Transmission Kikuchi diffraction (TKD), or tansmission EBSD (t-EBSD), is a related technique to EBSD. In TKD the sample has to be electron transparent and is mounted horizontally (sample surface perpendicular to the electron beam) or at a slight tilt (up to 20°). Electrons transmitted through the sample, and diffracted on their way out from the lower surface are detected . A spatial resolution of a few nanometres is possible, compared with tens of nanometres for EBSD. TKD can be performed with a conventional EBSD system by simply using a bespoke sample holder. This is referred to as the off-axis geometry with the vertical detector below, but to the side of the sample.