Oxygen Vacancies In Thin Films Research Articles

Crystallographic Pathways to Tailoring Metal-Insulator Transition through Oxygen Transport in VO2.

The metal-insulator (MI) transition of vanadium dioxide (VO2) is effectively modulated by oxygen vacancies, which decrease the transition temperature and insulating resistance. Oxygen vacancies in thin films can be driven by oxygen transport using electrochemical potential. This study delves into the role of crystallographic channels in VO2 in facilitating oxygen transport and the subsequent tuning of electrical properties. A model system is designed with two types of VO2 thin films: (100)- and (001)-oriented, where channels align parallel and perpendicular to the surface, respectively. Growing an oxygen-deficient TiO2 layer on these VO2 films prompted oxygen transport from VO2 to TiO2. Notably, in (001)-VO2 film, where oxygen ions move along the open channels, the oxygen migration deepens the depleted region beyond that in (100)-VO2, leading to more pronounced changes in metal-insulator transition behaviors. The findings emphasize the importance of understanding the intrinsic crystal structure, such as channel pathways, in controlling ionic defects and customizing electrical properties for applications.

Comment on "Anisotropic Scattering Caused by Apical Oxygen Vacancies in Thin Films of Overdoped High-Temperature Cuprate Superconductors".

Comment on "Anisotropic Scattering Caused by Apical Oxygen Vacancies in Thin Films of Overdoped High-Temperature Cuprate Superconductors".

A Simple Strategy to Realize Super Stable Ferroelectric Capacitor via Interface Engineering

AbstractFluorite‐structure ferroelectric thin films have been extensively studied as promising candidates for next‐generation non‐volatile memory. However, these ferroelectric thin films have fatal issues such as the irregular formation of the ferroelectric phase, low cycling endurance, and wake‐up and fatigue during endurance cycling tests. These problems are reportedly caused by oxygen vacancies, which form due to the interface reaction between the thin films and bottom electrodes during deposition and the post‐annealing process. Therefore, in this work, the enhanced ferroelectric characteristics of Hf1‐xZrxO2 thin films that control the oxygen vacancies in thin films through interfacial pretreatment are investigated. Interfacial treatment using an oxygen source can reduce oxygen vacancies and improve crystallinity through intentional oxidation of the bottom electrode. As a result, the remanent polarization value is increased by ≈1.6 times by applying the optimized pretreatment condition, and the measured 2Pr is a very high value of 73 µC cm−2. Furthermore, it exhibits very stable ferroelectric properties without a wake‐up effect or significant fatigue, up to 108 cycles even under a severe electric field of 3.5 MV cm−1. This simple strategy provides a new avenue to effectively improve the performance and cycling endurance of devices with ferroelectric thin films.

Anisotropic Scattering Caused by Apical Oxygen Vacancies in Thin Films of Overdoped High-Temperature Cuprate Superconductors.

There is a hot debate on the anomalous behavior of superfluid density ρ_{s} in overdoped La_{2-x}Sr_{x}CuO_{4} films in recent years. The linear drop of ρ_{s} at low temperatures implies the superconductors are clean, but the linear scaling between ρ_{s} (in the zero temperature limit) and the transition temperature T_{c} is a hallmark of the dirty limit in the Bardeen-Cooper-Schrieffer (BCS) framework [I. Bozovic etal., Nature (London) 536, 309 (2016)NATUAS0028-083610.1038/nature19061]. This dichotomy motivated exotic theories beyond the standard BCS theory. We show, however, that such a dichotomy can be reconciled naturally by the role of increasing anisotropic scattering caused by the apical oxygen vacancies. Furthermore, the anisotropic scattering also explains the "missing" Drude weight upon doping in the optical conductivity, as reported in the THz experiment [F. Mahmood etal., Phys. Rev. Lett. 122, 027003 (2019)PRLTAO0031-900710.1103/PhysRevLett.122.027003]. Therefore, the overdoped cuprates can actually be described consistently by the d-wave BCS theory with the unique anisotropic scattering.

Effect of pressure on the elemental composition and magnetic properties of lithium-doped ZnO thin films

The paper presents the results of a study of the effect of pressure in a vacuum chamber on magnetic characteristics of Zn1-xLixOy thin films obtained by pulsed laser deposition on sapphire substrates as well as the results of elemental analysis across thickness of the samples. Secondary ion mass spectrometry demonstrated that the method of pulsed laser deposition allows for the synthesis of zinc oxide based thin films characterized by a high uniformity of elemental composition across thickness. It was established that different pressure in the vacuum chamber affects the number of oxygen vacancies in thin films, but not the distribution of elements across thin film thickness. Weak room temperature ferromagnetism was observed in Zn1-xLixOy thin films synthesized at a pressure of 3.15·10−5 Torr; it increases upon the increase in lithium concentration. Interstitial lithium atoms are considered to play a important role in its occurrence. The results of the study allow for expansion of the body of knowledge about the nature of room temperature ferromagnetism in zinc oxide based thin film structures as well as for developing technologies for high-quality thin film materials for recording and storing information.

Two Kinds of Metastable Structures in an Epitaxial Lanthanum Cobalt Oxide Thin Film.

Thin films have attracted much interest because they often have novel properties different from those of their bulk counterparts. In this work, we tune two metastable states in three kinds of lanthanum cobalt oxide thin films by electron beam irradiation and record their dynamic transition process in situ in a transmission electron microscope. The lanthanum cobalt oxide thin films exhibit a homogeneous microstructure in the initial state and then transfer to a stripelike superstructure with 3a0 periodicity (a0 is the perovskite lattice parameter), further developing into a superstructure with 2a0 periodicity in dark stripes (brownmillerite structure). To explore the inherent energy discrepancy within the two metastable states, we perform first-principles calculations on a LaCoO3-δ (0 ≤ δ ≤ 0.5) thin film system by geometry optimization. The calculation results suggest that the forming energy of the 3a0 periodicity stripelike structure is a little lower than that of the 2a0 periodicity in the LaCoO3-δ thin film. Our work explains why the two stripelike structures coexist in lanthanum cobalt oxide thin films and extends prospective applications related to oxygen vacancies in thin films.

Tuning Oxygen Vacancy Diffusion through Strain in SrTiO3 Thin Films.

Understanding diffusion of oxygen vacancies in oxides under different external stimuli is crucial for the design of ion-based electronic devices, improvement of catalytic performance, and so forth. In this manuscript, using an external electric field produced by an atomic force microscopy tip, we obtain the room-temperature diffusion coefficient of oxygen-vacancies in thin films of SrTiO3 under compressive/tensile epitaxial strain. Tensile strain produces a substantial increase of the diffusion coefficient, facilitating the mobility of vacancies through the film. Additionally, the effect of tip bias, pulse time, and temperature on the local concentration of vacancies is investigated. These are important parameters of control in the production and stabilization of nonvolatile states in ion-based devices. Our findings show the key role played by strain for the control of oxygen vacancy migration in thin-film oxides.

Optical properties of As doped ZnO thin films prepared by pulsed laser deposition technique

ZnO thin films are deposited on glass substrates at adapted experimental conditions during the pulsed laser deposition (PLD). The as-deposited thin films are attached by GaAs wafers and annealed at different temperatures and for different times. Transmittance and photoluminescence (PL) are measured to evaluate the As doping. With increasing annealing temperature and annealing time the transmission of films in the VIS range decreases. The band gap energies are determined by a linear fit of the absorption edge. In PL spectra, two PL emission peaks are found in all samples, one is the near band edge emission, and the ether is green emission. The annealing decreases the intensity of the green emission. The aging is found in ZnO thin films by PL measurements. As time goes on, the green emission peak decreases, and the near band emission peak is enhanced because of the decrease of oxygen vacancies in thin films.