STM and STS

The 3B premise enables the STM and STS to probe individual atomic valence, which assists formulation of the reaction kinetics. Electron clouds of metal dipoles, induced by either the 0 or the non-bonding lone pairs of the 0 , dominate the STM protmsions ions of guest or oxygen (M , 0 or 0 ) or vacancies of missing atoms produce STM depressions. Even though it locates 

The various shapes of STM protrusions represent the configuration of dipoles. For example, (1) a single dipole forms on the Cu(l 10)-O surface (2) an engaged-cogwheel and paired dipoles (quadruple) grow on the Cu(001)-O surface and, (3) the grouped dipoles (octupole) form a congested array on the (Co, Ru)(1010)-c(2 X 4)-40 and the V(001)-(72 x 3y2)R45° 0 surfaces. 

The unique STS profiles covering energies of 2.5 eV from the 0-Cu(l 10) surface give the on-site DOS information about the lone pairs ( p) and antibonding dipoles ( Ep). The STS features from O-Nb(llO) show the resonant features due to the surface-image potential, which is in accordance with observations using the inverse PES. 

Spectral identities of STS, PES, TDS, EELS, and VLEED correspond to individual processes of bond formation or their consequences on the energetic behavior of valence electrons. Oxygen-induced phase ordering and structure patterning vary 

Raman spectroscopy gives information at low frequencies about the nonbonding lone-pair interaction, being similar to that revealed by EELS. As the weaker part of a hydrogen bond, the lone-pair interaction exists in oxides, nitrides, and bio-molecules such as protein and DNA chains. 

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We refrain here from giving an extensive overview of studies on the surface structure of vanadium oxide nanolayers, as this has already been done for up to year 2003 in our recent review [97]. Instead, we would like to focus on prototypical examples, selected from the V-oxide-Rh(l 1 1) phase diagram, which demonstrate the power of STM measurements, when combined with state-of-the-art DFT calculations, to resolve complex oxide nanostructures. Other examples will highlight the usefulness of combining STM and STS data on a local scale, as well as data from STM measurements, and sample area-averaging spectroscopic techniques, such as XPS and NEXAFS, to derive as complete a picture as possible of the investigated system. 

In the following we will focus on three molecular electronics test beds as developed and employed for applications at electrified solid/liquid interfaces (1) STM and STS, (2) assemblies based on horizontal nanogap electrodes, and (3) mechanically-controlled break junction experiments. For a more detailed description of the methods we refer to several excellent reviews published recently [16-22]. We will also address specific aspects of electrolyte gating and of data analysis. 

The first one is the reaction of oxygen with a clean Si surface, or the initial stage of oxidation of the Si surface. On the Si(lll)-7 X 7 surface, the reaction activity and the local reaction mechanism are now understood at the atom-by-atom level (Avouris and Lyo, 1990 Avouris, Lyo, and Bozso, 1991 Pelz and Koch, 1991). Two different early products of oxidation and their site selectivity are identified with STM and STS. 

In order to gain further insight into the growth and characterization of the deposited polymer film we acquired in situ STM and STS measurements. 

Fig. 11. Comparison between STM and STS results obtained on cleaved 2xl-Si(lll) (left) and NH4F-treated 1 x l-H-Si(lll) (right) surfaces. STS spectra are shown together with a large-scale STM image and one or two atomically resolved STM images in each case. Note that the H-termina-tion of the surface removes the states which exist in the band gap of the 2 x 1 surface after cleavage (after [54]).

It has been emphasized that STM is sensitive to topography convoluted with the electronic density of states. Spectroscopic characterization of surface states by STM is a challening field of research to be intensified for a better understanding of the chemical reactivity of interfaces. There are still fundamental effects which could be clarified definitively by direct observation. The characterization of transport properties, as demonstrated in Sec. 6, is complementary to STM and STS, and the combination of several techniques should provide a comprehensive description of charge transfer at electrodes. 

Almost all the characterizations performed by us until now are ensemble characterizations (i.e. probing many nanostructures simultaneously). HRTEM and HRS EM do probe the structure (and elemental composition) of individual nanostructures, but they do not correlate this structure with a specific property. STM and STS measurements are real single-object measurements that reveal the size, shape, and surface atomic structure, as well as the electronic density of states (deduced the I-V characteristics). The STM/STS measurements offer a way to correlate the electronic properties of SiNWs with the nanostructure size. 

STM and STS measurements have been also performed on B-doped and undoped SiNWS [45] produced by OAG [23, 80]. The as-grown sample consisted primarily of SiNWs and nanoparticle chains coated with an oxide sheath. Samples for STM and STS measurements were prepared by dispersing the SiNWs into a suspension, which was then spin-coated onto highly oriented pyrolytic graphite (HOPG) substrates. The presence of nanoparticle chains and nanowires in the B-doped SiNWs sample was observed. Clear and regular nanoscale domains were observed on the SiNW surface, which were attributed to B-induced surface recon-... 

Zell CA, Freyland W (2001) In situ STM and STS study of NixAll-x alloy formation on Au(lll) by electrodeposition from a molten salt electrolyte. Chem Phys Lett 337 293-298... 

The combined STM and STS measurements revealed no changes of the BPn adlayer structures if the bias potential sweep was restricted to values... 

The electrodeposition of AlSb cannot be achieved from aqueous solution because the reduction potential is far beyond the aqueous electrolyte potential limit. Furthermore, the high volatility of Sb complicates the electrodeposition of AlSb from high-temperature molten salt electrolytes. Consequently, the electrodeposition of AlSb is limited to be in the room-temperature molten salts which are also termed ionic liquids. Freyland and coworkers [164,165] first explored the nanoscale electrodeposition of AlSb on Au(l 11) using in situ scanning probe techniques such as STM and STS from AlCls-l-butyl-S-methylimidzolium chloride (1 1) ionic liquid containing SbCs. At a potential positive to 0.0 V (vs. an A1/A1(III) quasireference electrode), only Sb was deposited. The codeposition of AlSb occurred at more negative potentials. The deposition obtained at —0.9 V was Sb-rich whereas that at —1.5 V was Al-rich. Homogeneous distributed stoichiometric AlSb with a band gap of 2.0 0.2 eV was obtained at —1.1 V. 

The invention of STM and STS has led to revolutionary impact on studying the chemisorption of metal surfaces on an atomic scale and in real time. In spite of the difficulties in interpreting the STM images, valuable, direct, yet qualitative information for systems with adsorbate has been gained from such observations [18, 19]. It is possible to investigate the kinetic and the static features of the chemisorbed systems using STM and STS and hence to [15] ... 

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