Control of Elemental Distribution in the Nanoscale Solid-State Reaction That Produces (Ga_1–xZn_x)(N_1–xO_x) Nanocrystals

Abstract

Solid-state chemical transformations at the nanoscale can be a powerful tool for achieving compositional complexity in nanomaterials. It is desirable to understand the mechanisms of such reactions and characterize the local-level composition of the resulting materials. Here, we examine how reaction temperature controls the elemental distribution in (GaZn)(NO) nanocrystals (NCs) synthesized via the solid-state nitridation of a mixture of nanoscale ZnO and ZnGaO NCs. (GaZn)(NO) is a visible-light absorbing semiconductor that is of interest for applications in solar photochemistry. We couple elemental mapping using energy-dispersive X-ray spectroscopy in a scanning transmission electron microscope (STEM-EDS) with colocation analysis to study the elemental distribution and the degree of homogeneity in the (GaZn)(NO) samples synthesized at temperatures ranging from 650 to 900 °C with varying ensemble compositions (i.e., x values). Over this range of temperatures, the elemental distribution ranges from highly heterogeneous at 650 °C, consisting of a mixture of larger particles with Ga and N enrichment near the surface and very small NCs, to uniform particles with evenly distributed constituent elements for most compositions at 800 °C and above. We propose a mechanism for the formation of the (GaZn)(NO) NCs in the solid state that involves phase transformation of cubic spinel ZnGaO to wurtzite (GaZn)(NO) and diffusion of the elements along with nitrogen incorporation. The temperature-dependence of nitrogen incorporation, bulk diffusion, and vacancy-assisted diffusion processes determines the elemental distribution at each synthesis temperature. Finally, we discuss how the visible band gap of (GaZn)(NO) NCs varies with composition and elemental distribution.

Synthesis and Size-Dependent Optical Properties of Intermediate Band Gap Cu3VS4 Nanocrystals

“…38 Furthermore, presynthesized nanoparticles can be reacted to form ternary compounds, as shown by Dukovic et al for the synthesis of (Ga1-xZn)(N1-xOx) nanoparticles obtained by nitriding a mixture of ZnGa2O4 and ZnO nanoseeds. 45 To get further insights into the reaction between the CuxS seeds and the vanadium precursor, STEM-EDX analysis was performed on the reaction product obtained after 5 minutes from the DDT/OLAM injection and the results are reported in Figure 5 and Figure S6. The analysis evidences the presence of CuxS in the form of hexagonal nanoplateles and nanospheres, of Cu3VS4 nanocubes and of Vcontaining nanoparticles (V-NPs).…”

Understanding the visible-light photocatalytic activity of GaN:ZnO solid solution: the role of Rh2−yCryO3 cocatalyst and charge carrier lifetimes over tens of seconds

“… 19 , 43 Furthermore, Zn volatilization during synthesis has been shown to yield Ga-rich surfaces 31 and increase structural disorder, 40 and inhomogeneous elemental distributions have also been observed. 22 , 44 , 45 As a result of the energetic preference for the valence-matched nearest neighbor pairs (Ga–N and Zn–O), significant short range order is predicted 46 and observed, 34 , 38 which has been shown theoretically to impact the electronic properties in addition to structural properties. 46 Experimental investigations have also proposed the formation of domains with different chemical compositions and heterojunctions within GaN:ZnO.…”

Chemical transformations at the nanoscale: nanocrystal-seeded synthesis of β-Cu2V2O7 with enhanced photoconversion efficiencies

“…Multinary metal oxides are emerging as key materials to advance diverse applications ranging from batteries to flexible electronics, catalysis and plasmonics. 1 – 12 Achieving control over crystalline phases, stoichiometry, grain size and morphology is of the uttermost importance considering the correlation of these structural features with the physical–chemical properties and with the device performance. This urgent need requires novel synthetic approaches, which include various seeding strategies, photochemical synthesis and nanoscale solid-state reactions.…”

“… 3 Another example comes from Chuang et al who have exploited the nanoscale solid state reaction between ZnO and GaN nanocrystals to tune the composition and the band gap of (Ga 1– x Zn x )(N 1– x O x ), a material with intriguing optical properties relevant for solar fuel generation. 9 – 12 Finally, our group has recently developed a nanocrystal-seeded growth approach wherein Bi x Sb 1– x nanocrystalline thin films react with vanadium precursor to afford a new photoanode material, BiV 1– x Sb x O 4 . 13 This compound had been predicted by theoretical calculations but attempts to synthesize it by more conventional approaches, such as sol–gel, solid-state synthesis and spray pyrolysis, had been unsuccessful.…”