Wang Yuman, Yan Baojun, Wen Kaile, Liu Shulin, Qi Ming, Zhang Binting, Gu Jianyu, Yao Wenjing
School of Physics, Nanjing University, Nanjing, 210093, China.
State Key Laboratory of Particle Detection and Electronics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China.
Nanoscale Res Lett. 2021 Oct 7;16(1):151. doi: 10.1186/s11671-021-03606-y.
The electron multipliers gain is closely related to the secondary electron emission coefficient (SEE) of the emission layer materials. The SEE is closely related to the thickness of the emission layer. If the emission layer is thin, the low SEE causes the low gain of electron multipliers. If the emission layer is thick, the conductive layer can't timely supplement charge to the emission layer, the electronic amplifier gain is low too. The electron multipliers usually choose AlO and MgO film as the emission layer because of the high SEE level. MgO easy deliquescence into Mg(OH) Mg(OH)CO and MgCO resulting in the lower SEE level. The SEE level of AlO is lower than MgO, but AlO is stable. We designed a spherical system for testing the SEE level of materials, and proposed to use low-energy secondary electrons instead of low-energy electron beam for neutralization to measuring the SEE level of AlO, MgO, MgO/AlO, AlO/MgO, and precisely control the film thickness by using atomic layer deposition. We propose to compare the SEE under the adjacent incident electrons energy to partition the SEE value of the material, and obtain four empirical formulas for the relationship between SEE and thickness. Since the main materials that cause the decrease in SEE are Mg(OH)CO and MgCO, we use the C element atomic concentration measured by XPS to study the deliquescent depth of the material. We propose to use the concept of transition layer for SEE interpretation of multilayer materials. Through experiments and calculations, we put forward a new emission layer for electron multipliers, including 2-3 nm AlO buffer layer, 5-9 nm MgO main-body layer, 1 nm AlO protective layer or 0.3 nm AlO enhancement layer. We prepared this emission layer to microchannel plate (MCP), which significantly improved the gain of MCP. We can also apply this new emission layer to channel electron multiplier and separate electron multiplier.
电子倍增器的增益与发射层材料的二次电子发射系数（SEE）密切相关。SEE与发射层的厚度密切相关。如果发射层薄，SEE低会导致电子倍增器增益低。如果发射层厚，导电层不能及时向发射层补充电荷，电子放大器增益也低。由于SEE水平高，电子倍增器通常选择AlO和MgO薄膜作为发射层。MgO容易潮解成Mg(OH)、Mg(OH)CO和MgCO，导致SEE水平降低。AlO的SEE水平低于MgO，但AlO稳定。我们设计了一个用于测试材料SEE水平的球形系统，并提出用低能二次电子代替低能电子束进行中和来测量AlO、MgO、MgO/AlO、AlO/MgO的SEE水平，并通过原子层沉积精确控制膜厚。我们建议比较相邻入射电子能量下的SEE来划分材料的SEE值，并得到SEE与厚度关系的四个经验公式。由于导致SEE下降的主要物质是Mg(OH)CO和MgCO，我们用XPS测量的C元素原子浓度来研究材料的潮解深度。我们建议用过渡层的概念对多层材料的SEE进行解释。通过实验和计算，我们提出了一种新的电子倍增器发射层，包括2 - 3nm的AlO缓冲层、5 - 9nm的MgO主体层、1nm的AlO保护层或0.3nm的AlO增强层。我们将这种发射层制备到微通道板（MCP）上，显著提高了MCP的增益。我们也可以将这种新的发射层应用于通道电子倍增器和分离电子倍增器。
