Efficient data sampling scheme to reduce acquisition time in statistical ALCHEMI

The distribution of dopants in host crystals significantly influences the chemical and electronic properties of materials. Therefore, determining this distribution is crucial for optimizing material performance. The previously developed statistical ALCHEMI (St-ALCHEMI), an extension of the atom-location by channeling-enhanced microanalysis (ALCHEMI) technique, utilizes variations in electron channeling based on the beam direction relative to the crystal orientation. It statistically analyzes spectra collected across multiple beam directions. However, the total experimental time can be extensive, particularly for low dopant concentrations, where typical experiments can span several hours. In this study, we propose a scheme based on efficient sampling point selection that reduces the experimental time required while maintaining accuracy. Guidelines for selecting beam directions were derived from theoretical and experimental analyses of data redundancy. The strategies include choosing directions that exhibit greater variances in the host ionization channeling patterns and lower correlation coefficients between them. Additionally, an edge detection scheme using the dual tree complex wavelet transform, applied to electron channeling patterns, is proposed to significantly reduce measurement time. Our findings suggest that effective sampling can reduce experimental duration by at least two orders of magnitude without compromising accuracy. Implementing the proposed guidelines shortens total measurement times, minimizes electron irradiation damage and improves S/N ratio through extended data acquisition per tilt.