Nanoscale charging hysteresis measurement using multifrequency electrosctatic force spectroscopy

Dana group has developed a scanning probe technique that can be used to measure charging of localized states on conducting or partially insulating substrates at room temperature under ambient conditions. Electrostatic interactions in the presence of a charged particle between the tip and the sample is monitored by the second order flexural mode, while the fundamental mode is used for stabilizing the tip-sample separation

In a cyclic voltage sweep, measuring the amplitude of the electrostatic excitation, it is possible to obtain linear curves symmetric around the contact potential difference value as shown in the figure. Charging of the surface states, or states between the tip and the ground plane effectively shifts the surface potential causing a hysteresis.

Figure: (a) Electrostatic excitation of the second order mode during a voltage sweep on a clean silicon surface. The arrows denote voltage sweep directions. No hysteresis can be observed. (b) Electrostatic excitation of the second order mode during a voltage sweep on silicon nitride layer with silicon nanocrystals embedded. Significant hysteresis is observable, indicating charging of nanocrystals. The arrows denote onset of charging and discharging events. The insets show capacitance-voltage traces of macroscopic capacitors fabricated using silicon nitride films without and with nanocrystals.

Reference: Bostanci et al., Applied Physics Letters 92, 093108 2008