Confinement Effects at the Superfluid Transition of 4He

通常人们处理的系统中，空间维度在热力学行为中不是一个相关变量。也就是说，一半大或两倍大的系统在被质量归一化时表现相同。在空间维度被制作得如此之小以至于可以与系统的相关长度相媲美的情况下，情况并非如此。在二阶相变的情况下，一个长度尺度随着相变的接近而发散。在这种情况下，如果一个人通过强加的空间边界来限制这种分歧，他就会从根本上影响行为。这种情况将在氦超流跃迁的情况下进行研究。要做这项工作，必须有一种达到均匀约束的方法。已经证明，两个硅晶片可以以这样的方式间隔，以便在大的横向尺寸上实现均匀的亚微米限制。这些结构可以用于拟议的研究，并且具有技术重要性。例如，键合过程可用于实现大规模的绝缘体上硅结构。目前的半导体技术已经将有源电子的集成推进到非常小的尺寸。进一步突破这些限制在技术上是具有挑战性的，也是重要的，科学地提出这样的问题：越来越小的系统是否只是大系统的小版本。在可以有效放大较小维度的影响的其他情况下，也可以提出类似的问题。为了进行这样的研究，人们必须以可靠的方式制造小型结构，并开发新的测量技术。为这项工作制作的结构将由两个硅晶片组成，它们以一种非常小的间隙连接在一起。在这个间隙中，将引入一种液体，并研究它在经历相变时的性质。这些研究的总体结果将对硅键合过程具有技术意义，并将导致对非常小系统的行为有更好的理解。＊＊＊

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. ***