dimer_linear

The localised plasmon resonance of a dimer of nanoparticles in close proximity may be described in the framework of hybridisation theory. As the separation decreases, electromagnetic coupling between the particles influences the net local field experienced by each particle, resulting in a shift of the resonance.

library(cda)
library(rgl)
library(ggplot2)
library(reshape2)
library(plyr)

# dielectric function
wvl <- seq(500, 800)
gold <- epsAu(wvl)

Influence of the particle separation

  
dimer <- function(d=100, ...){
  
  r <- cbind(c(0,0), c(-d/2, d/2), c(0, 0))
  sizes <- equal_sizes(a=50, b=20, c=20, N=2)  
  angles <- matrix(0, ncol=3, nrow=2)

  cl <- list(r=r, sizes=sizes, angles=angles)
  dispersion_spectrum(cl, material = gold)
  
}
params <- data.frame(d=seq(50, 500, by=10))
comparison <- mdply(params, dimer)

## compare with the single-particle response
single <- dispersion_spectrum(list(r=cbind(0,0,0), angles = cbind(0,0,0),
                                   sizes=cbind(a=50, b=20, c=20)), material = gold)

p <- 
  ggplot(data=subset(comparison, polarisation == "p")) + 
  facet_grid(type~., scales="free") +
  geom_line(aes(wavelength, value/2, 
                colour=d, group=d)) +
  geom_line(aes(wavelength, value), colour="red", linetype="dashed",
            data=subset(single, polarisation == "p")) +
  labs(y=expression(sigma[ext]*" /"*nm^2),
       x=expression(wavelength*" /"*nm), colour="distance /nm") 

p