| 1. |
- Adamovic, Dragan, 1973-, et al.
(författare)
-
Kinetic pathways leading to layer-by-layer growth from hyperthermal atoms : A Multibillion time step molecular dynamics study
- 2007
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 76, s. 115418-115425
-
Tidskriftsartikel (refereegranskat)abstract
- We employ multibillion time step embedded-atom molecular dynamics simulations to investigate the homoepitaxial growth of Pt(111) from hyperthermal Pt atoms (EPt=0.2–50eV) using deposition fluxes approaching experimental conditions. Calculated antiphase diffraction intensity oscillations, based on adatom coverages as a function of time, reveal a transition from a three-dimensional multilayer growth mode with EPt<20eV to a layer-by-layer growth with EPt≥20eV. We isolate the effects of irradiation-induced processes and thermally activated mass transport during deposition in order to identify the mechanisms responsible for promoting layer-by-layer growth. Direct evidence is provided to show that the observed transition in growth modes is primarily due to irradiation-induced processes which occur during the 10ps following the arrival of each hyperthermal atom. The kinetic pathways leading to the transition involve both enhanced intralayer and interlayer adatom transport, direct incorporation of energetic atoms into clusters, and cluster disruption leading to increased terrace supersaturation.
|
|
| 2. |
- Alling, Björn, 1980-, et al.
(författare)
-
Mixing and decomposition thermodynamics of c-Ti1-xAlxN from first-principles calculations
- 2007
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:045123
-
Tidskriftsartikel (refereegranskat)abstract
- Wedescribe an efficient first-principles method that can be used tocalculate mixing enthalpies of transition metal nitrides with B1 structureand substitutional disorder at the metal sublattice. The technique isbased on the density functional theory. The independent sublattice modelis suggested for the treatment of disorder-induced local lattice relaxationeffects. It supplements the description of the substitutional disorder withinthe coherent potential approximation. We demonstrate the excellent accuracy ofthe method by comparison with calculations performed by means ofthe projector augumented wave method on supercells constructed as specialquasirandom structures. At the same time, the efficiency of thetechnique allows for total energy calculations on a very finemesh of concentrations which enables a reliable calculation of thesecond concentration derivative of the alloy total energy. This isa first step towards first-principles predictions of concentrations and temperatureintervals where the alloy decomposition proceeds via the spinodal mechanism.We thus calculate electronic structure, lattice parameter, and mixing enthalpiesof the quasibinary alloy c-Ti1−xAlxN. The lattice parameter follows Vegard'slaw at low fractions of AlN but deviates increasingly withincreasing Al content. We show that the asymmetry of themixing enthalpy and its second concentration derivative is associated withsubstantial variations of the electronic structure with alloy composition. Thephase diagram is constructed within the mean-field approximation.
|
|
| 3. |
- Berlind, Torun, 1965-
(författare)
-
Carbon Nitride : Characterization and Protein Interactions
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns synthesis and characterization of carbon-based materials and theinvestigation of the possible use, of a selection of these materials, in biomedicalapplications. Protein adsorption and blood plasma tests were used for this purposeutilizing a surface sensitive technique called spectroscopic ellipsometry.The materials were synthesized by physical vapor deposition and characterizedregarding microstructure, mechanical properties and optical properties. The ternaries BC-N and Si-C-N as well as carbon and carbon nitrides (CNx) of different microstructureshave been examined. In the B-C-N work, the intention was to investigate the possibilityto combine the two materials CNx and BN, interesting on their own regarding highhardness and extreme elasticity, to produce a material with even better properties.Theoretical calculations were performed to elucidate the different element substitutionsand defect arrangements in the basal planes promoting curvature in the fullerene-likemicrostructure. The Si-C-N ternary was investigated with the consideration of finding away to control the surface energy for certain applications. Amorphous carbon and threemicrostructures of CNx were analyzed by spectroscopic ellipsometry in the UV-VIS-NIRand IR spectral ranges in order to get further insight into the bonding structure of thematerial.In the second part of this work focus was held on studies of macromolecularinteractions on silicon, carbon and CNx film surfaces using ellipsometry. One purposewas to find relevance (or not) for these materials in biological environments. Materials for bone replacement used today, e.g. stainless steel, cobalt-chromium alloys andtitanium alloys suffer from corrosion in body fluids, generation of wear particles inarticulating systems, infections and blood coagulation and cellular damage leading toimpaired functionality and ultimately to implant failure. Artificial heart valves made ofpyrolytic carbon are used today, with friction and wear problems. Thus, there is still aneed to improve biomaterials. The aim of the fourth paper was to investigate theinteraction between carbon-based materials and proteins. Therefore, amorphous carbon(a-C), amorphous (a), graphitic (g) and fullerene-like (FL) CNx thin films were exposedto human serum albumin and blood plasma and the amount of protein was measured insitu using spectroscopic ellipsometry. Surface located and accessible proteins after blood plasma incubations were eventually identified through incubations in antibody solutions.Antibody exposures gave indications of surface response to blood coagulation,complement activation and clotting. The a-C and FL-CNx films might according to theresults have a future in soft tissue applications due to the low immuno-activity, whereasthe g-CNx film possibly might be a candidate for bone replacement applications."Layered" structures of fibrinogen, a fibrous but soft protein involved in manyprocesses in our body, were grown in situ and dynamically monitored by ellipsometry inorder to understand the adsorption process and molecule arrangement onto a siliconsurface.In the last paper of this thesis, the effects of ion concentration and proteinconcentration on the refractive index of water-based solutions used in in situ ellipsometrymeasurements were demonstrated and spectral refractive index data for water solutionswith different ionic strengths and protein concentrations have been provided.
|
|
| 4. |
- Brodin, N., et al.
(författare)
-
Coaching patients with early rheumatoid arthritis to healthy physical activity : A multicenter, randomized, controlled study
- 2008
-
Ingår i: Arthritis and Rheumatism. - Hoboken, NJ : Wiley. - 0004-3591 .- 1529-0131. ; 59:3, s. 325-331
-
Tidskriftsartikel (refereegranskat)abstract
- Objective. To investigate the effect of a 1-year coaching program for healthy physical activity on perceived health status, body function, and activity limitation in patients with early rheumatoid arthritis. Methods. A total of 228 patients (169 women, 59 men, mean age 55 years, mean time since diagnosis 21 months) were randomized to 2 groups after assessments with the EuroQol visual analog scale (VAS), Grippit, Timed-Stands Test, Escola Paulista de Medicina Range of Motion scale, walking in a figure-of-8, a visual analog scale for pain, the Health Assessment Questionnaire disability index, a self-reported physical activity questionnaire, and the Disease Activity Score in 28 joints. All patients were regularly seen by rheumatologists and underwent rehabilitation as prescribed. Those in the intervention group were further individually coached by a physical therapist to reach or maintain healthy physical activity (=30 minutes, moderately intensive activity, most days of the week). Results. The retention rates after 1 year were 82% in the intervention group and 85% in the control group. The percentages of individuals in the intervention and control groups fulfilling the requirements for healthy physical activity were similar before (47% versus 51%, P > 0.05) and after (54% versus 44%, P > 0.05) the intervention. Analyses of outcome variables indicated improvements in the intervention group over the control group in the EuroQol VAS (P = 0.025) and muscle strength (Timed-Stands Test, P = 0.000) (Grippit, P = 0.003), but not in any other variables assessed. Conclusion. A 1-year coaching program for healthy physical activity resulted in improved perceived health status and muscle strength, but the mechanisms remain unclear, as self-reported physical activity at healthy level did not change. © 2008, American College of Rheumatology.
|
|
| 5. |
- Broitman, E, et al.
(författare)
-
Water adsorption on fullerene-like carbon nitride overcoats
- 2008
-
Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 517:3, s. 1106-1110
-
Tidskriftsartikel (refereegranskat)abstract
- Humidity influences the tribological performance of the head-disk interface in magnetic data storage devices. In this work we compare the uptake of water of amorphous carbon nitride (a-CNx) films, widely used as protective overcoats in computer disk drive systems, with fullerene-like carbon nitride (FL-CNx) and amorphous carbon (a-C) films. Films with thickness in the range 10-300 run were deposited on quartz crystal substrates by reactive DC magnetron sputtering. A quartz crystal microbalance placed in a vacuum chamber was used to measure the water adsorption. Electron paramagnetic resonance (EPR) has been used to correlate water adsorption with film microstructure and surface defects (dangling bonds). Measurements indicate that the amount of adsorbed water is highest for the pure a-C films and that the FL-CNx films adsorbed less than a-CNx. EPR data correlate the lower water adsorption on FL-CNx films with a possible lack of dangling bonds on the film surface. To provide additional insight into the atomic structure of defects in the FL-CNx, a-CNx and a-C compounds, we performed first-principles calculations within the framework of Density Functional Theory. Emphasis was put on the energy cost for formation of vacancy defects and dangling bonds in relaxed systems. Cohesive energy comparison reveals that the energy cost formation for dangling bonds in different configurations is considerably higher in FL-CNx than for the amorphous films. These simulations thus confirm the experimental results showing that dangling bonds are much less likely in FL-CNx than in a-CNx and a-C films.
|
|
| 6. |
- Broitman, E., et al.
(författare)
-
Water adsorption on lubricated fullerene-like CNx films
- 2006
-
Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 515:3, s. 979-983
-
Tidskriftsartikel (refereegranskat)abstract
- Humidity influences the tribological performance of the head–disk interface in magnetic data storage devices. In this work we compare the uptake of water of amorphous hydrogenated carbon (a-CHy) and carbon nitride (a-CNx) films, widely used as protective overcoats in computer disk drive systems, with two types of amorphous non-hydrogenated carbon (a-C and a-Csp2) films, and fullerene-like carbon nitride (FL-CNx) films. Carbon films were deposited on quartz crystal substrates by reactive dc magnetron sputtering in Ar/N2 discharges. After deposition, some of the films were coated with a 2-nm-thick layer of Z-tetraol, a lubricant used in hard disk devices. A quartz crystal microbalance placed in a vacuum chamber was used to measure the adsorption of water at room temperature and at pressures of water corresponding to relative humidities in the range RH = 0 to 90%. Water adsorption and desorption is fast, indicating that equilibrium with ambient humidity is reached on time scales of minutes, much faster than the time scales for fluctuations in ambient humidity. The amount of water adsorbed on the non-lubricated amorphous carbon films is significantly higher than that on the fullerene-like films. The presence of the lubricant influences water adsorption but its impact differs on different carbon films.
|
|
| 7. |
- Broitman, E., et al.
(författare)
-
Water adsorption on phosphorous-carbide thin films
- 2009
-
Ingår i: Surface & Coatings Technology. - : Elsevier BV. - 0257-8972 .- 1879-3347. ; 204:6-7, s. 1035-1039
-
Tidskriftsartikel (refereegranskat)abstract
- Amorphous phosphorous-carbide films have been considered as a new tribological coating material with unique electrical properties. However, such CPx films have not found practical use until now because they tend to oxidize/hydrolyze rapidly when in contact with air. Recently, we demonstrated that CPx thin films with a fullerene-like structure can be deposited by magnetron sputtering, whereby the structural incorporation of P atoms induces the formation of strongly bent and inter-linked graphene planes. Here, we compare the uptake of water in fullerene-like phosphorous-carbide (FL-CPx) thin films with that in amorphous phosphorous-carbide (a-CPx), and amorphous carbon (a-C) thin films. Films of each material were deposited on quartz crystal substrates by reactive DC magnetron sputtering to a thickness in the range 100-300 nm. The film microstructure was characterized by X-ray photoelectron spectroscopy, and high resolution transmission electron microscopy. A quartz crystal microbalance placed in a vacuum chamber was used to measure their water adsorption. Measurements indicate that FL-CPx films adsorbed less water than the a-CPx and a-C ones. To provide additional insight into the atomic structure of defects in the FL-CPx and a-CPx compounds, we performed first-principles calculations within the framework of density functional theory. Cohesive energy comparison reveals that the energy cost formation for dangling bonds in different configurations is considerably higher in FL-CPx than for the amorphous films. Thus, the modeling confirms the experimental results that dangling bonds are less likely in FL-CPx than in a-CPx and a-C films.
|
|
| 8. |
- Darakchieva, Vanya, 1971-, et al.
(författare)
-
Effects of strain and composition on the lattice parameters and applicability of Vegard's rule in Al-rich Al1-x Inx N films grown on sapphire
- 2008
-
Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 103:10, s. 103513-
-
Tidskriftsartikel (refereegranskat)abstract
- The lattice parameters and strain evolution in Al1-x In x N films with 0.07≤x≤0.22 grown on GaN-buffered sapphire substrates by metal organic vapor phase epitaxy have been studied by reciprocal space mapping. Decoupling of compositional effects on the strain determination was accomplished by measuring the In contents in the films both by Rutherford backscattering spectrometry (RBS) and x-ray diffraction (XRD). Differences between XRD and RBS In contents are discussed in terms of compositions and biaxial strain in the films. It is suggested that strain plays an important role for the observed deviation from Vegard's rule in the case of pseudomorphic films. On the other hand, a good agreement between the In contents determined by XRD and RBS is found for Al1-x Inx N films with low degree of strain or partially relaxed, suggesting applicability of Vegard's rule in the narrow compositional range around the lattice matching to GaN. © 2008 American Institute of Physics.
|
|
| 9. |
- Eriksson, Fredrik, et al.
(författare)
-
Atomic scale interface engineering by modulated ion-assisted deposition applied to soft x-ray multilayer optics
- 2008
-
Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 47:23, s. 4196-4204
-
Tidskriftsartikel (refereegranskat)abstract
- Cr/Sc and Ni/V multilayers, intended as normal incidence soft x-ray mirrors and Brewster angle polarizers, have been synthesized by employing a novel modulated low-energy and high-flux ion assistance as a means of engineering the interfaces between the subnanometer layers on an atomic scale during magnetron sputter deposition. To reduce both roughness and intermixing, the ion energy was modulated within each layer. The flat and abrupt interfaces yielded soft x-ray mirrors with near-normal incidence reflectances of R = 20.7% at the Sc 2p absorption edge and R = 2.7% at the V 2p absorption edge. Multilayers optimized for the Brewster angle showed a reflectance of R = 26.7% and an extinction ratio of Rs/Rp=5450 for Cr/Sc and R = 10% and Rs/Rp=4190 for Ni/V. Transmission electron microscopy investigations showed an amorphous Cr/Sc structure with an accumulating high spatial frequency roughness. For Ni/V the initial growth mode is amorphous and then turns crystalline after ~1/3 of the total thickness, with an accumulating low spatial frequency roughness as a consequence. Elastic recoil detection analyses showed that N was the major impurity in both Cr/Sc and Ni/V with concentrations of 15 at. % and 9 at. %, respectively, but also O (3 at. % and 1.3 at. %) and C (0.5 at. % and 1.9 at. %) were present. Simulations of the possible normal incidence reflective properties in the soft x-ray range of 100-600 eV are given, predicting that reflectivities of more than 31% for Cr/Sc and 5.8% for Ni/V can be achieved if better control of the impurities and the deposition process is employed. The simulations also show that Cr/Sc is a good candidate for mirrors for the photon energies between the absorption edges of B (E = 188 eV) and Sc (E = 398.8 eV).
|
|
| 10. |
- Hills, Gerald E., et al.
(författare)
-
A value creation view of opportunity recognition processes
- 2005
-
Ingår i: International Journal of Entrepreneurship and Small Business. - Genéve, Switzerland : Inderscience Publishers. - 1476-1297 .- 1741-8054. ; 2:4, s. 404-417
-
Tidskriftsartikel (refereegranskat)abstract
- Opportunity recognition is an important part of value creation processes and vice-versa. A qualitative study, involving in-depth, semi-structured interviews of 59 firm-owners/founders in the U.S. and Sweden was conducted to better understand how entrepreneurs and SME owners engage in opportunity recognition and marketing practices. The findings revealed evidence of: planning to be opportunistic, a propensity to take action, opportunities perceived incrementally over years, instantaneous opportunity evaluation, first customer testing rather than formal market research, both Kirznerian alertness and Schumpeterian new combinations, job dissatisfaction and industry experience preceding opportunity recognition, support for the Bhave model, variations in the level of search, entrepreneurs taking “ownership” of ideas that were not originally theirs, use of supply and demand in recognizing opportunities and contingent opportunity recognition.
|
|
