Triangular Gold Research Articles

「マイクロ・ナノ加工技術の最前線」自己組織化分子多層膜を用いた超高精密ナノリソグラフィー

The combination of self-, directed and positional assembly techniques, i. e., “bottom up” fabrication, is demonstrated in this work because they will be essential for patterning and connecting future nanodevices. An array of polystyrene spheres was used instead of conventional lithographic techniques to make “parent” structures. A close-packed monolayer of polystyrene spheres (diameter∼400 nm) was used as a hard mask. Gold was vapor deposited through this mask and lift-off of the spheres produced arrays of triangular gold dots, which were used as “parent” structures. Multilayers of 16-mercaptohexadecanoic acid and Cu2+ ions were selectively deposited as a molecular resist onto these gold dots followed by chromium deposition creating a daughter structure on the substrate. After lift-off of the molecular resist, uniform spacings between “parent” and “daughter” structures are observed using a scanning electron microscope. Nanometer-scale spacing can be controlled around the nanostructures by simply changing the number of layers in the molecular resist or by using molecules of different lengths. In the near future, many applications using this method are expected to impact nanofabrication, such as nanoelectronic devices and micromachines.

4-Nitrothiophenol SAM on Au(111) Investigated by in Situ STM, Electrochemistry, and XPS

SAMs formed from 4-nitrothiophenol (4-NTP) on Au(111) were studied in different electrolytes with in situ STM, cyclic voltammetry, and X-ray photoelectron spectroscopy. The 4-NTP SAM exhibits structural changes with the electrode potential, which coincide with the reduction steps of the nitro group. In general, at potentials where no faradaic processes occur, small domains (10 nm × 2 nm) with ordered structures are observed together with unordered phases, the latter ones occupying ca. 50% of the substrate surface. When subjecting the surface to negative potentials, the ordered structure disappears and monatomic-high islands covering 40% of the surface emerge, the nature of which could not be elucidated unequivocally. This starts at 20 mV versus saturated calomel electrode (SCE) in 50 mM H2SO4 and at −240 mV versus SCE in 50 mM Na2SO4. Upon further reduction, SAM reductive desorption is observed directly in scanning tunneling microscopy. This leads to a bare gold surface with characteristic triangular gold...

Alteration of the aurophilic interactions in trimeric gold(I) compounds through charge transfer. Behavior of solvoluminescent Au(3)(MeN=COMe)(3) in the presence of electron acceptors.

The ability of the triangular gold(I) complex, Au(3)(MeN=COMe)(3), which as a solid displays the novel property of solvoluminescence (see: Vickery, J. C.; Olmstead, M. M.; Fung, E. Y.; Balch, A. L. Angew.Chem., Int. Ed. Engl. 1997, 36, 1179) to function as an electron donor has been demonstrated through spectroscopic studies and isolation of crystalline adducts with organic acceptor molecules. Four such adducts with nitro-9-fluorenones have been isolated and subject to single-crystal X-ray diffraction study. These are deep yellow [Au(3)(MeN=COMe)(3)].[2,4,7-trinitro-9-fluorenone], red [Au(3)(MeN=COMe)(3)].[2,4,5,7-tetranitro-9-fluorenone], red [Au(3)(MeN=COEt)(3)](2).[2,7-dinitro-9-fluorenone], and red [Au(3)(MeN=COEt)(3)](2).[2,4,7-trinitro-9-fluorenone]. The solid-state structures of [Au(3)(MeN=COMe)(3)].[2,4,7-trinitro-9-fluorenone] and [Au(3)(MeN=COMe)(3)].[2,4,5,7-tetranitro-9-fluorenone] consist of columns in which the planar gold(I) trimers and the nearly planar nitro-9-fluorenones are interleaved with the gold trimers making face-to-face contact with the nitroaromatic portion of the electron acceptor. Thus the organic acceptors disrupt the aurophilic interactions present in crystalline [Au(3)(MeN=COMe)(3)] itself. However, in [Au(3)(MeN=COEt)(3)](2).[2,7-dinitro-9-fluorenone] and [Au(3)(MeN=COEt)(3)](2).[2,4,7-trinitro-9-fluorenone], aurophilic interactions are found which produce dimers, [Au(3)(MeN=COEt)(3)](2), with nearly trigonal prismatic Au(6) cores. These dimers are interleaved with the nitro-9-fluorenone molecules to again form extended columns in which the components make face-to-face contact. Despite the fact that the gold atoms in [Au(3)(MeN=COMe)(3)] and [Au(3)(MeN=COEt)(3)] are in exposed sites and only two-coordinate, there is no evidence of additional coordination of the nitro-9-fluorenones with gold centers in the crystalline adducts.

An approach to long-range electron transfer mechanisms in metalloproteins: in situ scanning tunneling microscopy with submolecular resolution.

In situ scanning tunneling microscopy (STM) of redox molecules, in aqueous solution, shows interesting analogies and differences compared with interfacial electrochemical electron transfer (ET) and ET in homogeneous solution. This is because the redox level represents a deep indentation in the tunnel barrier, with possible temporary electronic population. Particular perspectives are that both the bias voltage and the overvoltage relative to a reference electrode can be controlled, reflected in spectroscopic features when the potential variation brings the redox level to cross the Fermi levels of the substrate and tip. The blue copper protein azurin adsorbs on gold(111) via a surface disulfide group. Well resolved in situ STM images show arrays of molecules on the triangular gold(111) terraces. This points to the feasibility of in situ STM of redox metalloproteins directly in their natural aqueous medium. Each structure also shows a central brighter contrast in the constant current mode, indicative of 2- to 4-fold current enhancement compared with the peripheral parts. This supports the notion of tunneling via the redox level of the copper atom and of in situ STM as a new approach to long-range electron tunneling in metalloproteins.

Submicron contacts for electrical characterization of semiconducting WS2 thin films

We report a new method to characterize the local electronic properties of polycrystalline semiconducting thin films. A lattice of triangular gold electrodes, with a typical area of 0.2 μm2, is evaporated on a p-type WS2 film. With the help of a conductive atomic force microscope, the current–voltage characteristics of the contacts established between the gold electrodes and the WS2 film are measured. A linear dependence of the current versus voltage is obtained on gold triangles in contact with grain edges. This indicates a high level of doping or degeneracy of the semiconductor at the grain edges. The electrodes deposited on flat WS2 crystallites form rectifying diodes with the underlying grains. Barrier heights of 0.56–0.74 eV and diode ideality factors between 1.15 and 2 are determined. Under illumination, open-circuit voltages up to 500 mV can be measured on some contacts. A short response time of the photocurrent is observed (<0.1 ms) when the diodes are reversed biased, which is related to intrinsic properties of the crystallites. When the diodes are forward biased a longer response time is measured (>100 ms), linked to trapping effects at grain boundaries.

Spectroscopy, photoredox properties and X-ray crystal structures of triangular gold(I) and silver(I) phosphine complexes

The reaction of HC(PPh2)3 with K[AuCl4] in the presence of 2,2′-thiodiethanol in methanol yielded [Au3{HC(PPh2)3}2Cl]2+. The related [Ag3{HC(PPh2)3}2]3+ was prepared by the reaction of HC(PPh2)3 with Ag(CF3SO3) in dichloromethane. Both complex cations were isolated as perchlorate salts. The X-ray structures of [Au3{HC(PPh2)3}2Cl][ClO4]2 and [Ag3{HC(PPh2)3}2][ClO4]3 have been determined: [Au3{HC(PPh2)3}2Cl][ClO4]2·2MeCN, monoclinic, space group C2/c(no. 15), a= 26.466(3), b= 12.741(2), c= 23.012(5)A, β= 98.89(1)° and Z= 4; [Ag3{HC(PPh2)3}2][ClO4]3·2MeCN, monoclinic, space group, P21/n, a= 14.597(4), b= 23.047(2), c= 22.485(3)A, β= 91.49(2)° and Z= 4. Both [Au3{HC(PPh2)3}2Cl]2+ and [Ag3{HC(PPh2)3}2]3+ consist of three metal atoms arranged in a nearly equilateral triangle with the M–M–M angles close to 60°. The measured intramolecular Ag–Ag and Au–Au distances of 3.1618(5)–3.2228(9) and 2.9220(8)–3.0889(8)A respectively, indicate that the Au–Au bonding interaction is much stronger than that for Ag–Ag. The UV/VIS spectrum of an acetonitrile solution of [Au3{HC(PPh2)3}2Cl]2+ exhibits intense absorption bands at 270 and 290 nm, assignable to the dσ·→ pσ transitions. For [Ag3{HC(PPh2)3}2]3+ the UV/VIS spectrum is virtually identical to that of the free HC(PPh2)3. Excitation of a degassed acetonitrile solution of [Au3{HC(PPh2)3}2Cl]2+ at 300–400 nm at room temperature leads to an observed photoluminescence centred at ca. 537 nm with a lifetime of 11 µs [ϕ=(1.0 ± 0.1)× 10–3]. The excited-state redox potential, [Au3{HC(PPh2)3}2Cl]3++ e–→[Au3{HC(PPh2)3}2Cl]2+*, determined by quenching studies with a series of pyridinium acceptors, is –1.6(2) V vs. saturated sodium chloride calomel electrode (SSCE).