Development Of STM Head For TERS Instrument

Scanning tunneling microscopy(STM)with high spatial resolution combined with surface-enhanced raman spectroscopy(SERS)is one of combination in tip-enhanced raman spectroscopy(TERS)instruments.This combination can be used to detect nanoscale appearance characterization and nano-local Raman spectroscopy.At present,TERS instruments used in most laboratories are a simple combination of Raman spectrometer and commercialized STM.The STM is not designed for TERS instrument specifically,which results in some problems,such as function waste,mismatch of scanning mode,insufficient operation space and so on.Some manufacturers also provide integrated TERS instruments,but the price of these instruments are too high for most laboratories.In addition,the integrated instruments cannot meet the requirements of a variety of scientific researches.Therefore,it is necessary to develop a STM head for TERS instrument,which can avoid some shortcomings of commercialized STM,improve the accuracy of measurement results,reduce the costs and facilitate its' expansibility.In this paper,a STM head suited for TERS instrument was developed.The system was driven by piezoelectric ceramics and assisted by the self-designed differential capacitive sensor as a displacement feedback to achieve closed-loop control,so as to improve the scanning accuracy.In the mechanical structure,reed design was used in the system,so as to achieve a wide range of scanning.Sufficient space was reserved around the tip,so it was easy for objective to close the tip and the sample to emit lasers and collect TERS signals.In the circuit design,a corresponding current detection circuit was designed to detect the tunnel current.The corresponding drive circuits were designed to control devices such as piezoelectric ceramics,differential capacitance sensors and so on.At last,main control circuit was designed to get the signals and control the scanning mode,so as to make the system suit for TERS instrument.The mechanical structure was simulated by simulation software ANSYS and the circuits which mentioned above was tested.Simulation and experiment results showed that the mechanical structure could realize a wide range of scanning,resolution of the differential capacitive sensor was high,and the current detection circuit could detect the current at the nA level accurately.The STM head was assembled and it was used to carry out the experiment of detecting appearance characterization and tip-enhanced Raman spectroscopy.The experiment results met the expected requirements.