Morphological Transitions during Au Electrodeposition: From Porous Films to Compact Films and Nanowires

Abstract

Gold electrodeposition was studied in a sulfite electrolyte to which micromolar concentrations of Tl 2 SO 4 were added. Hysteresis and a regime of negative differential resistance (NDR) evident in electroanalytical measurements are correlated with deposit morphology and interpreted through measurements of thallium underpotential deposition (upd). Deposit morphologies range from specular surfaces to highly faceted dendrite-like grains of moderate aspect ratio and, for potentials within the NDR region, sub-50 nm diameter, high aspect ratio 110 oriented single crystal nanowires. The nanowires exhibit an epitaxial relationship to the substrate that permits one step fabrication of surfaces densely covered with high aspect ratio nanowires having controlled orientations. The NDR and nanowires are a consequence of the non-monotonic relationship between Tl coverage and growth velocity; at low coverage Tl accelerates Au deposition while at higher coverage it inhibits deposition. Immiscibility of the Tl and Au supports on-going surface segregation during area expansion that accompanies nanowire growth leading to greater dilution of the additive coverage and more rapid growth at the nanowire tips, while the sidewalls remain passivated by a saturated Tl coverage. Interest in nanostructures is driven by the unique properties associated with high surface area to volume materials that express quantum or mesoscale phenomena of importance to diverse subjects ranging from biology and medicine 1-3 to optics and energy conversion. [4][5][6][7] Of particular interest is the substantial literature on solution or vapor processing to yield a wide variety of nanostructures including high aspect ratio nanowires. 4,8,9 Solution-based, chemical reduction processes are attractive because they are inexpensive and scalable.9-18 Subsequent processing involving particle packing and/or substrate interactions can lead to higher order organization and colloidal crystals.19 Alternatively, nanostructures can be grown on or in surfaces that have been shaped by lithography or other means to obtain control of orientation and/or placement.8 Electrochemical processing may involve throughmask plating in patterned templates 20,21 or superconformal electrodeposition of metals and alloys [22][23][24][25][26][27][28][29][30][31] including gold 32-34 in high aspect ratio features. However, these processes require nanoscale patterned topography to create such structures and the associated patterning often comes with increased processing complexity.Controlled anisotropic growth and orientation, if not position, is possible through vapor-liquid-solid (VLS) growth processes. Fabrication of semiconductor and oxide nanowires typically uses dewetting of a low melting point metal catalyst where the resulting clusters set the feature size while epitaxy to the underlying substrate can control the growth orientation. 5,[35][36][37] More recently, an electrochemical electrolyte-liquid-solid analog has been demonstrated for growth of Ge nanowires. [38][39][40] In another ap...

Bottom-up Filling of Damascene Trenches with Gold in a Sulfite Electrolyte

“…9 ). The nontrivial relationship between additive acceleration in electroanalytical measurements and evolution of deposition in patterned features is reinforced by the extremely modest superconformal feature filling obtained when Bi is replaced by Tl, also an accelerator of Au deposition in this potential range, 48 shown in Fig. 12 .…”

Electrodeposition of Nanoporous Gold Thin Films

“…The role of electrodeposition potential on the growth morphologies has been seen in a study where gold deposition from sulfite electrolyte exhibits a range of geometries from vertically oriented nanowires to lenticular grains and dendrites at more negative potentials [54].…”

Facile chemical routes to mesoporous silver substrates for SERS analysis

“…The latter includes selective chemical etching of one metal component [ 10 – 11 ] or etching during galvanic replacement [ 12 ]. Among other relevant strategies, nanoparticle aggregation [ 13 – 14 ] or direct deposition of porous films without templates [ 15 – 16 ] should be mentioned. Chemical etching is a technically low demand process – an important advantage of this technique.…”