Abstract
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 Al2O3 and MgO film as the emission layer because of the high SEE level. MgO easy deliquescence into Mg(OH)2 Mg2(OH)2CO3 and MgCO3 resulting in the lower SEE level. The SEE level of Al2O3 is lower than MgO, but Al2O3 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 Al2O3, MgO, MgO/Al2O3, Al2O3/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 Mg2(OH)2CO3 and MgCO3, 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 Al2O3 buffer layer, 5–9 nm MgO main-body layer, 1 nm Al2O3 protective layer or 0.3 nm Al2O3 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.
Highlights
The secondary electron emission coefficient (SEE) of a material is defined as the ratio of the emitted secondary electrons number to the incident electrons number on the material
We propose that the preparation process of the new emission layer is to grow a 9 nm MgO main layer on the 2 nm Al2O3 buffer layer, and grow 1 nm Al2O3 protective layer or 0.3 nm A l2O3 enhancement layer on it, which can solve the problem of the MgO shortcomings of the emission layer in the electron multipliers
SEE Zoning and Analysis We compare the SEE value under the adjacent incident electrons energy to describe the change of SEE with the energy of incident electrons and define it as SEE(x + b) RSEE = SEE(x) and the SEE of the material is divided into three areas by the size of the RSEE value, namely the low energy region of the incident electron ( RSEE ≥ 1.02 ), the medium energy region of the incident electron ( 0.98 ≤ RSEE < 1.02 ) and the high energy region of the incident electron ( RSEE ≥ 0.98 )
Summary
The secondary electron emission coefficient (SEE) of a material is defined as the ratio of the emitted secondary electrons number to the incident electrons number on the material. The application field of secondary electrons is very wide, mainly divided into the field of electron multiplication, the field of material surface composition and structure analysis, and the field of suppressing. Electron multipliers consist of the substrate, the conductive layer and the emission layer. The incident electron hitting the emission layer leads to the generation of secondary electron from the emission layer. The secondary electron will be further accelerated by bias voltage to hit the emission layer and lead to more and more secondary electron, resulting in an electron avalanche and the emission of a cloud of electrons from the output. The emission layer lost a large amount of electric charge due to more and more secondary electron, so the conductive layer for the loss of the electron emission continuously provides the charge [15]
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