Complementary and beneficial effects of Sb and Bi codoping in GeTe are shown to generate high thermoelectric figure of merit, zT, of 1.8 at 725 K in Ge1‑x‑y Bi x Sb y Te samples. Sb and Bi codoping in GeTe facilitates the valence band convergence enhancing the Seebeck coefficient as supported by density functional theoretical (DFT) calculations. Further, Sb and Bi codoping in GeTe releases the rhombohedral strain and increases its tendency to be cubic in structure, which ultimately enhances the valence band degeneracy. At the same time, Bi forms nanoprecipitates of size ∼5–20 nm in GeTe matrix and Sb doping increases solid solution point defects greatly, which altogether scatter low-to mid wavelength phonons and result in reduced lattice thermal conductivity down to 0.5 W/mK in the 300–750 K range.

M-N-C centers have garnered tremendous research attention due to a potential replacement to the Pt- group metal based cathode catalysts and is expected to be the integral part of the...

Rational design of efficient electrode materials for fuel cell, water oxidation, and the metal-air battery is now cutting–edge activity in renewable energy research. In this regard, tuning the activity at...

Combining atomically thin layers of van der Waals (vdW) materials in a chosen vertical sequence is an emerging route to create devices with desired functionalities. While this method aims to exploit the individual properties of partnering layers, strong interlayer coupling can significantly alter their electronic and optical properties.Here we explored the impact of the vdW epitaxy on electrical transport in atomically thin molybdenum disulfide (MoS 2 ) when it forms a vdW dimer with crystalline films of hexagonal boron nitride (hBN). We observe a thermal history-dependent long-term (over ∼40 h) current relaxation in the overlap region of MoS 2 /hBN heterostructures, which is absent in bare MoS 2 layers (or homoepitaxial MoS 2 /MoS 2 dimers) on the same substrate. Concurrent relaxation in the low-frequency Raman modes in MoS 2 in the heterostructure region suggests a slow structural relaxation between trigonal and octahedral polymorphs of MoS 2 as a likely driving mechanism that also results in inhomogeneous charge distribution in the MoS 2 layer. Our experiment yields an aspect of vdW heteroepitaxy that can be generic to electrical devices with atomically thin transition-metal dichalcogenides.

Simple, inexpensive, and scalable strategies for metal oxide thin film growth are critical for potential applications in the field of gas sensing. Here, we report a general method for the synthesis of free-standing oxide thin films via a one-step, surfactant-free hydrothermal reaction wherein the oxide film forms at the air–water interface. Using SnO2 and PdO as model systems, we show that the thin films, thus formed, have lateral dimensions of the order of centimeters and thickness of the order of tens of nanometers. Transmission electron microscopy (TEM) has been used to understand the growth mechanism of the films. On the basis of these studies, we propose that the metal oxide particles formed in the bulk of the solution move to the interface and get trapped to form a continuous, polycrystalline film. X-ray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) measurements have been performed to understand the structure, morphology, and thickness of the films. Thickness tunability by varying the precursor concentration has been explored, which in turn affects optical and gas sensing properties. Thin SnO2 films (30 nm) revealed an ultrasensitive response (R) of 25000% to 6 ppm of H2S at 150 °C while demonstrating 25 ppb (R = 19.3%) as the experimental lowest limit of detection. The selectivity of these nanostructured films toward H2S stands tall among the other interfering gases by exhibiting an ∼2 orders higher response magnitude. Furthermore, these thin films are highly stable at elevated temperatures.

Semiconducting nanowires with modulated structures are potential candidates for application in nanoelectronics and photonics devices and are crucial for the fundamental understanding of electron transport in quantum confined systems. Among these semiconductors, Te (having a low band gap of ∼0.32 eV) finds numerous applications in the field of optoelectronics, thermoelectrics, and memory devices. Te-based compounds like lead telluride, bismuth telluride, and antimony telluride have been extensively used as thermoelectric materials. Moreover, superlattice structures of semiconducting nanomaterials are known to show enhanced properties as compared to their individual counterparts. However, a simple and general scheme to achieve a superlattice 1-D nanostructure with a coherent interface is still challenging. Here, we demonstrate a facile wet chemical synthesis method for designing PbTe−Bi 2 Te 3 1D-superlattice nanostructure on Te nanowires. These superlattice nanowires are characterized using various electron microscopy techniques that reveal chemically distinct regions having PbTe and Bi 2 Te 3 phases with a coherent interface between them. The volume fractions of the PbTe and Bi 2 Te 3 phases in these nanowires can be easily tuned with changing the concentration of the Pb precursor and the addition rate of the reducing agent. The electrical transport measurement on these heterostructure nanowires indicates a rectifying behavior that can be useful for designing future optoelectronics devices. Further, a measured energy barrier of ∼0.1 ± 0.08 eV at the interface between the PbTe cube and the Bi 2 Te 3 wire using electrostatic force microscopy can be responsible for the observed nonlinearity in the transport character.

Au-Ag Nanostructures comprising of ~1 nm Ag nanoparticles embedded into an Au matrix show several unconventional optical, electric and magnetic properties. Here we review progress made towards the preparation of these materials as well as analysis of their structure. Further, electrical and magnetic transitions in these materials are discussed. Finally, we review the properties of these materials as revealed from optical and electron microscopic probes.

We describe the unusual dielectric properties of Au-Ag nanostructures at a single particle level using electron energy loss spectroscopy. It has been shown previously that these nanostructures deviate from their usual metallic characteristics of metallic Ag and Au. In particular certain variants of these materials appear to undergo a transition to an immeasurably low resistive state as well as a strong diamagnetic state that is not usually associated with Au and Ag themselves. More significantly these nanostructures exhibit absence of Mie like resonances associated with Au and Ag. Instead, these exhibit negligible optical absorption in the UV-VIS-NIR range. Here this unconventional electromagnetic response was probed at a single particle level. We find that the absence of dissipation is also reflected in the electron loss spectra. The lack of distinct electron energy loss features in particles with a known composition enables us to unambiguously assign these observations to actual particle properties. We tentatively interpret our observations as arising due to a reduction of free electron density in Au and Ag nanostructures. Further it was also shown that the conventional plasmonic modes can be recovered by altering material composition.