Deformation and fracture of crystalline tungsten and fabrication of composite STM probes

Ultramicroscopy. 2020. Vol. 218. No. 11. P. 113083.

Andrei M. Ionov, Chekmazov S., Usov V., Aronin Alexander S.,, Nesterova M. E., Semenov V., Shvetsc I., Bozhko S.

Fracturing microscale constrictions in metallic wires, such as tungsten, platinum, or platinum-iridium, is a
common fabrication method used to produce atomically sharp tips for scanning tunneling microscopy (STM),
field-emission microscopy and field ion microscopy. Typically, a commercial polycrystalline drawn wire is locally
thinned and then fractured by means of a dislocation slip inside the constriction. We examine a special case
where a dislocation-free microscale constriction is created and fractured in a single crystal tungsten rod with a
long side parallel to the [100] direction. In the absence of dislocations, vacancies become the main defects in the
constriction which breaks under the tensile stress of approximately 10 GPa, which is close to the theoretical
fracture strength for an ideal monocrystalline tungsten. We propose that the vacancies are removed early in the
tensile test by means of deformation annealing, creating a defect-free tungsten constriction which cleaves along
the W(100) plane. This approach enables fabrication of new composite STM probes which demonstrate excellent
stability, atomic resolution and magnetic contrast that cannot be attained using conventional methods.

Keywords: зонд, сканирующая туннельная микроскопия, вакансия, vacancies, Scanning tunneling microscopy (STM), STM probe preparation, Tension test, Fracture mechanism, механизм разрушения, испытание на растяжение