A5067871722- Diamond and Carbon-based Materials Research
- Particle accelerators and beam dynamics
- Photocathodes and Microchannel Plates
- Particle Accelerators and Free-Electron Lasers
- Gyrotron and Vacuum Electronics Research
- Electron and X-Ray Spectroscopy Techniques
- Semiconductor materials and devices
- Radiation Detection and Scintillator Technologies
- Particle Detector Development and Performance
- Atomic and Subatomic Physics Research
- Electronic and Structural Properties of Oxides
- Plasma Diagnostics and Applications
- Laser Design and Applications
- Quantum and electron transport phenomena
- High-pressure geophysics and materials
- X-ray Spectroscopy and Fluorescence Analysis
- Neutrino Physics Research
- Surface and Thin Film Phenomena
- Nuclear Physics and Applications
- Advanced Surface Polishing Techniques
- Advanced X-ray Imaging Techniques
- Dark Matter and Cosmic Phenomena
- Integrated Circuits and Semiconductor Failure Analysis
- Advanced X-ray and CT Imaging
- Advanced Chemical Physics Studies
SLAC National Accelerator Laboratory
2006-2025
Brookhaven National Laboratory
2011-2024
University of Rochester
2024
Stanford University
2023
Los Alamos National Laboratory
2018-2022
Stony Brook University
2003-2020
California Institute of Technology
2020
Max Planck Institute for Physics
2018
Argonne National Laboratory
2018
United States Naval Research Laboratory
2018
Metal photocathodes are commonly used in high-field rf guns because they robust, straightforward to implement, and tolerate relatively poor vacuum compared semiconductor cathodes. However, these cathodes have low quantum efficiency (QE) even at UV wavelengths, still require some form of cleaning after installation the gun. A process for improving QE is laser cleaning. In this technique UV-drive focused a small diameter close metal's damage threshold then moved across surface remove...
Nano-roughness limits the emittance of electron beams that can be generated by high efficiency photocathodes, such as thermally reacted alkali antimonide thin films. However there is an urgent need for photocathodes produce order magnitude or more lower than present day systems in to increase transverse coherence width beam. In this paper we demonstrate a method producing cathodes with near atomic smoothness reproducibility.
Alkali antimonides are well established as high efficiency, low intrinsic emittance photocathodes for accelerators and photon detectors. However, conventionally grown alkali antimonide films polycrystalline with surface disorder roughness that can limit achievable beam brightness. Ordering the crystalline structure of has potential to deliver higher brightness electron beams by reducing enabling engineering material properties at level atomic layers. In this report, we demonstrate growth...
The development of high-brightness electron sources is critical to state-of-the-art accelerator applications like X-ray free laser (XFEL) and ultra-fast microscopy. Cesium telluride chosen as the source material for multiple cutting-edge XFEL facilities worldwide. This manuscript presents first demonstration growth highly crystalized epitaxial cesium thin films on 4H-SiC graphene/4H-SiC substrates with ultrasmooth film surfaces. ordering was characterized by in situ reflection high energy...
Free-electron lasers and energy recovery linacs represent a new generation of ultra-high brightness electron accelerator based x-ray sources. Photocathodes are critical performance-limiting component these systems. Here, we describe the development photocathodes on potassium-cesium-antimonide that satisfy many key requirements future light sources, such as robustness, high quantum efficiency when excited with visible light, low transverse emittance.
Alkali-antimonide photocathodes were grown on Si(100) and studied by means of XPS UHV-AFM to validate the growth procedure morphology this material. The elements evaporated sequentially at elevated substrate temperatures (first Sb, second K, third Cs). generated intermediate K-Sb compound itself is a photocathode composition K2.4Sb close favored K3Sb stoichiometry. After cesium deposition, surface layer enriched. determined rms roughness 25 nm results in domination emittance photoinjector...
Measurements of the intrinsic emittance and transverse momentum distributions obtained from a metal (antimony thin film) photocathode near below photoemission threshold are presented. show that is limited by lattice temperature cathode as incident photon energy approaches threshold. A theoretical model to calculate this An excellent match between experimental measurements calculations demonstrated. These relevant low electron sources for Free Electron Lasers Ultrafast Diffraction experiments.
Design methodologies for high-performance photocathodes become increasingly important, driven by the needs of advanced x-ray light sources and ultrafast electron diffraction microscopy. Cathode design has been hampered interdependent performance metrics, where improving one compromises another. Rapid developments in modeling nanomaterial fabrication allow tailoring electronic structure ways that influence fundamental mechanisms photoemission: absorption, transport, emission. This survey...
High-quality single-crystal and polycrystalline chemical-vapor-deposition diamond detectors with platinum contacts have been tested at the white-beam X28C beamline National Synchrotron Light Source under high-flux conditions. The voltage dependence of these devices has measured both DC pulsed-bias conditions, establishing presence or absence photoconductive gain in each device. Linear response consistent theoretically determined ionization energy achieved over eleven orders magnitude when...
Alkali antimonides have a long history as visible-light-sensitive photocathodes. This work focuses on the process of fabrication bi-alkali photocathodes, K2CsSb. In-situ synchrotron x-ray diffraction and photoresponse measurements were used to monitor phase evolution during sequential photocathode growth mode Si(100) substrates. The amorphous-to-crystalline transition for initial antimony layer was observed at film thickness 40 Å . crystalline structure dissolved upon potassium deposition,...
We present the results of our investigation lead as a suitable photocathode material for superconducting rf injectors. Quantum efficiencies (QE) have been measured range incident photon energies and compared to predictions from three-step model photoemission. A variety cathode preparation methods used, including various plating techniques on niobium substrate. The effects operating at ambient cryogenic temperatures different vacuum levels QE also studied.
The diamond amplifier (DA) is a new device for generating high-current, high-brightness electron beams. Our transmission-mode tests show that, with single-crystal, high-purity diamonds, the peak current density greater than 400 mA/mm², while its average can be more 100 mA/mm². gain of primary electrons easily exceeds 200, and independent their within practical range DA applications. We observed emission. maximum emission measured was 40, bunch charge 50 pC/0.5 mm². There 35% probability an...
Two ${\mathrm{K}}_{2}\mathrm{CsSb}$ photocathodes were manufactured at Brookhaven National Lab and delivered to Jefferson within a compact vacuum apparatus pressure $\ensuremath{\sim}{10}^{\ensuremath{-}11}\text{ }\text{ }\mathrm{Torr}$. These evaluated using dc high voltage photogun biased voltages up 200 kV, illuminated with laser light wavelengths 440 or 532 nm, generate electron beams currents 20 mA. Some conditions produced exceptionally large photocathode charge lifetimes, without...
Electron emission from the negative electron affinity (NEA) surface of hydrogen terminated, boron doped diamond in [100] orientation is investigated using angle resolved photoemission spectroscopy (ARPES). ARPES measurements 16 eV synchrotron and 6 laser light are compared found to show a catastrophic failure sudden approximation. While high energy yield little information regarding NEA, low reveals for first time that NEA results novel Franck-Condon mechanism coupling electrons conduction...
Ultra-flat, ultra-thin alkali antimonide photocathodes with high crystallinity can exhibit quantum efficiency and low mean transverse energy of outgoing electrons, which are essential requirements for a variety applications photocathode materials. Here, we investigate the growth Cs3Sb on graphene-coated 4H–SiC (Gr/4H–SiC), 3C–SiC, Si3N4 substrates. Sb is deposited using pulsed laser deposition, while Cs thermally simultaneously. We demonstrate, employing x-ray analysis measurements, that...
A promising new concept of a diamond-amplified photocathode for generation high-current, high-brightness, and low thermal emittance electron beams was recently proposed is currently under active development. Detailed understanding physical processes with multiple energy time scales required to design reliable efficient diamond-amplifier cathodes. We have implemented models, within the VORPAL computational framework, simulate secondary charge transport in diamond order facilitate...
Hard x-ray photoelectron spectroscopy was applied to investigate the diamond-metal Schottky barrier heights for several metals and diamond surface terminations. The position of valence-band maximum determined by theoretically calculating density states applying cross section corrections. diamond-platinum height lowered 0.2 eV after thermal annealing, indicating annealing may increase carrier injection in devices leading photoconductive gain. platinum contacts on oxygen-terminated found...
K2CsSb is a promising photocathode candidate to serve as an electron source in next-generation light sources such Free Electron Lasers (FEL) and Energy Recovery Linacs (ERL). As the traditional recipe for creation of photocathodes typically results rough surface that deteriorates beam quality, significant effort has been made explore novel growth methods photocathodes. In this paper, method ternary co-evaporation K, Cs, Sb described. By using in-situ synchrotron X-ray techniques, quality...
K-Cs-Sb bialkali antimonide photocathodes grown by a triple-element codeposition method have been found to excellent quantum efficiency (QE) and outstanding near-atomic surface smoothness employed in the VHF gun Advanced Photoinjector Experiment (APEX), however, their robustness terms of lifetime at elevated photocathode temperature has not yet investigated. In this paper, relationship between The origin significant QE degradation temperatures over $70\text{...
Cesium telluride (CsTe) photocathodes have been the primary choice for electron sources by worldwide accelerators, due to their high quantum yield, stable performance in complex operation environments and long lifetime. In this paper we compared traditional sequential newly developed coevaporation growth of CsTe describing chemical structural evolution each method, using situ, real time x-ray characterization. From codeposition were able achieve ∼2 nm surface roughness, crystallinity a...
Bi-alkali antimonide photocathodes are one of the best known sources electrons for high current and/or bunch charge applications like Energy Recovery Linacs or Free Electron Lasers. Despite their quantum efficiency in visible light and low intrinsic emittance, surface roughness these prohibits use as emittance cathodes accelerating gradient superconducting normal conducting radio frequency photoguns limits minimum possible near threshold. Also, growth process materials is largely based on...
Two transmission-mode diamond X-ray beam position monitors installed at National Synchrotron Light Source (NSLS) beamline X25 are described. Each monitor is constructed around two horizontally tiled electronic-grade (p.p.b. nitrogen impurity) single-crystal (001) CVD synthetic diamonds. The position, angle and flux of the white can be monitored in real time with a resolution 500 nm horizontal direction 100 vertical for 3 mm × 1 beam. first has been operation more than one year without any...