Overview of the labs in surface physics in the workgroup Prof. Falta
Low Energy Electron Microscopy (LEEM)
A commercial low-energy electron microscopy system with energy analyzer (SPE-LEEM by Elmitec) allows for surface investigations under highly variable conditions, i.e. under ultra-high vacuum (base pressure better than 1×10-10 bar) as desired for the study of clean semiconductor and metal surface and growth experiments to medium pressure conditions of 1×10-3 mbar suitable for monitoring surface changes during surface reactions. The sample temperature can be varied from 100 K up to 1800 K. This system will has a lateral resolution better than 8 nm in LEEM mode and 15 nm in PEEM mode (photoemission electron microscope). A microLEED (Low-Energy Electron Diffraction) mode further allows for structural investigations of regions as small as 250nm in diameter.
Scanning Tunneling Microscopy (STM)
A commercial variable temperature scanning tunneling microscope (VT-STM by Omicron) is used to investigate surfaces down to the atomic scale. The apparatus is connected to a UHV preparation chamber of spherical shape equipped with a combined low-energy electron diffraction (LEED) with four grid optics and x-ray photoelectron spectroscopy (XPS).
For sample growth, various materials such as Ga, In, Ge, Si, Sb and V can be deposited, using thermal (Knudsen cell) or electron-beam evaporators. The samples may be exposed to molecular gases, as well as to atomic nitrogen provided by plasma sources (Epi-rf/ECR) or atomic oxygen from a thermal cracker.
The base pressure of around 5×10-11 mbar is achieved using rotary pumps, turbo molecular pumps, an ion getter pump and a titanium sublimation pump.
X-ray photoemission electron spectroscopy (XPS)
Attached to our STM system in Bremen, we use a commercial Omicron EA 125 XPS system, equipped with a seven channel detection system and differential pumping for measurements at higher pressures, i.e. up to 10-3 mbar. Furthermore we employ XPS, e.g. in combination with XSW, at various synchrotron radiation facilities in Europe and the USA.
Spot Profile Analysis - Low Energy Electron Diffraction (SPALeed)
A commercial spot profile analysis - low energy electron diffraction apparatus (by Omicron) allows in-situ measurements of surface structure and morphology under UHV conditions. For the detection of diffracted low-energy electrons a channeltron (zero dimensional detector with high dynamic range > 106) is used. Quantitative imaging of the two-dimensional diffraction pattern is achieved without changing the positions of electron gun, sample or detector, but by implying deflection voltages. For sample growth, various materials such as Ga, In, Ge, Si and Sb can be deposited, using thermal (Knudsen cell) or electron-beam evaporators. Due to the conical shape of the instrument experiments during growht are possible. Furthermore, the samples may be heated by direct current in a temperature range from room temperature to typically 1200°C. The base pressure of around 1×10-10 mbar is achieved using rotary pumps, turbo molecular pumps, an ion getter pump and a titanium sublimation pump.