"published_papers" "Title(English)","Title(Japanese)","Author(s)(English)","Author(s)(Japanese)","Journal name(English)","Journal name(Japanese)","Volume","Number","First page","Last page","Date of publication","Peer reviewed/Not peer reviewed","Invited/Not invited","Publishing type","Language","ISSN","DOI","URL","Description(English)","Description(Japanese)" "Electronic Band Structure of Various TiN/MgO Superlattices","多様なTiN/MgO超格子の電子構造","Kazuaki Kobayashi, Hirokazu Takaki, Nobuhiko Kobayashi, Kenji Hirose","Kazuaki Kobayashi, Hirokazu Takaki, Nobuhiko Kobayashi, Kenji Hirose","JPS Conference Proceedings","JPS Conference Proceedings","","","","","2015-02-25","TRUE","","international_conference_proceedings","eng","","10.7566/jpscp.5.011013","","Various TiN(001)/MgO(001) superlattices have been investigated by using the total energy pseudopotential method. Their relaxed superlattice structures (multilayered systems) and electronic properties were obtained. Calculated superlattices are (TiN)n/(MgO)m as (n = 1, m = 7), (n = 2, m = 6), (n = 3, m = 5), and (n = 2, m = 14) cases. “n” and “m” are the layer numbers of TiN and MgO superlattices, respectively. “n + m” is the total number of the TiN/MgO superlattice in the unit cell. Since MgO is a wide band gap material, we expect (TiN)n/(MgO)m will have a band gap in its electronic state when the MgO superlattice is sufficiently thick (large m). All the calculated electronic states of TiN/MgO correspond to metallicity.","" "Electric and Thermal Transport Calculations through Nanometer-Size Interface and Applications to Thermoelectric Energy Conversio","界面の電子・熱輸送計算と熱電変換への応用","Kenji Hirose, Kazuaki Kobayashi, Masato Shimono, Hiroyuki Ishii, Nobuhiko Kobayashi","Kenji Hirose, Kazuaki Kobayashi, Masato Shimono, Hiroyuki Ishii, Nobuhiko Kobayashi","e-JOURNAL OF SURFACE SCIENCE AND NANOTECHNOLOGY","e-JOURNAL OF SURFACE SCIENCE AND NANOTECHNOLOGY","","","115","118","2014-03-14","TRUE","","international_conference_proceedings","eng","","10.1380/ejssnt.2014.115","","We present the electrical and thermal transport calculations through interface of metallic aluminum and semiconductor silicon materials. The obtained transport results are utilized to find the thermoelectric properties of Seebeck coefficient and figure of merits. We find that the increase of Seebeck coefficients and also the decrease of thermal transport due to the scatterings of electrons and phonons at the nanometer-size interface enhances the efficiency of thermoelectric energy conversion around the Fermi energy.","" "First-Principles Study of TiN/MgO Interfaces","TiN/MgO界面の第一原理計算","Kazuaki Kobayashi, Nobuhiko Kobayashi, Kenji Hirose","Kazuaki Kobayashi, Nobuhiko Kobayashi, Kenji Hirose","e-JOURNAL OF SURFACE SCIENCE AND NANOTECHNOLOGY","e-JOURNAL OF SURFACE SCIENCE AND NANOTECHNOLOGY","","","230","237","2014-05-16","TRUE","","international_conference_proceedings","eng","","10.1380/ejssnt.2014.230","","We calculated electronic and lattice properties ofTiN(001)/MgO(001) interfaces using the total energy pseudopotential method. Crystal structures of TiN and MgO are rock-salt. TiN is metal and MgO is a wide band gap semiconductor. A lattice mismatch of TiN and MgO is 3.7 {\%} in this study. This value is larger than that (0.5 {\%}) in experiment. The lattice properties (supercell and internal atoms) of TiN/MgO were fully optimized. We calculated two interface structures. One is Ti (Mg) is bonded to O (N) at the interface. The other is Ti (N) is bonded to Mg (O) at the interface. As a result, the former is energetically more stable than the latter. ","" "First-Principles Study of AlBN and related polytypes","AlBNとその関連ポリタイプの第一原理計算","KOBAYASHI, Kazuaki, KOMATSU, Shojiro","KOBAYASHI, Kazuaki, KOMATSU, Shojiro","Transactions of MRS-J","Transactions of MRS-J","","","485","492","2013-09-01","TRUE","","international_conference_proceedings","eng","","","","We have investigated the electronic and lattice properties of AlBN and related polytypes which are sp3-bonded compounds. The 2H-, 3H-, 4H-, 5H-, 6H-, 3×2H-, and 12H polytypes are treated. In 2H ∼ 6H-AlN and 12H-AlN, one Al layer is replaced with the B atom in a unit cell as AlBN polytype structures. One N layer in 2H-AlN (= Al2N2) is replaced with the B atom as 2H-AlBN (= Al2BN). One, two or five Al layers in 3×2H-AlN are replaced with the B atoms as 3×2H-AlBN. The electronic and lattice properties of 4H-AlPN and 4H-AlAsN are calculated in order to compare them with those of the AlBN polytypes. One or two N layers in 4H-AlN are replaced with the P (As) atoms as AlPN (AlAsN). ","" "First-Principles Study of Various BN, SiC, and AlN Polytypes","多様なBN, SiC, AlNポリタイプの第一原理計算","KOBAYASHI, Kazuaki, KOMATSU, Shojiro","KOBAYASHI, Kazuaki, KOMATSU, Shojiro","TRANSACTIONS OF THE MATERIALS RESEARCH SOCIETY OF JAPAN","TRANSACTIONS OF THE MATERIALS RESEARCH SOCIETY OF JAPAN","","","583","588","2012-12-01","TRUE","","international_conference_proceedings","eng","","","","We have investigated the electronic and lattice properties of various BN, SiC, and AlN polytypes which are sp3-bonded compounds. The 2H, 3H, 4H, 5H, 6H, 8H, 10H, 12H, 18H, 20H, and 30H polytypes are treated. As for SiC polytypes, 10H-SiC(ABCACBCACB) is most stable and its hexagonality is 40 %. In contrast, 3C-BN(H = 0 %) and 2H-AlN(H = 100 %) are most stable in the calculated BN and AlN polytypes, respectively. The band gap of 2H-AlN is direct. The band gap of 10H-AlN(ABABCBABAC) by GGA (LDA) is direct (indirect).","" "First-principles study of 6H-AlN under various pressure conditions","様々な圧力条件下での6H-AlNの第一原理計算","Kazuaki Kobayashi, Shojiro Komatsu","Kazuaki Kobayashi, Shojiro Komatsu","JOURNAL OF PHYSICS:CONFERENCE SERIES (JPCS) ","JOURNAL OF PHYSICS:CONFERENCE SERIES (JPCS) ","","","012111-1","012111-9","2010-03-01","TRUE","","international_conference_proceedings","eng","","10.1088/1742-6596/215/1/012111",""," We calculated the electronic and lattice properties of 6H-AlN under various pressure conditions. The pressure conditions are hydrostatic, biaxial, and uniaxial compression and expansion. The 6H polytype has two structures. One is ABCBCB (ABC notation) and the other is ABCACB. 6H-AlN(ABCBCB) is energetically more favorable than 6H-AlN(ABCACB). Symmetry and hexagonality (H[{%}]) of 6H-AlN(ABCBCB) are P3m1 and 67 %, respectively. The electronic band structures of 6H-AlN polytypes under the ambient pressure show indirect band gaps. The band gap of 6H-AlN(ABCBCB) is closer to direct than that of 6H-AlN(ABCACB). The lattice properties of 6H-AlN(ABCBCB) under the various pressure conditions were optimized automatically by the first-principles molecular dynamics (FPMD) method.","" "Bulk modulus of Os by experiments and first-principles calculations","Bulk modulus of Os by experiments and first-principles calculations","TAKEMURA, Kenichi, ARAI, Masao, KOBAYASHI, Kazuaki, SASAKI, Taizo","TAKEMURA, Kenichi, ARAI, Masao, KOBAYASHI, Kazuaki, SASAKI, Taizo","Joint 20th AIRAPT - 43th EHPRG","Joint 20th AIRAPT - 43th EHPRG","","","1","6","2005-06-01","TRUE","","international_conference_proceedings","eng","","","","オスミウムの体積弾性率をヘリウムを圧力媒体とした室温粉末X線回折実験により決定した。その結果、以前の報告とは異なりオスミウムの体積弾性率はダイヤモンドより決して大きくはないことが明らかになった。またわれわれが行った第一原理計算もこの実験結果を支持している。体積弾性率の値を他の研究グループの結果とも比較しながら議論する。","" "First-principles study of Hg under high pressure","高圧下での水銀の第一原理計算","KOBAYASHI, Kazuaki, ARAI, Masao, TAKEMURA, Kenichi","KOBAYASHI, Kazuaki, ARAI, Masao, TAKEMURA, Kenichi","Transactions of the Materials Research Society of Japan","Transactions of the Materials Research Society of Japan","","","893","896","2005-09-01","TRUE","","international_conference_proceedings","eng","","","","We calculate Hg under various compression conditions using the first-principles molecular dynamics (FPMD) and all-electron (FLAPW: WIEN2k) methods. A calculated crystal structure of Hg is hexiagonal close-packed (hcp, P63/mmc). The present calculations are based on the local density approximation (LDA) in the density functional theory (DFT). Lattice and electronic properties are optimized using th","" "Lattice Anomalies of MBC (M = H, Li, Na) Under Anisotropic Compression","異方的圧縮下でのMBC(M = H, Li, Na)の格子異常","KOBAYASHI, Kazuaki, ARAI, Masao, SASAKI, Taizo","KOBAYASHI, Kazuaki, ARAI, Masao, SASAKI, Taizo","Transactions of the Materials Research Society of Japan","Transactions of the Materials Research Society of Japan","","","3799","3802","2004-12-01","TRUE","","international_conference_proceedings","eng","","","","Very recently, we found the lattice anomaly of LiBC under anisotropic compression[1][2]. Lattice constant c of LiBC contracts under a, b-axis compression although lattice constant c generally expands under a, b-axis compression. This contraction of lattice constant c implies a kind of negative Poisson ratios. From an analysis of model systems[3], an electrostatic interaction between negative and positive ionized layers and a size of a cation atom are very important key points for the lattice anomaly. There is no lattice anomaly for NaBC in our previous study[2] in which a Na atom is larger than a Li atom. In this study, we investigate HBC (Hydrogen Boron Carbide) under anisotropic compression because a hydrogen atom is smaller than a Li atom. As a result, the contraction of lattice constant c for HBC when Pxy = 50 GPa is larger than that for LiBC. Calculational method is the first-principles molecular dynamics (FPMD) method with DFT-LDA. [1] K. Kobayashi and M. Arai: submitted to Proceedings of the LT23 [Phys",""