STM images

The development of scanning probe microscopies and x-ray reflectivity (see Chapter VIII) has allowed molecular-level characterization of the structure of the electrode surface after electrochemical reactions [145]. In particular, the important role of adsorbates in determining the state of an electrode surface is illustrated by scanning tunneling microscopic (STM) images of gold (III) surfaces in the presence and absence of chloride ions [153]. Electrodeposition of one metal on another can also be measured via x-ray diffraction [154]. 

Fig. XVni-2. Successive STM images of (a) Ni(llO) with a chemisorbed layer of oxygen atoms and (b) after exposure to 3 1 of H2S. The area shown in 85 x 91 A. [From F. Besenbacher, P. T. Sprunger, L. Ruan, L. Olesen, I. Stensgaard, and E. Lcegsgaard, Tap. Catal., 1, 325 (1994).]...

Figure Al.7.7. Atomic-resolution, empty-state STM image (100 A x 100 A) of the reconstmcted Si(l 11)-7 7 surface. The bright spots correspond to a top layer of adatoms, with 12 adatoms per unit cell (courtesy of Alison Baski).

Figure Al.7.10. STM image (1000 A x 1000 A) of the (111) surface of a tungsten single crystal, after it had been coated with a very thin film of palladium and heated to about 800 K (courtesy of Ted Madey).

Figure Al.7.14. 3.4 mn x 3.4 mn STM images of 1-docosanol physisorbed onto a graphite surface in solution. This image reveals the hydrogen-bonding alcohol molecules assembled in lamellar fashion at the liquid-solid interface. Each bright circular region is attributed to the location of an individual hydrogen...

Figure A3.10.3 STM images of the early stages of sulfur segregation on Ni(l 11). Sulfur atoms are seen to preferentially mieleate at step edges [8],...

Figure A3.10.6 A series of STM images for Ag/Pt(l 11) at 75 K showing the transition from nueleation to growth [23], Coverages ( ) and mean island sizes (ii) are indieated.

Figure A3.10.9 STM images of Si(l 11) surfaces before (a) and after (b) etching by bromine at 675 K. In (a) the (7 X 7) reconstmcted surface is seen. In (b), the rest layer consisting of triangular arrays of Si atoms has been exposed by etehing [28], Both images show a 17 x 17 mn area.

Figure A3.10.10 STM image (55 x 55 mn ) of a Si(lOO) surface exposed to molecular bromine at 800 K. The dark areas are etch pits on the terraces, while the bright rows that run perpendicular to the terraces are Si dimer chains. The dimer chains consist of Si atoms released from terraces and step edges during etching [28],...

Figure A3.10.14 STM image of 0.25 ML Aii vapour-deposited onto Ti02(l 10). Atomie resolution of the substrate is visible as parallel rows. The Au elusters are seen to nueleate preferentially at step edges.

One class of large molecules that was investigated relatively early was liquid crystals [37, 38], and in particular the group 4-n-alkyl-4 -cyanbiphenyl (mCB). These molecules fonu a highly crystalline surface adlayer, and STM images clearly show the characteristic shape of the molecule (figure B 1.19.8). 

Figure Bl.19.8. (a) STM image (5.7 mu x 5.7 mu) of 10-alkylcyanobiphenyl on graphite (b) model showing the packing of the molecules. The shaded and unshaded segments represent the alkyl tails and the cyanobiphenyl head groups, respectively. (Taken from [38], figure 2.)...

Figure Bl.19.13. (a) Tliree STM images of a Pt(l 11) surface covered witli hydrocarbon species generated by exposure to propene. Images taken in constant-height mode. (A) after adsorption at room temperature. The propylidyne (=C-CH2-CH2) species that fomied was too mobile on the surface to be visible. The surface looks similar to that of the clean surface. Terraces ( 10 mn wide) and monatomic steps are the only visible features. (B) After heating the adsorbed propylidyne to 550 K, clusters fonn by polymerization of the C H...

Figure Bl.19.14. A sequence of STM images taken during tire construction of a patterned array of xenon atoms on a Ni(lOO) surface. Grey scale is assigned according to the slope of the surface. The atomic structure of the nickel surface is not resolved. Each letter is 5 mn from top to bottom. (Taken from [ ], figure 1.)...

Figure C2.7.6. STM images of an Ru(OOOl) surface after dissociative adsorjDtion of NO at 315 K. (A) Image (38 nmx33 nm) showing two terraces separated by a monatomic step (black stripe). (B) Close-up (6 nmx4 mn) showing an O island and individual N atoms. Individual O atoms are imaged as dashes (arrow) [9]...

Figure C2.7.9. STM images recorded during reaction of adsorbed O atoms with adsorbed CO molecules on a Pt(l 1 crystal at 247 K image size, 18 nmxl7 nm. Times are those after addition of CO to the surface see text for details [...

Pontifex G H ef a/1991 STM imaging of small metal partioles formed in anodio oxide pores J. Phys. Chem. 95 9989... 

The simplest interpretation of stm images is in terms of surface topography. However, care must be exercised in this interpretation, since in teahty, tunneling probabiUty is really measured. The many subdeties of stm data interpretation ate beyond the scope of this article. The interested reader is referred to references 14 and 15 for a more detailed discussion of these issues. 

Fig. 5.14. STM image of silicon covered with 1 /3 of a monolayer of silver [5.38].

Fig. 5.15. STM image of a Si (111)-7x7 surface exposed to 0.2 L of O2 at 300 K. The sample bias voltage was 2 V. Dark and bright sites generated by oxygen exposure are marked with A and B, respectively [5.41].

Fig. 5.16. Top STM image of a region of an 02-exposed Si (111 )-7 x 7 surface. The sites labeled with A, B, and C have not been changed by exposure to oxygen. D, E, and F correspond to oxygen-induced dark, bright, and perturbed (gray) sites, respectively. Bottom Tunneling spectra corresponding to the different sites [5.41].

We produced multilayer tubes with diameters between 20 A and 70 A and up to 2000 A in length [4]. An STM image of such tubes is shown in Fig. 3. The cylindrical shapes are well displayed. 

In Fig. 4 we show an atomic resolution image of a carbon tube. The structure imaged at the upper right corner of the picture comes from another tube. Both of them were —1000 A long. A perfect honeycomb surface structure is observed. By taking into account the curvature of the tube surface and the STM imaging profile, we find the same lattice parameter as that of. graphite (1.42 A). This directly proves that the tubu-... 

Fig. 1. Atomic resolution STM image of a 10 A nanotube of carbon with cross-sectional plot.

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