Abstract
Protein-mediated doping of ZnO with plasmonic nanoparticles offers control over surfaces, electronic states, carrier dynamics, and spectral fingerprints. Here, we report on ZnO-nano-Au bioinorganic heterostructures prepared using a chimeric polypeptide that combines most of the ZnO-binding sequence GLHVMHKVAPPR and the gold-binding AYSSGAPPMPPF sequence. The one-pot peptide-mediated synthesis was performed in the presence and absence of HAuCl4 to determine the impact of the peptide and metallic component on the structural and electronic properties of the ZnO assembly. Electron microscopy confirms that the chimera polypeptide promotes the synthesis of both spherical and nonspherical gold nanoparticles, which are properly embedded in ZnO. The optical absorption spectra describe a complex palette of plasmon modes, while the luminescence spectra show a dominant subset of near-infrared spectral fingerprints that suggest an increasing role of surfaces in carrier relaxation. Simulations using finite difference time-domain theory describe collective plasmon phenomena specific to gold nanoparticles embedded in ZnO. Furthermore, to confirm experimental data, theory suggests an interinclusion nanogold spacing of 10 nm or less. Flexibility of the primary sequence of the chimera in the synthesis of ZnO-nano-Au composites opens up possibilities for plasmon-modulated ZnO junctions with Ohmic contacts as sought in sensor technologies and for security applications.
Highlights
Zinc oxide-gold heterostructures have received much attention in the past 2 decades for the development of higher efficiency photovoltaic[1] and photocatalytic[2−5] devices
Formed in the presence of a peptide, and zinc oxide (ZnO)-gold composites formed by both stepwise addition of gold to the ZnO and the single-pot synthesis approach
All experiments where gold was a component of the composite synthesis generated marooncolored materials, as compared to the white of ZnO, Figure 2A,B
Summary
Zinc oxide-gold heterostructures have received much attention in the past 2 decades for the development of higher efficiency photovoltaic[1] and photocatalytic[2−5] devices. The constituent materials of this heterostructure are zinc oxide (ZnO) nanoand microassemblies and gold (Au) nanoparticles, which have differing electronic and optical properties. 3.3 eV) n-type semiconductor which demonstrates a high exciton binding energy (0.06 eV) and strong emission bands in both the ultraviolet (UV) and visible (vis) spectral ranges which are attributed to near-band and defect level emissions, respectively.[6−8] Through varying the layer deposition or synthetic conditions and/or introducing dopants into materials,[9] the optical and structural properties of ZnO can be tailored for a given application such as light-emitting diodes (LEDs).[10] While ZnO is a promising material for applications, including optical coatings,[11] light-emitting devices,[10,12] and sensors,[13−15] the electronic and optical applications of ZnO are limited due to the large (UV) band gap of the material These can be overcome by engineering ZnO with dopants or defect states. Nanoscale and thin metal structures such as gold (Au) are known to be able to generate a localized surface plasmon resonance which results in optical absorption in the visible range.[16−18] The location of the absorption is strongly dependent upon the structure of the layer/size of the particles and the surrounding media.[17,19,20]
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