退火对C_（60）薄膜电学性质的影响

Effects of Annealing on Electrical Conductivity of C_(60) Films

本文研究了退火对Ｃ６０膜电导率的影响．结果表明，从室温到２００℃的温度范围内，Ｃ６０膜具有明显的半导体性质，室温电导率在１０－５～１０－７（Ω·ｃｍ）－１的范围内．薄膜在２００℃温度下恒温保持过程中，当时间小于２．５小时时电导率的增大是由于薄膜中不稳定的ｈｃｐ相的减少引起的；而相互通连的晶粒数目的减少导致退火时间大于２．５小时的薄膜电导率的减小．相互通连的晶粒数目的减少使得晶间势垒变高，从而使电导率变小．通连晶粒间缺陷的减少导致激活能变大，这些缺陷在Ｃ６０膜的能带中引入缺陷态．σ－１／Ｔ图中高温区域电导偏离直线是由于在退火过程中不稳定的结构相向稳定的ｆＣＣ相转变．

Abstract We report the annealing effects on the electrical conductivity of C60 films. The studies show that the C60 films have clear semiconducting behavior in the temperature range from room temperature to 473K. The room temperature conductivity is in the range of 10-5￣ 10-7 (Ω· cm)-1. From the measurments of the conductivity versus time when the film is maintained at 473K, we explained that the increase of conductivity before 2. 5 hours of annealing is the result of decrease of unstable phases and increase of the number of connected crystallites, the decrease of conductivity after 2. 5 hours of annealing is due to the decrease of the number of connected crystallites; the decrease in the number of connected rystallites makes intercrystalline potential barrier higher, thus decrease the conductivity.The reason for the increase of activation energy is the decrease of defects between connectd crystallites. These defects may introduce states in the energy gap of C60 film. The deviation of the conductivity from straight lines in the high temperature region in the σ versus 1/T plots are due to unstable structural phases transform toward stable fcc phase in the annealing process.