Direct Electrodeposition of Thin Metal Films on Functionalized Dielectric Layer and Hydrogen Gas Sensor

Abstract

Harnessing cathodic hydrogen atom generation, metals such as Pt, Pd, Cu, Au and Ni are directly electrodeposited on functionalized dielectric layers of 6 nm thick silicon oxide formed by thermal oxidation of c-Si substrate. Modifying the oxide layer with functional molecules and Au nanoparticles by simple wet chemistry, we can enhance electrodeposition efficiently and thereby electroplate nanoparticles of Pd and Pt to obtain such thin metal films. In particular, Au nanoparticles on amine-modified silicon oxides remarkably enhance electrodeposition of metal nanoparticles to create sturdy metal films on the dielectric layer, n + -Si/SiO 2 -NH 2 . Such enhancement is ascribed to good affinity of Au nanoparticles with electrodeposited metal as well as enhanced current density across the silicon oxide. For an example of potential applications, we show one-step electrodeposition Pd film on dielectric layers to fabricate conductometric hydrogen gas sensor without transferring Pd film. 8 and so on. Electrochemical methods 9,10 allow the solution process under fine and easy control without reducing agents by directly delivering electrons to precursors. Importantly, it can create stabilizer-free NPs or films with pristine surfaces that potentially serve as catalytically active sites for sensors and chemical reactions.11 Therefore, electroplating method has been widely considered as a cost-effective alternative. Especially, electro-synthesis of nanoparticles on conducting surfaces 12,13 has been attracting steady attention as highlighted by shape-control of nanoparticles using the programmed electrochemical methods on glassy carbon electrode. 14 Despite its valuable merits, programmed electro-synthesis can produce nanoparticles on the conducting electrode, while need to be transferred to other substrates, mostly dielectric materials, for practical applications in many cases. Recently reported strategy gives an inspiration of direct electrodeposition on dielectric layer; Pd NPs deposited on n + -Si/thermal SiO 2 . 15 It appears to be counterintuitive to electroplate on insulating substrates but it works owing to electrogenerated hydrogen (H) atoms in the thermal SiO 2 layer. H atom-mediated electro-reduction on thermal SiO 2 layers can be finely controlled by not only the applied bias but also pH in the solution, producing pristine Pd NPs deposited without any stabilizer or additive. H atoms, which are created by reduction of protons migrating across thermal SiO 2 layers, are expected to make precursors reduced at the interface between SiO 2 and solution. Indeed, this suggests a new breakthrough toward direct electroplating technology for thin metal films on dielectric layer.There are a few critical issues to overcome. Low density of current carried by H atoms and poor affinity of metal onto pristine SiO 2 are likely to make the metal grow too slow to be a film. Furthermore, there is a limitation in uniformity of particles in terms of both size and shape. For fine and steady control of electroplating process, it is undesir...

Cathodic electroorganic reaction on silicon oxide dielectric electrode

“…Not only oxidation at dielectric electrode as the cathode but also reduction of organic reactant occurred as shown by the electroorganic reaction from nitrobenzene to aniline ( Table 2 ). In addition, we could electrodeposit various metals directly on the dielectric electrode as reported in the previous works ( 11 , 13 ).…”

“…In this regard, there is an unusual approach that deserves attention, i.e., electrochemistry at an insulator thin film ( 7 – 13 ). Electrochemistry at an insulator, in which few charge carriers are available, is counterintuitive and thereby rarely found in the literature.…”

“…The third category is the electrochemistry at the thin film of thermal SiO 2 ( 11 – 13 ). The thermal SiO 2 layer has a highly dielectric structure with minimal defects, and with the underlying conductive substrate, it constitutes an electrolyte–oxide–semiconductor (EOS) system.…”

“…In addition, silanol defects in thermal SiO 2 are subject to electrochemical reduction, leading to asymmetric voltammetric behavior in acidic aqueous solution (only reduction observed). This thermal SiO 2 layer permits the selective migration of protons as well as the diffusion of hydrogen atoms which could react with the nearby chemical environment as shown from metal electrodeposition ( 11 , 13 ). Thus, the thermal SiO 2 layer serves as a “chemical electrode” in which electrochemical reaction generates reactive species being stored in the insulating layer before intermolecular reaction.…”

Electrochemical Atomic Layer Deposition (EC-ALD) Low Cost Synthesis of Engineered Materials a Short Review

“…Layer-by-layer deposition of Cu film formed at a Pb UPD of -443 mV exhibited higher conformability, and step coverage, and (111) texture. The results of this study suggested that the EC-ALD can used for fabricating Cu interconnects [72].…”