O3 Thin Films Research Articles

Structural, Optical, Electric and Magnetic Characteristics of (In1-xGdx)2O3 Films for Optoelectronics.

After (In1-xGdx)2O3 powder with a wide x range of 0 to 10 at.% was chemically produced, (In1-xGdx)2O3 thin films were evaporated under ultra-vacuum using an electron beam apparatus. We investigated the influence of the Gd doping concentration on the magnetic, optical, electrical, and structural properties of the resultant In2O3 deposits. The produced Gd-doped In2O3 films have a cubic In2O3 structure without a secondary phase, as shown by the X-ray diffraction results. Additionally, the chemical analysis revealed that the films are nearly stoichiometric. A three-layer model reproduced the spectroscopic ellipsometer readings to determine the optical parameters and energy gap. The Egopt changed toward the lower wavelength with growing the Gd doping in (In1-xGdx)2O3 films. The Egopt in the (In1-xGdx)2O3 films was observed to increase from 3.22 to 3.45 eV when the Gd concentration climbed. Both carrier concentration and hall mobility were found during the Hall effect studies. It was possible to construct the heterojunction of Ni (Al)/n-(In1-xGdx)2O3/p-Si/Al. At voltages between -2 and 2 volts, investigations into the dark (cutting-edge-voltage) characteristics of the produced heterojunctions were made. The oxygen vacancies and cationic defects in the lattice caused by the uncompensated cationic charges resulted in significant magnetism and ferromagnetic behavior in the undoped In2O3 films. The (In1-xGdx)2O3 films, however, displayed faint ferromagnetism. The ferromagnetism seen in the (In1-xGdx)2O3 films was caused by oxygen vacancies formed during the vacuum film production process. Metal cations created ferromagnetic exchange interactions by snatching free electrons in oxygen.

Influence of Pulse Laser Energy on Structural and Magnetic Properties of CoFe2O4 and CoLa0.01Fe1.99O4 Thin Films

Cobalt ferrite and CoLa0.01Fe1.99O4 thin film were prepared using the pulsed laser deposition method with varying pulse laser energy. XRD analysis was used to investigate the structure of ferrite thin films. The study was expanded to include morphology and magnetic properties. The prepared films showed a strong peak at (311), which belongs to the cubic spinel cobalt ferrite phase with the presence of some peaks belonging to α-Fe2O3 as hematite phase that depressed when doping with La ion, and the crystallization improvement significantly after intensity increases by increasing the pulsed laser energy from 500 to 650 mJ. The lattice constant of Cobalt ferrite thin films increased with the increase in the laser pulse energy while the crystallite size deduced from the Williamson Hall method showed decreases with the increases of pulse laser energy. The saturation, remnant magnetization, and coercivity of prepared films were studied according to increasing pule laser energy and Lanthanum doping.

Evaluation of V<sub>1</sub><sub>-<i>x</i></sub>Cr<i><sub>x</sub></i>O<sub>2</sub> Thin Films Fabricated by MOD

Cr-doped vanadium dioxide, V1-xCrxO2 (x = 0-0.20), thin films were fabricated by metal-organic decomposition. From X-ray diffraction patterns of the films at room temperature, VO2(M2)(201) and VO2(M2)(201) diffraction peaks were observed for x = 0.03-0.20, while a VO2(M1)(011) peak was observed for x = 0-0.01, where M1 and M2 represent different monoclinic structures of VO2. Moreover, all the fabricated films showed a p-type conductivity, and the hole concentration in the films increased with increasing x. From R-T characteristics of the films at the temperature range from 20 to 90℃, abrupt resistance changes caused by the metal-insulator transition in VO2 with a hysteresis loop were gradually suppressed with increasing x; especially x≥0.15, they were completely suppressed, since the transition temperature of the film shifted to a temperature above 140℃. Relatively flat temperature dependence of the temperature coefficients of resistance (TCR) as high as -3.9%/K in the range of 20-90℃ was obtained for the V0.85Cr0.15O2 thin film. The TCR value of the film is almost same as that of a V0.75Ti0.25O2 thin film, whereas a resistivity of the former at room temperature is one order lower than that of the latter.

Growth, characterization and DNA sensing properties of PrFe0.6Ni0.4O3 thin film

Growth, characterization and DNA sensing properties of PrFe0.6Ni0.4O3 thin film

Flexible Pb(Zr0.52,Ti0.48)O3 thin film acoustic emission sensor for monitoring partial discharge in power cable

Piezoelectric acoustic emission sensors can be used detect the sound emitted by the target structure when it is damaged and have important applications in the field of structure health monitoring. However, due to the mismatch of the interface acoustic impedance, it is hard for the conventional ultrasonic sensor to monitor the acoustic emission in a pipe structure. In this work, a flexible sensor by the deposition of a Pb(Zr0.52,Ti0.48)O3 thin film on a mica substrate was fabricated, and the acoustic emission generated by the partial discharge of a 110 kV power cable was detected by using the flexible sensor. The flexible sensor was designed with an electromagnetic shielding structure and, therefore, can screen most of the electromagnetic interference. The flexible sensor shows a relatively flat response in the frequency range from 100 to 1000 kHz with a sensitivity over 47.5 dB, which is beneficial for pattern recognition studies of acoustic emission. This work not only provides a flexible, anti-electromagnetic interference and broadband sensor for acoustic emission detection but also promotes the development and application of flexible ferroelectric materials.

Deep learning for exploring ultra-thin ferroelectrics with highly improved sensitivity of piezoresponse force microscopy

Hafnium oxide-based ferroelectrics have been extensively studied because of their existing ferroelectricity, even in ultra-thin film form. However, studying the weak response from ultra-thin film requires improved measurement sensitivity. In general, resonance-enhanced piezoresponse force microscopy (PFM) has been used to characterize ferroelectricity by fitting a simple harmonic oscillation model with the resonance spectrum. However, an iterative approach, such as traditional least squares (LS) fitting, is sensitive to noise and can result in the misunderstanding of weak responses. In this study, we developed the deep neural network (DNN) hybrid with deep denoising autoencoder (DDA) and principal component analysis (PCA) to extract resonance information. The DDA/PCA-DNN improves the PFM sensitivity down to 0.3 pm, allowing measurement of weak piezoresponse with low excitation voltage in 10-nm-thick Hf0.5Zr0.5O2 thin films. Our hybrid approaches could provide more chances to explore the low piezoresponse of the ultra-thin ferroelectrics and could be applied to other microscopic techniques.

Characteristics of Hf0.5Zr0.5O2 Thin Films Prepared by Direct and Remote Plasma Atomic Layer Deposition for Application to Ferroelectric Memory.

Hf0.5Zr0.5O2 (HZO) thin film exhibits ferroelectric properties and is presumed to be suitable for use in next-generation memory devices because of its compatibility with the complementary metal-oxide-semiconductor (CMOS) process. This study examined the physical and electrical properties of HZO thin films deposited by two plasma-enhanced atomic layer deposition (PEALD) methods- direct plasma atomic layer deposition (DPALD) and remote plasma atomic layer deposition (RPALD)-and the effects of plasma application on the properties of HZO thin films. The initial conditions for HZO thin film deposition, depending on the RPALD deposition temperature, were established based on previous research on HZO thin films deposited by the DPALD method. The results show that as the measurement temperature increases, the electric properties of DPALD HZO quickly deteriorate; however, the RPALD HZO thin film exhibited excellent fatigue endurance at a measurement temperature of 60 °C or less. HZO thin films deposited by the DPALD and RPALD methods exhibited relatively good remanent polarization and fatigue endurance, respectively. These results confirm the applicability of the HZO thin films deposited by the RPALD method as ferroelectric memory devices.

Disorder–Order Transition in Ga2O3 and Its Solid Solution with In2O3 upon Thermal Annealing

The local ordering in amorphous Ga2O3 and (In x Ga1−x )2O3 thin films on Si(111) and its change on crystallization upon annealing are investigated. Synchrotron‐based extended X‐ray absorption fine structure data, as probed across the Ga K‐edge in conjunction with a numerical implementation of the scattering process including multiple scattering events, provide detailed insights into the bonding character of the Ga cations. Bond lengths and coordination numbers indicate the preferential formation of GaO4 tetrahedrons in the amorphous binary and ternary solid solution at the absence of long‐range ordering. Upon annealing there is no tendency toward the formation of long‐range ordering for the ternary alloy, while the amorphous Ga2O3 film turns into monoclinic β‐Ga2O3 crystallites with both tetra‐ and octahedral coordination.

Enhanced dielectric and energy storage performances of Hf0.6Zr0.4O2 thin films by Al doping

Hf- and Zr-based oxide thin films, which have various polarization characteristics depending on the crystal structure, have been intensively studied for application in various semiconductor devices due to their excellent electrical properties and complementary metal oxide semiconductor process compatibility. Especially, when the tetragonal phase is implemented, they exhibit a high dielectric constant with anti-ferroelectric properties. Therefore, in this study, the effect of Al doping in HfZrO2 thin films was investigated from the viewpoint of the realization of a high dielectric constant and a stable anti-ferroelectric phase. Through a small amount of Al doping, the crystal structure was modulated from monoclinic to tetragonal. Also, the polarization characteristics were observed in the change of ferroelectric to anti-ferroelectric. Owing to the formation of a tetragonal structure, the dielectric constant was improved up to 41, and the leakage current density remarkably decreased by more than one order of magnitude. Moreover, the Al-doped HfZrO2 thin film with anti-ferroelectricity exhibited excellent energy storage properties with an energy storage density and efficiency of about 53.3 J/cm3 and 76% at ±4.5 MV/cm, respectively. Therefore, we propose that Al-doped HfZrO2 thin film could be applied as a candidate material for next-generation charge storage devices.

Current-induced switching of photonic spin Hall effect in a magnetic insulator based on spin–orbit torques

The photonic spin Hall effect (PSHE) is analogous to the electronic spin Hall effect, which has substantial potential for optoelectronic applications. However, PSHE-based devices are rarely studied, and manipulating the PSHE by charge current has remained elusive thus far. In this paper, we demonstrate current-induced switching of PSHE in the Ce1Dy2Al0.42Fe4.58O12 thin film capping with Pt electrodes, which is mediated by spin–orbit torques at the Pt/Ce1Dy2Al0.42Fe4.58O12 interface. The results show that the transverse beam shifts related to the PSHE can be reversed by applying a small order of magnitude charge current (∼108 A·m−2) to the Pt layer in opposite directions, which predicts low dissipation in our proposed heterostructure. In addition, by applying an in-plane magnetic field, the saturation beam shifts can be increased, which can significantly enhance the switching ratio.

Fabrication and Properties of Epitaxial VO2 Thin Film on m-Al2O3 Substrate

A thin film of thermochromic VO2 was prepared on m-Al2O3 substrate using a radio frequency (RF) magnetron sputtering technique. The epitaxial growth of the monoclinic M1 phase of VO2 on the m-Al2O3 substrate was confirmed through synchrotron X-ray diffraction (XRD) measurements. The transformation of this monoclinic M1 phase into a rutile phase at ~68 °C was reflected in the temperature-dependent XRD measurements of the VO2 thin film. The temperature-dependent electrical resistance measurements of this sample also revealed an abrupt metal-to-insulator transition at ~68 °C, which is reversible in nature. Temperature-dependent X-ray absorption (XAS) measurements at V L-edge and O K-edge were performed to study the electronic structure of the epitaxial VO2/m-Al2O3 thin film during the metal-to-insulator (MIT) transition.

Syntheses of η1 -Alkyl-η3 -Allyl-η5 -Cyclopentadienyl Cobalt(III) Complexes and Their Use in Low-temperature Atomic Layer Deposition of Cobalt-Containing Thin Films.

Herein, we report the design and scalable synthesis of three new Co(III) complexes, which have an unusual hydrocarbon η1 -alkyl-η3 -allyl-η5 -cyclopentadienyl ligation structure, from the reactions of readily available cobalt(II) compound CoCl2 (PPh3 )2 and biomass material β-pinene via C-C bond activation. These Co(III) complexes are air-stable, fairly volatile, and thermally stable, so they are excellent candidates as the metal precursors for the vapor deposition of cobalt-containing thin films. As a demonstration, we show that the Co(III) complex of [(3'-5'-η,1-σ)-methylene(2,2,4-trimethyl-4-cyclohexene-1,3-diyl)](η5 -methylcyclopentadienyl)Co (i. e. (seco-pinene)(MeCp)Co) is well suited for the atomic layer deposition (ALD) of Co3 O4 and CoS2 thin films, and the deposited Co3 O4 and CoS2 films are able to conformally cover trench structures with a fairly high aspect ratio of 10 : 1.

Investigation of resistive switching properties in acceptor-induced Sr(Fe,Ti)O3 thin film memristor

In this work, the amorphous SrFe0.1Ti0.9O3-δ (a-SFT10) thin film was prepared on FTO/Glass substrate by chemical solution deposition process and then annealed at 500 ℃. Step Profiler measurements and SEM images revealed that the thickness of the a-SFT10 film was around 300 nm. The a-SFT10 thin film was found to have a smooth surface but was not crystalline. X-ray photoelectron spectroscopy (XPS) was used to analyze the chemical states of the film. Fe2+ and Fe3+ coexist in a-SFT10, according to XPS results, with Fe3+ being the dominating state. The mixed valence state of iron ions may be related to oxygen vacancies. Current-voltage characteristics were conducted to study the electrical properties. The uniform switching voltages, high switch ratio and good endurance were obtained. The ratio of high and low resistance (RH/RL) is up to 103 under positive bias voltage. The physical mechanisms underlying resistance switching behaviors were also investigated. The results show that the Ohmic, space charge limited current and Schottky conduction mechanisms dominated in different voltage ranges of A-SFT10 films, respectively. The oxygen vacancies associated with the acceptor doping play a significant role in the current characteristic in Au/a-SFT10/FTO/Glass device. Our findings suggest that the device has potential applications in future resistive random access memory.

The comparison of structural and electro-optical properties of (In, Yb)2O3 thin films with those of In2O3 and Yb2O3 thin films

The comparison of structural and electro-optical properties of (In, Yb)2O3 thin films with those of In2O3 and Yb2O3 thin films

Coherent growth of β-(Al x Ga1−x )2O3 alloy thin films on (010) β-Ga2O3 substrates using mist CVD

Herein, we demonstrate β-(Al x Ga1−x )2O3 thin films that were coherently grown on a (010) β-Ga2O3 substrate using mist chemical vapor deposition (CVD). X-ray diffraction and reciprocal space mapping results revealed that the β-(Al x Ga1−x )2O3 thin films were of high-crystalline quality and were grown coherently to attain an Al content of 18.3% as measured by Rutherford backscattering spectroscopy. Importantly, based on their surface morphologies, the coherently grown β-(Al x Ga1−x )2O3 thin films have atomically flat surfaces. These results indicate that mist CVD is a promising technique for β-(Al x Ga1−x )2O3/β-Ga2O3 heterojunction devices.

Optical study on mesa structures with adjustable absorption based on Mn1.56Co0.96Ni0.48O4 thin films

In order to improve the infrared detection performance, mesa structures of Mn1.56Co0.96Ni0.48O4/Aluminum/Silicon dioxide/Silicon (MCN/Al/SiO2/Si) were prepared by chemical solution deposition method. Raman spectroscopy results indicate that increasing the thickness causes a change in the Mn3+–O band stretching vibration and the Mn4+–O band bending vibration. Spectroscopic elllipsometry was used to obtain the dielectric function of the films by fitting the experiment data using the classical middle-infrared dispersion formula. The evaluated real part of the dielectric constants ε1 and refractive index n decreased as the wavelength increase, the imaginary part ε2 and extinction coefficient k monotonically increased as the wavelength increase in the entire measuring range of 2–10 μm. The calculated absorption spectra of the MCN/Al/SiO2/Si structure showed that the absorption peak position could be adjusted by varying the thickness of the MCN films. Our results are important in the design and application of MCN film infrared detectors.

Sol-Gel-Derived Ordered Mesoporous High Entropy Spinel Ferrites and Assessment of Their Photoelectrochemical and Electrocatalytic Water Splitting Performance.

The novel material class of high entropy oxides with their unique and unexpected physicochemical properties is a candidate for energy applications. Herein, it is reported for the first time about the physico- and (photo-) electrochemical properties of ordered mesoporous (CoNiCuZnMg)Fe2 O4 thin films synthesized by a soft-templating and dip-coating approach. The A-site high entropy ferrites (HEF) are composed of periodically ordered mesopores building a highly accessible inorganic nanoarchitecture with large specific surface areas. The mesoporous spinel HEF thin films are found to be phase-pure and crack-free on the meso- and macroscale. The formation of the spinel structure hosting six distinct cations is verified by X-ray-based characterization techniques. Photoelectron spectroscopy gives insight into the chemical state of the implemented transition metals supporting the structural characterization data. Applied as photoanode for photoelectrochemical water splitting, the HEFs are photostable over several hours but show only low photoconductivity owing to fast surface recombination, as evidenced by intensity-modulated photocurrent spectroscopy. When applied as oxygen evolution reaction electrocatalyst, the HEF thin films possess overpotentials of 420mV at 10mA cm-2 in 1m KOH. The results imply that the increase of the compositional disorder enhances the electronic transport properties, which are beneficial for both energy applications.

Wake-up-free ferroelectric Hf0.5Zr0.5O2 thin films characterized by precession electron diffraction

In the recent decade, there is a growing interest in Hf0.5Zr0.5O2 (HZO) thin films owing to their well-behaved ferroelectricity and high compatibility with semiconductor integrated circuit technology. The ferroelectric properties of HZO are highly pertinent to the wake-up effect, which has been reported to be associated with the monoclinic (m-), orthorhombic (o-), and tetragonal (t-) phases. However, it is very challenging to distinguish the o- and t- phases by conventional X-ray diffraction. In this study, the HZO thin films with and without the need for the wake-up process to enhance the ferroelectricity were prepared, and the precession electron diffraction (PED) phase mapping technique was utilized to identify the crystalline phases in the HZO layers. The PED characterization reveals the correlation between the phase transformation and the wake-up effect in HZO. The absence of the t-phase is responsible for the wake-up-free property in the ferroelectric HZO thin film. The wake-up-free and pronounced ferroelectricity of the nanoscale HZO thin film in this study may bring a practical impact on a variety of ferroelectric applications.

Reduced fatigue and leakage of ferroelectric TiN/Hf0.5Zr0.5O2/TiN capacitors by thin alumina interlayers at the top or bottom interface

Hf0.5Zr0.5O2 (HZO) thin films are promising candidates for non-volatile memory and other related applications due to their demonstrated ferroelectricity at the nanoscale and compatibility with Si processing. However, one reason that HZO has not been fully scaled into industrial applications is due to its deleterious wake-up and fatigue behavior which leads to an inconsistent remanent polarization during cycling. In this study, we explore an interfacial engineering strategy in which we insert 1 nm Al2O3 interlayers at either the top or bottom HZO/TiN interface of sequentially deposited metal-ferroelectric-metal capacitors. By inserting an interfacial layer while limiting exposure to the ambient environment, we successfully introduce a protective passivating layer of Al2O3 that provides excess oxygen to mitigate vacancy formation at the interface. We report that TiN/HZO/TiN capacitors with a 1 nm Al2O3 at the top interface demonstrate a higher remanent polarization (2Pr ∼ 42 μC cm−2) and endurance limit beyond 108 cycles at a cycling field amplitude of 3.5 MV cm−1. We use time-of-flight secondary ion mass spectrometry, energy dispersive spectroscopy, and grazing incidence x-ray diffraction to elucidate the origin of enhanced endurance and leakage properties in capacitors with an inserted 1 nm Al2O3 layer. We demonstrate that the use of Al2O3 as a passivating dielectric, coupled with sequential ALD fabrication, is an effective means of interfacial engineering and enhances the performance of ferroelectric HZO devices.

Selective Crystallization of Ferroelectric HfxZr1–xO2 via Excimer Laser Annealing

Herein, we report the ferroelectricity of HfxZr1–xO2 (HZO) thin films crystallized via excimer laser annealing at 25 °C under atmospheric conditions. We characterized the structure and antiferroelectric/ferroelectric properties of HZO thin films using X-ray diffraction and standard polarization–voltage hysteresis. The laser-annealed Hf0.5Zr0.5O2 thin film was gradually crystallized with increasing laser pulse number. The HZO thin film series exhibited systemic changes in antiferroelectric/ferroelectric properties with variations in Zr concentration. In addition, we constructed a phase diagram of laser-annealed HZO thin films.