SGER: Surface and Sub-Surface Imaging at Nanometer Scales Using Picosecond Thermoacoustic Microscopy

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ABSTRACTProposal Number: CTS-9910823Principal Investigators: A. MajumdarThe ability to manipulate matter and to observe and control physical and biological phenomena at nanometer scales is providing researchers with rich opportunity for basic science as well as new technology. One of the most important aspects of this research is the ability to observe objects and phenomena with nanometer scale spatial resolution. The scanning tunneling (STM) and the atomic force microscopes (AFM) and, in general, the whole class of scanning probe microscopes (SPMs), have made it possible to image single atoms and observe single biological molecules on a solid surface. The current SPMs, however, fail to address some fundamental needs in nanotechnology, namely: (i) the ability to image objects below the surface, i.e. in three dimensions, with nanometer vertical and lateral resolution; (ii) the ability to perform spectroscopy in order to identify the chemical content of the material. Imaging in three dimensions is extremely important because of the following reasons: (a) microelectronics chips are becoming increasingly multilayered; (b) biological molecules have three-dimensional structure and function; (c) nanophase materials are generally three dimensional. The ballistic electron emission microscope (BEEM) [1] is able to image and perform electron spectroscopy below the surface to a distance of about 100-200 A. However, it needs a metal and a semiconducting material to operate. Magnetic resonance imaging using the AFM [2,3] can provide a three-dimensional picture, although one needs to perform experiments at very low temperatures ( 1 K) to obtain sub-micron resolution. To image objects in three dimensions, there are two possible approaches: (i) to either emit some form of radiation and measure its time-resolved scattering (elastic or inelastic) at a certain point in space (eg. ultrasonic imaging); or (ii) to confine resonance excitation to a certain location by an external field (eg. nuclear magnetic resonance). This project will use the first approach. It will combine two techniques - scanning probe microscopy for high lateral resolution and picosecond thermoacoustics for high vertical resolution - to obtain three-dimensional images with nanometer-scale resolution.