李哲安-原子与分子物理-墙报-精品文档资料整理.ppt

University of Science and Technology of ChinaNonlinear inelastic electron scattering from Au nanostructures induced by localized surface plasmon resonanceZheAn Li 1,ChunKai Xu 1,2,and XiangJun Chen1,2,(1.Hefei National Laboratory for Physical Sciences at the Microscale and Department of Modern Physics,University of Science and Technology of China,Hefei,230026,China.2.Synergetic Innovation Center of Quantum Information and Quantum Physics,University of Science and Technology of China,Hefei,230026,China.)1.Introduction3.Result&Discussion2.Experimental4.Summary Spectroscopic techniques are powerful tools for investigating the chemical properties of materials at microscopic level.We developed a new instrument called scanning probe electron spectrometer(SPEES)as shown in Fig.1.It consist of a homemade STM and toroidal electron energy analyzer.Usually,the inelastic electron scattering probability is known to be very small.So,there is a huge technical challenge for high resolution measurements.This problem may be solved by recent discovery of a new physical process,named nonlinear electron scattering(NES)1,in which the intensity of the inelastic scattering electron signal can be nonlinearly enhanced by the external electric field.Recently,we report the nonlinear electron scattering(NES)experiments carried out on gold nanostructures on graphite surface2.Similar to the previous work on Ag nanostructures,the intensity of inelastic scattering electron due to Au surface plasmon polariton(SPP)excitation increases nonlinearly with respect to the external electric field.Fig.1(a)Three-dimensional view of SPEES.(b)Schematic diagram of the cross section of SPEES(The electrons trajectory is in highlight).The experimental arrangement is schematically shown in Fig.2.A tip made from a 0.42 mm tungsten wire by electrochemical etching was approached to a distance of micrometers from the grounded sample surface,which was prepared by evaporating 30 nm thin film of Au on freshly cleaved HOPG.The topography image of the sample surface is shown in the inset of Fig.2,where Au nanostructures can be observed.During the experiment,a negative voltage of hundred volts was applied to the tip,from which the electrons were field emitted and impacted with the sample surface.Then the backscattered electrons were collected and analyzed by the toroidal electron energy analyzer.Fig.2.The experimental arrangement.A tip is approached to a distance of micrometers from the grounded HOPG surface with Au nanostructures on it,the topography image of which is shown as the inset.The experiments are carried out under two tip-sample distances,80 m and 166 m.In Fig.3,five electron energy loss spectrums acquired at tip-sample distance 166 m with different tip voltages are shown,where the experimental data are denoted as scattered points and the fitted curves are indicated by solid lines.Each spectrum has been background-subtracted by polynomial function and normalized by the amplitude of the elastic scattering peak.The energy loss peak located at around 2.6 eV is attribute to the excitation of Au SPP.It can be seen that as the tip voltage increases,the intensity of the SPP peak will increase accordingly.Obviously,it indicates that the NES process has been observed for Au nanostructures.Fig.3 Five EELSs acquired at tip-sample distance 166m with different tip voltages and sample currents.Nonlinear electron scattering(NES)is a recently discovered physical process observed during the plasmonic excitation of silver nanostructures on graphite surface.In the present work,NES phenomenon is experimentally verified by on gold nanostructures by measuring inelastic scattering of electrons field-emitted from tungsten tip.The relative intensity of the electron-energy-loss peak associated with the plasmonic excitation of Au shows again to increase nonlinearly with the electric field generated by the tipsample bias,demonstrating the generality of NES process in plasmonic systems.1 ChunKai Xu et al.Nature Pyhsics.10,753-757(2014).2 ZheAn Li,ChunKai Xu,WenJie Liu,Meng Li and XiangJun Chen,“Nonlinear inelastic electron scattering from Au nanostructures induced by localized surface plasmon resonance”,submitted.5.Reference