Mechanistic study on the micro-optical morphology and electrical properties of microchannel plates by acid-base alternating corrosion processes

doi:10.21203/rs.3.rs-3141726/v1

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Mechanistic study on the micro-optical morphology and electrical properties of microchannel plates by acid-base alternating corrosion processes

https://doi.org/10.21203/rs.3.rs-3141726/v1

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published 16 Oct, 2023

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As a two-dimensional vacuum electron multiplier device, the microchannel plate is made by solid method with lead silicate glass as the base material, and acid-base etching to remove the core material is a key step in the formation of the microchannel plate, which mainly affects the microstructure, morphology and composition of the inner wall surface, and then affects the electrical properties of the microchannel plate. The microscopic morphology of silicate glass under different etching processes was studied by scanning electron microscopy, and it was found that with the increase of acid-base alternation during the etching process, the particle density of the inner wall of the channel gradually decreased, and the energy spectrum analysis of the particles revealed that the main contents were Pb and Bi; further by AFM analysis, the particle peak height was reduced from 31.1 nm to 1.9 nm with roughness. The results of the electrical and noise properties of the microchannel plates show that an appropriate increase in acid-base alternation can effectively reduce the bulk resistance and dark current without reducing the gain of the microchannel plates. This shows that increasing the "erosion intensity" of the acid-base alternation multiple times during corrosion can effectively improve the core-skin diffusion layer, further affecting the physical and chemical transformation of the nanoscale morphology, pointing to a new direction for improving the electrical properties of microchannel plates made of silicate glass.

Microchannel plate

Nanoscale morphological transformation

Dark current density

Microchannel plate (MCP) is a high aspect ratio porous lead-silicate glass array structure with electron multiplication properties. With the rapid development of modern science and technology, its application scope has been broadened such as particle detection and micro-optical imaging ^[1–8], and the demand for detector performance has been increasing, while MCP is facing problems such as high background noise and low gain, which have restricted the s further development. Studies of the gain and noise performance of microchannel plates have identified numerous factors affecting noise and gain, among them the reduction of the significant background noise caused by radioisotopes (potassium and rubidium) in photodetector devices by reducing the 40K content in the glass material^[9–12]. One of the most important factors is the inner surface of the micro via, which directly affects the physical processes associated with electron multiplication, and therefore the study of the inner surface of micro via is of great importance to improve gain and reduce background noise. The inner wall surface is formed by the acid and alkaline liquid erosion and hydrogen reduction processes at the core and skin glass diffusion interface, so the different erosion processes directly affect the micro-hole inner wall surface structure and composition. There have been many studies on the surface structure and composition of the inner wall of microchannel plates, mainly focusing on the direct effects of different physicochemical processes on the morphology, structure and composition of the inner wall of microchannel plates, and thus the influence of surface structure morphology and composition on plate volume resistance, electron gain and fixed pattern noise ^[13–17]. In this paper, the local morphological transformations and elemental valence states of lead silicate glass on the inner wall surface of MCP channels under increased alternating acid-base attack were investigated, while the electrical properties of MCP were measured under the corresponding conditions to establish the relationship between nanoscale microstructure and macroscale electrical properties, and it can be found that alternating acid-base plays a crucial role in the nanoscale morphology and electrical properties.

Leaded silicate glass MCP is manufactured using soluble glass with the raw materials of chemical composition as shown in Table 1. The core glass is hand cast into a glass rod and the skin glass is drawn into a shaped glass tube stretched into fibers, which are then bundled into blocks, sliced and chemically mechanically polished to form a fiber optic plate. The soluble fiber core is chemically etched to form holes, followed by hydrogen reduction and electrode material plating, etc., to make MCP with resistance and emission characteristics.

Table 1

Standard composition of lead silicate glass (%, molar fraction)
	K₂O	Na₂O	BaO	Bi2O3	Al₂O₃	SiO₂	PbO
%, Mol Fraction	5.9	1.8	1.1	9	1.4	Bal.	20.8

In this paper, the morphology of the inner wall of the channel is investigated by controlling the number of acid and alkali alternations during the MCP corrosion process, combined with the MCP inner wall roughness and testing, and the noise performance is assessed as a final validation of the process reliability. The acid and alkali etching process is shown in Table 2. The acid concentration was 1 mol/L dilute hydrochloric acid; the base was a NaOH solution with a mass concentration of 5%; and the temperature of the acid-base solution was 25°C. The corrosion was carried out using a magnetic stirring device to rotate the solution. Between the acid and alkali alternations a pure water ultrasonic cleaning process was used with an ultrasonic frequency of 40 kHz and a power of 300 W.

Table 2

Different corrosion processes.
Etching Process	Step 1: Acid 1st	Step 2: Lye 1st	Step 3: Acid 2nd	Step 4: Lye 2nd
Process 1	60min	30min	60min	60min
Process 2			60min	60min
Process 3			60min	60min

Table 2

(continued) Different corrosion processes.
Etching Process	Step 5: Acid 3rd	Step 6: Lye 3rd	Step 7: Acid 4th	Step 8: Lye 4th
Process 1
Process 2	60min	60min
Process 3	60min	60min	60min	60min

The body resistance and gain of the MCP were measured by a vacuum electronic test set-up (VPTF, Nanjing, China), as shown in Fig. 1, with the vacuum of the cavity maintained at better than 1.3 × 10^− 4 Pa. The body resistance of the MCP sample was obtained by measuring the conduction current of the MCP at the corresponding voltage with a microcurrent meter while the MCP input and output were in closed circuit, while the average output current of the MCP was collected from the fluorescent screen and tested with a microcurrent meter. The ratio of the average input current to the average output current is the gain of the MCP. The dark current was also measured at different voltages. The internal surface morphology of the channels was characterized using a swept surface electron microscope (SEM, HITACHI Regulus 8220) and the microscopic morphology of the internal surface of the holes of the MCP was analyzed using an atomic force microscope (AFM, DIMENSION ICON with ScanAsyst) with a contact imaging method.

3.1. The shape of the inner wall of the channel under different alternating acid and alkali corrosion processes

The inner wall of the MCP channel will form a reactive surface after acid and alkali etching treatment, which has a greater impact on the subsequent degassing process and the emission performance of secondary electrons, the greater the roughness of the inner wall of the channel, the greater the reactive surface area. Alternating acid and alkali corrosion can effectively reduce the roughness of the inner wall of the channel, while the length of the alkali etching time will have a certain impact on the roughness. It is also considered that after reducing the alkali etching time, the core skin permeation layer may be difficult to remove, and the existence of this permeation layer will not only increase the surface roughness and cause electron memory effect^[10],but also increase the adsorption of gas on the inner wall of the channel, which in turn brings ion noise. Therefore, a smooth channel surface is prepared by selecting a suitable etching process. In this paper, we first characterized the inner surface morphology of the channels of MCP treated with the above three corrosion processes using swept surface electron microscopy; secondly, we analyzed the microscopic morphology and roughness of the inner surface of the pores of MCP using atomic force microscopy.

According to Table 2 different acid-base alternating corrosion processes of MCP, after hydrogen reduction and cleaning, test its inner wall surface morphology. From Figure 2 (a) can be seen, Process 1 MCP, the channel wall there are more particles; Figure 2 (b) Process 2 MCP, the channel wall particle number significantly reduced; Figure 2 (c) Process 3 MCP, the channel wall no obvious particles. Figure 3 can be seen with the number of acid and alkali increase the number of particles in the channel wall significantly reduced. It can be speculated that increasing the corrosion intensity of MCP, the core-skin interface diffusion layer changes, and further in the hot hydrogen atmosphere, affecting the reduction of reducible metal oxides in the channel surface aggregation, resulting in changes in the conductive properties and secondary emission characteristics of the channel inner wall surface.

To further determine the particle composition, sample points 3 and 4, the characteristic points of the inner wall of the MCP channel from Process 1, were also selected and their EDS profiles were measured, as shown in Fig. 4. It is evident from the profiles that the highest content of lead and bismuth in the surface components of the inner wall of the channel may be due to the reduction process producing a new phase, i.e. the aggregation of lead atoms, resulting in an increase in the Z-axis height and surface roughness of the inner wall of the channel. The aggregation of lead atoms is in a diffusely connected state. In the diffusion state, the lead atoms combine into larger lead aggregates and are individually embedded in the bulk glass. After multiple new phases are created, the distance between the lead aggregates becomes smaller and a connected state is formed. At the same time the bismuth atoms produced by reduction also aggregate with the lead aggregates and form new aggregates. Therefore, suitable acid-base alternation during corrosion can improve the surface morphology and elemental distribution of the inner walls of the channels.

Further characterization of the inner wall morphology and roughness testing of the MCP for the three etching processes, Figure 5 (a) can be seen, Process 1 MCP, the channel inner wall surface appears larger island particles, and island particles peak height 31.1 nm; with the number of acid-base increase the number of island particles and peak height significantly reduced, Process 3 MCP the roughness of 1.9 nm. This acid etching stripping core after the glass skin glass surface appears island structure, these island particles in the fiber drawing have been formed at the interface, indicating that the core skin glass interface diffusion there is mutual reaction diffusion^[18] .

3.2. Dark currents and background noise under different acid-base alternating processes

Firstly, the electrical properties of the MCP itself after three corrosion processes were compared and analyzed, as shown in Table 3, it can be seen that the (c) body resistance decreases with the increase of the alternating acid and alkali of the corrosion process. Then the test data of dark current under different acid-base corrosion processes were further tested, and the schematic diagram is shown in Fig. 6 below. Noise tests were carried out on the microchannel plates after different numbers of acid-base corrosion, and the background noise tested by the customer Jilin University was taken as the final evaluation. It can be seen that compared to the Process 1 MCP, the MCP treated with the increased acid-base alternating corrosion process shows a better noise profile in the component and customer tests, as shown in the Fig. 8. Analysis of the reasons for the reduction in noise is mainly because with the addition of alternating acid-base etching, there is greater correlation between the inner wall roughness and the state of the alkali metal on the surface, where the inner wall islands of particles are prone to tip discharge, resulting in a greater background noise; the increased roughness of the inner wall may result in more gas adsorption on its surface, which ionizes at high voltages and is accelerated in the opposite direction of the electric field to the input of the channel and has the opportunity to collide with the photoelectric. These additional electrons are then re-generated as secondary electrons by the channel electric field, resulting in ion feedback noise. Similarly for alkali metal ions with small atomic radii attached to the channel surface, they can also be affected by the operating voltage and migrate off the inner wall of the channel, resulting in similar ion feedback. Finally, Process 1 MCP, which has a higher dark current, and Process 3 MCP, which has a lower one.

Table 3

Electrical properties of different acid-base alternating corrosion processes.
Sample	Bulk Resistances	Gain	Number
Process 1 MCP	379	15320	6
Process 2 MCP	216	13620	7
Process 3 MCP	138	17213	6

3.3. Changes in background noise under different voltages and screen voltages

As the MCP voltage and screen voltage change, the background noise also changes accordingly. We selected the background at a screen voltage of 3800V and an MCP voltage of 1550V as the base background subtraction, and measured the trend of background noise changes at fixed screen voltage and different MCP voltage, as well as the trend of background noise changes at constant MCP voltage and different screen voltage, as shown in Figs. 9 and 10. It was found that the number of noise generated with the increase of MCP voltage is much higher than that generated with the increase of screen voltage, as shown in Figs. 11 and 12. Which may be due to the low surface potential barrier of MCP material under high voltage, and “hot-spots” caused by debris on the MCP surface are excluded, which is easy to escape more electrons^[19].

The performance of the microchannel plate after different acid-base alternating treatments was investigated according to the mechanism of acid-base corrosion of the microchannel plate.The SEM characterization and AFM roughness test results show that increasing the acid-base alternating corrosion can effectively reduce the formation of inner wall island particles and further reduce the inner wall surface roughness. Performance tests on the dark current of the microchannel plate reflect that an appropriate increase in acid-base etching can reduce the dark current and reduce the background noise. Therefore, by adjusting the acid-base etching process, it is possible to improve the MCP noise profile without increasing other risk factors.

Acknowledgements

The authors express their gratitude to North Night Vision Science & Technology (Nanjing) Research institute Co., Ltd. for financially supporting this study. We also thank Institute of Atomic and Molecular Physics, Jilin University for providing test equipment.

CRediT authorship contribution statement

Tao Li: Formal analysis, Data curation, determining the research plan, data analysis, and writing and revised the manuscript. Jian Wang: Determining the research plan, revised the manuscript. Xiaoqing Cong: Determining the research plan, data analysis. Kai Pan：Formal analysis, Data curation, data analysis. Wankai Li: Formal analysis, Data curation, data analysis. Ge Jin: Formal analysis, Data curation. Xiangbiao Qiu: Formal analysis, Data curation. Yanjian Lin: Determining the research plan, data analysis.

Declaration of Interest Statement

This manuscript is an origin work and has not been published elsewhere in part or in entirety and is not under consideration by another journal. We have read and understood the journal’s policies, and we believe that neither the manuscript nor the study violates any of these. There are no conflicts of interest to declare. We are looking forward to hearing your reply and with thanks for your kind consideration.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Supplementary information

Increasing the acid-base alternating corrosion can effectively reduce :

1) the formation of inner wall island particles and further reduce the inner wall surface roughness. The particle peak height was reduced from 31.1 nm to 1.9 nm.

2) the dark current and the background noise.

Pointing to a new direction for improving the electrical properties of microchannel plates made of silicate glass.

Funding

The project conducted in this research has not received any form of financial support or sponsor-ship. All research activities have been carried out by the researchers themselves, without any influence or control from any third-party organizations or indi-viduals. We assure the objectivity and independence of the research findings, adhering to strict ethical standards and research guidelines.

Ethical approval (not Applicable)

The paper did not involve experiments related to human tissues and did not violate ethical and ethical requirements.

Consent for publication

All authors agreed to publish this research article.

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No competing interests reported.

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You are reading this latest preprint version

Mechanistic study on the micro-optical morphology and electrical properties of microchannel plates by acid-base alternating corrosion processes

Status:

Journal Publication

Version 1

Abstract

Figures

1. Introduction

2. Materials and methods

3. Results and Discussion

3.1. The shape of the inner wall of the channel under different alternating acid and alkali corrosion processes

3.2. Dark currents and background noise under different acid-base alternating processes

3.3. Changes in background noise under different voltages and screen voltages

4. Conclusions

Declarations

Acknowledgements

CRediT authorship contribution statement

Declaration of Interest Statement

Data availability

Supplementary information

Funding

Ethical approval (not Applicable)

Consent for publication

References

Additional Declarations

Status:

Journal Publication

Version 1