The interaction of solvent molecules with metallic surfaces impacts many interfacial chemical processes: We investigate the chemical and structure evolution that follows adsorption of the polar solvent dimethylformamide (DIM) on Ag(111). An Ag(DMF)(2) coordination complex forms spontaneously by DMF etching of Ag(111), yielding Allied films of the complexes and DMF. Utilizing ultrahigh vacuum scanning tunneling microscopy (UHV-STM), in combination with X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) computations, we map monolayer phases from the 2-D gas regime, consisting of a binary mixture of DMF and Ag(DMF)(2), through the saturation monolayer limit, in which these two chemical species phase separate into ordered islands. Structural models for the near-square DMF phase and the chain-like Ag(DMF)(2) phase are presented and supported by DFT computation. Interface evolution is summarized in a surface pressure-composition phase diagram, which allows structure prediction over arbitrary experimental conditions. This work reveals new surface coordination chemistry for an important electrolyte electrode system and illustrates how surface pressure can be used to tune monolayer phases.

We report an ultrahigh vacuum scanning tunneling microscopy study of thermally driven interface rearrangement in binary films of [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) and zinc phthalocyanine (ZnPc), a model electron acceptor electron donor system for organic solar cells. Neat PCBM films have been previously shown to undergo a transition from a disordered (glassy) phase to a crystalline hexagonal close-packed (hcp) arrangement above a critical packing density of 0.9 molecules/nm(2). We now show how local PCBM density has a critical impact on binary film structure evolution. Bilayer films of PCBM and ZnPc undergo a spontaneous vertical phase separation to PCBM/ZnPc/Au(111) stacking at lower (<0.9 molecules/nm(2)) PCBM densities. This vertical phase separation is shown to be electrostatically preferred, with the PCBM/ZnPc/Au(111) dimer stacking lower in energy by 0.16 eV/pair relative to ZnPc/PCBM/Au(111) stacking. At higher local PCBM densities, sufficient to nucleate hcp PCBM domains, ZnPc molecules do not displace PCBM to the second layer. PCBM density variations in binary films thus give rise to heterogeneous interface structures.

Objective: Improve the efficiency of Organic Solar Cells by studying the phase separation through contact angle (CA) measurements of the molecules deposited on the silicon substrate. Materials and Methods: The materials used are tetranitro-zinc phthalocyanine (tn-ZnPc) and PCBM, separately and combined in a mixture (in ratio 1:1) deposited on silicon surface by spin-coating. We used AFM imaging to analyze the morphology of the molecules and a Matlab algorithm to extract the contact angle. Results: We found an increasing in the CA in the mixture, compared to that for the PCBM alone, proving that the tn-ZnPc changes the tension between PCBM and ambient.

Our previous studies demonstrated great potential of methyl methacrylate and vinylbenzyl chloride based copolymer electrolytes for alkaline fuel cell applications. In this study, a number of factors including polymer composition drift, molecular weight, and polymer crosslinking is investigated to understand their effects and to precisely control the electrolyte properties including conductivity, mechanical strength, and water mass-uptake. This investigation demonstrated a controllable polymerization procedure of poly (methyl methacrylate-co-vinylbenzyl chloride) membrane with tunable and balanced properties, which is promising for the alkaline fuel cell technology.

Thin films of metal phthalocyanine (MPc) are grown on an Au(111) support with a newly developed aerosol molecular beam deposition source and characterized in situ via ultrahigh vacuum scanning tunneling microscopy. MPcs are delivered to Au(111) in a series of N2-entrained microsized solvent droplets of variable surface residence time. Phthalocyanine film registration to the herringbone reconstruction of the Au(111) surface, indicative of thermodynamically favored structure, is observed at submonolayer coverages for aromatic solvents with long residence times. Aerosol-deposited monolayer film structures are noncrystalline with tilted MPc orientations and vacancy nanocavities. Upon annealing, MPc molecules adopt flat-lying orientations with respect to the substrate and vacancies are eliminated. Film morphologies indicate solvation-mediated film nucleation and growth, with less long-range ordering that in vapor-generated films.

Structure evolution in monolayer films of [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) deposited on Au(111) was determined via ultrahigh vacuum scanning tunneling microscopy (UHV-STM). Molecular organization was monitored from a glassy phase, produced via a pulsed microaersol molecular beam deposition source, through ordered arrangements, following thermal annealing. At lower PCBM densities, two double-row structures arise, involving distinct PCBM hydrogen-bonding motifs, reminiscent of patterns produced by solvent-free deposition. At higher PCBM monolayer densities, hexagonal close-packed islands of PCBM form, with a 0.98 nm nearest-neighbor spacing in good agreement with structure predictions [Napoles-Duarte et al. Phys. Rev. B 2008, 78, 035425]. Under UHV conditions, solvent molecules are retained in the organic layer to temperatures up to 200 C, inhibiting PCBM ordering. Following complete solvent removal, nanosized hexagonal close-packed PCBM islands show arrested development, indicating a kinetic barrier to island growth, attributed to reorientational energy costs.