Special Issue "Machine Learning Methods and Sustainable Development: Metal Oxides and Multilayer Metal-Oxides"

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

Deadline for manuscript submissions: 31 January 2022.

Special Issue Editors

Dr. Maria Luisa Grilli
E-Mail Website
Guest Editor
Italian National Agency for New Technologies, Energy and Sustainable Economic Development, Energy Technologies and Renewable Sources Department, Casaccia Research Center, Via Anguillarese 301, Rome, Italy
Interests: materials science; physics; materials engineering; chemistry; energy; environmental science
Special Issues and Collections in MDPI journals

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

Manuscript Submission Information

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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 1800 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 (8 papers)

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Research

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Article
Volatile Resistive Switching Characteristics of Pt/HfO2/TaOx/TiN Short-Term Memory Device
Metals 2021, 11(8), 1207; https://doi.org/10.3390/met11081207 - 29 Jul 2021
Viewed by 291
Abstract
In this work, we study the threshold switching and short-term memory plasticity of a Pt/HfO2/TaOx/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) [...] Read more.
In this work, we study the threshold switching and short-term memory plasticity of a Pt/HfO2/TaOx/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
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Article
Gradually Modified Conductance in the Self-Compliance Region of an Atomic-Layer-Deposited Pt/TiO2/HfAlOx/TiN RRAM Device
Metals 2021, 11(8), 1199; https://doi.org/10.3390/met11081199 - 28 Jul 2021
Viewed by 230
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 [...] Read more.
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
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Article
Improved Synaptic Device Properties of HfAlOx Dielectric on Highly Doped Silicon Substrate by Partial Reset Process
Metals 2021, 11(5), 772; https://doi.org/10.3390/met11050772 - 08 May 2021
Viewed by 389
Abstract
This work demonstrates the synaptic properties of the alloy-type resistive random-access memory (RRAM). We fabricated the HfAlOx-based RRAM for a synaptic device in a neuromorphic system. The deposition of the HfAlOx film on the silicon substrate was verified by X-ray [...] Read more.
This work demonstrates the synaptic properties of the alloy-type resistive random-access memory (RRAM). We fabricated the HfAlOx-based RRAM for a synaptic device in a neuromorphic system. The deposition of the HfAlOx 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/HfAlOx/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
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Article
Irregular Resistive Switching Behaviors of Al2O3-Based Resistor with Cu Electrode
Metals 2021, 11(4), 653; https://doi.org/10.3390/met11040653 - 17 Apr 2021
Cited by 3 | Viewed by 504
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 [...] Read more.
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
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Article
Gradually Tunable Conductance in TiO2/Al2O3 Bilayer Resistors for Synaptic Device
Metals 2021, 11(3), 440; https://doi.org/10.3390/met11030440 - 07 Mar 2021
Cited by 4 | Viewed by 584
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 [...] Read more.
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
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Article
Liquid-Phase Deposition Synthesis of ZIF-67-Derived Synthesis of Co3O4@TiO2 Composite for Efficient Electrochemical Water Splitting
Metals 2021, 11(3), 420; https://doi.org/10.3390/met11030420 - 04 Mar 2021
Cited by 1 | Viewed by 503
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 [...] Read more.
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
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Article
Photocatalytic Applications of Metal Oxides for Sustainable Environmental Remediation
Metals 2021, 11(1), 80; https://doi.org/10.3390/met11010080 - 02 Jan 2021
Cited by 10 | Viewed by 1247
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. [...] Read more.
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
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Review

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Review
A Systematic Review of Metal Oxide Applications for Energy and Environmental Sustainability
Metals 2020, 10(12), 1604; https://doi.org/10.3390/met10121604 - 29 Nov 2020
Cited by 9 | Viewed by 977
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 [...] Read more.
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
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