Crystals

11 pages, 3609 KiB

Open AccessArticle

Pulse-Propagation Modeling and Experiment for Femtosecond-Laser Writing of Waveguide in Nd:YAG

by Tao Feng, Pankaj K. Sahoo, Francisco R. Arteaga-Sierra, Christophe Dorrer and Jie Qiao

Crystals 2019, 9(8), 434; https://doi.org/10.3390/cryst9080434 - 20 Aug 2019

Cited by 23 | Viewed by 4834

In this work, unidirectional pulse propagation equation (UPPE) modeling is performed to study the nonlinear laser-mater interaction in silicon and Nd:Y₃Al₅O₁₂ (Nd:YAG) crystals. The simulation results are validated with reported experimental results for silicon and applied to Nd:YAG [...] Read more.

In this work, unidirectional pulse propagation equation (UPPE) modeling is performed to study the nonlinear laser-mater interaction in silicon and Nd:Y₃Al₅O₁₂ (Nd:YAG) crystals. The simulation results are validated with reported experimental results for silicon and applied to Nd:YAG crystals with experimental validation. Stress-induced waveguides are written in Nd:YAG crystals using 515 nm, 300 fs pulses at a 1 kHz repetition rate. Waveguides having a mean propagation loss of 0.21 ± 0.06 dB/cm are obtained, which is lower than the previous reported values for Type-II waveguides written in Nd:YAG crystals. The modeling and experimental results consistently show that the modification (waveguide track) depth increases with input energy. A detailed analysis is presented to control the modal properties of the waveguide in the context of UPPE simulation. Full article

(This article belongs to the Special Issue Laser Crystals)

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14 pages, 4858 KiB

Open AccessArticle

Utilization of a CO₂ Storage Material: Shape-Controlled Preparation of CaCO₃ Microspheres

by Xianlong Meng, Long Zhao, Haitao Guo, Feng Sha, Huihu Shi, Zhaojun Wu and Jianbin Zhang

Crystals 2019, 9(8), 433; https://doi.org/10.3390/cryst9080433 - 20 Aug 2019

Cited by 4 | Viewed by 3483

Abstract

Homogeneous CaCO₃ microspheres were controllably synthesized via a simple hydrothermal method without using extraneous additives by Ca(OH)₂ saturated solution reacted with CO₂ storage material (CO₂SM), which was obtained by absorbing CO₂ gas in a system containing equimolar [...] Read more.

Homogeneous CaCO₃ microspheres were controllably synthesized via a simple hydrothermal method without using extraneous additives by Ca(OH)₂ saturated solution reacted with CO₂ storage material (CO₂SM), which was obtained by absorbing CO₂ gas in a system containing equimolar ethylenediamine (EDA) and polyethylene glycol 400 (PEG). Specifically, homogeneous pure vaterite spheres were obtained by using 160 g/L CO₂SM solution at 100 °C and a reaction time of two hours. It is noteworthy that the EDA and PEG, which are released from CO₂SM, have dual functions as a CO₂ absorber and crystal regulator in the process of controlling the crystallization of CaCO₃ crystals. Full article

(This article belongs to the Section Crystalline Materials)

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11 pages, 26026 KiB

Open AccessArticle

Combining Nanofocused X-Rays with Electrical Measurements at the NanoMAX Beamline

by Lert Chayanun, Susanna Hammarberg, Hanna Dierks, Gaute Otnes, Alexander Björling, Magnus T Borgström and Jesper Wallentin

Crystals 2019, 9(8), 432; https://doi.org/10.3390/cryst9080432 - 20 Aug 2019

Cited by 11 | Viewed by 4664

Abstract

The advent of nanofocused X-ray beams has allowed the study of single nanocrystals and complete nanoscale devices in a nondestructive manner, using techniques such as scanning transmission X-ray microscopy (STXM), X-ray fluorescence (XRF) and X-ray diffraction (XRD). Further insight into semiconductor devices can [...] Read more.

The advent of nanofocused X-ray beams has allowed the study of single nanocrystals and complete nanoscale devices in a nondestructive manner, using techniques such as scanning transmission X-ray microscopy (STXM), X-ray fluorescence (XRF) and X-ray diffraction (XRD). Further insight into semiconductor devices can be achieved by combining these techniques with simultaneous electrical measurements. Here, we present a system for electrical biasing and current measurement of single nanostructure devices, which has been developed for the NanoMAX beamline at the fourth-generation synchrotron, MAX IV, Sweden. The system was tested on single InP nanowire devices. The mechanical stability was sufficient to collect scanning XRD and XRF maps with a 50 nm diameter focus. The dark noise of the current measurement system was about 3 fA, which allowed fly scan measurements of X-ray beam induced current (XBIC) in single nanowire devices. Full article

(This article belongs to the Special Issue Investigation of Nanostructures with X-ray Scattering Techniques)

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10 pages, 3559 KiB

Open AccessArticle

Electrically Tunable-Focusing Liquid Crystal Microlens Array with Simple Electrode

by Li-Lan Tian, Fan Chu, Hu Dou, Lei Li and Qiong-Hua Wang

Crystals 2019, 9(8), 431; https://doi.org/10.3390/cryst9080431 - 20 Aug 2019

Cited by 8 | Viewed by 3460

Abstract

An electrically tunable-focusing liquid crystal (LC) microlens array exhibiting a wide-range tunable focal length is proposed. The lower substrate has strip indium tin oxide (ITO) electrodes, the upper substrate has periodic ITO electrodes with a certain gap coated on the inner surface., and [...] Read more.

An electrically tunable-focusing liquid crystal (LC) microlens array exhibiting a wide-range tunable focal length is proposed. The lower substrate has strip indium tin oxide (ITO) electrodes, the upper substrate has periodic ITO electrodes with a certain gap coated on the inner surface., and an LC microlens is generated between the two strip electrodes. For each LC microlens, the gap between the top planar electrodes is directly above the center of the microlens. Unlike the conventional LC lens, the individual LC microlens is not coated with ITO electrodes on the central part of its upper and lower substrates, which helps to maintain the LC’s horizontal orientation. In the voltage-off state, the focal length of the microlens array is infinity because of the homogeneous LC alignment. At a given operating voltage, an ideal gradient refractive index distribution is induced over the homogeneous LC layer, which leads to the focusing effect. The simulation result shows that the focal length of the LC microlens could be gradually drawn to 0.381 mm with a change of voltage. Full article

(This article belongs to the Special Issue Liquid Crystal Optics and Physics: Recent Advances and Prospects)

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18 pages, 2099 KiB

Open AccessArticle

Wetting of Nematic Liquid Crystals on Crenellated Substrates: A Frank–Oseen Approach

by Óscar A. Rojas-Gómez, Margarida M. Telo da Gama and José M. Romero-Enrique

Crystals 2019, 9(8), 430; https://doi.org/10.3390/cryst9080430 - 19 Aug 2019

Cited by 1 | Viewed by 2706

Abstract

We revisit the wetting of nematic liquid crystals in contact with crenellated substrates, studied previously using the Landau–de Gennes formalism. However, due to computational limitations, the characteristic length scales of the substrate relief considered in that study limited to less than 100 nematic [...] Read more.

We revisit the wetting of nematic liquid crystals in contact with crenellated substrates, studied previously using the Landau–de Gennes formalism. However, due to computational limitations, the characteristic length scales of the substrate relief considered in that study limited to less than 100 nematic correlation lengths. The current work uses an extended Frank–Oseen formalism, which includes not only the free-energy contribution due to the elastic deformations but also the surface tension contributions and, if disclinations or other orientational field singularities are present, their core contributions. Within this framework, which was successfully applied to the anchoring transitions of a nematic liquid crystal in contact with structured substrates, we extended the study to much larger length scales including the macroscopic scale. In particular, we analyzed the interfacial states and the transitions between them at the nematic–isotropic coexistence. Full article

(This article belongs to the Special Issue Advances in Nematic Liquid Crystals)

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11 pages, 2406 KiB

Open AccessArticle

Structural Analyses of Helicobacter Pylori FolC Conducting Glutamation in Folate Metabolism

by Joon Sung Park, Hyoun Sook Kim, Sang Ho Park, Mi Seul Park, Sung-Min Kang, Hyun-Jung Kim and Byung Woo Han

Crystals 2019, 9(8), 429; https://doi.org/10.3390/cryst9080429 - 19 Aug 2019

Cited by 1 | Viewed by 3136

Abstract

FolC plays important roles in the folate metabolism of cells by attaching l-Glu to dihydropteroate (DHP) and folate, which are known activities of dihydrofolate synthetase (DHFS) and folylpolyglutamate synthetase (FPGS), respectively. Here, we determined the crystal structure of Helicobacter pylori FolC ( [...] Read more.

FolC plays important roles in the folate metabolism of cells by attaching l-Glu to dihydropteroate (DHP) and folate, which are known activities of dihydrofolate synthetase (DHFS) and folylpolyglutamate synthetase (FPGS), respectively. Here, we determined the crystal structure of Helicobacter pylori FolC (HpFolC) at 1.95 Å resolution using the single-wavelength anomalous diffraction method. HpFolC has globular N- and C-terminal domains connected by a single loop, and a binding site for ATP is located between the two domains. Apo-HpFolC was crystallized in the presence of citrate in a crystallization solution, which was held in the ATP-binding site. Structural motifs such as the P-loop and Ω-loop of HpFolC for binding of ATP and two magnesium ions are well conserved in spite of the low overall sequence similarity to other FolC/FPGSs. The Ω-loop would also recognize a folate molecule, and the DHP-binding loop of HpFolC is expected to exhibit a unique recognition mode on DHP, compared with other FolCs. Because human FolC is known to only exhibit FPGS activity, the DHFS activity of bacterial FolC is an attractive target for the eradication of pathogenic bacteria. Consequently, our structural analyses of HpFolC provide a valuable foundation for a universal antibacterial strategy against H. pylori as well as other pathogenic bacteria. Full article

(This article belongs to the Special Issue Crystallographic Studies of Enzymes)

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13 pages, 5991 KiB

Open AccessArticle

Raman Characterization of Carrier Concentrations of Al-implanted 4H-SiC with Low Carrier Concentration by Photo-Generated Carrier Effect

by Tao Liu, Zongwei Xu, Mathias Rommel, Hong Wang, Ying Song, Yufang Wang and Fengzhou Fang

Crystals 2019, 9(8), 428; https://doi.org/10.3390/cryst9080428 - 17 Aug 2019

Cited by 7 | Viewed by 4576

Abstract

In this work, 4H SiC samples with a multilayer structure (shallow implanted layer in a lowly doped n-type epitaxial layer grown on a highly doped thick substrate) were investigated by Raman scattering. First, Raman depth profiling was performed to identify characteristic peaks for [...] Read more.

In this work, 4H SiC samples with a multilayer structure (shallow implanted layer in a lowly doped n-type epitaxial layer grown on a highly doped thick substrate) were investigated by Raman scattering. First, Raman depth profiling was performed to identify characteristic peaks for the different layers. Then, Raman scattering was used to characterize the carrier concentration of the samples. In contrast to the conventional Raman scattering measuring method of the Longitudinal Optical Plasmon Coupled (LOPC) mode, which is only suitable to characterize carrier concentrations in the range from 2 × 10¹⁶ to 5 × 10¹⁸ cm⁻³, in this work, Raman scattering, which is based on exciting photons with an energy above the band gap of 4H-SiC, was used. The proposed method was evaluated and approved for different Al-implanted samples. It was found that with increasing laser power the Al-implanted layers lead to a consistent redshift of the LOPC Raman peak compared to the peak of the non-implanted layer, which might be explained by a consistent change in effective photo-generated carrier concentration. Besides, it could be demonstrated that the lower concentration limit of the conventional approach can be extended to a value of 5 × 10¹⁵ cm⁻³ with the approach presented here. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystals)

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11 pages, 4106 KiB

Open AccessArticle

The Influence of B, N and Si Doping on the CH₃ Adsorption on the Diamond Surface Based on DFT Calculations

by Liang Wang, Jiangshan Liu and Tang Tang

Crystals 2019, 9(8), 427; https://doi.org/10.3390/cryst9080427 - 17 Aug 2019

Cited by 5 | Viewed by 4518

Abstract

To better understand the influence mechanism of boron, nitrogen and silicon dopants on the growth of chemical vapor deposition (CVD) diamond film, density functional calculations have been performed to reveal the different impact of the impurities on the CH₃ adsorption on diamond [...] Read more.

To better understand the influence mechanism of boron, nitrogen and silicon dopants on the growth of chemical vapor deposition (CVD) diamond film, density functional calculations have been performed to reveal the different impact of the impurities on the CH₃ adsorption on diamond surface. The substituted doping and radical doping of diamond (111) and (100) − 2 × 1 surface are both considered. The calculation results indicate that the CH₃ radicals are hardly adsorbed on nitrogen atoms and thus may cause vacancy in the diamond lattice easily. Boron substituted doping will disfavor the adsorption of CH₃ due to the lacking of valence electron. However, the empty p orbitals of boron atom will help the chemical adsorbing of CH₃ radicals. The substituted silicon doping has little influence on the CH₃ adsorption, as Si atom has the same outer valence electron structure with C atom. In the case of radical doping, the adsorption energy of CH₃ will be reduced due to the steric hindrance between NH₂ or SiH₃ with CH_3. The adsorption energy can be slightly enhanced when BH₂ radical is pre-adsorbed on diamond (111) surface. However, the BH₂ pre-adsorbed on diamond (100) − 2 × 1 surface may interact with surface radical carbon site and result in a large reduction of CH₃ adsorption energy. Thus, the boron doping may hinder the formation of the (100) facet during the CVD diamond deposition under a certain condition. Full article

(This article belongs to the Special Issue Synthesis and Characterization of Diamond Crystals)

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37 pages, 5030 KiB

Open AccessArticle

Band Tunability of Coupled Elastic Waves along Thickness in Laminated Anisotropic Piezoelectric Phononic Crystals

by Qiangqiang Li, Yongqiang Guo, Yajun Wang and Haibo Zhang

Crystals 2019, 9(8), 426; https://doi.org/10.3390/cryst9080426 - 16 Aug 2019

Cited by 5 | Viewed by 2893

Abstract

Although the passively adjusting and actively tuning of pure longitudinal (primary (P-)) and pure transverse (secondary or shear (S-)) waves band structures in periodically laminated piezoelectric composites have been studied, the actively tuning of coupled elastic waves (such as P-SV, P-SH, SV-SH, and [...] Read more.

Although the passively adjusting and actively tuning of pure longitudinal (primary (P-)) and pure transverse (secondary or shear (S-)) waves band structures in periodically laminated piezoelectric composites have been studied, the actively tuning of coupled elastic waves (such as P-SV, P-SH, SV-SH, and P-SV-SH waves), particularly as the coupling of wave modes is attributed to the material anisotropy, in these phononic crystals remains an untouched topic. This paper presents the analytical matrix method for solving the dispersion characteristics of coupled elastic waves along the thickness direction in periodically multilayered piezoelectric composites consisting of arbitrarily anisotropic materials and applied by four kinds of electrical boundaries. By switching among these four electrical boundaries—the electric-open, the external capacitance, the electric-short, and the external feedback control—and by altering the capacitance/gain coefficient in cases of the external capacitance/feedback-voltage boundaries, the tunability of the band properties of the coupled elastic waves along layering thickness in the concerned phononic multilayered crystals are investigated. First, the state space formalism is introduced to describe the three-dimensional elastodynamics of arbitrarily anisotropic elastic and piezoelectric layers. Second, based on the traveling wave solutions to the state vectors of all constituent layers in the unit cell, the transfer matrix method is used to derive the dispersion equation of characteristic coupled elastic waves in the whole periodically laminated anisotropic piezoelectric composites. Finally, the numerical examples are provided to demonstrate the dispersion properties of the coupled elastic waves, with their dependence on the anisotropy of piezoelectric constituent layers being emphasized. The influences of the electrical boundaries and the electrode thickness on the band structures of various kinds of coupled elastic waves are also studied through numerical examples. One main finding is that the frequencies corresponding to

q H = n π

(with

q H

the dimensionless characteristic wavenumber) are not always the demarcation between pass-bands and stop-bands for coupled elastic waves, although they are definitely the demarcation for pure P- and S-waves. The other main finding is that the coupled elastic waves are more sensitive to, if they are affected by, the electrical boundaries than the pure P- and S-wave modes, so that higher tunability efficiency should be achieved if coupled elastic waves instead of pure waves are exploited. Full article

(This article belongs to the Special Issue Sonic and Photonic Crystals)

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8 pages, 1479 KiB

Open AccessArticle

Polarization Dependence of Low-Frequency Vibrations from Multiple Faces in an Organic Single Crystal

by Irena Nemtsov, Hagit Aviv, Yitzhak Mastai and Yaakov R. Tischler

Crystals 2019, 9(8), 425; https://doi.org/10.3390/cryst9080425 - 16 Aug 2019

Cited by 7 | Viewed by 3517

Abstract

Recent developments in optical filters have enabled the facile use of Raman spectroscopy for detection of low frequency (LF) vibrational modes. LF-Raman spectroscopy offers fast and sensitive characterization of LF vibrations, and enables the measurement of single microcrystals and detection of defects. It [...] Read more.

Recent developments in optical filters have enabled the facile use of Raman spectroscopy for detection of low frequency (LF) vibrational modes. LF-Raman spectroscopy offers fast and sensitive characterization of LF vibrations, and enables the measurement of single microcrystals and detection of defects. It is useful for probing intermolecular interactions in crystals, which are lower in energy, such as hydrogen bonds, shear modes, and breathing modes. Crystal excitation from multiple faces allows learning the orientation of intermolecular interactions, as polarization dependence varies with the polarizability of the interactions along the planes. Elucidating the orientations of the intermolecular interactions in organic crystals is essential for guiding the reactions or adsorption to a specific crystal face. In this study, we investigated the dependence of the LF-Raman signal intensity on the orientation of an organic single microcrystal of L-alanine. Three incident beam directions provided the orientations of the intermolecular interactions by analyzing the corresponding LF-Raman spectra. The signal intensity correlated well with the proximity between the incident beam’s direction and the orientations of the intermolecular interactions. Excellent compatibility was found between the spectra and simulated orientations based on structural information. Full article

(This article belongs to the Special Issue Raman Spectroscopy of Crystals)

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12 pages, 4017 KiB

Open AccessArticle

Press to Success: Gd₅FW₃O₁₆—The First Gadolinium(III) Fluoride Oxidotungstate(VI)

by Katharina V. Dorn and Ingo Hartenbach

Crystals 2019, 9(8), 424; https://doi.org/10.3390/cryst9080424 - 16 Aug 2019

Cited by 1 | Viewed by 3646

Abstract

The gadolinium(III) fluoride oxidotungstate(VI), with the formula Gd₅FW₃O₁₆, represents the first published fluoride-derivative of a rare-earth metal oxidotungstate. It is synthesized by a mixture of GdF₃, Gd₂O₃, and WO₃ at [...] Read more.

The gadolinium(III) fluoride oxidotungstate(VI), with the formula Gd₅FW₃O₁₆, represents the first published fluoride-derivative of a rare-earth metal oxidotungstate. It is synthesized by a mixture of GdF₃, Gd₂O₃, and WO₃ at 800 °C and a pressure of 2 GPa with the help of a belt press. The title compound crystallizes in the monoclinic space group P2₁/c (no. 14) with four formula units per unit cell and the following lattice parameters: a = 539.29 (4), b = 1556.41 (12), c = 1522.66 (11) pm, and β = 93.452 (4). The crystal structure comprises five crystallographically distinguishable Gd³⁺ cations, which are surrounded by either oxide and fluoride anions (Gd1–3) or by oxide anions only (Gd4, Gd5), with coordination numbers ranging between seven and nine. The fluoride anions are trigonal non-planar coordinated by three Gd³⁺ cations (Gd1–3). The distorted [WO₆]⁶⁻ octahedra in this structure form isolates edge- and vertex-connected entities of the compositions [W₂O₁₀]⁸⁻ and [W₂O₁₁]¹⁰⁻, respectively. According to the presented units, a structured formula can be written as Gd₄[FGd₃]₂[W₂O₁₀][W₂O₁₁]₂. The single-crystal Raman spectrum reveals the typical symmetric stretching vibration mode of octahedral oxidotungstate(VI) units at about 871 cm⁻¹. Full article

(This article belongs to the Special Issue Rare-Earth Metal Compounds)

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19 pages, 4545 KiB

Open AccessArticle

Quest for Compounds at the Verge of Charge Transfer Instabilities: The Case of Silver(II) Chloride ^†

by Mariana Derzsi, Adam Grzelak, Paweł Kondratiuk, Kamil Tokár and Wojciech Grochala

Crystals 2019, 9(8), 423; https://doi.org/10.3390/cryst9080423 - 15 Aug 2019

Cited by 8 | Viewed by 6360

Abstract

Electron-transfer processes constitute one important limiting factor governing stability of solids. One classical case is that of CuI₂, which has never been prepared at ambient pressure conditions due to feasibility of charge transfer between metal and nonmetal (CuI₂ → CuI [...] Read more.

Electron-transfer processes constitute one important limiting factor governing stability of solids. One classical case is that of CuI₂, which has never been prepared at ambient pressure conditions due to feasibility of charge transfer between metal and nonmetal (CuI₂ → CuI + ½ I₂). Sometimes, redox instabilities involve two metal centers, e.g., AgO is not an oxide of divalent silver but rather silver(I) dioxoargentate(III), Ag(I)[Ag(III)O₂]. Here, we look at the particularly interesting case of a hypothetical AgCl₂ where both types of redox instabilities operate simultaneously. Since standard redox potential of the Ag(II)/Ag(I) redox pair reaches some 2 V versus Normal Hydrogen Electrode (NHE), it might be expected that Ag(II) would oxidize Cl⁻ anion with great ease (standard redox potential of the ½ Cl₂/Cl⁻ pair is + 1.36 V versus Normal Hydrogen Electrode). However, ionic Ag(II)Cl₂ benefits from long-distance electrostatic stabilization to a much larger degree than Ag(I)Cl + ½ Cl₂, which affects relative stability. Moreover, Ag(II) may disproportionate in its chloride, just like it does in an oxide; this is what AuCl₂ does, its formula corresponding in fact to Au(I)[Au(III)Cl₄]. Formation of polychloride substructure, as for organic derivatives of Cl₃⁻ anion, is yet another possibility. All that creates a very complicated potential energy surface with a few chemically distinct minima i.e., diverse polymorphic forms present. Here, results of our theoretical study for AgCl₂ will be presented including outcome of evolutionary algorithm structure prediction method, and the chemical identity of the most stable form will be uncovered together with its presumed magnetic properties. Contrary to previous rough estimates suggesting substantial instability of AgCl₂, we find that AgCl₂ is only slightly metastable (by 52 meV per formula unit) with respect to the known AgCl and ½ Cl₂, stable with respect to elements, and simultaneously dynamically (i.e., phonon) stable. Thus, our results point out to conceivable existence of AgCl₂ which should be targeted via non-equilibrium approaches. Full article

(This article belongs to the Special Issue First-Principles Prediction of Structures and Properties in Crystals)

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14 pages, 12588 KiB

Open AccessArticle

Theoretical Study of the Electronic and Magnetic Properties and Phase Stability of the Full Heusler Compound Pd₂CoAl

by Liyu Hao, Jiaxue You, Rabah Khenata, Yanfeng Wang, Xiaotian Wang and Tie Yang

Crystals 2019, 9(8), 422; https://doi.org/10.3390/cryst9080422 - 14 Aug 2019

Cited by 5 | Viewed by 3265

Abstract

Based on first principles calculation, a systematical investigation has been performed to study the electronic, magnetic, dynamic, and mechanical properties of the full Heusler compound Pd₂CoAl. It is found that the L2₁-type structure is energetically more stable than [...] Read more.

Based on first principles calculation, a systematical investigation has been performed to study the electronic, magnetic, dynamic, and mechanical properties of the full Heusler compound Pd₂CoAl. It is found that the L2₁-type structure is energetically more stable than the XA-type due to the lower total energy. The obtained lattice constant in cubic ground state is 6.057 Å, which matches well with previous study. The calculated electronic band structure reveals the metallic nature of Pd₂CoAl and its total magnetic moment of 1.78 μ_B is mainly contributed by Co atom from strong spin splitting effect, as indicated with the distinctive distributions of the density of states in two spin directions. Under uniform strains from −5% to +5%, the variation of total magnetic moment has been obtained and it is still caused by the much larger change from Co atom, compared with Pd and Al atoms. The tetragonal structure has further been analyzed and we found that there is possible martensitic phase transformation because the total energy can be further reduced when the cubic structure is varied into the tetragonal one. The large energy difference of 0.165 eV between the tetragonal and cubic phases is found at the c/a ratio of 1.30. The total density of states has been compared between the cubic and tetragonal phases for Pd₂CoAl and results show tetragonal phase transformation could reduce the states at the Fermi energy level in both directions. In addition, the dynamic and mechanical stabilities have also been evaluated for Pd₂CoAl in both cubic and tetragonal structures and results confirm that the tetragonal phase shows good stability against the cubic phase, which further verifies that the tetragonal phase transformation is highly expected. In the end, the strong elastic anisotropy in the tetragonal structure has been clearly shown with the calculated directional dependence of the Young’s modulus and shear modulus. Full article

(This article belongs to the Special Issue Heusler Alloys)

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9 pages, 3807 KiB

Open AccessArticle

Mechanism Design with Singularity Avoidance of Crystal-Inspired Deployable Structures

by Yao Chen, Jiayi Yan and Jian Feng

Crystals 2019, 9(8), 421; https://doi.org/10.3390/cryst9080421 - 14 Aug 2019

Cited by 3 | Viewed by 4373

Abstract

Although deployable structures have important applications in various fields, developing a new form of structural configuration faces some scientific challenges. Furthermore, kinematic singularity frequently exists in these structures, which has a negative impact on deployment performance and stiffness. To deal with these problems, [...] Read more.

Although deployable structures have important applications in various fields, developing a new form of structural configuration faces some scientific challenges. Furthermore, kinematic singularity frequently exists in these structures, which has a negative impact on deployment performance and stiffness. To deal with these problems, this paper obtains inspiration from crystals on two-dimensional (2D) space, and aims at developing symmetric deployable structures assembled by identical link members and periodic units. Mobility and compatibility conditions of crystal-inspired deployable structures are given, and a detailed design for novel joints with bevels gears is proposed to avoid singularity of these symmetric structures. According to feasible solutions to the compatibility conditions, several types of deployable structures are developed and verified to be mobile with a single degree of freedom. The results show that the proposed joint with bevel gears has a satisfactory singularity avoidance capability, and the assembled structures exhibit a good deployment performance. Because a crystal-inspired deployable structure can be gradually deployed to cover a large area, it has a potential engineering application as a macroscopic or mesoscale structure. Full article

(This article belongs to the Section Crystal Engineering)

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8 pages, 1635 KiB

Open AccessArticle

Comparing Cyclic Tension-Compression Effects on CoCrFeMnNi High-Entropy Alloy and Ni-Based Superalloy

by Tu-Ngoc Lam, You-Shiun Chou, Yao-Jen Chang, Tsung-Ruei Sui, An-Chou Yeh, Stefanus Harjo, Soo Yeol Lee, Jayant Jain, Bo-Hong Lai and E-Wen Huang

Crystals 2019, 9(8), 420; https://doi.org/10.3390/cryst9080420 - 13 Aug 2019

Cited by 10 | Viewed by 3447

Abstract

An equal-molar CoCrFeMnNi, face-centered-cubic (fcc) high-entropy alloy (HEA) and a nickel-based superalloy are studied using in situ neutron diffraction experiments. With continuous measurements, the evolution of diffraction peaks is collected for microscopic lattice strain analyses. Cyclic hardening and softening are found in both [...] Read more.

An equal-molar CoCrFeMnNi, face-centered-cubic (fcc) high-entropy alloy (HEA) and a nickel-based superalloy are studied using in situ neutron diffraction experiments. With continuous measurements, the evolution of diffraction peaks is collected for microscopic lattice strain analyses. Cyclic hardening and softening are found in both metallic systems. However, as obtained from the diffraction-peak-width evolution, the underneath deformation mechanisms are quite different. The CoCrFeMnNi HEA exhibits distinct lattice strain and microstructure responses under tension-compression cyclic loadings. Full article

(This article belongs to the Special Issue Crystallographic Understanding of Deformation, Phase Transformation, and Recrystallization in Materials Engineering)

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7 pages, 2165 KiB

Open AccessArticle

Field-Induced Magnetic Phase Transitions and Rich Phase Diagram of HoMnO₃ Single Crystal

by Chao Dong, Rui Chen, Yongjie Liu, Congbin Liu, Haipeng Zhu, Jiezun Ke, Wanxin Liu, Ming Yang and Junfeng Wang

Crystals 2019, 9(8), 419; https://doi.org/10.3390/cryst9080419 - 13 Aug 2019

Cited by 5 | Viewed by 3109

Abstract

An extensive magnetization study in pulsed fields up to 62 T and at temperatures down to ~0.7 K has been performed on the single crystals of hexagonal manganite HoMnO₃. For magnetic fields (H) applied along the c-axis, successive [...] Read more.

An extensive magnetization study in pulsed fields up to 62 T and at temperatures down to ~0.7 K has been performed on the single crystals of hexagonal manganite HoMnO₃. For magnetic fields (H) applied along the c-axis, successive magnetic transitions below 10 T and a step-like transition at ~41 T are observed. The phase diagram for H//c is very complex and new phase boundaries are explored below 6 K. This phase diagram is compared with the early results derived from dielectric constant and neutron scattering measurements. For H//a, two magnetic transitions are found below 3 T dome-shaped and the phase diagram is reported for the first time. The variety of magnetic symmetries of the field-induced magnetic phases is discussed. Full article

(This article belongs to the Special Issue Magnetic Field-induced Phase Transition)

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13 pages, 3101 KiB

Open AccessArticle

A Grain Boundary Regulates the Friction Behaviors between Graphene and a Gold Substrate

by Pinxuan He, Qiang Cao, Pengjie Wang, Huaipeng Wang, Shaolong Zheng, Shuting Lei, Sheng Liu and Qing Peng

Crystals 2019, 9(8), 418; https://doi.org/10.3390/cryst9080418 - 13 Aug 2019

Cited by 7 | Viewed by 3256

Abstract

The nanofriction of graphene is critical for its broad applications as a lubricant and in flexible electronics. Herein, using a Au substrate as an example, we have investigated the effect of the grain boundary on the nanofriction of graphene by means of molecular [...] Read more.

The nanofriction of graphene is critical for its broad applications as a lubricant and in flexible electronics. Herein, using a Au substrate as an example, we have investigated the effect of the grain boundary on the nanofriction of graphene by means of molecular dynamics simulations. We have systematically examined the coupling effects of the grain boundary with different mechanical pressures, velocities, temperatures, contact areas, and relative rotation angles on nanofriction. It is revealed that grain boundaries could reduce the friction between graphene and the gold substrate with a small deformation of the latter. Large lateral forces were observed under severe deformation around the grain boundary. The fluctuation of lateral forces was bigger on surfaces with grain boundaries than that on single-crystal surfaces. Friction forces induced by the armchair grain boundaries was smaller than those by the zigzag grain boundaries. Full article

(This article belongs to the Special Issue Graphene Mechanics)

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22 pages, 6007 KiB

Open AccessReview

Recent Advances in Colloidal Photonic Crystal-Based Anti-Counterfeiting Materials

by Mengyao Pan, Lebin Wang, Shuliang Dou, Jiupeng Zhao, Hongbo Xu, Bo Wang, Leipeng Zhang, Xiaobai Li, Lei Pan and Yao Li

Crystals 2019, 9(8), 417; https://doi.org/10.3390/cryst9080417 - 12 Aug 2019

Cited by 39 | Viewed by 7567

Abstract

Colloidal photonic crystal (PC)-based anti-counterfeiting materials have been widely studied due to their inimitable structural colors and tunable photonic band gaps (PBGs) as well as their convenient identification methods. In this review, we summarize recent developments of colloidal PCs in the field of [...] Read more.

Colloidal photonic crystal (PC)-based anti-counterfeiting materials have been widely studied due to their inimitable structural colors and tunable photonic band gaps (PBGs) as well as their convenient identification methods. In this review, we summarize recent developments of colloidal PCs in the field of anti-counterfeiting from aspects of security strategies, design, and fabrication principles, and identification means. Firstly, an overview of the strategies for constructing PC anti-counterfeiting materials composed of variable color PC patterns, invisible PC prints, and several other PC anti-counterfeiting materials is presented. Then, the synthesis methods, working principles, security level, and specific identification means of these three types of PC materials are discussed in detail. Finally, the summary of strengths and challenges, as well as development prospects in the attractive research field, are presented. Full article

(This article belongs to the Special Issue Sonic and Photonic Crystals)

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9 pages, 1992 KiB

Open AccessArticle

N,O Chelating Ligands Construct Five-Coordinated Zn(II) Exclusive {Zn6} Clusters: Decomposition, Stepwise Assembly and Photoluminescence Study

by Qian-Jun Deng, Min Chen, Dong-Chu Chen and Chang-Ai Chen

Crystals 2019, 9(8), 416; https://doi.org/10.3390/cryst9080416 - 12 Aug 2019

Viewed by 2262

Abstract

N-methylbenzimidazole-2-methanol (Hmbm) and Zn(NO₃)₂·6H₂O were reacted in acetonitrile solvothermal at 80 °C for 48 h to obtain a six-nuclear Zn(II) cluster ([Zn^II₆(Hmbm)₂(mbm)₈(NO₃ [...] Read more.

N-methylbenzimidazole-2-methanol (Hmbm) and Zn(NO₃)₂·6H₂O were reacted in acetonitrile solvothermal at 80 °C for 48 h to obtain a six-nuclear Zn(II) cluster ([Zn^II₆(Hmbm)₂(mbm)₈(NO₃)₄]·12H₂O·2CH₃CN (Zn6)). Structural analysis indicated that Zn(II) in the above Zn6 clusters showed pentacoordinates. The metal centers Zn1 and Zn2 are both in the N₂O₃ coordination environment, and both show a triangular bipyramid configuration. Zn3 is in a NO₄ coordination environment, which is also shown as a triangular bipyramid configuration. The ion source voltage of high-resolution electrospray ionization mass spectrometry (HRESI-MS) was further adjusted to bombard the Zn6 cluster, and seven major key intermediates were identified. Furthermore, we proposed that the gradual fragmentation mechanism is Zn6 → [Zn^II₆(mbm)₈(NO₃)₃]⁺ → [Zn^II₅(mbm)₇(NO₃)₂]⁺ → [Zn^II₄(mbm)₆(NO₃)]⁺ → [Zn^II₃(mbm)₄(NO₃)]⁺ → [Zn^II₂(mbm)₃]⁺ → [Zn^II₂(mbm)₂(OH)(H₂O)₂(DMSO)]⁺ → [Zn^II(mbm)]⁺. In order to understand the gradual formation of Zn6 clusters, herein, we track the changes of species in the solution in different time periods by HRESI-MS. The nine key intermediates were identified and further combined with its gradual fragmentation mechanism. We proposed the gradual assembly mechanism of [Zn^II(mbm)]⁺ → [Zn^II(mbm)(Hmbm)]⁺ → [Zn^II₂(mbm)₂(NO₃)]⁺ → [Zn^II₂(mbm)₃]⁺ → [Zn^II₃(mbm)₄(NO₃)]⁺ → [Zn^II₄(mbm)₅(NO₃)₂]⁺ → [Zn^II₄(mbm)₆(NO₃)]⁺ → [Zn^II₅(mbm)₇(NO₃)₂]⁺ → [Zn^II₆(mbm)₈(NO₃)₃]⁺ → Zn6. To the best of our knowledge, this is the first time that a decomposition and assembly binding strategy has been used to resolve the stepwise formation of Zn(II) clusters. Photoluminescence measurements indicate that the cluster Zn6 exhibits a strong emission peak at 300 nm and an emission shoulder at 600 nm. Full article

(This article belongs to the Section Crystal Engineering)

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3 pages, 174 KiB

Open AccessEditorial

Thin Film Transistor

by Ray-Hua Horng

Crystals 2019, 9(8), 415; https://doi.org/10.3390/cryst9080415 - 09 Aug 2019

Cited by 2 | Viewed by 2996

Abstract

The special issue is "Thin Film Transistor". There are eight contributed papers. They focus on organic thin film transistors, fluorinated oligothiophenes transistors, surface treated or hydrogen effect on oxide-semiconductor-based thin film transistors, and their corresponding application in flat panel displays and optical detecting. [...] Read more.

The special issue is "Thin Film Transistor". There are eight contributed papers. They focus on organic thin film transistors, fluorinated oligothiophenes transistors, surface treated or hydrogen effect on oxide-semiconductor-based thin film transistors, and their corresponding application in flat panel displays and optical detecting. The present special issue on “Thin Film Transistor” can be considered as a status report reviewing the progress that has been made recently on thin film transistor technology. These papers can provide the readers with more research information and corresponding application potential about Thin Film Transistors. Full article

(This article belongs to the Special Issue Thin Film Transistor)

10 pages, 1886 KiB

Open AccessArticle

Argentophilic Interactions in Two Ag^I Complexes of 3-(2-(Pyridin-4-yl)ethyl)pentane-2,4-dione, a Promising Ditopic Ligand

by Steven van Terwingen and Ulli Englert

Crystals 2019, 9(8), 414; https://doi.org/10.3390/cryst9080414 - 09 Aug 2019

Cited by 4 | Viewed by 3291

Abstract

Reactions of 3-(2-(pyridin-4-yl)ethyl)pentane-2,4-dione (HacacPyen) with AgPF₆ and AgBF₄ afforded cationic silver complexes [Ag(HacacPyen)₂]⁺ with essentially linear coordination of the Ag^I cation by two pyridine N atoms. Rather unexpectedly, the HacacPyen ligands in the PF₆⁻ salt [...] Read more.

Reactions of 3-(2-(pyridin-4-yl)ethyl)pentane-2,4-dione (HacacPyen) with AgPF₆ and AgBF₄ afforded cationic silver complexes [Ag(HacacPyen)₂]⁺ with essentially linear coordination of the Ag^I cation by two pyridine N atoms. Rather unexpectedly, the HacacPyen ligands in the PF₆⁻ salt 1 adopt the diketo form, in contrast to the uncoordinated HacacPyen molecule, whereas the corresponding BF₄⁻ salt 2 and the majority of 3-substituted acetylacetones crystallizes as the enol tautomer. In both compounds 1 and 2, complex cations aggregate via short Ag···Ag interactions to pairs. These contacts amount to 3.21 Å in 1 and 3.26 Å or 3.31 Å in 2. As they are unsupported by any additional bridging ligands and correspond to the closest interionic interactions between neighbouring complex cations, they may be addressed as argentophilic interactions. The PF₆⁻ anions in 1 and the BF₄⁻ counter ions in 2 are involved in long and presumably electrostatic Ag···F contacts of ca. 2.9 Å. Additional coordination between Ag^I and keto O atoms of symmetry-equivalent ligands occurs in 1 and leads to an extended two-periodic supramolecular structure. Full article

(This article belongs to the Section Crystal Engineering)

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14 pages, 2237 KiB

Open AccessArticle

Structural and Reactivity Analyses of Nitrofurantoin–4-dimethylaminopyridine Salt Using Spectroscopic and Density Functional Theory Calculations

by Eram Khan, Anuradha Shukla, Karnica Srivastava, Debraj Gangopadhyay, Khaled H. Assi, Poonam Tandon and Venu R. Vangala

Crystals 2019, 9(8), 413; https://doi.org/10.3390/cryst9080413 - 09 Aug 2019

Cited by 6 | Viewed by 4033

Abstract

Pharmaceutical salt, nitrofurantoin–4-dimethylaminopyridine (NF-DMAP), along with its native components NF and DMAP are scrutinized by FT-IR and FT-Raman spectroscopy along with density functional theory so that an insight into the H-bond patterns in the respective crystalline lattices can be gained. Two different functionals, [...] Read more.

Pharmaceutical salt, nitrofurantoin–4-dimethylaminopyridine (NF-DMAP), along with its native components NF and DMAP are scrutinized by FT-IR and FT-Raman spectroscopy along with density functional theory so that an insight into the H-bond patterns in the respective crystalline lattices can be gained. Two different functionals, B3LYP and wB97X-D, have been used to compare the theoretical results. The FT-IR spectra obtained for NF-DMAP and NF clearly validate the presence of C33–H34⋅⋅⋅O4 and N23–H24⋅⋅⋅N9 hydrogen bonds by shifting in the stretching vibration of –NH and –CH group of DMAP⁺ towards the lower wavenumber side. To explore the significance of hydrogen bonding, quantum theory of atoms in molecules (QTAIM) has been employed, and the findings suggest that the N23–H24⋅⋅⋅N9 bond is a strong intermolecular hydrogen bond. The decrement in the HOMO-LUMO gap, which is calculated from NF → NF-DMAP, reveals that the active pharmaceutical ingredient is chemically less reactive compared to the salt. The electrophilicity index (ω) profiles for NF and DMAP confirms that NF is acting as electron acceptor while DMAP acts as electron donor. The reactive sites of the salt are plotted by molecular electrostatic potential (MEP) surface and calculated using local reactivity descriptors. Full article

(This article belongs to the Special Issue Pharmaceutical Crystals)

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16 pages, 3154 KiB

Open AccessArticle

Continuous Generation of Millimeter-Sized Glycine Crystals in Non-Seeded Millifluidic Slug Flow

by Mingyao Mou, Huayu Li, Bing-Shiou Yang and Mo Jiang

Crystals 2019, 9(8), 412; https://doi.org/10.3390/cryst9080412 - 09 Aug 2019

Cited by 20 | Viewed by 4575

Abstract

Millimeter-sized α-glycine crystals were generated from continuous non-seeded cooling crystallization in slug flow. The crystallization process is composed of three steps in sequence: slug formation, crash-cooling nucleation, and growth. Stable uniform slugs of three different aspect ratios (slug length/tubing inner diameter) were formed, [...] Read more.

Millimeter-sized α-glycine crystals were generated from continuous non-seeded cooling crystallization in slug flow. The crystallization process is composed of three steps in sequence: slug formation, crash-cooling nucleation, and growth. Stable uniform slugs of three different aspect ratios (slug length/tubing inner diameter) were formed, by adjusting the flow rates of both the solution and air streams. Besides supersaturation, the slug aspect ratio can also affect primary nucleation outcome. Stable slug flow can accommodate a relative supersaturation (C/C*) of up to 1.5 without secondary nucleation. Large glycine crystals can grow to millimeter size within 10 min, inside millimeter-sized slugs without reducing the slug quality. Full article

(This article belongs to the Special Issue Anti-Solvent Crystallization)

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16 pages, 2840 KiB

Open AccessArticle

Gold Nanoparticle-Mediated Photoporation Enables Delivery of Macromolecules over a Wide Range of Molecular Weights in Human CD4+ T Cells

by Laurens Raes, Clarissa Van Hecke, Julie Michiels, Stephan Stremersch, Juan C. Fraire, Toon Brans, Ranhua Xiong, Stefaan De Smedt, Linos Vandekerckhove, Koen Raemdonck and Kevin Braeckmans

Crystals 2019, 9(8), 411; https://doi.org/10.3390/cryst9080411 - 07 Aug 2019

Cited by 26 | Viewed by 5742

Abstract

The modification of CD4+ T cells with exogenous nucleic acids or proteins is a critical step in several research and therapeutic applications, such as HIV studies and cancer immunotherapies. However, efficient cell transfections are not always easily achieved when working with these primary [...] Read more.

The modification of CD4+ T cells with exogenous nucleic acids or proteins is a critical step in several research and therapeutic applications, such as HIV studies and cancer immunotherapies. However, efficient cell transfections are not always easily achieved when working with these primary hard-to-transfect cells. While the modification of T cells is typically performed by viral transduction or electroporation, their use is associated with safety issues or cytotoxicity. Vapor nanobubble (VNB) photoporation with sensitizing gold nanoparticles (AuNPs) has recently emerged as a new technology for safe and flexible cell transfections. In this work, we evaluated the potential of VNB photoporation as a novel technique for the intracellular delivery of macromolecules in primary human CD4+ T cells using fluorescent dextrans as model molecules. Our results show that VNB photoporation enables efficient delivery of fluorescent dextrans of 10 kDa in Jurkat (>60% FD10+ cells) as well as in primary human CD4+ T cells (±40% FD10+ cells), with limited cell toxicity (>70% cell viability). We also demonstrated that the technique allows the delivery of dextrans that are up to 500 kDa in Jurkat cells, suggesting its applicability for the delivery of biological macromolecules with a wide range of molecular weights. Altogether, VNB photoporation represents a promising technique for the universal delivery of macromolecules in view of engineering CD4+ T cells for use in a wide variety of research and therapeutic applications. Full article

(This article belongs to the Special Issue Synthesis and Investigation of Gold Nanoparticles)

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17 pages, 2397 KiB

Open AccessArticle

Antimonate Removal from Polluted Mining Water by Calcined Layered Double Hydroxides

by Elisabetta Dore, Franco Frau and Rosa Cidu

Crystals 2019, 9(8), 410; https://doi.org/10.3390/cryst9080410 - 06 Aug 2019

Cited by 11 | Viewed by 2896

Abstract

Calcined layered double hydroxides (LDHs) can be used to remove Sb(V), in the Sb(OH)₆⁻ form, from aqueous solutions. Sorption batch experiments showed that the mixed MgAlFe oxides, obtained from calcined hydrotalcite-like compound (3HT-cal), removed Sb(OH)₆⁻ through the formation of [...] Read more.

Calcined layered double hydroxides (LDHs) can be used to remove Sb(V), in the Sb(OH)₆⁻ form, from aqueous solutions. Sorption batch experiments showed that the mixed MgAlFe oxides, obtained from calcined hydrotalcite-like compound (3HT-cal), removed Sb(OH)₆⁻ through the formation of a non-LDH brandholzite-like compound, whereas the mixed ZnAl oxides, resulting from calcined zaccagnaite-like compound (2ZC-cal), trapped Sb(OH)₆⁻ in the interlayer during the formation of a Sb(V)-bearing LDH (the zincalstibite-like compound). The competition effect of coexistent anions on Sb(OH)₆⁻ removal was HAsO₄²⁻ >> HCO₃⁻ ≥ SO₄²⁻ for 2ZC-cal and HAsO₄²⁻ >> HCO₃⁻ >> SO₄²⁻ for 3HT-cal. Considering the importance of assessing the practical use of calcined LDHs, batch experiments were also carried out with a slag drainage affected by serious Sb(V) pollution (Sb = 9900 μg/L) sampled at the abandoned Su Suergiu mine (Sardinia, Italy). Results showed that, due to the complex chemical composition of the slag drainage, dissolved Sb(OH)₆⁻ was removed by intercalation in the interlayer of carbonate LDHs rather than through the formation of brandholzite-like or zincalstibite-like compounds. Both 2ZC-cal and 3HT-cal efficiently removed very high percentages (up to 90–99%) of Sb(V) from the Su Suergiu mine drainage, and thus can have a potential application for real polluted waters. Full article

(This article belongs to the Special Issue Layered Double Hydroxides)

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3 pages, 185 KiB

Open AccessEditorial

Biological Crystallization

by Jaime Gómez-Morales, Giuseppe Falini and Juan Manuel García-Ruiz

Crystals 2019, 9(8), 409; https://doi.org/10.3390/cryst9080409 - 06 Aug 2019

Cited by 2 | Viewed by 2736

Abstract

“Biological Crystallization” is today a very wide topic that includes biomineralization, but also the laboratory crystallization of biological compounds such as macromolecules, carbohydrates or lipids, and the synthesis and fabrication of biomimetic materials by different routes [...] Full article

(This article belongs to the Special Issue Biological Crystallization)

13 pages, 8457 KiB

Open AccessArticle

An Unexpected Trinuclear Cobalt(II) Complex Based on a Half-Salamo-Like Ligand: Synthesis, Crystal Structure, Hirshfeld Surface Analysis, Antimicrobial and Fluorescent Properties

by Ruo-Yan Li, Xiao-Xin An, Juan-Li Wu, You-Peng Zhang and Wen-Kui Dong

Crystals 2019, 9(8), 408; https://doi.org/10.3390/cryst9080408 - 06 Aug 2019

Cited by 18 | Viewed by 3650

Abstract

An unexpected trinuclear Co(II) complex, [Co₃(L²)₂(μ-OAc)₂(CH₃OH)₂]·2CH₃OH (H₂L² = 4,4′-dibromo-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol) constructed from a half-Salamo-based ligand (HL¹ = 2-[O-(1-ethyloxyamide)]oxime-4-bromophenol) and Co(OAc)₂·4H [...] Read more.

An unexpected trinuclear Co(II) complex, [Co₃(L²)₂(μ-OAc)₂(CH₃OH)₂]·2CH₃OH (H₂L² = 4,4′-dibromo-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol) constructed from a half-Salamo-based ligand (HL¹ = 2-[O-(1-ethyloxyamide)]oxime-4-bromophenol) and Co(OAc)₂·4H₂O, has been synthesized and characterized by elemental analyses, infrared spectra (IR), UV-Vis spectra, X-ray crystallography and Hirshfeld surface analysis. The Co(II) complex contains three Co(II) atoms, two completely deprotonated (L²)²⁻ units, two bridged acetate molecules, two coordinated methanol molecules and two crystalline methanol molecules, and finally, a three-dimensional supramolecular structure with infinite extension was formed. Interestingly, during the formation of the Co(II) complex, the ligand changed from half-Salamo-like to a symmetrical single Salamo-like ligand due to the bonding interactions of the molecules. In addition, the antimicrobial activities of HL¹ and its Co(II) complex were also investigated. Full article

(This article belongs to the Special Issue Synthesis, Crystal Structures and Hirshfeld Surface Analysis of Coordination Compounds)

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15 pages, 2188 KiB

Open AccessArticle

Taking Advantage of the Coordinative Behavior of a Tridentate Schiff Base Ligand towards Pd²⁺ and Cu²⁺

by Jesús Sanmartín-Matalobos, Matilde Fondo, Morteza Zarepour-Jevinani and Ana M. García-Deibe

Crystals 2019, 9(8), 407; https://doi.org/10.3390/cryst9080407 - 05 Aug 2019

Cited by 1 | Viewed by 2794

Abstract

We have explored the suitability of an O,N,N–donor Schiff base (H₂SB) for obtaining dinuclear complexes with heavy metal ions such as Cu²⁺, Zn²⁺, Ni²⁺, and Co²⁺ (borderline acids) as well as Pd²⁺ [...] Read more.

We have explored the suitability of an O,N,N–donor Schiff base (H₂SB) for obtaining dinuclear complexes with heavy metal ions such as Cu²⁺, Zn²⁺, Ni²⁺, and Co²⁺ (borderline acids) as well as Pd²⁺ and Cd²⁺ (soft acids). Spectroscopic studies demonstrated that the complexation of H₂SB and Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺, Pd²⁺, and Cd²⁺ occurred at a 1:1 stoichiometry. We have found two square planar centers with Pd-N-Pd angles of 93.08(11)° and a Pd–Pd distance of 3.0102(4) Å in Pd₂(SB)₂·Me₂CO. This Pd–Pd distance is 30% shorter than the sum of the van der Waals radii, which is in accordance with a strong palladophilic interaction. Fluorescence studies on H₂SB-M²⁺ interaction showed that H₂SB can detect Cu²⁺ ions in a sample matrix containing various metal ions (hard, soft, or borderline acids) without interference. Determination of binding constants showed that H₂SB has a greater affinity for borderline acids than for soft acids. Full article

(This article belongs to the Section Crystal Engineering)

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19 pages, 2547 KiB

Open AccessReview

Implementing Metal-Organic Frameworks for Natural Gas Storage

by Eyas Mahmoud, Labeeb Ali, Asmaa El Sayah, Sara Awni Alkhatib, Hend Abdulsalam, Mouza Juma and Ala’a H. Al-Muhtaseb

Crystals 2019, 9(8), 406; https://doi.org/10.3390/cryst9080406 - 04 Aug 2019

Cited by 37 | Viewed by 7933

Abstract

Methane can be stored by metal-organic frameworks (MOFs). However, there remain challenges in the implementation of MOFs for adsorbed natural gas (ANG) systems. These challenges include thermal management, storage capacity losses due to MOF packing and densification, and natural gas impurities. In this [...] Read more.

Methane can be stored by metal-organic frameworks (MOFs). However, there remain challenges in the implementation of MOFs for adsorbed natural gas (ANG) systems. These challenges include thermal management, storage capacity losses due to MOF packing and densification, and natural gas impurities. In this review, we discuss discoveries about how MOFs can be designed to address these three challenges. For example, Fe(bdp) (bdp²⁻ = 1,4-benzenedipyrazolate) was discovered to have intrinsic thermal management and released 41% less heat than HKUST-1 (HKUST = Hong Kong University of Science and Technology) during adsorption. Monolithic HKUST-1 was discovered to have a working capacity 259 cm³ (STP) cm⁻³ (STP = standard temperature and pressure equivalent volume of methane per volume of the adsorbent material: T = 273.15 K, P = 101.325 kPa), which is a 50% improvement over any other previously reported experimental value and virtually matches the 2012 Department of Energy (Department of Energy = DOE) target of 263 cm³ (STP) cm⁻³ after successful packing and densification. In the case of natural gas impurities, higher hydrocarbons and other molecules may poison or block active sites in MOFs, resulting in up to a 50% reduction of the deliverable energy. This reduction can be mitigated by pore engineering. Full article

(This article belongs to the Special Issue New Horizons in Zeolites and Zeolite-Like Materials)

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13 pages, 3227 KiB

Open AccessEditor’s ChoiceArticle

Direct Growth of Flower-Shaped ZnO Nanostructures on FTO Substrate for Dye-Sensitized Solar Cells

by Ahmad Umar, Mohammad Shaheer Akhtar, Tubia Almas, Ahmed Abdulbaqi Ibrahim, Mohammed Sultan Al-Assiri, Yoshitake Masuda, Qazi Inamur Rahman and Sotirios Baskoutas

Crystals 2019, 9(8), 405; https://doi.org/10.3390/cryst9080405 - 04 Aug 2019

Cited by 18 | Viewed by 4670

Abstract

The proposed work reports that ZnO nanoflowers were grown on fluorine-doped tin oxide (FTO) substrates via a solution process at low temperature. The high purity and well-crystalline behavior of ZnO nanoflowers were established by X-ray diffraction. The morphological characteristics of ZnO nanoflowers were [...] Read more.

The proposed work reports that ZnO nanoflowers were grown on fluorine-doped tin oxide (FTO) substrates via a solution process at low temperature. The high purity and well-crystalline behavior of ZnO nanoflowers were established by X-ray diffraction. The morphological characteristics of ZnO nanoflowers were clearly revealed that the grown flower structures were in high density with 3D floral structure comprising of small rods assembled as petals. Using UV absorption and Raman spectroscopy, the optical and structural properties of the ZnO nanoflowers were studied. The photoelectrochemical properties of the ZnO nanoflowers were studied by utilizing as a photoanode for the manufacture of dye-sensitized solar cells (DSSCs). The fabricated DSSC with ZnO nanoflowers photoanode attained reasonable overall conversion efficiency of ~1.40% and a short-circuit current density (J_SC) of ~4.22 mA cm⁻² with an open circuit voltage (V_OC) of 0.615 V and a fill factor (FF) of ~0.54. ZnO nanostructures have given rise to possible utilization as an inexpensive and efficient photoanode materials for DSSCs. Full article

(This article belongs to the Special Issue Zinc Oxide Nanomaterials and Based Devices)

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