| 1. |
- Dahlqvist, Martin, et al.
(författare)
-
Complex magnetism in nanolaminated Mn2GaC
- 2014
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We have used first-principles calculations and Heisenberg Monte Carlo simulations to search for the magnetic ground state of Mn2GaC, a recently synthesized magnetic nanolaminate. We have, independent on method, identified a range of low energy collinear as well as non-collinear magnetic configurations, indicating a highly frustrated magnetic material with several nearly degenerate magnetic states. An experimentally obtained magnetization of only 0.29 per Mn atom in Mn2GaC may be explained by canted spins in an antiferromagnetic configuration of ferromagnetically ordered sub-layers with alternating spin orientation, denoted AFM[0001]. Furthermore, low temperature X-ray diffraction show a new basal plane peak appearing upon a magnetic transition, which is consistent with the here predicted change in inter-layer spacing for the AFM[0001] configuration.
|
|
| 2. |
- Chen, Yen-Ting, et al.
(författare)
-
Nucleation of single GaN nanorods with diameters smaller than 35 nm by molecular beam epitaxy
- 2013
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 103:20, s. 203108-
-
Tidskriftsartikel (refereegranskat)abstract
- Nucleation mechanism of catalyst-free GaN nanorod grown on Si(111) is investigated by the fabrication of uniform and narrow (andlt; 35 nm) nanorods without a pre-defined mask by molecular beam epitaxy. Direct evidences show that the nucleation of GaN nanorods stems from the sidewall of the underlying islands down to the Si(111) substrate, different from commonly reported ones on top of the island directly. Accordingly, the growth and density control of the nanorods is exploited by a "narrow-pass" approach that only narrow nanorod can be grown. The optimal size of surrounding non-nucleation area around single nanorod is estimated as 88 nm.
|
|
| 3. |
- Ingason, Arni Sigurdur, et al.
(författare)
-
Magnetic Self-Organized Atomic Laminate from First Principles and Thin Film Synthesis
- 2013
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 110
-
Tidskriftsartikel (refereegranskat)abstract
- he first experimental realization of a magnetic Mn+1AXn (MAX) phase, (Cr0.75Mn0.25)2GeC, is presented, synthesized as a heteroepitaxial single crystal thin film, exhibiting excellent structural quality. This self-organized atomic laminate is based on the well-known Cr2GeC, with Mn, a new element in MAX phase research, substituting Cr. The compound was predicted using first-principles calculations, from which a variety of magnetic behavior is envisaged, depending on the Mn concentration and Cr/Mn atomic configuration within the sublattice. The analyzed thin films display a magnetic signal at room temperature.
|
|
| 4. |
- Nedfors, Nils, et al.
(författare)
-
Superhard NbB2-x thin films deposited by dc magnetron sputtering
- 2014
-
Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 257, s. 295-300
-
Tidskriftsartikel (refereegranskat)abstract
- We have deposited weakly textured substoichiometric NbB2-x thin films by magnetron sputtering from a NbB2 target. The films exhibit superhardness (42 ± 4 GPa), previously only observed in overstoichiometric TiB2 thin films, and explained by a self-organized nanostructuring, where thin TiB2 columnar grains hinder nucleation and slip of dislocations and a B-rich tissue phase between the grains prevent grain-boundary sliding. The wide homogeneity range for the NbB2 phase allows a similar ultra-thin B-rich tissue phase to form between thin (5 – 10 nm) columnar NbB2-x grains also for films with a B/Nb atomic ratio of 1.8, as revealed here by analytical aberration-corrected scanning transmission electron microscopy. Furthermore, a coefficient of friction of 0.16 is measured for a NbB2-x film sliding against stainless steel with a wear rate of 4x10-7 mm3/Nm. X-ray photoelectron spectroscopy results suggest that the low friction is due to the formation of a lubricating boric acid film.
|
|
| 5. |
- Fallqvist, Amie, et al.
(författare)
-
Self-organization during Growth of ZrN/SiNx Multilayers by Epitaxial Lateral Overgrowth
- 2013
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 114:224302
-
Tidskriftsartikel (refereegranskat)abstract
- ZrN/SiNx nanoscale multilayers were deposited on ZrN seed layers grown on top of MgO(001) substrates by dc magnetron sputtering with a constant ZrN thickness of 40 Å and with an intended SiNx thickness of 2, 4, 6, 8, and 15 Å at a substrate temperature of 800 °C and 6 Å at 500 °C. The films were investigated by X-ray diffraction, high-resolution scanning transmission electron microscopy, and energy dispersive X-ray spectroscopy. The investigations show that the SiNx is amorphous and that the ZrN layers are crystalline. Growth of epitaxial cubic SiNx – known to take place on TiN(001) – on ZrN(001) is excluded to the monolayer resolution of this study. During the course of SiNx deposition, the material segregates to form surface precipitates in discontinuous layers for SiNx thicknesses ≤ 6 Å that coalesce into continuous layers for 8 and 15 Å thickness at 800 °C, and for 6 Å at 500 °C. The SiNx precipitates are aligned vertically. The ZrN layers in turn grow by epitaxial lateral overgrowth on the discontinuous SiNx in samples deposited at 800 °C with up to 6 Å thick SiNx layers. Effectively a self-organized nanostructure can be grown consisting of strings of 1-3 nm large SiNx precipitates along apparent column boundaries in the epitaxial ZrN.
|
|
| 6. |
- Gunnarsson Sarius, Niklas, 1976-, et al.
(författare)
-
Influence of ultrasound and cathode rotation on the formation of intrinsic stress in Ni films during electrodeposition
- 2011
-
Ingår i: Transactions of the Institute of Metal Finishing. - : Institute of Metal Finishing. - 0020-2967 .- 1745-9192. ; 89:3, s. 137-142
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of 25 kHz ultrasound and cathode rotation during electroplating of Ni films on Si wafers has been studied with respect to intrinsic stress formation. Current densities from 1.6 A dm-2 up to 28.3 A dm-2 were used in an additive-free Ni sulphamate electrolyte. In general more efficient agitation by either ultrasound or cathode rotation was found to reduce intrinsic stress towards compressive levels compared to conventional agitation with an electrolyte circulation pump. Further more, intrinsic stresses become less dependent on changes in current density. The latter effect is most pronounced for ultrasonic agitation. Structure analysis of samples deposited by ultrasonic agitation show dense deposits with initially smaller grains at high ultrasonic effect. Locally increased temperature at the substrates surface could be an important effect of ultrasound agitation.
|
|
| 7. |
- Hsiao, Ching-Lien, et al.
(författare)
-
Room-temperature heteroepitaxy of single-phase Al1-xInxN films with full composition range on isostructural wurtzite templates
- 2012
-
Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 524, s. 113-120
-
Tidskriftsartikel (refereegranskat)abstract
- Al1-xInxN heteroepitaxial layers covering the full composition range have been realized by magnetron sputter epitaxy on basal-plane AlN, GaN, and ZnO templates at room temperature (RT). Both Al1-xInxN single layers and multilayers grown on these isostructural templates show single phase, single crystal wurtzite structure. Even at large lattice mismatch between the film and the template, for instance InN/AlN (similar to 13% mismatch), heteroepitaxy is achieved. However, RT-grown Al1-xInxN films directly deposited on non-isostructural c-plane sapphire substrate exhibit a polycrystalline structure for all compositions, suggesting that substrate surface structure is important for guiding the initial nucleation. Degradation of Al1-xInxN structural quality with increasing indium content is attributed to the formation of more point-and structural defects. The defects result in a prominent hydrostatic tensile stress component, in addition to the biaxial stress component introduced by lattice mismatch, in all RT-grown Al1-xInxN films. These effects are reflected in the measured in-plane and out-of-plane strains. The effect of hydrostatic stress is negligible compared to the effects of lattice mismatch in high-temperature grown AlN layers thanks to their low amount of defects. We found that Vegards rule is applicable to determine x in the RT-grown Al1-xInxN epilayers if the lattice constants of RT-sputtered AlN and InN films are used instead of those of the strain-free bulk materials.
|
|
| 8. |
- Jouanny, I, et al.
(författare)
-
In situ transmission electron microscopy studies of the kinetics of Pt-Mo alloy diffusion in ZrB2 thin films
- 2013
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 103:12
-
Tidskriftsartikel (refereegranskat)abstract
- Using in situ high-temperature (1073–1173 K) transmission electron microscopy, we investigated the thermal stability of Pt and Mo in contact with polycrystalline ZrB2 thin films deposited on Al 2O3(0001). During annealing, we observed the diffusion of cubic-structured Pt1− x Mo x (with x = 0.2 ± 0.1) along the length of the ZrB2 layer. From the time-dependent increase in diffusion lengths, we determined that the Pt1− x Mo x does not react with ZrB2, but diffuses along the surface with a constant temperature-dependent velocity. We identify the rate-limiting step controlling the observed phenomenon as the flux of Mo atoms with an associated activation barrier of 3.8 ± 0.5 eV.
|
|
| 9. |
- Keast, V J., et al.
(författare)
-
AuAl2 and PtAl2 as potential plasmonic materials
- 2013
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 577, s. 581-586
-
Tidskriftsartikel (refereegranskat)abstract
- The dielectric functions of PtAl2, AuAl2 and hypothetical intermediate alloys of the two in the form of AuxPt1-xAl2 were calculated from first principles using density functional theory (DFT) and the random phase approximation (RPA). From these, the reflectivity, electron energy-loss spectra (EELS) and small sphere extinction spectra are predicted. The experimental reflectivity and EELS were measured for PtAl2 and showed good agreement with the theoretical spectra. The yellow color of PtAl2 is associated with a bulk plasmon at 3 eV. We predict that the optical properties of hypothetical intermediate alloys would show a smooth evolution with composition. The details of this change can be understood by examination of the underlying density of states (DOS). The predicted small sphere extinction spectra and quality factors show a strong surface plasmon resonance for these materials, with PtAl2 having the optimum performance. The results indicate that these materials are good candidates for applications in plasmonics.
|
|
| 10. |
- Kodambaka, S, et al.
(författare)
-
Kinetics of Ga droplet decay on thin carbon films
- 2013
-
Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 102:16
-
Tidskriftsartikel (refereegranskat)abstract
- Using in situ transmission electron microscopy, we investigated the kinetics of liquid Ga droplet decay on thin amorphous carbon films during annealing at 773 K. The transmission electron microscopy images reveal that liquid Ga forms spherical droplets and undergo coarsening/decay with increasing time. We find that the droplet volumes change non-linearly with time and the volume decay rates depend on their local environment. By comparing the late-stage decay behavior of the droplets with the classical mean-field theory model for Ostwald ripening, we determine that the decay of Ga droplets occurs in the surface diffusion limited regime.
|
|
