Static-charging mitigation and contamination avoidance by selective carbon coating of TEM samples

Prior to transmission electron microscopy (TEM) analyses, insulating specimens need to become coated with a charge-draining layer. Rather than coating the entire TEM foil with a thin film of homogeneous thickness, selective coating is proposed. Using a novel preparation tool, peripheral parts of the sample are coated with a relatively thick (4–8 nm) carbon film while the central, electron-transparent part of the sample is hidden behind a shape-adopted mask and thus not directly exposed to carbon deposition. Beneath the mask, an ultrathin (3–7 Å) carbon film is formed that is (i) thick enough to drain charges evolving upon electron irradiation in the electron microscope and (ii) thin enough to avoid typical contamination effects caused by superficial carbon diffusion. Consequently, image quality is becoming enhanced in high-resolution imaging and sensitivity is significantly increased in all nano-beam related techniques including elemental analytics, convergent-beam and nano-beam electron diffraction, and spectral imaging.