Photo induced Force Microscopy (PiFM): Nanoscale Topography and Vibrational Spectroscopy

Virtually every aspect of our everyday lives, from friction to adhesion, from LED lighting to display screens, and from corrosion to drug delivery through cell walls, depends upon the interface between the outer layer of a solid and the environment. We know the "outer layer" that governs the interactions between a solid and a gas, liquid, or solid, is usually less than a couple of nanometers (nm) thick and often as little as the very outermost layer of atoms or molecules. This means that there is simply very little surface material there to see, in a 1 cm cube of solid for example, only 1 atom in 100 million is at the surface. That makes studying these interfaces very difficult.

Surface science has developed many different techniques capable of examining the outer layer of atoms, but there remain considerable gaps in our knowledge. In particular, we cannot see how the molecular composition changes at very small scales (i.e. < 1000th of a mm) although we do know that such local differences are critical to the behaviour of most interfaces. We can obtain an idea of the molecular constituents of the surface as an average over areas of a few millimeters from bouncing light off the surface, but this approach cannot be used at the smallest scales needed.
In the last 30 years, scanning probe microscopy such as atomic force microscopy (AFM) have revolutionized our understanding of the topography of interfaces; it is now routinely possible to resolve the shape of features as small as a few nm and to study how such local structures affect the behaviour of the interface. The shape is only part of the story however, the local chemical composition and electron interactions are crucial too. With this proposal, we will establish a facility for UK researchers that is capable of determining the topography, local molecular composition and local electronic interactions simultaneously with <10 nm lateral resolution. The technique is called Photo-induced Force Microscopy (PiFM) and can provide a full infrared (IR) spectrum at every point on an AFM map. Infrared spectroscopy is a standard tool used by chemists to identify molecular species (a version of IR was used to identify the presence of methane on Mars for example, and more controversially the possible presence of phosphine in the atmosphere of Venus).
The combination of infrared spectroscopy with atomic force microscopy at such high resolution will provide a new and very important insight into areas of science as diverse as antibacterial coatings on surfaces, quantum nanocrystals for lighting and display, materials for medical implants, catalysts for water purification and the cause of defects or failure in the coatings applied to electrical steels. Understanding these processes will help researchers develop more resilient and sustainable materials with better performance.