• 제목/요약/키워드: First principles calculation

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DEMS와 H-terminated Si (001) 표면의 상호작용: 제일원리연구 (Interaction of DEMS with H-terminated Si (001) Surface: A First Principles Study)

  • 김대현;김대희;박소연;서화일;이도형;김영철
    • 한국세라믹학회지
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    • 제46권4호
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    • pp.425-428
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    • 2009
  • We performed a density functional theory study to investigate the interaction of DEMS (diethoxymethylsilane) with the H-terminated Si (001) surface. The optimum structure of DEMS was first calculated by a first principles study. The dissociation probability of the O-C bond of DEMS was higher than the other seven bonds based on the bond energy calculation. When the fragmented DEMS groups reacted with the H-terminated Si (001) surface, it was the most favorable among the eight reactions to form a bond between the Si atom on the surface and the O atom of a fragmented DEMS group (($C_2H_5O$)Si($CH_3$)(H)-O-) by forming a $C_2H_6$ as by-product.

Si(001)에 흡착되는 NO에 대한 제일원리 분자동역학 연구 (First-principles molecular dynamics study of NO adsorption on Si(001))

  • 정석민
    • 한국진공학회지
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    • 제14권2호
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    • pp.97-102
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    • 2005
  • 제일원리 분자동역학 방법을 이용하여 Si(001) 표면에 NO 분자 흡착을 연구하였다. NO 분자가 Si(001)의 dimer축과 나란히 흡착될 경우에 50K에서도 분해가 일어났다. 이를 에너지 장벽으로 환산해 보면 0.006eV로서 거의 무시해도 좋을 정도이다 만일 NO 분자가 표면에 수직으로 들어오면 이웃에 있는 dimer에 걸쳐서 분해가 일어났다. 이 경우는 에너지 장벽은 0.08eV 정도였으며 여전히 낮은 수준이다. 분해가 된 산소분자는 dimer와 기판 사이의 backbend로 파고들어서 (에너지 장벽 0.007eV) 안정된 구조를 만들었다. 또 dimer에 나란히 흡착된 분자 상태의 경우는 N=Si_3$를 만들기도 하는데 속전자준위분광학(core level spectroscopy) 실험 결과와 일치한다.

Effects of Al Impurity on Magnetism in bcc Fe by a First-principles Calculation

  • Seo, Seung-Woo;Rahman, Gul;Kim, In-Gee
    • 한국자기학회:학술대회 개요집
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    • 한국자기학회 2009년도 정기총회 및 동계학술연구발표회
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    • pp.72-73
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    • 2009
  • First-principles calculations were carried out to investigate the effects of Al impurities on bcc Fe magnetism by considering SOC. No significant solid solution hardening effect was found. Albeit the effects of the SOC by Al on spin magnetic moments were minor, there are sizeable orbital magnetic effects. It is concluded that the orbital magnetism due to the Al impurity is strongly related with the impurity screening of the system as seen in Si impurity case [3], but the effects of Al impurity is stronger than those of Si impurity in terms of orbital magnetism.

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High Performance Thin-Film Transistors Based on Zinc Oxynitride Semiconductors: Experimental and First-Principles Studies

  • Kim, Yang-Soo;Kim, Jong Heon;Kim, Hyun-Suk
    • 한국재료학회지
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    • 제26권1호
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    • pp.42-46
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    • 2016
  • The properties of zinc oxynitride semiconductors and their associated thin film transistors are studied. Reactively sputtered zinc oxynitride films exhibit n-type conduction, and nitrogen-rich compositions result in relatively high electron mobility. Nitrogen vacancies are anticipated to act as shallow electron donors, as their calculated formation energy is lowest among the possible types of point defects. The carrier density can be reduced by substituting zinc with metals such as gallium or aluminum, which form stronger bonds with nitrogen than zinc does. The electrical properties of gallium-doped zinc oxynitride thin films and their respective devices demonstrate the carrier suppression effect accordingly.

Magnetic Property of BixCa1-xMnO3: Experimental and First Principles Calculation Study

  • Na, Sung-Ho;Kim, Dong-Jin
    • Journal of Magnetics
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    • 제14권1호
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    • pp.1-6
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    • 2009
  • The magnetic properties of ${Bi_x}{Ca_{1-x}}{MnO_3}$ for x = 0.12, 0.13, 0.14, 0.15, and 0.16 were examined by measuring magnetic susceptibility, resistivity and electron magnetic resonance at different temperatures. ${Bi_x}{Ca_{1-x}}{MnO_3}$ showed complicated magnetic structure that varies with temperature and composition, particularly around Bi composition x. 0.15. The aim of this study was to determine how the magnetic and physical properties of ${Bi_x}{Ca_{1-x}}{MnO_3}$ change in this region. In addition, first principles calculations of the magnetic phase of ${Bi_x}{Ca_{1-x}}{MnO_3}$ for x = 0, 0.125, 0.25 were carried out, and the spin state, electric and magnetic characteristics are discussed.

A First-principles Calculation of Surface Magnetism of Half-monolayer Ru on Pd(001)

  • Kim, Dong-Chul;Lee, J.I;Jang, Y.R
    • Journal of Magnetics
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    • 제4권4호
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    • pp.107-110
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    • 1999
  • In order to investigate the magnetism of Ru submonolayer on Pb(001), we have performed first-principles calculations for half-layer of Ru on Pd(001) using the full-potential linearzed augmented plane wave (FLAPW) method. We have found that the magnetic moment of Ru for 0.5 layer is 2.21 B. It is found that substrate Pd layers are polarized by the 0.5 Ru overlayer to have significant magnetic moments. Our results are compared with those obtained by the anomalous Hall effect. The calculated electronic structures, i,e., the spin densities and density of states are presented and discussed in relation with magnetic properties.

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Understanding Role of Precursor (Crystal Violet) and its Polarity on MoS2 Growth; A First Principles Study

  • Ramzan, Muhammad Sufyan;Kim, Yong Hoon
    • EDISON SW 활용 경진대회 논문집
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    • 제5회(2016년)
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    • pp.373-376
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    • 2016
  • Transition metal dichalcogenides (TMDs) such as $MoS_2$ is the thinnest semiconductor, exhibits promising prospects in the applications of optoelectronics, catalysis and hydrogen storage devices. Uniform and high quality $MoS_2$ is highly desirable in large area for its applications on commercial scale and fundamental research. Many experimental techniques i.e CVD have been developed to successfully synthesis $MoS_2$ on large scale, here in this work atomistic detail to understand the growth mechanism is addressed which was greatly overlooked. Here based on first principles calculation we found that polarity of seeding promter (crystal violet considerd in this work) controls the growth mechanism. It is also found that molybdenum destroys the precursor while sulfur adsorption with precursor is favorable.

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호이슬러 화합물 Co2MnSi에서 전자구조계산을 통한 에너지 간격의 원인에 대한 고찰 (Investigation on the Origin of Band Gap in Heusler Alloy Co2MnSi through First-principles Electronic Structure Calculation)

  • 김동철;이재일
    • 한국자기학회지
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    • 제18권6호
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    • pp.201-205
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    • 2008
  • 호이슬러 구조의 대표적 반쪽금속인, $Co_2MnSi$에서 에너지 간격이 생기는 원인을 실제적인 전자구조 계산을 통해 검토하기 위해 호이슬러 구조에서 부분을 이루는 zinc-blende 구조의 CoMn과 하프 호이슬러 구조를 가진 CoMnSi, 그리고 가상적인 화합물인 $Co_2Mn$의 전자구조를 제일원리 방법을 통해 계산하였다. 각 화합물에서 계산된 상태밀도를 이용하여 띠 혼성이나 에너지 간격 등을 고찰한 결과 $Co_2MnSi$에서 에너지 간격이 생기는 원인이 Galanakis 등이 설명한 방식이 그대로 적용되지 않았으며, Si 원자의 역할 또한 중요함을 알게 되었다. 각 화합물에서 얻은 다수스핀과 소수스핀 전자수를 통해 이들 화합물의 자성도 고찰하였다.

Integral Hellmann-Feynman Approach에 의한 KNiF$_3$의 Cubic Crystal Field Splitting 10 Dq의 계산 (Calculation of the Cubic Crystal Field Splitting 10 Dq in KNiF$_3$. An Integral Hellmann-Feynman Approach)

  • 김호징;김희준
    • 대한화학회지
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    • 제17권6호
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    • pp.395-405
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    • 1973
  • Integral Hellmann-Feynman formula를 사용하여 $KNiF_3$의 cubic crystal splitting 10Dq를 first principle로부터 계산하였다. Covalency parameter들과 필요한 적분치들은 Sugano와 Shulman의 계산치를 사용하였다. 계산치 7100$cm^{-1}$는 실험치 7250$cm^{-1}$와 대단히 잘 일치하였다. 고차섭동에너지 보정치는 10 Dq 자체와 같은 order of magnitude를 가지며 따라서 first principle로부터 10 Dq를 계산하는데 있어서 반드시 고려되어야 할 몫이라는 것을 발견하였다. 또한 point charge potential이 crystal field potential의 압도적인 부분을 차지하는 것을 발견하였다.

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