Measuring 3D pyroelectric distributions with high resolution in thin films by a laser scanning microscope

Abstract

A laser scanning microscope for measuring 3D pyroelectric distributions inside thin vinylidene fluoride-trifluoroethylene copolymer films using the Laser Intensity Modulation Method was developed. The setup consists of a laser unit, a laser driver, an xyz-stepper motor unit, a transimpedance amplifier, and a lock-in amplifier. The focus lens at the laser unit is fixed by magnetic levitation and can correct a defocusing of the system or a tilt of the sample surface. It has been demonstrated in different samples that the system has a lateral resolution of 1 μm for measuring the topological surface structure or the pyroelectric distributions. The self-developed laser driver and transimpedance amplifier combined with a fast lock-in amplifier are able to measure small pyroelectric currents and their variation inside a pyroelectric sample in the range of some 1 pA. The maximum measure frequency of 4 MHz and the fast lock-in make it possible to measure the 3D pyroelectric distributions with high resolution. A 3D scan of 30 different layers with depths of 100 nm–5 μm inside the sample and 100 × 100 points in the xy-direction per layer is performed in 3 days.