| AVS 62nd International Symposium & Exhibition | |
| In-Situ Spectroscopy and Microscopy Focus Topic | Monday Sessions |
| Session IS+AS+SA+SS-MoA |
| Session: | Ambient Pressure X-ray Photoelectron Spectroscopy Studies for Catalytic and Energy Materials in Gas Phase |
| Presenter: | Hikmet Sezen, Elettra-Sincrotrone Trieste, Italy |
| Authors: | H. Sezen, Elettra-Sincrotrone Trieste, Italy M. Amati, Elettra-Sincrotrone Trieste, Italy L. Gregoratti, Elettra-Sincrotrone Trieste, Italy |
| Correspondent: | Click to Email |
A technique based on photoelectron spectroscopy (PES) providing simultaneously spectroscopy and microscopy capabilities and being compatible with ambient pressure conditions is still missing. Ambient pressure PES (APPES), based on differential pumping of the electron energy analyzer, offers an optimal spectroscopic solution to overcome pressure barrier for surface related studies[1]. Unfortunately, APPES has very limited spatial resolution. On the other hand, a better than 100 nm spatial resolution scanning photoelectron microscope (SPEM), where the X-ray beam is demagnified down to a 130 nm spot by Zone Plate Fresnel optics and the sample scanned under the focused beam, is accessible from a few synchrotrons. A direct adaptation of the APPES approach to SPEM technique is not possible because of geometric constrains, stabilities and sustainability of the x-ray optics under near ambient pressures, and mechanical stability of the photoelectron detection system under such severe pumping conditions. In this presentation we will introduce two novel solutions for near-ambient pressure SPEM with ~100 nm spatial resolution and compatible with in-situ/operando conditions operated at ESCAmicroscopy beamline at Elettra synchrotron facility.
Dynamic high pressure (DHP) is the one of our near-ambient pressure SPEM solution. The technique is based on generating high pressure pulsed gas packets directed to the sample. Under influence of gas pulses the sample fells a few mbar pressure in a burst instant, then gas packets dilute into the SPEM chamber to yield a 1x10-5 mbar background pressure. From the test results a 10-3-10-2 mbar equivalent static pressure was felt by Si and Rh samples during in-situ oxidation reaction.[2] It is available for users.
Effusive cell is another solution for near-ambient pressure SPEM. The sample is encapsulated with a vacuum sealed cell and located just 30-50 µm behind of a 200 µm diameter size pinhole. The focused x-ray beam are scanning the sample trough the pinhole. The generated photoelectrons come out from the same pinhole and are able to reach the electron energy analyzer. Due to the geometric orientation of energy analyzer and the pinhole we can achieve ca. a 200x100 µm2 aerial point of view on the sample. The pressure inside the cell can be raised up to mbar range while the pressure in the main chamber kept around 1x10-5 mbar which is the safety limit for SPEM system. An encapsulated filament is behind the sample for heating, and other electrical connections are ready for biasing of sample, and thermocouple connections.
[1] D. F. Ogletree, et al. Rev. Sci. Instrum. 73, 3872 (2002)
[2] M. Amati, et al. J. Instrum. 8, 05001 (2013)