The interaction between an adsorbed 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [BMP][TFSA], ionic liquid (IL) layer and a Ag(111) substrate, under ultrahigh-vacuum conditions, was investigated in a combined experimental and theoretical approach, by high-resolution scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and dispersion-corrected density functional theory calculations (DFT-D). Most importantly, we succeeded in unambiguously identifying cations and anions in the adlayer by comparing experimental images with submolecular resolution and simulated STM images based on DFT calculations, and these findings are in perfect agreement with the 1:1 ratio of anions and cations adsorbed on the metal derived from XPS measurements. Different adlayer phases include a mobile 2D liquid phase at room temperature and two 2D solid phases at around 100 K, i.e., a 2D glass phase with short-range order and some residual, but very limited mobility and a long-range ordered 2D crystalline phase. The mobility in the different adlayer phases, including melting of the 2D crystalline phase, was evaluated by dynamic STM imaging. The DFT-D calculations show that the interaction with the substrate is composed of mainly van der Waals and weak electrostatic (dipole-induced dipole) interactions and that upon adsorption most of the charge remains at the IL, leading to attractive electrostatic interactions between the adsorbed species.

The ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [BMP][TFSA] is a promising candidate for improved nextgeneration rechargeable lithium−ion batteries. We here report results of a model study of the reactive interaction of (sub-)monolayers and multilayers of [BMP][TFSA] with lithium (Li) on Cu(111), employing scanning tunnelling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIRS) under ultrahigh vacuum (UHV) conditions. Upon post-deposition of Li on [BMP][TFSA] multilayers at 80 K, we identified changes in the chemical state of the [TFSA] anion and the [BMP] cation as well as in the IR absorption bands related to the anion. These changes are most likely due to the decomposition of the IL adlayer into a variety of products like LiF, Li 2 S, and Li 2 O upon anion decomposition and LiN 3 , LiC x H y N, and Li x CH y upon cation decomposition, where the latter includes cracking of the pyrrolidinium ring. Deposition of Li on [BMP][TFSA] (sub-)monolayer-covered surfaces led to similar decomposition patterns, and the same was also observed for the reverse deposition order. The addition of the corresponding amounts of Li to a [BMP][TFSA] adlayer resulted in distinct changes in the STM images, which must be due to the surface reaction. After annealing to 300 K, the core-level peaks of the cation lose most of their peak area. Upon further heating to 450 K, the anion is nearly completely decomposed, resulting in LiF and Li 2 S decomposition products that dominate the interface.

Surface functionalization of an inorganic surface with bio-organic molecules is often aimed at creating a "permanent" bio-organic surface with receptor functional groups. We show here that L-cysteine can be used to transform a highly reactive Si(111)7×7 surface to not just a permanent bio-organic surface but also a semipermanent (or renewable) and a temporary bio-organic surfaces by manipulating the exposure. In the early growth stage, the strong bonding between the first cysteine adlayer and the Si substrate through Si-N or Si-S linkages in unidentate or bidentate arrangement provides permanent biofunctionalization by this interfacial layer. This interfacial layer can be used to build a transitional layer (second adlayer) mediated by interlayer vertical hydrogen bonding between an amino group and a carboxylic acid group. Further exposure of cysteine eventually leads to a zwitterionic multilayer film involving electrostatic interactions between cation (-NH3(+)) and anion moieties (-COO(-)). The interlayer hydrogen bonding therefore provides temporary trapping of bio-organic molecules as the second transitional layer that is stable up to 175 °C. This transitional layer can be easily removed by annealing above this temperature and then regenerated with the same molecular layer or a different one by "renewing" the interlayer hydrogen bonds. We also illustrate coverage-dependent adsorption structures of cysteine, from bidentate to unidentate attachments and to self-assembled multimers, involving formation of intralayer horizontal N···H-O hydrogen bonds, by combining our X-ray photoemission data with the local density-of-state images obtained by scanning tunnelling microscopy.

In this work, we aim at a molecular scale understanding of the interactions and structure formation at the electrode|electrolyte interface (EEI) in Li-ion batteries. Therefore, the interaction of the key electrolyte component ethylene carbonate (EC) with Cu(111) was investigated under ultrahigh vacuum conditions. Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIRS), and dispersion-corrected density functional theory (DFT-D) calculations were employed. After vapor deposition of EC (sub-) monolayers on Cu(111) at 80 K, STM measurements (100 K) reveal a well-ordered commensurate superstructure, in which EC molecules assume different configurations and whose total adsorption energy is mainly governed by van der Waals interactions, as demonstrated by DFT-D. In the temperature range between 150−220 K, competing desorption and decomposition into −CO, −C−O−C−, −C−H, and −C−C− compounds, as derived by XPS and confirmed by FTIRS, result in distinct changes of the adlayer composition. Similar heating of an EC multilayer film from 80 K to room temperature results in a surface that is almost completely covered with adsorbed, carboncontaining decomposition products. This can be interpreted as the initial stage of chemical EEI formation, and the relevance of these results for battery applications is discussed.