• Nuclear Engineering and Technology
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• 제1권2호
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• pp.91-101
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• 1969

인원자첨가농도가 6.4$\times$$10^{14}$ 부터 1.25$\times$$10^{17}$ ㎤까지인 n 형씰리콘 단결정들을 (1) 1 MeV 전자선과 (2) 두가지 연구용원자로와 (3) $Co^{6o}$ 감마선원으로 조사하고 이에 따르는 비저항의 변화를 측정하였고 이 측정결과를 Buehler가 제의한 실험식을 적용하여 분석했다. 이 지수실험식은 조사량이 적은 범위내에서는 대부분의 경우 잘 적용되나 1 MeV원자선조사에서는 측정결과와 잘 맞지 않으며 경우에 따라서는 선형변화식이 오히려 더 잘 적용된다는 것이 밝혀졌다. 특히 전자선조사 시료에서 조사량이 많을때 carrier 제거율에 큰 변화가 나타나는데 이것을 결함준위와 Fermi level과의 교환효과로 보고 자세히 살펴보았다. 위의 실험식이 적용되는 범위안에서 손상계수를 계산하고 손상계수에 의해서 n형 씰리콘의 비저항 변화에 미치는 여러가지 방사선원의 상대적효과를 비교하였다. 예컨대 TRIGA Mark II 연구로내의 중성자조사는 1 MeV 전자선 조사에 비하여 약 40배나 더 효과적으로 비저항 변화를 일으킨다는 것이 알려졌다. 조사전의 carrier농도와 손상계수와의 관계도 조사하였고 또 지수실험식의 물리적근거와 조사량이 많을때의 결함준위와 Fermi level와의 교차가 비저항변화에 미치는 효과도 아울러 고찰하였다.다.

• Progress in Superconductivity
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• 제12권2호
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• pp.99-103
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• 2011

We performed angle resolved photoelectron spectroscopy (ARPES) studies on Ru doped $BaFe_2As_2$ with various Ru contents. Ru, which is doped into a parent compound $BaFe_2As_2$ and substitute Fe, does not donate or accept electrons. However, it induces superconductivity. From ARPES data along the high symmetry cuts and Fermi surface maps, we investigate the electron correlation and carrier density at the Fermi level. We observe that the Fermi velocity increases with Ru doping, suggesting reduction in electron correlation. In addition, we address issues on local vs. itinerant pictures for the magnetism in $BaFe_2As_2$.

• 한국재료학회지
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• 제29권7호
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• pp.451-455
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• 2019

The electromagnetic and thermal properties of a heavy fermion $CeNi_2Ge_2$ are investigated using first-principle methods with local density approximation (LDA) and fully relativistic approaches. The Ce f-bands are located near the Fermi energy $E_F$ and hybridized with the Ni-3d states. This hybridization plays important roles in the characteristics of this material. The fully relativistic approach shows that the 4f states split into $4f_{7/2}$ and $4f_{5/2}$ states due to spin-orbit coupling effects. It can be found that within the LDA calculation, the density of states near the Fermi level are mainly of Ce-derived 4f states. The Ni-derived 3d states have high peaks around -1.7eV and spreaded over wide range around the Fermi level. The calculated magnetic of $CeNi_2Ge_2$ with LDA method does not match with that of experimental result because of strong correlation interaction between electrons in f orbitals. The calculations show that the specific heat coefficient underestimates the experimental value by a factor of 19.1. The discrepancy between the band calculation and experiment for specific heat coefficient is attributed to the formation of a quasiparticle. Because of the volume contraction, the exchange interaction between the f states and the conduction electrons is large in $CeNi_2Ge_2$, which increases the quasiparticle mass. This will result in the enhancement of the specific hear coefficient.

• 태양에너지
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• 제8권1호
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• pp.68-73
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• 1988

In the glass/TCO/p-i-n a-Si/Al type of amorphous silicon solar cell, the effects on solar cell efficiency and metastability for the various kinds of TCO analyzed by SAM and ESCA, which was used to measure the diffusion profiles of In and Sn and the Fermi energy shifts in the TCO/p interface respectively. Indium which diffused into a-Si p-layer did not have any significant effects on the Fermi level shift of p-layer when the content of $B_2H_6/SiH_4$ in p-layer was at 1 gas%. The cell fabricated on $SnO_2$ turned out to have the best cell photovoltaic characteristics. ITO fabricated by electron beam deposition system, which was shown to have the greatest rate of diffusion of Indium in ITO/p interface produced the worst metastability among the cells tested.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.169-169
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• 2014

Interfacial electronic structure of bathocuproine and Al was investigated using in-situ photoemission spectroscopy and density functional theory (DFT) calculations. Bathocuproine is used for exciton blocking and electron transport material in organic photovoltaics and Al is typical cathode material. When thin thickness of Al was thermally evaporated on BCP, gap states were observed by ultraviolet photoemission spectroscopy. The closest gap state yielded below 0.3 eV from Fermi level. By x-ray photoemission spectroscopy, interaction of Al with nitrogen of BCP was observed. To understand the origin of gap states, DFT calculation was carried out and gap states was verified with successive calculation of interaction of Al and nitrogen of BCP. Furthermore, emergency of another state above Fermi level was observed. Remarkable reduction of electron injection barrier between Al and BCP, therefore, is possible.

• Bulletin of the Korean Chemical Society
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• 제24권3호
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• pp.325-333
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• 2003

An analysis of the electronic structure and bonding in the ternary silicide YNiSi₃is made, using extended Huckel tight-binding calculations. The YNiSi₃structure consists of Ni-capped Si₂dimer layers and Si zigzag chains. Significant bonding interactions are present between the silicon atoms in the structure. The oxidation state formalism of $(Y^{3+})(Ni^0)(Si^3)^{3-}$ for YNiSi₃constitutes a good starting point to describe its electronic structure. Si atoms receive electrons from the most electropositive Y in YNiSi₃, and Ni 3d and Si 3p states dominate below the Fermi level. There is an interesting electron balance between the two Si and Ni sublattices. Since the ${\pi}^*$ orbitals in the Si chain and the Ni d and s block levels are almost completely occupied, the charge balance for YNiSi₃can be rewritten as $(Y^{3+})(Ni^{2-})(Si^{2-})(Si-Si)^+$, making the Si₂layers oxidized. These results suggest that the Si zigzag chain contains single bonds and the Si₂double layer possesses single bonds within a dimer with a partial double bond character. Strong Si-Si and Ni-Si bonding interactions are important for giving stability to the structure, while essentially no metal-metal bonding exists at all. The 2D metallic behavior of this compound is due to the Si-Si interaction leading to dispersion of the several Si₂π bands crossing the Fermi level in the plane perpendicular to the crystallographic b axis.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.342-342
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• 2010

We have investigated an Au intercalated monolayer graphene on Ni(111) using angle-resolved photoemission spectroscopy (ARPES), high resolution photoemission spectroscopy (HRPES), and low energy electron diffraction (LEED) at the 3A2 ARUPS beamline in Pohang Accelerator Laboratory. We find the monolayer graphene is well grown on the Ni(111) surface by the adsorption of acetylene. However, the graphene does not show the characteristic $\pi$ band near the Fermi level due to its strong interaction with the underlying substrate. When Au is adsorbed on the surface and then annealed at high temperature, we observe that Au is intercalated underneath the monolayer graphene. The process of the Au intercalation was monitored by HRPES of corresponding Au 4f and C 1s core levels as well as the electronic structure of the $\sigma$, $\pi$ states at $\Gamma$, K points. The $\sigma$, $\pi$ bands of graphene shift towards the Fermi level and the $\pi$ band is clearly observed at K point after the intercalation of full monolayer Au. The full width at half maximum (FWHM) of the C 1s peak narrows to approximately 0.42 eV after intercalation. These results imply that the interaction between the graphene and substrate is considerably weakened after the Au intercalation. We will discuss the graphene is really closer to ideal free standing graphene suggested recently.

• Journal of Magnetics
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• 제7권4호
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• pp.132-137
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• 2002

The electronic structures and magnetism of the non-oxide perovskite MgCFe$_3$(001) surface were investigated by using the all-electron full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA). We considered both of the MgFe terminated (MgFe-Term) and the CFe terminated (CFe-Term) surfaces. We found that the minority spin d-bands of Fe(S) of the MgFe-Term are strongly localized and Fermi level (EF) lies just below the sharp peak of the minority spin d-band of Fe(S), while the minority spin d-bands of Fe(S) of the CFe-Term are not localized much and Fermi level (E$_F$) lies in the middle of two peaks of the minority spins. The majority Fe(S) d-band width of MgFe- Term is narrower than that of the CFe-Term. It is found that the magnetic moment of Fe(S) of the MgFe- Term is 2.51 ${\mu}$$_B$, which is much larger than that of 1.97 ${\mu}$$_B$ of the CFe-Term.

• 한국재료학회지
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• 제30권12호
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• pp.666-671
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• 2020

The electronic structure and magnetic properties of chalcopyrite (CH) AlGaAs2 with dopant Mn at 3.125 and 6.25 % concentrations are investigated using first-principles calculations. The CH AlGaAs2 alloy is a p-type semiconductor with a small band-gap. The AlGaAs2:Mn shows that the ferromagnetic (FM) state is the most energetically favorable one. The Mn-doped AlGaAs2 exhibits FM and strong half-metallic ground states.The spin polarized Al(Ga,Mn)As2 state (Al-rich system) is more stable than the (Al,Mn)GaAs2 state (Ga-rich system), which has a magnetic moment of 3.82mB/Mn. The interaction between Mn-3d and As-4p states at the Fermi level dominates the other states.The states at the Fermi level are mainlyAs-4p electrons, which mediate strong interaction between the Mn-3d and As-4p states. It is noticeable that the FM ordering of dopant Mn with high magnetic moment originates from the As(4p)-Mn(3d)-As(4p) hybridization, which is attributed to the partially unfilled As-4pbands. The high FM moment of Mn is due to the double-exchange mechanism mediated by valence-band holes.

• 한국진공학회:학술대회논문집
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• 한국진공학회 1994년도 제6회 학술발표회 논문개요집
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• pp.43-43
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• 1994

We studied chemical reactio of Eu metal on the in situ cleaved CdTe(110) surface by pphotoemission sppectroscoppy using synchrotron radiation. The chamber was maintained with base ppressure $\leq$2${\times}$10-10 mb during the expperiment. The expperiment was carried out in pphoton Factory in Jappan. Core level pphotoemission sppectroscoppy was carried out with Al K${\alpha}$ Line. The CdTe simiconductor was determined to be pp-typpe with low dopping concentration from Hall measurement. We found that there are two reacted pphases of Te with Eu (related to divalent Eu and trivalent Eu, resppectively) from least square fitting of Te 4d sppectra, but three is no indication of Cd reaction. Trivalent Eu exists after roughly one monolayer depposition (600 sec. depposition time is considered as one monolayer), which is also observed at Eu 3d core level sppectra. Overlayer Eu is metallized after roughly 2 monolayers depposition, as can be deduced from the fact that metallic edge near Fermi level begins to appear. The intensity of core-level of Te decreases expponentially at the initial stage (near one monolayer) and after one monolayer depposition it decreases more slowly due to Te out-diffusion. We categorized the growth mode of Eu on CdTe as S-K growth mode (cluster formation after one monolayer deppisition) from the relative intensity pplot of Te 4d normalized to the cleaved surface. At cleaved surface band bending is already established due to surface defects. At first 100 sec. depposition time the shift toward lower binding side by 0.6 eV is found at all core level sppectra of all elements in semiconductor. This shift is considered as the re-adjustment of surface Fermi level to the pposition induced by Eu metal (0.2 eV above the valence band maximum).