SRF2011 - List of Authors (Ford, D.C.)

Paper

Title

Page

First Principles Investigation of Hydrogen in Niobium

868

D.C. Ford, L.D. Cooley
Fermilab, Batavia, USA
D.C. Ford
Northwestern University, Evanston, USA
D.N. Seidman
NU, Evanston, Illinois, USA

Niobium hydride is a contributor to degraded niobium SRF cavity performance by Q-slope and Q-disease. Hydrogen is easily absorbed into niobium when the protective oxide layer is disturbed, such as during electropolishing and chemical treatments, and the structure and distribution of hydrogen in niobium is altered during other processing steps such as baking. To optimize cavity performance and production efficiency, it is important to understand the structures of hydrogen in niobium, including the interactions of hydrogen with structural defects and other impurities such as oxygen. In this study density functional theory was used to evaluate these interactions. Hydrogen was examined as a dissolved interstitial impurity and in ordered niobium-hydride phases; and the interactions between hydrogen, niobium, vacancies on niobium sites, and oxygen dissolved in niobium were evaluated. The results yield information about the thermodynamic, electronic, magnetic, and geometric properties of these systems, which lead to important implications concerning the mobilities of impurities and vacancies in niobium and the precipitation of phases that are detrimental to cavity performance.

Poster THPO060 [1.167 MB]

THPO072

Raman Spectroscopy as a Probe of Surface Oxides and Hydrides on Niobium

912

J. Zasadzinski
IIT, Chicago, Illinois, USA
B. Albee, S. Bishnoi, C. Cao
Illinois Institute of Technology, Chicago, IL, USA
G. Ciovati
JLAB, Newport News, Virginia, USA
L.D. Cooley, D.C. Ford
Fermilab, Batavia, USA
Th. Proslier
ANL, Argonne, USA

Funding: ANL, FNAL
Raman microscopy/spectroscopy has been used in conjunction with AFM, tunneling and magnetic susceptibility to identify surface oxides and hydrides on annealed, recrystallized foils of high purity Nb and on single crystals of cavity grade Nb. Cold worked regions of the Nb foil as well as rough regions near grain boundaries showed clear evidence of ordered hydride phases which were identified by VASP phonon calculations. Cold worked regions also displayed enhanced surface paramagnetism. Surface enhanced Raman spectra have also been obtained using 1.0 nm Au depositon. The SERS spectra reveal hydride molecular species which are not observable by conventional Raman. These results indicate that Raman is a useful probe of Nb surfaces relevant for cavity performance

Paper	Title	Page
THPO060	First Principles Investigation of Hydrogen in Niobium	868
	D.C. Ford, L.D. Cooley Fermilab, Batavia, USA D.C. Ford Northwestern University, Evanston, USA D.N. Seidman NU, Evanston, Illinois, USA
	Niobium hydride is a contributor to degraded niobium SRF cavity performance by Q-slope and Q-disease. Hydrogen is easily absorbed into niobium when the protective oxide layer is disturbed, such as during electropolishing and chemical treatments, and the structure and distribution of hydrogen in niobium is altered during other processing steps such as baking. To optimize cavity performance and production efficiency, it is important to understand the structures of hydrogen in niobium, including the interactions of hydrogen with structural defects and other impurities such as oxygen. In this study density functional theory was used to evaluate these interactions. Hydrogen was examined as a dissolved interstitial impurity and in ordered niobium-hydride phases; and the interactions between hydrogen, niobium, vacancies on niobium sites, and oxygen dissolved in niobium were evaluated. The results yield information about the thermodynamic, electronic, magnetic, and geometric properties of these systems, which lead to important implications concerning the mobilities of impurities and vacancies in niobium and the precipitation of phases that are detrimental to cavity performance.
	Poster THPO060 [1.167 MB]

THPO072	Raman Spectroscopy as a Probe of Surface Oxides and Hydrides on Niobium	912
	J. Zasadzinski IIT, Chicago, Illinois, USA B. Albee, S. Bishnoi, C. Cao Illinois Institute of Technology, Chicago, IL, USA G. Ciovati JLAB, Newport News, Virginia, USA L.D. Cooley, D.C. Ford Fermilab, Batavia, USA Th. Proslier ANL, Argonne, USA
	Funding: ANL, FNAL Raman microscopy/spectroscopy has been used in conjunction with AFM, tunneling and magnetic susceptibility to identify surface oxides and hydrides on annealed, recrystallized foils of high purity Nb and on single crystals of cavity grade Nb. Cold worked regions of the Nb foil as well as rough regions near grain boundaries showed clear evidence of ordered hydride phases which were identified by VASP phonon calculations. Cold worked regions also displayed enhanced surface paramagnetism. Surface enhanced Raman spectra have also been obtained using 1.0 nm Au depositon. The SERS spectra reveal hydride molecular species which are not observable by conventional Raman. These results indicate that Raman is a useful probe of Nb surfaces relevant for cavity performance