VUV Photo-reactions over Solid Surfaces studied by Techniques of Surface Science

表面光化学已应用于微电子金属和半导体薄膜的制备。用红外反射吸收光谱、X射线光电子能谱和热脱附谱研究了吸附在固体表面的五甲基铁(Fe(CO)_5，IPC)的低温光解机理，并考察了固体表面的物理和化学性质对反应的影响。结果表明：1.在低于150K的温度下，IPC以分子形式吸附在清洁的Ag、Au(111)和SiO_2表面上，并在波长和光的照射下发生光脱羰反应；光产物是Fe(CO)_4的低聚物，在光照下很稳定，但在300K以上发生热分解，在表面沉积Fe金属。热过程的机理取决于衬底表面的催化性能。2.观察到银和金衬底的光脱羰产率与气相IPC的吸收光谱不同。在银表面，光脱羰产率在320 nm附近达到最大值，而在Au(111)面上，在320 nm附近有较高的产率，但在更长的波长范围内没有表现出最大的产率。这些结果表明，IPC在固体表面的吸附会导致吸收光谱的红移。此外，银表面等离子体激元(3.88 eV*320 nm)的光激发可引起吸附的IPC的脱羰基反应。

Surface photochemistry has been applied to the preraration of thin films of metal and semiconductor for microelectronics. The purpose of this study is to investigate a mechanism of the photodecomposition of iron pentacarbonyl(Fe(CO)_5, IPC)adsorbed on solid surfaces at low temperatures using IR reflection absorption spectroscopy, X-ray photoelectron spectroscopy, and thermal desorption spectroscopy, and to examine effects of the physical and chemical properties of solid surface on the reactions.The results are summarized as follows.1.IPC is molecularly adsorbed on clean Ag, Au(111), and SiO_2 surfaces at tenperatures bellow 150K and undergoes photodecarbonylation upon irradiation with the light of wavelengths < 360nm.The photoproduct is the oligomer of Fe(CO)_4, which is quite stable under illumination but undergoes thermal decomposition at temperatures above 300K to deposit Fe metal on the surface. A mechanism of the thermal process depends on the catalytic properties of substrate surface.2.The dependence of photo-decarbonylation yield on the wavelength of light was observed for Ag and Au substrates and found different from the absorption spectrum of gas phase IPC.On Ag surfaces the yield is maximized at around 320 nm, at which gaseous IPC shows little absorption, while on Au(111) the decarbonylation occurs at significant yield at around 320nm but exhibits no maximum yield in longer wavelength range. These results show that the adsorption of IPC on solid surfaces would lead to the red shift of absorption spectrum. In addition, the photoexcitation of Ag surface plasmon(3.88eV * 320nm)could cause the decarbonylation of adsorbed IPC.