Photon synthesis of iron oxide thin films for thermo-photo-chemical sensors
Highlights
► We report of UV photon synthesis of iron oxide thin films for multi-parameter sensors. ► Semiconductor properties of thin films are stipulated by iron oxides content. ► We obtained renewable thermo-photo-chemical sensors based on iron oxide thin films.
Introduction
At present, great interest is growing up for nanometric (thin) films, to test the advantages of reduced thickness in the performances of electronic devices and sensors [1]. As it was shown in our previous work [2], [3], [4], [5], [6] thin films based on transitional metals silicides and oxides formed by the pulsed laser deposition (PLD) and the reactive pulsed laser deposition (RPLD) are quite suitable materials for thermo-tenso sensors. Tenso sensor is based on the dependence of the relative change of the electrical resistance of the deposited film versus relative mechanical deformation of this film [2]. In general, these materials demonstrate semiconductor properties with the band gap (Eg) less than 1.0 eV [2], [3], [4], [5], [6]. Here we use photon-induced chemical vapor deposition (PCVD) based on continuous ultraviolet photodiode radiation for the deposition of iron oxide films from iron carbonyl [Fe(CO)5] vapors and RPLD in fast process of element ablation of iron target at low oxygen pressure. For example, RPLD was used to deposit iron oxide thin films for investigation of their magnetic and optical properties [7]. We used for the first time RPLD for synthesis of iron oxide thin films for thermo-chemical sensors [3]. Our interest is the deposition of nanometric iron oxide films with variable stoichiometry, in order to obtain semiconductor films with variable band gap for multi-parameter sensors on the single chip: thermo-photo-chemical sensors operating at moderate temperature.
In general, RPLD and PCVD methods were used in the oxides synthesis in chemical reactions.
But iron oxide synthesis in PCVD method takes place only in secondary processes and at not high vacuum [5]. Iron oxide synthesis in RPLD method takes place in direct process oxidizing atomic iron with oxygen molecules and at high vacuum. So RPLD gives the possibility to obtain metal oxides with more purity. But PCVD equipment is simpler than RPLD one but it requires metal organic compounds i.e. metal carbonyls as in our experiment. RPLD is a quite fast process and allows a good control of thickness and stoichiometry of deposits by varying the laser pulse number and the gas pressure in the deposition chamber [3], [6]. A pure iron target was ablated in low pressure oxygen atmosphere using a KrF laser pulses in order to obtain Fe2O3−x (0 ≤ x ≤ 1) semiconductor structures with variable thickness and composition. PCVD allows a good control of thickness and stoichiometry of deposits too by simply varying the light radiation parameters and pressure of carbonyl vapors resulted in the formation of iron oxide films. Here we carried out the investigation of nanometric iron oxide films deposited on 〈1 0 0〉 Si substrate by RPLD and PCVD for thermo-photo sensors and we compared these two methods for film deposition concerning their advantages. The thermo electromotive force (e.m.f.) coefficient (Seebeck coefficient, S) and photosensitivity (F) of Fe2O3−x (0 ≤ x ≤ 1) films were measured. It is very important to create a NOx (1 ≤ x ≤ 2) sensor, as nitrogen oxides are the most dangerous gases. They are emitted from the combustion of fossil fuels in coal-fired power plants, motor vehicles and they are being released in the form of trace from explosive matter like TNT, Tetryl and others. So it is needed to detect nitrogen oxides especially NO as it is the most active nitrogen oxide among these kinds of oxides. It is known sensor for NOx molecules based on tungsten oxide (WO3), but, unfortunately, it operates at relatively high temperature: 473–623 K [8], [9]. So it is needed to create chemical sensors operating at moderate temperature. In general, to create sensitive selected sensor for detection of definite molecules in gas mixture is important and difficult problem, because each kind of molecules has donor or acceptor action on metal oxide semiconductor. So it is needed to investigate separately the action of each kind of molecules on this semiconductor.
Section snippets
Material and methods
The experiment dealt with RPLD of iron oxide films is completely described in [3] where a KrF laser was used for RPLD of iron oxide films. The experiment dealt with PCVD based on laser radiation for the deposition of iron oxide films is completely described in [5], [6]. We used Ar+ laser tuned at 488 nm line in PCVD in previous experiments. Here we used continuous ultraviolet photodiode radiation with wave length of maximum radiation at 360 nm and the power density about 0.2 W/cm2 in PCVD, as iron
Films deposited by RPLD
Iron oxides with composition Fe2O3−x (0 ≤ x ≤ 1) were formed in thin films. The temperature dependence of the specific conductivity of deposited films demonstrated the typical behavior of semiconductor materials and can be approximated by the well-known relationwhere σg is the intrinsic conductivity; σi is the conductivity determined by impurities; k is the Boltzmann constant; Eg is the band gap for intrinsic conductivity; Ei is the band gap assigned for impurities in the
Thermo-sensor properties of films deposited by RPLD and PCVD
The shape of the Arhenius plot of electrical conductivity vs. 1/T is a clear evidence of the semiconducting characteristics of the deposited films (2). The experimental data show that the band gap Eg of the semiconductor films deposited by RPLD increases with increasing oxygen pressure from 0.05 up to 1.0 Pa during deposition, due to the higher content of iron oxides with higher oxidized phases [3]. The Eg values increase from 0.43 to 0.93 eV for samples prepared at p = 0.05 Pa to samples prepared
Conclusion
It was shown that RPLD and PCVD are very simple procedures for fabricating iron oxide thin films with semiconductor properties: Fe is ablated in a low-pressure reactive atmosphere (O2) and its deposition is via Fe(CO)5 vapors, accordingly. The stoichiometry and crystalline structure of the films are controlled by the O2 pressure during deposition and by exposure time to the substrate surface. The film thickness is controlled by amount of laser pulses, the O2 pressure and by exposure time. The
Acknowledgments
Authors thank to Prof. A. Luches, Dr. A.P. Caricato and Dr. D. Valerini from the Department of Physics of Salento University, Italy for samples prepared by RPLD and fruitful discussion of scientific results.
References (14)
- et al.
Deposition of thin films for sensors by pulsed laser ablation of iron and chromium silicide targets
Applied Surface Science
(2007) - et al.
Influence of binders on the sensing and electrical characteristics of WO3-based gas sensors
Sensors and Actuators B
(1999) - et al.
Effect of oxidation on thickness dependencies of thermoelectric properties in PbTe/mica thin films
Thin Solid Films
(2005) - (2000)
- et al.
Structural, electrical, and optical characterizations of laser deposited nanometric iron oxide films
Journal of Vacuum Science and Technology B
(2010) - et al.
Deposition of chromium oxide thin films with large thermoelectromotive force coefficient by reactive pulsed laser ablation
Journal of Optoelectronics and Advanced Materials
(2010) - et al.
Laser synthesis of nanostructures based on transitional metal oxides
Applied Surface Science
(2006)
Cited by (11)
Characterization and antibacterial activity of nanocrystalline Mn doped Fe<inf>2</inf>O<inf>3</inf> thin films grown by successive ionic layer adsorption and reaction method
2016, Journal of the Association of Arab Universities for Basic and Applied SciencesCitation Excerpt :Since the past decades, α-Fe2O3 has gained extensive scientific importance in materials science because of its important role in various applications namely gas sensor, supercapacitor, dye sensitized solar cell, photocatalyst, lithium ion battery and in microbial fuel cells (Lee et al., 2001; Fan et al., 2011; Mulenko et al., 2012; Rahman and Joo, 2013; Cavas et al., 2013; Akhavan, 2010; Hsien et al., 2013; Kitaura et al., 2008; Kulal et al., 2011; Ji et al., 2011).
Laser synthesis of nanometric iron oxide films for thermo-sensing applications
2014, Materials Research BulletinCitation Excerpt :RPLD was applied for synthesis of iron oxide thin films for thermo-chemical sensors [3]. RPLD and laser (light) chemical vapours deposition (LCVD) were used for the synthesis of iron oxide thin films on <1 0 0>Si substrate for thermo-photo sensors [8,17]. On the other hand, there is interest to materials for technical applications with large thermoelectric figure of merit (ZT), as it is connected with energetic problems.
Influence of hybrid Fe/Cr parameters structures synthesised with laser radiation on their photosensitivity
2023, Journal of Materials Science: Materials in ElectronicsLaser synthesis of hybrid Fe/Cr 2D structures based on their oxides for thermo-sensors with high sensitivity
2022, Journal of Materials Science: Materials in ElectronicsLaser synthesis of copper oxides 2D structures with high Seebeck coefficient and high thermoelectric figure of merit
2021, Journal of Materials Science: Materials in Electronics