Using Ion Imaging to Measure Velocity Distributions in Surface Scattering Experiments

Abstract

We present a new implementation of ion imaging for the study of surface scattering processes. The technique uses a combination of spatial ion imaging with laser slicing and delayed pulsed extraction. The scattering velocities of interest are parallel to the imaging plane, allowing speed and angular distributions to be extracted from a single image. The first results of direct scattering of N2 from a clean, single-crystal Au(111) surface are reported, and the speed resolution is shown to be competitive with current state-of-the-art time-of-flight methods for velocity measurements while providing simultaneous measurements of in-plane angular distributions.

Ion and velocity map imaging for surface dynamics and kinetics

“…The spread in the final translational energy is also large when compared to that observed in rotationally resolved scattering of diatomic molecules. 14,48 We attribute this larger spread to the use of fs-MPI, where all final rotational states of the scattered H 2 O molecules are detected. As each rotational state will have a different velocity distribution, the total velocity distribution is broader than that of any single state.…”

“…When combined with delayed extraction, the short pulse provided by the MCP gate can also be used to slice the ion distribution. 14,44 The desorption kinetics are measured by varying the delay between the molecular beam dosing pulse and the probe laser pulse. At each delay, an ion image of the desorbing CO is recorded.…”

“…In this paper, we show how this concept can be generalized and improved with ion imaging. 14 To prove its accuracy, we demonstrate this new approach by measuring the desorption kinetics of CO from Pt(111) and Pd(111), which have been previously studied. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] As in the double resonance experiment, the residence time and the speed are measured independently-ion imaging is used to record the speeds and angles of the desorbing CO molecules and the timing between a short pulsed molecular beam and the ionizing laser reports on the residence time at the surface.…”

An ultrahigh vacuum apparatus for H atom scattering from surfaces

“…beams to other elements using a VUV free electron laser and in combination with imaging detection. 37…”

Note: Velocity map imaging the scattering plane of gas surface collisions

“…7,10 Even small perturbations to these carefully created electric fields result in the loss of 'velocity mapping' conditions, so approaches to imaging the scattering from surfaces have endeavored to minimize these effects by either mounting the surface onto an electrode, [2][3][4] or outside the electrodes altogether. 1 These approaches mean that it is no longer possible to image the whole 2D scattering plane, and so multiple measurements are still required to obtain the total scattering distribution.…”