Abstract: This die-shaped coarse-approach positioning device is particularly suited for the sample holder of a scanning tunneling microscope or the like. It comprises two blocks (21, 23), one (21) stationary, the other tiltable with respect to the stationary one. The blocks (21, 23) are connected on one side by a spring-like sheet metal (20). The tiltable block (23) can be moved, and with it the sample (33), by turning a screw (28) which presses down onto an elastic pad (30). The tilting of the tiltable block (23) occurs against the effect of the sheet metal (20) until the block (23) touches down onto a wedge (39) insertable in the gap (24) between the blocks (21, 23), and consisting of an elastic material, however, having a spring constant much higher than the effective spring constant of the sheet metal (20). In the application shown, the sample can be lowered onto a tunnel tip (34) attached to a fine-approach positioning device (35).

Abstract: This method involves the deposition of free metal atoms (4) from the apex (5) of a pointed tip (1) supported at a distance of 10 to 20 nm from a substrate (2). The atoms (4) are being field-desorbed under the influence of a strong electric field existing between the tip (1) and the substrate (2). With the tip (1) being moved across the substrate (2), a narrow trace (6) of metal atoms will be deposited on the substrate.

Abstract: The dilution refrigerator operates by sucking a .sup.4 He-rich mixture from a tank and returning it to the tank through a superleak. Thereby the .sup.3 He is separated and returned to the .sup.3 He-rich content of the tank. By this cycling process, a drop in temperature is obtained at the exit of the superleak and through re-mixing of the .sup.3 He with the .sup.4 He. Cycling of the liquid .sup.3 He-.sup.4 He mixture is performed by a bellows pump maintained in a container 16 at a temperature below 2.degree. K. and by specially designed valves comprising a steel ball as a plug and a gold ring as the valve seat.