X-Ray absorption, photoemission spectroscopy, and Raman scattering analysis of amorphous tantalum oxide with a large extent of oxygen nonstoichiometry

Abstract

The electronic structure and modification of the local interatomic structure of a reactive sputtered amorphous tantalum oxide (a-TaO(x)) thin film with the variation of oxygen nonstoichiometry, x in a-TaO(x) have been investigated by X-ray absorption spectroscopy (XAS), X-ray photoemission spectroscopy (XPS), Raman scattering spectroscopy, and Rutherford back scattering spectroscopy. A parallel chemical shift of Ta4f(7/2) and O1s core levels observed with the variation of x indicates the Fermi level shift by reduction and oxidation in the framework of the rigid band model. Extended X-ray absorption fine structure (EXAFS) suggests both the increase of average coordination number of the first Ta-O shell in polyhedra and a considerable reduction of the average Ta-O bond length with the increase of x. The relative intensity of Raman shift peaks at 670 cm(-1) and 815 cm(-1), corresponding to Ta-O stretching of TaO(6) octahedra and TaO(5) probably with a pyramidal form, respectively, drastically changes between x = 2.47 to 1.86, suggesting the change in the predominant polyhedron from TaO(6) to TaO(5) with a modification in multiplicity of oxygen by the reorganization of the polyhedral network.

Conduction paths in Cu/amorphous-Ta2O5/Pt atomic switch: First-principles studies

“…All these structural parameters agree well with the previous experimental and theoretical studies. 18,19,28 The calculated band gap of the a-Ta 2 O 5 , 2.82 eV, is obviously larger than that of the crystalline b-Ta 2 O 5 (0.2 eV) and d-Ta 2 O 5 (1.06 eV) in our calculations. 16 This value for the a-Ta 2 O 5 is about 1.4 eV lower than that of the observed one, 29 which could be attributed to the well-known band-gap underestimation of the local/semi-local approximation of the density functional theory.…”

“…Structure of amorphous Ta 2 O 5 As shown in Figure 1, the partial pair correlation functions of amorphous and crystalline d- Ta 26 and Tsuchiya et al 19 As for the bonding around Ta atoms, 27 the main components are octahedral TaO 6 and pyramidal TaO 5 structures with the ratio of 20:9. As for O atoms, both three-and two-coordinated O atoms (bonding with Ta) are present, with the ratio of 25:55.…”

“…We focus on the Ta 2 O 5 -based atomic switch, which is particularly promising as a practical device because of its compatibility with semiconductor fabrication processes. In contrast to our previous work, 17 we examine the case of amorphous Ta 2 O 5 (a-Ta 2 O 5 ) in the present study, since the amorphous phase is usually adopted in experiments and prototype devices 18,19 as mentioned above. The atomic and electronic structures of Cu filaments of different thicknesses in a-Ta 2 O 5 have been discussed.…”

“…S2), the structural parameters of a-Ta 2 O 5 only slightly changed among the cases of rapid quenching processes of 4 K/3fs, 2 K/3fs, and 1 K/3fs and agree well with the experimental proposed a-Ta 2 O 5 . 18,19 On the other hand, the structural parameters for a-Ta 2 O 5 generated with the much slower quenching rate of 0.1 K/3fs are considerably different from those in the cases of the rapid quenching rates and approaches to those of crystalline Ta 2 O 5 . This sign of crystallization may be an artifact due to the use of small supercell under the periodic boundary conditions.…”

<i>In-Situ</i> Monitoring of Oxide Ion Induced Breakdown in Amorphous Tantalum Oxide Thin Film Using Acoustic Emission Measurement

“…14) For an ionic behavior in bulk materials, conventional electrochemical method usually helps us to understand detail of the electrochemical property, to say conductivity, transport number of ionic carrier, faradaic impedance at electrode/electrolyte interface, and so on. On the other hand, it is not straight forward to investigate electron/ion mixed conduction in thin films which consists of an electronic conductivity under strong influence of Poole Frenkel, or F-N mechanism, 5) where a small signature of ionic conduction can easily be hidden.…”