Metal-semiconductor-metal (MSM) structures for the application as detectors for low-energy backscattered electrons in electron-beam microcolumns have been investigated. Realized Ti-Si-Ti MSM devices showed current gains of up to 200 for 1 keV electrons. An unsatisfying signal/dark current ratio made the reduction of the dark current necessary. Two different approaches to reduce the dark current were examined : varying the used contact metal and investigating MSM structures with two different contact metals for cathode and anode (asymmetric MSM structures). The accomplished reduction of more than two orders of magnitude demonstrated the possibility to achieve a signal/dark current ratio of 0.4.