Molecule hopping images reveal adsorption behavior of organic semiconductor on silicon surface
Molecule hopping images reveal adsorption behavior of organic semiconductor on silicon surface lead image
The surfaces of semiconductors usually have many unsaturated dangling bonds that impede ordered growth of molecular layers. Incorporating boron atoms under the surface of silicon – which is widely used for growing organic semiconductors – removes dangling bonds, allowing ordered growth. However, single dangling bonds, known as Si-Si(S5) defects, sometimes remain.
Kubicki et al. studied how dangling bonds affect the adsorption behavior of an organic semiconductor called cobalt phthalocyanine (CoPc) on the Si(111)-B surface.
Through periodic scanning tunneling microscopy (STM) images, the authors “watched” the CoPc molecules hop from one adsorption position on the surface to another, allowing them to identify the former adsorption site of CoPc molecules on Si(111)-B.
Their results show that at first, the CoPc molecules adsorb on Si-Si(S5) defects, but then begin to occupy passivated Si atoms. Scanning tunneling spectroscopy revealed that adsorption on the Si-Si(S5) defects is a hybridization between its pz orbital and the dz2 orbital of the cobalt molecule.
The STM images also showed that the CoPc molecules form two distinct, flat shapes when they adsorb. The authors determined that if there is only one Si-Si(S5) defect underneath CoPc, the CoPc molecule can rotate, leading to a circular appearance. But if there are more than one defect under CoPc or neighboring molecules, these block rotation, leading to a four-leaf clover-like appearance.
“The current work is an important step to understand the adsorption behavior of CoPc on silicon surfaces,” said author Susi Lindner. “Such a fundamental understanding of this system is important for the development of future electronic and optoelectronic devices.”
Next, the authors will study other silicon surfaces and semiconductor systems.
Source: “Adsorption behavior of cobalt phthalocyanine submonolayer coverages on B-Si(111)- × R 30°,” by Milan Kubicki, Susi Lindner, Martin Franz, Holger Eisele, and Mario Dähne, Journal of Vacuum Science & Technology B (2020). The article can be accessed at https://doi.org/10.1116/6.0000242 .
