Optical System For Small-integrated TERS Instrument

Tip-enhanced Raman spectroscopy(TERS)is an ingenious combination of the scanning probe microscope(SPM)and the surface-enhanced Raman spectroscopy(SERS).TERS uses a sharp probe to convert the near-field evanescent photons with information of refined structure to the propagating scattering that can be detected in the far-field by using conventional optics,TERS also produces enormous enhancement of the electromagnetic field locally at the tip end,thus to obtain high spatial resolution that overcome the diffraction limit and high sensitivity spectral signal.Besides,the topographic information that describing the surface shape can be directly correlated with the spectroscopic data that demonstrating the molecular structure by scanning the tip over the sample surface.These advantages allow TERS to have wide applications,and it shows great potential in bioinstrumentation,nanomaterials and surface sciences.However,most commercial TERS instruments and homemade setups of measurement in laboratory are found to have complicated structure,poor coordination,low optical efficiency,poor stability,bulk size and high cost,which restrict its wide application.Therefore,it will be of important research significance and promising application to develop a high sensitivity,high spatial resolution,and good coordination small-integrated TERS instrument.This thesis focuses on the development of TERS instrument,and developed an optical system for small-integrated TERS instrument.The innovation of this work is the integration and miniaturization of optical system of TERS instrument,and solving the problem of deterioration of sensitivity and spectral resolution in the miniature.Optics was simplified,optical path was decreased,and exciting and collecting optics was directly coupled with Raman spectrometer to increase the throughput of the optical system;The structure of the Raman spectrometer was developed and the layout of optical components was optimized to make the structure of the optical system compact and reasonable;In order to make sure that the laser focus,the tip and the sample were coupled precisely,a white light illumination and micro-imaging optics was introduced,so that the laser focus,the lighting point and the collecting point of signal was strictly confocal;Besides,the far-field background noise was reduced by developing experimental method,so that to increase the signal to noise ratio(SNR)of the TERS instrument.The structure of the optical device is compact,which is in favor of in-situ measurement,and it has a high sensitivity and spectral resolution.A TERS setup of side illumination and collection was established by combining the optical system with a commercial STM head,and the tip enhanced Raman spectrum of 4'-(pyridine-4-yl)-biphenyl-4-yl)methanethiol(4-PBT)molecule was obtained.Next,the compact optical system will be coupled with a homemade specific STM head and coordinative circuit to develop a small-integrated TERS instrument,so that to promote the practical application of TERS instrument.