Scanning electron microscopy has long been plagued by target charging. In past, thin metal coatings were commonly applied to the target in order to bleed away charge imbalances that naturally arise during electron bombardment by the scanning beam. However, when trying to resolve features on the scale of nanometers, even a few nanometer thick coating completely distorts or obscures the target features.
Alternatively, many SEMs are operated at a “charging-neutral” beam voltage. I put “charging-neutral” in quotations, because true charge balance can only hold for one material at a time. Heterogeneous substrates still suffer local charging even if global charging is absent.
Various schemes including supplementary, low-voltage electron flood, ion flood, or low-pressure gas discharge have been used with more or less success.
A new proof-of-principle experiment harnesses the photoelectric effect to restore charge neutrality during SEM imaging. The target is flood illuminated with deep ultra-violet (DUV) irradiation, of sufficient energy to cause photoemission. This process is demonstrated to reduce local and global charging. The authors point out that judicious selection of the photon energy (wavelength) can enhance the secondary emission from some but not all of the materials in a heterogeneous material. This should lead to increased (or decreased) material contrast in secondary detection mode.
Reference: G Seniutinas, A Balˇcytis, S Juodkazis, “UV-photoelectric effect for augmented contrast and resolution in electron microscopy”, arXiv:1604.01426