Confinement and Scaling of 4He at the Superfluid Transition
Francis Gasparini Principal Investigator
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9972287<br/>Gasparini<br/><br/>This is a condensed matter physics project employing micro-scale cells to investigate the critical behavior of helium-4. Properties of a system which is small on a relevant length scale are greatly modified when compared to its bulk limit. This is especially true near a phase transition. Issues which are normally irrelevant, such as the shape of the sample or its surfaces now matter. Understanding of these small systems has wide implications. This is also relevant in the area for applications, given for example the continued miniaturization of devices. It is also true for theoretical reasons, since often calculations involve the extrapolation, not always justified, from a small to a large sample. The research to be done combines silicon technology and direct wafer bonding to form small structures in which liquid helium is introduced. It is the properties of this liquid near a phase transition which is studied. Graduate and undergraduate students are involved in this effort. The students are trained in silicon processing, low temperature technology, and a variety of experimental techniques and controls. Diagnostic tools involve laser optics and infrared imaging. Students receive an broad training interacting with researchers in different laboratories, both on campus and at national facilities. These student move on to a variety of careers in education and technology development.<br/>%%%<br/>One thinks of materials as having certain properties which do not depend on their size or shape. A metal will remain a metal no matter how small the sample. This is true within certain bounds. However, there is clearly a limit to this. One might think that a million atoms, or perhaps a thousand, might be as low as one could go. One does not know in general the answer to this, it requires investigations for specific properties and materials. Often very small samples will display new and different properties. This has technological implications in miniaturizations of devices. The research to be done will involve measurements of a small quantity of helium-4 undergoing a superfluid phase transformation. It requires the use of silicon technology, and a unique process developed in previous work, to construct structures as small a few hundred atoms. Students involved in this work, both graduate and undergraduates, will receive a broad technical training. This will include the use of facilities at the National Nanofabrication Facility at Cornell University, and local facilities for various diagnostic and experimental measurements. These students will be well diversified in their training, and able to move on to careers both in industry and academia.