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Collision frequency is defined in chemical kinetics and collision theory, in the background of theoretical kinetics. For a reaction between A and B, the collision frequency (Z) is the number of collisions between A and B occurring in the container per unit volume per unit time. Z=nAnBσAB√(8kBT/πμAB), SI unit of Z is number of collision m⁻³s⁻¹=1000NA mol L⁻¹ s⁻¹, where NA is Avogadro constant. where: nA is the number density of A in the gas (unit m⁻³), nB is the number density of B in the gas (unit m⁻³), σAB is the reaction cross section (unit m²), the area when two molecules collide with each other, simplified to σAB=π(rA+rB)², where rA the radius of A and rB the radius of B. kB is the Boltzmann's constant unit m² kg s⁻² K), T is the temperature (unit K), μAB is the reduced mass of the reactants A and B, μAB=mAmB/(mA+mB) (unit kg)

Method of deposition of thin films of amorphous and crystalline microstructures based on ultrafast pulsed laser deposition

InactiveUS6312768B1Improve surface qualityImprove efficiencyMaterial nanotechnologyElectric discharge heatingMacroscopic scaleCarbon nanotube

Powerful nanosecond-range lasers using low repetition rate pulsed laser deposition produce numerous macroscopic size particles and droplets, which embed in thin film coatings. This problem has been addressed by lowering the pulse energy, keeping the laser intensity optional for evaporation, so that significant numbers of the macroscopic particles and droplets are no longer present in the evaporated plume. The result is deposition of evaporated plume on a substrate to form thin film of very high surface quality. Preferably, the laser pulses have a repetition rate to produce a continuous flow of evaporated material at the substrate. Pulse-range is typically picosecond and femtosecond and repetition rate kilohertz to hundreds of megahertz. The process may be carried out in the presence of a buffer gas, which may be inert or reactive, and the increased vapour density and therefore the collision frequency between evaporated atoms leads to the formation of nanostructured materials of increasing interest, because of their peculiar structural, electronic and mechanical properties. One of these is carbon nanotubes, which is a new form of carbon belonging to the fullerene (C60) family. Carbon nanotubes are seamless, single or multishell co-axial cylindrical tubules with or without dome caps at the extremities. Typically diameters range from 1 nm to 50 nm with a length >1 mum. The electronic structure may be either metallic or semiconducting without any change in the chemical bonding or adding of dopant. In addition, the materials have application to a wide range of established thin film applications.

94 results about "Collision frequency" patented technology

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