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Crystals, Volume 9, Issue 8 (August 2019)

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Open AccessArticle
Raman Characterization of Carrier Concentrations of Al-implanted 4H-SiC with Low Carrier Concentration by Photo-Generated Carrier Effect
Crystals 2019, 9(8), 428; https://doi.org/10.3390/cryst9080428 (registering DOI)
Received: 20 July 2019 / Revised: 16 August 2019 / Accepted: 16 August 2019 / Published: 17 August 2019
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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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Open AccessArticle
The Influence of B, N and Si Doping on the CH3 Adsorption on the Diamond Surface Based on DFT Calculations
Crystals 2019, 9(8), 427; https://doi.org/10.3390/cryst9080427 (registering DOI)
Received: 28 June 2019 / Revised: 1 August 2019 / Accepted: 14 August 2019 / Published: 17 August 2019
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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 CH3. 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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Open AccessArticle
Band Tunability of Coupled Elastic Waves along Thickness in Laminated Anisotropic Piezoelectric Phononic Crystals
Crystals 2019, 9(8), 426; https://doi.org/10.3390/cryst9080426 (registering DOI)
Received: 22 May 2019 / Revised: 3 August 2019 / Accepted: 13 August 2019 / Published: 16 August 2019
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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 (with 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)
Open AccessArticle
Polarization Dependence of Low-Frequency Vibrations from Multiple Faces in an Organic Single Crystal
Crystals 2019, 9(8), 425; https://doi.org/10.3390/cryst9080425 (registering DOI)
Received: 16 July 2019 / Revised: 5 August 2019 / Accepted: 14 August 2019 / Published: 16 August 2019
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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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Open AccessArticle
Press to Success: Gd5FW3O16—The First Gadolinium(III) Fluoride Oxidotungstate(VI)
Crystals 2019, 9(8), 424; https://doi.org/10.3390/cryst9080424 (registering DOI)
Received: 21 June 2019 / Revised: 9 August 2019 / Accepted: 12 August 2019 / Published: 16 August 2019
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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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Open AccessArticle
Quest for Compounds at the Verge of Charge Transfer Instabilities: The Case of Silver(II) Chloride
Crystals 2019, 9(8), 423; https://doi.org/10.3390/cryst9080423
Received: 5 July 2019 / Revised: 2 August 2019 / Accepted: 9 August 2019 / Published: 15 August 2019
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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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Open AccessArticle
Theoretical Study of the Electronic and Magnetic Properties and Phase Stability of the Full Heusler Compound Pd2CoAl
Crystals 2019, 9(8), 422; https://doi.org/10.3390/cryst9080422
Received: 30 July 2019 / Revised: 9 August 2019 / Accepted: 13 August 2019 / Published: 14 August 2019
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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 μB 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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Open AccessArticle
Mechanism Design with Singularity Avoidance of Crystal-Inspired Deployable Structures
Crystals 2019, 9(8), 421; https://doi.org/10.3390/cryst9080421
Received: 11 July 2019 / Revised: 9 August 2019 / Accepted: 12 August 2019 / Published: 14 August 2019
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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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Open AccessArticle
Comparing Cyclic Tension-Compression Effects on CoCrFeMnNi High-Entropy Alloy and Ni-Based Superalloy
Crystals 2019, 9(8), 420; https://doi.org/10.3390/cryst9080420
Received: 12 July 2019 / Revised: 1 August 2019 / Accepted: 8 August 2019 / Published: 13 August 2019
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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
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Open AccessArticle
Field-Induced Magnetic Phase Transitions and Rich Phase Diagram of HoMnO3 Single Crystal
Crystals 2019, 9(8), 419; https://doi.org/10.3390/cryst9080419
Received: 24 July 2019 / Revised: 9 August 2019 / Accepted: 12 August 2019 / Published: 13 August 2019
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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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Open AccessArticle
A Grain Boundary Regulates the Friction Behaviors between Graphene and a Gold Substrate
Crystals 2019, 9(8), 418; https://doi.org/10.3390/cryst9080418
Received: 27 June 2019 / Revised: 28 July 2019 / Accepted: 9 August 2019 / Published: 13 August 2019
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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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Open AccessReview
Recent Advances in Colloidal Photonic Crystal-Based Anti-Counterfeiting Materials
Crystals 2019, 9(8), 417; https://doi.org/10.3390/cryst9080417
Received: 27 July 2019 / Revised: 9 August 2019 / Accepted: 10 August 2019 / Published: 12 August 2019
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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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Open AccessArticle
N,O Chelating Ligands Construct Five-Coordinated Zn(II) Exclusive {Zn6} Clusters: Decomposition, Stepwise Assembly and Photoluminescence Study
Crystals 2019, 9(8), 416; https://doi.org/10.3390/cryst9080416
Received: 27 July 2019 / Revised: 8 August 2019 / Accepted: 11 August 2019 / Published: 12 August 2019
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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 ([ZnII6(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 ([ZnII6(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 → [ZnII6(mbm)8(NO3)3]+ → [ZnII5(mbm)7(NO3)2]+ → [ZnII4(mbm)6(NO3)]+ → [ZnII3(mbm)4(NO3)]+ → [ZnII2(mbm)3]+ → [ZnII2(mbm)2(OH)(H2O)2(DMSO)]+ → [ZnII(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 [ZnII(mbm)]+ → [ZnII(mbm)(Hmbm)]+ → [ZnII2(mbm)2(NO3)]+ → [ZnII2(mbm)3]+ → [ZnII3(mbm)4(NO3)]+ → [ZnII4(mbm)5(NO3)2]+ → [ZnII4(mbm)6(NO3)]+ → [ZnII5(mbm)7(NO3)2]+ → [ZnII6(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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Open AccessEditorial
Thin Film Transistor
Crystals 2019, 9(8), 415; https://doi.org/10.3390/cryst9080415
Received: 25 July 2019 / Revised: 3 August 2019 / Accepted: 9 August 2019 / Published: 9 August 2019
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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)
Open AccessArticle
Argentophilic Interactions in Two AgI Complexes of 3-(2-(Pyridin-4-yl)ethyl)pentane-2,4-dione, a Promising Ditopic Ligand
Crystals 2019, 9(8), 414; https://doi.org/10.3390/cryst9080414
Received: 27 June 2019 / Revised: 2 August 2019 / Accepted: 5 August 2019 / Published: 9 August 2019
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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 AgI cation by two pyridine N atoms. Rather unexpectedly, the HacacPyen ligands in the PF6- salt 1 adopt the diketo form, in contrast [...] 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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Open AccessArticle
Structural and Reactivity Analyses of Nitrofurantoin–4-dimethylaminopyridine Salt Using Spectroscopic and Density Functional Theory Calculations
Crystals 2019, 9(8), 413; https://doi.org/10.3390/cryst9080413
Received: 4 July 2019 / Revised: 6 August 2019 / Accepted: 6 August 2019 / Published: 9 August 2019
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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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Open AccessArticle
Continuous Generation of Millimeter-Sized Glycine Crystals in Non-Seeded Millifluidic Slug Flow
Crystals 2019, 9(8), 412; https://doi.org/10.3390/cryst9080412
Received: 4 July 2019 / Revised: 29 July 2019 / Accepted: 2 August 2019 / Published: 9 August 2019
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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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Open AccessArticle
Gold Nanoparticle-Mediated Photoporation Enables Delivery of Macromolecules over a Wide Range of Molecular Weights in Human CD4+ T Cells
Crystals 2019, 9(8), 411; https://doi.org/10.3390/cryst9080411
Received: 17 June 2019 / Revised: 31 July 2019 / Accepted: 5 August 2019 / Published: 7 August 2019
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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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Open AccessArticle
Antimonate Removal from Polluted Mining Water by Calcined Layered Double Hydroxides
Crystals 2019, 9(8), 410; https://doi.org/10.3390/cryst9080410
Received: 20 June 2019 / Revised: 31 July 2019 / Accepted: 1 August 2019 / Published: 6 August 2019
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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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Open AccessEditorial
Biological Crystallization
Crystals 2019, 9(8), 409; https://doi.org/10.3390/cryst9080409
Received: 2 August 2019 / Accepted: 3 August 2019 / Published: 6 August 2019
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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)
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
Crystals 2019, 9(8), 408; https://doi.org/10.3390/cryst9080408
Received: 17 July 2019 / Revised: 31 July 2019 / Accepted: 2 August 2019 / Published: 6 August 2019
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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
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Open AccessArticle
Taking Advantage of the Coordinative Behavior of a Tridentate Schiff Base Ligand towards Pd2+ and Cu2+
Crystals 2019, 9(8), 407; https://doi.org/10.3390/cryst9080407
Received: 23 July 2019 / Revised: 1 August 2019 / Accepted: 3 August 2019 / Published: 5 August 2019
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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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Open AccessReview
Implementing Metal-Organic Frameworks for Natural Gas Storage
Crystals 2019, 9(8), 406; https://doi.org/10.3390/cryst9080406
Received: 16 June 2019 / Revised: 1 August 2019 / Accepted: 2 August 2019 / Published: 4 August 2019
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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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Open AccessArticle
Direct Growth of Flower-Shaped ZnO Nanostructures on FTO Substrate for Dye-Sensitized Solar Cells
Crystals 2019, 9(8), 405; https://doi.org/10.3390/cryst9080405
Received: 27 May 2019 / Revised: 18 July 2019 / Accepted: 25 July 2019 / Published: 4 August 2019
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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 (JSC) of ~4.22 mA cm−2 with an open circuit voltage (VOC) 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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Open AccessArticle
Synthesis and Characterization of Crystalline NaY-Zeolite from Belitung Kaolin as Catalyst for n-Hexadecane Cracking
Crystals 2019, 9(8), 404; https://doi.org/10.3390/cryst9080404
Received: 30 June 2019 / Revised: 26 July 2019 / Accepted: 1 August 2019 / Published: 4 August 2019
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Abstract
Crystalline sodium Y (NaY) zeolite has been synthesized using alternative natural source of aluminate and silicate, extracted from natural Belitung kaolin. Prior to use, the natural kaolin was pretreated to obtain fragmented metakaolin and extracted silica. Synthesis was conducted with the addition of [...] Read more.
Crystalline sodium Y (NaY) zeolite has been synthesized using alternative natural source of aluminate and silicate, extracted from natural Belitung kaolin. Prior to use, the natural kaolin was pretreated to obtain fragmented metakaolin and extracted silica. Synthesis was conducted with the addition of NaY gel (two types of NaY seeds were used, prepared from colloidal sillica or sodium silica water) using hydrothermal method for 21 h at 100 °C. The characterization on the as-synthesized zeolites confirmed that the one prepared using colloidal silica-seed has closer structure similarity to NaY zeolite that was synthesized using pro analysis silicate and aluminate sources. Thus, the rest of the synthesis of NaY was carried out using colloidal silica-NaY seed. The NaY zeolites then were converted to HY, through ammonium-exchange followed by calcination, to be tested as cracking catalysts using n-hexadecane as a probe molecule. It shows that HY from metakaolin and extracted silica gives high performance, i.e., n-hexadecane conversion of 58%–64%, also C5-C12 percentage yield and selectivity of 56%–62% and 98%. This work has shown the potential to utilize kaolin as alternative silicate aluminate sources for crystalline zeolite synthesis and to obtain inexpensive and environmentally friendly catalyst materials. Full article
(This article belongs to the Special Issue New Horizons in Zeolites and Zeolite-Like Materials)
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Open AccessArticle
Cocrystals of 2-Aminopyrimidine with Boric Acid—Crystal Engineering of a Novel Nonlinear Optically (NLO) Active Crystal
Crystals 2019, 9(8), 403; https://doi.org/10.3390/cryst9080403
Received: 16 July 2019 / Revised: 29 July 2019 / Accepted: 31 July 2019 / Published: 3 August 2019
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Abstract
Crystal engineering of novel materials for nonlinear optics (NLO) based on 2-aminopyrimidine yielded two molecular cocrystals with boric acid—trigonal (P3221 space group) 2-aminopyrimidine—boric acid (3/2) and monoclinic (C2/c space group) 2-aminopyrimidine—boric acid (1/2). In addition to [...] Read more.
Crystal engineering of novel materials for nonlinear optics (NLO) based on 2-aminopyrimidine yielded two molecular cocrystals with boric acid—trigonal (P3221 space group) 2-aminopyrimidine—boric acid (3/2) and monoclinic (C2/c space group) 2-aminopyrimidine—boric acid (1/2). In addition to crystal structure determination by single crystal X-ray diffraction, the cocrystals were characterized by powder X-ray diffraction and vibrational spectroscopy (FTIR and FT Raman). Large single crystals of the non-centrosymmetric cocrystal 2-aminopyrimidine—boric acid (3/2) were grown to study the optical properties and determine the second harmonic generation (SHG) efficiency (using 800 nm fundamental laser line) of powder samples. Full article
(This article belongs to the Special Issue Novel Hydrogen-bonded Materials with Significant Physical Properties)
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Open AccessArticle
Silicon Heterojunction Solar Cells with p-Type Silicon Carbon Window Layer
Crystals 2019, 9(8), 402; https://doi.org/10.3390/cryst9080402
Received: 31 May 2019 / Revised: 30 July 2019 / Accepted: 31 July 2019 / Published: 3 August 2019
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Abstract
Boron-doped hydrogenated amorphous silicon carbide (a-SiC:H) thin films are deposited using high frequency 27.12 MHz plasma enhanced chemical vapor deposition system as a window layer of silicon heterojunction (SHJ) solar cells. The CH4 gas flow rate is varied to deposit various a-SiC:H [...] Read more.
Boron-doped hydrogenated amorphous silicon carbide (a-SiC:H) thin films are deposited using high frequency 27.12 MHz plasma enhanced chemical vapor deposition system as a window layer of silicon heterojunction (SHJ) solar cells. The CH4 gas flow rate is varied to deposit various a-SiC:H films, and the optical and electrical properties are investigated. The experimental results show that at the CH4 flow rate of 40 sccm the a-SiC:H has a high band gap of 2.1 eV and reduced absorption coefficients in the whole wavelength region, but the electrical conductivity deteriorates. The technology computer aided design simulation for SHJ devices reveal the band discontinuity at i/p interface when the a-SiC:H films are used. For fabricated SHJ solar cell performance, the highest conversion efficiency of 22.14%, which is 0.33% abs higher than that of conventional hydrogenated amorphous silicon window layer, can be obtained when the intermediate band gap (2 eV) a-SiC:H window layer is used. Full article
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Open AccessCommunication
Stepwise Evolution of AgCl Microcrystals from Octahedron into Hexapod with Mace Pods and their Visible Light Photocatalytic Activity
Crystals 2019, 9(8), 401; https://doi.org/10.3390/cryst9080401
Received: 9 July 2019 / Revised: 23 July 2019 / Accepted: 1 August 2019 / Published: 2 August 2019
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Abstract
In this work, we have synthesized hexapods AgCl crystals with mace pods for the first time. Diallyldimethylammonium chloride (DDA)-controlled stepwise evolution of AgCl crystals from octahedron to hexapods with mace pods are achieved by one-pot method. The intermediates have been captured which show [...] Read more.
In this work, we have synthesized hexapods AgCl crystals with mace pods for the first time. Diallyldimethylammonium chloride (DDA)-controlled stepwise evolution of AgCl crystals from octahedron to hexapods with mace pods are achieved by one-pot method. The intermediates have been captured which show the basic process of crystal growth. In this process, octahedra AgCl crystals firstly grow along the <100> direction and then change to grow in the <110> direction. At the same time, the size of AgCl grow from 2 μm to 20 μm. Due to the poor absorption of visible light by AgCl, sodium borohydride(NaBH4) is used to reduce AgCl hexapods with mace pods crystals. By changing the mole ratio(R) of NaBH4 to AgCl, the new structure was reduced to obtain a series of [email protected] microstructures. Visible light catalysis effects of the [email protected] microstructures on degradation of methyl orange (MO) were investigated. The [email protected] microstructures with R = 0.02 have a high photocatalytic performance, which completely degrades MO in 40 minutes. Full article
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Open AccessReview
Dynamics of Dislocations in Smectic A Liquid Crystals Doped with Nanoparticles
Crystals 2019, 9(8), 400; https://doi.org/10.3390/cryst9080400
Received: 25 July 2019 / Revised: 30 July 2019 / Accepted: 31 July 2019 / Published: 2 August 2019
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Abstract
Edge dislocations are linear defects that locally break the positional order of the layers in smectic A liquid crystals. As in usual solids, these defects play a central role for explaining the plastic properties of the smectic A phase. This work focuses on [...] Read more.
Edge dislocations are linear defects that locally break the positional order of the layers in smectic A liquid crystals. As in usual solids, these defects play a central role for explaining the plastic properties of the smectic A phase. This work focuses on the dynamical properties of dislocations in bulk samples prepared between two glass plates and in free-standing films. The emphasis will be put on the measurement of the mobility of edge dislocations in liquid crystals either pure or doped with nanoparticles. The experimental results will be compared to the existing models. Full article
(This article belongs to the Special Issue Pattern Formation and Defects in Liquid Crystals)
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Open AccessArticle
Crystal Structure of Chaperonin GroEL from Xanthomonas oryzae pv. oryzae
Crystals 2019, 9(8), 399; https://doi.org/10.3390/cryst9080399
Received: 16 July 2019 / Revised: 28 July 2019 / Accepted: 28 July 2019 / Published: 2 August 2019
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Abstract
Xanthomonas oryzae pv. oryzae (Xoo) is a plant pathogen that causes bacterial blight of rice, with outbreaks occurring in most rice-growing countries. Thus far, there is no effective pesticide against bacterial blight. Chaperones in bacterial pathogens are important for the stabilization [...] Read more.
Xanthomonas oryzae pv. oryzae (Xoo) is a plant pathogen that causes bacterial blight of rice, with outbreaks occurring in most rice-growing countries. Thus far, there is no effective pesticide against bacterial blight. Chaperones in bacterial pathogens are important for the stabilization and delivery of effectors into host cells to cause disease. In bacteria, GroEL/GroES complex mediates protein folding and protects proteins against misfolding and aggregation caused by environmental stress. We determined the crystal structure of GroEL from Xanthomonas oryzae pv. oryzae (XoGroEL) at 3.2 Å resolution, which showed the open form of two conserved homoheptameric rings stacked back-to-back. In the open form structure, the apical domain of XoGroEL had a higher B factor than the intermediate and equatorial domains, indicating that the apical domain had a flexible conformation before the binding of substrate unfolded protein and ATP. The XoGroEL structure will be helpful in understanding the function and catalytic mechanism of bacterial chaperonin GroELs. Full article
(This article belongs to the Special Issue Crystallographic Studies of Enzymes)
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