Effect of sulfur passivation on 6H-SiC surface stability
Based on first-principles calculation, the surface stability of S-passivated 6H-SiC in different terminals are researched through investigating surface energy, charge distribution and density of states with the change of sulfur coverage from1/4 monolayer (ML) to 1 monolayer (ML). Our calculations show that S-passivated Si-terminal surface performs better than Si-terminal surface. Surface-state of 6H-SiC is reduced by about 1-4 electrons/eV due to S passivation. Meanwhile as the sulfur coverage increasing, surface energy is decreased from about -5.2eV/nm2 to about -40 eV/nm2 which leads to a more stable structure. According to theoretical calculation and mechanism analysis, the most stable structure is 3/4 ML sulfur atoms absorb in bridge site on Si-terminal surface.
First-principles study of the H2S passivation on 6H-SiC (0001) surface
Passivation is an effective way to reduce density of states (DOS) on the surface. In order to verify the differences and stabilities of H2S passivation on Si- and C-face of 6H-SiC, the adsorption of H2S on surface is studied by the first principles method, which is based on the density functional theory. Adsorption configuration and stability are researched with the coverage changing from 1/9monolayer (ML) to 1/3ML on Si-face while 1/9ML to 5/9ML on C-face. Adsorption energy, DOS and charge population of the system are calculated separately. On Si-face, energy calculations show that H2S which is adsorbed at the bridge (BR) site is more stable than that adsorbed at the on-top (OT) site. After H2S is decomposed, S atoms are combined at the BR site, while H atoms are adsorbed at the OT site. The surface states are noticeably reduced after passivation. Surface states are reduced to the lowest when the coverage is 2/9ML. On C-face, H2S which is adsorbed at the OT site is more stable than that adsorbed at the BR site. After H2S is decomposed, HS bonds and H atoms are all combined at the OT site. The surface states are noticeably reduced to the lowest when the coverage is 4/9ML.
Positive Rights and State Constitutions: The Limits of Federal Rationality Review
INTRODUCTION ............................................................................................................................. 1132 I. STATE CONSTITUTIONAL WELFARE PRACTICE ............................................................. 1144 A. A Mandatory Obligation: The New York Example .................................................. 1144 B. A Typology of Current State Court Decisions .......................................................... 1145 IT. RECONSIDERING FEDERAL RATIONALITY REVIEW IN STATE CONSTITUTIONAL WELFARE CASES ................................................................................ 1153 A. Rationality Review and Positive Rights .................................................................. 1155 B. Rationality Review and Democratic Legitimacy .................................................... 1157 C. Rationality Review and Judicial Finality ............................................................. xi61 D. Rationality Review and Federalism ......................................................................... i166 E. Rationality Review Revisited .................................................................................... 1169 III. TOWARD A NEW STANDARD OF REVIEW ......................................................................... 1169 A. The Need for Judicial Review .................................................................................. 1170 B. Institutional Competence and Welfare Litigation ................................................... 1175 I. State Courts as Fact Gatherers ......................................................................... 1175 2. State Courts as Policymakers ......................................................................... " 179 3. State Courts as Rights Enforcers ..................................................................... 1182 C. A Jurisprudence of Consequences .............................................................................. 1183 D. Why Education and Not Welfare? ........................................................................... i86 E. Implications for Welfare Litigation ........................................................................... i9i IV. CONCLUSION ........................................................................................................................ 1194