Local chemical reaction of benzene on Cu110 via STM-induced excitation.
Local chemical reaction of benzene on Cu110 via STM-induced excitation.
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DOI：
10.1063/1.1647044
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发表时间：
2004-03
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影响因子：
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通讯作者：
T. Komeda;Yousoo Kim;Y. Fujita;Y. Sainoo;M. Kawai
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文献类型：
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作者：
T. Komeda;Yousoo Kim;Y. Fujita;Y. Sainoo;M. Kawai
利用扫描隧道显微镜（STM）研究了苯分子在Cu（110）表面吸附时，隧道电子注入引起的化学反应机理。当从STM针尖向分子注入能量为2- 5eV的隧穿电子时，我们在STM图像中检测到苯分子的高度增加了40%，在非弹性隧穿谱（IETS）谱中出现了nu（C-H）模的振动特征。这可以用一个模型来理解，在这个模型中，苯分子中发生C-H键的解离，导致键的几何构型从平躺到直立构型的变化，这遵循Lauhon和Ho关于STM诱导的苯在Cu（100）表面上的变化的报道。[L. J. Lauhon和W. Ho，J.Phys.Chem.A104，2463（2000）]。反应概率显示出在样品偏置电压在2.4 V下急剧上升，其在3.0 V下饱和，随后在4.3 V的电压下又急剧上升。对于高达5 eV的负样品电压，没有观察到反应产率的增加。在完全氘代的苯分子的情况下，它显示出在2.4 eV的相同能量下的起始，但是反应概率比正常苯分子的情况小10（3）。我们提出了一个模型，在该模型中，苯分子的脱氢诱导的时间负离子的形成，由于在未占的π轨道形成的共振态的电子捕获。接近费米能级（约2.4eV）的共振能级和距离费米能级小于约5eV的多个能级的存在表明苯分子的Cu-pi（*）态具有相当强的相互作用。我们估计大约10（3）的大同位素效应可以用Menzel-Gomer-Redhead（MGR）模型来解释，其中假设激发态的电势曲线较浅。
We have investigated the mechanism of the chemical reaction of the benzene molecule adsorbed on Cu(110) surface induced by the injection of tunneling electrons using scanning tunneling microscopy (STM). With the dosing of tunneling electrons of the energy 2-5 eV from the STM tip to the molecule, we have detected the increase of the height of the benzene molecule by 40% in the STM image and the appearance of the vibration feature of the nu(C-H) mode in the inelastic tunneling spectroscopy (IETS) spectrum. It can be understood with a model in which the dissociation of C-H bonds occurs in a benzene molecule that induces a bonding geometry change from flat-lying to up-right configuration, which follows the story of the report of Lauhon and Ho on the STM-induced change of benzene on the Cu(100) surface. [L. J. Lauhon and W. Ho, J. Phys. Chem. A 104, 2463 (2000)]. The reaction probability shows a sharp rise at the sample bias voltage at 2.4 V, which saturates at 3.0 V, which is followed by another sharp rise at the voltage of 4.3 V. No increase of the reaction yield is observed for the negative sample voltage up to 5 eV. In the case of a fully deuterated benzene molecule, it shows the onset at the same energy of 2.4 eV, but the reaction probability is 10(3) smaller than the case of the normal benzene molecule. We propose a model in which the dehydrogenation of the benzene molecule is induced by the formation of the temporal negative ion due to the trapping of the electrons at the unoccupied resonant states formed by the pi orbitals. The existence of the resonant level close to the Fermi level ( approximately 2.4 eV) and multiple levels in less than approximately 5 eV from the Fermi level, indicates a fairly strong interaction of the Cu-pi(*) state of the benzene molecule. We estimated that the large isotope effect of approximately 10(3) can be accounted for with the Menzel-Gomer-Redhead (MGR) model with an assumption of a shallow potential curve for the excited state.