K W Hipps - Tip−Sample Distance Dependence in the STM-Based Orbital-Mediated Tunneling Spectrum of Nickel(II) Tetraphenylporphyrin Deposited on Au(111)

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      Publication Details (including relevant citation   information):

      Deng, Wenli, Hipps, K. W. The Journal of Physical Chemistry   B 2003 107 (39) 10736-10740

      Abstract: Orbital-mediated tunneling spectra   obtained in the STM environment are reported for nickel(II)   tetraphenylporphyrin, NiTPP, as a function of molecule−tip   separation. Spectra were acquired over a range of tip motion of   0.42 nm. Spectra did not show the variation in band splitting   with tip distance predicted by several models. It appears for   molecules such as NiTPP that the average potential at the   molecule is essentially the same as at the metal substrate, at   least for gap resistance values greater than 500 MΩ. Thus, at   least for molecules of the height of NiTPP, the STM−OMT spectra   should give reliable occupied and unoccupied orbital energies   over a wide range of tip−molecule distances. An unexpected small   shift of all orbital energies of NiTPP relative to the vacuum   level is observed as a function of tip−molecule separation.

      Address (URL): http://dx.doi.org/10.1021/jp034900o