2019 Volume 4 Pages 96-102
This paper describes an estimation of elastic and plastic properties of Poly (9-vinylcarbazole) (PVK) and 4, 4’Bis (N-carbazolyl)-1, 1’-biphenyl (CBP) thin films by using a nano-indenter. PVK and CBP were coated in a thickness of 350-500 nm on a glass substrate for Organic Light Emitting Diode (OLED) devices by spin coating and vacuum deposition respectively. The measurement of Young’s modulus was carried out by the continuous indentation method. Plastic deformation properties were obtained by a method proposed by Higuchi et al. (2009) and Ogasawara et al. (2007), that is stress-strain curve is estimated in an equation of σ= Rεn . The results have shown that the elastic modules of PVK and CBP were 9.3 MPa and 9.5 MPa respectively, which are a little lower than those of Alq3 and α-NPD reported in the previous paper. Further, the material constant n are 0.003 and 0.0007 for PVK and CBP respectively, which are much smaller than those of Alq3 and α-NPD, suggesting that PVK and CBP have nearly elastic-perfect plastic properties. Therefore, it has been suggested that the reason why PVK and CBP thin films showed higher critical cracking strains more than 7% is resulted from the lower elastic modulus and the smaller work hardening rate (n) than those of Alq3 and α-NPD whose critical cracking strains are 5.0 % and 3.6% respectively.
