Marco Diegel

The morphology of silver nanoparticles prepared by enzyme-induced reduction

Summary Silver nanoparticles were synthesized by an enzyme-induced growth process on solid substrates. In order to customize the enzymatically grown nanoparticles (EGNP) for analytical applications in biomolecular research, a detailed study was carried out concerning the time evolution of the formation of the silver nanoparticles, their morphology, and their chemical composition. Therefore, silver-nanoparticle films of different densities were investigated by using scanning as well as transmission electron microscopy to examine their structure. Cross sections of silver nanoparticles, prepared for analysis by transmission electron microscopy were additionally studied by energy-dispersive X-ray spectroscopy in order to probe their chemical composition. The surface coverage of substrates with silver nanoparticles and the maximum particle height were determined by Rutherford backscattering spectroscopy. Variations in the silver-nanoparticle films depending on the conditions during synthesis were observed. After an initial growth state the silver nanoparticles exhibit the so-called desert-rose or nanoflower-like structure. This complex nanoparticle structure is in clear contrast to the auto-catalytically grown spherical particles, which maintain their overall geometrical appearance while increasing their diameter. It is shown, that the desert-rose-like silver nanoparticles consist of single-crystalline plates of pure silver. The surface-enhanced Raman spectroscopic (SERS) activity of the EGNP structures is promising due to the exceptionally rough surface structure of the silver nanoparticles. SERS measurements of the vitamin riboflavin incubated on the silver nanoparticles are shown as an exemplary application for quantitative analysis.

A New Four Bit Magnetic Domain Wall Based Multiturn Counter

A multiturn counter is proposed which is based on domain wall movement. This sensor has a true-power-on functionality and works gear-less. Due to the new design of the multiturn, the drawbacks of the former design, namely the limitation to 12 turns in maximum and a large die size, are overcome, allowing counting of up to 64 turns at reasonable die size. Parameters as the maximum frequency of the rotating field to be detected and the magnetic working window fit the demands in industrial application.

360/spl deg/ domain wall investigation for sensor applications

The stability of 360/spl deg/ domain walls is suitable for future sensor applications. We present a new idea for such a sensor based on special spin valve geometries, where 360/spl deg/ domain walls can be generated with an appropriate magnetic field and stored. Micro magnetic simulations and the first experimental structures show the feasibility of the idea. The magnetoresistive effect in our spin-valve sandwich is up to 0.5% for one 360/spl deg/ domain wall.

Multiturn Counter Using the Movement and Storage of 180

We describe a novel giant magnetoresistive (GMR) stack geometry which enables the counting of the number of turns of a rotating magnetic field. A race-track-like spiral of N turns acts as a 180deg domain-wall memory. At one end of the spiral, an enlarged film area works as a domain-wall generator. Due to the small width of the spirals themselves in the order of 100-200 nm, there is only domain-wall movement within the spiral. By rotating the magnetic field with/against the sense of the spiral, every half turn increases/decreases the number of domains by one. The number of domain walls have a one-to-one correspondence with the resistance of the spiral due to the GMR effect

^circ

Growth temperature effects on the microstructure of Nb-doped BaTiO3 thin films of the composition BaTi0.98Nb0.02O3 are studied using X-ray diffraction and transmission electron microscopy (TEM). Reciprocal space maps and electron diffraction patterns show that the a-axis lattice parameter increases and the c-axis parameter decreases with increasing growth temperature, indicating a decrease of tetragonality. Bright-field TEM images show low and high densities of threading defects in films grown at low and high temperatures, respectively. The observations are discussed in terms of a hindering of the cubic-to-tetragonal phase transition by a high defect density and a high unit cell volume.

Magnetic Domain Walls

We report on a galvanic isolated current sensor that operates on the principle of the giant magnetoresistive effect. Due to an optimized combination of uniaxial and unidirectional magnetic anisotropy of the sense layer system the sensor response is temperature independent and linear at low currents. Higher currents are measured with a reduced sensitivity. By optimizing the sensor stack a good accuracy with an error less than 0.3% is obtained in the industrial temperature range. The sensor system is capable of measuring dc, ac, and pulse currents up to 20 MHz.

Growth temperature dependence of crystal symmetry in Nb-doped BaTiO3 thin films

This article is intended to set the scope of the meeting, in particular for the high spatial resolution section

Giant Magnetoresistance-Stack Optimization for Current Sensor Application With Low Hysteresis and a Temperature-Independent Sensitivity at Low Current

We have developed a new multi-turn counter which uses magnetic 180deg domain walls for this purpose enabling the detection of up to 12 turns.