Lin HaoNational Physical Laboratory，UK
Prof. Ling Hao is leading work on applications of nanoscience, superconducting electronics and microwave technology for precision measurements, recently focussing on low dimensional carbon, including carbon nanotubes and graphene transport measurements. She is a Principal Research Scientist in the Quantum Detection Group at the UK’s National Physical Laboratory (NPL). Ling is a Fellow of the Institute of Physics and a visiting professor at Imperial College, London, Harbin Institute Technology and Fudan University, China. She has published more than 140 research papers in refereed journals as well as writing four book chapters. She is a member of the Institute of Physics Superconductivity Committee.
Title：Graphene Self-Supporting Drums for NEMS and Sensors
SymposiumSensors
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Abstract
The extremely low areal density and high strength of graphene monolayers make the material very attractive for mechanical nanoelectromechanical systems (NEMS) resonators. These can form the basis of a number of highly sensitive measuring sensors for mass, force and displacement. In this presentation we report our method for preparing substrates with suitably patterned array of holes, across which chemical vapour deposition (CVD) grown graphene may be transferred. This provides a range of graphene ‘drums’, varying in size from 1 um to 40um in diameter. Optimisation of the transfer method onto the patterned substrates has led to minimum amount of polymer contaminant. Raman microscopy has been used to confirm the layer number of the transferred films and scanned probe microscopy (atomic force microscopy (AFM) and scanning Kelvin probe microscopy (SKPM) have been carried out on a wide selection of drums (see Fig. 1). The former technique has been used to map the force-deflection curves across the surface of several drums, allowing a value for Youngs modulus for the suspended graphene to be derived. The mechanical resonant properties of the drums have also been determined in a system where the substrate is mounted on a piezoelectric vibrator. A scanned near-field microwave microscope is then brought close to a drum and the drum’s resonant frequencies can be measured as the piezo driving frequency is varied. The results for resonant frequencies and Q values provide another method for examining the mechanical properties of the suspended films.
A key issue for the application of these drums is to optimize the mechanical quality factor Q as this parameter determines the sensitivity for force, mass of displacement detection. Initial Q values observed were only around 50 but we have been able to increase this by more than a factor of 10 times by paying attention to the underlying substrate structure. We have also been able to provide a means for removing any air trapped in the well beneath the film by means of deep reactive ion etching (Bosch process) to provide a hole from the base of the well through the entire 0.5mm thick substrate.
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