173 Experimental Constraints on MCP Avalanche Simulations Using A Pulsed Picosecond Laser

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Description: This is a draft in progress. It will be updatesd regularly, so watch out. Abstract: Gain and timing characteristics of microchannel plates (MCPs) are determined both by the kinematics of electrons accelerating in and striking the MCP pore, and by the material propeties of the pore surface. Of particular importance are the Secondary Electron Yield (SEY), which describes the number of additional electrons produced when an electron strikes a surface material, and the forward-scattering (FS) probability, which describes the probability of an incident primary undergoing quasi-eleastic, specular reflection and keeping most of its kinetic energy. Both of these properties depend on the energies and striking angles of the incident electrons. Comparisons between simulations and experimental measurements can be used to help understand the relationship between the material properties of an MCP and the resulting cascade and, in particular, how changes in operational voltage should affect the resulting characteristics of the cascade. With the development of atomic layer deposition (ALD) techniques for fabricating MCPs there is now an opportunity to widely vary the composition of the material on the pore surface. This allows us to study MCP functionality over a much larger range of parameters than are available to conventional microchannel plates. In this paper we present a comparison between experimental measurements of ALD-functionalized MCPs with the results of a full, particle-tracking MCP Monte Carlo (MC), taking measured, material-level electron scattering properties as its inputs. Tests were performed on two MCP samples with different ALD coatings, 20 nm $Al_2O_3$ and 20 nm of $MgO$. Material level measurements were performed on silicon wafers coated with the same ALD layers and used as inputs to the full MCP simulation. This full simulation is used to predict how differences between the two materials translate to different gain-voltage dependecies. It also clarifies the internal processes driving these dependences. Methods like the one desribed in this paper can be used to further clarify the relationship between surface physics and avalanche formation, and also used in the optimization of highly customizable MCP photodetectors.

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