McCartney's research primarily involves using electron holography for the observation and measurement of electrostatic and electromagnetic fields associated with nanostructured materials. Off-axis electron holography is an electron-microscope-based interference technique that provides unique access to the phase of a scattered electron wave. The technique has been shown by McCartney and others to enable visualization and quantification of electrostatic and magnetic fields with very high spatial resolution and sensitivity, enabling unique insights into nanoscale physical phenomena to be obtained.