电子功函数降低的表面:产生问题及理论描述。回顾

IF 0.6 Q4 PHYSICS, MULTIDISCIPLINARY Ukrainian Journal of Physics Pub Date : 2023-10-02 DOI:10.15407/ujpe68.8.549
M.V. Strikha, A.M. Goriachko
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引用次数: 1

摘要

本文综述了现代光电阴极或具有低功函数或低/负电子亲和的高效场发射阴极的实验研究。我们提出了理论模型,其中电子亲和力降低与半导体/绝缘体界面上带电层的影响有关。介绍了现代测量功函数或电子亲和力的实验技术,以及旨在制造低功函数/电子亲和力表面的技术。在作者建立的一个简单的理论模型框架中,已经证明了在半导体表面存在一个偶极子层(例如,由带负电荷的氧离子和带正电荷的稀土离子组成),在提供相同浓度的带相反电荷的吸附离子的情况下,可以将电子亲和力降低高达3 eV。当带负电的氧离子的表面浓度高于带正电的金属离子的表面浓度时,由于半导体中空间电荷区向上的带弯曲,电子亲和的降低变小;否则,由于带向下弯曲,电子亲和的降低会更大。这种效应允许制定技术建议,以便在现代场发射电子设备中获得具有最小功函数值的表面。在提出的模型框架内,对oh功能化MXene的功函数进行了评估。未功能化MXene的对应值约为4.5 eV,与Ti层数和C层数(从1层到9层)无关。oh功能化将其降低到约1.6 eV,并且该值实际上也与MXene中的原子层数无关。描述了获得低功函数/低电子亲和力阴极的实验方法。它们的目的是在垂直于表面的近表面阴极区域中产生电荷的空间分离。正负电荷的相应空间分布的特征是它们要么在两个不同的原子平面上定位,要么在一个平面和一个扩展的空间区域(后一种变体是半导体衬底的典型特征)。生产这种表面的技术是基于将吸附物沉积到金属或半导体衬底上的各种方法:物理气相沉积、化学气相沉积、液相沉积、衬底体扩散等。特别关注的是处理稀土金属(Ce, Gd, Eu)的吸附和氧在Si, Ge和Mo表面(也是在纳米结构状态下)的共吸附的实验工作,这导致偶极子层的形成和功函数的减少。
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Surfaces with Lowered Electron Work Function: Problems of Their Creation and Theoretical Description. A Review
Experimental studies devoted to the creation of the modern photocathodes or efficient field emission cathodes with lowered work function or low/negative electron affinity are reviewed. We present theoretical models, where the electron affinity lowering is associated with the influence of electrically charged layers at the semiconductor/insulator interface. Modern experimental techniques of measuring the work function or the electron affinity and technologies aimed at fabricating the surfaces with low work function/electron affinity are described. In the framework of a simple theoretical model developed by the authors, it has been demonstrated that the presence of a dipole layer (e.g., composed of negatively charged oxygen ions and positively charged rare earth ions) at the semiconductor surface can lower the electron affinity by up to 3 eV provided equal concentrations of oppositely charged adsorbate ions. It is also shown that if the surface concentration of negatively charged oxygen ions is higher than the surface concentration of positively charged metal ions, the lowering of the electron affinity becomes smaller due to the upward band bending in the space charge region in the semiconductor; otherwise, the lowering of the electron affinity becomes larger due to the downward band bending. This effect allows technological proposals to be formulated for obtaining surfaces with minimum work function values in modern field-emission-based electronic devices. In the framework of the proposed model, the work function was evaluated for the OH-functionalized MXene. The corresponding value for the unfunctionalized MXene equals about 4.5 eV, being practically independent of the number of Ti and C layers (from 1 to 9 layers). The OH-functionalization lowers it down to about 1.6 eV, and this value is also practically independent of the number of atomic layers in MXene. Experimental approaches to obtain cathodes with low work function/low electron affinity are described. They are aimed at creating a spatial separation of electric charges in the near-surface cathode region perpendicularly to the surface plane. The corresponding spatial distributions of positive and negative charges are characterized by their localization either in two different atomic planes or in one plane and an extended space region (the latter variant is typical of semiconductor substrates). The technologies for producing such surfaces are based on various methods of adsorbate deposition onto the metal or semiconductor substrate: physical vapor deposition, chemical vapor deposition, liquid phase deposition, diffusion from the substrate bulk, and so forth. Particular attention is paid to the experimental works dealing with the adsorbtion of rare earth metals (Ce, Gd, Eu) and the coadsorbtion of oxygen onto the Si, Ge, and Mo surfaces (in a nano-structured state as well), which results in the dipole layer formation and the work function reduction.
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来源期刊
Ukrainian Journal of Physics
Ukrainian Journal of Physics PHYSICS, MULTIDISCIPLINARY-
CiteScore
1.20
自引率
20.00%
发文量
244
期刊介绍: Ukrainian Journal of Physics is the general physics edition of the Department of Physics and Astronomy of the National Academy of Sciences of Ukraine. The journal publishes original papers and reviews in the fields of experimental and theoretical physics.
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