Lambrick S M, Bergin M, Jardine A P, Ward D J
Department of Physics, The Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK.
Micron. 2018 Oct;113:61-68. doi: 10.1016/j.micron.2018.06.014. Epub 2018 Jun 26.
A ray tracing method for predicting contrast in atom beam imaging is presented. Bespoke computational tools have been developed to simulate the classical trajectories of atoms through the key elements of an atom beam microscope, as described using a triangulated surface mesh, using a combination of MATLAB and C code. These tools enable simulated images to be constructed that are directly analogous to the experimental images formed in a real microscope. It is then possible to understand which mechanisms contribute to contrast in images, with only a small number of base assumptions about the physics of the instrument. In particular, a key benefit of ray tracing is that multiple scattering effects can be included, which cannot be incorporated easily in analytic integral models. The approach has been applied to model the sample environment of the Cambridge scanning helium microscope (SHeM), a recently developed neutral atom pinhole microscope. We describe two applications; (i) understanding contrast and shadowing in images; and (ii) investigation of changes in image formation with pinhole-to-sample working distance. More generally the method has a broad range of potential applications with similar instruments, including understanding imaging from different sample topographies, refinement of a particular microscope geometry to enhance specific forms of contrast, and relating scattered intensity distributions to experimental measurements.
提出了一种用于预测原子束成像中对比度的光线追踪方法。已开发出定制的计算工具，以模拟原子通过原子束显微镜关键元件的经典轨迹，该模拟过程使用三角化表面网格描述，采用MATLAB和C代码相结合的方式。这些工具能够构建出与实际显微镜中形成的实验图像直接类似的模拟图像。这样，只需对仪器的物理特性做出少量基本假设，就有可能了解哪些机制对图像中的对比度有贡献。特别是，光线追踪的一个关键优势在于可以纳入多重散射效应，而这在解析积分模型中很难实现。该方法已应用于对剑桥扫描氦显微镜（SHeM）的样品环境进行建模，SHeM是一种最近开发的中性原子针孔显微镜。我们描述了两个应用；（i）理解图像中的对比度和阴影；（ii）研究针孔到样品工作距离对图像形成的影响。更广泛地说，该方法在类似仪器上有广泛的潜在应用，包括理解不同样品形貌的成像、优化特定显微镜几何结构以增强特定形式的对比度，以及将散射强度分布与实验测量相关联。
