STM“Jump-to-contact”针尖诱导表面纳米构筑是目前水溶液中具有最高分辨率的一种表面纳米构筑技术.然而,一些金属因其具有较高的内聚能而难以发生针尖原子向表面的转移,限制了该技术的广泛应用.本文建立了以STM构筑-置换两步法获得不能直接利用“Jump-to-contact”原理进行构筑的金属表面纳米团簇阵列,利用STM针尖“Jump-to-contact”诱导在Au(111)表面构筑Cu纳米团簇阵列,然后通过Pt-Cu置换的方法,制备出Au(111)表面的Pt纳米团簇阵列.
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.
[1]Kolb D M,U llm ann R,W ill T.Nanofabrication of sm allcopper c lusters on Gold(111)E lectrodes by a scann ingtunneling m icroscope[J].Sc ience,1997,275:1097~1099.
[2]Kolb D M,Engelm ann G E,Z iegler J C.Nanoscaledecoration of electrode surfaces w ith an STM[J].SolidState Ion ics,2000,131:69~78.
[3]Engelm ann G E,Z iegler J C,Kolb D M.E lectrochem i-cal fabrication of large arrays of m etal nanoc lusters[J].Surf.Sc i.,1998,401:L420~L424.
[4]Engelm ann G E,Z iegler J C,Kolb D M.Nanofabrica-tion of sm all pallad ium c lusters on Au(111)E lectrodesw ith a scann ing tunnelling m icroscope[J].J.E lectro-chem.Soc.,1998,145:L33~L35.
[5]Zhang Y,M aupai S,Schmuk i P.EC-STM tip inducedCd nanostructures on Au(111)[J].Surf.Sc i.,2004,551:L33~L39.
[6]M aupai S,Dakkouri A S,Stratm ann M,et al.Tip-in-duced nanostructuring of Au3Cu(001)w ith an electro-chem ical scann ing tunneling m icroscope[J].J.E lec-trochem.Soc.,2003,150:C111~C114.
[7]Johnstone R A W,W ilby A H,Entw istle I D.Hetero-geneous catalytic transfer hydrogenation and its relationto other m ethods for reduction of organ ic compounds[J].Chem.Rev.,1985,85:129~170.
[8]Pellet R J.Hydrogen transfer catalysis by p latinum onzeolites[J].J.Catal.,1998,177:40~52.
[9]Tian Z Q,Jiang S P,L iang Y M,et al.Synthesis andcharacterization of p latinum catalysts on mu ltiwalledcarbon nanotubes by interm ittent m icrowave irrad iationfor fuel cell app lications[J].J.Phys.Chem.B,2006,110:5343~5350.
[10]W aszczuk P,Lu G Q,W ieckowsk iA,et al.UHV andelectrochem ical stud ies of CO and m ethanol adsorbedat p latinum/ruthen ium surfaces,and reference to fuelcell catalysis[J].E letroch im ica Acta,2002,47:3637~3652.
[11]C lavilier J,Faure R,Gu inet G,et al.Preparation ofmono-crystalline Pt m icroelectrodes and electrochem i-cal study of the p lane surfaces cut in the d irection ofthe(111)and(110)p lanes[J].J.E lectroanal.Chem.,1980,107:205~209.
[12]Kolb D M,Engelm ann G E,Z iegler J C.On the unu-sual electrochem ical stab ility of nanofabricated copperc lusters[J].Angew.Chem.Int.Ed,2000,39:1123~1125.
[13]B rankovic S R,W ang J X,Ad ic′R R.M etal mono-layer deposition by rep lacem ent ofm etal layers on elec-trode surface[J].Surf.Sc i.,2001,474:L173~L179.
