Electronic structure of Pr2MnNiO6 from x-ray photoemission, absorption and density functional theory

The electronic structure of double perovskite Pr2MnNiO6 is studied using core x-ray photoelectron spectroscopy and x-ray absorption spectroscopy. The 2p x-ray absorption spectra show that Mn and Ni are in 2+ and 4+ states respectively. Using charge transfer multiplet analysis of Ni and Mn 2p XPS spectra, we find charge transfer energies {\Delta} of 3.5 and 2.5 eV for Ni and Mn respectively. The ground state of Ni2+ and Mn4+ reveal a higher d electron count of 8.21 and 3.38 respectively as compared to the atomic values of 8.00 and 3.00 respectively thereby indicating the covalent nature of the system. The O 1s edge absorption spectra reveal a band gap of 0.9 eV which is comparable to the value obtained from first principle calculations for U-J >= 2 eV. The density of states clearly reveal a strong p-d type charge transfer character of the system, with band gap proportional to average charge transfer energy of Ni2+ and Mn4+ ions.Comment: 18 pages, 9 figure

Enhanced Mechanical and Antibacterial Properties of Nanocomposites Based on Poly(vinyl Alcohol) and Biopolymer-Derived Reduced Graphene Oxide

Functionalized graphene-polymer nanocomposites have gained significant attention for their enhanced mechanical, thermal, and antibacterial properties, but the requirement of multi-step processes or hazardous reducing agents to functionalize graphene limits their current applications. Here, we present a single-step synthesis of thermally reduced graphene oxide (TrGO) based on shellac, which is a low-cost biopolymer that can be employed to produce poly(vinyl alcohol) (PVA)/TrGO nanocomposites (PVA-TrGO). The concentration of TrGO varied from 0.1 to 2.0 wt.%, and the critical concentration of homogeneous TrGO dispersion was observed to be 1.5 wt.%, below which strong interfacial molecular interactions between the TrGO and the PVA matrix resulted in improved thermal and mechanical properties. At 1.5 wt.% filler loading, the tensile strength and modulus of the PVA-TrGO nanocomposite were increased by 98.7% and 97.4%, respectively, while the storage modulus was increased by 69%. Furthermore, the nanocomposite was 96% more effective in preventing bacterial colonization relative to the neat PVA matrix. The present findings indicate that TrGO can be considered a promising material for potential applications in biomedical devices

Low-cost and Fast-response Resistive Humidity Sensor Comprising Biopolymer-derived Carbon Thin Film and Carbon Microelectrodes

In this study, we present a highly responsive room-temperature resistive humidity sensor based on a shellac-derived carbon (SDC) active film deposited on sub-micrometer-sized carbon interdigitated electrodes (cIDEs). This monolithic carbon-based sensor demonstrates excellent linear relationship with humidity and ohmic contact between the active carbon film and carbon electrodes, which results in low noise and low power consumption (similar to 1 mW). The active SDC film is synthesized by a single-step thermal process, wherein the temperature is found to control the amount of oxygen functional moieties of the SDC film, thereby providing an efficient means to optimize the sensor response time, recovery time, and sensitivity. This SDC-cIDEs-based humidity sensor exhibits an excellent dynamic range (0%-90% RH), a large dynamic response (50%), and high sensitivity (0.54/% RH). In addition, the two-dimensional feature (thickness similar to 10 nm) of the SDC film enables a swift absorption/desorption equilibrium, leading to fast response (similar to 0.14 s) and recovery (similar to 1.7 s) under a humidity range of 0%-70% RH. Furthermore, the thin SDC-based sensor exhibited excellent selectivity to humidity from various gases, which in combination with its fast response/recovery promises it application for an instant calibration tool for gas sensors

Ecofriendly Polymer-Graphene-Based Conductive Ink for Multifunctional Printed Electronics

The ongoing research on printed and flexible electronics is primarily focused on conductive three-dimensional (3D) print patterning. However, due to the nonhomogeneous distribution of conductive elements in a polymer matrix and their tendency to shrink, 3D-printed patterns often suffer from low-printing accuracies and poor mechanical and electrical properties. Here, poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) (PVBVA) is reinforced with microwave-exfoliated graphene to develop a conductive ink for 3D printing. Compared with the pure PVBVA patterns, the PVBVA/graphene patterns exhibited a high-electrical conductivity, a twofold enhancement in tensile strength, an improved printing accuracy, and a high stability because of the graphene addition. The PVBVA/graphene inks flowed well during the printing; loading of up to 0.1 wt% graphene in the PVBVA gel resulted in notable changes in the rheological properties of the ink. The printed conductive patterns showed a high flexibility suitable for wearable electronics. Additionally, multifunctional electronic operations such as photoinduced heating, temperature sensing, and motion sensing are possible, and this study may pave the way for the development of a new class of smart wearable electronics for healthcare and soft robotics

Low-cost synthesis of high quality graphene oxide with large electrical and thermal conductivities

A simple and cost-effective method for synthesizing high quality thermally reduced graphene oxide (TrGO) thin films using Shellac, is presented. The synthesis temperature ranges from 550 degrees C to 900 degrees C, and is the sole control parameter to obtain a carbon content as high as 97 atomic percentage. For TrGO synthesized at 900 degrees C, its XPS, Raman, and TEM data indicate a large portion of sp(2) hybridized carbon atoms and large crystal sizes (similar to 1 mu m), which resulted in very high electrical and cross-plane thermal conductivities, 2488 S/cm and 1.3 W/m-K, respectively. Furthermore, this high electrical conductivity of TrGO was observed to remain unaffected under mechanical stress 10 times higher than that completely broke solution-processed reduced graphene oxide (rGO) films, promising its potential for robust, transparent, and cost-effective conductive coating. (C) 2021 Elsevier B.V. All rights reserved

Ultrathin, Breathable, Permeable, and Skin‐Adhesive Charge Storage Electronic Tattoos Based on Biopolymer Nanofibers and Carbon Nanotubes

Abstract Ultrathin, breathable, and skin‐compatible epidermal electronics are attractive for wearable and implantable healthcare and biomedical applications. However, materializing and integrating all electronic components on ultrathin platforms is still challenging. Here, a charge‐storing electronic tattoo (E‐tattoo) device with ultrathin, breathable, and skin‐compatible properties is reported. Silk protein nanofibers (SNFs) and carbon nanotubes (CNTs) form the top and bottom electrodes that sandwich the intermediate dielectric layer fabricated using poly(vinyl alcohol) nanofibers. The E‐tattoo capacitors on the deformed skin, show excellent mechanical and electrical stability, and 60 µm‐thick capacitors exhibit frequency‐dependent capacitances (up to 350 pF at 5 kHz) and capability for memory operation. Mechanical bending induces capacitance change, which increases as the bending radius is decreased, indicating mechanical sensing capability of the E‐tattoo. SNF/CNT‐based triboelectric nanogenerator E‐tattoos can be connected to the capacitor E‐tattoo, and the charges generated by multiple bare‐finger touches can be stored in the capacitor (0.23 V for 200 touches). Due to the micro/nanopores in the NF networks, the device exhibits a water vapor transmission rate of 115.04 g m−2 d−1, which is better than that of a commercial band‐aid, as well as ethanol sensing capability. Developed E‐tattoo capacitor can be used for constructing multicomponent integrated ultrathin and epidermal electronics