High Vacuum Sublimation Research Articles

In-lens cryo-high resolution scanning electron microscopy: methodologies for molecular imaging of self-assembled organic hydrogels.

The micro- and nanoarchitectures of water-swollen hydrogels were routinely analyzed in three dimensions at very high resolution by two cryopreparation methods that provide stable low-temperature specimens for in-lens high magnification recordings. Gemini surfactants (gS), poly-N-isopropylacrylamides (p-NIP Am), and elastin-mimetic di- (db-E) and triblock (tb-E) copolymer proteins that form hydrogels have been routinely analyzed to the sub-10-nm level in a single day. After they were quench or high pressure frozen, samples in bulk planchets were subsequently chromium coated and observed at low temperature in an in-lens field emission SEM. Pre-equilibrated planchets (4-40 degrees C) that hold 5-10 microl of hydrogel facilitate dynamic morphological studies above and below their transition temperatures. Rapidly frozen samples were fractured under liquid nitrogen, low-temperature metal coated, and observed in-lens to assess the dispersion characteristics of micelles and fragile colloidal assemblies within bulk frozen water. Utilizing the same planchet freezing system, the cryoetch-HRSEM technique removed bulk frozen water from the hydrogel matrix by low-temperature, high-vacuum sublimation. The remaining frozen solid-state sample faithfully represented the hydrogel matrix. Cryo- and cryoetch-HRSEM provided vast vistas of hydrogels at low and intermediate magnifications whereas high magnification recordings and anaglyphs (stereo images) provided a three-dimensional prospective and measurements on a molecular level.

A potential J aggregate molecular system: crystal packing and optical properties of 4,4′-bis(2,3,4,5,6-pentafluorostyryl)stilbene

A preliminary condition for an organic semiconductor to display the appealing spectroscopic properties of J aggregates in the solid state is to posses a favourable molecular packing. 4,4′-Bis(2,3,4,5,6-pentafluorostyryl)stilbene crystallizes in a “brickwall” fashion that is promising with respect to the possible formation of J aggregates in the solid. We report a systematic spectroscopic investigation of 4,4′-bis(2,3,4,5,6-pentafluorostyryl)stilbene in powder, solution, thin films and single crystals. Solutions of 4,4′-bis(2,3,4,5,6-pentafluorostyryl)stilbene with increasing concentration starting from 10 −6 M have been prepared and characterized. Thin films have been grown by high vacuum sublimation on substrates with different hydrophobicity (viz. sapphire, mica and HOPG) in order to explore the effect of substrate surface energy on the photoluminescence (PL) properties of thin films. Single crystals have been grown by vacuum sublimation and the corresponding polarized photoluminescence spectra have been measured at 4 K.

Thin Films of Molecular Metals TTF-TCNQ

We present recent results on the characterization of highly ordered polycrystalline thin films of the charge transfer salt TTF–TCNQ (TTF=tetrathiafulvalene, TCNQ=tetracyanoquinodimethane) prepared by thermal sublimation in high vacuum under different conditions. The increase in orientation and microcrystal size as a function of substrate and annealing temperatures is addressed. A consequence of such an increase is the reduction of the conductivity activation energy, which eventually leads to the observation of the Peierls transition by resistivity measurements. X-ray absorption near edge spectroscopy studies performed with synchrotron radiation reveal directly the influence of charge transfer on unoccupied states near the Fermi level.

Highly Ordered Titanyl Phthalocyanine Films Grown by Directional Crystallization on Oriented Poly(Tetrafluoroethylene) Substrate

Highly oriented films of titanyl phthalocyanine (TiOPc) were obtained by high-vacuum sublimation onto an oriented poly(tetrafluoroethylene) (PTFE) substrate. The dependence of the structure and morphology on deposition parameters (substrate temperature Ts, deposition time t, and deposition rate τ) was followed by X-ray diffraction, transmission electron microscopy (TEM), and atomic force microscopy (AFM) to uncover the origin of the oriented growth process. At Ts = 100 °C, an original growth mechanism was observed whereby α-TiOPc microcrystallites were formed by the static coalescence and reorganization of small amorphous aggregates in close contact. Nucleation of α-TiOPc is initiated at the PTFE macrosteps from which oriented crystallization propagates, leading to uniform α-TiOPc films with a twinned texture and a dense (0 1 0) contact plane. The molecules are in an edge-on orientation, with their molecular plane oriented parallel to the PTFE chains. At the mesoscale, the nucleation of crystalline α-TiOPc involves the alignment and oriented coalescence of amorphous prenucleation aggregates along the PTFE macrosteps, i.e., a graphoepitaxial process. At the molecular scale, it is proposed that the TiOPc orientation and the preferential nucleation of the α polymorph are enforced by the topography and structure of the PTFE macrosteps in conjunction with the requirement for a minimal nucleation free energy. The optical absorption of the films in the near infrared is found to be strongly correlated with the structural and morphological modifications in the films. The oriented character of the α-TiOPc films results in a strong polarization of the 850-nm band perpendicular to the PTFE chain axis direction.

Thin molecular films of neutral tetrathiafulvalene-derivatives

Thin films (thickness ∼1 μm) of the neutral π-donor molecules tetrathiafulvalene (TTF) derivatives tetramethyl-tetrathiafulvalene (TMTTF), ethylenedithio-tetrathiafulvalene (EDT-TTF) and bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF) as well as of tetramethyl-tetraselenafulvalene (TMTSF) have been obtained by sublimation in high vacuum (∼10 −6 mbar) on alkali halide substrates. The films grow by the well-known Volmer–Weber mechanism and are polycrystalline. The microcrystals are highly oriented with their most densely packed molecular planes parallel to the substrate surface in order to minimize the surface (interface) energy. Incommensurate in-plane texture is found for particular molecule–substrate systems.

Growth of mesoscopic correlated droplet patterns by high-vacuum sublimation

Growth of mesoscopic correlated droplet patterns by high-vacuum sublimation

Aspects of the purification of volatile rare earth metals by UHV sublimation: Sm, Eu, Tm, Yb

Purification of rare earth metals with high vapor pressure below melting point (Sm, Eu, Tm, Yb) have been carried out by high and ultra-high vacuum sublimation and distillation, using direct sublimation, sublimation with a porous solid W filter and novel promising liquid metal through distillation (LMTD). Using the last two methods, high purity RE metals with RRR of about 300 were obtained. Aspects of experimental setup and conditions and its influence on behavior and redistribution of impurities are analysed and future perspective of methods are discussed.

Molecular semiconductors from bifunctional dithia- and diselenadiazolyl radicals. Preparation and solid-state structural and electronic properties of 1,4-[(E2N2C)C6H4(CN2E2)] (E = sulfur, selenium)

The reactions of 1,4-phenylenebis(N,N,N{prime}-tris(trimethylsilyl)amidine) with sulfur and selenium dichlorides yield, respectively, the 1,4-phenylenebis(dithiadiazolium) and bis(diselenadiazolium) dichlorides 1,4-((E{sub 2}N{sub 2}C)C{sub 6}H{sub 4}(CN{sub 2}E{sub 2}))Cl{sub 2} (E = S, Se). Reduction of these materials with triphenylantimony affords the corresponding diradical species 1,4-((E{sub 2}N{sub 2}C)C{sub 6}H{sub 4}(CN{sub 2}E{sub 2})), which can be purified by high vacuum sublimation. The crystal structures of 1,4-((E{sub 2}N{sub 2}C)C{sub 6}H{sub 4}(CN{sub 2}E{sub 2})) (E = S, Se) are both monoclinic, space group P2{sub 1}/n. The crystal packing consists of sheets of interleaved columns of weakly associated diradical units (dimers); the mean intradimer separation is 3.34/3.37 {angstrom} (E = S/Se). The sulfur compound is an insulator, but the selenium material has a room temperature pressed pellet resistivity of about 100 {Omega} cm. Magnetic susceptibility measurements show the solids to be predominantly diamagnetic with variable amounts of paramagnetic defects in the lattice. While the exact mechanism of conduction remains to be established, these systems represent the first structurally characterized conducting materials constructed from neutral molecular radicals.

The part of targets in heavy-ion positron spectroscopy

Quasi-atomic K-hole and positron-production experiments together with the positron-line phenomena are presented which emphasize the importance of target proporties in heavy-ion collisions near the Coulomb barrier with beams of 208Pb, 232Th, and 238U. Various self-supported, supported, or sandwiched targets — either metallic or as chemical compounds — have been used; preparation techniques (high-vacuum sublimation- and evaporation condensations, pack rolling, sputter deposition, and molecular plating) are mentioned casually for targets ranging from C, Ti, Ni, Ta, and Pb up to radioactive samples of 232Th, 238U, and 248Cm. The influence of target deterioration is discussed in view of the energy loss and the charge states of the ions. In-beam heavy-ion scattering as well as proton backscattering are exemplified as target control procedures. A target wobbler and a target wheel are given as examples for the reduction of deteriorations due to heavy-ion bombardments.

Poly(sulphur nitride): an assessment of the synthesis from trichlorocyclotri(azathiene) and trimethylsilyl azide

An improved synthesis and purification, and some properties, of powdered (SN)X are reported. Gram quantities can be prepared by reacting (NSCl)3 and Me3SiN3(molar ratio 1:7.5) in acetonitrile, followed by the liquid-SO2 extraction of impurities. The product polymers are fine black powders; surface areas (14–22 m2 g–1) were measured by the B.E.T. method. Freshly prepared and purified samples readily converted to S4N4 both photolytically and by thermal activation; a rapid solid-state conversion to S4N4 occurred at ca. 120 °C (under N2). Differential scanning calorimetry gave ΔH(conversion)=–(20 ± 1) kJ mol–1 of S4N4. Aged samples of powdered polymer were sublimed in vacuo at 110 °C to give gold-bronze conductive layers, σ(bulk)≈ 5 Ω–1 cm–1. A new mode of growth of (SN)X single crystals during high-vacuum sublimation was observed.

THE CHEMISTRY OF THE "AMINOCHROMES": PART II. THE PREPARATION, PAPER CHROMATOGRAPHY, AND SPECTROSCOPIC PROPERTIES OF PURE ADRENOLUTIN; THE INFRARED SPECTRUM OF ADRENOCHROME

The preparation of adrenolutin monohydrate in pure crystalline form has been carried out by the alkaline rearrangement of aqueous solutions of adrenochrome, prepared from the silver oxide oxidation of adrenaline in aqueous solution. An anion-exchange resin (Dowex-1 (Cl−)) was employed to remove inorganic contaminants from the reaction mixture prior to treatment with alkali. The pure anhydrous material has been prepared by the high vacuum sublimation of the monohydrate. The paper chromatographic, spectroscopic, and fluorimetric characteristics of adrenolutin have been investigated. On the basis of the infrared spectrum it is suggested that in the solid state, adrenolutin exists in the keto form, i.e. 2,3-dihydro-5,6-dihydroxy-N-methyl-3-ketoindole. The infrared spectrum of adrenochrome, in the solid state, agrees with the zwitterionic formulation suggested for this compound.

Identity of a muscle-inhibiting flavone in lucerne.

IT was suggested in an earlier note1 that the flavone isolated from lucerne which, like most flavones, inhibits smooth-muscle movements, was 3′,4′,5-trihydroxy-7-methoxyflavone. Further work on larger quantities of the flavone purified by high-vacuum sublimation has now shown it to be tricin, 5,7,4′-trihydroxy-3′,5′-dimethoxyflavone, a flavone found in Triticum dicoccum2.