외부 자극에 의해 구조 및 화학적으로 변화된 sp2 혼성궤도를 이루는 유기물들의 전자구조 연구

Abstract

In researches of device applications and performances based on organic materials with sp2-hybrid orbitals, electrically and chemically abnormal phenomena can be caused by unexpected external stimuli. These results trigger the study on chemical interactions between atoms or molecules and working mechanisms in terms of physical view. Here, we chose three organic materials with sp2-hybrid orbitals, i.e. pentacene, 6F-TPA PI, and graphene, which have different chemical structures and electrical properties. And then we have investigated the correlations between organic materials and external stimuli using spectroscopic and microscopic methods.Pentacene molecules composed of five benzene rings form the molecular crystal. When pentacene is used as the channel layer of the organic field effect transistor (OFET), its performance is related to the strength of the van der Waals interaction between pentacene molecules. Water is one of the obstacles for prolonged life-time of OFETs. We have investigated how H2O molecules adsorb and affect pentacene crystal. As a result, diffused H2O molecules result in the deteriorated crystallinity, which reflects the weakened inter-molecular interactions in pentacene crystal. This explains the performance degradation of the pentacene-based device in a humid atmosphere.The polymer memory device based on metal/poly(4,40-aminotriphenylene hexafluoroisopropylidenediphthalimide) (6F-TPA PI)/metal system shows electrically bi-stable and volatile memory behaviors. This system hampers experimentally direct investigation of the changes in chemical or electronic structures of the polymer layer before and after the electrical phase transition (EPT), because it is impossible to perfectly eliminate metal covering polymer after this transition. Therefore, we designed a set-up in which holes generated by the photoelectron emission process are injected into 6F-TPA PI instead of direct charge carrier injection via metal electrode. We observed an irreversible EPT of 6F-TPA PI, which originated from an irreversible chemical modification of the carbonyl group (C=O) in phthalimide of 6F-TPA PI.Graphene is a regular sp2-bonded atomic-scale honeycomb lattice of carbon atoms, which results in the band structure of the remarkable linear dispersion of the π bands at Fermi level in the vicinity of K. Therefore, the crystallinity of graphene plays a key role in determining physical properties of that. When the patterned Au/native oxide of silicon (SiOx)/Si sample covered with the graphene sheet is annealed at 400 °C, we have monitored the chemical evolution of this system by contribution of Au as a catalyst. Our results exhibit the catalytic oxidation of carbon atoms from the vacancy defects of the graphene by consuming oxygen atoms dissociated from the SiOx layer even at a relatively low temperature of 400 °C.In selective catalytic etching of graphene above, the unsolved problem is how Au affects and contributes the dissociated process of oxygen atoms from the SiOx layer at relatively low temperatur of 400~500 °C. It was reported that SiOx was thermally dissociated at above 737 °C in a ultra-high vacuum (UHV) conditions, implying that Au could be used as a catalyt. From the sample annealed at 500 °C, we identfied that that inhomogeneous oxidation and silicide of Au were partially formed and originated from dissociation of the native SiOx layer. In addition, we found the structural change of Au from bulk state into coordinately unsaturated state related to the high chemical reactivity, which suggests that the low coordination number of Au caused by diffusion of Au atoms through defects of SiOx play a significant role in the dissociation of SiOx at relatively low temperature.