Light-controlled one-sided growth of large plasmonic gold domains on quantum rods observed on the single particle level

Abstract

We create large gold domains (up to 15 nm) exclusively on one side of CdS or CdSe/CdS quantum rods by photoreduction of gold ions under anaerobic conditions. Electrons generated in the semiconductor by UV stimulation migrate to one tip where they reduce gold ions. Large gold domains eventually form; these support efficient plasmon oscillations with a light scattering cross section large enough to visualize single hybrid particles in a dark-field microscope during growth in real time.

Controlling Au Photodeposition on Large ZnO Nanoparticles

“…Control of the position of metal NP photodeposition on the semiconductor and possible influence of semiconductor shape (and lattice matching), as well as metal NP size and shape, are all topics of interest when host particles of an intermediate size are used. 27,32 The metal photodeposition route could prove advantageous where precise control over the metal domain size is required, which in the case of noble metal NPs may also prove to be a way to fine-tune plasmonic properties. 32,33 Once the noble metal has been deposited at the surface of a semiconductor to form a hybrid NP, it can serve as an electron sink.…”

“…27,32 The metal photodeposition route could prove advantageous where precise control over the metal domain size is required, which in the case of noble metal NPs may also prove to be a way to fine-tune plasmonic properties. 32,33 Once the noble metal has been deposited at the surface of a semiconductor to form a hybrid NP, it can serve as an electron sink. UV irradiation of the hybrid NP generates electron−hole pairs that separate at the metal−semiconductor interface with the electrons accumulating in the metal, causing further metal reduction and growth at the deposition site.…”

“…42 Defects in ZnO semiconductor NPs are localized, high-energy surface traps for electrons and thus sites where photodeposition growth of the metal component can occur. 32 It is logical that a metal precursor is more likely to be reduced where high-energy electrons accumulate on the semiconductor surface. Studies of metal NP photodeposition on anisotropic ZnO and CdS that terminate in sharp tips have found that tip-growth of the metal occurs on these NPs and nanorod structures.…”

“…Studies of metal NP photodeposition on anisotropic ZnO and CdS that terminate in sharp tips have found that tip-growth of the metal occurs on these NPs and nanorod structures. 32,43,44 The nanostructure tips of these noncentrosymmetric, wurtzite-phase materials are likely to have low coordination number, a high number of dangling bonds, and increased electron density compared to other sites on these nanostructures. 44 The localization of electrons at the ends of ZnO nanorods prior to the electron-transfer step has been demonstrated to produce site-specific photodeposition of silver NPs.…”

Heterostructured Hybrid Colloidal Semiconductor Nanocrystals

“…51 Having established a hierarchical order of site-speci¯c deposition locations on CdSe-seeded CdS nanorods, one important question that arises naturally when considering the deposition of Au at the tips is the relative position of the tip with respect to the asymmetrically located core in which Au depo-sition¯rst occurs. In the case of CdSe-seeded CdS nanorods, imaging directly from high resolution TEM to distinguish the lattice planes of CdSe and CdS is di±cult due to the fact that their relative parameters di®er by a mere 4.2%.…”