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Metal Oxide Thin Films: Synthesis, Characterization and Applications

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Thin Films and Interfaces".

Deadline for manuscript submissions: closed (28 February 2021) | Viewed by 30919

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Special Issue Editors

Prof. Dr. Erwan Rauwel

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Guest Editor

Institute of Veterinary Medicine and Animal Science, Estonian University of Life Science, Kreutzwaldi 62, 51006 Tartu, Estonia
Interests: metal-oxide thin-film deposition; atomic layer deposition; nanomaterial synthesis; metal nanoparticles; metal-oxide nanoparticles; water purification; nanomedicine; photovoltaics; hybrid nanocomposites
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Protima Rauwel

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Institute of Forestry and Engineering, Estonian University of Life Science, Kreutzwaldi 56/1, 51014 Tartu, Estonia
Interests: nanoparticles; thin films; carbon-based hybrid materials; photovoltaics; LED; photocatalysis; electron microscopy; water purification
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear colleagues,

The last two decades have seen an intensive improvement in thin film deposition methods, enabling the precise coating of surfaces at the nanoscale. Today, it is possible to coat surfaces with complex compositions and synthesize multilayers, enabling the development of synergistic effects through the mutual interaction of such layers. The deposition of complex structures allows for the development of new technologies, with recent advances in deposition techniques further miniaturizing electronic devices.

The development of these new technologies towards scaling down the size of the produced devices requires accurate control of the deposition process. The latter then allows tailoring thin films and nanodevices to ones desires. The recent advances are not only limited to nanoelectronics but are applicable to every field, viz., anti-corrosion coating, biocidal coating, or photovoltaic devices, in order to cope with the present demands of the society. The last two decades have also witnessed the accelerated development of atomic layer deposition processes that enable the conformal coating at nanoscale now up-scalable to larger surface areas.

This Special Issue will compile recent developments in the field of metal oxide thin film deposition. The articles presented in this Special Issue will cover various topics, ranging from but not limited to the optimization of deposition methods, thin films preparations, the functionalization of surfaces with targeted applications, nanosensors, catalysis, electronic devices, biocidal coating, and the synthesis of nanostructures via the accurate control of thin film deposition methods, among others. Topics are open to metal oxide thin film deposition and characterization for the development of applications.

Prof. Dr. Erwan Rauwel
Dr. Protima Rauwel
Guest Editors

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Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

metal oxide thin films
metallic thin films
atomic layer deposition
chemical vapor deposition
sputtering
spin coating
dip-coating
multilayers
functional thin films
photovoltaic cells
catalysis
transistor technology
optoelectronic
sensors
biocidal coating
corrosion

Published Papers (11 papers)

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Editorial

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3 pages, 175 KiB

Open AccessEditorial

Editorial for the Special Issue on ‘Metal Oxide Thin Film: Synthesis, Characterization, and Application’

by Erwan Rauwel and Protima Rauwel

Materials 2021, 14(8), 1834; https://doi.org/10.3390/ma14081834 - 7 Apr 2021

Viewed by 1647

Abstract

The last two decades have witnessed the development of new technologies for thin-film deposition and coating [...] Full article

(This article belongs to the Special Issue Metal Oxide Thin Films: Synthesis, Characterization and Applications)

Research

Jump to: Editorial

11 pages, 4905 KiB

Open AccessArticle

Nanoscale Piezoelectric Properties and Phase Separation in Pure and La-Doped BiFeO₃ Films Prepared by Sol–Gel Method

by Alina V. Semchenko, Vitaly V. Sidsky, Igor Bdikin, Vladimir E. Gaishun, Svitlana Kopyl, Dmitry L. Kovalenko, Oleg Pakhomov, Sergei A. Khakhomov and Andrei L. Kholkin

Materials 2021, 14(7), 1694; https://doi.org/10.3390/ma14071694 - 30 Mar 2021

Cited by 11 | Viewed by 2399

Abstract

Pure BiFeO₃ (BFO) and doped Bi_0.9La_0.1FeO₃ (BLFO) thin films were prepared on Pt/TiO₂/SiO₂/Si substrates by a modified sol–gel technique using a separate hydrolysis procedure. The effects of final crystallization temperature and La doping on the phase structure, film morphology, and nanoscale piezoelectric properties were investigated. La doping and higher crystallization temperature lead to an increase in the grain size and preferred (102) texture of the films. Simultaneously, a decrease in the average effective piezoelectric coefficient (about 2 times in La-doped films) and an increase in the area of surface non-polar phase (up to 60%) are observed. Phase separation on the films’ surface is attributed to either a second phase or to a non-polar perovskite phase at the surface. As compared with undoped BFO, La-doping leads to an increase in the average grain size and self-polarization that is important for future piezoelectric applications. It is shown that piezoelectric activity is directly related to the films’ microstructructure, thus emphasizing the role of annealing conditions and La-doping that is frequently used to decrease the leakage current in BFO-based materials. Full article

(This article belongs to the Special Issue Metal Oxide Thin Films: Synthesis, Characterization and Applications)

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17 pages, 10824 KiB

Open AccessArticle

Hot-Probe Characterization of Transparent Conductive Thin Films

by Alexander Axelevitch

Materials 2021, 14(5), 1186; https://doi.org/10.3390/ma14051186 - 3 Mar 2021

Cited by 6 | Viewed by 2159

Abstract

Transparent conductive oxide (TCO) thin films represent a large class of wide-bandgap semiconductors applied in all fields of micro- and optoelectronics. The most widespread material applied for the creation of TCO coatings is indium-tin oxide (ITO). At the same time, there are plurality trends to change the high-cost ITO on other materials, for example, on the ZnO doped by different elements such as Al, Mn, and Sb. These films require mobile and low-cost evaluation methods. The dynamic hot-probe measurement system is one of such techniques that can supplement and sometimes replace existing heavy systems such as the Hall effect measurements or the Haynes–Shockley experiments. The theoretical basis and the method of analysis of the recorded dynamic hot-probe characteristics measured at different temperatures were presented in this work. This method makes it possible to extract the main parameters of thin films. Commercial thin ITO films and new transparent conducting ZnO:Al layers prepared by magnetron co-sputtering were studied by the proposed method. The measured parameters of commercial ITO films are in agreement with the presented and reference data. In addition, the parameters of ZnO:Al thin films such as the majority charge carriers type, concentration, and mobility were extracted from dynamic hot-probe characteristics. This method may be applied also to other wide-bandgap semiconductors. Full article

(This article belongs to the Special Issue Metal Oxide Thin Films: Synthesis, Characterization and Applications)

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15 pages, 4937 KiB

Open AccessArticle

Origin of Mangetotransport Properties in APCVD Deposited Tin Oxide Thin Films

by Krunoslav Juraić, Davor Gracin, Matija Čulo, Željko Rapljenović, Jasper Rikkert Plaisier, Aden Hodzic, Zdravko Siketić, Luka Pavić and Mario Bohač

Materials 2020, 13(22), 5182; https://doi.org/10.3390/ma13225182 - 17 Nov 2020

Cited by 5 | Viewed by 2346

Abstract

Transparent conducting oxides (TCO) with high electrical conductivity and at the same time high transparency in the visible spectrum are an important class of materials widely used in many devices requiring a transparent contact such as light-emitting diodes, solar cells and display screens. Since the improvement of electrical conductivity usually leads to degradation of optical transparency, a fine-tuning sample preparation process and a better understanding of the correlation between structural and transport properties is necessary for optimizing the properties of TCO for use in such devices. Here we report a structural and magnetotransport study of tin oxide (SnO₂), a well-known and commonly used TCO, prepared by a simple and relatively cheap Atmospheric Pressure Chemical Vapour Deposition (APCVD) method in the form of thin films deposited on soda-lime glass substrates. The thin films were deposited at two different temperatures (which were previously found to be close to optimum for our setup), 590 °C and 610 °C, and with (doped) or without (undoped) the addition of fluorine dopants. Scanning Electron Microscopy (SEM) and Grazing Incidence X-ray Diffraction (GIXRD) revealed the presence of inhomogeneity in the samples, on a bigger scale in form of grains (80–200 nm), and on a smaller scale in form of crystallites (10–25 nm). Charge carrier density and mobility extracted from DC resistivity and Hall effect measurements were in the ranges 1–3 × 10²⁰ cm⁻³ and 10–20 cm²/Vs, which are typical values for SnO₂ films, and show a negligible temperature dependence from room temperature down to −269 °C. Such behaviour is ascribed to grain boundary scattering, with the interior of the grains degenerately doped (i.e., the Fermi level is situated well above the conduction band minimum) and with negligible electrostatic barriers at the grain boundaries (due to high dopant concentration). The observed difference for factor 2 in mobility among the thin-film SnO₂ samples most likely arises due to the difference in the preferred orientation of crystallites (texture coefficient). Full article

(This article belongs to the Special Issue Metal Oxide Thin Films: Synthesis, Characterization and Applications)

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19 pages, 18648 KiB

Open AccessArticle

Phase and Orientation Control of NiTiO₃ Thin Films

by Jon Einar Bratvold, Helmer Fjellvåg and Ola Nilsen

Materials 2020, 13(1), 112; https://doi.org/10.3390/ma13010112 - 25 Dec 2019

Cited by 4 | Viewed by 2859

Abstract

Subtle changes in the atomic arrangement of NiTiO₃ in the ilmenite structure affects its symmetry and properties. At high temperatures, the cations are randomly distributed throughout the structure, resulting in the corundum structure with R−3c symmetry. Upon cooling, the cations order in alternating layers along the crystallographic c axis, resulting in the ilmenite structure with R−3 symmetry. Related to this is the R3c symmetry, where the cations alternate both perpendicularly and along the c axis. NiTiO₃ with the latter structure is highly interesting as it exhibits ferroelectric properties. The close relationship between structure and properties for ilmenite-related structures emphasizes the importance of being able to control the symmetry during synthesis. We show that the orientation and symmetry of thin films of NiTiO₃ formed by atomic layer deposition (ALD) can be controlled by choice of substrate. The disordered phase (R−3c), previously only observed at elevated temperatures, have been deposited at 250 °C on α-Al₂O₃ substrates, while post-deposition annealing at moderate temperatures (650 °C) induces ordering (R−3). We have in addition explored the symmetry and epitaxial orientation obtained when deposited on substrates of LaAlO₃(100), SrTiO₃(100) and MgO(100). The presented work demonstrates the possibilities of ALD to form metastable phases through choice of substrates. Full article

(This article belongs to the Special Issue Metal Oxide Thin Films: Synthesis, Characterization and Applications)

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10 pages, 1626 KiB

Open AccessArticle

Atomic Layer Deposition of GdCoO₃ and Gd_0.9Ca_0.1CoO₃

by Marion Duparc, Henrik Hovde Sønsteby, Ola Nilsen, Anja Olafsen Sjåstad and Helmer Fjellvåg

Materials 2020, 13(1), 24; https://doi.org/10.3390/ma13010024 - 19 Dec 2019

Cited by 1 | Viewed by 2541

Abstract

Thin films of the catalytically interesting ternary and quaternary perovskites GdCoO₃ and Gd_0.9Ca_0.1CoO₃ are fabricated by atomic layer deposition using metal β-diketonates and ozone as precursors. The resulting thin films are amorphous as deposited and become single-oriented crystalline on LaAlO₃(100) and YAlO₃(100/010) after post-annealing at 650 °C in air. The crystal orientations of the films are tunable by choice and the orientation of the substrate, mitigated through the interface via solid face epitaxy upon annealing. The films exhibit no sign of Co²⁺. Additionally, high-aspect-ratio Si(100) substrates were used to document the suitability of the developed process for the preparation of coatings on more complex, high-surface-area structures. We believe that coatings of GdCoO₃ and Gd_1−xCa_xCoO₃ may find applications within oxidation catalysis. Full article

(This article belongs to the Special Issue Metal Oxide Thin Films: Synthesis, Characterization and Applications)

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12 pages, 4441 KiB

Open AccessArticle

Improving the Tribological Performance of MAO Coatings by Using a Stable Sol Electrolyte Mixed with Cellulose Additive

by Wei Song, Bailing Jiang and Dongdong Ji

Materials 2019, 12(24), 4226; https://doi.org/10.3390/ma12244226 - 16 Dec 2019

Cited by 4 | Viewed by 2270

Abstract

In this study, micro-arc oxidation (MAO) of aluminum 6061 alloy was carried out within a silicate base electrolyte containing 0.75 g/L of cellulose, and the tribological properties of the coating were investigated. The as-prepared coating was detected by Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), a scanning electron microscope (SEM) and an energy-dispersive spectrometer (EDS), respectively. The results suggested that cellulose filled in the microcracks and micropores, or it existed by cross-linking with Al³⁺. In addition, it was found that the cellulose had little effect on the coating hardness. However, the thickness and roughness of the coating were improved with the increase in cellulose concentration. Moreover, the ball-on-disk test showed that the friction coefficient, weight loss and wear rate of the MAO coating decreased with the increase in cellulose concentration. Further, the performances of the coatings obtained in the same electrolyte, under different preserved storage periods, were compared, revealing that the cellulose was uniformly dispersed in the electrolyte and improved the tribological properties of the MAO coating within 30 days. Full article

(This article belongs to the Special Issue Metal Oxide Thin Films: Synthesis, Characterization and Applications)

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10 pages, 2507 KiB

Open AccessArticle

Influence of Carrier Gases on the Quality of Epitaxial Corundum-Structured α-Ga₂O₃ Films Grown by Mist Chemical Vapor Deposition Method

by Yu Xu, Chunfu Zhang, Yaolin Cheng, Zhe Li, Ya’nan Cheng, Qian Feng, Dazheng Chen, Jincheng Zhang and Yue Hao

Materials 2019, 12(22), 3670; https://doi.org/10.3390/ma12223670 - 7 Nov 2019

Cited by 26 | Viewed by 3574

Abstract

This report systematically investigates the influence of different carrier gases (O₂, N₂, and air) on the growth of gallium oxide (Ga₂O₃) thin films on c-plane sapphire substrates by using the mist-CVD method. Although XRD and Raman measurements show that the pure corundum-structured α-Ga₂O₃ with single (0006) plane orientation was successfully obtained for all three different carrier gases, the crystal quality could be greatly affected by the carrier gas. When O₂ is used as the carrier gas, the smallest full-width at half maximum (FWHM), the very sharp absorption cutoff edge, the perfect lattice structure, the highest growth rate, and the smooth surface can be obtained for the epitaxial α-Ga₂O₃ film as demonstrated by XRD, UV-VIS, TEM, AFM (Atomic Force Microscope), and SEM measurements. It is proposed that the oxygen content in carrier gas should be responsible for all of these results. XPS (X-ray photoelectron spectroscopy) analysis also confirms that more oxygen elements can be included in epitaxial film when O₂ is used as the carrier gas and thus help improve the crystal quality. The proper carrier gas is essential for the high quality α-Ga₂O₃ growth. Full article

(This article belongs to the Special Issue Metal Oxide Thin Films: Synthesis, Characterization and Applications)

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10 pages, 5113 KiB

Open AccessArticle

A Novel Self-Adaptive Control Method for Plasma Electrolytic Oxidation Processing of Aluminum Alloys

by Kai Yang, Jiaquan Zeng, Haisong Huang, Jiadui Chen and Biao Cao

Materials 2019, 12(17), 2744; https://doi.org/10.3390/ma12172744 - 27 Aug 2019

Cited by 11 | Viewed by 2469

Abstract

Plasma electrolytic oxidation processing is a novel promising surface modification approach for various materials. However, its large-scale application is still restricted, mainly due to the problem of high energy consumption of the plasma electrolytic oxidation processing. In order to solve this problem, a novel intelligent self-adaptive control technology based on real-time active diagnostics and on the precision adjustment of the process parameters was developed. Both the electrical characteristics of the plasma electrolytic oxidation process and the microstructure of the coating were investigated. During the plasma electrolytic oxidation process, the discharges are maintained in the soft-sparking regime and the coating exhibits a good uniformity and compactness. A total specific energy consumption of 1.8 kW h m⁻² μm⁻¹ was achieved by using such self-adaptive plasma electrolytic oxidation processing on pre-anodized 6061 aluminum alloy samples. Full article

(This article belongs to the Special Issue Metal Oxide Thin Films: Synthesis, Characterization and Applications)

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10 pages, 4017 KiB

Open AccessArticle

Optimizing the Properties of InGaZnO_x Thin Film Transistors by Adjusting the Adsorbed Degree of Cs⁺ Ions

by He Zhang, Yaogong Wang, Ruozheng Wang, Xiaoning Zhang and Chunliang Liu

Materials 2019, 12(14), 2300; https://doi.org/10.3390/ma12142300 - 18 Jul 2019

Cited by 3 | Viewed by 2237

Abstract

To improve the performance of amorphous InGaZnO_x (a-IGZO) thin film transistors (TFTs), in this thesis, Cs⁺ ions adsorbed IGZO (Cs-IGZO) films were prepared through a solution immersion method at low temperature. Under the modification of surface structure and oxygen vacancies concentrations of a-IGZO film, with the effective introduction of Cs⁺ ions into the surface of a-IGZO films, the transfer properties and stability of a-IGZO TFTs are greatly improved. Different parameters of Cs⁺ ion concentrations were investigated in our work. When the Cs⁺ ions concentration reached 2% mol/L, the optimized performance Cs-IGZO TFT was obtained, showing the carrier mobility of 18.7 cm² V⁻¹ s⁻¹, the OFF current of 0.8 × 10⁻¹⁰ A, and the threshold voltage of 0.2 V, accompanied by the threshold voltage shifts of 1.3 V under positive bias stress for 5000 s. Full article

(This article belongs to the Special Issue Metal Oxide Thin Films: Synthesis, Characterization and Applications)

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12 pages, 24973 KiB

Open AccessArticle

Discharge Behavior and Dielectric Breakdown of Oxide Films during Single Pulse Anodizing of Aluminum Micro-Electrodes

by Kai Yang, Haisong Huang, Jiadui Chen and Biao Cao

Materials 2019, 12(14), 2286; https://doi.org/10.3390/ma12142286 - 17 Jul 2019

Cited by 6 | Viewed by 2823

Abstract

Micro-arc discharge events and dielectric breakdown of oxide films play an important role in the formation process of plasma electrolytic oxidation coating. Single pulse anodization of micro-electrodes was employed to study the discharge behavior and dielectric breakdown of oxide films deposited on aluminum in an alkaline silicate electrolyte. Voltage and current waveforms of applied pulses were measured and surface morphology of micro-electrodes was characterized from images obtained using scanning electron microscope (SEM). A feasible identification method for the critical breakdown voltage of oxide film was introduced. Different current transients of voltage pulses were obtained, depending on applied pulse voltage and duration. In addition, the active capacitive effect and complex non-linear nature of plasma electrolytic oxidation process is confirmed using dynamic electrical characteristic curves. A good correlation between the pulse parameters and shape of discharge channels was observed. Circular opened pores were found to close with increasing potential and pulse width. Finally, the characteristic parameters of a single discharge event were estimated. Full article

(This article belongs to the Special Issue Metal Oxide Thin Films: Synthesis, Characterization and Applications)

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