Oxygen reconstructions

Abstract The controlled in-situ deposition of sexiphenyl (6P) on the (2x1) oxygen reconstruction of Cu (110) is shown to give rise to the ordered growth of large anisotropic needle-like structures on the surface. Photoemission electron microscopy (PEEM) and atomic force microscopy (AFM) results are presented for the growth of 6P (20-3) crystalline needles for a range of substrate temperatures. In addition, desorption and other interesting phenomena are discussed. 

More complete works consider the self-assembly of the molecules on the copper surface. Note that this is a difficult task as experimental structural data are scarce. Cho et al. studied BTAH adsorption on the clean Cu(l 10) and oxygen reconstructed Cu(l 10)—2 x 1 surfaces [87]. The atomically resolved scanning tunneling microscope (STM) images showed that BTA adsorbed on the clean Cu(l 10)—1 x 1 surface forms a c(4 x 2) structure, in agreement with the c(4 x 2) LEED pattern. On the other hand, STM images of BTA adsorbed on the... 

Restructuring of a surface may occur as a phase change with a transition temperature as with the Si(OOl) surface [23]. It may occur on chemisorption, as in the case of oxygen atoms on a stepped Cu surface [24]. The reverse effect may occur The surface layer for a Pt(lOO) face is not that of a terminal (100) plane but is reconstructed to hexagonal symmetry. On CO adsorption, the reconstruction is lifted, as shown in Fig. XVI-8. 

Perhaps the most fascinating detail is the surface reconstruction that occurs with CO adsorption (see Refs. 311 and 312 for more general discussions of chemisorption-induced reconstructions of metal surfaces). As shown in Fig. XVI-8, for example, the Pt(lOO) bare surface reconstructs itself to a hexagonal pattern, but on CO adsorption this reconstruction is lifted [306] CO adsorption on Pd( 110) reconstructs the surface to a missing-row pattern [309]. These reconstructions are reversible and as a result, oscillatory behavior can be observed. Returning to the Pt(lOO) case, as CO is adsorbed patches of the simple 1 x 1 structure (the structure of an undistorted (100) face) form. Oxygen adsorbs on any bare 1 x 1 spots, reacts with adjacent CO to remove it as CO2, and at a certain point, the surface reverts to toe hexagonal stmcture. The presumed sequence of events is shown in Fig. XVIII-28. 

Jensen F, Besenbacher F, Laesgaard E and Stensgaard I 1990 Surface reconstruction of Cu (110) induced by oxygen chemisorption Phys. Rev. B 41 10 233... 

Reconstruction of the Cu(l 11) close-packed surface at room temperature upon oxygen adsorption has been reported by Niehus.590 This result is in good agreement with data on cyclic voltammetry and second-harmonic generation591 it has been concluded that oxygen-containing spe-... 

Marino, B.D. and DeNiro, M.J. 1987 Isotopic analysis of archaeobotanicals to reconstruct past climates Effects of activities associated with food preparation on carbon, hydrogen and oxygen isotope ratios of plant cellulose. Journal of Archaeological Science 14 537-548. 

Suggestions that phosphatic minerals in mammals could be used, however, revived the interest in climate reconstruction in continental interiors. Aquatic, cold-blooded animals like fish have body temperatures and body water oxygen isotopic compositions that are directly dependent on the water in which they live. For these animals, a commonly used equation describes the relationships among temperature, water oxygen isotopic composition and phosphate oxygen isotopic composition as (Longinelli and Nuti 1973 verified by Kolodny et al. 1983, among others) ... 

Figure 1. Image of the Rh(110) surface after treatment with oxygen, producing mainly the c(2x6) reconstruction of the adlayer. The dark lines run parallel to the [011] direcUon and are missing rows of Rh atoms. More details of this structure are given elsewhere [4-7].

Figure 7.9 STM images of reconstructed Au(l 1 1) (left) and Au (1 1 1) covered with 0.4 ML of oxygen atoms (right). Images are 100 X 100 nm. Reproduced with permission from Min eto/. [176], Copyright (2005) American Physical Society.

Pfniir H, Held G, Lindroos M, Menzel D. 1989. Oxygen induced reconstruction of a close-packed surface A LEED IV study on Ru(001)-p(2 x 1)0. Surf Sci 220 43. 

The significance and impact of surface science were now becoming very apparent with studies of single crystals (Ehrlich and Gomer), field emission microscopy (Sachtler and Duell), calorimetric studies (Brennan and Wedler) and work function and photoemission studies (M.W.R.). Distinct adsorption states of nitrogen at tungsten surfaces (Ehrlich), the facile nature of surface reconstruction (Muller) and the defective nature of the chemisorbed oxygen overlayer at nickel surfaces (M.W.R.) were topics discussed. 

Figure 2.1 Real-time photoemission study (hv = 6.2 eV) of the interaction of oxygen (Po2 = 10- Torr) with a nickel surface at 300 K. The photocurrent decreases initially (A B), then recovers (B-C), before finally decreasing (CD). Surface reconstruction occurs (B-C) with further support from studies of the work function. The work function measured by the capacitor method15 increases by 1.5 eV with oxygen exposure at 80 K followed by a rapid decrease on warming to 295 K and an increase on further oxygen exposure at 295 K. These observations suggest that three different oxygen states are involved in the formation of the chemisorbed overlayer. (Reproduced from Refs. 15, 42).

The first STM evidence for the facile transport of metal atoms during chemisorption was for oxygen chemisorption at a Cu(110) surface at room temperature 10 the conventional Langmuir model is that the surface substrate atoms are immobile. The reconstruction involved the removal of copper atoms from steps [eqn (1)], resulting in an added row structure and the development of a (2 x 1)0 overlayer [eqn (2)]. The steps present at the Cu(llO) surface are... 

Figure 4.5 STM images (6.2 x 6.5 nm) observed in the chemisorption of oxygen at Ni(110) at room temperature (a) the (3 x 1)0 state at 0 = 0.33 (b) the (2 x 1)0 state at 0 = 0.5 (c) the (3 x 1)0 state at 0 = 0.66. Corresponding ball models of these are shown in (d), (e) and (f) and are typical of oxygen-induced reconstructions at metal surfaces. The small black balls represent the O adatoms. (Reproduced from Ref. 12).

To probe the early stage of oxygen chemisorption, that is, prior to the onset of surface reconstruction and oxide formation and relevant to our coadsorption reactivity studies, there were obvious advantages for STM observations to be made at cryogenic temperatures. 

Figure 5.10 STM images of a Cu(l 10)-O surface (a), after exposure (10 L) to CH3OH at 270 K (b) and 40 min later (c). Note the transformations of the (2 x 1)0 strings into zig-zag chains and c(2 x 2) structures (b) and with time the oxygen has been removed and the surface evolved into a (5 x 2) methoxy reconstruction (c). (Reproduced from Ref. 37).

The interatomic spacing within the rows of the c(2 x 4) structure is 0.5 nm, which is close to the Cs-Cs spacing in the monolayer of Cs formed at a Cu(l 10) surface at 80 K. The presence of the oxygen adlayer apparently prevents reconstruction of the surface with the caesium locked in within the rows of... 

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