BEST CAFM Results in Comparative Study

Unique Technology Avoids Photocurrent Artifacts

Review of Scientific Instruments 87(8), 083703 

Yanfeng Ji, Fei Hui, Yuanyuan Shi, Vanessa Iglesias, David Lewis, Jiebin Niu, Shibing Long, Ming Liu, Alexander Hofer, Werner Frammelsberger, Guenther Benstetter, Andrew Scheuermann, Paul C. McIntyre and Mario Lanza

Photoactive materials play a crucial role in the development of energy storage devices, such as solar, electrochemical cells, and others. Conductive atomic force microscopy (CAFM) is a powerful tool for nanoscale electronic characterization of photoactive materials. It is well known that environmental light can alter the measurements when scanning photoactive samples. For this reason, measuring in a dark environment has been recognized as the standard CAFM process. However, as an optical feedback laser is necessary to acquire topography, the laser used in CAFM can also generate a high photocurrent, even without any bias between the conductive tip and the sample. While the laser-induced current signal perturbation is well known within the CAFM community, the observation of currents generated by the optical feedback laser in absence of bias is still not fully understood and has never been studied in depth.

For the first time, this paper studies and analyzes the photocurrent induced in the photoactive materials by the feedback laser. CAFM measurements were carried out on photoactive samples using six standard optical feedback AFMs of different manufacturers, as well as a Nanonics tuning-fork based feedback AFM (without using a laser).

Seen in image: 3D Collage Map of topographic and current maps, collected on Ni electrode using the Nanonics MV4000 AFM without application of bias. The yellow regions were measured with illumination, in order to replicate a feedback laser, and high current is observed. In contrast, the blue regions were measured without any feedback laser, and thus in absolute darkness, and no current is observed.