Jun 8 2015
A recent study published by NPL's Quantum Detection Group in Scientific Reports journal describes new prospects on the electronic properties of quasi-free standing graphene (QFSG) that could find applications in sensors and high speed electronics.
The study was carried out in association with the Institute of Electronic Materials Technology, Poland and the University of Surrey, UK. It was evident from the study that the electronic and structural properties of graphene changes at nano level as a result of hydrogen intercalation, where the material is decoupled from the silicon carbide supporting substrate.
The researchers observed that the introduction of hydrogen molecules between SiC and epitaxial graphene facilitates sudden changes in the material's electronic properties. This could result in carrier type changes and considerable increase in the carrier mobility.
The scientists could generate a complete chart of the surface potential distribution of graphene layers using the Kelvin probe force microscopy, for both QFSG on SiC and SiC supported epitaxial graphene. Further, based on the changes in potential distribution between the two systems which are related with Raman spectroscopy information, the scientist could identify changes in graphene layers' electronic properties.
"While electrons are main carriers in pristine epitaxial graphene, in the QFSG the main carriers are holes," Olga Kazakova, principal research scientist, explained.
Following Hall effect-based measurements, they also identified a three-fold increase in QSFG conductivity, a key parameter for future electronics applications.
Kazakova explained that the increase in carrier mobility is nearing the world record for graphene materials under ambient conditions.
Epitaxial graphene on SiC achieved using chemical vapour deposition method (CVD) has three key benefits: good structural quality, ability to scale-up to 4 inch size, and avoids the need to be transferred to other substrates, considerably simplifying the technological process.
However, the material conductivity reduces the interfacial layer between SiC and graphene, thereby restricting pristine epitaxial graphene applications in high speed electronics. After the formation of QFSG via hydrogen intercalation, the electronic properties of the material changes providing high electrical mobility.
"In our work, we showed for the first time how this process occurs on nanoscale," Kazakova said.
The study also proves the versatility of Kelvin probe force microscope in providing detailed information on surface phenomena.