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, [N1888][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.
| Original language | English |
|---|---|
| Pages (from-to) | 2217-2226 |
| Number of pages | 10 |
| Journal | ACS Applied Electronic Materials |
| Volume | 4 |
| Issue number | 5 |
| DOIs | |
| State | Published - May 24 2022 |
Funding
The research was motivated by the mission of the BEES Center (Breakthrough Electrolyte for Energy Storage)\u2500an Energy Frontier Research Center (EFRC) funded by the U.S. DOE, Office of Science under Award No. DE-SC0019409. B.G. and J.M.K. were supported by the BEES EFRC. This research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. Preparation of the substrate materials was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. The beamline NR experiments were completed with support from the Department of Energy Office of Science Graduate Student Research program (SCGSR). The SCGSR program is administered by the Oak Ridge Institute for Science and Education for the DOE under contract number DE-SC0014664. J.M.K. acknowledges the SCGSR fellowship. R.L.S. was supported by the Fluid Interface Reactions, Structures and Transport Center, and Energy Frontier Research Center funded by the U.S. DOE, Office of Science, Basic Energy Sciences at ORNL. The authors would like to thank Bernadeta Srijanto for support in access and use of the CNMS facility and Dale Hensely for the preparation of the sputtered gold surface. The authors would also like to thank Mathieu Doucet for thorough support using the reflectivity fitting procedures as well as providing thoughtful and useful discussion towards the studied systems.
Keywords
- double layer
- in situ cell
- interfacial structure
- quaternary ammonium
- scattering length density