SINGLE QUANTUM DOTS AS SCANNING TUNNELING MICROSCOPE TIPS

We report the use of single quantum dot structures as tips on a scanni ng tunneling microscope (STM). A single quantum dot structure with a d iameter of less than 200 nm and a height of 2 mu m was fabricated by r eactive ion etching. This dot was placed on a 40 mu m-high mesa and mo unted on the tip of a STM. The topography of large structures such as quantum wires or gold test substrates is clearly resolved with such a tip. To check the transport properties of the tip, quantum dot arrays were fabricated on resonant tunneling double barrier structures using the same process parameters. Conventional tunneling spectroscopy clear ly resolved the OD states in our samples. Using a metal substrate as s econd electrode such STM tips can be used to perform high resolution e nergy spectroscopy on single dots and free standing wire structures. ( C) 1996 Academic Press Limited