We report a comparative study of the structure and chemistry of methyl-terminated n-alkanethiol selfassembling monolayers (SAMs) formed from liquid and vapor phases. Three different SAMs are considered: Au/ HS(CH2)"CH3, n = 5, 11, and 15. Liquid-phase-deposited films were prepared by exposure of Au substrates to dilute ethanol solutions of the n-alkanethiols followed by ethanol rinsing, and vapor-phase-deposited SAMs were prepared by exposure of the Au surface to 10%-of-saturation n-alkanethiol vapors followed by N2 purging, which removes loosely bound n-alkanethiol molecules from the surface. The matrix of six organic surfaces was studied by FTIR external reflectance spectroscopy (FTIR-ERS), ellipsometry, and cyclic voltammetry, which provide information about the average structure of the SAMs, and a newly developed scanning tunneling microscope (STM)-based method, which provides information about individual SAM defect structures. FTIR-ERS and ellipsometry indicate no detectable differences between liquid-and vapor-phase-deposited SAMs. Data obtained using cyclic voltammetry and STM show that the barrier properties of SAMs depend on the ambient phase from which the SAM assembles, the length of the rt-alkanethiol, and the chemical nature of the molecular probe used to evaluate the monolayer structure. For example, vapor-phase-deposited Au/HS(CH2)nCH3 SAMs are better CN mass-transfer barriers than their liquid-phasedeposited analogs. However, Au/HS(CH2)]5CH3 SAMs are better CNbarriers when they are formed from the liquid phase. In contrast, Au/HS(CH2)nCH3 SAMs prepared from either phase present nearly identical barriers to electron exchange between the Au surface and solution-phase Ru(NH3)63+. STM reveals some of the nanostructural details of SAMs and confirms that individual defects govern their barrier properties.

We present the results of a study of the interactions between three different acid-terminated self-assembled monolayer (SAM) surfaces and three basic vapor-phase probe molecules. The SAMs are composed of 4-mercaptobenzoic acid (MBA), 3-mercaptopropionic acid (MPA), and 11-mercaptoundecanoic acid (MUA), and the vapor-phase probes are, in order of increasing solution-phase acidity, decylamine, pyridine, and pyrazine. Our results are based on data from surface infrared spectroscopy and thickness-shear mode mass sensors. We find that all three SAMs irreversibly bind approximately one monolayer of decylamine, although there are slight differences that correlate with the structural nuances of the SAMs. The MPA and MBA SAMs bind decylamine through an electrostatic interaction brought about by transfer of a proton from the acid to the base. Because the MUA SAM is more impenetrable than the others, complete proton transfer is hindered, and binding of decylamine arises through a combination of proton transfer and strong hydrogen bonding. In the presence of its vapor, pyridine adsorbs to MBA surfaces at near-monolayer coverage, but upon N2 purging about two-thirds of it desorbs. Only one-half monolayer of pyrazine, which is less basic than pyridine, adsorbs to the MBA SAM, and upon N2 purging, about two-thirds of it desorbs. The aliphatic acid SAMs follow a similar trend. The results of this study indicate that the extent of base binding correlates most strongly with the structural nuances of the acidic SAMs and the relative basicity of the vapor-phase bases. These results are relevant to SAM-based chemical sensors.

A new in-situ application of FTIR external reflectance spectroscopy (FTIR-ESR), which is useful for real-time evaluation of monolayer and multilayer adsorption and reaction chemistry at the vapor/solid interface at pressures near 1 atm, is described. The utility and versatility of the method is illustrated by two proof-of-concept experiments. The first experiment involves adsorption of H2N(CH2)9CHS onto a naked Au substrate from the vapor phase. In-situ FTIR-ERS indicates that the amine forms a stable, ordered monolayer on the Au surface; that is, H2N(CH2)9-CHs self-assembles onto the Au surface from the vapor phase. The second experiment involves vapor-phase adsorption of a HS(C6H5)OH monolayer onto a naked Au surface, followed by an insitu coupling reaction with [CHs(CH2)7](CH3)2-SiCl. Real-time FTIR-ERS characterization of the organic bilayer is consistent with previously reported ex-situ FTIR-ERS results; however, kinetic data can be abstracted from the new in-situ data. The rate constant for the surface silane coupling reaction is estimated to be 0.30 min-1.

Dramatic growth of lithium (Li) dendrite and structural deterioration of LiCoO2 (LCO) lead to rapid failure of a high-voltage Li∥LCO battery. The nitrile group (−CN) is beneficial to maintain the integrity of the LCO lattice due to its strong affiliation to Co ions, whereas the −CN bond is incompatible with the Li metal anode, leading to form a deleterious solid electrolyte interphase (SEI) film. Herein, a dual-functional electrolyte additive potassium selenocyanate (KSeCN) is introduced to construct stable and dense SEI/cathode electrolyte interphase (CEI) films by synergistic effects with −Se and −CN groups, resulting in uniform Li deposition and a stabilized LCO lattice during cycling. With a trace amount of KSeCN (0.1 wt %) in conventional carbonated electrolyte, the Li∥LCO battery exhibits promoted cycling performance at high charge cutoff 4.6 V. This work provides a strategic guidance for rational design of electrolyte to construct stable SEI and CEI films, to achieve a high-energy-density Li∥LCO battery with great performance.

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Elevating the cutoff charge voltage (≥ 4.65 V) of LiCoO2 (LCO) arouses the big challenge between the pursuit of high energy density and long cycling life of LCO-based batteries. Herein,...