| 1. |
- Beckers, Manfred, et al.
(författare)
-
The influence of substrate temperature and Al mobility on the microstructural evolution of magnetron sputtered ternary Ti-Al-N thin films
- 2009
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 106:6, s. 064915-
-
Tidskriftsartikel (refereegranskat)abstract
- Ternary Ti-Al-N films were deposited onto Al2O3 (0001) substrates by reactive co‑sputtering from elemental Ti and Al targets and analyzed by in situ and ex situ x-ray scattering, Rutherford backscattering spectroscopy, transmission electron microscopy and x-ray photoemission spectroscopy. The deposition parameters were set to values that yield Ti:Al:N ratios of 2:1:1 and 4:1:3 at room temperature. 2TiAlN depositions at 675 °C result in epitaxial Ti2AlN growth with basal planes parallel to the substrate surface. Nominal 4TiAl3N depositions at 675 °C and above, however, yield TiN and Ti2AlN domains due to Al loss to the vacuum. Depositions at a lower temperature of 600 °C yield films with correct 4:1:3 stoichiometry, but Ti4AlN3 formation is supposedly prevented by insufficient adatom mobility. Instead, an incoherent Tin+1AlNn structure with random twinned stacking sequences n is obtained, that exhibits both basal plane orientations parallel as well as nearly perpendicular to the substrate interface. X‑ray photoemission spectroscopy shows that in contrast to stoichiometric nitrides the Al is metallically bonded and hence acts as twinning plane within the Tin+1AlNn stackings. Domains with perpendicular basal plane orientation overgrowth those with parallel ones in a competitive growth mode. The resulting morphology is a combination of smooth‑surfaced parallel basal plane orientation domains interrupted by repeated facetted hillock-like features with perpendicular basal plane orientation.
|
|
| 2. |
- Höglund, Carina, et al.
(författare)
-
Cubic Sc1-xAlxN solid solution thin films deposited by reactive magnetron sputter epitaxy onto ScN(111)
- 2009
-
Ingår i: JOURNAL OF APPLIED PHYSICS. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 105:11, s. 132862-
-
Tidskriftsartikel (refereegranskat)abstract
- Reactive magnetron sputter epitaxy was used to deposit thin solid films of Sc1-xAlxN (0 andlt;= x andlt;= 1) onto MgO(111) substrates with ScN(111) seed layers. Stoichiometric films were deposited from elemental Sc and Al targets at substrate temperatures of 600 S C. The films were analyzed by Rutherford backscattering spectroscopy, elastic recoil detection analysis, x-ray diffraction, and transmission electron microscopy. Results show that rocksalt structure (c)-Sc1-xAlxN solid solutions with AlN molar fractions up to similar to 60% can be synthesized. For higher AlN contents, the system phase separates into c- and wurtzite structure (w)-Sc1-xAlxN domains. The w-domains are present in three different orientations relative to the seed layer, namely, Sc1-xAlxN(0001)parallel to ScN(111) with Sc1-xAlxN[(1) over bar2 (1) over bar0]parallel to ScN[1 (1) over bar0], Sc1-xAlxN(10 (1) over bar1)parallel to ScN(111) with Sc1-xAlxN[(1) over bar2 (1) over bar0]parallel to ScN[1 (1) over bar0], and Sc1-xAlxN(10 (1) over bar1)parallel to ScN(113). The results are compared to first-principles density functional theory calculations for the mixing enthalpies of c-, w-, and zinc blende Sc0.50Al0.50N solid solutions, yielding metastability with respect to phase separation for all temperatures below the melting points of AlN and ScN.
|
|
| 3. |
- Höglund, Carina, 1981-
(författare)
-
Reactive Magnetron Sputter Deposition and Characterization of Thin Films from the Ti-Al-N and Sc-Al-N Systems
- 2009
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Thesis treats the growth and characterization of ternary transition metal nitride thin films. The aim is to probe deeper into the Ti-Al-N system and to explore the novel Sc-Al-N system. Thin films were epitaxially grown by reactive magnetron sputtering from elemental targets onto single-crystal substrates covered with a seed layer. Elastic recoil detection analysis and Rutherford backscattering spectroscopy were used for compositional analysis and depth profiling. Different x-ray diffraction techniques were employed, ex situ using Cu radiation and in situ during deposition using synchrotron radiation, to identify phases, to obtain information about texture, and to determine the thickness and roughness evolution of layers during and after growth. Transmission electron microscopy was used for overview and lattice imaging, and to obtain lattice structure information by electron diffraction. Film properties were determined using van der Pauw measurements of the electrical resistivity, and nanoindentation for the materials hardness and elastic modulus. The epitaxial Mn+1AXn phase Ti2AlN was synthesized by solid-state reaction during interdiffusion between sequentially deposited layers of (0001)-oriented AlN and Ti thin films. When annealing the sample, N and Al diffused into the Ti, forming Ti3AlN at 400 ºC and Ti2AlN at 500 ºC. The Ti2AlN formation temperature is 175 ºC lower than earlier reported results. Ti4AlN3 thin films were, however, not possible to synthesize when depositing films with a Ti:Al:N ratios of 4:1:3. Substrate temperatures at 600 ºC yielded an irregularly stacked Tin+1AlNn layered structure because of the low mobility of Al adatoms. An increased temperature led, however, to an Al deficiency due to an out diffusion of Al atoms, and formation of Ti2AlN phase and Ti1-xAlxN cubic solid solution. In the Sc-Al-N system the first ternary phase was discovered, namely the perovskite Sc3AlN, with a unit cell of 4.40 Å. Its existence was supported by ab initio calculations of the enthalpy showing that Sc3AlN is thermodynamically stable with respect to the binaries. Sc3AlN thin films were experimentally found to have a hardness of 14.2 GPa, an elastic modulus of 21 GPa, and a room temperature resistivity of 41.2 μΩcm.
|
|
| 4. |
- Höglund, Carina, 1981-, et al.
(författare)
-
Sc3AlN : A New Perovskite
- 2008
-
Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1434-1948 .- 1099-1948 .- 1099-0682. ; 2008:8, s. 1193-1195
-
Tidskriftsartikel (refereegranskat)abstract
- Sc3AlN with perovskite structure has been synthesized as the first ternary phase in the Sc–Al–N system. Magnetron sputter epitaxy at 650 °C was used to grow single-crystal, stoichiometric Sc3AlN(111) thin films onto MgO(111) substrates with ScN(111) seed layers as shown by elastic recoil detection analysis, X-ray diffraction, and transmission electron microscopy. The Sc3AlN phase has a lattice parameter of 4.40 Å, which is in good agreement with the theoretically predicted 4.42 Å. Comparisons of total formation energies show that Sc3AlN is thermodynamically stable with respect to all known binary compounds. Sc3AlN(111) films of 1.75 μm thickness exhibit a nanoindentation hardness of 14.2 GPa, an elastic modulus of 249 GPa, and a roomtemperature electrical resistivity of 41.2 μΩ cm.
|
|
| 5. |
- Höglund, Carina, 1981-, et al.
(författare)
-
Topotaxial growth of Ti2AlN by solid state reaction in AlN/Ti(0001) multilayer thin films
- 2007
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:174106
-
Tidskriftsartikel (refereegranskat)abstract
- The formation of Ti2AlN by solid state reaction between layers of wurtzite-AlN and α-Ti was characterized by in situ x-ray scattering. The sequential deposition of these layers by dual magnetron sputtering onto Al2O3(0001) at 200 °C yielded smooth, heteroepitaxial (0001) oriented films, with abrupt AlN/Ti interfaces as shown by x-ray reflectivity and Rutherford backscattering spectroscopy. Annealing at 400 °C led to AlN decomposition and diffusion of released Al and N into the Ti layers, with formation of Ti3AlN. Further annealing at 500 °C resulted in a phase transformation into Ti2AlN(0001) after only 5 min.
|
|
| 6. |
- Höglund, Erika, et al.
(författare)
-
Growth Hormone Increases Beta-Cell Proliferation in Transplanted Human and Fetal Rat Islets
- 2009
-
Ingår i: Journal of the Pancreas. - 1590-8577. ; 10:3, s. 242-248
-
Tidskriftsartikel (refereegranskat)abstract
- Objective The aim of the study was to increase the number of human islet beta-cells after transplantation with injections of human growth hormone (hGH). Interventions Human islets and fetal rat islets were transplanted under the left kidney capsule and under the right kidney capsule, respectively in nude normoglycemic mice which were then given a daily injection of 200 µg hGH for 1-4 weeks. Main outcome measure Beta-cell proliferation was determined using thymidine incorporation and the beta-cell area was assessed using light microscopy. Results Mice given hGH increased their body weight one week after transplantation and had a more efficient removal of glucose after 3 and 4 weeks. Treatment with hGH resulted in increased beta-cell proliferation in human and fetal rat beta-cells, and the beta-cell area tended to increase. However, serum insulin concentrations and pancreas insulin content remained unchanged. Conclusions hGH increased the proliferation of transplanted human beta-cells as well as improving the glucose tolerance of the transplanted mice.
|
|
| 7. |
- Magnuson, Martin, et al.
(författare)
-
Bonding mechanism in the nitrides Ti2AlN and TiN: An experimental and theoretical investigation
- 2007
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 76:195127
-
Tidskriftsartikel (refereegranskat)abstract
- Theelectronic structure of nanolaminate Ti2AlN and TiN thin films hasbeen investigated by bulk-sensitive soft x-ray emission spectroscopy. The measuredTi L2,3, N K, Al L1, and Al L2,3 emissionspectra are compared with calculated spectra using ab initio density-functionaltheory including dipole transition-matrix elements. Three different types of bondregions are identified; a relatively weak Ti 3d-Al 3p bonding between −1and −2 eV below the Fermi level, and Ti 3d-N 2p and Ti 3d-N 2sbondings which are deeper in energy observed at −4.8 eV and−15 eV below the Fermi level, respectively. A strongly modified spectralshape of 3s states of Al L2,3 emission from Ti2AlNin comparison with pure Al metal is found, which reflectsthe Ti 3d-Al 3p hybridization observed in the Al L1 emission. Thedifferences between the electronic and crystal structures of Ti2AlN andTiN are discussed in relation to the intercalated Al layersof the former compound and the change of the materialsproperties in comparison with the isostructural carbides.
|
|
| 8. |
- Magnuson, Martin, et al.
(författare)
-
Electronic structure and chemical bonding anisotropy investigation of wurtzite AlN
- 2009
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 80, s. 155105-
-
Tidskriftsartikel (refereegranskat)abstract
- The electronic structure and the anisotropy of the Al - N p and s chemical bonding of wurtzite AlN has been investigated by bulk-sensitive total fluorescence yield absorption and soft x-ray emission spectroscopies. The measured N K, Al L1, and Al L2,3 x-ray emission and N 1s x-ray absorption spectra are compared with calculated spectra using first principles density-functional theory including dipole transition matrix elements. The main N 2p - Al 3p hybridization regions are identified at -1.0 to -1.8 eV and -5.0 to -5.5 eV below the top of the valence band. In addition, N 2s - Al 3p and N 2s - Al 3s hybridization regions are found at the bottom of the valence band around -13.5 eV and -15 eV, respectively. A strongly modified spectral shape of Al 3s states in the Al L2,3 emission from AlN in comparison to Al metal is found, which is also reflected in the N 2p - Al 3p hybridization observed in the Al L1 emission. The differences between the electronic structure and chemical bonding of AlN and Al metal are discussed in relation to the position of the hybridization regions and the valence band edge influencing the magnitude of the large band gap.
|
|
| 9. |
- Magnuson, Martin, et al.
(författare)
-
Electronic structure investigation of the cubic inverse perovskite Sc3AlN
- 2008
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:23, s. 235102-
-
Tidskriftsartikel (refereegranskat)abstract
- The electronic structure and chemical bonding of the recently discovered inverse perovskite Sc3AlN, in comparison to those of ScN and Sc metal, have been investigated by bulk-sensitive soft-x-ray emission spectroscopy. The measured Sc L, N K, Al L-1, and Al L-2,L-3 emission spectra are compared with calculated spectra using first-principles density-functional theory including dipole transition-matrix elements. The main Sc 3d-N 2p and Sc 3d-Al 3p chemical bond regions are identified at -4 and -1.4 eV below the Fermi level, respectively. A strongly modified spectral shape of 3s states in the Al L-2,L-3 emission from Sc3AlN in comparison to that for pure Al metal is found, which reflects the Sc 3d-Al 3p hybridization observed in the Al L-1 emission. The differences between the electronic structures of Sc3AlN, ScN, and Sc metal are discussed in relation to the change in the conductivity and elastic properties.
|
|
| 10. |
- Mattesini, Maurizio, et al.
(författare)
-
Elastic properties and electrostructural correlations in ternary scandium-based cubic inverse perovskites : A first-principles study
- 2009
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79, s. 125122-
-
Tidskriftsartikel (refereegranskat)abstract
- Wehave performed ab initio calculations for the cubic inverse-perovskite Sc3EN(E=Al,Ga,In) systems to study their electronic band-structures and elastic properties.In this study, we used the accurate augmented plane waveplus local orbital method to find the equilibrium structural parametersand to compute the full elastic tensors. The obtained single-crystalelastic constants were used to quantify the stiffness of theSc-based ternary nitrides and to appraise their mechanical stability. Thesite-projected density of states, Fermi surfaces, and the charge-density plotshave also been used to analyze the chemical bonding betweenthe Sc6N cluster and the surrounding metallic lattice of eitherAl, Ga, or In atoms. Our calculations show that Sc3GaNhas the largest covalent Sc-N bonding-type character with the highestYoung, shear, and bulk moduli. Compared with the other twoisoelectronic systems, it also behaves as the most brittle materialwith a relatively large elastic anisotropy.
|
|
