Papers by Author: Run Sheng Yu

Abstract: The annihilation behavior of positronium in N and P type porous silicon is investigated via positron annihilation lifetime (PAL) and positronium time-of-flight (Ps-TOF) measurements. The result shows the N type sample has smaller positronium annihilation fraction and more interconnected pores. The microstructure of Rapid Thermal Oxidation (RTO) treated N type porous silicon also studied using PAL spectroscopy, and the relationship between its photoluminescence properties and porous structure was discussed.

Abstract: The positronium time of flight (Ps-TOF) spectroscopy is a novel technique for studying the microstructure in porous materials, in which the high-efficient detection of γ rays generated from ortho-positronium annihilation is the key point for the apparatus setup. In this paper, a new geometry of the scintillator was proposed to improve the γ ray detection efficiency which was indicated by the 22.1% promotion using the simulation results.

Abstract: In this work, a single scintillator detector setup for AMOC measurement is considered to improve coincidence efficiency. A planar HPGe detector provide both the timing signal of stop channel and the energy spectrum signal for an annihilation events of positronium. Experiment results show that the system can get a count rate ~20cps/μCi with a time resolution of 2.2ns.

Abstract: In this paper, a series of mesoporous silica particles with different pore diameters were fabricated using tetraethyl orthosilicate (TEOS) as the network precursor, hexadecyl trimethyl ammonium bromide (CTAB) as a structure directing agent and 1,3,5-Trimethylbenzene (TMB) as a pore enlarge reagent. Compared with SAXRD and BET, the PALS may not only show the mesoporous information but also provide the structure information of microporous.

Abstract: We prepared a series of mesoporous silica films to study the structural information of ordered pores by positronium Time of Flight (Ps-TOF) spectroscopy. By changing the ratio of surfactant to silicon source, the pore structure is tuned. Results show that once ordered pores are formed, clear Ps TOF peak is observed. And the film with less distributed pore geometry leads to a narrowed Ps TOF peak.