Quantification of 2D Interfaces: Quality of heterostructures, and what is inside a nanobubble

TL;DR

This paper introduces a novel optical imaging method to quantify the quality of 2D heterostructure interfaces and identifies water as the trapped material inside nanobubbles, advancing understanding and control of these systems.

Contribution

It presents a new optical imaging technique to assess interface quality and determine trapped materials in nanobubbles, enabling improved design of 2D heterostructures.

Findings

Optical imaging can quantify interface quality in 2D heterostructures.

Water is identified as the trapped material inside nanobubbles.

A new quality index parameter for heterostructure interfaces is proposed.

Abstract

Trapped materials at the interfaces of two-dimensional heterostructures (HS) lead to reduced coupling between the layers, resulting in degraded optoelectronic performance and device variability. Further, nanobubbles can form at the interface during transfer or after annealing. The question of what is inside a nanobubble, i.e. the trapped material, remains unanswered, limiting the studies and applications of these nanobubble systems. In this work, we report two key advances. Firstly, we quantify the interface quality using RAW-format optical imaging, and distinguish between ideal and non-ideal interfaces. The HS-substrate ratio value is calculated using a transfer matrix model, and is able to detect the presence of trapped layers. The second key advance is identification of water as the trapped material inside a nanobubble. To the best of our knowledge, this is the first study to show that optical imaging alone can quantify interface quality, and find the type of trapped material inside spontaneously formed nanobubbles. We also define a quality index parameter to quantify the interface quality of HS. Quantitative measurement of the interface will help answer the question whether annealing is necessary during HS preparation, and will enable creation of complex HS with small twist angles. Identification of the trapped materials will pave the way towards using nanobubbles for novel optical and engineering applications.