Joule
PerspectiveProbing Semiconductor Properties with Optical Scanning Tunneling Microscopy
Context & Scale
Studying photophysical processes at the nanoscale is critical to fully understand the complex optoelectronic properties in semiconductors used in light-harvesting applications. Optical spectroscopy has historically been used to characterize semiconductor materials, yet, is limited in resolution by diffraction and cannot achieve the required resolution to fully unravel the fundamental photophysics occurring at the nanoscale. Thus, a proper understanding of nanoscale systems requires tools with both the ability to resolve nanometer structures and to provide detailed information about chemical, (opto-)electronic, and magnetic properties. Scanning probe techniques (scanning probe microscopy [SPM]) achieve the requisite high spatial resolution and can provide insights on the electronic structure and surface topography; however, SPM alone cannot address questions regarding the optoelectronic processes that can occur at the interface. To overcome this limitation, innovative SPM strategies have been developed during the last decade, which allow optical imaging and manipulation of light below the diffraction limit.
In this perspective, we target specific SPM techniques that combine scanning tunneling microscopy (STM) with optical methods and critically review their potential for energy applications. Incident wavelengths spanning the electromagnetic spectrum from the terahertz region to X-rays have been coupled into the STM tip-sample junction to investigate the nanoscale properties of semiconductor materials, whereas the reverse process of luminescence can give insight on local recombination processes.
These advances in photoassisted STM combined with localized light emission at the nanoscale may be the key to unlock the root cause of reduced efficiencies in optoelectronic devices, and in light of a growing interest in quantum computing, may be able to shed light on exploring quantum emitters and quantum entanglement at the nanoscale.