Structural Stabilization of New Compounds: MoS2 and WS2 Micro- and Nanotubes Alloyed with Gold and Silver

Abstract

where they are evanescent, especially the narrow white band centered in the graph. This is what gives rise to reflection in our samples, since modes in this region cannot propagate within the material and are reflected.SEM images show that the lamellae in our system preferentially orient parallel to the surfaces of the film. If we then consider that these grains of lamellae with their layer normal parallel to the incident light will present more area from which to reflect, we reason that the wavelength of peak reflectivity is approximately the same as the midgap wavelength at normal incidence. Thus we can use this single plot to interpret the normal incidence reflective behavior of all of our samples and infer the lamellar spacing from our reflectivity data (shown on the right axis of Fig. 1b). This allows us to simply express the lamellar spacing in terms of the wavelength of peak reflectance, l p . The lamellar spacing of a sample is thus given by L = l p /(n ps + n pi ).We have shown that photonic crystals spanning the visible spectrum can be easily fabricated from a ternary blend of a diblock copolymer and two homopolymers. We were able to fabricate films with reflective bands of Dl/l = 0.15± 0.25 with a peak reflective wavelength tunable over a range of l = 350±600 nm. These films had peak reflectivities in the range of 60±70 %. This simple method demonstrates the ease with which large-area, tunable, highly reflective, flexible films can be fabricated from block copolymer± based materials. ExperimentalA near symmetric S/I diblock copolymer with a total molecular weight of 391 kg/mol and a polydispersity index (PDI) of 1.02 as determined by size exclusion chromatography (SEC) was synthesized by anionic polymerization in benzene at 25 C. The styrene block had a molecular weight of approximately 194 kg/mol and the isoprene block had a molecular weight of approximately 197 kg/mol. The homopolymers used were a polystyrene (hPS) with a molecular weight of 13 kg/mol and PDI = 1.04 obtained from Polysciences and a polyisoprene (hPI) with a molecular weight of 13 kg/mol and PDI = 1.06 obtained from the Pressure Chemical Company.The blends were made by mixing together calculated amounts of stock solutions of 100 mg/mL polymer in cumene. The stock solutions were prepared from the diblock copolymer and each homopolymer. We mixed blends containing 100 % to 40 % diblock copolymer at 5 % increments, with the remainder composed of equal fractions of the two homopolymers (i.e., samples contained 0±60 % total homopolymer). About 0.25 mL of the resulting blended solution was dispensed onto one side of a glass cover slip 25 mm in diameter. The solution-coated disks were placed in a cumene-rich atmosphere for one week. Samples can also be made by rapidly drying them in about 10 min, yielding approximately the same optical characteristics. The resulting films of polymer blend on glass were then further dried in ambient conditions for three days, yielding a film of approximately 20±50 mm thickness.Spectral measurements were then p...

Metallic Sub‐Nanometer MoS2–xIy Nanotubes

“…The addition of a few atomic percent of gold or silver leads to the growth of alloyed MoS 2 and WS 2 nanotubes with suppressed chirality and typical crater±cone tube extremities. [12] The C 60 molecules used in the transport reaction template the growth of single-wall MoS 2±x I y (0 £ x < 1, y < 1) nanotubes self-assembled in the form of bundles, which represent the first case of regular molecular crystals composed of inorganic nanotubes. [1] The unit cell of the hexagonal close-packed nanotubes within a bundle is 0.4 nm along the bundle axis, and 0.96 nm perpendicular to the bundle.…”

Dissulfeto de molibdênio, um material multifuncional e surpreendente

“…A fase 1T é condutora 2 enquanto que as fases 2H e 3R são diamagnéticas e semicondutoras 3 . Além das três formas conhecidas de hábito cristalino, o dissulfeto de molibdênio se apresenta na forma amorfa 4,5 , como nanotubos 6,7 e esferas de dimensões nanoscópicas 7,8 semelhantes as estruturas dos fulerenos.…”

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