Photoconductive NSOM for mapping optoelectronic phases in nanostructures

Abstract

Abstract:The advent of optically functional materials with low-intensive processing methods is accompanied by a growing need for high resolution imaging to probe the inherent inhomogeneities in the underlying microstructure. Atomic force microscopy based techniques are typically utilized for imaging the surface of organic thin films, quantum dots and other nanomaterials with ultrahigh resolution. Several modes like conductive, Kelvin, electrostatic amongst others have been particularly successful in imaging the local current, potential and charge distribution of variety of systems. However, the functionality of photoconduction in these materials cannot be directly imaged by these modes alone. There is a requirement for a local excitation source or collection arrangement that is compatible with scanning microscopy techniques followed by a current monitoring mechanism. Near-field scanning optical microscopy (NSOM) possesses all the advantages of scanning microscopy and is capable of local excitation that overcomes the diffraction limit faced by conventional optical microscopes. Additionally, NSOM can be carried out on actual photoconductive two terminal and three terminal device structures to image local optoelectronic properties. In this review, we present the various geometries that have been demonstrated to perform photoconductive NSOM (p-NSOM). We highlight a representative set of important results and discuss the implications of photocurrent imaging in macroscopic device performance.

Imaging Energy Harvesting and Storage Systems at the Nanoscale

“…88 One application of NSOM in excitation-only mode is light beam-induced current (LBIC) microscopy, where the photogenerated current can be spatially resolved at the nanoscale. 89 A spot size equivalent to the diameter of the aperture illuminates a solar cell and locally generates a flow of charge carriers. The photocurrent signal is typically detected by using the macroscopic contacts of the device.…”

Visualizing the Surface Photocurrent Distribution in Perovskite Photovoltaics

“…SNOM has been initially well applied in the areas of CdTe/CdS solar cells, GaAs solar cells, organic solar cells, and so on. [36][37][38][39][40][41] These works all presented a thorough and organized understanding of carrier dynamics. Recently, there have appeared some excellent works explored the carrier behavior around the grain boundaries using SNOM for PSCs.…”

Time-resolved terahertz time-domain near-field microscopy

“…Near-field techniques probe spatial lengths much smaller than the diffraction limit, allowing to circumvent many of the challenges that complicate conventional TRTS. Implementations of steady-state (photo-)conductivity mapping range from scattering near-field microscopy using sharp tips [15][16][17][18][19], to experiments relying on microwaves or narrow band THz sources [20,21]. However, transient photoconductivity near-field measurements at THz frequencies have until recently remained largely unexplored [22,23].…”