Lothar Hahn

Role of oxygen in the determination of oxide-forming elements by electrothermal atomic absorption spectrometry. Part 1. Effect of oxygen on the reactions of thallium

To study the effect of oxygen on the chemical reactions of oxide-forming elements in a graphite furnace a method was developed that allows a separation between the oxygen treatment and the subsequent measurement. This method demonstrated that the effects caused by oxygen are due to a change in the surface properties of the furnace. Thallium forms residues in untreated and oxygen-treated furnaces after the drying step as Tl2O3 on the surface. In untreated furnaces the reduction to the atomic state occurs via the volatile suboxide Tl2O, which is the reason for losses of atomizable material. Furnaces treated with oxygen avoid the formation of the volatile suboxide owing to the chemically modified graphite surface and enhance the absorbance considerably. The modification of the graphite surface is caused by chemisorption of oxygen on active sites of the graphite which are destroyed in a high-temperature step. Hence, the reduction process is shifted to higher temperatures with lower losses of atomizable material. Details of a pre-treatment that avoids the losses of material without the use of oxygen are also given.

High-flexibility combinatorial peptide synthesis with laser-based transfer of monomers in solid matrix material

Laser writing is used to structure surfaces in many different ways in materials and life sciences. However, combinatorial patterning applications are still limited. Here we present a method for cost-efficient combinatorial synthesis of very-high-density peptide arrays with natural and synthetic monomers. A laser automatically transfers nanometre-thin solid material spots from different donor slides to an acceptor. Each donor bears a thin polymer film, embedding one type of monomer. Coupling occurs in a separate heating step, where the matrix becomes viscous and building blocks diffuse and couple to the acceptor surface. Furthermore, we can consecutively deposit two material layers of activation reagents and amino acids. Subsequent heat-induced mixing facilitates an in situ activation and coupling of the monomers. This allows us to incorporate building blocks with click chemistry compatibility or a large variety of commercially available non-activated, for example, posttranslationally modified building blocks into the arrays peptides with >17,000 spots per cm2.

Role of oxygen in the determination of oxide forming elements by electrothermal atomic absorption spectrometry. Part 2. Effect of oxygen on the reactions of thallium, bismuth and lead in uncoated furnaces, pyrolytic coated furnaces and on platforms

The chemical processes occurring in the graphite furnaces of atomic absorption spectrometers were studied when the oxide forming elements, Tl, Bi and Pb were being determined. Furnaces fabricated from uncoated electrographite, pyrolytic graphite coated graphite furnaces, uncoated furnace coated platforms and uncoated furnace uncoated platforms were tested. Pyrolysis curves were measured in all the furnace types, with flowing argon and under gas stop. The reactions occurring for Tl and Bi are reduction reactions via volatile suboxides to the elements, whereas Pb is directly reduced to the metal. The volatile suboxides are responsible for material losses during pretreatment. Under gas stop conditions the losses may be reduced by further reduction of the suboxides by additional collisions with the graphite surface. Separate atomization from the furnace wall and from the platform after thermal pretreatment gave an indication of the location and the kinetics of the different reaction steps. The oxygen conditioning of the uncoated furnaces and the uncoated platforms resulted in the thermal stabilization of the elements under study. This can be explained by the intercalation of the metals into the graphite layers.

Particle-Based Microarrays of Oligonucleotides and Oligopeptides

In this review, we describe different methods of microarray fabrication based on the use of micro-particles/-beads and point out future tendencies in the development of particle-based arrays. First, we consider oligonucleotide bead arrays, where each bead is a carrier of one specific sequence of oligonucleotides. This bead-based array approach, appearing in the late 1990s, enabled high-throughput oligonucleotide analysis and had a large impact on genome research. Furthermore, we consider particle-based peptide array fabrication using combinatorial chemistry. In this approach, particles can directly participate in both the synthesis and the transfer of synthesized combinatorial molecules to a substrate. Subsequently, we describe in more detail the synthesis of peptide arrays with amino acid polymer particles, which imbed the amino acids inside their polymer matrix. By heating these particles, the polymer matrix is transformed into a highly viscous gel, and thereby, imbedded monomers are allowed to participate in the coupling reaction. Finally, we focus on combinatorial laser fusing of particles for the synthesis of high-density peptide arrays. This method combines the advantages of particles and combinatorial lithographic approaches.

Damage and failure behaviour of a woven C/SiC material

The mechanical behaviour of a C/SiC material, infiltrated by liquid silicon, was investigated. Structural features have been attributed to the damage and failure behaviour of the material. The material can be described by a two-component model: the fibre bundles in the loading direction (component 1), and the rest of structure (component 2). The fibre bundles in the loading direction largely determine the deformation and failure behaviour, whereas the rest of the structure essentially determines the damage behaviour of the material. The structural features do not undergo changes up to 1400°C in mechanical tests, whereas the mechanical properties undergo slight changes. Heat treatment of the material at elevated temperatures causes a change in the structural features and leads to a reduction in strength and in interlaminar shear strength.

Silicon-plasmonic photomixer for generation and homodyne reception of continuous-wave THz radiation

We demonstrate the first silicon-plasmonic photomixer. THz radiation is generated and received by employing two lasers near 1.5 μm. The receiver sensitivity of 28 mA/(W V) compares well with the sensitivity of a commercial system.

Silicon–plasmonic integrated circuits for terahertz signal generation and coherent detection

Optoelectronic signal processing offers great potential for generation and detection of ultra-broadband waveforms in the terahertz range (so-called T-waves). However, fabrication of the underlying devices still relies on complex processes using dedicated III–V semiconductor substrates. This severely restricts the application potential of current T-wave transmitters and receivers and impedes co-integration of these devices with advanced photonic signal processing circuits. Here, we demonstrate that these limitations can be overcome by plasmonic internal-photoemission detectors (PIPEDs). PIPEDs can be realized on the silicon photonic platform, which allows exploiting the enormous opportunities of the associated device portfolio. In our experiments, we demonstrate both T-wave signal generation and coherent detection at frequencies up to 1 THz. To prove the viability of our concept, we monolithically integrate PIPED transmitters and receivers on a common silicon chip and use them to measure the complex transfer impedance of an integrated T-wave device.Transmitters and receivers based on plasmonic internal-photoemission detectors are developed for optoelectronic terahertz signal processing and monolithically integrated on a silicon chip. Proof-of-concept experiments are demonstrated.