@article{maheshwari_stevie_myneni_ciovati_rigsbee_dhakal_griffis_2014, title={SIMS analysis of high-performance accelerator niobium}, volume={46}, ISSN={["1096-9918"]}, DOI={10.1002/sia.5461}, abstractNote={Niobium is used to fabricate superconducting radio frequency accelerator modules because of its high critical temperature, high critical magnetic field, and easy formability. Recent experiments have shown a very significant improvement in performance (over 100%) after a high‐temperature bake at 1400 °C for 3 h. SIMS analysis of this material showed the oxygen profile was significantly deeper than the native oxide with a shape that is indicative of diffusion. Positive secondary ion mass spectra showed the presence of Ti with a depth profile similar to that of O. It is suspected that Ti is associated with the performance improvement. The source of Ti contamination in the anneal furnace has been identified, and a new furnace was constructed without Ti. Initial results from the new furnace do not show the yield improvement. Further analyses should determine the relationship of Ti to cavity performance. Copyright © 2014 John Wiley & Sons, Ltd.}, journal={SURFACE AND INTERFACE ANALYSIS}, author={Maheshwari, P. and Stevie, F. A. and Myneni, G. R. and Ciovati, G. and Rigsbee, J. M. and Dhakal, P. and Griffis, D. P.}, year={2014}, month={Nov}, pages={288–290} }
 @article{dhakal_ciovati_myneni_gray_groll_maheshwari_mcrae_pike_proslier_stevie_et al._2013, title={Effect of high temperature heat treatments on the quality factor of a large-grain superconducting radio-frequency niobium cavity}, volume={16}, number={4}, journal={Physical Review Special Topics. Accelerators and Beams}, author={Dhakal, P. and Ciovati, G. and Myneni, G. R. and Gray, K. E. and Groll, N. and Maheshwari, P. and McRae, D. M. and Pike, R. and Proslier, T. and Stevie, F. and et al.}, year={2013} }
 @article{stevie_maheshwari_pierce_adekore_griffis_2013, title={SIMS analysis of zinc oxide LED structures: quantification and analysis issues}, volume={45}, ISSN={["1096-9918"]}, DOI={10.1002/sia.4919}, abstractNote={Zinc oxide (ZnO) is a wide band gap semiconductor that shows great promise for development of light emitting diode structures. Interest in this technology has increased significantly, but even though controlled n‐type doping can be readily achieved, p‐type doping has been difficult. Numerous potential p‐type dopants were investigated in this SIMS study using a CAMECA IMS‐6F. The dopants and other elements of interest were quantified by use of ion implantation into ZnO substrates. Relative sensitivity factor values were obtained for H, Li, N, F, Na, Mg, Al, Si, K, Ga, As, Se, Ag, Cd, Te. Sample charging was encountered for some specimens, and adjacent electron neutralization procedures were employed. ZnO structures were prepared and subsequently analyzed with both O2+ and Cs+ primary beams. Depth profiles exposed a number of analysis issues. Because of the large number of elements, especially those at low atomic number, that were present in the structures, many mass interferences were encountered. Ag in particular was very difficult to monitor. Matrix effects were also noted, especially when high Mg doping was used. The need to monitor Al, Na, and K in the near surface region required analysis without conductive Au coating to reduce contamination. With careful choice of secondary ion species, it was possible to monitor the elements of primary interest using O2+ primary beam. SIMS demonstrated the ability to characterize the layers in the ZnO structure, including quantum wells, and to determine dopant and contaminant levels. Copyright © 2012 John Wiley & Sons, Ltd.}, number={1}, journal={SURFACE AND INTERFACE ANALYSIS}, author={Stevie, F. A. and Maheshwari, P. and Pierce, J. M. and Adekore, B. T. and Griffis, D. P.}, year={2013}, month={Jan}, pages={352–355} }
 @article{maheshwari_stevie_myeneni_ciovati_rigsbee_griffis_2011, title={Analysis of Interstitial Elements in Niobium with Secondary Ion Mass Spectrometry (SIMS)}, volume={1352}, ISBN={["978-0-7354-0909-5"]}, ISSN={["0094-243X"]}, DOI={10.1063/1.3579233}, abstractNote={Superconducting Radio Frequency (SRF) cavities provide enhanced efficiency and reduced energy utilization in present day particle accelerators. Niobium (Nb) is the material of choice for these cavities due to its high critical temperature and critical magnetic field. In order to understand why certain treatments, especially a low temperature bake, improve performance, it is important to study Nb surface characteristics and identify elemental contamination that can affect the performance of the cavity. H, C, O, and N are of interest because they are interstitial impurities in Nb. In earlier work, SIMS analysis using a CAMECA IMS‐6F with Cs+ primary beam showed that C and N were probably not significant factors impacting performance but there was a very high level of H in the Nb. Ion implants of C, N, O, and D into Nb provided quantification of C, N, O and indicated that D is very mobile in the Nb. Further analyses showed that heat treated Nb has lower levels of surface H than non heat treated Nb and subseq...}, journal={INTERNATIONAL SYMPOSIUM ON THE SUPERCONDUCTING SCIENCE & TECHNOLOGY OF INGOT NIOBIUM}, author={Maheshwari, P. and Stevie, F. A. and Myeneni, G. and Ciovati, G. and Rigsbee, J. M. and Griffis, D. P.}, year={2011}, pages={151-+} }
 @article{maheshwari_tian_reece_kelley_myneni_stevie_rigsbee_batchelor_griffis_2011, title={Surface analysis of Nb materials for SRF cavities}, volume={43}, ISSN={["1096-9918"]}, DOI={10.1002/sia.3513}, abstractNote={Abstract}, number={1-2}, journal={SURFACE AND INTERFACE ANALYSIS}, author={Maheshwari, P. and Tian, H. and Reece, C. E. and Kelley, M. J. and Myneni, G. R. and Stevie, F. A. and Rigsbee, J. M. and Batchelor, A. D. and Griffis, D. P.}, year={2011}, pages={151–153} }
 @article{ciovati_myneni_stevie_maheshwari_griffis_2010, title={High field Q slope and the baking effect: Review of recent experimental results and new data on Nb heat treatments}, volume={13}, ISSN={["1098-4402"]}, DOI={10.1103/physrevstab.13.022002}, abstractNote={Here, the performance of superconducting radio-frequency (SRF) cavities made of bulk Nb at high fields (peak surface magnetic field greater than about 90 mT) is characterized by exponentially increasing rf losses (high-field Q-slope), in the absence of field emission, which are often mitigated by low temperature (100-140 °C, 12-48 h) baking. In this contribution, recent experimental results and phenomenological models to explain this effect will be briefly reviewed. New experimental results on the high-field Q-slope will be presented for cavities that had been heat treated in a vacuum furnace at high temperature without subsequent chemical etching. These studies are aimed at understanding the role of hydrogen on the high-field Q-slope and at the passivation of the Nb surface during heat treatment. Improvement of the cavity performances, particularly of the cavities’ quality factor, have been obtained following the high temperature heat-treatments, while SIMS surface analysis measurements on Nb samples treated with the cavities revealed significantly lower hydrogen concentration than for samples that followed standard cavity treatments.}, number={2}, journal={PHYSICAL REVIEW SPECIAL TOPICS-ACCELERATORS AND BEAMS}, author={Ciovati, G. and Myneni, G. and Stevie, F. and Maheshwari, P. and Griffis, D.}, year={2010}, month={Feb} }