Furthermore, it is interesting to note that the LSPR location of simulation data fits quite Veliparib well with the experimental results (788 nm in experiment, 792 nm in simulation). Due to the strong SPRs in the pulse AC-grown Au nanoarray,

it is believed that the uniform Au nanoarray can generate large enhancement of electric field and local density of states, which makes the Au nanoarray a good candidate for nanoantennas. Thus, we use the FDTD and Green function methods to do our further theoretical investigation. Figure 3 shows the field distribution of the Au nanoarray with L = 150 nm, where the incident light is a plane wave at the wavelength of 792 nm with an incident angle of 40°. The field intensity enhancements are drawn at the logarithmic scale. The large field enhancement at every tip of the Au nanoarray is clearly seen, and this field enhancement can cause the increment of LDOS. However, the electric field tends to concentrate at some certain nanowire in the nonuniform Au nanoarray, and this asymmetric field distribution decreases the whole extinction intensity and displays nonuniform field enhancement which may affect

the stability and repeatability of the Au nanoarray in the application of nanoantennas (see Additional file 1: Figure S3). Furthermore, with the help of the Green function, the LDOS is given as [44]: where Im stands for the imaginary part and tr denotes the trace of the Green tensor matrix in brackets. Figure Selleckchem FK506 3 Field distribution and LDOS enhancement. (a) The field distribution of Au nanoarray (L = 150 nm, d = 34 nm, a = 110 nm) at the plane wave wavelength of 792 nm with an incident angle of 40°. (b) The x-position dependence of LDOS enhancement at the wavelength of 792 nm. As shown from the sketch of the simulation model in the inset, the zero point is at 10 nm above the center Au

nanowire. The enhancement of LDOS Lonafarnib in vivo at the center and the edge is 66.7 and 81.2, respectively. (c) The z-position dependence of LDOS enhancement. From the Maxwell equations, one can get By setting a dipole source the Green function can be calculated by the electric field at the position of the dipole as . Also, the matrix form of can be written as: After choosing three of different directions, all the elements of the Green matrix can be obtained so as to get the LDOS. The LDOS is calculated by the finite element method with the help of the COMSOL software (version 4.2a). As shown in Figure 3b, one can see that the LDOS enhancement at 792 nm is much larger at the edge which is in accord with the field distribution in Figure 3a, and the maximum enhancement is 81.2 times (define the LDOS enhancement as the ratio of LDOS around the nanoarray to LDOS in vacuum).