Final Report Summary - X-TIP (Nanoscale chemical mapping and surface structural modification by joint use of X-ray microbeams and tip-assisted local detection)
The aim of the X-TIP project was to develop a novel line of instruments which integrate the specificities of X-ray spectroscopy with the lateral resolution of local scanning probe microscopy. This combined nanoscale spectro-microscopy would provide information concerning the elemental composition, chemical status and structure in addition to surface morphology which was the only outcome of the probe microscopy.
The main types of probes that have been used in this project are metallic tips for electron detection and quartz optical fibre probes for detection of optical photons emitted from the surface. The challenge has been to develop such type of tips so that the beam-tip interaction could be avoided. Therefore, the bare metallic tips had to be covered by a thick insulating layer to prevent, at least partially, penetration of the X-rays, but, more importantly, to prevent secondary electrons to escape from the metallic surface. Another challenge has been to find a way to get higher signals and better accuracy and finally, to integrate both techniques (X-ray spectroscopy and local probe microscopy) into one system. Concerning the latter, the core of the system would comprise a multi-head local probe microscope, consisting of Atomic force microscopy (AFM), Scanning tunnelling microscopy (STM) and near-field Scanning optical microscopy (SNOM), integrated in a synchrotron radiation beam line that would provide a fine focused X-ray beam on the area explored by the probe tip. The head would provide three different functionalities:
- X-ray absorption spectra (XAS)-SNOM: Element-specific contrast in local probe microscopy via X-ray excited optical luminescence (XEOL) detection by optical probe in SNOM mode;
- XAS-STM: Element-specific contrast in local probe microscopy via X-ray excited photoelectrons detection by conductive tip in STM mode;
- XAS-AFM: Element-specific contrast in local probe microscopy via X-ray induced changes in capacitance by conductive tip in AFM mode.
The main types of probes that have been used in this project are metallic tips for electron detection and quartz optical fibre probes for detection of optical photons emitted from the surface. The challenge has been to develop such type of tips so that the beam-tip interaction could be avoided. Therefore, the bare metallic tips had to be covered by a thick insulating layer to prevent, at least partially, penetration of the X-rays, but, more importantly, to prevent secondary electrons to escape from the metallic surface. Another challenge has been to find a way to get higher signals and better accuracy and finally, to integrate both techniques (X-ray spectroscopy and local probe microscopy) into one system. Concerning the latter, the core of the system would comprise a multi-head local probe microscope, consisting of Atomic force microscopy (AFM), Scanning tunnelling microscopy (STM) and near-field Scanning optical microscopy (SNOM), integrated in a synchrotron radiation beam line that would provide a fine focused X-ray beam on the area explored by the probe tip. The head would provide three different functionalities:
- X-ray absorption spectra (XAS)-SNOM: Element-specific contrast in local probe microscopy via X-ray excited optical luminescence (XEOL) detection by optical probe in SNOM mode;
- XAS-STM: Element-specific contrast in local probe microscopy via X-ray excited photoelectrons detection by conductive tip in STM mode;
- XAS-AFM: Element-specific contrast in local probe microscopy via X-ray induced changes in capacitance by conductive tip in AFM mode.