Low thermal power electron beam annealing of scanning tunneling microscope tips

Abstract

An add-on unit was developed that allows the cleaning of scanning tunneling microscope tips by electron beam annealing even if they cannot be disconnected from the piezo scanner in situ. The whole scanner tip combination, which is attached to a linear motion stage, is subjected to a pulsed annealing treatment. The heat impact is focused on the outermost tip by sticking the tip through a hole in a grounded Mo screening plate with the cathode mounted on the opposite side. Tungsten tips attached to the scanner of the Omicron ultrahigh vacuum Multiscan Lab were annealed to achieve atomic resolution of ultrahigh vacuum cleaved GaAs (110) faces. A highly doped superlattice package grown on semi-insulating GaAs was also able to be investigated on the cleaved (110) face due to the ability of exact tip positioning with a scanning electron microscope.

Preparation and characterization of electrochemically etched W tips for STM

“…However, heating is too local to clean the tip sufficiently. Scholz et al [23] have designed a special experimental apparatus to focus the electron impact at the outermost tip. We do not believe this to be necessary, since the heating of the tip is always very local according to our TEM images.…”

Compact device for cleaning scanner-mounted scanning tunneling microscope tips using electron bombardment

“…The maximum increase of temperature at the point of contact between the piezo tube and the tip holder can be estimated by taking into account the thermal capacity of the tip and the tip holder, the power deposited on it, and the duration of the treatment. 11 From this we estimate that for I t = 4 mA and 5 s of treatment, the change of temperature is roughly 80 K, being well below the critical temperature of depolarisation which is about 150 • C.…”

“…The setups for electron bombardment proposed in the literature are located either outside the scanner 9, 10 or even require to take the complete scanner from its position within the UHV chamber. 11 In either case, the tip has to be removed from its usual position, subsequently being transferred to an additional assembly where the actual treatment is done.…”