Mineralization of inorganic materials in (bio)polymers became one of the most fruitful approaches towards designing materials with outstanding properties in the past decades. The concept of biomieralization is adapted from nature and has witnessed numerous fascinating developments, which in many cases have changed our lives. Among those functional materials hybrid materials play an increasingly important role. Hybrid materials are in most cases blends of inorganic and organic materials and are considered to be key for the next generation of materials research. The main goal while fabricating such materials is to bridge the worlds of polymers and ceramics, ideally uniting the most desirable properties within a singular material. In our work, we extend the concept of biomineralization towards fabrication of (bio)polymer-inorganic hybrid materials by applying a solvent-free vapor phase infiltration (VPI) process rather than making use of wet chemistry. The VPI process can be seen as a chemical reactor that allows precise dosing of a chemical, allowing for chemical interaction and modification of the subsurface area of a substrate.
In this talk, some approaches will be discussed that show great promise for establishing VPI as the method-of-choice for innovation. The VPI process allows infusing metals or ceramics into polymeric substrates, which leads to novel material blends that cannot easily be obtained in other ways. The chemical or physical properties of the initial substrate are improved or new functionalities added. With some showcases, this talk will discuss approaches towards fabrication of novel materials with great promise in personal protection or flexible electronics.
Enzymes play a crucial role in biochemical processes and are essential for many synthetic processes in industry. In spite of their great catalytic performance and high selectivity for material conversion, their chemical and/or thermal stability is a limiting factor for many processes that opt for a high throughput. Increasing the stability of enzymes thus promises considerable increase in productivity of numerous industrial processes.
A promising pathway for such stability enhancement is the generation of hybrid bioinorganic nanomaterials that show catalytic properties similar to enzymes, but at the same time benefit from the chemical and thermal stability of the inorganic constituent. In this presentation we will show that a combination of inorganic nanoparticles with a surrounding protein shell can indeed mimic a variety of enzyme-analogue reactions in both activity and inhibition. Moreover, the catalytic activity can even be enhanced if the materials are exposed to environmental conditions under which traditional protein-based enzymes become inactive.
X-ray microscopy enables high spatial resolutions, high penetration depths and characterization of a broad range of materials. Calculations show that nanometer range resolution is achievable in the hard X-ray regime by using Fresnel zone plates (FZPs) if certain conditions are satisfied. However, this requires, among other things, aspect ratios of several thousands. The multilayer (ML) type FZPs, having virtually unlimited aspect ratios, are strong candidates to achieve single nanometer resolutions. Our research is focused on the fabrication of ML-FZPs which encompasses deposition of multilayers over a glass fiber via the atomic layer deposition (ALD), which is subsequently sliced in the optimum thickness for the X-ray energy by a focused ion beam (FIB). We recently achieved aberration free imaging by resolving 21 nm features with an efficiency of up to 12.5 %, the highest imaging resolution achieved by an ML-FZP. We also showed efficient focusing of 7.9 keV X-rays down to 30 nm focal spot size (FWHM). For resolutions below ~10 nm, efficiencies would decrease significantly due to wave coupling effects. To compensate this effect high efficiency, low stress materials have to be researched, as lower intrinsic stresses will allow fabrication of larger FZPs with higher number of zones, leading to high light intensity at the focus. As a first step we fabricated an ML-FZP with a diameter of 62 μm, an outermost zone width of 12 nm and 452 active zones. Further strategies for fabrication of high resolution high efficiency multilayer FZPs will also be discussed.
Developments and advances in the e-beam lithography (EBL) made it possible to reach resolutions in a single digit
nanometer range in the soft x-ray microscopy using Fresnel Zone Plates (FZP). However, it is very difficult to fabricate
efficient FZPs for hard x-rays via this conventional fabrication technique due to limitations in the achievable aspect
ratios. Here, we demonstrate the use of alternative fabrication techniques that depend on utilization of atomic layer
deposition and focused ion beam processing to deliver FZPs that are efficient for the hard X-ray range.
A combination of deposition strategies was applied in order to synthesize Au nanoparticle chains embedded in helical Al2O3 nanotubes (“nanopeapods”). Carbon nanocoils were grown by chemical vapour deposition and coated with Au by sputtering with a subsequent Al2O3 coating by atomic layer deposition. Rayleigh instabilities were made use of in order to fragment the Au coating into nanoparticles with a sharp size distribution. The pitch of the nanocoils arising from three-dimensional periodical topography of the carbon nanocoil templates induced a regular spacing between the nanoparticles. The nanoparticle chains show a strong plasmonic resonance behaviour visible as clear polarization contrast at red wavelengths, which is absent in the blue upon excitation with a confocal laser scanning microscope. The fabricated nanopeapods are suggested promising candidates for highly efficient, ultrathin waveguides.
Advances in the deposition of metallic thin films are discussed. The ALD growth of ultrathin Ir films is analyzed by
transmission electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy, and optical and
electrical measurements. The morphology of iridium metallic layers is assessed based on Ir/ Al2O3 nanolaminate films.
High resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy measurements show sharp
interfaces and pure Ir layers in the nanolaminates. The iridium films as polycrystalline. Excellent thickness control, high
uniformity and low roughness of ALD films are demonstrated. Four point probe measurements of the resistivity of Ir
coatings with various thicknesses have been performed and proved conductive layers with an Ir film thickness of ca. 10
nm. The optical properties of the Ir films deposited by ALD are similar to those of the bulk Ir. Thin iridum layers
deposited on high aspect ratio linear gratings have been successfully used as electrodes in the electrochemical deposition
of gold nanoparticles and gold layers. The gold deposition evolves through the formation of gold islands with ca. 40 nm
diameters that coalesce after ca. 60 seconds deposition. The density of the gold islands within the grating pattern is much
lower than on the flat region of the substrate. The combination of ALD with electrochemical deposition allows the
diversification of conductive layers on complex nanostructured surfaces.
The progress of 3D photonic intermediate reflectors for micromorph silicon tandem cells towards a first prototype
cell is presented. Intermediate reflectors enhance the absorption of spectrally-selected light in the top cell
and decrease the current mismatch between both junctions. A numerical method to predict filter properties for
optimal current matching is presented. Our device is an inverted opal structure made of ZnO and fabricated
using self-organized nanoparticles and atomic layer deposition for conformal coating. In particular, the influence
of ZnO-doping and replicated cracks during drying of the opal is discussed with respect to conductivity
and optical properties. A first prototype is compared to a state-of-the-art reference cell.
The concept of a 3D photonic crystal structure as diffractive and spectrally selective intermediate filter within
'micromorphous' (a-Si/μc-Si) tandem solar cells has been investigated numerically and experimentally. Our device aims
for the enhancement of the optical pathway of incident light within the amorphous silicon top cell in its spectral region of
low absorption. From our previous simulations, we expect a significant improvement of the tandem cell efficiency of
about absolutely 1.3%. This increases the efficiency for a typical a-Si / μc-Si tandem cell from 11.1% to 12.4%, as a
result of the optical current-matching of the two junctions. We suggest as wavelength-selective optical element a 3D-structured
optical thin-film, prepared by self-organized artificial opal templates and replicated with atomic layer
deposition. The resulting samples are highly periodic thin-film inverted opals made of conducting and transparent zinc-oxide.
We describe the fabrication processes and compare experimental data on the optical properties in reflection and
transmission with our simulations and photonic band structure calculations.