Type of presentation: Oral

MS-1-O-2629 Insight into the structural, electrical and photoresponse properties of individual Fe:SrTiO3 nanotubes

Žagar K.1, Fabrega C.2, Hernandez-Ramirez F.2,3, Prades J. D.3, Morante J. R.2,3, Rečnik A.1, Čeh M.1
1Jožef Stefan Institute, Ljubljana, Slovenia, 2Catalonia Institute for Energy Research, Barceloba Spain, 3University of Barcelona, Barcelona, Spain
kristina.zagar@ijs.si

Titanates are suitable for many applications such as oxygen sensing and tunable high temperature superconducting microwave filters. The potential advantages of the nanostructured forms have been scarcely explored compared to other oxides. We report on the structural and electrical properties of individual iron-doped strontium titanate nanotubes (Fe:SrTiO3). The Fe:SrTiO3 nanotubes were assessed for the first time, showing high stability and reproducibility [1].

Fe:SrTiO3 nanotubes were synthesized using sol-gel electrophoretic deposition (EPD) technique [2]. The Fe:SrTiO3 sol, where 2 mol% of Ti was replaced by Fe, was deposited into the anodic alumina template while a potential was applied between the AAO/Al working electrode and Pt counter electrode. After the deposition samples were annealed at 700 °C for 1 h with subsequent template removal. Resulting Fe:SrTiO3 nanotubes were characterized by electron microscopy techniques. To study electrical properties, Fe:SrTiO3 nanotube devices were fabricated by focused ion beam nanolithography techniques [3].

Obtained Fe:SrTiO3 nanotubes with lengths between 5 and 10 µm and diameters of approximately 200 nm were polycrystalline, dense and made up of cubic grains ranging between 10 and 20 nm in size (Figure 1). Their chemical composition explored by Energy-dispersive X-ray (EDX) analysis showed the presence of Sr, Ti and Fe; and confirmed that Fe was effectively incorporated into the perovskite structure.

For the electrical characterization the prototype device was formed by integration of individual Fe:SrTiO3 nanotubes into simple circuit architecture and the electrical resistivity of approx. 35 ohm∙cm was calculated (Figure 2). This value was significantly lower than the values for intrinsic bulk SrTiO3 samples due to the presence of Fe. This result opens the door to the future synthesis of Fe:SrTiO3 nanotubes suitable for monitoring small trace level of oxygen. Furthermore, some devices were tested as UV-detectors with the final aim to explore the optoelectronics characteristics and validate their suitability for device integration. The dynamic behavior of the photoresponse obtained with a single Fe:SrTiO3 nanotube as a function of different UV photon fluxes is shown in Figure 3. Repeatable and reversible responses were found in all cases, demonstrating that our devices are nice proof-of concept systems showing that an Fe:SrTiO3 nanotube can be used as a UV photodetector.

References:

1. K. Zagar et al., J. Mat. Chem. Phys. 141 (2013), p. 9.

2. K. Zagar et al., Nanotechnology 21 (2010) p. 375605.

3. F. Hernandez-Ramirez et al., Chem. Phys. 11 (2009), p. 7105.

The research was also supported by the Framework 7 program under the project S3 (FP7-NMP-2009-247768) and European Union Seventh Framework Programme [FP7/2007-2013] under grant agreement n°312483 (ESTEEM2).

Fig. 1: (a) Bright-field image of a uniformly shaped and polycrystalline Fe:SrTiO3 nanotube. (b) Higher-magnification bright-field TEM image of polycrystalline Fe:SrTiO3 nanotube with grain sizes in the range from 10 to 20 nm.

Fig. 2: (a) Fe:SrTiO3 nanotube electrically contacted in 2-probe configuration using FIB lithography. (b) I-V curve of the contacted Fe:SrTiO3 nanotube. An ohmic response is found at room temperature and open air atmosphere.

Fig. 3: (a) Photoresponse Iph of a Fe:SrTiO3 nanotube as function of different UV photon intensities (b) Dynamic response of Iph as function of different UV photon fluxes.