Abstract
Fabrication of heterostructures by merging two or more materials in a single object. The domains at the nanoscale represent a viable strategy to purposely address materials’ properties for applications in several fields such as catalysis, biomedicine, and energy conversion. In this case, solution-phase seeded growth and the hot-injection method are ingeniously combined to fabricate TiO2/PbS heterostructures. The interest in such hybrid nanostructures arises from their absorption properties that make them advantageous candidates as solar cell materials for more efficient solar light harvesting and improved light conversion. Due to the strong lattice mismatch between TiO2 and PbS, the yield of the hybrid structure and the control over its properties are challenging. In this study, a systematic investigation of the heterostructure synthesis as a function of the experimental conditions (such as seeds’ surface chemistry, reaction temperature, and precursor concentration), its topology, structural properties, and optical properties are carried out. The morphological and chemical characterizations confirm the formation of small dots of PbS by decorating the oleylamine surface capped TiO2 nanocrystals under temperature control. Remarkably, structural characterization points out that the formation of heterostructures is accompanied by modification of the crystallinity of the TiO2 domain, which is mainly ascribed to lattice distortion. This result is also confirmed by photoluminescence spectroscopy, which shows intense emission in the visible range. This originated from self-trapped excitons, defects, and trap emissive states.
Highlights
The present study aims at synthesizing and extensively characterizing TiO2 /PbS hybrid NCs prepared by a seeded growth approach using purposely functionalized TiO2 NCs as seeds and allows the PbS domains growth, in situ, by the hot injection method
A seeded growth combined with a hot-injection approach has been used to prepare TiO2 /PbS
The hybrid structure topology has been demonstrated to be strongly affected by the high interfacial strain between the TiO2 and PbS, which agreed with the Volmer-Weber growth mode
Summary
The colloidal approach, which is extensively used to prepare nanoparticles (NPs) and nanocrystals (NCs) with a variety of sizes and shapes [1,2,3,4], has, in recent decades, made a step forward by fabricating hybrid NPs [5,6,7,8,9,10,11] based on the combination of two or more materials in one solid nano-object for application in several fields, including biomedicine, environment, catalysis, and sensing [12,13,14,15,16].In principle, any desired inorganic material can be purposely assembled to form the hybrid structures, characterized by properties that possibly derive from a simple combination, enhancement, or mitigation of the properties of the individual materials or can bring on completely new physical and chemical properties. The new phase, nucleated at the NC surface facet, may topotaxially grow toward the interior of the NCs or form original morphologies due to facet-dependent exchange reaction, nanoscale asymmetry, and anisotropy. This strategy shows great potentiality for the easy fabrication of novel heterostructures, it has been mainly limited to the fabrication of hybrid structures belonging to the II–VI, I−III−VI, and IV−VI classes of semiconductors and characterized by the same anion for both domains. A huge variety of hybrid structures with each component having a different size, shape, spatial orientation, composition, and crystalline structure, have been synthesized by the multi-step seed-mediated growth [10,39,40,41].
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