Quantum plasmon excitations in gold-fullerene mixture films

Abstract

Controllable access to the hybrid plasmonic nanostructures built of small metal nanoparticles and organic spacer offers a tempting set of electronic excitations, which proper handling promises valuable applications and bright fundamental prospect. Here, we report on remarkable plasmonic properties of the Au x C 60 hybrid nanostructures formed through self-assembling the depositing mixture of metal and fullerene. Using optical absorption spectra, we demonstrate establishing of quantum plasmon (QP) excitations upon the controllable increase of spatial density and size of the Au clusters formed in the films. Detection of two plasmonic modes evidences the QP hybridization enabling by nm-scaled proximity of the neighboured Au clusters. Variation of the QP mode parameters with gradual decrease of the inter-cluster spacing ΔL to the sub-nanometre scale driven by the Au concentration in the film x allowed us to evidence the quantum tunnelling regime in the QP hybridization launching at ΔL≈0.9 nm. The later result designates an important role of the C 60 molecules, separating the Au clusters, in design of plasmonic and transport properties of the hybrid films. The obtained results represent the self-assembled Au x C 60 nanocomposites as the promising plasmonic materials with potential for application in nanoplasmonics, nanoelectronics, and nanomedicine.

Structure assembly regularities in vapour-deposited gold–fullerene mixture films

“…39 This remarkable result has fundamental importance and demonstrates the NP size threshold launching the quantum size effects in the smaller Au NPs and yielding intriguing quantum phenomena such as quantum plasmons. 22,[39][40][41] In contrast to the monotonous lattice contraction observed for fcc-Au NPs in Au x C 60 nanocomposites with increasing Au content, the crystal structure of fcc-C 60 experiences a nonmonotonous expansion, which reaches its maximum for the Au concentration of about x ¼ 1.6 in the XRD-studied Au x C 60 samples (Fig. 8).…”

“…25 This technique is quite appropriate for the analysis of the metal-fullerene mixture lms. 15,22 Fig. 1a demonstrates a series of RBS spectra recorded from the deposited mixture lms with increasing Au content.…”

“…This value of x c1 is satisfactorily supported by the optical spectra. 22 According to the Raman spectra and the XRD study of the lms with x < x c1 (see Fig. 8), the TH-intercalated Au atoms dominating in the structure of the lms from this x interval do not couple strongly with the surrounding C 60 molecules because no Au-C 60 charge transfer occurs (see the previous section).…”

“…We fabricated a set of the Au x C 60 mixture films (0 < x < 30) by means of the simultaneous deposition of Au and C 60 from vapour onto the Si(100) substrates under vacuum at 10 −6 mbar, as previously described elsewhere. 22 The Au pellets (99.99 mass% Au) were evaporated using an electron gun operated by a digital power supplier (FuG Elektronik GmbH). The evaporation of C 60 (99.9 mass% C 60 ) was carried out by means of a Knudsen cell-like source.…”

“…Herein, we focus on the SD-fabricated Au–C 60 mixed systems, whose intriguing plasmonic properties were recently discovered. 22 The practical importance of this discovery motivated us to clarify the details of self-assembly in the Au x C 60 mixture films by performing a systematic analysis of the nanostructures formed in such mixed systems. Success in the realization of this task would allow, for instance, the management of the discovered plasmonic effects, which promises new applications of TM–C 60 NC materials.…”