SCIENTIFIC HIGHLIGHTS RL3, Articles

Transparent and highly conducting metallic oxides

Metals are known to be bright by reflecting light. Many applications however, require transparent rather than reflecting metals. Transition metal oxides offer a solution to this dilemma

Information technologies require new materials with high electrical conductivity and optical transparency to face scarcity of critical materials and improve performances. Oxide thin films based on early transition metals (e.g. V, Nb, Mo, etc.), the partially occupation of ndx orbitals (i.e. nd1, nd2...) gives rise to metallic conductivity. Transparency at visible range requires that the plasm edge to be at red or infrared. The narrow conducting 3d band of SrVO3 is expected to enhance the carrier effective mass, thus lowering the plasma frequency below the visible as required. However, growing thin films of these oxides typically requires an extremely low oxygen pressure, that compromises point defect concentration in the film and thus challenges obtaining high conducting materials as required. Using pulsed laser deposition (PLD) as a tool to grow epitaxial thin films of SrVO3, we have discovered that the use of a non-reactive gas controls the ablation plume expansion and allows to obtain SrVO3 films with low room-temperature resistivity (r ≈ 31 mW cm) and large carrier mobility (m ≈ 8.3 cm2 V-1 s-1) and residual resistivity ratio (RRR ≈ 11.5), which are record figures of merit for PLD grown films, while preserving the plasma frequency at infrared and improving optical transparency in the visible range.

Moreover, we show that by exploiting the strain caused by the substrates on the structure and microstructure of the films, the carrier concentration and the effective mass of carriers can be modulated while preserving the optical transmittance window. As indicated by linear X-ray dichroism experiments performed at Boreas Beamline at ALBA synchrotron, the electronic bandwidth and orbital occupation appear to rule the observed effects.

 

High Carrier Mobility, Electrical Conductivity, and Optical Transmittance in Epitaxial SrVO3 Thin Films
Mathieu Mirjolet, Florencio Sánchez, Josep Fontcuberta
Adv. Funct. Mater. 29, 1808432, 2019
DOI: 10.1002/adfm.201808432

Independent Tuning of Optical Transparency Window and Electrical Properties of Epitaxial SrVO3 Thin Films by Substrate Mismatch
Mathieu Mirjolet, Hari Babu Vasili, LLuís López-Conesa, Sònia Estradé, Francesca Peiró, José Santiso, Florencio Sánchez, Pamela Machado, Pierluigi Gargiani, Manuel Valvidares, Josep Fontcuberta
Adv. Funct. Mater. 29, 1904238, 2019
DOI: 10.1002/adfm.201904238

Figure: Plasma energy of SrVO3 thin films (left axis) and room-temperature electrical resistivity (right axis) grown on different substrates, imposing tensile or compressive stress on SrVO3, as indicated.

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