Casimir Forces in Dynamic Geometries for MEMS/NEMS Design

该项目的目标是利用理论物理学在卡西米尔力计算方面的最新进展，为纳米技术工程师提供适合设计优化的计算工具，同时为实验学家制作和提供教材，为有效利用这些计算工具提供足够的背景知识。本教材将使与卡西米尔力计算相关的量子场论的各个方面为工程师所理解。量子噪声现象在量子光学（激光物理学）中是众所周知的：正如海森堡的不确定性原理使粒子不可能同时具有明确定义的位置和速度一样，它也阻止了电磁振荡具有精确的零（均方根）振幅。在激光器中，这种量子噪声起着重要的作用，因为它可以在启动时最初播种放大过程。从电磁的角度来看，任何设备都由反射或吸收光的组件组成，因此具有一组高谐波的特征，类似于乐器。同样，就像乐器一样，可能振荡的频率结构在很大程度上取决于设备的几何形状（例如，声学情况下的鼓）。即使没有振荡被激发（仪器不产生声音），所有的谐波仍然单独受到量子波动的影响，并且随着几何设置的任何变化（调整仪器）改变振荡频率，量子噪声能量的变化产生了可测量的力：卡西米尔效应。虽然这些量子力对大型物体来说并不重要，但对于典型间隙尺寸在几十纳米范围内的系统来说，它们变得相当强大。特别是，它们是纳米机器粘滞的主要原因，即机器的一部分与另一部分接触并粘滞导致设备故障。不幸的是，它们的行为往往违背了天真的直觉：虽然人们会期望相互远离的表面会引起较低振荡频率的转变，从而减少能量，但详细的研究表明，卡西米尔力通常是有吸引力的。然而，在非常特殊的条件下，排斥力可以在一些涉及某些浸入液体的巧妙设计的系统中得到证明。此外，由于这些力以不同寻常的方式强烈依赖于几何形状和光学吸收特性，因此可靠的定量计算非常困难-或者更确切地说，如果不采用相当新颖和冒险的计算方法，基本上是不可行的。

The objective of this project is to utilise recent advances in theoretical physics on Casimir force computations in order to provide computational tools suitable for design optimisation to nanotechnology engineers, as well as to produce and provide teaching material for experimentalists that will give sufficient background to effectively make use of such computational tools. This teaching material will make those aspects of quantum field theory that are relevant for Casimir force calculations accessible to engineers.The phenomenon of quantum noise is well-known in quantum optics (laser physics): Just as Heisenberg's Uncertainty Principle makes it impossible for a particle to have at the same time a well-defined position and velocity, it also prevents electromagnetic oscillations from having a precisely zero (root-mean-square) amplitude. In lasers, this quantum noise plays an important role as it can initially seed the amplification process at start-up.From the electromagnetic perspective, any device consists of components that reflect or absorb light, and hence comes with a characteristic set of higher harmonics , analogous to a musical instrument. Again, as with a musical instrument, the frequency structure of possible oscillations strongly depends on the geometry of the device (e.g. a drum in the acoustic case). Even if no oscillation is excited (the instrument produces no sound), all the harmonics nevertheless are individually subject to quantum fluctuations, and as any change of the geometric set-up ( tuning the instrument ) shifts the oscillation frequencies, the changes in quantum noise energies give rise to a measurable force: the Casimir effect .While these quantum forces are unimportant for large bodies, they become quite strong for systems where typical gap dimensions are in the range of tens of nanometres. In particular, they are a major cause of stiction in nanomachines - i.e. device failure by one part of the machine coming in contact with and sticking to another. Their behaviour unfortunately often defies naive intuition: while one would expect that surfaces moving away from one another would induce a shift to lower oscillation frequencies, hence less energy, a detailed investigation shows that Casimir forces normally are attractive. Nevertheless, under very specific conditions, repulsion could be demonstrated in some cleverly designed systems involving certain immersion liquids. Also, as these forces strongly depend on the geometry and on optical absorption properties in unusual ways, reliable quantitative computations are infamous for being very difficult - or rather, essentially infeasible without resorting to rather novel and adventurous computational approaches.