Molecular and Ionic Dipole Effects on the Electronic Properties of Si-/SiO₂-Grafted Alkylamine Monolayers

Abstract

In this work, we demonstrate the tunability of electronic properties of Si/SiO substrates by molecular and ionic surface modifications. The changes in the electronic properties such as the work function (WF) and electron affinity were experimentally measured by the contact potential difference technique and theoretically supported by density functional theory calculations. We attribute these molecular electronic effects mainly to the variations of molecular and surface dipoles of the ionic and neutral species. We have previously shown that for the alkylhalide monolayers, changing the tail group from Cl to I decreased the WF of the substrate. Here, we report on the opposite trend of WF changes, that is, the increase of the WF, obtained by using the anions of these halides from Cl to I. This trend was observed on self-assembled alkylammonium halide (-NH X, where X = Cl, Br, or I) monolayer-modified substrates. The monolayer's formation was supported by ellipsometry measurements, X-ray photoelectron spectroscopy, and atomic force microscopy. Comparison of the theoretical and experimental data suggests that the ionic surface dipole depends mainly on the polarizability and the position of the counter halide anion along with the organization and packaging of the layer. The described ionic modification can be easily used for facile tailoring and design of the electronic properties Si/SiO substrates for various device applications.

Sulfation Patterns of Saccharides and Heavy Metal Ion Binding

“…Each assembly step was analyzed by three different methods: spectroscopic ellipsometry, wettability by contact angle (CA), and atomic force microscopy (AFM). In the first step, the silicon wafer was oxidized by using a reported procedure . The silicon‐dioxide layer activation resulted in a thickness of 17.9 Å, root mean square (RMS) roughness of 0.67 nm and contact angle lower than 20°.…”

“…To avoid any metal-mediated process, we relied on copper-free, strain-promoted click reaction of azido sHA4 with ad ibenzocyclooctyne (DBCO) moiety that was previously anchored to am odified oxide surface ( Figure 2). [63,64] The silicon-dioxide layer activation resulted in a thickness of 17.9 ,r oot mean square (RMS) roughness of 0.67 nm and contact angle lower than 208.T he resultingo xide layer was reacted with (3-aminopropyl)triethoxysilane (APTES) and an additional smoother and more hydrophobic layer was formed with at hickness of 6.3 ,aroughnesso f0 .17 nm, and aC Ao f5 68. In the first step, the silicon wafer was oxidized by using ar eported procedure.…”

“…In the first step, the silicon wafer was oxidized by using ar eported procedure. [63,64] The silicon-dioxide layer activation resulted in a thickness of 17.9 ,r oot mean square (RMS) roughness of 0.67 nm and contact angle lower than 208.T he resultingo xide layer was reacted with (3-aminopropyl)triethoxysilane (APTES) and an additional smoother and more hydrophobic layer was formed with at hickness of 6.3 ,aroughnesso f0 .17 nm, and aC Ao f5 68.…”

Synergy of Ionic and Dipolar Effects by Molecular Design for pH Sensing beyond the Nernstian Limit

“…[29] The dipole moment changes between the neutral and the protonated states are 6.59 and 17.76 D for the azonium and ammonium ions, respectively, and the dipole direction is the same as their neutral states. The ammonium ions generated from protonation can further attract anions to form ion pairs through electrostatic interaction and consequently generate ionic dipoles between the cations and the anions, when there are anions around, [37,38] as shown by the simulation results in Figure 1d-right. In addition, the ionic dipole has an opposite dipole direction compared to the neutral case (Figure 1d-left), and the dipole moment of the ion-pair shows a strong dependence on the anion size.…”

Probing an Interfacial Ionic Pairing‐Induced Molecular Dipole Effect in Ionovoltaic System

“…[1,2,4] As an offshoot of them, ion-surface molecular interactions at SAM were revealed to altering dipolar moment of the surface molecules or modulating the intrinsic potential emanating from the SAM, thereby controlling electron energetics of the solid electrode or an electrostatic potential profiles at electrical double layer. [5][6][7][8][9][10] These phenomena were based on various specific interactions, originated from physicochemical natures of associating species [11][12][13][14][15] (e.g., coordination bonding, coulombic pairing, and hydrogen bonding), and made the surface molecule redistribute its charges by building new bond dipoles or structural changes, thereby altering the dipolar characteristic of SAM. [5][6][7]9] Although these interfacial molecular effects play a substantial role in various electronic and electrochemical systems, comprehensive molecular pictures in these interactions are still limited due to interfacing intricate electrolytes and observing conditions.…”