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The discovery of another monoclinic polymorph in the niobium trisulfide system expands the structural possibilities for quasi-1D transition metal trichalcogenide materials. We describe here NbS3-VI prepared by chemical vapor transport (CVT) using ammonium chloride as the transport agent rather than the typical iodine or excess chalcogen. This example establishes precedent for transport agent control over CVT product polymorphism, thereby opening an alternative avenue for structural engineering. The single crystal x-ray diffraction structure of NbS3-VI shows that this polymorph unexpectedly incorporates features of both NbS3-IV and NbS3-V; specifically, NbS3-VI contains corrugated chains with paired Nb–Nb and uniform chains with unpaired, equidistant Nb centers. We also use single crystal x-ray diffraction to compare NbS3-VI with (Nb0.6Ti0.4)S3, which contains solely uniform chains with slightly shorter metal–metal distances than those of uniform NbS3-VI chains.

We conducted a tip-enhanced Raman scattering spectroscopy (TERS) and photoluminescence (PL) study of quasi-1D TaSe

The "leaky pipeline" of women in science, technology, engineering, and mathematics (STEM), which is especially acute for academic mothers, continues to be problematic as women face continuous cycles of barriers and obstacles to advancing further in their fields. The severity and prevalence of the COVID-19 pandemic both highlighted and exacerbated the unique challenges faced by female graduate students, postdocs, research staff, and principal investigators because of lockdowns, quarantines, school closures, lack of external childcare, and heightened family responsibilities, on top of professional responsibilities. This perspective provides recommendations of specific policies and practices that combat stigmas faced by women in STEM and can help them retain their careers. We discuss actions that can be taken to support women within academic institutions, journals, government/federal centers, university-level departments, and individual research groups. These recommendations are based on prior initiatives that have been successful in having a positive impact on gender equity─a central tenet of our postpandemic vision for the STEM workforce.

We report on switching among three charge-density-wave phases, commensurate, nearly commensurate, incommensurate, and the high-temperature normal metallic phase in thin-film 1T-TaS2 devices induced...

We report the polarization-dependent Raman spectra of exfoliated MoI3, a van der Waals material with a “true one-dimensional” crystal structure that can be exfoliated to individual atomic chains. The temperature evolution of several Raman features reveals an anomalous behavior suggesting a phase transition of magnetic origin. Theoretical considerations indicate that MoI3 is an easy-plane antiferromagnet with alternating spins along the dimerized chains and with inter-chain helical spin ordering. The calculated frequencies of phonons and magnons are consistent with the interpretation of the experimental Raman data. The obtained results shed light on the specifics of the phononic and magnonic states in MoI3 and provide a strong motivation for further study of this unique material with potential for future spintronic applications.

We report on the preparation of flexible polymer composite films with aligned metallic fillers composed of atomic chain bundles of quasi-one-dimensional (1D) van der Waals material, tantalum triselenide (TaSe3). The material functionality, embedded at the nanoscale level, is achieved by mimicking the design of an electromagnetic aperture grid antenna. The processed composites employ chemically exfoliated TaSe3 nanowires as the grid building blocks incorporated within the thin film. Filler alignment is achieved using the "blade coating" method. Measurements conducted in the X-band frequency range demonstrate that the electromagnetic transmission through such films can be varied significantly by changing the relative orientations of the quasi-1D fillers and the polarization of the electromagnetic wave. We argue that such polarization-sensitive polymer films with unique quasi-1D metallic fillers are applicable to advanced electromagnetic interference shielding in future communication systems.

Conducting electroactive polymers are promising candidates for next-generation sodium-ion batteries due to their environmentally benign properties, high stability, and low cost. In this work, polyaniline (PANI) nanofibers have been successfully prepared by interfacial polymerization and characterized using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The effect of initiator concentration and interfacial contact area on the yield and surface morphology of PANI nanofibers has been studied. The yield and nanofibrous structure of PANI are found to be directly proportional to the interfacial contact area and the concentration of initiator. PANI nanofibers prepared from 1 M ammonium persulfate (APS) in a container having highest interfacial area of 200 cm2 has the highest yield of 0.9 and uniform nanofibrous structure which is clear from SEM study. Preparation of PANI nanofibers and doping with sodium-ion salt is confirmed by FTIR spectroscopy. Sodium-ion battery prepared with doped PANI delivered a highest discharge capacity value of 112 mAh g−1 at 0.047 mA cm−2 during initial cycling. The rate capability tests indicated that after cycling at different C-rates, the cell regained its initial discharge capacity value of 123 mAh g−1 at 0.047 mA cm−2.

Proton radiation damage is an important failure mechanism for electronic devices in near-Earth orbits, deep space and high energy physics facilities. Protons can cause ionizing damage and atomic displacements, resulting in device degradation and malfunction. Shielding of electronics increases the weight and cost of the systems but does not eliminate destructive single events produced by energetic protons. Modern electronics based on semiconductors - even those specially designed for radiation hardness - remain highly susceptible to proton damage. Here we demonstrate that room temperature (RT) charge-density-wave (CDW) devices with quasi-two-dimensional (2D) 1T-TaS2 channels show remarkable immunity to bombardment with 1.8 MeV protons to a fluence of at least 10^14 H+cm^2. Current-voltage I-V characteristics of these 2D CDW devices do not change as a result of proton irradiation, in striking contrast to most conventional semiconductor devices or other 2D devices. Only negligible changes are found in the low-frequency noise spectra. The radiation immunity of these "all-metallic" CDW devices can be attributed to their two-terminal design, quasi-2D nature of the active channel, and high concentration of charge carriers in the utilized CDW phases. Such devices, capable of operating over a wide temperature range, can constitute a crucial segment of future electronics for space, particle accelerator and other radiation environments., 18 pages, 2 display items

The first direct AMS radiocarbon dating of two rock art motifs in separate rock shelters (VQ1 and VQ2) at the Viuda Quenzana (VQ) archaeological locality in Patagonia, has provided median probability ages of 3190 cal BP for two reddish dots, and 520 cal BP (1430 CE) for a pink negative hand. These ages are consistent with evidence of occupation of sites in the locality and in the nearby region during the later part of the Middle Holocene (8200–4200 cal BP) and Late Holocene (4200 cal BP to present), as indicated by ages for bones and charcoal from sediments in the VQ8 and VQ7 rockshelters, and the nearby La Martita 4 and La Gruta 1 and 3 rockshelters ranging from ca. 5470 to 305 cal BP (Rubinos Perez 2003; Franco et al. 2013; Brook et al. 2015). The pink hand is relatively recent, which supports the notion that such artwork continued through the Late Holocene despite changes in other artistic motifs. Characterization by Raman spectroscopy, powder x-ray diffraction, and high-resolution scanning electron microscopy with energy dispersive spectroscopy shows that: 1) hematite is the main pigment in both the dot and hand motifs, 2) the reddish dot paint includes a specific type of hematite, microplaty hematite, and 3) animal fat appears to have been added as a binder to the reddish dot paint. Thus, rock art paint production at VQ involved two distinct processes. One, used to paint dots, entailed mixing a mineral coloring substance (hematite) with an organic binder (animal fat), which was then applied to the rock substrate with a painting tool and/or fingers. The second process, used to produce the hand motif, entailed using a mineral coloring substance (hematite) with no binder (or with a binder that left little chemical trace), which was then applied to the rock substrate by spraying, probably with the mouth. Fil: Brook, George. University of Georgia; Estados Unidos Fil: Franco, Nora Viviana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto Multidisciplinario de Historia y Ciencias Humanas; Argentina Fil: Cherkinsky, Alexander. University of Georgia; Estados Unidos Fil: Acevedo, Agustín. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto Multidisciplinario de Historia y Ciencias Humanas; Argentina Fil: Fiore, Dánae. Asociación de Investigaciones Antropológicas; Argentina Fil: Pope, Timothy R.. University Of Georgia. Department Of Chemistry And Physics; Estados Unidos Fil: Weimar, Richard D.. University Of Georgia. Department Of Chemistry And Physics; Estados Unidos Fil: Neher, Gregory. University Of Georgia. Department Of Chemistry And Physics; Estados Unidos Fil: Evans, Hayden A.. University Of Georgia. Department Of Chemistry And Physics; Estados Unidos Fil: Salguero, Tina T.. University Of Georgia. Department Of Chemistry And Physics; Estados Unidos

We investigated low-frequency noise in two-dimensional (2D) charge density wave (CDW) systems, 1T-TaS2 thin films, as they were driven from the nearly commensurate (NC) to incommensurate (IC) CDW phases by voltage and temperature stimuli. This study revealed that noise in 1T-TaS2 has two pronounced maxima at the bias voltages, which correspond to the onset of CDW sliding and the NC-to-IC phase transition. We observed unusual Lorentzian features and exceptionally strong noise dependence on electric bias and temperature, leading to the conclusion that electronic noise in 2D CDW systems has a unique physical origin different from known fundamental noise types. We argue that noise spectroscopy can serve as a useful tool for understanding electronic transport phenomena in 2D CDW materials characterized by coexistence of different phases and strong pinning.

Quasi-1D van der Waals materials, such as transition metal trichalcogenides, have strong covalent bonds in one direction and weaker bonds in cross-plane directions. They can be prepared as crystalline nanowires or nanoribbons consisting of 1D atomic threads, i.e., chains. We have examined the current carrying capacity of ZrTe3 nanoribbons using a set of structures fabricated by the shadow mask method. The bulk crystals were synthesized by the chemical vapor transport method and exfoliated onto Si/SiO2 substrates. It was found that ZrTe3 nanoribbons reveal an exceptionally high current density, on the order of ~100 MA/cm2, at the peak of the stressing DC current. The low-frequency noise was of 1/ ${f}$ type near room temperature ( ${f}$ is the frequency). The noise amplitude scaled with the resistance, following the trend established for other low-dimensional materials. The high current density in ZrTe3 can be attributed to the single-crystal nature of quasi-1D van der Waals materials.

We describe the top-down nanostructuring of a metal boride using SrB6 as an example. To accomplish this transformation, we demonstrate (1) the direct lithiation of a metal boride using n-butyllithium and then (2) the reactive disassembly of Li-SrB6 into nanoparticles using water. The identity of the Li-SrB6 intermediate, a mixture of Li2B6, LixSr1-2xB6, and SrB6 phases, was established by powder X-ray diffraction (PXRD), solid-state 11B and 7Li NMR, transmission electron microscopy, selected-area electron diffraction, and scanning electron microscopy. The necessary 2Li+/Sr2+ substitution is enabled by cation mobility within the hexaboride lattice. The subsequent reaction with water results in Li2B6 decomposition and the release of

The $1{T}$ polytype of TaS2 exhibits voltage-triggered threshold switching as a result of a phase transition from nearly commensurate to incommensurate charge density wave states. Threshold switching, persistent above room temperature, can be utilized in a variety of electronic devices, e.g., voltage controlled oscillators. We evaluated the total-ionizing-dose response of thin film $1{T}$ -TaS2 at doses up to 1 Mrad (SiO2). The threshold voltage changed by less than 2% after irradiation, with persistent self-sustained oscillations observed through the full irradiation sequence. The radiation hardness is attributed to the high intrinsic carrier concentration of $1{T}$ -TaS2 in both of the phases that lead to threshold switching. These results suggest that charge density wave devices, implemented with thin films of $1{T}$ -TaS2, are promising for applications in high radiation environments.

A fourth polymorph of manganese phosphate, δ-Mn3(PO4)2, crystallizes in the monoclinic space group P21/c with lattice parameters a = 8.9234(6) A, b = 9.1526(6) A, c = 8.6587(5) A, β = 111.6670(10)°, V = 657.21(7) A3, and Z = 4. Its structure features planes of [MnO5] pentahedra edge- and corner-shared with [PO4] tetrahedra, resulting in a three-dimensional framework containing sub-nanometer channels. Both hydrothermal and solid-state synthesis routes can yield δ-Mn3(PO4)2. In one method, the hydrothermal treatment of Mn5(PO4)2(PO3OH)2·4H2O (hureaulite) at 250 °C for 1–6 h yields δ-Mn3(PO4)2 microcrystals; changing the precursor to Mn3(PO4)2·3H2O nanosheets leads to δ-Mn3(PO4)2 nanoplates. A time study of δ-Mn3(PO4)2 formation under hydrothermal conditions suggests a dissolution–nucleation mechanism. Alternatively, the solid state reaction of LiMnPO4 and β′-Mn3(PO4)2 in a 1:2 molar ratio under air-free conditions at 1000 °C produces δ-Mn3(PO4)2. Differential scanning calorimetry and variable temperature X-...

We report on switching among three charge-density-wave phases, commensurate, nearly commensurate, incommensurate, and the high-temperature normal metallic phase in thin-film 1T-TaS

We report results of investigation of the low-frequency electronic excess noise in quasi-1D nanowires of TaSe3 capped with quasi-2D h-BN layers. Semimetallic TaSe3 is a quasi-1D van der Waals material with exceptionally high breakdown current density. It was found that TaSe3 nanowires have lower levels of the normalized noise spectral density, SI/I2, compared to carbon nanotubes and graphene (I is the current). The temperature-dependent measurements revealed that the low-frequency electronic 1/f noise becomes the 1/f2 type as temperature increases to ∼400 K, suggesting the onset of electromigration (f is the frequency). Using the Dutta–Horn random fluctuation model of the electronic noise in metals, we determined that the noise activation energy for quasi-1D TaSe3 nanowires is approximately EP ≈ 1.0 eV. In the framework of the empirical noise model for metallic interconnects, the extracted activation energy, related to electromigration is EA = 0.88 eV, consistent with that for Cu and Al interconnects. Our...

We report 1–2 unit-cell-thick CaF2 nanosheets, which can be converted topochemically into LaF3–2xOx nanosheets that scroll spontaneously. The formation of CaF2 nanosheets is achieved through interlayer confinement and templating within CaSi2 during reaction with aqueous HF. The structure and morphology of these nanosheets are characterized by HRTEM, AFM, and powder XRD. Solid-state MAS and solution 19F NMR spectroscopies provide further information about interstitial fluoride sites within CaF2 nanosheets as well as help identify side products of the CaSi2 + HF reaction. CaF2 nanosheets react with lanthanide salts at room temperature to yield nanostructured hexagonal LnF3 (Ln = Ce, Pr, Nd, Sm, Eu), orthorhombic LnF3 (Ln = Gd, Dy, Ho, Er, Yb), and cubic YbF3–x products. Furthermore, the reaction of CaF2 nanosheets with lanthanum salts is unique in producing LaF3–2xOx. The evidence for this composition includes powder XRD, EDS, XPS, and 19F NMR data. The structure of LaF3–2xOx differs from hexagonal LaF3 onl...

Polymer composite films containing fillers comprising quasi-1D van der Waals materials, specifically transition metal trichalcogenides with 1D structural motifs that enable their exfoliation into bundles of atomic threads, are reported. These nanostructures are characterized by extremely large aspect ratios of up to ≈106 . The polymer composites with low loadings of quasi-1D TaSe3 fillers (

We report results regarding the electron transport in vertical quasi-two-dimensional (2D) layered 1T-TaS 2 charge-density-wave (CDW) devices. The low-frequency noise spectroscopy was used as a tool to study changes in the cross-plane electrical characteristics of the quasi-2D material below room temperature. The noise spectral density revealed strong peaks - changing by more than an order-of-magnitude - at the temperatures closely matching the electrical resistance steps. Some of the noise peaks appeared below the temperature of the commensurate to nearly-commensurate CDW transition, possibly indicating the presence of the debated hidden phase transitions. These results confirm the potential of the noise spectroscopy for investigations of electron transport and phase transitions in novel materials.

We describe the low-frequency current fluctuations, i.e. electronic noise, in quasi-one-dimensional ZrTe3 van der Waals nanoribbons, which have recently attracted attention owing to their extraordinary high current carrying capacity. Whereas the low-frequency noise spectral density, SI/I2, reveals 1/f behavior near room temperature, it is dominated by the Lorentzian bulges of the generation-recombination noise at low temperatures (I is the current and f is the frequency). Unexpectedly, the corner frequency of the observed Lorentzian peaks shows strong sensitivity to the applied source-drain bias. This dependence on electric field can be explained by the Frenkel-Poole effect in the scenario where the voltage drop happens predominantly on the defects, which block the quasi-1D conduction channels. We also have found that the activation energy of the characteristic frequencies of the G-R noise in quasi-1D ZrTe3 is defined primarily by the temperature dependence of the capture cross-section of the defects rather than by their energy position. These results are important for the application of quasi-1D van der Waals materials in ultimately downscaled electronics.

Bulk 1T-TaSe2 exhibits unusually high charge density wave (CDW) transition temperatures of 600 and 473 K below which the material exists in the incommensurate (I-CDW) and the commensurate (C-CDW) charge-density-wave phases, respectively. The (13)(1/2) × (13)(1/2) C-CDW reconstruction of the lattice coincides with new Raman peaks resulting from zone-folding of phonon modes from middle regions of the original Brillouin zone back to Γ. The C-CDW transition temperatures as a function of film thickness are determined from the evolution of these new Raman peaks, and they are found to decrease from 473 to 413 K as the film thicknesses decrease from 150 to 35 nm. A comparison of the Raman data with ab initio calculations of both the normal and C-CDW phases gives a consistent picture of the zone-folding of the phonon modes following lattice reconstruction. The Raman peak at ∼154 cm(-1) originates from the zone-folded phonons in the C-CDW phase. In the I-CDW phase, the loss of translational symmetry coincides with a strong suppression and broadening of the Raman peaks. The observed change in the C-CDW transition temperature is consistent with total energy calculations of bulk and monolayer 1T-TaSe2.

We review results of our studies of the low-frequency electronic noise in quasi-1D TaSe 3 nanowires of. The semi-metallic TaSe 3 is a quasi-1D van der Waals material with an exceptionally high breakdown current density. Our noise studies showed that TaSe 3 nanowires have lower levels of the normalized noise spectral density, S I /I2, compared to carbon nanotubes and graphene. The temperature-dependent measurements revealed that the low-frequency 1/f noise becomes the 1/f2-type as temperature increases to ∼400 K, suggesting the onset of electromigration. Using the Dutta-Horn random fluctuation model of the electronic noise, we determined that the noise activation energy for quasi-1D TaSe 3 nanowires is approximately E P ≈1.0 eV. From the empirical noise model for interconnects, the extracted activation energy, related to electromigration, is E A =0.88 eV, consistent with that for Cu and Al interconnects. Our results suggest that TaSe 3 nanowires and similar systems have potential for ultimately downscaled local interconnect applications.

Nanosheets of Bi2WO6 with lateral dimensions of 1–2 μm and thicknesses of 5–15 nm were prepared using Cs4W11O362− nanosheets as the tungsten oxide precursor and lateral template. The formation of these nanosheets was followed by electron microscopy and powder X-ray diffraction techniques. The isolated Bi2WO6 nanosheet product was characterized with respect to structure, morphology, spectroscopic properties, and optical properties. The bandgap energy of Bi2WO6 nanosheets is relatively large at ∼3.1 eV. The chromism of these sheets with respect to UV irradiation and Li+ intercalation was examined in detail. The UV-induced photochromism of dispersed Bi2WO6 nanosheets is highly dependent on the solvent environment, and the initial color change from white to black is reversible. The photochromic properties of “flowerlike” and single crystal Bi2WO6 were evaluated as well. Another color change, pale yellow to brown-black, occurred when lithium ions were intercalated into the Bi2WO6 lattice using n-butyl lithium. Reaction of lithiated Bi2WO6 with water yielded nanofragments of Bi2WO6 rather than nanosheets.

The colored component of several important ancient pigments, including Egyptian blue and Han blue, are based on alkali earth copper tetrasilicate materials. In recent work, we have found that these layered materials can be chemically exfoliated into their constituent monolayers to provide alkali earth copper tetrasilicate nanosheets—defined by nanometer thickness and lateral dimensions that are on the order of several microns. The facile exfoliation of these materials into nanosheets is especially surprising in view of their long history on artifacts under a variety of environmental conditions, and we have examined the issue of whether archaeological samples are affected by this exfoliation mechanism. We have characterized the properties of these nanosheets by an array of analytical techniques, including powder x-ray diffraction, photoluminescence measurements, and Raman spectroscopy. In all cases, we observe differences between nanosheet and bulk samples that originate from the loss of coupling between layers when going from three-dimensional to two- dimensional structures. Both CaCuSi4O10 nanosheets (derived from Egyptian blue) and BaCuSi4O10 nanosheets (derived from Han blue) have strong near-infrared luminescence properties like their bulk counterparts, yet they are amenable to modern solution processing methods. We have demonstrated ink jet printing with CaCuSi4O10 nanosheet inks, as well as the fabrication of nanosheet-based papers. Potential applications for these materials include NIR-based biomedical imaging and security inks.

We report results of investigation of the low-frequency electronic excess noise in quasi-1D nanowires of TaSe

The continuous downscaling of interconnect dimensions in combination with the introduction of low-k dielectrics has increased the number of heat dissipation, integration and reliability challenges in modern electronics. As a result, there is a strong need for new materials that have high current-carrying capacity for applications as nanoscale interconnects. In this presentation, we show that quasi-one-dimensional (1D) van der Waals metals such as TaSe3 have excellent breakdown current density exceeding that of 5 MA/cm2. This value is above that currently achievable in conventional copper or aluminum wires. The quasi-1D van der Waals materials are characterized by strong bonds along one dimension and weak van der Waals bonds along two other dimensions. The material for this study was grown by the chemical vapor transport (CVT) method. Both mechanical and chemical exfoliation methods were used to fabricate nanowires with lateral dimensions below 100 nm. The dimensions of the quasi-1D nanowires were verified with scanning electron microscopy (SEM) and atomic force microscopy (AFM). The metal (Ti/Au) contacts for the electrical characterization were deposited using electron beam evaporation (EBE). The measurements were conducted on a number of prototype interconnects with multiple electric contacts to ensure reproducibility. The obtained results suggest that quasi-1D van der Waals metals present a feasible alternative to conventional copper interconnects in terms of the current-carrying capacity and the breakdown current-density. This work was supported, in part, by the SRC and DARPA through STARnet Center for Function Accelerated nanoMaterial Engineering (FAME).

We report on the current-carrying capacity of the nanowires made from the quasi-1D van der Waals metal tantalum triselenide capped with quasi-2D boron nitride. The chemical vapor transport method followed by chemical and mechanical exfoliation were used to fabricate the mm-long TaSe3 wires with the lateral dimensions in the 20 to 70 nm range. Electrical measurements establish that the TaSe3/h-BN nanowire heterostructures have a breakdown current density exceeding 10 MA cm(-2)-an order-of-magnitude higher than that for copper. Some devices exhibited an intriguing step-like breakdown, which can be explained by the atomic thread bundle structure of the nanowires. The quasi-1D single crystal nature of TaSe3 results in a low surface roughness and in the absence of the grain boundaries. These features can potentially enable the downscaling of the nanowires to lateral dimensions in a few-nm range. Our results suggest that quasi-1D van der Waals metals have potential for applications in the ultimately downscaled local interconnects.

Layered heterostructures containing graphene oxide (GO) nanosheets and 20-35 nm bimetal coatings can detach easily from a Si substrate upon sonication-spontaneously forming freestanding, micrometer-sized scrolls with GO on the outside-due to a combination of material stresses and weak bonding between GO layers. Simple procedures can tune the scroll diameters by varying the thicknesses of the metal films, and these results are confirmed by both experiment and modeling. The selection of materials determines the stresses that control the rolling behavior, as well as the functionality of the structures. In the GO/Ti/Pt system, the Pt is located within the interior of the scrolls, which can become self-propelled microjet engines through O2 bubbling when suspended in aqueous H2O2.

a b s t r a c t Electrically conductive and hydrophilic coatings for proton exchange membrane fuel cell (PEMFC) stain- less steel bipolar plates have been developed in order to minimize voltage losses at the plate and gas diffusion layer (GDL) interface and facilitate liquid water transport in plate channels for efficient stack operation. The coatings are based on a multifunctional silane, 1,2-bis(triethoxysilyl)ethane (BTSE), mixed with conductive, hydrophilic carbon black. Vulcan ® XC72 carbon black was modified with either polar phenylsulfonic acid (PSA) or carboxylic acid (COOH) groups to increase hydrophilic character and wet- ting behavior. Wetting and electrical contact resistance performance was compared with coatings based on nano-particle titania and silica. These conductive silane and carbon composite coating precursors are conveniently formulated in alcohol solution for scalable application via spray coating. Cured films exhibit negligible contact resistance increase (

A graphene transistor integrated on-chip on a hexagonal boron nitride-capped TaS2 layer provides a voltage-tunable, low-resistance load for controlling a TaS2 metal–insulator transition, enabling a compact voltage-controlled oscillator operating at room temperature. The charge-density-wave (CDW) phase is a macroscopic quantum state consisting of a periodic modulation of the electronic charge density accompanied by a periodic distortion of the atomic lattice in quasi-1D or layered 2D metallic crystals1,2,3,4. Several layered transition metal dichalcogenides, including 1T-TaSe2, 1T-TaS2 and 1T-TiSe2 exhibit unusually high transition temperatures to different CDW symmetry-reducing phases1,5,6. These transitions can be affected by the environmental conditions, film thickness and applied electric bias1. However, device applications of these intriguing systems at room temperature or their integration with other 2D materials have not been explored. Here, we demonstrate room-temperature current switching driven by a voltage-controlled phase transition between CDW states in films of 1T-TaS2 less than 10 nm thick. We exploit the transition between the nearly commensurate and the incommensurate CDW phases, which has a transition temperature of 350 K and gives an abrupt change in current accompanied by hysteresis. An integrated graphene transistor provides a voltage-tunable, matched, low-resistance load enabling precise voltage control of the circuit. The 1T-TaS2 film is capped with hexagonal boron nitride to provide protection from oxidation. The integration of these three disparate 2D materials in a way that exploits the unique properties of each yields a simple, miniaturized, voltage-controlled oscillator suitable for a variety of practical applications.

Experimental approaches for altering the thermodynamics and kinetics of light element hydride systems are discussed. Equilibrium hydrogen pressures and reaction enthalpies can be varied with additives that form new alloy or compound phases upon dehydrogenation. The formation of new phases lowers the dehydrogenated state enthalpy and effectively destabilizes the component hydrides. This strategy is illustrated for LiBH 4 destabilized by MgH 2 , MgF 2 , MgS, and MgSe. The slow rates of hydrogen exchange in light element hydrides can be improved with catalysts and by reducing diffusion distances to the nanometer scale. The catalytic effects of a variety of transition metal sources on hydrogen exchange in the LiBH 4 /MgH 2 system are described. The effects of reduced diffusion distances are illustrated using LiBH 4 incorporated into a nanoporous carbon aerogel.

The decomposition of a series of ruthenium metathesis catalysts has been examined using methylidene species as model complexes. All of the phosphine-containing methylidene complexes decomposed to generate methylphosphonium salts, and their decomposition routes followed first-order kinetics. The formation of these salts in high conversion, coupled with the observed kinetic behavior for this reaction, suggests that the major decomposition pathway involves nucleophilic attack of a dissociated phosphine on the methylidene carbon. This mechanism also is consistent with decomposition observed in the presence of ethylene as a model olefin substrate. The decomposition of phosphine-free catalyst (H_2IMes)(Cl)_2Ru CH(2-C_6H_4-O-i-Pr) (H_2IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) with ethylene was found to generate unidentified ruthenium hydride species. The novel ruthenium complex (H_2IMes)(pyridine)_3(Cl)_2Ru, which was generated during the synthetic attempts to prepare the highly unstable pyridine-based methylidene complex (H_2IMes)(pyridine)_2(Cl)_2Ru CH_2, is also reported.

We describe the first hydrothermal synthesis of CaCuSi4 O10 as micron-scale clusters of thin platelets, distinct from morphologies generated under salt-flux or solid-state conditions. The hydrothermal reaction conditions are surprisingly specific: too cold, and instead of CaCuSi4 O10 , a porous calcium copper silicate forms; too hot, and calcium silicate (CaSiO3 ) forms. The precursors also strongly impact the course of the reaction, with the most common side product being sodium copper silicate (Na2 CuSi4 O10 ). Optimized conditions for hydrothermal CaCuSi4 O10 formation from calcium chloride, copper(II) nitrate, sodium silicate, and ammonium hydroxide are 350 °C at 3000 psi for 72 h; at longer reaction times, competitive delamination and exfoliation causes crystal fragmentation. These results illustrate that CaCuSi4 O10 is an even more unique material than previously appreciated.

We describe monolayer nanosheets of calcium copper tetrasilicate, CaCuSi(4)O(10), which have strong near-IR luminescence and are amenable to solution processing methods. The facile exfoliation of bulk CaCuSi(4)O(10) into nanosheets is especially surprising in view of the long history of this material as the colored component of Egyptian blue, a well-known pigment from ancient times.

In a visualized example of the ancient past connecting with modern times, we describe the preparation and exfoliation of CaCuSi4O10 and BaCuSi4O10, the colored components of the historic Egyptian blue and Han blue pigments. The bulk forms of these materials are synthesized by both melt flux and solid-state routes, which provide some control over the crystallite size of the product. The melt flux process is time intensive, but it produces relatively large crystals at lower reaction temperatures. In comparison, the solid-state method is quicker yet requires higher reaction temperatures and yields smaller crystallites. Upon stirring in hot water, CaCuSi4O10 spontaneously exfoliates into monolayer nanosheets, which are characterized by TEM and PXRD. BaCuSi4O10 on the other hand requires ultrasonication in organic solvents to achieve exfoliation. Near infrared imaging illustrates that both the bulk and nanosheet forms of CaCuSi4O10 and BaCuSi4O10 are strong near infrared emitters. Aqueous CaCuSi4O10 and BaCuSi4O10 nanosheet dispersions are useful because they provide a new way to handle, characterize, and process these materials in colloidal form.