| 1. |
- Adrian-Kalchhauser, Irene, et al.
(författare)
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The mitochondrial genome sequences of the round goby and the sand goby reveal patterns of recent evolution in gobiid fish
- 2017
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Ingår i: BMC Genomics. - : Springer Science and Business Media LLC. - 1471-2164. ; 18:1
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Tidskriftsartikel (refereegranskat)abstract
- Background Vertebrate mitochondrial genomes are optimized for fast replication and low cost of RNA expression. Accordingly, they are devoid of introns, are transcribed as polycistrons and contain very little intergenic sequences. Usually, vertebrate mitochondrial genomes measure between 16.5 and 17 kilobases (kb). Results During genome sequencing projects for two novel vertebrate models, the invasive round goby and the sand goby, we found that the sand goby genome is exceptionally small (16.4 kb), while the mitochondrial genome of the round goby is much larger than expected for a vertebrate. It is 19 kb in size and is thus one of the largest fish and even vertebrate mitochondrial genomes known to date. The expansion is attributable to a sequence insertion downstream of the putative transcriptional start site. This insertion carries traces of repeats from the control region, but is mostly novel. To get more information about this phenomenon, we gathered all available mitochondrial genomes of Gobiidae and of nine gobioid species, performed phylogenetic analyses, analysed gene arrangements, and compared gobiid mitochondrial genome sizes, ecological information and other species characteristics with respect to the mitochondrial phylogeny. This allowed us amongst others to identify a unique arrangement of tRNAs among Ponto-Caspian gobies. Conclusions Our results indicate that the round goby mitochondrial genome may contain novel features. Since mitochondrial genome organisation is tightly linked to energy metabolism, these features may be linked to its invasion success. Also, the unique tRNA arrangement among Ponto-Caspian gobies may be helpful in studying the evolution of this highly adaptive and invasive species group. Finally, we find that the phylogeny of gobiids can be further refined by the use of longer stretches of linked DNA sequence.
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| 2. |
- Dochev, Dimitar Milkov, 1981, et al.
(författare)
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Growth and characterization of epitaxial ultra-thin NbN films on 3C-SiC/Si substrate for terahertz applications
- 2011
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Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 24:3, s. 035016 (6pp)-
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Tidskriftsartikel (refereegranskat)abstract
- We report on electrical properties and microstructure of epitaxial thin NbN films grown on 3C-SiC/Si substrates by means of reactive magnetron sputtering. A complete epitaxial growth at the NbN/3C-SiC interface has been confirmed by means of high resolution transmission electron microscopy (HRTEM) along with x-ray diffractometry (XRD). Resistivitymeasurements of the films have shown that the superconducting transition onset temperature (TC) for the best specimen is 11.8 K. Using these epitaxial NbN films, we have fabricated submicron-size hot-electron bolometer (HEB) devices on 3C-SiC/Si substrate and performed their complete DC characterization. The observed critical temperature TC = 11.3 K and critical current density of about 2.5 MA cm−2 at 4.2 K of the submicron-size bridges were uniform across the sample. This suggests that the deposited NbN films possess the necessary homogeneity to sustain reliable hot-electron bolometer device fabrication for THz mixer applications.
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| 3. |
- Krause, Sascha, 1989, et al.
(författare)
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Ambient temperature growth of mono- and polycrystalline NbN nanofilms and their rigorous composition and surface analysis
- 2015
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Ingår i: European Conference on Applied Superconductivity.
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Konferensbidrag (refereegranskat)abstract
- This paper reflects on the rigorous investigation of high-quality 5nm thin NbN films which were deposited by means of reactive DC magnetron sputtering at ambient temperatures. Monocrystalline NbN films have been epitaxially grown onto hexagonal GaN buffer-layers (0002) and showing a distinct, low defect interface as confirmed from HRTEM. The critical temperature (Tc) of those films reached 10.4K. Furthermore, a poly-crystalline structure was observed on films grown onto Si (100) substrates, exhibiting a Tc of 8.1K albeit a narrow transition from the normal to the superconducting state. The deposition at ambient temperatures offers major advantages from a processing point of view and motivates the in-depth characterization and comparison of present films with high quality films grown at elevated temperatures. X-ray photoelectron spectroscopy and reflected electron energy loss spectroscopy verified that the composition of NbN did not differ irrespectively of applied substrate heating. Moreover, the native oxide layer at the surface of NbN has been identified as NbO2 and thus is in contrast to the Nb2O5, usually being formed at the surface of Nb when exposed to air. These findings are of great significance since it was proven the possibility of growing epitaxial NbN onto GaN buffer layer in the absence of high temperatures hence paving the way to employ NbN in more advanced fabrication processes involving a higher degree of complexity. Particularly low-noise THz receiver could benefit from the eased integration of e.g IF circuitry or general multi-layer structures which take advantage of lift-off techniques.
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| 4. |
- Krause, Sascha, 1989, et al.
(författare)
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Ambient temperature growth of mono- and polycrystalline NbN nanofilms and their surface and composition analysis
- 2016
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Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 26:3
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the studies of high-quality 5 nmthin NbN films deposited by means of reactive DC magnetronsputtering at room temperature. The deposition withoutsubstrate heating offers major advantages from a processingpoint of view and motivates the extensive composition- andsurface characterization and comparison of the present filmswith high quality films grown at elevated temperatures.Monocrystalline NbN films have been epitaxially grown ontohexagonal GaN buffer-layers (0002) and show a distinct, lowdefect interface as confirmed by High-Resolution TEM. Thecritical temperature Tc of films on the GaN buffer-layer reached10.4 K. Furthermore, a poly-crystalline structure was observedon films grown onto Si (100) substrates, exhibiting a Tc of 8.1 Kalbeit a narrow transition from the normal to thesuperconducting state. X-ray photoelectron spectroscopy andreflected electron energy loss spectroscopy verified that thecomposition of NbN was identical irrespectively of appliedsubstrate heating. Moreover, the native oxide layer at the surfaceof NbN has been identified as NbO2 and thus, is in contrast to theNb2O5, usually claimed to be formed at the surface of Nb whenexposed to air. These findings are of significance since it wasproven the possibility of growing epitaxial NbN onto GaN bufferlayer in the absence of high temperatures hence paving the wayto employ NbN in more advanced fabrication processes involvinga higher degree of complexity. The eased integration andemployment of lift-off techniques could, in particular, lead toimproved performance of cryogenic ultra-sensitive terahertzelectronics.
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| 5. |
- Krause, Sascha, 1989, et al.
(författare)
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Deposition of high-quality ultra-thin NbN films at ambient temperatures
- 2014
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Ingår i: 25th International Sympsoium on Space Terahertz Technology, ISSTT 2014; Moscow; Russian Federation; 27 April 2014 through 30 April 2014. ; , s. 139-140
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Konferensbidrag (refereegranskat)abstract
- This paper discusses the possibility of growing NbN ultra-thin films on Si-substrates and AlxGa1-xN buffer-layers by means of DC magnetron sputtering without intentional substrate heating. Resistance-temperature measurements were carried out and the superconducting properties such as Tc, ΔTc and R□ were deduced while HRTEM gave insight into the crystal structure and film thickness. The adjustment of the partial pressure of argon and nitrogen was found to be critical in establishing a reliable deposition process. The quality of the interface between the NbN film and the substrate was improved by optimizing the total pressure while sputtering, and is therefore particularly valuable for phonon-cooled HEB heterodyne receivers. NbN films of 5 nm thickness were obtained and exhibited a Tc from 8K on Si-substrates, and up to 10.5 K on the GaN buffer-layers. This result is significant since the absence of a high-temperature environment permits the establishment of more complex fabrication processes for intricate thin-film structures without compromising the overall integrity of e.g. dielectric layers, or hybrid circuitries with e.g. SIS junctions.
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| 6. |
- Krause, Sascha, 1989, et al.
(författare)
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Epitaxial growth of ultra-thin NbN films on AlxGa1-xN buffer-layers
- 2014
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Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 27:6
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Tidskriftsartikel (refereegranskat)abstract
- The suitability of AlxGa1-xN epi-layer to deposit onto ultra-thin NbN films has been demonstrated for the first time. High quality single-crystal films with 5 nm thickness confirmed by high-resolution transmission electron microscopy (HRTEM) have been deposited in a reproducible manner by means of reactive DC magnetron sputtering at elevated temperatures and exhibit critical temperatures (Tc) as high as 13.2 K and residual resistivity ratio (RRR) ~ 1 on hexagonal GaN epi-layer. With increasing the Al-content x in the AlxGa1-xN epi-layer above 20% a gradual deterioration of Tc down to 10 K was observed. Deposition of NbN on bare silicon substrates served as reference and comparison. Excellent spatial homogeneity of the fabricated films was confirmed by R(T) measurements of patterned micro-bridges across the entire film area. The superconducting properties of those films were further characterized by critical magnetic field and critical current measurements. It is expected that the employment of GaN material as a buffer-layer for the deposition of ultra-thin NbN films prospectively benefit terahertz electronics, particularly hot electron bolometer (HEB) mixers.
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| 7. |
- Krause, Sascha, 1989, et al.
(författare)
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Ultra-thin film NbN depositions for HEB heterodyne mixer on Si-substrates
- 2013
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Ingår i: Proceedings of the 24th International Symposium on Space Terahertz Technology.
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Konferensbidrag (refereegranskat)abstract
- The key of improving hot-electron bolometer (HEB) mixer performance lies inevitably in the quality of ultra-thin NbN films itself. This work presents a thorough investigation of crucial process parameters of NbN films deposited by means of reactive DC-sputtering on Si-substrates at elevated temperatures up to 750°C.The polycrystalline NbN films with thickness of 4 to 10nm were characterized by DC resistivity measurements, ellipsometry and high resolution transmission electron microscopy (HRTEM) in order to confirm thickness and film structure. Since the macroscopic properties such as critical temperature, thickness as well as the transition width to the superconducting state are directly linked to HEB mixer noise temperature and IF bandwidth, a set of experiments were conducted to enhance aforementioned properties. We considered deposition temperature, RF biasing, nitrogen and argon partial and total pressure during deposition as major process variable parameters. Careful optimization of the deposition conditions allowed setting up a process resulting in high-quality NbN ultra-thin films with thickness of 5.5nm exhibiting Tc of 10.5K. Moreover, the transition width could be kept as low as 1.4K. The produced films were stored at ambient conditions and re-characterized over a period of 4 month without measurable degradation.
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