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Schematic of an OVPD reactor with a laser-induced fluorescence (LIF) capability to dynamically measure organic species concentration in the gas phase. Here, qs and qtot are the mass flow rates of carrier gas injected in the source and the tube respectively, Ts and Tt are the source and tube temperatures, Pt is the tube pressure, and PL is the photoluminescence.
(a) Concentration of Alq3 as a function of time, t, for a series of organic material pulses into the OVPD reactor and transported by Ar. The pulses are shown for several arrest times, ta . All pulses are generated with the following conditions: Source temperature Ts = 300 °C, source carrier gas mass flow rate qs = 100 sccm, tube pressure Pt = 1.5 Torr, total carrier gas mass flow rate qtot = 200 sccm, and tube temperature Tt = 340 °C. All pulses are generated by a 3 s long injection from the organic material source. Following 6 s after injection, the travel of each pulse is arrested for a time, ta , by switching all carrier gas flow to the bypass line. The solid lines are fits by the EMG function with a fixed τ = 4.6 s for all pulses. (b) Evolution of the pulse width, σ 2, with arrest time, ta , obtained from the EMG fits in (a). The solid line is a linear fit.
Diffusion coefficients of Alq3 in N2 and Ar as functions of (a) tube temperature, Tt , with a tube pressure of Pt = 1.5 Torr and (b) as a function of the inverse of Pt with a Tt = 340 °C. The lines are theoretical diffusivities, calculated using the Chapman-Enskog theory.
Diffusion coefficients of Alq3, ADN, SubPc, and rubrene in N2 and Ar measured experimentally and calculated using the Chapman-Enskog theory. Tt and Pt are the tube temperature and pressure, respectively.
Molecular properties used to parameterize the Chapman-Enskog theory. m is the molecular mass, Tm is the melting point, εα/kB and σα are the maximum intermolecular attractive energy and the molecular diameter of species α, FA is the fractional anisotropy of the molecular shape, and p is the magnitude of the molecular dipole.
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