Ultra-Clean Graphene Coating for Robust Operation of High Brightness Photocathodes
- Qrona Technologies LLC
- Brookhaven National Lab. (BNL), Upton, NY (United States)
The main goal of this Phase-I SBIR project was to develop high-performance (In)GaN-based thin-film photocathodes (PhCs), deposited directly on large area MCPs, in order to improve detection efficiency, spatial and temporal resolutions, and immunity to magnetic fields, using a simpler and more reliable design as compared to the current state-of-the-art UV/visible photomultiplier tubes (MPTs) for DOE high-energy physics (HEP) and Nuclear Physics (NP) projects, as well as many other scientific, industrial, and defense applications. To achieve this goal, a novel ultra-high vacuum (UHV) surface-coating of negative electron affinity (NEA) (In)GaN-based PhCs was proposed in order to enable long-life operation of these high-performance electron sources in non-ideal vacuum encountered in high-intensity electron guns, used in many DOE projects, as well as other scientific, industrial, and defense applications. The main technical objectives of the Phase-I program included the demonstration of NEA photocathodes with (1) improved photoemission quantum efficiency (QE), (2) increased lifetime and tolerance for operation in non-ideal vacuum, and (3) substantial reduction in mean transverse energy (MTE), i.e., lower spread in the momentum of emitted photoelectrons. NEA photocathodes based on GaN, and its alloys with indium and/or aluminum, have the potential to simultaneously achieve all these three characteristics due to a unique combination of materials properties, including a wide bandgap, chemical and thermal robustness, and high crystallinity and smooth surface morphology that can be routinely obtained using a number of mature thin-film deposition techniques. We were able to perform the main Phase-I tasks, with some of the highlights listed below: 1) Fabrication of GaN NEA photocathodes (PhCs) on sapphire with QE > 80% @ λ ~ 250nm. 2) Development of a novel metallic buffer layer for high quality growth of GaN-based PhCs on arbitrary substates, including fused silica glass and metal substrates. 3) GaN NEA photocathodes (PhCs) on fused silica glass substrates with QE > 60% @ λ ~ 250nm. 4) Photoresponse extended well into the visible light range using p-doped InGaN PhCs with indium mole fraction > 30%. 5) Large reduction in MTE of (In)GaN PhCs by increasing the indium composition up to 30%. 6) Demonstration of the operation of p-type (mg-doped) InGaN NEA PhCs at liquid nitrogen temperature (77K) to achieve further reduction in MTE. 7) A new PhC surface coating process was developed to protect NEA PhCs against short air exposure, allowing the unpacking and installation of these PhCs in different systems at user sites, without the need for difficult and time-consuming surface cleaning procedures after air exposure. 8) First demonstration of UHV transfer of graphene as a protective layer for NEA Photocathodes. 9) Developing a new commercial application of NEA PhCs in high-resolution x-ray microscopes
- Research Organization:
- Qrona Technologies LLC
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- SC0020601
- OSTI ID:
- 1844958
- Type / Phase:
- SBIR (Phase I)
- Report Number(s):
- DOE-Qrona-0020933
- Country of Publication:
- United States
- Language:
- English
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