Zhemi Xu

Recent developments in black phosphorus transistors

The discovery of graphene has inspired great research interest in two-dimensional (2D) layered nanomaterials during the past decade. As one of the newest members in the 2D layered nanomaterial family, black phosphorus (BP), with puckered structure similar to graphene, has shown great potential in novel nanoelectronics owing to its thickness-dependent bandgap. Especially, the unique in-plane anisotropy and high carrier mobility enable BP to be a promising candidate for field-effect transistor (FET) applications. In addition, monolayer or few-layer BP can be combined into van der Waals heterostructures and this opens up a pathway for overcoming existing problems such as impurity scattering and surface degradation or achieving functionalities. In this article, we will review the typical physical and chemical properties of BP and provide an overview of the recent developments in BP-based transistors. In this review, we also discuss the current challenges in BP transistors and future research directions.

Reversible Hydrophobic to Hydrophilic Transition in Graphene via Water Splitting Induced by UV Irradiation

Although the reversible wettability transition between hydrophobic and hydrophilic graphene under ultraviolet (UV) irradiation has been observed, the mechanism for this phenomenon remains unclear. In this work, experimental and theoretical investigations demonstrate that the H2O molecules are split into hydrogen and hydroxyl radicals, which are then captured by the graphene surface through chemical binding in an ambient environment under UV irradiation. The dissociative adsorption of H2O molecules induces the wettability transition in graphene from hydrophobic to hydrophilic. Our discovery may hold promise for the potential application of graphene in water splitting.

Electric double-layer transistors: a review of recent progress

With the miniaturization of electronic devices, it is essential to achieve higher carrier density and lower operation voltage in field-effect transistors (FETs). However, this is a great challenge in conventional FETs owing to the low capacitance and electric breakdown of gate dielectrics. Recently, electric double-layer technology with ultra-high charge-carrier accumulation at the semiconductor channel/electrolyte interface has been creatively introduced into transistors to overcome this problem. Some interesting electrical transport characteristics such as superconductivity, metal–insulator transition, and tunable thermoelectric behavior have been modulated both theoretically and experimentally in electric double-layer transistors (EDLTs) with various semiconductor channel layers and electrolyte materials. The present article is a review of the recent progress in the EDLTs and the impacts of EDLT technology on modulating the charge transportation of various electronics.

Electrodeposition of Mesoporous Co3O4 Nanosheets on Carbon Foam for High Performance Supercapacitors

Metal oxide nanosheets have promising potential applications in novel energy storage devices. In this work, Co3O4 nanosheets/carbon foam with excellent supercapacitor characteristics was successfully fabricated, without using metal substrates. The experimental results demonstrate that the electrochemical tests showed that the as-prepared Co3O4 nanosheets exhibited an ideal capacitive behavior with a maximum specific capacitance of 106 F/g in 1 M NaOH solution at a scan rate of 0.1 V s−1.

UV irradiation induced reversible graphene band gap behaviors

The nature of zero bandgap has limited the applications of graphene for potential electronic devices, such as p–n junctions and transistors, etc. Here we report a simple methodology that can tune the bandgap of graphene by using ultraviolet (UV) irradiation. Most importantly, such a bandgap transition is reversible and can be controlled by the alternative treatment of UV irradiation and dark storage. In addition, density functional theory (DFT) calculations are performed to reveal the underlying mechanism of bandgap behavior in this reversible transition. Both experimental and computational results demonstrate that it is a promising technology for applications of graphene in electronic devices.

Manipulating resistive states in oxide based resistive memories through defective layers design

In this work, multilevel switching was achieved by a strategically designed alternative multi-layer structure with pure and Mn-doped SnO2. In this multilayer structure, by utilizing the pure SnO2 layer as an ionic defect diffusion barrier, the migration of ionic defects from the doped layers can be controlled and the intermediate resistance states were stabilized. The multilevel devices exhibit superior performances with a high ON/OFF ratio, low operation voltage and excellent retention. Such an alternative multi-layer structure could be a potential strategy for achieving high-density memories.

Development of ferroelectric oxides based resistive switching materials

ABSTRACT Resistive random access memory (RRAM) is one of the most promising candidates that satisfies the requirements of new generation non-volatile memories, as a consequence of its high density, outstanding scalability, and low power consumption. The review is based on a summary of recent studies in ferroelectric oxides based resistive switching (RS) materials and devices. It highlights the various ferroelectric oxide materials with RS behaviour and the underlying mechanisms including filament-type and interface-type mechanism. In the end, the challenge in current RRAM for future high-density data storage applications is addressed.

Improved super-capacitive performance of carbon foam supported CeOx nanoflowers by selective doping and UV irradiation

In this work, a facile electrochemical approach for depositing Gd-doped CeOx nanoflowers on porous carbon foam with excellent supercapacitor characteristics has been demonstrated. Moreover, the ultraviolet illumination on the electrodeposited nanoflowers significantly enhances the device supercapacitor performances as compared to thermally treated samples. Based on the experimental results in the present study, a new process to improve the surface character and electrochemical properties of the electrode material via UV light irradiation has been proposed.