The effect of work function during electron spectroscopy measurements in Scanning Field-Emission Microscopy.

Electron spectroscopy proves to be a handy tool in material science. Combination of electron spectroscopy and scanning probe microscopy is possible through Scanning Field Emission Microscopy (SFEM), where a metallic probe positioned close to the surface is used as an electron source. However, using this not too much technologically demanding technique, it looks like the compromise between the lateral resolution and spectroscopic clarity must be considered. Here, we demonstrate, using experimental and simulation data, that the spectroscopic information can be understood without the need to grossly deteriorate the potential spatial resolution of the microscope. We prepared a three-section sample with clean W(110), sub-monolayer Cs on W(110) and monolayer of Cs on W(110) on which electron energy loss spectra are obtained via Scanning Probe Energy Loss Spectroscopy (SPELS) measurements. To explain the detected spectra a new model describing SPELS measurements in a SFEM is developed which aids to uncover the origin of spectral features typically detected during experiments. Experimental and simulation data are in a mutual agreement and observed spectral features on different surfaces could be explained. This novel understanding of SPELS can solve the main issue previously related to this technique, and good spatial resolution can be accompanied by the understanding of the measured spectra.

Symmetric Mixed Sulfur-Selenium Fused Ring Systems as Potential Materials for Organic Field-Effect Transistors.

A reliable synthetic protocol toward a series of fused chalcogenopheno[1]benzochalcogenophene (CBC) building blocks was developed based on a Fiesselmann reaction. The obtained CBC units were applied in McMurry and Stille coupling reactions toward symmetric regioisomeric ene-linked dimers. These π-conjugated compounds were characterized regarding their photophysical and electrochemical properties and proved to be materials with reduced HOMO-LUMO gaps compared to their sulfur-based analogues. Single-crystal X-ray diffraction experiments revealed strong intermolecular selenium-selenium and selenium-carbon interactions depending on the position and number of incorporated selenium atoms. Good field-effect transistor performance with charge carrier mobilities up to 4×10-3  cm2 V-1 s-1 and high on/off ratios could be observed.