| 1. |
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| 2. |
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| 3. |
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| 4. |
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| 5. |
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| 6. |
- Bruzzi, M, et al.
(författare)
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Radiation-hard semiconductor detectors for SuperLHC
- 2005
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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
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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.
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| 7. |
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| 8. |
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| 9. |
- Novak, R., et al.
(författare)
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Robotic fluidic coupling and interrogation of multiple vascularized organ chips
- 2020
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Ingår i: Nature Biomedical Engineering. - : Nature Research. - 2157-846X.
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Tidskriftsartikel (refereegranskat)abstract
- Organ chips can recapitulate organ-level (patho)physiology, yet pharmacokinetic and pharmacodynamic analyses require multi-organ systems linked by vascular perfusion. Here, we describe an ‘interrogator’ that employs liquid-handling robotics, custom software and an integrated mobile microscope for the automated culture, perfusion, medium addition, fluidic linking, sample collection and in situ microscopy imaging of up to ten organ chips inside a standard tissue-culture incubator. The robotic interrogator maintained the viability and organ-specific functions of eight vascularized, two-channel organ chips (intestine, liver, kidney, heart, lung, skin, blood–brain barrier and brain) for 3 weeks in culture when intermittently fluidically coupled via a common blood substitute through their reservoirs of medium and endothelium-lined vascular channels. We used the robotic interrogator and a physiological multicompartmental reduced-order model of the experimental system to quantitatively predict the distribution of an inulin tracer perfused through the multi-organ human-body-on-chips. The automated culture system enables the imaging of cells in the organ chips and the repeated sampling of both the vascular and interstitial compartments without compromising fluidic coupling.
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| 10. |
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| 11. |
- Brandsma, Joost, et al.
(författare)
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Stratification of asthma by lipidomic profiling of induced sputum supernatant
- 2023
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Ingår i: Journal of Allergy and Clinical Immunology. - : Elsevier. - 0091-6749 .- 1097-6825. ; 152:1, s. 117-125
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Tidskriftsartikel (refereegranskat)abstract
- Background: Asthma is a chronic respiratory disease with significant heterogeneity in its clinical presentation and pathobiology. There is need for improved understanding of respiratory lipid metabolism in asthma patients and its relation to observable clinical features.Objective: We performed a comprehensive, prospective, cross-sectional analysis of the lipid composition of induced sputum supernatant obtained from asthma patients with a range of disease severities, as well as from healthy controls.Methods: Induced sputum supernatant was collected from 211 adults with asthma and 41 healthy individuals enrolled onto the U-BIOPRED (Unbiased Biomarkers for the Prediction of Respiratory Disease Outcomes) study. Sputum lipidomes were characterized by semiquantitative shotgun mass spectrometry and clustered using topologic data analysis to identify lipid phenotypes.Results: Shotgun lipidomics of induced sputum supernatant revealed a spectrum of 9 molecular phenotypes, highlighting not just significant differences between the sputum lipidomes of asthma patients and healthy controls, but also within the asthma patient population. Matching clinical, pathobiologic, proteomic, and transcriptomic data helped inform the underlying disease processes. Sputum lipid phenotypes with higher levels of nonendogenous, cell-derived lipids were associated with significantly worse asthma severity, worse lung function, and elevated granulocyte counts.Conclusion: We propose a novel mechanism of increased lipid loading in the epithelial lining fluid of asthma patients resulting from the secretion of extracellular vesicles by granulocytic inflammatory cells, which could reduce the ability of pulmonary surfactant to lower surface tension in asthmatic small airways, as well as compromise its role as an immune regulator.
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| 12. |
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| 13. |
- Reed, B. P., et al.
(författare)
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Diamond (111) surface reconstruction and epitaxial graphene interface
- 2022
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Ingår i: Physical Review B. - 2469-9950. ; 105:20
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of the diamond (111) surface as it undergoes reconstruction and subsequent graphene formation is investigated with angle-resolved photoemission spectroscopy, low energy electron diffraction, and complementary density functional theory calculations. The process is examined starting at the C(111)-(2×1) surface reconstruction that occurs following detachment of the surface adatoms at 920 ∘C, and continues through to the liberation of the reconstructed surface atoms into a freestanding monolayer of epitaxial graphene at temperatures above 1000 ∘C. Our results show that the C(111)-(2×1) surface is metallic as it has electronic states that intersect the Fermi level. This is in strong agreement with a symmetrically π-bonded chain model and should contribute to resolving the controversies that exist in the literature surrounding the electronic nature of this surface. The graphene formed at higher temperatures exists above a newly formed C(111)-(2×1) surface and appears to have little substrate interaction as the Dirac point is observed at the Fermi level. Finally, we demonstrate that it is possible to hydrogen-terminate the underlying diamond surface by means of plasma processing without removing the graphene layer, forming a graphene-semiconductor interface. This could have particular relevance for doping the graphene formed on the diamond (111) surface via tuneable substrate interactions as a result of changing the terminating species at the diamond-graphene interface by plasma processing.
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| 14. |
- Brandsma, Joost, et al.
(författare)
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Lipid phenotyping of lung epithelial lining fluid in healthy human volunteers
- 2018
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Ingår i: Metabolomics. - : Springer-Verlag New York. - 1573-3882 .- 1573-3890. ; 14:10
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Tidskriftsartikel (refereegranskat)abstract
- Background: Lung epithelial lining fluid (ELF)-sampled through sputum induction-is a medium rich in cells, proteins and lipids. However, despite its key role in maintaining lung function, homeostasis and defences, the composition and biology of ELF, especially in respect of lipids, remain incompletely understood. Objectives: To characterise the induced sputum lipidome of healthy adult individuals, and to examine associations between different ELF lipid phenotypes and the demographic characteristics within the study cohort.Methods: Induced sputum samples were obtained from 41 healthy non-smoking adults, and their lipid compositions analysed using a combination of untargeted shotgun and liquid chromatography mass spectrometry methods. Topological data analysis (TDA) was used to group subjects with comparable sputum lipidomes in order to identify distinct ELF phenotypes.Results: The induced sputum lipidome was diverse, comprising a range of different molecular classes, including at least 75 glycerophospholipids, 13 sphingolipids, 5 sterol lipids and 12 neutral glycerolipids. TDA identified two distinct phenotypes differentiated by a higher total lipid content and specific enrichments of diacyl-glycerophosphocholines, -inositols and -glycerols in one group, with enrichments of sterols, glycolipids and sphingolipids in the other. Subjects presenting the lipid-rich ELF phenotype also had significantly higher BMI, but did not differ in respect of other demographic characteristics such as age or gender.Conclusions: We provide the first evidence that the ELF lipidome varies significantly between healthy individuals and propose that such differences are related to weight status, highlighting the potential impact of (over)nutrition on lung lipid metabolism.
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| 15. |
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| 16. |
- Goss, J.P., et al.
(författare)
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Extended defects in diamond: the interstitial platelet
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:16, s. 165208-1
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Tidskriftsartikel (refereegranskat)abstract
- The structure and properties of the {001} planar platelet in diamond are investigated using ab initio theory. We find that a carbonaceous model, based on a layer of self-interstitials, satisfies the requirements of transmission electron microscopy, infrared absorption data, and energetic considerations. The energetics of self-interstitial production during nitrogen aggregation are considered. It is found that the growth mechanism of the platelet involves a thermally activated release of vacancies from platelets. The role of vacant sites and platelet nitrogen are also investigated and it is shown that these defects embedded within the platelet could account for the observed optical activity.
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| 17. |
- Goss, J.P., et al.
(författare)
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Small aggregates of interstitials and models for platelets in diamond
- 2000
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 12:49, s. 10257-10261
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Tidskriftsartikel (refereegranskat)abstract
- By examining the structure of small clusters of self-interstitials in diamond using local-density-functional techniques, we have developed models for the planar defects called platelets. We present the structures, energies and vibrational properties
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| 18. |
- Leigh, R. S., et al.
(författare)
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Vibrational modes of sulfur defects in GaP
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 68:3
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Tidskriftsartikel (refereegranskat)abstract
- First principles calculations carried out on GaP containing sulfur donors 32SP (95%) and34SP (5%) show that both the neutral and ionized donors are located on substitutional sites and have weak S-Ga bonds. For the sulfur impurity in its positive charge state the calculations give gap modes for 32S and34S at frequencies close to those found experimentally. Modes within the gap are also predicted for neutral sulfur at frequencies within a few cm-1 of their charged-state counterparts. However, the SP0 donor has a very low apparent charge (i.e. oscillator strength), its calculated integrated absorption cross section being only ∼3% of that for the SP+ defect. These results support an earlier explanation of the failure to detect gap modes from SP0 in infrared measurements. Calculated and observed apparent charges for the SP+ donor are compared, and the importance of taking due account of the different geometries that apply to the theoretical calculations and infrared experiments is emphasized.
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| 19. |
- Budde, M., et al.
(författare)
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Identification of the hydrogen-saturated self-interstitials in silicon and germanium
- 1998
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 57:18, s. 4397-4412
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Tidskriftsartikel (refereegranskat)abstract
- Silicon and germanium single crystals are implanted with protons. The infrared-absorption spectra of the samples contain sharp absorption lines due to the excitation of hydrogen-related local vibrational modes. The lines at 743.1, 748.0, 1986.5, and 1989.4 cm-1 in silicon and at 700.3, 705.5, 1881.8, and 1883.5 cm-1 in germanium originate from the same defect in the two materials. Measurements on samples coimplanted with protons and deuterons show that the defect contains two equivalent hydrogen atoms. Uniaxial stress measurements are carried out and a detailed analysis of the results is presented. It is shown that the defect has monoclinic-II symmetry, and the orientations of the Si-H and Ge-H bonds of the defect are determined. Ab initio local-density-functional theory is used to calculate the structure and local vibrational modes of the self-interstitial binding one and two hydrogen atoms in silicon and germanium together with the structure of the self-interstitial itself. The observed properties of the defect are in excellent agreement with those calculated for the self-interstitial binding two hydrogen atoms.
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| 20. |
- Budde, M., et al.
(författare)
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The hydrogen-saturated self-interstitial in silicon and germanium
- 1997
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Ingår i: Defects in semiconductors. - : Trans Tech Publications Inc.. ; , s. 35-40
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Konferensbidrag (refereegranskat)abstract
- Infrared absorption spectroscopy is used to study H-related point defects in H+-implanted Si (Si:H) and Ge (Ge:H). The absorption lines at 743.1, 748.0, 1986.5 and 1989.4 cm-1 in Si:H and at 700.3, 705.5, 1881.8 and 1883.5 cm-1 in Ge:H are shown to originate from the same defect containing two equivalent H atoms. Uniaxial stress experiments show that the defects have monoclinic-II symmetry, and the orientations of the two Si-H or Ge-H bonds are determined. The structure and the local vibrational modes of the self-interstitial binding two H atoms (IH2) are calculated with LDF cluster theory. The symmetry, bond-orientations and isotopic frequency-shifts calculated for IH2 are in excellent agreement with those observed for the 743.1-, 748.0-, 1986.5- and 1989.4-cm-1 modes in Si:H and for the 700.3-, 705.5-, 1881.8- and 1883.5-cm-1 modes in Ge:H.
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| 21. |
- Carvalho, A., et al.
(författare)
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Self-interstitial in germanium
- 2007
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 99:17, s. 175502-
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Tidskriftsartikel (refereegranskat)abstract
- Low-temperature radiation damage in n- and p-type Ge is strikingly different, reflecting the charge-dependent properties of vacancies and self-interstitials. We find, using density functional theory, that in Ge the interstitial is bistable, preferring a split configuration when neutral and an open cage configuration when positively charged. The split configuration is inert while the cage configuration acts as a double donor. We evaluate the migration energies of the defects and show that the theory is able to explain the principal results of low-temperature electron-irradiation experiments.
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| 22. |
- Carvalho, A., et al.
(författare)
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Self-interstitials and Frenkel pairs in electron-irradiated germanium
- 2007
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 401-402, s. 495-498
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Tidskriftsartikel (refereegranskat)abstract
- First principles calculations were used to study the structures and electrical levels of the self-interstitial in Ge. We considered the possibility of structural changes consequent with change in charge state and show these have important implications in the mobility and electrical activity of the defect. The theoretical model is compared to the results of low temperature electron irradiation in germanium reported in the literature.
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| 23. |
- Coomer, B.J., et al.
(författare)
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Identification of the tetra-interstitial in silicon
- 2001
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 13:1, s. L1-L7
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Tidskriftsartikel (refereegranskat)abstract
- First-principles computational methods are employed to investigate the structural, vibrational, optical and electronic properties of the self-interstitial aggregate, I4 in silicon. We find the defect to be electrically active and identify it with the B3 EPR centre. We also show that its properties are consistent with DLTS and optical spectra observed following implantation of silicon.
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| 24. |
- Coomer, B.J., et al.
(författare)
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Interstitial aggregates and a new model for the I1/W optical centre in silicon
- 1999
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 273-274, s. 505-508
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Tidskriftsartikel (refereegranskat)abstract
- The properties of di-interstitial (I2), tri-interstitial (I3) and tetra-interstitial (I4) structures in silicon were studied by employing first principles local-density-functional (LDF) theory. A tri-interstitial defect can account for many of the fundamental properties of the I1/W-optical center which is observed in irradiated, annealed silicon. Energy comparisons between di-interstitial defects reveal four low-energy structures within 0.5 eV of each other.
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| 25. |
- Coomer, B.J., et al.
(författare)
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The divacancy in silicon and diamond
- 1999
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 273-274, s. 520-523
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Tidskriftsartikel (refereegranskat)abstract
- First-principles studies of the divacancy (V2) in both silicon and diamond are reported. We demonstrate that the contrasting experimental spin-density localisation of both systems can be explained through the one-electron pictures arising from opposing distortions
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| 26. |
- Eberlein, T.A.G., et al.
(författare)
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Self-interstitial clusters in silicon
- 2001
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308-310, s. 454-457
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Tidskriftsartikel (refereegranskat)abstract
- Although there have been made many calculations for structures of the self-interstitial in Si and small aggregates of interstitials, In, there have been relatively few attempts to relate these defects with experimental data. Here, we discuss the assignments of the self-interstitial to the AA12 EPR centre and the di-interstitial to the P6 EPR centre.
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| 27. |
- Goss, J.P., et al.
(författare)
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A first principles study of interstitial Si in diamond
- 1997
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Ingår i: Defects in Semiconductors. - : Trans Tech Publications Inc.. ; , s. 781-786
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The results of first principles calculations using AIMPRO (a local-density-functional code) are presented to describe the stability of interstitial Si in diamond. It is found that the 〈100〉 and 〈110〉 split-interstitial configurations are only local minima in the total energy surface. Td interstitial Si reconstructs to form a substitutional Si site close to a self-interstitial. The difference in total energy between the split configuration and the substitutional-Si-self-interstitial complex is more than 6 eV. It is concluded that Si would not adopt an interstitial location in diamond as has been previously suggested from experimental evidence. Interestingly the self-interstitial remains bound to the substitutional Si with a binding energy around 1 eV.
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| 28. |
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| 29. |
- Goss, J.P., et al.
(författare)
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Interstitial aggregates in diamond
- 2001
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Ingår i: Diamond and related materials. - 0925-9635 .- 1879-0062. ; 10:3, s. 434-438
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical modelling of magnetic resonance signals lead to convincing models for the first three self-interstitial aggregates in diamond. These in turn suggest the manner in which larger more stable aggregates including the platelet, observed in annealed type I diamonds, are formed.
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| 30. |
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| 31. |
- Goss, J.P., et al.
(författare)
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Self-interstitial aggregation in diamond
- 2001
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:19, s. 195208-
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Tidskriftsartikel (refereegranskat)abstract
- First-principles methods are used to investigate the self-interstitial and its aggregates in diamond. The experimental assignment of the spin-1 R2 EPR center to the single interstitial has been questioned because of the small fine-structure term observed. We calculate the spin-spin interaction tensor for the three interstitial defects I1〈001〉, I2NN, and I3 and compare with the experimental D tensors. The results give support for the assignments of the single and di-interstitials to microscopic models and allow us to conclusively identify a recently observed EPR center, O3, with I3. This identification, in turn, suggests a low-energy structure for I4 and a generic model for an extended defect called the platelet. We also determine the optical properties of I1〈001〉 as well as its piezospectroscopic or stress tensor and find these to be in agreement with experiment. Several multi-interstitial defects are found to possess different structural forms which may coexist. We propose that a different form of the charged I2 defect gives rise to the 3H optical peak. Several structures of the platelet are considered, and we find that the lowest-energy model is consistent with microscopic and infrared studies.
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| 32. |
- Goss, J P, et al.
(författare)
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The twelve-line 1.682 eV luminescence center in diamond and the vacancy-silicon complex
- 1996
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 77:14, s. 3041-3044
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Tidskriftsartikel (refereegranskat)abstract
- Ab initio cluster methods are used to investigate vacancy-impurity complexes in diamond. We assign the 1.682 eV, twelve-line optical band to a vacancy-Si complex which has a very unusual, possibly unique structure with a Si atom at the center of a split vacancy. The method also successfully accounts for the 1.945, 2.156, and 2.985 eV optical transitions in trigonal vacancy-N defects and estimates of radiative lifetimes are given.
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| 33. |
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| 34. |
- Jones, R., et al.
(författare)
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Intrinsic defects and the D1 to D4 optical bands detected in plastically deformed Si
- 2000
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Ingår i: Physica status solidi. B, Basic research. - 0370-1972 .- 1521-3951. ; 222:1, s. 133-140
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Tidskriftsartikel (refereegranskat)abstract
- The properties of multi-vacancy and multi-interstitial defects that possess luminescent bands around 1 eV are reviewed. Prominent among these are the hexavacancy and tri- and tetra-self-interstitial defects. It is suggested that the formation of these defects on dislocation cores could lead to the D1 to D4 photoluminescent bands linked to dislocations in Si and SiGe.
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| 35. |
- Jones, R., et al.
(författare)
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Self-interstitial clusters in silicon
- 2002
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - 0168-583X .- 1872-9584. ; 186:1, s. 10-18
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Tidskriftsartikel (refereegranskat)abstract
- Although there have been many calculations of the structures of the self-interstitial in Si and small aggregates of interstititals, In, there has been little attempt to relate the defects with experimental data. Here we discuss the assignments of the self-interstitial to the AA12 electron paramagnetic resonance (EPR) centre, and the tri-interstitial and tetra-interstitial to the W-optical centre and the B3 EPR centre, respectively. Difficulties in the assignment of I2 to the P6 EPR centre are also noted.
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| 36. |
- Markevich, A., et al.
(författare)
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First-principles study of hydrogen and fluorine intercalation into graphene-SiC(0001) interface
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:4
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Tidskriftsartikel (refereegranskat)abstract
- The properties of epitaxial graphene on SiC substrates can be modified by intercalation of different atomic species. In this work, mechanisms of hydrogen intercalation into the graphene-SiC(0001) interface, and properties of hydrogen and fluorine intercalated structures have been studied with the use of density functional theory. Our calculations show that the intercalation of hydrogen and fluorine into the interface is energetically favorable. Energy barriers for diffusion of atomic and molecular hydrogen through the interface graphene layer with no defects and graphene layers containing Stone-Wales defect or two- and four-vacancy clusters have been calculated. It is argued that diffusion of hydrogen towards the SiC surface occurs through the hollow defects in the interface graphene layer. It is further shown that hydrogen easily migrates between the graphene layer and the SiC substrate and passivates the surface Si bonds, thus causing the graphene layer decoupling. According to the band structure calculations the graphene layer decoupled from the SiC(0001) surface by hydrogen intercalation is undoped, while that obtained by the fluorine intercalation is p-type doped.
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| 37. |
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| 38. |
- Rasmussen, F. Berg, et al.
(författare)
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The nitrogen-pair oxygen defect in silicon
- 1996
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5107 .- 1873-4944. ; 36:1-3, s. 91-95
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Tidskriftsartikel (refereegranskat)abstract
- The nitrogen-pair oxygen defect in silicon has been studied by infrared absorption spectroscopy on samples implanted with various combinations of 14N, 15N, 16O and 17O. The measurements give direct evidence for the involvement of nitrogen and oxygen in the defect and show that the impurity atoms comprising the defect are only weakly coupled. Ab initio cluster calculation on several models of the nitrogen-pair oxygen defect have been performed and are compared with experiment. Based on these investigations a model consisting of a bridging oxygen atom adjacent to the nitrogen pair is suggested
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| 39. |
- Rasmussen, F. Berg, et al.
(författare)
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The NNO defect in silicon
- 1995
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Ingår i: Proceedings of the 18th International Conference on Defects in Semiconductors. - : Trans Tech Publications Inc.. ; , s. 791-796
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Konferensbidrag (refereegranskat)abstract
- Nitrogen-oxygen complexes in silicon have been studied by infrared absorption spectroscopy on samples implanted with various combinations of O and N isotopes as well as O-rich samples doped with N during growth. Local vibrational modes at 805, 999 and 1030 cm-1 (14N, 16O) are directly shown to belong to a defect consisting of a N-pair interacting with an O interstitial. A recently proposed model of this NNO defect is further investigated by ab initio cluster calculations and found to account for the dynamical properties of the defect. A mode around 730 cm-1 predicted by the calculation is observed giving further support to the model.
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| 40. |
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| 41. |
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| 42. |
- Sque, S.J., et al.
(författare)
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First-principles study of C60 and C60F36 as transfer dopants for p-type diamond
- 2005
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Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 17:2, s. L21-L26
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Tidskriftsartikel (refereegranskat)abstract
- Ab initio density-functional-theory has been used to investigate transfer doping between C60 monolayers and the hydrogenated (100) diamond surface. An electron transfer from diamond to C60 is predicted for a C60 coverage of around one monolayer, and the possibility of electron transfer is expected to increase for higher coverages, leading to an accumulation of holes at the diamond surface. It has been found that the greater electron affinity of fluorinated C60 is likely to enhance the effect. Results are reported on the structural and electronic properties of isolated C60 and C60F36 molecules, solid C60, and a monolayer of each material adjacent to the (100)-(2 × 1):H diamond surface.
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| 43. |
- Al-Hamadandy, Raied, et al.
(författare)
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Oxygen vacancy migration in compressively strained SrTiO3
- 2013
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:2
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Tidskriftsartikel (refereegranskat)abstract
- The intrinsic properties of strontium titanate render it promising in applications such as gate dielectrics and capacitors. However, there is growing evidence that oxygen vacancies significantly impact upon its use, with the diffusion and deep donor level of the oxygen vacancy leading to electrical leakage. Where grown epitaxially on a lattice mismatched substrate, SrTiO 3 undergoes bi-axial strain, altering its crystal structure and electronic properties. In this paper, we present the results of first-principles simulations to evaluate the impact of strain in a (001) plane upon the migration of oxygen vacancies. We show that in the range of strains consistent with common substrate materials, diffusion energies in different directions are significantly affected, and for high values of strain may be altered by as much as a factor of two. The resulting diffusion anisotropy is expected to impact upon the rate at which oxygen vacancies are injected into the films under bias, a critical factor in the leakage and resistive switching seen in this material
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| 44. |
- Al-Hamadany, R., et al.
(författare)
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Impact of tensile strain on the oxygen vacancy migration in SrTiO3 : Density functional theory calculations
- 2013
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:22
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Tidskriftsartikel (refereegranskat)abstract
- Strontium titanate is a promising dielectric material for device applications including capacitors and gate dielectrics. However, oxygen vacancies, which are inevitable donor defects mobile under bias at room temperature, lead to undesirable leakage current in SrTiO3 thin films. Epitaxially grown SrTiO3 on lattice mismatched substrates leads to strained SrTiO3, inducing structural phase transitions from a cubosymmetric non-ferroelectric geometry to tetragonal and orthorhombic structures, depending upon the sign of the strain. In this study, density functional calculations have been performed to determine the impact of isotropic biaxial tensile strain in a (001) plane upon the phase of SrTiO3 and the activation energy for the migration of oxygen vacancies in such strained SrTiO3. The phase transition of the host material yields anisotropy in oxygen vacancy diffusion for diffusion within and between planes parallel to the strain. We found a general reduction in the barrier for diffusion within and normal to the plane of tensile strain. The inter-plane diffusion barrier reduces up to 25% at high values of strain. The variation in the barrier corresponding to in-plane diffusion is smaller in comparison to inter-plane diffusion. Finally, we reflect upon how the interplay between lattice strain with native defects plays a crucial role in the conduction mechanism of thin film, strained SrTiO3
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| 45. |
- Albinsson, Bo, 1963, et al.
(författare)
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Matrix-isolation IR and UV spectra of Si3H8 and Si4H10: Isomers and conformers of oligosilanes
- 1996
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Ingår i: Journal of Physical Chemistry. - 0022-3654. ; 100:21, s. 8681-8691
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Tidskriftsartikel (refereegranskat)abstract
- Matrix-isolation IR and UV spectra of Si3H8, i-Si4H10, and the two conformers of n-Si4H10 have been recorded. A quantitative separation of the IR spectrum of n-Si4H10 into contributions from the anti and gauche forms was accomplished by a combination of matrix annealing and selective monochromatic photodestruction experiments. A qualitative separation of their UV spectra was achieved as well. The IR spectra of Si3H8, i-Si4H10, and the two conformers of n-Si4H10 have been assigned by comparison with results of ab initio calculations, which reproduce the frequencies and even the relative intensities quite well. The calculations predict dihedral angles omega of 180 degrees and 57 degrees for the anti and the gauche conformer of n-Si4H10, respectively, and confirm earlier predictions of nearly equal stability for an isolated molecule. In the matrix, the anti conformer is more stable, The conformational effects on the UV spectrum of n-Si4H10 are not those anticipated from simple models of the Sandorfy or ladder C type, in that it is primarily not the energy but the intensity of the low-energy excited singlet states that depends strongly on the SiSiSiSi dihedral angle omega. This result is interpreted in terms of data from 6-in-8 CASSCF 6-31G* calculations, which predict an avoided crossing between a strongly allowed sigma sigma* B state and a very weakly allowed sigma pi* B state as omega changes, with the former lower in energy at 180 degrees and the latter lower at 0 degrees. Consequences for attempts to understand the effects of conformation on optical spectra of polysilanes are noted.
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| 46. |
- Atumi, M.K., et al.
(författare)
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Hyperfine interaction of H-divacancy in diamond
- 2020
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Ingår i: Results in Physics. - : Elsevier. - 2211-3797. ; 16
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Tidskriftsartikel (refereegranskat)abstract
- We present a first principles density functional theory study of microscopic properties of hydrogen defect centres in diamond. Several configurations, involving interstitial hydrogen impurities, have been considered either forming with other defects, such as hydrogen defects and vacancies. The atomic structures, and hyperfine parameters of hydrogen result compared with the experimental data on electrically active centres in synthetic diamond. Based on Local density functional theory our calculations are in excellent agreement with one interpretation of electron paramagnetic resonance of hydrogen in diamond.
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| 47. |
- Atumi, M.K., et al.
(författare)
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Hyperfine interactions at nitrogen interstitial defects in diamond
- 2013
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 25:6
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Tidskriftsartikel (refereegranskat)abstract
- Diamond has many extreme physical properties and it can be used in a wide range of applications. In particular it is a highly effective particle detection material, where radiation damage is an important consideration. The WAR9 and WAR10 are electron paramagnetic resonance centres seen in irradiated, nitrogen-containing diamond. These S = 1/2 defects have C2v and C1h symmetry, respectively, and the experimental spectra have been interpreted as arising from nitrogen split-interstitial centres. Based upon the experimental and theoretical understanding of interstitial nitrogen defect structures, the AIMPRO density functional code has been used to assess the assignments for the structures of WAR9 and WAR10. Although the calculated hyperfine interaction tensors are consistent with the measured values for WAR9, the thermal stability renders the assignment problematic. The model for the WAR10 centre yields principal directions of the hyperfine tensor at variance with observation. Alternative models for both centres are discussed in this paper, but no convincing structures have been found.
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| 48. |
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| 49. |
- Budde, M., et al.
(författare)
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Local modes of the H2* dimer in germanium
- 1996
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 54:8, s. 5485-5494
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Tidskriftsartikel (refereegranskat)abstract
- Local vibrational modes of the H2* defect in crystalline germanium are identified by a combination of infrared-absorption spectroscopy, uniaxial stress measurements, and ab initio theory. Germanium crystals are implanted with protons and/or deuterons at 30 K, and subsequently annealed at room temperature. A number of local vibrational modes of hydrogen are revealed by infrared-absorption spectroscopy. In particular, modes at 765, 1499, 1774, and 1989 cm-1 originate from the same defect which has trigonal symmetry according to the uniaxial stress measurements. The 765-cm-1 mode is two dimensional, while the 1774- and 1989-cm-1 modes are one dimensional. Measurements on samples coimplanted with protons and deuterons show that the defect contains a pair of weakly coupled and inequivalent hydrogen atoms. The 765-, 1499-, 1774-, and 1989-cm-1 modes are ascribed to the H2* defect. The 765-cm-1 mode is a Ge-H bend mode with an overtone at 1499 cm-1 and the modes at 1774 and 1989 cm-1 are Ge-H stretch modes. An excellent fit to the stretch frequencies is obtained with a simple model based on two coupled Morse-potential oscillators. In addition, the model gives intensity ratios in fair agreement with those observed. The structure, the local-mode frequencies, and the isotope shifts of H2* are calculated with ab initio local-density-functional cluster theory. The theoretical frequencies are consistently 5-10 % too high, as expected from the theory which often leads to overbinding. The isotope shifts, however, are in fair agreement with observations. These results provide additional support for our assignments, and show that the 765- and 1774-cm-1 modes primarily involve the hydrogen at the antibonding site, while the 1989-cm-1 mode is related mainly to vibration of the hydrogen near the bond-center site.
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| 50. |
- Carvalho, A, et al.
(författare)
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First-principles study of the diffusion mechanisms of the self-interstitial in germanium
- 2008
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 20:13
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Tidskriftsartikel (refereegranskat)abstract
- The self-interstitial in germanium can assume multiple configurations depending on the temperature and charge state. Here, we employ a first-principles density functional method to investigate the diffusion mechanisms of this defect. The energy barriers associated with the transformation between different structures are determined by the climbing nudged elastic band method, as a function of the charge state. The relation between the thermodynamic properties of the self-interstitial and the temperature evolution of electron radiation damage in germanium are discussed.
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