| 1. |
- Sarakinos, Kostas, et al.
(författare)
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Structural factors determining the nanomechanical performance of transition metal nitride films
- 2005
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Konferensbidrag (refereegranskat)abstract
- Chromium nitride (CrN) and Titanium nitride (TiN) thin films were deposited employing unbalanced magnetron sputtering (UBMS) for various values of substrate bias voltage (V-b). The structural characterization of the films in terms of phase identification and the density determination was achieved utilizing X-Ray techniques (XRD and XRR respectively), while the internal stresses were calculated by the change of the substrates curvature using Stoneys equation. The nanomecahnical properties of the films (hardness and elastic modulus) were investigated using the Nanoindentation (NI) technique in the Continuous Stiffness Measurement (CSM) configuration. According to the NI results the hardness of the films ranges between between 15-25 GPa while the elastic modulus between 180-250 GPa. ne analysis revealed that the hardness of the films is maximum when their orientation is pure (either [111] or [100]), while it is minimized under mixed orientation regime. Furthermore, the hardness of the films increases as the internal compressive stresses and the mass density increase. The latter can be validated through the comparison of the results concerning the above films to reported results for TiN films prepared by balanced magnetron sputtering (BMS).
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| 2. |
- Jonsson, Mats, et al.
(författare)
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Modeling of the effects of radiolysis on UO2-dissolution employing recent experimental data
- 2004
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Konferensbidrag (refereegranskat)abstract
- This study examines the effect of water radiolysis on the dissolution of uranium dioxide. A model is created to describe the system of uranium dioxide fragments in water, and the production and reactions of radiolysis products (using recent kinetic data). The system is evaluated under different conditions using MAKSIMA-CHEMIST. Conditions examined include presence of carbonate in the water and effects of hydrogen. The simulations are compared to experimental results on spent fuel dissolution. Surprisingly, the simulated U(VI)-release agrees within a factor of three with the experimentally found U(VI)-release. The inhibiting effect of hydrogen is clearly demonstrated by the simulations. From the results of the simulations we are also able to conclude that the main inhibiting effect of H-2 is the reaction with OH* and not the reduction of U(VI) to U(IV).
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| 3. |
- Martinsson, Åsa, et al.
(författare)
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The effect of cold work on the creep properties of copper
- 2009
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Konferensbidrag (refereegranskat)abstract
- Spent nuclear fuel is in Sweden planned to be disposed of by encapsulating in waste packages consisting of a cast iron insert surrounded by a copper canister. The waste package is heavy. Throughout the manufacturing process from the extrusion/pierce-and-draw manufacturing to the final placement in the repository, the copper is subjected to handling which could introduce cold work in the material. It is well known that the creep properties of engineering materials at higher temperatures are affected by cold working. The study includes creep testing of four series of cold worked, oxygen-free, phosphorus doped copper (Cu-OFP) at 75°C. The results are compared to reference series for as-received material carried out in a recent study. Two series of copper cold worked in tension (12 and 24 %) and two series cold worked in compression (12 % parallel to creep load axis and 15 % perpendicular to creep load axis) were tested. The results show that pre-straining in tension of copper leads to prolonged creep life at 75°C. The creep rate and ductility are reduced. The influence on the creep properties increases with the amount of cold work. Cold work in compression applied along the creep load axis has no effect on the creep life or the creep rate. Nonetheless the ductility is still impaired. However, cold work in compression applied perpendicular to the creep load direction has a positive effect on the creep life. Cold work in both tension and compression results in a pronounced reduction of the initial strain on loading. Yet the high value of the area reduction, 90 %, is unaffected by the degree of cold work. © 2009 Materials Research Society.
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| 4. |
- Moeck, P., et al.
(författare)
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Nominal PbSe nano-islands on PbTe : Grown by MBE, analyzed by AFM and TEM
- 2005
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Konferensbidrag (refereegranskat)abstract
- Nominal PbSe nano-islands were grown in the Stranski-Krustanow mode on (111) oriented PbTe/BaF 2 pseudo-substrates by molecular beam epitaxy (MBE). The number density and morphology of these islands were assessed by means of atomic force microscopy (AFM). Transmission electron microscopy (TEM) was employed to determine the strain state and cryslallographic structure of these islands. On the basis of both AFM and TEM analyses, we distinguish between different groups of tensibly strained islands. The suggestion is made to use such nano-islands as part of nanometrology standards for scanning probe microscopy.
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| 5. |
- Paskova, Tanja, et al.
(författare)
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Hydride vapour phase homoepitaxial growth of GaN on MOCVD-grown 'templates'
- 2000
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Konferensbidrag (refereegranskat)abstract
- We report on an improved quality of thick HVPE-GaN grown on MOCVD-GaN 'template' layers compared to the material grown directly on sapphire. The film-substrate interface revealed by cathodoluminescence measurements shows an absence of highly doped columnar structures which are typically present in thick HVPE-GaN films grown directly on sapphire. This improved structure results in a reduction of two orders of magnitude of the free carrier concentration from Hall measurements. It was found that the structure, morphology, electrical and optical properties of homoepitaxial thick GaN layers grown by HVPE were strongly influenced by the properties of the MOCVD-GaN 'template'. Additionally the effect of Si doping of the GaN buffer layers on the HVPE-GaN properties was analysed.
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| 6. |
- Paskova, T., et al.
(författare)
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Strain-free low-defect-density bulk GaN with nonpolar orientations
- 2006
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Ingår i: MRS Proceedings. - : Springer Science and Business Media LLC. - 1946-4274.
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Konferensbidrag (refereegranskat)abstract
- Bulk GaN sliced in bars along (11-20) and (1-100) planes from a boule grown in the [0001] direction by HVPE was confirmed as strain free material with a low dislocation density by using several characterization techniques. The high-structural quality of the material allows photoluminescence studies of free excitons, principal donor bound excitons and their twoelectron satellites with regard to the optical selection rules. Raman scattering study of the bulk GaN with nonpolar orientations allows a direct access to the active phonon modes and a direct determination of their strain-free positions.
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| 7. |
- Rubensson, J. E., et al.
(författare)
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Soft X-ray Spectroscopic Characterization of Montmorillonite
- 2009
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Konferensbidrag (refereegranskat)abstract
- Soft X-ray spectroscopy was applied to study a calcium bentonite from the Kutch area in India. We recorded the X-ray absorption spectra from the L-edge of calcium, silicon, and aluminum, and from K-edge of oxygen. The Ca absorption spectrum shows a quasi-atomic behavior, while the Si spectrum closely simulates the absorption spectrum of a pure silicon oxide The O K spectrum shows a pre-peak, which is absent in the spectra of both the pure, bulk aluminum and silicon oxides. The At L spectrum is complex and shows almost no resemblance to the absorption spectrum of aluminum oxides. The chemical state of the At atoms (in octahedral coordination) must, thus, be quite different from what is common in the oxides. The obtained data show that soft X-ray spectroscopy is a promising technique for studying clay minerals. It is capable of supplying unique information that is complementary to information accessible using other techniques; especially, it can be used to determine the local electronic structure at various atomic sites in the complex samples.
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