Time-Resolving Monte Carlo Simulation for Structural Fluctuation on Low Temperature Solid Sate Surfaces

在第一性原理计算的基础上，得到了Si(001)上二聚体系统的模型势。用MP进行了70K下的时间分辨动态蒙特卡罗模拟(DMCS)，模拟结果很好地再现了70K下Si(001)的时间分辨恒高电流模式STM(TCHC STM)的实验结果。我们引入了由电子系统项和电子-振动耦合项组成的哈密顿量。电子-振动耦合常数是由振动态的能量和MP得到的。利用哈密顿量得到了二聚体振动的有效温度Te。结果表明，在20K以下，当隧道电流为100Pa时，Te达到约250K。出现在20K以下的高Te本质上解释了为什么在低温下观察到对称的STM图像。当衬底温度升高到20K左右时，Te开始急剧下降，并与60K时的衬底温度几乎相同。这些低的Te解释了为什么不对称的STM图像在高于50K的温度范围内恢复。研究了STM的隧道电流相干激发的高振动数的Ge(001)表面上二聚体的振动。在扫描隧道显微镜中报道的局域结构的转变是由隧道电流相干激发的二聚体振动驱动的，样品偏置电压对激发速率的依赖关系被π^*-带的准维特性半定量地再现。证明了一维能带的激发速率不随距离STM尖端的距离而衰减，在多重分形统计的基础上，通过映射到二维伊辛系统的模拟，阐明了表面二聚体系统的主要相干模。

We obtained the model potential(MP) tor the dimer system on Si(001) based on the first-principles calculations. Using MP, we performed the time-resolving dynamical Monte-Carlo simulation(DMCS) at 70 K. The results from DMCS reproduce well the experimental results the time-resolving constant-height current mode STM(TCHC STM) for Si(001) at 70K. We introduced the Hamiltonian consists of the terms of the electronic system and the elecron-vibration coupling term. The electron-vibration coupling constant is obtained by the energy of the vibrational state and MP. We obtained the effective temperature Te of the dimer vibratio, using the Hamiltonian. We showed that below 20 K, Te reaches about 250 K at 100 pA of the tunneling current. The high Te appearing below 20 K, essentially explains why the symmetric STM images are observed at low temperatures. When the substrate temperature increases around 20 K, Te starts to decrease steeply, and takes the nearly same values as the substrate temperature at 60K. These low Te explains why the asymmetric STM images recover in the temperature range higher than 50 K.The vibration of the dimer on the Ge(001) surface with a high vibrational number excited coherently by tunneling current of STM, was investigated. The transformation of the local structures reported in STM is shown to be driven by the dimer vibration excited coherently by the tunneling current the sample bias voltage dependence on the excitation rate is semiquantitatively reproduced by the quasi-dimensional character of the π^*-band. We show that the excitation rate has a term that does not decay with the distance from the STM tip for the one-dimensional band.On the basis of multifractal statistics, we have clarified the dominant coherent mode of the surface dimer system by the simulation mapped onto the 2D Ising system.