Low-temperature anomalous specific heat without tunneling modes: a simulation for a-Si with voids

Using empirical potential molecular dynamics we compute dynamical matrix eigenvalues and eigenvectors for a 4096 atom model of amorphous silicon and a set of models with voids of different size based on it. This information is then employed to study the localization properties of the low-energy vibrational states, calculate the specific heat C(T) and examine the low-temperature properties of our models usually attributed to the presence of tunneling states in amorphous silicon. The results of our calculations for C(T) and "excess specific heat bulge" in the C(T)/T^3 vs. T graph for voidless a-Si appear to be in good agreement with experiment; moreover our investigation shows that the presence of localized low-energy excitations in the vibrational spectrum of our models with voids strongly manifests itself as a sharp peak in C(T)/T^3 dependence at T < 3K. To our knowledge this is the first numerical simulation that provides adequate agreement with experiment for the very low-temperature properties of specific heat in disordered systems within the limits of harmonic approximation.Comment: 5 pages with 2 ps figures, submitted to PR

Reverse Monte Carlo modeling of amorphous silicon

An implementation of the Reverse Monte Carlo algorithm is presented for the study of amorphous tetrahedral semiconductors. By taking into account a number of constraints that describe the tetrahedral bonding geometry along with the radial distribution function, we construct a model of amorphous silicon using the reverse monte carlo technique. Starting from a completely random configuration, we generate a model of amorphous silicon containing 500 atoms closely reproducing the experimental static structure factor and bond angle distribution and in improved agreement with electronic properties. Comparison is made to existing Reverse Monte Carlo models, and the importance of suitable constraints beside experimental data is stressed.Comment: 6 pages, 4 PostScript figure

Fungal Planet description sheets: 1284–1382

Novel species of fungi described in this study include those from various countries as follows: Antartica, Cladosporium austrolitorale from coastal sea sand. Australia, Austroboletus yourkae on soil, Crepidotus innuopurpureus on dead wood, Curvularia stenotaphri from roots and leaves of Stenotaphrum secundatum and Thecaphora stajsicii from capsules of Oxalis radicosa. Belgium, Paraxerochrysium coryli (incl. Paraxerochrysium gen. nov.) from Corylus avellana. Brazil, Calvatia nordestina on soil, Didymella tabebuiicola from leaf spots on Tabebuia aurea, Fusarium subflagellisporum from hypertrophied floral and vegetative branches of Mangifera indica and Microdochium maculosum from living leaves of Digitaria insularis. Canada, Cuphophyllus bondii fromagrassland. Croatia, Mollisia inferiseptata from a rotten Laurus nobilis trunk. Cyprus, Amanita exilis oncalcareoussoil. Czech Republic, Cytospora hippophaicola from wood of symptomatic Vaccinium corymbosum. Denmark, Lasiosphaeria deviata on pieces of wood and herbaceousdebris. Dominican Republic, Calocybella goethei among grass on a lawn. France (Corsica) , Inocybe corsica onwetground. France (French Guiana) , Trechispora patawaensis on decayed branch of unknown angiosperm tree and Trechispora subregularis on decayed log of unknown angiosperm tree. Germany, Paramicrothecium sambuci (incl. Paramicrothecium gen. nov.)ondeadstemsof Sambucus nigra. India, Aureobasidium microtermitis from the gut of a Microtermes sp. termite, Laccaria diospyricola on soil and Phylloporia tamilnadensis on branches of Catunaregam spinosa. Iran, Pythium serotinoosporum from soil under Prunus dulcis. Italy, Pluteus brunneovenosus on twigs of broad leaved trees on the ground. Japan, Heterophoma rehmanniae on leaves of Rehmannia glutinosa f. hueichingensis. Kazakhstan, Murispora kazachstanica from healthy roots of Triticum aestivum. Namibia, Caespitomonium euphorbiae (incl. Caespitomonium gen. nov.)from stems of an Euphorbia sp. Netherlands, Alfaria junci, Myrmecridium junci, Myrmecridium juncicola, Myrmecridium juncigenum, Ophioceras junci, Paradinemasporium junci (incl. Paradinemasporium gen. nov.), Phialoseptomonium junci, Sporidesmiella juncicola, Xenopyricularia junci and Zaanenomyces quadripartis (incl. Zaanenomyces gen. nov.), fromdeadculmsof Juncus effusus, Cylindromonium everniae and Rhodoveronaea everniae from Evernia prunastri, Cyphellophora sambuci and Myrmecridium sambuci from Sambucus nigra, Kiflimonium junci, Saro cladium junci, Zaanenomyces moderatricis academiae and Zaanenomyces versatilis from dead culms of Juncus inflexus, Microcera physciae from Physcia tenella, Myrmecridium dactylidis from dead culms of Dactylis glomerata, Neochalara spiraeae and Sporidesmium spiraeae from leaves of Spiraea japonica, Neofabraea salicina from Salix sp., Paradissoconium narthecii (incl. Paradissoconium gen. nov.)from dead leaves of Narthecium ossifragum, Polyscytalum vaccinii from Vaccinium myrtillus, Pseudosoloacrosporiella cryptomeriae (incl. Pseudosoloacrosporiella gen. nov.)fromleavesof Cryptomeria japonica, Ramularia pararhabdospora from Plantago lanceolata, Sporidesmiella pini from needles of Pinus sylvestris and Xenoacrodontium juglandis (incl. Xenoacrodontium gen. nov. and Xenoacrodontiaceae fam. nov.)from Juglans regia. New Zealand, Cryptometrion metrosideri from twigs of Metrosideros sp., Coccomyces pycnophyllocladi from dead leaves of Phyllocladus alpinus, Hypoderma aliforme from fallen leaves Fuscopora solandri and Hypoderma subiculatum from dead leaves Phormium tenax. Norway, Neodevriesia kalakoutskii from permafrost and Variabilispora viridis from driftwood of Picea abies. Portugal, Entomortierella hereditatis from abio film covering adeteriorated limestone wall. Russia, Colpoma junipericola from needles of Juniperus sabina, Entoloma cinnamomeum on soil in grasslands, Entoloma verae on soil in grasslands, Hyphodermella pallidostraminea on a dry dead branch of Actinidia sp., Lepiota sayanensis onlitterinamixedforest, Papiliotrema horticola from Malus communis , Paramacroventuria ribis (incl. Paramacroventuria gen. nov.)fromleaves of Ribes aureum and Paramyrothecium lathyri from leaves of Lathyrus tuberosus. South Africa, Harzia combreti from leaf litter of Combretum collinum ssp. sulvense, Penicillium xyleborini from Xyleborinus saxesenii , Phaeoisaria dalbergiae from bark of Dalbergia armata, Protocreopsis euphorbiae from leaf litter of Euphorbia ingens and Roigiella syzygii from twigs of Syzygium chordatum. Spain, Genea zamorana on sandy soil, Gymnopus nigrescens on Scleropodium touretii, Hesperomyces parexochomi on Parexochomus quadriplagiatus, Paraphoma variabilis from dung, Phaeococcomyces kinklidomatophilus from a blackened metal railing of an industrial warehouse and Tuber suaveolens in soil under Quercus faginea. Svalbard and Jan Mayen, Inocybe nivea associated with Salix polaris. Thailand, Biscogniauxia whalleyi oncorticatedwood. UK, Parasitella quercicola from Quercus robur. USA , Aspergillus arizonicus from indoor air in a hospital, Caeliomyces tampanus (incl. Caeliomyces gen. nov.)fromoffice dust, Cippumomyces mortalis (incl. Cippumomyces gen. nov.)fromatombstone, Cylindrium desperesense from air in a store, Tetracoccosporium pseudoaerium from air sample in house, Toxicocladosporium glendoranum from air in a brick room, Toxicocladosporium losalamitosense from air in a classroom, Valsonectria portsmouthensis from airinmen'slockerroomand Varicosporellopsis americana from sludge in a water reservoir. Vietnam, Entoloma kovalenkoi on rotten wood, Fusarium chuoi inside seed of Musa itinerans , Micropsalliota albofelina on soil in tropical evergreen mixed forest sand Phytophthora docyniae from soil and roots of Docynia indica. Morphological and culture characteristics are supported by DNA barcodes

Fungal Planet description sheets: 868-950

Novel species of fungi described in this study include those from various countries as follows: Australia, Chaetomella pseudocircinoseta and Coniella pseudodiospyri on Eucalyptus microcorys leaves, Cladophialophora eucalypti, Teratosphaeria dunnii and Vermiculariopsiella dunnii on Eucalyptus dunnii leaves, Cylindrium grande and Hypsotheca eucalyptorum on Eucalyptus grandis leaves, Elsinoe salignae on Eucalyptus saligna leaves, Marasmius lebeliae on litter of regenerating subtropical rainforest, Phialoseptomonium eucalypti (incl. Phialoseptomonium gen. nov.) on Eucalyptus grandis × camaldulensis leaves, Phlogicylindrium pawpawense on Eucalyptus tereticornis leaves, Phyllosticta longicauda as an endophyte from healthy Eustrephus latifolius leaves, Pseudosydowia eucalyptorum on Eucalyptus sp. leaves, Saitozyma wallum on Banksia aemula leaves, Teratosphaeria henryi on Corymbia henryi leaves. Brazil, Aspergillus bezerrae, Backusella azygospora, Mariannaea terricola and Talaromyces pernambucoensis from soil, Calonectria matogrossensis on Eucalyptus urophylla leaves, Calvatia brasiliensis on soil, Carcinomyces nordestinensis on Bromelia antiacantha leaves, Dendryphiella stromaticola on small branches of an unidentified plant, Nigrospora brasiliensis on Nopalea cochenillifera leaves, Penicillium alagoense as a leaf endophyte on a Miconia sp., Podosordaria nigrobrunnea on dung, Spegazzinia bromeliacearum as a leaf endophyte on Tilandsia catimbauensis, Xylobolus brasiliensis on decaying wood. Bulgaria, Kazachstania molopis from the gut of the beetle Molops piceus. Croatia, Mollisia endocrystallina from a fallen decorticated Picea abies tree trunk. Ecuador, Hygrocybe rodomaculata on soil. Hungary, Alfoldia vorosii (incl.Alfoldia gen. nov.) from Juniperus communis roots, Kiskunsagia ubrizsyi (incl. Kiskunsagia gen. nov.) from Fumana procumbens roots. India, Aureobasidium tremulum as laboratory contaminant, Leucosporidium himalayensis and Naganishia indica from windblown dust on glaciers. Italy, Neodevriesia cycadicola on Cycas sp. leaves, Pseudocercospora pseudomyrticola on Myrtus communis leaves, Ramularia pistaciae on Pistacia lentiscus leaves, Neognomoniopsis quercina (incl. Neognomoniopsis gen. nov.) on Quercus ilex leaves. Japan, Diaporthe fructicola on Passiflora edulis × P. edulis f. flavicarpa fruit, Entoloma nipponicum on leaf litter in a mixed Cryptomeria japonica and Acer spp. forest. Macedonia, Astraeus macedonicus on soil. Malaysia, Fusicladium eucalyptigenum on Eucalyptus sp. twigs, Neoacrodontiella eucalypti (incl. Neoacrodontiella gen. nov.) on Eucalyptus urophylla leaves. Mozambique, Meliola gorongosensis on dead Philenoptera violacea leaflets. Nepal, Coniochaeta dendrobiicola from Dendriobium lognicornu roots. New Zealand, Neodevriesia sexualis and Thozetella neonivea on Archontophoenix cunninghamiana leaves. Norway, Calophoma sandfjordenica from a piece of board on a rocky shoreline, Clavaria parvispora on soil, Didymella finnmarkica from a piece of Pinus sylvestris driftwood. Poland, Sugiyamaella trypani from soil. Portugal, Colletotrichum feijoicola from Acca sellowiana. Russia, Crepidotus tobolensis on Populus tremula debris, Entoloma ekaterinae, Entoloma erhardii and Suillus gastroflavus on soil, Nakazawaea ambrosiae from the galleries of Ips typographus under the bark of Picea abies. Slovenia, Pluteus ludwigii on twigs of broadleaved trees. South Africa, Anungitiomyces stellenboschiensis (incl. Anungitiomyces gen. nov.) and Niesslia stellenboschiana on Eucalyptus sp. leaves, Beltraniella pseudoportoricensis on Podocarpus falcatus leaf litter, Corynespora encephalarti on Encephalartos sp. leaves, Cytospora pavettae on Pavetta revoluta leaves, Helminthosporium erythrinicola on Erythrina humeana leaves, Helminthosporium syzygii on a Syzygium sp. barkcanker, Libertasomyces aloeticus on Aloe sp. leaves, Penicillium lunae from Musa sp. fruit, Phyllosticta lauridiae on Lauridia tetragona leaves, Pseudotruncatella bolusanthi (incl. Pseudotruncatellaceae fam. nov.) and Dactylella bolusanthi on Bolusanthus speciosus leaves. Spain, Apenidiella foetida on submerged plant debris, Inocybe grammatoides on Quercus ilex subsp. ilex forest humus, Ossicaulis salomii on soil, Phialemonium guarroi from soil. Thailand, Pantospora chromolaenae on Chromolaena odorata leaves. Ukraine, Cadophora helianthi from Helianthus annuus stems. USA, Boletus pseudopinophilus on soil under slash pine, Botryotrichum foricae, Penicillium americanum and Penicillium minnesotense from air. Vietnam, Lycoperdon vietnamense on soil. Morphological and culture characteristics are supported by DNA barcodes

Dislocation Core Reconstruction In Zinc-blende Semiconductors

Using ab initio total-energy calculations, we computed core reconstruction energies of partial dislocations in zinc-blende semiconductors. The reconstruction energy of 30° partials was found to scale almost linearly with the experimental activation energy of 60° dislocations. The electronic structure of a dislocation shows that in an unreconstructed core, the gap states comprise a half-filled one-dimensional band, which splits up into bonding and antibonding states upon reconstruction. The energy states which lie in the electronic gap come from the core of β-partials, while those related to α-partials remain resonant in the valence band.12491003910044Alexander, H., (1986) Dislocations in Solids, 7, p. 115. , ed F R N Nabarro (Amsterdam: North-Holland)Hirth, J.P., Lothe, J., (1982) Theory of Dislocations, , New York: WileyJusto, J.F., De Koning, M., Cai, W., Bulatov, V.V., (2000) Phys. Rev. Lett., 84, p. 2172Bigger, J.R.K., McInnes, D.A., Sutton, A.P., Payne, M.C., Stich, I., King-Smith, R.D., Bird, D.M., Clarke, L.J., (1992) Phys. Rev. Lett., 69, p. 2224Bennetto, J., Nunes, R.W., Vanderbilt, D., (1997) Phys. Rev. Lett., 79, p. 245Sitch, P., Jones, R., Öberg, S., Heggie, M.I., (1994) Phys. Rev. B, 50, pp. R17717Bulatov, V.V., Yip, S., Argon, A.S., (1995) Phil. Mag. A, 72, p. 453Duesbery, M.S., Richardson, G.Y., (1991) Crit. Rev. Solid State Sci., 17, p. 1Justo, J.F., Bulatov, V.V., Yip, S., (1999) J. Appl. Phys., 86, p. 4249Alexander, H., Gottschalk, H., (1989) Structure and Properties of Dislocations in Semiconductors (Inst. Phys. Conf. Ser. 104), 104, p. 281. , Bristol: Institute of Physics PublishingBazant, M.Z., Kaxiras, E., Justo, J.F., (1997) Phys. Rev. B, 56, p. 8542Justo, J.F., Bazant, M.Z., Kaxiras, E., Bulatov, V.V., Yip, S., (1998) Phys. Rev. B, 58, p. 2539Bockstedte, M., Kley, A., Neugebauer, J., Scheffler, M., (1997) Comput. Phys. Commun., 107, p. 187Car, R., Parrinello, M., (1985) Phys. Rev. Lett., 55, p. 2471Troullier, N., Martins, J.L., (1991) Phys. Rev. B, 43, p. 1993Kleinman, L., Bylander, D.M., (1982) Phys. Rev. Lett., 48, p. 1425Monkhorst, H.J., Pack, J.D., (1976) Phys. Rev. B, 13, p. 5188Imai, M., Sumino, K., (1983) Phil. Mag. A, 47, p. 599Yonenaga, I., Sumino, K., (1996) Appl. Phys. Lett., 69, p. 1264Yonenaga, I., Sumino, K., (1993) J. Appl. Phys., 73, p. 1681Yonenaga, I., Sumino, K., (1989) J. Appl. Phys., 65, p. 85Choi, S.K., Mihara, M., Ninomiya, T., (1977) Japan. J. Appl. Phys., 16, p. 737Choi, S.K., Mihara, M., Ninomiya, T., (1978) Japan. J. Appl. Phys., 17, p. 329Omri, M., Michel, J.P., George, A., (1990) Phil Mag. A, 62, p. 203Yonenaga, I., (1998) J. Appl. Phys., 84, p. 4209Suzuki, T., Takeuchi, S., Yoshinaga, H., (1991) Dislocation Dynamics and Plasticity, , Berlin: Springe

Effects Of Extended Defects On The Properties Of Intrinsic And Extrinsic Point Defects In Silicon

We investigated the interaction of intrinsic and extrinsic point defects with stacking faults in silicon. The calculations were carried out using ab initio total energy methods. The results show that the formation energies of intrinsic defects and impurities (P, As, and Al) are lower at the stacking fault as compared to the respective defects in crystalline environment. Therefore, stacking faults should have a large concentration of defects, and they should play an important role on the mechanisms of dislocation motion.273-274473475Alexander, H., (1986) Dislocations in Solids, 7, p. 115. , F.R.N. Nabarro (Ed.), Elsevier, AmsterdamChou, M.Y., Cohen, M.L., Louie, S.G., (1985) Phys. Rev. B, 32, p. 7979Antonelli, A., Justo, J.F., Fazzio, A., (1999) Phys. Rev. B, 60, p. 4711Hirth, J.P., Lothe, J., (1982) Theory of Dislocations, , Wiley, New YorkBulatov, V.V., Justo, J.F., Cai, W., Yip, S., (1997) Phys. Rev. Lett., 79, p. 5042Maiti, A., Kaplan, T., Mostoller, M., Chisholm, M.F., Pennycook, S.J., Pantelides, S.T., (1997) Appl. Phys. Lett., 70, p. 336Lehto, N., Öberg, S., (1997) Phys. Rev. B, 56, p. 12706Car, R., Parrinello, M., (1985) Phys. Rev. Lett., 55, p. 2471Bockstedte, M., Kley, A., Neugebauer, J., Scheffler, M., (1997) Comp. Phys. Commun., 107, p. 187Bachelet, G.B., Hamann, D.R., Schluter, M., (1982) Phys. Rev. B, 26, p. 4199Kleinmann, L., Bylander, D.M., (1982) Phys. Rev. Lett., 48, p. 1425Puska, M.J., Pöykkö, S., Pesola, M., Nieminen, R.M., (1998) Phys. Rev. B, 58, p. 1318Blochl, P.E., Smargiassi, E., Car, R., Laks, D.B., Andreoni, W., Pantelides, S.T., (1993) Phys. Rev. Lett., 70, p. 2435Maiti, A., Crisholm, M.F., Pennycook, S.J., Pantelides, S.T., (1996) Phys. Rev. Lett., 77, p. 130

Unstable Stacking Fault Free Energies In Silicon Through Empirical Modeling

The temperature dependence of unstable stacking fault free energies on glide and shuffle {111} planes in silicon is investigated using a finite temperature molecular dynamics approach which includes a full treatment of anharmonic vibrational effects. The results are compared to earlier zero temperature ab initio calculations in which finite temperature effects were estimated using a harmonic approximation to transition state theory (TST). The unstable stacking free energies are interpreted within the framework of Rice's dislocation nucleation criterium to characterize a possible change from shuffle to glide plane dominance in the context of dislocation nucleation processes at a sharp crack tip. Such a change may be related to the abrupt brittle-ductile transition observed in silicon.539175180Samuels, J., Roberts, S.G., (1989) Proc. R. Soc. London A, 421, p. 1Hirsch, P.B., Roberts, S.G., Samuels, J., (1989) Proc. R. Soc. London A, 421, p. 25Hirth, J.P., Lothe, J., (1982) Theory of Dislocations, , Wiley, New YorkRice, J.R., (1992) J. Mech. Phys. Solids, 40, p. 239Rice, J.R., Beltz, G.E., (1994) J. Mech. Phys. Solids, 42, p. 333Sun, Y., Beltz, G.E., (1993) Mater. Sci. Eng., A170, p. 67Kaxiras, E., Duesbery, M.S., (1993) Phys. Rev. Lett., 70, p. 3752Juan, Y.-M., Kaxiras, E., (1996) Phil. Mag. A, 74, p. 1367Vineyard, G.H., (1957) J. Phys. Chem. Solids, 3, p. 121Bazant, M.Z., Kaxiras, E., Justo, J.F., (1997) Phys. Rev. B, 56, p. 8542Justo, J.F., Bazant, M.Z., Kaxiras, E., Bulatov, V., Yip, S., (1998) Phys. Rev. B, 58, p. 2539De Koning, M., Antonelli, A., (1996) Phys. Rev. E, 53, p. 465De Koning, M., Antonelli, A., (1997) Phys. Rev. B, 55, p. 73