半导体纳米晶体的冷等离子体合成:原理、进展和展望

Nonthermal plasma synthesis of semiconductor nanocrystals:Principle,progress and perspectives

冷等离子体已发展成为纳米材料合成领域的重要技术途径.无需化学溶剂和配体,冷等离子体为高品质半导体纳米晶体的生长提供了独特的非热力学平衡环境:等离子体中的高能电子与纳米颗粒碰撞使得纳米颗粒带电,可降低或消除纳米颗粒之间的团聚;高能表面化学反应能够选择性地将纳米颗粒加热到远超环境气体温度的温度;气相中生长物和固相纳米颗粒表面结合物之间化学势的巨大差异,有利于实现纳米晶体的超高浓度掺杂.本文综述了冷等离子体合成半导体纳米晶体的研究现状,详细讨论了冷等离子体中纳米颗粒形核、生长和晶化的基本原理,总结了冷等离子体在单元素、化合物和复杂核壳结构纳米晶体方面的研究进展,特别强调了冷等离子体在纳米颗粒尺寸、形貌、结晶状态、表面化学和组分等性能调变上的技术优势,概述了超掺杂纳米晶体呈现的新颖物性,展望了冷等离子体技术在纳米晶体合成领域的应用前景.

Nanotechnology has been thriving for many years,but scientists’pursuit of innovation and breakthrough in the synthesis of various forms of nanomaterials in a controlled manner has never ceased.The 2023 Nobel Prize in Chemistry was awarded to Moungi G.Bawendi,Louis E.Brus,and Alexei I.Ekimov for their pioneer contributions to the discovery and synthesis of quantum dots,also known as semiconductor nanocrystals(NCs),signifying the importance of advanced synthesis methods for nanomaterials in a variety of technical applications.Over the past two decades,nonthermal plasma has been established as an important technique for controlled synthesis of versatile nanomaterials with high quality on a par with conventional colloidal methods.Inherently free of chemical solvents and organic ligands,nonthermal plasma provides a unique non-equilibrium environment for growing high-quality and high-purity semiconductor NCs.First,high-energy electrons in the plasma collide with nanoparticles to negatively charge the nanoparticles,which can effectively reduce agglomeration of the nanoparticles,yielding ultrasmall nanoparticles with a few nanometers accompanied with a narrow size distribution.Second,energetic surface chemical and physical reactions can selectively heat the nanoparticles to temperatures far exceeding the ambient gas temperature,allowing significant deviation of the particle growing from a thermal equilibrium.Third,large difference between chemical potentials of growth species in the gas environment and species bound to the solid nanoparticle surface facilitates hyperdoping of semiconductor NCs for emerging new physical phenomena and applications.Inspired by recent impressive success of nonthermal plasma in the synthesis of semiconductor NCs,it is necessary to summarize latest research progress for on-demand plasma science and technology.Herein the current paperreviews state of the art in nonthermal plasma synthesis of a variety of semiconductor NCs.Fundamental mechanisms of the particle nucleation,growth,and crystallization in nonthermal plasma are discussed in detail in the review.Emphasis is placed on flexible control over the evolution of nanoparticle size,morphology,crystallinity,surface chemistry,and component,as well as recent impressive progress in the synthesis of single-element,multi-elements and complex core-shell structured semiconductor NCs by means of nonthermal plasma.Importantly,nonthermal-plasma-enabled hyperdoping of semiconductor NCs far exceeding the bulk solubility of a dopant as well as their novel optoelectronic properties such as sub-bandgap optical absorption and emission,localized surface plasmon resonance(LSPR),and metal-insulator transition(MIT)is highlighted,together with prospecting the development of nonthermal plasma systems in the future.We are confident that nonthermal plasma technology is expected to evolve into a universal strategy in addition to conventional colloidal methods for controlled synthesis of versatile nanomaterials,and should greatly contribute to the practical implementation of nanomaterials in a wide range of technical fields including electronics,optoelectronics,energy,catalysis,medicine,bioimaging,and beyond.