Small mesas and holes in split-gate quantum wires acting as ‘‘artificial impurities’’ fabricated with scanning tunneling microscope

Abstract

This article discusses fabrication of ‘‘artificial impurities’’ such as small mesas and holes with a scanning tunneling microscope (STM) in split-gate quantum wires and their transport properties. In order to make and properly place these small structures on the wire surface, we employed a combined STM/scanning electron microscope system operated in vacuum. The fabrication method involves simple electrical evaporation with a Tungsten tip. In a wire having a small mesa (70 nm diameter and 15 nm height) at the center, clear Coulomb blockades and staircases corresponding to the size of the mesa were observed at 0.3 K. In a wire with a hole (200–300 nm upper diameter and 100–150 nm depth) near the gate electrode, both quantized plateaus and damage-induced telegraphic switching were observed in the two-terminal conductance also at 0.3 K. This means that a deep hole at the wire edge can behave, depending on the evaporation condition, either as a simple constriction or as a constriction with electron traps.