表面原子扩散和氢对石墨表面功函数影响

【作者】 王昶清；

【导师】 贾瑜；

【作者基本信息】 郑州大学 ， 凝聚态物理， 2006， 硕士

【摘要】 本论文第一部分利用分子动力学(MD)方法，采用Stillinger-Weber势对不同温度下解理Si(001)表面的原子结构和单个Si原子在Si(001)表面以及该表面单层台阶附近扩散的动力学过程分别进行了研究。 对于不同温度下解理Si(001)表面的原子结构，研究结果表明：Si(001)表面除主要的p(2×1)结构之外，较低温度下还会有双悬挂键的单原子结构存在；较高温度下表面还会存在c(2×2)和三聚体等亚稳态结构；接近表面熔化温度时，双悬挂键单原子、c(2×2)和三聚体等亚稳态结构都消失，表面只存在稳定的p(2×1)结构。 对于Si原子在Si(001)表面和该表面单层台阶附近扩散的动力学过程，研究表明：较高温度下，单个Si原子在Si(001)表面可以通过与表面原子的交换，沿着垂直于二聚体排方向扩散。Si原子沿着这一方向扩散能够减弱Si原子在Si(001)表面扩散的各向异性、减小沿着二聚体排方向的扩散系数；增原子通过与表面原子之间的交换可以从S_A台阶的下台面扩散到上台面，而且还可以从S_B台阶上台面扩散到下台面。这一结果有助于理解Si(001)表面双原子台阶的形成机制。无论是单个Si原子在Si(001)表面垂直于二聚体排方向扩散还是在Si(001)表面的单层台阶附近扩散，增原子和表面原子之间的交换机制都起着重要的作用。 本论文第二部分采用基于密度泛函理论(DFT)的第一性原理方法计算了氢在石墨(0001)表面不同位置、不同覆盖度的吸附对其功函数的影响，并与实验结果比较，得到与实验结果一致的结论。计算结果表明氢在石墨(0001)表面的顶位和桥位可以形成较强的化学吸附。吸附在其表面的氢可以明显降低石墨(0001)表面功函数，而且少量的氢吸附(0.125覆盖度)比相对大量的氢吸附(0.5覆盖度)更能降低石墨(0001)表面的功函数。更多还原

【Abstract】 In the first part of the thesis, by using Stillinger-Weber potential, we carried out the constant temperature molecular dynamics simulations of Si(001) surface structures at different temperatures and single Si adatom diffusing on Si(001) surface or single-layer Si(001) steps at the temperatures ranging 1000K to 1300K.As for the simulations of Si(001) surface structures , our results show that dimers rearranged into p(2×1) cell are the primary structure of Si(001) surface. Besides this, trimers and c(2×2) metastable structures are observed on the surface at different temperature as well as two-dangling-bond single atoms. Up to the surface melting temperature, these metastable structures disappear and the simple p(2×1) structure remains on the surface. About the simulations of single Si adatom diffusing on Si(001) surface or single-layer Si(001) steps at the temperatures ranging 1000K to 1300K, we have presented one new diffusion pathway of single Si adatom diffusing on the Si(001) along the direction perpendicular to dimer rows, that can weaken the diffusion anisotropy. We have investigated the process of single Si adatom diffusing across single-layer Si(001) steps as well and given adatom diffusion pathways of step-flow and transformation of single-layer into double-layer steps. Our results show that the exchange between an adatom and a surface atom plays an important role in the adtom diffusion process above 1000K.In the second part of the thesis, we performed first principles calculations based on density functional theory (DFT) about Hydrogen adsorptions on different sites on Graphite(0001) at different coverage. Calculation results indicate that top and bridge sites on Graphite(0001) are more stable chemisorption. Moreover, little Hydrogen adsorbed on it (0.125coverage) can more lower the work function of the Graphite(0001) surface.更多还原