QPlus: atomic force microscopy on single-crystal insulators with small oscillationamplitudes at 5 K

Abstract

Based on a proven low temperature scanning tunneling microscope (STM) platform, wehave integrated a QPlus sensor, which employs a quartz tuning fork for force detection innon-contact atomic force microscopy (AFM). For combined STM operation, this sensor haskey advantages over conventional sensors. For quantitative force spectroscopy oninsulating thin films or semiconductors, decoupling of the tunneling current and thepiezo-electrically induced AFM signal is important. In addition, extremely low signalsrequire the first amplification stage to be very close to the sensor, i.e. to be compatiblewith low temperatures. We present atomic resolution imaging on single-crystalNaCl(100) with oscillation amplitudes below 100 pm (peak-to-peak) and operation athigher flexural modes in constant frequency shift (df) imaging feedback. We alsopresent atomic resolution measurements on MgO(100) and Au(111), and firstevaluation measurements of the QPlus sensor in Kelvin probe microscopy on Si(111)7 × 7.