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Machine Learning Methods and Sustainable Development: Metal Oxides and Multilayer Metal-Oxides

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A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Computation and Simulation on Metals".

Deadline for manuscript submissions: closed (31 January 2022) | Viewed by 42718

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Special Issue Editors

Dr. Alexey Mikhaylov

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Guest Editor

Financial University under the Government of the Russian Federation, Moscow, Russian
Interests: machine learning; sustainability; financial markets; crypto; innovation
Special Issues, Collections and Topics in MDPI journals

Dr. Maria Luisa Grilli

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ENEA-Italian National Agency for New Technologies, Energy and Sustainable Economic Development, Rome, Italy
Interests: thin films; nanomaterials; graphene; PVD; sputtering; optics; photonics; solar cells
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Special Issue Information

Dear Colleagues,

The development of nanotechnologies and new methods of machine learning are responsible for the significant attention and demand for metal oxides and multilayer metal-oxide nanostructures. Metal oxides are a class of materials that are considered extremely important from both a scientific and a technological viewpoint. The physicochemical properties of metal oxides are governed by their growth process mechanisms, both chemical and physical. The control of film properties, film nanostructuring, and use of different oxides in composites and multilayer systems are key parameters for tailoring materials’ properties to the selected application. Metal oxides can become strategic critical resources because they are implemented in many high-tech products such as computers, batteries for electric vehicles, magnets, scintillators, and aviation and medical devices. The secured supply of metal oxides is crucial to the continuing production and exporting of their technologies. Moreover, the specific properties of some metal oxides make them essential and difficult to substitute in several demanding applications.

This Special Issue aims to gather recent advances in the field of machine learning methods, process synthesis, and sustainable development of metal oxides, multilayer metal oxides, and metal oxide nanostructures for the global industry. These challenges are not only related to technology but also environmental, societal, economic, and financial tools as well as process management, all of which are of interest for this Special Issue.

Dr. Alexey Mikhaylov
Dr. Maria Luisa Grilli
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. Metals is an international peer-reviewed open access monthly 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

artificial intelligence
nanotechnologies
material synthesis
industrial development
financial tools
environmental impact
economic tools
societal impact
process management

Published Papers (12 papers)

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Editorial

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5 pages, 176 KiB

Open AccessEditorial

Machine Learning Methods and Sustainable Development: Metal Oxides and Multilayer Metal Oxides

by Alexey Mikhaylov and Maria Luisa Grilli

Metals 2022, 12(5), 836; https://0-doi-org.brum.beds.ac.uk/10.3390/met12050836 - 13 May 2022

Cited by 20 | Viewed by 1629

Abstract

(This article belongs to the Special Issue Machine Learning Methods and Sustainable Development: Metal Oxides and Multilayer Metal-Oxides)

Research

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12 pages, 3012 KiB

Open AccessArticle

Mixed Oxide Electrodes Based on Ruthenium and Copper: Electrochemical Properties as a Function of the Composition and Method of Manufacture

by Elisabetta Petrucci, Francesco Porcelli, Monica Orsini, Serena De Santis and Giovanni Sotgiu

Metals 2022, 12(2), 316; https://0-doi-org.brum.beds.ac.uk/10.3390/met12020316 - 11 Feb 2022

Cited by 6 | Viewed by 1619

Abstract

The development of mixed oxide electrodes is being intensively investigated to reduce the high cost associated with the use of noble metals and to obtain versatile and long-lasting devices. To evaluate their use for charge storage or anodic oxidation, in this paper, thin-film electrodes coated with ruthenium (RuO_x) and copper oxide (CuO_x) are fabricated by thermal decomposition of organic solutions containing the precursors by drop-casting on titanium (Ti) foils. The coating consisted of four layers of metal oxide. To investigate the effect of copper (Cu) on electrochemical performances, different approaches are adopted by varying the ratios of precursors’ concentration and including a RuO_x interlayer. A comparison with samples obtained by only RuO_x has been also performed. The electrodes are characterized using scanning electron microscopy (SEM), cyclic (CV) and linear sweep (LSV) voltammetry, electrochemical impedance spectroscopy (EIS), and corrosion tests. The addition of Cu enhances the capacitive response of the materials and promotes electron transfer reversibility. The coatings obtained by the highest Ru:Cu ratio (95:5) exhibit a more uniform surface distribution and increased corrosion resistance. The interlayer is beneficial to further reduce the corrosion susceptibility and to promote the oxygen evolution but detrimental in the charge storage power. The results suggest the possibility to enhance the electrochemical performance of expensive RuO_x through a combination with a low amount of cheaper and more abundant CuO_x. Full article

(This article belongs to the Special Issue Machine Learning Methods and Sustainable Development: Metal Oxides and Multilayer Metal-Oxides)

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8 pages, 2587 KiB

Open AccessArticle

Multi-Level Resistive Switching of Pt/HfO₂/TaN Memory Device

by Hojeong Ryu, Hoeje Jung, Kisong Lee and Sungjun Kim

Metals 2021, 11(12), 1885; https://0-doi-org.brum.beds.ac.uk/10.3390/met11121885 - 23 Nov 2021

Cited by 1 | Viewed by 1868

Abstract

This work characterizes resistive switching and neuromorphic simulation of Pt/HfO₂/TaN stack as an artificial synaptic device. A stable bipolar resistive switching operation is performed by repetitive DC sweep cycles. Furthermore, endurance (DC 100 cycles) and retention (5000 s) are demonstrated for reliable resistive operation. Low-resistance and high-resistance states follow the Ohmic conduction and Poole–Frenkel emission, respectively, which is verified through the fitting process. For practical operation, the set and reset processes are performed through pulses. Further, potentiation and depression are demonstrated for neuromorphic application. Finally, neuromorphic system simulation is performed through a neural network for pattern recognition accuracy of the Fashion Modified National Institute of Standards and Technology dataset. Full article

(This article belongs to the Special Issue Machine Learning Methods and Sustainable Development: Metal Oxides and Multilayer Metal-Oxides)

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7 pages, 1976 KiB

Open AccessArticle

Volatile Resistive Switching Characteristics of Pt/HfO₂/TaO_x/TiN Short-Term Memory Device

by Hojeong Ryu and Sungjun Kim

Metals 2021, 11(8), 1207; https://0-doi-org.brum.beds.ac.uk/10.3390/met11081207 - 29 Jul 2021

Cited by 10 | Viewed by 2581

Abstract

In this work, we study the threshold switching and short-term memory plasticity of a Pt/HfO₂/TaO_x/TiN resistive memory device for a neuromorphic system. First, we verify the thickness and elemental characterization of the device stack through transmission electron microscopy (TEM) and an energy-dispersive X-ray spectroscopy (EDS) line scan. Volatile resistive switching with low compliance current is observed under the DC sweep in a positive bias. Uniform cell-to-cell and cycle-to-cycle DC I-V curves are achieved by means of a repetitive sweep. The mechanism of volatile switching is explained by the temporal generation of traps. Next, we initiate the accumulation of the conductance and a natural decrease in the current by controlling the interval time of the pulses. Finally, we conduct a neuromorphic simulation to calculate the pattern recognition accuracy. These results can be applicable to short-term memory applications such as temporal learning in a neuromorphic system. Full article

(This article belongs to the Special Issue Machine Learning Methods and Sustainable Development: Metal Oxides and Multilayer Metal-Oxides)

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7 pages, 1186 KiB

Open AccessArticle

Gradually Modified Conductance in the Self-Compliance Region of an Atomic-Layer-Deposited Pt/TiO2/HfAlOx/TiN RRAM Device

by Hojeong Ryu and Sungjun Kim

Metals 2021, 11(8), 1199; https://0-doi-org.brum.beds.ac.uk/10.3390/met11081199 - 28 Jul 2021

Cited by 7 | Viewed by 2358

Abstract

This study presents conductance modulation in a Pt/TiO₂/HfAlOx/TiN resistive memory device in the compliance region for neuromorphic system applications. First, the chemical and material characteristics of the atomic-layer-deposited films were verified by X-ray photoelectron spectroscopy depth profiling. The low-resistance state was effectively controlled by the compliance current, and the high-resistance state was adjusted by the reset stop voltage. Stable endurance and retention in bipolar resistive switching were achieved. When a compliance current of 1 mA was imposed, only gradual switching was observed in the reset process. Self-compliance was used after an abrupt set transition to achieve a gradual set process. Finally, 10 cycles of long-term potentiation and depression were obtained in the compliance current region for neuromorphic system applications. Full article

(This article belongs to the Special Issue Machine Learning Methods and Sustainable Development: Metal Oxides and Multilayer Metal-Oxides)

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8 pages, 1399 KiB

Open AccessFeature PaperArticle

Improved Synaptic Device Properties of HfAlO_x Dielectric on Highly Doped Silicon Substrate by Partial Reset Process

by Seunghyun Kim, Osung Kwon, Hojeong Ryu and Sungjun Kim

Metals 2021, 11(5), 772; https://0-doi-org.brum.beds.ac.uk/10.3390/met11050772 - 08 May 2021

Cited by 3 | Viewed by 1923

Abstract

This work demonstrates the synaptic properties of the alloy-type resistive random-access memory (RRAM). We fabricated the HfAlO_x-based RRAM for a synaptic device in a neuromorphic system. The deposition of the HfAlO_x film on the silicon substrate was verified by X-ray photoelectron spectroscopy (XPS) analysis. It was found that both abrupt and gradual resistive switching could be implemented, depending on the reset stop voltage. In the reset process, the current gradually decreased at weak voltage, and at strong voltage, it tended to decrease rapidly by Joule heating. The type of switching determined by the first reset process was subsequently demonstrated to be stable switching by successive set and reset processes. A gradual switching type has a much smaller on/off window than abrupt switching. In addition, retention maintained stability up to 2000 s in both switching cases. Next, the multiple current states were tested in the gradual switching case by identical pulses. Finally, we demonstrated the potentiation and depression of the Cu/HfAlO_x/Si device as a synapse in an artificial neural network and confirmed that gradual resistive switching was suitable for artificial synapses, using neuromorphic system simulation. Full article

(This article belongs to the Special Issue Machine Learning Methods and Sustainable Development: Metal Oxides and Multilayer Metal-Oxides)

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7 pages, 1963 KiB

Open AccessArticle

Irregular Resistive Switching Behaviors of Al₂O₃-Based Resistor with Cu Electrode

by Hojeong Ryu and Sungjun Kim

Metals 2021, 11(4), 653; https://doi.org/10.3390/met11040653 - 17 Apr 2021

Cited by 13 | Viewed by 2767

Abstract

In this work, we examined the irregular resistive switching behaviors of a complementary metal–oxide–semiconductor (CMOS)-compatible Cu/Al₂O₃/Si resistor device. X-ray photoelectron spectroscopy (XPS) analysis confirmed the chemical and material compositions of a Al₂O₃ thin film layer and Si substrate. Bipolar resistive switching occurred in a more stable manner than the unipolar resistive switching in the device did. Five cells were verified over 50 endurance cycles in terms of bipolar resistive switching, and a good retention was confirmed for 10,000 s in the high-resistance state (HRS) and the low-resistance state (LRS). Both high reset current (~10 mA) and low reset current (<100 μA) coexisted in the bipolar resistive switching. We investigated nonideal resistive switching behaviors such as negative-set and current overshoot, which could lead to resistive switching failure. Full article

(This article belongs to the Special Issue Machine Learning Methods and Sustainable Development: Metal Oxides and Multilayer Metal-Oxides)

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7 pages, 1993 KiB

Open AccessFeature PaperArticle

Gradually Tunable Conductance in TiO₂/Al₂O₃ Bilayer Resistors for Synaptic Device

by Hojeong Ryu and Sungjun Kim

Metals 2021, 11(3), 440; https://0-doi-org.brum.beds.ac.uk/10.3390/met11030440 - 07 Mar 2021

Cited by 17 | Viewed by 2707

Abstract

In this work, resistive switching and synaptic behaviors of a TiO₂/Al₂O₃ bilayer device were studied. The deposition of Pt/Ti/TiO₂/Al₂O₃/TiN stack was confirmed by transmission electron microscopy (TEM) and energy X-ray dispersive spectroscopy (EDS). The initial state before the forming process followed Fowler-Nordheim (FN) tunneling. A strong electric field was applied to Al₂O₃ with a large energy bandgap for FN tunneling, which was confirmed by the I-V fitting process. Bipolar resistive switching was conducted by the set process in a positive bias and the reset process in a negative bias. High-resistance state (HRS) followed the trap-assisted tunneling (TAT) model while low-resistance state (LRS) followed the Ohmic conduction model. Set and reset operations were verified by pulse. Moreover, potentiation and depression in the biological synapse were verified by repetitive set pulses and reset pulses. Finally, the device showed good pattern recognition accuracy (~88.8%) for a Modified National Institute of Standards and Technology (MNIST) handwritten digit database in a single layer neural network including the conductance update of the device. Full article

(This article belongs to the Special Issue Machine Learning Methods and Sustainable Development: Metal Oxides and Multilayer Metal-Oxides)

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10 pages, 1829 KiB

Open AccessArticle

Liquid-Phase Deposition Synthesis of ZIF-67-Derived Synthesis of Co₃O₄@TiO₂ Composite for Efficient Electrochemical Water Splitting

by Zaffar Ahmed Shaikh, Asif Ali Laghari, Oleg Litvishko, Valery Litvishko, Tatyana Kalmykova and Artur Meynkhard

Metals 2021, 11(3), 420; https://0-doi-org.brum.beds.ac.uk/10.3390/met11030420 - 04 Mar 2021

Cited by 12 | Viewed by 2260

Abstract

In this article, a novel Co₃O₄@TiO₂ composite is synthesized by applying two-step methods. ZIF-67 is synthesized and used as a template for the synthesis of the composite. The composite is designed by using the effective photocatalytic properties of Co₃O₄ and TiO₂. The resulting synthesized composite is supposed to offer superior properties compared to their counterparts. The synthesized Co₃O₄@TiO₂ composite is characterized by powder X-ray diffraction (PXRD), Brunauer–Emmet–Teller (BET), atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Electrochemical water splitting, including hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) studies on the Co₃O₄@TiO₂ composite, is evaluated by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) analysis in a 2M aqueous KOH electrolyte. The current generation stability of these samples is deliberated by chronoamperometric measurements. It is observed, from LSV results at a 1 mV/s scan rate, that metal oxides incorporated on other metal oxides have a higher current density and lower onset potential as compared to pure metal oxides. From the obtained results, it has become evident that synthesized studies on the Co₃O₄@TiO₂ composite possess significant potential for electrochemical water splitting with the lowest onset potential, highest current density, better OER, and HER activity. Full article

(This article belongs to the Special Issue Machine Learning Methods and Sustainable Development: Metal Oxides and Multilayer Metal-Oxides)

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25 pages, 649 KiB

Open AccessFeature PaperArticle

Photocatalytic Applications of Metal Oxides for Sustainable Environmental Remediation

by Mir Sayed Shah Danish, Liezel L. Estrella, Ivy Michelle A. Alemaida, Anton Lisin, Nikita Moiseev, Mikaeel Ahmadi, Massoma Nazari, Mohebullah Wali, Hameedullah Zaheb and Tomonobu Senjyu

Metals 2021, 11(1), 80; https://0-doi-org.brum.beds.ac.uk/10.3390/met11010080 - 02 Jan 2021

Cited by 206 | Viewed by 9420

Abstract

Along with industrialization and rapid urbanization, environmental remediation is globally a perpetual concept to deliver a sustainable environment. Various organic and inorganic wastes from industries and domestic homes are released into water systems. These wastes carry contaminants with detrimental effects on the environment. Consequently, there is an urgent need for an appropriate wastewater treatment technology for the effective decontamination of our water systems. One promising approach is employing nanoparticles of metal oxides as photocatalysts for the degradation of these water pollutants. Transition metal oxides and their composites exhibit excellent photocatalytic activities and along show favorable characteristics like non-toxicity and stability that also make them useful in a wide range of applications. This study discusses some characteristics of metal oxides and briefly outlined their various applications. It focuses on the metal oxides TiO₂, ZnO, WO₃, CuO, and Cu₂O, which are the most common and recognized to be cost-effective, stable, efficient, and most of all, environmentally friendly for a sustainable approach for environmental remediation. Meanwhile, this study highlights the photocatalytic activities of these metal oxides, recent developments, challenges, and modifications made on these metal oxides to overcome their limitations and maximize their performance in the photodegradation of pollutants. Full article

(This article belongs to the Special Issue Machine Learning Methods and Sustainable Development: Metal Oxides and Multilayer Metal-Oxides)

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Review

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20 pages, 1859 KiB

Open AccessReview

Green Synthesis of Silver Oxide Nanoparticles for Photocatalytic Environmental Remediation and Biomedical Applications

by Mir Sayed Shah Danish, Liezel L. Estrella-Pajulas, Ivy Michelle Alemaida, Maria Luisa Grilli, Alexey Mikhaylov and Tomonobu Senjyu

Metals 2022, 12(5), 769; https://0-doi-org.brum.beds.ac.uk/10.3390/met12050769 - 29 Apr 2022

Cited by 38 | Viewed by 5215

Abstract

Among the most notable nanotechnology applications is its employment in environmental remediation and biomedical applications. Nonetheless, there is a need for cleaner and sustainable methods in preparing nanomaterials that use cheaper, more environment-friendly precursors than the conventional synthesis process. The green chemistry approach for the preparation of nanoparticles is becoming more attractive as it uses non-toxic chemicals and reagents. It also offers cost-effective synthesis process as it uses readily available plant sources and microbe as redox mediators in converting metallic cations to metal or metal oxide nanoparticles. The extracts of these plants and microbe sources contain phytochemicals and metabolites in variable quantities, which serve as redox mediators and capping agents that stabilize the biosynthesized nanoparticles. The present article reviews the recent studies on the fabrication of silver oxide nanoparticles (Ag₂O-NPs) via plant-mediated and microbe-mediated green synthesis, giving a concise discussion on the green preparation of Ag₂O-NPs employing extracts of different plants and microbial sources. The performances of the biosynthesized Ag₂O-NPs are also reviewed, highlighting their potential use in photocatalysis and biomedical applications. Full article

(This article belongs to the Special Issue Machine Learning Methods and Sustainable Development: Metal Oxides and Multilayer Metal-Oxides)

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20 pages, 3290 KiB

Open AccessReview

A Systematic Review of Metal Oxide Applications for Energy and Environmental Sustainability

by Mir Sayed Shah Danish, Arnab Bhattacharya, Diana Stepanova, Alexey Mikhaylov, Maria Luisa Grilli, Mahdi Khosravy and Tomonobu Senjyu

Metals 2020, 10(12), 1604; https://0-doi-org.brum.beds.ac.uk/10.3390/met10121604 - 29 Nov 2020

Cited by 114 | Viewed by 6175

Abstract

Energy is the fundamental requirement of all physical, chemical, and biological processes which are utilized for better living standards. The toll that the process of development takes on the environment and economic activity is evident from the arising concerns about sustaining the industrialization that has happened in the last centuries. The increase in carbon footprint and the large-scale pollution caused by industrialization has led researchers to think of new ways to sustain the developmental activities, whilst simultaneously minimizing the harming effects on the enviroment. Therefore, decarbonization strategies have become an important factor in industrial expansion, along with the invention of new catalytic methods for carrying out non-thermal reactions, energy storage methods and environmental remediation through the removal or breakdown of harmful chemicals released during manufacturing processes. The present article discusses the structural features and photocatalytic applications of a variety of metal oxide-based materials. Moreover, the practical applicability of these materials is also discussed, as well as the transition of production to an industrial scale. Consequently, this study deals with a concise framework to link metal oxide application options within energy, environmental and economic sustainability, exploring the footprint analysis as well. Full article

(This article belongs to the Special Issue Machine Learning Methods and Sustainable Development: Metal Oxides and Multilayer Metal-Oxides)

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