ELECTRONICALLY DRIVEN ADSORBATE EXCITATION MECHANISM IN FEMTOSECOND-PULSE LASER-DESORPTION
ELECTRONICALLY DRIVEN ADSORBATE EXCITATION MECHANISM IN FEMTOSECOND-PULSE LASER-DESORPTION
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DOI：
10.1103/physrevb.52.6042
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发表时间：
1995-08-15
影响因子：
3.7
通讯作者：
NEWNS, DM
中科院分区：
文献类型：
--
作者：
BRANDBYGE, M;HEDEGARD, P;NEWNS, DM
飞秒脉冲激光脱附是指在衬底-吸附物电子系统中，由5000 K量级的亚皮秒温度脉冲驱动脱附，其能量通过直接耦合机制转移到吸附物质心自由度的过程。我们提出了一个系统的理论处理这个耦合过程中的语言的电子摩擦，产生朗之万噪声的吸附质中心的质量自由度，而电子自由度是在高温下。从影响泛函路径积分描述出发，定义了一个在所有电子温度下都有效的电子摩擦的简单公式。在低温下的形式主义接触的吸附质振动阻尼理论中出现的电子摩擦，而在高温下的吸附质电子激发能量的摩擦成为强烈的温度依赖性，由于不同的吸附质势能面之间的虚拟激发的主导地位。前一个政权是有关的电子摩擦模型的解吸过程中，和后者诱导的多个电子transitions模型的过程中的解吸，本制剂包括两个政权。解吸计算一个简单的准解析Kramers速率的方法，并通过数值解的朗之万方程。的解吸分数和解吸的时间尺度的大小进行比较，实验结果。
Femtosecond-pulse laser desorption is a process in which desorption is driven by a subpicosecond temperature pulse of order 5000 K in the substrate-adsorbate electron system, whose energy is transferred into the adsorbate center-of-mass degrees of freedom by a direct coupling mechanism. We present a systematic theoretical treatment of this coupling process in the language of an electronic friction, which generates Langevin noise in the adsorbate center-of-mass degrees of freedom, while the electronic degrees of freedom are at a high temperature. Starting from an influence-functional path-integral description, a simple formula for the electronic friction is defined which is valid at all electronic temperatures. At low temperatures the formalism makes contact with the electronic friction appearing in the theory of adsorbate vibrational damping, whereas at high temperatures comparable with the adsorbate electronic excitation energies the friction becomes strongly temperature dependent due to dominance by virtual excitations between different adsorbate potential energy surfaces. The former regime is related to the electronic friction model for the desorption process, and the latter to the desorption induced by multiple electronic transistions model for the process; the present formulation comprises both regimes. Desorption is calculated both by a simple quasianalytic Kramers rate approach, and by numerical solution to the Langevin equation. The magnitude of the desorbed fraction and the time scale for desorption are compared to experimental results.