Electronic structure of titania aerogels from soft x-ray absorption spectroscopy

Kucheyev, S. O.; Buuren, T. van; Baumann, Theodore F.; Satcher, J. H.; Willey, Trevor M.; Meulenberg, Robert W.; Felter, T. E.; Poco, J.F.; Gammon, Stuart A.; Terminello, L. J.

doi:10.1103/physrevb.69.245102

Cited by 193 publications

(274 citation statements)

References 28 publications

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“…The observed peak shapes for the annealed sample and the broadening in the as-deposited sample agree with spectra reported for anatase and amorphous TiO 2 in the literature. [35][36][37][38] The difference in electrical behavior of devices based on as-deposited versus annealed TiO 2 thin fi lms is due to the combination of changes in the oxygen content and in the structure of the fi lms upon annealing.…”

Section: Resultsmentioning

confidence: 99%

Role and Optimization of the Active Oxide Layer in TiO₂‐Based RRAM

Regoutz

Gupta

Serb

et al. 2015

Adv Funct Materials

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TiO2 is commonly used as the active switching layer in resistive random access memory. The electrical characteristics of these devices are directly related to the fundamental conditions inside the TiO2 layer and at the interfaces between it and the surrounding electrodes. However, it is complex to disentangle the effects of film “bulk” properties and interface phenomena. The present work uses hard X‐ray photoemission spectroscopy (HAXPES) at different excitation energies to distinguish between these regimes. Changes are found to affect the entire thin film, but the most dramatic effects are confined to an interface. These changes are connected to oxygen ions moving and redistributing within the film. Based on the HAXPES results, post‐deposition annealing of the TiO2 thin film was investigated as an optimisation pathway in order to reach an ideal compromise between device resistivity and lifetime. The structural and chemical changes upon annealing are investigated using X‐ray absorption spectroscopy and are further supported by a range of bulk and surface sensitive characterisation methods. In summary, it is shown that the management of oxygen content and interface quality is intrinsically important to device behavior and that careful annealing procedures are a powerful device optimisation technique.

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Section: Resultsmentioning

confidence: 99%

Role and Optimization of the Active Oxide Layer in TiO₂‐Based RRAM

Regoutz

Gupta

Serb

et al. 2015

Adv Funct Materials

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“…Dependence of the O K-edge NEXAFS spectra of hydrogenated Ti-DLC films on fluence is shown in Figure 7. The spectrum of a TiO2 amorphous film is also shown for reference [40]. A peak is observable in spectrum (a) [0 atoms· cm −2 ].…”

Section: Resultsmentioning

confidence: 99%

Resistance of Hydrogenated Titanium-Doped Diamond-Like Carbon Film to Hyperthermal Atomic Oxygen

Kidena

Endo

Takamatsu

et al. 2015

Metals

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The effect of irradiation by a hyperthermal-atomic-oxygen beam on hydrogenated titanium-doped diamond-like carbon (hydrogenated Ti-DLC) films, applied as a solid lubricant for equipment used in low-earth orbit was investigated. Unlike the film thickness of hydrogenated non-doped DLC films, that of hydrogenated Ti-DLC films was found to be constant after the films were exposed to atomic oxygen. In addition, bulk composition of the hydrogenated Ti-DLC film stayed constant, and in particular, hydrogen content in the film did not decrease. These results indicate that a hydrogenated Ti-DLC film can keep its low friction properties under vacuum. Surface chemical analysis showed that a titanium-oxide layer is form on the film by exposure to atomic oxygen. The thickness of the titanium oxide layer was estimated to be about 5 nm from the element distribution in the depth direction of the hydrogenated Ti-DLC films. The titanium-oxide OPEN ACCESSMetals 2015, 5 1958 layer was interpreted to protect the bulk film from erosion by hyperthermal atomic oxygen.

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“…Therefore the presence Nb atoms on Ti sites interrupt the O 2p -Ti 3d orbitals hybridizations and leads to reduction in the intensity of e g feature with broadening in peak. 37 In Fig. 8(a), The characteristic features in the Ti L 3,2 edge spectra are attributed to the transition of Ti 2p core electrons to unoccupied 3d electronic states in the conduction band.…”

Section: Resultsmentioning

confidence: 99%

“…The characteristic features of Ti L 3,2 edge and O K-edge spectra are well matched with the reported anatase phase features. 37,38 The Ti L 3,2 edge spectra are attributed to the transition of Ti 2p core electrons to unoccupied 3d electronic states and the O K-edge spectra in TiO 2 show the electronic transition from O 1s to O 2p states hybridized with Ti 3d unoccupied states in the conduction band and the introduced Nb doping heavily interrupts their hybridization. 39,40 The spin-orbit and crystal field interactions of surrounding O atoms with Ti atoms splits the Ti 3d band into two different sub-level, t 2g (dxy, dxz , and dyz) and e g (dx 2 -y 2 and dz 2 ) top and bottom orbitals, respectively.…”

Section: Resultsmentioning

confidence: 99%

Anomalous behavior of B1g mode in highly transparent anatase nano-crystalline Nb-doped Titanium Dioxide (NTO) thin films

Gautam

Singh

et al. 2015

AIP Advances

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The effect of Niobium doping and size of crystallites on highly transparent nano-crystalline Niobium doped Titanium Dioxide (NTO) thin films with stable anatase phase are reported. The Nb doping concentration is varied within the solubility limit in TiO2 lattice. Films were annealed in controlled environment for improving the crystallinity and size of crystallites. Elemental and thickness analysis were carried out using Rutherford backscattering spectrometry and cross sectional field emission scanning electron microscopy. Structural characteristics reveal a substitutional incorporation of Nb+5 in the TiO2 lattice which inhibits the anatase crystallites growth with increasing the doping percentage. The micro-Raman (MR) spectra of films with small size crystallites shows stiffening of about 4 cm−1 for the Eg(1) mode and is ascribed to phonon confinement and non-stoichiometry. In contrast, B1g mode exhibits a large anomalous softening of 20 cm−1 with asymmetrical broadening; which was not reported for the case of pure TiO2 crystallites. This anomalous behaviour is explained by contraction of the apical Ti-O bonds at the surface upon substitutional Nb5+ doping induced reduction of Ti4+ ions also known as hetero-coordination effect. The proposed hypotheses is manifested through studying the electronic structure and phonon dynamics by performing the near edge x-ray absorption fine structure (NEXAFS) and temperature dependent MR down to liquid nitrogen temperature on pure and 2.5 at.% doped NTO films, respectively.

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Electronic structure of titania aerogels from soft x-ray absorption spectroscopy

Cited by 193 publications

References 28 publications

Role and Optimization of the Active Oxide Layer in TiO₂‐Based RRAM

Role and Optimization of the Active Oxide Layer in TiO₂‐Based RRAM

Resistance of Hydrogenated Titanium-Doped Diamond-Like Carbon Film to Hyperthermal Atomic Oxygen

Anomalous behavior of B1g mode in highly transparent anatase nano-crystalline Nb-doped Titanium Dioxide (NTO) thin films

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Electronic structure of titania aerogels from soft x-ray absorption spectroscopy

Cited by 193 publications

References 28 publications

Role and Optimization of the Active Oxide Layer in TiO2‐Based RRAM

Role and Optimization of the Active Oxide Layer in TiO2‐Based RRAM

Resistance of Hydrogenated Titanium-Doped Diamond-Like Carbon Film to Hyperthermal Atomic Oxygen

Anomalous behavior of B1g mode in highly transparent anatase nano-crystalline Nb-doped Titanium Dioxide (NTO) thin films

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Role and Optimization of the Active Oxide Layer in TiO₂‐Based RRAM

Role and Optimization of the Active Oxide Layer in TiO₂‐Based RRAM