| This paper mainly includes the co-construction of one ultrahigh vacuum(UHV)-varying temperature(VT)-optical scanning tunnel microscope(OSTM)system,and the research of growing few-layered well-ordered nanostructures for 4,4 "-diamino biphenyl(DAT)and pentacene on Au(110)and quasi-free-standing graphene nanoislands on Ag(110)by using this homemade STM system.In addition,as for STM system,there are several disadvantages,such as low chemical-analysis ability and temporal resolution,which limit its further development,and combining STM with ultrafast laser technique can improve its capability.Therefore,the ultrafast-laser optical path has been designed and constructed.1.The structure of UHV-VT-OSTM includes the chamber structure,vacuum pumps,gas station,the stage for processing tip and sample,STM scanning head,continuous-flow cryostat and the optical stage for adjusting the lens.After construction,the whole system was tested and it could work at each setting temperature and good spatial resolution had been achieved at each temperature.In addition,it is easy for the system to be ramped from one temperature to another,and its real temperature variation for one setting temperature is low,on the order of 10 mK during one hour.Therefore,the system has reached the original goal.2.Self-assembling structures of single layer 4,4"-diamino biphenyl(DAT)on Au(110)were formed by controlling sample temperature after depositing molecules.After annealing the sample at 100 ?,there was(1×5)surface reconstruction on Au(110)with DAT molecular configuration of side by side mode,forming one ladder-type structure.While the sample was annealed at 200 ?,STM images show three distinct domains,including DAT molecules on a 1×3 reconstructed surface,dehydrogenated molecules with two hydrogen atoms detached from one amino group(-2H-DAT)on a 1×5 reconstructed surface and dehydrogenated molecules with four hydrogen atoms detached from two amino groups(-4H-DAT)on a 1×3 reconstructed surface through N-Au bonds.Furthermore,after annealing the sample to 350 ?,STM image shows only one self-assembled structure with-4H-DAT molecules on a 1×3 reconstructed surface.Relative STM simulations of different self-assembled structures show excellent agreements with the experimental STM images at different annealing temperatures.Further DFT calculations on the dehydrogenation process of DAT molecule prove that the dehydrogenation barrier on a 1×5 reconstructed surface is lower than that on 1×3 one,which demonstrates the experimental results that the formation temperature of a 1×3 reconstructed surface is higher than that of a 1×5 one.3.One-dimensioned metal-organic molecular chains on Au(110)for pentacene molecules with gold atoms can be constructed by controlling coverage and annealing temperatures.As for pentacene molecules on Au(110)with molecular coverage from sub-monolayer to monolayer,annealing the sample at 200 ? could induce the formation of both(1×3)and(1×6)surface reconstructions and pentacene molecules were with end-to-end or side-by-side in those two structure,in respect.Because of the interaction of pentacene molecules and the surface,there was one bright center for pentacene molecule in(1×6)reconstruction.After annealing the monolayer sample at 250 ?,pentacene molecules just existed in the(1×6)reconstruction through coordination between native Au atoms and the-CH-of the pentacene,forming onedimensional metal-organic chains.In a second layer,pentacene molecules adopted only the side-by-side configuration on top of pentacene molecules in(1×3)surface reconstruction at 200 ?,which revealed detailed interface information about the initial growth of the pentacene crystal system on metals.4.Quasi-free-standing Graphene islands can be grown by depositing carbon atoms directly onto a hot single crystal Ag(110)surface,using solid carbon source.First,graphene nano-islands with morphologies tuned by carbon flux and substrate temperatures are fabricated.Moiré superstructures are found to be superposed on the graphene islands,corresponding to the islands' varied orientations and periodicities in respect to the underling Ag(110)substrate.Both STS and Raman spectroscopy indicate weak interaction between graphene and the substrate,which is further confirmed by STM tip induced graphene flake movement.5.Due to its low temporal resolution and lack of chemical-relative analysis,combination of STM system and ultrafast laser technique is expected to improve the whole STM system's capability,which is vital for the research of obtaining high spatialtemporal resolution at the same time,tip-enhanced Raman Spectrum and photo-induced chemical reaction or transformation.On the basis of the optical pump-probe technique,the ultrafast-laser optical path for OSTM has been designed and constructed. |
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