Computational Model Shows Stark Shifts Induce Ultrafast Current in Molecular Wires
- PDF / 754,914 Bytes
- 2 Pages / 576 x 783 pts Page_size
- 52 Downloads / 138 Views
arrays by decomposing recrystallized silver phenylacetylide nanowires, as they reported in the September 19 issue of Chemistry of Materials (DOI: 10.1021/ cm071688i). The researchers succeeded in recrystallizing silver phenylacetylide by using the ligand dissociation of Me3P–Ag–C≡C–Ph. It crystallized as thin wire-shaped crystals because of its highly anisotropic crystalline structure. A fast PMe3 dissociation rate in a high-polarity solvent produced a
thin silver phenylacetylide nanowires (39 ± 11 nm in EtOH), whereas slow crystal growth in a lower-polarity solvent brought thicker nanowires (94 ± 12 nm in 1-BuOH). The aspect ratio was ~30–40, which increased to more than 100 when CH3CN was used as a solvent. The strong reducing power of ethynyl anions present in the wires converted the raw material into an assembly of Ag nanoparticles under mild conditions when they were irradiated with ultraviolet (UV) light, b
20 nm c
50 nm d
20 nm
Computational Model Shows Stark Shifts Induce Ultrafast Current in Molecular Wires
50 nm
e
100 nm
Figure 1. (a–d) Transmission electron microscope images of ultraviolet (UV)-irradiated silver phenylacetylide nanowires: (a) wire/EtOH, 15 min of irradiation; (b) wire/1-BuOH, 15 min of irradiation; (c) wire/EtOH, 3h of irradiation; (d) wire/1-BuOH, 3 h of irradiation. (e) Scanning electron microscope image of decomposed wire/EtOH. Ag nanoparticles are fixed on a Si substrate by heating after UV irradiation. Reprinted with permission from Chemistry of Materials 19(19) (2007) p. 4627. ©2007 American Chemical Society. 882
while the phenylacetylene molecules formed during the decomposition process polymerized. This generated an organic matrix that surrounded the Ag nanoparticles, protecting them from oxidation while keeping the original shape of the wire, without using any template. After 15 minutes of irradiation, the surface plasmon resonance band of Ag nanoparticles appeared at 485 nm, slightly red-shifted with respect to typical Ag nanoparticles because of the dipole–dipole interaction caused by the short distance between nanoparticles (1 nm for 15 min of irradiation and 3 nm for 3 h of irradiation). Additionally, the high dielectric constant of the matrix can also reduce the plasmon frequency, the researchers said. Particle size was independent of the wire diameter and increased with irradiation time. Transmission electron microscope images recorded by the researchers showed the conversion of a nanowire into a 1D array of homogeneously distributed Ag nanoparticles after irradiation (see Figure 1). Heating silver phenylacetylide nanowires at 110ºC for 3 h was an alternative for obtaining 1D arrays of Ag nanoparticles with a diameter of 2.4 ± 0.7 nm, similar to that obtained after UV irradiation for 15 min. By using higher temperatures, however, the organic part of the decomposed nanowire melted and evaporated and the Ag nanoparticles spread on the substrate without keeping the 1D array structure. This process was used by the researchers to fix the 1D Ag nanoparticle arrays on a
Data Loading...
