Highly conductive PdCoO2 ultrathin films for transparent electrodes

Harada, T.; Fujiwara, K.; Tsukazaki, Atsushi

doi:10.1063/1.5027579

Cited by 52 publications

(55 citation statements)

References 22 publications

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“…1(a)) was confirmed using X-ray diffraction (XRD) ( Fig. S2 [20]), as reported in detail previously [19]. A typical, high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) image around the film-substrate interface is shown in Fig.…”

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confidence: 78%

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Anomalous Hall effect at the spontaneously electron-doped polar surface of PdCoO2 ultrathin films

Harada

Sugawara

Fujiwara

et al. 2020

Phys. Rev. Research

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We revealed the electrical transport through surface ferromagnetic states of a nonmagnetic metal PdCoO2. Electronic reconstruction at the Pd-terminated surface of PdCoO2 induces Stoner-like ferromagnetic states, which could lead to spinrelated phenomena among the highly conducting electrons in PdCoO2. Fabricating a series of nanometer-thick PdCoO2 thin films, we detected a surface-magnetization-driven anomalous Hall effect via systematic thickness-and terminationdependent measurements. Besides, we discuss that finite magnetic moments in electron doped CoO2 triangular lattices may have given rise to additional unconventional Hall resistance.Layered transition-metal oxides have given great insight into the role of dimensionality in correlated electron physics [1][2][3][4]. Among the many different oxides, the delafossite metal PdCoO2 is a unique system in which monovalent Pd + ions are stabilized in the form of a twodimensional (2D) Pd sheet that is sandwiched by [CoO2]layers [5-7] (Fig. 1 (a)). This 2D Pd + sheet ( Fig. 1 (b)) provides a highly dispersive 4d-dominant conduction band [8][9][10][11], while [CoO2]forms an insulating block layer ( Fig.

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confidence: 78%

“…To overcome this, here we examine ultrathin PdCoO2 films. By altering film thickness [19], we have succeeded in detecting the signal from spin-related transport in these ultrathin films, demonstrating that the surface ferromagnetism occurred within a limited thickness ds near the surface ( Fig. 1(e) and Fig.…”

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confidence: 93%

Anomalous Hall effect at the spontaneously electron-doped polar surface of PdCoO2 ultrathin films

Harada

Sugawara

Fujiwara

et al. 2020

Phys. Rev. Research

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“…It was found that this limited the in situ growth temperature to about 300 °C, which was insufficient to drive diffusion, and thus, necessitates an ex situ post-growth anneal to high temperatures to create films with high crystalline quality. These films exhibit improved transport properties compared with the previous PLD grown films [10]. Specifically, the room temperature resistivity of the annealed films approaches that of the best single crystals, suggesting comparable crystalline quality, as confirmed by the STEM data.…”

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confidence: 62%

Growth of metallic delafossite PdCoO2 by molecular beam epitaxy

Brahlek

Rimal

et al. 2019

Phys. Rev. Materials

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The Pd, and Pt based ABO2 delafossites are a unique class of layered, triangular oxides with 2D electronic structure and a large conductivity that rivals the noble metals. Here, we report successful growth of the metallic delafossite PdCoO2 by molecular beam epitaxy (MBE). The key challenge is controlling the oxidation of Pd in the MBE environment where phase-segregation is driven by the reduction of PdCoO2 to cobalt oxide and metallic palladium. This is overcome by combining low temperature (300 °C) atomic layer-by-layer MBE growth in the presence of reactive atomic oxygen with a post-growth high-temperature anneal. Thickness dependence (5-265 nm) reveals that in the thin regime (<75 nm), the resistivity scales inversely with thickness, likely dominated by surface scattering; for thicker films the resistivity approaches the values reported for the best bulk-crystals at room temperature, but the low temperature resistivity is limited by structural twins. This work shows that the combination of MBE growth and a post-growth anneal provides a route to creating high quality films in this interesting family of layered, triangular oxides.

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“…The electrochemical performance of nano CuAlO 2 with an average particle size of ≈20 nm demonstrated 12 times more catalytic activity in the electrolysis of water to the hydrogen evolution reactions and oxygen evolution reactions compared to bulk CuAlO 2 [28]. Research on thin films of delafossite is another interesting and widely investigated area for their potential uses in optoelectronic device fabrication [29][30][31][32]. As has been well established by the high pressure scientific community, compression is yet another way to engineer the crystal/electronic structure of materials, producing compounds with entirely different set of physical properties without altering their chemical composition [33,34].…”

Section: Introductionmentioning

confidence: 99%

Copper Delafossites under High Pressure—A Brief Review of XRD and Raman Spectroscopic Studies

Garg

Rao

2018

Crystals

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Delafossites, with a unique combination of electrical conductivity and optical transparency constitute an important class of materials with their wide range of applications in different fields. In this article, we review the high pressure studies on copper based semiconducting delafossites with special emphasis on their structural and vibrational properties by synchrotron based powder X-ray diffraction and Raman spectroscopic measurements. Though all the investigated compounds undergo pressure induced structural phase transition, the structure of high pressure phase has been reported only for CuFeO 2 . Based on X-ray diffraction data, one of the common features observed in all the studied compounds is the anisotropic compression of cell parameters in ambient rhombohedral structure. Ambient pressure bulk modulus obtained by fitting the pressure volume data lies between 135 to 200 GPa. Two allowed Raman mode frequencies E g and A 1g are observed in all the compounds in ambient phase with splitting of E g mode at the transition except for CuCrO 2 where along with splitting of E g mode, A 1g mode disappears and a strong mode appears which softens with pressure. Observed transition pressure scales exponentially with radii of trivalent cation being lowest for CuLaO 2 and highest for CuAlO 2 . The present review will help materials researchers to have an overview of the subject and reviewed results are relevant for fundamental science as well as possessing potential technological applications in synthesis of new materials with tailored physical properties.

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Highly conductive PdCoO2 ultrathin films for transparent electrodes

Cited by 52 publications

References 22 publications

Anomalous Hall effect at the spontaneously electron-doped polar surface of PdCoO2 ultrathin films

Anomalous Hall effect at the spontaneously electron-doped polar surface of PdCoO2 ultrathin films

Growth of metallic delafossite PdCoO2 by molecular beam epitaxy

Copper Delafossites under High Pressure—A Brief Review of XRD and Raman Spectroscopic Studies

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