Seminars Archive

Microfabricated sample platforms for low energy (photo-) electron spectromicroscopy in liquids and gases

Abstract
The instrumentation for (near) atmospheric pressure “photon IN-electron OUT” spectromicroscopy currently evolves in two directions: (i) via development of the differential pumping apparatus coupled with sophisticated electron optics and sample delivery systems [1]; and more recently, (ii) via implementation of the electron transparent membranes that separate the liquids or dense gaseous environments from the standard UHV instrumentation [2]. In the latter user-friendly case, the complexity of the analytical instrumentation is transferred to the sample stage that can effectively employ already existing microfabrication and lab-on-a-chip technologies. Here we highlight the tested capabilities of the membrane approach and future trends [3]. We discuss graphene liquid cells multi-orifice designs and applications. Such designs allow for high throughput combinatorial data mining algorithms such as principle component analysis, clustering, Bayesian inference methods etc. This is particularly important when multi-dimensional/ hyperspectral datasets like in PEEM are collected [4],[3]. We are currently testing the next generation of the MCA sample platform which has UHV compatible microfluidic capabilities. The key feature of the design is very small degassing rate even if multiple graphene windows are disrupted during the experiment. Such a device is capable to maintain UHV conditions in the vacuum chamber of the analyzer/detector without necessity in differential pumping stage.

REFERENCES
[1] D. F. Ogletree, H. Bluhm, G. Lebedev, C. S. Fadley, Z. Hussain, and M. Salmeron, "A differentially pumped electrostatic lens system for photoemission studies in the millibar range," Review of Scientific Instruments, vol. 73, no. 11, pp. 3872-3877, 2002.
[2] A. Kolmakov et al., "Graphene oxide windows for in situ environmental cell photoelectron spectroscopy," Nat Nano, 10.1038/nnano.2011.130 vol. 6, no. 10, pp. 651-657, 2011.
[3] S. Nemšák et al., "In aqua electrochemistry probed by XPEEM: experimental setup, examples, and challenges," arXiv preprint arXiv:1802.02545, 2018.
[4] H. Guo et al., "Enabling Photoemission Electron Microscopy in Liquids via Graphene-Capped Microchannel Arrays," Nano Letters, vol. 17, no. 2, pp. 1034-1041, 2017/02/08 2017.