有機薄膜の可視ATR特性

摘要

有機薄膜の光吸収は，通常，透過スペクトル測定によって評価されるが，透過スペクトルには反射光の影響が含まれ，特に吸収の強い波長領域で反射光が増大する.ここでは，反射分光法の一種である全反射減衰（ATR）法を用いて薄膜の反射スペクトルを測定し，透過スペクトルとの比較を行った.測定対象は銅フタロシアニン（CdPc）の蒸着薄膜である.ATRスペクトルは，入射光の偏光と薄膜の膜厚によって大きく変化し，透過スペクトルの吸収に対応する反射率の低下が観測された.しかし，ATRスペクトルでは，CuPcの吸収帯の高エネルギー（短波長）側で，透過スペクトルには見られない大きな反射率の低下も現れた.吸収帯の高エネルギー（短波長）側では，異常分散の影響により，顕著に屈折率が低下する.ここでは，CuPc薄膜の光吸収に伴う屈折率変化の影響を考慮した考察を行った.%In case of organic thin films with a strong optical absorption, transmission spectra are influenced by an increase of reflected light, and it is difficult to measure the optical absorption correctly. Therefore, the optical absorption spectra measured by attenuated total reflection (ATR) method of reflection measurements were compared with the transmission spectra. The ATR spectra of a copper phthalocyanine (CuPc) thin film with difference thicknesses were measured for an incident light of p- and s-polarizations. The ATR spectra depending on the conditions of the polarized light and the film thickness were obtained from the ATR measurements. In the p-polarized ATR spectra of the 25-nm CuPc films, particularly, a new attenuated peak was observed at the high energy side of the CuPc absorption spectra. The new peaks are attributed to low refractive index influenced on the strong absorption bands of the CuPc.