Novel local density of state mapping technique for low-dimensional systems.

Abstract

A novel local density of state (LDOS) probing method for low-dimensional electron systems is proposed. By applying a two-dimensional fast Fourier transform to a real-space image obtained by scanning tunneling microscopy (STM), visualization of a complementary image in k-space can be realized. Especially, low-dimensional Fermi contours can be extracted by applying the k-space imaging to real-space images containing sufficient LDOS information around the Fermi level. To realize a more enhanced LDOS visualization in both spaces, we have proposed the use of special materials for STM tips, which have relatively large LDOSs at the Fermi level. To demonstrate this idea, several kinds of STM tips (Ag, Au, W and Nb) with different types of LDOSs were developed. An Au(111)-(22 x square root(3)) reconstructed surface, where Shockley surface-state electrons form a nearly free electron gas, was selected as a test sample for the LDOS extraction. Visualization of standing waves in the surface LDOS modulated by herringbone reconstruction was attempted using the various types of STM tips. Significant effects of the LDOSs of the STM tips were clarified.