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There is an urgent need for faster, brighter, and more controllable scintillation materials in advanced nuclear medicine, high-energy physical experiments, and dark matter particle detection. Nevertheless, the trade-off between high emission efficiency and fast timing characteristics remains a common challenge in the entire optical field. To address this issue, we develop a composition engineering strategy that involves multisite selective doping. This strategy aims to transform nearly all Ce 3+ into fast-emitting Ce 4+ while synergistically suppressing the electron traps. Even at very low doping concentrations, the designed Ca 2+ , Al 3+ , and Ce 3+ tridoped oxyorthosilicate exhibits a scintillation decay (τ d ) acceleration of 20%, accompanied by a 25% increase in light yield (LY). The ratio of emission efficiency and timing characteristics (LY/τ d ) can be enhanced by 56%, which realizes the perfect balance of high LY and fast τ d . Our work provides a method for designing efficient, ultrafast, and controllable scintillators in multicomponent systems, thus paving the way for high-resolution radiation detection and imaging applications.

Entering an era of miniaturization prompted scientists to explore strategies to assemble colloidal crystals for numerous applications, including photonics. However, wet methods are intrinsically less versatile than dry methods, whereas the manual rubbing method of dry powders has been demonstrated only on sticky elastomeric layers, hindering particle transfer in printing applications and applicability in analytical screening. To address this clear impetus of broad applicability, we explore here the assembly on nonelastomeric, rigid substrates by utilizing the manual rubbing method to rapidly (≈20 s) attain monolayers comprising hexagonal closely packed (HCP) crystals of monodisperse dry powder spherical particles with a diameter ranging from 500 nm to 10 μm using a PDMS stamp. Our findings elucidate that the tribocharging-induced electrostatic attraction, particularly on relatively stiff substrates, and contact mechanics force between particles and substrates are critical contributors to attain large-scale HCP structures on conductive and insulating substrates. The best performance was obtained with polystyrene and PMMA powder, while silica was assembled only in HCP structures on fluorocarbon-coated substrates under zero-humidity conditions. Finally, we successfully demonstrated the assembly of tunable crystal patterns on a wafer-scale with great control on fluorocarbon-coated wafers, which is promising in microelectronics, bead-based assays, sensing, and anticounterfeiting applications.

Knowledge of controllable thermal expansion is a fundamental issue in the field of materials science and engineering. Direct blocking of the thermal expansions in positive thermal expansion materials is a challenging but fascinating task. Here we report a near zero thermal expansion (ZTE) of SnO2 achieved from twin crystal nanowires, which is highly correlated to the twin boundaries. Local structural evolutions followed by pair distribution function revealed a remarkable thermal local distortion along the twin boundary. Lattice dynamics investigated by Raman scattering evidenced the hardening of phonon frequency induced by the twin crystal compressing, giving rise to the ZTE of SnO2 nanowires. Further DFT calculation of Grüneisen parameters confirms the key role of compressive stress on ZTE. Our results provide an insight into the thermal expansion behavior regarding to twin crystal boundaries, which could be beneficial to the applications. [ABSTRACT FROM AUTHOR]

The insufficient understanding of the physical and chemical phenomena taking place at the electrode-electrolyte interface is the main roadblock for improvement of current battery technologies and development of new ones. Of particular interest is the solid-electrolyte interphase (SEI) layer because many aspects of the battery performance depend on its quality. Recently we have shown that a stable SEI layer can be designed in specific Li- or Na-based electrolytes. In this paper, we continue exploring this concept by identifying the interactions that take place at the lithiated (or sodiated) carbon-electrolyte interface and discussing the transport mechanisms of Li and Na ions through the most commonly found SEI layer inorganic components. For the ab initio molecular dynamics (AIMD) simulations, we considered the case of the sodiated hard carbon structure. The simulations show the decomposition of ethylene carbonate on the edge of the graphite layers leading to products such as CO and other organic fragments. The decomposition of the PF6- anion is a precursor step for the formation of NaF layers. Regarding the Li- and Na-ion transport through the SEI, the results show that the energy to create defects is lowest when Li ions are guests at an interstitial position in NaF and lattice positions in Na2CO3. For the LiF and Li2CO3 crystals, the energy to create defects is lowest when Na ions substitute Li. This lower energy cost for Li-ion defects in Na-based components is due to the smaller size of the Li ion when compared to the Na ion. Regarding diffusion barriers, the Na ions in Li-based SEI components show a preference for the vacancy diffusion and knock-off mechanisms as the preferred pathways to migrate through the SEI while Li ions in Na-based SEI components prefer a mechanism involving the migration of the interstitial ion through the knock-off or direct hopping mechanism. This work also emphasizes the interplay between the crystallographic orientation of the SEI components and the direction dependent ion migration guiding the controlled design of efficient artificial SEI layers. [ABSTRACT FROM AUTHOR]

Crystals are physical arrays delineated by polar surfaces and often contain imperfections of a polar nature. Understanding the structure of such defects on the molecular level is of topical importance since they strongly affect the macroscopic properties of materials. Moreover, polar imperfections in crystals can be created intentionally and specifically designed by doping nonpolar crystals with "tailor-made" additives as dopants, since their incorporation generally takes place in a polar mode. Insertion of dopants also induces a polar deformation of neighboring host molecules, resulting in the creation of polar domains within the crystals. The contribution of the distorted host molecules to the polarity of such domains should be substantial, particularly in crystals composed of molecules with large dipole moments, such as the zwitterionic amino acids, which possess dipole moments as high as ∼14 D. Polar materials are pyroelectric, i.e., they generate surface charge as a result of temperature change. With the application of recent very sensitive instruments for measuring electric currents, coupled with theoretical computations, it has become possible to determine the structure of polar imperfections, including surfaces, at a molecular level. The detection of pyroelectricity requires attachment of electrodes, which might induce various artifacts and modify the surface of the crystal. Therefore, a new method for contactless pyroelectric measurement using X-ray photoelectron spectroscopy was developed and compared to the traditional periodic temperature change technique. Here we describe the molecular-level determination of the structure of imperfections of different natures in molecular crystals and how they affect the macroscopic properties of the crystals, with the following specific examples: (i) Experimental support for the nonclassical crystal growth mechanism as provided by the detection of pyroelectricity from near-surface solvated polar layers present at different faces of nonpolar amino acid crystals. (ii) Enantiomeric disorder in dl-alanine crystals disclosed by detection of anomalously strong pyroelectricity along their nonpolar directions. The presence of such disorder, which is not revealed by accurate diffraction techniques, explains the riddle of their needlelike morphology. (iii) The design of mixed polar crystals of l-asparagine·H2O/l-aspartic acid with controlled degrees of polarity, as determined by pyroelectricity and X-ray diffraction, and their use in mechanistic studies of electrofreezing of supercooled water. (iv) Pyroelectricity coupled with dispersion-corrected density functional theory calculations and molecular dynamics simulations as an analytical method for the molecular-level determination of the structure of polar domains created by doping of α-glycine crystals with different l-amino acids at concentrations below 0.5%. (v) Selective insertion of minute amounts of alcohols within the bulk of α-glycine crystals, elucidating their role as inducers of the metastable β-glycine polymorph. In conclusion, the various examples demonstrate that although these imperfections are present in minute amounts, they can be detected by the sensitive pyroelectric measurement, and by combining them with theoretical computations one can elucidate their diverse emerging functionalities. [ABSTRACT FROM AUTHOR]

Rheological studies of liquid crystalline systems based on monopalmitolein and 5 or 8% of 1,2 distearoylphosphatidylglycerol are reported. Such cubic phases have been shown to possess unusually large water channels because of their ability of accommodating up to 80 wt % of water, a feature that renders these systems suitable for crystallizing membrane proteins with large extracellular domains. Their mechanical properties are supposed to be substantially different from those of traditional cubic phases. Rheological measurements were carried out on cubic phases of both Pn3m and Ia3d symmetries. It was verified that these ultraswollen cubic phases are less rigid than the normal cubic phases, with the Pn3m being softer that the Ia3d ones. Furthermore, for the Pn3m case, the longest relaxation time is shown to decrease logarithmically with increasing surface area per unit volume, proving the critical role of the density of interfaces in establishing the macroscopic viscoelastic properties of the bicontinuous cubic phases. [ABSTRACT FROM AUTHOR]

Polymer/fullerene bimolecular crystal formation has been investigated using a variety of conjugated polymers and fullerenes to understand the design rules that influence donor-acceptor interaction. Modifications of the polymer by varying the substitution side-chain position, density, and branching have demonstrated the importance of the "pocket" dimensions (free volume between side chains where the fullerene resides) for controlling intercalation. Yet the effect of pocket height has not been systematically explored because of the solubility limitations in polymers. In this report, we present an experimental investigation into the effect of the pocket height by synthesizing poly[2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene] dimers with varied side chain lengths and track the morphological changes of the dimer/fullerene blends using grazing-incidence X-ray scattering, thermal measurements, and photoluminescence quenching. We identify two regimes: (1) oligomers with side chains greater than or equal to heptyl (C7) form bimolecular crystals and (2) oligomers with less than or equal to hexyl (C6) form amorphous blends. This work provides the first observation of an order-to-disorder transition mediated by side-chain length in donor-fullerene intercalated blends. [ABSTRACT FROM AUTHOR]

Carbon nanothreads are a new one-dimensional sp³ carbon nanomaterial. They assemble into hexagonal crystals in a room temperature, nontopochemical solid-state reaction induced by slow compression of benzene to 23 GPa. Here we show that pyridine also reacts under compression to form a well-ordered sp³ product: C5NH5 carbon nitride nanothreads. Solid pyridine has a different crystal structure from solid benzene, so the nontopochemical formation of low-dimensional crystalline solids by slow compression of small aromatics may be a general phenomenon that enables chemical design of properties. The nitrogen in the carbon nitride nanothreads may improve processability, alters photoluminescence, and is predicted to reduce the bandgap. [ABSTRACT FROM AUTHOR]

The inadvertent occurrence of polymorphic phase transformations in active pharmaceutical ingredients (APIs) during hot melt extrusion (HME) processes has been claimed to limit the application of this technique. Hence, the control of polymorphism would need to be addressed if there is any prospect of HME to be successfully implemented as an alternative solid dosage formulation strategy in integrated, continuous end-to-end pharmaceutical manufacturing settings. This work demonstrates that flufenamic acid (FFA), one of the most polymorphic APIs known, thus far, can be processed using temperature-simulated HME with polyethylene glycol (PEG) as polymeric carrier. At temperatures above the transition point of FFA forms III and I (42 °C), the induction time of the polymorphic phase transformation is longer than the average reported residence time in conventional HME processes (5 min). Moreover, it was demonstrated that thorough understanding of the thermodynamic and kinetic design space for the PEG-FFA system leads to polymorphic control in the produced crystalline solid dispersions. Ultimately, this investigation helps to gain fundamental understanding of the processing needs of crystalline solid dispersions, which will lead to the broader application of HME as a continuous manufacturing strategy for drug products containing APIs prone to polymorphism, representing about 80% of all APIs. [ABSTRACT FROM AUTHOR]

Apart from not having crystallized, supercooled liquids can be considered as being properly equilibrated and thus can be described by a few thermodynamic control variables. In contrast, glasses and other amorphous solids can be arbitrarily far away from equilibrium and require a description of the history of the conditions under which they formed. In this paper we describe how the locality of interactions intrinsic to finite-dimensional systems affects the stability of amorphous solids far off equilibrium. Our analysis encompasses both structural glasses formed by cooling and colloidal assemblies formed by compression. A diagram outlining regions of marginal stability can be adduced which bears some resemblance to the quasi-equilibrium replica meanfield theory phase diagram of hard sphere glasses in high dimensions but is distinct from that construct in that the diagram describes not true phase transitions but kinetic transitions that depend on the preparation protocol. The diagram exhibits two distinct sectors. One sector corresponds to amorphous states with relatively open structures, the other to high density, more closely packed ones. The former transform rapidly owing to there being motions with no free energy barriers; these motions are string-like locally. In the dense region, amorphous systems age via compact activated reconfigurations. The two regimes correspond, in equilibrium, to the collisional or uniform liquid and the so-called landscape regime, respectively. These are separated by a spinodal line of dynamical crossovers. Owing to the rigidity of the surrounding matrix in the landscape, high-density part of the diagram, a sufficiently rapid pressure quench adds compressive energy which also leads to an instability toward string-like motions with near vanishing barriers. Conversely, a dilute collection of rigid particles, such as a colloidal suspension leads, when compressed, to a spatially heterogeneous structure with percolated mechanically stable regions. This jamming corresponds to the onset of activation when the spinodal line is traversed from the low density side. We argue that a stable glass made of sufficiently rigid particles can also be viewed as exhibiting sporadic and localized buckling instabilities that result in local jammed structures. The lines of instability we discuss resemble the Gardner transition of meanfield systems but, in contrast, do not result in true criticality owing to being short-circuited by activated events. The locally marginally stable modes of motion in amorphous solids correspond to secondary relaxation processes in structural glasses. Their relevance to the low temperature anomalies in glasses is also discussed. [ABSTRACT FROM AUTHOR]

Photomechanical molecular crystals have been investigated as mesoscopic photoactuators. Here, we report how the photomechanical twisting of 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene (1a) crystals depends on illumination direction. The ribbon-like crystal of 1a could be successfully prepared by a sublimation method. The ribbon crystal exhibited reversible photomechanical crystal twisting upon alternating irradiation with ultraviolet (UV) and visible light. Moreover, changing the UV illumination direction with respect to the crystal resulted in different twisting modes, ranging from helicoid to cylindrical. Control of photomechanical crystal deformation by illumination direction provides a convenient and useful way to generate a variety of photomechanical motions from a single crystal. [ABSTRACT FROM AUTHOR]

We investigate the effect of the presence of vertically aligned multiwalled carbon nanotubes (CNTs) on the orientation of poly(ethylene oxide) (PEO) lamellae and PEO crystallinity. The high alignment of carbon nanotubes acting as templates probably governs the orientation of PEO lamellae. This templating effect might result in the lamella planes of PEO crystals oriented along a direction parallel to the long axis of the nanotubes. The presence of aligned carbon nanotubes also gives rise to the decreases in PEO crystallinity, crystallization temperature, and melting temperature due to the perturbation of carbon nanotubes to the crystallization of PEO. These effects have significant implications for controlling the orientation of PEO lamellae and decreasing the crystallinity of PEO and thickness of PEO lamellae, which have significant impacts on ion transport in PEO/CNT composite and the capacitive performance of PEO/CNT composite. Both the decreased PEO crystallinity and the orientation of PEO lamellae along the long axes of vertically aligned CNTs give rise to the decrease in the charge transfer resistance, which is associated with the improvements in the ion transport and capacitive performance of PEO/CNT composite. [ABSTRACT FROM AUTHOR]

In the inertial limit, the resonance frequency of the quartz crystal microbalance (QCM) is related to the coupled mass on the quartz sensor through the Sauerbrey expression that relates the mass to the change in resonance frequency. However, when the thickness of the film is sufficiently large, the relationship becomes more complicated and both the frequency and damping of the crystal resonance must be considered. In this regime, a rheological model of the material must be used to accurately extract the adhered film's thickness, shear modulus, and viscoelastic phase angle from the data. In the present work we examine the suitability of two viscoelastic models, a simple Voigt model (Physica Scripta 1999, 59, 391-396) and a more realistic power-law model (Langmuir 2015, 31, 4008-4017), to extract the rheological properties of a thermoresponsive hydrogel film. By changing temperature and initial dry film thickness of the gel, the operation of QCM was traversed from the Sauerbrey limit, where viscous losses do not impact the frequency, through the regime where the QCM response is sensitive to viscoelastic properties. The density-shear modulus and the viscoelastic phase angle from the two models are in good agreement when the shear wavelength ratio, d/λn, is in the range of 0.05-0.20, where d is the film thickness and λn is the wavelength of the mechanical shear wave at the nth harmonic. We further provide a framework for estimating the physical properties of soft materials in the megahertz regime by using the physical behavior of polyelectrolyte complexes. This provides the user with an approximate range of allowable film thicknesses for accurate viscoelastic analysis with either model, thus enabling better use of the QCM-D in soft materials research. [ABSTRACT FROM AUTHOR]

The noncovalent interactions arising from solute···solute (i.e., drug···drug, drug···neutraceutical, or drug···coformer) and solute···solvent play a significant role in predicting desired properties of an active compound. We demonstrated here the role of π···π interactions in the presence of hydrogen bonding, the two important cohesive and adhesive forces in the crystallization of small molecules to regulate certain physiochemical properties in their multicomponent crystals. Acridine was employed as a representative cocrystal partner with isomeric dihydroxybenzoic acids. The choice was intentional as with a single hydrogen bond acceptor acridine provides increased surface area to favor the stacking of π-frameworks at van der Waals separation (~3.5 Å) and herringbone C-H···π interactions, and isomeric dihydroxybenzoic acids easily form COOH···Nacridine and O-H···Nacridine hydrogen bonds in competition. Structure elucidation of several cocrystals/salts underlines the influence of continuous and discrete π···π stacking and C-H···π interactions supported by other hydrogen bonds on their physiochemical properties such as solubility, cell membrane permeation, and release behavior in vitro. Experiments were performed in various pH ranges (pH = 1.2 SAL and 7.4 PBS) in order to imitate human physiological conditions. Molecular packing and interaction energies suggest a significant contribution of π···π interactions in the modulation of property. In fact coformers' conformational energy, lipophilicity, and Log P values were found to be valued contributors. Therefore, the present study anticipates the contribution towards understanding of the impact of π···π and C-H···π interactions supported by hydrogen bonds on modulating physiochemical properties, essentially improving efficacy of a drug. [ABSTRACT FROM AUTHOR]

Weakly basic drugs are predisposed to order of magnitude decreases in solubility and dissolution as pH increases from 1 to 7 along the gastrointestinal tract. Such behavior is known to be detrimental to drug absorption. The work presented here shows how cocrystals of basic drugs with acidic coformers can mitigate these negative effects. Cocrystals of ketoconazole (KTZ) with adipic, fumaric, and succinic acids exhibit a parabolic solubility dependence on pH such that with increasing pH, solubility decreases, reaches a minimum, and increases. Cocrystals exhibit pHmax values between 3.6 and 3.8, above which they generate supersaturation with respect to drug. The cocrystal supersaturation index (SA), defined as Scocrystal/Sdrug, changes from 1 (pHmax) to 10-30 (pH 5) to 800-3000 (pH 6.5). SA represents the driving force for cocrystal conversion to the less soluble drug during dissolution. SA is not expected to be equal to the observed supersaturation, but it is of great value to classify cocrystals in terms of their risk of conversion. Cocrystal dissolution behavior was analyzed in terms of Cmax, σmax (maximum KTZ concentration and supersaturation), AUCdiss (KTZ concentration area under the curve during dissolution-precipitation), and SA. The three cocrystals studied achieved σmax values between 5 and 15 and sustained supersaturation for 1-3 h, resulting in an AUCdiss advantage over drug in the range of 2-12. SA values as high as 800 were associated with enhanced drug exposure. An SA of 3000 led to limited exposure, very rapid conversion, and no measurable supersaturation. Since cocrystals may be more soluble than needed and/or too soluble to be developed, there is great value in recognizing the relationship between supersaturation threshold, cocrystal solubility, and SA. This becomes more important as cocrystal SA is dependent on pH and other environmental conditions. [ABSTRACT FROM AUTHOR]

Here we show a new adsorptive separation approach using nonporous adaptive crystals of a pillar[5]- arene. Desolvated perethylated pillar[5]arene crystals (EtP5α) with a nonporous character selectively adsorb 1-pentene (1-Pe) over its positional isomer 2-pentene (2- Pe), leading to a structural change from EtP5α to 1-Pe loaded structure (1-Pe@EtP5). The purity of 1-Pe reaches 98.7% in just one cycle and EtP5α can be reused without losing separation performance. [ABSTRACT FROM AUTHOR]

Intrinsic organic -- inorganic metal halide perovskites (OIHP) based semiconductors have shown wide applications in optoelectronic devices. There have been several attempts to incorporate heterovalent metal (e.g., Bi[sup 3+]) ions in the perovskites in an attempt to induce electronic doping and increase the charge carrier density in the semiconductor. It has been reported that inclusion of Bi[sup 3+] decreases the band gap of the material considerably. However, contrary to the earlier conclusions, despite a clear change in the appearance of the crystal as observed by eye, here we show that the band gap of MAPbBr[sub 3] crystals does not change due the presence of Bi[sup 3+] in the growth solution. An increased density of states in the band gap and use of very thick samples for transmission measurements, erroneously give the impression of a band gap shift. These sub band gap states also act as nonradiative recombination centers in the crystals. [ABSTRACT FROM AUTHOR]

In-situ imaging and characterization of Cs2LiLaBr6:Ce crystal growth are performed utilizing energy-resolved neutron imaging. The unique capability of neutrons to penetrate the furnace and to provide direct information on the materials within the furnace is used to visualize the growth dynamics, location, and shape of the liquid/solid interface and to map the elemental composition. Nontrivial dynamics of phase separation within the liquid and solid phases were observed and investigated. Quantitative projected two-dimensional maps of Li concentrations were obtained with sub-millimeter spatial resolution delineating Li-rich and Li-depleted areas. Concurrent variations in Cs and Br concentrations were identified. Good transparency was obtained in part of the ingot where the liquid phase separation has reached steady state, suggesting that nonstoichiometric materials may be optimal for the original charge. The results demonstrate that energy-resolved neutron imaging and its associated modalities can provide unique information for the optimization of crystal growth conditions, in particular having the potential to accelerate scale-up from laboratory to commercial production by improving the yield and quality of single crystal materials. [ABSTRACT FROM AUTHOR]

As a member of the lead-halide perovskite family, inorganic perovskite CsPbBr3 exhibits excellent optical and electrical properties with higher stability to the environment. However, former efforts to obtain large-size CsPbBr3 single crystals with satisfactory quality using low temperature solution methods reached limited results. In this work, we have studied the growth of CsPbBr3 crystals using the antisolvent vapor-assisted crystallization (AVC) method. By adjusting the mole ratio of PbBr2 and CsBr, the phase diagram of the final products is acquired. Five regions are identified, including the Cs4PbBr6 single phase region, Cs4PbBr6 and CsPbBr3 two phases region, CsPbBr3 single phase region, CsPbBr3 and PbBr2·2[(CH3)2SO] metastable two phases region, and CsPbBr3 and PbBr2·2[(CH3)2SO] two phases region. Three methods are adopted to improve the size and crystalline quality of CsPbBr3. The growth rate is effectively tailored by diluting the antisolvent MeOH solution using DMSO to reduce the MeOH vapor pressure. Centimeter-size bright CsPbBr3 crystals have been obtained. The room temperature bandgap of CsPbBr3 is estimated at ~2.29 eV by the transmission spectra. The photoluminescence spectra show two strong emission peaks, located at 530 and 555 nm, respectively, which are related to the free and bond excitons. The resistivity is as large as 2.1 × 109 Ω·cm. Hall effect measurements demonstrate the CsPbBr3 is p-type conductivity with a hole carrier concentration of 4.55 × 107 cm-3 and the mobility of 143 cm2 V-1 s-1. The resulting Au/CsPbBr3/Au device exhibits strong photoresponse to optical light, with an on-off ratio of two orders under a light emitting diode (~1 mW/cm2) with a wavelength of 365-420 nm. Our research would shed more light on the growth and the photoresponse properties of CsPbBr3 crystals. [ABSTRACT FROM AUTHOR]

The recently proposed relationship between the oxygen volume fraction and topological ordering in solid and liquid oxide glasses at high pressure is examined with Bader's atoms-in-molecules (AIM) theory using glass structures generated from first principles molecular dynamics calculations. It is shown that the atomic (O/Si and O/Ge) volume ratio derived from AIM theory is not constant with pressure. This finding is due to the continuous change in the electron topology under compression. Unlike crystalline solids, there is no distinctive transition pressure for Si-O and Ge-O coordination in a glass; instead, the changes are gradual and continuous over a broad pressure range. Therefore, relating a unique Si-O or Ge-O coordination number to the properties of the glass at a given pressure is difficult. [ABSTRACT FROM AUTHOR]

The development of metal-free organic room temperature phosphorescence (RTP) materials has attracted increasing attention because of their applications in sensors, biolabeling (imaging) agents and anticounterfeiting technology, but remains extremely challenging owing to the restricted spin-flip intersystem crossing (ISC) followed by low-yield phosphorescence that cannot compete with nonradiative relaxation processes. Here, we report a facile strategy to realize highly efficient RTP by doping iodo difluoroboron dibenzoylmethane (I-BF2dbm-R) derivatives into a rigid crystalline 4-iodobenzonitrile (Iph-C≡N) matrix. We found that halogen bonding between cyano group of Iph-C≡N matrix and iodine atom of I-BF2dbm-R dopant is formed in doped crystals, i.e., Iph-C≡N···I-BF2dbm-R, which not only suppresses nonradiative relaxation of triplets but also promotes the spin-orbit coupling (SOC). As a result, the doped crystals show intense RTP with an efficiency up to 62.3%. By varying the substituent group R in I-BF2dbm-R from electron donating -OCH3 to electron accepting -F, -CN groups, the ratio between phosphorescence and fluorescence intensities has been systematically increased from 3.8, 15, to 50. [ABSTRACT FROM AUTHOR]

Phase transformation in anisotropic nanocrystals is critical for enhanced surface properties of bimetallic catalysts. In this work, we report a series of phase transformed PtFe nanocomposites as catalysts for facile oxidation of glycerol to value-added tartronic acid at mild operating conditions. The lattice mismatch between Pt and Fe intrinsically drives structure reconstruction from face centered cubic (fcc) to ordered and lattice distorted face centered tetragonal (fct) phase. Surface characterization reveals that there exists an interdiffusion of Pt and Fe during phase transformation and a downward shift of binding energy for Pt species. Such transformation induces the formation of strained PtFe nanocomposites and enhanced structural coherence leading to 3-fold enhancement in catalytic activity for one-pot glycerol oxidation to tartronic acid compared with the fcc structure. [ABSTRACT FROM AUTHOR]

Segmented metallic nanorods with well-defined shapes and controllable components play an important role on the systematic investigation of their shape-dependent catalytic, electric, and plasmonic properties of metal nanostructures. Unfortunately, the shape and composition of segmented nanorods are difficult to be precisely controlled via colloidal methods. Here, we reported the growth of Pd-Au-Pd bimetallic heterostructures by using Au 5-fold twinned bipyramids (BPs) as seeds, with KI as a structure-directing reagent. Through a series of control experiments we revealed that two parameters were identified as critical factors for the growth of segmented Pd-Au-Pd nanorods. First, 5-fold twinned Au BPs with low-index end facets and high-index side facets function as a unique template for directed growth. Second, iodide can switch the deposition of Pd on the Au BPs. A high concentration of iodide is believed to block the high-index facets of the Au BPs and lower the reaction kinetics to promote the selective growth of two Pd segments on the Au BPs. As a result, uniformed segmented Pd-Au-Pd nanorods were obtained. The segmented nanorods exhibit intense extinction in the near-IR range and could be a potential candidate for plasmon-based biological applications such as thermal therapy. [ABSTRACT FROM AUTHOR]

Chalcopyrite-type AgGaQ2 (Q = S, Se) and ZnGeP2 are the main commercial infrared nonlinear optical (IR NLO) crystals. Unfortunately, performance defects including low laser damage threshold (LDT), harmful two-photon absorption (TPA), or small birefringence limit their application. With this background, four new compressed chalcopyrite-like IR NLO materials Li2BaMIVQ4 (MIV = Ge, Sn; Q = S, Se) were successfully synthesized with the typical AgGaQ2 as templates. Remarkably, Li2BaGeS4 and Li2BaSnS4 not only maintain the good NLO responses (0.5 and 0.7 x AgGaS2) but also overcome low LDTs and TPA of commercial chalcopyrites, demonstrating that they satisfy critical demands as promising IR NLO candidates. All of them exhibit phasematching abilities. Furthermore, the discovery of chalcopyrite- like compounds also provides a feasible design strategy to explore new promising IR NLO materials. [ABSTRACT FROM AUTHOR]

Examination of the microstructure of metal-organic frameworks (MOFs) after postsynthetic exchange (PSE) reveals that the exchanged ligand is concentrated at the edges of the crystal and decreases in concentration with crystal depth, resulting in a core-shell arrangement. Diffusion studies of the carboxylate ligand into MOF-5 indicate that diffusion is limiting to the exchange process and may ultimately be responsible for the observed core-shell structure. Examination of PSE in UMCM-8 and single crystals of UiO-66 shows a similar trend, illustrating the applicability of PSE as a method for the creation of core-shell MOFs. [ABSTRACT FROM AUTHOR]

The effect of seed loading and batch trajectory on the growth of crystals with two size coordinates is studied using a simple model for two crystallization systems known to exhibit shape evolution: hen egg white lysozyme and hydroquinone. For moderate seed loading, batch trajectories that lead to a high supersaturation near the beginning of the batch result in a larger nucleated mass and less growth of the seed crystals than other alternatives, while trajectories that keep the supersaturation almost constant give good performance. Increasing seed mass and decreasing seed size also improves performance. Critical seed loading analysis shows that the two-dimensional systems considered in this work behave similarly to one-dimensional crystallization systems considered previously. [ABSTRACT FROM AUTHOR]

The crystallization behaviors of low density polyethylene (LDPE) under ambient N2 and compressed CO2 were characterized using high-pressure differential scanning calorimetry (CO2 pressure ranging from 0.1 to 8 MPa) and high-pressure rheometer (CO2 pressure ranging from 0.1 to 30 MPa), respectively. The modulus variation during the crystallization characterized by HP-rheometer indicated that there were three typical regions where the modulus was nearly invariable with time corresponding to the crystallization beginning, the modulus increased dramatically corresponding to the crystallization ongoing, and the modulus stabilized at a higher value corresponding to the crystallization ending. The foaming was conducted at different storage modulus while other operation factors such as saturation pressure and temperature were maintained consistent. The results suggested that the crystal would affect the bubble-size distribution and even constrain the bubble growth when the relative crystallinity was more than 50%. Below this value, the crystal could facilitate cell nucleation and improve the melt strength. [ABSTRACT FROM AUTHOR]

Here, we introduce Na3V(PO3)3N as a novel 4V-class and zero-strain cathode material for Na-ion batteries. Structural analysis based on a combination of neutron and X-ray diffraction (XRD) reveals that the Na3V(PO3)3N crystal contains three-dimensional channels that are suitable for facile Na diffusion. The Na (de)intercalation is observed to occur at ~4 V vs Na/Na+ in the Na cell via the V3+/V4+ redox reaction with ~67% retention of the initial capacity after over 3000 cycles. The remarkable cycle stability is attributed to the near-zero volume change (~0.24%) and unique centrosymmetric distortion that occurs during a cycle despite the large ionic size of Na ions for (de)intercalation, as demonstrated by ex situ XRD analysis and first-principles calculations. We also demonstrate that the Na3V(PO3)3N electrode can display outstanding power capability with ~84% of the theoretical capacity retained at 10C, even though the particle sizes are on the micrometer scale (>5 μm), which is attributed to its intrinsic three-dimensional open-crystal framework. The combination of this high power capability and extraordinary cycle stability makes Na3V(PO3)3N a new potential cathode material for Na-ion batteries. [ABSTRACT FROM AUTHOR]

The effects of disodium malonate, disodium succinate, disodium glutarate, and disodium adipate on the crystal habit of calcium sulfate α-hemihydrate (CaSO4.0.5H2O, α-CSH) were studied using experimental studies and molecular dynamics simulations. The calculation and experimental results provided insight into the mechanism of the interaction between the additives mentioned above and the different faces of α-CSH that dominate the morphology of α-CSH. The calculation results indicated that the formation of high-aspect-ratio α-CSH, namely, calcium sulfate α-hemihydrate whiskers (α-CSH whiskers), in aqueous solution was due to the interaction between liquid water and side faces of the α-CSH crystal, which inhibits the growth of α-CSH along the radial direction. However, when a trace amount of crystal habit modifier, such as disodium succinate or disodium glutarate, was added to the aqueous solution, the growth rates along the directions normal to the {001} and {114} faces were considerably inhibited. Thus, α-CSH crystals with a low aspect ratio were synthesized using a hydrothermal method. In addition, the calculation methodology used in this work could provide a powerful tool for selecting suitable crystal habit modifiers for preparing α-CSH and other inorganic crystals. [ABSTRACT FROM AUTHOR]

Crystalline 3-D materials bearing interlinked domains of differential porosity and functionality offer the potential for organizing and shuttling molecular and nanoscale matter to specific locations within 3-D space. Here, we present methods for creating prototype MOF materials that have such structural features. Specifically, the process of pore expansion via ligand exchange was studied for an isoreticular series of mesoporous MOFs based on bMOF-100. It was found that pore expansion occurs incrementally in small steps and that it proceeds gradually in an "outside in" fashion within individual crystals. The ligand exchange reaction can be terminated prior to complete crystal conversion to yield intermediate product MOFs, denoted bMOF-100/102 and bMOF-102/106, which bear descending porosity gradients from the crystal periphery to the crystal core. As a proof of concept, size-sensitive incorporation of a gold-thiolate nanocluster, Au133(SR)52, selectively in the bMOF-102/106 crystal periphery region was accomplished via cation exchange. These new methods open up the possibility of controlling molecular organization and transport within porous MOF materials. [ABSTRACT FROM AUTHOR]

Engineering nanostructured optical materials via the purposeful distortion of their constituent nanocrystals requires the knowledge of how various distortions affect the nanocrystals' electronic subsystem and its interaction with light. We use the geometric theory of defects in solids to calculate the linear permittivity tensor of semiconductor nanocrystals whose crystal lattice is arbitrarily distorted by imperfections or strains. The result is then employed to systematically analyze the optical properties of nanocrystals with spatial dispersion caused by screw dislocations and Eshelby twists. We demonstrate that Eshelby twists create gyrotropy in nanocrystals made of isotropic semiconductors whereas screw dislocations can produce it only if the nanocrystal material itself is inherently anisotropic. We also show that the dependence of circular dichroism spectrum on the aspect ratio of dislocation-distorted semiconductor nanorods allows resonant enhancing their optical activity (at least by a factor of 2) and creating highly optically active nanomaterials. [ABSTRACT FROM AUTHOR]

Vertically stacked van der Waals heterostructures are a lucrative platform for exploring the rich electronic and optoelectronic phenomena in two-dimensional materials. Their performance will be strongly affected by impurities and defects at the interfaces. Here we present the first systematic study of interfaces in van der Waals heterostructure using cross-sectional scanning transmission electron microscope (STEM) imaging. By measuring interlayer separations and comparing these to density functional theory (DFT) calculations we find that pristine interfaces exist between hBN and MoS2 or WS2 for stacks prepared by mechanical exfoliation in air. However, for two technologically important transition metal dichalcogenide (TMDC) systems, MoSe2 and WSe2, our measurement of interlayer separations provide the first evidence for impurity species being trapped at buried interfaces with hBN interfaces that are flat at the nanometer length scale. While decreasing the thickness of encapsulated WSe2 from bulk to monolayer we see a systematic increase in the interlayer separation. We attribute these differences to the thinnest TMDC flakes being flexible and hence able to deform mechanically around a sparse population of protruding interfacial impurities. We show that the air sensitive two-dimensional (2D) crystal NbSe2 can be fabricated into heterostructures with pristine interfaces by processing in an inert-gas environment. Finally we find that adopting glovebox transfer significantly improves the quality of interfaces for WSe2 compared to processing in air. [ABSTRACT FROM AUTHOR]

Grain boundaries in two-dimensional crystals are usually thought to separate distinct crystallites and as such they must either form closed loops or terminate at the boundary of a sample. However, when an atomically thin two-dimensional crystal grows on a substrate of nonzero Gaussian curvature, it can develop finite-length grain boundaries that terminate abruptly within a monocrystalline domain. We show that by properly designing the substrate topography, these grain boundaries can be placed at desired locations and at specified misfit angles, as the thermodynamic ground state of a two-dimensional (2D) system bound to a substrate. Compared against the hypothetical competition of growing defectless 2D materials on a Gaussian-curved substrate with consequential fold development or detachment from the substrate, the nucleation and formation of finite-length grain boundaries can be made energetically favorably given sufficient substrate adhesion on the order of tens of meV/Å2 for typical 2D materials. New properties specific to certain grain boundary geometries, including magnetism and metallicity, can thus be engineered into 2D crystals through topographic design of their substrates. [ABSTRACT FROM AUTHOR]

ReS2 is considered as a promising candidate for novel electronic and sensor applications. The low crystal symmetry of this van der Waals compound leads to a highly anisotropic optical, vibrational, and transport behavior. However, the details of the electronic band structure of this fascinating material are still largely unexplored. We present a momentum-resolved study of the electronic structure of monolayer, bilayer, and bulk ReS2 using k-space photoemission microscopy in combination with first-principles calculations. We demonstrate that the valence electrons in bulk ReS2 are-contrary to assumptions in recent literature-significantly delocalized across the van der Waals gap. Furthermore, we directly observe the evolution of the valence band dispersion as a function of the number of layers, revealing the transition from an indirect band gap in bulk ReS2 to a direct gap in the bilayer and the monolayer. We also find a significantly increased effective hole mass in single-layer crystals. Our results establish bilayer ReS2 as an advantageous building block for two-dimensional devices and van der Waals heterostructures. [ABSTRACT FROM AUTHOR]

A biodegradable and biocompatible electrospun scaffold with shape memory behavior in the physiological temperature range is here presented. It was obtained starting from a specifically designed, biobased PLLA-based triblock copolymer, where the central block is poly(propylene azelate-co-propylene sebacate) (P(PAz60PSeb40)) random copolymer. Shape memory properties are determined by the contemporary presence of the low melting crystals of the P(PAz60PSeb40) block, acting as switching segment, and of the high melting crystal phase of PLLA blocks, acting as physical network. It is demonstrated that a straightforward annealing process applied to the crystal phase of the switching element gives the possibility to tune the shape recovery temperature from about 25 to 50 °C, without the need of varying the copolymer's chemical structure. The thermal annealing approach here presented can be thus considered a powerful strategy for "ad hoc" programming the same material for applications requiring different recovery temperatures. Fibroblast culture experiments demonstrated scaffold biocompatibility. [ABSTRACT FROM AUTHOR]

In this work, we fabricated four diphenylcyclopropenone (DPCP) crystals, which involved various molecular interactions encoded in individual molecular structures 1-4. On the basis of crystalline structural analysis and photoresponsive characterization of the resultant single-crystal microribbons 1-4, we demonstrated that the magnitude of molecular interactions could effectively control the quantum chain reaction and the photoresponsive property of the DPCP crystals. The microribbons 1 and 2 having weak molecular interactions exhibited an efficient chain reaction and large mechanical photoresponses (i.e., photomelting and photodeforming), whereas the microribbons 3 and 4 with strong molecular interactions exhibited no chain reaction and mechanical morphology change. Our work presented a new way to achieve molecular crystals with enhanced mechanical photoresponses. [ABSTRACT FROM AUTHOR]

Nonlinear optical materials are essential for the development of solid-state lasers. KBe2BO3F2 (KBBF) is a unique nonlinear optical material for generation of deep-ultraviolet coherent light; however, its industrial application is limited. Here, we report a new material NH4B4O6F, which exhibits a wide deep-ultraviolet transparent range and suitable birefringence that enables frequency doubling below 200 nm. NH4B4O6F possesses large nonlinear coefficients about 2.5 times that of KBBF. In addition, it is easy to grow bulk crystals and does not contain toxic elements. [ABSTRACT FROM AUTHOR]

SnSe emerges as a new class of thermoelectric materials since the recent discovery of an ultrahigh thermoelectric figure of merit in its single crystals. Achieving such performance in the polycrystalline counterpart is still challenging and requires fundamental understandings of its electrical and thermal transport properties as well as structural chemistry. Here we demonstrate a new strategy of improving conversion efficiency of bulk polycrystalline SnSe thermoelectrics. We show that PbSe alloying decreases the transition temperature between Pnma and Cmcm phases and thereby can serve as a means of controlling its onset temperature. Along with 1% Na doping, delicate control of the alloying fraction markedly enhances electrical conductivity by earlier initiation of bipolar conduction while reducing lattice thermal conductivity by alloy and point defect scattering simultaneously. As a result, a remarkably high peak ZT of ~1.2 at 773 K as well as average ZT of ~0.5 from RT to 773 K is achieved for Na0.01(Sn1-xPbx)0.99Se. Surprisingly, spherical-aberration corrected scanning transmission electron microscopic studies reveal that NaySn1-xPbxSe (0 < x ≤ 0.2; y = 0, 0.01) alloys spontaneously form nanoscale particles with a typical size of ~5-10 nm embedded inside the bulk matrix, rather than solid solutions as previously believed. This unexpected feature results in further reduction in their lattice thermal conductivity. [ABSTRACT FROM AUTHOR]

Transition metal compounds sometimes exhibit attractive colors. Here, we report a new oxychloride, Ca3ReO5Cl2, that shows unusually distinct pleochroism; that is, the material exhibits different colors depending on the viewing direction. This pleochroism is a consequence of the coincidental complex crystal field splitting of the 5d orbitals of the Re6+ ion in a square-pyramidal coordination of low symmetry in the energy range of the visible spectrum. Since the relevant d-d transitions show characteristic polarization dependence according to the optical selection rule, the orbital states are "visible" in Ca3ReO5Cl2. [ABSTRACT FROM AUTHOR]

A strategy is outlined for the design of hand-twisted helical crystals. The starting point in the exercise is the one-dimensional (1D) plastic crystal, 1,4-dibromobenzene, which is then changed to a 1D elastic crystal, exemplified by 4-bromophenyl 4'-chlorobenzoate, by introduction of a molecular synthon -O-CO- in lieu of the supramolecular synthon Br···Br in the precursor. The 1D elastic crystals are next modified to two-dimensional (2D) elastic crystals, of the type 4-bromophenyl 4'-nitrobenzoate where the halogen bonding and C-H···O hydrogen bonding are well-matched. Finally, varying the interaction strengths in these 2D elastic crystals gives plastic crystals with two pairs of bendable faces but without slip planes. Typical examples are 4-chlorophenyl and 4-bromophenyl 4'-nitrobenzoate. This type of 2D plasticity represents a new type of bendable crystals in which plastic behavior is seen with a fair degree of isotropic character in the crystal packing. The presence of two sets of bendable faces, generally orthogonal to each other, allows for the possibility of hand-twisting of the crystals to give grossly helical morphologies. Accordingly, we propose the name hand-twisted helical crystals for these substances. [ABSTRACT FROM AUTHOR]

Thiols can engage favorably with aromatic rings in S-H/π interactions, within abiological systems and within proteins. However, the underlying bases for S-H/π interactions are not well understood. The crystal structure of Boc-l-4-thiolphenylalanine tert-butyl ester revealed crystal organization centered on the interaction of the thiol S-H with the aromatic ring of an adjacent molecule, with a through-space Hthiol···Caromatic distance of 2.71 Å, below the 2.90 Å sum of the van der Waals radii of H and C. The nature of this interaction was further examined by DFT calculations, IR spectroscopy, solid-state NMR spectroscopy, and analysis of the Cambridge Structural Database. The S-H/π interaction was found to be driven significantly by favorable molecular orbital interactions, between an aromatic π donor orbital and the S-H σ* acceptor orbital (a π → σ* interaction). For comparison, a structural analysis of O-H/π interactions and of cation/π interactions of alkali metal cations with aromatic rings was conducted. Na+ and K+ exhibit a significant preference for the centroid of the aromatic ring and distances near the sum of the van der Waals and ionic radii, as expected for predominantly electrostatic interactions. Li+ deviates substantially from Na+ and K+. The S-H/π interaction differs from classical cation/π interactions by the preferential alignment of the S-H σ* toward the ring carbons and an aromatic π orbital rather than toward the aromatic centroid. These results describe a potentially broadly applicable approach to understanding the interactions of weakly polar bonds with π systems. [ABSTRACT FROM AUTHOR]

We synthesized TiO2 mesocrystals using a hydrothermal method and investigated the effect of calcination temperature (100-800 °C) on their morphology, crystallinity, and photocatalytic activity. While no appreciable changes in the shape, dimension, and crystal structure of the TiO2 nanoparticles (NPs) were observed as the calcination temperature increased to 300 °C, the crystallinity improved with increasing temperature. The mesocrystal form of the NPs began to disappear at 400 °C, and the specific surface area significantly decreased with increasing temperature owing to the reduced boundaries between the subunits and surface roughness of the NPs. The photocatalytic activity of the TiO2 NPs improved when the temperature increased to 300 °C because of the enhanced crystallinity and elimination of byproducts; on the other hand, it degraded above 400 °C due to the decreased surface area. These results suggest that controlling the calcination temperature is an effective way to tailor the morphology, crystallinity, and photocatalytic activity of TiO2 NPs. [ABSTRACT FROM AUTHOR]

Solvent-mediated transformation of disodium guanosine 5'-monophosphate (5'-GMPNa2) from amorphous to hydrated crystal phases was studied. The SMT process is dominated by the dissolution of the amorphous form and nucleation and growth of the crystal polymorph. The kinetic estimation based on population balance equation was carried out according to experimental data, including polymorphic fraction in the solid phase, solute concentration, and crystal size distribution. Furthermore, independent seeded batch experiments were carried out to estimate the kinetic parameters. The experimental data showed that the nucleation and growth of the crystal polymorph occurred shortly after the dissolution of the amorphous form. The estimated growth, nucleation, and dissolution rates indicated that the solution-mediated transformation was governed by the nucleation and growth of crystal polymorph. We believe that the results hold great importance toward understanding the transformation process of 5'-GMPNa2, which provides theoretical guidance for producing its specific forms, and possibly those for other pharmaceuticals and chemicals as well. [ABSTRACT FROM AUTHOR]