Department of Physics and Center for Nanointegration CeNIDE, University of Duisburg-Essen, Lotharstrasse 1, Duisburg 47057, Germany.
Ultramicroscopy. 2013 Apr;127:2-8. doi: 10.1016/j.ultramic.2012.07.017. Epub 2012 Jul 28.
Many fundamental processes of structural changes at surfaces occur on a pico- or femtosecond time scale. In order to study such ultra-fast processes, we have combined modern surface science techniques with fs-laser pulses in a pump-probe scheme. Reflection high energy electron diffraction (RHEED) with grazing incident electrons ensures surface sensitivity for the probing electron pulses. Utilizing the Debye-Waller effect, we studied the cooling of vibrational excitations in monolayer adsorbate systems or the nanoscale heat transport from an ultra-thin film through a hetero-interface on the lower ps-time scale. The relaxation dynamics of a driven phase transition far away from thermal equilibrium is demonstrated with the In-induced (8×2) reconstruction on Si(111). This surface exhibits a Peierls-like phase transition at 100K from a (8×2) ground state to (4×1) excited state. Upon excitation by a fs-laser pulse, this structural phase transition is driven into an excited (4×1) state at a sample temperature of 20K. Relaxation into the (8×2) ground state occurs after more than 150 ps.
许多表面结构变化的基本过程都发生在皮秒或飞秒时间尺度上。为了研究这种超快过程，我们将现代表面科学技术与飞秒激光脉冲结合在泵浦-探测方案中。掠入射电子的反射高能电子衍射（RHEED）确保了探测电子脉冲的表面灵敏度。利用德拜-沃勒效应，我们研究了单层吸附物系统中振动激发的冷却，或在纳秒时间尺度上通过异质界面从超薄薄膜中传输纳米尺度的热。通过 Si(111)上的 In 诱导（8×2）重构，展示了远离热平衡的驱动相变的弛豫动力学。该表面在 100K 时表现出类 Peierls 相变，从（8×2）基态到（4×1）激发态。在飞秒激光脉冲的激发下，该结构相变在 20K 的样品温度下被驱动到激发的（4×1）态。在 150 多皮秒后，才会进入（8×2）基态。
