Size-dependent change in parallel band absorption of Al particles

Abstract

Optical absorption of Al island films consisting of Al particles smaller than about 1200 Å in diameter has been measured in the energy range of 0.5-6.5 eV. Below about 200 Å in diameter, parallel band absorption, due to transitions between almost parallel bands, weakens and then disappears with decreasing particle size. Nguyen et al. ͓Phys. Rev. B 47, 3947 ͑1993͔͒ have reported that the parallel band absorption of Al particles is not visible when relaxation times for conduction electrons and the parallel band absorption are much smaller than those in the bulk. We investigate the relaxation times by simulating the optical plasma-resonance absorption of the Al island films with a Maxwell-Garnet-type effective medium theory. The very small relaxation times are pointed out to be a possible cause of the weakening and disappearance.

Surface Plasmon Resonances and Local Field Enhancement in Aluminum Nanoparticles Embedded in Silicon Nitride

“…, which is consistent with the low contrast of the HAADF-STEM images and with earlier studies focused on the growth of Al films on oxide surfaces. 42,70 For a longitudinal excitation, the calculated absorption spectrum also correctly reproduces the plasmonic dichroism with the position of the main absorption peak at about λ = 613 nm (2.02 eV) being close to the experimental one. Moreover, a faint shoulder can be noticed in the NIR region beyond 800 nm (1.55 eV).…”

“…27,[36][37][38][39][40] It is also worth noting that, despite -or thanks to -its IT around 800 nm (1.55 eV) and high losses in the NIR, aluminum nanoparticles are suggested as a promising alternative for light absorption and near-field enhancement in this spectral region, as well as for designing efficient integrated thermoplasmonic devices. 17,21,26,41 Several approaches have been reported to fabricate aluminum plasmonic nanostructures like lithographic methods, [19][20][21][22][23][24][25][26][27][28][29][30][31] physical vapor deposition, [33][34][35][36]39,40,[42][43][44] cluster beam depo-sition, 45 laser ablation in liquids, 46 and wet-chemical synthesis. 37,47 However, still to this day, technical challenges make it difficult to achieve the production of ultrafine aluminum nanoparticles (< 20 nm) with controlled morphology and composition.…”

Plasmon resonances of aluminum nanoparticles and nanorods

“…Al particles smaller than 10 nm exhibit anomalous far-infrared absorption, 11,12 which has been attributed to quantum size effects 13 and the effects of oxide overlayer. 14 Another interesting effect that has attracted attention is the diminishing of the interband absorption at 850 nm wavelength in small Al clusters, [15][16][17] resulting from the breakdown of the band structure. Broad absorption peaks attributed to surface plasmon modes were measured for nanoporous thin films, 18 for thermally evaporated discontinuous films, 19,17 and for hollow nanocaps.…”

In situ spectroscopic ellipsometry to monitor surface plasmon resonant group-III metals deposited by molecular beam epitaxy

“…Optical plasma-resonance absorption occurring in metal island films is shifted to lower energies with increasing size of the interacting, flat Al particles, due to the increase in the depolarization factor of the particles, while broadening depends on a relaxation time of conduction electrons, which depend on the particle size. 21 The transition from disperse particles to a coalesced thin film is evident as the plasmon resonance redshifts and gradually is replaced by Drude-like behavior above the percolation limit, which is defined as the onset of Drude-like behavior and can be readily observed in the kinetic ͗ 2 ͘ spectra. From the kinetic spectra, the percolation limit is estimated to be 45 ML of Al on GaN.…”