Enhancement of Thermoelectric Properties in Surface Nanostructures

Takaki

Proceedings of Computational Science Workshop 2014 (CSW2014)

et al. 2015

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Various TiN(001)/MgO(001) superlattices have been investigated by using the total energy pseudopotential method. They are (TiN) n /(MgO) m as (TiN) 1 /(MgO) 7 , (TiN) 2 /(MgO) 6 , (TiN) 3 /(MgO) 5 , and (TiN) 2 /(MgO) 14. "n", "m", and "n + m" are TiN, MgO, and TiN/MgO layer numbers of superlattices in a supercell, respectively. Their relaxed superlattice structures and electronic properties were obtained. All the calculated electronic states of TiN/MgO superlattices correspond to metallicity. Values of an electrical conductance of the TiN/MgO superlattice along the c-axis around the Fermi level are quite small although its electronic structure is metallic. A Ti (N) atom at the TiN layer in (TiN) 1 /(MgO) 7 is replaced with Sc, V, and Nb (B, C, and O) as (ScN) 1 /(MgO) 7 , (VN) 1 /(MgO) 7 , and (NbN) 1 /(MgO) 7 ((TiB) 1 /(MgO) 7 , (TiC) 1 /(MgO) 7 , and (TiO) 1 /(MgO) 7). Their detailed electronic properties were investigated systematically.

“…Furthermore, it is necessary to consider thermoelectric properties (thermal conduc- tivity, Seebeck coefficient, etc.) of the TiN/MgO [48] and related superlattices in the near future.…”

Section: Discussionmentioning

confidence: 97%

“…Our next task is to investigate in detail the anisotropy of the electrical conductance for the other superlattices [48]. Furthermore, it is necessary to consider thermoelectric properties (thermal conduc- tivity, Seebeck coefficient, etc.)…”

Section: Discussionmentioning

confidence: 99%

Electronic Band Structure of Various TiN/MgO Superlattices

Takaki

Proceedings of Computational Science Workshop 2014 (CSW2014)

et al. 2015

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“…Their thermoelectric properties, such as the thermal conductivity, Seebeck coefficient, and power factor will be treated using the non-equilibrium Greenʼs function formalism. 56,57) Materials Studio (BIOVIA), and the TDOS, PDOS, and magnetic moments depicted using MATLAB (MathWorks).…”

Section: Sl1013-7mentioning

confidence: 99%

First-principles study of Fe₂VAl and Fe₂VAl/Si thin films and their magnetic properties

Kobayashi¹,

Takaki²,

Shimono³

et al. 2022

Jpn. J. Appl. Phys.

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We studied thin films of Fe2VAl, Fe2VAl/Si, and a related compound using the total energy pseudopotential method. The internal atoms in a supercell of the repeated slab model were fully relaxed, except for Fe2VAl/Si. The detailed electronic and magnetic properties of structurally relaxed thin films of Fe2VAl, Fe2VAl/Si, and a related compound were calculated. These films are free-standing in the supercell, except for Fe2VAl/Si, which comprises Fe2VAl and Si (substrate) layers in a supercell. A thin film comprising Fe2V, Al, and Si (substrate) layers in the supercell (denoted as Fe2V/Al/Si) was also studied. Although electronic states of bulk Fe2VAl (full-Heusler) are metallic with pseudo-gap states around the Fermi level and nonmagnetic, the calculation results for Fe2VAl, Fe2VAl/Si, and Fe2V/Al/Si thin films in this study indicate that the films have ferromagnetic properties and their ferromagnetic states are energetically more favorable than nonmagnetic states. The magnetic moments are large and enhanced in the thin films. The magnetic moments of Fe in Fe2VAl (Fe12V4Al4), Fe2VAl (Fe20V8Al8), Fe2VAl/Si, and Fe2V/Al/Si thin films are 2.07 μB/per atom, 1.29 μB/per atom, 1.83 μB/per atom, and 2.22 μB/per atom, respectively.

“…7) Thermoelectric properties (Seebeck coefficients, thermal conductance, and figure of merit [ZT] 24) ) of TiN/MgO-1 × 1 and 2 × 2 superlattices using a non-equilibrium Green's function (NEGF) method have been obtained in the previous studies. 25,26) The 0.002 ZT value for TiN/MgO-1 × 1 interface 25) is enhanced to 0.15 for the TiN dot/MgO-2 × 2 superlattice. 26) The former (latter) electronic state is metallic (semiconducting).…”

Section: Introductionmentioning

confidence: 96%

“…25,26) The 0.002 ZT value for TiN/MgO-1 × 1 interface 25) is enhanced to 0.15 for the TiN dot/MgO-2 × 2 superlattice. 26) The former (latter) electronic state is metallic (semiconducting). Therefore, it is essential to control the electronic properties (DOS, band gap value) as band engineering.…”

Section: Introductionmentioning

confidence: 96%

Electronic and lattice properties of nanostructured TiN/MgO and ScN/MgO superlattices

Takaki

Shimono

et al. 2021

Jpn. J. Appl. Phys.

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Various nanostructured TMN(001) dot/MgO(001) (TM = Sc, Ti) superlattices have been investigated. Here, we consider single and double layered TM dot structures with rectangular and rectangular parallelepiped shapes. MgO-2 × 2 and −3 × 3 substrates were used. Their electronic states were obtained using a total energy pseudopotential method. The internal atomic coordinates from the repeated slab model in the unit cell were fully relaxed. Various relaxed structures and electronic properties of the TMN(001) dot/MgO-2 × 2 and −3 × 3 superlattices were obtained. We determined their total and partial densities of states. Peaks of density of states (DOS) of the ScN dot/MgO superlattices around the band gap consist of Sc 3d and N 2p states and those of the TiN dot/MgO superlattices consist of mainly Ti 3d states. The largest band gap value in the TiN(001) dot/MgO(001) (ScN(001) dot/MgO(001)) superlattice is 1.22 eV (1.48 eV) from the density-functional theory-local density approximation calculation. The electronic properties (band gap values, DOS curves, and many more) vary with varying dot shape and substrate size. Most band gap values corrected using a generalized density-functional theory were improved.