Patent ID: 7825378

Claim:
Method for obtaining a transmission image of a sample in a particle-optical apparatus, said apparatus equipped to image a sample by scanning the sample with a finely focused beam of particles and detecting particles transmitted through the sample, said finely focused beam showing a smallest diameter, the so-named cross-over, the diameter of the cross-over R being a function of the opening half-angle α which is adjusted to a value as a function of a variable representing the thickness T of the sample, the method comprising: acquiring an image of the sample by scanning the sample with the finely focused beam of particles and detecting particles transmitted through the sample, characterized in that, before the image is acquired, the thickness T of the sample is determined or estimated, the length L of the sample material through which the transmitted particles have to travel is derived from the thickness T of the sample, and the opening half-angle α is set to a value such that 0.5·R(α)/L≦tan(α)≦2·R(α)/L, as a result of which the sample is scanned with a beam having a substantially constant diameter over a length equal to the length L of the sample material through which the transmitted particles have to travel.