C_(60)分子在GaAs(001)表面的外延生长的扫描隧道显微镜研究

STUDY ON GROWTH OF C 60 MOLECULES ON GaAs(001) SUBSTRATE BY SCANNING TUNNELING MICROSCOPY

利用扫描隧道显微镜（ＳＴＭ）系统地研究了Ｃ６０薄膜在ＧａＡｓ（００１）表面的异质外延生长．在ＧａＡｓ（００１）２×４β相表面，观察到Ｃ６０薄膜以非密排面进行生长，并在生长中有结构相变产生．实验数据表明，薄膜下层面心立方（ｆｃｃ）的晶格常数比Ｃ６０晶体的晶格常数要大１３％；而薄膜的表层结构则展示了非理想的六角密堆（ｈｃｐ）结构，其表面为ｈｃｐ（１１００）面，生长过程是非理想的层状生长模式．在ＧａＡｓ（００１）ｃ（４×４）衬底上，Ｃ６０薄膜的表面仍然是ｆｃｃ（１１１）面，其结构参数与Ｃ６０晶体一致。

We have studied the growth of C 60 film on GaAs(001) 2×4 β phase surface epitaxially grown by MBE.Due to the delicate equilibrium between the interaction of C 60 molecules and the interaction of C 60 molecule with the substrate,the toplayer of C 60 film,unlike that on the metal and silicon substrate,shows a non close packed structure.The facet structure of C 60 film exhibits that the top two layers are hcp but the others are fcc,which implies an existence of the phase transition from hcp to fcc structure in the film growth.The measurement results that the lattice constant of fcc is 1.13 nm,larger of 13% than that of C 60 crystal,and hcp is not ideal which is compressed along c axis.The strain in C 60 film and the minimum of the total energy should be responsible for the existence of the phase transition.On GaAs(001) c(4×4) surface,the structure of C 60 film shows fcc(111) surface and the film grows in three dimensional mode which is quite different from that on other substrates.