3-D Surface Velocity Map Imaging (TeDiouS-VMI)

SAM

Using our new VMI spectrometer, our goal is to image the neutral fragments which are photodesorbed from surfaces, and to determine their 3-D velocity distributions. VMI images yield the velocities in the 2 dimensions parallel to the surface, and TOF measurements yield the velocity along the surface normal. There is currently no technique available to record the 3-D velocity distribution of photodesorbed neutral species with the resolution achiable using the VMI technique.


We have recently completed a set of experiments trying to measure how far away from the centre axis of a spectrometer VMI conditionst still prevail. While the beauty of VMI lies in the fact that "fragments are velocity images no matter where they were created," this is only true for rather small volumes, and more sophisticated electron optics such as our 12 plate setup are necessary to incease the area to +/- 6mm from the spectrometer's centre axis.
SAM