氧化锌有序结构在Au(111)和Cu(111)上的生长

摘要

The growth and structural properties of ZnO thin films on both Au(111) and Cu(111) surfaces were studied using either NO2 or O2 as oxidizing agent.The results indicate that NO2 promotes the formation of well-ordered ZnO thin films on both Au(111) and Cu(111).The stoichiometric ZnO thin films obtained on these two surfaces exhibit a flattened and non-polar ZnO(0001) structure.It is shown that on Au(111),the growth of bilayer ZnO nanostructures (NSs) is favored during the deposition of Zn in presence of NO2 at 300 K,whereas both monolayer and bilayer ZnO NSs could be observed when Zn is deposited at elevated temperatures under a NO2 atmosphere.The growth of bilayer ZnO NSs is caused by the stronger interaction between two ZnO layers than between ZnO and Au(111) surface.In contrast,the growth of monolayer ZnO NSs involves a kinetically controlled process.ZnO thin films covering the Au(111) surface exhibits a multilayer thickness,which is consistent with the growth kinetics of ZnO NSs.Besides,the use of O2 as oxidizing agent could lead to the formation of substoichiometric ZnOx structures.The growth of full layers of ZnO on Cu(111) has been a difficult task,mainly because of the interdiffusion of Zn promoted by the strong interaction between Cu and Zn and the formation of Cu surface oxides by the oxidation of Cu(111).We overcome this problem by using NO2 as oxidizing agent to form well-ordered ZnO thin films covering the Cu(111) surface.The surface of the well-ordered ZnO thin films on Cu(111) displays mainly a moiré pattern,which suggests a (3 × 3) ZnO superlattice supported on a (4 × 4) supercell of Cu(111).The observation of this superstructure provides a direct experimental evidence for the recently proposed structural model of ZnO on Cu(111),which suggests that this superstructure exhibits the minimal strain.Our studies suggested that the surface structures of ZnO thin films could change depending on the oxidation level or the oxidant used.The oxidation of Cu(111) could also become a key factor for the growth of ZnO.When Cu(111) is pre-oxidized to form copper surface oxides,the growth mode of ZnOx is altered and single-site Zn could be confined into the lattice of copper surface oxides.Our studies show that the growth of ZnO is promoted by inhibiting the diffusion of Zn into metal substrates and preventing the formation of sub-stoichiometric ZnOx.In short,the use of an atomic oxygen source is advantageous to the growth of ZnO thin films on Au(111) and Cu(111) surfaces.%利用NO2或O2作为氧化剂,研究了氧化锌在Au(111)和Cu(111)上的生长和结构.NO2表现了更好的氧化性能,有利于有序氧化锌纳米结构或薄膜的生长.在Au(111)和Cu(111)这两个表面上,化学计量比氧化锌都形成非极性的平面化ZnO(0001)的表面结构.在Au(111)上,NO2气氛下室温沉积锌倾向于形成双层氧化锌纳米结构;而在更高的沉积温度下,在NO2气氛中沉积锌则可同时观测到单层和双层氧化锌纳米结构.O2作为氧化剂时可导致形成亚化学计量比的ZnOx结构.由于铜和锌之间的强相互作用会促进锌的体相扩散,并且铜表面可以被氧化形成表面氧化物,整层氧化锌在Cu(111)上的生长相当困难.我们通过使用NO2作为氧化剂解决了这个问题,生长出了覆盖Cu(111)表面的满层有序氧化锌薄膜.这些有序氧化锌薄膜表面显示出莫尔条纹,表明存在一个ZnO和Cu(111)之间的莫尔超品格.实验上观察到的超晶格结构与最近理论计算提出的Cu(111)上的氧化锌薄膜结构相符,具有最小应力.我们的研究表明,氧化锌薄膜的表界面结构可能会随氧化程度或氧化剂的不同而变化,而Cu(111)的表面氧化也可能影响氧化锌的生长.当Cu(111)表面被预氧化成铜表面氧化物时,ZnOx的生长模式会发生变化,锌原子会受到铜氧化物晶格的限域形成单位点锌.我们的研究表明了氧化锌的生长需要抑制锌向金属基底的扩散,并阻止亚化学计量比ZnOx的形成.因此,使用原子氧源有利于在Au(111)和Cu(111)表面上生长有序氧化锌薄膜.