Paper NS+BI+EM-WeA4
Enhanced Electrical Conductivity by Au Nanoparticle Islands Deposited from Solution

Wednesday, October 30, 2013, 3:00 pm, Room 203 B

Colloidal Au nanoparticles (NPs) capped with tetraoctylammonium bromide (TOAB) were synthesized using the Brust method, and deposited on oxidized p-type Si(100) covered by either 3-aminopropyltrimethoxysilane (APTMS) or 3-mercaptopropyltrimethoxysilane (MPTMS). Dip coating was used to deposit the Au NPs with nominal diameters of 5-20 nm using the linker 1,2-ethanedithiol (EDT). One coating cycle consisted of immersion in the Au NP colloid for 1 h, rinsing in toluene, immersion in EDT for 1 h, and rinsing in toluene. Deposits were made of one half-cycle (NPs only) up to 9 complete cycles. After deposition the samples were annealed for 1 h at 300°C in flowing N₂, which removed at least 85% of the organic compounds based on FTIR. SEM and cross-sectional TEM showed that after 9 cycles, 40% of the surface was covered with small islands consisting of clusters of Au NPs that were 10-20 nm in diameter and 20-30 nm apart from one another. AFM showed that the heights of the islands were also 20-30 nm. FTIR also showed that EDT replaced only half of the TOAB on the surface, suggesting that island growth is caused by TOAB ligands blocking binding sites. Current-voltage (IV) measurements were made by clamping two Cu terminals with a contact area of 6 mm² to the surface of a sample, separated by a distance of 10 mm. The film stack consisted of a) p-type Si substrate, b) 1.6 nm silicon oxide layer, c) 0.7-3 nm silane layer, and d) Au islands. A control experiment in which the Au NP islands were replaced by two 20 nm thick e-beam deposited Au films separated by a 10 mm gap yielded a sigmoidal IV curve due to current flow through the p-type Si substrate and possibly to lateral charge transfer through the APTMS monolayer. The Au NP islands increased the current flow at negative bias relative to the control. The Au NP islands could reduce the contact resistance or electrons could hop or tunnel between islands, through the underlying silane layer. Compared to the nanometer scale 1D Au NP arrays on BNNTs reported in the literature, electron transfer over such a large area found in this study could be used to scale up the class of semiconductor-free transistors that operate based on electron tunneling and could contribute to other applications that require effective local charge transfer, such as the seed layer for electro- and electroless deposition.