Deposition of lead thin films used as photo-cathodes by means of cathodic arc under UHV conditions (original) (raw)
Related papers
2006
The paper reports on recent progress in the application of the UHV arc technology, which was proposed as an alternative solution for the deposition of thin superconducting films of pure niobium (Nb) upon the inner surfaces of RF cavities designed for particle accelerators. There are presented new experimental studies aimed at the deposition of superconducting films of pure niobium (Nb) and lead (Pb) needed for the modern accelerator technology. The main experimental results and characteristics of arc-deposited thin superconducting films are discussed, and the progress achieved recently in the formation of such films is presented. Contribution to the XXII th "International Symposium on Discharges and Electrical Insulation in Vacuum" Matsue (Japan), 25
Deposition of superconducting niobium films for RF cavities by means of UHV cathodic Arc
Vacuum, 2006
Recently the UHV arc technology was proposed as a possible alternative for depositing thin superconducting films of pure niobium on the inside surface of RF cavities for particle accelerators. The paper describes status of research on deposition of superconducting films for RF accelerating cavities. New UHV arc based devices with planar and cylindrical niobium cathodes are presented. The main results and characteristics of arc deposited thin superconducting niobium films as well as the progress obtained recently in formation such films are also shown.
Deposition of Thin Metal Films by Means of Arc Discharges under Ultra-High Vacuum Conditions
EUROCON 2007 - The International Conference on "Computer as a Tool", 2007
The paper reports on plasma technology of the production of thin metal layers by means of controlled arc discharges, initiated at ultra-high vacuum (UHV) conditions, i.e. at the background pressure < 10-8 Pa, and carried out at the operating pressure < 10-5 Pa. Different UHV arc facilities, which have been designed and operated at IPJ in Swierk, are described. The UHV arc facility equipped with a cylindrical cathode made of a pure niobium (Nb) is applied for the deposition of superconducting Nb layers upon inner surfaces of RF accelerator cavities. The UHV arc device equipped with a truncated-cone cathode made of pure lead (Pb) is used for the formation of photo-cathodes in RF electron guns. Filtering systems, which are used to reduce an amount of metal micro-droplets, are described. Characteristics of the deposited samples show that very pure and smooth metal films of the bulk-like crystalline structure can be produced by means of the described technique.
High quality superconducting niobium films produced by an ultra-high vacuum cathodic arc
2005
The vacuum arc is a well-known technique to produce coating with enhanced adhesion and film density. Many cathodic arc deposition systems are actually in use in industry and research. They all work under (high) vacuum conditions in which water vapor pressure is an important source of film contamination, especially in the pulsed arc mode of operation. Here we present a Cathodic Arc system working under Ultra High Vacuum conditions (UHVCA). UHVCA has been used to produce ultra-pure niobium films with excellent structural and electrical properties at a deposition temperature lower than 100 o C. The UHVCA technique therefore opens new perspectives for all applications requiring ultra-pure films or, as in the case of Plasma Immersion Ion Implantation, ultra-pure plasmas.
UHV arc deposition for RF superconducting cavity: samples characterization
Thin niobium film on copper coated RF cavities are a very interesting alternative to bulk-Nb ones since copper is cheaper than niobium, has higher thermal conductivity and better mechanical stability. The magnetron sputtering technology for such coating was successfully used for the production of the 350 MHz LEP SC accelerating cavities at CERN. Unfortunately, the observed degradation of the quality factor with increasing cavity voltage is so far limiting the maximum useful field and therefore the application of this technology to future large accelerators designed to operate with field gradients higher than 25 MV/m. The alternative vacuum arc coating method, discussed in this paper, is a powerful technique for the deposition of films on several materials. Its main advantages, as compared to the standard sputtering process, are the ionized state of the evaporated material, the absence of gases to sustain discharge, the higher energy of atoms reaching the substrate surface and the capability of higher deposition rates. To ignite the arc one needs to produce a small plasma burst of a sufficient density to form a high-conductivity path between cathode and anode. To eliminate all possible source of contaminants we used a triggering system based on Nd-YAG pulsed laser focused on the cathode surface. We built and put into operation 3 different UHV arc system: a planar arc, a filtered arc and a cylindrical arc system. It was demonstrated that using the UHV arc technique bulklike films, suitable for superconducting applications, can be produced. The main disadvantage-the production of macroparticles that can increase the roughness and induce field emission-is being studied and methods to eliminate it are discussed. We present the different systems and discuss their possible application to cavity coating. Our recent results on the characterization of niobium film samples produced under different arc regime are also briefly presented.
Fabrication of thin metallic films by arc discharges under ultra-high vacuum conditions
Cathodic arc deposition technology offers an excellent approach to producing pure metal, alloy and compound films at very high rates and with excellent adhesion and density. High ion energy is the main factor allowing one to produce more compact films, with much stronger adhesion to the substrate than those obtained by other methods. It was shown that the cathodic arc working in ultra-high vacuum (UHV) conditions solves the problem of the oxygen contamination originating from water vapour thus paving the road to applications where very pure metallic films are needed. The paper presents systems used for deposition of thin coatings by means of arc discharges performed under the UHV conditions. The most important experimental results and characteristics of the arc-deposited thin superconducting films are discussed, and the progress achieved recently in the formation of such films is described.
SUPERCONDUCTING NB FILM FOR RF APPLICATIONS
2004
Copper RF cavities coated with thin Nb (Nb) films are an interesting possible alternative to bulk-Nb ones because copper is cheaper than Nb, has higher thermal conductivity and better mechanical properties. Unfortunately, the observed degradation of the quality factor (Q) with increasing electric field shown by Nb- sputtered cavities makes them unsuitable for future very high energy linear accelerators needing gradients higher than ≈15MV/m. We are therefore developing an alternate deposition technology, based on a cathodic arc system working in UHV conditions. Its main advantages compared to standard sputtering are the ionized state of the evaporated material, the absence of gases to sustain the discharge, the much higher energy of atoms reaching the substrate surface and, possibly, higher deposition rates. To ignite the arc we use a Nd-YAG pulsed laser focused on the cathode surface which proves a reliable and ultraclean trigger. Recent results on the characterization of Nb film sa...
UHV arc for high quality film deposition
2006
The vacuum arc is a well-known technique for producing coatings with enhanced adhesion and film density. Many cathodic arc deposition systems are actually in use in industry and research. They all work under (high) vacuum conditions in which water vapour pressure is an important source of film contamination, especially in the pulsed arc mode of operation. Here we present a cathodic arc system working under ultra-high vacuum conditions (UHVCA). We have used for arc ignition a Nd-YAG pulsed laser focused on the cathode surface, which provides a reliable system and allows eliminating all possible sources of contaminants. We have proven that the arc technique produces bulk-like films suitable for superconducting applications. UHVCA has been used to produce ultra-pure niobium films with excellent structural and electrical properties at a deposition temperature lower than 100oC. The UHVCA technique therefore opens up new perspectives for all applications requiring pure films and low deposition temperatures.
International Journal of Modern Physics A, 2007
We present the results of our investigation of lead and niobium as suitable photocathode materials for superconducting RF injectors. Quantum efficiencies (QE) have been measured for a range of incident photon energies and a variety of cathode preparation methods, including various lead plating techniques on a niobium substrate. The effects of operating at ambient and cryogenic temperatures and different vacuum levels on the cathode QE have also been studied.
Deposition methods of high-T, superconductors
Depositing high-T, oxide superconductors poses the most demanding challenge for thin film technology. The complexity of the superconductor film formation parallels the complexity of the materials themselves. Making films of these materials requires transporting all the elements in the proper stoichiometry onto the substrate, forming the correct crystal structure and layer stacking sequence, and providing sufficient oxygen to form the superconducting phase. Evaporation of separate metal constituents generally is a low-pressure process. A high oxygen-atom arrival rate at the substrate under this restriction can successfully be provided by oxygen rf-plasmas, microwave-generated atomic oxygen, electron cyclotron resonance (ECR) sources, and ozone-generation techniques. Sputter deposition suffers from negative ion bombardment of the substrate. This can be minimized by geometries where the substrate is held outside the plasma, and by applying high sputtering pressures with attendant short mean free paths, Chemical vapour deposition (CVD) stillshows some problems with volatile barium sources. Nevertheless, it represents one of the most promising techniques for large-scale applications. In the pulsed laser deposition (PLO) technique, a high-energy pulse of ultraviolet or visible laser radiation vaporizes and ejects the surface material which impinges on the substrate subsequently. The process runs far off the thermal equilibrium, and therefore produces an extremely good stoichiometric material transfer. Furthermore, parameters can be chosen to allow for a wide dynamic range between molecular beam and heavy sputter conditions. There are practically no restrictions regarding the reactive gas atmosphere in the deposition chamber. Highest quality epitaxial films of the YBa2Cu,0,_,: superconductor made to date have been produced this way. Other approaches include, e.g. thermal spraying, chemical spray pyrolysis, sol-gel spin casting, dipping, and electrodeposition. Nevertheless, traditional vacuum techniques, or the more novel laser deposition processes, are most likely of finding general acceptance for a thin film process.