Ultrasensitive Calorimetry Enabled by Suspended Semiconductor Nanostructures

在低温下的介观系统中，热传递和热平衡的发生方式与室温下的宏观系统非常不同。这是由于所涉及的小热容，和非常长的热松弛时间，以达到平衡与热储，环境。在极限情况下，热输运涉及系统和环境之间单一能量通道的交换。在该项目的前一阶段，研究人员首次观察到这种预测的热导量化。这为未来分子电子器件的热导率提供了一个重要的硬性上限。目前的项目继续研究纳米加工介观系统的热容：悬浮的半导体纳米结构是热隔离的，具有集成的传感器，允许局部引入热量和局部温度测量。用前所未有的灵敏度对微小样品进行热容测量应该是可能的。这将提供与小型化热探测器工程相关的数据，并将提供与分子尺度和超小型电子设备的功耗限制有关的关键信息。有了这种灵敏度水平，阐明涉及单个原子和分子的过程的量热实验也将首次成为可能。这项工作将向本科生、研究生和博士后研究人员介绍纳米制造的先进技术以及超灵敏测量的技术和原理。未来的电子学将可能基于分子尺度的器件。有源电子设备，在任何规模下，都需要电力来运行，而这些电力最终必须消散到周围环境中。然而，在分子尺度上，控制功耗的过程变得非常弱；因此，这可能是有问题的。这个领域直到1999年才被广泛探索，当时，在之前的一个nsf资助的研究项目中，研究人员观察到热导率的量化——热导率是能量从一个小系统传导到周围环境的基本限制。在他们目前的提案中，作者建议继续在这一领域进行研究，现在转向非常小系统的热容量，即它们“储存”能量的能力。他们的方法涉及悬浮半导体纳米结构，由他们开发的新的表面纳米加工工艺制造。这使得在纳米尺度上构建复杂的探索装置成为可能，其内部组件允许对其特性进行定量和精确的测量。在提出的研究计划中，这些将被用来获得对纳米尺度结构的热传输和热容的更完整的理解。它们也将被证明对小型化热探测器的工程非常有用，并将提供与分子尺度和超小型电子设备的功耗限制有关的关键信息。有了这种灵敏度，阐明涉及单个原子和分子之间热流过程的实验也将首次成为可能。这项工作将向本科生、研究生和博士后研究人员介绍纳米制造的先进技术以及超灵敏测量的技术和原理。

In mesoscopic systems at low temperatures, heat transport and thermal equilibration occur in a very different manner from macroscopic systems at room temperature. This is due to the small heat capacities involved, and very long thermal relaxation times to reach equilibrium with a heat reservoir, the environment. At the ultimate limit, thermal transport involves exchange of a single energy channel between a system and the environment. During the preceding phase of this project, investigators observed, for the first time, this predicted quantization of thermal conductance. This places an important, hard upper bound on the thermal conductance available through future molecular electronic devices. The current project continues the investigation of heat capacities of nanomachined mesoscopic systems: Suspended semiconductor nanostructures that are thermally-isolated and have integral transducers that permit the localized introduction of heat and local temperature measurements. Heat capacity measurements on minute samples with unprecedented sensitivity should be possible. This should provide data relevant to the engineering of miniaturized thermal detectors, and will provide crucial information relating to limits of power dissipation in molecular-scale and ultrasmall electronic devices. With this level of sensitivity, calorimetry experiments that elucidate processes involving individual atoms and molecules should also become possible for the first time. The effort will introduce undergraduates, graduate students, and postdoctoral researchers to advanced techniques in nanofabrication and in techniques and principles of ultrasensitive measurements.%%%Future electronics will likely be based upon molecular scale devices. Active electronic devices, at any scale, require power to operate and this must ultimately be dissipated to their surroundings. However at the molecular scale the processes that govern power dissipation become very weak; hence it can be problematic. This domain had remained largely unexplored until 1999, when, in a previous NSF-funded research program, investigators observed the quantization of thermal conductance -- a fundamental limit to the rate at which power can be conducted from a small system to its surroundings. In their current proposal, the authors propose to continue with research in this realm, turning now to the heat capacity of very small systems, i.e. their ability to "store" energy. Their approach involves suspended semiconductor nanostructures, fabricated by new surface nanomachining processes they have developed. These enable the construction of complex exploratory devices at the nanometer-scale, with internal components allowing quantitative and precise measurements on their properties to be carried out. In the proposed research program these will be utilized to obtain a more complete understanding of heat transport and the heat capacity of nanometer-scale structures. They should also prove to be extremely useful for the engineering of miniaturized thermal detectors, and will provide crucial information relating to limits of power dissipation in molecular-scale and ultrasmall electronic devices. With this level of sensitivity, experiments that elucidate processes involving heat flow between individual atoms and molecules should also become possible for the first time. The effort will introduce undergraduates, graduate students, and postdoctoral researchers to advanced techniques in nanofabrication and in techniques and principles of ultrasensitive measurements.