10 research outputs found
First Direct Observation of Nanometer size Hydride Precipitations on Superconducting Niobium
Superconducting niobium serves as a key enabling material for superconducting
radio frequency (SRF) technology as well as quantum computing devices. At room
temperature, hydrogen commonly occupies tetragonal sites in the Nb lattice as
metal (M)-gas (H) phase. When the temperature is decreased, however, solid
solution of Nb-H starts to be precipitated. In this study, we show the first
identified topographical features associated with nanometer-size hydride phase
(Nb1-xHx) precipitates on metallic superconducting niobium using
cryogenic-atomic force microscopy (AFM). Further, high energy grazing incidence
X-ray diffraction reveals information regarding the structure and stoichiometry
that these precipitates exhibit. Finally, through time-of-flight secondary ion
mass spectroscopy (ToF-SIMS), we are able to locate atomic hydrogen sources
near the top surface. This systematic study further explains localized
degradation of RF superconductivity by the proximity effect due to hydrogen
clusters
Selective thermal evolution of native oxide layer in Nb and Nb3Sn-coated SRF grade Nb: An in-situ angular XPS study
This contribution discusses the results of an in-situ angular XPS study on
the thermal evolution of the native oxide layer on Nb3Sn and pure Nb. XPS data
were recorded with conventional spectrometers using an AlK(alpha) X-ray source
for spectra collected up to 600 C, and an MgK(Alpha) X-rays source for
temperatures above 600 C. The effect of the thickness, composition, and thermal
stability of that oxide layer is relevant to understanding the functional
properties of superconducting radiofrequency (SRF) cavities used in particle
accelerators. There is a consensus that oxide plays a role in surface
resistance (Rs). The focus of this study is Nb3Sn, which is a promising
material that is used in the manufacturing of superconducting radiofrequency
(SRF) cavities as well as in quantum sensing, and pure Nb, which was included
in the study for comparison. The thermal evolution of the oxide layer in these
two materials is found to be quite different, which is ascribed to the
influence of the Sn atom on the reactivity of the Nb atom in Nb3Sn films. Nb
and Sn atoms in this intermetallic solid have different electronegativity, and
the Sn atom can reduce electron density around neighbouring Nb atoms in the
solid, thus reducing their reactivity for oxygen. This is shown in the
thickness, composition, and thermal stability of the oxide layer formed on
Nb3Sn. The XPS spectra were complemented by grazing incident XRD patterns
collected using the ESRF synchrotron radiation facility. The results discussed
herein shed light on oxide evolution in the Nb3Sn compound and guide its
processing for potential applications of the Nb3Sn-based SRF cavities in
accelerators and other superconducting devices
Systematic Improvements in Transmon Qubit Coherence Enabled by Niobium Surface Encapsulation
We present a novel transmon qubit fabrication technique that yields
systematic improvements in T coherence times. We fabricate devices using an
encapsulation strategy that involves passivating the surface of niobium and
thereby preventing the formation of its lossy surface oxide. By maintaining the
same superconducting metal and only varying the surface structure, this
comparative investigation examining different capping materials and film
substrates across different qubit foundries definitively demonstrates the
detrimental impact that niobium oxides have on the coherence times of
superconducting qubits, compared to native oxides of tantalum, aluminum or
titanium nitride. Our surface-encapsulated niobium qubit devices exhibit T
coherence times 2 to 5 times longer than baseline niobium qubit devices with
native niobium oxides. When capping niobium with tantalum, we obtain median
qubit lifetimes above 200 microseconds. Our comparative structural and chemical
analysis suggests that amorphous niobium suboxides may induce higher losses.
These results are in line with high-accuracy measurements of the niobium oxide
loss tangent obtained with ultra-high Q superconducting radiofrequency (SRF)
cavities. This new surface encapsulation strategy enables further reduction of
dielectric losses via passivation with ambient-stable materials, while
preserving fabrication and scalable manufacturability thanks to the
compatibility with silicon processes
Analysis of failure of C-V characteristics of MIS structure with SiO2 passivation layer deposited on InSb substrate via Raman spectroscopy
The effect of interfacial phases on the electrical properties of Au/Ti/SiO2/InSb metal-insulator (oxide)-semiconductor (MIS or MOS) structures was investigated by capacitance-voltage (C-V) measurements. With increasing the deposition temperature of silicon oxide from 100 to 350°C using PECVD, the change in the interfacial phases between SiO2 and InSb were analyzed by resonant Raman spectroscopy to verify the relation between the breakdown of C-V characteristics and the change of interfacial phases. The shape of C-V characteristics was dramatically changed when the deposition temperature was above 300°C. The C-V measurements and Raman spectra represented that elemental Sb accumulation resulted from the chemical reaction of Sb oxide with InSb substrate was responsible for the failure in the C-V characteristics of MIS structure. Copyright © 2014 Materials Research Society.N
Systematic improvements in transmon qubit coherence enabled by niobium surface encapsulation
Abstract We present a transmon qubit fabrication technique that yields systematic improvements in T 1 relaxation times. We encapsulate the surface of niobium and prevent the formation of its lossy surface oxide. By maintaining the same superconducting metal and only varying the surface, this comparative investigation examining different capping materials, such as tantalum, aluminum, titanium nitride, and gold, as well as substrates across different qubit foundries demonstrates the detrimental impact that niobium oxides have on coherence times of superconducting qubits, compared to native oxides of tantalum, aluminum or titanium nitride. Our surface-encapsulated niobium qubit devices exhibit T 1 relaxation times 2â5 times longer than baseline qubit devices with native niobium oxides. When capping niobium with tantalum, we obtain median qubit lifetimes above 300âÎŒs, with maximum values up to 600 ÎŒs. Our comparative structural and chemical analysis provides insight into why amorphous niobium oxides may induce higher losses compared to other amorphous oxides