A ‘nano’ drum

Print edition : July 22, 2016

Artist's impression of two coupled, vibrational models of a graphene drum. Photo: Nanoelectronics Group, TIFR, Mumbai

RESEARCHERS in the Tata Institute of Fundamental Research (TIFR), Mumbai, have demonstrated the ability to manipulate the vibrations of a drum of nanometre-scale thickness, which would be the world’s smallest and most versatile drum. This work, according to a TIFR press release, has implications in improving the sensitivity of small detectors of mass, very important in detecting the mass of small molecules like viruses. This also opens the door to probing exciting new aspects of fundamental physics.

The work, done by John Matthew and his associates, made use of graphene, a one-atom thick wonder material, to fabricate drums that have highly tunable mechanical frequencies and coupling between various modes. Coupling between the modes was shown to be controllable, which led to the creation of new, hybrid modes and, further, allowed amplification of the vibrations. The work has been published in a recent issue of the journal Nature Nanotechnology,

The experiment consisted of studying the mechanical vibrational modes, or “notes”, similar to a musical drum. The small size of the drum (diameter 0.003 mm, or 30 times smaller than the diameter of human hair) gave rise to high frequencies of vibration for the “nano drum” in the range of 100 megahertz (100 million times/second). The work showed that the notes of these drums could be controlled by making use of an electrical force that bends, or strains, the drum. The bending of the drum also caused different modes of the drum to interact with each other. “Using this interaction we can now show that energy can be transferred between the modes, leading to the creation of new ‘notes’ in the drum,” says Mandar Deshmukh, under whose supervision this work was carried out. The rate of energy transfer could be precisely controlled by electrical signals that modulate the coupling. The work, in addition, made use of the mechanical mode coupling to manipulate the energy lost to the environment and demonstrated amplification of the vibrational motion, equivalent to an increase in sound from the drum. At low temperatures, the high mechanical frequencies would allow studies of energy transfer of a quantum mechanical nature between the notes, says the press release. The coupling between various notes of the drum could also be engineered to work as mechanical logic circuits and lead to improvements in quantum information processing. The ability to amplify the mechanical motion will also help improve the sensitivity of sensors based on nanoscale drums.

Compiled by R. Ramachandran.