Tetrathiafulvalene-based conducting deposits on silicon substrates

Abstract

Tetrathiafulvalene-based molecular conductors, namely [TTF][TCNQ], (TTF)₆[N(C₂H₅)₄](HPM₁₂O₄₀) (M = W, Mo), and TTF[Ni(dmit)₂]₂ have been processed as thin films on microrough (001)-oriented silicon substrates using three different techniques. CVD-grown [TTF][TCNQ] deposits consist of platelets (10 × 5 µm) and filaments (diameter ∼1 µm). CN stretching modes in the infrared spectrum and CC stretching modes in the Raman spectrum are in agreement with a charge transfer of ∼0.6 from the TTF donor to the TCNQ acceptor. The N(1s) photoelectron spectrum confirms the presence of a reduced tetracyanoquinodimethane moiety. The films exhibit a semiconducting behaviour with a room-temperature conductivity of ∼0.4 S cm⁻¹. Deposits of (TTF)₆[N(C₂H₅)₄](HPW₁₂O₄₀) are electrodeposited on microrough Si(001) at constant current from TTF and [N(C₂H₅)₄]₃(PW₁₂O₄₀) in acetonitrile solution. The films are made of stacked sheets (5 < thickness < 25 µm). Vibrational spectra, conductivity measurements and magnetic susceptibility data are similar to those obtained on single crystals of (TTF)₆[N(C₂H₅)₄](HPW₁₂O₄₀) grown on a platinum electrode. Thin films of TTF[Ni(dmit)₂]₂ are grown on microrough Si(001) by an adsorption process in organic solution. The deposits are characterized by Raman micro-probe and exhibit a pseudo-metallic behaviour with a room-temperature conductivity of about 2 S cm⁻¹.