Strain Dependence of Dielectric Properties and Reliability of High-k Thin Films
The effect of strain on both electronic and structural characteristics of HfO2 used for sub-50-nm semiconductor devices was analyzed by a quantum chemical molecular dynamics analysis. The band structure of HfO2 is strongly affected by strain in the film. Based on the change rate of band gap obtained from our simulations, the strain sensitivity of the relative permittivity of HfO2 film is predicted to about 2.4%/1%-strain. The predicted strain sensitivity was validated quantitatively by measuring the change of the capacitance of MOS capacitors using a HfO2 gate dielectric film. It is very important, therefore, to minimize the mechanical strain in the dielectric film to assure the reliability of MOS transistor.
Tight-binding quantum chemical molecular dynamics study of cathode materials for lithium secondary battery
Abstract Our tight-binding quantum chemical molecular dynamics (TBMD) program was applied to the investigation of the structural and electronic properties of LixMn2O4. The calculated lattice constants of the LiMn2O4 and λ-MnO2 were 8.17 and 8.08 A, respectively, which are in good agreement with experimental results. The electronic analysis showed that the manganese atoms in the LiMn2O4 were separated into two groups based on their electronic states, which correspond to Mn3+ and Mn4+. We calculated the average potential for the reaction of Li+Mn2O4→LiMn2O4 and obtained the average potential of 4.2 V. The experimental value of the potential is approximately 4.0 V, indicating that our program is a powerful tool to predict the potential of various materials, as well as their atomistic and electronic structures.
Work, Status, and Income: Men in the American Occupational Structure since the Late Nineteenth Century
The historical record rarely presents researchers with precisely the evidence they desire. This is particularly true for social historians and like-minded scholars, whose subjects left precious few signs of their passing. Consequently, certain data have borne a disproportionate evidentiary load in social-historical research. The occupation a person pursued is one key piece of information on which scholars have come to depend. Our understanding of the historical social structure and where people fit into it is bound up with the interpretation of occupations. But this reliance on occupation as the primary social locator in historical research depends on some largely unexamined premises. Whether scholars group occupations or convert them into numerical status measures, they make assumptions about the nature of the occupational structure. When researchers incorporate change over time into their analyses, they suggest that the meaning of occupations remained stable for the purpose of measuring social mobility, class position, or group status-attainment. This assumption has been the subject of little discussion and even less research. For all the use to which historians have put occupation, there has been little effort to assess systematically its stability as a social or economic indicator.