Y. X. Liu

Bio: Y. X. Liu is an academic researcher. The author has contributed to research in topics: Adsorption & Materials science. The author has an hindex of 1, co-authored 1 publications receiving 82 citations.

Highly uniform resistive switching characteristics of TiN/ZrO2/Pt memory devices

Abstract: We fabricated the TiN/ZrO2/Pt sandwiched resistive switching memory devices. Excellent bipolar resistive switching characteristics, including a large number of switching cycles and highly uniform switching parameters, as well as long retention time were achieved. The improved switching behavior of TiN/ZrO2/Pt could be attributed to the oxygen reservoir effect of TiN electrodes on the formation and rupture of the filamentary conducting paths by modifying the concentration distributions of the oxygen ions and vacancies in ZrO2 thin films. The results demonstrate the feasibility of high performance resistive switching memory devices based on transition metal oxides by using TiN as the top electrode.

Hollow CoS2 anchored on hierarchically porous carbon derived from Pien Tze Huang for high-performance supercapacitors.

Abstract: The development of electrode materials with a high specific capacitance, power density, and long-term stability is essential and remains a challenge for developing supercapacitors. Cobalt sulfides (CoS2) are considered one of the most promising and widely studied electrode materials for supercapacitors. Herein, CoS2 and hierarchical porous carbon derived from Pien Tze Huang waste are assembled into a cobalt sulfide/carbon (CoS2/PZH) matrix composite using a one-step hydrothermal method to resolve the challenges of supercapacitors. The resulting CoS2/PZH composite material exhibits a hierarchical porous structure with hollow CoS2 embedded in a PZH framework. The uniform dispersion of the hierarchical porous structure CoS2/PZH is achieved due to the PZH framework, while the uniform decoration of the porous PZH with the hollow CoS2 prevents the PZH from stacking easily. Moreover, the excellent synergistic effect of the hierarchical porous and hollow structure of CoS2/PZH can shorten the electron/ion diffusion channels, expose additional active sites, and provide stable structures for subsequent reactions. As a result, the CoS2/PZH composite material displays a high initial specific capacity of 447.5 F g-1 at 0.5 A g-1, a high energy density of 22.38 W h kg-1, and long-term cycling stability (a retention rate of 92.3% over 10 000 cycles at 5 A g-1).

Remarkable adsorption capacity of Cu2+-doped ZnAl layered double hydroxides and the calcined materials toward phosphate

Abstract: In this study, Cu2+ was doped into ZnAl hydrotalcite by one-step urea homogeneous hydrolysis to produce ZnAlCu ternary hydrotalcite (ZnAlCu-1%-LDH). After that, it was roasted to obtain ZnAlCu layered trimetallic oxide (ZnAlCu-1%-LDO). The Jahn-Teller effect of Cu2+ is able to distort the ZnAlCu, thus increasing the hydrotalcite layer spacing and specific surface area. The influence of Cu2+ doping on phosphate adsorption was investigated, and adsorption mechanism was also analyzed. XRD proved that Cu2+ doping increased the interlayer spacing of adsorbent. The optimum copper doping amount of ZnAlCu-1%-LDO was 1% of the total metal molarity. The ZnAlCu-1%-LDO obtained the phosphate adsorption capacity of 199.28 mg P/g, which was 4.6 and 2.9 times higher than that of ZnAl-LDH and ZnAlCu-1%-LDH (phosphate concentration of 200 mg P/L, adsorbent dosage of 0.4 g/L), respectively. Experimental characterizations revealed that the phosphate adsorption mechanisms of ZnAlCu-1%-LDO were memory effect, electrostatic attraction, ligand exchange and surface precipitation. In addition, the phosphate removal efficiency of ZnAlCu-1%-LDO in the actual wastewater (3.43 mg P/L initial concentration) was also investigated, and the residual concentration after adsorption was 0.0664 mg P/L, which reached the A-level standard of phosphate effluent in China (0.5 mg P/L). The experiment provided a universal solution for other layered double hydroxides (LDHs) to improve their phosphate adsorption performance.

Facile fabrication of self-supporting porous CuMoO4@Co3O4 nanosheets as a bifunctional electrocatalyst for efficient overall water splitting.

Abstract: Research shows that redox complementarity and synergism among the ingredients of heterogeneous catalysts can enhance the performance of the catalyst. In this research, a porous CuMoO4@Co3O4 nanosheet electrocatalyst is prepared, which is uniformly decorated on nickel foam (NF) by hydrothermal reactions and the impregnation method. The CuMoO4@Co3O4 is an efficient bifunctional catalyst with prominent electrocatalytic activity and durability. It requires overpotentials of only 54 and 251 mV to obtain current densities of 10 and 50 mA cm-2 for the cathodic hydrogen evolution reaction (HER) and the anodic oxygen evolution reaction (OER) in 1.0 mol L-1 KOH, corresponding to Tafel slope values of 98.8 and 87.4 mV dec-1, respectively. Furthermore, the CuMoO4@Co3O4 shows excellent stability of 120 h chronopotentiometry at a current density of 100 mA cm-2 for the HER/OER. Notably, an alkaline electrolyzer (with CuMoO4@Co3O4 as the HER and OER electrodes) can deliver a current density of 10 mA cm-2 at a low voltage of 1.51 V. The catalytic activity of CuMoO4@Co3O4 can be attributed to the structure of the porous nanosheets and the synergistic effect between CuMoO4 and Co3O4.

Metal oxides for optoelectronic applications

Abstract: Optical transparency, tunable conducting properties and easy processability make metal oxides key materials for advanced optoelectronic devices. This Review discusses recent advances in the synthesis of these materials and their use in applications. Metal oxides (MOs) are the most abundant materials in the Earth's crust and are ingredients in traditional ceramics. MO semiconductors are strikingly different from conventional inorganic semiconductors such as silicon and III–V compounds with respect to materials design concepts, electronic structure, charge transport mechanisms, defect states, thin-film processing and optoelectronic properties, thereby enabling both conventional and completely new functions. Recently, remarkable advances in MO semiconductors for electronics have been achieved, including the discovery and characterization of new transparent conducting oxides, realization of p-type along with traditional n-type MO semiconductors for transistors, p–n junctions and complementary circuits, formulations for printing MO electronics and, most importantly, commercialization of amorphous oxide semiconductors for flat panel displays. This Review surveys the uniqueness and universality of MOs versus other unconventional electronic materials in terms of materials chemistry and physics, electronic characteristics, thin-film fabrication strategies and selected applications in thin-film transistors, solar cells, diodes and memories.

Resistive Random Access Memory (ReRAM) Based on Metal Oxides

Abstract: In this paper, we review the recent progress in the resistive random access memory (ReRAM) technology, one of the most promising emerging nonvolatile memories, in which both electronic and electrochemical effects play important roles in the nonvolatile functionalities. First, we provide a brief historical overview of the research in this field. We also provide a technological overview and the epoch-making achievements, followed by an account of the current understanding of both bipolar and unipolar ReRAM operations. Finally, we summarize the challenges facing the ReRAM technology as it moves toward the beyond-2X-nm generation of nonvolatile memories and the so-called beyond complementary metal-oxide-semiconductor (CMOS) device.

Resistive Random Access Memory (ReRAM) Based on Metal Oxides This paper reviews a class of metal-oxide-metal resistive memory structures that depend on a chemical oxidation/reduction process to cause a change in resistance when a voltage pulse is applied.

Abstract: In this paper, we review the recent progress in the resistive random access memory (ReRAM) technology, one of the most promising emerging nonvolatile memories, in which both electronic and electrochemical effects play important roles in the nonvolatile functionalities. First, we provide a brief historical overview of the research in this field. We also provide a technological overview and the epoch-making achievements, followed by an account of the current understanding of both bipolar and unipolar ReRAM operations. Finally, we summarize the challenges facing the ReRAM technology as it moves toward the beyond-2X-nm generation of nonvolatile memories and the so-called beyond complementary metal-oxide-semiconductor (CMOS) device.

Resistive Random Access Memory (RRAM): an Overview of Materials, Switching Mechanism, Performance, Multilevel Cell (mlc) Storage, Modeling, and Applications

Abstract: In this manuscript, recent progress in the area of resistive random access memory (RRAM) technology which is considered one of the most standout emerging memory technologies owing to its high speed, low cost, enhanced storage density, potential applications in various fields, and excellent scalability is comprehensively reviewed. First, a brief overview of the field of emerging memory technologies is provided. The material properties, resistance switching mechanism, and electrical characteristics of RRAM are discussed. Also, various issues such as endurance, retention, uniformity, and the effect of operating temperature and random telegraph noise (RTN) are elaborated. A discussion on multilevel cell (MLC) storage capability of RRAM, which is attractive for achieving increased storage density and low cost is presented. Different operation schemes to achieve reliable MLC operation along with their physical mechanisms have been provided. In addition, an elaborate description of switching methodologies and current voltage relationships for various popular RRAM models is covered in this work. The prospective applications of RRAM to various fields such as security, neuromorphic computing, and non-volatile logic systems are addressed briefly. The present review article concludes with the discussion on the challenges and future prospects of the RRAM.

Adaptive oxide electronics: A review

Abstract: Novel information processing techniques are being actively explored to overcome fundamental limitations associated with CMOS scaling. A new paradigm of adaptive electronic devices is emerging that may reshape the frontiers of electronics and enable new modalities. Creating systems that can learn and adapt to various inputs has generally been a complex algorithm problem in information science, albeit with wide-ranging and powerful applications from medical diagnosis to control systems. Recent work in oxide electronics suggests that it may be plausible to implement such systems at the device level, thereby drastically increasing computational density and power efficiency and expanding the potential for electronics beyond Boolean computation. Intriguing possibilities of adaptive electronics include fabrication of devices that mimic human brain functionality: the strengthening and weakening of synapses emulated by electrically, magnetically, thermally, or optically tunable properties of materials.In this review, we detail materials and device physics studies on functional metal oxides that may be utilized for adaptive electronics. It has been shown that properties, such as resistivity, polarization, and magnetization, of many oxides can be modified electrically in a non-volatile manner, suggesting that these materials respond to electrical stimulus similarly as a neural synapse. We discuss what device characteristics will likely be relevant for integration into adaptive platforms and then survey a variety of oxides with respect to these properties, such as, but not limited to, TaOx, SrTiO3, and Bi4-xLaxTi3O12. The physical mechanisms in each case are detailed and analyzed within the framework of adaptive electronics. We then review theoretically formulated and current experimentally realized adaptive devices with functional oxides, such as self-programmable logic and neuromorphic circuits. Finally, we speculate on what advances in materials physics and engineering may be needed to realize the full potential of adaptive oxide electronics.