NaEuF_4微米晶的水热合成与表征

以柠檬酸钠(Na3Cit)为螯合剂和形貌控制剂,通过水热方法成功合成了尺寸均匀的六角形NaEuF4微米晶.采用X-射线粉末衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、能量色散X射线(EDX)和光致发光光谱(PL)对所得产物的结构、形貌以及发光性质进行分析.XRD和SEM分析表明:所得NaEuF4微米晶为六方相,颗粒较均匀.NaEuF4微米晶的尺寸和形貌可通过改变Na3Cit的量和反应时间进行调整.提出NaEuF4微米晶的可能形成机理,并研究其光致发光光谱性质.     

Synthesis and characterization of branched yttrium hydroxide fluoride microcrystals with hierarchical tubular structure

Hexagonal yttrium hydroxide fluoride microcrystals were prepared by a two-step hydrothermal route using yttrium nitrate, sodium hydroxide and sodium fluoride as raw materials to react in propanetriol solvent. The samples were characterized by powder X-ray diffraction (XRD), energy dispersive spectrum (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier trans-form infrared spectroscopy (FT-IR), thermogravimetre and differential-thermogravimetric analysis (TG-DTA), which revealed that Y(OH)2.14F0.86 microcrystals were multi-branched and that the branches of Y(OH)2.14F0.86 microcrystals were composed of hierarchical tubes. This novel multi-branched and intriguing hierarchical tubular structure of yttrium hydroxide fluoride maybe has a potential application in photoelectric crystals. The formation of branched Y(OH)2.14F0.86 microcrystals with hierarchical tubular structure were due to the substitution reaction and Oswald ripening.     

Energy-filtering TEM and electron energy-loss spectroscopy of double structure tabular microcrystals of silver halide emulsions

Composite Ag(Br,I) tabular microcrystals of photographic emulsions were studied by the combination of energy-filtering electron microscopy (EFTEM) and electron energy-loss spectroscopy (EELS) in conjunction with energy-dispersive X-ray (EDX) microanalysis. The contrast tuning under the energy-filtering in the low-loss region was used to observe more clearly edge and random dislocations, {11⁻1} stacking faults in the grain shells parallel to {11⁻2} edges and bend and edge contours. Electron spectroscopic diffraction patterns revealed numerous extra reflections at commensurate positions in between the Bragg reflections and diffuse honeycomb contours; these were assigned to the number of defects in the shell region parallel to the grain edges and polyhedral clusters of interstitial silver cations, respectively. Inner-shell excitation bands of silver halide were detected and confirmed by EDX analyses, i.e. the Ag N_2,3 edge at 62 eV (probably overlapped with the weak I N_4,5 edge at 52 eV and the Br M_4,5 edge at 70 eV), the I M_4,5 edge at about 620 eV, and the Br L_2,3 edge at about 1550 eV energy losses. Energy-loss near-edge structure of the Ag M_4,5 edge at about 367 eV energy losses and low-loss fine structure arisen as a result of interband transitions and excitons, possibly superimposed with many electron effects, have been revealed. The crystal thickness was determined by a modified EELS log-ratio technique in satisfactory agreement with measurements on grain replicas.     

Air-grid surface patterning provided by superhydrophobic surfaces

Recently, several unique studies on surface patterning have been developed based on superhydrophobic surfaces, where air was introduced as the separating barrier for the surface pattern. This new type of surface patterning approach is called "air-grid surface patterning." Traditional technologies of surface patterning always utilize the solid or liquid phase as the separating barrier, for example, a 2D chemical molecular barrier in soft lithography, a 3D solid barrier in photolithography, or a liquid barrier in microfluidic, laminar flow patterning methods. These recent studies reveal that air can act as a gas-phase separating barrier. This concept is expected to open up a new branch of applications of superhydrophobic surfaces, and it exhibits promising potential for functional micropatterning of various materials, from nanomaterials to crystals to cells.     

纤维素在炭化和活化过程中的结构变化

以纤维素为原料,通过在氮气氛下炭化和水蒸气活化得到纤维素基炭。采用热分析、傅里叶红外光谱、X射线衍射及低温N₂吸附测试手段研究了纤维素的炭化和活化过程以及过程中炭微晶结构和比表面积的变化。纤维素分子结构中的C-OH、C-O-C、C-H等基团在280~380℃之间大量分解,380℃后少量裂解产生的小分子碎片或基团持续分解,同时碳元素发生结构重排,形成石墨微晶。炭化温度是影响纤维素基活性炭微晶结构及孔结构的关键因素,随炭化温度的升高,石墨微晶尺寸变大,孔结构得到发育,但活性炭的比表面积则呈先增加后下降趋势,当炭化温度为600℃时所得活性炭比表面积最大;炭化时间对炭微晶结构及比表面积的影响不显著;随着活化时间的延长,先是炭结构中的非微晶碳被氧化,比表面积及总孔容积变大,然后微晶碳被氧化,微晶结构被破坏,炭中部分微孔变成中孔或大孔,导致比表面积及总孔容积变小,当微晶间的非微晶碳被充分氧化而又不破坏原微晶结构时得到的炭孔隙最丰富。     

Influence of copper anion complexes on the incorporation of metal particles in polyaniline Part II: Copper oxalate complex

Copper deposition at polyaniline (PAN) coated electrodes is studied using copper oxalate complexes as reducing species. It is found that a high number (3.4 × 10⁸ cm^–2) of single sized (~150 nm), regular shaped crystals can be obtained. Statistical analysis of the distances between neighbouring crystals shows deviation from a random surface distribution. This finding is discussed both in terms of origin and overlap of nucleation exclusion zones and of the influence of the finite size of the copper crystals. Experiments performed under potentiostatic conditions give evidence for instantaneous copper nucleation and growth under phase boundary transition limitations. Results concerning number, size and shape of copper crystals deposited in a similar way using three different reducing species (i.e., copper cations, copper citrate and copper oxalate complex anions) are compared. It is established that the copper oxalate complex anions allow for deposition of the largest number of small metal crystals. This result is related to both the initial oxidation state of the PAN layer in the oxalate solution and to the specific properties of the anion complex.     

Evaluation of characterization methods for thin sections of silver halide microcrystals by analytical electron microscopy

Silver halide microcrystals are usually composed of different phases with varying halide compositions. These microcrystals can be sectioned with an ultramicrotome with a certain thickness in a specific direction. The scanning electron microscopical analysis of these sections provides information on the internal halide profile.
During sample sectioning, many deformations can be induced in the material, and usually dominate the different scanning electron images.
By acquiring X-ray maps, it is possible to locate the different phases in the sections. This technique, however, is very time-consuming, and can only be used when the local halide variations are very high.
When an EDX line scan is acquired over the section, information on the position of the phases with different halide composition is obtained in a reasonable time, and shows no dependence on the section deformations. From this knowledge, several positions on the section are selected where local X-ray analyses are performed. After quantifying the results, the internal halide distribution is obtained. The analytical lateral resolution is about 30 nm for sections ≈100 nm thick.     

Controllable Synthesis of Organic Microcrystals with Tunable Emission Color and Morphology Based on Molecular Packing Mode

Organic microcrystals are of essential importance for high fluorescence efficiency, ordered molecular packing mode, minimized defects, and smooth shapes, which are extensively applied in organic optoelectronics. The molecular packing mode significantly influences the optical/electrical properties of organic microcrystals, which makes the controllable preparation of organic microcrystals with desired molecular packing mode extremely important. In the study, yellow‐emissive α phase organic microcrystals with rectangular morphology and green‐emissive β phase perylene microcrystals with rhombic morphology are separately prepared by simply controlling the solution concentration. The distinct molecular staking modes of the H/J‐aggregate are found in these two types of perylene microcrystals, which contribute to the different emission color, morphology, and radiative decay rate. What is more interesting, the α‐doped β phase and the β‐doped α phase organic microcrystals can also be fabricated by modulating the evaporation rate from 100 to 10 µL min^?1. The findings can contribute to the future development of organic optoelectronics at the microscale.     

Tuning the size and optical properties in molecular nano/microcrystals: manifestation of hierarchical interactions

Intermolecular interactions, such as hydrogen bonding, dipolar and van der Waals, occurring in molecular crystals cover a range of magnitudes. As the crystal evolves from a relatively softer state in the nanoscopic size regime to a harder one in the microcrystalline and bulk solid state, the impact of the hierarchy of intermolecular interactions can be expected to emerge in a progressive fashion. The strongest interactions alone would be manifested at small sizes; as the crystal grows, the effect of the weaker ones will be added on, with the bulk crystals exhibiting the cumulative impact of the different interactions. We demonstrate this phenomenon through investigations of the solution, colloid, and solid state of a novel zwitterionic molecule based on the diaminodicyanoquinodimethane framework. A reprecipitation-digestion protocol is developed for the fabrication of nano/microcrystals of varying sizes. Microscopic and spectroscopic characterizations reveal tuning of the size and optical properties of this material. The optical absorption of the colloidal particles evolves with size towards that of the bulk solid, the emission showing a steady enhancement of intensity. Crystallographic investigations coupled with semiempirical computations provide a viable model to describe the range of observations in terms of the gradual accumulation of hierarchical intermolecular interactions.