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A novel technique of low-energy N2 neutral beam (NB) (<10 eV) irradiation was investigated as a means of controlling the surface nitridation of self-assembled monolayers (SAMs). This low-energy process without UV photons was able to nitride the surfaces of terphenyl SAMs. Furthermore, by varying the on/off period for irradiation, a pulse-time modulated NB process could be used to control the atomic ratio of nitrogen in terphenyl molecules. Time-of-flight secondary ion mass spectra revealed that one H in the terphenyl group was substituted by a NH2 group because of irradiation by the N2 beam. The data suggested that the low-energy NB technique caused less damage to modified surfaces than the conventional plasma process did. Therefore, we believe that it is a potential damage-free process for modifying the surfaces of soft organic materials and films. [ABSTRACT FROM AUTHOR]

Abstract: The formation of self-assembled monolayer and multilayer using redox-active Ru complex molecules with phosphonic acids on SiO2 surface has been examined using X-ray photoelectron spectroscopy (XPS), ellipsometry, and time of flight secondary mass-ion spectroscopy (TOF-SIMS). We found that an introduction of a Zr adlayer leads to higher surface molecular density of Ru complex SAMs on the SiO2 surface, compared to that of obtained from the direct adsorption of Ru complex monolayer on the SiO2 surface. We further tried to fabricate a multilayer film using this molecule with Zr(IV) ion acting as a chemical glue by a successive immersion process. The XPS data revealed that the molecular densities of the multilayers were also higher for the immobilization with Zr adlayer between Ru complex and SiO2 surface than those without the Zr adlayer, suggesting that Zr adlayer is effective in forming highly packed molecular layer of phosphonic acids on SiO2 surface. We found the film growth reached a saturation point after 6 layers on the SiO2 surface. The film growth saturation can be explained by a molecular domain boundary effect encountered due to the large tilt angle of the molecular layer. [Copyright &y& Elsevier]

Abstract: The frictional properties of self-assembled monolayers (SAMs) covalently bonded to silicon (Si) substrates through Si–C or Si–O–C bonds were investigated using a pin-on-plate tribometer. Four kinds of molecules with different alkyl chain lengths and different head groups were used: 1-hexadecene, 1-hexadecanol, 1-dodecene and 1-dodecanol. The SAMs with longer alkyl chains exhibited lower friction coefficients than those with shorter alkyl chains. Of the SAMs with longer alkyl chains, the SAMs with the Si–C bond of the head group exhibited lower friction coefficients, higher wear resistance and higher durability than those with the Si–O–C bond. The head group and alkyl chain length of the molecules affected the frictional properties of the modified surfaces of the SAMs. [Copyright &y& Elsevier]

Oligo(para-phenylene-vinylene)-methanethiol of trimer and dimer have been synthesized to prepare monolayers onto Au(111). The trimer diluted in dichloromethane glows with a brilliant blue fluorescence when excited with UV light (365 nm). The absorption and emission spectra of the dimer diluted in CH[sub 2]Cl[sub 2] show a blue shift. The molecular level morphologies of the monolayers prepared on gold surfaces were probed by scanning tunneling microscopy or atomic force microscopy (AFM). The dimer is entire trans isomer, which formed highly ordered self-assembled monolayers (SAMs) on Au. The trimer is a mixture of cis–trans isomers, and did not form ordered monolayers on Au. However, the trimer molecules could be embedded in dodecanethiol SAM, and showed higher conductance than oligo(para-phenylene) molecules characterized using a conductive AFM. [ABSTRACT FROM AUTHOR]

We investigated molecular arrangement change of self-assembled monolayers (SAMs) made from [1,1′:4′,1″-terphenyl]-4-thiol (TP0) on Au(1 1 1) using scanning tunneling microscopy. In an ethanol solvent, lying down phase of TP0 molecules where the conjugated rings are expected to contact directly the Au surface, were observed at the initial stage of TP0 SAM growth (at 1 min immersion). After 24 h immersion, a molecular lattice, which is similar to (√3×√3)R30° structure (perpendicular arrangement) was observed. We further investigated the molecular arrangement dependence of electrical conduction of the TP0 SAMs using conductive atomic force microscopy technique. The resistances of the TP0 SAMs were &ap;104 Ω (at parallel arrangement) and &ap;108 Ω (at perpendicular arrangement). The resistance of the lying down TP0 SAM was lower than that of benzylmercaptane SAM where the thickness was identical to lying down TP0 SAM. The result indicated that the direct contact of the conjugated ring to the Au surface could further reduces the tunneling resistance. [Copyright &y& Elsevier]

Damage-free surface nitridation of terphenyl methanethiol self-assembled monolayers (TP1-SAMs) was investigated using a novel low-energy N2 neutral beam (NB) irradiation technique. When a conventional inductively coupled plasma process was used, x-ray photoelectron spectra confirmed that the TP1-SAM was quickly broken because ions or ultraviolet (UV) photons enhance the surface decomposition and molecular desorption. Conversely, with the N2 NB radiation process, which is free of ions and UV photons, there was little difference in the atomic ratios of x-ray photoelectron spectra before and after NB irradiation. These results suggest that low-damage surface modification is possible through the authors’ NB technique. [ABSTRACT FROM AUTHOR]

Sequential assembly of layers containing redox-active dinuclear Ru complexes that differ in their redox potential on ITO substrates afforded a series of layered structures with different potential gradients. The Ru complexes Ru-NP and Ru-CP contain tetrapodal phosphonate anchors and bridging 2,3,5,6-tetra(2-pyridyl)pyrazine or 1,2,4,5-tetra(2-pyridyl)benzene ligands, respectively. Oxidation potentials of E 1/2 = +0.83 and +1.04 V vs. Fc + /Fc ( Ru-NP ) and E 1/2 = −0.37 and 0.09 V ( Ru-CP ) were observed for the Ru(II)-Ru(II)/Ru(II)-Ru(III) and Ru(II)-Ru(III)/Ru(III)-Ru(III) couples. As the Ru-NP and Ru-CP units contain several accessible redox-active electronic states, electron transfer (ET) blockage and mediation occurred at the Ru-NP / Ru-CP heterojunction on account of the large potential gradient. An examination of the electrochemical behavior of the multilayer diblock ITO||( Ru-CP ) n |( Ru-NP ) n ( n = 1–5) heterofilms revealed that in ITO||( Ru-CP ) 4 |( Ru-NP ) 4 , the Ru(III)-Ru(III)/Ru(III)-Ru(IV) couple is involved in the electron mediation pathway on the Ru-NP / Ru-CP heterojunction. In the case of the multilayer triblock ITO||( Ru-NP ) n |( Ru-CP ) n |( Ru-NP ) n ( n = 4) heterofilms, two catalytic peaks were observed, indicating that the inner and outer Ru-NP / Ru-CP junctions display two different catalytic ET processes. In the alternating Ru-NP / Ru-CP multilayer heterofilms, the ET mediation processes are governed by the sequence order of the Ru-NP / Ru-CP heterojunction attached to the ITO electrode. In multilayer homo- and heterofilms, the dependence of the ET distance on the layer number is discussed on the basis of potential-step chronoamperometry (PSCA) results. In the multilayer Ru-NP and Ru-CP homofilms, relatively low β values were observed, while in the multilayer heterofilms, the ET rate of the catalytic wave was not affected by the number of layers, as the energy gap between the Ru-NP / Ru-CP units is the rate-determining factor. Therefore, the molecular sequence in such multilayer heterofilms, composed of layers containing Ru-NP or Ru-CP complexes, plays an important role. [ABSTRACT FROM AUTHOR]