Special Issue "Functional Oxide Based Thin-Film Materials"

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystalline Materials".

Deadline for manuscript submissions: closed (30 September 2018)

Special Issue Editor

Guest Editor
Prof. Dr. Dong-Sing Wuu

Department of Materials Science and Engineering, National Chung Hsing University, 145 Xingda Road, Taichung 40227, Taiwan
Website | E-Mail
Interests: epitaxial materials; thin films and plasma processing; optoelectronic devices

Special Issue Information

Dear Colleagues,

Functional oxide based thin-film materials are extraordinary multifunctional crystals with a huge range of emerging application domains such as sensors, displays, light emitters, photovoltaics, nanotechnology, spintronics, piezoelectric motors, biotechnology, capacitors, transparent electronics, and next-generation memories.

The functional oxide crystal has several favorable properties, including good transparency, high conductivity, wide bandgap, and strong luminescence. Thin-film oxide materials have been grown on various substrates by sputtering, hydrothermal, sol-gel, Plasma CVD, MOCVD, PLD, HVPE, MBE etc. A number of breakthroughs over the past few years have driven an exponential energy in research activity of this field.

We invite investigators to submit papers which discuss the development of functional oxide -based thin-film materials, including thin film, nanostructured, and multilayered forms. Mixing oxide-based alloys with other materials could allow for the possible fabrication of advanced devices. Furthermore, the diluted magnetic crystals and combination with two-dimensional materials are welcomed.

The potential topics include, but again are not limited to:

  • Crystal growth of functional oxide based thin-film materials, including the modelling of crystal growth
  • Property characterization (optic, electric, piezoelectric, ferromagnetic properties, etc.) and their relationships to external conditions, such as electric field, photo pumping, current injection, stress, temperature, etc.
  • Advances in device development of finctional oxide based thin-film materials
  • Microstructure analysis and micromacro correlation of the observed properties and their modelling
  • Characterization or modeling of micro-, nano-domain behavior in functional oxide based crystals
  • Novel applications of diluted magnetic oxide crystals and combination with two-dimensional materials
  • Reliability and stability of the crystal properties, including aging and fatigue, etc.

Prof. Dr. Dong-Sing Wuu
Guest Editor

Manuscript Submission Information

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Keywords

  • Functional oxide-based compounds
  • Thin film growth
  • Material characterization
  • Device fabrication and applications

Published Papers (7 papers)

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Research

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Open AccessArticle Fabrication of GaOx Confinement Structure for InGaN Light Emitter Applications
Crystals 2018, 8(11), 418; https://doi.org/10.3390/cryst8110418
Received: 29 September 2018 / Revised: 2 November 2018 / Accepted: 4 November 2018 / Published: 7 November 2018
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Abstract
An indium gallium nitride (InGaN) light-emitting diode (LED) with an embedded porous GaN reflector and a current confined aperture is presented in this study. Eight pairs of n+-GaN:Si/GaN in stacked structure are transformed into a conductive, porous GaN/GaN reflector through an
[...] Read more.
An indium gallium nitride (InGaN) light-emitting diode (LED) with an embedded porous GaN reflector and a current confined aperture is presented in this study. Eight pairs of n+-GaN:Si/GaN in stacked structure are transformed into a conductive, porous GaN/GaN reflector through an electrochemical wet-etching process. Porous GaN layers surrounding the mesa region were transformed into insulating GaOx layers in a reflector structure through a lateral photoelectrochemical (PEC) oxidation process. The electroluminescence emission intensity was localized at the central mesa region by forming the insulating GaOx layers in a reflector structure as a current confinement aperture structure. The PEC-LED structure with a porous GaN reflector and a current-confined aperture surrounded by insulating GaOx layers has the potential for nitride-based resonance cavity light source applications. Full article
(This article belongs to the Special Issue Functional Oxide Based Thin-Film Materials)
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Open AccessArticle Highly Visible Photoluminescence from Ta-Doped Structures of ZnO Films Grown by HFCVD
Crystals 2018, 8(10), 395; https://doi.org/10.3390/cryst8100395
Received: 27 July 2018 / Revised: 30 August 2018 / Accepted: 3 September 2018 / Published: 22 October 2018
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Abstract
Tantalum-doped ZnO structures (ZnO:Ta) were synthesized, and some of their characteristics were studied. ZnO material was deposited on silicon substrates by using a hot filament chemical vapor deposition (HFCVD) reactor. The raw materials were a pellet made of a mixture of ZnO and
[...] Read more.
Tantalum-doped ZnO structures (ZnO:Ta) were synthesized, and some of their characteristics were studied. ZnO material was deposited on silicon substrates by using a hot filament chemical vapor deposition (HFCVD) reactor. The raw materials were a pellet made of a mixture of ZnO and Ta2O5 powders, and molecular hydrogen was used as a reactant gas. The percentage of tantalum varied from 0 to 500 mg by varying the percentages of tantalum oxide in the mixture of the pellet source, by holding a fixed amount of 500 mg of ZnO in all experiments. X-ray diffractograms confirmed the presence of zinc oxide in the wurtzite phase, and metallic zinc with a hexagonal structure, and no other phase was detected. Displacements to lower angles of reflection peaks, compared with those from samples without doping, were interpreted as the inclusion of the Ta atoms in the matrix of the ZnO. This fact was confirmed by energy dispersive X-ray spectrometry (EDS), and X-ray diffraction (XRD) measurements. From scanning electron microscopy (SEM) images from undoped samples, mostly micro-sized semi-spherical structures were seen, while doped samples displayed a trend to grow as nanocrystalline rods. The presence of tantalum during the synthesis affected the growth direction. Green photoluminescence was observed by the naked eye when Ta-doped samples were illuminated by ultraviolet radiation and confirmed by photoluminescence (PL) spectra. The PL intensity on the Ta-doped ZnO increased from those undoped samples up to eight times. Full article
(This article belongs to the Special Issue Functional Oxide Based Thin-Film Materials)
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Open AccessArticle Simulation and Analysis of Single-Mode Microring Resonators in Lithium Niobate Thin Films
Crystals 2018, 8(9), 342; https://doi.org/10.3390/cryst8090342
Received: 4 August 2018 / Revised: 21 August 2018 / Accepted: 22 August 2018 / Published: 24 August 2018
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Abstract
The single-mode microring resonators on lithium niobate thin films were designed and simulated using 2.5-D variational finite difference time domain mode simulations from Lumerical mode Solutions. The single-mode conditions and the propagation losses of lithium niobate planar waveguide with different SiO2 cladding
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The single-mode microring resonators on lithium niobate thin films were designed and simulated using 2.5-D variational finite difference time domain mode simulations from Lumerical mode Solutions. The single-mode conditions and the propagation losses of lithium niobate planar waveguide with different SiO2 cladding layer thicknesses were studied and compared systematically. The optimization of design parameters such as radii of microrings and gap sizes between channel and ring waveguides were determined. The key issues affecting the resonator design such as free spectral range and Quality Factor were discussed. The microring resonators had radius R = 20 μm, and their transmission spectrum had been tuned using the electro-optical effect. Full article
(This article belongs to the Special Issue Functional Oxide Based Thin-Film Materials)
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Open AccessArticle Investigation of HfO2 Thin Films on Si by X-ray Photoelectron Spectroscopy, Rutherford Backscattering, Grazing Incidence X-ray Diffraction and Variable Angle Spectroscopic Ellipsometry
Crystals 2018, 8(6), 248; https://doi.org/10.3390/cryst8060248
Received: 23 April 2018 / Revised: 31 May 2018 / Accepted: 5 June 2018 / Published: 12 June 2018
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Abstract
Hafnium oxide (HfO2) thin films have been made by atomic vapor deposition (AVD) onto Si substrates under different growth temperature and oxygen flow. The effect of different growth conditions on the structure and optical characteristics of deposited HfO2 film has
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Hafnium oxide (HfO2) thin films have been made by atomic vapor deposition (AVD) onto Si substrates under different growth temperature and oxygen flow. The effect of different growth conditions on the structure and optical characteristics of deposited HfO2 film has been studied using X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS), grazing incidence X-ray diffraction (GIXRD) and variable angle spectroscopic ellipsometry (VASE). The XPS measurements and analyses revealed the insufficient chemical reaction at the lower oxygen flow rate and the film quality improved at higher oxygen flow rate. Via GIXRD, it was found that the HfO2 films on Si were amorphous in nature, as deposited at lower deposition temperature, while being polycrystalline at higher deposition temperature. The structural phase changes from interface to surface were demonstrated. The values of optical constants and bandgaps and their variations with the growth conditions were determined accurately from VASE and XPS. All analyses indicate that appropriate substrate temperature and oxygen flow are essential to achieve high quality of the AVD-grown HfO2 films. Full article
(This article belongs to the Special Issue Functional Oxide Based Thin-Film Materials)
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Open AccessArticle Effect of Lithium Doping on Microstructural and Optical Properties of ZnO Nanocrystalline Films Prepared by the Sol-Gel Method
Crystals 2018, 8(5), 228; https://doi.org/10.3390/cryst8050228
Received: 28 April 2018 / Revised: 16 May 2018 / Accepted: 16 May 2018 / Published: 19 May 2018
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Abstract
The Zn1−xLixO (x = 0, 0.01, 0.03, and 0.05) nanocrystalline films were synthesized on silicon (Si) substrates by using the sol-gel method. The crystal structure and surface morphology of these films were investigated by X-ray diffraction (XRD) and field
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The Zn1−xLixO (x = 0, 0.01, 0.03, and 0.05) nanocrystalline films were synthesized on silicon (Si) substrates by using the sol-gel method. The crystal structure and surface morphology of these films were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). We observed that the average grain size was gradually reduced with increasing doping Li content. Photoluminescence (PL) spectra show that increasing the Li content will deteriorate the crystalline quality and result in the decrease of ultraviolet emission from the excitonic recombination and the enhancement of visible emission from the recombination between the intrinsic defects. The current-voltage properties of Zn1−xLixO nanocrystalline films were also studied under dark and photo-illumination for photo-detection applications. The normalized photo-to-dark-current ratio (Iphoto − Idark)/Idark has been enhanced from 315 to 4161 by increasing the Li content of the Zn1−xLixO nanocrystalline films from zero to 0.05. Full article
(This article belongs to the Special Issue Functional Oxide Based Thin-Film Materials)
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Open AccessArticle Epitaxial Crystallization of Precisely Methyl-Substituted Polyethylene Induced by Carbon Nanotubes and Graphene
Crystals 2018, 8(4), 168; https://doi.org/10.3390/cryst8040168
Received: 9 March 2018 / Revised: 11 April 2018 / Accepted: 11 April 2018 / Published: 16 April 2018
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Abstract
How large of a substituent/branch a polyethylene possesses that can still be induced by nanofillers to form ordered chain structures is interesting, but uncertain. To solve this problem, precisely methyl-substituted polyethylene (PE21M) was chosen as a model to prepare its one-dimensional and two-dimensional
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How large of a substituent/branch a polyethylene possesses that can still be induced by nanofillers to form ordered chain structures is interesting, but uncertain. To solve this problem, precisely methyl-substituted polyethylene (PE21M) was chosen as a model to prepare its one-dimensional and two-dimensional nanocomposites with carbon nanotubes (CNTs) and graphene via solution crystallization. It is shown that kebab-like and rod-like nanofiller-induced crystals were separately observed on the surfaces of CNTs and graphene and the density of rod-like crystals is significantly less than kebab-like ones. The results of differential scanning calorimetry (DSC) and X-ray diffraction (XRD) reveal that CNTs and graphene cannot induce polymers with the substituent volume greater than, or equal to, 2 Å (methyl) to form ordered lattice structure, but CNTs exhibit the better nucleation effect, providing us with guidance to manipulate the physical performance of polymer composites on the basis of the size of the substituent and the type of nanofiller. Full article
(This article belongs to the Special Issue Functional Oxide Based Thin-Film Materials)
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Review

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Open AccessReview One-Dimensional Zinc Oxide Nanomaterials for Application in High-Performance Advanced Optoelectronic Devices
Crystals 2018, 8(5), 223; https://doi.org/10.3390/cryst8050223
Received: 27 April 2018 / Revised: 13 May 2018 / Accepted: 13 May 2018 / Published: 18 May 2018
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Abstract
Unlike conventional bulk or film materials, one-dimensional (1D) semiconducting zinc oxide (ZnO) nanostructures exhibit excellent photoelectric properties including ultrahigh intrinsic photoelectric gain, multiple light confinement, and subwavelength size effects. Compared with polycrystalline thin films, nanowires usually have high phase purity, no grain boundaries,
[...] Read more.
Unlike conventional bulk or film materials, one-dimensional (1D) semiconducting zinc oxide (ZnO) nanostructures exhibit excellent photoelectric properties including ultrahigh intrinsic photoelectric gain, multiple light confinement, and subwavelength size effects. Compared with polycrystalline thin films, nanowires usually have high phase purity, no grain boundaries, and long-distance order, making them attractive for carrier transport in advanced optoelectronic devices. The properties of one-dimensional nanowires—such as strong optical absorption, light emission, and photoconductive gain—could improve the performance of light-emitting diodes (LEDs), photodetectors, solar cells, nanogenerators, field-effect transistors, and sensors. For example, ZnO nanowires behave as carrier transport channels in photoelectric devices, decreasing the loss of the light-generated carrier. The performance of LEDs and photoelectric detectors based on nanowires can be improved compared with that of devices based on polycrystalline thin films. This article reviews the fabrication methods of 1D ZnO nanostructures—including chemical vapor deposition, hydrothermal reaction, and electrochemical deposition—and the influence of the growth parameters on the growth rate and morphology. Important applications of 1D ZnO nanostructures in optoelectronic devices are described. Several approaches to improve the performance of 1D ZnO-based devices, including surface passivation, localized surface plasmons, and the piezo-phototronic effect, are summarized. Full article
(This article belongs to the Special Issue Functional Oxide Based Thin-Film Materials)
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