Quantum Composites with Charge-Density-Wave Fillers.

A unique class of advanced materials-quantum composites based on polymers with fillers composed of a van der Waals quantum material that reveals multiple charge-density-wave quantum condensate phases-is demonstrated. Materials that exhibit quantum phenomena are typically crystalline, pure, and have few defects because disorder destroys the coherence of the electrons and phonons, leading to collapse of the quantum states. The macroscopic charge-density-wave phases of filler particles after multiple composite processing steps are successfully preserved in this work.

Electrical Gating of the Charge-Density-Wave Phases in Two-Dimensional -BN/1T-TaS Devices.

We report on the electrical gating of the charge-density-wave phases and current in -BN-capped three-terminal 1T-TaS heterostructure devices. It is demonstrated that the application of a gate bias can shift the source-drain current-voltage hysteresis associated with the transition between the nearly commensurate and incommensurate charge-density-wave phases. The evolution of the hysteresis and the presence of abrupt spikes in the current while sweeping the gate voltage suggest that the effect is electrical rather than self-heating.

Metallic semiconducting properties of quasi-one-dimensional tantalum selenide van der Waals nanoribbons.

We conducted a tip-enhanced Raman scattering spectroscopy (TERS) and photoluminescence (PL) study of quasi-1D TaSe nanoribbons exfoliated onto gold substrates. At a selenium deficiency of ∼ 0.25 (Se/Ta = 2.

Charge-Density-Wave Thin-Film Devices Printed with Chemically Exfoliated 1T-TaS Ink.

We report on the preparation of inks containing fillers derived from quasi-two-dimensional charge-density-wave materials, their application for inkjet printing, and the evaluation of their electronic properties in printed thin-film form. The inks were prepared by liquid-phase exfoliation of CVT-grown 1T-TaS crystals to produce fillers with nm-scale thickness and μm-scale lateral dimensions. Exfoliated 1T-TaS was dispersed in a mixture of isopropyl alcohol and ethylene glycol to allow fine-tuning of filler particles thermophysical properties for inkjet printing.

Turning the Tide for Academic Women in STEM: A Postpandemic Vision for Supporting Female Scientists.

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.

Electromagnetic-Polarization-Selective Composites with Quasi-1D Van der Waals Fillers: Nanoscale Material Functionality That Mimics Macroscopic Systems.

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 (TaSe). 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 TaSe nanowires as the grid building blocks incorporated within the thin film.

Electrically Insulating Flexible Films with Quasi-1D van der Waals Fillers as Efficient Electromagnetic Shields in the GHz and Sub-THz Frequency Bands.

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 ≈10 . The polymer composites with low loadings of quasi-1D TaSe fillers (<3 vol%) reveal excellent electromagnetic interference shielding in the X-band GHz and extremely high frequency sub-THz frequency ranges, while remaining DC electrically insulating.

Bias-Voltage Driven Switching of the Charge-Density-Wave and Normal Metallic Phases in 1T-TaS Thin-Film Devices.

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 devices induced by application of an in-plane bias voltage. The switching among all phases has been achieved over a wide temperature range, from 77 to 400 K. The low-frequency electronic noise spectroscopy has been used as an effective tool for monitoring the transitions, particularly the switching from the incommensurate charge-density-wave phase to the normal metal phase.

Unique features of the generation-recombination noise in quasi-one-dimensional van der Waals nanoribbons.

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.

Low-Frequency Current Fluctuations and Sliding of the Charge Density Waves in Two-Dimensional Materials.

We investigated low-frequency noise in two-dimensional (2D) charge density wave (CDW) systems, 1 T-TaS 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 1 T-TaS 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.

Nanostructuring of Strontium Hexaboride via Lithiation.

We describe the top-down nanostructuring of a metal boride using SrB 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-SrB into nanoparticles using water. The identity of the Li-SrB intermediate, a mixture of LiB, LiSrB, and SrB phases, was established by powder X-ray diffraction (PXRD), solid-state B and Li NMR, transmission electron microscopy, selected-area electron diffraction, and scanning electron microscopy.

Low-Frequency Electronic Noise in Quasi-1D TaSe van der Waals Nanowires.

We report results of investigation of the low-frequency electronic excess noise in quasi-1D nanowires of TaSe capped with quasi-2D h-BN layers. Semimetallic TaSe is a quasi-1D van der Waals material with exceptionally high breakdown current density. It was found that TaSe nanowires have lower levels of the normalized noise spectral density, S/I, compared to carbon nanotubes and graphene (I is the current).

Breakdown current density in h-BN-capped quasi-1D TaSe3 metallic nanowires: prospects of interconnect applications.

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.

A charge-density-wave oscillator based on an integrated tantalum disulfide-boron nitride-graphene device 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 crystals. Several layered transition metal dichalcogenides, including 1T-TaSe, 1T-TaS and 1T-TiSe exhibit unusually high transition temperatures to different CDW symmetry-reducing phases. These transitions can be affected by the environmental conditions, film thickness and applied electric bias.

Hydrothermal Formation of Calcium Copper Tetrasilicate.

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 ).

Exfoliation of Egyptian Blue and Han Blue, two alkali earth copper silicate-based pigments.

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.

Nanoscience of an ancient pigment.

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.

Nanostructured Scrolls from Graphene Oxide for Microjet Engines.

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.

Decomposition of ruthenium olefin metathesis catalysts.

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.