Variable-Temperature KPFM Reveals Temperature-Dependent Charge Inhomogeneities in Monolayer Graphene

Understanding the behaviour of electrons in atomically thin materials presents a significant challenge in modern physics, and recent research addresses this by developing a new technique for precisely measuring local chemical potential. Namkyung Lee, Seungwon Jung, and Baeksan Jang, all from Seoul National University, alongside their colleagues, have created a variable-temperature Kelvin probe force microscopy system that operates without the need for liquid cryogens. This innovative approach allows researchers to map the electronic landscape of materials like graphene with unprecedented stability and sensitivity across a wide range of temperatures. The team demonstrates the power of their system by revealing subtle electronic variations and charge distributions within graphene heterostructures, offering crucial insights into the fundamental properties of these materials and paving the way for advancements in nanoscale electronics.

Mapping Nanoscale Potential in 2D Materials

Researchers are increasingly focused on two-dimensional materials, such as graphene, as potential building blocks for future electronic devices. These materials exhibit fascinating quantum properties, but understanding and controlling them requires probing their electronic behaviour at the nanoscale.

To overcome the limitation of conventional measurement techniques that provide only an averaged view, scientists are turning to advanced scanning probe microscopy techniques, specifically Kelvin probe force microscopy (KPFM), to map the distribution of electrical potential and reveal the intricate electronic landscapes within these materials. The team developed a new variable-temperature KPFM system that incorporates a cryogen-free cryostat, allowing for stable operation across a broad temperature range.

This innovative setup features custom-designed vibration isolation and feedback control mechanisms that minimize external disturbances and maintain a consistent tip-sample distance. The researchers demonstrated the capabilities of their system by studying monolayer graphene encapsulated within a hexagonal boron nitride layer.

Their measurements revealed spatially resolved electronic inhomogeneities and “charge puddles”, regions of varying electron density, within the graphene.

Exploring Electronic Structure with Nanoscale Resolution

The team’s work opens new avenues for exploring the fundamental properties of 2D materials and developing novel electronic devices. Their KPFM system represents a significant advancement in the field, providing a versatile tool for investigating the electronic properties of 2D materials.

Quantitative Analysis of Electronic Properties

The researchers also performed quantitative analysis of the data, allowing them to extract detailed information about the electronic structure of the graphene. By analysing the temperature-dependent slope changes of the chemical potential curves, they were able to evaluate the interaction-induced renormalization effect on graphene’s unique dispersion and density of states.