| 1. |
- Dalgaard, Kirstine Junker, et al.
(författare)
-
Local structure of Nb in superconducting Nb-doped Bi2Se3
- 2021
-
Ingår i: Physical Review B. - 2469-9950. ; 103:18
-
Tidskriftsartikel (refereegranskat)abstract
- In the prospect of realizing bulk superconductivity in a topological insulator, metal-doped Bi2Se3 has been investigated with increased interest, where the Cu-, Sr-, and Nb-doped systems appear particularly promising. It is generally assumed that metal intercalation into the van der Waals (vdW) gap is responsible for the superconductivity. We have investigated the local structure of Nb in samples with nominal composition Nb0.25Bi2Se3 and Nb0.25Bi1.75Se3 using the X-ray absorption fine structure technique. It is found that that Nb is primarily located in a local environment consistent with that of the misfit layered structure (BiSe)1+δNbSe2, which has a δ-dependent superconducting transition in the same temperature range. We explore the possibility of Nb occupancy on various sites in the Bi2Se3 structure, but neither intercalation nor substitution lead to physically meaningful improvements of the models. Furthermore, we report single crystal X-ray diffraction analysis of Nb-doped Bi2Se3. Difference density maps are found to show negligible occupancy in the vdW gap. The misfit layer compound has recently been suggested as an alternative origin for superconductivity in the Nb-doped Bi2Se3 system, in good agreement with the present study. Our findings stress the necessity of thorough structural characterization of these samples. In more general terms, it raises the question of whether metal intercalation is responsible for the superconductivity in the Cu- A nd Sr-doped Bi2Se3 systems or phase segregation plays a role as well.
|
|
| 2. |
- Micheal Raj, Pushparani, et al.
(författare)
-
Fabrication and characterisation of a silicon-borosilicate glass microfluidic device for synchrotron-based hard X-ray spectroscopy studies
- 2021
-
Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 11:47, s. 29859-29869
-
Tidskriftsartikel (refereegranskat)abstract
- Some of the most fundamental chemical building blocks of life on Earth are the metal elements. X-ray absorption spectroscopy (XAS) is an element-specific technique that can analyse the local atomic and electronic structure of, for example, the active sites in catalysts and energy materials and allow the metal sites in biological samples to be identified and understood. A microfluidic device capable of withstanding the intense hard X-ray beams of a 4th generation synchrotron and harsh chemical sample conditions is presented in this work. The device is evaluated at the K-edges of iron and bromine and the L-3-edge of lead, in both transmission and fluorescence mode detection and in a wide range of sample concentrations, as low as 0.001 M. The device is fabricated in silicon and glass with plasma etched microchannels defined in the silicon wafer before anodic bonding of the glass wafer into a complete device. The device is supported with a well-designed printed chip holder that made the microfluidic device portable and easy to handle. The chip holder plays a pivotal role in mounting the delicate microfluidic device on the beamline stage. Testing validated that the device was sufficiently robust to contain and flow through harsh acids and toxic samples. There was also no significant radiation damage to the device observed, despite focusing with intense X-ray beams for multiple hours. The quality of X-ray spectra collected is comparable to that from standard methods; hence we present a robust microfluidic device to analyse liquid samples using synchrotron XAS.
|
|
| 3. |
- Raj, Pushparani, et al.
(författare)
-
Fabrication and characterisation of a silicon-borosilicate glass microfluidic device for synchrotron-based hard X-ray spectroscopy studies
- 2021
-
Ingår i: RSC Advances. - Cambridge : RSC Publishing. - 2046-2069. ; 11:47, s. 29859-29869
-
Tidskriftsartikel (refereegranskat)abstract
- Some of the most fundamental chemical building blocks of life on Earth are the metal elements. X-ray absorption spectroscopy (XAS) is an element-specific technique that can analyse the local atomic and electronic structure of, for example, the active sites in catalysts and energy materials and allow the metal sites in biological samples to be identified and understood. A microfluidic device capable of withstanding the intense hard X-ray beams of a 4th generation synchrotron and harsh chemical sample conditions is presented in this work. The device is evaluated at the K-edges of iron and bromine and the L3-edge of lead, in both transmission and fluorescence mode detection and in a wide range of sample concentrations, as low as 0.001 M. The device is fabricated in silicon and glass with plasma etched microchannels defined in the silicon wafer before anodic bonding of the glass wafer into a complete device. The device is supported with a well-designed printed chip holder that made the microfluidic device portable and easy to handle. The chip holder plays a pivotal role in mounting the delicate microfluidic device on the beamline stage. Testing validated that the device was sufficiently robust to contain and flow through harsh acids and toxic samples. There was also no significant radiation damage to the device observed, despite focusing with intense X-ray beams for multiple hours. The quality of X-ray spectra collected is comparable to that from standard methods; hence we present a robust microfluidic device to analyse liquid samples using synchrotron XAS.
|
|
