Tip-enhanced Raman spectroscopy of semiconductor nanostructures

Abstract

Raman scattering is a powerful probe of local bonding, strain, temperature, and other properties of materials via their influence on vibrational modes or optical phonons. Tip-enhanced Raman spectroscopy (TERS), in which plasmonic modes are excited at the apex of a metal-coated scanning probe tip, enables Raman scattering signals to be detected from nanoscale volumes with precise positional control. We discuss the application of TERS to characterize a variety of semiconductor nanostructures. In studies of Ge-SiGe core-shell nanowires, we measure spatially resolved Raman spectra along the length of a tapered nanowire to demonstrate the ability to measure local strain distributions with nanoscale spatial resolution. In tip-induced resonant Raman spectroscopy of monolayer and bilayer MoS 2 , we observe large enhancements in Raman signal levels measured for MoS 2 associated with excitation of plasmonic gap modes between an Au-coated probe tip and Au substrate surface onto which MoS 2 has been transferred. Transitions in B exciton photoluminescence intensity between monolayer and bilayer regions of MoS 2 are observed and discussed. Significant differences in nanoscale Raman spectra between monolayer and bilayer MoS 2 are also observed. The origins of specific resonant Raman peaks, their dependence on Mo S 2 layer thickness, and spatial resolution associated with the transition in Raman spectra between monolayer and bilayer regions are described.