Enhancing surface production of negative ions using nitrogen doped diamond in a deuterium plasma

Abstract

The production of negative ions is of significant interest for applications including mass spectrometry, particle acceleration, material surface processing, and neutral beam injection for magnetic confinement fusion. Methods to improve the efficiency of the surface production of negative ions, without the use of low work function metals, are of interest for mitigating the complex engineering challenges these materials introduce. In this study we investigate the production of negative ions by doping diamond with nitrogen. Negatively biased (−20 V or −130 V), nitrogen doped micro-crystalline diamond films are introduced to a low pressure deuterium plasma (helicon source operated in capacitive mode, 2 Pa, 26 W) and negative ion energy distribution functions (NIEDFs) are measured via mass spectrometry with respect to the surface temperature (30 • C to 750 • C) and dopant concentration. The results suggest that nitrogen doping has little influence on the yield when the sample is biased at −130 V, but when a relatively small bias voltage of −20 V is applied the yield is increased by a factor of 2 above that of un-doped diamond when its temperature reaches 550 • C. The doping of diamond with nitrogen is a new method for controlling the surface production of negative ions, which continues to be of significant interest for a wide variety of practical applications.

Структурные И Оптические Характеристики Синтетических Алмазов В Нано-, Микро- И Миллиметровом Масштабе

“…1). Образец наноалмазов (5 nm) демонстрирует широкий пик примерно при 17 В остальных порошковых образцах видна широкая полоса с центром около 2100 cm −1 , которая может быть связана с примесями азота, образующими центры NV 0 [22]. В порошковом образце микроалмазов (100 µm) наблюдается дополнительная полоса около 865 cm −1 , возможно, относящаяся к дефектам, связанным с никелем [23,24] из никель-марганцевого катализатора, используемого в процессе синтеза HPHT.…”

Surface production of negative ions from pulse-biased nitrogen doped diamond within a low-pressure deuterium plasma

“…The mesh also acts to increase the confinement of the plasma to the source region, thereby reducing the plasma density in the diffusion region where the sample is located. The stability of the plasma is therefore tracked in the diffusion region, described in section 2.3 and 2.5, as distinct from the source region 33 .…”

“…48. Nitrogen doped diamond films were produced using a similar PECVD technique to the MCD samples 33 . The PECVD process utilised a bell jar reactor with a pressure of 200 mbar, microwave power at 3 kW, substrate temperature of 850 • C, background hydrogen gas mixture with a methane concentration of 5%.…”

“…Alternative materials to caesium are under investigation, and these include highly oriented pyrolitic graphite (HOPG) 20,[23][24][25] , novel electrides 26 , LaB 6 , MoLa 27 , as well as those that have dielectric properties such as diamond-like-carbon (DLC) and diamond [23][24][25][28][29][30][31][32][33] .…”

“…It can also be doped to further influence its properties and electronic band structure [38][39][40][41] . Firstly, as a method to increase conductivity at low temperatures through the addition of boron (p-type doping) 28,42 , and secondly, to enhance negative ion yield through the use of nitrogen doping (n-type doping) 33 .…”