中国科学技术大学：《正电子物理》课程教学讲稿（正电子在材料科学中的应用）12 正电子技术在材料科学中的应用（Positron for Nano-particles）

正电子概况XⅫⅡ 正电子技术在材料科学中 的应用-nanoparticles 叶邦角 核固体物理研究室 Laboratory of Nuclear Solid State Physics,USTC PDF文件使用"pdfFactory”试用版本创建耀w.fineprint.cn

正电子技术在材料科学中 的应用--- nanoparticles 叶邦角 核固体物理研究室 Laboratory of Nuclear Solid State Physics, USTC 正电子概况XII

Positron for Nano-particles 纳米粒子 二.纳米粒子嵌入 三，纳米粒子在表面 PDF文件使用"pdfFactory”试用版本创建ww.fineprint.cn

Positron for Nano-particles 二. 纳米粒子嵌入 三. 纳米粒子在表面 一 . 纳米粒子 PDF 文件使用 "pdfFactory" 试用版本创建 www.fineprint.cn ÿ

一.纳米粒子 PDF文件使用"pdfFactory”试用版本创建ww.fineprint.cn

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INSTITUTE OF PHYSICS PUBLISHING NANOTECHNOLOGY Nanotechnology 15(2004)467-472 PIL:S0957-448404)62779-6 Trapping of positrons at grain boundaries in nanoparticle systems V Thakur,S B Shrivastava and M K Rathore School of Studies in Physics,Vikram University.Ujjain(MP)-456010.India E-mail:vandanathakurl @rediffmail.com Abstract The positron annihilation in nanoparticle materials has been discussed in terms of the thermal diffusion of positrons at grain surfaces and trapping at the grain interfaces and interfacial defects.The diffusion trapping model has been applied to obtain the mean lifetime of positrons as a function of grain size and temperature and the S-parameter of the annihilation radiation as a function of grain size in Ag,Nb,Zn-Al and Zn-Al-Mg nanocrystallites.The calculated mean positron lifetimes have beencompared with the available experimental results. PDF文件使用"pdfFactory" 试用版本创建l.fineprint..cn

Abstract The positron annihilation in nanoparticle materials has been discussed in terms of the thermal diffusion of positrons at grain surfaces and trapping at the grain interfaces and interfacial defects. The diffusion trapping model has been applied to obtain the mean lifetime of positrons as a function of grain size and temperature and the S-parameter of the annihilation radiation as a function of grain size in Ag, Nb, Zn–Al and Zn–Al–Mg nanocrystallites. The calculated mean positron lifetimes have beencompared with the available experimental results. PDF 文件使用 "pdfFactory" 试用版本创建 Ìwww.fineprint.cn ÿÌ

280 Theory 260 Ag 240 802 220 200 180 160 15 20 25 30 35 Grain Size (nm) Comparison with the experimental results of the calculated mean positron lifetime in Ag nanocrystallites as a function of grain size PDF文件使用"pdfFactory”试用版本创建进.fineprint.cn

l Comparison with the experimental results of the calculated mean positron lifetime in Ag nanocrystallites as a function of grain size. PDF 文件使用 "pdfFactory" 试用版本创建 Ìwww.fineprint.cn ÿÌ

220 240 -Theory Expt. 218 Theory b 216 Zn-Al 220 214 212 色 1210 200. 208 206 180 204 202 5 10 15 20 200 400 600 800 10001200 Grain Size (nm) Grain Size (nm) PDF文件使用"pdfFactory”试用版本创建w.fineprint.cn

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220 一Theory Zn-Al-Mg Expt. 350 Zn-Al-Mg 215 -Theory 210 R=0.7 um 300 205 1 200 250 R =1um 195 200 190 20040600 8001000 12001400 50 100 150 200250 300 350 Grain Size (nm) Temperature(K) PDF文件使用"pdfFactory”试用版本创建w.fineprint.cn

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S-参数 0.375 0.59 T=300K Zn-Al 0.370- 0.58 0.365- Zn-AHMg 0.57 Jwered-S 0.360 0.355 0.56 Nb T=300K 0.350 Expt. 0.55- Theory Theory 0.345 5 101520 2530 35 40 0 200 400 600 800 1000 Grain Size (nm) Grain Size(nm) PDF文件使用"pdfFactory”试用版本创建ww.fineprint.cn

S-参数 PDF 文件使用 "pdfFactory" 试用版本创建 ÿwww.fineprint.cn

Conclusions (1)The mean positron lifetime has been found to decrease with an increase in the size of the grains. At large grain size,comparable to the diffusion length,annihilation occurs in the bulk state. (2)The diffusion coefficient D+could be described by the relation D.DoT-12.The variation of the S- parameter in nanocrystalline samples suggests that the material undergoes significant changes at low grain size. PDF文件使用"pdfFactory”试用版本创建ww.fineprint.cn

Conclusions (1)The mean positron lifetime has been found to decrease with an increase in the size of the grains. At large grain size, comparable to the diffusion length, annihilation occurs in the bulk state. (2) The diffusion coefficient D+ could be described by the relation D+ = D0T -1/2 . The variation of the S￾parameter in nanocrystalline samples suggests that the material undergoes significant changes at low grain size. PDF 文件使用 "pdfFactory" 试用版本创建 ÿwww.fineprint.cn

JOURNAL OF APPLIED PHYSICS VOLUME 93.NUMBER 10 Positron lifetime spectroscopic studies of nanocrystalline ZnFe2O4 P.M.G.Nambissan) Nuclear and Atomic Plnysics Division.Saha Institute of Nuclear Plysics,IAF Bidhannagar. Kolkata 700 064.India C.Upadhyay and H.C.Verma Depariment of Physics,Indian Institute of Techmology.Kanpur 208 016.India (Received 9 December 2002;accepted 6 March 2003) TABLE I.Grain size (d)and lattice parameter (a)of the ZnFe2O samples as estimated from the x-ray diffraction data Samples de (nm) a() CTR Series Bulk 8.448 14 8.448 9 8.432 7 8.356 6 8.343 5 8.267 CER Series Bulk 8.448 HTR Series 6 8.438 4 8.437 PDF文件使用"pdfFactory”试用版本创建w.fineprint.cn

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