Electrodeposition of long-chain alkylaryl layers on Au surfaces

4-Alkylaryl layers were electrodeposited on Au surface via formation in situ of diazonium cations and the subsequent electroreduction in solution of 4-alkylanilines (4-CH ₃(CH ₂) _nC ₆H ₄NH ₂, n = 5-13). The electrodeposited layers were characterized with X-ray photoelectron spectra (XPS), an atomic force microscope (AFM), attenuated-total-reflection infrared spectra (ATR-IR), spectroscopic ellipsometry, and water contact angle. The thickness of the deposited alkylaryl layer increased with the length of the alkyl chain, which was about 1.6 times the molecular length of the alkylaniline precursor. The surfaces of deposited adlayers were uniform and smooth without aggregation and exhibited hydrophobic character with a water contact angle ∼95°. Charge transport across the alkylaryl layer was characterized with a measurement of a conductive AFM. The current-voltage characteristics at low voltages are describable with a nonresonant tunneling mechanism, according to which the resistance increased exponentially with the thickness of the adlayer. As a measure of the efficiency of the charge transport, the average attenuation factor (β) was 0.63 Å ^-1, which was less than that observed for the alkyl SAM because of the presence of the aryl ring. The breakdown voltage of the adlayer also increased with the length of the alkyl chain. The 4-tetradocylaryl layer exhibited a resistance and breakdown voltage comparable to that observed for a 1-octadecanethiolate SAM.