Growth And Surface Chemistry Of Zn And ZnO Overlayers On Pt(111)Surface

In this paper,surface analysis techniques including X-ray photoelectron spectroscopy(XPS),high-resolution electron energy loss spectroscopy(HREELS)and scanning tunneling microscopy(STM)were used to study the growth of ultrathin Zn and ZnO overlayers on Pt(111)and their surface chemistry processes,which include the alloying between Zn and Pt and the surface hydroxylation of ZnO ultrathin overlayers.The main results are as follows:(1)Growth of Zn thin films on Pt(111)and the surface alloying studies.In the Zn/Pt(111)system,Zn started to alloy with Pt surface between 220-300 K and was completely alloyed before 450 K.At 550 K,surface Zn atoms had diffused from the surface to the subsurface of Pt(111),and formed subsurface alloy with Pt.Furthermore,Zn-Au(111)surface was studied in order to compare with the Zn-Pt(111)surface.It was found that Zn has been completely alloyed with Au(111)surface after Zn deposition at 150 K.At 550K Zn atoms had partially desorbed from surface of Au(111)and the rest of Zn distributed on the surface of Au(111),and kept the surface alloy structure with Au(111).As the temperature rises to 600 K,the signal of Zn on the Au(111)surface almost disappeared.On the contrary,the Zn signal on the Pt(111)surface did not decrease significantly at this temperature,which might attributed to the subsurface structure of Zn/Pt(111).According to the relationship between the relative content ratio of Zn/Pt and the Zn 2p binding energy shift,the Zn 2p binding energy was more strongly affected by Zn/Pt ratio at the Zn-Pt(111)surface but less by Zn/Au at the Zn-Au(111)surface.(2)Growth and surface hydroxylation of ZnO thin layer structure on Pt(111)surface.Different ZnOx overlayers were obtained on Pt(111)surface,and its reaction with small molecules such as H2 and H2O was studied.XPS was used to characterize the conversion of ZnOx/Pt(111)surface structure to Zn(OH)x/Pt(111)surface structure under ultra-high vacuum(UHV)conditions.HREELS characterization was used to confirm that H2,atomic H and H2O can participate in the surface hydroxylation reaction.When the O/Zn ratio of the ZnOx structure in the sub-monolayer ZnOx/Pt(111)sample was relatively low,reaction with D2O becomes dominant in the surface hydroxylation.When the O/Zn ratio was relatively high,D2 or atomic H species mainly contributed to the hydroxylation reaction.When the thickness of ZnOx increased to 3 monolayers(ML),D2 showed low hydroxylation activity,and it is D2O or atomic H species participated in the hydroxylation process.