No abstract

Silica biomorphs are extraordinary inorganic superstructures formed via autocatalytic co‐precipitation and bottom‐up self‐assembly of alkaline‐earth carbonates and silica. However, they show no inherent functionality except for their striking textural motifs and curved morphologies. This work presents strategies to magnetize silica biomorphs, thus creating thermally stable ceramic microswimmers with unique elaborate shapes. This is achieved by growing super paramagnetic magnetite mesocrystals on and around the complex curved surfaces of biomorphs, while keeping their morphology and maintaining mesocrystal integrity. Selective mesocrystal formation on certain parts of the substrates is induced by chemical modification of the biomorph surface, increasing the loading of magnetite on the silica–carbonate structures and, in suitable cases, rendering them able to respond to external magnetic fields and move as microswimmer entities. In this way, the complex ultrastructure of silica biomorphs is successfully used as a template for functional ceramics. Furthermore, selective dissolution of the carbonate core from the biomorphs leads to hollow magnetic structures that could be filled with actives, thus serving as microcarriers with considerable loading capacity.

The development of preferred orientation in AlN thin films deposited on silica glass substrates by rf sputtering at low substrate temperature (<150 °C) has been studied. The main factors controlling the preferential orientation of the AlN thin films are the ion-bombardment energies, incidence angle of the arriving particles, and deposition rate. At low pressure, a perpendicular and highly directional energetic ion-bombardment induces an orientation of the crystallites with their c-axis perpendicular to the substrate surface. At higher pressure (>15 mTorr), a spreading in the incidence angle of the arriving particles, due to gas phase collisions, favors the formation of AlN crystal twinning. A change in the preferred orientation of the films from (0001) to (1011) for deposition rates above 1.8 Å/s is observed.

The search for signs of life in the ancient rock record, extreme terrestrial environments, and other planetary bodies requires a well-established, universal, and unambiguous test of biogenicity. This is notably true for cellular remnants of microbial life, since their relatively simple morphologies resemble various abiogenic microstructures that occur in nature. Although lists of qualitative biogenicity criteria have been devised, debates regarding the biogenicity of many ancient microfossils persist to this day. We propose here an alternative quantitative approach for assessing the biogenicity of putative microfossils. In this theoretical approach, different hypotheses-involving biology or not and depending on the geologic setting-are put forward to explain the observed objects. These hypotheses correspond to specific types of microstructures/systems. Using test samples, the morphology and/or chemistry of these systems are then characterized at the scale of populations. Morphologic parameters include, for example, circularity, aspect ratio, and solidity, while chemical parameters could include elementary ratios (e.g., N/C ratio), isotopic enrichments (e.g., d13C), or chirality (e.g., molar proportion of stereoisomers), among others. Statistic trends distinguishing the different systems are then searched for empirically. The trends found are translated into ''decision spaces'' where the different systems are quantitatively discriminated and where the potential microfossil population can be located as a single point. This approach, which is formulated here on a theoretical level, will solve several problems associated with the classical qualitative criteria of biogenicity. Most importantly, it could be applied to reveal the existence of cellular life on other planets, for which characteristics of morphology and chemical composition are difficult to predict.