Correlative Chemical Metrology

表面的相互作用是我们如何生活的基础。作为机器中工程部件的一部分，表面在相互移动时的行为在很大程度上取决于它们是由什么制成的以及它们是如何制成的。这一点很重要，因为由错误的材料或错误的表面光洁度制成的表面可能会导致组件在设计之前失效。这导致维修和更换的成本损失，但由于材料需要回收和重新制造，也会产生额外的能源浪费。因此，测量表面成分和粗糙度是非常重要的，但要准确地做到这一点，涉及到许多不同的科学技术，这可能会使其耗时和昂贵。从可持续发展的角度来看，如果能够以相对较低的成本快速准确地测量表面，并提供其成分和粗糙度的信息，那将更好。本项目旨在通过将两种科学技术结合到一种传感器测量中来尝试实现这一目标。粗糙度通常通过跟踪金刚石尖端在表面上测量高度差来测量。金刚石是一种很好的材料，因为它非常坚硬，在与表面接触时不易损坏。金刚石是一种绝缘体，但如果掺杂硼，这一点可以改变。这使得金刚石具有导电性，这意味着我们可以使用一种称为电化学阻抗谱（EIS）的技术来测量金刚石和钢等工程表面之间在不同AC频率下的接触电阻（称为阻抗）的变化。阻抗很可能随着探头在钢结构的不同部分上移动而改变，例如，与含有大量碳的部分相比，钢的铁部分的粗糙度可能会有所不同。这意味着我们可以将粗糙度的高点和低点与表面的不同材料相关联。由于EIS需要几分钟，因此实现这一点非常具有挑战性扫描所有的交流频率，但测量地形只需要几秒钟。在进行测量时，需要考虑振动、热漂移和相对湿度的影响。这些数据将从一个非常敏感的纳米压痕机器收集，该机器使用电容板提供非常准确的表面位置数据。测量时空气中的水量将通过一个充满干燥氮气的腔室进行控制。这是因为当测量时，空气中的水会在探头附近解吸，从而可以测量周围表面的阻抗。如果该技术能够工作，它将在许多不同的领域非常有用。这些包括制造，其中它可能被用作质量控制设备，检查制造的组件是否具有正确的表面粗糙度，以及表面是否存在污染。当一些制造过程出错时，它们有时会“燃烧”或氧化表面，这种新的传感器可能能够在人类注意到之前检测到。其他可能受益的部门将是化学工业，特别是催化部门，其中不同催化物质的表面积可以与表面高度相关，从而可以优化特定应用。这种方法也将与经历滑动或滚动接触的工程部件相关，因为该技术可以确定表面如何响应于损伤累积而变化。这既可以从表面工程设计优化的角度来看，也可以实际上作为一种状态监测方法，其中表面在其应用环境中进行原位测量，以警告在操作期间出现的潜在问题。

The interaction of surfaces is fundamental to how we live our lives. How surfaces behave when they move against each other as part of engineered components in machines depends to a large extend on what they are made from and how they are made. This is important because surfaces made from the wrong material or the wrong surface finish could cause the component to fail before it was designed to do so. This leads to a cost penalty for repair and replacement but there is also the additional energy wastage incurred as the material needs to be recycled and re-made. Thus measuring surface composition and roughness is quite important but to do so accurately involves lots of different scientific techniques which can make it time consuming and expensive. It would be much better from a sustainability perspective if surfaces could be measured quickly and accurately when they were being made at a relatively low cost to give information about both their composition and roughness.This project aims to try and achieve this goal by combining two scientific techniques into one sensor measurement. Roughness is often measured by tracing a diamond tip across a surface to measure differences in height. Diamond is a good material for doing this as it is very hard and is not easily damaged when in contact with surfaces. Diamond is an insulator but this can be changed if it is doped with boron. This makes the diamond conductive and means we could potentially use a technique called electrochemical impedance spectroscopy, or EIS, to measure changes in the contact resistance at different AC frequencies (called the impedance) between the diamond and an engineered surface like a steel. The impedance is likely to change as the probe moves across different parts of the steel structure, for example, it will probably be different for the iron part of the steel compared to a part that has lots of carbon in it. This means we might be able to correlate the high and low points of the roughness to the different materials phases of a surface.It will be quite challenging to achieve this as EIS take several minutes to scan all the AC frequencies, but measuring the topography only takes a few seconds. The influence of vibrations, thermal drift and relative humidity will need to be taken account of when the measurement is performed. The data will be collected from a very sensitive nano-indentation machine that uses capacitance plates to provide very accurate data of surface positions. The amount of water in the air when the measurements are taken will be controlled with a chamber than can be filled with dry nitrogen. This is because water in the air will desorb near the probe when the measurements are made and could allow impedance of ambient surfaces to be measured.If the technique were to work it could be very useful across a number of different sectors. These include manufacturing, where it might be used as a quality control device, checking that manufactured components have been made to the correct surface roughness and that no contamination of the surface is present. When some manufacturing processes go wrong they sometimes 'burn' or oxide the surface and this new sensor might be capable of detecting that before a human notices. Other sectors that could benefit would be the chemical industry, especially the catalysis sector, where the surface area of different catalytic species could be correlated to surface height, allowing optimisation for particular applications. This approach would also be relevant to engineering components that experience sliding or rolling contacts as the technique could determine how surfaces change in response to damage accumulation. This could be from both a surface engineering design optimisation point of view or indeed as a condition monitoring approach, where the surfaces are measuring in-situ within their application environment to warn of potential problems developing during operation.