Alexander S. Filatov

Dinosaur “mummies” preserve large areas of three-dimensional, wrinkled, desiccated integument renderings enveloping articulated skeletons. The majority of dinosaur “mummies” are “duck-billed” hadrosaurids in desiccated death poses that were buried in Late Cretaceous fluvial sandstones, such as in the Lance and Hell Creek formations of western North America, and unlike the lacustrine, marshy, or shallow marine sediments of many Konservat-Lagerstätten. Although first described in 1912, the structural and chemical nature of these renderings and the steps leading to their formation have only recently begun to be explored in detail. Hypotheses about the mode and mechanism of “mummy” preservation have varied widely, from simple impressions in sediment to near-pristine retention of organic tissues or biomolecules. Two newly described “mummies” of the Late Cretaceous hadrosaurid Edmontosaurus annectens were subjected to a wide range of modern structural and chemical analyses. These specimens come from a several-kilometer region in east-central Wyoming, USA, near the top of the Maastrichtian Lance Formation that has produced multiple of the best-preserved “mummy” dinosaurs over the course of the last century. These two “mummies” preserve exceptional integument renderings, including skin/scales, tail spikes, and hooves. We characterized how the three-dimensional form of the integument is preserved and whether any original tissue structure or organic biomolecules remain. We find little evidence for any endogenous organic preservation or internal tissue structure. Instead, these “mummies” likely desiccated sub-aerially for a period of time before rapid burial and infilling of the carcass by fluvial sands. Next, organic decay induced preservation of their outermost integumentary surface largely via microbially induced clay templating (a < 1 mm, predominantly kaolinite/partly illite, external “death mask”). In places, microbially induced precipitation of iron compounds (e.g., pyrite) as stains/concretions occurred, although some of these precipitates might also appear during or be altered by late-stage weathering (e.g., iron oxides, manganese oxides). Dinosaur “mummies” are rare examples of high-fidelity mineral templating of soft tissues in Mesozoic animals, a taphonomic mode better studied in far older, invertebrate fossils of Paleozoic or Precambrian marine Lagerstätten. The “mummies” are also closely associated with fossil plant material, suggesting that the sediments were not organic-limited. Future work should characterize variation in the composition of fossilized dinosaur integument, determine if any endogenous organic or inorganic compounds from the integument preserve in other “mummies”, determine which mineral precipitates are early-stage and induced by decay versus late-stage and induced by subsurface oxidative weathering, and look for bacterial biomarkers (e.g., hopanoids) in the integument template.

Metal nitrides represent a large class of materials with extensive applications in optoelectronics, energy and healthcare technologies. For example, GaN and related nitride semiconductors are key materials for solid-state lighting and high-power electronics^1,2. TiN and other early transition metal nitrides (TMNs) are widely used in wear-resistant alloys, tool coatings, catalysts and medical implants³. Strong metal-nitrogen bonds grant nitrides structural rigidity as well as chemical and thermal stability⁴. However, the covalency of metal-nitrogen bonds necessitates high temperatures to synthesize crystalline metal nitrides. Common synthetic routes include high-temperature solid-state nitridation⁵, crystal growth in supercritical ammonia⁶, molecular-beam epitaxy (MBE)⁷, reactive sputtering^8,9 and chemical vapour deposition^1,10-12. The solution synthesis of colloidal nanocrystals (NCs) has been demonstrated for late TMNs with relatively weak chemical bonds^13-17, whereas the synthesis of early TMN NCs is challenging because it requires temperatures far above the stability range of commonly used solvents. Here we report a general approach to solution synthesis of refractory metal nitride NCs by reacting metal halides and ammonia dissolved in molten inorganic salts at elevated pressures. Successful syntheses of colloidal TiN, VN, GaN, NbN, Mo₂N, Ta₃N₅, TaN, W₂N and ternary Ti_1-xV_xN NCs are demonstrated. These NCs expand the scope of solution-processable technologically important materials.

Colloidal quantum dots offer tunable optical properties for optoelectronic applications, but the synthesis of high-quality III–V quantum dots (QDs) other than indium pnictides, and particularly GaAs, has remained elusive due to synthetic challenges. Colloidal GaAs QDs have been reported very recently and have shown only weak band-edge photoluminescence. Here, we demonstrate a large-scale synthesis of colloidal GaAs QDs in molten salts, followed by a high-temperature surface treatment with K₂S, which removes native oxide and enables uniform zinc chalcogenide shell growth on GaAs. These QDs demonstrate bright band-edge photoluminescence and electroluminescence in QD LED devices. Low-temperature spectroscopy reveals a well-resolved exciton fine structure with distinct bright-state splitting and temperature-independent decay dynamics from 4 to 100 K. These results establish a practical pathway for the preparation of high-quality colloidal GaAs QDs from molten salts with potential applications in quantum technologies and optoelectronics.

Heating, ventilation, and air-conditioning (HVAC) systems are major contributors to global energy consumption, underscoring the urgent need for energy-efficient building envelope technologies. Synergistic solar and radiative electrochromism offers a promising solution by leveraging the sun and outer space as sustainable thermodynamic resources. In this study, we demonstrate a dual-mode electrochromic device that enables reversible, non-volatile switching between solar heating and sub-ambient radiative cooling, achieving an annual energy savings of 73.7 MBtu and CO2 emission savings of 4063 kgCO2 in specific U.S. climate zones. The device can achieve true sub-ambient passive daytime radiative cooling by 1 °C in the cooling mode and raise it by 33 °C above ambient in the heating mode during daytime operation, controlled by electrical voltage. The device employs electrodeposited lossy amorphous Cu-Bi nanoclusters on defect-activated monolayer graphene, yielding high optical contrast between cooling (solar absorptance α = 7.99%, thermal emittance ε = 93.58%) and heating (α = 47.7%, ε = 20.14%) modes, with outstanding long-term durability. This work paves the way for scalable, durable, and dynamic thermal regulation, advancing sustainable building technologies.

The diverse structures of metal-organic frameworks (MOFs) originate from the coordination chemistry of ionic metal-ligand bonds, while covalent organic frameworks (COFs) leverage covalent bonding. Between these extremes, extended structures based on metalloids are comparatively rare. This paucity obscures how the chemistry of the metalloid elements, intermediate between the metals and the main group, manifests in the properties of new porous materials. This study presents the chemistry of new examples of germanium-organic frameworks (GeOFs). Two new GeOFs with metalloid GeO4 nodes and redox-active triphenylene hexahydroxyl (THO) linkers, Ge-THO-1 and Ge-THO-2, have been synthesized and characterized. Ge-THO-1 has Ge2+ nodes which become tetravalent with concomitant formation of Ge–Ge bonds in Ge-THO-2 upon activation or air exposure. This structural transformation leads to a 10,000-fold increase in electrical conductivity. These materials are rare examples of GeOFs as well as a unique case where metal-metal bond formation regulates structure and conductivity in porous materials.

The discovery of materials with programmable combinations of charge transport and magnetic properties is a major goal in synthetic chemistry. Molecular materials, such as coordination polymers (CPs), are emerging candidates in this field due to their synthetic modularity. While there are many conductive or magnetic CPs, single-component examples with both properties are still emerging. Here we demonstrate how alloying paramagnetic Fe(III) centers into a highly conductive Ni-based CP results in novel amorphous materials with high conductivity and giant magnetoresistance. Aliovalent doping with paramagnetic Fe centers engenders spin-glass transitions, while Ni and the strong π-stacking interactions of tetrathiafulvalene-2,3,6,7-tetrathiolate (TTFtt) ligands support conductivity. Ni_0.69Fe_0.31TTFtt has σ ≈ 200 S/cm and a 1.8 K magnetoresistance of -52% at 5 T, among the largest for any coordination solid. This work demonstrates not only how magnetic properties can be rationally incorporated into conductive CPs, but also an unexpected potential for amorphous materials in spintronic applications.

Conductive coordination polymers (CPs) with sulfur-based ligands offer strong metal–ligand interactions and redox tunability, making them promising candidates for electronic applications. Tetrathiafulvalene-2,3,6,7-tetrathiolate (TTFtt) is a particularly attractive ligand. However, its strong metal–ligand covalency leads to rapid irreversible metal coordination, limiting control over structure and morphology. Here, we demonstrate structural control in Cu TTFtt CPs using a pre-synthetic redox control strategy. Two new copper-based CPs, CuTTFtt and Cu₂TTFtt, have been synthesized and thoroughly characterized from differentially oxidized TTFtt synthons. CuTTFtt forms a 1D chain, while Cu₂TTFtt adopts a 2D ribbon-like structure. Detailed spectroscopic studies confirm the structures of these materials as well as their ligand and metal oxidation states. Physical property measurements reveal that Cu₂TTFtt exhibits higher conductivity than CuTTFtt. Furthermore, Cu₂TTFtt also shows unusual diamagnetism which contrasts the paramagnetism observed in CuTTFtt and the related material NiTTFtt. Density functional theory (DFT) further elucidates the physical properties of these CPs and supports the observed conductivity trends. This study expands the structural landscape of TTFtt-based CPs and further establishes how redox-doping can tune CP structure and physical properties.

The structural and transport properties of an organic ionic plastic crystal (OIPC), triisobutyl(methyl)phosphonium bis(fluorosulfonyl)imide (P1444FSI) with the addition of lithium bis(fluorosulfonyl)imide (LiFSI) have been investigated with a combined experimental and computational approach. After establishing the effect of thermal processing on structural and transport properties of P1444FSI, a consistent processing procedure was established to understand how P1444FSI properties change with increasing temperature and LiFSI concentration. Elevated rotational motions of ions on the plastic crystalline lattice coincides with and may facilitate solid-solid phase transitions in P1444FSI, while the transport of lithium cations within LiFSI-doped P1444FSI was found to be dominated by increased translational diffusivity with little change in rotational diffusivity. The trade-off between increased ion conductivity in the solid-state and decreased mechanical robustness with increasing LiFSI concentration presents an important challenge for P1444FSI-based solid-state electrolytes moving forward.

The ability to perform versatile covalent surface modifications in two-dimensional (2D) inorganic materials marks a significant advance in the functionalization of this broad family of materials. One particularly successful example of 2D materials with chemically modifiable surfaces are 2D transition metal carbides and nitrides (MXenes). MXenes' strong in-plane metal-carbon bonds and labile surface metal-halide bonds create altogether unprecedented opportunities for versatile postsynthetic modifications and assembling complex materials, including various organic-inorganic hybrids. We demonstrate the general applicability of this surface modification strategy to non-MXene halide-terminated 2D materials, termed MXenoids. These surface modifications enable compositional and electronic structure engineering, introduce chiral hybrid organic-inorganic structures, and photoluminescence ranging from near-IR to blue. This study highlights the avenue of surface chemistry-driven materials design, enhancing the functional capabilities of 2D materials.