Electrospray ionization deposition of ultrathin ionic liquid films:[C 8C1Im]Cl and [C8C1Im][Tf 2N] on Au(111)

\u3cp\u3eWe introduce a new method for preparing ultrathin ionic liquid (IL) films on surfaces by means of electrospray ionization deposition (ESID) under ultraclean and well-defined ultra-high-vacuum (UHV) conditions. In contrast to physical vapor deposition (PVD) of ILs under UHV, ESID even allows deposition of ILs, which are prone to thermal decomposition. As proof of concept, we first investigated ultrathin [C\u3csub\u3e8\u3c/sub\u3eC\u3csub\u3e1\u3c/sub\u3eIm][Tf\u3csub\u3e2\u3c/sub\u3eN] (=1-methyl-3-octyl imidazolium bis(trifluoromethyl)imide) films on Au(111) by angle-resolved X-ray photoelectron spectroscopy (ARXPS). Films obtained by ESID are found to be virtually identical to films grown by standard PVD. Thereafter, ESID of [C\u3csub\u3e8\u3c/sub\u3eC\u3csub\u3e1\u3c/sub\u3eIm]Cl on Au(111) was studied as a first example of an IL that cannot be prepared as ultrathin film otherwise. [C \u3csub\u3e8\u3c/sub\u3eC\u3csub\u3e1\u3c/sub\u3eIm]Cl forms a wetting layer with a checkerboard arrangement with the cationic imidazolium ring and the chloride anion adsorbed next to each other on the substrate and the alkyl chain pointing toward vacuum. This arrangement within the wetting layer is similar to that observed for [C\u3csub\u3e8\u3c/sub\u3eC\u3csub\u3e1\u3c/sub\u3eIm][Tf\u3csub\u3e2\u3c/sub\u3eN], albeit with a higher degree of order of the alkyl chains. Further deposition of [C\u3csub\u3e8\u3c/sub\u3eC \u3csub\u3e1\u3c/sub\u3eIm]Cl leads to a pronounced island growth on top of the wetting layer, which is independently confirmed by ARXPS and atomic force microscopy. This behavior contrasts the growth behavior found for [C\u3csub\u3e8\u3c/sub\u3eC \u3csub\u3e1\u3c/sub\u3eIm][Tf\u3csub\u3e2\u3c/sub\u3eN], where layer-by-layer growth on top of the wetting layer is observed. The dramatic difference between both ILs is attributed to differences in the cation-anion interactions and in the degree of order in the wetting layer of the two ILs.\u3c/p\u3

First-Principles Characterization and Experimental Validation of the Solid-Solid Interface in a Novel Organosulfur Cathode for the Li-S Battery

Organosulfur silanes grafted on an aluminum current collector have been proposed and demonstrated to function as a sulfur source in the cathode for a lithium-sulfur (Li-S) battery. Bis[3-(triethoxysilyl)propyl]disulfide silane (TESPD) and bis[3-(triethoxysilyl)propyl]tetrasulfide silane (TESPT) are typical examples of organosulfur complexes used for the study. These organosulfur silanes act as an insulator. Formation of polysulfides (Li2Sx), which is a major bottleneck in the case of elemental sulfur, can be eliminated using this novel cathode. In the absence of charge-carrying polysulfide species, the role of insulating TESPD/TESPT in the charge conduction pathway is an open question. Insight into the interface between the Al current collector and grafted TESPD/TESPT at an atomic level is a prerequisite for addressing the charge conduction pathway. The systematic theoretical methodology is developed based on electronic structure calculations and ab initio molecular dynamics simulations to propose the realistic cathode model (hydration environment) for the Li-S battery. A cluster model is developed to predict the reduction potentials of TESPD/TESPT disclosing the reduction reaction with Li, resulting in the intramolecular S-S bond breaking which is validated by experimental cyclic voltammetry measurements. A realistic cathode model between the aluminum current collector and TESPD/TESPT is also proposed to mimic the experimental conditions where the Al surface was exposed to O2 and H2O. The top few layers of Al are transformed into α-Al2O3 and covered with H2O molecules in the vicinity of grafted TESPD/TESPT. The structural models are further validated by comparing simulated S 2p binding energies with experimental X-ray photoelectron spectroscopy studies

Interfacial Behavior of Thin Ionic Liquid Films on Mica

Ultrathin films of two imidazolium-based ionic liquids (ILs), [C₁C₁Im]­[Tf₂N] (=1-methyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide) and [C₄C₁Im]­[Tf₂N] (=1-butyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide) were deposited on mica surfaces by physical vapor deposition in ultrahigh vacuum. Using angle-resolved X-ray photoelectron spectroscopy (ARXPS), the initial wetting behavior, the growth characteristics, and the molecular arrangement of the ions at the interface were investigated. The measurements were performed on freshly air-cleaved mica surfaces with different carbon precoverages. ARXPS clearly reveals that the initial IL adsorption behavior strongly depends on the amount of preadsorbed carbon: On clean mica, 3D growth (complete dewetting) occurs, whereas on a fully carbon covered surface, initially a complete 2D wetting layer forms, followed by 3D growth