Cryo-FIB-SEM-CT: a 'three-in-one' imaging facility for opaque soft matter

爱丁堡大学（UoE）是软物质研究的国际中心。软物质科学家研究复杂的液体，其中存在尺寸介于组成溶剂的小分子和肉眼可见的宏观结构世界之间的结构。这些结构可能是油漆中的色素颗粒（胶体），洗涤液中肥皂分子的自组装聚集体（表面活性剂胶束），气泡（比如在搅打奶油中）或长链分子（聚合物），如DNA（用于基因转染）。该领域具有根本意义，因为这些材料的性质受许多相互竞争的长度和时间尺度的控制，并且在日常条件下可能发生显着变化。这类材料也普遍存在于各种配方中，如药品（CALPOL是一种胶体扑热息痛悬浮液）和个人护理产品（洗发水是一种表面活性剂-聚合物混合物）。它们也是许多领域的关键中间体：例如，所有陶瓷开始都是软糊状物（想想陶泥），在高温烧结形成最终的硬质产品之前，它们被泵入模具或挤出。软物质的一个基本挑战是弄清楚这些中间结构元素的组织方式，以及这种组织如何响应外力而变化。大多数这样的材料是不透光的，所以除了提供表面信息外，各种光学显微镜都没有用。因此，科学家们有时会求助于各种电子显微镜，然而，这些电子显微镜在真空中工作，因此湿样品会干燥，它们的天然结构会被破坏。低温扫描电子显微镜（cryo-SEM）是近几十年来的一个主要发展。将天然的湿软样品冷冻在液氮中，使用特殊技术确保快速冷却以保存复杂的微观结构。然后将这些冷冻的样品破碎，暴露出内部结构以通过SEM成像。(One缺点是样品断裂或多或少是随机的，因此暴露在视野中的是偶然的。UoE有一台冷冻SEM仪器。这个有十年历史的仪器在分辨率（比今天最好的仪器差十倍）和软物质科学家的访问方面都受到限制，因为它需要将系统转换为低温模式。我们建议购买一台最先进的低温扫描电镜，以使这种尖端技术成为日常工作的常规手段。这次购买是及时的，因为低温扫描电镜最近通过增加聚焦离子束（FIB）为软物质研究人员带来了革命性的变化。这种强大的技术使用带电原子（离子）的聚焦束在SEM内非常精确地切割和切片样品。这不仅允许用户随意曝光所需的部分，而且还可以通过逐部分成像样品以达到10 nm（原子大小的100倍）的分辨率来构建完整的3D图片（字面上）。我们建议购买冷冻纤维蛋白原扫描电镜。这项技术是如此的新，以至于我们知道英国目前只有两种仪器，这两种仪器都不是专门用于软物质的研究。我们建议将X射线断层扫描功能添加到我们的冷冻FIB SEM中。这使我们能够无损地建立350 nm分辨率的3D图像，就像X射线CT扫描仪在医院建立人体3D图像一样。这套组合仪器的可用性将改变软物质科学家常规观察样品内部的能力。一系列令人兴奋的应用程序立即跟进。一个例子是基于新型软材料的“设计电极”，其在充电/放电循环期间最小化膨胀/收缩。一项推广和培训方案将使全联合王国的学术和工业研究人员都能利用这一设施。

The University of Edinburgh (UoE) is an international centre for soft matter research. Soft matter scientists study complex liquids in which there are structures intermediate in size between the small molecules making up the solvent and the macroscopic world of structures visible to the naked eye. The structures may be pigment particles in paint (colloids), self-assembled aggregates of soap molecules in washing-up liquid (surfactant micelles), bubbles (say, in whipped cream) or long-chain molecules (polymers) such as DNA (as used in gene transfection). The field is of fundamental interest because the properties of these materials are controlled by many competing length and time scales, and can change dramatically under everyday conditions. Such materials are also ubiquitous in formulations of all kinds, such as medicines (CALPOL is a suspension of colloidal paracetamol) and personal care products (a shampoo is a surfactant-polymer mixture). They are also key intermediates in many sectors: all ceramics, for example, begin as soft pastes (think potter's clay) that are pumped into moulds or extruded before they are sintered at high temperatures to form the final hard products. A fundamental challenge in soft matter is to figure out the way these intermediate structural elements are organised, and how such organisation changes in response to external forces. Most of such materials are opaque to light, so that optical microscopies of all kinds are not useful except to give surface information. As a result, scientists sometimes resort to various kinds of electron microscopy, which, however, operate in a vacuum, so that wet samples are desiccated and their native structures destroyed. A major development in the last decades is cryogenic scanning electron microscopy (cryo-SEM). A native, wet soft sample is frozen in liquid nitrogen, using special techniques to ensure rapidity of cooling to preserve intricate microstructures. Then these frozen samples are fractured, exposing internal structures to be imaged by SEM. (One disadvantage is that samples fracture more or less randomly, so that what is exposed to view is haphazard.) A single cryo-SEM instrument exists at UoE. This decade-old instrument is limited in both resolution (ten times worse than the best instruments today) and in access for soft matter scientists, as it requires laborious conversion of the system to cryogenic mode. We propose to purchase a state-of-the-art cryo-SEM to enable this cutting-edge technique to become routinely available for day-to-day work. This purchase is timely, because cryo-SEM has recently been revolutionised for soft matter researchers by the addition of focussed ion beam (FIB). This powerful technique uses a focused beam of charged atoms (ions) to cut and section specimens very accurately inside the SEM. This not only allows the user to expose desired sections at will, but also to build up a complete 3D picture (literally) by imaging the sample section by section to a resolution of 10 nm (100 times the size of atoms). We propose to purchase a cryo-FIB SEM. The technique is so new that we know of only two current instruments in the UK, neither of which is dedicated to the study of soft matter. We propose to add X-ray tomography capability to our cryo-FIB SEM. This allows us to build up a 3D picture non-destructively to 350 nm resolution, much like the way X-ray CT scanners build up 3D images of the body in hospitals. The availability of this combined suite of instruments will transform the ability of soft matter scientists to see inside their samples routinely. A host of exciting applications immediately follow. One example is 'designer electrodes' based on novel soft materials that minimise expansion/shrinkage during charge/discharge cycles. A programme of outreach and training will make this facility available to academic and industrial researchers UK-wide.