Prashanth Kannan

STM works by scanning a sharp conductive probe very close to the surface of a conductive sample and forcing electrons to cross the gap between them. When the tip is close enough to the surface (usually less than 1 nm), the fuzzy electron cloud of the first atom of the tip and the surface begin to overlap. Applying a bias voltage between the tip and the surface in this configuration creates a current as the electrons are forced to tunnel through the potential barrier from the tip to the surface through the overlapping electron cloud. This tunneling current is very sensitive to the gap between the tip of the probe and the surface, which varies exponentially with the distance between the tip and the sample. As the tip scans line by line across the surface of the sample, the intensity of the tunneling current reflects the electron density of states of the sample.

The Cu-TCPP organometallic framework is a poor conductor of electricity. Therefore, there is no electron tunneling and no image. It is possible that increasing the copper content will help to obtain an image.

Prof.Mirogorod,

Thank you for replying so soon. I seem to have made an error in my question. My problem is that I want to deposit TCPP first and then Cu. But there are no discernable porphyrin motifs when I found the optimal sublimation temperature. I've gone through all the available temperature ranges upto its decomposition point. Although few porphyrins were able to be seen in the STM images, most of the molecules seem to be randomly oriented with different motifs.

Annealing at low temperaures (< 80C) seem to cause all the molecules to desorb from the Ag(100) substrate.

Hi, I have some experience depositing porphyrin-like molecules on surfaces under UHV. First of all, without an image it is difficult to find out what is going on, but in my experience, porphyrins are thermally robust and difficult to decompose. If so, the normally decomposed molecules react in the crucible leading to polymerisation. These polymers are heavier and almost impossible to sublimate.

On the other hand, what I see as more plausible is that the quality of their molecules is low. Even with purities around 99% we are used to see a lot of fragments on the surface. I would recommend lengthening the degassing time and perhaps increasing the temperature for deposition.