Crystals

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7 pages, 2134 KiB

Open AccessArticle

Synthesis of GaN Crystals by Nitrogen Pressure-Controlled Recrystallization Technique in Na Alloy Melt

by Xi Wu, Hongcheng Wang, Dongxiong Ling, Chuanyu Jia, Wei Lü, Ye Liu, Fei Zhou and Zhenrong Li

Crystals 2021, 11(9), 1058; https://doi.org/10.3390/cryst11091058 - 02 Sep 2021

Cited by 2 | Viewed by 1938

Abstract

GaN crystals are synthesized by recrystallization technique in Na-Li-Ca alloy melt under different N₂ pressure. X-ray powder diffraction results confirm that the structure of crystals is GaN with wurtzite type and there still have raw powders remaining. The total mass of GaN [...] Read more.

GaN crystals are synthesized by recrystallization technique in Na-Li-Ca alloy melt under different N₂ pressure. X-ray powder diffraction results confirm that the structure of crystals is GaN with wurtzite type and there still have raw powders remaining. The total mass of GaN decreases with the nitrogen pressure reduces. No GaN crystals are found in the solution under N₂ pressure of 0.4 MPa. The morphologies of the crystal are mainly prism and pyramid. The size of the crystal increases when closer to the liquid surface. Raman spectra indicates that these crystals are stress-free and crystal grown at 3.6 MPa has high structural quality or low impurity concentrations. The results reveal that the solubility and supersaturation of the solution are controlled by N₂ pressure. The principle of GaN crystal synthesis by recrystallization is discussed. Full article

(This article belongs to the Special Issue Synthesis, Structure and Property Analysis of Crystalline Layers)

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16 pages, 5445 KiB

Open AccessArticle

Crystallization and Investigation of the Structural and Optical Properties of Ce³⁺-Doped Y_3−xCa_xAl_5−ySi_yO₁₂ Single Crystalline Film Phosphors

by Vitalii Gorbenko, Tetiana Zorenko, Sandra Witkiewicz-Łukaszek, Anna Shakhno, Andres Osvet, Miroslaw Batentschuk, Aleksandr Fedorov and Yuriy Zorenko

Crystals 2021, 11(7), 788; https://doi.org/10.3390/cryst11070788 - 06 Jul 2021

Cited by 5 | Viewed by 1976

Abstract

This work is devoted to the crystallization and investigation of the optical properties of single crystalline films (SCFs) of Ce³⁺-doped Y_3−xCa_xAl_5−ySi_yO₁₂ garnet, where the content of Ca²⁺ and Si⁴⁺ cations [...] Read more.

This work is devoted to the crystallization and investigation of the optical properties of single crystalline films (SCFs) of Ce³⁺-doped Y_3−xCa_xAl_5−ySi_yO₁₂ garnet, where the content of Ca²⁺ and Si⁴⁺ cations varied in the x = 0.13–0.52 and y = 0.065–0.5 ranges, respectively. The SCF samples were grown using the liquid phase epitaxy technique onto Y₃Al₅O₁₂ substrates from the melt solution with equimolar Ca and Si content using PbO-B₂O₃ flux. However, the Ca and Si concentration in Y_3−xCa_x Al_5−ySi_yO₁₂:Ce SCFs is not equal: the Ca²⁺ content was systematically larger than that of Si⁴⁺, and the Ca²⁺ excess is compensated for by the Ce⁴⁺ ion formation. The absorption, scintillation, and luminescent properties of Y_3−xCa_xAl_5−ySi_yO₁₂:Ce SCFs with different Ca/Si concentrations were investigated and compared with the sample of YAG:Ce SCF. Due to the creation of Ce⁴⁺ ions, the as-grown Y_3−xCa_xAl_5−ySi_yO₁₂:Ce SCFs show relatively low light yield (LY) under α–particle excitation but a fast scintillation response with a decay time in the ns range. After SCF annealing in the reducing (N₂ + H₂) atmosphere at T > 1000 °C, the recharging of Ce⁴⁺→Ce³⁺ ions occurs. Furthermore, the samples annealed at 1300 °C SCF possess an LY of about 40% in comparison with the reference YAG:Ce SCF and scintillation decay kinetics much closer to that of the SCF counterpart. Due to Ca²⁺ and Si⁴⁺ alloying, the Ce³⁺ emission spectra in Y_3−xCa_xAl_5−ySi_yO₁₂ SCFs are extended to the red range in comparison with the spectra of YAG:Ce SCF. Such an extension is caused by the Ce³⁺ multicenter formation at the substitutions of both Y³⁺ and Ca²⁺ dodecahedral positions in the hosts of these mixed garnets. Full article

(This article belongs to the Special Issue Synthesis, Structure and Property Analysis of Crystalline Layers)

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18 pages, 25450 KiB

Open AccessArticle

The Influence of Recrystallization on Zinc Oxide Microstructures Synthesized with Sol–Gel Method on Scintillating Properties

by Ewelina Nowak, Mirosław Szybowicz, Alicja Stachowiak, Daria Piechowiak, Andrzej Miklaszewski, Marcin E. Witkowski, Michał Makowski, Winicjusz Drozdowski, Kazimierz Paprocki, Kazimierz Fabisiak, Szymon Łoś and Marek Trzcinski

Crystals 2021, 11(5), 533; https://doi.org/10.3390/cryst11050533 - 11 May 2021

Cited by 3 | Viewed by 2762

Abstract

Zinc oxide (ZnO) is one of the wide-bandgap semiconductors, which may be useful in a plethora of electronic, optical, piezoelectric, and scintillating applications. The following article consists in a structural and luminescence analysis of ZnO microfilms grown on a sapphire substrate with a [...] Read more.

Zinc oxide (ZnO) is one of the wide-bandgap semiconductors, which may be useful in a plethora of electronic, optical, piezoelectric, and scintillating applications. The following article consists in a structural and luminescence analysis of ZnO microfilms grown on a sapphire substrate with a sol–gel method. The films were annealed at different temperatures. The structures were investigated with the XRD and Raman methods, by which the influence of the substrate on the structure of the film was determined. The luminescence of films was investigated with room-temperature fluorescence, radioluminescence, and thermoluminescence. Full article

(This article belongs to the Special Issue Synthesis, Structure and Property Analysis of Crystalline Layers)

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10 pages, 3703 KiB

Open AccessArticle

Improving the Ionic Conductivity of the LLZO–LZO Thin Film through Indium Doping

by Zongkai Yan, Yu Song, Shuai Wu, Yongmin Wu, Shipai Song, Xinyu Wang, Yanlin Zhu, Junsong Chen, Rui Guo and Yong Xiang

Crystals 2021, 11(4), 426; https://doi.org/10.3390/cryst11040426 - 15 Apr 2021

Cited by 5 | Viewed by 4418

Abstract

A solid-state electrolyte with an ionic conductivity comparable to that of a liquid electrolyte is demanded of all-solid-state lithium-ion batteries. Li₇La₃Zr₂O₁₂ (LLZO) is considered to be a promising candidate due to its good thermal stability, high [...] Read more.

A solid-state electrolyte with an ionic conductivity comparable to that of a liquid electrolyte is demanded of all-solid-state lithium-ion batteries. Li₇La₃Zr₂O₁₂ (LLZO) is considered to be a promising candidate due to its good thermal stability, high ionic conductivity, and wide electrochemical window. However, the synthesis of a stable cubic-phase LLZO thin film with enhanced densification at a relatively low thermal treatment temperature is yet to be developed. Indium is predicted to be a possible dopant to stabilize the cubic-phase LLZO (c-LLZO). Herein, via a nanolayer stacking process, a LLZO–Li₂CO₃–In₂O₃ multilayer solid electrolyte precursor was obtained. After thermal annealing at different temperatures, the effects of indium doping on the formation of c-LLZO and the ionic conductivities of the prepared LLZO–LZO thin film were systematically investigated. The highest ionic conductivity of 9.6 × 10⁻⁶ S·cm^–1 was obtained at an annealing temperature of 800 °C because the incorporation of indium promoted the formation of c-LLZO and the highly conductive LLZO–LZO interfaces. At the end, a model of LLZO–LZO interface-enhancing ionic conductivity was proposed. This work provides a new approach for the development of low-temperature LLZO-based, solid-state thin-film batteries. Full article

(This article belongs to the Special Issue Synthesis, Structure and Property Analysis of Crystalline Layers)

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16 pages, 5065 KiB

Open AccessArticle

Impact of CdCl₂ Treatment in CdTe Thin Film Grown on Ultra-Thin Glass Substrate via Close Spaced Sublimation

by Nowshad Amin, Mohammad Rezaul Karim and Zeid Abdullah ALOthman

Crystals 2021, 11(4), 390; https://doi.org/10.3390/cryst11040390 - 07 Apr 2021

Cited by 18 | Viewed by 2843

Abstract

In this study, close-spaced sublimation (CSS) grown cadmium telluride (CdTe) thin films with good adhesion to 100 µm thin Schott D263T ultra-thin glass (UTG) were investigated. Cadmium chloride (CdCl₂) treatment in vacuum ambient was executed to enhance the film quality and [...] Read more.

In this study, close-spaced sublimation (CSS) grown cadmium telluride (CdTe) thin films with good adhesion to 100 µm thin Schott D263T ultra-thin glass (UTG) were investigated. Cadmium chloride (CdCl₂) treatment in vacuum ambient was executed to enhance the film quality and optoelectrical properties of CdTe thin film. The post-deposition annealing temperature ranging from 360–420 °C was examined to improve the CdTe film quality on UTG substrate. Various characterization techniques have been used to observe the compositional, morphological, optical, as well as electrical properties. Scanning electron microscopy (SEM) verified that the CdTe morphology and grain size could be controlled via CdCl₂ treatment temperature. Energy Dispersive X-Ray Analysis (EDX) results confirmed that the annealing temperature range of 375–390 °C yielded the stoichiometric CdTe films. UV-Vis analysis estimated the post-treatment bandgap energy in the range of 1.39–1.46 eV. Carrier concentration and resistivity were obtained in the order of 10¹³ cm⁻³ and 10⁴ Ω-cm, respectively. All the experimental results established that the CdCl₂ treatment temperature range of 390–405 °C might be considered as the optimum process temperature for the deposition of CdTe solar cell on UTG substrate in close-spaced sublimation (CSS) method. Full article

(This article belongs to the Special Issue Synthesis, Structure and Property Analysis of Crystalline Layers)

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13 pages, 10225 KiB

Open AccessArticle

The Role of Deposition Temperature in the Photovoltaic Properties of RF-Sputtered CdSe Thin Films

by Hasrul Nisham Rosly, Kazi Sajedur Rahman, Siti Fazlili Abdullah, Muhammad Najib Harif, Camellia Doroody, Puvaneswaran Chelvanathan, Halina Misran, Kamaruzzaman Sopian and Nowshad Amin

Crystals 2021, 11(1), 73; https://doi.org/10.3390/cryst11010073 - 17 Jan 2021

Cited by 17 | Viewed by 2753

Abstract

Cadmium selenide (CdSe) thin films were grown on borosilicate glass substrates using the RF magnetron sputtering method. In this study, CdSe thin film was deposited at a deposition temperature in the range of 25 °C to 400 °C. The influence of deposition or [...] Read more.

Cadmium selenide (CdSe) thin films were grown on borosilicate glass substrates using the RF magnetron sputtering method. In this study, CdSe thin film was deposited at a deposition temperature in the range of 25 °C to 400 °C. The influence of deposition or growth temperature on the structural, morphological, and opto-electrical properties of CdSe films was investigated elaborately to achieve a good-quality window layer for solar-cell applications. The crystal structure, surface morphology, and opto-electrical characteristics of sputtered CdSe films were determined using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV–Vis spectrophotometry, and Hall effect measurement, respectively. The XRD results revealed the polycrystalline nature of CdSe, with a hexagonal structure having a strong preferential orientation toward the (002) plane. As evident from the FESEM images, the average grain size and surface morphology of the films were dependent on deposition temperatures. The carrier concentration was obtained as 10¹⁴ cm⁻³. The band gap in the range of 1.65–1.79 eV was found. The explored results suggested that sputtered CdSe thin film deposited at 300 °C has the potential to be used as a window layer in solar cells. Full article

(This article belongs to the Special Issue Synthesis, Structure and Property Analysis of Crystalline Layers)

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11 pages, 1742 KiB

Open AccessArticle

Non-Isothermal Crystallization Behavior of Poly(vinylidene fluoride) in Dialkyl Phthalate Diluents during Thermally Induced Phase Separation Process

by Yakai Lin, Yuanhui Tang, Lin Wang and Xiaolin Wang

Crystals 2020, 10(9), 782; https://doi.org/10.3390/cryst10090782 - 03 Sep 2020

Cited by 6 | Viewed by 1866

Abstract

The non-isothermal crystallization behavior of poly(vinylidene fluoride) (PVDF) in dialkyl phthalate diluents during the thermally induced phase separation (TIPS) process was investigated by differential scanning calorimetry (DSC) at various cooling rates. Dialkyl phthalates with different alkyl chain-length, namely dimethyl phthalate (DMP), diethyl phthalate [...] Read more.

The non-isothermal crystallization behavior of poly(vinylidene fluoride) (PVDF) in dialkyl phthalate diluents during the thermally induced phase separation (TIPS) process was investigated by differential scanning calorimetry (DSC) at various cooling rates. Dialkyl phthalates with different alkyl chain-length, namely dimethyl phthalate (DMP), diethyl phthalate (DEP) and dibutyl phthalate (DBP), were used as the diluent. The effects of alkyl chain-length of dialkyl phthalate and cooling rate on the non-isothermal crystallization behavior as implied by the Avrami analysis modified by Jeziorny and Mo’s analysis were determined. The values of half-time,

t_{1 / 2}

, and the parameters

Z_{c}

and

F (t)

, which characterized the kinetics of non-isothermal crystallization, showed that the crystallization rate increased with the increase of the alkyl chain-length of dialkyl phthalate due to the lower compatibility between PVDF and dialkyl phthalate. Moreover, the alkyl chain-length of dialkyl phthalate also has a great impact on the compact spherulitic structure of PVDF membranes prepared from different PVDF/dialkyl phthalate blends. With the decrease of the alkyl chain-length of dialkyl phthalate, the number of spherulites increased and the size of spherulites became smaller. This research thus not only proves the effects of alkyl chain-length of dialkyl phthalate on the non-isothermal crystallization behavior of PVDF, but also provides a systematic strategy to evaluate a single diluent during the TIPS process. Full article

(This article belongs to the Special Issue Synthesis, Structure and Property Analysis of Crystalline Layers)

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Review

Jump to: Research

31 pages, 1936 KiB

Open AccessReview

Graphene to Advanced MoS₂: A Review of Structure, Synthesis, and Optoelectronic Device Application

by Tahreem Nawz, Amna Safdar, Muzammil Hussain, Dae Sung Lee and Muhammad Siyar

Crystals 2020, 10(10), 902; https://doi.org/10.3390/cryst10100902 - 06 Oct 2020

Cited by 34 | Viewed by 5790

Abstract

In contrast to zero-dimensional (0D), one-dimensional (1D), and even their bulk equivalents, in two-dimensional (2D) layered materials, charge carriers are confined across thickness and are empowered to move across the planes. The features of 2D structures, such as quantum confinement, high absorption coefficient, [...] Read more.

In contrast to zero-dimensional (0D), one-dimensional (1D), and even their bulk equivalents, in two-dimensional (2D) layered materials, charge carriers are confined across thickness and are empowered to move across the planes. The features of 2D structures, such as quantum confinement, high absorption coefficient, high surface-to-volume ratio, and tunable bandgap, make them an encouraging contestant in various fields such as electronics, energy storage, catalysis, etc. In this review, we provide a gentle introduction to the 2D family, then a brief description of transition metal dichalcogenides (TMDCs), mainly focusing on MoS₂, followed by the crystal structure and synthesis of MoS₂, and finally wet chemistry methods. Later on, applications of MoS₂ in dye-sensitized, organic, and perovskite solar cells are discussed. MoS₂ has impressive optoelectronic properties; due to the fact of its tunable work function, it can be used as a transport layer, buffer layer, and as an absorber layer in heterojunction solar cells. A power conversion efficiency (PCE) of 8.40% as an absorber and 13.3% as carrier transfer layer have been reported for MoS₂-based organic and perovskite solar cells, respectively. Moreover, MoS₂ is a potential replacement for the platinum counter electrode in dye-sensitized solar cells with a PCE of 7.50%. This review also highlights the incorporation of MoS₂ in silicon-based heterostructures where graphene/MoS₂/n-Si-based heterojunction solar cell devices exhibit a PCE of 11.1%. Full article

(This article belongs to the Special Issue Synthesis, Structure and Property Analysis of Crystalline Layers)

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