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

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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.