Improved accuracy in nano beam electron diffraction

Nano beam electron diffraction (NBD or NBED) is applied on a well controlled sample in order to evaluate the limit of the technique to measure strain. Measurements are realised on a 27nm thick Si0.7Ge0.3 layer embedded in a silicon matrix, with a TITAN microscope working at 300kV. Using a standard condenser aperture of 50μm, a probe size diameter of 2.7 nm is obtained and a strain accuracy of 6×10−4 (mean root square, rms) is achieved. NBED patterns are acquired along a [110] direction and the bidimensionnal strain in the (110) plane is measured. Finite element simulations are carried out to check experimental results and reveal that strain relaxation and probe averaging in a 170nm thick TEM lamella reduces strain by 15%.