The Effect of Oxygen Binding and Orbital
Mediated Tunneling on the Apparent Corrugation.

VOPcColorScar: High resolution STM image of a VOPc monolayer on Au(111). Also shown is a model of the VOPc molecule. Note that the Vanadium ion sits slightly above the plane and that the van der Walls radius of the O atom extends more than 0.2 nm above top of the isoindole rings. However, because the bonding to O decreases the density of electrons near the center of the molecule near the Fermi energy, this region appears as a depression. This image has been plane fit and low pass filtered only.

Figure 1

Figure 2

VOPcFig4: Constant current image of a VOPc island on Au(111), top, and apparent constant current heights as a function of bias voltage, lower. Note that the apparent height of the VOPc island changes with bias voltage, but that the gold step height does not.


IV&dIdV: Area averaged IV curves and generated dI/dV. In order to reduce noise errors in the dI/dV curves, two different methods were used. The IV curve obtained over VOPc was fit by a polynomial and the exact derivative of the polynomial was take. Alternatively, the raw data was smoothed and then a numerical derivative was taken. This curve has been artificially offset to aid viewing. The setpoint used was 300 pA and 850 mV. The peaks in dI/dV are due to electronic resonance processes. The peak at positive bias is due to transient reduction of the VOPc at the Pc ring.

For more information, see J. Phys. Chem B, 2000, 104, 5993-6000

Figure 3