Coulomb blockade regions in sputter-deposited titanium nitride films

TL;DR

This study uses scanning tunneling microscopy to investigate Coulomb blockade phenomena in sputter-deposited TiN films at cryogenic temperatures, revealing quantum dot states and tunneling asymmetries.

Contribution

First detailed observation of Coulomb blockade regions in sputter-deposited TiN films, linking nanoscale electronic features to film microstructure.

Findings

Coulomb blockade signs observed in TiN films at 4.2 K

Asymmetric peak structures indicate different tunneling barriers

Constant peak spacing suggests quantum dot states within the blockade area

Abstract

We present topographic and spectroscopic scanning tunneling microscopy measurements taken on a 21 nm thick TiN film at a temperature of 4.2 K -- above the superconducting transition temperature (T_c = 3.8 K) of the sample. The film was polycrystalline with crystallite diameters of d~19 nm, consistent with other films prepared under similar conditions. The spectroscopic maps show on average a shallow V-shape around V_b = 0 V consistent with a sample near the Mott insulation transition. In selected regions on several samples we additionally observed signs of Coulomb blockade. The corresponding peak structures are typically asymmetric with respect to bias voltage indicating coupling to two very different tunneling barriers. Furthermore, the peak structures appear with constant peak-peak spacing which indicates quantum dot states within the Coulomb blockade island. In this paper we discuss one such Coulomb blockade area and its implications in detail.