Abstract
To enable atomic-scale observations of model catalysts under conditions approaching those used by the chemical industry, we have developed a second generation, high-pressure, high-temperature scanning tunneling microscope (STM): the ReactorSTM. It consists of a compact STM scanner, of which the tip extends into a 0.5 ml reactor flow-cell, that is housed in a ultra-high vacuum (UHV) system. The STM can be operated from UHV to 6 bars and from room temperature up to 600 K. A gas mixing and analysis system optimized for fast response times allows us to directly correlate the surface structure observed by STM with reactivity measurements from a mass spectrometer. The in situ STM experiments can be combined with ex situ UHV sample preparation and analysis techniques, including ion bombardment, thin film deposition, low-energy electron diffraction and x-ray photoelectron spectroscopy. The performance of the instrument is demonstrated by atomically resolved images of Au(111) and atom-row resolution on Pt(110), both under high-pressure and high-temperature conditions.
Highlights
Much of our current knowledge of the precise mechanisms underlying chemical reactions at catalyst surfaces is derived from experiments under ultra-high vacuum (UHV) or high vacuum (HV) conditions
The discrepancy with respect to the typical working conditions of practical catalysts comes from the fact that many surface-sensitive techniques such as low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS) cannot be combined with the environment to which a catalyst would normally be exposed, for example, in the threeway catalyst of a car or in catalytic processes in the petrochemical industry
The lower o-ring separates the reactor on the lower side from all other scanning tunneling microscope (STM) components, such as the piezo element that is used to actuate the motion of the tip; these components stay in UHV, while the pressure in the reactor can be as high as several bar
Summary
Much of our current knowledge of the precise mechanisms underlying chemical reactions at catalyst surfaces is derived from experiments under ultra-high vacuum (UHV) or high vacuum (HV) conditions. The UHV provides a clean and controllable environment for accurate experiments.[1,2] such low-pressure model studies have contributed extensively to our fundamental understanding of catalysts, recent investigations at high gas pressures have yielded new a)Present address: ASM Europe BV, Versterkerstraat 8, 1322 AP Almere, The Netherlands. Scanning tunneling microscopy is one of the few atomically sensitive surface-science techniques that do not introduce fundamental problems or limitations when bridging the pressure gap. It can operate in the full range from UHV to high pressures of, e.g., 1 bar and beyond, and from cryogenic temperatures to temperatures well above 1000 K.16,17. We start this paper with a discussion of the concept and the specifications of the instrument, followed by a description of the actual design and performance
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