ABSTRACT
Triangle-like nanoparticles are predominantly represented by noble metals,1 such as silver (Ag)2,3 and gold4 (frequently prepared by biogenic/bioreduction methods,5 whose use in nanomaterial synthesis offers an environmentally benign alternative to the traditional chemical synthesis routes), although a few other inorganic compounds have been reported. Thus, biogenic gold nanotriangles and spherical Ag nanoparticles were synthesized by a simple procedure using Aloe vera leaf extract as the reducing agent.6 It was revealed that multiply twinned particles play an important role in the formation of gold nanotriangles. On the contrary, reduction of Ag ions by Aloe vera extract led to the formation of spherical Ag nanoparticles of 15.2 ± 4.2 nm size. The effect of halide ions on the formation of biogenically prepared gold nanotriangles (Figure 11.1) using the leaf extract of lemongrass (Cymbopogon ™exuosus) plant was studied.7 It was shown that the presence of halide ions either during the growth of gold nanoparticles by the reduction of aqueous AuCl4
− ions using lemongrass leaf extract or after the synthesis of the particles signi£cantly affected the morphology of the particles formed. The authors emphasized that, although F− ions do not bind to the gold particle surface, Cl−, Br−, and I− ions bind strongly to the (111) surface of gold and, by virtue of the mismatch between the halide adlayer and the (111) surface, alter the morphology of the particles formed; Cl− ions promoted the formation of nanotriangles, whereas Br− and I− ions led to distortion of the triangular morphology in that order. In addition, the electric £eld interaction of hexagonal arrays of gold nanotriangles positioned on glass slides was studied using £nite-difference time domain (FDTD) simulations.8 It was shown that the plasmonic properties of this array of nanostructures were susceptible to modi£cation by changing any of the studied variables: the length of the triangles (L = 100-300 nm), the irradiation wavelength (λ = 400-1100 nm), and the direction of the linearly polarized input £eld (either Px or Py).
