Showing papers by "Münster University of Applied Sciences published in 1998"

Field enhancement of optical radiation in the nearfield of scanning probe microscope tips

Abstract: A brief outline of the methods and approaches in the theory for field enhancement of laser radiation in the nearfield of a scanning probe microscope tips is given. The simple analytical small spheroid model (mainly used in Surface Enhanced Raman Spectroscopy) as well as a more realistic numerical model based on the boundary element method are used for field enhancement calculations on the tip apex. The small spheroid model gives a rough estimation from below for tips with spheroid geometry, whereas the numerical model can take into account arbitrary tip geometry and include the effect of substrate surface. Tremendous field concentration with nanometer localization for certain tip and substrate materials is used for applications in surface nano modification with laser radiation. Experimental data supporting the surface modification due to the enhanced field mechanism are presented.

Calculation of the field enhancement on laser-illuminated scanning probe tips by the boundary element method

Abstract: In the near field of an illuminated scanning probe tip with a dimension much smaller than a light wavelength a tremendous field enhancement is possible. This effect is similar to field enhancement on small metal particles first in- vestigated in SERS (surface-enhanced Raman spectroscopy). In this article we propose to apply the boundary element method (BEM) to calculate the electric potential and field for an arbitrary tip-sample geometry. BEM works especially well for the Laplace problem with piecewise constant mate- rial properties. We developed a simple and fast program and carried out calculations for some tip-sample configurations.

Steep central islands after myopic photorefractive keratectomy.

Abstract: Purpose: To investigate the formation of steep central islands and their reduction under modified experimental conditions. Setting: University Eye Hospital Munster and Schwind Co., Kleinosthelrn, Germany. Methods: Corneas of enucleated intact bovine eyes were treated with the Schwind Keratom. All experimental conditions were repeated six tunes in six different corneas. Eight expehrriental groups were looked at. Fluence was 180 to 200 mJ/cm2. Ablation mode (phototherapeutic keratectomy [PTK] and standard myopic photorefractive keratectomy [PRK]), internal repetition rate (3 to 30 Hz), and ablation diameter (5 to 8 mm) and depth (4 to 15 diopters [D] in PRK) were varied. Modifications to reduce or avoid steep central islands included blowing nitrogen gas and aerosol over the cornea, cleaning the cornea of fluid, and using an anticentrai-island software program. Results: In PTK, an increase in the internal repetition rate resulted in a decrease in the height of the steep central island. In standard PRK; increasing refractive correction up to −8.0 D and increasing the ablation diameter resulted in an increase in steep central island polder. The anti-central-island program, blowing aerosol, and cleaning the comea reduced the formation of steep central islands and blowing nitrogen gas eliminated them. Conclusion: Steep central islands are created by a wide-field ablation process and are probably caused by many factors. Both software and hardware modifications can be used to reduce their formation.

Nano-material processing with laser radiation in the near field of a scanning probe tip

Abstract: We report preliminary results of using a scanning probe microscope/laser combination to perform nanostructuring on insulator and metal surfaces in air. This technique enables processing of structures with a lateral resolution of approximately 10 nm. In this paper we present our last structuring results with both scanning tunnelling and scanning force microscopy. Some possible interaction mechanisms responsible for the structuring will be discussed.

Design and performance of an excimer-laser based optical system for high precision microstructuring

Abstract: We report on the design of an excimer-laser based system for high precision micromachining of spinnerets using a mask imaging technique. Both the illumination and imaging unit are optimized for specified demagnification ratios of 5 and 15, respectively. Detailed investigations were performed to measure the resolution, depth of focus and the sensitivity for the position accuracy of the substrate depending on illumination parameters. A special test mask for measuring the resolution in combination with a new definition of measurement procedure is used. SEM views of ablation results with high machining quality are presented.

Health situation of refugee children in Münster

Abstract: The unique opportunities of databased community health promotion in cooperation with local community health authorities are pointed out. Especially within the local refugee population many organisational and psychological obstacles to otherwise widely distributed health services are obvious. Population-focused community health practice involves home health care with interdisciplinary collaboration, and promotes clients's responsibility and self-care. Health promotion depends on communal health reporting focused on specific needs of subpopulations. Health and population data concerning the refugees in Muenster show a considerably higher proportion of children than among the general population of the town, thus indicating special needs for the paediatric care of this group. Communal data concerning health-relevant indicators such as vaccination rates or routine paediatric checkup coverage illustrate the necessity for improving low levels of health care for the communal refugee population. The concept of transcultural community health nursing with vice versa information about health traditions and practices improves health services and care for the refugee population and the health-related communal culture in general.

Development of Cryogenic Current Comparators with DC Squid Readout for the Calibration of Electrical Standards

Abstract: For the realization of the electrical quantum metrology triangle (V-A-Ω) a device to amplify very small currents with high precision is needed. The cryogenic current comparator (CCC) is by far the best instrument to do this. In order to make a very current sensitive CCC for calibration of electrical standards, we have developed optimum dc Superconducting QUantum Interference Devices (SQUIDs). The design, fabrication and characterisation of these devices is presented. The measurements concern the flux-to-voltage transfer and the noise properties, especially the input current noise. The optimisation of the flux transformer circuit that links the CCC with the SQUID will be treated. In addition, typical fabrication aspects of the CCC as the wires and tube assembly, the shields and the support system will be addressed.