Energy systems converting efficiently from surrounding environment for powering semiconductor electronic components at nanoscale has attracted intense research interests. Due to the strong size dependency, flexoelectricity has been demonstrated as an excellent candidate implemented as nanoscale piezoelectric semiconductor energy harvesters. In this work, through a judicious exploitation of structural symmetry and nonuniformity, we theoretically study the energy conversion behaviors of a novel asymmetric nanodisk model composed of functionally graded (FG) flexoelectric semiconductor (FS) (FG-FS) materials while being loaded with thickness-extensional mechanical vibration. In numerical analysis, the material parameters have been treated with a general variation method under the Cartesian coordinate systems for simplicity. Taking into accounts of the nonuniform structural form and multi-field coupling features, we derived an octic governing equation with variable coefficients for the current analyzed FG-FS nanodisk structure, which is, however, almost impossible to obtain analytical solutions. To successfully address this issue and also further explore the improved performance and new phenomena induced by the FG type of non-uniform structural profile, we specially proposed an efficient tensor algorithm and reduced the octic governing equation into one quartic equation with variable coefficients and other four common quadratic equations. Later, we explicitly explored the effect of each physical parameter on the energy conversion performance of the FS energy harvester by studying the variations of the output electric power density and the energy conversion efficiency. Results illustrated that the electromechanical energy conversion behaviors of the studied FG-FS nanodisk can be properly tuned by not only the related material parameters but also their gradations. We believe our work have the potential to pave new way for the designs and manufacture of novel nano-electronic semiconductor components for the future practical applications.

中文翻译：

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功能梯度柔性电半导体纳米结构能量转换的模型和性能分析


从周围环境中高效转换能量以为纳米级半导体电子元件供电的能源系统引起了人们的强烈研究兴趣。由于尺寸依赖性很强，柔性电已被证明是纳米级压电半导体能量收集器的绝佳候选者。在这项工作中，通过明智地利用结构对称性和不均匀性，我们从理论上研究了由功能梯度（FG）挠曲电半导体（FS）（FG-FS）材料组成的新型非对称纳米盘模型在加载厚度时的能量转换行为- 延伸机械振动。在数值分析中，为简单起见，材料参数在笛卡尔坐标系下采用一般变分法处理。考虑到结构形式的不均匀和多场耦合特征，我们针对当前分析的FG-FS纳米盘结构推导了变系数八次控制方程，然而，这几乎不可能获得解析解。为了成功解决这一问题，并进一步探索FG型非均匀结构轮廓所带来的性能改进和新现象，我们专门提出了一种高效的张量算法，将八次控制方程简化为一个带变系数的四次方程和其他四个方程常见的二次方程。随后，我们通过研究输出电功率密度和能量转换效率的变化，明确探讨了每个物理参数对FS能量收集器能量转换性能的影响。 结果表明，所研究的 FG-FS 纳米盘的机电能量转换行为不仅可以通过相关材料参数而且可以通过其梯度来适当调节。我们相信我们的工作有潜力为未来实际应用的新型纳米电子半导体元件的设计和制造铺平新的道路。