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Crystals, Volume 7, Issue 7 (July 2017)

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Cover Story In this review, we briefly summarize the history of mesocrystal research. We introduce the current [...] Read more.
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Open AccessArticle Lempel-Ziv Complexity of Photonic Quasicrystals
Crystals 2017, 7(7), 183; doi:10.3390/cryst7070183
Received: 27 April 2017 / Revised: 20 June 2017 / Accepted: 21 June 2017 / Published: 23 June 2017
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Abstract
The properties of one-dimensional photonic quasicrystals ultimately rely on their nontrivial long-range order, a hallmark that can be quantified in many ways depending on the specific aspects to be studied. Here, we assess the quasicrystal structural features in terms of the Lempel-Ziv complexity.
[...] Read more.
The properties of one-dimensional photonic quasicrystals ultimately rely on their nontrivial long-range order, a hallmark that can be quantified in many ways depending on the specific aspects to be studied. Here, we assess the quasicrystal structural features in terms of the Lempel-Ziv complexity. This is an easily calculable quantity that has proven to be useful for describing patterns in a variety of systems. One feature of great practical relevance is that it provides a reliable measure of how hard it is to create the structure. Using the generalized Fibonacci quasicrystals as our thread, we give analytical fitting formulas for the dependence of the optical response with the complexity. Full article
(This article belongs to the collection Structure and Properties of Quasicrystals)
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Open AccessArticle Photonic Bandgap–Cholesteric Device with Electrical Tunability and Optical Tristability in Its Defect Modes
Crystals 2017, 7(7), 184; doi:10.3390/cryst7070184
Received: 14 May 2017 / Revised: 15 June 2017 / Accepted: 20 June 2017 / Published: 23 June 2017
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Abstract
This study proposes a hybrid structure for a one-dimensional (1D) photonic crystal (PC) comprising a tristable cholesteric liquid crystal (CLC) as the defect layer. The CLC exhibits three optically stable states: the Grandjean planar (P), focal conic (FC), and uniform lying helix (ULH)
[...] Read more.
This study proposes a hybrid structure for a one-dimensional (1D) photonic crystal (PC) comprising a tristable cholesteric liquid crystal (CLC) as the defect layer. The CLC exhibits three optically stable states: the Grandjean planar (P), focal conic (FC), and uniform lying helix (ULH) configurations. Specifically, the reflection band of the CLC is set within the photonic bandgap (PBG) of the 1D PC. While the ULH and the FC states can be regarded as the light-on and light-off states for defect-mode peaks in the visible spectrum, respectively, switching the device from the ULH to the P state enables suppression of the transmission of partial defect modes within the PBG. This device possesses many alluring features, such as optical tristability at null applied voltage and transmission tunability of the defect modes, providing a new pathway for the design of multifunctional and energy-efficient optical switches, light shutters, multichannels, and wavelength selectors. Full article
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Open AccessArticle Microstructure and Electrical Properties of Fe,Cu Substituted (Co,Mn)3O4 Thin Films
Crystals 2017, 7(7), 185; doi:10.3390/cryst7070185
Received: 19 May 2017 / Revised: 14 June 2017 / Accepted: 17 June 2017 / Published: 23 June 2017
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Abstract
In this work, thin films (~1000 nm) of a pure MnCo2O4 spinel together with its partially substituted derivatives (MnCo1.6Cu0.2Fe0.2O4, MnCo1.6Cu0.4O4, MnCo1.6Fe0.4O4
[...] Read more.
In this work, thin films (~1000 nm) of a pure MnCo2O4 spinel together with its partially substituted derivatives (MnCo1.6Cu0.2Fe0.2O4, MnCo1.6Cu0.4O4, MnCo1.6Fe0.4O4) were prepared by spray pyrolysis and were evaluated for electrical conductivity. Doping by Cu increases the electrical conductivity, whereas doping by Fe decreases the conductivity. For Cu containing samples, rapid grain growth occurs and these samples develop cracks due to a potentially too high thermal expansion coefficient mismatch to the support. Samples doped with both Cu and Fe show high electrical conductivity, normal grain growth and no cracks. By co-doping the Mn, Co spinel with both Cu and Fe, its properties can be tailored to reach a desired thermal expansion coefficient/electrical conductivity value. Full article
(This article belongs to the Special Issue Crystal Structure of Electroceramics)
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Open AccessArticle Effective Pattern Intensity Artifacts Treatment for Electron Diffractive Imaging
Crystals 2017, 7(7), 186; doi:10.3390/cryst7070186
Received: 3 May 2017 / Revised: 12 June 2017 / Accepted: 21 June 2017 / Published: 24 June 2017
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Abstract
We present a method to treat spurious intensities in electron diffraction experiments. Coherent electron diffraction imaging requires proper data reduction before the application of phase retrieval algorithms. The presence of spurious intensities in the electron diffraction patterns makes the data reduction complicated and
[...] Read more.
We present a method to treat spurious intensities in electron diffraction experiments. Coherent electron diffraction imaging requires proper data reduction before the application of phase retrieval algorithms. The presence of spurious intensities in the electron diffraction patterns makes the data reduction complicated and time consuming and jeopardizes the application of mathematical constraints to maximize the information that can be extracted from the experimental data. Here we show how the experimental diffraction patterns can be treated to remove the unwanted artifacts without corrupting the genuine intensities scattered by the specimen. The resulting diffraction patterns are suitable for the application of further processes and constraints aimed at deriving fundamental structural information by applying phase retrieval algorithms or other approaches capable of deriving quantitative atomic resolution information about the specimen structure. Full article
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Open AccessArticle Transparency of Semi-Insulating, n-Type, and p-Type Ammonothermal GaN Substrates in the Near-Infrared, Mid-Infrared, and THz Spectral Range
Crystals 2017, 7(7), 187; doi:10.3390/cryst7070187
Received: 10 May 2017 / Revised: 16 June 2017 / Accepted: 21 June 2017 / Published: 25 June 2017
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Abstract
GaN substrates grown by the ammonothermal method are analyzed by Fast Fourier Transformation Spectroscopy in order to study the impact of doping (both n- and p-type) on their transparency in the near-infrared, mid-infrared, and terahertz spectral range. It is shown that the introduction
[...] Read more.
GaN substrates grown by the ammonothermal method are analyzed by Fast Fourier Transformation Spectroscopy in order to study the impact of doping (both n- and p-type) on their transparency in the near-infrared, mid-infrared, and terahertz spectral range. It is shown that the introduction of dopants causes a decrease in transparency of GaN substrates in a broad spectral range which is attributed to absorption on free carriers (n-type samples) or dopant ionization (p-type samples). In the mid-infrared the transparency cut-off, which for a semi-insulating GaN is at ~7 µm due to an absorption on a second harmonic of optical phonons, shifts towards shorter wavelengths due to an absorption on free carriers up to ~1 µm at n ~ 1020 cm−3 doping level. Moreover, a semi-insulating GaN crystal shows good transparency in the 1–10 THz range, while for n-and p-type crystal, the transparency in this spectral region is significantly quenched below 1%. In addition, it is shown that in the visible spectral region n-type GaN substrates with a carrier concentration below 1018 cm−3 are highly transparent with the absorption coefficient below 3 cm−1 at 450 nm, a satisfactory condition for light emitting diodes and laser diodes operating in this spectral range. Full article
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Open AccessArticle Research on Nonlinear Absorption Effect in KDP and 70%-DKDP Crystals
Crystals 2017, 7(7), 188; doi:10.3390/cryst7070188
Received: 7 May 2017 / Revised: 17 June 2017 / Accepted: 17 June 2017 / Published: 1 July 2017
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Abstract
Nonlinear optical absorption effect in KDP and 70%-DKDP crystals, which were grown by the conventional temperature cooling method, was systematically studied using picosecond pulse laser excitation. Using open aperture Z-scan measurements, the dependence of nonlinear absorption effect on sample orientations (I, II, and
[...] Read more.
Nonlinear optical absorption effect in KDP and 70%-DKDP crystals, which were grown by the conventional temperature cooling method, was systematically studied using picosecond pulse laser excitation. Using open aperture Z-scan measurements, the dependence of nonlinear absorption effect on sample orientations (I, II, and z) as well as laser intensity was systematically measured at λ = 1064 and 532 nm. According to the experimental results, the nonlinear absorption effect at λ = 532 nm was confirmed, while at λ = 1064 nm no nonlinear absorption was observed for KDP and 70%-DKDP crystals. In addition, the optical absorption along I- and II-type affected by laser intensity was larger than that along the z-direction. The important nonlinear absorption coefficients β and χ I ( 3 ) (esu) measured along different orientations were exhibited in detail at wavelengths of 1064 nm and 532 nm. The results indicate that nonlinear absorption coefficients increase first and then decrease with the increment of laser intensity for KDP and 70%-DKDP crystals. Full article
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Open AccessArticle High Power 1443.5 nm Laser with Nd:YAG Single Crystal Fiber
Crystals 2017, 7(7), 189; doi:10.3390/cryst7070189
Received: 30 April 2017 / Revised: 18 June 2017 / Accepted: 23 June 2017 / Published: 1 July 2017
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Abstract
A high-power eye-safe 1443.5 nm laser was demonstrated with an Nd:YAG single crystal fiber (SCF) as the gain medium. For continuous wave (CW) operation, a maximum output power of 13.3 W was obtained under an absorbed pump power of 95.0 W, corresponding to
[...] Read more.
A high-power eye-safe 1443.5 nm laser was demonstrated with an Nd:YAG single crystal fiber (SCF) as the gain medium. For continuous wave (CW) operation, a maximum output power of 13.3 W was obtained under an absorbed pump power of 95.0 W, corresponding to an optical-to-optical conversion efficiency of 14.0%. For acousto-optically (AO) Q-switched regime, an output power of 1.95 W was obtained at a pulse repetition frequency (PRF) of 10 kHz. The pulse duration was 69.5 ns. The pulse energy and peak power were calculated to be 195 µJ and 2.81 kW, respectively. Full article
(This article belongs to the Special Issue Advances in Optical Crystal Fibers)
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Open AccessArticle Experimental and Theoretical Evidence for Surface-Induced Carbon and Nitrogen Fractionation during Diamond Crystallization at High Temperatures and High Pressures
Crystals 2017, 7(7), 190; doi:10.3390/cryst7070190
Received: 31 March 2017 / Revised: 21 June 2017 / Accepted: 22 June 2017 / Published: 26 June 2017
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Abstract
Isotopic and trace element variations within single diamond crystals are widely known from both natural stones and synthetic crystals. A number of processes can produce variations in carbon isotope composition and nitrogen abundance in the course of diamond crystallization. Here, we present evidence
[...] Read more.
Isotopic and trace element variations within single diamond crystals are widely known from both natural stones and synthetic crystals. A number of processes can produce variations in carbon isotope composition and nitrogen abundance in the course of diamond crystallization. Here, we present evidence of carbon and nitrogen fractionation related to the growing surfaces of a diamond. We document that difference in the carbon isotope composition between cubic and octahedral growth sectors is solvent-dependent and varies from 0.7‰ in a carbonate system to 0.4‰ in a metal-carbon system. Ab initio calculations suggest up to 4‰ instantaneous 13C depletion of cubic faces in comparison to octahedral faces when grown simultaneously. Cubic growth sectors always have lower nitrogen abundance in comparison to octahedral sectors within synthetic diamond crystals in both carbonate and metal-carbon systems. The stability of any particular growth faces of a diamond crystal depends upon the degree of carbon association in the solution. Octahedron is the dominant form in a high-associated solution while the cube is the dominant form in a low-associated solution. Fine-scale data from natural crystals potentially can provide information on the form of carbon, which was present in the growth media. Full article
(This article belongs to the Special Issue Diamond Crystals)
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Open AccessArticle On the Importance of Halogen–Halogen Interactions in the Solid State of Fullerene Halides: A Combined Theoretical and Crystallographic Study
Crystals 2017, 7(7), 191; doi:10.3390/cryst7070191
Received: 31 May 2017 / Revised: 17 June 2017 / Accepted: 22 June 2017 / Published: 26 June 2017
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Abstract
In this manuscript, we combined DFT (Density Functional Theory) calculations (BP86-D3/def2-TZVP level of theory) and a search in the CSD (Cambridge Structural Database) to analyze the role of halogen–halogen interactions in the crystal structure of fullerene halides. We have used a theoretical model
[...] Read more.
In this manuscript, we combined DFT (Density Functional Theory) calculations (BP86-D3/def2-TZVP level of theory) and a search in the CSD (Cambridge Structural Database) to analyze the role of halogen–halogen interactions in the crystal structure of fullerene halides. We have used a theoretical model of a halogenated C60 and evaluated the formation of halogen–halogen complexes between F, Cl, Br and I derivatives. In addition, we also carried out AIM (Atoms in Molecules) and NBO (Natural Bonding Orbital) analyses to further describe and characterize the interactions described herein. Finally, we have carried out a search in the CSD and found several X-ray structures where these interactions are present and important in governing the crystal packing of the fullerene halides, thus giving reliability to the results derived from the calculations. Full article
(This article belongs to the Special Issue Analysis of Halogen and Other σ-Hole Bonds in Crystals)
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Open AccessArticle Synthesis, Crystal Structure, and Magnetic Properties of Amidate and Carboxylate Dimers of Ruthenium
Crystals 2017, 7(7), 192; doi:10.3390/cryst7070192
Received: 15 June 2017 / Revised: 23 June 2017 / Accepted: 25 June 2017 / Published: 27 June 2017
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Abstract
Solvothermal and microwave-assisted methods have been used to prepare several amidate and carboxylate complexes of the type [Ru2X(µ-NHOCC6H3-3,5-(OMe)2)4]n [X = Cl (1), Br (2), I (3)]
[...] Read more.
Solvothermal and microwave-assisted methods have been used to prepare several amidate and carboxylate complexes of the type [Ru2X(µ-NHOCC6H3-3,5-(OMe)2)4]n [X = Cl (1), Br (2), I (3)] and [Ru2X(µ-O2CC6H3-3,5-(OMe)2)4]n [X = Cl (4), Br (5), I (6)]. Complexes 46 have also been obtained by conventional synthesis which is ineffective to prepare the amidate compounds. However, single crystals of complexes 15 were obtained using the solvothermal method. The single crystal X-ray structure determination of compounds 15 have been carried out. All complexes display a paddlewheel-type structure with the metal atoms connected by four bridging amidate or carboxylate ligands. Chloride, bromide, or iodide anions connect the dimetallic units, producing one-dimensional zigzag chains. The magnetic properties of all compounds were studied. The magnetic moment at room temperature are in accordance with an electronic configuration with three unpaired electrons σ2π4δ2(π*δ*)3 per dimer unit. The fit of the magnetic data suggests the existence, in these complexes, of a weak antiferromagnetic intermolecular interaction between the diruthenium units mediated by the halide ligand and an appreciable zero-field splitting in the diruthenium moieties. Full article
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Open AccessArticle Phenomenological Consideration of Protein Crystal Nucleation; the Physics and Biochemistry behind the Phenomenon
Crystals 2017, 7(7), 193; doi:10.3390/cryst7070193
Received: 23 May 2017 / Revised: 19 June 2017 / Accepted: 21 June 2017 / Published: 27 June 2017
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Abstract
Physical and biochemical aspects of protein crystal nucleation can be distinguished in an appropriately designed experimental setting. From a physical perspective, the diminishing number of nucleation-active particles (and/or centers), and the appearance of nucleation exclusion zones, are two factors that act simultaneously and
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Physical and biochemical aspects of protein crystal nucleation can be distinguished in an appropriately designed experimental setting. From a physical perspective, the diminishing number of nucleation-active particles (and/or centers), and the appearance of nucleation exclusion zones, are two factors that act simultaneously and retard the initially fast heterogeneous nucleation, thus leading to a logistic time dependence of nuclei number density. Experimental data for protein crystal (and small-molecule droplet) nucleation are interpreted on this basis. Homogeneous nucleation considered from the same physical perspective reveals a difference—the nucleation exclusion zones lose significance as a nucleation decelerating factor when their overlapping starts. From that point on, a drop of overall system supersaturation becomes the sole decelerating factor. Despite the different scenarios of both heterogeneous and homogeneous nucleation, S-shaped time dependences of nuclei number densities are practically indistinguishable due to the exponential functions involved. The biochemically conditioned constraints imposed on the protein crystal nucleation are elucidated as well. They arise because of the highly inhomogeneous (patchy) protein molecule surface, which makes bond selection a requisite for protein crystal nucleation (and growth). Relatively simple experiments confirm this assumption. Full article
(This article belongs to the Special Issue Biological and Biogenic Crystallization)
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Open AccessArticle Electro-Infiltration of Cytochrome C into a Porous Silicon Network, and Its Effect on Nucleation and Protein Crystallization—Studies of the Electrical Properties of Porous Silicon Layer-Protein Systems for Applications in Electron-Transfer Biomolecular Devices
Crystals 2017, 7(7), 194; doi:10.3390/cryst7070194
Received: 6 May 2017 / Revised: 10 June 2017 / Accepted: 23 June 2017 / Published: 28 June 2017
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Abstract
In this work, we report the electrical properties of cytochrome C (Cyt C) inside porous silicon (PSi). We first used two techniques of protein infiltration: classic sitting drop and electrochemical migration methods. The electrochemically assisted cell, used for the infiltration by electro-migration, improved
[...] Read more.
In this work, we report the electrical properties of cytochrome C (Cyt C) inside porous silicon (PSi). We first used two techniques of protein infiltration: classic sitting drop and electrochemical migration methods. The electrochemically assisted cell, used for the infiltration by electro-migration, improved the Cyt C nucleation and the crystallization behavior due to the PSi. We were able to carry out the crystallization thanks to the previous infiltration of proteins inside the Si pores network. We then continued the protein crystal growth through a vapor diffusion set-up. Secondly, we applied both forward and reverse bias currents only to the infiltrated Cyt C. Finally, the electrical characteristics were compared to the control (the protein molecules of which were not infiltrated) and to the samples without protein infiltration. The linker used in the sitting drop method influenced the electrical properties, which showed a modification in the current density. The simple drop method showed a current density of ~42 A/cm2; when employing the electrochemical cell technique, the current density was ~318 A/cm2; for the crystallized structures, it was ~0.908 A/cm2. Full article
(This article belongs to the Special Issue Protein Crystallization under the Presence of an Electric Field)
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Open AccessArticle Ultrasound Assisted Particle Size Control by Continuous Seed Generation and Batch Growth
Crystals 2017, 7(7), 195; doi:10.3390/cryst7070195
Received: 10 April 2017 / Revised: 16 June 2017 / Accepted: 22 June 2017 / Published: 29 June 2017
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Abstract
Controlling particle size is essential for crystal quality in the chemical and pharmaceutical industry. Several articles illustrate the potential of ultrasound to tune this particle size during the crystallization process. This paper investigates how ultrasound can control the particle size distribution (PSD) of
[...] Read more.
Controlling particle size is essential for crystal quality in the chemical and pharmaceutical industry. Several articles illustrate the potential of ultrasound to tune this particle size during the crystallization process. This paper investigates how ultrasound can control the particle size distribution (PSD) of acetaminophen crystals by continuous seed generation in a tubular crystallizer followed by batch growth. It is demonstrated that the supersaturation ratio at which ultrasound starts seed generation has a substantial effect on the final PSD while the applied power is insignificant in the studied conditions. The higher the supersaturation ratio, the smaller the final crystals become up to a supersaturation ratio of 1.56. Furthermore, it was shown that ultrasound can also impact the final PSD when applied during the growth phase. Frequencies of 850 kHz or below reduce the final particle size; the lower the applied frequency, the smaller the crystals become. In conclusion, one could state that ultrasound is able to control the particle size during seed generation and subsequent growth until the final particle size. Full article
(This article belongs to the Special Issue Advances in Ultrasound Stimulated Crystallization)
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Open AccessArticle Superradiant MeV γ Scattered by a Room-Temperature Spinor Quantum Fluid
Crystals 2017, 7(7), 196; doi:10.3390/cryst7070196
Received: 18 May 2017 / Revised: 28 June 2017 / Accepted: 28 June 2017 / Published: 1 July 2017
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Abstract
Recent reports have revealed the rich long-lived Mossbauer phenomenon of 93mNb, in which it has long been speculated that the delocalized 93mNb undergoes Bose-Einstein condensation following an increase in the 93mNb density beyond the threshold of 1012 cm−3
[...] Read more.
Recent reports have revealed the rich long-lived Mossbauer phenomenon of 93mNb, in which it has long been speculated that the delocalized 93mNb undergoes Bose-Einstein condensation following an increase in the 93mNb density beyond the threshold of 1012 cm−3 at room temperature. We now report on the superradiant Rayleigh of the M4 γ at 662 keV scattered into end-fire modes along the long axis of the sample, as evidence of Bose-Einstein condensation. We observed the Arago (Poisson’s) spot in order to demonstrate a near-field γ-ray diffraction from a mm-sized γ source, as well as a γ interference beyond the Huygens-Fresnel principle. During the 107-day monitoring period, seven Sisyphus cycles of mode hopping appeared in the superradiance, which demonstrates the optomechanic bistabilty provided by the collective interaction between the spinor quantum fluid and the impinging γs. Condensate-light interaction produces a pm matter-wave grating to become a Fabry-Pérot resonator with a Q-factor on the order of 1020, from which end-fired γs lase. Full article
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Open AccessArticle Lanthanide Coordination Polymers as Luminescent Sensors for the Selective and Recyclable Detection of Acetone
Crystals 2017, 7(7), 199; doi:10.3390/cryst7070199
Received: 23 May 2017 / Revised: 22 June 2017 / Accepted: 28 June 2017 / Published: 5 July 2017
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Abstract
Three new isostructural lanthanide coordination polymers {[Ln(L)2·2H2O]·Cl·4H2O}, Ln = La (LaL 1), Tb (TbL 2), Eu (EuL 3), L = 4-carboxy-1-(4-carboxybenzyl)pyridinium, have been synthesized under hydrothermal conditions and characterized by single
[...] Read more.
Three new isostructural lanthanide coordination polymers {[Ln(L)2·2H2O]·Cl·4H2O}, Ln = La (LaL 1), Tb (TbL 2), Eu (EuL 3), L = 4-carboxy-1-(4-carboxybenzyl)pyridinium, have been synthesized under hydrothermal conditions and characterized by single crystal X-ray diffraction, IR, TG, PXRD, and luminescence. The solid-state luminescence properties of those Ln-CPs were investigated, realizing the zwitterionic ligand (L) is an excellent antenna chromophore for sensitizing both Tb3+ and Eu3+ ions. We utilized TbL 2 as a representative chemosensor to consider the potential luminescence sensing properties in different solvent suspension, which has the potential to serve as the first case of a luminescent Ln-CP material based on the zwitterionic type of organic ligand for selective and recyclable sensing of acetone in methanol solution. Full article
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Open AccessArticle Growth by the μ-PD Method and Visible Laser Operation of a Single-Crystal Fiber of Pr3+:KY3F10
Crystals 2017, 7(7), 200; doi:10.3390/cryst7070200
Received: 28 April 2017 / Revised: 29 June 2017 / Accepted: 29 June 2017 / Published: 2 July 2017
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Abstract
We report on the first growth, spectroscopy, and visible laser operation of a single-crystal fiber (SCF) of KY3F10 (KYF) grown by the micro-pulling-down (μ-PD) method, doped with Pr3+ ions. This material has a cubic lattice, which makes it appealing
[...] Read more.
We report on the first growth, spectroscopy, and visible laser operation of a single-crystal fiber (SCF) of KY3F10 (KYF) grown by the micro-pulling-down (μ-PD) method, doped with Pr3+ ions. This material has a cubic lattice, which makes it appealing for use in the industry. However, KYF crystals are considered difficult to grow with high optical quality, even with well-established methods. Nevertheless, we grew a 50-mm-long SCF of Pr:KYF, which was transparent in its inner part. We studied the spectroscopic features of it in comparison with existing literature and with samples of the same crystal grown by the Czochralski method, and we did not notice any large differences. These characterizations confirmed that is indeed possible to grow high-quality crystals of Pr:KYF by the μ-PD method. Unfortunately, the crystal proved to be more brittle than typical KYF and especially difficult to polish, leading to rough and irregular facets, as evidenced by transmission measurements. Despite these issues, we obtained continuous-wave laser operation in the orange, red, and deep red regions, using a sample carved from the SCF as active medium and an InGaN-based laser diode as pump source, though with lower performances than in existing reports on this crystal. Full article
(This article belongs to the Special Issue Advances in Optical Crystal Fibers)
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Open AccessArticle Fast Turn-Off Switching of Vertically-Aligned Negative Liquid Crystals by Fine Patterning of Pixel Electrodes
Crystals 2017, 7(7), 201; doi:10.3390/cryst7070201
Received: 25 May 2017 / Revised: 29 June 2017 / Accepted: 30 June 2017 / Published: 3 July 2017
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Abstract
We investigated the two-dimensional (2D) confinement effect on the switching of vertically-aligned negative liquid crystals (LCs) by an electric field applied between the top and bottom patterned electrodes. When an electric field is applied to a patterned vertical alignment (PVA) cell, virtual walls
[...] Read more.
We investigated the two-dimensional (2D) confinement effect on the switching of vertically-aligned negative liquid crystals (LCs) by an electric field applied between the top and bottom patterned electrodes. When an electric field is applied to a patterned vertical alignment (PVA) cell, virtual walls form in the middle of the gaps between and at the center of the patterned electrodes. These virtual walls formed in a PVA cell results in the turn-off time being dependent on the pitch of the patterned electrodes as well as the cell gap. We found that a short response time can be achieved by the fine patterning of pixel electrodes with little decrease in the transmittance. The obtained numerical results agree well with the model based on the 2D confinement effect of LCs. Full article
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Open AccessCommunication External-Voltage-Free Dielectrophoresis of Liquid Crystal Droplets
Crystals 2017, 7(7), 202; doi:10.3390/cryst7070202
Received: 12 May 2017 / Revised: 26 June 2017 / Accepted: 30 June 2017 / Published: 3 July 2017
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Abstract
This work reports, for the first time, a dielectrophoresis (DEP) effect-induced motion of liquid crystal (LC) droplets in an LC/monomer mixture sample with a poly-(N-vinyl carbazole) PVK-coated substrate without an external voltage. With the UV pre-irradiation of the PVK layer through
[...] Read more.
This work reports, for the first time, a dielectrophoresis (DEP) effect-induced motion of liquid crystal (LC) droplets in an LC/monomer mixture sample with a poly-(N-vinyl carbazole) PVK-coated substrate without an external voltage. With the UV pre-irradiation of the PVK layer through a binary mask, a laterally non-uniform electric field can be induced between the pre-illuminated regions and the neighboring non-pre-illuminated PVK regions near the borders of the two regions. The phase separation occurs once the temperature is lower than 50 °C and the LC droplets can form in the sample. The pre-formed non-uniform field provides a DEP-like force to manipulate the small LC microdroplets in the pre-illuminated regions to effectively migrate to the adjacent non-pre-illuminated regions. The continuous supply of the LC from the pre-illuminated regions to the adjacent non-pre-illuminated regions significantly increases the diffraction efficiency of the grating sample. This study provides an insight into developing new external-voltage-free DEP-based devices that can be applied on various fields, such as photonics, displays, and biomedicines. Full article
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Open AccessArticle Incompatibility Stresses and Lattice Rotations Due to Grain Boundary Sliding in Heterogeneous Anisotropic Elasticity
Crystals 2017, 7(7), 203; doi:10.3390/cryst7070203
Received: 29 April 2017 / Revised: 23 June 2017 / Accepted: 26 June 2017 / Published: 4 July 2017
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Abstract
Non-uniform grain boundary sliding can induce strain and rotation incompatibilities at perfectly planar interfaces. Explicit analytic expressions of stress and lattice rotation jumps are thus derived at a planar interface in the general framework of heterogeneous anisotropic thermo-elasticity with plasticity and grain boundary
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Non-uniform grain boundary sliding can induce strain and rotation incompatibilities at perfectly planar interfaces. Explicit analytic expressions of stress and lattice rotation jumps are thus derived at a planar interface in the general framework of heterogeneous anisotropic thermo-elasticity with plasticity and grain boundary sliding. Both elastic fields are directly dependent on in-plane gradients of grain boundary sliding. It is also shown that grain boundary sliding is a mechanism that may relax incompatibility stresses of elastic, plastic and thermal origin although the latter are not resolved on the grain boundary plane. This relaxation may be a driving force for grain boundary sliding in addition to the traditionally considered local shears on the grain boundary plane. Moreover, the obtained analytic expressions are checked by different kinds of bicrystal shearing finite element simulations allowing grain boundary sliding and where a pinned line in the interface plane aims at representing the effect of a triple junction. A very good agreement is found between the analytic solutions and the finite element results. The performed simulations particularly emphasize the role of grain boundary sliding as a possible strong stress generator around the grain boundary close to the triple line because of the presence of pronounced gradients of sliding. Full article
(This article belongs to the Special Issue Plasticity of Crystals and Interfaces)
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Open AccessArticle Morphological and Crystallographic Characterization of Primary Zinc-Rich Crystals in a Ternary Sn-Zn-Bi Alloy under a High Magnetic Field
Crystals 2017, 7(7), 204; doi:10.3390/cryst7070204
Received: 3 June 2017 / Revised: 2 July 2017 / Accepted: 3 July 2017 / Published: 6 July 2017
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Abstract
Due to the unique capacity for structural control, high magnetic fields (HMFs) have been widely applied to the solidification process of alloys. In zinc-based alloys, the primary zinc-rich crystals can be dendritic or needle-like in two dimensions. For the dendritic crystals, their growth
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Due to the unique capacity for structural control, high magnetic fields (HMFs) have been widely applied to the solidification process of alloys. In zinc-based alloys, the primary zinc-rich crystals can be dendritic or needle-like in two dimensions. For the dendritic crystals, their growth pattern and orientation behaviors under HMFs have been investigated. However, the three-dimensional crystallographic growth pattern and the orientation behaviors of the needle-like primary zinc-rich crystals under a high magnetic field have not been studied. In this work, a ternary Sn-Zn-Bi alloy was solidified under different HMFs. The above-mentioned two aspects of the needle-like primary zinc-rich crystals were characterized using the Electron Backscattered Diffraction (EBSD) technique. The results show that the primary zinc-rich crystals are characterized by the plate-shaped faceted growth in three dimensions. They grow in the following manner: spreading rapidly in the {0001} basal plane with a gradual decrease in thickness at the edges. The application of HMFs has no effect on the growth form of the primary zinc-rich crystals, but induces their vertical alignment. Crystallographic analysis indicates that the vertically aligned primary zinc-rich crystals orient preferentially with the c-axis perpendicular to the direction of the magnetic field. Full article
(This article belongs to the Special Issue Crystal Chemistry of Zinc, Cadmium and Mercury)
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Open AccessArticle Shape-Controlled TiCx Particles Fabricated by Combustion Synthesis in the Cu-Ti-C System
Crystals 2017, 7(7), 205; doi:10.3390/cryst7070205
Received: 17 May 2017 / Revised: 23 June 2017 / Accepted: 4 July 2017 / Published: 6 July 2017
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Abstract
TiCx particle-reinforced Cu-matrix composites were prepared in the Cu-Ti-C system by thermal explosion and hot press. Extracted TiCx particles with various shapes of in situ TiCx particles in the Cu-Ti-C system were observed through the Field Emission Scanning Electron Microscope
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TiCx particle-reinforced Cu-matrix composites were prepared in the Cu-Ti-C system by thermal explosion and hot press. Extracted TiCx particles with various shapes of in situ TiCx particles in the Cu-Ti-C system were observed through the Field Emission Scanning Electron Microscope (FESEM). It was found that octahedral and close-to-spherical, spherical or cubic TiCx could be fabricated by changing the C/Ti molar ratio and Cu content. Then, the effect of the C/Ti molar ratio and constituent element concentrations on the shape of in situ TiCx particles was determined: the shape of TiCx particles is octahedral at a C/Ti ratio of 0.4–0.6 with the presence of 70 vol% Cu; or spherical and close-to-spherical at 0.8–1.0 with the presence of 70 vol% Cu; or cubic at C/Ti ratios ≥1.0 with the presence of Cu from 80 vol%–90 vol% and even at C/Ti ratios >1.0 with the presence of 70 vol% Cu. The shape-controlled synthesis of TiCx particles in the Cu-Ti-C system is realized. Full article
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Open AccessArticle Crystallization under an External Electric Field: A Case Study of Glucose Isomerase
Crystals 2017, 7(7), 206; doi:10.3390/cryst7070206
Received: 9 May 2017 / Revised: 8 June 2017 / Accepted: 9 June 2017 / Published: 6 July 2017
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Abstract
Electric fields have been employed to promote macromolecular crystallization for several decades. Although crystals grown in electric fields seem to present higher diffraction quality, these methods are not widespread. For most configurations, electrodes are in direct contact with the protein solution. Here, we
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Electric fields have been employed to promote macromolecular crystallization for several decades. Although crystals grown in electric fields seem to present higher diffraction quality, these methods are not widespread. For most configurations, electrodes are in direct contact with the protein solution. Here, we propose a configuration that can be easily extended to standard crystallization methods for which the electrodes are not in direct contact with the protein solution. Furthermore, the proposed electrode configuration supplies an external DC electric field. Glucose Isomerase from Streptomyces rubiginosus crystals were grown at room temperature using the microbatch method in the presence of 1, 2, 4, and 6 kV. Several crystallization trials were carried out for reproducibility and statistical analysis purposes. The comparison with crystals grown in the absence of electric fields showed that crystallization in the presence of electric fields increases the size of crystals, while decreasing the number of nucleations. X-ray diffraction analysis of the crystals showed that those grown in the presence of electric fields are of higher crystal quality. Full article
(This article belongs to the Special Issue Protein Crystallization under the Presence of an Electric Field)
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Open AccessArticle Doping Liquid Crystal Cells with Photocurable Monomer via Holographic Exposure to Realize Optical-Scattering-Free Infrared Phase Modulators with Fast Response Time
Crystals 2017, 7(7), 208; doi:10.3390/cryst7070208
Received: 30 May 2017 / Revised: 3 July 2017 / Accepted: 4 July 2017 / Published: 7 July 2017
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Abstract
Photocurable monomer-doped liquid crystal (LC) cells were processed via holographic exposure using a low-power He–Ne laser to generate holographic polymer networks. The polymer network LC (PNLC) cells are used to fabricate infrared phase modulators at 1550 nm wavelength possessing favorable electro-optical performance. Compared
[...] Read more.
Photocurable monomer-doped liquid crystal (LC) cells were processed via holographic exposure using a low-power He–Ne laser to generate holographic polymer networks. The polymer network LC (PNLC) cells are used to fabricate infrared phase modulators at 1550 nm wavelength possessing favorable electro-optical performance. Compared with our previous work, the percentages of ingredients in the LC mixture filled in PNLC cells underwent a slight change. The 2 wt% concentration of anisotropic monomer RM257 were in place of isotropic monomer N–vinyl–2–pyrrolidinone (NVP). As a result, the fabricated phase modulators also maintained well homogeneous LC alignments and optical-scattering-free characteristics. Furthermore, NVP dopant successfully reduced the operating voltages from 95 Vrms to 79 Vrms to prevent polymer network deformation when electrically operating with higher voltages. The fabricated infrared phase modulators had a good average response time (i.e., rising time of 0.88 ms and falling time of 0.40 ms). Full article
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Open AccessArticle An Electrically Tunable Liquid Crystal Lens with Coaxial Bi-Focus and Single Focus Switching Modes
Crystals 2017, 7(7), 209; doi:10.3390/cryst7070209
Received: 30 May 2017 / Revised: 3 July 2017 / Accepted: 4 July 2017 / Published: 7 July 2017
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Abstract
A hole-patterned electrode liquid crystal (LC) lens with electrically switching coaxial bi-focus and single focus modes of tuning is demonstrated. The proposed LC lens mainly consists of a two LC layer (TLCL) structure with different thicknesses to achieve higher focusing power than the
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A hole-patterned electrode liquid crystal (LC) lens with electrically switching coaxial bi-focus and single focus modes of tuning is demonstrated. The proposed LC lens mainly consists of a two LC layer (TLCL) structure with different thicknesses to achieve higher focusing power than the conventional hole-patterned electrode LC lens with the same aperture size. In the TLCL structure, one LC layer, doped with 3 wt % RM257, was photopolymerized to achieve a fixed focusing power of 18.5 Diopter. Due to polarization dependence in TLCL lenses, an additional 90° twisted nematic (TN) cell was used to change the incident polarization in order to switch lens functions on or off. As a result, a fixed focusing power of 18.5 Diopter was achieved when voltages of 10 Vrms were applied to the 90° TN cell. In addition, the switching capabilities of the bi-focus and single focus modes were achieved when operating individually with applied voltages from 20 Vrms to 90 Vrms, and higher voltages of over 90 Vrms, respectively. The maximum focusing power in the fabricated TLCL lens is 30.9 Diopter. Full article
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Open AccessArticle Synthesis, Crystal Structures, and Properties of a New Supramolecular Polymer Based on Mixed Imidazole and Carboxylate Ligands
Crystals 2017, 7(7), 210; doi:10.3390/cryst7070210
Received: 5 June 2017 / Revised: 1 July 2017 / Accepted: 2 July 2017 / Published: 13 July 2017
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Abstract
One new coordination polymer, namely, [Cd3(H2L)3(Pza)2(H2O)2]n (1) was synthesized by the reaction of Cd(NO3)2·4H2O with 1,4-di(1H-imidazol-4-yl)benzene (H2L) and
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One new coordination polymer, namely, [Cd3(H2L)3(Pza)2(H2O)2]n (1) was synthesized by the reaction of Cd(NO3)2·4H2O with 1,4-di(1H-imidazol-4-yl)benzene (H2L) and 3,5-pyrazoledicarboxylic acid (H3pza) and characterized by single-crystal X-ray diffraction, IR spectroscopy, elemental analysis, and powder X-ray diffraction (PXRD). The H3pza ligand was completely deprotonated to pza3−, which bridged the Cd2+ to form one-dimensional (1D) chain. The adjacent 1D chains were further linked into the two-dimensional (2D) layer by the linear H2L ligands. The weak interaction, including hydrogen bonds and π−π stacking interactions, extends the 2D layers into three-dimensional (3D) supramolecular polymer. Complex 1 shows intense light blue emission in the solid state at room temperature. Full article
(This article belongs to the Section Crystal Engineering)
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Open AccessCommunication Dual Inhibition of AChE and BChE with the C-5 Substituted Derivative of Meldrum’s Acid: Synthesis, Structure Elucidation, and Molecular Docking Studies
Crystals 2017, 7(7), 211; doi:10.3390/cryst7070211
Received: 23 May 2017 / Revised: 22 June 2017 / Accepted: 5 July 2017 / Published: 9 July 2017
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Abstract
Alzheimer’s disease (AD) lies in the category of those diseases which are still posing challenges to medicinal chemists, and the search for super-effective drugs for the treatment of AD is a work in progress. The inhibition of cholinesterase is considered a viable strategy
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Alzheimer’s disease (AD) lies in the category of those diseases which are still posing challenges to medicinal chemists, and the search for super-effective drugs for the treatment of AD is a work in progress. The inhibition of cholinesterase is considered a viable strategy to enhance the level of acetylcholine in the brain. The C-5 substituted derivative of Meldrum’s acid was synthesized and screened against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzyme inhibition activity. The simple and unique structure of synthesized derivative 3 was found to be good for the dual inhibition of both enzymes (AChE and BChE). 2,2-Dimethyl-5-(([2-(trifluoromethyl) phenyl]amino)methylidene)-1,3-dioxane-4,6-dione (3) showed significant inhibition against AChE, with an IC50 value of 1.13 ± 0.03 µ M (Standard Neostigmine 22.2 ± 3.2 µM), and moderate inhibition against BChE, with an IC50 value of 2.12 ± 1.22 µM (Standard Neostigmine 49.6 ± 6.11 µM). The structural insights reveal that compound 3 possesses intriguing reactive groups, which can potentially evoke the non-covalent interactions and possibly assist by binding in the active site of the target protein. Docking simulations revealed that the compound 3 showed binding inside the active site gorges of both AChE and BChE. An excellent agreement was obtained, as the best docked poses showed important binding features mostly based on interactions due to oxygen atoms and the aromatic moieties of the compound. The docking computations coupled with the experimental findings ascertained that the compound 3 can serve as a scaffold for the dual inhibitors of the human acetylcholine esterases. Full article
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Open AccessArticle σ-Hole Interactions: Perspectives and Misconceptions
Crystals 2017, 7(7), 212; doi:10.3390/cryst7070212
Received: 4 June 2017 / Revised: 21 June 2017 / Accepted: 22 June 2017 / Published: 12 July 2017
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Abstract
After a brief discussion of the σ-hole concept and the significance of molecular electrostatic potentials in noncovalent interactions, we draw attention to some common misconceptions that are encountered in that context: (1) Since the electrostatic potential reflects the contributions of both the nuclei
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After a brief discussion of the σ-hole concept and the significance of molecular electrostatic potentials in noncovalent interactions, we draw attention to some common misconceptions that are encountered in that context: (1) Since the electrostatic potential reflects the contributions of both the nuclei and the electrons, it cannot be assumed that negative potentials correspond to “electron-rich” regions and positive potentials to “electron-poor” ones; (2) The electrostatic potential in a given region is determined not only by the electrons and nuclei in that region, but also by those in other portions of the molecule, especially neighboring ones; (3) A σ-hole is a region of lower electronic density on the extension of a covalent bond, not an electrostatic potential; (4) Noncovalent interactions are between positive and negative regions, which are not necessarily associated with specific atoms, so that “close contacts” between atoms do not always indicate the actual interactions. Full article
(This article belongs to the Special Issue Analysis of Halogen and Other σ-Hole Bonds in Crystals)
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Open AccessArticle Element Strategy Using Ru-Mn Substitution in CuO-CaCu3Ru4O12 Composite Ceramics with High Electrical Conductivity
Crystals 2017, 7(7), 213; doi:10.3390/cryst7070213
Received: 15 May 2017 / Revised: 29 June 2017 / Accepted: 8 July 2017 / Published: 10 July 2017
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Abstract
CaCu3Ru4xMnxO12 bulks with various substitution amounts x and sintering additive CuO (20 vol.%) were prepared, and the influence of x on the electrical conductivity in a wide temperature range (8–900 K) was investigated. Microstructural
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CaCu3Ru4xMnxO12 bulks with various substitution amounts x and sintering additive CuO (20 vol.%) were prepared, and the influence of x on the electrical conductivity in a wide temperature range (8–900 K) was investigated. Microstructural observations showed an enhancement of bulk densification upon Mn substitution. Although the resistivity increased with increasing x, the resistivity was as low as a few mΩcm even in the sample with x = 2.00, where half of Ru is substituted by Mn. This high conductivity despite the loss of Ru 4d conduction following the substitution is explained by the A-site (Cu2+) conduction in CaCu3Ru4xMnxO12. The thermopower of CaCu3Ru4xMnxO12 was found to be influenced by the substitution, and a sign inversion was observed in the substituted samples at low temperature. The partial substitution of Ru by Mn in CaCu3Ru4O12 enables the reduction of the materials cost while maintaining good electrical conductivity for applications as a conducting device component. Full article
(This article belongs to the Special Issue Crystal Structure of Electroceramics)
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Open AccessArticle Halogen-Bonded Co-Crystals of Aromatic N-oxides: Polydentate Acceptors for Halogen and Hydrogen Bonds
Crystals 2017, 7(7), 214; doi:10.3390/cryst7070214
Received: 7 June 2017 / Revised: 6 July 2017 / Accepted: 7 July 2017 / Published: 11 July 2017
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Abstract
Seventeen new halogen-bonded co-crystals characterized by single crystal X-ray analysis are presented from 8 × 4 combinations using methyl-substituted pyridine N-oxides and 1,ω-diiodoperfluoroalkanes. The N−O group in six of 17 co-crystals is monodentate and 11 have μ-O,O bidentate halogen
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Seventeen new halogen-bonded co-crystals characterized by single crystal X-ray analysis are presented from 8 × 4 combinations using methyl-substituted pyridine N-oxides and 1,ω-diiodoperfluoroalkanes. The N−O group in six of 17 co-crystals is monodentate and 11 have μ-O,O bidentate halogen bond acceptor modes. Remarkably, the N−O group in co-crystals of 3-methyl-, 4-methyl- and 3,4-dimethylpyridineN-oxides with octafluoro-1,4-diiodobutane acted as a μ-O,O,O,O halogen and hydrogen bond acceptor, while acting as a μ-O,O,O acceptor in the co-crystal of 2,5-dimethylpyridineN-oxide and tetrafluoro-1,2-diiodoethane. The C−H···O−N hydrogen bonds demonstrated the polydentate cooperativity of the N−O group as a mixed halogen-hydrogen bond acceptor. The co-crystal of 2,4,6-trimethylpyridineN-oxide and dodecafluoro-1,6-diiodohexane exhibited C−I···O−N+ halogen bonds with RXB value 0.76, the shortest of its kind compared to previously reported structures. The RXB values between 0.76 and 0.83 suggested that the C−I···O−N halogen bonds are moderately strong compared to our previously studied N−I···O−N system, with RXB in the order 0.66. Full article
(This article belongs to the Special Issue Analysis of Halogen and Other σ-Hole Bonds in Crystals)
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Open AccessArticle Fabrication of Nano-Micro Hybrid Structures by Replication and Surface Treatment of Nanowires
Crystals 2017, 7(7), 215; doi:10.3390/cryst7070215
Received: 16 June 2017 / Revised: 7 July 2017 / Accepted: 7 July 2017 / Published: 11 July 2017
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Abstract
Nanowire structures have attracted attention in various fields, since new characteristics could be acquired in minute regions. Especially, Anodic Aluminum Oxide (AAO) is widely used in the fabrication of nanostructures, which has many nanosized pores and well-organized nano pattern. Using AAO as a
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Nanowire structures have attracted attention in various fields, since new characteristics could be acquired in minute regions. Especially, Anodic Aluminum Oxide (AAO) is widely used in the fabrication of nanostructures, which has many nanosized pores and well-organized nano pattern. Using AAO as a template for replication, nanowires with a very high aspect ratio can be fabricated. Herein, we propose a facile method to fabricate a nano-micro hybrid structure using nanowires replicated from AAO, and surface treatment. A polymer resin was coated between Polyethylene terephthalate (PET) and the AAO filter, roller pressed, and UV-cured. After the removal of aluminum by using NaOH solution, the nanowires aggregated to form a micropattern. The resulting structure was subjected to various surface treatments to investigate the surface behavior and wettability. As opposed to reported data, UV-ozone treatment can enhance surface hydrophobicity because the UV energy affects the nanowire surface, thus altering the shape of the aggregated nanowires. The hydrophobicity of the surface could be further improved by octadecyltrichlorosilane (OTS) coating immediately after UV-ozone treatment. We thus demonstrated that the nano-micro hybrid structure could be formed in the middle of nanowire replication, and then, the shape and surface characteristics could be controlled by surface treatment. Full article
(This article belongs to the Special Issue Advance in Crystalline Thin Wires)
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Open AccessArticle Syntheses, Crystal Structures and Thermal Behaviors of Two Supramolecular Salamo-Type Cobalt(II) and Zinc(II) Complexes
Crystals 2017, 7(7), 217; doi:10.3390/cryst7070217
Received: 4 June 2017 / Revised: 3 July 2017 / Accepted: 5 July 2017 / Published: 12 July 2017
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Abstract
This paper reports the syntheses of two new complexes, [Co(L1)(H2O)2] (1) and [{Zn(L2)(μ-OAc)Zn(n-PrOH)}2] (2), from asymmetric halogen-substituted Salamo-type ligands H2L1 and H3L
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This paper reports the syntheses of two new complexes, [Co(L1)(H2O)2] (1) and [{Zn(L2)(μ-OAc)Zn(n-PrOH)}2] (2), from asymmetric halogen-substituted Salamo-type ligands H2L1 and H3L2, respectively. Investigation of the crystal structure of complex 1 reveals that the complex includes one Co(II) ion, one (L1)2− unit and two coordinated water molecules. Complex 1 shows slightly distorted octahedral coordination geometry, forming an infinite 2D supramolecular structure by intermolecular hydrogen bond and π–π stacking interactions. Complex 2 contains four Zn(II)ions, two completely deprotonated (L2)3− moieties, two coordinated μ-OAc ions and n-propanol molecules. The Zn(II) ions in complex 2 display slightly distorted trigonal bipyramidal or square pyramidal geometries. Full article
(This article belongs to the Special Issue Crystal Structures of Boron Compounds)
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Open AccessArticle Crystal Structure of 17α-Dihydroequilin, C18H22O2, from Synchrotron Powder Diffraction Data and Density Functional Theory
Crystals 2017, 7(7), 218; doi:10.3390/cryst7070218
Received: 9 April 2017 / Revised: 4 June 2017 / Accepted: 22 June 2017 / Published: 13 July 2017
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Abstract
The crystal structure of 17α-dihydroequilin has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional techniques. 17α-dihydroequilin crystallizes in space group P212121 (#19) with a = 6.76849(1) Å, b = 8.96849(1) Å,
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The crystal structure of 17α-dihydroequilin has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional techniques. 17α-dihydroequilin crystallizes in space group P212121 (#19) with a = 6.76849(1) Å, b = 8.96849(1) Å, c = 23.39031(5) Å, V = 1419.915(3) Å3, and Z = 4. Both hydroxyl groups form hydrogen bonds to each other, resulting in zig-zag chains along the b-axis. The powder diffraction pattern has been submitted to ICDD for inclusion in the Powder Diffraction File™ as the entry 00-066-1608. Full article
(This article belongs to the Special Issue Structural Analysis of Crystalline Materials from Powders)
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Open AccessArticle Analysis of Diffracted Intensities from Finite Protein Crystals with Incomplete Unit Cells
Crystals 2017, 7(7), 220; doi:10.3390/cryst7070220
Received: 31 May 2017 / Revised: 7 July 2017 / Accepted: 8 July 2017 / Published: 14 July 2017
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Abstract
Developments in experimental techniques in micro electron diffraction and serial X-ray crystallography provide the opportunity to collect diffraction data from protein nanocrystals. Incomplete unit cells on the surfaces of protein crystals can affect the distribution of diffracted intensities for crystals with very high
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Developments in experimental techniques in micro electron diffraction and serial X-ray crystallography provide the opportunity to collect diffraction data from protein nanocrystals. Incomplete unit cells on the surfaces of protein crystals can affect the distribution of diffracted intensities for crystals with very high surface-to-volume ratios. The extraction of structure factors from diffraction data for such finite protein crystals sizes is considered here. A theoretical model for the continuous diffracted intensity distribution for data merged from finite crystals with two symmetry-related sub-units of the conventional unit cell is presented. This is used to extend a whole-pattern fitting technique to account for incomplete unit cells in the extraction of structure factor amplitudes. The accuracy of structure factor amplitudes found from this whole-pattern fitting technique and from an integration approach are evaluated. Full article
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Open AccessArticle σ-Holes on Transition Metal Nanoclusters and Their Influence on the Local Lewis Acidity
Crystals 2017, 7(7), 222; doi:10.3390/cryst7070222
Received: 10 June 2017 / Revised: 10 July 2017 / Accepted: 11 July 2017 / Published: 14 July 2017
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Abstract
Understanding the molecular interaction behavior of transition metal nanoclusters lies at the heart of their efficient use in, e.g., heterogeneous catalysis, medical therapy and solar energy harvesting. For this purpose, we have evaluated the applicability of the surface electrostatic potential [VS
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Understanding the molecular interaction behavior of transition metal nanoclusters lies at the heart of their efficient use in, e.g., heterogeneous catalysis, medical therapy and solar energy harvesting. For this purpose, we have evaluated the applicability of the surface electrostatic potential [VS(r)] and the local surface electron attachment energy [ES(r)] properties for characterizing the local Lewis acidity of a series of low-energy TM13 transition metal nanoclusters (TM = Au, Cu, Ru, Rh, Pd, Ir, Pt, Co), including also Pt7Cu6. The clusters have been studied using hybrid Kohn–Sham density functional theory (DFT) calculations. The VS(r) and ES(r), evaluated at 0.001 a.u. isodensity contours, are used to analyze the interactions with H2O. We find that the maxima of VS(r), σ-holes, are either localized or diffuse. This is rationalized in terms of the nanocluster geometry and occupation of the clusters’s, p and d valence orbitals. Our findings motivate a new scheme for characterizing σ-holes as σs (diffuse), σp (localized) or σd (localized) depending on their electronic origin. The positions of the maxima in VS(r) (and minima in ES(r)) are found to coincide with O-down adsorption sites of H2O, whereas minima in VS(r) leads to H-down adsorption. Linear relationships between VS,max (and ES,min) and H2O interaction energies are further discussed. Full article
(This article belongs to the Special Issue Analysis of Halogen and Other σ-Hole Bonds in Crystals)
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Open AccessArticle Inorganic Anions Regulate the Phase Transition in Two Organic Cation Salts Containing [(4-Nitroanilinium)(18-crown-6)]+ Supramolecules
Crystals 2017, 7(7), 224; doi:10.3390/cryst7070224
Received: 28 May 2017 / Revised: 30 June 2017 / Accepted: 6 July 2017 / Published: 15 July 2017
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Abstract
Inorganic Anions Regulate the Phase Transition in Two Organic Cation Salts Containing [(4-Nitroanilinium)(18-crown-6)]+ Supramolecules Full article
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Open AccessArticle The Interplay between Various σ- and π-Hole Interactions of Trigonal Boron and Trigonal Pyramidal Arsenic Triiodides
Crystals 2017, 7(7), 225; doi:10.3390/cryst7070225
Received: 26 June 2017 / Revised: 17 July 2017 / Accepted: 17 July 2017 / Published: 19 July 2017
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Abstract
Boron and arsenic triiodides (BI3 and AsI3, respectively) are similar molecules that differ mainly in their geometries. BI3 is a planar trigonal molecule with D3h symmetry, while AsI3 exhibits a trigonal pyramidal shape with C3v symmetry.
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Boron and arsenic triiodides (BI3 and AsI3, respectively) are similar molecules that differ mainly in their geometries. BI3 is a planar trigonal molecule with D3h symmetry, while AsI3 exhibits a trigonal pyramidal shape with C3v symmetry. Consequently, the As atom of the AsI3 molecule has three σ-holes, whereas the B atom of the BI3 molecule has two symmetrical π-holes. Additionally, there are σ-holes on the iodine atoms in the molecules studied. In the first step, we have studied σ-hole and π-hole interactions in the known monocrystals of BI3 and AsI3. Quantum mechanical calculations have revealed that the crystal packing of BI3 is dominated by π-hole interactions. In the case of AsI3, the overall contribution of dihalogen bonding is comparable to that of pnictogen bonding. Additionally, we have prepared the [Na(THF)6]+[I(AsI3)6](AsI3)2 complex, which can be described as the inverse coordination compound where the iodine anion is the center of the aggregate surrounded by six AsI3 molecules in the close octahedral environment and adjacent two molecules in remote distances. This complex is, besides expected dihalogen and pnictogen bonds, also stabilized by systematically attractive dispersion interactions. Full article
(This article belongs to the Special Issue Analysis of Halogen and Other σ-Hole Bonds in Crystals)
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Open AccessArticle The Role of Halogen Bonding in Controlling Assembly and Organization of Cu(II)-Acac Based Coordination Complexes
Crystals 2017, 7(7), 226; doi:10.3390/cryst7070226
Received: 23 June 2017 / Revised: 15 July 2017 / Accepted: 17 July 2017 / Published: 20 July 2017
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Abstract
In order to explore the use of non-covalent interactions in the deliberate assembly of metal-supramolecular architectures, a series of β-diketone based ligands capable of simultaneously acting as halogen-bond donors and chelating ligands were synthesized. The three ligands, L1, L2, and L3
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In order to explore the use of non-covalent interactions in the deliberate assembly of metal-supramolecular architectures, a series of β-diketone based ligands capable of simultaneously acting as halogen-bond donors and chelating ligands were synthesized. The three ligands, L1, L2, and L3, carry ethynyl-activated chlorine, bromine, and iodine atoms, respectively and copper(II) complexes of all three ligands were crystallized from different solvents, acetonitrile, ethyl acetate, and nitromethane in order to study specific ligand-solvent interaction. The free ligands L2 and L3, with more polarizable halogen atoms, display C-X⋯O halogen bonds in the solid state, whereas the chloro-analogue (L1) does not engage in halogen bonding. Both acetonitrile and ethyl acetate act as halogen-bond acceptors in Cu(II)-complexes of L2 and L3 whereas nitromethane is present as a ‘space-filling’ guest without participating in any significant intermolecular interactions in Cu(II)-complexes of L2. L3, which is decorated with an iodoethynyl moiety and consistently engages in halogen-bonds with suitable acceptors. This systematic structural analysis allows us to rank the relative importance of a variety of electron-pair donors in these metal complexes. Full article
(This article belongs to the Special Issue Analysis of Halogen and Other σ-Hole Bonds in Crystals)
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Open AccessCommunication Electrohydrodynamics-Induced Abnormal Electro-Optic Characteristics in a Polymer-Dispersed Liquid Crystal Film
Crystals 2017, 7(7), 227; doi:10.3390/cryst7070227
Received: 14 June 2017 / Revised: 17 July 2017 / Accepted: 18 July 2017 / Published: 21 July 2017
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Abstract
This study demonstrates for the first time abnormal electro-optic (EO) characteristics induced by electrohydrodynamics (EHD) in a polymer-dispersed liquid crystal (PDLC) film in the presence of a low-frequency (1 kHz) AC voltage. Large LC droplets (20−40 µm) buried in the film can be
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This study demonstrates for the first time abnormal electro-optic (EO) characteristics induced by electrohydrodynamics (EHD) in a polymer-dispersed liquid crystal (PDLC) film in the presence of a low-frequency (1 kHz) AC voltage. Large LC droplets (20−40 µm) buried in the film can be obtained after the illumination of one UV light with a weak intensity (~0.96 mW/cm2) for 12 h. This film exhibits abnormal EO features, including the transmittance’s decay at a high voltage regime at normal incidence and the conversion between polarization independence and polarization dependence for the transmittance-voltage curve at normal and oblique incidences, respectively, of which properties are different from those shown in traditional PDLC films with small droplets. The abnormal EO characteristics of the large-droplet PDLC at the high voltage regime are attributed to a strong scattering effect associated with the formation of the foggy LC droplets in the cell. This effect is induced by a vortex-like LC director field with a rotational axis normal to the cell substrates in each dome-like droplet of the cell at the high voltage regime. The vortex-like director field is induced by a vortex-like turbulence of charged impurity generated by the EHD effect under the action of the AC electric field along the cell normal and the confinement of the dome-like boundary of the droplet on the charged impurities in each droplet. The scattering is decided by the degrees of mismatch between the refractive indices of the LC droplet and polymer, and the local fluctuation of the vortex-like director field in the droplet, resulting in the abnormal EO behaviors of the large-droplet PDLC. This investigation provides novel insight into the EHD effect in three dimensional (3D) microdroplets with anisotropic fluid. Such a large-droplet PDLC has potential in photonic applications, such as electrically controlled polarization-based optical components or optical converters between polarization independence and polarization dependence. Full article
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Open AccessArticle Synthesis, Crystal Structures, and Photoluminescent Properties of Two Supramolecular Architectures Based on Difunctional Ligands Containing Imidazolyl and Carboxyl Groups
Crystals 2017, 7(7), 228; doi:10.3390/cryst7070228
Received: 13 June 2017 / Revised: 21 July 2017 / Accepted: 21 July 2017 / Published: 23 July 2017
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Abstract
Two new supramolecular architectures, namely, [Cd(L1)2(H2O)]n (1) and [Ni(L2)2(H2O)]n (2), were synthesized by the reaction of corresponding metal salts of CdCl2·2.5H2O
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Two new supramolecular architectures, namely, [Cd(L1)2(H2O)]n (1) and [Ni(L2)2(H2O)]n (2), were synthesized by the reaction of corresponding metal salts of CdCl2·2.5H2O and NiCl2·6H2O with 2-(1H-imidazol-4-yl)benzoic acid (HL1) and 3-(1H-imidazol-4-yl)benzoic acid (HL2) respectively, and characterized by single-crystal X-ray diffraction, IR spectroscopy, elemental analysis and powder X-ray diffraction (PXRD). Both HL1 and HL2 ligands are deprotonated to be L1- and L2- anions that coordinate with Cd(II) and Ni(II) atoms to form two-dimensional (2D) layer structure. Topologically, complex 1 is a 2D network with (4, 4) sql topology, while 2 is a typical 63-hcb topology net. Complex 1 exhibits intense light blue emission in the solid state at room temperature. Full article
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Review

Jump to: Research

Open AccessReview An Overview of the Top Ten Detergents Used for Membrane Protein Crystallization
Crystals 2017, 7(7), 197; doi:10.3390/cryst7070197
Received: 7 June 2017 / Revised: 26 June 2017 / Accepted: 28 June 2017 / Published: 1 July 2017
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Abstract
To study integral membrane proteins, one has to extract them from the membrane—the step that is typically achieved by the application of detergents. In this mini-review, we summarize the top 10 detergents used for the structural analysis of membrane proteins based on the
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To study integral membrane proteins, one has to extract them from the membrane—the step that is typically achieved by the application of detergents. In this mini-review, we summarize the top 10 detergents used for the structural analysis of membrane proteins based on the published results. The aim of this study is to provide the reader with an overview of the main properties of available detergents (critical micelle concentration (CMC) value, micelle size, etc.) and provide an idea of what detergents to may merit further study. Furthermore, we briefly discuss alternative solubilization and stabilization agents, such as polymers. Full article
(This article belongs to the Special Issue Recent Advances in Protein Crystallography)
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Open AccessReview Synthesis Methods of Two-Dimensional MoS2: A Brief Review
Crystals 2017, 7(7), 198; doi:10.3390/cryst7070198
Received: 19 May 2017 / Revised: 20 June 2017 / Accepted: 28 June 2017 / Published: 1 July 2017
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Abstract
Molybdenum disulfide (MoS2) is one of the most important two-dimensional materials after graphene. Monolayer MoS2 has a direct bandgap (1.9 eV) and is potentially suitable for post-silicon electronics. Among all atomically thin semiconductors, MoS2’s synthesis techniques are more
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Molybdenum disulfide (MoS2) is one of the most important two-dimensional materials after graphene. Monolayer MoS2 has a direct bandgap (1.9 eV) and is potentially suitable for post-silicon electronics. Among all atomically thin semiconductors, MoS2’s synthesis techniques are more developed. Here, we review the recent developments in the synthesis of hexagonal MoS2, where they are categorized into top-down and bottom-up approaches. Micromechanical exfoliation is convenient for beginners and basic research. Liquid phase exfoliation and solutions for chemical processes are cheap and suitable for large-scale production; yielding materials mostly in powders with different shapes, sizes and layer numbers. MoS2 films on a substrate targeting high-end nanoelectronic applications can be produced by chemical vapor deposition, compatible with the semiconductor industry. Usually, metal catalysts are unnecessary. Unlike graphene, the transfer of atomic layers is omitted. We especially emphasize the recent advances in metalorganic chemical vapor deposition and atomic layer deposition, where gaseous precursors are used. These processes grow MoS2 with the smallest building-blocks, naturally promising higher quality and controllability. Most likely, this will be an important direction in the field. Nevertheless, today none of those methods reproducibly produces MoS2 with competitive quality. There is a long way to go for MoS2 in real-life electronic device applications. Full article
(This article belongs to the Special Issue Integration of 2D Materials for Electronics Applications)
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Open AccessReview Mesocrystals: Past, Presence, Future
Crystals 2017, 7(7), 207; doi:10.3390/cryst7070207
Received: 15 June 2017 / Revised: 2 July 2017 / Accepted: 4 July 2017 / Published: 9 July 2017
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Abstract
In this review, we briefly summarize the history of mesocrystal research. We introduce the current structural definition of mesocrystals and discuss the appropriate base for the classification of mesocrystals and their relations with other classes of solid state materials in terms of their
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In this review, we briefly summarize the history of mesocrystal research. We introduce the current structural definition of mesocrystals and discuss the appropriate base for the classification of mesocrystals and their relations with other classes of solid state materials in terms of their structure. Building up on this, we comment on the problems in mesocrystal research both fundamental and methodological. Additionally, we make the short overview of the mesocrystal formation principles and synthetic routes used for their fabrications. As an outlook into the future, we highlight the most notable trends in mesocrystal research and developments. Full article
(This article belongs to the Special Issue Mesocrystals and Hierarchical Structures)
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Open AccessReview Advanced Scanning Probe Microscopy of Graphene and Other 2D Materials
Crystals 2017, 7(7), 216; doi:10.3390/cryst7070216
Received: 17 May 2017 / Revised: 3 July 2017 / Accepted: 7 July 2017 / Published: 11 July 2017
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Abstract
Two-dimensional (2D) materials, such as graphene and metal dichalcogenides, are an emerging class of materials, which hold the promise to enable next-generation electronics. Features such as average flake size, shape, concentration, and density of defects are among the most significant properties affecting these
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Two-dimensional (2D) materials, such as graphene and metal dichalcogenides, are an emerging class of materials, which hold the promise to enable next-generation electronics. Features such as average flake size, shape, concentration, and density of defects are among the most significant properties affecting these materials’ functions. Because of the nanoscopic nature of these features, a tool performing morphological and functional characterization on this scale is required. Scanning Probe Microscopy (SPM) techniques offer the possibility to correlate morphology and structure with other significant properties, such as opto-electronic and mechanical properties, in a multilevel characterization at atomic- and nanoscale. This review gives an overview of the different SPM techniques used for the characterization of 2D materials. A basic introduction of the working principles of these methods is provided along with some of the most significant examples reported in the literature. Particular attention is given to those techniques where the scanning probe is not used as a simple imaging tool, but rather as a force sensor with very high sensitivity and resolution. Full article
(This article belongs to the Special Issue Integration of 2D Materials for Electronics Applications)
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Open AccessReview A Review on Metal Nanoparticles Nucleation and Growth on/in Graphene
Crystals 2017, 7(7), 219; doi:10.3390/cryst7070219
Received: 8 June 2017 / Revised: 4 July 2017 / Accepted: 11 July 2017 / Published: 13 July 2017
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Abstract
In this review, the fundamental aspects (with particular focus to the microscopic thermodynamics and kinetics mechanisms) concerning the fabrication of graphene-metal nanoparticles composites are discussed. In particular, the attention is devoted to those fabrication methods involving vapor-phase depositions of metals on/in graphene-based materials.
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In this review, the fundamental aspects (with particular focus to the microscopic thermodynamics and kinetics mechanisms) concerning the fabrication of graphene-metal nanoparticles composites are discussed. In particular, the attention is devoted to those fabrication methods involving vapor-phase depositions of metals on/in graphene-based materials. Graphene-metal nanoparticles composites are, nowadays, widely investigated both from a basic scientific and from several technological point of views. In fact, these graphene-based systems present wide-range tunable and functional electrical, optical, and mechanical properties which can be exploited for the design and production of innovative and high-efficiency devices. This research field is, so, a wide and multidisciplinary section in the nanotechnology field of study. So, this review aims to discuss, in a synthetic and systematic framework, the basic microscopic mechanisms and processes involved in metal nanoparticles formation on graphene sheets by physical vapor deposition methods and on their evolution by post-deposition processes. This is made by putting at the basis of the discussions some specific examples to draw insights on the common general physical and chemical properties and parameters involved in the synergistic interaction processes between graphene and metals. Full article
(This article belongs to the Special Issue Integration of 2D Materials for Electronics Applications)
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Open AccessReview Understanding Mn-Based Intercalation Cathodes from Thermodynamics and Kinetics
Crystals 2017, 7(7), 221; doi:10.3390/cryst7070221
Received: 24 June 2017 / Revised: 7 July 2017 / Accepted: 11 July 2017 / Published: 13 July 2017
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Abstract
A series of Mn-based intercalation compounds have been applied as the cathode materials of Li-ion batteries, such as LiMn2O4, LiNi1xyCoxMnyO2, etc. With open structures, intercalation compounds exhibit
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A series of Mn-based intercalation compounds have been applied as the cathode materials of Li-ion batteries, such as LiMn2O4, LiNi1xyCoxMnyO2, etc. With open structures, intercalation compounds exhibit a wide variety of thermodynamic and kinetic properties depending on their crystal structures, host chemistries, etc. Understanding these materials from thermodynamic and kinetic points of view can facilitate the exploration of cathodes with better electrochemical performances. This article reviews the current available thermodynamic and kinetic knowledge on Mn-based intercalation compounds, including the thermal stability, structural intrinsic features, involved redox couples, phase transformations as well as the electrical and ionic conductivity. Full article
(This article belongs to the Special Issue Solution-Processed Inorganic Functional Crystals)
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Open AccessReview Structural Aspects of Porphyrins for Functional Materials Applications
Crystals 2017, 7(7), 223; doi:10.3390/cryst7070223
Received: 19 April 2017 / Revised: 22 June 2017 / Accepted: 12 July 2017 / Published: 15 July 2017
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Abstract
Porphyrinic compounds comprise a diverse group of materials which have in common the presence of one or more cyclic tetrapyrroles known as porphyrins in their molecular structures. The resulting aromaticity gives rise to the semiconducting properties that make these compounds of interest for
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Porphyrinic compounds comprise a diverse group of materials which have in common the presence of one or more cyclic tetrapyrroles known as porphyrins in their molecular structures. The resulting aromaticity gives rise to the semiconducting properties that make these compounds of interest for a broad range of applications, including artificial photosynthesis, catalysis, molecular electronics, sensors, non-linear optics, and solar cells. In this brief review, the crystallographic attributes of porphyrins are emphasized. Examples are given showing how the structural orientations of the porphyrin macrocycle, and the inter-porphyrin covalent bonding present in multiporphyrins influence the semiconducting properties. Beginning with porphine, the simplest porphyrin, we discuss how the more complex structures that have been reported are described by adding peripheral substituents and internal metalation to the macrocycles. We illustrate how the conjugation of the π-bonding, and the presence of electron donor/acceptor pairs, which are the basis for the semiconducting properties, are affected by the crystallographic topology. Full article
(This article belongs to the Special Issue Crystallography of Functional Materials)
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