Abstract
We have studied the dynamic properties of hybrid devices in which the piezoelectric material lead zirconate titanate is integrated with silicon photodiodes on-chip. Such an integrated system enables direct conversion of light energy into mechanical deformation and motion, opening up new pathways for light propulsion in microrobots and nanorobots. By operating our devices under alternating illumination and simultaneously recording the time-dependent deformation and surface potential, we were able to derive frequency and voltage dependent time constants and phase relations between photovoltage and deformation. We observed that the silicon top contact resistance limits the response time to 6 ms in small area devices in which the capacitance is low. Furthermore, we observed a phase transition at low frequency that seems to be consistent with the occurrence of a negative capacitance. Our method of using time-dependent atomic force and Kelvin probe force microscopy proves to be suitable for the investigation of nanoscale, dynamic properties of light-driven piezo systems and can lead the design of next generation devices.
Highlights
We present time-resolved atomic force microscopy (AFM) in combination with time-resolved Kelvin probe force microscopy (KPFM) as a promising method to investigate the interplay between electrical and mechanical behaviors on the nanoscale of photovoltage-driven piezo devices
Our study shows that a combination of time-dependent AFM and KPFM measurements provides valuable information on the dynamic microscopic device properties and can guide the design of generation device architectures
The system was operated in the tapping (AC) atomic force microscopy (AFM) mode, and the contact potential difference (CPD) was measured in the amplitude modulated (AM) dual pass Kelvin probe force microscopy (KPFM) mode
Summary
We present time-resolved atomic force microscopy (AFM) in combination with time-resolved Kelvin probe force microscopy (KPFM) as a promising method to investigate the interplay between electrical and mechanical behaviors on the nanoscale of photovoltage-driven piezo devices. The photovoltage present at the top contact is determined as the difference between CPD in the dark and under illumination.14–16 It has been previously shown that neither an externally applied voltage nor the photovoltage interferes with the topography measurements in AM, single or dual pass KPFM, neither for inorganic nor for organic solar cells or light emitting diodes14–16,20,21 as long as the CPD is fully compensated.22 In accordance with this, for solar cells without PZT, we did not measure any displacement beyond the noise level (see S6 in the supplementary material).
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