Microwave Hydrothermal Synthesis and Acidity of Nanosize Gallosilicate Mesoporous Molecular Sieves

A range of nanosize alkaline‐free gallosilicate mesoporous molecular sieves (GaMMS) were synthesized using microwave hydrothermal method and various analytical and spectroscopic techniques were employed to systematically investigate the structure, coordination geometry of gallium, acidic properties and catalytic activity. These nanosize GaMMSs exhibit high surface area (240 ～ 720 m²/g), pore volume (1.06 ～ 1.49 m³/g), narrow pore size distribution and nano‐particle size between 20 and 100 nm and four‐coordinated gallium site mainly, which were characterized by XRD, N₂ adsorption/desorption, TEM, ⁷¹Ga MAS‐NMR and ICP‐AES. Mesoporosity, mesostructure and nanosize can be controlled simply by microwave irradiation time and temperature. Pyridine‐IR result reveals the coexistence of Lewis and Brönstead acid sites in these nanosize GaMMS while NH₃‐TPD profiles suggest nanosize one has stronger acid site and contains more acid sites than the conventional one. Catalytic performance was evaluated using the catalytic cumene cracking test. The result indicates that the nanosize GaMMS shows a much higher activity than that of conventional GaMCM‐41, probably due to higher concentrations of H‐form sites, external surface and fast diffusion.     

A study of the switching mechanism and electrode material of?fully CMOS compatible tungsten oxide ReRAM

Tungsten oxide (WO _X ) resistive memory (ReRAM), a two-terminal CMOS compatible nonvolatile memory, has shown promise to surpass the existing flash memory in terms of scalability, switching speed, and potential for 3D stacking. The memory layer, WO _X , can be easily fabricated by down-stream plasma oxidation (DSPO) or rapid thermal oxidation (RTO) of W plugs universally used in CMOS circuits. Results of conductive AFM (C-AFM) experiment suggest the switching mechanism is dominated by the REDOX (Reduction-oxidation) reaction??the creation of conducting filaments leads to a low resistance state and the rupturing of the filaments results in a high resistance state. Our experimental results show that the reactions happen at the TE/WO _X interface. With this understanding in mind, we proposed two approaches to boost the memory performance: (i) using DSPO to treat the RTO WO _X surface and (ii) using Pt TE, which forms a Schottky barrier with WO _X . Both approaches, especially the latter, significantly reduce the forming current and enlarge the memory window.