Efficient Discovery of Optimal N-Layered TMDC Hetero-Structures

MRS Advances ◽  
2018 ◽  
Vol 3 (6-7) ◽  
pp. 397-402 ◽  
Author(s):  
Lindsay Bassman ◽  
Pankaj Rajak ◽  
Rajiv K. Kalia ◽  
Aiichiro Nakano ◽  
Fei Sha ◽  
...  
Keyword(s):  
Band Structure ◽  
Physical Properties ◽  
Band Gap ◽  
Electronic Band Structure ◽  
Transport Coefficients ◽  
Optimization Technique ◽  
Bayesian Optimization ◽  
Material Structure ◽  
Electronic Band ◽  
Structure Calculations

ABSTRACTVertical hetero-structures made from stacked monolayers of transition metal dichalcogenides (TMDC) are promising candidates for next-generation optoelectronic and thermoelectric devices. Identification of optimal layered materials for these applications requires the calculation of several physical properties, including electronic band structure and thermal transport coefficients. However, exhaustive screening of the material structure space using ab initio calculations is currently outside the bounds of existing computational resources. Furthermore, the functional form of how the physical properties relate to the structure is unknown, making gradient-based optimization unsuitable. Here, we present a model based on the Bayesian optimization technique to optimize layered TMDC hetero-structures, performing a minimal number of structure calculations. We use the electronic band gap and thermoelectric figure of merit as representative physical properties for optimization. The electronic band structure calculations were performed within the Materials Project framework, while thermoelectric properties were computed with BoltzTraP. With high probability, the Bayesian optimization process is able to discover the optimal hetero-structure after evaluation of only ∼20% of all possible 3-layered structures. In addition, we have used a Gaussian regression model to predict not only the band gap but also the valence band maximum and conduction band minimum energies as a function of the momentum.

NaGe6As6: Insertion of sodium into the layered semiconductor germanium arsenide GeAs

2016 ◽  
Vol 71 (5) ◽  
pp. 375-380 ◽  
Author(s):  
Mansura Khatun ◽  
Arthur Mar
Keyword(s):  
Band Structure ◽  
Fermi Level ◽  
Band Gap ◽  
Electronic Band Structure ◽  
Structure Type ◽  
Monoclinic Structure ◽  
Layered Semiconductor ◽  
Electronic Band ◽  
Band Structure Calculations ◽  
Structure Calculations

AbstractNaGe6As6 is a ternary arsenide prepared by reaction of the elements at 650 °C. It crystallizes in a new monoclinic structure type [space group C2/m, Z = 2, a = 22.063(2), b = 3.8032(4), c = 7.2020(8) Å, β = 92.7437(15)°] that can be considered to be derived by inserting guest Na atoms between [Ge6As6] layers identical to those found in the layered binary arsenide GeAs. An unusual feature in both structures is the presence of ethane-like Ge2As6 units in staggered conformation, with Ge–Ge dumbbells oriented either parallel or perpendicular to the layers. Electronic band structure calculations have shown that the electron excess in NaGe6As6 is accommodated by raising the Fermi level across a 0.6 eV band gap in semiconducting GeAs so that it cuts the bottom of the conduction band, resulting in an n-doped semiconductor.

Nanostructure Dependence of the Electronic Conductivity of Carbon Nanotubes and Graphene Sheets

2010 ◽  
Author(s):  
Masato Ohnishi ◽  
Katsuya Ohsaki ◽  
Yusuke Suzuki ◽  
Ken Suzuki ◽  
Hideo Miura
Keyword(s):  
Aspect Ratio ◽  
Band Structure ◽  
Band Gap ◽  
Critical Strain ◽  
Electronic Band Structure ◽  
Electronic Conductivity ◽  
Membered Ring ◽  
Applied Strain ◽  
Dominant Factor ◽  
Electronic Band

In this study, the change of the resistivity of the CNT-dispersed resin was analyzed by applying a quantum chemical molecular dynamics and the first principle calculation. Various combinations of double-walled carbon nanotube structures were modeled for the analysis. The change of the band structure was calculated by changing the amplitude of the applied strain. It was found in some cases that the band structure changes drastically from a metallic structure to a semiconductive structure, and this result clearly indicated that the electronic conductivity of this MWCNT decreased significantly under tensile strain. It was also found that further application of the strain made a band gap in the band structure. This result indicated that the metallic CNT changes a semiconductive CNT due to the applied strain. The effect of the diameter of the zigzag type CNT on the critical strain of buckling deformation was analyzed under a uni-axial strain. In this analysis, the aspect ratio of each structure was fixed at 10. It was found that the critical strain decreased monotonically with the increase of the diameter. This was because that the flexural rigidity of a cylinder decreased with the increase of its diameter when the thickness of the wall of the cylinder is fixed. It was found that the critical strain decreased drastically from about 5% to 0.5% when the aspect ratio was changed from 10 to 30. Since the typical aspect ratio of CNTs often exceeds 1000, most CNTs show buckling deformation when an axial compressive strain was applied to the CNTs. Finally, the shape of six-membered ring of the CNT was found to be the dominant factor that determines the electronic band structure of a CNT. Next, the change of the band structure of a graphene sheet was analyzed by applying the abinitio calculation (Density functional theory). It was found that the fluctuation of the atomic distance among the six-membered ring is the most dominant factor of the electronic band structure. When the fluctuation exceeded about 10%, band gap appeared in the deformed six-membered ring, and thus, the electronic conductivity of the graphene sheet changes from metallic one to semiconductive one. It is therefore, possible to predict the change of the electronic conductivity of a CNT by considering the local shape of a six-membered ring in the deformed CNT.

Electronic Band Structure of Cubic Silicon Carbide Nanowires

2008 ◽  
Vol 600-603 ◽  
pp. 575-578 ◽  
Author(s):  
A. Miranda ◽  
A. Estrella Ramos ◽  
M. Cruz Irisson
Keyword(s):  
Silicon Carbide ◽  
Band Structure ◽  
Band Gap ◽  
Density Functional ◽  
Electronic Band Structure ◽  
Local Density ◽  
Thickness Variation ◽  
Hydrogen Atoms ◽  
Electronic Band ◽  
Cubic Silicon Carbide

In this work, the effects of the diameter and morphology on the electronic band structure of hydrogenated cubic silicon carbide (b-SiC) nanowires is studied by using a semiempirical sp3s* tight-binding (TB) approach applied to the supercell model, where the Si- and C-dangling bonds on the surface are passivated by hydrogen atoms. Moreover, TB results (for the bulk) are compared with density functional calculations in the local density approximation. The results show that though surface morphology modifies the band gap, the change is more systematic with the thickness variation. As expected, hydrogen saturation induces a broadening of the band gap energy because of the quantum confinement effect.

Sign in / Sign up

Export Citation Format

Share Document