Laser Synthesis of Nanometric Iron Oxide Films with High Seebeck Coefficient and High Thermoelectric Figure of Merit

Abstract

Radiation of a KrF-laser (λ=248 nm) was used for the synthesis by reactive pulsed laser deposition (RPLD) of nanometric iron oxide [Fe 2 O 3-X (0≤×≤1)] films with variable thickness, stoichiometry and electrical properties. Film deposition was carried out on <100>Si at its temperature to have being increased from 293 to 800 K. XRD analysis showed that films deposited on Si substrate had polycrystalline structure. Films demonstrated semiconductor temperature trend with variable band gap E g about 1.0 eV or less depending on oxygen pressure, the number of laser pulses and substrate temperature. Film thickness (13-60 nm) depended on oxygen pressure, substrate temperature and number of laser pulses. The higher substrate temperature, the more crystallinity of the deposited iron oxides' films was resulting in increasing of thermo electromotive force coefficient (Seebeck coefficient, S). It was found out the optimum oxygen pressure in the reactor, substrate temperature and film thickness when the S coefficient was high as 12-4 mV/K in the range 240-330 K. The thermoelectric figure of merit (ZT) was high as 1-6 in the range 280-330 K. This makes nanometric Fe 2 O 3-X films, synthesized by UV photons using RPLD method, an exceptionally strong candidate for effective thermo sensors and thermo converters operating at moderate temperature.

Laser Synthesis of Transitional Metal Oxides in 2D Structure and Heterostructure for Thermo Sensors with High Seebeck Coefficient

“…oxygen pressure, substrate temperature, structure thickness). In general, the increase of oxygen pressure in the reactor resulted in decreasing oxides' lines due to the decrease of crystalline status in deposited structures, as the increase of oxygen pressure caused a kinetic energy loss of iron atoms and their ions owing to increasing of collision frequency with oxygen molecules [Mulenko et al 2014]. Correspondingly, the cooling time of structures on a substrate decreases and the crystallization status is worsening.…”

“…Correspondingly, the cooling time of structures on a substrate decreases and the crystallization status is worsening. On the other hand, in the case of substrates temperature of 800 K, the number of the iron oxide lines in XRD (Fig.5), as the kinetic energy of iron atoms, their ions and cooling time are increased resulting in the growth of a more amount of Fe2O3-X semiconductor phases in the deposited structures [Mulenko et al 2014]. The substrate temperature increases resulting in the increasing of  value owing to higher crystalline phases' content.…”

“…But the highest S coefficient for Fe2O3-X 2D structure as high as 3-8 mV/K in the range Frontiers in Sensors (FS) Volume 4, 2016 www.seipub.org/fs 17 of 280-330 K was obtained while deposition on heated Si substrate with RPLD [Mulenko et al, 2014]. The highest S coefficient for Cr3-XO3-Y 2D structure as high as 3-8 mV/K in the range 240-330 K was obtained while deposition on heated Si substrate [Mulenko et al 2014]. Nevertheless, it further remains very important problem to increase the S coefficient as much as possible.…”

Structural and Magnetoresistive Properties of Nanometric Films Based on Iron and Chromium Oxides on the Si Substrate

“…In our previous work [5][6][7][8][9], it was shown that thin films based on silicides and oxides of the transitional metals formed by the pulsed laser deposition (PLD) and by the reactive pulsed laser deposition (RPLD) are quite suitable materials for thermo-tenso sensors. The reactive pulse laser deposition is one of the attractive methods for the nanometric film synthesis.…”

“…The advantages of this method are effectivity, simplicity, environmental safety, and deposition of the layers with precise thicknesses on the different substrates from the various chemical precursors. In other words, the RPLD method application in combination with the material selecting allows creating sensors with required parameters [5][6][7]. The iron oxide thin films with different sensing properties for thermo-photochemical sensors operating at moderate temperature were demonstrated.…”