Linking gold nanoparticles with conductive 1,4-phenylene diisocyanide–gold oligomers

Abstract

A major challenge to fabricating molecular electronic circuits 1 is the difficulty of simultaneously chemically bonding molecular components to two metal electrodes. This can be accomplished by adjusting the electrode separation to match the molecular dimensions using break junctions 2-5 or by using a sharp tip to vary the electrode-surface spacing. 6 Such approaches provide detailed information on molecular conduction, but are not easily extended to planar systems required for a realistic circuit. 7Molecularly linked nanoparticles have been synthesized in solution and deposited onto surfaces 7,8 but the location of the nanoparticles in the circuit is dictated by the cross-linking structure. Ordered assemblies have been formed from functionalized nanoparticles but they are often not covalently connected. Finally, the length of the molecular linker can be matched to the nanoparticle spacing but requires the molecular size to be tailored to the separation of the nanoparticles. 10An alternative strategy is proposed based on recent observations that molecules that bind strongly to metals with low cohesive energies such as gold or copper can oligomerize by extracting metal atoms from the substrate.11-14 An example of this is the lateral self-assembly of 1,4-phenylene diisocyanide (PDI) on Au(111) that forms -(Au-PDI) n -oligomers comprising long, one-dimensional chains by extracting low-coordination gold atoms from surface defect sites. [15][16][17] The relatively short (B1.1 nm) repeat distance between gold atoms in the oligomer suggests the possibility of being able to chemically bond between gold nanoparticles with various separations by incorporating a number of repeat units until the gap is bridged. PDI has been previously proposed as a prototypical molecular electronic component, 4,6,[18][19][20][21] and theory suggests that PDI is a suitable candidate for device applications. 22This lateral self-assembly is explored by measuring the conductivity of a gold nanoparticle film on mica that has been exposed to PDI. Evaporating gold films on mica (and other insulating substrates)23-28 provides a simple method for growing isolated nanoparticles with different spacings merely by ensuring that the gold film thickness remains below a critical value, above which a continuous film is formed. The success of this approach relies on the oligomers being sufficiently mobile to bridge between nanoparticles. This mobility is illustrated in Fig. 1, which displays a typical series of 15 consecutive STM images (taken 53 seconds apart) of a saturated layer of Au-PDI chains on Au (111) showing the repeated lateral motion of an entire chain, where a line is drawn to highlight the chain motion, showing nine hopping events corresponding

Self-Assembled Oligomeric Structures from 1,4-Benzenedithiol on Au(111) and the Formation of Conductive Linkers between Gold Nanoparticles

“…Similar behavior has been found for PDI-linked gold nanoparticles and provides corroborative evidence that 1,4-BDT forms similar oligomeric linkages. 95 It has been shown previously that this behavior can be adequately reproduced by a model due to Abeles for thermally assisted tunneling through an array of nanoparticles. 108 This model predicts that the sheet resistance R is given by R = R 0 exp(+2(C/kT) 1/2 ), where C = χsE c 0 , s is the average spacing between particles, χ = (2mϕ/ℏ 2 ) 1/2 , ϕ is the height of the tunneling barrier, m is the electron mass, E c 0 is the Coulomb charging energy, and R 0 is a constant.…”

“…109 The prediction that the resistance should vary with temperature as ln(R) = (α/√T) + β is in agreement with the results shown in Figure 7, as well as for PDI-linked gold nanoparticles. 95 The Abeles model predicts that the value of α in the above equation should depend on ln(initial film resistance) and such a plot is displayed in Figure 8, which yields a good straight line with a slope of 4.2 ± 0.2, which is slightly larger than for the corresponding plot for PDI-linked nanoparticles, which gave a slope of 3.7 ± 0.2. 95 ■ DISCUSSION 1,4-BDT adsorbs molecularly at low temperatures on Au (111) and reacts to form an η 1 -bonded thiolate on heating to ∼166 K ( Figure 1).…”

Nanoscale architecture of bimetallic hybrid Fe–Au nanostructures with and without 1,4-phenylene diisocyanide pre-functionalization

“…In contrast, obvious aggregation of Au NIs is found for the bare or non-functionalized Au NI template (Fig. 42,43 The complementary case has also been examined by preparing Au on Fe NrPs by magnetron sputtering (Fig. This is believed to be due to eld-induced relocation of Au nanoparticles smaller than 10 nm.…”

“…34 It has been demonstrated that near-IR absorption of Au-Fe 3 O 4 can be utilized for potential applications as a photothermal treatment of cancer and a drug delivery system. [42][43][44][45][46] PDI is found to have the tendency to self-assemble with gold to form -(Au-PDI) noligomers. 38,39 Various methods of synthesizing Fe oxides have been reported.…”

The role of ligands in coinage-metal nanoparticles for electronics

“…The molecule bridged the gold islands and increased conductivity from 6.5 × 10 −10 to 270 × 10 −10 S after 2000 s of exposure. The authors showed that the presence of two isocyanide groups in the PDI molecule is essential to achieve conductivity: Exposure to phenyl isocyanide hardly improved the conductivity [ 119 ].…”