ZnO Nanostructures for Mid‐ IR Plasmonics

Degenerate metal oxide nanocrystals (NCs) are promising systems to expand the significant achievements of plasmonics into the infrared (IR) range 1 . We report on the tunable mid IR Plasmon induced in degenerate Al and Ga doped ZnO (AZO and GZO) nanocrystals. The NCs were obtained by Low Energy Cluster Beam Deposition (LECBD). By varying the Al and Ga content from 3 to 9 at.% within the particles we are able to tune the plasmon wavelength from 3 to 4 μm. However, the plasmon resonances are characterized by an unusually large damping, which originates from two mechanisms. The first one is the Oriented Attachment (OA) process (cf. figure 1, B) 3 . When NCs attach by epitaxy, the resulting structure has a lower symmetry, which induces a shift and broadening of the plasmon resonance. Embedding the particles in an Al 2 O 3 matrix has prevented the OA, and hence the damping was reduced along with broadening. The second mechanism is the partial activation of the dopants. We have observed that less than half of the dopants actually participate to the electron gas 2 . The cause of the partial activation is related to the position of the dopants within the particles. It has been proposed that the damping is larger if the dopants are homogeneously distributed 4 . In the present work we investigate the possibility of mapping the spatial distribution of dopants within the nanocrystals usingFEI‐TITAN ETEM equipped with High resolution Gatan GIF (see Figure 2). We subsequently anneal the nanocrystals to let them reach the thermodynamic equilibrium. The distribution of dopants, and its consequences on the plasmon resonances is then investigated [5,6].