论文标题
在相干的声子振荡中跟踪表面原子运动
Tracking the surface atomic motion in a coherent phonon oscillation
论文作者
论文摘要
X射线光电子衍射是确定清洁和吸附物覆盖表面的结构的强大工具。将技术扩展到超快时间域将为固体中电子偶联强度的直接测定和表面化学反应中原子运动的映射而直接确定的研究开放。在这里，我们证明了使用自由电子激光闪光的超X射线脉冲的时间分辨光电子衍射。我们在宽的角度范围内收集SE 3D光电子衍射图案，从光学激发bi $ _2 $ _2 $ se $ _3 $，时间分辨率为140 fs。将它们与多个散射模拟结合在一起，使我们能够在触发A $ _ {1G} $光学声子的连贯振动后，在前3 ps中跟踪近表面原子的运动。使用1.55 eV泵激光器的4.2 MJ/cm $^2 $的通量，我们在前两个层间间距中发现所得的相干振动幅度在1 pm处。
X-ray photoelectron diffraction is a powerful tool for determining the structure of clean and adsorbate-covered surfaces. Extending the technique into the ultrafast time domain will open the door to studies as diverse as the direct determination of the electron-phonon coupling strength in solids and the mapping of atomic motion in surface chemical reactions. Here we demonstrate time-resolved photoelectron diffraction using ultrashort soft X-ray pulses from the free electron laser FLASH. We collect Se 3d photoelectron diffraction patterns over a wide angular range from optically excited Bi$_2$Se$_3$ with a time resolution of 140 fs. Combining these with multiple scattering simulations allows us to track the motion of near-surface atoms within the first 3 ps after triggering a coherent vibration of the A$_{1g}$ optical phonons. Using a fluence of 4.2 mJ/cm$^2$ from a 1.55 eV pump laser, we find the resulting coherent vibrational amplitude in the first two interlayer spacings to be on the order of 1 pm.
