STEM Beam Diameter Balancing for Thick Sample Resolution
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Solution Overview
Problem
Conventional Scanning Transmission Electron Microscopy (STEM) techniques struggle to achieve high resolution for thick samples, as the effective thickness of the sample limits resolution, especially when tilted, resulting in poor image quality due to beam broadening.
Innovation Solution
The method involves determining the sample thickness and setting the opening half-angle of the finely focused beam such that the beam maintains a substantially constant diameter over the sample length, balancing the cross-over broadening with the beam broadening inside the sample, allowing for optimized overall resolution by adjusting the opening half-angle within specific constraints based on the sample's tilt and thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the opening half-angle is optimized for minimum cross-over diameter, then the cross-over resolution is improved, but the beam diameter inside the sample increases significantly
Solution Approach 1:
The patent changes the opening half-angle parameter from the conventional value optimized for minimum cross-over diameter to a smaller value that balances cross-over diameter with beam diameter inside the sample. This parameter change resolves the contradiction by accepting a slightly larger cross-over diameter in exchange for significantly reduced beam broadening through the sample thickness, thereby improving overall image resolution for thick samples.
2Measurement precision
If a finely focused beam with small cross-over diameter is used, then high resolution is achieved for thin samples, but the beam broadens significantly for thick samples
Solution Approach 1:
The patent applies parameter changes by selecting an opening half-angle that produces a larger cross-over diameter compared to conventional STEM, but this larger angle is compensated by the reduced beam broadening effect in thick samples. The net result is improved overall resolution for thick samples while maintaining acceptable cross-over size.
3Length of stationary object
If the sample thickness is increased to study thick samples, then more structural information is obtained, but the resolution deteriorates due to beam broadening
Solution Approach 1:
The patent resolves this contradiction by changing the opening half-angle parameter to a value that minimizes the cumulative beam broadening effect through increased sample thickness. This allows thick samples to be imaged with maintained resolution by balancing the trade-off between sample thickness and beam diameter growth.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly improves the resolution of thick samples, achieving better image quality compared to conventional methods, with improved resolution for samples thicker than 100 nm, and up to 1000 nm, by balancing beam and cross-over diameters, thereby enhancing the overall imaging capability.
Implementation Method 1
a 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 of the finely focused beam
Implementation Method 2
Some of the electrons are absorbed by the sample, some are scattered in the sample
Implementation Method 3
Some of the electrons are absorbed by the sample, some are scattered in the sample
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The invention discloses a method for Scanning Transmission Electron Microscopy (STEM). In STEM a sample (1) is scanned with a focused beam of electrons (2). The diameter of the cross-over (3) can be as low as 0.1 nm. As known to the person skilled in the art the diameter of the cross-over depends on the opening half-angle α of the beam. Therefore for optimum resolution an opening half-angle is chosen at which the diameter of the cross-over R(α) shows a minimum. For thick samples however the resolution is, for those parts of the sample removed from the cross-over plane, limited by the convergence of the beam, resulting in a diameter D of the beam at the surface of the sample. According to the invention the opening angle is chosen to balance the contribution of convergence and of diameter of the cross-over by choosing an opening half-angle smaller than the optimum opening half-angle. Effectively the sample is then scanned with a beam that has a substantially constant diameter over the length of the sample material through which the electrons have to travel.