Theoretical Prediction and Synthesis of a Family of Atomic Laminate Metal Borides with In-Plane Chemical Ordering

All atomically laminated MAB phases (M = transition metal, A = A-group element, and B = boron) exhibit orthorhombic or tetragonal symmetry, with the only exception being hexagonal Ti₂InB₂. Inspired by the recent discovery of chemically ordered hexagonal carbides, i-MAX phases, we perform an extensive first-principles study to explore chemical ordering upon metal alloying of M₂AlB₂ (M from groups 3 to 9) in orthorhombic and hexagonal symmetry. Fifteen stable novel phases with in-plane chemical ordering are identified, coined i-MAB, along with 16 disordered stable alloys. The predictions are verified through the powder synthesis of Mo_4/3Y_2/3AlB₂ and Mo_4/3Sc_2/3AlB₂ of space group R3̅m (no. 166), displaying the characteristic in-plane chemical order of Mo and Y/Sc and Kagomé ordering of the Al atoms, as evident from X-ray diffraction and electron microscopy. The discovery of i-MAB phases expands the elemental space of these borides with M = Sc, Y, Zr, Hf, and Nb, realizing an increased property tuning potential of these phases as well as their suggested potential two-dimensional derivatives.

C-H activation of light alkanes on MXenes predicted by hydrogen affinity

C-H activation of light alkanes is one of the most important reactions for a plethora of applications but requires catalysts to operate at feasible conditions. MXenes, a new group of two-dimensional materials, have shown great promise as heterogeneous catalysts for several applications. However, the catalytic activity of MXenes depends on the type and distribution of termination groups. Theoretically, it is desired to search for a relation between the catalytic activity and the termination configuration by employing a simple descriptor in order to avoid tedious activation energy calculations. Here, we show that MXenes are promising for splitting C-H bonds of light alkanes. Furthermore, we present how a quantitative descriptor - the hydrogen affinity - can be used to characterize the termination configuration of Ti₂CT_z (T = O, OH) MXenes, as well as the catalytic activity towards dehydrogenation reactions, using propane as model system. First-principles calculations reveal that the hydrogen affinity can be considered as an intrinsic property of O and OH terminated Ti₂C MXenes, in which the mean hydrogen affinity for the terminated Ti₂C MXenes is linearly correlated to the statistical average of their OH fraction. In addition, the C-H activation energies exhibit a strong scaling relationship to the hydrogen affinity. This quantity can therefore yield quick predictions of catalytic activity of terminated Ti₂C MXenes towards C-H activations, and even predict their chemical selectivity toward scissoring different C-H bonds. We believe that the hydrogen affinity will accelerate the discovery of further applications of the broad family of MXenes in heterogeneous catalysis.

Controlled-Atmosphere Flame Fusion Single-Crystal Growth of Non-Noble fcc, hcp, and bcc Metals Using Copper, Cobalt, and Iron

The growth of noble‐metal single crystals via the flame fusion method was developed in the 1980s. Since then, there have been no major advancements to the technique until the recent development of the controlled‐atmosphere flame fusion (CAFF) method to grow non‐noble Ni single crystals. Herein, we demonstrate the generality of this method with the first preparation of fcc Cu as well as the first hcp and bcc single crystals of Co and Fe, respectively. The high quality of the single crystals was verified using scanning electron microscopy and Laue X‐ray backscattering. Based on Wulff constructions, the equilibrium shapes of the single‐crystal particles were studied, confirming the symmetry of the fcc, hcp, and bcc single‐crystal lattices. The low cost of the CAFF method makes all kinds of high‐quality non‐noble single crystals independent of their lattice accessible for use in electrocatalysis, electrochemistry, surface science, and materials science.

Impact of strain, pressure, and electron correlation on magnetism and crystal structure of Mn2GaC from first-principles

The atomically laminated Mn2GaC has previously been synthesized as a heteroepitaxial thin film and found to be magnetic with structural changes linked to the magnetic anisotropy. Related theoretical studies only considered bulk conditions and thus neglected the influence from possible strain linked to the choice of substrate. Here we employ first principles calculations considering different exchange-correlation functionals (PBE, PW91, PBEsol, AM05, LDA) and effect from use of + U methods (or not) combined with a magnetic ground-state search using Heisenberg Monte Carlo simulations, to study influence from biaxial in-plane strain and external pressure on the magnetic and crystal structure of Mn2GaC. We find that PBE and PBE + U, with Ueff ≤ 0.25 eV, gives both structural and magnetic properties in quantitative agreement with available experimental data. Our results also indicate that strain related to choice of substrate or applied pressure is a route for accessing different spin configurations, including a ferromagnetic state. Moreover, the easy axis is parallel to the atomic planes and the magnetocrystalline anisotropy energy can be increased through strain engineering by expanding the in-plane lattice parameter a. Altogether, we show that a quantitative description of the structural and magnetic properties of Mn2GaC is possible using PBE, which opens the way for further computational studies of these and related materials.

Ultrafast assembly of swordlike Cu3(1,3,5-benzenetricarboxylate)n metal-organic framework crystals with exposed active metal sites

Owing to their large surface area and high uptake capacity, metal-organic frameworks (MOFs) have attracted considerable attention as potential materials for gas storage, energy conversion, and electrocatalysis. Various strategies have recently been proposed to manipulate the MOF surface chemistry to facilitate exposure of the embedded metal centers at the crystal surface to allow more effective binding of target molecules to these active sites. Nevertheless, such strategies remain complex, often requiring strict control over the synthesis conditions to avoid blocking pore access, reduction in crystal quality, or even collapse of the entire crystal structure. In this work, we exploit the hydrodynamics and capillary resonance associated with acoustically-driven dynamically spreading and nebulizing thin films as a new method for ultrafast synthesis of swordlike Cu₃(1,3,5-benzenetricarboxylate)_n (Cu-BTC) MOFs with unique monoclinic crystal structures (P2₁/n) distinct to that obtained via conventional bulk solvothermal synthesis, with 'swordlike' morphologies whose lengths far exceed their thicknesses. Through pulse modulation and taking advantage of the rapid solvent evaporation associated with the high nebulisation rates, we are also able to control the thicknesses of these large aspect ratio (width and length with respect to the thickness) crystals by arresting their vertical growth, which, in turn, allows exposure of the metal active sites at the crystal surface. An upshot of such active site exposure on the crystal surface is the concomitant enhancement in the conductivity of the MOF, evident from the improvement in its current density by two orders of magnitude.

Tactile sensory coding and learning with bio-inspired optoelectronic spiking afferent nerves

The integration and cooperation of mechanoreceptors, neurons and synapses in somatosensory systems enable humans to efficiently sense and process tactile information. Inspired by biological somatosensory systems, we report an optoelectronic spiking afferent nerve with neural coding, perceptual learning and memorizing capabilities to mimic tactile sensing and processing. Our system senses pressure by MXene-based sensors, converts pressure information to light pulses by coupling light-emitting diodes to analog-to-digital circuits, then integrates light pulses using a synaptic photomemristor. With neural coding, our spiking nerve is capable of not only detecting simultaneous pressure inputs, but also recognizing Morse code, braille, and object movement. Furthermore, with dimensionality-reduced feature extraction and learning, our system can recognize and memorize handwritten alphabets and words, providing a promising approach towards e-skin, neurorobotics and human-machine interaction technologies.

Predictive theoretical screening of phase stability for chemical order and disorder in quaternary 312 and 413 MAX phases

In this work we systematically explore a class of atomically laminated materials, Mn+1AXn (MAX) phases upon alloying between two transition metals, M' and M'', from groups III to VI (Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W). The materials investigated focus on so called o-MAX phases with out-of-plane chemical ordering of M' and M'', and their disordered counterparts, for A = Al and X = C. Through use of predictive phase stability calculations, we confirm all experimentally known phases to date, and also suggest a range of stable ordered and disordered hypothetical elemental combinations. Ordered o-MAX is favoured when (i) M' next to the Al-layer does not form a corresponding binary rock-salt MC structure, (ii) the size difference between M' and M'' is small, and (iii) the difference in electronegativity between M' and Al is large. Preference for chemical disorder is favoured when the size and electronegativity of M' and M'' is similar, in combination with a minor difference in electronegativity of M' and Al. We also propose guidelines to use in the search for novel o-MAX; to combine M' from group 6 (Cr, Mo, W) with M'' from groups 3 to 5 (Sc only for 312, Ti, Zr, Hf, V, Nb, Ta). Correspondingly, we suggest formation of disordered MAX phases by combing M' and M'' within groups 3 to 5 (Sc, Ti, Zr, Hf, V, Nb, Ta). The addition of novel elemental combinations in MAX phases, and in turn in their potential two-dimensional MXene derivatives, allow for property tuning of functional materials.

Flexible Freestanding MoO3-x -Carbon Nanotubes-Nanocellulose Paper Electrodes for Charge-Storage Applications

Herein, a one-step synthesis protocol was developed for synthesizing freestanding/flexible paper electrodes composed of nanostructured molybdenum oxide (MoO_3-x ) embedded in a carbon nanotube (CNT) and Cladophora cellulose (CC) matrix. The preparation method involved sonication of the precursors, nanostructured MoO_3-x , CNTs, and CC with weight ratios of 7:2:1, in a water/ethanol mixture, followed by vacuum filtration. The electrodes were straightforward to handle and possessed a thickness of approximately 12 μm and a mass loading of MoO_3-x -CNTs of approximately 0.9 mg cm^-2 . The elemental mapping showed that the nanostructured MoO_3-x was uniformly embedded inside the CNTs-CC matrix. The MoO_3-x -CNTs-CC paper electrodes featured a capacity of 30 C g^-1 , normalized to the mass of MoO_3-x -CNTs, at a current density of 78 A g^-1 (corresponding to a rate of approximately 210 C based on the MoO₃ content, assuming a theoretical capacity of 1339 C g^-1 ), and exhibited a capacity retention of 91 % over 30 000 cycles. This study paves the way for the manufacturing of flexible/freestanding nanostructured MoO_3-x -based electrodes for use in charge-storage devices at high charge/discharge rates.

Ti n+1C n MXenes with fully saturated and thermally stable Cl terminations

MXenes are a rapidly growing family of 2D materials that exhibit a highly versatile structure and composition, allowing for significant tuning of the materials properties. These properties are, however, ultimately limited by the surface terminations, which are typically a mixture of species, including F and O that are inherent to the MXene processing. Other and robust terminations are lacking. Here, we apply high-resolution scanning transmission electron microscopy (STEM), corresponding image simulations and first-principles calculations to investigate the surface terminations on MXenes synthesized from MAX phases through Lewis acidic melts. The results show that atomic Cl terminates the synthesized MXenes, with mere residual presence of other termination species. Furthermore, in situ STEM-electron energy loss spectroscopy (EELS) heating experiments show that the Cl terminations are stable up to 750 °C. Thus, we present an attractive new termination that widely expands the MXenes' functionalization space and enables new applications.

P14.18 Prognostic value of serial dynamic O-(2-[18F]-fluoroethyl)-L-tyrosine PET in patients with non-resectable malignant glioma undergoing chemoradiation

BACKGROUND

A complete resection of high-grade gliomas (HGG) is associated with improved survival, which, however, cannot be achieved in a considerable number of patients. We here evaluated the prognostic value of serial O-(2-[18F]-fluoroethyl)-L-tyrosine (FET) PET in patients with newly diagnosed, non-resectable astrocytic HGG undergoing chemoradiation with temozolomide.

MATERIAL AND METHODS

Serial dynamic FET PET scans were performed in 18 newly diagnosed patients with molecularly defined, non-resectable HGG at baseline and after chemoradiation (8±3 weeks). Both static (tumor/brain ratios, FET tumor volumes) and dynamic FET PET parameters (time-to-peak, slope), as well as MRI changes according to RANO criteria at first follow-up after chemoradiation (8±3 weeks), were obtained. The predictive ability of FET PET parameters and RANO criteria was evaluated with regard to the progression-free survival (PFS). Using ROC analyses, threshold values for FET PET parameters were obtained. Subsequently, univariate and multivariate survival analyses were performed to assess their predictive power for PFS.

RESULTS

ROC analysis revealed that the mean tumor/brain ratio (AUC, 0.84), FET tumor volume (AUC, 0.89), and slope (AUC, 0.72) at baseline were predictive for a prolonged PFS (9.3 vs. 5.7 months, P=0.05; 10.3 vs. 5.9 months; P=0.03; 13.5 vs. 6.2 months, P=0.02, respectively). Furthermore, FET tumor volume and slope remained significant in the multivariate survival analysis (both P<0.05). In contrast, relative changes of static or dynamic FET PET parameters at follow-up and MRI changes according to RANO criteria were not significant in this albeit small series of patients.

CONCLUSION

Results suggest that before initiation of chemoradiation FET PET parameters at baseline can be used to predict PFS in patients with non-resectable HGG.

A-51 A Novel Memory Catastrophizing Scale

Objective

A weak relationship exists between subjective memory complaints and performance on objective measures of learning and memory. A memory catastrophizing scale may explain this relationship. Our objective is to preliminarily explore a scale which assesses catastrophizing.

Method

The sample consisted of 46 patients (21 normal profiles, 25 mild cognitive impairment; mean age 56.1 ± 15.4) in a community-based neurology clinic. Each patient completed a clinical interview and comprehensive neuropsychological battery. The California Verbal Learning Test II (CVLT-II) was used to assess memory; the Beck Depression Inventory and Beck Anxiety Inventory were used to assess depressive and anxiety symptoms; a novel Memory Catastrophizing Scale (MCS) was used to assess subjective memory.

Results

A reliability analysis revealed internal consistency throughout the MCS (Cronbach’s alpha = .958). A bivariate correlation revealed that memory catastrophizing was significantly positively correlated with depressive (r = 0.623, p < 0.01) and anxiety (r = 0.433, p < 0.01) symptomology. Bivariate correlations demonstrated significant positive correlations between subjective memory complaints and memory (CVLT-II SDFR r = 0.502, p < .05; SDCR r = 0.434, p = 0.05; LDCR r = 0.512, p < .05) only among NP patients. The mean MCS score was 26 (±17), with a median of 17, a skewness of 0.40 and kurtosis of -0.77.

Conclusion

Our results support past research suggesting that there is a weak relationship between subjective and objective memory performances. Catastrophizing as a concept may explain the relationship between mood and performance on testing, especially amongst individuals without a known neurological pathology seeking treatment at a community-based neurological clinic.

Synthesis of (V2/3Sc1/3)2AlC i-MAX phase and V2-xC MXene scrolls

We report the synthesis and characterization of a new laminated i-MAX phase, (V2/3Sc1/3)2AlC, with in-plane chemical ordering between the M-elements. We also present evidence for the solid solution (V2-xScx)2AlC, where x ≤ 0.05. Chemical etching of the Al and Sc results in a two-dimensional (2D) MXene counterpart: V2-xC from the latter phase. Furthermore, etching with HF yields single-sheet MXene of flat morphology, while LiF + HCl gives MXene scrolls. We also show a 4× reduction in etching time for (V2-xScx)2AlC compared to V2AlC, suggesting that traces of Sc changes the phase stability, and make the material more susceptible to etching. The results show a path for improved control of MXene synthesis and morphology, which may be applicable also for other MAX/MXene systems.

On-Surface Synthesis of Ethynylene-Bridged Anthracene Polymers

Engineering low-band-gap π-conjugated polymers is a growing area in basic and applied research. The main synthetic challenge lies in the solubility of the starting materials, which precludes advancements in the field. Here, we report an on-surface synthesis protocol to overcome such difficulties and produce poly(p-anthracene ethynylene) molecular wires on Au(111). To this aim, a quinoid anthracene precursor with =CBr2 moieties is deposited and annealed to 400 K, resulting in anthracene-based polymers. High-resolution nc-AFM measurements confirm the nature of the ethynylene-bridge bond between the anthracene moieties. Theoretical simulations illustrate the mechanism of the chemical reaction, highlighting three major steps: dehalogenation, diffusion of surface-stabilized carbenes, and homocoupling, which enables the formation of an ethynylene bridge. Our results introduce a novel chemical protocol to design π-conjugated polymers based on oligoacene precursors and pave new avenues for advancing the emerging field of on-surface synthesis.

Electronic and optical characterization of 2D Ti2C and Nb2C (MXene) thin films

Two-dimensional (2D) transition metal carbides and/or nitrides (MXenes) are a new class of 2D materials, with extensive opportunities for property tailoring due to the numerous possibilities for varying chemistries and surface terminations. Here, Ti₂AlC and Nb₂AlC MAX phase epitaxial thin films were deposited on sapphire substrates by physical vapor deposition. The films were then etched in LiF/HCl solutions, yielding Li-intercalated, 2D Ti₂CT _z and Nb₂CT _z films, whose terminations, transport and optical properties were characterized. The former exhibits metallic conductivity, with weak localization below 50 K. In contrast, the Nb-based film exhibits an increase in resistivity with decreasing temperature from RT down to 40 K consistent with variable range hopping transport. The optical properties of both films were determined from spectroscopic ellipsometry in the 0.75 to 3.50 eV range. The results for Ti₂CT _z films confirm the metallic behavior. In contrast, no evidence of metallic behavior is observed for the Nb₂CT _z film. The present work therefore demonstrates that one fruitful approach to alter the electronic and optical properties of MXenes is to change the nature of the transition metal.

Generation of structured light by multilevel orbital angular momentum holograms

Structured light has been created by a myriad of near-and far-field techniques and has found both classical and quantum applications. In the case of orbital angular momentum (OAM), continuous spiral phase patterns in dynamic or geometric phase are often employed with the phase patterns existing across the entire transverse plane. Here, we exploit the uncertain relationship between OAM and angle in order to create structured OAM fields by using multilevel OAM holograms. We show theoretically and experimentally that only a multilevel angular phase contour in the near-field is needed to create structured OAM light in the far-field, exploiting the reciprocal nature of angular momentum and angle. We use this approach to demonstrate exotic 3D structured light control to show the Poynting vector's evolution in such fields and to highlight the physics underlying this phenomenon.

A Tungsten-Based Nanolaminated Ternary Carbide: (W,Ti)4C4- x

Nanolamellar transition metal carbides are gaining increasing interests because of the recent developments of their two-dimensional (2D) derivatives and promising performance for a variety of applications from energy storage, catalysis to transparent conductive coatings, and medicine. To develop more novel 2D materials, new nanolaminated structures are needed. Here we report on a tungsten-based nanolaminated ternary phase, (W,Ti)₄C_{4- x}, synthesized by an Al-catalyzed reaction of W, Ti, and C powders at 1600 °C for 4 h, under flowing argon. X-ray and neutron diffraction, along with Z-contrast scanning transmission electron microscopy, were used to determine the atomic structure, ordering, and occupancies. This phase has a layered hexagonal structure ( P6₃ /mmc) with lattice parameters, a = 3.00880(7) Å, and c = 19.5633(6) Å and a nominal chemistry of (W,Ti)₄C_{4- x} (actual chemistry, W_2.1(1)Ti_1.6(1)C_2.6(1)). The structure is comprised of layers of pure W that are also twin planes with two adjacent atomic layers of mixed W and Ti, on either side. The use of Al as a catalyst for synthesizing otherwise difficult to make phases, could in turn lead to the discovery of a large family of nonstoichiometric ternary transition metal carbides, synthesized at relatively low temperatures and shorter times.