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.
Self-diffusion in amorphous germanium is studied at temperatures between 325 and 370 °C utilizing amorphous isotopically controlled germanium multilayer structures. The isotope multilayer is ...epitaxially grown on a single crystalline germanium-on-insulator structure by means of molecular beam epitaxy and subsequently amorphized by self-ion implantation. After heat treatment, the diffusional broadening of the isotope structure is measured with time-of-flight secondary ion mass spectrometry. The temperature dependence of self-diffusion is accurately described by the Arrhenius equation with the activation enthalpy Q = (2.21 ± 0.12) eV and pre-exponential factor D0=(2.32−2.10+20.79) cm2 s−1. The activation enthalpy equals the activation enthalpy of solid phase epitaxial recrystallization (SPER). This agreement suggests that self-diffusion in amorphous germanium is similar to SPER, also mainly mediated by local bond rearrangements. Classical molecular dynamics simulations with a modified Stillinger–Weber-type interatomic potential yield results that are consistent with the experimental data and support the proposed atomic mechanism.
Crystalline and preamorphized isotope multilayers are utilized to investigate the dependence of ion beam mixing in silicon (Si), germanium (Ge), and silicon germanium (SiGe) on the atomic structure ...of the sample, temperature, ion flux, and electrical doping by the implanted ions. The magnitude of mixing is determined by secondary ion mass spectrometry. Rutherford backscattering spectrometry in channeling geometry, Raman spectroscopy, and transmission electron microscopy provide information about the structural state after ion irradiation. Different temperature regimes with characteristic mixing properties are identified. A disparity in atomic mixing of Si and Ge becomes evident while SiGe shows an intermediate behavior. Overall, atomic mixing increases with temperature, and it is stronger in the amorphous than in the crystalline state. Ion-beam-induced mixing in Ge shows no dependence on doping by the implanted ions. In contrast, a doping effect is found in Si at higher temperature. Molecular dynamics simulations clearly show that ion beam mixing in Ge is mainly determined by the thermal spike mechanism. In the case of Si thermal spike, mixing prevails at low temperature whereas ion beam-induced enhanced self-diffusion dominates the atomic mixing at high temperature. The latter process is attributed to highly mobile Si di-interstitials formed under irradiation and during damage annealing.
Nanocrystalline PbS layers have been deposited chemically on Si, Ge and GaAs substrates from alkaline solutions containing 0.05 mol l
−
1 of Pb(NO
3)
2, 0.04 mol l
−
1 of thiourea, 0.05 mol l
−
1 of ...triethanolamine, and 0.15 mol l
−
1 of NaOH. Rutherford backscattering spectroscopy, transmission electron and atomic force microscopy reveal that the chemical nature of the substrate has a profound influence on the structure and thickness of the deposited layers. It is found that a large lattice mismatch between the substrate and PbS results in formation of coarse-grained layers with a small effective thickness (e.g. PbS on Si). On the other hand, close matching of lattice constants leads to deposition of thicker layers with smaller grain size (e.g. PbS on Ge, GaAs).
Er-doped SiO1.87 films containing amorphous Si nanodots were deposited and heat-treated at the two temperatures 950 and 1100 °C. On the basis of morphological observations, structural ...characterizations and optical measurements it is concluded that the heat-treatment at 1100 °C results in a 3-fold higher Er3+ luminescent efficiency than the one at 950 °C due to the formation of SiOEr complex rather than the nature of sensitizers.
•Intense emission at 1.5 μm from Er ions is excited by amorphous Si nanodots.•The crystallinities of Si nanodots in two different annealed-samples are same.•The SiOEr complex results in the higher luminescent efficiency for Er ions.
Epitaxial silicon-germanium layers have already for some time been used in Si-based high performance devices. More recently integration of Ge layers in Si-based structures has been considered due to ...its superior carrier mobilities compared to silicon. The most feasible method for integrating SiGe and Ge layers into Si-based structures is through epitaxial growth. Among the epitaxial growth systems molecular-beam epitaxy (MBE) and ultra-high vacuum chemical-vapor deposition (UHV-CVD) are widely used, in particular in research environments, due to their flexibility with respect to controlling growth parameters. The emphasis of this review will be on structures grown by these two techniques. Due to the 4.2% lattice misfit between Si and Ge, SiGe and Ge layers on Si substrates are usually grown on a buffer layer to accommodate the strain, thus producing SiGe or Ge top layers of reduced defect densities. Top layers with or without strain can then be produced by adjusting the composition of the buffer relative to that of the top layer. A high quality top layer of low defect density is the required product, and different buffer-layer concepts on Si are discussed.
The present work reports on a distinct and very reproducible bistable-like behavior of two defects at around EC − 0.5 eV in MOCVD-grown GaN. The kinetics of the thermally activated transformation ...between the two states are analyzed in an Arrhenius model, yielding an energy barrier of 0.4 ± 0.1 eV, and a frequency factor of 106±1 s−1. Depth profiles suggest that the charge state of the defects determines the observed amplitude variation. Relevant models for the observed behavior, and their shortcomings are discussed: (i) passivating properties of hydrogen, and (ii) bistable defect component(s). A proper explanation of the experimental observations represents, however, a further challenge.
The article presents a nanoparticle-based buried light-scattering (BLiS) back-reflector design realized through a simplified nanofabrication technique for the purpose of light-management in solar ...cells. The BLiS structure consists of a flat silver back-reflector with an overlying light-scattering bilayer which is made of a TiO
2
dielectric nanoparticles layer with micron-sized inverted pyramidal cavities, buried under a flat-topped silicon nanoparticles layer. The optical properties of this BLiS back-reflector show high broadband and wide angular distribution of diffuse light-scattering. The efficient light-scattering by the buried inverted pyramid back-reflector is shown to effectively improve the short-circuit-current density and efficiency of the overlying n-i-p amorphous silicon solar cells up to 14% and 17.5%, respectively, compared to the reference flat solar cells. A layer of TiO
2
nanoparticles with exposed inverted pyramid microstructures shows equivalent light scattering but poor fill factors in the solar cells, indicating that the overlying smooth growth interface in the BLiS back-reflector helps to maintain a good fill factor. The study demonstrates the advantage of spatial separation of the light-trapping and the semiconductor growth layers in the photovoltaic back-reflector without sacrificing the optical benefit.
This work investigates the localized surface plasmon resonance (LSPR) of
β
-Sn also known as white tin. Recently, studies on arrays of
β
-Sn nanoparticles have shown that these arrays possess strong ...optical features caused by diffractive effects in the particle grating (Johansen et al., Phys Rev B 84:113405–113408,
2011
). In the presence of the grating, the LSPR could not clearly be distinguished in the spectra. To get a better understanding of the plasmonic properties of the particles, we have now eliminated the diffractive effects by placing the particles in a random distribution. The particles were fabricated by electron beam lithography on a fused silica substrate and investigated by optical transmission measurements. In the random configuration, a clear LSPR is observed at 530 nm for particles with a diameter of 155 nm and a height of 50 nm.
The optical properties of metallic tin nanoparticles embedded in silicon-based host materials were studied. Thin films containing the nanoparticles were produced using RF magnetron sputtering ...followed by ex situ heat treatment. Transmission electron microscopy was used to determine the nanoparticle shape and size distribution; spherical, metallic tin nanoparticles were always found. The presence of a localized surface plasmon resonance in the nanoparticles was observed when SiO
2
and amorphous silicon were the host materials. Optical spectroscopy revealed that the localized surface plasmon resonance is at approximately 5.5 eV for tin nanoparticles in SiO
2
, and at approximately 2.5 eV in amorphous silicon. The size of the tin nanoparticles in SiO
2
can be varied by changing the tin content of the films; this was used to tune the localized surface plasmon resonance.
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