Steffen Chemnitz

Single step integration of ZnO nano- and microneedles in Si trenches by novel flame transport approach: whispering gallery modes and photocatalytic properties.

Direct growth of quasi-one-dimensional nano- and microstructures in desired places of complex shaped substrates using simple growth methods is highly demanded aspect for various applications. In this work, we have demonstrated direct integration of ZnO nano- and microneedles into Si trenches by a novel flame transport synthesis approach in a single fabrication step. Growth of partially and fully covered or filled trenches in Si substrate with ZnO nano- and microneedles has been investigated and is discussed here. Detailed microstructural studies revealed the evolution of the ZnO nano- and microneedles as well as their firm adhesion to the wall in the Si trenches. Micro-photoluminescence measurements at different locations along the length of needles confirmed the good crystalline quality and also the presence of whispering gallery mode resonances on the top of needles due to their hexagonal shape. Faceted ZnO nano- and microstructures are also very important candidates with regard to photocatalytic activity. First, photocatalytic measurements from the grown ZnO nano- and microneedles have shown strong degradation of methylene blue, which demonstrate that these structures can be of significant interest for photocatalysis and self-cleaning chromatography columns.

Magnetic moment investigation by frequency mixing techniques

Gas turbines and other large industrial equipment are subjected to high-temperature oxidation and corrosion. Research and development of efficient protective coatings is the main task in the field. Also, knowledge about the depletion state of the coating during the operation time is important. To date, practical nondestructive methods for the measurement of the depletion state do not exist. By integrating magnetic phases into the coating, the condition of the coating can be determined by measuring its magnetic properties. In this paper, a new technique using frequency mixing is proposed to investigate the thickness of the coatings based on their magnetic properties. A sensor system is designed and tested on specific magnetic coatings. New approaches are proposed to overcome the dependency of the measurement on the distance between coil and sample that all noncontact techniques face. The novelty is a low cost sensor with high sensibility and selectivity which can provide very high signal-to-noise ratios. Prospects and limitations are discussed for future use of the sensor in industrial applications.

Identifying and overcoming the interface originating c-axis instability in highly Sc enhanced AlN for piezoelectric micro-electromechanical systems

Enhancing the piezoelectric activity of AlN by partially substituting Al with Sc to form Al1–xScxN is a promising approach to improve the performance of piezoelectric micro-electromechanical systems. Here, we present evidence of an instability in the morphology of Al1–xScxN, which originates at, or close to, the substrate/Al1–xScxN interface and becomes more pronounced as the Sc content is increased. Based on Transmission electron microscopy, piezoresponse force microscopy, X-ray diffraction, and SEM analysis, it is identified to be the incipient formation of (100) oriented grains. Approaches to successfully reestablish exclusive c-axis orientation up to x = 0.43 are revealed, with electrode pre-treatment and cathode-substrate distance found to exert significant influence. This allows us to present first measurements of the transversal thin film piezoelectric coefficient e31,f and dielectric loss tangent tan δ beyond x = 0.3.

A novel technology for MEMS based on the agglomeration of powder by atomic layer deposition

A novel disruptive fabrication technique for MEMS is presented, based on the agglomeration of powders into three-dimensional porous structures by atomic layer deposition (ALD). Since ALD is performed at low temperatures, such structures can be created from a broad variety of materials on top or embedded within a substrate. The porous structures are thermally and mechanically robust enough to allow further processing of such substrates in a common back-end-of-line (BEOL) environment. The new technique extends the variety of functional materials for MEMS. Moreover, 3D microstructures with certain porosity and a large inner surface with tailored properties can be fabricated in a simple manner. That opens up unique prospects for future MEMS.

Reconstruction of Magnetization Curve Using Magnetic Spectroscopy

A new measurement principle based on the frequency mixing technique for investigating the shape of the magnetization curve of soft non-hysteretic magnetic materials is introduced. Based on Taylor expansion of the magnetization curve and spectral investigation of an inductively detected signal, a mathematical model for the reconstruction of M(H) is proposed, [7]. Here, the model is experimentally verified using a nanocrystalline soft magnetic material with defined properties. It is shown that the magnetization curve can be reconstructed very accurately and the influence of an additional parameter, i.e. strain, can be investigated in detail as well.