Growth and characterization of thin oriented Co3O4 (111) films obtained by decomposition of layered cobaltates Na CoO2

Buršík, J.; Soroka, Miroslav; Kužel, R.; Mika, Filip

doi:10.1016/j.jssc.2015.03.014

Cited by 8 publications

(6 citation statements)

References 21 publications

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“…The complex LEED pattern observed for thicker Co 3 O 4 (111) films grown on Ru(0001), consisting of two sixfold patterns rotated by 30 0 from each other (see figures 3(b) and (c)), is similar to those reported for Co 3 O 4 (111) grown by various methods on Ir [2,12] and on Al 2 O 3 (0001) [9,10,34], and for Fe 3 O 4 (111) on Pt(111) or Ru(0001) [35]. This behavior is indicative of twinning [9,10,33], and appears to be a general phenomenon for both Co 3 O 4 (111) and Fe 3 O 4 (111), regardless of the specific substrate used or the growth method.…”

Section: Discussionsupporting

confidence: 76%

Epitaxial growth of cobalt oxide phases on Ru(0001) for spintronic device applications

Olanipekun

Ladewig

Kelber

et al. 2017

Semicond. Sci. Technol.

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Cobalt oxide films are of technological interest as magnetic substrates that may support the direct growth of graphene, for use in various spintronic applications. In this work, we demonstrate the controlled growth of both Co 3 O 4 (111) and CoO(111) on Ru(0001) substrates. The growth is performed by Co molecular beam epitaxy, at a temperature of 500 K and in an O 2 partial pressure of 10 −4 Torr for Co 3 O 4 (111), and 7.5×10 −7 Torr for CoO(111). The films are distinguished by their dissimilar Co 2p x-ray photoemission (XPS) spectra, while XPS-derived O/Co stoichiometric ratios are 1.33 for Co 3 O 4 (111) and 1.1 for CoO(111). Electron energy loss (EELS) spectra for Co 3 O 4 (111) indicate interband transitions at ∼2.1 and 3.0 eV, while only a single interband transition near 2.0 eV is observed for CoO(111). Low energy electron diffraction (LEED) data for Co 3 O 4 (111) indicate twinning during growth, in contrast to the LEED data for CoO(111). For Co 3 O 4 (111) films of less than 20 Å average thickness, however, XPS, LEED and EELS data are similar to those of CoO(111). XPS data indicate that both Co oxide phases are hydroxylated at all thicknesses. The two phases are moreover found to be thermally stable to at least 900 K in UHV, while ex situ atomic force microscopy measurements of Co 3 O 4 (111)/Ru(0001) indicate an average surface roughness below 1 nm. Electrical measurements indicate that Co 3 O 4 (111)/Ru(0001) films exhibit dielectric breakdown at threshold voltages of ∼1 MV cm −1 . Collectively, these data show that the growth procedures yield Co 3 O 4 (111) films with topographical and electrical characteristics that are suitable for a variety of advanced device applications.

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Section: Discussionsupporting

confidence: 76%

Epitaxial growth of cobalt oxide phases on Ru(0001) for spintronic device applications

Olanipekun

Ladewig

Kelber

et al. 2017

Semicond. Sci. Technol.

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“…To compensate the sodium losses that can occur during the final annealing at 800 °C, the film was encapsulated in Na 2 CO 3 powder, slightly pressed and heated at 625 °C for 16 h [15]. More details of precursor solution synthesis and film deposition procedure are reported in our previous papers [16,17].…”

Section: Methodsmentioning

confidence: 99%

Charge transport in thin layer Na_xCoO₂(x∼ 0.63) studied by terahertz spectroscopy

Němec

Knı́žek

Jirák

et al. 2016

J. Phys.: Condens. Matter

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Charge transport in Na0.63CoO2 thin film deposited by a spin-coating method was investigated experimentally by time-domain terahertz spectroscopy and theoretically using Monte Carlo calculations of charge response in nano-structured materials. The dominating type of transport mechanism over the entire investigated range of temperatures (20-300 K) is a metallic-like conductivity of charges partly confined in constituting nano-sized grains. Due to the granular character of our thin film, the scattering time at low temperatures is limited by scattering on grain boundaries and the conductivity is strongly suppressed due to capture of a major fraction of charge carriers in deep traps. Nevertheless, our experimental setup and the applied model allowed us to distinguish the parameters related to the grain interior from those influenced by grain boundaries, and to conclude that the metallic type of conductivity is the intrinsic property relevant to single crystal materials.

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“…that during the epitaxial growth of Co 3 O 4 , two surfaces with the lowest surface energy, namely (111) and (110), are typically formed. 26 More detailed experimental and theoretical study have been performed in [27], where the effect of different Co surface has been studied by X-ray diffraction (XRD) and atomic force microscopy (AFM) methods, 29 LEED and scanning tunneling microscopy (STM). [30][31][32][33] Bulk Co 3 O 4 have also been studied using Raman spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

“…Experimentally, cobalt spinel (110) surface has been thoroughly investigated by Petitto and Langel 28 using low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS). The Co 3 O 4 (111) surface has been studied by X-ray diffraction (XRD) and atomic force microscopy (AFM) methods, 29 LEED and scanning tunneling microscopy (STM). [30][31][32][33] Considering the lack of microscopic understanding of the surface and interface magnetism, the present study is aimed to establish the nature of ferromagnetism at the Co 3 O 4 /ZnO interface toward an application in the new device types for spintronics.…”

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confidence: 99%

Interface magnetism and electronic structure: ZnO(0001)/ Co3O4 (111)

et al. 2018

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We have studied the structural, electronic and magnetic properties of spinel Co 3 O 4 (111) surfaces and their interfaces with ZnO (0001) using density functional theory (DFT) within the Generalized Gradient Approximation with on-site Coulomb repulsion term (GGA+U). Two possible forms of spinel surface, containing Co 2+ or Co 3+ ions and terminated with either cobalt or oxygen ions were considered, as well as their interface with zinc oxide. Our calculations demonstrate that Co 3+ ions attain non-zero magnetic moments at the surface and interface, in contrast to the bulk, where they are not magnetic, leading to the ferromagnetic ordering. Since heavily Co-doped ZnO samples can contain Co 3 O 4 secondary phase, such a magnetic ordering at the interface might explain the origin of the magnetism in such diluted magnetic semiconductors (DMS). PACS numbers: 73.20.-r, 75.70.-i Acknowledgments 16References 17 I. INTRODUCTIONMagnetic semiconductors (MS) and diluted magnetic semiconductors (DMS) exhibit both ferromagnetic and semiconducting properties. Therefore, they are promising materials for spintronics, which utilizes for information processing not only the electron charge but also its spin. Historically, the first DMS with a high Curie temperature up to about 200 K was GaAs doped with Mn ions. 1,2 In that compound, the ferromagnetism is promoted by hole carriers, which align along the local Mn magnetic moments and called carrier-induced ferromagnetism or Zener p − d exchange. It is crucial for this mechanism that Mn at the Ga site becomes Mn 2+ instead of Ga 3+ , thus providing at the same time a local spin and a hole charge carrier. Extension of the mechanism, proposed in a very influential paper 3 of Dietl and co-workers, allows a prediction that the above room-temperature ferromagnetism in ZnO:Co and GaN:Mn is due to the same carrier-induced mechanism. This would be responsible for the ferromagnetism with a sufficiently high number of hole charge carriers.First experiments after that prediction 4 seemed to confirm the mechanism proposed and has also been supported by ab-initio calculations. 5 However, it soon turned out that the Co impurity is in fact isovalent to the Zn ion 6 and provides no charge carriers at all, while the situation in GaN:Mn is similar. 7We are going to concentrate here on ZnO:Co, where the experimental reports demon-2 strate that the above room-temperature ferromagnetism in ZnO:Co persist. Even though its origin is still not clarified, there are clear indications in more recent experiments that the magnetism in the ZnO:Co system is attributed to the formation of the Co 3 O 4 phase in ZnO. 8-12 Therefore, we will focus here on the role of the Co 3 O 4 phase, although several attempts to explain the mechanism of the ferromagnetism in realistic ZnO:Co systems exist including, for instance, spinodal decomposition 13 or Lieb-Mattis ferrimagnetism, 14 to cite just two ideas. The typical doping level of Co in ZnO can be relatively high (in the range between 10% and 30%). This leads to the secondar...

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Growth and characterization of thin oriented Co3O4 (111) films obtained by decomposition of layered cobaltates Na CoO2

Cited by 8 publications

References 21 publications

Epitaxial growth of cobalt oxide phases on Ru(0001) for spintronic device applications

Epitaxial growth of cobalt oxide phases on Ru(0001) for spintronic device applications

Charge transport in thin layer Na_xCoO₂(x∼ 0.63) studied by terahertz spectroscopy

Interface magnetism and electronic structure: ZnO(0001)/ Co3O4 (111)

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Growth and characterization of thin oriented Co3O4 (111) films obtained by decomposition of layered cobaltates Na CoO2

Cited by 8 publications

References 21 publications

Epitaxial growth of cobalt oxide phases on Ru(0001) for spintronic device applications

Epitaxial growth of cobalt oxide phases on Ru(0001) for spintronic device applications

Charge transport in thin layer NaxCoO2(x∼ 0.63) studied by terahertz spectroscopy

Interface magnetism and electronic structure: ZnO(0001)/ Co3O4 (111)

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Charge transport in thin layer Na_xCoO₂(x∼ 0.63) studied by terahertz spectroscopy