Atomic motion in low-coverage helium films adsorbed in FSM nanochannels
Atomic motion in low-coverage helium films adsorbed in FSM nanochannels
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吸附在 FSM 纳米通道中的低覆盖氦膜中的原子运动
DOI：
10.1007/s10909-012-0815-0
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发表时间：
2013
影响因子：
2
通讯作者：
and N. Wada
中科院分区：
文献类型：
--
作者：
T. Matsushita;A. Kuze;R. Kawai;M. Hieda;and N. Wada
吸附在纳米多孔硅酸盐中的4 He和3 He膜显示出相似的热容，直到量子流体层出现在覆盖第一层完成n1。为了获得量子流体区以下低覆盖度下吸附原子的动力学信息，我们对吸附在2.4nm的FSM硅酸盐直纳米通道中的~ 3 He膜进行了3.3MHz的脉冲NMR实验。在0.54- 7 K范围内观察到的自旋-晶格和自旋-自旋弛豫时间T1和T2可用二维Bloembergen-Purcell-磅模型很好地描述。在覆盖率为0.4-1.7n1时，T1的最小值，表明自旋相关时间τ c为4.8 π 10 − 8 π sec，在6 - 3 π K之间观察到。随着温度的降低，T1和T2的变化在1.5K以下变得很小，这表明从热激活运动到量子隧穿的交叉。与下面的大的变化相反，上面的两个弛豫时间几乎与覆盖度无关，这可能表明τ是由吸附原子的层间交换决定的。下文1中，áT 2中的减少表明吸附原子定位的开始。
4He and3He films adsorbed in nanoporous silicates have shown similar heat capacities until the quantum-fluid layer appears at coverages over the first-layer completionn1. To obtain information on dynamics of adatoms at low coverages below the quantum fluid region, we have done pulsed-NMR experiment at 3.3áMHz for3He films adsorbed in straight 2.4ánm nanochannels of FSM silicates. The spin-lattice and spin-spin relaxation timesT1andT2observed at 0.54–7áK were well described by the two-dimensional version of the Bloembergen-Purcell-Pound model. At coverages 0.4–1.7n1, minima ofT1, indicating the spin correlation timeτcof 4.8Î10−8ásec, were observed at temperatures between 6 and 3áK. With decreasing temperature, changes inT1andT2become small below about 1.5áK, suggesting crossover from thermally-activated motion to quantum tunneling. In contrast to large variations belown1, both relaxation times aboven1are almost independent of coverage, which is likely to indicate thatτcis determined by interlayer exchange of adatoms. Belown1, onsets for localization of adatoms were suggested by a decrease ináT2.