The NanoESCA is an Ultra High Vacuum (UHV) photoemission spectroscopy system with sub-micron spatial resolution for real-space and k-space (reciprocal space) mapping from areas of a few microns of flat material surfaces, and the capability to perform quantitative chemical state mapping at the nanoscale. The system has been installed in one of Bristol's Ultra-quiet Nano Science Laboratories. A strategic research partnership between the Bristol NanoESCA Laboratory and Diamond Light Source ( beam lines IO5 and IO6) will be established as one of the outputs of this grant, to allow users to transfer samples for analysis between the two sites by vacuum suitcase.
The system has various modes of operation. UV photon sources are used for Photoemission Spectroscopy (XPS). UPS gives energy filtered information on weakly bound states and the valence band structure in real space and the Ultra-violet Photoemission Spectroscopy (UPS), Angle Resolved UPS, and Photo Emission Electron Microscopy (PEEM), soft X-rays are used for X-ray surface electronic band structure in k-space. XPS is used to probe core level spectra to obtain quantitative information on the chemical composition of a surface. In contrast to the high resolution Scanning Electron Microscope, PEEM directly images surface areas emitting photoelectrons in real time without scanning. By energy filtering PEEM images it is possible to obtain quantitative maps of surface work function. The field of view is adjustable from millimetres to microns allowing high resolution imaging of features as small as 30nm (UPS modes) and 480nm (XPS mode).
The NanoESCA machine represents the next generation in imaging and spectroscopic PEEM. It uses an extension of the established parallel imaging technique, to simultaneously image and filter photoelectrons, by using a double hemispherical (aberration corrected) electron analyser in combination with high photon flux VUV and X-ray sources, to realise nano scale imaging and spectroscopy in real space and in k-space; the latter mode allows information on the electronic band structure of materials to be visualised and compared directly with theoretical models. Uniquely, this capability to obtain nanoscale spectroscopy using either X-ray or VUV sources is obtained by parallel imaging through the same PEEM 'column' which also acts as the entrance lens of the imaging spectrometer.
Ultra high Vacuum imaging photoemission spectroscopy is a valuable tool for Materials for Energy research allowing the first few atomic layers of a surface or interface to be analysed in both real space and also momentum space (k-space).
Real space spectro-microscopy is performed with Energy filtering on the NanoESCA II allows work function maps of conductive materials to be generated and related to chemical state information obtained by XPS/XPEEM and Spot Profile LEED available on the same instrument platform. Momentum space imaging of single crystal and polycrystalline materials reveals ARPES information on the electronic structure, electron orbital patterns and surface states.