摘要
为研究纳米厚度有机薄膜生长过程中有效导电层的判定方法,揭示反射光谱蕴含的薄膜生长机理,基于多相膜层等效结构和光学菲涅耳方程建立了材料光学系数和膜层厚度为参数的差分反射光谱数学模型,提出了依据相对拟合误差的拟合度评价方法.通过分析室温真空环境纳米厚度并五苯薄膜在Si/SiO_2基底上生长过程的差分反射光谱,发现采用四相膜层结构和并五苯薄膜晶体结构光学系数拟合的差分反射光谱与实验数据符合良好,确认并五苯分子主要以薄膜结构的形态进行生长,膜厚生长速率约为0.2 nm/min.该方法避免了反射光谱中多膜层结构产生的干涉信号对生长机理分析的影响.更为重要的是,相对拟合误差随生长时间的变化趋势与由薄膜构建的场效应管结构的电学特性呈现出明显的相关性,不仅反映了生长过程中薄膜成膜模式的演变趋势,还清晰地揭示了有效导电层的形成过程,为光谱法研究薄膜生长机理和无法进行电学测试的条件下监测薄膜电学特性提供了新手段.
We propose an optical approach for analyzing the formation of the conductive layer during organic thin film growth. The relationship between the properties of multi-layer film, such as thickness and optical coefficients, and the corresponding differential reflectance spectrum（DRS） is derived as math formula based on the effective medium approximation. With the deduced formula, the thickness of the deposited film, for example, electron transport layer in this paper, can be estimated according to the measured DRS data. But, in fact, the fitting error always exists. It is, on the other hand, a useful evidence to indicate the actual situation of the thin film. A concept of the normalized fitting error（NFE） is offered here to equivalently assess the fitting results of all DRS data in the growth process. The curve of NFE versus time is proposed to analyze the growth revolution of the thin film and reveal the inner physical mechanism. In order to demonstrate the performance of the proposed method, an organic field effect transistor（OFET）with a bottom-gate structure is fabricated and pentacene organic thin film is deposited by vacuum thermal evaporation,as an electron transport layer, on the top of the transistor, i. e., an insulator substrate of Si/SiO2. The reflected optical spectrum and the current between the drain and the source of the OFET device are investigated in real time in the growth process. It has been reported that pentacene has three kinds of crystal structures and their optical properties differ from each other. The actual phase of the pentacene film in our experiment is discussed at first. The fitting results show that the pentacene layer exists mainly in thin film phase here. Then, the thickness of SiO_2 layer is determined to be 296 nm, which is close to the design value of 300 nm. With those parameters, a four-layer model is used to calculate the thickness of the organic film. The thickness data indicate that the film appears to be linearly growing and the growth rate is 0.2 nm/min. Next,
出处
《物理学报》
SCIE
EI
CAS
CSCD
北大核心
2016年第20期1-9,共9页
Acta Physica Sinica
基金
国家自然科学基金(批准号:61008028,11504201)
全国优秀博士学位论文作者专项资金(批准号:201140)
教育部新世纪优秀人才支持计划(批准号:11-0366)
“111”引智计划(批准号:B07014)资助的课题~~
关键词
有机薄膜
光学模型
有效导电层
反射光谱
organic thin film
optical model
effective conduction layer
reflectance spectroscopy
