Pt/Si界面化学键性质的研究

在超高真空系统中,超薄层 Pt淀积膜原位蒸发在原子清洁的 Si(111)表面上形成 Pt/Si界面.利用光电子谱技术(XPS和UPS)研究了Pt/Si 界面的化学性质.测量了Si2p和Pt 4f芯能级和价带电子态,并着重研究这些芯能级及电子态在低覆盖度时的变化.由 Si(2p)峰的强度随 Pt 覆盖度的变化可以清楚证明:在 300 K下淀积亚单原子层至数个单原子层 Pt的 Pt/Si(111)界面发生强烈混合作用,其原子组伤是缓变的.由于Si原子周围的 Pt原子数不断增加,所以 Pt 4f芯能级化学位移随 Pt原子覆盖度的增加而逐步减小,而Si 2p芯能级化学位移则逐步增大.同时,Pt 4f峰的线形也产生明显变化,对称性增加;Si 2p峰的线形则对称性降低.淀积亚单原子层至数单原子层Pt的UPS谱,主要显示两个峰:-4.2eV(A峰),-6.0eV(B峰).A峰随着覆盖度的增加移向费米能边,而B峰则保持不变.这说明Ptd-Sip键合不受周围Pt原子增加的影响.利用Pt/Si界面Pt原子向Si原子的间隙扩散模型讨论了所观察到的结果.

Investigation of Chemical Bonding at the Pt/Si Interface

Photoelectron spectroscopy (UPS and XPS) technique has been used to study the chemicalbehavior of interfaces formed by Pt deposition at 300 K under ultrahigh vacuum on atomicallyclean Si(111) surface prepared by sputter/annealing.Both core lines (Si2p and Pt4f) andvalence-band states have been measured. Special attention has been given to the low-coverageregime.The intensity variations of Si(2p) core lines as a function of Pt coverage show clearindications of strong Pt/Si intermixing across the interface with gradual-changed atomic com-position from the submonolayer range to several atomic layers at 300 K. With increasing cove-rage the Pt4f core level shifts decrease gradually while Si2p shifts increase as expected for amore Pt-rich environment. In the meanwhile,the Pt4f core line changes markedly with highersymmetrical line shape upon metal deposition, and, moreover, the shape of Si2p core lines ismodified towards that typical of a metallic phase (the greater width and asymmetry). TheUPS spectrum is dominated by two peaks at -4.2 eV (labeled as A), and -6.0 eV (labeledas B), from submonolayer to several atomic layers of Pt coverages.The peak A shifts towardsthe Fermi energy with increasing coverage as expected for a more Pt-rich environment, butpeaks B remains unchanged suggesting that the Ptd-Sip bonding has not been affected byincreasing around Pt atoms.All these results are discussed with an interstitial diffusion modelbetween Si and Pt at the Pt/Si interface.