研究目的
Examining the capabilities of a simplified approach of in line electron holography to evidence heterogeneities in a polycrystalline HfO2 layer.
研究成果
The phase maps derived from the simplified in line holography approach can constitute a simple tool to evidence local heterogeneities in a complex microstructure. However, these defects will need further investigation by advanced TEM techniques to be identified.
研究不足
The phase map has a limited spatial resolution, typically 1 nm for a 100 nm defocus. The inversion leads to a singularity at q = 0 that requires specific filtering techniques to manage.
The in line holography method consists first in acquiring images at different defocus (-D, 0, D) and then deriving the phase image using a post treatment that realizes the inversion of the phase transfer function. Various numerical treatments are possible, however a simple inversion process based on a small angle approximation can be achieved [5]. As a consequence of the approximation, the phase map has a limited spatial resolution, typically 1 nm for a 100 nm defocus. Also the inversion leads to a singularity at q = 0 that can be dealt with using a Gaussian edge filtering or more efficiently a Tikhonov regularisation (i.e. a q2/(q2+a2)2 filter) [6]. Depending on the parameter a, long range fluctuations can be amplified or cancelled out which have a significant impact on the value of the phase output. However if only a qualitative information on the phase map is desired, this simplified in line holography can be used as a tool to point out chemical or charge fluctuations within the sample.
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