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ZnO Materials: Synthesis, Properties and Applications (Second Volume)
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ZnO Materials: Synthesis, Properties and Applications (Second Volume)

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Materials Physics".

Deadline for manuscript submissions: closed (20 February 2024) | Viewed by 10489

Special Issue Editor

Dr. Ana Pimentel

E-Mail Website
Guest Editor
Department of Materials Science, NOVA School of Science and Technology, Lisbon, Portugal
Interests: metal oxide nanostructures; photocatalysis; sensing; microwave irradiation
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Zinc oxide, ZnO, is an inexpensive and abundant material that is nontoxic and chemically stable, which makes it suitable to be used in a vast area of applications. Thus, in the last few years, researchers have focused their attention on developing new ways to synthesize innovative ZnO nanostructures to improve its intrinsic properties and thus properly integrate it in devices. The use of doped, functionalized, and/or hybrid ZnO nanostructures is an effective way to improve devices’ performance. Further, the use of flexible and/or cellulosic substrates to grow ZnO nanostructures brings certain advantages, such as being lightweight, bendable, disposable, and suitable for roll-to-roll manufacturing.

This Special Issue of Materials, entitled “ZnO Materials: Synthesis, Properties, and Applications, vol. II”, is focused on the synthesis and characterization of ZnO nanostructures as well as thin films, with special emphasis on their applications in different areas of research, such as field effect transistors, solar cells, piezoelectric generators, photocatalysis, UV, and gas and bio sensors, as a platform for SERS (Surface-Enhanced Raman Scattering) applications and so on.

We aim to gather a collection of articles (full papers, communications, and reviews) focusing on recent developments in the synthesis and characterization of ZnO nanostructures and thin films, as well as its integration into devices (rigid, flexible and/or cellulosic) covering distinct areas of applications and a wide range of topics.

Dr. Ana Pimentel
Guest Editor

Manuscript Submission Information

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

  • ZnO
  • doping
  • functionalization
  • hybrid
  • sensors
  • photocatalysis
  • transistors
  • optoelectronic
  • antibacterial

Published Papers (7 papers)

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Research

11 pages, 3088 KiB  
Article
Tailoring of the Structural, Optical, and Electrical Characteristics of Sol-Gel-Derived Magnesium-Zinc-Oxide Wide-Bandgap Semiconductor Thin Films via Gallium Doping
by Chien-Yie Tsay, Shih-Ting Chen and Hsuan-Meng Tsai
Materials 2023, 16(19), 6389; https://doi.org/10.3390/ma16196389 - 25 Sep 2023
Cited by 2 | Viewed by 806
Abstract
The Ga-doped Mg0.2Zn0.8O (GMZO) transparent semiconductor thin films were prepared using the sol-gel and spin-coating deposition technique. Changes in the microstructural features, optical parameters, and electrical characteristics of sol-gel-synthesized Mg0.2Zn0.8O (MZO) thin films affected by [...] Read more.
The Ga-doped Mg0.2Zn0.8O (GMZO) transparent semiconductor thin films were prepared using the sol-gel and spin-coating deposition technique. Changes in the microstructural features, optical parameters, and electrical characteristics of sol-gel-synthesized Mg0.2Zn0.8O (MZO) thin films affected by the amount of Ga dopants (0–5 at%) were studied. The results of grazing incidence X-ray diffraction (GIXRD) examination showed that all as-prepared MZO-based thin films had a wurtzite-type structure and hexagonal phase, and the incorporation of Ga ions into the MZO nanocrystals refined the microstructure and reduced the average crystallite size and flatness of surface roughness. Each glass/oxide thin film sample exhibited a higher average transmittance than 91.5% and a lower average reflectance than 9.1% in the visible range spectrum. Experimental results revealed that the optical bandgap energy of the GMZO thin films was slightly higher than that of the MZO thin film; the Urbach energy became wider with increasing Ga doping level. It was found that the 2 at% and 3 at% Ga-doped MZO thin films had better electrical properties than the undoped and 5 at% Ga-doped MZO thin films. Full article
(This article belongs to the Special Issue ZnO Materials: Synthesis, Properties and Applications (Second Volume))
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15 pages, 4251 KiB  
Article
Effect of Al Incorporation on the Structural and Optical Properties of Sol–Gel AZO Thin Films
by Hermine Stroescu, Madalina Nicolescu, Daiana Mitrea, Ecaterina Tenea, Irina Atkinson, Mihai Anastasescu, Jose Maria Calderon-Moreno and Mariuca Gartner
Materials 2023, 16(9), 3329; https://doi.org/10.3390/ma16093329 - 24 Apr 2023
Cited by 2 | Viewed by 1400
Abstract
ZnO and Al-doped ZnO (AZO) thin films were prepared using the sol–gel method and deposited on a Silicon (Si(100)) substrate using the dipping technique. The structure, morphology, thickness, optical constants in the spectral range 300–1700 nm, bandgap (Eg) and photoluminescence (PL) [...] Read more.
ZnO and Al-doped ZnO (AZO) thin films were prepared using the sol–gel method and deposited on a Silicon (Si(100)) substrate using the dipping technique. The structure, morphology, thickness, optical constants in the spectral range 300–1700 nm, bandgap (Eg) and photoluminescence (PL) properties of the films were analyzed using X-ray diffractometry (XRD), X-ray fluorescence (XRF), atomic force microscopy (AFM), scanning electron microscopy (SEM), spectroscopic ellipsometry (SE), Raman analysis and PL spectroscopy. The results of the structure and morphology analyses showed that the thin films are polycrystalline with a hexagonal wurtzite structure, as well as continuous and homogeneous. The PL background and broader peaks observable in the Raman spectra of the AZO film and the slight increase in the optical band gap of the AZO thin film, compared to undoped ZnO, highlight the effect of defects introduced into the ZnO lattice and an increase in the charge carrier density in the AZO film. The PL emission spectra of the AZO thin film showed a strong UV line corresponding to near-band-edge ZnO emission along with weak green and red emission bands due to deep-level defects, attributed to the oxygen-occupied zinc vacancies (OZn lattice defects). Full article
(This article belongs to the Special Issue ZnO Materials: Synthesis, Properties and Applications (Second Volume))
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17 pages, 4673 KiB  
Article
Synthesis, Characterization, and Electronic Properties of ZnO/ZnS Core/Shell Nanostructures Investigated Using a Multidisciplinary Approach
by Jelena Zagorac, Dejan Zagorac, Vesna Šrot, Marjan Ranđelović, Milan Pejić, Peter A. van Aken, Branko Matović and J. Christian Schön
Materials 2023, 16(1), 326; https://doi.org/10.3390/ma16010326 - 29 Dec 2022
Cited by 2 | Viewed by 1822
Abstract
ZnO/ZnS core/shell nanostructures, which are studied for diverse possible applications, ranging from semiconductors, photovoltaics, and light-emitting diodes (LED), to solar cells, infrared detectors, and thermoelectrics, were synthesized and characterized by XRD, HR-(S)TEM, and analytical TEM (EDX and EELS). Moreover, band-gap measurements of the [...] Read more.
ZnO/ZnS core/shell nanostructures, which are studied for diverse possible applications, ranging from semiconductors, photovoltaics, and light-emitting diodes (LED), to solar cells, infrared detectors, and thermoelectrics, were synthesized and characterized by XRD, HR-(S)TEM, and analytical TEM (EDX and EELS). Moreover, band-gap measurements of the ZnO/ZnS core/shell nanostructures have been performed using UV/Vis DRS. The experimental results were combined with theoretical modeling of ZnO/ZnS (hetero)structures and band structure calculations for ZnO/ZnS systems, yielding more insights into the properties of the nanoparticles. The ab initio calculations were performed using hybrid PBE0 and HSE06 functionals. The synthesized and characterized ZnO/ZnS core/shell materials show a unique three-phase composition, where the ZnO phase is dominant in the core region and, interestingly, the auxiliary ZnS compound occurs in two phases as wurtzite and sphalerite in the shell region. Moreover, theoretical ab initio calculations show advanced semiconducting properties and possible band-gap tuning in such ZnO/ZnS structures. Full article
(This article belongs to the Special Issue ZnO Materials: Synthesis, Properties and Applications (Second Volume))
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15 pages, 6143 KiB  
Article
Density-Controlled Growth of ZnO Nanowalls for High-Performance Photocatalysts
by Yu-Cheng Chang, Ying-Ru Lin, Sheng-Wen Chen and Chia-Man Chou
Materials 2022, 15(24), 9008; https://doi.org/10.3390/ma15249008 - 16 Dec 2022
Cited by 3 | Viewed by 1165
Abstract
ZnO nanowires and nanowalls can be fabricated on the glass substrate with a ZnO seed film and low-cost aluminum (Al) foil by the aqueous solution method (ASM), respectively. The different concentrations of ZnO precursors can use to control the densities of ZnO nanowalls. [...] Read more.
ZnO nanowires and nanowalls can be fabricated on the glass substrate with a ZnO seed film and low-cost aluminum (Al) foil by the aqueous solution method (ASM), respectively. The different concentrations of ZnO precursors can use to control the densities of ZnO nanowalls. In addition, FESEM, FETEM, EDS, XRD, XPS, and CL were used to evaluate the characteristics of ZnO nanowalls. The ZnO nanowalls exhibited higher photocatalytic efficiency (99.4%) than that of ZnO nanowires (53.3%) for methylene blue (MB) degradation under UVC light irradiation at the ZnO precursors of 50 mM. This result is attributed to ZnO nanowalls with Al-doped, which can improve the separation of photogenerated electron-hole pairs for enhanced photocatalytic activity. In addition, ZnO nanowalls can also reveal higher photocatalytic activity for the degradation of tetracycline capsules (TC) rather than commercial ZnO nanopowder under UVC light irradiation. The superoxide and hydroxyl radicals play essential roles in the degradation of MB and TC solutions by the radical-trapping experiment. Furthermore, the ZnO nanowalls exhibit excellent recycling and reuse capacity for up to four cycles for the degradation of MB and TC. This study highlights the potential use of ZnO nanowalls directly grown on commercial and low-cost Al foil as noble metal-free photocatalysis. Full article
(This article belongs to the Special Issue ZnO Materials: Synthesis, Properties and Applications (Second Volume))
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18 pages, 3320 KiB  
Article
Thermoelectric, Electrochemical, & Dielectric Properties of Four ZnO Nanostructures
by Rusiri Rathnasekara, Grant Mayberry and Parameswar Hari
Materials 2022, 15(24), 8816; https://doi.org/10.3390/ma15248816 - 09 Dec 2022
Cited by 3 | Viewed by 1461
Abstract
In this work, we investigated the thermoelectric, electrochemical, and dielectric properties of four different ZnO morphologies, namely nanoribbons, nanorods, nanoparticles, and nanoshuttles. Temperature-dependent Seebeck coefficients were observed using thermoelectric measurements, which confirmed that all synthesized ZnO nanostructures are n-type semiconductors. The Van der [...] Read more.
In this work, we investigated the thermoelectric, electrochemical, and dielectric properties of four different ZnO morphologies, namely nanoribbons, nanorods, nanoparticles, and nanoshuttles. Temperature-dependent Seebeck coefficients were observed using thermoelectric measurements, which confirmed that all synthesized ZnO nanostructures are n-type semiconductors. The Van der Pauw method was applied to measure electrical conductivity, which was also used to calculate the thermal activation energy. Electrochemical properties were analyzed by cyclic voltammetry techniques under five different optical filters. Electrical conductivity of ZnO morphologies showed an increasing trend with increasing temperature. The highest electrical conductivity (1097.60 Ω−1 m−1) and electronic thermal conductivity (1.16×10−4 W/mK) were obtained for ZnO nanorods at 425 K, whereas ZnO nanoshuttles carried the lowest electrical conductivity (1.10 × 10−4 Ω−1 m−1) and electronic thermal conductivity (8.72 × 10−7 W/mK) at 325 K. ZnO nanorods obtained the maximum Power factor value in all temperature ranges. All nanostructures showed electro-catalytic performance with different optical filters. From impedance spectroscopy analysis, ZnO nanorods showed the highest dielectric constant at high frequencies (>1 MHz) at 2.02 ± 0.06, while ZnO nanoshuttles gave the highest dielectric constant at low frequencies (<100 Hz) at 9.69 ± 0.05. These results indicate that ZnO nanorods have the most favorable thermoelectric, electrochemical, and dielectric properties compared to all other ZnO morphologies. Full article
(This article belongs to the Special Issue ZnO Materials: Synthesis, Properties and Applications (Second Volume))
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18 pages, 6692 KiB  
Article
Polar and Non-Polar Zn1−xMgxO:Sb Grown by MBE
by Ewa Przezdziecka, Karolina M Paradowska, Rafal Jakiela, Serhii Kryvyi, Eunika Zielony, Ewa Placzek-Popko, Wojciech Lisowski, Piotr Sybilski, Dawid Jarosz, Abinash Adhikari, Marcin Stachowicz and Adrian Kozanecki
Materials 2022, 15(23), 8409; https://doi.org/10.3390/ma15238409 - 25 Nov 2022
Viewed by 1270
Abstract
The article presents a systematic study of Sb-doped Zn1−xMgxO layers, with various concentrations of Mg, that were successfully grown by plasma-assisted MBE on polar a- and c-oriented and non-polar r-oriented sapphire substrates. X-ray diffraction confirmed the [...] Read more.
The article presents a systematic study of Sb-doped Zn1−xMgxO layers, with various concentrations of Mg, that were successfully grown by plasma-assisted MBE on polar a- and c-oriented and non-polar r-oriented sapphire substrates. X-ray diffraction confirmed the polar c-orientation of alloys grown on c-and a-oriented sapphire and non-polar structures grown on r-oriented substrates. A uniform depth distribution of the Sb dopant at level of 2 × 1020 cm−3 was determined by SIMS measurements. Raman spectroscopy revealed the presence of Sb-related modes in all samples. It also showed that Mg alloying reduces the compressive strain associated with Sb doping in ZnO. XPS analysis indicates that the chemical state of Sb atoms in ZnMgO is 3+, suggesting a substitutional position of SbZn, probably associated with two VZn vacancies. Luminescence and transmission spectra were measured to determine the band gaps of the Zn1−xMgxO layers. The band gap energies extracted from the transmittance measurements differ slightly for the a, c, and r substrate orientations, and the differences increase with increasing Mg content, despite identical growth conditions. The differences between the energy gaps, determined from transmission and PL peaks, are closely correlated with the Stokes shift and increase with the Mg content in the analyzed series of ZnMgO layers. Full article
(This article belongs to the Special Issue ZnO Materials: Synthesis, Properties and Applications (Second Volume))
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10 pages, 3088 KiB  
Article
p-ZnO/n-ZnMgO Nanoparticle-Based Heterojunction UV Light-Emitting Diodes
by Islam Mohammad Shafiqul, Toshiyuki Yoshida and Yasuhisa Fujita
Materials 2022, 15(23), 8348; https://doi.org/10.3390/ma15238348 - 24 Nov 2022
Viewed by 1671
Abstract
Heterojunction light-emitting diodes (LEDs), based on p-type ZnO and n-type ZnMgO nanoparticles, have been demonstrated. ZnMgO nanoparticles were prepared by the thermal diffusion of Mg onto ZnO nanoparticles. p-ZnO/GZO homostructure LEDs and p-ZnO/n-ZnMgO/GZO heterostructure LEDs have been fabricated using ZnO and ZnMgO nanoparticles. [...] Read more.
Heterojunction light-emitting diodes (LEDs), based on p-type ZnO and n-type ZnMgO nanoparticles, have been demonstrated. ZnMgO nanoparticles were prepared by the thermal diffusion of Mg onto ZnO nanoparticles. p-ZnO/GZO homostructure LEDs and p-ZnO/n-ZnMgO/GZO heterostructure LEDs have been fabricated using ZnO and ZnMgO nanoparticles. By comparing the characteristic results of these diodes, it can be seen that LEDs with the p-ZnO/n-ZnMgO/GZO structure showed better I–V characteristics with a lower current density leakage than those with the p-ZnO/GZO LED structure. Moreover, the emission intensity was improved by adding the ZnMgO NP layer to the LEDs. These results show that the ZnMgO NP layer acts as a hetero-barrier layer that suppresses the diffusion of holes into the n-type layer and confines holes to the p-type layer. Full article
(This article belongs to the Special Issue ZnO Materials: Synthesis, Properties and Applications (Second Volume))
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