A cryogenic scanning force microscope for the characterization of frozen biological samples

We present the design of a new scanning force microscope specially suited for the investigation of soft matter, particularly biological, in an ultrahigh vacuum. The key point is that the samples are immobilized by shock freezing in order to maintain their native structure before they are introduced into the vacuum system. The vacuum system itself consists of a transfer chamber, which allows an exchange of the cold sample with cryo-electron microscopes, a preparation chamber including a stage for in-situ freeze drying, freeze etching, or freeze fracturing, and the analysis chamber with the microscope. Sample cooling is maintained in all chambers. The microscope is mounted on a commercially available vibration isolation system; a flow cryostat cools the sample to the temperature of liquid nitrogen, while the tip is scanned. Besides measurements on test samples, which demonstrate the imaging capabilities of the instrument, first results on T4-bacteriophages (viruses) are shown.