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Atomic structure and oxygen deficiency of the ultrathin aluminium oxide barrier in Al/AlOx/Al Josephson junctions.

Zeng L, Tran DT, Tai CW, Svensson G, Olsson E - Sci Rep (2016)

Bottom Line: The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier.In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide.Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Physics, Chalmers University of Technology, 41296, Göteborg, Sweden.

ABSTRACT
Al/AlOx/Al Josephson junctions are the building blocks of a wide range of superconducting quantum devices that are key elements for quantum computers, extremely sensitive magnetometers and radiation detectors. The properties of the junctions and the superconducting quantum devices are determined by the atomic structure of the tunnel barrier. The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier. Here we show that the miniaturized dimension of the barrier and the interfacial interaction between crystalline Al and amorphous AlOx give rise to oxygen deficiency at the metal/oxide interfaces. In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide. Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.

No MeSH data available.


Related in: MedlinePlus

Nanobeam electron diffraction (NBED) and pair distribution function (PDF) analysis of the barrier oxide.(a) A typical NBED pattern of the AlOx barrier. It includes contributions from the adjacent crystalline Al as evidenced by the Bragg spots from Al. Diffused and speckle intensities are from the amorphous barrier oxide. (b) pair distribution function obtained from a set of NBED data. Peaks P1-P6 are identified as the attributes of interatomic pair distances, involving both the AlOx barrier (in red) and crystalline Al layers (in blue).
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f2: Nanobeam electron diffraction (NBED) and pair distribution function (PDF) analysis of the barrier oxide.(a) A typical NBED pattern of the AlOx barrier. It includes contributions from the adjacent crystalline Al as evidenced by the Bragg spots from Al. Diffused and speckle intensities are from the amorphous barrier oxide. (b) pair distribution function obtained from a set of NBED data. Peaks P1-P6 are identified as the attributes of interatomic pair distances, involving both the AlOx barrier (in red) and crystalline Al layers (in blue).

Mentions: Here we used NBED to further unveil the atomic structure of aluminium oxide in the tunnel barrier (Fig. 2a). PDF analysis (see Methods) was performed on NBED patterns to obtain a distribution of interatomic distances between atoms of both the AlOx barrier (in red, Fig. 2b) and crystalline Al (in blue, Fig. 2b). Most of the peaks in the short range can be reasonably identified: P1: 1.76 Å, Al-O first shell distance; P2: 2.27 Å, Al-O first shell extended distance possibly due to Al-AlOx interaction at the metal/oxide interfaces; P3: 2.83 Å, superimposition of O-O and first shell distance of fcc Al-Al (a is the lattice constant of fcc Al, ~4.05 Å); P4: 3.41 Å, Al-Al distances of the barrier oxide and at the interface; P5: 4.00 Å, fcc Al-Al second shell distance ~a; P6: 4.95 Å, fcc Al-Al third shell distance ~. A small peak observed between P5 and P6 can be considered (like P2) as a termination ripple and/or interatomic distance due to Al-AlOx interaction at the interfaces.


Atomic structure and oxygen deficiency of the ultrathin aluminium oxide barrier in Al/AlOx/Al Josephson junctions.

Zeng L, Tran DT, Tai CW, Svensson G, Olsson E - Sci Rep (2016)

Nanobeam electron diffraction (NBED) and pair distribution function (PDF) analysis of the barrier oxide.(a) A typical NBED pattern of the AlOx barrier. It includes contributions from the adjacent crystalline Al as evidenced by the Bragg spots from Al. Diffused and speckle intensities are from the amorphous barrier oxide. (b) pair distribution function obtained from a set of NBED data. Peaks P1-P6 are identified as the attributes of interatomic pair distances, involving both the AlOx barrier (in red) and crystalline Al layers (in blue).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4940733&req=5

f2: Nanobeam electron diffraction (NBED) and pair distribution function (PDF) analysis of the barrier oxide.(a) A typical NBED pattern of the AlOx barrier. It includes contributions from the adjacent crystalline Al as evidenced by the Bragg spots from Al. Diffused and speckle intensities are from the amorphous barrier oxide. (b) pair distribution function obtained from a set of NBED data. Peaks P1-P6 are identified as the attributes of interatomic pair distances, involving both the AlOx barrier (in red) and crystalline Al layers (in blue).
Mentions: Here we used NBED to further unveil the atomic structure of aluminium oxide in the tunnel barrier (Fig. 2a). PDF analysis (see Methods) was performed on NBED patterns to obtain a distribution of interatomic distances between atoms of both the AlOx barrier (in red, Fig. 2b) and crystalline Al (in blue, Fig. 2b). Most of the peaks in the short range can be reasonably identified: P1: 1.76 Å, Al-O first shell distance; P2: 2.27 Å, Al-O first shell extended distance possibly due to Al-AlOx interaction at the metal/oxide interfaces; P3: 2.83 Å, superimposition of O-O and first shell distance of fcc Al-Al (a is the lattice constant of fcc Al, ~4.05 Å); P4: 3.41 Å, Al-Al distances of the barrier oxide and at the interface; P5: 4.00 Å, fcc Al-Al second shell distance ~a; P6: 4.95 Å, fcc Al-Al third shell distance ~. A small peak observed between P5 and P6 can be considered (like P2) as a termination ripple and/or interatomic distance due to Al-AlOx interaction at the interfaces.

Bottom Line: The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier.In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide.Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Physics, Chalmers University of Technology, 41296, Göteborg, Sweden.

ABSTRACT
Al/AlOx/Al Josephson junctions are the building blocks of a wide range of superconducting quantum devices that are key elements for quantum computers, extremely sensitive magnetometers and radiation detectors. The properties of the junctions and the superconducting quantum devices are determined by the atomic structure of the tunnel barrier. The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier. Here we show that the miniaturized dimension of the barrier and the interfacial interaction between crystalline Al and amorphous AlOx give rise to oxygen deficiency at the metal/oxide interfaces. In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide. Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.

No MeSH data available.


Related in: MedlinePlus