| 1. |
- Bruzzi, M, et al.
(författare)
-
Radiation-hard semiconductor detectors for SuperLHC
- 2005
-
Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 541:1-2, s. 189-201
-
Tidskriftsartikel (refereegranskat)abstract
- An option of increasing the luminosity of the Large Hadron Collider (LHC) at CERN to 1035 cm-2 s-1 has been envisaged to extend the physics reach of the machine. An efficient tracking down to a few centimetres from the interaction point will be required to exploit the physics potential of the upgraded LHC. As a consequence, the semiconductor detectors close to the interaction region will receive severe doses of fast hadron irradiation and the inner tracker detectors will need to survive fast hadron fluences of up to above 1016cm-2. The CERN-RD50 project "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" has been established in 2002 to explore detector materials and technologies that will allow to operate devices up to, or beyond, this limit. The strategies followed by RD50 to enhance the radiation tolerance include the development of new or defect engineered detector materials (SiC, GaN, Czochralski and epitaxial silicon, oxygen enriched Float Zone silicon), the improvement of present detector designs and the understanding of the microscopic defects causing the degradation of the irradiated detectors. The latest advancements within the RD50 collaboration on radiation hard semiconductor detectors will be reviewed and discussed in this work.
|
|
| 2. |
- Chan, P., et al.
(författare)
-
Multicentennial record of Labrador Sea primary productivity and sea-ice variability archived in coralline algal barium
- 2017
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- Accelerated warming and melting of Arctic sea-ice has been associated with significant increases in phytoplankton productivity in recent years. Here, utilizing a multiproxy approach, we reconstruct an annually resolved record of Labrador Sea productivity related to sea-ice variability in Labrador, Canada that extends well into the Little Ice Age (LIA; 1646 AD). Barium-to-calcium ratios (Ba/Ca) and carbon isotopes (delta C-13) measured in long-lived coralline algae demonstrate significant correlations to both observational and proxy records of sea-ice variability, and show persistent patterns of co-variability broadly consistent with the timing and phasing of the Atlantic Multidecadal Oscillation (AMO). Results indicate reduced productivity in the Subarctic Northwest Atlantic associated with AMO cool phases during the LIA, followed by a step-wise increase from 1910 to present levels-unprecedented in the last 363 years. Increasing phytoplankton productivity is expected to fundamentally alter marine ecosystems as warming and freshening is projected to intensify over the coming century.
|
|
| 3. |
- Adey, J., et al.
(författare)
-
Degradation of boron-doped Czochralski-grown silicon solar cells
- 2004
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 93:5, s. 055504-1
-
Tidskriftsartikel (refereegranskat)abstract
- The formation mechanism and properties of the boron-oxygen center responsible for the degradation of Czochralski-grown Si(B) solar cells during operation is investigated using density functional calculations. We find that boron traps an oxygen dimer to form a bistable defect with a donor level in the upper half of the band gap. The activation energy for its dissociation is found to be 1.2 eV. The formation of the defect from mobile oxygen dimers, which are shown to migrate by a Bourgoin mechanism under minority carrier injection, has a calculated activation energy of 0.3 eV. These energies and the dependence of the generation rate of the recombination center on boron concentration are in good agreement with observations.
|
|
| 4. |
- Adey, J., et al.
(författare)
-
Theory of boron-vacancy complexes in silicon
- 2005
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 71:16, s. 165211-
-
Tidskriftsartikel (refereegranskat)abstract
- The substitutional boron-vacancy BsV complex in silicon is investigated using the local density functional theory. These theoretical results give an explanation of the experimentally reported, well established metastability of the boron-related defect observed in p-type silicon irradiated at low temperature and of the two hole transitions that are observed to be associated with one of the configurations of the metastable defect. BsV is found to have several stable configurations, depending on charge state. In the positive charge state the second nearest neighbor configuration with C1 symmetry is almost degenerate with the second nearest neighbor configuration that has C1h symmetry since the bond reconstruction is weakened by the removal of electrons from the center. A third nearest neighbor configuration of BsV has the lowest energy in the negative charge state. An assignment of the three energy levels associated with BsV is made. The experimentally observed Ev+0.31 eV and Ev+0.37 eV levels are related to the donor levels of second nearest neighbor BsV with C1 and C1h symmetry respectively. The observed Ev+0.11 eV level is assigned to the vertical donor level of the third nearest neighbor configuration. The boron-divacancy complex BsV2 is also studied and is found to be stable with a binding energy between V2 and Bs of around 0.2 eV. Its energy levels lie close to those of the V2. However, the defect is likely to be an important defect only in heavily doped material.
|
|
| 5. |
- Gamboa, G., et al.
(författare)
-
Mg/Ca ratios in coralline algae record northwest Atlantic temperature variations and North Atlantic Oscillation relationships
- 2010
-
Ingår i: Journal of Geophysical Research-Oceans. - 0148-0227. ; 115
-
Tidskriftsartikel (refereegranskat)abstract
- [1] Climate variability in the North Atlantic has been linked in part to the North Atlantic Oscillation (NAO). The NAO influences marine ecosystems in the northwestern Atlantic and transport variability of the cold Labrador Current. Understanding historic patterns of NAO variability requires long-term and high-resolution climate records that are not available from instrumental data. Here we present the first century-scale proxy record of sea surface temperature (SST) variability from the Newfoundland shelf, a region from which other annual-resolution shallow marine proxies are unavailable. The 116 year record was obtained from three sites along the eastern Newfoundland shelf using laser ablation inductively coupled mass spectrometry-determined Mg/Ca ratios in the crustose coralline alga Clathromorphum compactum. The alga is characterized by a high Mg-calcite skeleton exhibiting annual growth increments and a century-scale lifespan. Results indicate positive correlations between interannual variations in Mg/Ca ratios and both station-based and gridded instrumental SST. In addition, the record shows high spatial correlations to SST across the Newfoundland shelf and the Gulf of St. Lawrence. Before 1950 the Mg/Ca proxy record reveals significant departures from gridded temperature records. While the Newfoundland shelf is generally considered a region of negative correlations to the NAO, the algal time series as well as a recent modeling study suggest a variable negative relationship with the NAO which is strongest after similar to 1960 and before the mid-1930s.
|
|
| 6. |
- Halfar, J., et al.
(författare)
-
Coralline algal growth-increment widths archive North Atlantic climate variability
- 2011
-
Ingår i: Palaeogeography Palaeoclimatology Palaeoecology. - 0031-0182. ; 302:1-2, s. 71-80
-
Tidskriftsartikel (refereegranskat)abstract
- Over the past decade coralline algae have increasingly been used as archives of paleoclimate information. Encrusting coralline algae, which deposit annual growth increments in a high Mg-calcite skeleton, are amongst the longest-lived shallow marine organisms. In fact, a live-collected plant has recently been shown to have lived for at least 850 years based on radiometric dating. While a number of investigations have successfully used geochemical information of coralline algal skeletons to reconstruct sea surface temperatures, less attention has been paid to employ growth increment widths as a temperature proxy. Here we explore the relationship between growth and environmental parameters in Clathromorphum compactum collected in the subarctic Northwestern Atlantic. Results indicate that growth-increment widths of individual plants are poorly correlated with instrumental sea surface temperatures (SST). However, an averaged record of multiple growth increment-width time series from a regional network of C. compactum specimens up to 800 km apart reveals strong correlations with annual instrumental SST since 1950. Hence, similar to methods applied in dendrochronology, averaging of multiple sclerochronological records of coralline algae provides accurate climate information. A 115-year growth-increment width master chronology created from modern-collected and museum specimens is highly correlated to multidecadal variability seen in North Atlantic sea surface temperatures. Positive changes in algal growth anomalies record the well-documented regime shift and warming in the northwestern Atlantic during the 1990s. Large positive changes in algal growth anomalies were also present in the 1920s and 1930s, indicating that the impact of a concurrent large-scale regime shift throughout the North Atlantic was more strongly felt in the subarctic Northwestern Atlantic than previously thought, and may have even exceeded the 1990s event with respect to the magnitude of the warming. (C) 2010 Elsevier B.V. All rights reserved.
|
|
| 7. |
- Hetzinger, S., et al.
(författare)
-
Coralline algal Barium as indicator for 20th century northwestern North Atlantic surface ocean freshwater variability
- 2013
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 3
-
Tidskriftsartikel (refereegranskat)abstract
- During the past decades climate and freshwater dynamics in the northwestern North Atlantic have undergone major changes. Large-scale freshening episodes, related to polar freshwater pulses, have had a strong influence on ocean variability in this climatically important region. However, little is known about variability before 1950, mainly due to the lack of long-term high-resolution marine proxy archives. Here we present the first multidecadal-length records of annually resolved Ba/Ca variations from Northwest Atlantic coralline algae. We observe positive relationships between algal Ba/Ca ratios from two Newfoundland sites and salinity observations back to 1950. Both records capture episodical multi-year freshening events during the 20th century. Variability in algal Ba/Ca is sensitive to freshwater-induced changes in upper ocean stratification, which affect the transport of cold, Ba-enriched deep waters onto the shelf (highly stratified equals less Ba/Ca). Algal Ba/Ca ratios therefore may serve as a new resource for reconstructing past surface ocean freshwater changes.
|
|
| 8. |
- Hetzinger, S., et al.
(författare)
-
High-resolution analysis of trace elements in crustose coralline algae from the North Atlantic and North Pacific by laser ablation ICP-MS
- 2011
-
Ingår i: Palaeogeography Palaeoclimatology Palaeoecology. - 0031-0182. ; 302:1-2, s. 81-94
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated the trace elemental composition in the skeleta of two specimens of attached-living coralline algae of the species Clathromorphum compactum from the North Atlantic (Newfoundland) and Clathromorphum nereostratum from the North Pacific/Bering Sea region (Amchitka Island, Aleutians). Samples were analyzed using Laser Ablation-Inductively Coupled Plasma Mass Spectrometry (IA-ICP-MS) yielding for the first time continuous individual trace elemental records of up to 69 years in length. The resulting algal Mg/Ca, Sr/Ca, U/Ca, and Ba/Ca ratios are reproducible within individual sample specimens. Algal Mg/Ca ratios were additionally validated by electron microprobe analyses (Amchitka sample). Algal Sr/Ca, U/Ca, and Ba/Ca ratios were compared to algal Mg/Ca ratios, which previously have been shown to reliably record sea surface temperature (SST). Ratios of Sr/Ca from both Clathromorphum species show a strong positive correlation to temperature-dependent Mg/Ca ratios, implying that seawater temperature plays an important role in the incorporation of Sr into algal calcite. Linear Sr/Ca-SST regressions have provided positive, but weaker relationships as compared to Mg/Ca-SST relationships. Both, algal Mg/Ca and Sr/Ca display clear seasonal cycles. Inverse correlations were found between algal Mg/Ca and U/Ca, Ba/Ca, and correlations to SST are weaker than between Mg/Ca, Sr/Ca and SST. This suggests that the incorporation of U and Ba is influenced by other factors aside from temperature. (C) 2010 Elsevier B.V. All rights reserved.
|
|
| 9. |
- Larsen, A. Nylandsted, et al.
(författare)
-
E center in silicon has a donor level in the band gap
- 2006
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 97:10, s. 106402/1-106402/4
-
Tidskriftsartikel (refereegranskat)abstract
- It has been an accepted fact for more than 40 years that the E center in Si (the group-V impurity-vacancy pair)-one of the most studied defects in semiconductors-has only one energy level in the band gap: namely, the acceptor level at about 0.45 eV below the conduction band. We now demonstrate that it has a second level, situated in the lower half of the band gap at 0.27 eV above the valence band. The existence of this level, having a donor character, is disclosed by a combination of different transient-capacitance techniques and electronic-structure calculations. The finding seriously questions some diffusion-modeling approaches performed in the past.
|
|
