Luo Qing

Base-induced Bronsted acid sites on dealuminated HY zeolite: A solid-state NMR spectroscopy study

Using trimethylphosphine(TMP) and d(5)-pyridine (deuterated pyridine) as the basic probe molecules, the concentrations of Bronsted acid sites on both HY zeolite and dealuminated HY zeolite have been quantitatively determined using solid-state H-1 and P-31 magic-angle spinning (MAS) NMR. After the adsorption of the probe molecules, the concentration of Bronsted acid sites on the dealuminated HY zeolite increases by about 25%, whereas the parent HY sample remains almost unchanged. The increase in the concentration of Bronsted acid sites is due to the appearance of base-induced Bronsted acid sites in the dealuminated HY zeolite. The terminal SiOH in the vicinity of the aluminum atom is induced to form a bridging hydroxyl group (SiOHAl) in the presence of the basic probe molecules. The mechanism of formation of the induced Bronsted acid sites has also been discussed.

Effect of Pulse and dc Formation on the Performance of One-Transistor and One-Resistor Resistance Random Access Memory Devices

We investigate the effect of the formation process under pulse and dc modes on the performance of one transistor and one resistor (1T1R) resistance random access memory (RRAM) device. All the devices are operated under the same test conditions, except for the initial formation process with different modes. Based on the statistical results, the high resistance state (HRS) under the dc forming mode shows a lower value with better distribution compared with that under the pulse mode. One of the possible reasons for such a phenomenon originates from different properties of conductive filament (CF) formed in the resistive switching layer under two different modes. For the dc forming mode, the formed filament is thought to be continuous, which is hard to be ruptured, resulting in a lower HRS. However, in the case of pulse forming, the filament is discontinuous where the transport mechanism is governed by hopping. The low resistance state (LRS) can be easily changed by removing a few trapping states from the conducting path. Hence, a higher HRS is thus observed. However, the HRS resistance is highly dependent on the length of the gap opened. A slight variation of the gap length will cause wide dispersion of resistance.

Synthesis of Vinyl-functionalized MSU-X Silicates

Vinyl-functionalized MSU-X silicates were prepared by one-pot synthesis methodology at the presence of Tx-15 and AEO(9) surfactants respectively. The solids were characterized by XRD, FT-IR, Si-29 MASNMR, HRTEM, SEM, N-2 physisorption techniques. The surface morphology and textural properties of such materials varied with the synthesis mechanism and content of vinyl groups in the channel. The effects of the organic groups on the modified MSU-2 were investigated carefully. The vinyl-modified mesopore with 10% (x) VTES templated by AEO(9) was of 3.1 nm. pore diameter, but that templated by Tx-15 displayed a bimodal mesoporous channels, in which the smaller pore size was about 3 nm, while the bigger one was in the range of 40 similar to 46 nm.