# Corner Reflector Plasmonic Nanoantennas for Enhanced Single-Photon Emission
## 3 Results and Discussion
Conversely, the NP size \(d\) showed a lesser effect on \(f_{L}\). Overall, the loss factors for silver NPs were smaller, though still comparable, to those for gold NPs. As discussed in Section 2, achieving efficient emission requires a good balance between relatively low \(f_{L}\) values and sufficiently high \(f_{R}\) values. Based on the analysis of the coupled dipole-nanoparticle system, a particle size of \(d=70\) nm with a separation of \(s=15\) nm from the dipole was chosen for the analysis of the full structure incorporating the CR. For these parameters, at their respective target wavelengths, the results show \(f_{L}=5.4\) and \(f_{R}=8.3\) for silver nanoparticles and \(f_{L}=6.1\) and \(f_{R}=4.9\) for gold nanoparticles. This indicates a higher radiative emission rate enhancement with lower losses for silver compared to gold. Under these conditions, \(f_{R}>f_{L}\) for silver NPs, whereas \(f_{R}<f_{L}\) for gold NPs. The corresponding values of the emission gain figure of merit, \(G\), as defined in (7)--with a directivity value of \(D=1.5\) for an electrically short dipole [15; 16]--were \(G_{Ag}=0.9\) for silver and \(G_{Au}=0.7\) for gold NPs. The radiation properties of the CRs in RF antennas were systematically studied in [38] through extensive experimental measurements of the gain achieved with different corner configurations using a resonant half-wave dipole feeder. As the distance from the corner apex to the feeder increased, a series of positions corresponding to local maxima of the antenna gain was identified. The first three positions were thoroughly analyzed in [38]. Whereas the second and third positions were sharply defined, the first position corresponded to a broader region. This is due to a trade-off between the increase in directivity obtained by moving the feeder closer to the apex and the associated rise in ohmic losses in the conductors. In the first position, the corner angle for maximum gain depended on the width and length of the reflecting planes: as the planes became larger, the optimal angle decreased and the maximum gain increased. Conversely, fixed optimal values of the corner angle were observed for the second and third positions when the planes were sufficiently large. For the second position, a maximum gain occurred at \(\psi=65^{\circ}\) when the width and length of the corner planes exceeded about one wavelength. At the third position, an optimal corner angle was found at \(\psi=90^{\circ}\) when the reflecting planes were larger than half a wavelength. In the following analyses, we selected a corner angle of \(\psi=65^{\circ}\) and corner plane dimensions of \(L=1.5\)\(\upmu\)m and \(H=1\)\(\upmu\)m. We examined the directivity \(D\) along the corner axis and investigated how the presence of the CR influenced the values of \(f_{R}\) and \(f_{L}\) at the target wavelengths for silver and gold NAs. Figure 5 presents the on-axis directivities calculated for silver (a) and gold (b) CRs, with film thicknesses ranging from \(W=10\) nm to \(80\) nm and feeder positions between \(S=0.2\)\(\upmu\)m and \(S=1\)\(\upmu\)m. For the presentation of the results, the values of \(S\) have been rescaled with the respective target wavelengths for the gold and silver reflectors at which the directivities were evaluated. The figure reveals similar patterns in the variation in directivity with the normalized separation \(S/\lambda_{M}\) and the film thickness \(W\), where \(M\) denotes the corresponding noble metal. The higher peak directivities obtained for silver than for gold can be attributed mainly to the larger relative values of the corner plane length \(L/\lambda_{Ag}>L/\lambda_{Au}\). The metal film thickness also played a significant role in the radiation properties of the NA. As the thickness increased, the peak directivity increased, and the variation in \(S/\lambda_{M}\) followed a more regular oscillatory pattern in terms of the local maxima and minima, as in the case of RF antennas [38].