Germanium was the first material used for transistors -- back in 1947 when AT&T Bell Labs invented them. Since then silicon has taken over as the semiconductor material of choice, even though germanium has witnessed a resurgence in recent years in everything from high-speed digital transceivers to analog optical detectors.
Other researchers have tried to fabricate germanium in atomically thin monolayers but have run into similar problems to fabricating monolayers of graphene--namely, the inability to grow perfectly crystalline lattices across an entire wafer. To solve the problem, Goldberger first wedged calcium atoms between separate germanane monolayers, thus easing their large-scale growth, then dissolved away the calcium and plugged the holes in the lattice with hydrogen atoms to prevent oxidation. As a result, the researchers were able to exfoliate (peel off) the germanane monolayers for testing.
Next the researchers aim to fabricate real devices with the new material as well as experiment with different termination molecules to act as dopants, which the team will then characterize for both electrical and optical properties. Currently, the material is stable up to 75 degrees Celsius (167 Fahrenheit) which the team also hopes to raise for use in a wider range of applications.
Assisting in the research was Goldberger's student, Elizabeth Bianco who recently won the Notre Dame Connect competition for her work on germanane. Also contributing were Ohio State researchers Sheneve Butler, Shishi Jiang, Oscar Restrepo and Wolfgang Windl. Funding was provided by the National Science Foundation, the Army Research Office and Ohio State University.