• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.287.2-287.2
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• 2016

Silicon has considerably good characteristics on electron, hole mobility and its price. With 2-D sinlge-layer Graphene/n-Si heterojunction solar cell shows that in one sun condition exhibit power conversion efficiency(PCE) of 10.1%. This photovoltaic effect was achieved by applying gate voltage to the Schottky junction of the heterostructure solar cell. Energy band diagram shows that Schottky barrier between Si and graphene can be adjust by the external electric field. because of the fermi level of the graphene can be changed by external gate voltage, we can control the Schottkky barrier of the heterostructure solar cell. The ratio between generated power of solar cell and consumption electrical power is remarkable. Since we use the graphene as the top gate electrode, most of the sun light can penetrate into the active area.

• Journal of Korean Vacuum Science & Technology
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• v.6 no.4
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• pp.153-157
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• 2002

The electronic structures of Gd$_{5}$Si$_2$Ge$_2$ compound, which has a giant magnetocaloric effect, in the monoclinic and orthorhombic phases were calculated using the tight-binding linear-muffin-tin-orbital method within the atomic-sphere approximation. The calculated total energies of the monoclinic and orthorhombic structures in the paramagnetic phase confirm that the orthorhombic structure is more stable than monoclinic structure. The density of states (DOS) at the Fermi level of the orthorhombic phase is higher than that of the monoclinic phase in the paramagnetic phase, fulfilling the Stoner criterion. The calculated charge density verified the breaking of Ge(Si)-Ge(Si) bonding in the basal plane upon the orthorhombic-monoclinic phase transition. The DOS curve fairly well reproduces the photoemission spectrum.m.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.29A no.1
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• pp.19-24
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• 1992

The analysis of the resonant tunneling based on the exact solution of Schrodinger equations is performed in a single quantum well structure under applied bias. The transmittivity and the net tunneling current density are calculated with Airy function and the boundary conditions which is suggested by Bastard. The results are compared with those from other methods and boundary conditions. From the calculated J-V characteristics for the tunneling current, the dependence of the voltage location showing the first peak current on the various temperatures and Fermi level is investigated. In addition, the wave function within the structure is obtained and compared with that from the flat-potential model.

• Bulletin of the Korean Chemical Society
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• v.32 no.2
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• pp.451-454
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• 2011

The traditional BCS superconductors $AOs_2O_6$ (A=K, Rb, and Cs) were investigated to find the relationship between their structures and superconducting transition temperatures. The $T_c$ decreases with increasing the unit cell parameter of $AOs_2O_6$. This is in contrast to the case of conventional BCS superconductivity in a single bond model, where $T_c$ may increase with increasing the the unit cell parameter since the DOS at Fermi level increases as the unit cell parameter increases. Instead, the $T_c$ of a $\beta$-pyrochlore oxide is proportional to the lattice softness of the compound.

• Bulletin of the Korean Chemical Society
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• v.31 no.9
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• pp.2565-2570
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• 2010

The orthorhombic $MgB_2C_2$ structure contains well-separated parallel graphite-like $B_2C_2^{2-}$ layers which extend infinitely in two dimensions. Three possible ways to distribute B and C atoms in the hexagonal sublattice sites are adopted. Band structures for the hypothetical distribution patterns are examined to assess the electronic stability of these phases and to account for the observed arrangement by means of extended Huckel tight-binding calculations. The preferred choice is the layer with B and C alternating strictly so that B is nearest neighbor to C and vice versa. A rationale for this is given. Due to the alternation of B and C within the honeycomb layers, $MgB_2C_2$ is a band insulator, which through partial substitution of Mg with Li, is predicted to turn metallic with holes in the $\sigma$ bands at the Fermi level.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.273-275
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• 1997

We fabricated the conventional silicon tips coated with a diamond-like carbon (DLC) film. The DLC films are prepared by the filtered cathodic vacuum arc (FCVA) technique. With increasing nitrogen content in DLC film, the work function($\phi$) and the turn-on voltage decrease and the emission current increases. This phenomenon is due to the fact that the Fermi-level moves to the conduction band by increasing nitrogen doping concentration. We have tested on the stability of the DLC film coated silicon tip during 2 hours at 500V.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.1
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• pp.19-22
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• 1999

N-doped and low-hydrogenated DLC thin films were coated on the Mo-tip FEAs in order to improve the field emission performance and their electrical properties were evaluated. The fabricated devices showed improved field emission performance in terms of turn-on voltage, emission current and current fluctuation. This result might be caused both by the shift of Fermi level toward conduction band by N-doping and by the inherent stability of DLC material. Furthermore, the transconductance of the DLC-coated Mo-tip FEA and electrical conductivity and optical band-gap of the deposited DLC films were investigated.

• Journal of the Korean institute of surface engineering
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• v.29 no.6
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• pp.660-665
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• 1996

Thin films of indium oxide and indium tin oxide have been prepared by d.c. magnetron sputtering onto the fused silica substrates kept at 90, 200 and $300^{\circ}C$. In order to elucidate the optical absorption process in low energy region below 3 eV, we have analyzed the absorption coefficients obtained from reflectance and transmittance measurements for these films based on the Lucovsky model. It has been found for the first time that a defect center in the band gap is located at 0.8~1.4 eV below the Fermi level in all films and arises from oxygen vacancies in their films. The optical absorption in low energy region is explained to be dominated by the transition of electrons trapped at the positively charged (+2e) oxygen vacancies with s-like nature to the conduction band formed from the 5s-orbit in indium atoms.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.321-321
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• 2011

We have investigated the electronic structure of graphite oxide by photoelectron spectroscopy at the Pohang Accelerator Laboratory, Korea. The typical sp2 hybridization states found in graphite were also seen in graphite oxide. However, the ${\pi}$ state disappeared near the Fermi level because of bonding between the ${\pi}$ and oxygen-related states originating from graphite oxide, indicating electron transfer from graphite to oxygen and resulting in a downward shift of the highest occupied molecular orbital (HOMO) state to higher binding energies. The band gap opening increased to about 1.8 eV, and additional oxygen-related peaks were observed at 8.5 and 27 eV.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.114-114
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• 2011

Graphene is the hottest topic in condensed-matter physics due to its unusual electronic structures such as Dirac cones and massless linear dispersions. Graphene can be epitaxially grown on various metal surfaces with chemical vapor deposition (CVD) processes. Such epitaxial graphene shows modified electronic structures caused by substrates. In the method for removal of the effect of substrate, there are bi, tri-layer graphene, gold intercalation, and oxygen intercalation. Here, We will present the changes of geometric and electronic structure of graphene grown on Ru(0001) by oxygen intercalation between graphene and Ru(0001). Using Scanning tunneling microscopy (STM) and spectroscopy (STS), we observed the aspect that the band gap features near the fermi level of graphene on Ru(0001) system is shifted and narrow. Based on the observed results, two effects by intercalated oxygen were considered.