Patterned Transparent Conductive Au Films through Direct Reduction of Gold Thiocyanate

Abstract

Construction of structurally defi ned, patterned metal fi lms is a fundamental objective in the emerging and active fi eld of bottom-up nanotechnology. A new strategy for constructing macroscopically organized Au nanostructured fi lms is presented. The approach is based upon a novel phenomenon in which incubation of water-soluble Au(SCN) 4 1 − complex with amine-displaying surfaces gives rise to spontaneous crystallization and concurrent reduction, resulting in the formation of patterned metallic gold fi lms. The Au fi lms exhibit unique nanoribbon morphology, likely corresponding to aurophilic interactions between the complex moieties anchored to the amine groups through electrostatic attraction. Critically, no external reducing agents are needed to initiate or promote formation of the metallic Au fi lms. In essence, the thiocyanate ligands provide the means for surface targeting of the complex, guide the Au crystallization process and, importantly, donate the reducing electrons. It is shown that the Au fi lms exhibit electrical conductivity and high transparency over a wide spectral range, lending the new approach to possible applications in optoelectronics, catalysis, and sensing. In a broader context, a new gold chemistry route is presented in which ligandenabled crystallization/reduction could open the way to a wealth of innovative reaction pathways and applications.

Spontaneous Assembly of Extremely Long, Horizontally‐Aligned, Conductive Gold Micro‐Wires in a Langmuir Monolayer Template

“…The spectroscopic data in Figure 5 -indicating Au 0 formation -are consistent with the gold deposition mechanism outlined above, according to which electrostatic attraction induced binding between the amine moieties of OM (which are positivelycharged in the pH conditions employed) and the negativelycharged Au(SCN) 4 − , followed by spontaneous crystallization/ reduction of the Au ions by the thiocyanate ligands. [ 23 ] Control experiments corroborated the proposed mechanism. No organized Au structures were formed, for example, upon (or within) the water subphase when OM monolayers were not present.…”

“…Incubation gave rise to deposition of metallic gold upon the OM monolayer through a recently-reported process in which Au(SCN) 4 − binds through electrostatic attraction to the OM amino residues, followed by crystallization and thiocyanate-induced reduction. [ 23 ] Remarkably, subsequent isothermal compression of the monolayer resulted in formation of aligned OM/gold micro-wires (Figure 1 B). The micro-wires could be transferred from the water interface onto solid supports by the Langmuir-Schaffer method (horizontal transfer), and following plasma treatment (to remove the organic residues) [ 26 ] and gold enhancement [ 19,27 ] transparent and highly conductive fi lms comprising the gold micro-wires are produced (Figure 1 C).…”

“…Also, no gold micro-wires were assembled when the ionic strength of the subphase was increased (for example using a subphase containing 0.5 M KCl, Figure S3) -this inhibition effect is ascribed to electrostatic shielding of the OM monolayer by the positive potassium ions in the aqueous solution. [ 23 ] The physical properties and potential applicability of glasssupported aligned gold micro-wire fi lms in electro-optical devices were further examined ( Figure 6 ). Figure 6 demonstrates excellent transparency and conductivity profi les of the aligned gold micro-wire fi lms.…”

“…[ 23 ] The aligned gold micro-wires could be transferred from the air/water interface onto solid substrates. Following plasma treatment and gold enhancement the micro-wire fi lms exhibited high optical transparency and excellent conductivity even at electrode spacings of several centimeters.…”

“…We have recently demonstrated that Au(SCN) 4 − selfassembles into conductive Au 0 nanostructures through singlestep crystallization/reduction process which do not require addition of reducing agents. [23][24][25] Here we show that a surfactant, octyl-melamine (OM), adopts elongated and aligned micro-wire morphology when isothermally compressed at the air/water interface. Furthermore, the OM assemblies constitute a template for gold deposition through electrostatic attraction between the primary amine residues of the surfactant and soluble Au(SCN) 4 − , accompanied by spontaneous crystallization and reduction of gold by the thiocyanate moieties, without addition of reducing agents.…”