Double quartz tuning fork sensor for low temperature atomic force and scanning tunneling microscopy

A double quartz tuning fork sensor for low temperature ultrahigh vacuum atomic force and scanning tunneling microscopy is presented. The features of the new sensor are discussed and compared to a single asymmetric tuning fork assembly. In addition, a low temperature ac signal amplifier has been developed to pick up the oscillation amplitude of the tuning fork. Current consumption and amplification factor versus the supply voltage of the amplifier as well as the magnitude response of the sensor have been measured at room temperature, 77 and 4 K. Atomically resolved images of a Ag(111) surface and single Ag atoms on Ag(111) were recorded in the scanning tunneling microscopy mode. Initial atomic force measurements are shown that reveal step resolution on a NiAl(110) surface.