Instruments in nanotechnology
Dr Owen Guy, Associate Professor, and Nathan Smith, Test Engineer at the College of Engineering at the Swansea Centre for NanoHealth, give an overview of the instruments aiding cutting-edge research in nanotechnology.
Increasingly, nanotechnology is a multi-disciplinary concern, with biology, physics, medicine and engineering only a few of the specialities involved. This means that the tools required by those engaged in research have to be multi-functional too, and easily used by non-specialists. At the Centre for NanoHealth (CNH), we develop tools to enable multi-disciplinary work in nanotechnology.
One such tool is an X-ray photoelectron spectroscopy system for spatial mapping and chemical analysis of a surface, which can scan and analyse different areas. It has high throughput, which is another area of focus at the moment. Previously, tools haven’t been very user-friendly and would require a PhD student to assist or three years of development and study to learn the technique, but the new generation of instruments is more plug-and-play – the software does a lot of the hard work for you. This means that non-specialists can use these tools easily, allowing for greater – and faster – multi-disciplinary research.
The equipment used most commonly by biologists, such as Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and fluorescence techniques are being employed with great success to further research in many different areas. Likewise, semiconductor fabrication equipment, including etch and deposition tools, which you would usually see in a physics department, and photo-lithography instruments are now being used to create products for medical applications. SPTS Technologies, based in Newport, and Suss Microtec, based in Germany, have provided some of these semiconductor and micro-electro-mechanical system (MEMS) instruments to CNH.
One key specialist tool is the Suss Microtec substrate conformal imprint lithography (SCIL) system. This is used to create arrays of nanostructures over a large area (on a 200mm diameter wafer). At CNH, we’re using this capability to scale up fabrication of nano-devices. In addition to some of the more specialist tools, a clean room facility allows for the fabrication of devices, sensors and bio-MEMS products, while characterisation tools, such as scanning electron microscopy (SEM), are regularly used for anything from imaging coral to analysis of defects in components.
Finally, we shouldn’t forget the workhorse instruments – SEM and atomic force microscopy (AFM), which are key tools to any nanotechnology researcher. There are a variety of techniques for more particular applications of these tools, such as AFM combined and fluorescence microscopy, from which you can gain both topographical and mechanical measurements as well as fluorescence information. Dual capability and multi-functional tools such as these are invaluable.
One of the most cutting-edge specialist tools being used is the Omicron low temperature multi-probe system (the nanoprobe), developed at CNH.
Until recently, only single probe ultra-high vacuum (UHV) systems existed, such as scanning tunnelling microscopy (STM) and AFM. It is often difficult to perform localised measurements on individual nanostructures with these, as even locating them on a surface can be difficult.
Building low-resolution SEM columns into the chamber to help with probe positioning improves results, but the measurements are still performed over very localised regions. For example, scanning tunnelling spectroscopy is often performed on nano-to-sub-nanometre scale. With the development of nanomaterials, often STM and AFM approaches are too localised and do not describe the nanostructure as a whole. By incorporating high-resolution SEM and multi-probing capability, one-to-four probes can be brought into direct contact with nanostructures and contact measurements across the whole nanostructure can be made.
The addition of an Auger detector to the system has allowed chemical analysis on the same nanostructure as electrical measurement. Therefore, nanomaterials can be studied from both a chemical and electrical perspective simultaneously.
Furthermore, the whole measurement stage, including probes, can be cooled to liquid He temperature of 4 Kelvin, allowing significant improvement of statistical parametric mapping resolution by reducing thermal drift. It is also the first time that low-temperature contact measurements can be made using a nanoprobe. This allows information such as the conduction mechanism to be accurately investigated.