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We report single molecule conductance measurement of 4,4‘-bipyridine (BPY), 1,2-di(pyridin-4-yl)ethene (BPY-EE), and 1,2-di(pyridin-4-yl)ethane (BPY-EA), in which the two pyridine rings sandwich the conjugated ethene group and the nonconjugated ethane group, respectively. The conductance measurements of the molecules bridged in two Au electrodes have been carried out in aqueous solutions using the scanning tunneling microscopy-based break junction (STM-BJ) technique. All three molecules show two sets of conductance values with the high conductance (HC) values about 8−10 times higher than the low conductance (LC) values. The HC values for BPY, BPY-EE, and BPY-EA are (4.7 ± 1.1) × 10-3 G0, (2.3 ± 0.9) × 10-3 G0, and (4.5 ± 2.2) × 10-4 G0, respectively, in an order of BPY > BPY-EE > BPY-EA. The decrease of conductance of BPY-EE can be attributed mainly to the length increase of the molecule, while the decrease of the conductance of BPY-EA reveals the degree of electron decoupling upon insertion of one CH2CH2...

In this article, the underpotential deposition (UPD) of Sb on Au(111) and Au(100) over a wide potential range in a BMIBF4 ionic liquid containing SbCl3 is investigated by cyclic voltammetry and in situ scanning tunneling microscopy (STM). The cyclic voltammograms of the two surfaces show similar features of Sb UPD, which is kinetically sluggish at high underpotential shift but rapid at low underpotential shift with a large and broad reduction peak. The total charge flux associated with the UPD suggests an equivalent of nearly 1 ML quantity of Sb deposit. In situ STM results showed precursor adsorption and several stages of the UPD. The prior UPD reversible adsorption of SbCl3 precursor occurs only on Au(111) with an ordered hexagonal array of six- and seven-membered clusters in (√31 × √31)R8.9° registration with the Au(111) surface. On both Au(111) and Au(100), the initial stage of Sb UPD (from −0.2 to −0.4 V) proceeds with the formation of similar short atomic strips of Sb atoms with a length of 2−2.5 nm...

Adsorption of Zn atoms on a Si(1 0 0)-2×1 surface was studied by scanning tunneling microscopy at room temperature. Narrow lines are grown perpendicular to the Si-dimer rows of the [1 1 0] direction at low coverage. The narrow line is formed by arraying rectangular Zn 3 dots, where a dot is composed of one Zn atom on a Si dimer and the other two in the neighboring two hollow sites. When the Si(1 0 0)-2×1 surface is covered with one monolayer of Zn, a 4×1 structure is established. More deposition of Zn on the 4×1 monolayer grows into three-dimensional Zn islands.

A new type of cyclic water hexamer chain was found to occupy the host channel of a supramolecule, formulated as [Zn(bdc)en·3(H2O)] n (1) [H2bdc=1,3-benzenedicarboxylic acid; en=ethylenediamine] and characterized by X-ray crystallography. As each water molecule was only involved in hydrogen bonding, facile removal of the lattice water was anticipated. The hydrogen-bonded water chain was completely removed by heating 1 at 96°C, forming the dehydrated solid [Zn(bdc)en] n (2). Interestingly, complex 1 can be regenerated in water vapor by a gas–solid reaction.

We report an in situ scanning tunneling microscopy study on Sn underpotential deposition (UPD) on sulfate-covered Cu(111) electrode surfaces, which represents a system of anion adsorption in an extreme situation in terms of anion−anion and anion−substrate interactions. Owing to the strong sulfate adsorption, the UPD is initiated with “parasitical” adsorption of Sn adatoms almost exclusively along the periphery of the sulfate adlayer, as manifested in the appearance of brightened Moire structure modulation at the terrace edge. A Sn-induced local enhancement of tunneling is offered to explain the brightening of the Moire structure. The initially deposited Sn adatoms displace the sulfate ions from the edge and push themselves toward the interior region of the terrace, maintaining the brightened Moire pattern at the forefront sites. Consequently, a region free of sulfate is provided for further Sn deposition. In addition to terrace edge reshaping, surface alloying is confirmed by the course-dependent anodic s...

The adsorption of Sn and Zn on a Si(1 1 1)-7×7 surface was studied by a scanning tunneling microscopy (STM). Single Sn atom is adsorbed in the faulted and unfaulted half unit cells at low coverage. When the half unit cells comprising an adsorbed single Sn atom are separated each other, no diffusion of the Sn atom to the neighboring half unit cell takes place at room temperature although the Sn atom undergoes rapid migration over the three center Si-adatoms in the half unit cell. When an adjacent half unit cell adsorbs a Sn atom, however, the two single Sn atoms in the two adjacent half unit cells are rapidly agglomerated to a Sn 2 -dimmer, that is, the diffusion barrier is lowered at the border. In addition, the single Sn atoms in the adjacent two half unit cells undergo replacement with a center Si-adatom, and a Si 4 -cluster is formed. On the other hand, adsorbed Zn atoms on a Si(1 1 1)-7×7 surface prefer to form one Zn 3 -dot in each half unit cell. As a result, a honeycomb layer composed of Zn 3 -cluster is established as increasing the coverage. These results suggest that the adsorbate–adsorbate interaction plays important role in the formation of the precursor state, which is responsible for the feature of the surface reaction and catalysis.

Underpotential deposition of Sb has been observed to induce a relaxation of Au(111) (√3 × 22) reconstruction to corrugation lines of trigonal networks. The triangles typically appear pairwise with an average length of the baselines of ∼20.2 ± 1.0 nm and a height of the triangles of ∼10.6 ± 1.4 nm at a corrugation height of ∼0.05 nm. The baselines of the trigonal network rotate by 30° with respect to the corresponding double rows of the (√3 × 22) reconstruction and align along one of the three {110} directions. An atomic resolution image reveals an apparent (√3 × √3) structure in the regions with hcp stacking sites enclosed by the triangles, which is attributed to the atomically dispersed surface alloy structure of Sb with the topmost Au atoms. Similar relaxation structures are observed with decreasing coverage via irreversible adsorption, although the size of the relaxation is alleviated. The surface alloying is confirmed by the creation of holes upon anodic stripping, the holes being confined at the conn...

Nano-materials and nano-composites formed on solid surfaces are discussed. (1) (–Cu–O–) strings and square shape (Cu2)3 dots on Ag(110), (2) unfixed shape nano-size Ni-islands on a Cu(100)–O surface covered with nano-size c(2×2)–O domains, and (3) nano-width wire and nano-size dots controlled by template of super structures; nano-width Ni-wires on a \({\text{(2}}\sqrt {\text{2}} \times \sqrt {\text{2}} ){\text{R45Cu(100)}}--{\text{O}}\) surface, nano-size Ni-dots on a Cu(100) surface covered with regularly arrayed nano-c(2 × 2)–N patches, and the supra-honeycomb layers composed of Zn3 on a reconstructed Si(111)-7 × 7 surface. We could say that weak adsorbate–adsorbate interaction plays an important role for nano-size self-assembly.

The crystal structure of the title compound, [Ag(C 18 H 15 P) 4 ] 2 (Sn 2 (CH 3 ) 4 (CF 3 CO 2 ) 6 ], consists of discrete tetrahedral cations and trans-C 2 SnO 4 octahedral dianions [C-Sn-C = 154.6 (2)°]. The dianion lies about a center of inversion and the two Sn atoms are linked unevenly by the carboxylate unit [Sn-O = 2.291 (3) A and Sn←O = 2.818 (3) A].

The six-coordinate Sn atom in bis­(diiso­propyl­ammonium) di­methyl­dioxalatostannate, [(C3H7)2NH2]2+ [(CH3)2Sn(O2CCO2)]2−, exists in a cis–C2SnO4 coordination sphere [Sn—C 2.127 (5) A; C—Sn—C 109.2 (3)°]. The anion lies on a special position of 2 symmetry. The ammonium cations and the stannate anions are linked by hydrogen bonds into a linear chain.

The six-coordinate Sn atom in bis­(diiso­propyl­ammonium) di­phenyl­dioxalatostannate(IV), [(C3H7)2NH2]2+ [(C6H5)2Sn(O2CCO2)]2−, exists in a cis-C2SnO4 octahedral coordination sphere [Sn—C 2.139 (7) and 2.144 (7) A; C—Sn—C 103.8 (3)°]. The ammonium cations and the stannate anions are linked by hydrogen bonds into a zigzag chain, running along the c axis of the monoclinic cell.

The sticking probability of ethanol $({\mathrm{C}}_{2}{\mathrm{H}}_{5}\mathrm{O}\mathrm{H})$ on a $\mathrm{Si}(111)\text{\ensuremath{-}}7\ifmmode\times\else\texttimes\fi{}7$ surface is entirely coverage independent, and the adsorption is suddenly stopped when three adatoms (half of the adatoms) are changed to $\mathrm{Si}\text{\ensuremath{-}}\mathrm{O}{\mathrm{C}}_{2}{\mathrm{H}}_{5}$ in every half unit cell. This $\mathrm{Si}(111)\text{\ensuremath{-}}7\ifmmode\times\else\texttimes\fi{}7$ surface saturated with ${\mathrm{C}}_{2}{\mathrm{H}}_{5}\mathrm{O}\mathrm{H}$, however, is active for the adsorption of NO. A more surprising fact is that the sticking probability of NO on this surface is equal to that on the virgin $\mathrm{Si}(111)\text{\ensuremath{-}}7\ifmmode\times\else\texttimes\fi{}7$ surface. That is, the sticking probability of ${\mathrm{C}}_{2}{\mathrm{H}}_{5}\mathrm{O}\mathrm{H}$ and NO on a $\mathrm{Si}(111)\text{\ensuremath{-}}7\ifmmode\times\else\texttimes\fi{}7$ surface has no influence of the coverage of Si-adatoms with $\mathrm{Si}\text{\ensuremath{-}}\mathrm{O}{\mathrm{C}}_{2}{\mathrm{H}}_{5}$. From these results, we deduced that the dissociation of NO and ${\mathrm{C}}_{2}{\mathrm{H}}_{5}\mathrm{O}\mathrm{H}$ takes place via the precursor state adsorption. The coverage of adatoms gives no effect on the sticking probability of NO and ${\mathrm{C}}_{2}{\mathrm{H}}_{5}\mathrm{O}\mathrm{H}$, the adsorption of NO on the faulted halves prefers that on unfaulted halves $(F∕U=2.2\ensuremath{\sim}2.4)$, although no such preference was observed in the adsorption of ${\mathrm{C}}_{2}{\mathrm{H}}_{5}\mathrm{O}\mathrm{H}$ $(F∕U=1)$. N and O atoms formed by the dissociation of NO migrate over the surface and are finally trapped by Si-adatoms. On the other hand, adsorption of ${\mathrm{C}}_{2}{\mathrm{H}}_{5}\mathrm{O}\mathrm{H}$ occurs by dissociating the precursor state molecule on an adatom-rest atom site, which is the final step of the adsorption. Therefore, the scanning tunneling microscopy image of ${\mathrm{C}}_{2}{\mathrm{H}}_{5}\mathrm{O}\mathrm{H}$ reflects the structure of the sites, while that of NO reflects the electron density of sites. The physical meaning of the sticking probability, preferential adsorption on the faulted or unfaulted halves, and site selectivity of the center to corner adatoms in a half unit cell are discussed.

Adsorption of 2-propanol, (CH3)2CHOH, on a Si(111)-7x7 surface was studied by scanning tunneling microscopy. (CH3)2CHOH adsorbs equally on the faulted and unfaulted half unit cells by forming Si-OCH(CH3)2 and Si-H on an adatom and rest atom pair. Si-OCH(CH3)2 is consecutively increased in each half unit cell, and the adsorption is saturated when every half unit cell has three Si-OCH(CH3)2, which corresponds to 0.5 of the adatom coverage. The sticking probability for the dissociation of (CH3)2CHOH is independent of the adatom coverage from 0 to 0.4, but it depends on coverage at higher than 0.4. By counting the darkened adatoms, Si-OCH(CH3)2 on the center adatom (m) and that on the corner adatom (n), it was found the m/n ratio is ca. 4 for the first dissociation of (CH3)2CHOH in virgin half unit cell, but it becomes ca. 1.9 and 1.8 when two and three Si-OCH(CH3)2 are contained in a half unit cell. This result reveals that the dissociation probability of (CH3)2CHOH at the adatom-rest atom pair site is influenced by the nearest Si-OCH(CH3)2 in the half unit cell.

The crystal structure of the title compound, [Ag(C18H15P)4]2[Sn2(CH3)4(CF3CO2)6], consists of discrete tetrahedral cations and trans-C2SnO4 octahedral dianions [C-Sn-C = 154.6 (2) degrees ]. The dianion lies about a center of inversion and the two Sn atoms are linked unevenly by the carboxylate unit [Sn-O = 2.291 (3) A and Sn-- O = 2.818 (3) A].

Highly oriented pyrolytic graphite (HOPG) in different orientations, graphite, glassy carbon, and aromatic compounds were ablated by a pulsed laser beam in high vacuum, and the products were recorded in situ by mass spectrometry. The (0001) plane of HOPG generated mainly C[sub 60] and C[sub 70]. The surface perpendicular to the (0001) plane could not produce C[sub 60] or other fullerenes; neither did glassy carbon. The products ablated from a polycrystalline graphite were different sized carbon clusters including C[sub 60] and other fullerenes. In addition, the fullerent products from the (0001) plane were monitored as a function of laser ablation time. It was found that after thousands of shots of laser ablation, relative abundances of larger fullerenes increased as a result of damaged graphite surface. 12 refs., 4 figs.

CH(3)OH undergoes dissociation on a Si(111)-7 x 7 surface via a two dimensionally free precursor. The sticking probability attained by the STM (scanning tunneling microscopy) was entirely coverage independent, where the observed image represented the final state of the adsorption. CH(3)OH dissociates equally on the faulted and unfaulted halves at room temperature. However, the dissociation at the center adatom-rest atom site is four times preferential to that at the corner adatom-rest atom site in each half unit cell. Such site selectivity, center/corner, changes with the occupation of adatoms in corresponding half unit cell, that is, center/corner=4 for the half unit cell with one reacted adatom, but 2.6 and 1.8 for the half unit cells with two and three reacted adatoms, respectively. Such site selectivity is well rationalized by the dissociation depending on the local conformation of the site instead of the local density of states (LDOS). The site selectivity of center/corner is well reproduced by considering the occurrence probability of the whole dissociation pattern. As the STM image represents the final state of the adsorption, if the final step of adsorption involves dissociation of molecule or precursor, the STM image reflects the dissociation probability depending on the local structure. On the other hand, if no dissociation of molecule or precursor is involved at the final step, the adsorption probability might depend on the LDOS. The adsorption of H(2)S, H(2)O, and NH(3) is also discussed from this general viewpoint of adsorption. The concept of a two dimensionally free precursor will be important to understand the kinetics of heterogeneous catalysis.

A series of carbon cluster ions have been created by direct laser vaporization of elementary carbons and organic compounds with different structures and compositions. The mass spectra of the carbon cluster ions were recorded in situ by a time-of-flight mass spectrometer and the experimental results showed that the formation of fullerenes and their relative abundances are closely related to the surface structure of the sample. Under direct laser vaporization, the products from a perfect (0001) surface of graphite were mainly C60 and C70. The surface perpendicular to the (0001) plane of graphite could not produce C60, other fullerene ions or compounds containing six-membered aromatic carbon rings. The products of amorphous carbon and aromatic compounds included C60 and other fullerenes, among which those with a mass twice that of C60 were most abundant. Furthermore, C60 and C70 could also be aggregated from direct laser vaporization. Based on these experimental results, mechanism for formation of C60 and other fullerenes is suggested.