Hans Högberg

Growth of Ti3SiC2 thin films by elemental target magnetron sputtering

Epitaxial Ti3SiC2(0001) thin films have been deposited by dc magnetron sputtering from three elemental targets of Ti, C, and Si onto MgO(111) and Al2O3(0001) substrates at temperatures of 800–900°C. This process allows composition control to synthesize Mn+1AXn (MAX) phases (M: early transition metal; A: A-group element; X: C and∕or N; n=1–3) including Ti4SiC3. Depositions on MgO(100) substrates yielding the Ti–Si–C MAX phases with (101¯5), as the preferred orientation. Samples grown at different substrate temperatures, studied by means of transmission electron microscopy and x-ray diffraction investigations, revealed the constraints of Ti3SiC2 nucleation due to kinetic limitations at substrate temperatures below 700°C. Instead, there is a competitive TiCx growth with Si segregation to form twin boundaries or Si substitutional incorporation in TiCx. Physical properties of the as-deposited single-crystal Ti3SiC2 films were determined. A low resistivity of 25μΩcm was measured. The Young’s modulus, ascertaine...

Epitaxial Ti2GeC, Ti3GeC2, and Ti4GeC3 MAX-phase thin films grown by magnetron sputtering

We have grown single-crystal thin films of Ti2GeC and Ti3GeC2 and a new phase Ti4GeC3, as well as two new intergrown MAX-structures, Ti5Ge2C3 and Ti7Ge2C5. Epitaxial films were grown on Al2O3(0001) ...

Plasma oxytocin levels in women during labor with or without epidural analgesia: a prospective study

Background.  Epidural analgesia (EDA) has been reported to prolong labor. Whether this is by interference with endogenous oxytocin release or other mechanisms is unclear. With increasing numbers of women receiving an EDA, it is important to study its effects on labor. The aim was to study the concentration of plasma oxytocin and the progress of labor in women with and without EDA.

Theory of the effects of substitutions on the phase stabilities of Ti1−xAlxN

We have performed ab initio studies of the effect of substitutions on the phase stabilities of Ti1−xAlxN, x=0−1. The nonmetal substitutions studied include B, C, O, and Si. Metal substitutions studied include Sc, Zr, V, Cr, and Mn. The main objective has been to suggest substitutions that increase the thermal stability of the NaCl structure of Ti1−xAlxN at high Al contents. From these extensive and consistent calculations, some possible avenues for such stabilization present themselves, among which substitution with nonmetal C and Si, and metal V, Cr, and Mn are found to be the most promising.We have performed ab initio studies of the effect of substitutions on the phase stabilities of Ti1−xAlxN, x=0−1. The nonmetal substitutions studied include B, C, O, and Si. Metal substitutions studied include Sc, Zr, V, Cr, and Mn. The main objective has been to suggest substitutions that increase the thermal stability of the NaCl structure of Ti1−xAlxN at high Al contents. From these extensive and consistent calculations, some possible avenues for such stabilization present themselves, among which substitution with nonmetal C and Si, and metal V, Cr, and Mn are found to be the most promising.

Structural, electrical, and mechanical properties of nc-TiC∕a-SiC nanocomposite thin films

We have synthesized Ti–Si–C nanocomposite thin films by dc magnetron sputtering from a Ti3SiC2 compound target in an Ar discharge on Si(100), Al2O3(0001), and Al substrates at temperatures from roo ...

Tribofilm formation on cemented carbides in dry sliding conformal contact

Abstract The friction properties and the tribofilm formation of a binderless cemented carbide and two conventional cemented carbides have been evaluated in an unlubricated sliding contact in either air or nitrogen surroundings. A continuously varied normal load and two rotational speeds were used. The tribofilms were analysed with SEM, XPS, TEM and EELS. For all cemented carbides, friction was lower at higher sliding speed. The two conventional carbides also tended to give a lower friction in air than in nitrogen, whereas the binderless carbide gave about the same friction in both environments. All materials formed tribofilms during the tests. Mild tests with the conventional cemented carbides resulted in relatively thick tribofilms (a couple of μm) with low amounts of oxides. At more severe test conditions the tribofilms became thinner (

Participation in everyday occupations in a late phase of recovery after brain injury

The aim of this study was to describe to what extent individuals of working age, in a late phase after an acquired brain injury, participate in everyday occupations related to home maintenance, work, and leisure. The aim was also to evaluate if participation in different occupations influences their life satisfaction. A sample of 157 people consecutively admitted to a rehabilitation clinic between June 1995 and December 2000 answered a mailed questionnaire. The subjects who were of working age had had a brain injury on average 6 years before this study. The perceived participation was reported using the Reintegration to Normal Living Index (RNL) and life satisfaction according to an expanded version of the LiSat 11. This study showed that in this late phase of recovery after brain injury the subjects still experienced many restrictions in participation in everyday occupations. The area with the lowest reported participation was work activity while most comfort with the situation was reported for self-care. The RNL subscales showed a significant connection with satisfaction with life as a whole. Furthermore an interaction was found between the two subscales “Daily living” and “Perception of self”. This study showed restrictions in participation in the community even several years after brain injury, which underlines the need for rehabilitation services long after injury.

Magnetron sputtering of Ti3SiC2 thin films from a compound target

In this Thesis, I have investigated multifunctional nanostructured Ti-Si-C thin films synthesized by magnetron sputtering in the substrate-temperature range from room temperature to 900 °C. The studies cover high-temperature growth of Ti3SiC2 and Ti4SiC3, low-temperature growth of Ti-Si-C nanocomposites, and Ti-Si-C-based multi¬layers, as well as their electrical, mechanical, and thermal-stability properties. Ti3SiC2 and Ti4SiC3 were synthesized homoepitaxially onto bulk Ti3SiC2 from individual sputtering targets and heteroepitaxially onto Al2O3(0001) substrates from a Ti3SiC2 target at substrate temperatures of 700 – 900 °C. In the latter case, the film composition exhibits excess C compared to the nominal target composition due to differences between species in angular and energy distribution and gas-phase scattering processes. Ti buffering is shown to compensate for this excess C. The electrical-resistivity values of Ti3SiC2 and Ti4SiC3 thin films were measured to 21-32 uOhmcm and ~50 uOhmcm, respectively. The good conductivity is because the presence of Si layers enhances the relative strength of the metallic Ti-Ti bonds. The higher density of Si layers in Ti3SiC2 than in Ti4SiC3 explains why Ti3SiC2 is the better conductor of the two. Ti3SiC2 thin films are shown to be thermally stable up to 1000 – 1100 °C. Annealing at higher temperature results in decomposition of Ti3SiC2 by Si out-diffusion to the surface with subsequent evaporation. Above 1200 °C, TiCx layers recrystallized. Nanocomposites comprising nanocrystalline (nc-)TiC in an amorphous (a-)SiC matrix phase were deposited at substrate temperatures in the range 100 – 300 °C. These nc-TiC/a-SiC films exhibit low contact resistance in electrical contacts and a ductile deformation behavior due to rotation and gliding of nc-TiC grains in the matrix. The ductile mechanical properties of nc-TiC/a-SiC are actually more similar to those of Ti3SiC2, which is very ductile due to kinking and delamination, than to those of the brittle TiC. Epitaxial TiC/SiC multilayers deposited at ~550 °C were shown to contain cubic SiC layers up to a thickness of ~2 nm. Thicker SiC layers gives a-SiC due to the corresponding increase in interfacial strain energy leading to loss of coherent-layer growth. Nanoindentation of epitaxial Ti3SiC2/TiC0.67 nanolaminates showed inhibition of kink-band formation in Ti3SiC2, as the lamination with the less ductile TiC effectively hindered this mechanism.

Low resistivity ohmic titanium carbide contacts to n- and p-type 4H-silicon carbide

Abstract Low resistivity Ohmic contacts of epitaxial titanium carbide to highly doped n- ( 1.3×10 19 cm −3 ) and p-(> 10 20 cm −3 ) type epilayer on 4H-SiC were investigated. The titanium carbide contacts were epitaxially grown using co-evaporation with an e-beam for Ti and a Knudsen cell for C60 in a UHV system. A comparison of epitaxial evaporated Ti Ohmic contacts on p+ epilayer of 4H-SiC is also given. The as-deposited TiC Ohmic contacts showed a good Ohmic behavior and the lowest contact resistivity (ρC) was 7.4×10 −7 Ω cm 2 at 200°C for n-type, and 1.1×10 −4 Ω cm 2 at 25°C for p-type contacts. Annealing at 950°C did not improve the Ohmic contact to n-type 4H-SiC, but instead resulted in an increase in ρC to 4.01×10 −5 Ω cm 2 at 25°C. In contrast to n-type, after annealing at 950°C the specific ρC for p-type SiC reached its lowest value of 1.9×10 −5 Ω cm 2 at 300°C. Our results indicate that co-evaporated TiC contacts to n- and p-type epilayers of 4H-SiC should not require a higher post-annealing temperature, contrary to earlier works. Material characteristics, utilizing X-ray diffraction, Low energy electron diffraction, Rutherford backscattering spectrometry, transmission electron microscopy, and X-ray photoelectron spectroscopy measurements are also discussed.

Electronic structure investigation ofTi3AlC2,Ti3SiC2, andTi3GeC2by soft x-ray emission spectroscopy

The electronic structures of epitaxially grown films of Ti3AlC2 , Ti3SiC2 , and Ti3GeC2 have been investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured high-resolution Ti L ...