In 1987 we started the development of a small and rigid scanning tunneling microscope (STM). Our first goal was to demonstrate atomic resolution in air, and we did that in under 3 months. The next goal was to implement the STM under ultra-high vacuum (UHV) conditions and that took about a year.

The figure at the left show the latest version (1996), a very small and rigid construction completely controlled by electrical signals.

The sample (1) is placed in a tantalum holder (2) which may be removed from the STM and which is normally held down on the STM top by springs (3). The top plate is thermally and electrically insulated from the STM body by three quartz balls (10). The top plate is mounted on a 0.6 kg Al block which may be cooled to -160 C or heated to 100 C. The tip (4) is held by a macor holder (5) which is glued to the top of the scanner tube (6). The scanner tube is 4 mm long with an outer/inner diameter of 3.2/2.1 mm and is glued to the rod (7) which together with the piezo tube (9) forms a small inchworm motor used for coarse approach. The electrode of the tube is divided into three rings. In the tube two bearings are placed under the upper and the lower electrode with an extremely good fit to the rod (7). Applying a positive voltage to an electrode will clamp that electrode to the rod whereas a negative voltage will free that electrode from the rod. A voltage applied to the center electrode will cause it to elongate or contract. With the right sequence of voltages applied to the three electrodes the rod will move up or down since the tube is fixed to the STM body by the macor ring (8). The motor may work in steps of down to 2 Å, but at full speed it moves around 2 mm/min.
The scan range is up to +-1 µm when using antisymmetrical scan voltages of +-200 V. The Zener diode BZY93C75 (11) is used to counterheat the STM body during cooling.