Scanning tunneling microscopy, orbital-mediated tunneling spectroscopy, and ultraviolet photoelectron spectroscopy of metal(II) tetraphenylporphyrins deposited from vapor.
Scanning tunneling microscopy, orbital-mediated tunneling spectroscopy, and ultraviolet photoelectron spectroscopy of metal(II) tetraphenylporphyrins deposited from vapor.
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DOI：
10.1021/ja0100726
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发表时间：
2001-03
影响因子：
15
通讯作者：
L. Scudiero;D. Barlow;U. Mazur;K. W. Hipps
中科院分区：
文献类型：
--
作者：
L. Scudiero;D. Barlow;U. Mazur;K. W. Hipps
研究了气相沉积的四苯基卟啉Ni（II）和Co（II）配合物（NiTPP和CoTPP）在金载体上和Al-Al（2）O（3）-MTPP-Pb隧道二极管（M = Ni或Co）中的薄膜，用紫外光电子能谱（UPS）分析了沉积在多晶金上的薄膜。扫描隧道显微镜（STM）和轨道介导的隧道光谱（STM-OMTS）进行的亚单层膜的CoTPP和NiTPP的支持Au（111）。在传统的隧道二极管结构中测量了非弹性电子隧穿谱（IETS）和OMTS。卟啉环的最高占据的π分子轨道在STM-OMTS和UPS中均在真空能级以下约6.4 eV处被观察到。通过STM-OMTS和IETS-OMTS观察到卟啉环的最低未占π分子轨道位于真空能级以下3.4 eV附近。CoTPP的OMTS光谱在5.2 eV附近（低于真空能级）有一个谱带，这归因于中心Co（II）离子的瞬时氧化。也就是说，这是由于电子OMT经由CoTPP的Co（II）中存在的半填充d（z）（2）轨道。NiTPP OMTS光谱显示没有这样的带，与已知的Ni（II）离子氧化的困难一致。STM为基础的OMTS允许这两个卟啉配合物很容易区分。本工作是首次报道的STM-OMTS，隧道结OMTS，UPS相同的化合物的观察。基于扫描隧道显微镜的轨道介导隧穿提供了比UPS或基于隧道结的OMTS更多的信息，并且具有分子级分辨率。
Thin films of vapor-deposited Ni(II) and Co(II) complexes of tetraphenylporphyrin (NiTPP and CoTPP) were studied supported on gold and embedded in Al-Al(2)O(3)-MTPP-Pb tunnel diodes, where M = Ni or Co. Thin films deposited onto polycrystalline gold were analyzed by ultraviolet photoelectron spectroscopy (UPS) using He I radiation. Scanning tunneling microscopy (STM) and orbital-mediated tunneling spectroscopy (STM-OMTS) were performed on submonolayer films of CoTPP and NiTPP supported on Au(111). Inelastic electron tunneling spectroscopy (IETS) and OMTS were measured in conventional tunnel diode structures. The highest occupied pi molecular orbital of the porphyrin ring was seen in both STM-OMTS and UPS at about 6.4 eV below the vacuum level. The lowest unoccupied pi molecular orbital of the porphyrin ring was observed by STM-OMTS and by IETS-OMTS to be located near 3.4 eV below the vacuum level. The OMTS spectra of CoTPP had a band near 5.2 eV (below the vacuum level) that was attributed to transient oxidation of the central Co(II) ion. That is, it is due to electron OMT via the half-filled d(z)(2) orbital present in Co(II) of CoTPP. The NiTPP OMTS spectra show no such band, consistent with the known difficulty of oxidation of the Ni(II) ion. The STM-based OMTS allowed these two porphyrin complexes to be easily distinguished. The present work is the first report of the observation of STM-OMTS, tunnel junction OMTS, and UPS of the same compounds. Scanning tunneling microscope-based orbital-mediated tunneling provides more information than UPS or tunnel junction-based OMTS and does so with molecular-scale resolution.