Self-Organization of Ions at the Interface between Graphene and Ionic Liquid DEME-TFSI

Abstract

Electrochemical effects manifest as nonlinear responses to an applied electric field in electrochemical devices, and are linked intimately to the molecular orientation of ions in the electric double layer (EDL). Herein, we probe the origin of the electrochemical effect using a double-gate graphene field effect transistor (GFET) of ionic liquid N,N-diethyl-N-(2-methoxyethyl)-N-methylammonium bis(trifluoromethylsulfonyl)imide (DEME-TFSI) top-gate, paired with a ferroelectric PbLaZrTiO (PLZT) back-gate of compatible gating efficiency. The orientation of the interfacial molecular ions can be extracted by measuring the GFET Dirac point shift, and their dynamic response to ultraviolet-visible light and a gate electric field was quantified. We have observed that the strong electrochemical effect is due to the TFSI anions self-organizing on a treated GFET surface. Moreover, a reversible order-disorder transition of TFSI anions self-organized on the GFET surface can be triggered by illuminating the interface with ultraviolet-visible light, revealing that it is a useful method to control the surface ion configuration and the overall performance of the device.

Lateral Graphene p–n Junctions Realized by Nanoscale Bipolar Doping Using Surface Electric Dipoles and Self‐Organized Molecular Anions

“…Specifically, an array of nine GFET devices with the channel width of 10 µm and channel length of 20 µm was fabricated on each sample. In order to remove various polar adsorbates on GFETs from air and chemical residues, a nondestructive light‐assisted cleaning method was developed using ultraviolet–visible light of intensity in the range of 30–60 mW cm −2 . The emission spectrum of the light source can be found in Figure S2 (Supporting Information).…”

“…It should be mentioned that the PLZT also serves as the GFET back gate that has a high gating efficiency due to a large dielectric constant in exceeding 1000. On the other hand, bis‐(trifluoromethylsulfonyl)‐imide (TFSI) anions in the ionic liquid of 1‐butyl‐1‐methylpyrrolidinium bis‐(trifluoromethylsulfonyl)‐imide (BMP‐TFSI) have been found to form a self‐organized layer at the interface between graphene and ionic liquid, resulting in strong p‐doping to graphene . Through a combination of the n‐doping by the surface electric dipoles on oxide PLZT and p‐doping by self‐assembled TFSI anions, a network of p–n junctions can be generated on the GFET channel in a remarkably robust way.…”

Room‐Temperature Reversible and Nonvolatile Tunability of Electrical Properties of Cr‐Doped In2O3 Semiconductor Thin Films Gated by Ferroelectric Single Crystal and Ionic Liquid

“…Aside from the PMN‐0.29PT as a gate material, ionic liquid DEME‐TFSI was also used as gate material to modulate the resistivity of In 2– x Cr x O 3 film due to its high capacitance of ≈2.0–2.5 µF cm −2 and comparable high gate efficiency within its electrochemical window of ≈±1–3 V . As shown in Figure c, the resistivity of the ICO011 film was measured when the PMN‐0.29PT substrate was prepolarized and the gate voltage was applied to the DEME‐TFSI.…”

Dynamic control of heat flow using a spin-chain ladder cuprate film and an ionic liquid

“…Static control by chemical and defect engineering has been widely researched 7 ; however, no research focusing on its dynamic controllability has been conducted yet. To demonstrate dynamic control, we prepared multi-layered samples that include an interface between an ionic liquid (IL) widely used for iontronics, N , N -diethyl- N -methyl- N -(2-methoxyethyl)ammonium bis(trifluoromethanesulfonic)imido (DEME-TFSI) 12 – 14 , and a spin-chain ladder system, a La–Ca–Cu–O (LCCO) polycrystalline film, fabricated by radio-frequency (rf) sputtering and post-annealing, where we initially expected that an electric double layer would yield a dense accumulation of holes 13 , resulting in a decrease in thermal conductivity. Clearly, epitaxial or highly oriented films 15 – 17 and the single crystal usually grown by the travelling solvent floating zone method 8 , 18 should be used to take advantage of their high, anisotropic thermal conduction, but we consider that the use of the polycrystalline film is preferable for increasing the active interfacial area, as described in the Discussion section, and important for practical applications 19 , 20 .…”

“…(DEME-TFSI) [12][13][14] , and a spin-chain ladder system, a La-Ca-Cu-O (LCCO) polycrystalline film, fabricated by radio-frequency (rf) sputtering and post-annealing, where we initially expected that an electric double layer would yield a dense accumulation of holes 13 , resulting in a decrease in thermal conductivity. Clearly, epitaxial or highly oriented films [15][16][17] and the single crystal usually grown by the travelling solvent floating zone method 8,18 should be used to take advantage of their high, anisotropic thermal conduction, but we consider that the use of the polycrystalline film is preferable for increasing the active interfacial area, as described in the Discussion section, and important for practical applications 19,20 .…”