Nonclassical Optical Properties of Mesoscopic Gold

Abstract

Gold nanostructures have important applications in nanoelectronics, nano-optics as well as in precision metrology due to their intriguing opto-electronic properties. These properties are governed by the bulk band structure but to some extend are tunable via geometrical resonances. Here we show that the band structure of gold itself exhibits significant size-dependent changes already for mesoscopic critical dimensions below 30 nm. To suppress the effects of geometrical resonances and grain boundaries, we prepared atomically flat ultrathin films of various thicknesses by utilizing large chemically grown single-crystalline gold platelets. We experimentally probe thickness-dependent changes of the band structure by means of two-photon photoluminescence and observe a surprising 100-fold increase of the nonlinear signal when the gold film thickness is reduced below 30 nm allowing us to optically resolve single-unit-cell steps. The effect is well explained by density functional calculations of the thickness-dependent 2D band structure of gold.

Photon bunching of the nonlinear photoluminescence emitted by plasmonics metals

“…We then finalize this gold-based sample by drop-casting atomically flat singlecrystal micrometer-large Au flakes [16,36]. These large objects possess a thickness-dependent electronic band structure [37]. For the sake of the completeness of the study, we also produced 50 nm thick patches of Ag using the same methodology.…”

Anisotropic Second Harmonic Generation From Monocrystalline Gold Flakes

“…The anisotropic nonlinear optical response we report here may be of crucial importance for directional enhancement of harmonic generation in metal nanostructures [24][25][26][27]. Furthermore, we suggest that our findings can be used as a fast and non-destructive method for characterization of crystallinity and lattice orientation of metal substrates, which is an important asset for ongoing experimental activities on quantum surface effects and future plasmonic applications [28][29][30].…”

Extremely confined gap plasmon modes: when nonlocality matters

“…Along with the improvement in nanofabrication techniques, such as focused ion beam (FIB) milling, this progress allowed the fabrication of plasmonic nanocircuitry [25,26] and plasmonic nanoantennas [27,28] with superior quality. Furthermore, monocrystalline Au flakes present as a "playground" material platform for experimental studies of fundamental aspects of plasmonics [29][30][31][32][33][34][35][36].…”