对硅片上自组装生长的Pentacene薄膜生长机制及其结晶相态的研究

Study on Growth Mechanism and Crystallization Phase State of Pentacene Thin Films on p-Si Wafer

采用热蒸发的方法在硅片衬底上自组装生长的Pentacene薄膜,薄膜在80℃温度下经2h恒温真空热处理,通过原子力显微镜(AFM)对Pentacene薄膜表面形貌及其生长机制进行研究。结果得到,在硅片上生长的Pentacene薄膜是以台阶岛状结构生长,其岛状直径约为100nm。且Pentacene分子以垂直于衬底的方向生长,台阶岛状结构中每个台阶的平均高度约为1.54nm.s-1,与Pentacene分子的沿长轴方向的长度相近。从Pentacene薄膜的XRD图谱中可以看出,薄膜在形成的过程中会因条件的不同而形成不同的结晶相,分别为薄膜相和三斜体相,且薄膜的结晶相将随着薄膜厚度的增加向三斜体相转变,其临界厚度为80和150nm,当薄膜大于150nm时,薄膜的三斜体相占主导地位,而当Pentacene薄膜的厚度小于80nm时,Pentacene薄膜呈薄膜相存在。

The growth mechanism and crystallization phase state were investigated by the methods of atomic force microscopy （AFM） and X-ray diffraction （XRD）. The pentacene films were deposited with a self-assembling monolayer by thermal evaporation on p^＋-Si wafer substrates at room temperature and annealed at a constant temperature （80 ℃） for 120 min. The experimental results show that pentacene films were grown with terraces island structure with the diameter of island of about 100 nm and constituted a layer consisting of faceted grains with a average step height between terraces of 1.54 nm·s^-1,which were accord with the long axis length of pentacene molecule,and the film were vertically grown on the substrate surface. The crystallization of pentacene thin films is shown in XRD pattern. The increase in the thin film thickness introduced a second set of diffraction peaks,which were attributed to the pentacene triclinic bulk phase. The critical thickness of both phases is 150 and 80 nm,respectively. At a film thickness of 150 nm,the triclinic phase diffraction peaks become the dominant phase. This is contrast to the XRD spectrum of very thin film of 80 nm thickness,where the thin film phase is the only contribution.