Photocathode Underlayer for Quantum Efficiency
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Solution Overview
Problem
Conventional photocathodes have limitations in achieving high spectral sensitivity due to low effective quantum efficiency, which is the ratio of emitted photoelectrons to incident photons, and recent demands for further improvement in quantum efficiency have not been adequately met.
Innovation Solution
A photocathode structure is developed with a supporting substrate and a photoelectron emitting layer containing an alkali metal, where an underlayer is placed between the substrate and the emitting layer to suppress alkali metal diffusion during thermal treatment, thereby enhancing quantum efficiency. The underlayer can be made of materials like beryllium oxide or its mixed crystals with other oxides, and the thickness ratio of the emitting layer to the underlayer is optimized to improve performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a photocathode uses a conventional structure with direct contact between supporting substrate and photoelectron emitting layer, then the device complexity is low, but the effective quantum efficiency is insufficient
Solution Approach 1:
An underlayer is introduced between the supporting substrate and the photoelectron emitting layer. This underlayer acts as an intermediary that prevents harmful interactions while maintaining functional performance, specifically suppressing alkali metal diffusion to the substrate during thermal treatment and improving the overall quantum efficiency of the photocathode.
2Reliability
If the photocathode undergoes thermal treatment to improve photoelectron emission, then the emission performance improves, but alkali metal diffusion occurs reducing quantum efficiency
Solution Approach 1:
The underlayer is pre-installed between the supporting substrate and the photoelectron emitting layer before thermal treatment occurs. This preliminary protective structure prevents alkali metal diffusion during subsequent thermal processing, allowing the thermal treatment to improve photoelectron emission without compromising the compositional stability of the alkali metal layer.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration significantly enhances the effective quantum efficiency of the photocathode, leading to improved spectral sensitivity across the usable wavelength range, with specific examples showing increases in quantum efficiency by up to 50% or more compared to conventional designs.
Implementation Method 1
a photocathode that emits photoelectrons in response to incidence of light with a predetermined wavelength
Implementation Method 2
an underlayer which is provided between the supporting substrate and the photoelectron emitting layer
Data Source
Figure 1A~1B
Figure 2
Figure 3
AI summary
The present invention relates to a photocathode havmg a structure to dramatically improve the effective quantum efficiency in comparison with that of a conventional art, an photomultiplier and an electron tube. The photocathode comprises a supporting substrate transmitting or blocking an incident light, a photoelectron emitting layer containing an alkali metal provided on the supporting substrate, and an underlayer provided between the supporting substrate and the photoelectron emitting layer. Particularly, the underlayer contains a beryllium oxide, and is adjusted in its thickness such that a thickness ratio of the underlayer to the photoelectron emitting layer falls within a specific range. This structure allows to obtain a photocathode having a dramatically improved quantum efficiency.