6. Conclusion

Since the advent of near-field microscopy, techniques for measuring electrical quantities have continued to evolve and diversify. From simple air current measurements to ultra-high vacuum potential measurements, various strategies have been implemented to combat the low signal-to-noise ratio inevitable when the surface areas involved become so small, and many artifacts have been identified and controlled. Today, all electrical quantities are accessible with varying degrees of precision. However, electrical measurements on this scale have not yet fully entered the metrological phase that constitutes their natural evolution: from simple contrast measurement (a role in which they can easily be confined) to quantified measurement (value and associated uncertainty). There are still many directions in which efforts must be sustained to improve their reproducibility and reliability. Compromises...