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Crystals, Volume 9, Issue 7 (July 2019)

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Open AccessArticle
Phase Stability and Morphology of Gel Grown Crystals: The Case of CdCl2-bpp Polymeric System
Crystals 2019, 9(7), 363; https://doi.org/10.3390/cryst9070363 (registering DOI)
Received: 30 May 2019 / Revised: 25 June 2019 / Accepted: 12 July 2019 / Published: 16 July 2019
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Abstract
A phenomenological study is carried out on a complex two-component diffusion-reacting system in gel, that is, the Cd-1,3-bis(4-pyridyl)propane (Cd-bpp) coordination polymer. The latter can exist in three solid forms, which exploit a 1:1 correspondence among the Cd/bpp ratio, the crystal structure and [...] Read more.
A phenomenological study is carried out on a complex two-component diffusion-reacting system in gel, that is, the Cd-1,3-bis(4-pyridyl)propane (Cd-bpp) coordination polymer. The latter can exist in three solid forms, which exploit a 1:1 correspondence among the Cd/bpp ratio, the crystal structure and the crystal morphology (1/2: bipyramids; 2/3: needles; 1/3: plates). The aim was to clarify the role of key physicochemical variables (reactant concentrations, composition of the solvent and density of the transport medium) in determining the chemical nature and the morphology of the final crystallization products. The gel method was tested in a variety of different crystallization configurations, including single and double diffusion techniques. The density of the gel primarily affects the morphology of the synthesized crystals, with denser media favouring the needle-like 2/3 Cd-bpp species and diluted ones the 1/2 Cd-bpp bipyramidal one. However, higher densities of the gel are generally associated to strained crystals. The solvent composition is also important, as for example the 1/2 Cd-bpp bipyramids require at least a minimum amount of ethanol to appear. We demonstrated that in gel the strict “equality” stoichiometric criteria for metal-to-ligand ratios can be sometimes eluded, as non–equilibrium concentrations can be locally attained. In this respect, the crystallization geometry was proven to act as a key tool to influence the crystallization output, as it determines the direction and magnitude of the concentration gradients. Finally, the use of U tubes to perform one-pot screenings of a large part of the crystallization space is discussed. Full article
(This article belongs to the Special Issue Crystal Growth in Gels)
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Open AccessArticle
Phase and Residual Stress Evaluation of Dual-Phase Al70Cr30N and Al80Cr20N PVD Films
Crystals 2019, 9(7), 362; https://doi.org/10.3390/cryst9070362
Received: 5 June 2019 / Revised: 30 June 2019 / Accepted: 10 July 2019 / Published: 15 July 2019
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Abstract
We investigated arc ion-plated Al70Cr30N and Al80Cr20N thin films deposited with three different bias voltages (50 V, 100 V, and 150 V) to study crystal phase stabilities, residual stresses, and mechanical properties. Commercial compositions of [...] Read more.
We investigated arc ion-plated Al70Cr30N and Al80Cr20N thin films deposited with three different bias voltages (50 V, 100 V, and 150 V) to study crystal phase stabilities, residual stresses, and mechanical properties. Commercial compositions of AlxCr100–xN coatings typically range from x = 50 to 70 where the cubic face centered crystal phase occurs. The present study focuses on films near the solubility limit of Al in the cubic Cr(Al)N lattice around 70 at.%, above which hexagonal AlN (h–AlN) starts to form in significant amounts. Residual stress values are obtained by two methods: grazing incidence diffraction with the wholepattern fitting and the conventional side inclination method (sin2Ψ method). When multiple phases are present in the film, wholepattern fitting turns out to be particularly effective and a comparison of both measurement methods will be discussed. The Al70Cr30N films consist of the cubic phase with crystallite sizes of about 70 nm for all bias voltages. Compressive stress increased with bias voltage from about 3 to almost 6 GPa and coatings become brittle. Al80Cr20N films showed a different dependence on bias voltage. Using 50 V bias voltage in deposition, the major phase is h–AlN phase with a crystallite grain size of < 30 nm and (0002) preferred orientation. With increasing bias the cubic phase is stabilized also reaching about 70 nm crystallite size. In general, the compressive residual stress was significantly lower than for Al70Cr30N films for the same bias voltages which may be a result of the presence of the hexagonal phase. Wear and scratch tests confirmed higher ductility of the Al80Cr20N variants but reduced resistance of the films in impact wear testing. Full article
(This article belongs to the Special Issue X-ray and neutron Line Profile Analysis of Microstructures)
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Open AccessReview
Layered Double Hydroxides: A Toolbox for Chemistry and Biology
Crystals 2019, 9(7), 361; https://doi.org/10.3390/cryst9070361
Received: 20 June 2019 / Revised: 10 July 2019 / Accepted: 13 July 2019 / Published: 15 July 2019
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Abstract
Layered double hydroxides (LDHs) are an emergent class of biocompatible inorganic lamellar nanomaterials that have attracted significant research interest owing to their high surface-to-volume ratio, the capability to accumulate specific molecules, and the timely release to targets. Their unique properties have been employed [...] Read more.
Layered double hydroxides (LDHs) are an emergent class of biocompatible inorganic lamellar nanomaterials that have attracted significant research interest owing to their high surface-to-volume ratio, the capability to accumulate specific molecules, and the timely release to targets. Their unique properties have been employed for applications in organic catalysis, photocatalysis, sensors, drug delivery, and cell biology. Given the widespread contemporary interest in these topics, time-to-time it urges to review the recent progresses. This review aims to summarize the most recent cutting-edge reports appearing in the last years. It firstly focuses on the application of LDHs as catalysts in relevant chemical reactions and as photocatalysts for organic molecule degradation, water splitting reaction, CO2 conversion, and reduction. Subsequently, the emerging role of these materials in biological applications is discussed, specifically focusing on their use as biosensors, DNA, RNA, and drug delivery, finally elucidating their suitability as contrast agents and for cellular differentiation. Concluding remarks and future prospects deal with future applications of LDHs, encouraging researches in better understanding the fundamental mechanisms involved in catalytic and photocatalytic processes, and the molecular pathways that are activated by the interaction of LDHs with cells in terms of both uptake mechanisms and nanotoxicology effects. Full article
(This article belongs to the Special Issue Layered Double Hydroxides)
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Open AccessArticle
Synthesis, Crystal Structure, and Solubility Analysis of a Famotidine Cocrystal
Crystals 2019, 9(7), 360; https://doi.org/10.3390/cryst9070360
Received: 15 May 2019 / Revised: 8 July 2019 / Accepted: 10 July 2019 / Published: 15 July 2019
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Abstract
A novel cocrystal of the potent H2 receptor antagonist famotidine (FMT) was synthesized with malonic acid (MAL) to enhance its solubility. The cocrystal structure was characterized by X-ray single crystal diffraction, and the asymmetry unit contains one FMT and one MAL connected [...] Read more.
A novel cocrystal of the potent H2 receptor antagonist famotidine (FMT) was synthesized with malonic acid (MAL) to enhance its solubility. The cocrystal structure was characterized by X-ray single crystal diffraction, and the asymmetry unit contains one FMT and one MAL connected via intermolecular hydrogen bonds. The crystal structure is monoclinic with a P21/n space group and unit cell parameters a = 7.0748 (3) Å, b = 26.6502 (9) Å, c = 9.9823 (4) Å, α = 90, β = 104.2228 (12), γ = 90, V = 1824.42 (12) Å3, and Z = 4. The cocrystal had unique thermal, spectroscopic, and powder X-ray diffraction (PXRD) properties that differed from FMT. The solubility of the famotidine-malonic acid cocrystal (FMT-MAL) was 4.2-fold higher than FMT; the FAM-MAL had no change in FMT stability at high temperature, high humidity, or with illumination. Full article
(This article belongs to the Special Issue Pharmaceutical Crystals)
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Open AccessArticle
Fe Melting Transition: Electrical Resistivity, Thermal Conductivity, and Heat Flow at the Inner Core Boundaries of Mercury and Ganymede
Crystals 2019, 9(7), 359; https://doi.org/10.3390/cryst9070359
Received: 10 June 2019 / Revised: 2 July 2019 / Accepted: 12 July 2019 / Published: 15 July 2019
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Abstract
The electrical resistivity and thermal conductivity behavior of Fe at core conditions are important for understanding planetary interior thermal evolution as well as characterizing the generation and sustainability of planetary dynamos. We discuss the electrical resistivity and thermal conductivity of Fe, Co, and [...] Read more.
The electrical resistivity and thermal conductivity behavior of Fe at core conditions are important for understanding planetary interior thermal evolution as well as characterizing the generation and sustainability of planetary dynamos. We discuss the electrical resistivity and thermal conductivity of Fe, Co, and Ni at the solid–liquid melting transition using experimental data from previous studies at 1 atm and at high pressures. With increasing pressure, the increasing difference in the change in resistivity of these metals on melting is interpreted as due to decreasing paramagnon-induced electronic scattering contribution to the total electronic scattering. At the melting transition of Fe, we show that the difference in the value of the thermal conductivity on the solid and liquid sides increases with increasing pressure. At a pure Fe inner core boundary of Mercury and Ganymede at ~5 GPa and ~9 GPa, respectively, our analyses suggest that the thermal conductivity of the solid inner core of small terrestrial planetary bodies should be higher than that of the liquid outer core. We found that the thermal conductivity difference on the solid and liquid sides of Mercury’s inner core boundary is ~2 W(mK)−1. This translates into an excess of total adiabatic heat flow of ~0.01–0.02 TW on the inner core side, depending on the relative size of inner and outer core. For a pure Fe Ganymede inner core, the difference in thermal conductivity is ~7 W(mK)−1, corresponding to an excess of total adiabatic heat flow of ~0.02 TW on the inner core side of the boundary. The mismatch in conducted heat across the solid and liquid sides of the inner core boundary in both planetary bodies appears to be insignificant in terms of generating thermal convection in their outer cores to power an internal dynamo suggesting that chemical composition is important. Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations)
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Open AccessArticle
An Accurate Method for Crystallographic Reconstruction of Parent Austenite from Inherited Martensite in a Low-Alloy Steel
Crystals 2019, 9(7), 358; https://doi.org/10.3390/cryst9070358
Received: 22 June 2019 / Revised: 10 July 2019 / Accepted: 13 July 2019 / Published: 15 July 2019
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Abstract
The microstructure of austenite at high temperatures, which cannot be reserved at room temperatures, determines the properties of its transformed phase in low-alloy steels. Consequently, an accurate method is herein developed to reconstruct local orientations of the parent austenite (γ) phase [...] Read more.
The microstructure of austenite at high temperatures, which cannot be reserved at room temperatures, determines the properties of its transformed phase in low-alloy steels. Consequently, an accurate method is herein developed to reconstruct local orientations of the parent austenite ( γ ) phase from electron backscatter diffraction maps of the martensite ( α ) microstructure. The orientation map of α is cropped into a grid of data squares as the reconstruction unit. The cropped square is then divided into the square inherited from only one γ grain and the square inherited from more than one γ grain. The local orientations around parent γ grain boundaries are more accurately determined using a newly proposed reconstruction criterion. Furthermore, the solution spaces for the orientation relationship and the parent γ orientation are refined, which simultaneously improves the calculation accuracy and efficiency of reconstruction procedure. The validated reconstruction method is applied to obtain local orientations of the deformed γ microstructure accurately. Full article
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Open AccessArticle
Anomalous Behaviors of Spin Waves Studied by Inelastic Light Scattering
Crystals 2019, 9(7), 357; https://doi.org/10.3390/cryst9070357
Received: 30 May 2019 / Revised: 9 July 2019 / Accepted: 10 July 2019 / Published: 14 July 2019
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Abstract
Magnonics, an emerging research field, aims to control and manipulate spin waves in magnetic materials and structures. However, the current understanding of spin waves remains quite limited. This review attempts to provide an overview of the anomalous behaviors of spin waves in various [...] Read more.
Magnonics, an emerging research field, aims to control and manipulate spin waves in magnetic materials and structures. However, the current understanding of spin waves remains quite limited. This review attempts to provide an overview of the anomalous behaviors of spin waves in various types of magnetic materials observed thus far by inelastic light scattering experiments. The anomalously large asymmetry of anti-Stokes to Stokes intensity ratio, broad linewidth, strong resonance effect, unique polarization selection, and abnormal impurity dependence of spin waves are discussed. In addition, the mechanisms of these anomalous behaviors of spin waves are proposed. Full article
(This article belongs to the Special Issue Raman Spectroscopy of Crystals)
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Open AccessArticle
Experimental Evidence for Partially Dehydrogenated ε-FeOOH
Crystals 2019, 9(7), 356; https://doi.org/10.3390/cryst9070356
Received: 18 June 2019 / Revised: 5 July 2019 / Accepted: 12 July 2019 / Published: 13 July 2019
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Abstract
Hydrogen in hydrous minerals becomes highly mobile as it approaches the geotherm of the lower mantle. Its diffusion and transportation behaviors under high pressure are important in order to understand the crystallographic properties of hydrous minerals. However, they are difficult to characterize due [...] Read more.
Hydrogen in hydrous minerals becomes highly mobile as it approaches the geotherm of the lower mantle. Its diffusion and transportation behaviors under high pressure are important in order to understand the crystallographic properties of hydrous minerals. However, they are difficult to characterize due to the limit of weak X-ray signals from hydrogen. In this study, we measured the volume changes of hydrous ε-FeOOH under quasi-hydrostatic and non-hydrostatic conditions. Its equation of states was set as the cap line to compare with ε-FeOOH reheated and decompression from the higher pressure pyrite-FeO2Hx phase with 0 < x < 1. We found the volumes of those re-crystallized ε-FeOOH were generally 2.2% to 2.7% lower than fully hydrogenated ε-FeOOH. Our observations indicated that ε-FeOOH transformed from pyrite-FeO2Hx may inherit the hydrogen loss that occurred at the pyrite-phase. Hydrous minerals with partial dehydrogenation like ε-FeOOHx may bring it to a shallower depth (e.g., < 1700 km) of the lower mantle. Full article
(This article belongs to the Special Issue High Pressure Synthesis in Crystalline Materials)
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Open AccessArticle
Mg-Fe Layered Double Hydroxides Enhance Surfactin Production in Bacterial Cells
Crystals 2019, 9(7), 355; https://doi.org/10.3390/cryst9070355
Received: 20 June 2019 / Revised: 11 July 2019 / Accepted: 11 July 2019 / Published: 12 July 2019
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Abstract
In this study, four additives—montmorillonite, activated carbon, and the layered double hydroxides (LDHs), Mg2Fe–LDH and Mg2Al–LDH—were tested for their ability to promote surfactin production in a Bacillus subtilis ATCC 21332 culture. Among these tested materials, the addition of 4 [...] Read more.
In this study, four additives—montmorillonite, activated carbon, and the layered double hydroxides (LDHs), Mg2Fe–LDH and Mg2Al–LDH—were tested for their ability to promote surfactin production in a Bacillus subtilis ATCC 21332 culture. Among these tested materials, the addition of 4 g/L of the Mg-Fe LDH, which featured an Mg/Fe molar ratio of 2:1, produced the highest surfactin yield of 5280 mg/L. During the time course of B. subtilis cultivation with the added LDH, two phases of cell growth were evident: Growth and decay. In the growth phase, the cells grew slowly and secreted a high amount of surfactin; in the decay phase, the cells degraded rapidly. The production in the presence of the Mg2Fe–LDH had three characteristics: (i) High surfactin production at low biomass, indicating a high specific surfactin yield of 3.19 g/g DCW; (ii) rapid surfactin production within 24 h, inferring remarkably high productivity (4660 mg/L/d); and (iii) a lower carbon source flux to biomass, suggesting an efficient carbon flux to surfactin, giving a high carbon yield of 52.8%. The addition of Mg2Fe–LDH is an effective means of enhancing surfactin production, with many potential applications and future industrial scale-up. Full article
(This article belongs to the Special Issue Layered Double Hydroxides)
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Open AccessArticle
Optical Transport Properties of Graphene Surface Plasmon Polaritons in Mid-Infrared Band
Crystals 2019, 9(7), 354; https://doi.org/10.3390/cryst9070354
Received: 18 June 2019 / Revised: 5 July 2019 / Accepted: 10 July 2019 / Published: 12 July 2019
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Abstract
The excellent transmission characteristics of graphene surface plasmon polaritons in mid-infrared band were analyzed and verified effectively through theoretical derivation and soft simulation in this paper. Meanwhile, a sandwich waveguide structure of dielectric–graphene–substrate–dielectric based on graphene surface plasmon polaritons (SPPs) was presented. Simulation [...] Read more.
The excellent transmission characteristics of graphene surface plasmon polaritons in mid-infrared band were analyzed and verified effectively through theoretical derivation and soft simulation in this paper. Meanwhile, a sandwich waveguide structure of dielectric–graphene–substrate–dielectric based on graphene surface plasmon polaritons (SPPs) was presented. Simulation results indicate that graphene SPPs show unique properties in the mid-infrared region including ultra-compact mode confinement and dynamic tunability, which allow these SPPs to overcome the defects of metal SPPs and traditional silicon-based optoelectronic devices. Thus, they can be used to manufacture subwavelength devices. The work in this paper lays a theoretical foundation for the application of graphene SPPs in the mid-infrared region. Full article
(This article belongs to the Special Issue Graphene Mechanics)
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Open AccessArticle
Generating a High Valency Biotin Binder by Selecting Uniform Protein Assemblies via Crystallization
Crystals 2019, 9(7), 353; https://doi.org/10.3390/cryst9070353
Received: 28 May 2019 / Revised: 3 July 2019 / Accepted: 9 July 2019 / Published: 11 July 2019
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Abstract
Crystallization is a common practice in the purification process in small molecule synthesis while selecting the wanted product. For proteins it is rarely applied due to the methodological predicaments in obtaining crystals. Our observation of the stabilized octamers in the crystal structure of [...] Read more.
Crystallization is a common practice in the purification process in small molecule synthesis while selecting the wanted product. For proteins it is rarely applied due to the methodological predicaments in obtaining crystals. Our observation of the stabilized octamers in the crystal structure of hoefavidin, a novel dimeric member of the avidin family, led to the notion of developing a novel biotechnological tool via covalent crosslinking. The avidin–biotin system has been exploited for decades utilizing the ultra-high affinity between avidin and biotin as a basis for numerous applications. Optimizing the system led to the discovery of a novel group of dimeric avidins including hoefavidin. Hoefavidin has a dynamic quaternary structure, where a dimer is the basis for generating the octamer via crystallographic symmetry operation. Upon biotin binding in solution hoefavidin dissociates solely into dimers. In order to stabilize the octamer, we designed the P61C mutant to form a disulfide bridge stabilizing the octamer and preventing dissociation upon biotin binding. The process of selecting P61C hoefavidin uniform octamers includes crystallization followed by dissolving the crystals. The P61C modified hoefavidin octamer can have a substantial added value to the various biotechnological applications and advances of the biotin based high affinity systems. Full article
(This article belongs to the Special Issue X-ray Crystallography)
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Open AccessArticle
Effect of Type I Antifreeze Proteins on the Freezing and Melting Processes of Cryoprotective Solutions Studied by Site-Directed Spin Labeling Technique
Crystals 2019, 9(7), 352; https://doi.org/10.3390/cryst9070352
Received: 19 April 2019 / Revised: 1 July 2019 / Accepted: 9 July 2019 / Published: 11 July 2019
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Abstract
Antifreeze proteins (AFPs) protect organisms living in subzero environments from freezing injury, which render them potential applications for cryopreservation of living cells, organs, and tissues. Cryoprotective agents (CPAs), such as glycerol and propylene glycol, have been used as ingredients to treat cellular tissues [...] Read more.
Antifreeze proteins (AFPs) protect organisms living in subzero environments from freezing injury, which render them potential applications for cryopreservation of living cells, organs, and tissues. Cryoprotective agents (CPAs), such as glycerol and propylene glycol, have been used as ingredients to treat cellular tissues and organs to prevent ice crystal’s formation at low temperatures. To assess AFP’s function in CPA solutions, we have the applied site-directed spin labeling technique to a Type I AFP. A two-step process to prevent bulk freezing of the CPA solutions was observed by the cryo-photo microscopy, i.e., (1) thermodynamic freezing point depression by the CPAs; and (2) inhibition to the growth of seed ice crystals by the AFP. Electron paramagnetic resonance (EPR) experiments were also carried out from room temperature to 97 K, and vice versa. The EPR results indicate that the spin labeled AFP bound to ice surfaces, and inhibit the growths of ice through the bulk freezing processes in the CPA solutions. The ice-surface bound AFP in the frozen matrices could also prevent the formation of large ice crystals during the melting processes of the solutions. Our study illustrates that AFPs can play an active role in CPA solutions for cryopreservation applications. Full article
(This article belongs to the Special Issue Ice Crystals)
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Open AccessArticle
Polymorph Selection of ROY by Flow-Driven Crystallization
Crystals 2019, 9(7), 351; https://doi.org/10.3390/cryst9070351
Received: 13 May 2019 / Revised: 25 June 2019 / Accepted: 4 July 2019 / Published: 9 July 2019
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Abstract
The selection of polymorphs of the organic compound 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile, ROY, is studied experimentally in the confined space between two horizontal glass plates when an acetone solution of ROY of variable concentration is injected at a variable flow rate into water. Depending on the [...] Read more.
The selection of polymorphs of the organic compound 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile, ROY, is studied experimentally in the confined space between two horizontal glass plates when an acetone solution of ROY of variable concentration is injected at a variable flow rate into water. Depending on the local concentration within the radial flow, a polymorph selection is observed such that red prisms are favored close to the injection center while yellow needles are the preferred polymorph close to the edge of the injected ROY domain. At larger flow rates, a buoyancy-driven instability induces stripes at the outer edge of the displacement pattern, in which specific polymorphs are seen to crystallize. Our results evidence the possibility of a selection of ROY polymorph structures in out-of-equilibrium flow conditions. Full article
(This article belongs to the Special Issue Polymorphism in Crystals)
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Open AccessArticle
Hydrogenation of HOPG-supported Gold Nanoparticles: Features of Initial Stages
Crystals 2019, 9(7), 350; https://doi.org/10.3390/cryst9070350
Received: 10 June 2019 / Revised: 28 June 2019 / Accepted: 5 July 2019 / Published: 9 July 2019
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Abstract
The features of deuterium adsorption on the surface of gold nanoparticles deposited on highly oriented pyrolytic graphite (HOPG) were determined. The results showed that deuterium adsorption on gold nanoparticles takes place at room temperature. The results also showed that the filling of the [...] Read more.
The features of deuterium adsorption on the surface of gold nanoparticles deposited on highly oriented pyrolytic graphite (HOPG) were determined. The results showed that deuterium adsorption on gold nanoparticles takes place at room temperature. The results also showed that the filling of the nanoparticles’ surfaces with the adsorbate occurs from the graphite–gold interface until the entire surface is covered by deuterium. The results of quantum chemical simulations are used to explain the experimental data. A simple model of the observed effects is proposed. Full article
(This article belongs to the Special Issue Synthesis and Investigation of Gold Nanoparticles)
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Open AccessArticle
A Tunable NIR Filter with Sphere Phase Liquid Crystal
Crystals 2019, 9(7), 349; https://doi.org/10.3390/cryst9070349
Received: 7 June 2019 / Revised: 3 July 2019 / Accepted: 6 July 2019 / Published: 8 July 2019
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Abstract
A near-infrared (NIR) filter with sphere phase liquid crystal (SPLC) is proposed, which shows a low operating electric field and large temperature-gradient modulations. The central wavelength of the Bragg reflection can be thermally tuned from 1580 nm to 1324 nm with a temperature-gradient [...] Read more.
A near-infrared (NIR) filter with sphere phase liquid crystal (SPLC) is proposed, which shows a low operating electric field and large temperature-gradient modulations. The central wavelength of the Bragg reflection can be thermally tuned from 1580 nm to 1324 nm with a temperature-gradient of 42.7 nm/K. Meanwhile, the central wavelength can be electrically tuned over 76 nm within a low operating electric field of 0.3 V/μm. Thus, the SPLC filter may achieve a wavelength variation of 256 nm by thermal modulation and 76 nm by electrical modulation. The SPLC filter shows great potential applications in optical communication devices. Full article
(This article belongs to the Special Issue Liquid Crystal Optics and Physics: Recent Advances and Prospects)
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Open AccessArticle
Unified Assessment of the Effects of Van der Waals Interactions on the Structural and Electronic Properties of Some Layered Organic Solids κ-(BEDT-TTF)2X
Crystals 2019, 9(7), 348; https://doi.org/10.3390/cryst9070348
Received: 17 May 2019 / Revised: 26 June 2019 / Accepted: 3 July 2019 / Published: 6 July 2019
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Abstract
Proper inclusion of van der Waals interactions (vdW) in ab initio calculations based on the density functional theory (DFT) is crucial to describe soft, organic, layered solids such as κ-(BEDT-TTF)2X. Since no consensus has been reached on the reliability [...] Read more.
Proper inclusion of van der Waals interactions (vdW) in ab initio calculations based on the density functional theory (DFT) is crucial to describe soft, organic, layered solids such as κ -(BEDT-TTF) 2 X . Since no consensus has been reached on the reliability of available vdW DFT functionals, most of the first principles calculations have been based on experimental crystal structure data without any structural optimization. Here, we explore optimal DFT-based schemes that account for the effects of vdW interactions on the structural and electronic band properties of three paradigmatic charge transfer salts, κ -(BEDT-TTF) 2 Cu 2 (CN) 3 , κ -(BEDT-TTF) 2 Ag 2 (CN) 3 , and κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl, for which a unified optimization of the structure is possible. Detailed examination of the prototype test system κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl shows that the optB88-vdW functional performs slightly better than the PBE-vdW and that the choice of pseudopotentials is critical to obtaining realistic results. Full article
(This article belongs to the Special Issue Structure and Properties of Molecular Conductors)
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Open AccessReview
Femtosecond Laser Pulses Amplification in Crystals
Crystals 2019, 9(7), 347; https://doi.org/10.3390/cryst9070347
Received: 22 April 2019 / Revised: 24 June 2019 / Accepted: 1 July 2019 / Published: 5 July 2019
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Abstract
This paper describes techniques for high-energy laser pulse amplification in multi-PW femtosecond laser pulses. Femtosecond laser pulses can be generated and amplified in laser media with a broad emission spectral bandwidth, like Ti:sapphire crystals. By chirped pulse amplification (CPA) techniques, hundred-Joule amplified laser [...] Read more.
This paper describes techniques for high-energy laser pulse amplification in multi-PW femtosecond laser pulses. Femtosecond laser pulses can be generated and amplified in laser media with a broad emission spectral bandwidth, like Ti:sapphire crystals. By chirped pulse amplification (CPA) techniques, hundred-Joule amplified laser pulses can be obtained. Multi-PW peak-power femtosecond pulses are generated after recompression of amplified chirped laser pulses. The characteristics and problems of large bandwidth laser pulses amplification in Ti:sapphire crystals are discussed. An alternative technique, based on optical parametric chirped pulse amplification (OPCPA) in nonlinear crystals, is presented. Phase-matching conditions for broad bandwidth parametric amplification in nonlinear crystals are inferred. Ultra-broad phase matching bandwidth of more than 100 nm, able to support the amplification of sub-10 fs laser pulses, are demonstrated in nonlinear crystals, such as Beta Barium Borate (BBO), Potassium Dideuterium Phosphate (DKDP), and Lithium Triborate (LBO). The advantages and drawbacks of CPA amplification in laser crystals and OPCPA in nonlinear crystals are discussed. A hybrid amplification method, which combines low-medium energy OPCPA in nonlinear crystals with high energy CPA in large aperture laser crystals, is described. This technique is currently used for the development of 10-PW laser systems, with sub-20 fs pulse duration and more than 1012 intensity contrast of output femtosecond pulses. Full article
(This article belongs to the Special Issue Laser Crystals)
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Open AccessArticle
Importance of Blade-Coating Temperature for Diketopyrrolopyrrole-based Thin-Film Transistors
Crystals 2019, 9(7), 346; https://doi.org/10.3390/cryst9070346
Received: 4 June 2019 / Revised: 26 June 2019 / Accepted: 2 July 2019 / Published: 5 July 2019
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Abstract
In this work, the effect of blade-coating temperature on the electrical properties of a conjugated donor–acceptor copolymer containing diketopyrrolopyrrole (DPP)-based thin-film transistors (TFTs) was systematically analyzed. The organic semiconductor (OSC) layers were blade-coated at various blade-coating temperatures from room temperature (RT) to 80 [...] Read more.
In this work, the effect of blade-coating temperature on the electrical properties of a conjugated donor–acceptor copolymer containing diketopyrrolopyrrole (DPP)-based thin-film transistors (TFTs) was systematically analyzed. The organic semiconductor (OSC) layers were blade-coated at various blade-coating temperatures from room temperature (RT) to 80 °C. No remarkable changes were observed in the thickness, surface morphology, and roughness of the OSC films as the blade-coating temperature increased. DPP-based TFTs exhibited two noticeable tendencies in the magnitude of field-effect mobility with increasing blade-coating temperatures. As the temperature increased up to 40 °C, the field-effect mobility increased to 148% compared to the RT values. On the contrary, when the temperature was raised to 80 °C, the field-effect mobility significantly reduced to 20.9% of the mobility at 40 °C. These phenomena can be explained by changes in the crystallinity of DPP-based films. Therefore, the appropriate setting of the blade-coating temperature is essential in obtaining superior electrical characteristics for TFTs. A blade-coating temperature of 40 °C was found to be the optimum condition in terms of electrical performance for DPP-based TFTs. Full article
(This article belongs to the Special Issue Advances in Thin Film Materials and Devices)
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Open AccessArticle
Niobium Base Superalloys: Achievement of a Coherent Ordered Precipitate Structure in the Nb Solid-Solution
Crystals 2019, 9(7), 345; https://doi.org/10.3390/cryst9070345
Received: 30 April 2019 / Revised: 29 May 2019 / Accepted: 29 June 2019 / Published: 5 July 2019
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Abstract
In a previous work, the chemical elements necessary for the achievement of Niobium base superalloys were defined in order to get a structure equivalent to that of Nickel base superalloys, which contain ordered precipitates within a disordered solid-solution. It was especially emphasized that [...] Read more.
In a previous work, the chemical elements necessary for the achievement of Niobium base superalloys were defined in order to get a structure equivalent to that of Nickel base superalloys, which contain ordered precipitates within a disordered solid-solution. It was especially emphasized that precipitation hardening in the Niobium matrix would be possible with the addition of Ni. The remaining question about the design of such Niobium superalloys concerned the achievement of ordered precipitates in crystalline coherence with the Nb matrix i.e., with a crystalline structure equivalent to the Nb crystal prototype and with a lattice parameter in coherency with that of the Nb matrix. In order to reduce the trial/error experimental work, a reasoning based on various data for the achievement of coherency is presented. Then, starting from the Nb-Hf-Ni ternary alloy thus defined, this paper demonstrates that the precipitation of an ordered Nb phase within a disordered Nb matrix can be achieved with lattice parameter coherency between the ordered precipitates and the disordered matrix. The chemistry and the crystallographic structure of the precipitates were characterized using Transmission Electron Microscopy and Atom Probe Tomography. These results can help to conceive a new family of Nb base superalloys. Full article
(This article belongs to the Special Issue Fundamentals of Superalloys)
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Open AccessArticle
Acid Modification of the Unsupported NiMo Catalysts by Y-Zeolite Nanoclusters
Crystals 2019, 9(7), 344; https://doi.org/10.3390/cryst9070344
Received: 7 May 2019 / Revised: 23 June 2019 / Accepted: 2 July 2019 / Published: 4 July 2019
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Abstract
Unsupported NiMo catalyst has high hydrogenation activity due to its high active site distribution. However, low specific surface area and pore distribution greatly limit the efficient utilization of the active components. The Y-zeolite nanoclusters were hydrothermally synthesized and introduced into the unsupported NiMo [...] Read more.
Unsupported NiMo catalyst has high hydrogenation activity due to its high active site distribution. However, low specific surface area and pore distribution greatly limit the efficient utilization of the active components. The Y-zeolite nanoclusters were hydrothermally synthesized and introduced into the unsupported NiMo catalysts from a layered nickel molybdate complex oxide. The XRD, N2 adsorption-desorption, FT-IR, Py-IR, SEM, NH3-TPD, and TEM were used to characterize all catalysts. The dibenzothiophene (DBT) hydrodesulfurization (HDS) reaction was performed in a continuous high pressure microreactor. The results showed that the specific surface area, pore volume, and average pore size of the unsupported NiMo catalysts were greatly increased by the Y-zeolite nanoclusters, and a more dispersed structure was produced. Furthermore, the Lewis acid and total acid content of the unsupported NiMo catalysts were greatly improved by the Y-zeolite nanoclusters. The HDS results showed that the unsupported NiMo catalysts modified by the nanoclusters had the same high desulfurization efficiency as the unmodified catalyst, but had more proportion of direct desulfurization (DDS) products. The results offer an alternative to reducing hydrogen consumption and save cost in the production of ultra clean diesel. Full article
(This article belongs to the Special Issue Green Catalysts based on Metal Complexs)
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Open AccessArticle
Optical Characteristics of ZnCuInS/ZnS (Core/Shell) Nanocrystal Flexible Films Under X-Ray Excitation
Crystals 2019, 9(7), 343; https://doi.org/10.3390/cryst9070343
Received: 6 June 2019 / Revised: 2 July 2019 / Accepted: 3 July 2019 / Published: 4 July 2019
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Abstract
The aim of this article is to evaluate optical characteristics, such as the intrinsic conversion efficiency and the inherent light propagation efficiency of three polymethyl methacrylate (PMMA)/methyl methacrylate (MMA) composite ZnCuInS/ZnS (core/shell) nanocrystal flexible films. The concentrations of these were 100 mg/mL, 150 [...] Read more.
The aim of this article is to evaluate optical characteristics, such as the intrinsic conversion efficiency and the inherent light propagation efficiency of three polymethyl methacrylate (PMMA)/methyl methacrylate (MMA) composite ZnCuInS/ZnS (core/shell) nanocrystal flexible films. The concentrations of these were 100 mg/mL, 150 mg/mL, and 250 mg/mL, respectively. Composite films were prepared by homogeneously diluting dry powder quantum dot (QD) samples in toluene and subsequently mixing these with a PMMA/MMA polymer solution. The absolute luminescence efficiency (AE) of the films was measured using X-ray excitation. A theoretical model describing the optical photon propagation in scintillator materials was used to calculate the fraction of the generated optical photons passed through the different material layers. Finally, the intrinsic conversion efficiency was calculated by considering the QD quantum yield and the optical photon emission spectrum. Full article
(This article belongs to the Special Issue Single Crystals for Biomedical Applications)
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Open AccessArticle
Rapid Removal and Efficient Recovery of Tetracycline Antibiotics in Aqueous Solution Using Layered Double Hydroxide Components in an In Situ-Adsorption Process
Crystals 2019, 9(7), 342; https://doi.org/10.3390/cryst9070342
Received: 9 June 2019 / Revised: 28 June 2019 / Accepted: 1 July 2019 / Published: 4 July 2019
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Abstract
This work demonstrates a simple approach for the efficient removal of tetracycline (TC) antibiotic from an aqueous solution. The in situ-adsorption removal method involved instant precipitation formation of mixed metal hydroxides (MMHs), which could immediately act as a sorbent for capturing TC from [...] Read more.
This work demonstrates a simple approach for the efficient removal of tetracycline (TC) antibiotic from an aqueous solution. The in situ-adsorption removal method involved instant precipitation formation of mixed metal hydroxides (MMHs), which could immediately act as a sorbent for capturing TC from an aqueous solution, by employing layered double hydroxide (LDH) components including magnesium and aluminum ions in alkaline conditions. By using this approach, 100% removal of TC can be accomplished within 4 min under optimized conditions. The fast removal possibly resulted from an instantaneous adsorption of TC molecules onto the charged surface of MMHs via hydrogen bonding and electrostatically induced attraction. The results revealed that our removal technique was superior to the use of LDH as a sorbent in terms of both removal kinetics and efficiency. Moreover, the recovery of captured TC was tested under the influence of various common anions. It was found that 98% recovery could be simply achieved by using phosphate, possibly due to its highly charged density. Furthermore, this method was successful for efficient removal of TC in real environmental water samples. Full article
(This article belongs to the Special Issue Layered Double Hydroxides)
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Open AccessArticle
Induced Nucleation of Biomimetic Nanoapatites on Exfoliated Graphene Biomolecule Flakes by Vapor Diffusion in Microdroplets
Crystals 2019, 9(7), 341; https://doi.org/10.3390/cryst9070341
Received: 4 June 2019 / Revised: 24 June 2019 / Accepted: 1 July 2019 / Published: 3 July 2019
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Abstract
The nucleation of apatite nanoparticles on exfoliated graphene nanoflakes has been successfully carried out by the sitting drop vapor diffusion method, with the aim of producing cytocompatible hybrid nanocomposites of both components. The graphene flakes were prepared by the sonication-assisted, liquid-phase exfoliation technique, [...] Read more.
The nucleation of apatite nanoparticles on exfoliated graphene nanoflakes has been successfully carried out by the sitting drop vapor diffusion method, with the aim of producing cytocompatible hybrid nanocomposites of both components. The graphene flakes were prepared by the sonication-assisted, liquid-phase exfoliation technique, using the following biomolecules as dispersing surfactants: lysozyme, L-tryptophan, N-acetyl-D-glucosamine, and chitosan. Results from mineralogical, spectroscopic, and microscopic characterization (X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman, Variable pressure scanning electron microscopy (VPSEM), and transmission electron microscopy (TEM)) indicate that flakes were stacked in multilayers (>5 layers) and most likely intercalated and functionalized with the biomolecules, while the apatite nanoparticles were found forming a coating on the graphene surfaces. It is worthwhile to mention that when using chitosan-exfoliated graphene, the composites were more homogeneous than when using the other biomolecule graphene flakes, suggesting that this polysaccharide, extremely rich in –OH groups, must be arranged on the graphene surface with the –OH groups pointing toward the solution, forming a more regular pattern for apatite nucleation. The findings by XRD and morphological analysis point to the role of “functionalized graphene” as a template, which induces heterogeneous nucleation and favors the growth of apatite on the flakes’ surfaces. The cytocompatibility tests of the resulting composites, evaluated by the 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay in a dose–dependent manner on GTL-16 cells, a human gastric carcinoma cell line, and on m17.ASC cells, a murine mesenchymal stem cell line with osteogenic potential, reveal that in all cases, full cytocompatibility was found. Full article
(This article belongs to the Special Issue Biological Crystallization)
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Open AccessArticle
Determination of the Chemical Composition of Lithium Niobate Powders
Crystals 2019, 9(7), 340; https://doi.org/10.3390/cryst9070340
Received: 21 March 2019 / Revised: 26 April 2019 / Accepted: 30 April 2019 / Published: 3 July 2019
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Abstract
Existent methods for determining the composition of lithium niobate single crystals are mainly based on their variations due to changes in their electronic structure, which accounts for the fact that most of these methods rely on experimental techniques using light as the probe. [...] Read more.
Existent methods for determining the composition of lithium niobate single crystals are mainly based on their variations due to changes in their electronic structure, which accounts for the fact that most of these methods rely on experimental techniques using light as the probe. Nevertheless, these methods used for single crystals fail in accurately predicting the chemical composition of lithium niobate powders due to strong scattering effects and randomness. In this work, an innovative method for determining the chemical composition of lithium niobate powders, based mainly on the probing of secondary thermodynamic phases by X-ray diffraction analysis and structure refinement, is employed. Its validation is supported by the characterization of several samples synthesized by the standard and inexpensive method of mechanosynthesis. Furthermore, new linear equations are proposed to accurately describe and determine the chemical composition of this type of powdered material. The composition can now be determined by using any of four standard characterization techniques: X-Ray Diffraction (XRD), Raman Spectroscopy (RS), UV-vis Diffuse Reflectance (DR), and Differential Thermal Analysis (DTA). In the case of the existence of a previous equivalent description for single crystals, a brief analysis of the literature is made. Full article
(This article belongs to the Special Issue Recent Progress in Lithium Niobate)
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Open AccessArticle
Growth of Multi-Layer hBN on Ni(111) Substrates via MOCVD
Crystals 2019, 9(7), 339; https://doi.org/10.3390/cryst9070339
Received: 5 June 2019 / Revised: 24 June 2019 / Accepted: 29 June 2019 / Published: 2 July 2019
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Abstract
In this paper we demonstrate a metal organic chemical vapor deposition (MOCVD) process for growth of few layer hBN films on Ni(111) on sapphire substrates using triethylborane (TEB) and ammonia (NH3). Ni(111) was selected as a substrate due to its symmetry [...] Read more.
In this paper we demonstrate a metal organic chemical vapor deposition (MOCVD) process for growth of few layer hBN films on Ni(111) on sapphire substrates using triethylborane (TEB) and ammonia (NH3). Ni(111) was selected as a substrate due to its symmetry and close lattice matching to hBN. Using atomic force microscopy (AFM) we find hBN is well aligned to the Ni below with in plane alignment between the hBN zig zag edge and the <110> of Ni. We further investigate the growth process exploring interaction between precursors and the Ni(111) substrate. Under TEB pre-exposure Ni-B and graphitic compounds form which disrupts the formation of layered phase pure hBN; while NH3 pre-exposure results in high quality films. Tunnel transport of films was investigated by conductive-probe AFM demonstrating films to be highly resistive. These findings improve our understanding of the chemistry and mechanisms involved in hBN growth on metal surfaces by MOCVD. Full article
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Open AccessArticle
Sustainable Route for Synthesis of All-Silica SOD Zeolite
Crystals 2019, 9(7), 338; https://doi.org/10.3390/cryst9070338
Received: 19 June 2019 / Revised: 26 June 2019 / Accepted: 28 June 2019 / Published: 30 June 2019
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Abstract
The development of the sustainable synthesis of zeolites has become a very hot topic in recent years. Herein, we report a sustainable route for synthesizing all-silica SOD zeolite under solvent-free conditions. The method of solvent-free synthesis includes mixing, grinding, and heating raw solids. [...] Read more.
The development of the sustainable synthesis of zeolites has become a very hot topic in recent years. Herein, we report a sustainable route for synthesizing all-silica SOD zeolite under solvent-free conditions. The method of solvent-free synthesis includes mixing, grinding, and heating raw solids. The all-silica SOD zeolite obtained was well characterized by multiple measurement techniques (XRD, SEM, IR, thermogravimetric-differential thermal analysis (TG-DTA), and magic angel spinning nuclear magnetic resonance (MAS NMR)). The crystallization process of all-silica SOD zeolite was also investigated in detail by XRD, SEM, UV-Raman, and MAS NMR techniques. In addition, the effects of the crystallization compositions, including the molar ratios of Na2O/SiO2 and ethylene glycol/SiO2, on the synthesis of the pure all-silica SOD zeolite were investigated at different temperatures. Full article
(This article belongs to the Special Issue New Horizons in Zeolites and Zeolite-Like Materials)
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Open AccessArticle
Bi2Te3 Topological Insulator for Domain-Wall Dark Pulse Generation from Thulium-Doped Fiber Laser
Crystals 2019, 9(7), 337; https://doi.org/10.3390/cryst9070337
Received: 31 May 2019 / Revised: 23 June 2019 / Accepted: 28 June 2019 / Published: 29 June 2019
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Abstract
We have experimentally demonstrated domain-wall (DW) dark pulses from a thulium-doped fiber laser incorporating a topological insulator saturable absorber (SA). The bulk-structured Bi2Te3 was used as the SA, which was constructed on a fiber ferrule platform through the deposition of [...] Read more.
We have experimentally demonstrated domain-wall (DW) dark pulses from a thulium-doped fiber laser incorporating a topological insulator saturable absorber (SA). The bulk-structured Bi2Te3 was used as the SA, which was constructed on a fiber ferrule platform through the deposition of the Bi2Te3 mixed with distilled water. The DW dark pulses were generated from the thulium-doped fiber laser cavity with a dual wavelength at 1956 nm and 1958 nm. The dark pulse width and the repetition rate were measured as ~10.3 ns and ~20.7 MHz over the pump power of ~80 mW, respectively. To the best of our knowledge, this work is the first demonstrated generation of the DW dark pulse from a thulium-doped fiber laser using nanomaterial-based SA. Full article
(This article belongs to the Special Issue Recent Advances in Novel Topological Materials)
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Open AccessCommunication
Synthesis, Crystal Structure, Spectroscopic Properties, and Hirshfeld Surface Analysis of Diaqua [3,14-dimethyl-2,6,13,17 tetraazatricyclo(16.4.0.07,12)docosane]copper(II) Dibromide
Crystals 2019, 9(7), 336; https://doi.org/10.3390/cryst9070336
Received: 5 June 2019 / Revised: 17 June 2019 / Accepted: 26 June 2019 / Published: 28 June 2019
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Abstract
A newly prepared Cu(II) complex salt, Cu(L1)(H2O)2Br2, where L1 is 3,14-dimethyl-2,6,13,17-tetraazatricyclo(16.4.0.07,12) docosane, is characterized by elemental and crystallographic analyses. The Cu(II) center is coordinated by four nitrogen atoms of macrocyclic ligand and [...] Read more.
A newly prepared Cu(II) complex salt, Cu(L1)(H2O)2Br2, where L1 is 3,14-dimethyl-2,6,13,17-tetraazatricyclo(16.4.0.07,12) docosane, is characterized by elemental and crystallographic analyses. The Cu(II) center is coordinated by four nitrogen atoms of macrocyclic ligand and the axial position by two water molecules. The macrocyclic ligand adopts an optimally stable trans-III conformation with normal Cu–N bond lengths of 2.018 (3) and 2.049 (3) Å and long axial Cu1–O1W length of 2.632 (3) Å due to the Jahn–Teller effect. The complex is stabilized by hydrogen bonds formed between the O atoms of water molecules and bromide anions. The bromide anion is connected to the neighboring complex cations and water molecules through N–H···Br and O–H···Br hydrogen bonds, respectively. The g-factors obtained from the electron spin resonance spectrum show the typical trend of g > g > 2.0023, which is in a good accordance to the dx2-y2 ground state. It reveals a coordination sphere of tetragonal symmetry for the Cu(II) ion. The infrared and electronic absorption spectral properties of the complex are also discussed. Hirshfeld surface analysis represents that the H···H, H···Br/Br···H and H···O/O···H contacts are the major molecular interactions in the prepared complex. Full article
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Open AccessArticle
Ferroelectric Self-Poling in GeTe Films and Crystals
Crystals 2019, 9(7), 335; https://doi.org/10.3390/cryst9070335
Received: 30 May 2019 / Revised: 21 June 2019 / Accepted: 24 June 2019 / Published: 28 June 2019
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Abstract
Ferroelectric materials are used in actuators or sensors because of their non-volatile macroscopic electric polarization. GeTe is the simplest known diatomic ferroelectric endowed with exceedingly complex physics related to its crystalline, amorphous, thermoelectric, and—fairly recently discovered—topological properties, making the material potentially interesting for [...] Read more.
Ferroelectric materials are used in actuators or sensors because of their non-volatile macroscopic electric polarization. GeTe is the simplest known diatomic ferroelectric endowed with exceedingly complex physics related to its crystalline, amorphous, thermoelectric, and—fairly recently discovered—topological properties, making the material potentially interesting for spintronics applications. Typically, ferroelectric materials possess random oriented domains that need poling to achieve macroscopic polarization. By using X-ray absorption fine structure spectroscopy complemented with anomalous diffraction and piezo-response force microscopy, we investigated the bulk ferroelectric structure of GeTe crystals and thin films. Both feature multi-domain structures in the form of oblique domains for films and domain colonies inside crystals. Despite these multi-domain structures which are expected to randomize the polarization direction, our experimental results show that at room temperature there is a preferential ferroelectric order remarkably consistent with theoretical predictions from ideal GeTe crystals. This robust self-poled state has high piezoelectricity and additional poling reveals persistent memory effects. Full article
(This article belongs to the Special Issue Recent Advances in Novel Topological Materials)
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Open AccessArticle
Mechanochemical Reactions of Lithium Niobate Induced by High-Energy Ball-Milling
Crystals 2019, 9(7), 334; https://doi.org/10.3390/cryst9070334
Received: 24 May 2019 / Revised: 26 June 2019 / Accepted: 26 June 2019 / Published: 28 June 2019
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Abstract
Lithium niobate (LiNbO3, LN) nanocrystals were prepared by ball-milling of the crucible residue of a Czochralski grown congruent single crystal, using a Spex 8000 Mixer Mill with different types of vials (stainless steel, alumina, tungsten carbide) and various milling parameters. Dynamic [...] Read more.
Lithium niobate (LiNbO3, LN) nanocrystals were prepared by ball-milling of the crucible residue of a Czochralski grown congruent single crystal, using a Spex 8000 Mixer Mill with different types of vials (stainless steel, alumina, tungsten carbide) and various milling parameters. Dynamic light scattering and powder X-ray diffraction were used to determine the achieved particle and grain sizes, respectively. Possible contamination from the vials was checked by energy-dispersive X-ray spectroscopy measurements. Milling resulted in sample darkening due to mechanochemical reduction of Nb (V) via polaron and bipolaron formation, oxygen release and Li2O segregation, while subsequent oxidizing heat-treatments recovered the white color with the evaporation of Li2O and crystallization of a LiNb3O8 phase instead. The phase transformations occurring during both the grinding and the post-grinding heat treatments were studied by Raman spectroscopy, X-ray diffraction and optical reflection measurement, while the Li2O content of the as-ground samples was quantitatively measured by coulometric titration. Full article
(This article belongs to the Special Issue Recent Progress in Lithium Niobate)
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