title: Colloidal Synthesis of Bipolar Off-Stoichiometric Gallium Iron Oxide Spinel-Type Nanocrystals with Near-IR Plasmon Resonance.
abstract: We report the colloidal synthesis of ∼5.5 nm inverse spinel-type oxide Ga2FeO4(GFO) nanocrystals (NCs) with control over the gallium and iron content. As recently theoretically predicted, some classes of spinel-type oxide materials can be intrinsically doped by means of structural disorder and/or change in stoichiometry. Here we show that, indeed, while stoichiometric Ga2FeO4NCs are intrinsic small bandgap semiconductors, off-stoichiometric GFO NCs, produced under either Fe-rich or Ga-rich conditions, behave as degenerately doped semiconductors. As a consequence of the generation of free carriers, both Fe-rich and Ga-rich GFO NCs exhibit a localized surface plasmon resonance in the near-infrared at ∼1000 nm, as confirmed by our pump-probe absorption measurements. Noteworthy, the photoelectrochemical characterization of our GFO NCs reveal that the majority carriers are holes in Fe-rich samples, and electrons in Ga-rich ones, highlighting the bipolar nature of this material. The behavior of such off-stoichiometric NCs was explained by our density functional theory calculations as follows: the substitution of Ga3+by Fe2+ions, occurring in Fe-rich conditions, can generate free holes (p-type doping), while the replacement of Fe2+by Ga3+cations, taking place in Ga-rich samples, produces free electrons (n-type doping). These findings underscore the potential relevance of spinel-type oxides as p-type transparent conductive oxides and as plasmonic semiconductors.
authors.affiliation: Nanochemistry Department, Istituto Italiano di Tecnologia (IIT) , via Morego 30, Genova, Italy.|Department of Chemistry and Industrial Chemistry, University of Genoa , via Dodecaneso 31, Genova, Italy.
authors.forename: Carmine
authors.initials: C
authors.lastname: Urso
authors.affiliation: Center for Biomolecular Nanotechnologies, Istituto Italiano di Tecnologia (IIT) , Via Barsanti 14, 73010 Arnesano (Lecce), Italy.
authors.forename: Mariam
authors.initials: M
authors.lastname: Barawi
authors.affiliation: Nanochemistry Department, Istituto Italiano di Tecnologia (IIT) , via Morego 30, Genova, Italy.|CompuNet, Istituto Italiano di Tecnologia (IIT) , via Morego, 30, 16163 Genova, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Gaspari
authors.affiliation: Dipartimento di Fisica, Politecnico di Milano , P.za Leonardo da Vinci 32, 20133 Milano, Italy.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Sirigu
authors.affiliation: Nanochemistry Department, Istituto Italiano di Tecnologia (IIT) , via Morego 30, Genova, Italy.
authors.forename: Ilka
authors.initials: I
authors.lastname: Kriegel
authors.affiliation: Dipartimento di Energia, Politecnico di Milano , via Ponzio 34/3, 20133 Milano, Italy.|Istituto di Fotonica e Nanotecnologie CNR , Piazza Leonardo da Vinci 32, 20133 Milano, Italy.
authors.forename: Margherita
authors.identifier: 0000-0001-9910-0391
authors.initials: M
authors.lastname: Zavelani-Rossi
authors.affiliation: Dipartimento di Fisica, Politecnico di Milano , P.za Leonardo da Vinci 32, 20133 Milano, Italy.|Istituto di Fotonica e Nanotecnologie CNR , Piazza Leonardo da Vinci 32, 20133 Milano, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Scotognella
authors.affiliation: Center for Biomolecular Nanotechnologies, Istituto Italiano di Tecnologia (IIT) , Via Barsanti 14, 73010 Arnesano (Lecce), Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Manca
authors.affiliation: Nanochemistry Department, Istituto Italiano di Tecnologia (IIT) , via Morego 30, Genova, Italy.
authors.forename: Mirko
authors.initials: M
authors.lastname: Prato
authors.affiliation: Nanochemistry Department, Istituto Italiano di Tecnologia (IIT) , via Morego 30, Genova, Italy.
authors.forename: Luca
authors.identifier: 0000-0002-1514-6358
authors.initials: L
authors.lastname: De Trizio
authors.affiliation: Nanochemistry Department, Istituto Italiano di Tecnologia (IIT) , via Morego 30, Genova, Italy.
authors.forename: Liberato
authors.initials: L
authors.lastname: Manna