XPS depth profiling analysis of crystalline tantalum pentoxide films Israel Perez ∗ National Council of Science and Technology (CONACYT)-Institute of Engineering and Technology, Universidad Aut´ onoma de Ciudad Ju´ arez, Av. del Charro 450 Col. Romero Partido, C.P. 32310, Ju´ arez, Chihuahua, M´ exico V´ ıctor Sosa Applied Physics Department, CINVESTAV Unidad M´ erida, km 6 Ant. Carretera a Progreso, A.P. 73, C.P. 97310 M´ erida, Yucat´ an, M´ exico Fidel Gamboa Perera Applied Physics Department, CINVESTAV Unidad M´ erida, km 6 Ant. Carretera a Progreso, A.P. 73, C.P. 97310 M´ erida, Yucat´ an, M´ exico Jos´ e Trinidad Elizalde Galindo Institute of Engineering and Technology, Universidad Aut´onoma de Ciudad Ju´arez, Av. del Charro 450 Col. Romero Partido, C.P. 32310, Ju´ arez, Chihuahua, M´ exico Jos´ e Luis Enr´ ıquez Carrejo Institute of Engineering and Technology, Universidad Aut´onoma de Ciudad Ju´arez, Av. del Charro 450 Col. Romero Partido, C.P. 32310, Ju´ arez, Chihuahua, M´ exico Pierre Giovani Mani Gonz´alez Institute of Engineering and Technology, Universidad Aut´onoma de Ciudad Ju´arez, Av. del Charro 450 Col. Romero Partido, C.P. 32310, Ju´ arez, Chihuahua, M´ exico Carlos Iv´an Rodr´ ıguez Rodr´ ıguez Universidad Tecnol´ ogica de Ciudad Ju´arez, Av. Universidad Tecnol´ ogica No. 3051, Col. Lote Bravo II, C.P. 32695, Ju´ arez, Chihuahua, M´ exico (Dated: July 19, 2022) We investigate chemical and physical properties of crystalline Ta2O5 films grown on Si substrates by radio frequency magnetron sputtering. We first grew three Ta films and, to induce the crystalline phase of Ta2O5, two of them were exposed to a post-deposition annealing at 1273 K in air for 1 h. Coating characterization was performed by X-ray diffraction, scanning electron microscopy, Raman scattering spectroscopy, and X-ray photoelectron spectroscopy. The microstructure of the crystalline films is granular and the atomic structure corresponds to orthorhombic Ta2O5. XPS depth profiles for Ta 4f and O 1s core-levels were carried out in order to assess the chemical states of all samples. Upon analysis at the surface of the films, we observe the Ta 4f spectrum characteristic of Ta2O5. However, as one goes deeper into the films, oxygen vacancies are generated by ion bombardment and reconstruction processes are induced; resulting in the formation of metastable Ta oxide phases with oxidation states Ta 1+ , Ta 2+ , Ta 3+ , Ta 4+ , and Ta 5+ . Exposing the films, after sputtering, to ambience for some days stimulates the amorphous phase of Ta2O5 at the very surface suggesting that the suboxides of Ta are unstable. We discuss that these suboxides are only generated during sputtering and at the very surface. The Raman results indicate the presence of the orthorhombic Ta2O5 phase and also a straightforward transition from Ta amorphous to crystalline Ta2O5. I. INTRODUCTION Recent investigations in high dielectric constant mate- rials point to tantalum pentoxide (Ta 2 O 5 ) as one of the most promising candidates to deal with modern techno- logical challenges. Due to its low leakage current and high dielectric constant tantalum pentoxide has been used as a storage capacitor, insulator, catalyst and gas detector 1–3 . In addition to its electrical properties, Ta 2 O 5 possesses high refraction index (n =2.18 at λ = 550 nm) and a wide band gap of ∼4.0 eV which makes it an excellent material for optical applications 4–7 . In regard to its atomic structure, Ta 2 O 5 solidifies in ei- ther amorphous or crystalline structure; the latter show- ing two phases below 1500 K 7–9 . The study of the crystalline properties of Ta 2 O 5 films is of great impor- tance not only from the technological perspective but also from the scientific one. In an earlier work the ex- istence of several polymorphs 10,11 were established and although most researchers agree that the system crys- tallizes in either hexagonal (δ phase) or orthorhombic (β phase) structures, the exact spatial group is still un- der investigation 12 . The atomic structure and the chem- ical and physical properties of Ta 2 O 5 strongly depend on the fabrication methods. In the last two decades ex- perimental techniques such as PLD, LPCVD, sputtering, arXiv:1804.02067v1 [cond-mat.mtrl-sci] 5 Apr 2018