Surface science, tools

For example, energy transfer in molecule-surface collisions is best studied in nom-eactive systems, such as the scattering and trapping of rare-gas atoms or simple molecules at metal surfaces. We follow a similar approach below, discussing the dynamics of the different elementary processes separately. The surface must also be simplified compared to technologically relevant systems. To develop a detailed understanding, we must know exactly what the surface looks like and of what it is composed. This requires the use of surface science tools (section B 1.19-26) to prepare very well-characterized, atomically clean and ordered substrates on which reactions can be studied under ultrahigh vacuum conditions. The most accurate and specific experiments also employ molecular beam teclmiques, discussed in section B2.3. 

We have already mentioned that fundamental studies in catalysis often require the use of single crystals or other model systems. As catalyst characterization in academic research aims to determine the surface composition on the molecular level under the conditions where the catalyst does its work, one can in principle adopt two approaches. The first is to model the catalytic surface, for example with that of a single crystal. By using the appropriate combination of surface science tools, the desired characterization on the atomic scale is certainly possible in favorable cases. However, although one may be able to study the catalytic properties of such samples under realistic conditions (pressures of 1 atm or higher), most of the characterization is necessarily carried out in ultrahigh vacuum, and not under reaction conditions. 

Obviously, there is still much interesting work to be done on infrared spectroscopy of molecules adsorbed on metal surfaces in the future, both for those interested in instrumental development as well as those who will use the technique as one of many surface science tools. 

As surface science tools became more sophisticated it became abundantly clear that nearly all tools required extremely clean surfaces and high vacuum techniques. Michel Boudart has pointed out a number of times the need to bridge the gap between the high vacuum spectroscopic techniques and the real world of catalytic reactions. 

However, a better structure designing requests a finer characterization of nanopores. We need to know structural features of nanopores as accurate as possible in order to develop the best nanostructured materials for the specific function. Nevertheless, nanopores are hidden in the bulk of solids. Consequently, established surface science tools cannot be directly applied to the nanopore characterization, leading to necessity of an inherent characterization method for nanopores on the basis of gas adsorption. This paper summarizes main characterization methods, which can be applied to nanopore systems, and essential roles of gas adsorption will be described. 

The properties of alloy and intermetallic compound surfaces play an important role for the development of new materials. Attention has been stimulated from various topics in microelectronics, magnetism, heterogeneous catalysis and corrosion research. The investigation of binary alloys serves also as a first step in the direction to explore multi-component systems and is of particular regard in material science as a consequence of their widespread use in technical applications. The distribution of two elements in the bulk and at the surface probably results in new characteristics of the alloy or compound as compared to a simple superposition of properties known from the pure constituents. Consequently, surfaces of bulk- and surface- alloys have to be investigated like completely new substances by means of appropriate material research techniques and surface science tools. [1-6]. 

There is a trend in increasing sophistication of spectroscopic tools used to study sintering and redispersion. In the next decade we might expect additional insights into atomic and molecular processes during reaction at the atomic scale using STM, an ytical HRTEM, and other such powerful surface science tools. 

Simplifications in the physical and chemical characterization the 2D nature of the nanofabricated model catalysts make them easier to inspect with traditional surface science tools and electron microscopy. 

Silver catalysts have been used for the partial oxidation of methanol to formaldehyde this is a very important process in the chemical industry. The role of the silver catalyst and, in particular, the influence of its atomic structure on the catalytic process have been extensively studied with various surface science tools [44—50]. In these investigations, Raman spectroscopy was employed to identify and confirm the role of the oxygen species for the catalytic process. These studies were performed under reaction conditions close to those in industrial processes using Ag(lll) and Ag(llO) samples. Upon extended exposure to oxygen at high temperatures, both samples restructure to (111) planes with a well-defined microstructure and with mesoscopic roughness (on a scale of 1 pm). Therefore, in the course of the oxygen pretreatment, the local nature of the surface of the two samples becomes nearly identical and, hence, their Raman spectra are quite similar [44]. 

Employing TERS in UHV systems There are a number of surface science tools available for samples in UHV which allow us to characterize the state of a surface. Surface and adlayer structures can be determined by LEED (low electron energy diffraction) as weU as by SPM (scanning probe microscopy) techniques. While the kind of chemical interactions can be studied, for example, with AES (Auger electron spectroscopy), EELS (energy electron loss spectroscopy) permits the identification of the chemical nature of the adsorbed species. TERS, on the other hand, may provide similar but also complementary information on the chemical identity under UHV conditions. As an additional advantage, TERS and SPM permit the identification and characterization of the spatial region from which this information is accumulated. 

Two distinct experimental approaches can be used for investigating photodissociation processes at the gas-solid interface, depending on the nature of the observable. In the first approach, speed, angular distribution, and internal excitation of the photofragments leaving the surface are measured. In the second approach, the photoproduct left behind at the surface is monitored. In the second approach, the standard tools of surface science are used. Surface photochemical studies usually require ultra-high vacuum (UHV) conditions, of the order 10 ° to 10 mbar. Initially, the adsorption and thermal behaviour of the molecule-metal system must be characterized. Various surface-science tools can be used to provide information about adsorption geometry, molecular structure and thermal chemistry of adsorbates. 

A key property of a passive film that may be manipulated in the future is its semiconductive nature in the context of the cathodic reaction that necessarily occurs on top of the film. It is not always appreciated that chromium oxide is a very good electrical insulator, so that in theory one could enrich chromium to such an extent that the reduction of oxygen on top of the passive film on stainless steel would cease, thus eliminating localized corrosion in salt water. In practice, not much iron content is required to make the film rather conductive, but still, manipulation of cathodic reaction kinetics on passive films has to be considered an important challenge for the future. Many tools and theoretical underpinnings are available for further progress in this area, including a variety of in situ probes, surface-science tools, and classical electrochemistry methods. 

Among many important surface science tools, a soft X-ray photoelectron spectroscopy (XPS) has been one of the most popular choices in studying physical and chemical properties of surface, providing the element-specific, nondestructive, and quantitative information. As well known, the fundamental principle of XPS is based on Einstein s photoelectric effect, i.e., photon-in and electron-out. 

Farnsworth has observed the (7x7) in a FEED experiment, which was at first treated with much suspicion as to whether the surface was contaminated. Many subsequent experiments showed that the (7x7) stmcture was not due to trace contamination. In the following years, the Si(lll)-(7x7) structure has been investigated by almost any available surface science tool, however, without achieving a successful structural model. 

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