关键词: STM针尖诱导, Jump-to-contact, 表面纳米构筑, Pt-Cu置换

Abstract: STM tip-induced surface nanostructuring based on "Jump-to-contact" mechanism is a nanostructuring technique that has the highest resolution in aqueous solutions.However,for metals that have high cohesive energy,atoms would transfer from surface to tip instead,which limits the wide application of this technique.In this paper,we present a two-step Nanostructuring-Replacement method to construct metal nanoclusters that cannot be obtained directly via the "Jump-to-contact" mechanism.The method is demonstrated to construct Pt nanoclusters that are of great interest in catalysis and electrocatalysis but cannot be constructed via the "Jump-to-contact" mechanism.Since Cu is the most intensively studied and successful system in the tip-induced nanostructuring,it is utilized as the system in the first step of nanostructuring on Au(111) surface.The as-prepared Cu nanoclusters are replaced with Pt in the second step to form Pt nanoclusters.To fulfill the STM tip induced nanostructuring,an external workstation equipped with AD/DA board is employed for controlled generation of voltage signals,which are superimposed on the signals from a commercial STM instruments to direct the tip movement at desire.Cu nanostructuring is carried out in a CuSO_(4)solution with the substrate and tip potentials held at 10 mV and-30 mV vs.Cu/Cu~(2+),respectively,and STM feedback gain of 0.3 and setpoint current of 2 nA.A voltage pulse,typically 0.2 V and 10 ms depending on the z-sensitivity of the piezo,is applied on the z direction of the piezo to generate a Cu nanocluster.By repeating the procedure at desired positions,Cu nanocluster arrays or patterns can be constructed.In the second step,the CuSO_(4)solution is replaced with that of 0.1 mol/L HClO_(4) + 5 mmol/L K_(2)PtCl_(6) for replacement of Cu clusters with the Pt.Since the reduction of each Pt(IV) ion consumes two Cu atoms,the Pt nanoclusters thus obtained are lower than the original Cu nanoclusters.Besides,the Cu UPD monolayer-covered Au(111) surface becomes atomically rough as only 50% of the Au(111) surface is covered by Pt clusters after replacement.XPS data showed that Cu has almost been completely replaced with Pt.