Theoretical Investigation Of A Mn-doped Si Ge Heterostructure

We investigate, through ab initio density-functional theory calculations, the electronic and structural properties of neutral Mn impurities at tetrahedral interstitial and substitutional sites in both Si and Ge layers of a Si Ge heterostructure. We conclude that substitutional Mn at the Ge layers is more stable than interstitial Mn at the Si layers by approximately 0.45 eV, and we estimate an energy barrier of at least 1.12 eV to diffuse away from these most stable substitutional sites. Mn has a magnetic moment in the heterostructure that is similar to that in the bulk, and for the compressed Ge layer the Mn-Mn exchange interaction is always weakly antiferromagnetic. Varying the lattice constant of the substrate, the Mn-Mn ground state becomes ferromagnetic. This result opens up the possibility of manipulating the interaction between Mn impurities at Ge layers grown over a Si1-x Gex substrate by changing x. © 2007 The American Physical Society.757Žutić, I., Fabian, J., Das Sarma, S., (2004) Rev. Mod. Phys., 76, p. 323. , RMPHAT 0034-6861 10.1103/RevModPhys.76.323MacDonald, A.H., Schiffer, P., Samarth, N., (2005) Nat. Mater., 3, p. 195. , NMAACR 1476-1122Park, Y.D., Wilson, A., Hanbicki, A.T., Mattson, J.E., Ambrose, T., Spanos, G., Jonker, B.T., (2001) Appl. Phys. Lett., 78, p. 2739. , APPLAB 0003-6951 10.1063/1.1369151Silva Da, R.A.J., Fazzio, A., Antonelli, A., (2004) Phys. Rev. B, 70, p. 193205. , PRBMDO 0163-1829 10.1103/PhysRevB.70.193205Woodbury, H.H., Ludwig, G.W., (1960) Phys. Rev., 117, p. 102. , PHRVAO 0031-899X 10.1103/PhysRev.117.102Nakashima, H., Hashimoto, K., (1991) J. Appl. Phys., 69, p. 1440. , JAPIAU 0021-8979 10.1063/1.347285Kamon, Y., Harima, H., Yanase, A., Katayama-Yoshida, H., (2001) Physica B, 308-310, p. 391. , PHYBE3 0921-4526Perdew, J.P., Wang, Y., (1992) Phys. Rev. B, 45, p. 13244. , PRBMDO 0163-1829 10.1103/PhysRevB.45.13244Vanderbilt, D., (1990) Phys. Rev. B, 41, p. 7892. , PRBMDO 0163-1829 10.1103/PhysRevB.41.7892Kresse, G., Hafner, J., (1993) Phys. Rev. B, 47, p. 558. , PRBMDO 0163-1829 10.1103/PhysRevB.47.558Kresse, G., Furthmüller, J., (1996) Phys. Rev. B, 54, p. 11169. , PRBMDO 0163-1829 10.1103/PhysRevB.54.11169Da Silva, A.J.R., Fazzio, A., Dos Santos, R.R., Oliveira, L.E., (2003) Physica B, 340-342, p. 874. , PHYBE3 0921-4526Da Silva, A.J.R., Fazzio, A., Dos Santos, R.R., Oliveira, L.E., (2004) J. Phys.: Condens. Matter, 16, p. 8243. , JCOMEL 0953-8984 10.1088/0953-8984/16/46/011Venezuela, P., Dalpian, G.M., Silva Da, R.A.J., Fazzio, A., (2001) Phys. Rev. B, 64, p. 193202. , PRBMDO 0163-1829 10.1103/PhysRevB.64.193202Wang, Q., Sun, Q., Jena, P., Kawazoe, Y., (2004) Phys. Rev. Lett., 93, p. 155501. , PRLTAO 0031-9007 10.1103/PhysRevLett.93.15550

Structure And Energetics Of Molecular Point Defects In Ice Ih

We present a first-principles study of the molecular vacancy and three distinct molecular interstitial structures in ice Ih. The results indicate that, due to its bonding to the surrounding hydrogen-bond network, the bond-center (Bc) configuration is the favored molecular interstitial in ice Ih. A comparison between the vacancy and the Bc interstitial suggests that the former is the predominant molecular point defect for T 200K although a crossover scenario in which the latter becomes favored below the melting point is conceivable. © 2006 The American Physical Society.9715Petrenko, V.F., Whitworth, R.W., (1999) The Physics of Ice, , Oxford University Press, OxfordHaas, C., (1962) Phys. Lett., 3, p. 126. , PHLTAM 0031-9163 10.1016/0031-9163(62)90057-4Mogensen, O.E., Eldrup, M., (1978) J. Glaciol., 21, p. 85. , JOGLAO 0022-1430Eldrup, M., Mogensen, O.E., Bilgram, J.H., (1978) J. Glaciol., 21, p. 101. , JOGLAO 0022-1430Hondoh, T., Itoh, T., Higashi, A., (1982) Point Defects and Defect Interactions in Metals, p. 599. , edited by J. Takamura, M. Doyama, and M. Kiritani (University of Tokyo Press, TokyoGoto, K., Hondoh, T., Higashi, A., (1982) Point Defects and Defect Interactions in Metals, p. 174. , edited by J. Takamura, M. Doyama, and M. Kiritani (University of Tokyo Press, TokyoGoto, K., Hondoh, T., Higashi, A., (1986) Jpn. J. Appl. Phys., 25, p. 351. , JAPNDE 0021-4922 10.1143/JJAP.25.351Hondoh, T., Azuma, K., Higashi, A., (1987) J. Phys. Paris, 48 (C1), p. 183. , JOPQAG 0302-0738 No. C1Oguro, M., Hondoh, T., (1988) Lattice Defects in Ice Crystals, p. 49. , edited by A. Higashi (Hokkaido University Press, SapporoFletcher, N.H., (1970) The Chemical Physics of Ice, , Cambridge University Press, Cambridge, EnglandItoh, H., Kawamura, K., Hondoh, T., Mae, S., (1996) J. Chem. Phys., 105, p. 2408. , JCPSA6 0021-9606 10.1063/1.472108Demurov, A., Radhakrishnan, R., Trout, B.L., (2002) J. Chem. Phys., 116, p. 702. , JCPSA6 0021-9606 10.1063/1.1425821Ikeda-Fukazawa, T., Horikawa, S., Hondoh, T., Kawamura, K., (2002) J. Chem. Phys., 117, p. 3886. , JCPSA6 0021-9606 10.1063/1.1495844De Koning, M., Antonelli, A., Da Silva, A.J.R., Fazzio, A., (2006) Phys. Rev. Lett., 96, p. 075501. , PRLTAO 0031-9007 10.1103/PhysRevLett.96.075501Kresse, G., Hafner, J., (1993) Phys. Rev. B, 47, p. 558. , PRBMDO 0163-1829 10.1103/PhysRevB.47.558Kresse, G., Furthmüller, J., (1996) Comput. Mater. Sci., 6, p. 15. , CMMSEM. 0927-0256. 10.1016/0927-0256(96)00008-0Kresse, G., Joubert, D., (1999) Phys. Rev. B, 59, p. 1758. , PRBMDO 0163-1829 10.1103/PhysRevB.59.1758Hayward, J.A., Reimers, J.R., (1997) J. Chem. Phys., 106, p. 1518. , JCPSA6 0021-9606 10.1063/1.473300Finnis, M., (2003) Interatomic Forces in Condensed Matter, pp. 156-157. , Oxford University Press, New YorkLesar, R., Najafabadi, R., Srolovitz, D.J., (1989) Phys. Rev. Lett., 63, p. 624. , PRLTAO 0031-9007 10.1103/PhysRevLett.63.624Li, J.-C., Ross, D.K., (1992) Physics and Chemistry of Ice, p. 27. , edited by N. Maeno and T. Hondoh (Hokkaido University Press, Hokkaid

Energetics and stability of vacancies in carbon nanotubes

In this work we present ab initio calculations of the formation energies and stability of different types of multi-vacancies in carbon nanotubes. We demonstrate that, as in the case of graphene, the reconstruction of the defects has drastic effects on the energetics of the tubes. In particular, the formation of pentagons eliminates the dangling bonds thus lowering the formation energy. This competition leads to vacancies having an even number of carbon atoms removed to be more stable. Finally the appearance of magic numbers indicating more stable defects can be represented by a model for the formation energies that is based on the number of dangling bonds of the unreconstructed system, the pentagons and the relaxation of the final form of the defect formed after the relaxation

Hospitais: espaços de cura e lugares de memória da saúde

O presente artigo pretende analisar o Hospital Gaffrée e Guinle, construído na década de 1920, na cidade do Rio de Janeiro, em um processo de tomada de controle, pela administração pública, da gestão da assistência hospitalar na capital federal. Esse hospital representa o encontro da filantropia com um projeto de saúde pública posto em prática no Distrito Federal à mesma época. A instituição sintetiza também o desenvolvimento da medicina e sua tradução na arquitetura hospitalar, bem como a efervescência intelectual do período, mais especificamente das idéias nacionalistas, interpretadas tanto na escolha do estilo arquitetônico - o neocolonial - quanto na questão da salvação da raça através do combate e controle da sífilis.This paper analyzes the Gaffrée & Guinle Hospital, built in Rio de Janeiro during the 1920s as the result of a process whereby the government took over the management of hospital care in the federal capital. The hospital is the point of convergence between philanthropy and a public healthcare project implemented in the Federal District at that time. It also synthesizes the development of medicine and how the latter translates into hospital architecture, as well as the intellectual effervescence at the time, more specifically the nationalist ideas which can be identified both in the choice of architectural style - namely the neocolonial - and in the theme of salvation of a race through the combat and control of syphilis

Breaking Of Gold Nanowires

We have investigated the formation evolution and breaking of a gold nanowire using molecular dynamics simulation. Results reproduce many features observed experimentally. Suspended gold nanowires have recently been produced in an ultra-high vacuum and were imaged by electron microscopy. Here we simulate gold nanowires under stress. In particular, we discuss the mechanisms of formation, evolution and breaking of these atomically thin Au nanowires. © 2004 Elsevier B.V. All rights reserved.301-2 SPEC ISS.7376Kondo, Y., Takayanagi, K., (2000) Science, 289, p. 606Ohnishi, H., Kondo, Y., Takayanagi, K., (1998) Nature, 395, p. 780Rodrigues, V., Fuhrer, T., Ugarte, D., (2000) Phys. Rev. Lett., 85, p. 4124Rodrigues, V., Ugarte, D., (2001) Phys. Rev. B, 63, p. 073405Gulseren, O., Ercolessi, F., Tosatti, E., (1998) Phys. Rev. Lett., 80, p. 3775Landman, U., Luedtke, W., Burnham, N., Colton, R.J., (1990) Science, 248, p. 454Brandbyge, M., (1995) Phys. Rev. B, 52, p. 8499Barnett, R.N., Landman, U., (1997) Nature, 387, p. 788Nakamura, A., Brandbyge, M., Hansen, L.B., Jacobsen, K.W., (1999) Phys. Rev. Lett., 82, p. 1538Tosatti, E., Prestipino, S., Kostlmeier, S., Dal Corso, A., Di Tolla, F.D., (2001) Science, 291, p. 288Sánchez-Portal, D., (1999) Phys. Rev. Lett., 83, p. 3884Mehl, M.J., Papaconstantopoulos, D.A., (1996) Phys. Rev. B, 54, p. 4519http://cst-www.nrl.navy.mil/bindhttp://cst-www.nrl.navy.mil/bind/dodtbKirchhoff, F., Mehl, M.J., Papanicolaou, N.I., Papaconstantopoulos, D.A., Khan, F.S., (2001) Phys. Rev. B, 63, p. 195101Hamada, N., Savada, S., Oshiyama, A., (1992) Phys. Rev. Lett., 68, p. 1579Ercolessi, F., Tosatti, E., Parrinello, M., (1986) Phys. Rev. Lett., 57, p. 719Da Silva, E.Z., Da Silva, A.J.R., Fazzio, A., (2001) Phys. Rev. Lett., 87, p. 256102Häkkinen, H., Landman, U., (2001) Phys. Rev. B, 62, pp. R2287Rubio-Bollinger, G., Bahn, S.R., Agrait, N., Jacobsen, K.W., Vieira, S., (2001) Phys. Rev. Lett., 87, p. 2610