Symmetry driven control of optical properties in WO<sub>3</sub> films

Herklotz, Andreas; Rus, Simona; Kc, Santosh; Cooper, Valentino R.; Huon, Amanda; Guo, Er‐Jia; Ward, Thomas Z.

doi:10.1063/1.4989395

Cited by 10 publications

(6 citation statements)

References 29 publications

(28 reference statements)

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“…Except triclinic Mo9O26, which showed a semiconductor behavior, the other intermediate oxides were found to exhibit metallic conductivity attending to both the value and the temperature dependence of resistivity. In addition to the formation of oxygen vacancies and minority phases, the effect of uniaxial strain on the band diagram of MoO3 should be studied in the future, similar to ion beam strain engineering of the band gap reported for WO3 [18].…”

Section: Discussionmentioning

confidence: 99%

“…In addition, it has also been shown recently that the conductivity of MoO3 can be increased over several orders of magnitude by electron irradiation [17]. Furthermore, the controlled induced lattice strain along a single axis can allow tuning of the electrical, optical and magnetic properties of oxides, as observed in films of WO3 [18] and La0.7Sr0.3MnO3 [19] when implanted with low-energy helium ions.…”

Section: Introductionmentioning

confidence: 96%

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Engineering strain and conductivity of MoO3 by ion implantation

et al. 2019

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α-MoO3 lamellar crystals are implanted with 170 keV oxygen ions at room temperature and with fluences between 1×10 12 cm -2 and 1×10 17 cm -2 , in order to modify the electrical and structural properties of the crystals. A controllable and significant increase of the electrical conductivity, over several orders of magnitude, is observed after implantation at high fluences. Based on high resolution X-ray diffraction (HRXRD) and micro-Raman spectroscopy measurements, this effect is attributed to the formation of donor-type defect complexes and new phases more conductive than the α-MoO3 orthorhombic phase. A significant expansion of the b lattice parameter, increasing with fluence, is observed as a response to the defects created by implantation. Strain build-up occurs in several steps and in distinct depth regions within the implanted layer. Contrary to the typical values reported for other implanted oxide materials, an unusually high maximum perpendicular deformation of ~3% is verified.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Engineering strain and conductivity of MoO3 by ion implantation

et al. 2019

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“…Most works so far focused on thick films, amorphous layers and nanorods [9,10]. Only recently the growth of crystalline thin films has been demonstrated by means of several techniques such as sputtering, molecular beam epitaxy and pulsed laser deposition [11][12][13][14]. Because WO 3 structure and electronic properties are very sensitive to oxygen stoichiometry [15][16][17][18], a precise control of oxygen partial pressure during the growth process is crucial to obtain high quality thin films.…”

Section: Introductionmentioning

confidence: 99%

Charge doping and large lattice expansion in oxygen-deficient heteroepitaxial WO3

Mattoni

Filippetti

Manca

et al. 2018

Phys. Rev. Materials

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Tungsten trioxide is a versatile material with widespread applications ranging from electrochromic and optoelectronic devices to water splitting and catalysis of chemical reactions. For technological applications, thin films of WO 3 are particularly appealing, taking advantage from high surface-tovolume ratio and tunable physical properties. However, the growth of stoichiometric, crystalline thin films is challenging because the deposition conditions are very sensitive to the formation of oxygen vacancies. In this work, we show how background oxygen pressure during pulsed laser deposition can be used to tune the structural and electronic properties of WO 3 thin films. By performing X-ray diffraction and low-temperature transport measurements, we find changes in WO 3 lattice volume up to 10 %, concomitantly with an insulator-to-metal transition as a function of increased level of electron doping. We use advanced ab initio calculations to describe in detail the properties of the oxygen vacancy defect states, and their evolution in terms of excess charge concentration. Our results depict an intriguing scenario where structural, electronic, optical, and transport properties of WO 3 single-crystal thin films can all be purposely tuned by a suited control of oxygen vacancies formation during growth. arXiv:1711.05106v1 [cond-mat.mtrl-sci]

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“…Since interface roughnesses are small relative to film thickness, it is possible to determine the optical constants of the films by fitting the response data to a simple two-layer model consisting of the substrate and film. The impact of straggle doping into the substrates was also found to be unimportant by intentionally implanting He into bare LAO and LSAT substrates and determining their optical properties-no significant change was found after implantation [24]. Thus, in the model system, the optical properties of the substrates (LAO and LSAT) are fixed to the parametric data determined independently from ellipsometry measurements and fitted to the BFO layers by Kramers-Kronig consistent B splines with 16 data points over the full energy range.…”

Section: Methodsmentioning

confidence: 99%

Optical response of BiFeO3 films subjected to uniaxial strain

Herklotz

Rus

Sohn

et al. 2019

Phys. Rev. Materials

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The impact of single-axis lattice expansion on the optical response of BiFeO 3 films is examined. Low-energy He implantation is used to tailor morphotropic phases of BiFeO 3 films and study changes in their optical spectra with continuously increasing lattice expansion. He ion implantation of epitaxial rhombohedral (R)and tetragonal (T)-like BiFeO 3 films induces uniaxial out-of-plane strain that, on R-like films, eventually leads to a complete R-T phase transition. This approach allows us to provide insights into the optical response of BiFeO 3 films. Strain doping of T-like films leads to a significant redshift of the optical absorption spectra that is theoretically explained by a lowering of Fe 3d t 2g states. R-like films, on the other hand, show a less-pronounced sensitivity to uniaxial strain and a blueshift of about 250 meV at the strain-induced R-T transition. The results demonstrate that strain doping allows a deeper examination of the optical properties of epitaxial phases that are otherwise impossible to access by standard epitaxy.

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Symmetry driven control of optical properties in WO₃ films

Cited by 10 publications

References 29 publications

Engineering strain and conductivity of MoO3 by ion implantation

Engineering strain and conductivity of MoO3 by ion implantation

Charge doping and large lattice expansion in oxygen-deficient heteroepitaxial WO3

Optical response of BiFeO3 films subjected to uniaxial strain

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Symmetry driven control of optical properties in WO3 films

Cited by 10 publications

References 29 publications

Engineering strain and conductivity of MoO3 by ion implantation

Engineering strain and conductivity of MoO3 by ion implantation

Charge doping and large lattice expansion in oxygen-deficient heteroepitaxial WO3

Optical response of BiFeO3 films subjected to uniaxial strain

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Symmetry driven control of optical properties in WO₃ films