Technical University of Darmstadt, Eduard-Zintl-Institute, Alarich-Weiss-Straße 8, 64287 Darmstadt, Germany.
Phys Chem Chem Phys. 2023 May 17;25(19):13376-13382. doi: 10.1039/d3cp00926b.
In silicon clusters a structural transition from prolate to near-spherical structures takes place at a size of about 25-30 atoms. While some of the prolate clusters are very polar, there has been no experimental evidence of the presence of dipole moments in larger silicon clusters with near-spherical shape. By means of electric molecular beam deflection experiments at cryogenic temperatures, it was possible to prove for the first time that Si clusters with more than = 30 atoms are also polar. Interestingly, the dipole moment per atom for clusters in the range between 30 and 80 or 90 atoms is almost constant and amounts to 0.02 D. This unusual behaviour manifests in effective polarizabilities increasing linearly with cluster size. The dipolar contribution to the polarizability means that Si clusters with = 80 atoms can be polarized more than twice as well as a correspondingly small sphere with the dielectric properties of bulk α-Si. This finding is analysed with quantum chemical calculations concerning the geometric structure as well as the charge distribution and is related to the dielectric behaviour of polar semiconductor nanocrystals.
在硅团簇中，从长椭球结构到近球形结构的结构转变发生在大约 25-30 个原子的尺寸上。虽然一些长椭球团簇具有很强的极性，但在具有近球形的较大硅团簇中，并没有实验证据表明存在偶极矩。通过在低温下进行的电分子束偏转实验，首次证明了具有超过 = 30 个原子的 Si 团簇也是极性的。有趣的是，在 30 到 80 或 90 个原子之间的团簇中，每个原子的偶极矩几乎是恒定的，为 0.02 D。这种异常行为表现为有效极化率随团簇尺寸线性增加。偶极子对极化率的贡献意味着，具有 = 80 个原子的 Si 团簇的极化能力比相应的具有块状 α-Si 介电特性的小球体强两倍以上。这一发现通过与几何结构以及电荷分布有关的量子化学计算进行了分析，并与极性半导体纳米晶体的介电行为有关。
