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Issue 8, 2016
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Synthesis and characterization of (Ga1−xZnx)(N1−xOx) nanocrystals with a wide range of compositions

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We describe the synthesis and characterization of wurtzite (Ga1−xZnx)(N1−xOx) nanocrystals with a wide range of compositions and a focus on properties relevant for solar fuel generation. (Ga1−xZnx)(N1−xOx), a solid solution of GaN and ZnO, is an intriguing material because it exhibits composition-dependent visible absorption even though the parent semiconductors absorb in the UV. When functionalized with co-catalysts, (Ga1−xZnx)(N1−xOx) is also capable of water splitting under visible irradiation. Here, we examine the synthesis of (Ga1−xZnx)(N1−xOx) nanocrystals to understand how they form by nitridation of ZnO and ZnGa2O4 nanocrystalline precursors. We find that the ZnO precursor is critical for the formation of crystalline (Ga1−xZnx)(N1−xOx) at 650 °C, consistent with a mechanism in which wurtzite (Ga1−xZnx)(N1−xOx) nucleates topotactically on wurtzite ZnO at an interface with ZnGa2O4. Using this information, we expand the range of compositions from previously reported 0.30 ≤ x ≤ 0.87 to include the low-x and high-x ends of the range. The resulting compositions, 0.06 ≤ x ≤ 0.98, constitute the widest range of (Ga1−xZnx)(N1−xOx) compositions obtained by one synthetic method. We then examine how the band gap depends on sample composition and find a minimum of 2.25 eV at x = 0.87, corresponding to a maximum possible solar-to-H2 power conversion efficiency of 12%. Finally, we examine the photoelectrochemical (PEC) oxidation behavior of thick films of (Ga1−xZnx)(N1−xOx) nanocrystals with x = 0.40, 0.52, and 0.87 under visible illumination. (Ga1−xZnx)(N1−xOx) nanocrystals with x = 0.40 exhibit solar PEC oxidation activity that, while too low for practical applications, is higher than that of bulk (Ga1−xZnx)(N1−xOx) of the same composition. The highest photocurrents are observed at x = 0.52, even though x = 0.87 absorbs more visible light, illustrating that the observed photocurrents are a result of an interplay of multiple parameters which remain to be elucidated. This set of characterizations provides information useful for future studies of composition-dependent PEC properties of nanoscale (Ga1−xZnx)(N1−xOx).

Graphical abstract: Synthesis and characterization of (Ga1−xZnx)(N1−xOx) nanocrystals with a wide range of compositions

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The article was received on 14 Jun 2015, accepted on 27 Jul 2015 and first published on 28 Jul 2015

Article type: Paper
DOI: 10.1039/C5TA04314J
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J. Mater. Chem. A, 2016,4, 2927-2935

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    Synthesis and characterization of (Ga1−xZnx)(N1−xOx) nanocrystals with a wide range of compositions

    K. Lee, Y. Lu, C. Chuang, J. Ciston and G. Dukovic, J. Mater. Chem. A, 2016, 4, 2927
    DOI: 10.1039/C5TA04314J

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