Leeds study

Fig. XVI-8. (a) The quasi-hexagonal surface structure of clean Pt(lOO) surface, (b) Adsorption of CO lifts this reconstruction to give the structure corresponding to the termination of (100) planes (from LEED studies). [Reprinted with permission from G. Ertl, Langmuir, 3, 4 (1987) (Ref. 56). Copyright 1987, American Chemical Society.]...

As LEED studies have shown, the stmcture of a chemisorbed phase can change with 6. In terms of transition state theory, we can write A = (I/tq) and a common observation is that while E may change with a phase change, AS will tend to change also, and similarly. The result, again known as a compensation effect, is that the product remains relatively constant... 

Lang B, Joyner R W and Somorjai G A 1972 LEED studies of high index crystal surfaces of platinum Surf. Sc 30 440-53... 

Yamada T, Ogaki K, Okubo S and itaya K 1996 Continuous variation of iodine adiattices on Ag(111) eiectrodes In situ STM and ex situ LEED studies 1996 Surf. Sc/. 369 321-35... 

Surface reconstruction, which had dominated much of surface science through LEED studies, was very much a central theme of STM in the early 1990s but with surprisingly little attention given to chemical reactivity and the origin of active sites in heterogeneous catalysis. This was in part due to the lack of in situ chemical information that could be directly related to the STM images and... 

Figure 6.11 (a-c) Structures based on LEED studies of the adsorption of lithium at a... 

The authors then chose to examine hydrogen adsorption at Cu(110). This was a well-chosen example in that hydrogen adsorption is activated, being pressure dependent, and also was already known from LEED studies to exhibit a missing row (1 x 2) structure with every second close packed (110) copper row missing at high hydrogen pressures. What, then, was learnt from STM ... 

LEED studies of the UPD layers indicate unique superlattices which are highly dependent on the coverage as well as the particular single crystal surface. The UPD layers have also been examined with AES and XPS. These indicate that under some conditions lead in oxidized form is also present on the surface after the electrochemical measurements, thus complicating the interpretation of the LEED patterns. 

The results of LEED studies related to the results described in the next section are given in Table I. More complete tabulations are published elsewhere (22). 

Fig. II. (a) Schematic representation of hydrocarbons adsorbed on the [111] plane of platinum. Intersections of the lines of triangular net denote positions of the centers of platinum atoms. (1) Cyclohexane (2) all-cis conformation of cij-l,3,5-hexatriene (3) transoid conformations of cis- and trans-1,3,5-hexatriene (S4). (b) Adsorption configurations of acetylene and ethylene found most probable according to LEED studies 141).

In the last few years LEED studies of high Miller index or stepped surfaces have become more frequent. Almost all of these studies have been on fee metals, where the atomic structure of these surfaces consists of periodic arrays of terraces and steps. A nomenclature which is more descriptive of the actual surface configuration has been developed for these surfaces, as described in Section III. In Table 5.5 the stepped surface nomenclature for several high Miller index surfaces of fee crystals has been tabulated. In Fig. 5.1 the location of these high Miller index surfaces are shown on the... 

Fig. 7.4. Proposed structure of CO on Ni(lOO) from LEED studies, in top and side views. The CO molecules are tilted 34° away from the surface normal the unknown tilt azimuth is chosen random here for illustration purposes. The C and 0 atoms are given equal touching-sphere radii...

LEED studies have revealed that the atoms in this platinum surface are in the positions expected from the projection of the X-ray unit cell to the surface (5). The diffraction pattern that is exhibited (Fig. 4) clearly indicates a sixfold rotational symmetry that is expected in such a surface. Calculations of surface structure from LEED beam intensities indicate that atoms are in those positions in the surface layer (with respect to the second layer) as indicated by the X-ray unit cell within 5% of the interlayer distance (6,7). 

LEED studies of clean surfaces have revealed that most of these surfaces, if prepared under proper conditions, are ordered on an atomic scale and exhibit sharp diffraction beams and high diffraction beam intensities. Metal, semiconductor, alkali halide, inert gas, and organic crystal surfaces have been studied this way, and all exhibit ordered surface structures. 

One of the most exciting observations of LEED studies of adsorbed monolayers on low Miller index crystal surfaces is the predominance of ordering within these layers (18). These studies have detected a large number of surface structures formed upon adsorption of different atoms and molecules on a variety of solid surfaces. Conditions range from low temperature, inert gas physisorption to the chemisorption of reactive diatomic gas molecules and hydrocarbons at room temperature and above. A listing of over 200 adsorbed surface structures, mostly of small molecules, adsorbed on low Miller index surfaces can be found in a recent review (/). 

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