. When accidents occurred within the United States, FAA activity increased following the accident. The opposite occurred for airline accidents outside the U.S. The increase in FAA activity following U.S. based events, supports the reactive, tombstone agency reputation the FAA has acquired. In addition, the research revealed nine FAA activities judged by industry experts as having the ability to improve safety in the airline industry. Inspections and certificate actions are considered activities that will improve safety. Regulatory actions, fines, warning notices, and letters of correction were judged as non-safety enhancing activities. The result of this research was an increased understanding of how the FAA responds to airline accidents and the consequences of the response

Biased EPR entanglement and its application to teleportation

We consider pure continuous variable entanglement with non-equal correlations between orthogonal quadratures. We introduce a simple protocol which equates these correlations and in the process transforms the entanglement onto a state with the minimum allowed number of photons. As an example we show that our protocol transforms, through unitary local operations, a single squeezed beam split on a beam splitter into the same entanglement that is produced when two squeezed beams are mixed orthogonally. We demonstrate that this technique can in principle facilitate perfect teleportation utilising only one squeezed beam.Comment: 8 pages, 5 figure

Bunches of misfit dislocations on the onset of relaxation of Si0.4_{0.4}Ge0.6_{0.6}/Si(001) epitaxial films revealed by high-resolution x-ray diffraction

The experimental x-ray diffraction patterns of a Si$_{0.4}$Ge$_{0.6}$/Si(001) epitaxial film with a low density of misfit dislocations are modeled by the Monte Carlo method. It is shown that an inhomogeneous distribution of 60$^\circ$ dislocations with dislocations arranged in bunches is needed to explain the experiment correctly. As a result of the dislocation bunching, the positions of the x-ray diffraction peaks do not correspond to the average dislocation density but reveal less than a half of the actual relaxation

Teleportation of continuous variable polarisation states

This paper discusses methods for the optical teleportation of continuous variable polarisation states. We show that using two pairs of entangled beams, generated using four squeezed beams, perfect teleportation of optical polarisation states can be performed. Restricting ourselves to 3 squeezed beams, we demonstrate that polarisation state teleportation can still exceed the classical limit. The 3-squeezer schemes involve either the use of quantum non-demolition measurement or biased entanglement generated from a single squeezed beam. We analyse the efficacies of these schemes in terms of fidelity, signal transfer coefficients and quantum correlations

Crystal truncation rods in kinematical and dynamical x-ray diffraction theories

Crystal truncation rods calculated in the kinematical approximation are shown to quantitatively agree with the sum of the diffracted waves obtained in the two-beam dynamical calculations for different reflections along the rod. The choice and the number of these reflections are specified. The agreement extends down to at least $\sim 10^{-7}$ of the peak intensity. For lower intensities, the accuracy of dynamical calculations is limited by truncation of the electron density at a mathematically planar surface, arising from the Fourier series expansion of the crystal polarizability

An experimental investigation of criteria for continuous variable entanglement

We generate a pair of entangled beams from the interference of two amplitude squeezed beams. The entanglement is quantified in terms of EPR-paradox [Reid88] and inseparability [Duan00] criteria, with observed results of $\Delta^{2} X_{x|y}^{+} \Delta^{2} X_{x|y}^{-} = 0.58 \pm 0.02$ and $\sqrt{\Delta^{2} X_{x \pm y}^{+} \Delta^{2} X_{x \pm y}^{-}} = 0.44 \pm 0.01$, respectively. Both results clearly beat the standard quantum limit of unity. We experimentally analyze the effect of decoherence on each criterion and demonstrate qualitative differences. We also characterize the number of required and excess photons present in the entangled beams and provide contour plots of the efficacy of quantum information protocols in terms of these variables.Comment: 4 pages, 5 figure