Development and application of a variable-temperature scanning-tunneling/atomic-force microscope

为了研究非平衡条件下单个表面原子和介观团簇的动力学，我们开发了一种新的变温探针显微镜。为了进一步研究表面动力学，我们还利用热解吸和高分辨率电子能量损失谱研究了Pd（100）表面（NO+CO）共吸附体系的有序性和H+H/Pd（100）体系的能量传递动力学。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3 pm (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来自稳定的混合有序相，而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。发现NO和co之间的吸引相互作用具有可加性。我们计划利用扫描探针显微镜来研究表面有序的微观机制。

We have developped a new variable-temperature sanned probe microscope in order to study the dynamics of individual surface atoms and mesoscopic clusters under non-equillibrium conditions. In order to study further on the surface dynamics, we have also conducted thermal desorpition and high-resolution electron energy loss spectroscopy to investigate the ordering in the (NO+CO) coadsorption system on the Pd (100) surface and the energy-transfer dynamisc in the H+H/Pd (100) system.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 3 pm (p-p), which enables the imaging of (100) and (111) surfaces of transition metals. This microscope can also be operated at tunneling current aslow as 1 pA,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 from 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. It was found that the additivity holds for the attractive interaction among NO and CO.We are planning to use the scanned probe microscope to investigate the microscopic mechanism of ordering at surfaces.