Tunable Power Switching in Nonvolatile Flexible Memory Devices Based on Graphene Oxide Embedded with ZnO Nanorods

The growing demand for portable and bendable nonvolatile memory systems has motivated extensive research in the field of flexible resistive random access memory (RRAM) devices. This study investigated the resistive switching and flexibility behavior of zinc oxide nanorods (ZNs) incorporated graphene oxide (GO) sheets. GOZNs-based RRAM devices having top metal aluminum electrodes were fabricated on flexible indium tin oxide (ITO) coated polyethylene terephthalate (ITOPET) substrate. The devices having the structure Al/GOZNs/ITOPET showed typical bipolar resistive switching characteristics with switching voltages lower than those of Al/GO/ITOPET devices. The significant (∼50%) decrement in operating voltages in the case of GOZNs-based RRAM was attributed to enhanced concentration of oxygen vacancies into the GO matrix due to the incorporation of ZNs, which was supported by X-ray photoelectron spectroscopy studies. These memory devices showed repeatable and reliable switching characteristics having an on/off ratio of ∼100, lower switching voltages, good retention properties up to ∼10⁴ s, and endurance performance over 200 cycles. The resistance ratio of the GOZNs RRAM devices was maintained almost constant even for the extreme bending radius of 4 mm and mechanical flexing test over 10³ cycles, indicating excellent flexibility. These GOZNs-based RRAM devices showed great potential for use in future flexible nonvolatile memory devices

Electron–Phonon Interaction and Double-Resonance Raman Studies in Monolayer WS₂

Atomically thin layers of 2D WS₂ offer a realization of novel valley-selective electronics and power-efficient optoelectronic device fabrication due to large spin splitting at the top of the valence band and high quantum efficiency. However, the synthesis of the large-area monolayer WS₂ film through chemical vapor deposition (CVD) method is in a rudimentary stage. Here we report a modified CVD method to synthesize high-crystalline monolayer WS₂ (1L) with uniform size distribution over a large area. The intensity of the second-order Raman modes in 1L WS₂ is enhanced, particularly the overtone of the acoustic mode LA­(M), when the excitation wavelength is in the vicinity of B exciton. The variation in the intensity profile of the first-order Raman modes for 1L and bulk WS₂ in (laser-energy-dependent) resonant Raman scattering processes is discussed within the third-order perturbation theory

Temperature-Dependent Raman Studies and Thermal Conductivity of Few-Layer MoS₂

We report on the temperature dependence of in-plane E_2g and out-of-plane A_1g Raman modes in high-quality few-layer MoS₂ (FLMS) prepared using a high-temperature vapor-phase method. The materials obtained were investigated using transmission electron microscopy. The frequencies of these two phonon modes were found to vary linearly with temperature. The first-order temperature coefficients for E¹_2g and A_1g modes were found to be (1.32 and 1.23) × 10^–2 cm^–1/K, respectively. The thermal conductivity of the suspended FLMS at room temperature was estimated to be ∼52 W/mK

In Situ Raman Studies of Electrically Reduced Graphene Oxide and Its Field-Emission Properties

Electric-field-dependent in situ Raman studies have been carried out on chemically prepared graphene oxide. The Raman spectra show significant changes with increase in the applied electric field; in particular, the intensity of the G peak decreases with electric field. This behavior is typical for chemically or thermally reduced graphene oxide. To understand the nature of reduction, we compared the temperature-dependent and electric-field-dependent Raman spectra of graphene oxide and found that the evolutions of Raman spectra are not in agreement with each other, except the intensity of the G peak that decreases in both cases. The D peak broadens significantly with increase in temperature, whereas it sharpens in the case of applied electric field. The electron-field-emission properties of the electrically reduced graphene oxide were also carried out, and the turn-on field was found to be 9.1 V/μm

Surface Energy Engineering for Tunable Wettability through Controlled Synthesis of MoS₂

MoS₂ is an important member of the transition metal dichalcogenides that is emerging as a potential 2D atomically thin layered material for low power electronic and optoelectronic applications. However, for MoS₂ a critical fundamental question of significant importance is how the surface energy and hence the wettability is altered at the nanoscale in particular, the role of crystallinity and orientation. This work reports on the synthesis of large area MoS₂ thin films on insulating substrates (SiO₂/Si and Al₂O₃) with different surface morphology via vapor phase deposition by varying the growth temperatures. The samples were examined using transmission electron microscopy and Raman spectroscopy. From contact angle measurements, it is possible to correlate the wettability with crystallinity at the nanoscale. The specific surface energy for few layers MoS₂ is estimated to be about 46.5 mJ/m². Moreover a layer thickness-dependent wettability study suggests that the lower the thickness is, the higher the contact angle will be. Our results shed light on the MoS₂–water interaction that is important for the development of devices based on MoS₂ coated surfaces for microfluidic applications

Exploring Lead Zirconate Titanate, the Potential Advancement as an Anode for Li-Ion Batteries

Graphite, widely adopted as an anode for lithium-ion batteries (LIBs), faces challenges such as an unsustainable supply chain and sluggish rate capabilities. This emphasizes the urgent need to explore alternative anode materials for LIBs, aiming to resolve these challenges and drive the advancement of more efficient and sustainable battery technologies. The present research investigates the potential of lead zirconate titanate (PZT: PbZr0.53Ti0.47O3) as an anode material for LIBs. Bulk PZT materials were synthesized by using a solid-state reaction, and the electrochemical performance as an anode was examined. A high initial discharge capacity of approximately 686 mAh/g was attained, maintaining a stable capacity of around 161 mAh/g after 200 cycles with diffusion-controlled intercalation as the primary charge storage mechanism in a PZT anode. These findings suggest that PZT exhibits a promising electrochemical performance, positioning it as a potential alternative anode material for LIBs

Spin-Polarized Tunneling through Chemical Vapor Deposited Multilayer Molybdenum Disulfide

The two-dimensional (2D) semiconductor molybdenum disulfide (MoS₂) has attracted widespread attention for its extraordinary electrical-, optical-, spin-, and valley-related properties. Here, we report on spin-polarized tunneling through chemical vapor deposited multilayer MoS₂ (∼7 nm) at room temperature in a vertically fabricated spin-valve device. A tunnel magnetoresistance (TMR) of 0.5–2% has been observed, corresponding to spin polarization of 5–10% in the measured temperature range of 300–75 K. First-principles calculations for ideal junctions result in a TMR up to 8% and a spin polarization of 26%. The detailed measurements at different temperature, bias voltages, and density functional theory calculations provide information about spin transport mechanisms in vertical multilayer MoS₂ spin-valve devices. These findings form a platform for exploring spin functionalities in 2D semiconductors and understanding the basic phenomena that control their performance