Patent ID: 8074292

Claim:
Tomographic atom probe comprising: a sample-holding device for receiving a sample of material to be analysed having an extraction area of substantially pointed shape, a position-sensitive detector of useful diameter D and spaced apart from the sample by a distance L; an electrostatic lens consisting of three electrodes, a first electrode or extractor, arranged in proximity to the sample, an intermediate second electrode, and a distal third electrode arranged between the intermediate electrode and the detector, the three electrodes having a symmetry of revolution about the axis Oz passing through the point of the sample and perpendicular to the plane P of the detector, wherein the extractor comprises a number of diaphragms of different aperture diameters produced on a moving bar that can slide in front of the aperture of the extractor so as to place the desired diaphragm in front of the aperture; the sliding movement of the bar being automated, and since the distance L is greater than 2.75 D, the respective potentials of the sample, of the first electrode of the lens and of the detector are such that the ions deriving from the sample mounted on the sample-holder are attracted towards the first electrode and towards the detector; the cross-sectional profile of the intermediate electrode, in a cross-sectional plane rOz passing through the axis Oz, defining three points M 1 , M 2 and M 3 of respective coordinates (r 1 , z 1 ), (r 2 , z 2 ) and (r 3 , z 3 ) relative to an origin z 0 on the point of the sample, which satisfy the following conditions: z 1 <z 2 <z 3 , | z 1 âˆ’z 0 |<D/ 3, |z 2 âˆ’z 1 |<0.65Â·D, | z 3 âˆ’z 1 >1.4Â·D, r 2 =r 1 , 0.1 Â·D<r 1 <0.65Â·D, D<r 3 <1.6Â·D; all the points of the cross-sectional profile of the electrode being situated outside the area of the cross-sectional plane delimited by the profile of a cone with cylindrical tip limited by the points M 1 , M 2 and M 3 .