Koshida Nobuyoshi, Nakamura Toshihiro
Graduate School of Engineering, Tokyo University of Agriculture and Technology, Fuchu, Japan.
Department of Electrical and Electronic Engineering, Hosei University, Tokyo, Japan.
Front Chem. 2019 Apr 24;7:273. doi: 10.3389/fchem.2019.00273. eCollection 2019.
Recent topics of application studies on porous silicon (PS) are reviewed here with a focus on the emissive properties of visible light, quasiballistic hot electrons, and acoustic wave. By exposing PS in solvents to pulse laser, size-controlled nc-Si dot colloids can be formed through fragmentation of the PS layer with a considerably higher yield than the conventional techniques such as laser ablation of bulk silicon and sol-gel precursor process. Fabricated colloidal samples show strong visible photoluminescence (~40% in quantum efficiency in the red band). This provides an energy- and cost-effective route for production of nc-Si quantum dots. A multiple-tunneling transport mode through nc-Si dot chain induces efficient quasiballistic hot electron emission from an nc-Si diode. Both the efficiency and the output electron energy dispersion are remarkably improved by using monolayer graphene as a surface electrode. Being a relatively low operating voltage device compatible with silicon planar fabrication process, the emitter is applicable to mask-less parallel lithography under an active matrix drive. It has been demonstrated that the integrated 100 × 100 emitter array is useful for multibeam lithography and that the selected emission pattern is delineated with little distortion. Highly reducing activity of emitted electrons is applicable to liquid-phase thin film deposition of metals (Cu) and semiconductors (Si, Ge, and SiGe). Due to an extremely low thermal conductivity and volumetric heat capacity of nc-Si layer, on the other hand, thermo-acoustic conversion is enhanced to a practical level. A temperature fluctuation produced at the surface of nc-Si layer is quickly transferred into air, and then an acoustic wave is emitted without any mechanical vibrations. The non-resonant and broad-band emissivity with low harmonic distortions makes it possible to use the emitter for generating audible sound under a full digital drive and reproducing complicated ultrasonic communication calls between mice.
本文综述了多孔硅（PS）应用研究的最新课题，重点关注可见光的发射特性、准弹道热电子和声表面波。通过将PS暴露在溶剂中并施加脉冲激光，可通过PS层的破碎形成尺寸可控的纳米晶硅（nc-Si）点胶体，其产率比传统技术（如体硅激光烧蚀和溶胶-凝胶前驱体工艺）高得多。制备的胶体样品显示出强烈的可见光致发光（红色波段量子效率约为40%）。这为生产nc-Si量子点提供了一种节能且经济高效的途径。通过nc-Si点链的多隧道传输模式可诱导nc-Si二极管产生高效的准弹道热电子发射。使用单层石墨烯作为表面电极，效率和输出电子能量色散均得到显著提高。作为一种与硅平面制造工艺兼容的相对低工作电压器件，该发射器适用于有源矩阵驱动下的无掩膜并行光刻。已证明集成的100×100发射器阵列可用于多光束光刻，且所选发射图案的描绘几乎没有失真。发射电子的高还原活性适用于金属（Cu）和半导体（Si、Ge和SiGe）的液相薄膜沉积。另一方面，由于nc-Si层极低的热导率和体积热容，热声转换提高到了实用水平。nc-Si层表面产生的温度波动迅速传递到空气中，然后在没有任何机械振动的情况下发射出声波。非共振和宽带发射率以及低谐波失真使得该发射器能够在全数字驱动下用于产生可听声音，并在小鼠之间再现复杂的超声通信呼叫。
