Chiara Elisabetta - PowerPoint Presentation

Chiara Elisabetta Marcora Supervisor: Dr. Martina MartinelloHelen Edwards Summer Internship Program29 August 2019 Ion Implantation for Alternative Doping in Niobium Superconductive RF Cavities

Superconductive RF cavities Figures of Merit:Average accelerating electric field ( E acc ): energy transferred to the particlesQuality factor Q0: power consumptionIdeally: Maximize the factors Q0 and Eacc  minimizes capital and operational costHow?Introduction of interstitial N atoms in Nb lattice, which lowers the surface resistance, enhancing the Q factor at higher Eacc. Currently achieved by: Nitrogen Doping at high TNitrogen Infusion at low TExplore new doping technique doping with Ion Implantation. Background August 19 Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities 2 N-doped N-infused

MotivationAugust 19 3 “Process of depositing dopant ions by directly bombarding the substrate with high-energy ions of the element to be deposited” Ion Implantation AdvantagesDisadvantagesPossibility to extend doping technology to every kind of solid element Damage of the crystal structure, i.e. formation of crystal defects ( Frenkel pairs, Nb interstitials) … Reduction of the Q 0 factor?Possibility to control the dopant concentration profile Control of the Q0 factor? Aim: Is it worth it to replace current doping techniques with ion implantationfrom a microstructural point of view? Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities    

4 samples of Niobium doped with Nitrogen using Ion Implantation with different parameters :Energy of the ion beamDose (amount of ions)Analysis Procedure for each sample:MethodsAugust 19Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities4We want to measure: through: through:

August 19 Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities 5 We want to measure: through:through:Results of: Concentration of N vs. target depth? Target Depth   IMPORTANT TO KNOW: N depth profile  influences Q factor Dpa Vacancy distribution N profile depth N depth profile

SRIM Results: N and vacancy depth profiles; and dpa (displacement per atom) distributions August 19 Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities 6High Energy IonsImplanted SurfaceTarget Depth Higher energy , ions travel deeper and distribute over larger volume SRIM Results SIMS Results Comparison SRIM-SIMS: Agreement in N concentration peak is not evident due to very high N concentration at surface

SRIM Results: N and vacancy depth profiles; and dpa (displacement per atom) distributions August 19 Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities7Low Energy IonsImplanted SurfaceTarget Depth SRIM Results SIMS Results Higher dose, higher N concentration Comparison SRIM-SIMS: Agreement in N concentration peak is not evident due to very high N concentration at surface Discrepancy between SRIM and SIMS results due high N concentration at surface Still, Ion implantation allows control of N depth profile by using different ion energy and dose Possibility to achieve interesting N depth profiles which are not achievable through N-doping and N-infusion

August 19 Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities 8 We want to measure: through:through:Results of: IMPORTANT TO KNOW: H igh damage level reduces Q factor? How much damage is left in the near surface region?

August 19Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities9 EBSD Results Damage due to ion implantation should appear as a fluctuation in the misorientation angle (= indicator of level of damage in the subgrain structure) in correspondence to the peak in vacancy concentration predicted in SRIM simulations (slide 6-7)No fluctuations in misorientation angleLimited ResolutionNo damage due to ion implantationBUT, due to rough surface and limited resolution further more accurate analysis are needed Figure 1. EBSD results . Kernel average misorientation (KAM) analyses of Niobium after ion implantation at ( a) sample 2; ( b ) sample 4; ( c) sample 6; (d) sample 8

August 19 Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities 10 We want to measure: through:through:Higher accuracyResults of: How much damage is left in the near surface region? IMPORTANT TO KNOW: h igh damage level reduces Q factor?

FIB – Sample Preparation August 19 Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities11Rough Implanted SurfaceRequiresMicromachining through FIB Loss of information in the first nm which are of crucial importance for the Q-factorImplanted SurfaceImplanted Surface   Uniform Implanted Surface

August 19 Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities12EBSD vs HR EBSDHR EBSD ResultsFigure 2. HR EBSD results. Kernel average misorientation (KAM) analyses of Niobium after ion implantation of sample 2Figure 3. HR EBSD results. Kernel average misorientation (KAM) analyses of Niobium after ion implantation of sample 8 Absence of fluctuations in misorientation angle as a function of depth Re-confirmation of absence of damage due to ion implantation

August 19Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities 13 We want to measure: through :through:HEAT TREATMENTFurther work:Allows manipulation of: Results of:

August 19Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities14 Predicting the effect of Heat Treatment Gaussian approximation of concentration profile: Use Fick’s Second law of diffusion to predict concentration profile changes after heat heat treatment: Solution for Ion implantation: where  Relationship between C oncentration, T emperature and t ime  

Predicting the effect of Heat Treatment August 19 Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities15t￬T￪AsymmetricHigh EnergyLow EnergySimilar to N-infusion and N-doping

SIMS Results after Heat Treatment August 19 Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities 16400 C; 30 min350 C; 10 minExperimental results not very consistent with predictionsHeat treating allows further manipulation of the N depth profile obtained from ion implantation

August 19Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities17 Conclusion Repetition of the analysis with different dopants elementsExplore the effect of more implantation conditionsIs it worth it to replace current doping techniques with ion implantation from a microstructural point of view? Possibility to achieve different N depth profiles from what obtained through N-infusion and N-doping and might enhance the Q-factor. The shape of these profile can be tuned by tuning the ion energy and dose or by heat treating+ No damage left in the crystal structure Further investigation into the prospect of this technique seems to be worth itFuture Plans

Shape factor; depends on cavity shape Surface resistance; defined as: Residual surface resistance Mattis Bardeen surface resistanceEffect on N interstitials:Reduction of with increasing fieldHowever, (less significant) increase inwhich is caused by impurities, trapped magnetic flux and lattice distortions Further detail: Effect of N interstitialsAugust 19 Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities 18

SCOPE: Measure nitrogen concentration depth profilePRINCIPLE: Further detail: Secondary Ion Mass Spectroscopy (SIMS) August 19 Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities19Sputtering

SCOPE: Measure damage in the near implanted surface region PRINCIPLE: Further detail: Electron Back Scattered Diffraction (EBSD) August 19Chiara Marcora | Ion Implantation for Alternative Nitrogen Doping in Niobium Superconductive RF Cavities20Misorientation= Strain in subgrain structure = Irradiation Damage Effect of different crystal orientations: