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Use low-voltage, preferably aberration-corrected HRTEM, with about 60–80 kV as a defensible operating range. An approximately 80 kV starting point balances useful lattice resolution against carbon displacement damage; use the lower end if the instrument still resolves the lattice and defect stability is the priority.

A higher accelerating voltage reduces the electron wavelength, but can remove carbon atoms by knock-on displacement. Measurements on pristine single-layer graphene show a strong increase in displacement probability above the vicinity of 80 kV, so simply selecting a conventional 200–300 kV setting is a poor way to preserve the original lattice.^[ref]

reduced graphene oxide is already defective and chemically modified. Its vulnerable sites need not share the pristine-graphene threshold, and ionization, contamination and chemical etching remain possible at low voltage. Minimize dose, spread the beam while aligning and compare successive short exposures. The voltage choice suppresses one damage mechanism; it does not guarantee damage-free imaging.

Use a low-dose, dose-efficient acquisition rather than assuming that a lower accelerating voltage is always gentler. Focus and align on a sacrificial neighbouring region, blank the beam between exposures, illuminate only when recording and use an efficient detector. A broad, low-current-density transmission electron microscopy exposure can avoid a high instantaneous local dose; scanning can also work if probe current, dwell time and repeated visits are controlled.

Radiolysis starts with inelastic scattering and ionization. For an appropriate thin specimen, increasing the electron energy can reduce the inelastic interaction probability and energy deposition per incident electron, so a relatively high voltage can help. However, increasing voltage can also activate knock-on displacement. The optimum therefore depends on the material and the amount of useful information obtained per damaging event; $150\mathrm{nm}$ alone does not determine it. Cooling may reduce diffusion-driven chemical changes but does not eliminate primary ionization. An experimental study of nonbiological layered polymer films explicitly found that the voltage choice must balance damage with image signal.^[ref]

Chemical damage initiated by ionization and electronic excitation from radiation. It is distinct from direct momentum-transfer knock-on displacement; the useful image information per damaging event depends on beam energy and specimen.