A research team comprising Kirill Bolotin, A.K.M. Newaz, Sokrates Pantelides, Bin Wang and Yevgeniy Puzyev from the Vanderbilt University has confirmed that charged impurities present in graphene are the source of interference, and slow down the electron flow through the nanomaterial-based devices.
An image of a suspended graphene device made by a scanning probe microscope. The graphene sheet is the orange-colored layer suspended between six rectangular columns made of silicon dioxide and capped by gold. (A.K.M. Newaz / Bolotin Lab)
Using a suppression technique, the research team was able to achieve a room-temperature electron mobility, which is three folds quicker than that reported in earlier graphene-based devices. However, the team was not able to confirm one of the alternative theories, which says that ripples present in the graphened sheets are a major source of electron scattering. The study findings have been reported in Nature Communications.
Bolotin explained that graphene is highly sensitive to external factors. Hence the electrons flow via the graphene sheets get scattered by the electrical fields formed by the charged impurities, making the nanomaterial-based transistors heat up more and operate slowly.
To solve the electron mobility problem, the research team submerged graphene sheets in various liquids and recorded the electric transport properties of the nanomaterial. The team discovered that the electron mobility of the nanomaterial is drastically increased when it was suspended in electrically neutral liquids, which are capable of absorbing huge quantities of electrical energy. With anisole, a colorless aromatic odor liquid used mainly in perfumery, the team attained electron mobility of 60,000, which is a record value.
Bolotin informed that the electrical fields, formed from the charged impurities and suppressed by the liquids, make the electrons to travel with fewer barriers. The identification of the source of interference affecting graphene’s electrical performance paves the way to develop more reliable device designs.
According to Bolotin, graphene’s high sensitivity to its surroundings can be used to produce different types of highly sensitive sensors. The nanomaterial is biocompatible as it is made completely of carbon, making it suitable for producing biological sensors.