Arne Nylandsted Larsen

Fibronectin adsorption, cell adhesion, and proliferation on nanostructured tantalum surfaces

The interaction between dental pulp derived mesenchymal stem cells (DP-MSCs) and three different tantalum nanotopographies with and without a fibronectin coating is examined: sputter-coated tantalum surfaces with low surface roughness <0.2 nm, hut-nanostructured surfaces with a height of 2.9 +/- 0.6 nm and a width of 35 +/- 8 nm, and dome structures with a height of 13 +/- 2 nm and a width of 52 +/- 14 nm. Using ellipsometry, the adsorption and the availability of fibronectin cell-binding domains on the tantalum surfaces were examined, as well as cellular attachment, proliferation, and vinculin focal adhesion spot assembly on the respective surfaces. The results showed the highest fibronectin mass uptake on the hut structures, with a slightly higher availability of cell-binding domains and the most pronounced formation of vinculin focal adhesion spots as compared to the other surfaces. The proliferation of DP-MSCs was found to be significantly higher on dome and hut surfaces coated with fibronectin compared to the uncoated flat tantalum surfaces. Consequently, the results presented in this study indicate that fibronectin-coated nanotopographies with a vertical dimension of less than 5 nm influence cell adhesion. This rather interesting behavior is argued to originate from the more available fibronectin cell-binding domains observed on the hut structures.

Diffusion of Sb in relaxed Si1−xGex

Diffusion of antimony in relaxed Si1−xGex alloy layers grown by molecular beam epitaxy has been studied as a function of the composition for 0≤x≤0.5. The diffusivity of antimony was found to increase with the Ge alloy content, and the extracted activation energies for diffusion were found to decrease with increasing germanium content in the investigated composition range. The activation energies, however, are significantly higher than the corresponding activation energies obtained by an extrapolation between the activation energy in pure silicon and germanium.

Near-infrared–ultraviolet absorption cross sections for Ge nanocrystals in SiO2 thin films: Effects of shape and layer structure

Measured absolute optical absorption cross sections of 2–6 nm Ge nanocrystals embedded in SiO2 in the near-infrared–ultraviolet spectral range are reported. Thin layers of Ge sandwiched between SiO2 layers were prepared in a multilayered configuration, which upon heat treatment at 800 °C led to multilayers of Ge nanocrystals with a narrow size distribution. Four samples with different nanocrystal average sizes were prepared by this technique. In addition, samples containing Ge nanocrystals randomly distributed in SiO2 films were also prepared in order to clarify the effects of the multilayer configuration on the optical properties. The size distribution and density of the nanocrystals were obtained from transmission electron microscopy investigations and Rutherford backscattering spectrometry measurements. In combination with this structural information the nanocrystal absorption cross sections were obtained from optical transmission measurements, which were corrected for thin film interference effects by...

Point defect injection into silicon due to low‐temperature surface modifications

Deep level transient spectroscopy has been applied to study the appearance of phosphorus‐vacancy pairs in n‐type silicon following different low‐temperature surface modifications. It is established that at most 107 cm−2 vacancy is injected into the bulk of the silicon substrate during Pd2Si silicide formation. On the other hand, phosphorus‐vacancies pairs are observed after electron irradiation, low energy ion bombardment, and electron gun evaporation of metal films.

Growth and characterization of compositionally graded, relaxed Si1-xGex

Compositionally graded, relaxed, n-type, Si1-xGex alloy layers have been grown on (100) Si substrates; the main emphasis has been put on compositions with x = 0.25. It is found that for substrate growth-temperatures higher than similar 750°C and a grading rate of 10% Ge/μm relaxed Si0.75Ge0.25 epitaxial layers of high structural, optical, and electrical quality can be grown. The layers are characterized by channeling parameters close to expected bulk values, a threading dislocation density of similar 5 × 105 cm−2, and strong near-band gap luminescence. Electrical measurements have revealed Hall mobilities similar to published bulk values and concentrations of electrically active deep levels ≤2 × 1011 cm−3. The surface morphology is, however, strongly influenced by the grading procedure which produces a high degree of cross-hatching.

Quasiparticle electronic and optical properties of the Si–Sn system

The Si(1-x)Sn(x) material system is an interesting candidate for an optically active material compatible with Si. Based on density functional theory with quasiparticle corrections we calculate the electronic band structure of zinc-blende SiSn under both compressive and tensile strain. At 2.2% tensile strain the band gap becomes direct with a magnitude of 0.85 eV. We develop an accurate tight-binding parameterization of the electronic structure and calculate the optical properties of SiSn. Furthermore, the silicide SiSn(2) is investigated and found to have metallic character.

Room-temperature vacancy migration in crystalline Si from an ion-implanted surface layer

Migration of vacancies in crystalline, n-type silicon at room temperature from Ge+-implanted (150 keV, 5×109–1×1011 cm−2) surface layers was studied by tracing the presence of P–V pairs (E centers) in the underlying layer using deep level transient spectroscopy (DLTS). Under the conditions we have examined, the vacancies migrate to a maximum depth of about 1 μm and at least one vacancy per implanted Ge ion migrates into the silicon crystal. The annealing of the E centers is accompanied, in an almost one-to-one fashion, by the appearance of a new DLTS line corresponding to a level at EC−Et≈0.15 eV that has donor character. It is argued that the center associated with this line is most probably the P2–V complex; it anneals at about 550 K. A lower limit of the RT-diffusion coefficient of the doubly charged, negative vacancy is estimated to be 4×10−11 cm2/s.

Up-conversion enhancement in Er3+ doped TiO2 through plasmonic coupling: Experiments and finite-element modeling

Silver nanoparticles, placed on top of an Er3+ doped TiO2 thin film, were investigated as a means of achieving enhanced up-conversion. Finite-element modeling was used to determine the nanoparticle dimensions (height and diameter) yielding the largest plasmonic enhancement for an incident light wavelength of 808 nm. In order to mimic the experimentally observed up-conversion enhancement, the electric-field enhancement from the Ag nanoparticles was integrated over the entire thickness of the thin film. Based on these calculations, four samples were prepared and tested. The trends predicted by the models were found to correlate well with the trends of the experimentally obtained plasmonic enhanced up-conversion yields. The largest plasmonic enhancement for 808 nm excitation was observed for Ag nanoparticles of diameter 91 ± 5 nm and height 14 ± 1 nm, yielding 163- and 51-fold enhancements for the green (525 nm and 550 nm) and red (660 nm) emissions peaks, respectively.

Infrared upconversion in radio frequency magnetron sputtered Er-doped zinc oxide thin films

Upconversion in radio frequency magnetron sputtered Er-doped zinc oxide thin films on Si substrate has been demonstrated using 1550 nm cw laser excitation. As-sputtered thin films did not show any upconversion emission, and annealing was required to optically activate the Er3+-ions. Emissions at 985, 809, and 665–675 nm were observed in annealed thin films, corresponding to transitions from 4I11∕2, 4I9∕2, and 4F9∕2 to the ground state 4I15∕2, respectively. The emission from 4I11∕2 was the dominant one, whereas emission from 4I9∕2 was the weakest. The highest intensity at 985 nm was obtained with 2.4 at. % of Er by annealing the film at 700 °C. Annealing at higher temperatures causes Er to diffuse and segregate to the Si-ZnO interface between the Si substrate and the ZnO film.

On-line DLTS investigations of the mono- and di-vacancy in p-type silicon after low temperature electron irradiation

Abstract Using deep level transient spectroscopy (DLTS) and Laplace-DLTS, we have investigated vacancy-related defects created in boron-doped epitaxial Si by 2 MeV electron irradiations at low temperatures (⩽ 40 K ) . The vacancy level is found at E v +0.12 eV together with a DLTS peak at E v +0.20 eV which anneals at ∼140 K and is tentatively identified as a vacancy in a different configuration. The emission rate of the dominant vacancy-related deep level in the temperature range from 200 to 550 K, namely the (0/+) transition of the di-vacancy (V2), displays a very large dependence of the emission rate on the electric field strength in the depletion region of the diodes. This dependence is unexpected in terms of the classical Poole–Frenkel effect, given the neutral charge state of V2 before hole capture. The effect of high fields appears to be caused by phonon assisted tunneling. When V anneals around 200 K, a new complex assigned to a vacancy–boron pair gives rise to two charge states. Quenching experiments with reverse bias show that the complex is bistable. It anneals at 260 K.