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

爱丁堡大学(UOE)是一个国际软物质研究中心。软物质科学家研究复杂的液体，在组成溶剂的小分子和肉眼可见的宏观结构之间存在中等大小的结构。这种结构可能是涂料中的颜料颗粒(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，在起泡奶油中)或长链分子(聚合物)，如DNA(用于基因转移)。这一领域非常重要，因为这些材料的性质受到许多相互竞争的长度和时间尺度的控制，在日常条件下可能会发生巨大变化。这类材料也普遍存在于各种配方中，如药品(Calpoll是胶体对乙酰氨基酚的悬浮液)和个人护理产品(洗发水是表面活性剂和聚合物的混合物)。它们也是许多行业的关键中间体：例如，所有陶瓷最初都是软浆料(比如陶土)，在高温下烧结形成最终的硬产品之前，被泵入模具或挤压。软物质的一个根本挑战是弄清楚这些中间结构元素是如何组织的，以及这种组织如何随着外力的变化而变化。大多数这样的材料对光是不透明的，所以除了提供表面信息外，所有类型的光学显微镜都没有用处。因此，科学家有时求助于各种电子显微镜，然而，这些电子显微镜是在真空中操作的，因此湿样品被干燥，其固有结构被破坏。在过去的几十年中，一个主要的发展是低温扫描电子显微镜(低温扫描电子显微镜)。一个天然的、潮湿的软样品被冷冻在液氮中，使用特殊的技术确保快速冷却，以保存复杂的微观结构。然后，这些冷冻的样本被撕裂，暴露出内部结构，供扫描电子显微镜成像。(一个缺点是，样品的破裂或多或少是随机的，所以暴露在视野中的东西是随机的。)UOE只有一台低温扫描电子显微镜仪器。这台有十年历史的仪器在分辨率(比今天最好的仪器差十倍)和软物质科学家的使用方面都受到限制，因为它需要费力地将系统转换到低温模式。我们建议购买最先进的低温扫描电子显微镜，使这项尖端技术能够在日常工作中使用。这次收购是及时的，因为低温扫描电子显微镜最近通过添加聚焦离子束(FIB)为软物质研究人员带来了革命性的变化。这项强大的技术使用一束聚焦的带电原子(离子)在扫描电子显微镜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，还可以通过将样本逐段成像到10 nm(原子大小的100倍)的分辨率来构建完整的3D图像(字面上是这样)。我们建议购买一台低温扫描电子显微镜。这项技术是如此之新，以至于我们知道英国目前只有两台仪器，这两台仪器都不是专门用于软物质研究的。我们建议在我们的低温FIB扫描电子显微镜中增加X射线层析成像功能。这使我们可以无损地构建分辨率为350纳米的3D图像，就像X光CT扫描仪在医院构建身体的3D图像一样。这套组合仪器的使用将改变软物质科学家常规观察样品内部的能力。紧随其后的是一系列令人兴奋的应用程序。一个例子是基于新型软材料的“设计电极”，这种材料在充放电循环过程中最大限度地减少了膨胀/收缩。一个外展和培训计划将使这一设施可供英国各地的学术和工业研究人员使用。

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.