Needle-like Single Crystals Research Articles

Study on the Single Crystals of Poly(3-octylthiophene) Induced by Solvent-Vapor Annealing

Needle-like single crystals of poly(3-octylthiophene) (P3OT) have been prepared by tetrahydrofuran-vapor annealing. The morphology and structure of the crystals were characterized with optical microscopy, scanning electron microscopy, atomic force microscopy, transmission electron microscopy, and wide-angle X-ray diffraction. It is observed that the P3OT molecules are packed with the backbones parallel to the length axis of the crystal and the alkyl side chains perpendicular to the substrate. The field effect transistor based on the P3OT single crystal exhibited a charge carrier mobility of 1.54 x 10(-4) cm(2)/(Vs) and on/off current ratio of 37, and the molecular orientation of the crystal is ascribed to account for the device performance. The time-dependent morphological evolution demonstrated that the crystals underwent Ostwald ripening when annealed.

Single Crystal Growth of CaMn2O4 and CaMn3O6 in Molten CaCl2

Abstract We developed a novel growth route for oxide crystals in the Ca–Mn–O system. Single crystals of CaMn2O4 and CaMn3O6 were obtained by heating starting Na0.44MnO2 polycrystalline samples in molten CaCl2 salt at 950 and 850 °C, respectively. The as-grown CaMn2O4 crystals were black in color; they also had a polyhedral shape with a maximum dimension of 0.7×0.5×0.3 mm3. In the case of CaMn3O6, needle-like single crystals having average lengths of up to 0.2 mm were successfully grown at 850 °C for the first time.

Preparation of Copper Phthalocyanine Crystals Using Solvothermal Synthesis

Abstract A novel solvothermal synthesis method for the direct growth of β-form crystals of copper phthalocyanine(CuPc) is presented in this article. With quinoline as solvent, crystals were grown after cooling the reaction mixture of 1,3-diiminoisoindoline and copper oxide, heated for 9 h at 270°C, to room temperature in an autoclave. These high quality crystals were suitable for characterization measurements. The single-crystal diffraction data show a monoclinic system unit cell: a =1.4668(3) nm, b =0.48109(10) nm, c =1.9515(7) nm, α=90°, β=121.04(2)°, γ=90°, where the corresponding cell volume is 1.17991 nm 3 . Needle-like single crystals of CuPc up to 10.5 mm in length were obtained. The influences of different temperatures, reaction time and solvent volume on the crystal yields were also discussed. Optimum reaction conditions were 10 mL of quinoline, at 270°C for 8 h.

Single crystal growth of copper phthalocyanine using exaltation–evaporation growth method

A new method of growing single crystal for β-form copper phthalocyanine (CuPc) is presented in this paper. Melted anthracene was used as solvent of CuPc. The method, vaporizing the solvent using an automatic exaltation machine, was employed to grow CuPc single crystals. The needle-like single crystals of CuPc up to 11.6 mm in length were obtained by applying this method. The influences of different temperatures, exaltation speeds and concentrations on the single crystals growth were also discussed. The method was called exaltation–evaporation growth method.

Photoluminescence of ZnTe Crystals Grown under Deviation from Thermodynamic Equilibrium

Crystalline textured and columnar structures, as well as needlelike ZnTe single crystals, were grown from the vapor phase and in a tellurium melt under deviation of the growth conditions from equilibrium. Low-temperature photoluminescence and x-ray structural studies showed the samples thus grown to exhibit high structural perfection, a uniform impurity distribution, and weak interaction between impurities and defects of the crystal structure. Polariton scattering from neutral donors was detected in structures having a noticeable residual concentration of donors in the substituted state. It is shown that the spectrum of samples grown under nonequilibrium conditions exhibits transitions that are not typical of equilibrium crystals. Measurements of the luminescence spectra as a function of temperature, excitation level, and annealing conditions made it possible to draw tentative conclusions about the nature of these transitions.

Growth of bulk single crystals -FeSi2 by chemical vapour deposition

Bulk single crystals β-FeSi2, as a new photoelectric and thermoelectric material, has been successfully grown using chemical vapor transport technique by using iodine as transport agent in a sealed ampoule. The effects of crystal growth condition on quality and morphologies of the single crystals were studied. Both needle-like and grain-like single crystals were gained. By changing substrate temperature, tetrahedral high quality α-FeSi2 single crystals were also obtained.

Multiple crystalline morphologies of N -Alkyl chitosan solution cast films

In addition to spherulites, two novel crystalline morphologies, i. e. need-like crystal and sheet-like crystals were found in formic acid solution cast films of N-methyl chitosan and N-ethyl chitosan during casting at 25°C and relative humidity 65%. Their size was larger in 1∼2 order of magnitude than chitin needle-like single crystals and chitosan lamellar single crystals reported previously due to the high molecular weight. The formation mechanism of these crystalline morphologies was discussed.

Crystal and solution structures of photochromic spirobenzothiopyran. First full characterization of the meta-stable colored species.

Full elucidation for stable, colorless, and meta-stable colored structures of a new spirobenzothiopyran has been achieved both in the solid state and in a solution. 1',3',3'-Trimethyl-6-nitrospiro[(2H)-1-benzothiopyran-2,2'-indoline] with an ester group as a substituent at the 8-position of 1-sp shows photochromism. The blue-green colored species resulted from UV irradiation (365 nm) in one minute and spontaneously bleaches within one minute in acetone and methanol at 27 degrees C. UV exposure (365 nm) of 1-sp in methanol for 3 h at room temperature results in the growth of deep blue needlelike single crystals of the open form of spirobenzothiopyran, photomerocyanine 1-pmc, whose structures in the solid state and in solution were obtained unambiguously. The X-ray structural analysis of 1-pmc revealed the molecular structure of the zwitterionic photomerocyanine with s-trans,s-trans conformation. 1-pmc is soluble to polar solvents and thermally returns to 1-sp. In the DMSO solution, 1-pmc is found to return slowly to 1-sp (1-pmc gave only 18% of 1-sp for 30 min at 22 degrees C). The detailed NMR studies in DMSO-d(6) including COSY and NOE techniques as well as isotope labeling of the compound showed the structure with s-trans,s-cis conformation in a solution.

Single crystal growth of organic semiconductors by the Repeated Solid Solvent Growth Method using melted anthracene as a solvent

We propose a new method of growing single crystals of organic molecular semiconductors, using melted anthracene as a solvent. The method is called the Repeated Solid Solvent Growth Method. Needle-like single crystals of Cu phthalocyanine up to 10 mm in length have been grown by repeated cooling of a glass ampoule which contains the anthracene melt dissolving the molecule. We have found that the crystals tend to grow larger as the procedure is repeated. The crystal growth process is discussed on the basis of the temperature gradient of the growing ampoule.

Raman and infrared investigations of glass and glass-ceramics with composition 2Na2O · 1CaO · 3SiO2

Precursor glass and glass-ceramics with molar composition 2Na2O · ICaO · 3SiO2 are studied by infrared, conventional, and microprobe Raman techniques. The Gaussian deconvoluted Raman spectrum of the glass presents bands at 625 and 660 cm−1, attributed to bending vibrations of Si-O-Si bonds, and at 860, 920, 975, and 1030 cm−1, attributed to symmetric stretching vibrations of SiO4 tetrahedra with 4, 3, 2, and 1 nonbridging oxygens, respectively. The Raman microprobe spectrum of a highly crystallized sample presents two narrow and intense bands at about 590 and 980 cm−1, associated with vibrations of SiO4 tetrahedra with two nonbridging oxygens, in agreement with the predicted chain-like structure of crystalline metasilicates. Scanning electron microscopy shows that the crystals distributed in partially crystallized samples have a spherical shape, built up by radially oriented needle-like single crystals. The Raman microprobe spectra of these spherulites show that they still contain residual amorphous material. A comparison of Raman and infrared spectra of amorphous and highly crystallized samples is presented.

Synthesis and Polymorphism of PdP2O6

Transparent needlelike brownish-yellow single crystals of PdP2O6 have been grown in air under P2O5-rich composition in the system PdO-P2O5. It crystallizes in the orthorhombic system, the possible space group Pmna or P2na, with a = 12.4904(9) Å, b = 4.5759(5) Å, c = 4.2344(3) Å, and Z = 2. This phase changes into a monoclinic phase under heating conditions. The quenchable monoclinic phase has the possible space group P 21/m or P21 with a = 13.156(2) Å, b = 5.1630(7) Å, c = 8.1426(9) Å, and β = 97.46(1)°. A transition temperature depends entirely on a heating rate, e.g., at 908°C at a rate of 10°C min-1, or over 660-735°C at a rate of 20°C hr-1. Moreover the monoclinic phase tends to be decomposed into Pd metal as the final product, depending on not only a temperature but a heating rate. Isothermal heat treatments show that the orthorhombic phase might be a metastable state and the monoclinic phase a stable state at lower temperatures.

Morphology of poly(phenylene sulphide) single crystals grown by a two-stage self-seeding technique

Abstract We have successfully developed a two-stage self-seeding technique to grow poly(phenylene sulphide) (PPS) single crystals from dilute solution, and used these single crystals as model materials to investigate the morphological changes dependent upon the seeding and crystallization conditions. The seeding conditions control the coexistence of different crystal types and determine whether isolated single crystals will be grown. The crystal structure and morphology of PPS single crystals have been investigated by using the wide angle X-ray scattering (WAXS) and transmission electron microscopy techniques including surface decoration by polyethylene. The morphology of the PPS single crystals reveals a highly anisotropic needle-like habit with a very smooth fold surface and very rough growth edges. The aspect ratio of the PPS needle-like single crystals increases as the crystallization temperature and molecular weight increase. Formation of needle-like crystals, lack of sectorization, formation of macroscopically rough growth surfaces, and molecular weight and crystallization temperature dependency of crystal habit suggest a crystal growth model in which the PPS molecules fold parallel to the growth direction during the crystal growth stage from dilute solution.

Structural, Morphological, And Optical Recording Characterization Of Selenium Films

Selenium films obtained by vacuum deposition and hot-wall epitaxy (HWE) were investigated for structural, morphological, and holographic characteristics. Vacuum-deposited Se films, which are generally amorphous, were found to crystallize under an intense beam of an electron microscope. The transmission electron diffraction results indicated that the crystallized phase was b-monoclinic. These films have high transmittance in the visible spectrum and exhibit good exposure characteristics for recording holograms. Parameters such as diffraction efficiency, modulation transfer function, and spatial frequency, determining the exposure characteristics, were evaluated. Films grown by hot-wall epitaxy, however, have altogether different properties. The surface morphology showed growth to needlelike single crystals 5 kall in size, with preferred growth in the (100) direction. These films were gray and exhibited poor transmittance and scattering centers, thus losing their recording properties. X-ray diffraction results of Se films grown by HWE indicated that the crystallized phase was hexagonal in structure.

Growth forms of single crystals of β-rhombohedral boron

Plate-like and prismatic needle-like single crystals of β-rhombohedral boron have been obtained on the surface and in the cages of bulk polycrystalline boron melted in BN crucibles. A crystallographic characterization of prismatic crystals is presented. The preferential growth direction of these crystals is 〈211〉 and {101}, {001}, {012} are preferentially developed facets. It is shown that in the case of an ideal development of {101} planes the single crystals grow in the form of a tetrahedral prism truncated by the rhombohedral facet. The morphological characteristics of boron single crystals are discussed.

Generation of orthorhombic polyoxymethylene in a cationic polymerization system of trioxane

Orthorhombic polyoxymethylene, which was originally found two decades ago in Italy in a polymerization system of aqueous formaldehyde, has been rediscovered in a cationic polymerization system of trioxane designed to grow needle-like polyoxymethylene single crystals. Besides the single crystals obtained in the liquid phase, it has been known that a thin film bearing a number of particles, up to ∼ 1 mm diameter, is formed as a by-product on the inner wall in contact with the gaseous phase. X-ray analysis has now revealed that the particles consist essentially of the orthorhombic crystalline form. The morphology has been investigated and the growth mechanism briefly discussed.

Darstellung und eigenschaften des caesiumbarium-amids, CsBa(NH 2) 3: Strukturverwandtschaft zum NH 4CdCl 3-Typ

In the caesium amide-barium amide system the ternary amide CsBa(NH 2) 3 was synthesized in the form of needle-like single crystals by the reaction of the corresponding metals with NH 3 at an NH 3 pressure of 5 kbar and at 473 K within 11 days. The X-ray structure determination shows strings of edge-sharing anion double octahedra containing the barium atoms, while caesium connects them three dimensionally. The atomic arrangement is discussed in comparison with that of the NH 4CdCl 3 type of structure.

Kinetics of the epitaxy and the over‐growth of polyoxymethylene from molten state on needle‐like single‐crystals

AbstractKinetic studies have been made on the over‐crystallisation of polyoxymethylene on needle‐like crystals, which takes place cylindrically around the needles by forming a pile of lamellar crystallites, using the ordinary spherulitic crystallisation as reference. The growth kinetics were investigated, by means of microscopy and differential scanning calorimetry (DSC), and the resultant structure was examined by small‐angle X‐ray scattering and melting temperature measurements. The discontinuity found for their theoretical plot was assumed to be attributable to the difference in the type of crystallisation. The lamellar surface free energies obtained for the over‐growth were smaller than those for the spherulitic growth, i.e., σe = 42.1 and σs = 2.94 erg/cm2 against σe = 53.4 and σs = 4.97 erg/cm2. The epitaxy effect was elucidated from the analysis of DSC curves during cooling and the combined free‐energy, σeσs = 89.4 erg2/cm4, was estimated for the initial deposit on the needle surface.

Photoconduction of 9, 10-Anthraquinone Single Crystals

Bulky as well as needle-like single crystals of 9, 10-anthraquinone were grown by the Bridgman and the vapor phase growth technique respectively. The bulky single crystal is transparent and yellow and can be cleaved easily along (ab)-, (bc)- and (ac)-planes of the crystal. Crystals with dimension about 1×1×1 cm can be prepared easily. The DC-photoconductivity is about two orders of magnitude smaller than that of anthracene. It is recognized that carriers are generated with radiation at 4100 A which induces the n -π * transition of the molecule. Also carriers are generated for radiations which induce π-π * excitations in the wavelength region of 2500 A to 3000 A. In π-π * excitation region, the photocurrent with the illuminated electrode negative is much larger than that with the illuminated electrode positive. The photoconduction changes with thermal activation energy of 0.17 eV.