Ultrathin Two-Dimensional Porous Fullerene Membranes for Ultimate Organic Solvent Separation

Two-dimensional (2D) materials with high chemical stability have attracted intensive interest in membrane design for the separation of organic solvents. As a novel 2D material, polymeric fullerenes (C60)∞ with distinctive properties are very promising for the development of innovative membranes. In this work, we report the construction of a 2D (C60)∞ nanosheet membrane for organic solvent separation. The pathways of the (C60)∞ nanosheet membrane are constructed by sub-1-nm lateral channels and nanoscale in-plane pores created by the depolymerization of the (C60)∞ nanosheets. Attributing to ordered and shortened transport pathways, the ultrathin porous (C60)∞ membrane is superior in organic solvent separation. The hexane, acetone, and methanol fluxes are up to 1146.3±53, 900.4±41, and 879.5±42 kg ⋅ m-2 ⋅ h-1, respectively, which are up to 130 times higher than those of the state-of-the-art membranes with similar dye rejection. Our findings demonstrate the prospect of 2D (C60)∞ as a promising nanofiltration membrane in the separation of organic solvents from macromolecular compounds such as dyes, drugs, hormones, etc.

Bioinspiration and biomimetics in marine robotics: a review on current applications and future trends

Over the past few years, the research community has witnessed a burgeoning interest in biomimetics, particularly within the marine sector. The study of biomimicry as a revolutionary remedy for numerous commercial and research-based marine businesses has been spurred by the difficulties presented by the harsh maritime environment. Biomimetic marine robots are at the forefront of this innovation by imitating various structures and behaviors of marine life and utilizing the evolutionary advantages and adaptations these marine organisms have developed over millennia to thrive in harsh conditions. This thorough examination explores current developments and research efforts in biomimetic marine robots based on their propulsion mechanisms. By examining these biomimetic designs, the review aims to solve the mysteries buried in the natural world and provide vital information for marine improvements. In addition to illuminating the complexities of these bio-inspired mechanisms, the investigation helps to steer future research directions and possible obstacles, spurring additional advancements in the field of biomimetic marine robotics. Considering the revolutionary potential of using nature's inventiveness to navigate and thrive in one of the most challenging environments on Earth, the current review's conclusion urges a multidisciplinary approach by integrating robotics and biology. The field of biomimetic marine robotics not only represents a paradigm shift in our relationship with the oceans, but it also opens previously unimaginable possibilities for sustainable exploration and use of marine resources by understanding and imitating nature's solutions.

Fullerene Fragment Restructuring: How Spatial Proximity Shapes Defect-Rich Carbon Electrocatalysts

Fullerene transformation emerges as a powerful route to construct defect-rich carbon electrocatalysts, but the carbon bond breakage and reformation that determine the defect states remain poorly understood. Here, we explicitly reveal that the spatial proximity of disintegrated fullerene imposes a crucial impact on the bond reformation and electrocatalytic properties. A counterintuitive hard-template strategy is adopted to enable the space-tuned fullerene restructuring by calcining impregnated C60 not only before but also after the removal of rigid silica spheres (∼300 nm). When confined in the SiO2 nanovoids, the adjacent C60 fragments form sp3 bonding with adverse electron transfer and active site exposure. In contrast, the unrestricted fragments without SiO2 confinement reconnect at the edges to form sp2-hybridized nanosheets while retaining high-density intrinsic defects. The optimized catalyst exhibits robust alkaline oxygen reduction performance with a half-wave potential of 0.82 V via the 4e- pathway. Copper poisoning affirms the intrinsic defects as the authentic active sites. Density functional theory calculations further substantiate that pentagons in the basal plane lead to localized structural distortion and thus exhibit significantly reduced energy barriers for the first O2 dissociation step. Such space-regulated fullerene restructuring is also verified by heating C60 crystals confined in gallium liquid and a quartz tube.

Long-range ordered porous carbons produced from C60

Carbon structures with covalent bonds connecting C₆₀ molecules have been reported^1-3, but their production methods typically result in very small amounts of sample, which restrict the detailed characterization and exploration necessary for potential applications. We report the gram-scale preparation of a new type of carbon, long-range ordered porous carbon (LOPC), from C₆₀ powder catalysed by α-Li₃N at ambient pressure. LOPC consists of connected broken C₆₀ cages that maintain long-range periodicity, and has been characterized by X-ray diffraction, Raman spectroscopy, magic-angle spinning solid-state nuclear magnetic resonance spectroscopy, aberration-corrected transmission electron microscopy and neutron scattering. Numerical simulations based on a neural network show that LOPC is a metastable structure produced during the transformation from fullerene-type to graphene-type carbons. At a lower temperature, shorter annealing time or by using less α-Li₃N, a well-known polymerized C₆₀ crystal forms owing to the electron transfer from α-Li₃N to C₆₀. The carbon K-edge near-edge X-ray absorption fine structure shows a higher degree of delocalization of electrons in LOPC than in C₆₀(s). The electrical conductivity is 1.17 × 10^-2 S cm^-1 at room temperature, and conduction at T < 30  K appears to result from a combination of metallic-like transport over short distances punctuated by carrier hopping. The preparation of LOPC enables the discovery of other crystalline carbons starting from C₆₀(s).

Nanocrystals with metastable high-pressure phases under ambient conditions

The ambient metastability of the rock-salt phase in well-defined model systems comprising nanospheres or nanorods of cadmium selenide, cadmium sulfide, or both was investigated as a function of composition, initial crystal phase, particle structure, shape, surface functionalization, and ordering level of their assemblies. Our experiments show that these nanocrystal systems exhibit ligand-tailorable reversibility in the rock salt-to-zinc blende solid-phase transformation. Interparticle sintering was used to engineer kinetic barriers in the phase transformation to produce ambient-pressure metastable rock-salt structures in a controllable manner. Interconnected nanocrystal networks were identified as an essential structure that hosted metastable high-energy phases at ambient conditions. These findings suggest general rules for transformation-barrier engineering that are useful in the rational design of next-generation materials.

Nested order-disorder framework containing a crystalline matrix with self-filled amorphous-like innards

Solids can be generally categorized by their structures into crystalline and amorphous states with different interactions among atoms dictating their properties. Crystalline-amorphous hybrid structures, combining the advantages of both ordered and disordered components, present a promising opportunity to design materials with emergent collective properties. Hybridization of crystalline and amorphous structures at the sublattice level with long-range periodicity has been rarely observed. Here, we report a nested order-disorder framework (NOF) constructed by a crystalline matrix with self-filled amorphous-like innards that is obtained by using pressure to regulate the bonding hierarchy of Cu₁₂Sb₄S₁₃. Combined in situ experimental and computational methods demonstrate the formation of disordered Cu sublattice which is embedded in the retained crystalline Cu framework. Such a NOF structure gives a low thermal conductivity (~0.24 W·m⁻¹·K⁻¹) and a metallic electrical conductivity (8 × 10⁻⁶ Ω·m), realizing the collaborative improvement of two competing physical properties. These findings demonstrate a category of solid-state materials to link the crystalline and amorphous forms in the sublattice-scale, which will exhibit extraordinary properties.

The synthesis and characterization of new crystalline-amorphous hybrid materials is challenging. Here, the authors report the preparation of a nested order-disorder framework by applying high pressure to a nested copper chalcogenide Cu₁₂Sb₄S₁₃.

Topological Ordering of Memory Glass on Extended Length Scales

Identifying ordering in non-crystalline solids has been a focus of natural science since the publication of Zachariasen's random network theory in 1932, but it still remains as a great challenge of the century. Literature shows that the hierarchical structures, from the short-range order of first-shell polyhedra to the long-range order of translational periodicity, may survive after amorphization. Here, in a piece of AlPO₄, or berlinite, we combine X-ray diffraction and stochastic free-energy surface simulations to study its phase transition and structural ordering under pressure. From reversible single crystals to amorphous transitions, we now present an unambiguous view of the topological ordering in the amorphous phase, consisting of a swarm of Carpenter low-symmetry phases with the same topological linkage, trapped in a metastable intermediate stage. We propose that the remaining topological ordering is the origin of the switchable "memory glass" effect. Such topological ordering may hide in many amorphous materials through disordered short atomic displacements.

Pentaheptite diamond: a new carbon allotrope

The search forsp³-hybridized carbon allotropes other than diamond has attracted extensive interest because of their fascinating properties. In this paper, an orthorhombic carbon phase insp³bonding, named pentaheptite diamond, by combining the particle swarm optimization method with first-principles calculations has been predicted. The phonon spectra, total energy and elastic constants calculations of the pentaheptite diamond confirm its dynamical, thermal and mechanical stability at zero pressure, respectively. It possesses a high bulk modulus of 385 GPa and Vickers hardness of 72.6 GPa, comparable to diamond. Electronic band structure calculations show that the pentaheptite diamond has a direct band gap of 4.18 eV.

Discovery of carbon-based strongest and hardest amorphous material

Carbon is one of the most fascinating elements due to its structurally diverse allotropic forms stemming from its bonding varieties (sp, sp ² and sp ³). Exploring new forms of carbon has been the eternal theme of scientific research. Herein, we report on amorphous (AM) carbon materials with a high fraction of sp ³ bonding recovered from compression of fullerene C₆₀ under high pressure and high temperature, previously unexplored. Analysis of photoluminescence and absorption spectra demonstrates that they are semiconducting with a bandgap range of 1.5-2.2 eV, comparable to that of widely used AM silicon. Comprehensive mechanical tests demonstrate that synthesized AM-III carbon is the hardest and strongest AM material known to date, and can scratch diamond crystal and approach its strength. The produced AM carbon materials combine outstanding mechanical and electronic properties, and may potentially be used in photovoltaic applications that require ultrahigh strength and wear resistance.

Ultrahard bulk amorphous carbon from collapsed fullerene

Amorphous materials inherit short- and medium-range order from the corresponding crystal and thus preserve some of its properties while still exhibiting novel properties^1,2. Due to its important applications in technology, amorphous carbon with sp² or mixed sp²-sp³ hybridization has been explored and prepared^3,4, but synthesis of bulk amorphous carbon with sp³ concentration close to 100% remains a challenge. Such materials inherit the short-/medium-range order of diamond and should also inherit its superior properties⁵. Here, we successfully synthesized millimetre-sized samples-with volumes 10³-10⁴ times as large as produced in earlier studies-of transparent, nearly pure sp³ amorphous carbon by heating fullerenes at pressures close to the cage collapse boundary. The material synthesized consists of many randomly oriented clusters with diamond-like short-/medium-range order and possesses the highest hardness (101.9 ± 2.3 GPa), elastic modulus (1,182 ± 40 GPa) and thermal conductivity (26.0 ± 1.3 W m^-1 K^-1) observed in any known amorphous material. It also exhibits optical bandgaps tunable from 1.85 eV to 2.79 eV. These discoveries contribute to our knowledge about advanced amorphous materials and the synthesis of bulk amorphous materials by high-pressure and high-temperature techniques and may enable new applications for amorphous solids.

Superatomic solid solutions

In atomic solids, substitutional doping of atoms into the lattice of a material to form solid solutions is one of the most powerful approaches to modulating its properties and has led to the discovery of various metal alloys and semiconductors. Herein we have prepared solid solutions in hierarchical solids that are built from atomically precise clusters. Two geometrically similar metal chalcogenide clusters, Co₆Se₈(PEt₃)₆ and Cr₆Te₈(PEt₃)₆, were combined as random substitutional mixture, in three different ratios, in a crystal lattice together with fullerenes. This does not alter the underlying crystalline structure of the [cluster][C₆₀]₂ material, but it influences its electronic and magnetic properties. All three solid solutions showed increased electrical conductivities compared with either the Co- or Cr-based parent material, substantially so for two of the Co:Cr ratios (up to 100-fold), and lowered activation barriers for electron transport. We attribute this to the existence of additional energy states arising from the materials' structural heterogeneity, which effectively narrow transport gaps.

Influence of Prednisolone and Alendronate on the de novo Mineralization of Zebrafish Caudal Fin

Dysregulated balance between bone resorption and formation mediates the onset and progression of osteoporosis. The administration of prednisolone is known to induce osteoporosis, whereas alendronate is commonly used to reverse the process. However, the assessment of the effects of such medicines on the nanostructure of bone remodeling and mechanical properties remains a major technical challenge. The aim of this study was to apply various analytical approaches to evaluate the compositional, morphological, and mechanical properties of regenerative zebrafish caudal fin bony rays affected by prednisolone and alendronate. Adult wild-type AB strain zebrafish were first exposed to 125μM of prednisolone for 14 days to develop glucocorticoid-induced osteoporosis. Fish fins were then amputated and let to regenerate for 21 days in tank water containing 30μM of alendronate or no alendronate. The lepidotrichia in the proximal and distal regions were evaluated separately using confocal microscope, scanning electron microscope, electron-dispersive spectroscopy, Raman spectroscopy, atomic force microscopy, and a triboindenter. As expected, prednisolone led to significant osteoporotic phenotypes. A decrease of Ca/P ratio was observed in the osteoporotic subjects (1.46 ± 0.04) as compared to the controls (1.74 ± 0.10). Subsequent treatment of alendronate overmineralized the bony rays during regeneration. Enhanced phosphate deposition was detected in the proximal part with alendronate treatment. Moreover, prednisolone attenuated the reduced elastic modulus and hardness levels (5.60 ± 5.04 GPa and 0.12 ± 0.17 GPa, respectively), whereas alendronate recovered them to the pre-amputation condition (8.68 ± 8.74 GPa and 0.34 ± 0.47 GPa, respectively). As an emerging model of osteoporosis, regrowth of zebrafish caudal fin was shown to be a reliable assay system to investigate the various effects of medicines in the de novo mineralization process. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Long-Range Ordered Amorphous Atomic Chains as Building Blocks of a Superconducting Quasi-One-Dimensional Crystal

Crystalline and amorphous structures are two of the most common solid-state phases. Crystals having orientational and periodic translation symmetries are usually both short-range and long-range ordered, while amorphous materials have no long-range order. Short-range ordered but long-range disordered materials are generally categorized into amorphous phases. In contrast to the extensively studied crystalline and amorphous phases, the combination of short-range disordered and long-range ordered structures at the atomic level is extremely rare and so far has only been reported for solvated fullerenes under compression. Here, a report on the creation and investigation of a superconducting quasi-1D material with long-range ordered amorphous building blocks is presented. Using a diamond anvil cell, monocrystalline (TaSe₄ )₂ I is compressed and a system is created where the TaSe₄ atomic chains are in amorphous state without breaking the orientational and periodic translation symmetries of the chain lattice. Strikingly, along with the amorphization of the atomic chains, the insulating (TaSe₄ )₂ I becomes a superconductor. The data provide critical insight into a new phase of solid-state materials. The findings demonstrate a first ever case where superconductivity is hosted by a lattice with periodic but amorphous constituent atomic chains.

Tuning the π-π overlap and charge transport in single crystals of an organic semiconductor via solvation and polymorphism

Polymorphism is a central phenomenon in materials science that often results in important differences of the electronic properties of organic crystals due to slight variations in intermolecular distances and positions. Although a large number of π-conjugated organic compounds can grow as polymorphs, it is necessary to have at disposal a series of several polymorphs of the same molecule to establish clear and predictive structure-property relationships. We report here on the occurrence of two solvates and three polymorphs in single crystalline form of the organic p-type semiconductor 2,2',6,6'-tetraphenyldipyranylidene (DIPO). When grown from chlorobenzene or toluene, the DIPO crystals spontaneously capture solvent molecules to form two pseudopolymorphic 1 : 1 binary solvates. Independently, three solvent-free DIPO polymorphs are obtained either from the vapor phase or from acetonitrile and benzene. Surprisingly, single crystal field-effect transistors (SC-FETs) reveal that the DIPO 1 : 1 binary solvate grown from chlorobenzene possesses a higher hole mobility (1.1 cm² V^-1 s^-1) than the three solvent-free polymorphs (0.02-0.64 cm² V^-1 s^-1). A refined crystallographic analysis combined with a theoretical transport model clearly shows that the higher mobility of the solvate results from an improved π-π overlap. Our observations demonstrate that solvation allows to tune the π-π overlap and transport properties of organic semiconductors by selecting appropriate solvents.

Synthesis and high pressure studies of white luminescence host-guest complex nanocrystals based on C60 and p-But-calix[8]arene

Host-guest structured nanocrystals consisting of p-But-calix[8]arene and fullerene C₆₀ were fabricated with the facial solution deposition method. The as-prepared host-guest complex nanocrystals are well crystallized in a tetragonal structure, in which the guest C₆₀ and host p-But-calix[8]arene molecules interact with each other via the van der Waals force. The host-guest crystal has a wider band gap compared to that of C₆₀ crystals. The luminescence range of the host-guest structured nanocrystals was widely extended, and its photoluminescence (PL) intensity was highly enhanced by one order of magnitude. High pressure studies on such host-guest nanocrystals were carried out using the diamond anvil cell technique with the associated spectroscopic measurements. Raman and PL spectra show a phase transition occurred on the samples owing to the deformation of fullerene molecules. A PL behavior change was also observed synchronously with the phase transition. The host-guest structure strongly influences the structure and optical behaviors of C₆₀ under pressure.

Nano-makisu: highly anisotropic two-dimensional carbon allotropes made by weaving together nanotubes

Graphene and carbon nanotubes (CNT) are the representatives of two-dimensional (2D) and one-dimensional (1D) forms of carbon, both exhibiting unique geometric structures and peculiar physical and chemical properties. Herein, we propose a family or series of 2D carbon-based highly anisotropic Dirac materials by weaving together an array of CNTs by direct C-C bonds or by graphene ribbons. By employing first-principles calculations, we demonstrate that these nano-makisus are thermally and dynamically stable and possess unique electronic properties. These 2D carbon allotropes are all metals and some nano-makisus show largely anisotropic Dirac cones, causing very different transport properties for the Dirac fermions along different directions. The Fermi velocities in the k_x direction could be ∼170 times higher than those in the k_y direction, which is the strongest anisotropy among 2D carbon allotropes to the best of our knowledge. This intriguing feature of the electronic structure has only been observed in heavy element materials with strong spin-orbit coupling. These results indicate that carbon based materials may have much broader applications in future nanoelectronics.

Reversible Polymorphic Transition and Hysteresis-Driven Phase Selectivity in Single-Crystalline C8-BTBT Rods

Organic semiconductors (OSCs) are highly susceptible to the formation of metastable polymorphs that are often transformed by external stimuli. However, thermally reversible transformations in OSCs with stability have not been achieved due to weak van der Waals forces, and poor phase homogeneity and crystallinity. Here, a polymorph of a single crystalline 2,7-dioctyl[1] benzothieno[3,2-b][1]benzothio-phene rod on a low molecular weight poly(methyl methacrylate) (≈120k) that limits crystal coarsening during solvent vapor annealing is fabricated. Molecules in the polymorph lie down slightly toward the substrate compared to the equilibrium state, inducing an order of greater resistivity. During thermal cycling, the polymorph exhibits a reversible change in resistivity by 5.5 orders with hysteresis; this transition is stable toward bias and thermal cycling. Remarkably, varying cycling temperatures leads to diverse resistivities near room temperature, important for nonvolatile multivalue memories. These trends persist in the carrier mobility and on/off ratio of the polymorph field-effect transistor. A combination of in situ grazing incident wide angle X-ray scattering analyses, visualization for electronic and structural analysis simulations, and density functional theory calculations reveals that molecular tilt governs the charge transport characteristics; the polymorph transforms as molecules tilt, and thereby, only a homogeneous single-crystalline phase appears at each temperature.

Ordered Structures with Functional Units as a Paradigm of Material Design

Realizing new functions through the construction of ordered structures not only exists naturally in nature, but also in artificial materials. However, much research focuses more on the relationship between structure and performance rather than on the impact of functional units themselves. Reviewing previous research findings, a "paradigm" of material research is proposed, which is based on ordered structures with functional units (OSFU) such as compositions, phases, domains, and twins. The goal is to draw more intensive attention of researchers to this concept and thus to promote the development of this field toward a deeper and broader direction, producing highly influential research results.

Li-ion battery material under high pressure: amorphization and enhanced conductivity of Li4Ti5O12

Lithium titanium oxide (Li4Ti5O12, LTO), a 'zero-strain' anode material for lithium-ion batteries, exhibits excellent cycling performance. However, its poor conductivity highly limits its applications. Here, the structural stability and conductivity of LTO were studied using in situ high-pressure measurements and first-principles calculations. LTO underwent a pressure-induced amorphization (PIA) at 26.9 GPa. The impedance spectroscopy revealed that the conductivity of LTO improved significantly after amorphization and that the conductivity of decompressed amorphous LTO increased by an order of magnitude compared with its starting phase. Furthermore, our calculations demonstrated that the different compressibility of the LiO6 and TiO6 octahedra in the structure was crucial for the PIA. The amorphous phase promotes Li+ diffusion and enhances its ionic conductivity by providing defects for ion migration. Our results not only provide an insight into the pressure depended structural properties of a spinel-like material, but also facilitate exploration of the interplay between PIA and conductivity.

Fabrication and Characterization of Graphene Microcrystal Prepared from Lignin Refined from Sugarcane Bagasse

Graphene microcrystal (GMC) is a type of glassy carbon fabricated from lignin, in which the microcrystals of graphene are chemically bonded by sp³ carbon atoms, forming a glass-like microcrystal structure. The lignin is refined from sugarcane bagasse using an ethanol-based organosolv technique which is used for the fabrication of GMC by two technical schemes: The pyrolysis reaction of lignin in a tubular furnace at atmospheric pressure; and the hydrothermal carbonization (HTC) of lignin at lower temperature, followed by pyrolysis at higher temperature. The existence of graphene nanofragments in GMC is proven by Raman spectra and XRD patterns; the ratio of sp² carbon atoms to sp³ carbon atoms is demonstrated by XPS spectra; and the microcrystal structure is observed in the high-resolution transmission electron microscope (HRTEM) images. Temperature and pressure have an important impact on the quality of GMC samples. With the elevation of temperature, the fraction of carbon increases, while the fraction of oxygen decreases, and the ratio of sp² to sp³ carbon atoms increases. In contrast to the pyrolysis techniques, the HTC technique needs lower temperatures because of the high vapor pressure of water. In general, with the help of biorefinery, the biomass material, lignin, is found to be qualified and sustainable material for the manufacture of GMC. Lignin acts as a renewable substitute for the traditional raw materials of glassy carbon, copolymer resins of phenol formaldehyde, and furfuryl alcohol-phenol.

New Ordered Structure of Amorphous Carbon Clusters Induced by Fullerene-Cubane Reactions

As a new category of solids, crystalline materials constructed with amorphous building blocks expand the structure categorization of solids, for which designing such new structures and understanding the corresponding formation mechanisms are fundamentally important. Unlike previous reports, new amorphous carbon clusters constructed ordered carbon phases are found here by compressing C₈ H₈ /C₆₀ cocrystals, in which the highly energetic cubane (C₈ H₈ ) exhibits unusual roles as to the structure formation and transformations under pressure. The significant role of C₈ H₈ is to stabilize the boundary interactions of the highly compressed or collapsed C₆₀ clusters which preserves their long-range ordered arrangement up to 45 GPa. With increasing time at high pressure, the gradual random bonding between C₈ H₈ and carbon clusters, due to "energy release" of highly compressed cubane, leads to the loss of the ability of C₈ H₈ to stabilize the carbon cluster arrangement. Thus a transition from short-range disorder to long-range disorder (amorphization) occurs in the formed material. The spontaneous bonding reconstruction most likely results in a 3D network in the material, which can create ring cracks on diamond anvils.

Reciprocating Compression of ZnO Probed by X-ray Diffraction: The Size Effect on Structural Properties under High Pressure

Zinc oxide, ZnO, an important technologically relevant binary compound, was investigated by reciprocating compress the sample in a diamond anvil cell using in situ high-pressure synchrotron X-ray diffraction at room temperature. The starting sample (∼200 nm) was compressed to 20 GPa and then decompressed to ambient condition. The quenched sample, with average grain size ∼10 nm, was recompressed to 20 GPa and then released to ambient condition. The structural stability and compressibility of the initial bulk ZnO and quenched nano ZnO were compared. Results reveal that the grain size and the fractional cell distortion have little effect on the structural stability of ZnO. The bulk modulus of the B4 (hexagonal wurtzites structure) and B1 (cubic rock salt structure) phases for bulk ZnO under hydrostatic compression were estimated as 164(3) and 201(2) GPa, respectively. Importantly, the effect of pressure in atomic positions, bond distances, and bond angles was obtained. On the basis of this information, the B4-to-B1 phase transformation was demonstrated to follow the hexagonal path rather than the tetragonal path. For the first time, the detail of the intermediate hexagonal ZnO, revealing the B4-to-B1 transition mechanism, was detected by experimental method. These findings enrich our knowledge on the diversity of the size influences on the high-pressure behaviors of materials and offer new insights into the mechanism of the B4-to-B1 phase transition that is commonly observed in many other wurzite semiconductor compounds.

An order–disorder phase transition in the van der Waals based solvate of C60 and CClBrH2

The (010) plane of the C₆₀·2CBrClH₂ monoclinic (C2/m) co-crystal with both molecular entities, C₆₀ and CBrClH₂, orientationally ordered.

Investigation of the polymerization mechanism of ferrocene doped C60 under high pressure and high temperature

In situ high pressure and high temperature (HPHT) study has been carried out on C₆₀/ferrocene (Fc) in order to detect the process of polymerization and reveal the polymerization mechanism. Pristine C₆₀ was also studied under same conditions for comparison. In both cases, similar types of polymers can be observed after pressure and temperature release, but with different fractions, i.e. a larger amount of 2D polymers were formed in pure C₆₀, while more branch-like polymers were synthesized in C₆₀/Fc, although the most fraction of the polymers is still 1D chain-like polymer in both of the materials. The polymers formed in C₆₀ can be detected both during the “up” run (pressure and temperature increase) and the “down” run (pressure and temperature decrease), while in C₆₀/Fc, the polymers can only be synthesized in the “down” run. The differences between the two cases were attributed to the different initial lattice structures of the two materials and the confinement effect of the dopant. The polymerization mechanism on C₆₀/Fc under HPHT was also revealed in this work.

Novel Superhard sp^{3} Carbon Allotrope from Cold-Compressed C_{70} Peapods

Design and synthesis of new carbon allotropes have always been important topics in condensed matter physics and materials science. Here we report a new carbon allotrope, formed from cold-compressed C_{70} peapods, which most likely can be identified with a fully sp^{3}-bonded monoclinic structure, here named V carbon, predicted from our simulation. The simulated x-ray diffraction pattern, near K-edge spectroscopy, and phonon spectrum agree well with our experimental data. Theoretical calculations reveal that V carbon has a Vickers hardness of 90 GPa and a bulk modulus ∼400  GPa, which well explains the "ring crack" left on the diamond anvils by the transformed phase in our experiments. The V carbon is thermodynamically stable over a wide pressure range up to 100 GPa, suggesting that once V carbon forms, it is stable and can be recovered to ambient conditions. A transition pathway from peapod to V carbon has also been suggested. These findings suggest a new strategy for creating new sp^{3}-hybridized carbon structures by using fullerene@nanotubes carbon precursor containing odd-numbered rings in the structures.

Compressed glassy carbon: An ultrastrong and elastic interpenetrating graphene network

Carbon's unique ability to have both sp² and sp³ bonding states gives rise to a range of physical attributes, including excellent mechanical and electrical properties. We show that a series of lightweight, ultrastrong, hard, elastic, and conductive carbons are recovered after compressing sp²-hybridized glassy carbon at various temperatures. Compression induces the local buckling of graphene sheets through sp³ nodes to form interpenetrating graphene networks with long-range disorder and short-range order on the nanometer scale. The compressed glassy carbons have extraordinary specific compressive strengths-more than two times that of commonly used ceramics-and simultaneously exhibit robust elastic recovery in response to local deformations. This type of carbon is an optimal ultralight, ultrastrong material for a wide range of multifunctional applications, and the synthesis methodology demonstrates potential to access entirely new metastable materials with exceptional properties.

Elastic and mechanical softening in boron-doped diamond

Alternative approaches to evaluating the hardness and elastic properties of materials exhibiting physical properties comparable to pure diamond have recently become necessary. The classic linear relationship between shear modulus (G) and Vickers hardness (H_V), along with more recent non-linear formulations based on Pugh’s modulus extending into the superhard region (H_V > 40 GPa) have guided synthesis and identification of novel superabrasives. These schemes rely on accurately quantifying H_V of diamond-like materials approaching or potentially exceeding the hardness of the diamond indenter, leading to debate about methodology and the very definition of hardness. Elasticity measurements on such materials are equally challenging. Here we used a high-precision, GHz-ultrasonic interferometer in conjunction with a newly developed optical contact micrometer and 3D optical microscopy of indentations to evaluate elasticity-hardness relations in the ultrahard range (H_V > 80 GPa) by examining single-crystal boron-doped diamond (BDD) with boron contents ranging from 50–3000 ppm. We observe a drastic elastic-mechanical softening in highly doped BDD relative to the trends observed for superhard materials, providing insight into elasticity-hardness relations for ultrahard materials.

Incorporating Pyrrolic and Pyridinic Nitrogen into a Porous Carbon made from C60 Molecules to Obtain Superior Energy Storage

Nitrogen-doped porous carbon is obtained by KOH activation of C₆₀ in an ammonia atmosphere. As an anode for Li-ion batteries, it shows a reversible capacity of up to ≈1900 mA h g^-1 at 100 mA g^-1 . Simulations suggest that the superior Li-ion storage may be related to the curvature of the graphenes and the presence of pyrrolic/pyridinic group dopants.

High-pressure studies with x-rays using diamond anvil cells

Pressure profoundly alters all states of matter. The symbiotic development of ultrahigh-pressure diamond anvil cells, to compress samples to sustainable multi-megabar pressures; and synchrotron x-ray techniques, to probe materials' properties in situ, has enabled the exploration of rich high-pressure (HP) science. In this article, we first introduce the essential concept of diamond anvil cell technology, together with recent developments and its integration with other extreme environments. We then provide an overview of the latest developments in HP synchrotron techniques, their applications, and current problems, followed by a discussion of HP scientific studies using x-rays in the key multidisciplinary fields. These HP studies include: HP x-ray emission spectroscopy, which provides information on the filled electronic states of HP samples; HP x-ray Raman spectroscopy, which probes the HP chemical bonding changes of light elements; HP electronic inelastic x-ray scattering spectroscopy, which accesses high energy electronic phenomena, including electronic band structure, Fermi surface, excitons, plasmons, and their dispersions; HP resonant inelastic x-ray scattering spectroscopy, which probes shallow core excitations, multiplet structures, and spin-resolved electronic structure; HP nuclear resonant x-ray spectroscopy, which provides phonon densities of state and time-resolved Mössbauer information; HP x-ray imaging, which provides information on hierarchical structures, dynamic processes, and internal strains; HP x-ray diffraction, which determines the fundamental structures and densities of single-crystal, polycrystalline, nanocrystalline, and non-crystalline materials; and HP radial x-ray diffraction, which yields deviatoric, elastic and rheological information. Integrating these tools with hydrostatic or uniaxial pressure media, laser and resistive heating, and cryogenic cooling, has enabled investigations of the structural, vibrational, electronic, and magnetic properties of materials over a wide range of pressure-temperature conditions.

Effects of Molecular Geometry on the Properties of Compressed Diamondoid Crystals

Diamondoids are an intriguing group of carbon-based nanomaterials, which combine desired properties of inorganic nanomaterials and small hydrocarbon molecules with atomic-level uniformity. In this Letter, we report the first comparative study on the effect of pressure on a series of diamondoid crystals with systematically varying molecular geometries and shapes, including zero-dimensional (0D) adamantane; one-dimensional (1D) diamantane, [121]tetramantane, [123]tetramantane, and [1212]pentamantane; two-dimensional (2D) [12312]hexamantane; and three-dimensional (3D) triamantane and [1(2,3)4]pentamantane. We find the bulk moduli of these diamondoid crystals are strongly dependent on the diamondoids' molecular geometry with 3D [1(2,3)4]pentamantane being the least compressible and 0D adamantane being the most compressible. These diamondoid crystals possess excellent structural rigidity and are able to sustain large volume deformation without structural failure even after repetitive pressure loading cycles. These properties are desirable for constructing cushioning devices. We also demonstrate that lower diamondoids outperform the conventional cushioning materials in both the working pressure range and energy absorption density.

Structural Stability and Deformation of Solvated Sm@C2(42)-C90 under High Pressure

Solvated fullerenes recently have been shown to exhibit novel compression behaviors compared with the pristine fullerenes. However, less attention has been focused on the large cage endohedral metallofullerenes. Here, we have firstly synthesized solvated Sm@C₉₀ microrods by a solution drop-drying method, and then studied the transformations under high pressure. The pressure-induced structural evolutions of Sm@C₉₀ molecules both undergo deformation and collapse. The band gaps of both samples decrease with increasing pressure. The trapped Sm atom plays a role in restraining the compression of the adjacent bonds. The solvent plays a role in protecting Sm@C₉₀ against collapse in the region of 12–20 GPa, decreasing and postponing the change of band gap. Above 30 GPa, the carbon cages collapse. Released from 45 GPa, the compressed solvated Sm@C₉₀ forms a new ordered amorphous carbon cluster (OACC) structure with metal atoms trapped in the units of amorphous carbon clusters, which is different from the OACC structure formed by compressing solvated C₆₀ and C₇₀. This discovery opens the door for the creation of new carbon materials with desirable structural and physical properties when suitable starting materials are selected.

Assembling carbon quantum dots to a layered carbon for high-density supercapacitor electrodes

It is found that carbon quantum dots (CQDs) self-assemble to a layer structure at ice crystals-water interface with freeze- drying. Such layers interconnect with each other, forming a free-standing CQD assembly, which has an interlayer distance of about 0.366 nm, due to the existence of curved carbon rings other than hexagons in the assembly. CQDs are fabricated by rupturing C₆₀ by KOH activation with a production yield of ~15 wt.%. The CQDs obtained have an average height of 1.14 nm and an average lateral size of 7.48 nm, and are highly soluble in water. By packaging annealed CQD assembly to high density (1.23 g cm⁻³) electrodes in supercapacitors, a high volumetric capacitance of 157.4 F cm⁻³ and a high areal capacitance of 0.66 F cm⁻² (normalized to the loading area of electrodes) are demonstrated in 6 M KOH aqueous electrolyte with a good rate capability.

Probing the thermal stability and the decomposition mechanism of a magnesium–fullerene polymer via X-ray Raman spectroscopy, X-ray diffraction and molecular dynamics simulations

The dynamic decomposition mechanism was established in an element-specific way for a magnesium-intercalated fullerene polymer.

Rupturing C60 Molecules into Graphene-Oxide-like Quantum Dots: Structure, Photoluminescence, and Catalytic Application

The large-scale synthesis of graphene-oxide-like quantum dots (GOLQDs) is reported by oxidizing C(60) molecules using a modified Hummers method with a yield of ≈25 wt% readily achieved. The GOLQDs are highly soluble in water and in addition to hexagons have other carbon rings in the structure. They have an average height of ≈1.2 nm and a diameter distribution of 0.6-2.2 nm after drying on substrates. First-principle calculations indicate that a possible rupturing route may include the insertion of oxygen atoms to CC bonds in the C(60) molecule, followed by rupture of that CC bonds. The GOLQD suspension has a strong photoluminescence (PL) with peak position dependent on excitation wavelength. The PL is related to the size and emissive traps caused by oxygen-containing groups. The GOLQDs also catalyze the oxidation of benzyl alcohol with a high selectivity.

Structural Deformation of Sm@C88 under High Pressure

We have studied the structural transformation of Sm@C₈₈ under pressure up to 18 GPa by infrared spectroscopy combined with theoretical simulations. The infrared-active vibrational modes of Sm@C₈₈ at ambient conditions have been assigned for the first time. Pressure-induced blue and red shifts of the corresponding vibrational modes indicate an anisotropic deformation of the carbon cage upon compression. We propose that the carbon cage changes from ellipsoidal to approximately spherical around 7 GPa. A smaller deformation of the carbon bonds in the area close to the Sm atom in the cage suggests that the trapped Sm atom plays a role in minimizing the compression of the adjacent bonds. Pressure induced a significant reduction of the band gap of the crystal. The HOMO-LUMO gap of the Sm@C₈₈ molecule decreases remarkably at 7 GPa as the carbon cage is deformed. Also, compression enhances intermolecular interactions and causes a widening of the energy bands. Both effects decrease the band gap of the sample. The carbon cage deforms significantly above 7 GPa, from spherical to a peanut-like shape and collapses at 18 GPa.

Tailoring Building Blocks and Their Boundary Interaction for the Creation of New, Potentially Superhard, Carbon Materials

A strategy for preparing hybrid carbon structures with amorphous carbon clusters as hard building blocks by compressing a series of predesigned two-component fullerides is presented. In such constructed structures the building blocks and their boundaries can be tuned by changing the starting components, providing a way for the creation of new hard/superhard materials with desirable properties.

Toward the Ultra-incompressible Carbon Materials. Computational Simulation and Experimental Observation

The common opinion that diamond is the stiffest material is disproved by a number of experimental studies where the fabrication of carbon materials based on polymerized fullerenes with outstanding mechanical stiffness was reported. Here we investigated the nature of this unusual effect. We present a model constituted of compressed polymerized fullerite clusters implemented in a diamond matrix with bulk modulus B0 much higher than that of diamond. The calculated B0 value depends on the sizes of both fullerite grain and diamond environment and shows close correspondence with measured data. Additionally, we provide results of experimental study of atomic structure and mechanical properties of ultrahard carbon material supported the presented model.

Spin-glass behavior of a hierarchically-organized, hybrid microporous material, based on an extended framework of octanuclear iron-oxo units

Inspired by the stepwise addition of octanuclear iron units into mammalian ferritin, a "stop-and-go" synthesis strategy was used to prepare two microporous (Langmuir surface area, 490 m(2) g(-1); effective pore size, 4-5 Å) hierarchical materials {[Fe8(μ4-O)4(μ-pz)12Cl0.3(μ-O)1.85}n () and {[Fe8(μ4-O)4(μ-4-Me-pz)12Cl0.4(μ-O)1.8}n (), which are new members of the EO2 family of polymeric materials (E = C, Si and Ge). The secondary building units (SBUs) E = [Fe8(μ4-O)4(μ-4-R-pz)12] (Fe8) are nanoscale pseudo-spherical clusters, rather than single atoms, forming μ-oxo Fe-O-Fe linkages between Fe8-SBUs. The characteristic Fe-O-Fe asymmetric stretching mode in the infrared (IR) spectra of these compounds appearing at around 800 cm(-1) suggest the formation of approximately linear μ-oxo Fe-O-Fe linkages between Fe8-SBUs in and . We employ the concept of continuous random network (CRN) to describe for the first time the framework features of a Fe8-based amorphous materials, in which the average connecting numbers of each Fe8-cluster are ∼3.7 and ∼3.6 for and , respectively. (57)Fe-Mössbauer spectroscopic analysis provides insights to the intercluster connectivity of and on one hand and to their magnetic properties on the other, evident by a magnetic split sextet below 30 K. The combination of Mössbauer spectroscopy and magnetism measurements reveals a spin-glass behavior with Tg of ∼30 K. The hierarchical porous materials and straddle the gap between metal oxides and metal-organic frameworks (MOFs). This study may open an alternative way for the development of multifunctional materials based on high nuclearity metal clusters.

A new carbon phase constructed by long-range ordered carbon clusters from compressing C70 solvates

An ordered amorphous carbon cluster (OACC) structure with building blocks of highly deformed/collapsed C70 is synthesized by compressing C70 *m-xylene, which exhibits an exceptionally high hardness. Different from compressing C60 *m-xylene, a new structure transition is observed in C70*m-xylene at above 30 GPa, indicating the formation of a new OACC structure under pressure.

Deviatoric stress-induced phase transitions in diamantane

The high-pressure behavior of diamantane was investigated using angle-dispersive synchrotron x-ray diffraction (XRD) and Raman spectroscopy in diamond anvil cells. Our experiments revealed that the structural transitions in diamantane were extremely sensitive to deviatoric stress. Under non-hydrostatic conditions, diamantane underwent a cubic (space group Pa3) to a monoclinic phase transition at below 0.15 GPa, the lowest pressure we were able to measure. Upon further compression to 3.5 GPa, this monoclinic phase transformed into another high-pressure monoclinic phase which persisted to 32 GPa, the highest pressure studied in our experiments. However, under more hydrostatic conditions using silicone oil as a pressure medium, the transition pressure to the first high-pressure monoclinic phase was elevated to 7-10 GPa, which coincided with the hydrostatic limit of silicone oil. In another experiment using helium as a pressure medium, no phase transitions were observed to the highest pressure we reached (13 GPa). In addition, large hysteresis and sluggish transition kinetics were observed upon decompression. Over the pressure range where phase transitions were confirmed by XRD, only continuous changes in the Raman spectra were observed. This suggests that these phase transitions are associated with unit cell distortions and modifications in molecular packing rather than the formation of new carbon-carbon bonds under pressure.

Demonstration of ultrarapid interfacial formation of 1D fullerene nanorods with photovoltaic properties

We demonstrate ultrarapid interfacial formation of one-dimensional (1D) single-crystalline fullerene C60 nanorods at room temperature in 5 s. The nanorods of ∼ 11 μm in length and ∼ 215 nm in diameter are developed in a hexagonal close-pack crystal structure, contrary to the cubic crystal structure of pristine C60. Vibrational and electronic spectroscopy provide strong evidence that the nanorods are a van der Waals solid, as evidenced from the preservation of the electronic structure of the C60 molecules within the rods. Steady state optical spectroscopy reveals a dominance of charge transfer excitonic transitions in the nanorods. A significant enhancement of photogenerated charge carriers is observed in the nanorods in comparison to pristine C60, revealing the effect of shape on the photovoltaic properties. Due to their ultrarapid, large-scale, room-temperature synthesis with single-crystalline structure and excellent optoelectronic properties, the nanorods are expected to be promising for photosensitive devices applications.