GeH4以不同入射角度在Ge(100)表面上解離吸附的理論研究

Theoretical study of GeH4 dissociative adsorption onto Ge(100) by using different incident angles

葛玉環(Yuh-Hwan Ger)

指導教授 ： 林志興

淡江大學/理學院/化學學系碩士班/碩士(2009年)

https://doi.org/10.6846/TKU.2009.00163

摘要

運用密度泛函理論搭配ultrasoft pseudotentials、平面波基底，計算GeH4在Ge(100)表面上的解離吸附，透過結構、能量與態密度分析探討SDM (single dimer mode)、ATDM (adjacent two dimers mode)與NNDIRM(nearest neighboring dimers in row mode)三種反應途徑；而NNDIRM的入射角度選取以GeH4的Ge-H鍵由空懸鍵(dangling bond)的方向接近表面，以buckled-down Ge的空懸鍵的所形成的平面上的法向量為旋轉軸，buckled-down Ge為旋轉中心，空懸鍵為即為0∘，旋轉10∘、20∘和30∘。透過部分結構限制法(partial structural constrain path minimization)搜尋反應途徑及過渡態的資訊，探討由不同的入射角度及不同反應模式所造成的活化能與過渡態結構的關係；並且透過態密度的分析，討論過渡態與起始點、終點的能態結構變化。計算之活化能趨勢為：NNDIRM_10° > NNDIRM_20°> ATDM > NNDIRM_ 30° > SDM，與過渡態時前趨物中參與反應的Ge-H鍵與buckled -up Ge與前趨物的Ge的鍵長有相同的趨勢；且以入射角度最小的SDM具有最佳的反應性。由波茲曼分布的概念來看，要增加反應途徑中活化能較高的反應機率(reaction probability)，實驗中需要提供較大的入射動能使前趨物的Ge-H鍵作較大的扭曲，與較高的表面溫度提供dimer鍵長較大的變化量。從我們的研究也發現活化能較高的NNDIRM_10° 、NNDIRM_20°與ATDM在過渡態時結構變化較大，因此，入射動能的增加與表面溫度的升高均會提高這些反應途徑的反應機率。

關鍵字

密度泛函理論 ； 態密度 ； 鍺烷 ； 半導體表面 ； 入射動能 ； 表面溫度 ； 入射角度 ； 反應機率 ； 分子束

並列摘要

Using density functional theory (DFT) with ultrasoft pseudotentials and plane wave basis to calculate the reaction of GeH4 dissociative adsorption onto Ge(100). Through the analysis of structure, energy and density of state (DOS) to investigate the following three reaction path: single dimer mode (SDM), adjacent two dimers mode (ATDM) and nearest neighboring dimers in row mode (NNDIRM). In NNDIRM, choosing incident angles as 10˚, 20˚ and 30˚. To define the 0˚ angle that GeH4 impact the surface, choosing the direction from Ge-H bond within GeH4 to dangling bond to be 0˚. To define the incident angle, choosing the normal vector of the plane formed with the dangling bond of buckled-down Ge as the rotation axis, and the buckled-down Ge as rotation center. Using partial structural constrain path minimization (PSCPM) to find the reaction path and the information of transition state and to probe into the relation between activation energy, transition state structure and the different of incident angle and reaction path. Through DOS analysis to understand the variation of DOS of initial state (IS), transition state (TS) and final state (FS). After calculation, trend of activation energy: NNDIRM_10° > NNDIRM_20°> ATDM > NNDIRM_ 30° > SDM. The same result showed in the trend of bond length of Ge-H bond within precursor in transition state and buckled -up Ge with Ge in precursor. The better reactivity happened in SDM which has smaller incident angle. As Boltzmann distribution law, to increase the reaction probability in reaction path of higher activation energy, the more incident kinetic energy and higher substrate temperature is needed in experiment so that Ge-H bond within precursor could be distorted more and elongation of Ge=Ge dimmer could be larger, respectively. In the research, we found NNDIRM_10°, NNDIRM_20°and ATDM which have higher activation energy could make structure change more in transition state. As a result, the increasing of incident kinetic energy and substrate temperature will also increase reaction probability of those reaction paths.

並列關鍵字

Density Functional Theory ； Density of State ； GeH4 ； Ge(100) ； incident kinetic energy ； substrate temperature ； incident angle ； reaction probability ； CASTEP ； molecular beam

參考文獻

[4] Jiang, J. C.; Cheng, C. L.; Tsai, D. S. Surf. Sci. 2006, 600, 3194.

[7] Lam, A. M.; Zheng, Y.-J.; Engstrom, J. R. Surf. Sci. 1997, 393, 205.

[8] Lin, J. S.; Chou, W. C. Surf. Sci. 2004, 560, 79.

[11] Hohenberg, P.; Kohn. W. Phys. Rev. 1964, 136, 864.

[12] Martin, R. M. Electronic Structure, basic theory and practical methods (Cambridge) 2004.