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Abstract: Carbon impurities in Si are common in floating-zone and cast-Si materials. The simplest and most discussed carbon complex is the interstitial–substitutional CiCs pair, which readily forms when self-interstitials are present in the material. This pair has three possible configurations, each of which is electrically active. The less common CsCs pair has been studied in irradiated material but has also recently been seen in as-grown C-rich cast-Si, which is commonly used to fabricate solar cells. The third pair consists of two interstitial C atoms: CiCi. Although its formation probability is low for several reasons, the CiCi pair is very stable and electrically inactive. In this contribution, we report preliminary results of first-principles calculations of these three C pairs in Si. The structures, binding energies, vibrational spectra, and electrical activity are predicted. [Copyright &y& Elsevier]

Abstract: The ISiCiOi (C4) defect consists of a Si self-interstitial trapped at the interstitial carbon–oxygen CiOi pair (C3). The C4 defect is characterized by two infrared absorption lines at 940 and 1024cm−1. The former is C-related and the latter is O-related. The intensity of these lines begins to drop above 150°C and they disappear around 200°C. In this work, we present the results of first-principles calculations of the configurations, binding energies, vibrational spectra, and estimated gap levels of C3 and C4. [Copyright &y& Elsevier]

The vibrational spectra of crystalline diamond, silicon, and germanium are calculated with a first-principles local density functional scheme using 64 as well as 128 atoms supercells. The (harmonic) dynamical matrices are obtained from linear response theory. The phonon density of states, calculated for various isotopic masses M, are used to evaluate the vibrational heat capacities Cv and their dependence on M at low temperatures. Simple rules obeyed by the isotope effect of Cv are discussed. The results are compared with recent experimental data for Ge. It is hoped that this work will encourage and help to interpret analogous measurements in diamond and silicon with different isotopic compositions. [Copyright &y& Elsevier]

The properties of copper in silicon calculated from first-principles methods are reviewed and discussed. The defects studied so far include interstitial and substitutional copper, Cu complexes with the vacancy and vacancy clusters, Cu-self-interstitial pairs, Cu-shallow acceptor pairs, Cu–H, and Cu–O interactions, and Cu–Cu pairs. The variety of these interactions is possible because the shell of Cu is full only for the free atom. Inside the Si matrix, some electrons are promoted from the shell into the shell, and copper easily forms multiple (weak but) covalent bonds, in particular with native defects and impurities such as H. However, the interactions between interstitial Cu and interstitial O or the A-center do not involve the formation of a Cu–O bond, as oxygen much prefers to bind to silicon. [Copyright &y& Elsevier]

Carbon is a common substitutional impurity in Si. It traps hydrogen, and several {C,H} and {C,H,H} complexes have been observed by electrical and optical techniques. In this paper, we report (preliminary) first-principles molecular-dynamics studies of the structures and energetics of substitutional carbon (Cs) and two {Cs,H,H} complexes. Complete vibrational spectra are obtained from linear response theory. The relative stability of the two {Cs,H,H} complexes is calculated as a function of temperature. [Copyright &y& Elsevier]

Vibrational free energies are calculated from first-principles in the same Si periodic supercells routinely used to perform defect calculations. The specific heat, vibrational entropy, and zero-point energy obtained in defect-free cells are very close to the measured values. The importance of the vibrational part of the free energy is studied in the case of two defect problems: the relative energies of the H2 and H2* dimers and the binding energy of a copper pair. In both cases, the vibrational entropy term causes total energy differences to change by about 0.2 eV between 0 and 800 K. We also comment on the rotational entropy in the case of H2 and the configurational entropy in the case of the Cu pair. These examples illustrate the importance of extending first-principles calculations of defects in semiconductors to include free energy contributions. [Copyright &y& Elsevier]

Defects play essential roles in many materials, especially semiconductors. Today’s most advanced electronics involve defect engineering at the atomic level. The need to control the behavior of nearly every atom in the active area of a device implies a high degree of understanding of how defects behave and interact in a host crystal. This is achieved by a combination of microscopic experimental and theoretical methods. The theory of defects in silicon has evolved tremendously in the past half century and has become quantitative in many respects. This review gives an overview of the evolution of theory and a discussion of ongoing developments.Abraham Lincoln once said, “It has been my experience that folks who have no vices have very few virtues.” His wit and wisdom apply equally well to defects in materials. By ‘defect’, I mean a native defect or an impurity. The words ‘defect’ and ‘impurity’ have an intrinsically negative connotation, but defects are often desirable. They affect or even control the optical, mechanical, and electrical properties of materials. The color of diamond is determined by N or B impurities. Its thermal conductivity depends strongly upon its isotopic purity. Less than 1% of C transforms Fe into hard steel. As for semiconductors, virtually all their electrical and optical properties are determined by the type and concentration of defects they contain. The story of Si (and other semiconductors) is the story of defect control and defect engineering. Defects are not annoying details that must be eliminated. Instead, some are critically useful, while others render a device inoperable. Defect-free Si is pretty and shiny, but useless until the right defect is made to behave in the right way at the right place. [Copyright &y& Elsevier]

Abstract: The CuPL defect is characterized by intense photoluminescence (PL) emission with a 1014meV zero-phonon line and has since long been called the ‘copper-pair’ defect. However, recent PL studies in isotopically pure 28Si samples show clear evidence for four Cu atoms in this defect. This defect is one of a family of complexes that contain four (sometimes five) metal impurities. No complex containing two or three metal impurities (at least one of which is a transition metal) has been reported. We have performed systematic calculations of a priori possible Cu4 complexes, including the Cus1Cui3 complex proposed by Shirai et al. . This complex has the lowest formation energy of all the Cu4 defects. We have studied its properties using first-principle theory. In addition to the structures, binding energies, and vibrational spectra, we studied the formation pathway in an attempt to figure out why smaller (or larger) complexes do not form. We find that Cus1Cuin with n=0, 1 or 2 continue to trap Cui + if the Fermi level is midgap, and that the process stops when n=3. © 2011 Elsevier Science. All rights reserved [Copyright &y& Elsevier]

Emergency medicine dogma traditionally teaches that aortic dissection presents as tearing chest pain, radiating to the back. This case report describes a 55-year-old woman presenting with a left homonymous hemianopsia and resultant gait disturbance. Initial head computed tomography demonstrated a right parietal infarct, and chest radiograph demonstrated a markedly widened mediastinum. Acute Stanford type A aortic dissection was subsequently confirmed. This report provides further evidence for atypical, painless presentations of aortic dissection. Given recent literature on the increasing prevalence of painless dissection, the disease entity should be included in the differential diagnosis for stroke, and a simple portable chest x-ray should always be obtained before administering thrombolytics. [ABSTRACT FROM AUTHOR]

Abstract: We report measurements of the heat capacity Cp of diamond with several isotopic compositions (12C1-x13Cx) in the 20–280K temperature range. The results, in particular the derivative of the specific heat with respect to the average isotopic mass, are compared with recent ab initio calculations. Agreement is good for T>150K. At lower temperatures, the samples with isotopic compositions different from the natural one display an anomalous increase in Cp/T3 with decreasing temperature which is attributed to the presence of metallic inclusions stemming from the metal used as a solvent in the high-pressure high-temperature growth process. [Copyright &y& Elsevier]