Nanostructured graphene enables the detection and imaging of “colors” in the infrared range

University of Central Florida (UCF) researcher Debashis Chanda, a professor at UCF’s NanoScience Technology Center, has developed a new technique for detecting long-wave infrared (LWIR) photons of different wavelengths, or “colors.”

The research was recently published in Nano letters.

The new detection and imaging technology will find application in analyzing materials based on their spectral properties or in spectroscopic imaging and thermal imaging applications.

Humans perceive primary and secondary colors, but not infrared light. Scientists believe that animals such as snakes and nocturnal species can perceive different wavelengths in the infrared, almost in the same way that humans perceive colors.

According to Chanda, infrared, particularly LWIR, detection at room temperature has long been a challenge due to the weak photon energy.

LWIR detectors can be broadly divided into cooled and uncooled detectors, says the researcher.

Cooled detectors are characterized by high detection performance and fast response times, but their reliance on cryogenic cooling significantly increases their cost and limits their practical applications.

In contrast, uncooled detectors such as microbolometers can operate at room temperature and are relatively less expensive, but have lower sensitivity and slower response times, says Chanda.

Both types of LWIR detectors lack dynamic spectral tunability, so they cannot distinguish photon wavelengths of different “colors.”

Chanda and his team of postdoctoral researchers wanted to go beyond the limits of existing LWIR detectors and worked to demonstrate a highly sensitive, efficient and dynamically tunable method based on nanostructured graphene.

Tianyi Guo is the lead author of the study. Guo completed his doctoral studies at UCF in 2023 under Chanda’s mentorship. This newly discovered method is the culmination of research conducted by Guo, Chanda and others in Chanda’s lab, Chanda says.

“No currently available cooled or uncooled detectors offer such dynamic spectral tunability and ultrafast response,” says Chanda. “This demonstration highlights the potential of engineered monolayer graphene LWIR detectors that operate at room temperature and provide high sensitivity and dynamic spectral tunability for spectroscopic imaging.”

The detector is based on a temperature difference in materials (known as the Seebeck effect) within an asymmetrically structured graphene film. When exposed to light and interacting, the patterned half generates hot charge carriers with significantly increased absorption, while the unpatterned half remains cool. The diffusion of the hot charge carriers creates a photothermoelectric voltage that is measured between the source and drain electrodes.

By structuring the graphene in a special arrangement, the researchers achieved improved absorption and were able to further electrostatically tune the LWIR spectral range and enable better infrared detection. The detector significantly exceeds the capabilities of conventional uncooled infrared detectors – also called microbolometers.

“The proposed detection platform paves the way for a new generation of graphene-based uncooled LWIR photodetectors for diverse applications such as consumer electronics, molecular sensing and space travel, to name a few,” says Chanda.