The Essential Role of Cu Vapor for the Self-Limit Graphene via the Cu Catalytic CVD Method

Because of the inconsistent observations, the Cu catalytic decomposition of methane for graphene synthesis is reexamined, i.e., via the surface absorption, decomposition to atomic carbon, and segregation. Here, we experimentally show the quantity of ambient Cu vapor is the key factor in graphene synthesis, which influences the dropwise condensations for airborne Cu clusters during growth. The massive carburization in Cu clusters and the calculation of carbon solubility in nanosized clusters are performed, experimented, and further examined from the growth of diamond-like-carbon films and ball-like diamonds via Cu vapor assisted growth on SiO₂. The affinitive interactions between Cu vapor, ambient gases, and solid surface are embodied. By combining the molecular dynamics for the redeposited Cu clusters to surface, the vehicle theory of Cu clusters, which transports the atomic carbon to the surface and completes the graphene growth, is thus proposed as the essential puzzle we considered

Honeycomb-like Porous Carbon–Cobalt Oxide Nanocomposite for High-Performance Enzymeless Glucose Sensor and Supercapacitor Applications

Herein, we report the preparation of Pongam seed shells-derived activated carbon and cobalt oxide (∼2–10 nm) nanocomposite (PSAC/Co₃O₄) by using a general and facile synthesis strategy. The as-synthesized PSAC/Co₃O₄ samples were characterized by a variety of physicochemical techniques. The PSAC/Co₃O₄-modified electrode is employed in two different applications such as high performance nonenzymatic glucose sensor and supercapacitor. Remarkably, the fabricated glucose sensor is exhibited an ultrahigh sensitivity of 34.2 mA mM^–1 cm^–2 with a very low detection limit (21 nM) and long-term durability. The PSAC/Co₃O₄ modified stainless steel electrode possesses an appreciable specific capacitance and remarkable long-term cycling stability. The obtained results suggest the as-synthesized PSAC/Co₃O₄ is more suitable for the nonenzymatic glucose sensor and supercapacitor applications outperforming the related carbon based modified electrodes, rendering practical industrial applications

Honeycomb-like Porous Carbon–Cobalt Oxide Nanocomposite for High-Performance Enzymeless Glucose Sensor and Supercapacitor Applications

Herein, we report the preparation of Pongam seed shells-derived activated carbon and cobalt oxide (∼2–10 nm) nanocomposite (PSAC/Co₃O₄) by using a general and facile synthesis strategy. The as-synthesized PSAC/Co₃O₄ samples were characterized by a variety of physicochemical techniques. The PSAC/Co₃O₄-modified electrode is employed in two different applications such as high performance nonenzymatic glucose sensor and supercapacitor. Remarkably, the fabricated glucose sensor is exhibited an ultrahigh sensitivity of 34.2 mA mM^–1 cm^–2 with a very low detection limit (21 nM) and long-term durability. The PSAC/Co₃O₄ modified stainless steel electrode possesses an appreciable specific capacitance and remarkable long-term cycling stability. The obtained results suggest the as-synthesized PSAC/Co₃O₄ is more suitable for the nonenzymatic glucose sensor and supercapacitor applications outperforming the related carbon based modified electrodes, rendering practical industrial applications

Low Temperature Growth of Graphene on Glass by Carbon-Enclosed Chemical Vapor Deposition Process and Its Application as Transparent Electrode

A novel carbon-enclosed chemical vapor deposition (CE-CVD) to grow high quality monolayer graphene on Cu substrate at a low temperature of 500 °C was demonstrated. The quality of the grown graphene was investigated by Raman spectra, and the detailed growth mechanism of high quality graphene by the CE-CVD process was investigated in detail. In addition to growth of high quality monolayer graphene, a transparent hybrid few-layer graphene/CuNi mesh electrode directly synthesized by the CE-CVD process on a conventional glass substrate at the temperature of 500 °C was demonstrated, showing excellent electrical properties (∼5 Ω/□ @ 93.5% transparency) and ready to be used for optical applications without further transfer process. The few-layer graphene/CuNi mesh electrode shows no electrical degradation even after 2 h annealing in pure oxygen at an elevated temperature of ∼300 °C. Furthermore, the few-layer graphene/CuNi mesh electrode delivers an excellent corrosion resistance in highly corrosive solutions such as electroplating process and achieves a good nucleation rate for the deposited film. Findings suggest that the low temperature few-layer graphene/CuNi mesh electrode synthesized by the CE-CVD process is an excellent candidate to replace indium tin oxide (ITO) as transparent conductive material (TCM) in the next generation

Ultrafast and Low Temperature Synthesis of Highly Crystalline and Patternable Few-Layers Tungsten Diselenide by Laser Irradiation Assisted Selenization Process

Recently, a few attempts to synthesize monolayers of transition metal dichalcogenides (TMDs) using the chemical vapor deposition (CVD) process had been demonstrated. However, the development of alternative processes to synthesize TMDs is an important step because of the time-consuming, required transfer and low thermal efficiency of the CVD process. Here, we demonstrate a method to achieve few-layers WSe₂ on an insulator <i>via</i> laser irradiation assisted selenization (LIAS) process directly, for which the amorphous WO₃ film undergoes a reduction process in the presence of selenium gaseous vapors to form WSe₂, utilizing laser annealing as a heating source. Detailed growth parameters such as laser power and laser irradiation time were investigated. In addition, microstructures, optical and electrical properties were investigated. Furthermore, a patternable WSe₂ concept was demonstrated by patterning the WO₃ film followed by the laser irradiation. By combining the patternable process, the transfer-free WSe₂ back gate field effect transistor (FET) devices are realized on 300 nm-thick SiO₂/P⁺Si substrate with extracted field effect mobility of ∼0.2 cm² V^–1 s^–1. Similarly, the reduction process by the laser irradiation can be also applied for the synthesis of other TMDs such as MoSe₂ from other metal oxides such as MO₃ film, suggesting that the process can be further extended to other TMDs. The method ensures one-step process to fabricate patternable TMDs, highlighting the uniqueness of the laser irradiation for the synthesis of different TMDs

Manipulated Transformation of Filamentary and Homogeneous Resistive Switching on ZnO Thin Film Memristor with Controllable Multistate

A bias polarity-manipulated transformation from filamentary to homogeneous resistive switching was demonstrated on a Pt/ZnO thin film/Pt device. Two types of switching behaviors, exhibiting different resistive switching characteristics and memory performances were investigated in detail. The detailed transformation mechanisms are systematically proposed. By controlling different compliance currents and RESET-stop voltages, controllable multistate resistances in low resistance states and a high resistance states in the ZnO thin film metal–insulator–metal structure under the homogeneous resistive switching were demonstrated. We believe that findings would open up opportunities to explore the resistive switching mechanisms and performance memristor with multistate storage

ZnO_1–<i>x</i> Nanorod Arrays/ZnO Thin Film Bilayer Structure: From Homojunction Diode and High-Performance Memristor to Complementary 1D1R Application

We present a ZnO_1–<i>x</i> nanorod array (NR)/ZnO thin film (TF) bilayer structure synthesized at a low temperature, exhibiting a uniquely rectifying characteristic as a homojunction diode and a resistive switching behavior as memory at different biases. The homojunction diode is due to asymmetric Schottky barriers at interfaces of the Pt/ZnO NRs and the ZnO TF/Pt, respectively. The ZnO_1–<i>x</i> NRs/ZnO TF bilayer structure also shows an excellent resistive switching behavior, including a reduced operation power and enhanced performances resulting from supplements of confined oxygen vacancies by the ZnO_1–<i>x</i> NRs for rupture and recovery of conducting filaments inside the ZnO TF layer. A hydrophobic behavior with a contact angle of ∼125° can be found on the ZnO_1–<i>x</i> NRs/ZnO TF bilayer structure, demonstrating a self-cleaning effect. Finally, a successful demonstration of complementary 1D1R configurations can be achieved by simply connecting two identical devices back to back in series, realizing the possibility of a low-temperature all-ZnO-based memory system

Low Vacuum Annealing of Cellulose Acetate on Nickel Towards Transparent Conductive CNT–Graphene Hybrid Films

We report a versatile method based on low vacuum annealing of cellulose acetate on nickel (Ni) surface for rapid fabrication of graphene and carbon nanotube (CNT)–graphene hybrid films with tunable properties. Uniform films mainly composed of tri-layer graphene can be achieved via a surface precipitation of dissociated carbon at 800 °C for 30 seconds under vacuum conditions of ∼0.6 Pa. The surface precipitation process is further found to be efficient for joining the precipitated graphene with pre-coated CNTs on the Ni surface, consequently, generating the hybrid films. As expected, the hybrid films exhibit substantial opto-electrical and field electron emission properties superior to their individual counterparts. The finding suggests a promising route to hybridize the graphene with diverse nanomaterials for constructing novel hybrid materials with improved performances

Dynamic Observation of Phase Transformation Behaviors in Indium(III) Selenide Nanowire Based Phase Change Memory

Phase change random access memory (PCRAM) has been extensively investigated for its potential applications in next-generation nonvolatile memory. In this study, indium(III) selenide (In₂Se₃) was selected due to its high resistivity ratio and lower programming current. Au/In₂Se₃-nanowire/Au phase change memory devices were fabricated and measured systematically in an <i>in situ</i> transmission electron microscope to perform a RESET/SET process under pulsed and dc voltage swept mode, respectively. During the switching, we observed the dynamic evolution of the phase transformation process. The switching behavior resulted from crystalline/amorphous change and revealed that a long pulse width would induce the amorphous or polycrystalline state by different pulse amplitudes, supporting the improvement of the writing speed, retention, and endurance of PCRAM