| 1. |
- Brunell, I.F., et al.
(författare)
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In-situ stress measurement during the deposition of CN x thin films by unbalanced magnetron sputtering; formation of high levels of stress with 28 eV ion irradiation
- 2004
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 84:6, s. 395-403
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Tidskriftsartikel (refereegranskat)abstract
- Stress development during growth of CN x films by unbalanced magnetron sputtering has been investigated with an in-situ laser deflection technique. The stress is initially tensile, then it becomes compressive, reaching a maximum of as much as 7 GPa. These are anomalously high stress levels compared with pure carbon, considering the low ion energies (28 eV) and ion-to-neutral arrival rate ratio (<1) employed. This phenomenon is explained by the formation of a fullerene-like microstructure and nitrogen substitution at the growth surface. An accompanying increased reactivity of carbon atoms promotes sp3 bonding or other cross-linking of curved basal planes with resulting film densification.
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| 2. |
- Chen, Chun Lin, et al.
(författare)
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In situ TEM observation of decomposition of high-purity sapphire
- 2009
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 89:2, s. 113-119
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Tidskriftsartikel (refereegranskat)abstract
- The decomposition of agr-Al2O3 under 200 keV electron irradiation has been investigated by in situ high-resolution electron microscopy (HREM). It was confirmed that aluminium precipitated from agr-Al2O3 under 200 keV electron irradiation for less than 1 min over the temperature range from 700 to 1273 K. The electron dose rate was of the order of 1023 e m-2 s-1 and the vacuum level of the microscope was better than 10-6 Pa. The mechanisms of agr-Al2O3 decomposition were discussed based on two possible decomposition models: the thermally activated atom movement and the forced atom displacement
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| 3. |
- Ghassemali, Ehsan, 1983-, et al.
(författare)
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Dynamic precipitation at elevated temperatures in a dual-phase AlCoCrFeNi high-entropy alloy : an in situ study
- 2018
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Ingår i: Philosophical Magazine Letters. - : Taylor & Francis. - 0950-0839 .- 1362-3036. ; 98:9, s. 400-409
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Tidskriftsartikel (refereegranskat)abstract
- The effect of a possible phase transformation or precipitation of the face-centred cubic (FCC) phase on intermediate-temperature deformation of a dual-phase AlCoCrFeNi high-entropy alloy has been studied using in situ tensile testing at 550°C. Electron backscatter diffraction (EBSD) results showed localised precipitation of the FCC phase during the intermediate-temperature deformation. The overall fracture behaviour and crack propagation of the material was not altered much compared to the room-temperature behaviour, namely brittle trans-granular fracture. Deformation at higher temperatures (above 750°C) is suggested as a way to enhance the dynamic FCC phase precipitation, in order to improve the ductility or deformability of the alloy.
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| 4. |
- Gutiérrez, R., et al.
(författare)
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The formation of nanopipes caused by donor impurities in GaN: A theoretical study for the case of oxygen
- 1999
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 79:3, s. 147-152
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Tidskriftsartikel (refereegranskat)abstract
- Local density-functional methods are used to examine the behaviour of O and O-related defect complexes at {1010}-type surfaces in GaN. We find that O has a tendency to segregate to the (1010) surface and we identify the gallium vacancy surrounded by three oxygen impurities (VGa-(ON)3) to be a particularly stable and electrically inert complex. We suggest that these complexes impede growth at the walls of the nanopipes preventing them from growing in. Also, other donor-related defect complexes, in particular gallium vacancies surrounded by three silicon atoms as second nearest neighbours, are expected to have the same effect.
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| 5. |
- Hörnqvist Colliander, Magnus, 1979, et al.
(författare)
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Complete precipitate dissolution during adiabatic shear localisation in a Ni-based superalloy
- 2020
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 100:12, s. 561-570
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Tidskriftsartikel (refereegranskat)abstract
- Whereas microstructure evolution in adiabatic shear bands have been thoroughly studied, reports on the stability of hardening precipitates during shear localisation are scarce. We report an atomic scale investigation of solute distribution in adiabatic shear bands in a precipitation strengthened Ni-Fe-based superalloy, showing that the hardening particles are completely dissolved. Temperature estimations indicate that peak temperatures in the shear band above the solvus limits of the precipitates are not unrealistic, and thus diffusion-assisted transformations during the severe plastic deformation cannot be ruled out.
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| 6. |
- Johansson, Sven, 1981, et al.
(författare)
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Theory of ultrathin films at metal-ceramic interfaces
- 2010
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 90:8, s. 599-609
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical model for understanding the formation of interfacial thin films is presented, which combines density functional theory calculations for interface energies with thermodynamic modeling techniques for multicomponent bulk systems. The theory is applied to thin film formation in VC-doped WC-Co cemented carbides. It is predicted that ultrathin VC films may exist in WC/Co interfaces at the high temperature sintering conditions where most of the WC grain growth occurs, which provides an explanation of the grain growth inhibiting effect of VC additions in the WC-Co system.
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| 7. |
- Jones, R, et al.
(författare)
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Ab initio calculations of the structure and dynamics of C60 and C3- 60
- 1992
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 65:6, s. 291-298
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Tidskriftsartikel (refereegranskat)abstract
- A local-density-functional cluster method is used to calculate the structure and vibrational modes of C60. We find C–C lengths in good agreement with observed values. The effect of doping the molecule with three extra electrons is investigated and shown to result in a surprising shortening of the longer bonds. The second derivatives of the energy are evaluated and have enabled, for the first time, all the normal modes of the molecule to be found. We find these to be in fair agreement with the available experimental results.
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| 8. |
- Jones, R., et al.
(författare)
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First-principles theory of nitrogen aggregates in diamond
- 1992
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 66:2, s. 67-74
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Tidskriftsartikel (refereegranskat)abstract
- Local-density-functional theory is used to evaluate the structure, vibrational bands and electronic properties of two point defects in diamond a pair of adjacent substitutional N atoms and a vacancy surrounded by four N atoms. These defects are important as they are possible models of the A and B centres seen in type Ia diamond. For the A centre we find a N─N bond length of 2·14 Å, an occupied electronic energy level near midgap and four infrared absorption bands with frequencies close to the experimental values. For the model of the B centre we find a N─C length of 1·49 Å an occupied triplet electronic level within the gap consistent with the recent suggestion that the N9 absorption band is due to this defect and again vibratory modes in close agreement with experiment. These results provide strong evidence as to the validity of the models for the A and B centres.
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| 9. |
- Joseph, Ceena, 1982, et al.
(författare)
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Precipitation of γ’ during cooling of nickel-base superalloy Haynes 282
- 2021
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 101:1, s. 30-39
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Tidskriftsartikel (refereegranskat)abstract
- Cooling-induced precipitation of the strengthening γ’ phase is commonly investigated in Ni-base superalloys with a high γ’ volume fraction, where it is used to control the final microstructure and properties. Less is known about the phase separation in low-volume-fraction alloys during cooling, although the microstructural state after cooling from solution treatment is known to affect subsequent heat-treatment steps. We use atomic-scale characterisation of Ni-base superalloy Haynes 282 (equilibrium γ’ volume fraction around 20%) to show that air cooling after solution or carbide stabilisation results in precipitation of nm-sized γ’ particles, whereas precipitation was suppressed during water quenching. The solution treatment has a significant effect on the hardness and γ’ precipitation during air cooling from the subsequent carbide stabilisation temperature. Also, the carbide-stabilisation treatment itself affects the γ’ precipitation during subsequent air cooling.
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| 10. |
- Mathieu, Roland, et al.
(författare)
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Isothermal remanent magnetization and the spin dimensionality of spin glasses
- 2010
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 90:10, s. 723-729
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Tidskriftsartikel (refereegranskat)abstract
- The isothermal remanent magnetization is used to investigate dynamical magnetic properties of spatially three-dimensional spin glasses with different spin dimensionality (Ising, XY, Heisenberg). The isothermal remanent magnetization is recorded versus temperature after the application of a weak magnetic field at a constant temperature T-h. We observe that in the case of the Heisenberg spin glasses, the equilibrated spin structure and the direction of the excess moment are recovered at T-h. The isothermal remanent magnetization thus reflects the directional character of the Dzyaloshinsky-Moriya interaction present in Heisenberg systems.
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| 11. |
- McCulloch, I. P., et al.
(författare)
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Ferromagnetism in Kondo lattice models
- 2001
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 81:12, s. 869-875
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of a new ferromagnetic phase in the one-dimensional Kondo lattice model for intermediate values of the coupling constant. This new ferromagnetic phase was observed using a non-Abelian density-matrix renormalization group algorithm, which allowed us to measure directly the magnetization of the ground state with high accuracy.
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| 12. |
- Nussinov, Z., et al.
(författare)
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Exact ground states of extended t-J(z) models on a square lattice
- 2007
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 87:7, s. 515-526
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Tidskriftsartikel (refereegranskat)abstract
- We examine special extended spin S = 1/2 fermionic and hard core bosonic t - J(z) models with nearest neighbour and next nearest neighbour interactions to find exact ground states. Some of these models display an exponentially large degeneracy with diagonal stripe-like patterns.
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| 13. |
- Pan, Jinshan, et al.
(författare)
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Self-diffusion activation energies in alpha-Al2O3 below 1000 degrees C : measurements and molecular dynamics calculation
- 2004
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 84:12, s. 781-789
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Tidskriftsartikel (refereegranskat)abstract
- Results from impedance spectroscopy measurements at temperatures between 400 and 1000&DEG; C, for single crystal and highly pure and dense polycrystalline α-Al2O3 samples with well-defined grain size, are compared with that from molecular dynamics calculation. Between 650 and 1000&DEG; C, the measured activation energy for conductivity is 1.5 eV for the single crystal, and increases from 1.6 to 2.4 eV as the grain size decreases from 15 to 0.5 μ m. The molecular dynamics calculation leads to the conclusion that the self-diffusion activation energy is about 1.5 eV for O and 1.0 eV for Al in single crystal α-Al2O3. The much higher mobility of O ions makes the O ions responsible for the conductivity of the single crystal oxide. It seems that the grain boundary leads to an increase in the activation energy. However, the quantitative influence of grain boundary still needs to be explained. Between 400 and 650&DEG; C, the measured activation energy is about 1.0 eV and independent of the grain size.
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| 14. |
- Sagalowicz, Laurent, et al.
(författare)
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Structure of the wafer fused InP (001)-GaAs (001) interface
- 1997
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 76:6, s. 445-452
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Tidskriftsartikel (refereegranskat)abstract
- A structural study of wafer fused InP-GaAs interfaces has been carried out. The geometry of the dislocation network which accommodates the twist and the lattice mismatch is first given using a geometrical approach. Cross-sectional transmission electron microscopy and plan view observations are presented. Two different misfit cases are observed. (1) When no twist is present, the 3.7% lattice mismatch is relaxed by a regular square network of dislocations with pure edge character. (2) When an additional twist is present, a square network of dislocations results as well but here the dislocations have a mixed character; 60° dislocations are also observed, some form closed defect circuits and others very likely accommodate a small tilt. The interaction between the 60° dislocations and the edge dislocations is explained in detail. Voids or inclusions are also observed as well as additional dislocations which may accommodate part of the thermal mismatch. © 1997 Taylor & Francis Ltd.
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| 15. |
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| 16. |
- Stokes, J. Dustan, et al.
(författare)
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The virial theorem in graphene and other Dirac materials
- 2013
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 93:12, s. 672-679
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Tidskriftsartikel (refereegranskat)abstract
- The virial theorem is applied to graphene and other Dirac Materials for systems close to the Dirac points where the dispersion relation is linear. From this, we find the exact form for the total energy given by E = B/r(s) where r(s)a(0) is the mean radius of the d-dimensional sphere containing one particle, with a(0) the Bohr radius, and B is a constant independent of r(s). This result implies that, given a linear dispersion and a Coulombic interaction, there is no Wigner crystallization and that calculating B or measuring at any value of rs determines the energy and compressibility for all r(s). In addition to the total energy, we calculate the exact forms of the chemical potential, pressure and inverse compressibility in arbitrary dimension.
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| 17. |
- Thuvander, Mattias, 1968, et al.
(författare)
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Observations of copper clustering in a 25Cr-7Ni super duplex stainless steel during low-temperature aging under load
- 2012
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Ingår i: Philosophical Magazine Letters. - : Informa UK Limited. - 0950-0839 .- 1362-3036. ; 92:7, s. 336-343
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Tidskriftsartikel (refereegranskat)abstract
- Atom-probe tomography was used to investigate phase separation and copper (Cu) clustering in the ferrite phase of a 25Cr-7Ni super duplex stainless steel. The steel was subjected to a tensile load during aging at 325 degrees C for 5800 h. The degree of phase separation into alpha (Fe-rich) and alpha' (Cr-rich) was small, but still, it was the highest in the steel subjected to the highest load. Cu was found to cluster, and the number density of clusters increased with increasing load. In the material subjected to the highest load, Cu was enriched in regions that were neither Fe-rich nor Cr-rich. These regions also had the highest number density of Cu clusters.
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| 18. |
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| 19. |
- Wang, YD, et al.
(författare)
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A novel method for constructing the mean field of grain-orientation-dependent residual stress
- 2001
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Ingår i: PHILOSOPHICAL MAGAZINE LETTERS. - : TAYLOR & FRANCIS LTD. - 0950-0839. ; 81:3, s. 153-163
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Tidskriftsartikel (refereegranskat)abstract
- The heterogeneity of grain-orientation-dependent residual stress (ODRS) in polycrystalline materials has received a great deal of attention in the past few years. This letter describes a novel method, called the spherical harmonics approach (SHA), for ana
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