High quality thin films of topological insulators （TI） such as Bi2Se3 have been successfully synthesized by molecular beam epitaxy （MBE）. Although the surface of MBE films can be protected by capping with inert ma...High quality thin films of topological insulators （TI） such as Bi2Se3 have been successfully synthesized by molecular beam epitaxy （MBE）. Although the surface of MBE films can be protected by capping with inert materials such as amorphous Se, restoring an atomically clean pristine surface after decapping has never been demonstrated, which prevents in-depth investigations of the intrinsic properties of TI thin films with ex situ tools. Using high resolution scanning tunneling microscopy/spectroscopy （STM/STS）, we demonstrate a simple and highly reproducible Se decapping method that allows recovery of the pristine surface of extremely high quality Bi2Se3 thin films grown and capped with Se in a separate MBE system then exposed to the atmosphere during transfer into the STM system. The crucial step of our decapping process is the removal of the surface contaminants on top of amorphous Se before thermal desorption of Se at a mild temperature （-210 ~C）. This effective Se decapping process opens up the possibility of ex situ characterizations of pristine surfaces of interesting selenide materials and beyond using cutting-edge techniques.展开更多
文摘本文实验测量了少周期飞秒激光场下惰性气体Ne原子非顺序双电离引起的Ne^(2+)离子动量分布,发现该分布强烈依赖于激光场的载波-包络相位(Carrier-Envelope Phase,CEP),在某些CEP条件下呈现出明显不对称的双峰结构.半经典理论计算可以定性地重现实验结果.理论分析表明,二价离子的不对称动量分布来自于非顺序双电离过程中碰撞直接电离(Recollision-Impact-Ionization,RII)与碰撞-激发电离(Recollision-Excitation and Subsequent Ionization,RESI)两个通道的贡献,其中不对称双峰结构来自于RII通道,而RESI通道影响的是低动量部分,导致双峰结构变平.RII通道中产生的Ne^(2+)离子动量分布对CEP有较强的依赖性,而RESI通道中Ne^(2+)离子动量分布随CEP的变化不明显.进一步的计算表明,离子实库仑势在非顺序双电离过程中起到非常重要的作用,它将引起RESI通道产量增大.
文摘High quality thin films of topological insulators （TI） such as Bi2Se3 have been successfully synthesized by molecular beam epitaxy （MBE）. Although the surface of MBE films can be protected by capping with inert materials such as amorphous Se, restoring an atomically clean pristine surface after decapping has never been demonstrated, which prevents in-depth investigations of the intrinsic properties of TI thin films with ex situ tools. Using high resolution scanning tunneling microscopy/spectroscopy （STM/STS）, we demonstrate a simple and highly reproducible Se decapping method that allows recovery of the pristine surface of extremely high quality Bi2Se3 thin films grown and capped with Se in a separate MBE system then exposed to the atmosphere during transfer into the STM system. The crucial step of our decapping process is the removal of the surface contaminants on top of amorphous Se before thermal desorption of Se at a mild temperature （-210 ~C）. This effective Se decapping process opens up the possibility of ex situ characterizations of pristine surfaces of interesting selenide materials and beyond using cutting-edge techniques.
