Secondary electron emission properties of double-layer B-doped diamond films

https://doi.org/10.1016/j.diamond.2020.107826Get rights and content

Highlights

  • B-doped double-layer diamond films were prepared by microwave plasma chemical vapor deposition.

  • The composition and microstructure of the film have a great influence on its secondary electron emission performance.

  • Reasonable B doping concentration is a key factor in the preparation of a high secondary electron emission yield film.

Abstract

B-doped double-layer diamond films were prepared by microwave plasma chemical vapor deposition. The effects of different B-doping concentrations on the crystal quality, surface morphology, surface composition and the conductivity, secondary electron emission performance of the films were investigated. It is found that the increased conductivity with increased B-doping is beneficial for secondary electron emission. However, the degraded crystal quality of diamond, increased surface sp2 carbon and the segregation of B element at surface due to increased B-doping could degrade the secondary electron emission performance of the film. So it can be considered as a competition between improved vertical conductance that tends to increase secondary electron escape depth and finally degrading surface properties as a function of B-doping. The double-layer film with a light B-doping concentration has good crystal quality and enough conductivity, which helps to obtain the best secondary electron emission performance.

Introduction

Secondary electron emission (SEE) of solid materials is widely used in various fields of vacuum electronics such as microscopic imaging, mass spectrometry and photomultiplier tubes [[1], [2], [3], [4], [5], [6]]. B-doped diamond can have an excellent SEE performance, and this make it have very important applications to be used as the SEE material [7]. However, the doping of B atom as an impurity into the diamond lattice may reduce the crystal quality of the diamond film, and then affects the SEE yield of the film. In order to improve the crystal quality of the diamond and make the diamond film have sufficient conductivity, we designed a two-layer structure of a diamond film. In this two-layer diamond film, a high quality diamond film without B-doping is grown first, and then a B-doped film is grown on the first diamond film. Since the crystal quality of the substrate can affect the subsequent film growing quality definitely, we expect that the first layer film with a high quality diamond will be beneficial to the improvement of the crystal quality of the subsequent B-doped film, thereby improving the SEE performance of the film.

Although the effects of different doping concentrations on the SEE properties of diamond films have been studied in many previous reports [[8], [9], [10], [11]], there is no relevant research about the influence of the B-doping concentration on the composition, microstructure and the SEE performance of the film. Our goal is to explore the relationship between the film composition, microstructure and SEE performance, this can provide a useful guide for the preparation of diamond film with high SEE. In this work, a two-layer structure diamond film was prepared, and the effects of different B-doping concentrations on the composition and microstructure as well as the conductivity and SEE performance of the film were systematically studied.

Section snippets

Experiment

In the experiment, the polycrystalline diamond film without B-doping was first grown on the Mo substrate by microwave plasma chemical vapor deposition (MPCVD), the growing temperature was 1050 °C, and the methane and hydrogen were 25 sccm and 475 sccm respectively. After the polycrystalline diamond film was grown, the sample was then taken out and put into another MPCVD equipment to grow the B-doped diamond film [12]. For the B-doped diamond film, the hydrogen of 475 sccm, methane of 25 sccm,

Crystal quality and surface morphology of the films

The single-layer film grown without B-doping was recorded as B 0, and the double-layer films grown at different B-doping concentrations are denoted as B 0.5, B 1, B 2 and B 5, respectively. Fig. 2(a) and (b) is the XRD patterns and Raman spectra of the prepared films, Fig. 2(c) is a partial enlarged view of Fig. 2(b), the Raman spectra were baseline corrected. In Fig. 2(a), the peaks at 43.91° and 75.30° correspond to the diamond (111) and (220) crystal planes, respectively. They are marked

Conclusions

The B-doped double-layer polycrystalline diamond films were grown by MPCVD. The microstructure, composition and SEE yield of different B-doped diamond films were studied. It has been found that different B-doping concentrations can change the composition and microstructure of the prepared film, which has a huge impact on its conductivity and SEE yield. As the concentration of B increases, the content of B incorporated into the diamond lattice increases, which leads to the increased conductivity

CRediT authorship contribution statement

Kongting Wei: Conceptualization, Data curation, Formal analysis, Writing - original draft, Writing - review & editing. Ruozheng Wang: Methodology, Project administration. Jie Li: Visualization, Validation. Biye Liu: Investigation. Qiang Wei: Software. Rongrong Wu: Investigation. Shengli Wu: Conceptualization, Resources, Formal analysis, Writing - review & editing, Funding acquisition. Wenbo Hu: Supervision. Hongxing Wang: Resources, Funding acquisition.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The SEM work was done at the International Center for Dielectric Research (ICDR), Xi'an, China; Thanks Yanzhu Dai for her help in the SEM testing. This work was supported by the National Natural Science Foundation of China (Nos. 61627812, 61771383) and Dongguan Introduction Program of Leading Innovative and Entrepreneurial Talents.

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