Polaron transitions in charge intercalated amorphous tungsten oxide thin films

Saenger, M. F.; Höing, T.; Hofmann, Tino; Schubert, M.

doi:10.1002/pssa.200777894

Cited by 16 publications

(14 citation statements)

References 19 publications

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“…supports the concept that the low energy Lorentz oscillator in the parameterization of e is associated with the small polaron hopping mechanism for conduction in amorphous VO x , in which case E 0 serves as the self-trapping energy. Such a mechanism has been proposed previously for other metaloxide semiconductors [33][34][35][36][37][38][39][40] and has been identified as variable range hopping conduction in pulsed dc sputtered VO x using low temperature electrical measurements. 41 Within a small polaron hopping model, the increase in the amplitude of the Lorentz oscillator and the associated carrier concentration with the decrease in q in Fig.…”

Section: Discussionmentioning

confidence: 62%

Electrical and optical properties of sputtered amorphous vanadium oxide thin films

Podraza

Gauntt

Motyka

et al. 2012

Journal of Applied Physics

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Articles you may be interested inMicrostructural evolution of thin film vanadium oxide prepared by pulsed-direct current magnetron sputtering J. Appl. Phys. 112, 093504 (2012); 10.1063/1.4759255 Enhanced electrical and noise properties of nanocomposite vanadium oxide thin films by reactive pulsed-dc magnetron sputtering Appl. Phys. Lett. 100, 262108 (2012); 10.1063/1.4731240 Process-structure-property correlations in pulsed dc reactive magnetron sputtered vanadium oxide thin films J. Vac. Sci. Technol. A 29, 061504 (2011); 10.1116/1.3636372 Vanadium oxide thin films for bolometric applications deposited by reactive pulsed dc sputtering J. Vac. Sci. Technol. A 27, 951 (2009); 10.1116/1.3119675Optical and electrical properties of sputtered vanadium oxide films Amorphous vanadium oxide (VO x ) is a component found in composite nanocrystalline VO x thin films. These types of composite films are used as thermistors in pulsed biased uncooled infrared imaging devices when containing face centered cubic vanadium monoxide phase crystallites, and substantial fractions of amorphous material in the composite are necessary to optimize device electrical properties. Similarly, optoelectronic devices exploiting the metal-to-semiconductor transition contain the room-temperature monoclinic or high-temperature (>68 C) rutile vanadium dioxide phase. Thin films of VO x exhibiting the metal-to-semiconductor transition are typically polycrystalline or nanocrystalline, implying that significant amounts of disordered, amorphous material is present at grain boundaries or surrounding the crystallites and can impact the overall optical or electronic properties of the film. The performance of thin film material for either application depends on both the nature of the crystalline and amorphous components, and in this work we seek to isolate and study amorphous VO x . VO x thin films were deposited by pulsed dc reactive magnetron sputtering to produce amorphous materials with oxygen contents !2, which were characterized electrically by temperature dependent current-voltage measurements and optically characterized by spectroscopic ellipsometry. Film resistivity, thermal activation energy, and complex dielectric function spectra from 0.75 to 6.0 eV were used to identify the impact of microstructural variations including composition and density. V C 2012 American Institute of Physics. [http://dx.

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Section: Discussionmentioning

confidence: 62%

Electrical and optical properties of sputtered amorphous vanadium oxide thin films

Podraza

Gauntt

Motyka

et al. 2012

Journal of Applied Physics

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“…A polaron can form in W O 3 due to electron localization at the dstates of tungsten, thus, turning W 6+ into W 5+ or W 4+ . Light absorption can lead to the activation of the following transitions:We notice that more complex configurations of localized charge can form, for example, two bound polarons at neighboring sites, W 5+ -W 5+ , also called bipolarons (see Fig.1b,c for illustration).The presence of different localized charge states in W O 3 has been confirmed by numerous experiments [42][43][44][45][46][47][48][49]. The formation of polarons in this oxide has also been studied theoretically by semi-empirical models [50,51] and more recently by ab-initio methods employing hybrid functionals [53].…”

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confidence: 59%

Polaron mobility in oxygen-deficient and lithium-doped tungsten trioxide

2015

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Electron localization and polaron mobility in oxygen-deficient as well as Li-doped monoclinic tungsten trioxide have been studied in the adiabatic limit in the framework of density functional theory. We show that small polarons formed in the presence of oxygen vacancy prefer the bipolaronic W 5+ -W 5+ configuration, whereas the W 6+ -W 4+ configuration is found to be metastable. Our calculations suggest that bipolarons are tightly bound by the vacancy and therefore largely immobile. On the contrary, polarons formed as a result of Li intercalation can be mobile; the activation energy for polaron jumping in this case varies between 98 and 124 meV depending on the crystallographic direction.

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“…Polarons represent local charge transfer between the W 5+ and W 6+ sites. 65,66 Let us consider the possibility of both of these transitions in WO 3−x •H 2 O NPs.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Chiral Ceramic Nanoparticles and Peptide Catalysis

et al. 2017

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The chirality of nanoparticles (NPs) and their assemblies has been investigated predominantly for noble metals and II-VI semiconductors. However, ceramic NPs represent the majority of nanoscale materials in nature. The robustness and other innate properties of ceramics offer technological opportunities in catalysis, biomedical sciences, and optics. Here we report the preparation of chiral ceramic NPs, as represented by tungsten oxide hydrate, WO·HO, dispersed in ethanol. The chirality of the metal oxide core, with an average size of ca. 1.6 nm, is imparted by proline (Pro) and aspartic acid (Asp) ligands via bio-to-nano chirality transfer. The amino acids are attached to the NP surface through C-O-W linkages formed from dissociated carboxyl groups and through amino groups weakly coordinated to the NP surface. Surprisingly, the dominant circular dichroism bands for NPs coated by Pro and Asp are different despite the similarity in the geometry of the NPs; they are positioned at 400-700 nm and 500-1100 nm for Pro- and Asp-modified NPs, respectively. The differences in the spectral positions of the main chiroptical band for the two types of NPs are associated with the molecular binding of the two amino acids to the NP surface; Asp has one additional C-O-W linkage compared to Pro, resulting in stronger distortion of the inorganic crystal lattice and greater intensity of CD bands associated with the chirality of the inorganic core. The chirality of WO·HO atomic structure is confirmed by atomistic molecular dynamics simulations. The proximity of the amino acids to the mineral surface is associated with the catalytic abilities of WO·HO NPs. We found that NPs facilitate formation of peptide bonds, leading to Asp-Asp and Asp-Pro dipeptides. The chiroptical activity, chemical reactivity, and biocompatibility of tungsten oxide create a unique combination of properties relevant to chiral optics, chemical technologies, and biomedicine.

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Polaron transitions in charge intercalated amorphous tungsten oxide thin films

Cited by 16 publications

References 19 publications

Electrical and optical properties of sputtered amorphous vanadium oxide thin films

Electrical and optical properties of sputtered amorphous vanadium oxide thin films

Polaron mobility in oxygen-deficient and lithium-doped tungsten trioxide

Chiral Ceramic Nanoparticles and Peptide Catalysis

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