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Damage recovery for SRF photoinjector cavities
Get PDFTwo niobium elliptical 1.3 GHz superconducting radio frequency SRF electron photoinjector cavities were successfully recovered after mechanical inner surface damage. Both cavities had deep imprints in the critical high surface electric field area around the photoelectric cathode position. The lengthy repair procedure, which consists of surface inspection and defect characterization, mechanical polishing and light chemical etching is described in detail. In the process, a new high pressure rinsing HPR nozzle system optimized for the special photoinjector geometry was also developed. Subsequent cold RF tests demonstrate complete performance recovery. This is the first time that photoinjector cavities damaged in the high electric field region could be recovere
The Electronic Impact of Light Induced Degradation in CsPbBr3 Perovskite Nanocrystals at Gold Interfaces
Get PDFThe understanding of the interfacial properties in perovskite devices under irradiation is crucial for their engineering. In this study we show how the electronic structure of the interface between CsPbBr3 perovskite nanocrystals PNCs and Au is affected by irradiation of X rays, near infrared NIR , and ultraviolet UV light. The effects of X ray and light exposure could be differentiated by employing low dose X ray photoelectron spectroscopy XPS . Apart from the common degradation product of metallic lead Pb0 , a new intermediate component Pbint was identified in the Pb 4f XPS spectra after exposure to high intensity X rays or UV light. The Pbint component is determined to be monolayer metallic Pb on top of the Au substrate from underpotential deposition UPD of Pb induced from the breaking of the perovskite structure allowing for migration of Pb
Elemental distribution and fracture properties of magnetron sputtered carbon supersaturated tungsten films
Get PDFThe combination of strength and toughness is a major driving force for alloy design of protective coatings, and nanocrystalline tungsten W alloys have shown to be promising candidates for combining strength and toughness. Here we investigate the elemental distribution and the fracture toughness of carbon C alloyed W thin films prepared by non reactive magnetron sputtering. W C films with up to 4 at. C crystallize in a body centered cubic structure with a strong ?hh0?texture, and no additional carbide phases are observed in the diffraction pattern. Atom probe tomography and X ray photoelectron spectroscopy confirmed the formation of such a supersaturated solid solution. The pure W film has a hardness 13 GPa and the W C films exhibit a peak hardness of 24 GPa. In situ micromechanical cantilever bending tests show that the fracture toughness decreases from 4.5 MPa m1 2 for the W film to 3.1 MPa m1 2 for W C films. The results show that C can significantly enhance the hardness of W thin films while retaining a high fracture toughnes
Doubly Bridged Anthracenes Blue Emitters for OLEDs
Get PDFThe photooxidative stability of a series of doubly bridged anthracenes was evaluated after their preparation via twofold macrocyclization of a bis resorcinyl anthracene. Lightfastness correlates with the energy levels of the highest occupied molecular orbital HOMO , resulting in superior stability of the tetraesters compared to the tetraethers. The lengths and steric demand of the linker only plays a minor role for the ester based compounds, which can be prepared in reasonable yields and thus tested in proof of concept organic light emitting diodes. Double ester bridging allows deep blue electro luminescence, highlighting the importance of the choice of the functional groups used for macrocyclizatio
Updates on Hydrogen Value Chain A Strategic Roadmap
Get PDFA strategic roadmap for noncarbonized fuels is a global priority, and thereduction of carbon dioxide emissions is a key focus of the Paris Agreement tomitigate the effects of rising temperatures. In this context, hydrogen is apromising noncarbonized fuel, but the pace of its implementation will dependon the engineering advancements made at each step of its value chain. Toaccelerate its adoption, various applications of hydrogen across industries,transport, power, and building sectors have been identified, where it can beused as a feedstock, fuel, or energy carrier and storage. However, widespreadusage of hydrogen will depend on its political, industrial, and socialacceptance. It is essential to carefully assess the hydrogen value chain andcompare it with existing solar technologies. The major challenge towidespread adoption of hydrogen is its cost as outlined in the roadmap forhydrogen. It needs to be produced at the levelized cost of hydrogen of lessthan 2 kg amp; 8722;1to be competitive with the established process of steammethane reforming. Therefore, this review provides a comprehensive analysisof each step of the hydrogen value chain, outlining both the currentchallenges and recent advance
Enhancing the Selectivity and Transparency of the Electron Contact in Silicon Heterojunction Solar Cells by Phosphorus Catalytic Doping
Get PDFAn intrinsic hydrogenated amorphous silicon a Si H i film and a doped silicon film are usually combined in the heterojunction contacts of silicon heterojunction SHJ solar cells. In this work, a post doping process called catalytic doping Cat doping on a Si H i is performed on the electron selective side of SHJ solar cells, which enables a device architecture that eliminates the additional deposition of the doped silicon layer. Thus, a single phosphorus Cat doping layer combines the functions of two other layers by enabling excellent interface passivation and high carrier selectivity. The overall thinner layer on the window side results in higher spectral response at short wavelengths, leading to an improved short circuit current density of 40.31 mA cm amp; 8722;2 and an efficiency of 23.65 certified . The cell efficiency is currently limited by sputter damage from the subsequent transparent conductive oxide fabrication and low carrier activation in the a Si H i with Cat doping. Numerical device simulations show that the a Si H i with Cat doping can provide sufficient field effect passivation even at lower active carrier concentrations compared to the as deposited doped layer, due to the lower defect densit
Fast Photoresponse from Hybrid Monolayer MoS2 Organic Photodetector
Get PDFAs a direct bandgap transition semiconductor with high carrier mobility, monolayer ML transition metal dichalcogenides TMDCs have attracted significant attention as a promising class of material for photodetection. It is reported that these layers exhibit a persistent photoconductance PPC effect, which is assigned to long lasting hole capture by deep traps. Therefore, TMDCs based photodetectors show a high photoresponse but also a slow response. Herein, intensity modulated photocurrent spectroscopy IMPS with steady state background illumination is performed to investigate the photoresponse dynamics in a hybrid photodetector based on ML MoS2 covered with an ultrathin layer of phthalocyanine H2Pc molecules. The results demonstrate that adding the H2Pc layer speeds up the photoresponse of the neat ML MoS2 photodetector by almost two orders of magnitude without deteriorating its responsivity. The origin of these improvements is revealed by applying the Hornbeck Haynes model to the photocarrier dynamics in the IMPS experiment. It is shown that the improved response speed of the hybrid device arises mostly from a faster detrapping of holes in the presence of the H2Pc layer, while the trap densities remain rather unchanged. Meanwhile, the additional absorption of photons in the H2Pc layer contributes to photocarrier generation, resulting in an enlarged responsivity of the hybrid devic
How Atomic Bonding Plays the Hardness Behavior in the Al Co Cr Cu Fe Ni High Entropy Family
Get PDFA systematic study on a face centered cubic based compositionally complex alloy system Al Co Cr Cu Fe Ni in its single phase state is carried out, where a mother senary compound Al8Co17Cr17Cu8Fe17Ni33 and five of its suballoys, obtained by removing one element at a time, are investigated and exhaustively analyzed determining the contribution of each alloying element in the solid solution. The senary and the quinaries are compared using experimental techniques including X ray absorption spectroscopy, X ray diffraction, transmission electron microscopy, and first principles hybrid Monte Carlo molecular dynamics simulations. Chemical short range order and bond length distances have been determined both at the experimental and computational level. Electronic structure and local atomic distortions up to 5.2 amp; 8201; have been correlated to the microhardness values. A linear regression model connecting hardness with local lattice distortions is presente
Fast charge high voltage layered cathodes for sodium ion batteries
No full textSodium ion batteries have not only garnered substantial attention for grid scale energy storage owing to the higher abundance of sodium compared with lithium, but also present the possibility of fast charging because of the inherently higher sodium ion mobility. However, it remains a phenomenal challenge to achieve a combination of these merits, given the complex structural chemistry of sodium ion oxide materials. Here we show that O3 type sodium ion layered cathodes for example, Na5 6Li2 27Ni8 27Mn11 27Ti6 27O2 have the potential to attain high power density, high energy density 260 amp; 8201;Wh amp; 8201;kg amp; 8722;1 at the electrode level and long cycle life capacity retention of 80 over 700 cycles in full cells . The design involves introduction of characteristic P3 structural motifs into an O3 type framework that serves to promote sodium ion diffusivity and address detrimental transition metal migration and phase transition at a high state of charge. This study provides a principle for the rational design of sodium ion layered oxide electrodes and advances the understanding of the composition structure property relationships of oxide cathode material
Solution driven processing of calcium sulfate The mechanism of the reversible transformation of gypsum to bassanite in brines
Get PDFHere, we show that calcium sulfate dihydrate gypsum can be directly, rapidly and reversibly converted to calcium sulfate hemihydrate bassanite in high salinity solutions brines . The optimum conditions for the efficient production of bassanite in a short time lt;5 min involve the use of brines with c NaCl gt; 4 M and maintaining a temperature, T gt; 80 C. When the solution containing bassanite crystals is cooled down to around room temperature, eventually gypsum is formed. When the temperature is raised again to T gt; 80 C, bassanite is rapidly re precipitated. This contrasts with the better known behaviour of the bassanite phase in low salt environments. In low salinity aqueous solutions, bassanite is considered to be metastable with respect to gypsum and anhydrite, and therefore gypsum to bassanite conversion does not occur in pure water. Interestingly, the high salinity transformation of gypsum to bassanite has been reported by many authors and used in practice for several decades, although its very occurrence actually contradicts numerical thermodynamic predictions regarding solubility of calcium sulfate phases. By following the evolution of crystalline phases with in situ and time resolved X ray diffraction scattering and Raman spectroscopy, we demonstrated that the phase stability in brines at elevated temperatures was inaccurately represented in the thermodynamic databases. Most notably for c NaCl gt; 4 M, and T gt; 80 C gypsum becomes readily more soluble than bassanite, which induces the direct precipitation of the latter from gypsum. The fact that these transformations are controlled by the solution provides extensive opportunities for precise manipulation of crystal formation. Our experiments confirmed that bassanite remained the sole crystalline phase for many hours before reverting into gypsum. This property is extremely advantageous for practical processing and efficient crystal extraction in industrial scenario