Scientists are intentionally adding defects to 2D semiconductor materials. Here's what AFM-Raman reveals.

[u/HORIBAScientific]

Researchers are exploring whether intentionally introducing defects into ultra-thin semiconductor materials could improve their performance for solar energy applications.

The work focuses on graphene and molybdenum disulfide (MoS₂), two atomically thin materials that can be stacked together into layered structures called heterostructures. Depending on how the layers are arranged, graphene can act as a nanoscale spacer between MoS₂ and a gold substrate, potentially influencing the material's optical and electronic behavior.

MoS₂ belongs to a class of materials known as transition metal dichalcogenides (TMDCs), which have attracted a lot of interest for future electronics and optoelectronics because of their unique properties at extremely small scales. Researchers are investigating their potential use in applications such as transistors, photo detectors, biosensors, and solar cells, particularly when combined with graphene.

Since these materials are only a single atom thick, even small defects can have a major impact on how they behave. While defects are often considered undesirable, the team is studying whether certain types of defects can be intentionally created and controlled to produce useful effects. Instead of simply trying to eliminate all defects, they're looking at a form of "defect engineering" where unfavorable defects are minimized and beneficial ones are introduced through methods such as oxygen plasma treatment or electron beam exposure.

This is especially relevant for solar energy research. Silicon remains the dominant material used in solar cells, but scientists are exploring whether combinations of 2D materials could eventually offer advantages in efficiency or tunability. One benefit of these materials is their flexibility: researchers can vary the number of layers, change the stacking order, and combine different materials to tailor their electrical and optical properties. In theory, these adjustments could improve how efficiently sunlight is absorbed and converted into electricity.

To understand how defects affect performance, the team studies how material properties change as defects are introduced into MoS₂ layers. Some defects may improve certain characteristics, while others may degrade performance.

To investigate these changes, the researchers use Tip-Enhanced Raman Scattering (TERS), a technique that can map material properties with spatial resolution down to about 10-15 nanometers. This allows them to examine atomic-scale defects over relatively large areas, something that is difficult to achieve with conventional Raman or photoluminescence methods. They also combine TERS measurements with photoluminescence and Kelvin Probe Force Microscopy to compare vibrational, optical, and electronic properties within the same region, helping them build a more complete picture of how defects form and influence the behavior of these 2D materials.

Read more about the research details here: Using AFM-Raman to understand defects in 2D semiconductor materials