The long cycle life of the energy storage devices depends on the structural and chemical stability of the electrode material used. Developing energy storage devices with a longer cycle life helps in avoiding frequent replacement of the devices, cuts down cost of replacing and recycling dead batteries and supercapacitors. This makes the cycle life to be a vital parameter to focus on developing efficient energy storage devices. Supercapacitors, an electrochemical energy storage device has important characteristics of high-power density, fast charging, and long cycle life. Most of the electrode materials used in supercapacitor undergo surface, structural and chemical changes during cycling which leads to change in the capacitance retained. A thorough qualitative analysis is important to investigate the reason behind these changes occurring at the electrode. We employed a surface analysis tool such as Kelvin probe force microscopy (KPFM) to probe the reason behind capacitance change of a two-dimensional (2D) electrode during cycling. We investigated the cycling performance of 2D electrode material, tungsten disulfide (WS2) via KPFM and Raman studies. The results obtained via KPFM revealed that during cycling, WS2 layers develop strain due to intercalation/deintercalation of electrolyte ions. This leads to increase in the available electrochemical active sites leading to increased capacitance. The charge contribution studies revealed that the strain in the WS2 layers led to increased redox charge storage behavior of the electrode during cycling. Such qualitative studies will benefit in understanding the reason behind the structural changes during cycling and will help in developing highly efficient and long-lasting energy storage devices. This study can be further extended to other electrode materials employed in supercapacitor as well as batteries.

Uncovering the mechanism behind the increase in capacitance of a 2D WS2 supercapacitor electrode upon cycling using KPFM analysis.

High-performance photodetectors require efficient photogeneration and charge transport. Perovskite quantum dots (PQDs) have received enormous interest for applications in optoelectronics due to their high photogeneration efficiency. However, they offer meager carrier transport. Reduced graphene oxide (RGO) exhibits inferior photoresponse compared to materials such as quantum dots. An effective synthesis protocol to grow PQDs from the RGO lattice may facilitate direct charge transfers from PQDs to RGO, which could not be accomplished by mixing individual PQDs with RGO or making a bilayer. At ambient condition, the photodetector fabricated with the PQD-RGO superstructure showed high responsivity of 1.07 × 103 A/W, detectivity of 1 × 1013 Jones as well as sharp switching in the visible wavelength. After 3 months in an unencapsulated sample, the photocurrent was decreased ∼10% of its initial value while preserving speed and cycle stability at ambient condition.

Super-bright all-solution-processed quantum dot light-emitting diodes (QLEDs) with an inverted structure are achieved by imprinting speckle image holography (SIH) structures inside the devices. QLEDs with imprinted random grating structures can reach a luminance of up to 146 000 Cd/m(2) at driving voltage of 8 V, which is 1.76 times higher than the value of control devices with planar architecture, setting a new brightness record for all solution -processed inverted red QLEDs. The luminous power efficiency and external quantum efficiency of the QLEDs with imprinted structures are 1.8 and 1.65 times higher to those of the control devices, respectively. Further optical simulation results reveal that not only can the structure help extract the trapped internal photon energy but also the mechanical pressure during the imprinting process plays a crucial role in improving the device performance.

With the ever-increasing demand for low power electronics, neuromorphic computing has garnered huge interest in recent times. Implementing neuromorphic computing in hardware will be a severe boost for applications involving complex processes such as image processing and pattern recognition. Artificial neurons form a critical part in neuromorphic circuits, and have been realized with complex complementary metal–oxide–semiconductor (CMOS) circuitry in the past. Recently, metal-insulator-transition materials have been used to realize artificial neurons. Although memristors have been implemented to realize synaptic behavior, not much work has been reported regarding the neuronal response achieved with these devices. In this work, we use the volatile threshold switching behavior of a vertical-MoS 2 /graphene van der Waals heterojunction system to produce the integrate-and-fire response of a neuron. We use large area chemical vapor deposited (CVD) graphene and MoS 2 , enabling large scale realization of these devices. These devices can emulate the most vital properties of a neuron, including the all or nothing spiking, the threshold driven spiking of the action potential, the post-firing refractory period of a neuron and strength modulated frequency response. These results show that the developed artificial neuron can play a crucial role in neuromorphic computing.

Catalytic processes are critical steps in numerous industrial processes. The discovery of high reactivity of defects in metal-free two-dimensional materials has bolstered their emergence as catalysts. Here we consider the effect of defect-inducing methods in hexagonal boron nitride ( h -BN) on their performance for olefin and CO_2 hydrogenation. We compare the changes introduced by ball milling and heat treatment in h -BN and show how varying the treatment conditions can impact the properties. We provide some evidence of the reactivity of the powders. Our results highlight how characterization can be exploited to assess the potential catalytic activity of h -BN for heterogeneous catalysis.

The ability to probe structures and functional properties of complex systems at the nanoscale, both at their surface and in their volume, has drawn substantial attention in recent years. Besides detecting heterogeneities, cracks and defects below the surface, more advanced explorations of chemical or electrical properties are of great interest. In this article, we review some approaches developed to explore heterogeneities below the surface, including recent progress in the different aspects of metrology in optics, electron microscopy, and scanning probe microscopy. We discuss the principle and mechanisms of image formation associated with each technique, including data acquisition, data analysis and modeling for nanoscale structural and functional imaging. We highlight the advances based on atomic force microscopy (AFM). Our discussion first introduces methods providing structural information of the buried structures, such as position in the volume and geometry. Next we present how functional properties including conductivity, capacitance, and composition can be extracted from the modalities available to date and how they could eventually enable tomography reconstructions of systems such as overlay structures in transistors or living systems. Finally we propose a perspective regarding the outstanding challenges and needs to push the field forward.

This work describes a simple method to develop a high V(oc) low band gap PSCs. In addition, two new atomic force microscopy (AFM)-based nanoscale characterization techniques to study the surface morphology and physical properties of the structured active layer are introduced. With the help of ternary solvent processing of the active layer and C60 buffer layer, a bulk heterojunction PSC with V(oc) more than 0.9 V and conversion efficiency 7.5% is developed. In order to understand the fundamental properties of the materials ruling the performance of the PSCs tested, AFM-based nanoscale characterization techniques including Pulsed-Force-Mode AFM (PFM-AFM) and Mode-Synthesizing AFM (MSAFM) are introduced. Interestingly, MSAFM exhibits high sensitivity for direct visualization of the donor-acceptor phases in the active layer of the PSCs. Finally, conductive-AFM (cAFM) studies reveal local variations in conductivity in the donor and acceptor phases as well as a significant increase in photocurrent in the PTB7:ICBA sample obtained with the ternary solvent processing.