182,958 research outputs found
Surface melting of methane and methane film on magnesium oxide
Experiments on surface melting of several organic materials have shown
contradictory results. We study the Van der Waals interactions between
interfaces in surface melting of the bulk CH_4 and interfacial melting of the
CH_4 film on the MgO substrate. This analysis is based on the theory of
Dzyaloshinskii, Lifshitz, and Pitaevskii for dispersion forces in materials
characterized by the frequency dependent dielectric functions. These functions
for magnesium oxide and methane are obtained from optical data using an
oscillator model of the dielectric response. The results show that a repulsive
interaction between the solid-liquid and liquid-vapor interfaces exists for the
bulk methane. We also found that the van der Waals forces between two
solid-liquid interfaces are attractive for the CH_4 film on the MgO substrate.
This implies that the van der Waals forces induce the presence of complete
surface melting for the bulk methane and the absence of interfacial melting for
CH_4 on the MgO substrate.Comment: 11 pages, 4 ps figure
Two-dimensional band structure in honeycomb metal-organic frameworks
Metal-organic frameworks (MOFs) are an important class of materials that
present intriguing opportunities in the fields of sensing, gas storage,
catalysis, and optoelectronics. Very recently, two-dimensional (2D) MOFs have
been proposed as a flexible material platform for realizing exotic quantum
phases including topological and anomalous quantum Hall insulators.
Experimentally, direct synthesis of 2D MOFs has been essentially confined to
metal substrates, where the interaction with the substrate masks the intrinsic
electronic properties of the MOF. Here, we demonstrate synthesis of 2D
honeycomb metal-organic frameworks on a weakly interacting epitaxial graphene
substrate. Using low-temperature scanning tunneling microscopy (STM) and atomic
force microscopy (AFM) complemented by density-functional theory (DFT)
calculations, we show the formation of 2D band structure in the MOF decoupled
from the substrate. These results open the experimental path towards MOF-based
designer quantum materials with complex, engineered electronic structures
Piezoelectric sensing coating for real time impact detection and location on aircraft structures
Flexible, light weight and low cost electroactive coating has been fabricated by the dispersion of inorganic ferroelectric submicron particles in a polyurethane matrix. BaTiO3 particles have a mean diameter of 300 nm. The poling process and the influence of volume fraction of BaTiO3 on the piezoelectric activity of the coating have been reported. This spray coating has been realized on 1.6 * 1.6 m2 poly(epoxy)/carbon fiber reinforced composite. Impact detection has been also performed. A well-known cross correlated algorithm has been successfully employed to localize impact in a 90 * 90 cm2 area of the composite
Charge transport in nanoscale vertical organic semiconductor pillar devices
We report charge transport measurements in nanoscale vertical pillar
structures incorporating ultrathin layers of the organic semiconductor
poly(3-hexylthiophene)(P3HT). P3HT layers with thickness down to 5 nm are
gently top-contacted using wedging transfer, yielding highly reproducible,
robust nanoscale junctions carrying high current densities (up to
A/m). Current-voltage data modeling demonstrates excellent hole injection.
This work opens up the pathway towards nanoscale, ultrashort-channel organic
transistors for high-frequency and high-current-density operation.Comment: 30 pages, 8 figures, 1 tabl
Self-cleaning Properties of Thin Printed Layers of Titanium Dioxide
Tenké vrstvy oxidu titaničitého byly imobilizovány na sodnovápenatá skla a skelný uhlík použitím jak techniky materiálového tisku tak metodou chemického napařování. Pro přípravu titaničitých solů byly použity metody sol-gelu a nebo hydrotermální syntézy. Struktura připravených vrstev byla zkoumána rastrovací elektronovou mikroskopií a mikroskopií atomárních sil. Krystalická struktura připravených TiO2 byla analyzovány pomocí XRD metody. Fotoindukováná superhidrofility pripravených vzorků byla charakterizována měřením kontaktních úhlů. Fotokatalytická aktivity připravených vzorků byla testována na fotokatalytické oxidaci 2,6-dichlorindofenolu a kyseliny mravenčí. V případě sol-gel vrstev byl zkoumán vliv množství naneseného TiO2 a množství PEG, který byl do solu přidán jako praskliny potlačující činidlo. V případě hydrotermálních vrstev byl zkoumán vliv času a teploty syntézy a množství vrstev na výslednou účinnost vzorku. U chemicky napařených vzorků byl zjišťován vliv intenzity záření. Byla porovnána fotokatalitická aktivita vrstev připravených materiálovým tiskem a chemickým napařováním a byl vyhodnocen nejaktivnější vzorek.Titanium dioxide was immobilized on soda-lime glass substrates and glassy carbon substrates by two techniques: material printing and chemical vapour deposition. Two methods of sol preparation were used; sol-gel and hydrothermal synthesis. Morphology of all prepared titania layers were studied by scanning electron microscopy and atomic force microscopy analysis. Crystallite phase of prepared TiO2 was determined using XRD analysis. Photoinduced superhydrophilicity was examined using the sessile drop method. Photocatalytic activity was investigated as a degradation rate of 2,6-dichloroindophenol or formic acid. We studied the influence of sol-loading and amount of PEG on final activity in case of sol-gel process. PEG was added as an anticracking agent. The influence of time and temperature of hydrothermal synthesis or amount of layers on final efficiency was examined for hydrothermally synthesized samples. The influence of different intensities of irradiation was investigated for the layers deposited by CVD process. The activity of titania thin films prepared by material printing and CVD process was compared and the best sample was evaluated.
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