Towards a metallic top contact electrode in molecular electronic devices exhibiting a large surface coverage by photoreduction of silver cations

Abstract

In this contribution the photoreduction of silver ions coordinated onto a Langmuir-Blodgett monolayer is presented as an effective method for the deposition of the top contact electrode in metal/monolayer/ metal devices. Silver cations were incorporated from an aqueous AgNO 3 sub-phase of Langmuir films of 4,4 0 -(1,4-phenylenebis(ethyne-2,1-diyl))dibenzoic acid upon the transference of these films onto a metallic substrate. Subsequent irradiation of the silver-ion functionalized Langmuir-Blodgett films with 254 nm light results in the photoreduction of silver cations to produce metallic silver nanoparticles, which are distributed over the organic monolayer and exhibit a surface coverage as large as 76% of the monolayer surface. Electrical properties of these metal/monolayer/metal devices were determined by recording I-V curves, which show a sigmoidal behaviour indicative of well-behaved junctions free of metallic filaments and short-circuits. The integrity of the organic monolayer upon the irradiation process and formation of the silver top-contact electrode has also been demonstrated through cyclic voltammetry experiments.

High surface coverage of a self-assembled monolayer by in situ synthesis of palladium nanodeposits

“…25 nm radius, 0.4 N m −1 spring constant and 70 kHz resonance frequency). 46,53,[71][72][73] Under these conditions, the tip makes intermittent contact with the surface at a frequency of 2 kHz and a low maximum force ( peak-force) to limit damage to the surface and detrimental lateral forces. Therefore, the peakforce tapping mode is useful for the conductivity mapping of soft or fragile samples, since lateral forces are avoided.…”

“…51 These metallic palladium sheets are aggregated onto the monolayer to generate larger palladium nanodeposits (PdND) across the surface. This method results in a larger surface coverage of palladium than that previously achieved with gold 45,47 or silver 53 by the assembly of metal nanoparticles onto organic monolayers.…”

“…15,[26][27][28][29][30] A wide variety of techniques to deposit the top metal electrode onto a molecular monolayer have been described in the literature including direct and indirect evaporation, 11,[31][32][33][34][35][36][37][38] use of liquid metals, 11,34,39,40 flip chip lamination, 34,41 electrodeposition, [42][43][44] surface-diffusion-mediated deposition, 44 chemisorption of metal nanoparticles onto surface-functionalised monolayers, 45 thermal induced decomposition of an organometallic monolayer, 46 and photoreduction of a metal precursor. 47,48 The most significant problems in the deposition of the top-contact electrode are those related to damage of the functional molecules during the metallization process of the monolayer or penetration of the growing top-contact through the monolayer, which results in short circuits. In addition, many of the proposed 'soft' methods that avoid penetration of the growing metal electrode through the monolayer result in a relatively low surface coverage of the monolayer by the newly fashioned top contact.…”

Nanofabrication Techniques in Large-Area Molecular Electronic Devices

“…Therefore, alternatives to increase the surface coverage of the metal deposits have been developed. For instance, the photoreduction by UV-vis light of a metal precursor provides surface coverage of the monolayer surface as large as 76% [115,277]. In this methodology, the metal precursor is incorporated from an aqueous subphase to an LBM upon the transference process, generating in situ metal nanoislands on top of the monolayer by photoreduction of the precursor.…”

New routes to organometallic molecular junctionsviaa simple thermal processing protocol

“…22 Strategies to these structures include direct deposition 23 or growth 24 of naked metal nanoparticles onto monolayers bearing an exposed functional group on the top surface capable of ligating to the nanoparticle, and electrochemical deposition of metal particle seeds on top of a monolayer prior to electroless metal in-fill. 25 As an alternative to electrochemical reduction, photochemical reduction of AuCl4or Ag + ions co-deposited on the top-surface of a Langmuir-Blodgett monolayer gives rise to high surface coverage of the monolayer by Au 26 or Ag 27 nanoparticles.…”