Structure and sublimation of water ice films grown in vacuo at 120-190 K studied by positron and positronium annihilation.
Structure and sublimation of water ice films grown in vacuo at 120-190 K studied by positron and positronium annihilation.
复制标题
通过正电子和正电子湮灭研究 120-190 K 真空中生长的水冰膜的结构和升华。
DOI：
10.1088/0953-8984/26/12/125402
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
Townrow S
中科院分区：
文献类型：
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作者：
Townrow S
通过测量在165和172 K下生长的~ 5−20 μm水冰膜的正电子形成正电子离子（orthoo - ps）并衰变成3个伽玛光子的比例，对其晶体结构进行了探测。已经确定，在较慢速率（水蒸气压力≥1 mPa）下生长的薄膜比在较高速率（蒸汽压力~ 100 mPa）下生长的薄膜具有较低浓度的晶格缺陷和封闭孔隙，它们充当Ps陷阱，证明了前者的正交Ps扩散长度大约是前者的四倍。通过在162 ~ 182 K之间改变生长温度，发现在~ 172 K以上的温度下，薄膜的无序性降低，在此范围内，正交ps扩散长度增加了~ 60%。利用正电子湮灭参数在165 ~ 195 K之间的时间依赖性，在铜上生长的水冰膜的升华能测量为0.462 (5)eV，与早期的研究一致，并且与生长速率和热历史没有可测量的依赖性。
The crystalline structure of∼ 5− 20 μm water ice films grown at 165 and 172 K has been probed by measuring the fraction of positrons forming ortho-positronium (ortho-Ps) and decaying into three gamma photons. It has been established that films grown at slower rates (water vapour pressure≥ 1 mPa) have lower concentrations of lattice defects and closed pores, which act as Ps traps, than those grown at higher rates (vapour pressure∼ 100 mPa), evidenced by ortho-Ps diffusion lengths being approximately four times greater in the former. By varying the growth temperature between 162 and 182 K it was found that films become less disordered at temperatures above∼ 172 K, with the ortho-Ps diffusion length rising by∼ 60%, in this range. The sublimation energy for water ice films grown on copper has been measured to be 0.462 (5) eV using the time dependence of positron annihilation parameters from 165 to 195 K, in agreement with earlier studies and with no measurable dependence on growth rate and thermal history.