Decoding defect statistics from diffractograms via machine learning

Diffraction techniques can powerfully and nondestructively probe materials while maintaining high resolution in both space and time. Unfortunately, these characterizations have been limited and sometimes even erroneous due to the difficulty of decoding the desired material information from features of the diffractograms. Currently, these features are identified non-comprehensively via human intuition, so the resulting models can only predict a subset of the available structural information. In the present work we show (i) how to compute machine-identified features that fully summarize a diffractogram and (ii) how to employ machine learning to reliably connect these features to an expanded set of structural statistics. To exemplify this framework, we assessed virtual electron diffractograms generated from atomistic simulations of irradiated copper. When based on machine-identified features rather than human-identified features, our machine-learning model not only predicted one-point statistics (i.e. density) but also a two-point statistic (i.e. spatial distribution) of the defect population. Hence, this work demonstrates that machine-learning models that input machine-identified features significantly advance the state of the art for accurately and robustly decoding diffractograms.

Structural variations and transformation behavior of the Al68Cu11Co21 decagonal phase

The Al68Cu11Co21 decagonal phase was studied after annealing at 1000 °C for 24-760 h by transmission and scanning electron microscopy. The strong superstructure odd-n reflections in the [1,-2, 1, 0, 0] electron diffractograms were stable under annealing up to about 40 h. As a possible origin of the increased intensities of the odd-n reflections the formation of vacancy-ordered structures is discussed. The structure was modified by prolonged annealing. In several annealed samples a dense net of extra reflections overlapping the quasiperiodic reflections was observed. This observation was explained as an indication of the formation of metastable states during cooling. Differently ordered decagonal structures exhibited different transformation kinetics during cooling from high temperatures.

Interpretation of irradiation-induced changes in electron diffractograms and images of extinction contours at low temperatures

A few years ago results on cryoprotection of L-valine were reported, where the values of the critical fluence De i.e, the electron exposure which decreases the intensity of the diffraction reflections by a factor e, amounted to the order of 2000 + 1000 e/nm2. In the meantime a discrepancy arose, since several groups published De values between 100 e/nm2 and 1200 e/nm2 /1 - 4/. This disagreement and particularly the wide spread of the results induced us to investigate more thoroughly the behaviour of organic crystals at very low temperatures during electron irradiation.For this purpose large L-valine crystals with homogenuous thickness were deposited on holey carbon films, thin carbon films or Au-coated holey carbon films. These specimens were cooled down to nearly liquid helium temperature in an electron microscope with a superconducting lens system and irradiated with 200 keU-electrons. The progress of radiation damage under different preparation conditions has been observed with series of electron diffraction patterns and direct images of extinction contours.

Solid state properties of poly-β-hydroxybutyrate and of its oligomers

The solid state properties of poly-β-hydroxybutyrate (PHB) were investigated for samples with degrees of polymerization [Formula: see text] from 4 to 994. The observed melting points ranged from 47 °C to 180 °C. Electron diffractograms on carefully prepared single crystals of a high molecular weight sample provided data which confirmed the reported a and b parameters from X-ray fiber diffraction and provided clear justification for the P212121 space group. The observed intensities in the electron diffractogram, corresponding to (hk0) reflections, were compared with the predicted intensities for two proposed structures in the literature. The observed and calculated structure factors for both structures were in good agreement. Small angle X-ray diffraction of the meridional maximum for annealed "cold drawn" and "hot drawn" fibers showed a distinctly different dependence on temperature than the maximum for stacks of lamellar single crystals. For oligomers a long spacing was observed which was about twice the length of the sample [Formula: see text] multiplied by the crystalline advance per monomer.