Molecules that mimic Schottky diodes

• Published in: Physical chemistry chemical physics : PCCP Vol. 8; no. 28; p. 3314
• Main Authors: Ashwell, Geoffrey J, Urasinska, Barbara, Tyrrell, Wayne D
• Format: Journal Article
• Language: English
• Published: England 01-01-2006
• Subjects: Carbon - chemistry; Electric Conductivity; Electrochemistry - instrumentation; Electrochemistry - methods; Hydrogen - chemistry; Materials Testing; Nanostructures - chemistry; Nanostructures - ultrastructure; Nanotechnology - instrumentation; Nanotechnology - methods; Semiconductors; Sulfur - chemistry
• ISSN: 1463-9076
• DOI: 10.1039/b604092f

Self-assembled monolayers of cationic donor-(pi-bridge)-acceptor dyes coupled with anionic donors exhibit asymmetric current-voltage (I-V) characteristics when contacted by Au or PtIr probes. Rectification ratios of 3000 at +/- 1 V are obtained from Au-S-C10H20-A+-pi-D|D-|Au structures in which the cationic moiety is 5-(4-dimethylaminobenzylidene)-5,6,7,8-tetrahydro-isoquinolinium and the counterion is copper phthalocyanine-3,4',4'',4'''-tetrasulfonate (SAM ). Similar behaviour, with a high rectification ratio of 700-900 at +/- 1 V, is also obtained for the CuPc(SO3-)4 salt of 4-[2-(4-dimethylaminonaphthalen-1-yl)-vinyl]-quinolinium (SAM ). The properties are dependent upon the D-pi-A+ moieties which, for these highly rectifying salts, have sterically locked non-planar structures causing the conjugation to be effectively broken. Its effect on the electrical asymmetry is less spectacular when the cationic species is sterically unhindered: the rectification ratio decreases to 15-70 at +/- 1 V for films of the 4-[2-(4-dimethylaminophenyl)-vinyl]-pyridinium salt (SAM ), which has single-ring substituents on opposite sides of the -CH=CH- bridge and an almost planar D-pi-A+ structure. Rectification ratios from the sterically hindered structures are on a par with electrical asymmetries from metal-insulator-metal (MIM) devices where oxide-induced Schottky barriers dominate the behaviour.