Motion of individual atoms and mesoscopic structural dynamics on non-equillibrium surfaces

为了实现对非平衡表面上单个原子和分子动态运动的直接观察，了解其微观机理，我们研制了一种新型的变温扫描探针显微镜。为了进一步研究Pd（100）表面动力学，我们还通过热解吸和高分辨率电子能量损失谱来研究Pd（100）表面（NO+CO）共吸附体系的有序性。本研究研制的扫描探针显微镜可在超高真空和样品温度100 ~ 1000K范围内工作。另一个重要的特点是它的低噪声信号输出。地形成像模式的垂直噪声为3pm (p-p)，可以对过渡金属（100）和（111）表面进行成像。该显微镜还可以在低至1pA的隧道电流下工作，从而可以成像低电导率的材料，如有机晶体。采用低能电子衍射、热解吸和振动谱等方法研究了(NO+CO) /Pd（100）共吸附体系的有序性，为扫描探针显微镜的应用做了准备。我们发现NO和CO形成稳定的混合有序相，并且在混合有序相中发生爆炸性的CO2生成反应。基于晶格-气体模型的动力学蒙特卡罗模拟已经完成了量化NO-CO分子间相互作用。我们还研究了H+H/Pd（100）反应，发现撞击的H原子迫使预吸附的H原子渗透到Pd体中（冲压吸收）。讨论了MH2体系的势能面特性。

In order to realize the direct observation of the dynamic motion of individual atoms and molecules on the non-equillibrium surfaces and to understand the underlying microscopic mechanism, we have developped a new variable-temperature scanned probe microscope. In order to study further on the surface dynamics, we have also conducted thermal desorption and high-resolution electron energy loss spectroscopy to investigate the ordering in the (NO+CO) coadsorption system on the Pd (100) surface.The scanned probe microscope developped in the present study can be operated under ultrahigh vacuum and at sample temperature from 100 to 1000K.Another important characteristic is its low-noise signal output. The vertical noise for the topographic imaging mode is 3pm (p-p), which enables the imaging of (100) and (111) surfaces of transition metals. This microscope can also be operated at tunneling current as low as 1pA, which enables imaging of low-conductivity materials such as organic crystals.The ordering in (NO+CO) /Pd (100) coadsorption system has been studied by low-energy electron diffraction, thermal desorption and vibrational spectroscopy preparatory to the application of the scanned probe microscope. We have found that NO and CO form stable mixed ordered phases and that an explosive CO2 formation reaction undergoes in the mixed ordered phases. A kinetic Monte Carlo simulation based on a lattice-gas model has been done to quantify NO-CO intermolecular interactions.We have also investigated on the H+H/Pd (100) reaction and found that the impinging H atoms force the preadsorbed H atoms to penetrate into Pd bulk (stamping absorption). The characteristics of the potential energy surface for the MH2 system was discussed.