Future of the Search for Life: Workshop Report.

The 2-week, virtual Future of the Search for Life science and engineering workshop brought together more than 100 scientists, engineers, and technologists in March and April 2022 to provide their expert opinion on the interconnections between life-detection science and technology. Participants identified the advances in measurement and sampling technologies they believed to be necessary to perform in situ searches for life elsewhere in our Solar System, 20 years or more in the future. Among suggested measurements for these searches, those pertaining to three potential indicators of life termed "dynamic disequilibrium," "catalysis," and "informational polymers" were identified as particularly promising avenues for further exploration. For these three indicators, small breakout groups of participants identified measurement needs and knowledge gaps, along with corresponding constraints on sample handling (acquisition and processing) approaches for a variety of environments on Enceladus, Europa, Mars, and Titan. Despite the diversity of these environments, sample processing approaches all tend to be more complex than those that have been implemented on missions or envisioned for mission concepts to date. The approaches considered by workshop breakout groups progress from nondestructive to destructive measurement techniques, and most involve the need for fluid (especially liquid) sample processing. Sample processing needs were identified as technology gaps. These gaps include technology and associated sampling strategies that allow the preservation of the thermal, mechanical, and chemical integrity of the samples upon acquisition; and to optimize the sample information obtained by operating suites of instruments on common samples. Crucially, the interplay between science-driven life-detection strategies and their technological implementation highlights the need for an unprecedented level of payload integration and extensive collaboration between scientists and engineers, starting from concept formulation through mission deployment of life-detection instruments and sample processing systems.

Investigating the activity of Ca2Fe2O5 additives on the thermochemical energy storage performance of limestone waste.

Efficient and reliable energy storage systems are necessary to address the intermittency and variability of renewable energy sources. Thermochemical energy storage (TCES) has emerged as a promising solution for long-term renewable energy storage, with limestone being a widely studied material due to its abundance and high energy density. However, the practical implementation of limestone-based TCES systems faces challenges related to performance degradation upon multiple energy storage/release cycles, impacting their long-term viability and efficiency. In this study, we investigate the activity of Ca2Fe2O5 additives on the thermochemical energy storage performance of limestone waste. Ca2Fe2O5 additives were synthesized by a wet precipitation method using three different Ca/Fe molar ratios and added to limestone waste in a 5, 10, and 20 weight concentration. The synthesized samples were characterized using XRD, SEM, EDS, BET, and XPS techniques. The thermal properties and heat storage performance of the samples were evaluated through thermogravimetric analysis of calcination/carbonation cycling experiments. The results demonstrate the potential of Ca2Fe2O5 additives to improve the cycling stability and energy storage density of limestone-based TCES systems. The sample with 5 wt% of Ca2Fe2O5 additive having Ca : Fe molar ratio of 1 : 1 outperformed all samples with an effective conversion rate of 0.21 after 40 cycles, 1.31 times higher than limestone waste.

X-ray diffraction imaging of fully packaged n-p-n transistors under accelerated ageing conditions.

X-ray diffraction imaging was used to monitor the local strains that developed around individual n-p-n bipolar transistors within fully encapsulated packages under conditions of extremely high forward bias to simulate accelerated ageing. Die warpage associated with the packaging was observed to relax systematically as the polymer became viscous due to the temperature rise associated with the dissipation of heat in the transistor. The direct image size and intensity from the individual transistors were interpreted in terms of a model in which local thermal expansion is treated as a cylindrical inclusion of distorted material, contrast arising principally from lattice tilt. The extension of the thermal strain image along the emitter with increasing power dissipation was ascribed to the effect of current crowding in the emitter region. Weaker large-area contrast associated with the base-collector region was interpreted as arising from the smaller change in effective misorientation at the high X-ray energy of thermal lattice dilation in the base region.

Femtosecond Laser Assisted Crystallization of Gold Thin Films.

We propose a novel low temperature annealing method for selective crystallization of gold thin films. Our method is based on a non-melt process using highly overlapped ultrashort laser pulses at a fluence below the damage threshold. Three different wavelengths of a femtosecond laser with the fundamental (1030 nm), second (515 nm) and third (343 nm) harmonic are used to crystallize 18-nm and 39-nm thick room temperature deposited gold thin films on a quartz substrate. Comparison of laser wavelengths confirms that improvements in electrical conductivity up to 40% are achievable for 18-nm gold film when treated with the 515-nm laser, and the 343-nm laser was found to be more effective in crystallizing 39-nm gold films with 29% improvement in the crystallinity. A two-temperature model provides an insight into ultrashort laser interactions with gold thin films and predicts that applied fluence was insufficient to cause melting of gold films. The simulation results suggest that non-equilibrium energy transfer between electrons and lattice leads to a solid-state and melt-free crystallization process. The proposed low fluence femtosecond laser processing method offers a possible solution for a melt-free thin film crystallization for wide industrial applications.

Pulsed-Plasma Physical Vapor Deposition Approach Toward the Facile Synthesis of Multilayer and Monolayer Graphene for Anticoagulation Applications.

We demonstrate the growth of multilayer and single-layer graphene on copper foil using bipolar pulsed direct current (DC) magnetron sputtering of a graphite target in pure argon atmosphere. Single-layer graphene (SG) and few-layer graphene (FLG) films are deposited at temperatures ranging from 700 °C to 920 °C within <30 min. We find that the deposition and post-deposition annealing temperatures influence the layer thickness and quality of the graphene films formed. The films were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and optical transmission spectroscopy techniques. Based on the above studies, a diffusion-controlled mechanism was proposed for the graphene growth. A single-step whole blood assay was used to investigate the anticoagulant activity of graphene surfaces. Platelet adhesion, activation, and morphological changes on the graphene/glass surfaces, compared to bare glass, were analyzed using fluorescence microscopy and SEM techniques. We have found significant suppression of the platelet adhesion, activation, and aggregation on the graphene-covered surfaces, compared to the bare glass, indicating the anticoagulant activity of the deposited graphene films. Our production technique represents an industrially relevant method for the growth of SG and FLG for various applications including the biomedical field.

Crack propagation and fracture in silicon wafers under thermal stress.

The behaviour of microcracks in silicon during thermal annealing has been studied using in situ X-ray diffraction imaging. Initial cracks are produced with an indenter at the edge of a conventional Si wafer, which was heated under temperature gradients to produce thermal stress. At temperatures where Si is still in the brittle regime, the strain may accumulate if a microcrack is pinned. If a critical value is exceeded either a new or a longer crack will be formed, which results with high probability in wafer breakage. The strain reduces most efficiently by forming (hhl) or (hkl) crack planes of high energy instead of the expected low-energy cleavage planes like {111}. Dangerous cracks, which become active during heat treatment and may shatter the whole wafer, can be identified from diffraction images simply by measuring the geometrical dimensions of the strain-related contrast around the crack tip. Once the plastic regime at higher temperature is reached, strain is reduced by generating dislocation loops and slip bands and no wafer breakage occurs. There is only a small temperature window within which crack propagation is possible during rapid annealing.

Citrate-capped gold nanoparticle electrophoretic heat production in response to a time-varying radiofrequency electric-field.

The evaluation of heat production from gold nanoparticles (AuNPs) irradiated with radiofrequency (RF) energy has been problematic due to Joule heating of their background ionic buffer suspensions. Insights into the physical heating mechanism of nanomaterials under RF excitations must be obtained if they are to have applications in fields such as nanoparticle-targeted hyperthermia for cancer therapy. By developing a purification protocol which allows for highly-stable and concentrated solutions of citrate-capped AuNPs to be suspended in high-resistivity water, we show herein, for the first time, that heat production is only evident for AuNPs of diameters ≤ 10 nm, indicating a unique size-dependent heating behavior not previously observed. Heat production has also shown to be linearly dependent on both AuNP concentration and total surface area, and severely attenuated upon AuNP aggregation. These relationships have been further validated using permittivity analysis across a frequency range of 10 MHz to 3 GHz, as well as static conductivity measurements. Theoretical evaluations suggest that the heating mechanism can be modeled by the electrophoretic oscillation of charged AuNPs across finite length scales in response to a time-varying electric field. It is anticipated these results will assist future development of nanoparticle-assisted heat production by RF fields for applications such as targeted cancer hyperthermia.