Published online by Cambridge University Press: 31 January 2011
Thermal conductivity of rubrene single crystals is measured for both bulk and film-like crystals down to 0.5 K in order to estimate quantitatively density of crystalline defects through their phonon mean free paths. The temperature profile of the bulk rubrene crystals exhibit pronounced peak at ∼ 10 K in the thermal conductivity as the result of very long mean-free paths of their phonons which indicates extremely low-level defect density in the region of 1015-1016 cm−3 depending on different growth methods. The crystals grown from gas phase tend to have less defects than those grown from solution. It turned out that the film-like crystals have a few times more defect density as the result of the measurement by using newly developed devices for minute crystals.