Showing papers by "Hans-Gerd Boyen published in 2013"

A Molecular Toolkit for the Functionalization of Titanium-Based Biomaterials That Selectively Control Integrin-Mediated Cell Adhesion

Abstract: We present a click chemistry- based molecular toolkit for the bio- functionalization of materials to selec- tively control integrin-mediated cell ad- hesion. To this end, a 5 b 1-selective RGD peptidomimetics were covalently immobilized on Ti-based materials, and the capacity to promote the selective binding of a 5 b 1 was evaluated using a solid-phase integrin binding assay. This functionalization strategy yielded surfa- ces with a nine-fold increased affinity for a 5 b 1, in comparison to control samples, and total selectivity against the binding of the closely related integ- rin a v b 3. Moreover, our methodology allowed the screening of several phos- phonic acid containing anchoring units to find the best spacer–anchor moiety required for establishing an efficient binding to titanium and to promote se- lective integrin binding. The integrin subtype specificity of these biofunc- tionalized surfaces was further exam- ined in vitro by inducing selective ad- hesion of genetically modified fibro- blasts, which express exclusively the a 5 b 1 integrin. The versatility of our molecular toolkit was proven by shift- ing the cellular specificity of the mate- rials from a 5 b 1- to a v b 3-expressing fi- broblasts by using an a v b 3-selective peptidomimetic as coating molecule. The results shown here represent the first functionalization of Ti-based mate- rials with a 5 b 1- or a v b 3-selective pep- tidomimetics that allow an unprece- dented control to discriminate between a 5 b 1- and a v b 3-mediated adhesions. The role of these two integrins in dif- ferent biological events is still a matter of debate and is frequently discussed in literature. Thus, such bioactive titanium surfaces will be of great relevance for the study of integrin-mediated cell ad- hesion and the development of new bi- omaterials targeting specific cell types

Surface plasma pretreatment for enhanced diamond nucleation on AlN

Abstract: The surface of polycrystalline aluminum nitride (AlN) thin films is exposed to different gas discharge plasmas (N2, O2, and CF4) followed by a water-based colloidal seeding of ultra-dispersed nanodiamond particles. Fluorination of the AlN surface enhances the seeding density, whereas the oxidized surface does not yield any nucleation sites. In the former case, the seeding density improves by almost three orders of magnitude as compared to the untreated and N2 pretreated samples, and allows to grow pinhole-free nanocrystalline diamond film on AlN. Finally, we demonstrate a route towards selective diamond growth on AlN thin films by employing CF4 plasma pretreatment together with photolithography.

Controlled synthesis of ultrathin ZnO nanowires using micellar gold nanoparticles as catalyst templates

Abstract: We demonstrate a simple and effective approach to control the diameter of ultrathin ZnO nanowires with high aspect ratios and high densities over large areas. Diblock copolymer-based nanoparticle arrays exhibiting a high degree of hexagonal order and offering easy control of particle size (typically 1–10 nm) and interparticle spacing (25–150 nm) are utilized as nanocatalysts for the subsequent growth of semiconductor nanowires. The as-grown ZnO nanowires exhibit a single crystal hexagonal wurtzite structure and grow along the [0002] direction. Facetted catalyst particles were observed at the tip of the nanowires after synthesis, thus suggesting a catalyst-assisted vapor–solid–solid (VSS) rather than a vapor–liquid–solid (VLS) growth mechanism, the latter being frequently used in semiconductor nanowire production. Such a growth process allows us to easily prepare ultrathin ZnO nanowires with tunable diameters well below 10 nm by taking advantage of the inherent size control of the micellar method during deposition of the catalyst nanoparticles. Raman spectroscopy reveals a phonon confinement effect as the diameter of nanowires decreases. Photoluminescence spectra of these ultrathin nanowires indicate a blue shift of the free excitons and their phonon replicas by 37 meV induced by quantum confinement.

Impact of ammonium sulfide solution on electronic properties and ambient stability of germanium surfaces: towards Ge-based microelectronic devices

Abstract: The monolayer adsorption of sulfur on Ge(100) surfaces from aqueous (NH4)2S solution is an approach to saturate, i.e., to passivate broken surface bonds and hence to reduce the electrical and chemical activity of this semiconductor surface. Despite its importance in view of developing Ge-based microelectronic devices, we still lack a fundamental understanding of how this treatment modifies the electrical and chemical properties of the Ge surface. In this study, the electronic properties and ambient stability of sulfurized p-type Ge surfaces are investigated using a variety of complementary spectroscopic techniques. Based on these results we evaluate the degree of electrical and chemical passivation that can be achieved by sulfur adsorption from (NH4)2S solution. We find that sulfur atoms chemically bind to Ge surface atoms within the first few seconds after immersion in solution. Saturation is achieved after approximately 30 s at a maximum sulfur coverage below half of a monolayer. The Ge–S bonds have a partial ionic character, causing depletion of the majority charge carriers near the surface. The band gap measured at the surface exhibits a lower density of surface states compared to the clean Ge surface, indicating that the S/Ge surface is electrically passivated. The Ge–S bonds are preserved upon moderate exposure to ambient conditions (ca. 2 hours), but a small fraction of the sulfur is oxidized. The steady increase of the oxygen coverage with increasing exposure time suggests a growth of Ge oxides, indicating limited resistance of the sulfurized Ge surfaces to oxidizing conditions.

Liquid-Phase Adsorption of Sulfur on Germanium: Reaction Mechanism and Atomic Geometry

Abstract: We present a fundamental study of the monolayer adsorption of sulfur on Ge(100) surfaces from aqueous (NH4)2S solution. This treatment shows promising perspectives for the passivation of high-mobility semiconductor surfaces and is therefore presently of great technological importance. The adsorption mechanisms as well as the adsorption geometry are thoroughly investigated at the atomic scale, by both experiment and theory, applying X-ray absorption spectroscopy and molecular dynamics simulations. Our findings indicate that sulfidation in solution results in the formation of Ge–S–Ge bridges along the [110] direction, with no indication for −SH surface groups. A S–Ge bond length of 2.25 ± 0.05 A was deduced, which is affected by the chemical environment of the sulfur atoms, i.e., by residual surface oxides. Our study provides novel insights into the surface termination and atomic structure of (NH4)2S-treated Ge(100) surfaces and discusses possible differences from in situ sulfur adsorption methods such as H...

Ultrafast Self‐Assembly Using Ultrasound: A Facile Route to the Rapid Fabrication of Well‐Ordered Dense Arrays of Inorganic Nanostructures

Abstract: Financial support by the Research Foundation Flanders (FWO) within the Odysseus program, the projects G.0456.12, G.0346.09N, and the Methusalem project "NANO" is gratefully acknowledged. We furthermore thank J. Baccus and C. Willems for technical support. A.E. is a postdoctoral research fellow of the FWO.