Single Microcrystals Research Articles

Polarized three-photon-pumped laser in a single MOF microcrystal.

Higher order multiphoton-pumped polarized lasers have fundamental technological importance. Although they can be used to in vivo imaging, their application has yet to be realized. Here we show the first polarized three-photon-pumped (3PP) microcavity laser in a single host–guest composite metal–organic framework (MOF) crystal, via a controllable in situ self-assembly strategy. The highly oriented assembly of dye molecules within the MOF provides an opportunity to achieve 3PP lasing with a low lasing threshold and a very high-quality factor on excitation. Furthermore, the 3PP lasing generated from composite MOF is perfectly polarized. These findings may eventually open up a new route to the exploitation of multiphoton-pumped solid-state laser in single MOF microcrystal (or nanocrystal) for future optoelectronic and biomedical applications.

29Si nuclear spin relaxation in microcrystals of plastically deformed Si: B samples

Single crystals and microcrystals Si: B enriched with 29Si isotopes have been studied using nuclear magnetic resonance and electron paramagnetic resonance (EPR) in the temperature range from 300 to 800 K. It has been found that an increase in the temperature from 300 to 500 K leads to a change in the kinetics of the relaxation of the saturated nuclear spin system. At 300 K, the relaxation kinetics corresponds to direct electron–nuclear interaction with inhomogeneously distributed paramagnetic centers introduced by the plastic deformation of the crystals. At 500 K, the spin relaxation occurs through the nuclear spin diffusion and electron–nuclear interaction with an acceptor impurity. It has been revealed that the plastic deformation affects the EPR spectra at 9 K.

Utilization of Anodized Aluminum Oxide Substrate for the Growth of ZnO Microcrystals on Polygonized Spirals

Anodized Aluminum Oxide (AAO) has been utilized as a substrate for the screw dislocation assisted growth of polygonize spirals (PS) of ZnO with diameter of the order of ~230 μm by Chemical Vapour Deposition (CVD) process. Stoichiometric ZnO microcrystals nucleated on the terraces and tops of these polygonized spirals. Stress inherent in the ZnO polygonized spiral morphology (~ 3.57 GPa) was deciphered from the values of the magnitude of shift in observed 2θ values of Glancing Incidence angle XRD (GIXRD) peaks from the standard values (JCPDS 36-1451) for hexagonal Zincite. The growth mechanism of these PS was explained albeit to a limited extent on the basis of the Burton, Cabrera and Frank (BCF) theory and its later modification, wherein data obtained from exsitu SEM measurements concomitant with numerical analysis was utilized to decipher values of the critical radius and supersaturation ratios. Nucleation of ZnO microcrystals on the PS was explained on the basis of the supersaturation ratio and the plausible values of diffusion lengths, existent on the summits of these PS. Retardation of the step rotation of the PS, due to elastic stress around the dislocation source and the Gibbs–Thomson effect, was explained on the basis of numerical coefficient ω0, the dimensionless frequency of spiral rotation. Role of stress in inhibition of ZnO nucleation on PS of smaller heights and with larger supersaturation ratio, has been discussed albeit qualitatively. The optical characteristics of a single ZnO microcrystal has been analyzed by room temperature CL measurements in the wavelength range 350 nm to 650 nm, revealing a single high intensity peak at 382 nm corresponding to a excitonic bandgap of 3.25 eV.

ChemInform Abstract: Ultrathin Two‐Dimensional Inorganic Materials: New Opportunities for Solid State Nanochemistry

AbstractReview: 44 refs.

Diamond single micro-crystals and graphitic micro-balls’ formation in plasmoids under atmospheric pressure

Plasmoids are produced in the argon filamentary discharge. By going through hydrocarbon gas, the plasmoids collect carbon material. These plasmoids produce diamond single micro-crystals upon contact on the inner surface of cavity in air atmosphere. When the plasmoid’s contact point on the substrate is in inert atmosphere, they deposit their material as micro-balls with a graphite core. The dimension and nature of the micro-materials deposited by the plasmoids are analysed using scanning electron microscopy and Raman microspectroscopy. The compressive residual stress in the deposited micro-diamonds varies in the range −7 to −21 GPa.

Tuning Red Upconversion Emission in Single LiYF4:Yb3+/Ho3+ Microparticle

The upconversion (UC) emission of single LiYF4:Yb3+/Ho3+ microparticle with codoped Ce3+ is investigated. The UC emission tuning from green to red in single LiYF4:Yb3+/Ho3+ microparticle is successfully obtained by codoping Ce3+ ions with different concentrations, and the enhancement mechanism of red emission is discussed in detail. The results indicate that two efficient cross-relaxations between Ho3+ and Ce3+ enhance the red and suppress the green emission in the UC process. The investigation on the luminescence property of a single microcrystal can effectively avoid the influence of the particles around and provide more precise information for better exploring the UC mechanism. The current study on the multicolor tuning of RE-doped micromaterials is also important for extending the application of rare-earth-doped micromaterials in micro-optoelectronic devices, color displays, and anticounterfeiting applications.

IR Near-Field Spectroscopy and Imaging of Single LixFePO4 Microcrystals

IR Near-Field Spectroscopy and Imaging of Single LixFePO4 Microcrystals

Dielectric-dependent electron transfer behaviour of cobalt hexacyanides in a solid solution of sodium chloride.

Here we emphasise the importance of the dielectric environment on the electron transfer behavior in interfacial electrochemical systems. Through doping cobalt hexacyanide (Co(CN)63-) into single microcrystals of sodium chloride (NaCl), for the first time, we obtained the direct electrochemical behavior of Co(CN)63- which is hardly ever obtained in either aqueous or conventional nonaqueous solutions. DFT calculations elucidate that, as the Co(CN)63- anions occupy the lattice units of NaCl65- in the NaCl microcrystal, the redox energy barrier of Co(CN)63-/4- is decreased dramatically due to the low dielectric constant of NaCl. Meanwhile, the low-spin Co(CN)64- anions are stabilized in the lattices of the NaCl microcrystal. The results also show that the NaCl microcrystal is a potential solvent for solid-state electrochemistry at ambient temperature.

Ultrathin two-dimensional inorganic materials: new opportunities for solid state nanochemistry.

CONSPECTUS: The ultimate goal of solid state chemistry is to gain a clear correlation between atomic, defect, and electronic structure and intrinsic properties of solid state materials. Solid materials can generally be classified as amorphous, quasicrystalline, and crystalline based on their atomic arrangement, in which crystalline materials can be further divided into single crystals, microcrystals, and nanocrystals. Conventional solid state chemistry mainly focuses on studying single crystals and microcrystals, while recently nanocrystals have become a hot research topic in the field of solid state chemistry. As more and more nanocrystalline materials have been artificially fabricated, the solid state chemistry for studying those nanosolids has become a new subdiscipline: solid state nanochemistry. However, solid state nanochemistry, usually called "nanochemistry" for short, primarily studies the microstructures and macroscopic properties of a nanomaterial's aggregation states. Due to abundant microstructures in the aggregation states, it is only possible to build a simple but imprecise correlation between the microscopic morphology and the macroscopic properties of the nanostructures. Notably, atomically thin two-dimensional inorganic materials provide an ideal platform to establish clear structure-property relationships in the field of solid state nanochemistry, thanks to their homogeneous dispersion without the assistance of a capping ligand. In addition, their atomic structures including coordination number, bond length, and disorder degree of the examined atoms can be clearly disclosed by X-ray absorption fine structure spectroscopy. Also, their more exposed interior atoms would inevitably induce the formation of various defects, which would have a non-negligible effect on their physicochemical properties. Based on the obtained atomic and defect structural characteristics, density-functional calculations are performed to study their electronic structures. Then, after the properties of the individual ultrathin two-dimensional materials or their assembled highly oriented thin film-based nanodevices are measured, the explicit relationship between atomic, defect, and electronic structure and intrinsic properties could be established. In this Account, we focus on our recent advances in the field of solid state nanochemistry, including atomic structure characterization of ultrathin two-dimensional inorganic materials by X-ray absorption fine structure spectroscopy, characterization of their different types of structural defects by positron annihilation spectra and electron spin resonance, and investigation of their electronic structure by density-functional calculations. In addition, we summarize the close correlation between atomic, defect, and electronic structure variations and the optoelectronic, electrical, magnetic, and thermal properties of ultrathin two-dimensional materials. Finally, we also propose the major challenges and opportunities that face solid state nanochemistry. We believe that all the past achievements in ultrathin two-dimensional materials could bring new opportunities for solid state nanochemistry.

IR near-field spectroscopy and imaging of single Li(x)FePO4 microcrystals.

This study demonstrates the unique capability of infrared near-field nanoscopy combined with Fourier transform infrared spectroscopy to map phase distributions in microcrystals of Li(x)FePO4, a positive electrode material for Li-ion batteries. Ex situ nanoscale IR imaging provides direct evidence for the coexistence of LiFePO4 and FePO4 phases in partially delithiated single-crystal microparticles. A quantitative three-dimensional tomographic reconstruction of the phase distribution within a single microcrystal provides new insights into the phase transformation and/or relaxation mechanism, revealing a FePO4 shell surrounding a diamond-shaped LiFePO4 inner core, gradually shrinking in size and vanishing upon delithiation of the crystal. The observed phase propagation pattern supports recent functional models of LiFePO4 operation relating electrochemical performance to material design. This work demonstrates the remarkable potential of near-field optical techniques for the characterization of electrochemical materials and interfaces.

Shape-engineering of self-assembled organic single microcrystal as optical microresonator for laser applications.

Single micro/nanocrystals based on π-conjugated organic molecules have caused tremendous interests in the optoelectronic applications in laser, optical waveguide, nonlinear optics, and field effect transistors. However, the controlled synthesis of these organic micro/nanocrystals with regular shapes is very difficult to achieve, because the weak interaction (van der Waals' force, ca. 5 kJ/mol) between organic molecules could not dominate the kinetic process of crystal growth. Herein, we develop an elaborate strategy, selective adhesion to organic crystal plane by the hydrogen-bonding interaction (ca. 40 kJ/mol), for modulating the kinetic process of the formation of microcrystal, which leads to the self-assembly of one organic molecule 3-[4-(dimethylamino)phenyl]-1-(2-hy-droxyphenyl)prop-2-en-1-on (HDMAC) into one-dimensional (1D) microwires and 2D microdisks respectively. Furthermore, these as-prepared microcrystals demonstrate shape-dependent microresonator properties that 1D microwires act as Fabry-Pérot (FP) mode lasing resonator and 2D microdisks provide the whispering-gallery-mode (WGM) resonator for lasing oscillator. More significantly, through the investigation of the size-effect on the laser performance, single-mode lasing at red wavelength was successfully achieved in the self-assembled 2D organic microdisk at room temperature. These easily fabricated organic single-crystalline microcrystals with controlled shapes are the natural laser sources, which offer considerable promise for the multi-functionalities of coherent light devices integrated on the optics microchip.

In situ synchrotron IR microspectroscopy of CO2 adsorption on single crystals of the functionalized MOF Sc2(BDC-NH2)3.

Synchrotron radiation (SR) IR microspectroscopy has enabled determination of the thermodynamics, kinetics, and molecular orientation of CO2 adsorbed in single microcrystals of a functionalized metal–organic framework (MOF) under conditions relevant to carbon capture from flue gases. Single crystals of the small-pore MOF, Sc2(BDC-NH2)3, (BDC-NH2=2-amino-1,4-benzenedicarboxylate), with well-defined crystal form have been investigated during CO2 uptake at partial pressures of 0.025-0.2 bar at 298–373 K. The enthalpy and diffusivity of adsorption determined from individual single crystals are consistent with values obtained from measurements on bulk samples. The brilliant SR IR source permits rapid collection of polarized spectra. Strong variations in absorbance of the symmetric stretch of the NH2 groups of the MOF and the asymmetric stretch of the adsorbed CO2 at different orientations of the crystals relative to the polarized IR light show that CO2 molecules align along channels in the MOF.

In situ Synchrotron IR Microspectroscopy of CO2 Adsorption on Single Crystals of the Functionalized MOF Sc2(BDC‐NH2)3

AbstractSynchrotron radiation (SR) IR microspectroscopy has enabled determination of the thermodynamics, kinetics, and molecular orientation of CO2 adsorbed in single microcrystals of a functionalized metal–organic framework (MOF) under conditions relevant to carbon capture from flue gases. Single crystals of the small‐pore MOF, Sc2(BDC‐NH2)3, (BDC‐NH2=2‐amino‐1,4‐benzenedicarboxylate), with well‐defined crystal form have been investigated during CO2 uptake at partial pressures of 0.025‐0.2 bar at 298–373 K. The enthalpy and diffusivity of adsorption determined from individual single crystals are consistent with values obtained from measurements on bulk samples. The brilliant SR IR source permits rapid collection of polarized spectra. Strong variations in absorbance of the symmetric stretch of the NH2 groups of the MOF and the asymmetric stretch of the adsorbed CO2 at different orientations of the crystals relative to the polarized IR light show that CO2 molecules align along channels in the MOF.

Mechanism of Photoinduced Bending and Twisting in Crystalline Microneedles and Microribbons Composed of 9-Methylanthracene

The solid-state photodimerization of 9-methylanthracene is used as a model system to investigate how crystal morphology and reaction dynamics affect photomechanical deformations of single microcrystals. By varying the crystallization conditions, two different crystal shapes, microneedles and microribbons, are grown on a clean water surface. The microribbons twist under irradiation, while the microneedles bend. In both shapes, the maximum deformation occurs at roughly the midpoint of the reaction, while further dimerization causes the crystals return to their original shapes. Powder X-ray diffraction patterns establish that the needles and ribbons have the same crystal orientation and that the photoreaction proceeds in a crystal-to-crystal manner. NMR spin-lattice relaxation measurements are consistent with the rapid formation of large (>100 nm) dimer crystal domains. Simultaneous measurement of the needle bending and monomer fluorescence signal allows us to correlate the bending with the reaction progress. The behavior is qualitatively reproduced by a model in which the motion is driven by strain between spatially distinct reactant and product domains, also called heterometry. We consider several different mechanisms that could give rise to these spatially distinct domains. The ability to control the photoinduced crystal deformation by manipulating crystal shape and solid-state reaction kinetics suggests that photoreactive molecular crystals may be useful for generating well-defined motions on small length scales.

Can Protein Conformers Be Fractionated by Crystallization?

Molecular crystallization typically singles out a specific conformation, or a set of conformations that are identical over large parts and may show some flexibility, from a mixture of equilibrating conformations in solution. To critically evaluate the selectivity of this process, human lactate dehydrogenase isozyme 1 (LDH-1) microcrystals were separately dissolved and subsequently assayed inside capillaries with electrophoretically mediated microanalysis (EMMA) at both the ensemble and the single-molecule level. While fragments from the same crystal exhibited identical enzyme activities, different crystals, even when grown from the same drop of mother liquor, showed markedly different activities. Activities of individual molecules from a crystal were found to be essentially identical, whereas molecules obtained directly from solution showed a 4-fold variation in activity. Furthermore, after storage at 37 °C, the distribution of single-molecule LDH activities from solutions of individual crystals broadened and approached that of LDH obtained from the original solution. X-ray crystallography also showed distinct conformations for single microcrystals and confirms that crystallization properly selects even small conformational variants of proteins and that the slow equilibration to multiple stable conformations in solution is responsible for the observed single-molecule heterogeneity.

Electric-field-induced orientation control of organic semiconductor rubrene crystals

The electric field-induced orientation of rubrene single crystals was observed in a nonpolar solvent. Rubrene single microcrystals responded to an AC electric field beyond a crystal-size dependent threshold. The longitudinal axis, i.e., b-axis, of rubrene single crystals on a SiO2/Si substrate was aligned almost parallel to the direction of the applied electric field. Field-effect transistors with these orientated crystals exhibited low variability of the carrier mobility.

Electrochemical Behaviors of Single Microcrystals of Iron Hexacyanides/NaCl Solid Solution

Solid-state solution with excellent ionic conductivity and redox activity has potential applications in electrochemical microdevices, such as transistors, switches, sensors, and actuators, due to its controllable assembly, integration, and package in microchips. In this paper, we present an electrochemical method to synthesize single microcrystals of an iron hexacyanides/NaCl solid solution and to assemble them into microdevices based on scanning electrochemical cell microscopy. The redox behaviors of the single microcrystals were investigated systematically, especially in the "all-in-solid-state", that is, without exposure to any external liquid environment. The unique metal/solid solution interface has similar electrochemical properties as the conventional metal/liquid solution interface. The apparent concentration of ion hexacyanides (1.05 × 10(-3) mol/L), the diffusion coefficient of the counterion Na(+) (8.05 × 10(-8) cm(2)/s), and the electron transfer rate in the lattice (1.22 × 10(-4) cm/s) were evaluated from the data obtained through all-in-solid-state cyclic voltammetry and electrochemical impedance. All the results are comparable to the conventional metal/solution theory of electrochemistry.

FeCO3 Microparticle Synthesis by Fe-EDTA Hydrothermal Decomposition

We developed a new procedure for synthesizing highly crystalline FeCO3 by hydrothermal decomposition of the Fe(III)-EDTA complex in the presence of urea, starting from ferric ammonium sulfate and Na4EDTA as the main precursors. Single phase FeCO3 microcrystals with a size in the range of 50–200 μm have been obtained after high pressure–temperature treatment time between 15 and 26 h at 230 and 250 °C. Without changing the concentrations of the precursors and synthesis temperature, we have investigated the kinetics of phase transitions between 2 and 40 h of high pressure–temperature treatment time. A transition from hematite (in the first 4 h) to magnetite microoctahedrons with superparamagnetic behavior at room temperature, via a single phase of iron carbonate microcrystals, has been recorded.

Electrochemical Fabrication of Copper-Based Hybrid Microstructures and Mechanism of Formation of Related Hierarchical Structures on Polypyrrole Films

The surface electrochemistry of polypyrrole–polystyrene sulfonate (PPy–PSS) thin films is exploited for the fabrication of novel hybrid copper-based microstructures. The electrochemical deposition of the copper-based materials at the PPy–PSS film is strongly dependent on the electrode potential. This dependence is studied at three different potentials: 0.10, 0.00, and −0.10 V vs SCE. Hierarchical micro/nanostructures made of copper hydroxysulfate salts are only formed at 0.10 V vs SCE and are replaced with branched and single microcrystals of Cu2O covered by a thin layer of Cu(OH)2 at 0.00 and −0.10 V vs SCE, respectively. The different structures can be coupled on the same film through a simple fabrication procedure to give hybrid microstructures. These novel hybrids consist of a central microcrystal (deposited at −0.10 V vs SCE) and a surrounding contour of welded nanosheets (deposited at 0.10 V vs SCE). The mechanism of nucleation and growth of the hierarchical micro/nanostructures formed at 0.10 V vs SCE is also reported. These structures are made from the assembly of nanoparticles into nanowires, nanosheets, and microclusters. These microclusters have a flowerlike shape within which each nanosheet forms a petal of the flower. The nucleation of the clusters is shown to be progressive.

Shape-Controlled Synthesis of Zinc Oxide Microcrystals via a Simple Solvothermal Process and Their Optical Properties

In this work, the synthesis of zinc oxide (ZnO) microcrystals on a large scale with novel twinned ice-cream cones morphology without any additives have been synthesized with a facile alcohol-thermal method. It was found that other morphologies of ZnO (single ice-cream cones, dumbbell-like, hamburger-like and doughnuts-like microcrystals, etc.) could also be readily obtained by adjusting addition amount of ZnO precursor, temperature, solvent composition and surfactant. Furthermore, ZnO twinned microtubes with one end open were obtained using the mixed water and ethanol as solvent by the help of cetylpyridinium bromide (CPB). X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy(TEM), selected area electron diffraction (SAED), and the photoluminescence (PL) spectroscopy were used to characterize these products. Photoluminescence results showed that the as-synthesized ZnO microcrystals presented a narrow and sharp UV emission at 390 nm and a broad blue–green emission at above 466 nm when excited by UV light.