Confinement Effects at the Superfluid Transition of 4He

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9623831 Gasparini Usually one deals with systems where the spatial dimension is not a relevant variable in the thermodynamic behavior. That is, systems half as large or twice as large behave identically when normalized by the mass. This is not the case in situations where the spatial dimensions are made so small that they become comparable to a relevant length of the system. In the case of a second-order phase transition, one has a length scale which diverges as the transition is approached. In this case, if one limits this divergence by an imposed spatial boundary, one affects the behavior in a fundamental way. This situation will be studied in the case of helium at the superfluid transition. To do this work one must have a way of achieving uniform confinement. It has been shown that two silicon wafers can be spaced in such a way as to achieve uniform sub-micrometer confinement over large lateral dimensions. These structures can be used for the proposed studies and have, as well, technological importance. The bonding process, for instance, can be used to achieve large-scale silicon-on-insulator structures.. %%% Present semiconductor technology has pushed the integration of active electronics to very small dimensions. It is technologically challenging and important to push these limits further, and scientifically to ask the question whether the ever-smaller systems will behave simply as smaller versions of the larger system. A similar question can be asked in other circumstances where the influence of the smaller dimensions can be effectively amplified. To perform such studies one has to make small structures in a reliable way, and develop new measuring techniques. The structures which will be made for this work will consist of two wafers of silicon bonded to each other in such a way that a very small gap remains. In this gap a liquid will be introduced and its properties as it undergoes a phase transformation will be studied. The overall results of these s tudies will have technological implications for the silicon-bonding process, and will lead to a better understanding of the behavior of very small systems. ***