Bringing ultimate depth to scanning tunnelling microscopy: deep subsurface vision of buried nano-objects in metals

TL;DR

This paper introduces a non-destructive STM-based method for visualizing and characterizing buried nano-objects up to 110 nm deep in metals by analyzing quantum well states, enabling 3D subsurface nanostructure imaging.

Contribution

The paper presents a novel STM/STS technique exploiting quantum well states for subsurface nano-object visualization up to 110 nm deep in metals, which was not previously achievable.

Findings

Able to detect buried nanoclusters up to 80 nm deep

Demonstrated non-destructive imaging of subsurface structures

Achieved depth estimation of 110 nm for buried nano-objects

Abstract

A method for subsurface visualization and characterization of hidden subsurface nano-structures based on Scanning Tuneling Microscopy/Spectroscopy (STM/STS) has been developed. The nano-objects buried under a metal surface up to several tens of nanometers can be visualized through the metal surface and characterized with STM without destroying the sample. This non-destructive method exploits quantum well (QW) states formed by partial electron confinement between the surface and buried nano-objects. The specificity of STM allows for nano-objects to be singled out and easily accessed. Then, their shape, size and burial depth can be determined by analyzing the spatial distribution and oscillatory behavior of the electron density at the surface of the sample. The proof of concept was demonstrated by fabricating argon nanoclusters embedded into a single-crystalline Cu matrix. Taking advantage of the specific electronic band structure Cu and inner electron focusing, we experimentally demonstrated that noble-gas nanoclusters of several nanometers large buried as deep as 80 nm can be detected, characterized and imaged. The ultime depth of this ability is estimated as 110 nm. This approach using QW states paves the way for an enhanced 3D characterization of nanostructures hidden well below a metallic surface.