Liu Sitong, Shang Xiao, Liu Xizhe, Wang Xiaochun, Liu Fuchun, Zhang Jun
Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China.
School of Physics Science and Information Technology, Liaocheng University, Liaocheng 252000, China.
Nanomaterials (Basel). 2024 Aug 17;14(16):1358. doi: 10.3390/nano14161358.
Recently, the application of two-dimensional (2D) piezoelectric materials has been seriously hindered because most of them possess only in-plane piezoelectricity but lack out-of-plane piezoelectricity. In this work, using first-principles calculation, by atomic substitution of penta-graphene (PG) with tiny out-of-plane piezoelectricity, we design and predict stable 2D X-PG (X = Si or Ge) semiconductors with excellent in-plane and out-of-plane piezoelectricity and extremely high in-plane hole mobility. Among them, Ge-PG exhibits better performance in all aspects with an in-plane strain piezoelectric coefficient = 8.43 pm/V, an out-of-plane strain piezoelectric coefficient = -3.63 pm/V, and in-plane hole mobility = 57.33 × 10 cm V s. By doping Si and Ge atoms, the negative Poisson's ratio of PG approaches zero and reaches a positive value, which is due to the gradual weakening of the structure's mechanical strength. The bandgaps of Si-PG (0.78 eV) and Ge-PG (0.89 eV) are much smaller than that of PG (2.20 eV), by 2.82 and 2.47 times, respectively. This indicates that the substitution of X atoms can regulate the bandgap of PG. Importantly, the physical mechanism of the out-of-plane piezoelectricity of these monolayers is revealed. The super-dipole-moment effect proposed in the previous work is proved to exist in PG and X-PG, i.e., it is proved that their out-of-plane piezoelectric stress coefficient increases with the super-dipole-moment. The -induced polarization direction is also consistent with the super-dipole-moment direction. X-PG is predicted to have prominent potential for nanodevices applied as electromechanical coupling systems: wearable, ultra-thin devices; high-speed electronic transmission devices; and so on.
最近，二维（2D）压电材料的应用受到严重阻碍，因为它们中的大多数仅具有面内压电性，而缺乏面外压电性。在这项工作中，我们利用第一性原理计算，通过用具有微小面外压电性的五边形石墨烯（PG）进行原子取代，设计并预测了具有优异面内和面外压电性以及极高面内空穴迁移率的稳定2D X-PG（X = Si或Ge）半导体。其中，Ge-PG在各方面表现更佳，面内应变压电系数= 8.43 pm/V，面外应变压电系数= -3.63 pm/V，面内空穴迁移率= 57.33×10 cm V s。通过掺杂Si和Ge原子，PG的负泊松比接近零并变为正值，这是由于结构机械强度的逐渐减弱。Si-PG（0.78 eV）和Ge-PG（0.89 eV）的带隙比PG（2.20 eV）小得多，分别小2.82倍和2.47倍。这表明X原子的取代可以调节PG的带隙。重要的是，揭示了这些单层材料面外压电性的物理机制。先前工作中提出的超偶极矩效应在PG和X-PG中被证明存在，即证明了它们的面外压电应力系数随超偶极矩增加。诱导极化方向也与超偶极矩方向一致。预计X-PG在用作机电耦合系统的纳米器件方面具有突出潜力：可穿戴超薄器件；高速电子传输器件等。
