Synthesis of hybrid polymethacrylate–noble metal (M = Au, Pd) nanoparticles for the growth of metal-oxide semiconductor nanowires

Abstract

Metal-oxide semiconductor nanowires (NWs) such as ZnO, β-Ga₂O₃ and SnO₂ with diameters of tens of nanometres and lengths of many micrometres have been grown using micellar nanohybrids consisting of methacrylate-based diblock copolymers and noble metal nanoparticles (MNPs). Micellar Au and Pd MNPs with diameters as small as 2.3 ± 0.3 nm were deposited on Si(001) by spin coating or drop casting and metal-oxide NWs were grown by reactive vapor transport. A high yield of β-Ga₂O₃ NWs with diameters of approximately 40 nm, lengths > 10 μm and a monoclinic crystal structure were obtained at 900 °C with the largest MNPs. These exhibited a broad, symmetric photoluminescence (PL) spectrum centred at 2.3 eV attributed to defect states situated energetically in the energy band gap of β-Ga₂O₃. We find that a reduction in the size of the MNPs below 10 nm leads to the formation of necklace like β-Ga₂O₃ NWs via the encapsulation of the MNPs which act as catalytic centres for the formation of branched nanostructures along the length of the β-Ga₂O₃ NWs that are also responsible for a blue shift in the PL at 2.8 eV as a result of quantum confinement. This was not observed upon reducing the density of MNPs or in the case of ZnO or SnO₂ NWs grown with the smallest of MNPs probably due to differences in surface energy. We show that polymethacrylate-noble MNPs may be patterned directly by electron beam lithography and may be exploited for the selective location growth of semiconductor NWs while we also discuss the difference between the sizes of the hybrid polymer-MNPs and MO NWs which is attributed to agglomeration.