Effect of Carrier Localization on Electrical Transport and Noise at Individual Grain Boundaries in Monolayer MoS₂

Despite its importance in the large-scale synthesis of transition metal dichalcogenides (TMDC) molecular layers, the generic quantum effects on electrical transport across individual grain boundaries (GBs) in TMDC monolayers remain unclear. Here we demonstrate that strong carrier localization due to the increased density of defects determines both temperature dependence of electrical transport and low-frequency noise at the GBs of chemical vapor deposition (CVD)-grown MoS₂ layers. Using field effect devices designed to explore transport across individual GBs, we show that the localization length of electrons in the GB region is ∼30–70% lower than that within the grain, even though the room temperature conductance across the GB, oriented perpendicular to the overall flow of current, may be lower or higher than the intragrain region. Remarkably, we find that the stronger localization is accompanied by nearly 5 orders of magnitude enhancement in the low-frequency noise at the GB region, which increases exponentially when the temperature is reduced. The microscopic framework of electrical transport and noise developed in this paper may be readily extended to other strongly localized two-dimensional systems, including other members of the TMDC family

Anaerobe Syntrophic Co-culture-Mediated Green Synthesis of Ultrathin Niobium Carbide (NbC) Sheets for Flexoelectricity Generation

Niobium carbide (NbCx)-based materials have garnered significant attention in energy- and power-based applications. The physiochemistry-mediated preparation of two-dimensional (2D) NbC structures is often limited by extremely high-temperature and -pressure reaction conditions conjugated with toxic chemicals. In the present study, a unique biobased strategy, utilizing a solid–gas reaction, is developed, which involves the carburization of niobium salt (NbCl5)-based oxides using methane (CH4) and other metabolic gases produced by methanogen syntrophic culture. Thermodynamic calculations were performed to comprehend the reaction conditions of the biosystem during NbC formation. The bioprepared NbC sheets were found to be ∼10 nm thin and were studied for their potential in energy harvesting applications. The strain-induced charge generation was evaluated by fabricating a flexoelectric energy harvester with NbC sheets as a flexoelectric material. The maximum power output was ∼2.64 mW/m2 for 8.8 N applied force. We obtained clear evidence of flexoelectricity in NbC using Raman analysis. Finally, external pressure-, magnetic force-, and temperature-dependent responses were recorded to visualize the practical applications of NbC-based flexible flexoelectric nanogenerators in wearable electronics and sensing

Thermoelectricity Enhanced Electrocatalysis

We show that thermoelectric materials can function as electrocatalysts and use thermoelectric voltage generated to initiate and boost electrocatalytic reactions. The electrocatalytic activity is promoted by the use of nanostructured thermoelectric materials in a hydrogen evolution reaction (HER) by the thermoelectricity generated from induced temperature gradients. This phenomenon is demonstrated using two-dimensional layered thermoelectric materials Sb₂Te₃ and Bi_0.5Sb_1.5Te₃ where a current density approaching ∼50 mA/cm² is produced at zero potential for Bi_0.5Sb_1.5Te₃ in the presence of a temperature gradient of 90 °C. In addition, the turnover frequency reaches to 2.7 s^–1 at 100 mV under this condition which was zero in the absence of temperature gradient. This result adds a new dimension to the properties of thermoelectric materials which has not been explored before and can be applied in the field of electrocatalysis and energy generation

Sustainable Piezoelectric Energy Harvesting Using 3D Printing with Chicken Bone Extract

Animal waste, if not disposed of carefully, is a threat to the environment, as it may cause fouling and microorganism growth and can be a home for many diseases. Hence, proper waste management is required. One such abundantly found biowaste product is chicken bones, which are thrown into nature after the meat is consumed. However, this biowaste (chicken bone extract, CBE) can be utilized to make bioceramics in an efficient way without much labor and cost. Bioceramics made from natural sources such as chicken bones have chemical, physical, and biological similarities to the inorganic content of human bones and hence do not create any toxicity or harmful effects when used inside the human body. Bone, being a piezoelectric material, makes the healing of fractures faster (osteoconduction and osteoinduction) due to the electric field it generates. Hence, a piezoelectric device fabricated from natural CBE could be utilized for generating piezoelectricity to heal bones. The piezoelectric behavior of a CBE bioceramic material is studied for the first time by developing a device made via 3D printing. Piezoelectric studies were performed at various loads and tapping frequencies, and a maximum piezoelectric coefficient (d33) of ∼68.7 pC/N and electromechanical coupling of 0.17 were obtained, which are suitable for piezoelectric energy-harvesting applications. Normally, the lifetime of piezoelectric devices is low, and their disposal and recycling may also create health hazards. However, the current device made out of degradable natural CBE poses no environmental threat after disposal. This novel process opens up new opportunities and directions to rethink alternatives for piezoelectric materials that are used for sustainable energy harvesting

Thickness dependent nanoscale magnetism in two-dimensional manganese telluride (MnTe)

Magnetism from two-dimensional (2D) materials has received significant attention and admiration due to their unique electronic and magnetic properties owing to quantum confinement, such as spin-orbit coupling, magnetic anisotropy, and emergent magnetic orders, leading to behaviors and properties not observed in bulk materials. One of the crucial gaps that need to be addressed is deciphering the ordering of magnetic behavior with the thickness of manganese dichalcogenides, manganese telluride (MnTe). The present work explores the pivotal role of thickness in modulating the magnetic properties of 2D MnTe, obtained using liquid-phase exfoliation techniques. Intriguing magnetic and electronic properties have been observed in MnTe thinner than 5 nm. Our experimental findings and density functional theory (DFT) calculations revealed the transition from anti-ferromagnetic characteristics to ferromagnetic behavior for one to two layers and then back to anti-ferromagnetic behavior for thicknesses larger than 5 nm. These results demonstrate the existence of thickness-dependent transitions in magnetic ordering and anisotropy for the 2D materials. The experimental results, in conjunction with theoretical modeling, unravel useful insights into the implications of magnetic 2D MnTe for emerging technologies driven by nanoscale magnetism, such as spintronics and quantum computing. The outcomes from the present work open new possibilities for developing memory devices with enhanced functionality and efficiency.</p

Magnitude and Origin of Electrical Noise at Individual Grain Boundaries in Graphene

Grain boundaries (GBs) are undesired in large area layered 2D materials as they degrade the device quality and their electronic performance. Here we show that the grain boundaries in graphene which induce additional scattering of carriers in the conduction channel also act as an additional and strong source of electrical noise especially at the room temperature. From graphene field effect transistors consisting of single GB, we find that the electrical noise across the graphene GBs can be nearly 10 000 times larger than the noise from equivalent dimensions in single crystalline graphene. At high carrier densities (<i>n</i>), the noise magnitude across the GBs decreases as ∝1/<i>n</i>, suggesting Hooge-type mobility fluctuations, whereas at low <i>n</i> close to the Dirac point, the noise magnitude could be quantitatively described by the fluctuations in the number of propagating modes across the GB

Indentation Tests Reveal Geometry-Regulated Stiffening of Nanotube Junctions

Here we report a unique method to locally determine the mechanical response of individual covalent junctions between carbon nanotubes (CNTs), in various configurations such as “X”, “Y”, and “Λ”-like. The setup is based on <i>in situ</i> indentation using a picoindenter integrated within a scanning electron microscope. This allows for precise mapping between junction geometry and mechanical behavior and uncovers geometry-regulated junction stiffening. Molecular dynamics simulations reveal that the dominant contribution to the nanoindentation response is due to the CNT walls stretching at the junction. Targeted synthesis of desired junction geometries can therefore provide a “structural alphabet” for construction of macroscopic CNT networks with tunable mechanical response

Strain Rate Dependent Shear Plasticity in Graphite Oxide

Graphene oxide film is made of stacked graphene layers with chemical functionalities, and we report that plasticity in the film can be engineered by strain rate tuning. The deformation behavior and plasticity of such functionalized layered systems is dominated by shear slip between individual layers and interaction between functional groups. Stress–strain behavior and theoretical models suggest that the deformation is strongly strain rate dependent and undergoes brittle to ductile transition with decreasing strain rate

Synthesis of Low-Density, Carbon-Doped, Porous Hexagonal Boron Nitride Solids

Here, we report the scalable synthesis and characterization of low-density, porous, three-dimensional (3D) solids consisting of two-dimensional (2D) hexagonal boron nitride (h-BN) sheets. The structures are synthesized using bottom-up, low-temperature (∼300 °C), solid-state reaction of melamine and boric acid giving rise to porous and mechanically stable interconnected h-BN layers. A layered 3D structure forms due to the formation of h-BN, and significant improvements in the mechanical properties were observed over a range of temperatures, compared to graphene oxide or reduced graphene oxide foams. A theoretical model based on Density Functional Theory (DFT) is proposed for the formation of h-BN architectures. The material shows excellent, recyclable absorption capacity for oils and organic solvents

Thickness dependent tribological and magnetic behavior of two-dimensional cobalt telluride (CoTe2)

Two-dimensional (2D) layered transition-metal based tellurides (chalcogens) are known to harness their surface atoms’ characteristics to enhance topographical activities for energy conversion, storage, and magnetic applications. The gradual stacking of each sheet alters the surface atoms’ subtle features such as lattice expansion, leading to several phenomena and rendering tunable properties. Here, we have evaluated thickness- dependent mechanical properties (nanoscale mechanics, tribology, potential surface distributions, interfacial interaction) of 2D CoTe2sheets and magnetic behavior using surface probe techniques. The experimental observations are further supported and explained with theoretical investigations: density functional theory (DFT) and molecular dynamics (MD). The variation in properties observed in theoretical investigations unleashes the crucial role of crystal planes of the CoTe2. The presented results are beneficial in expanding the use of the 2D telluride family in flexible electronics, piezo sensors, tribo-generators, and next-generation memory devices.</p