The Adsorption and Thermal Desorption of Cis-Trans Organic Molecules on Metal Covered Ge(111)-(√3×√3)R30° Surfaces

• Main Authors: Tyng-Dar Chien, 簡廷達
• Other Authors: Chaochin Su
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/5zr7nm

碩士 === 國立臺北科技大學 === 有機高分子研究所 === 93 === This thesis is composed of two major parts. In the first part, the adsorption and thermal desorption of azobenzene on Ag/Ge(111)-(√3×√3)R30° (Ag/Ge(111)-√3) has been studied using combinative techniques of temperature programmed desorption (TPD) for azobenzene desorption kinetics, Auger electron spectroscopy (AES) for Ag coverage determination, and low energy electron diffraction (LEED) for surface structure characterization under ultra-high vacuum (UHV) condition. The Ag/Ge(111)-√3 surface was prepared by thermal deposition of one monolayer of Ag onto Ge(111) single crystal surface at 100 K followed by annealing at 700 K for 1 min. The resultant Ag/Ge(111) surface showed a sharp (√3×√3)R30° LEED pattern. For all the azobenzene exposures (0.6 L to 30 L) which have been studied, the TPD traces show only molecular desorption with single desorption peak at peak temperature (Tp)=250 K. The Tp shifts constantly from 250 to 267 K with increase of azobenzene exposure from 0.6 to 30 L. The leading edge shows excellent match for all the acquired TPD curves. Those results strongly suggest the zeroth-order kinetics for azobenzene desorption from Ag/Ge(111)-√3. Such behavior can be explained by the thermal-induced pre-aggregation of azobenzene molecules to form 3D cluster on Ag/Ge(111)-√3 before desorption. The zeroth-order desorption kinetics was also confirmed by the leading-edge analyses of TPD results. The plausible explanation in terms of molecular-molecular interaction and molecular-substrate interaction is discussed in this thesis. In the second part of this thesis, the adsorption and thermal desorption of cis-stilbene (CSB) on Au/Ge(111)-(√3×√3)R30° (Au/Ge(111)-√3) surface has been studied using the same approach. One monolayer of CSB deposited on Au/Ge(111)-√3 at 220 K followed by cooling to 100 K leads to the formation of a well ordered (2×1) structure as observed by LEED. The TPD spectra for CSB thermal desorption from Au/Ge(111)-√3 exhibit showed two well-resolved peaks at Tp = 243 and 274 K corresponding to multilayer and monolayer desorption, respectively. Only molecular desorption was detected during the heating process. Interestingly that the Tp for both multilayer and monolayer desorption peaks continually increase upon increase of CSB exposure and show unsaturated feature even up to 30 L. Similar behavior was also found for CSB desorption on the Ag/Ge(111)-√3 surface. Comparison between these two systems and possible explanation for the desorption mechanism is discussed in this thesis.