Smooth Modified Surfaces of Silicon for the Study of Ionic Liquid Interfaces by Neutron Reflectometry

Abstract

Silicon surfaces with termination of hydrogen (H−Si), quartz, native silicon (native-Si), and chemically deposited (Au−Si) cd and sputtered gold (Au−Si) s were fabricated with roughness less than 6 Å to study the solid−liquid interface of the ionic liquid (IL) methyltrioctylammonium bis(trifluoromethylsulfonyl)imide, [N 1888 ][TFSI], by neutron reflectometry (NR). The modifications made to the silicon surface were to obtain a native positive or negative charge similar to a charged surface in electrochemical systems. The differences in scattering length density (SLD) based on mass density and composition of IL were examined. Perpendicular to the substrate surface, a distinct transition between the first ion layer and the bulk liquid is resolved out of the reflectivity data for the gold surfaces and in particular the chemically deposited Au−Si. Other interfaces are best described by a diffuse transition between regions of different SLDs. The diffuse transitions between SLDs observed here suggest that the interfacial structure of IL, while ordered, is best described by a continuous variation in composition as opposed to distinct layers of ions.

Understanding the Electrode–Electrolyte Interfaces of Ionic Liquids and Deep Eutectic Solvents

“…In our recent study, Klein et al, 35 we minimized the surface roughness by utilizing Si surfaces to study the interfacial behavior of [N 1888 ][TFSI] by NR. Si surfaces were chemically modified to achieve a native surface charge to mimic polarization on the electrode surface.…”

“…The overlaps between the shaded regions represent the roughness that emerges from the model. Reprinted with permission from ref . Copyright 2022, American Chemical Society.…”

“…Recently, a wider range of techniques has been used to study ILs at interfaces. Scanning tunneling microscopy (STM) has been used to investigate the lateral arrangement of ions in the interface with limited success due to insufficient atomic resolution. , Fourier Transform Infrared Spectroscopy (FTIR), Surface Enhanced Infrared Absorption Spectroscopy (SEIRAS), Shell Isolated Nanoparticle Raman Spectroscopy (SHINERS), Surface Enhanced Raman Spectroscopy (SERS), − Sum Frequency Generation (SFG), − and Neutron Reflectivity (NR) have been demonstrated for probing the interface and acquiring a compositional knowledge to complement the electrochemical techniques. However, theoretical guidance in interpreting and analyzing the data from these advanced techniques is still needed in order to develop a unified understanding.…”

Elucidating the assembly of nanoparticle organic hybrid materials (NOHMs) near an electrode interface with varying potential using neutron reflectivity

“…36 NR has been used extensively to investigate the ordering of different ionic liquid-based electrolytes near electrode interfaces. [37][38][39][40] The technique is also used to highlight the ordering of nanoparticles near modified surfaces. 41,42 In this study, we investigate the ordering of HPE polymer and NOHM-I-HPE, considered as electrolyte additives, near two different electrode surfaces (SiO x and Au).…”

Tailoring Electrochemical CO2 Reduction on Copper by Reactive Ionic Liquid and Native Hydrogen Bond Donors

“…The thermodynamics and kinetics of CO 2 RR are highly dependent on the electrode‐electrolyte interface which presents complexities in IL electrolytes. While the cations are attracted to the negatively polarized electrode surface, anions can influence the crowding of the interface [26] and the cation adsorption on the surface through electrostatic interaction and hydrogen bonding [27] . It was shown by sum frequency generation (SFG) technique on the Pt surface by tracking the change in intensities of the spectra that Im cations orient in a tilted orientation to the electrode with the C 2 position facing the surface and that the ring becomes parallel to the surface with applied negative potentials [28] .…”