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Results for “Nb-Si”

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10 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Stability, metallicity, and magnetism in niobium silicide nanofilms

Modern superconducting qubits based on two-dimensional (2D) transmons typically involve the growth of Nb thin films on high-resistivity Si substrates. Since imperfections at the Nb-Si heterointerface have been implicated as a source of two-level systems that limit quantum coherence times, detailed characterization and understanding of niobium silicide interfacial layers are critical to improving superconducting qubit technology. While bulk binary intermetallic niobium silicide phases are well understood, the thermodynamic phase stability and properties of ultrathin niobium silicides, such as those found at the Nb-Si heterointerface in 2D transmons, have not yet been explored. Here, we report finite-sized effects for ultrathin niobium silicide films using density functional theory calculations and predict nanoscale stabilization of Nb 6 Si 5 over the bulk α-Nb 5 Si 3 phase. This result is consistent with our experimental observations of a niobium silicide interfacial layer between a sputtered Nb thin film and the underlying Si substrate. Furthermore, our calculations show that Nb 6 Si 5 nanofilms are nonmagnetic, making them superior to nanofilms of α-Nb 5 Si 3 that exhibit antiferromagnetic correlations detrimental to long coherence times in superconducting qubits. Furthermore, by providing atomic-scale insight into niobium silicide nanofilms, this paper can help guide ongoing efforts to optimize Nb-Si heterointerfaces for long coherence times in superconducting qubits.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Exploring the relationship between deposition method, microstructure, and performance of Nb/Si-based superconducting coplanar waveguide resonators

Superconducting quantum circuits (SQC) are one of the most promising hardware platforms for quantum computing, yet their performance is currently limited by the presence of various structural defects inside the circuit's structure. Despite impressive progress in the past decade, a precise understanding of the origin of these defects from various fabrication processes and their impact on coherence is still lacking. Here, in this study, we performed a comprehensive investigation on the microstructure, superconductivity, and resonator quality factor of Nb films deposited by high-power impulse magnetron sputtering (HiPIMS) and direct current (DC) magnetron sputtering. A suite of characterization techniques, including electron microscopy with spectroscopy, secondary ion mass spectrometry, magneto-optical microscopy, and pump-probe reflectivity spectroscopy is used. We reveal that niobium (Nb) resonators fabricated using HiPIMS exhibit a smaller average grain size, thicker surface oxide with larger thickness variations (rougher surface), and a thicker amorphous Nb/Si interface layer compared to samples deposited by DC sputtering. We identified that the amorphous Nb oxides (mainly located at the Nb surface and along the grain boundaries) and Nb-Si amorphous layers (at the Nb/Si interface) are major and potential sources of two-level system (TLS), while off-stochiometric oxides and suboxides of Nb close to the surface, crystalline defects (i.e., dislocations at grain boundary, point defects introduced during deposition) are main contributors of non-TLS sources. Our findings clarify the relationship between different defects and coherence loss mechanisms, highlighting the importance of material microstructure control on performance optimization in SQC.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb3Si by Materials Project

Nb3Si is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Nb is bonded to eight equivalent Nb and four equivalent Si atoms to form NbNb8Si4 cuboctahedra that share corners with twelve equivalent NbNb8Si4 cuboctahedra, edges with eight equivalent SiNb12 cuboctahedra, edges with sixteen equivalent NbNb8Si4 cuboctahedra, faces with four equivalent SiNb12 cuboctahedra, and faces with fourteen equivalent NbNb8Si4 cuboctahedra. All Nb–Nb bond lengths are 2.89 Å. All Nb–Si bond lengths are 2.89 Å. Si is bonded to twelve equivalent Nb atoms to form SiNb12 cuboctahedra that share corners with twelve equivalent SiNb12 cuboctahedra, edges with twenty-four equivalent NbNb8Si4 cuboctahedra, faces with six equivalent SiNb12 cuboctahedra, and faces with twelve equivalent NbNb8Si4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb3Si by Materials Project

Nb3Si crystallizes in the cubic Pm-3n space group. The structure is three-dimensional. Nb is bonded in a 6-coordinate geometry to two equivalent Nb and four equivalent Si atoms. Both Nb–Nb bond lengths are 2.56 Å. All Nb–Si bond lengths are 2.87 Å. Si is bonded to twelve equivalent Nb atoms to form a mixture of face and edge-sharing SiNb12 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb5Si3 by Materials Project

Nb5Si3 crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. there are two inequivalent Nb+2.40+ sites. In the first Nb+2.40+ site, Nb+2.40+ is bonded to six Si4- atoms to form NbSi6 octahedra that share corners with six equivalent NbSi6 octahedra, corners with sixteen equivalent NbSi5 trigonal bipyramids, and faces with eight equivalent NbSi5 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 0–52°. There are four shorter (2.60 Å) and two longer (2.99 Å) Nb–Si bond lengths. In the second Nb+2.40+ site, Nb+2.40+ is bonded to five Si4- atoms to form NbSi5 trigonal bipyramids that share corners with four equivalent NbSi6 octahedra, corners with twelve equivalent NbSi5 trigonal bipyramids, edges with seven equivalent NbSi5 trigonal bipyramids, faces with two equivalent NbSi6 octahedra, and a faceface with one NbSi5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 43–64°. There are a spread of Nb–Si bond distances ranging from 2.61–2.74 Å. There are two inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 10-coordinate geometry to ten Nb+2.40+ atoms. In the second Si4- site, Si4- is bonded in a 9-coordinate geometry to eight Nb+2.40+ and one Si4- atom. The Si–Si bond length is 2.41 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb3Si by Materials Project

Nb3Si crystallizes in the tetragonal P4_2/n space group. The structure is three-dimensional. there are three inequivalent Nb sites. In the first Nb site, Nb is bonded in a 2-coordinate geometry to two equivalent Si atoms. There are one shorter (2.62 Å) and one longer (2.66 Å) Nb–Si bond lengths. In the second Nb site, Nb is bonded in a 4-coordinate geometry to four equivalent Si atoms. There are a spread of Nb–Si bond distances ranging from 2.60–2.72 Å. In the third Nb site, Nb is bonded in a 2-coordinate geometry to three equivalent Si atoms. There are a spread of Nb–Si bond distances ranging from 2.59–2.87 Å. Si is bonded in a 9-coordinate geometry to nine Nb atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb5Si3 by Materials Project

Nb5Si3 crystallizes in the hexagonal P6_3/mcm space group. The structure is three-dimensional. there are two inequivalent Nb+2.40+ sites. In the first Nb+2.40+ site, Nb+2.40+ is bonded to five equivalent Si4- atoms to form distorted NbSi5 trigonal bipyramids that share corners with eight equivalent NbSi6 octahedra, corners with eight equivalent NbSi5 trigonal bipyramids, edges with six equivalent NbSi5 trigonal bipyramids, and faces with four equivalent NbSi6 octahedra. The corner-sharing octahedra tilt angles range from 41–55°. There are a spread of Nb–Si bond distances ranging from 2.61–2.86 Å. In the second Nb+2.40+ site, Nb+2.40+ is bonded to six equivalent Si4- atoms to form distorted NbSi6 octahedra that share corners with six equivalent NbSi6 octahedra, corners with twelve equivalent NbSi5 trigonal bipyramids, edges with three equivalent NbSi6 octahedra, faces with two equivalent NbSi6 octahedra, and faces with six equivalent NbSi5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 35°. All Nb–Si bond lengths are 2.69 Å. Si4- is bonded in a 9-coordinate geometry to nine Nb+2.40+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb5Si3 by Materials Project

Nb5Si3 crystallizes in the tetragonal I4/mcm space group. The structure is three-dimensional. there are two inequivalent Nb+2.40+ sites. In the first Nb+2.40+ site, Nb+2.40+ is bonded to six Si4- atoms to form distorted NbSi6 pentagonal pyramids that share corners with fifteen equivalent NbSi6 pentagonal pyramids, corners with four equivalent NbSi4 tetrahedra, edges with three equivalent NbSi6 pentagonal pyramids, edges with two equivalent NbSi4 tetrahedra, and faces with seven equivalent NbSi6 pentagonal pyramids. There are a spread of Nb–Si bond distances ranging from 2.66–2.95 Å. In the second Nb+2.40+ site, Nb+2.40+ is bonded to four equivalent Si4- atoms to form NbSi4 tetrahedra that share corners with sixteen equivalent NbSi6 pentagonal pyramids, edges with eight equivalent NbSi6 pentagonal pyramids, and edges with two equivalent NbSi4 tetrahedra. All Nb–Si bond lengths are 2.67 Å. There are two inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 10-coordinate geometry to ten Nb+2.40+ atoms. In the second Si4- site, Si4- is bonded in a 10-coordinate geometry to eight equivalent Nb+2.40+ and two equivalent Si4- atoms. Both Si–Si bond lengths are 2.56 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb3Si by Materials Project

Nb3Si crystallizes in the orthorhombic Cmmm space group. The structure is three-dimensional. there are two inequivalent Nb sites. In the first Nb site, Nb is bonded in a distorted L-shaped geometry to two equivalent Nb and two equivalent Si atoms. Both Nb–Nb bond lengths are 2.90 Å. Both Nb–Si bond lengths are 2.60 Å. In the second Nb site, Nb is bonded in a distorted body-centered cubic geometry to eight Nb atoms. All Nb–Nb bond lengths are 2.91 Å. Si is bonded in a distorted square co-planar geometry to four equivalent Nb atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nb3Si2 by Materials Project

Nb3Si2 crystallizes in the tetragonal P4/mbm space group. The structure is three-dimensional. there are two inequivalent Nb+2.67+ sites. In the first Nb+2.67+ site, Nb+2.67+ is bonded in a square co-planar geometry to four equivalent Si4- atoms. All Nb–Si bond lengths are 2.66 Å. In the second Nb+2.67+ site, Nb+2.67+ is bonded in a distorted hexagonal planar geometry to six equivalent Si4- atoms. There are two shorter (2.60 Å) and four longer (2.70 Å) Nb–Si bond lengths. Si4- is bonded in a 9-coordinate geometry to eight Nb+2.67+ and one Si4- atom. The Si–Si bond length is 2.44 Å.

36 MATERIALS SCIENCE↗