TEM and SIMS Analysis of (100), (110), and (111) Single Crystal Niobium

Abstract

Single crystal niobium specimens of (100), ( 110) and (111) crystal orientations have been analyzed using TEM and SIMS. The TEM specimens were prepared using Focused Ion Beam (FIB) and show niobium oxide thicknesses ranging from 4.9 to 8.3 nm for the three specimens after buffer chemical polishing. The oxide layers appear uniform and no significant sub-oxide region was noted. SIMS analysis was made for all three orientations on hydrogen, carbon, and oxygen before and after heat treatments at 90, 600, and 1250ºC. Hydrogen is at a high level between the oxide layer and niobium, but at a relatively low level in the oxide. No high oxygen concentration region was noted in the niobium below the oxide. C contamination on the surface is detected mainly at the surface. Analysis after heat treatments showed some decrease in hydrogen after the 600ºC heat treatment, and significant oxidation of the niobium after the 1250ºC heat treatment.

EELS of Niobium and Stoichiometric Niobium-Oxide Phases—Part I: Plasmon and Near-Edges Fine Structure

“…The existence of an unavoidable oxide layer at the surface of niobium handled in air or in the presence of oxygen was often mentioned and studied in the literature (see, e.g., Halbritter, 1987; Franchy et al, 1996; Kovács et al, 2003; Wu, 2006; Batchelor et al, 2007). However, the composition and thickness of this native oxide layer is not completely clear up to now and depend on the preparation of the niobium surface as well as on the crystallographic orientation of the surface and on the ambient oxygen atmosphere.…”

SIMS analysis of high‐performance accelerator niobium

“…[3] Cavities were traditionally made of polycrystalline Nb, but advantages have been noted for large-grain Nb, and single-crystal Nb modules have also been formed. [4] Performance is measured in terms of the Q factor or Q 0 , which is the ratio of energy stored in the cavity to energy dissipated in cavity walls.…”

Surface analysis of Nb materials for SRF cavities

“…In our initial studies of the Nb surface2, transmission electron microscopy (TEM) was used to characterize the oxide and suboxide regions on the Nb surface. Since Nb is a soft material, sample preparation by traditional TEM polishing methods is problematic since polishing can smear the surface and polishing media can become embedded in the material.…”

“…Since Nb is a soft material, sample preparation by traditional TEM polishing methods is problematic since polishing can smear the surface and polishing media can become embedded in the material. For our study,2 TEM lift‐out sample preparation using a gallium‐focused ion beam (FIB) system was used to obtain high‐quality TEM samples 3, 4. The cross‐sectional TEM images obtained were used to measure oxide thickness on single crystal samples, which showed a continuous uniform oxide approximately 8 nm thick with no apparent suboxide.…”

“…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 contaminants which may affect the performance of the cavity 1. Initial studies using SIMS and Focused Ion Beam (FIB) prepared specimens for Transmission Electron Microscopy (TEM) have helped to characterize the Nb surface and measure the surface oxide layer thickness 2. C, N and O are of particular interest as interstitial contaminants and earlier studies suggested very high H concentration.…”