6 ×10 -2 '' '' '' Ag (7 ( 0.63) '' '' 1.5×10 -2 '' '' '' Ag (7 ( 0.64) '' '' 2.4×10 -3 '' '' '' Ag (7 ( 0.70) '' '' 1.2×10 -3 '' '' '' Ag (7 ( 0.96) '' '' 1.2×10 -4 '' '' '' Au (2 ( 0.2) C 4S 1.01 1.6×10 -3 Langmuir Chen 135 '' '' 0.90 2.7×10 -3 '' '' '' '' 0.87 3.3×10 -3 '' '' '' '' 0.84 3.7×10 -3 '' '' '' '' 0.82 4.1×10 -3 '' '' '' '' 0.80 5.0×10 -3 '' '' '' C 5S 1.23 8.2×10 -4 '' '' '' '' 1.14 8.2×10 -4 '' '' '' '' 1.06 8.2×10 -4 '' '' '' '' 1.02 1.1×10 -3 '' '' '' '' 0.98 1.3×10 -3 '' '' '' '' 0.95 3.5×10 -3 '' '' '' '' 0.92 6.8×10 -3 '' '' Au (4.6-6.5) C 12S 1.5-2.6 A (38) DC Parthasarathy et al. 272 Au (1.6 ( 0.16) C6S 0.9 1 ×10 -5 LS Liljeroth et al. 142 '' C12S 1.4 6 ×10 -6 '' '' Au (6.6 ( 0.8) C 12S 2.5 2 ×10 -3 '' '' '' '' 1.8 5 ×10 -3 '' '' '' '' 1.5 8 ×10 -3 '' '' '' '' 1.3 1 ×10 -2 '' ''a R ) NP radius, s ) inter-NP separation, σ ) conductivity, and Ea ) activation energy. b CnS ) CH3(CH2)n-1SH; CnS2 ) HS(CH2)nSH; 1 ) 1,4-di-(4-isocyanophenylethynyl)-2-ethylbenzene; and 2 ) 2,5′′-bis(acetylthio)-5,2′,5′,2′′-terthienyl. c A ) Arrhenius; nA ) non-Arrhenius; M ) metallic; nM ) nonmetallic; and MIT ) metal-insulator transition. d DC ) drop-casting; LB ) Langmuir-Blodgett; LS ) Langmuir-Schaefer; and SC ) spin-casting.

No abstract

Self-assembled monolayers (SAMs) of C6H5–C≡C–C6H4–C≡C–C6H4SH (1) on Au(111) and Ag(111) exhibit electrical rectifying behavior when probed by the scanning tunneling microscope whereas SAMs derived from decanethiol, benzenethiol and 4-phenylethynylbenzenethiol do not. We suggest that rectification arises from the conjugated length of the molecular framework of 1 and an increase of the donor character of the sulfur atom to this system upon adsorption to the metal. This is supported by surface second-harmonic generation measurements which show a significantly larger second order optical nonlinearity of SAMs of 1 compared to the other systems.

We report a metal to insulator transition (MIT) in disordered films of molecularly linked gold nanoparticles (NPs). As the number of carbons (n) of alkanedithiol linker molecules (C(n)S2) is varied, resistance (R) at low temperature (T = 2 K) and at 200 K, as well as trends in R vs T data at intermediate temperatures, all point to an MIT occurring at n = 5. We describe these results in a context of a Mott-Hubbard MIT. We find that all insulating samples (n > or = 5) exhibit a universal scaling behavior R approximately exp[(T0/T)nu] with nu = 0.65, and all metallic samples (n < or = 5) exhibit weaker R-T dependencies than bulk gold. We discuss these observations in terms of competitive thermally activated processes and strong, T-independent elastic scattering, respectively.

No abstract