Axel Schindler

Killing of adherent oral microbes by a non-thermal atmospheric plasma jet

Atmospheric plasma jets are being intensively studied with respect to potential applications in medicine. The aim of this in vitro study was to test a microwave-powered non-thermal atmospheric plasma jet for its antimicrobial efficacy against adherent oral micro-organisms. Agar plates and dentin slices were inoculated with 6 log(10) c.f.u. cm(-2) of Lactobacillus casei, Streptococcus mutans and Candida albicans, with Escherichia coli as a control. Areas of 1 cm(2) on the agar plates or the complete dentin slices were irradiated with a helium plasma jet for 0.3, 0.6 or 0.9 s mm(-2), respectively. The agar plates were incubated at 37 degrees C, and dentin slices were vortexed in liquid media and suspensions were placed on agar plates. The killing efficacy of the plasma jet was assessed by counting the number of c.f.u. on the irradiated areas of the agar plates, as well as by determination of the number of c.f.u. recovered from dentin slices. A microbe-killing effect was found on the irradiated parts of the agar plates for L. casei, S. mutans, C. albicans and E. coli. The plasma-jet treatment reduced the c.f.u. by 3-4 log(10) intervals on the dentin slices in comparison to recovery rates from untreated controls. The microbe-killing effect was correlated with increasing irradiation times. Thus, non-thermal atmospheric plasma jets could be used for the disinfection of dental surfaces.

Removing Biofilms from Microstructured Titanium Ex Vivo: A Novel Approach Using Atmospheric Plasma Technology

The removal of biofilms from microstructured titanium used for dental implants is a still unresolved challenge. This experimental study investigated disinfection and removal of in situ formed biofilms from microstructured titanium using cold atmospheric plasma in combination with air/water spray. Titanium discs (roughness (Ra): 1.96 µm) were exposed to human oral cavities for 24 and 72 hours (n = 149 each) to produce biofilms. Biofilm thickness was determined using confocal laser scanning microscopy (n = 5 each). Plasma treatment of biofilms was carried out ex vivo using a microwave-driven pulsed plasma source working at temperatures from 39 to 43°C. Following plasma treatment, one group was air/water spray treated before re-treatment by second plasma pulses. Vital microorganisms on the titanium surfaces were identified by contact culture (Rodac agar plates). Biofilm presence and bacterial viability were quantified by fluorescence microscopy. Morphology of titanium surfaces and attached biofilms was visualized by scanning electron microscopy (SEM). Total protein amounts of biofilms were colorimetrically quantified. Untreated and air/water treated biofilms served as controls. Cold plasma treatment of native biofilms with a mean thickness of 19 µm (24 h) to 91 µm (72 h) covering the microstructure of the titanium surface caused inactivation of biofilm bacteria and significant reduction of protein amounts. Total removal of biofilms, however, required additional application of air/water spray, and a second series of plasma treatment. Importantly, the microstructure of the titanium discs was not altered by plasma treatment. The combination of atmospheric plasma and non-abrasive air/water spray is applicable for complete elimination of oral biofilms from microstructured titanium used for dental implants and may enable new routes for the therapy of periimplant disease.

Destruction of oral biofilms formed in situ on machined titanium (Ti) surfaces by cold atmospheric plasma

The decontamination of implant surfaces represents the basic procedure in the management of peri-implant diseases, but it is still a challenge. The study aimed to evaluate the degradation of oral biofilms grown in situ on machined titanium (Ti) discs by cold atmospheric plasma (CAP). ∼ 200 Ti discs were exposed to the oral cavities of five healthy human volunteers for 72 h. The resulting biofilms were divided randomly between the following treatments: CAP (which varied in mean power, treatment duration, and/or the gas mixture), and untreated and treated controls (diode laser, air-abrasion, chlorhexidine). The viability, quantity, and morphology of the biofilms were determined by live/dead staining, inoculation onto blood agar, quantification of the total protein content, and scanning electron microscopy. Exposure to CAP significantly reduced the viability and quantity of biofilms compared with the positive control treatments. The efficacy of treatment with CAP correlated with the treatment duration and plasma power. No single method achieved complete biofilm removal; however, CAP may provide an effective support to established decontamination techniques for treatment of peri-implant diseases.

Ion beam and plasma jet etching for optical component fabrication

Ion beam figuring (IBF) using inert gas (e.g. Ar) and (Reactive) ion beam etching [(R)IBE] gain growing interest in precision optical surface processing, RIBE mainly for proportional transfer of 3D-resist masks structures in hard optical materials and IBF for finishing and nanometer precision surface figuring in high performance optics technology. Ion beam and plasma jet etching techniques related to different optical surface figuring requirements have been developed at IOM during the last decade. Some of these techniques have been proven to be mature for application in industrial production. The developmental work include material related process tuning with respect to enhance the processing speed and to improve surface roughness and waviness, further various processing algorithms related to different surface figure requirements and processing related equipment modification. Plasma jet assisted chemical etching is under development with respect to efficient machining techniques for precision asphere fabrication. The paper gives an overview of precision engineering techniques for optical surface processing focusing on the status of ion beam and plasma techniques. The status of the proportional transfer of 3D micro-optical resist structures (e.g. micro-lens arrays, blazed fresnel lens structures) into hard optical and optoelectronic materials by (reactive) ion beam etching will be summarized.

Finishing procedure for high-performance synchrotron optics

Modern synchrotron radiation sources of the 3rd generation like BESSY II, Spring-8 and others with their high brilliance beam characteristics need very high quality optics to exploit the full power of this radiation. For the grazing incidence reflecting type of that optics (flat, spherical or aspherical) besides roughness the slope deviation error is the most important spec, which has to be improved to meet the present and future performance requirements. Together with partners from industry we investigate and develop on the one hand surface figuring and polishing techniques for final finishing by using mainly ion beam milling technology and on the other hand we improve and make use of the combination of the surface shape measurements by means of interferometry, long trace and auto-collimation profilometry. We aim to achieve the following slope deviation errors on silicon optical elements: flat surface 310 mm long 0.03 arcsec rms, flat surface 100 mm long 0.02 arcsec rms and elliptical cylinder surface 210 mm long 0.1 arcsec rms. This is a five to ten-fold improvement compared to the present state of the art in production. To achieve the demanding specification it is necessary to measure and to deterministically machine the surface over a wide range of spatial wavelength down to the sub-millimeter range. In depth scale the sub-nanometer shape error level has to be achieved. The roughness of about 0.2 nm rms has not to be increased during the shape finishing.

Advanced metrology: an essential support for the surface finishing of high performance x-ray optics

The performance of x-ray beamlines at 3rd generation synchrotron radiation sources and Free Electron Lasers (FELs) is limited by the quality of the state of the art optical elements. Proposed FEL beamlines require optical components which are of better quality than is available from the optical manufacturing technology of today. As a result of a joint research project (Nanometer Optik Komponenten - NOK) coordinated by BESSY, involving both metrologists and manufacturers it is possible now to manufacture optical components beyond the former limit of 0.1 arcsec rms slope error [1, 2]. To achieve the surface finishing of optical components with a slope error in the range of 0.04 arcsec rms (for flat or spherical surfaces up to 300 mm in length) by polishing and finally by ion beam figuring technology it is essential that the optical surface be mapped and the mapping data used as input for the multiple ion beam figuring stages. Metrology tools of at least five times superior accuracy to that required of the component have been developed in the course of the project. The Nanometer Optical Component measuring Machine (NOM) was developed at BESSY for line and area measurements of the figure of optical components used at grazing incidence in synchrotron radiation beamlines. Surfaces up to 730 cm2 have been measured with the NOM a measuring uncertainty in the range of 0.01 arcsec rms and a correspondingly high reproducibility [3]. Three dimensional measurements were used to correct polishing errors some nanometers high and only millimeters in lateral size by ion beam treatment. The design of the NOM, measurement results and results of NOM supported surface finishing by ion beam figuring will be discussed in detail. The improvement of beamline performance by the use of such high quality optical elements is demonstrated.

Precision optical asphere fabrication by plasma jet chemical etching (PJCE) and ion beam figuring

We develop a Plasma Jet Chemical Etching (PJCE) technique for high rate precision machining of optical materials aiming in a technology mature for precision asphere and free-form surface topology fabrication. The present contribution summarizes the achievements after about twelve months experience with a prototype production tool facility. PJCE is performed with the help of a microwave driven reactive plasma-jet working in a broad pressure range (10-600 mbar). We developed a moveable lightweight microwave plasma jet source for dwell time techniques performed in a roughly pumped process chamber equipped with a six axis system for precision workpiece and plasma source movement. Volume etch rates of some 10 mm3/min have been achieved for fused silica and silicon, respectively, using reactive (CF4,SF6,O2) and inert (Ar,He) gas mixtures and applying a microwave (2.45 GHz) power in the 100-200 W range. Large quartz plates (80-160 mm) have been figured using dwell time methods to achieve aspheric deformations of some 10 micrometers . The figured surfaces show shape errors of 1-2 micrometers and a microroughness of 50-100 nm RMS but no sub-surface damage enabling a small tool shape conserving post polishing up to the sub-nanometer roughness level. Thus, surface shaping to the nanometer error range can be done by ion beam finishing.

Ion Beam Figuring of Strongly Curved Surfaces with a (X, Y, Z) Linear Three-Axes System

Ion beam figuring of strongly curved surfaces using small spot beam and a three linear axes motion system and taking the ion incidence etch rate dependence into account in the process modeling has been developed.

Stitching interferometry of aspherical surfaces

Sub-aperture stitching interferometry (SASI) is an appropriate method to measure either large optical plane surface topologies or aspheres with strong deviation from the flatness with standard interferometers. Using SASI the surface shape is measured with a higher lateral resolution by multiple adjacent sub-aperture measurements with a sufficient overlap of the neighboring areas. In a second step, the total surface shape is composed with the help of a computer code by stitching the sub-aperture areas together. The overlap areas allow fitting. By means of a regression analysis, tilt and vertical displacement of adjacent areas are calculated and minimized. A confidence band calculated using a MATLAB based code describes the accuracy of the composition. The variance of this estimation is inverse proportional to the peak to valley value (PV) of the measured area and decreases with a 10-3 scaling of the width of the overlapping area. A statistical experimental design method is used to minimize the number of sub-apertures to be measured. The accuracy of the stitched total surface measurement can be increased with the help of model calculations by optimizing (i) the position of the sub-aperture, which was regarded as a standard, and (ii) the sequence of the stitched adjacent areas.

Ion beam figuring of SiC mirrors provides ultimate WFE performances for any type of telescope

Matra Marconi Space (MMS) has designed, manufactured and tested a (Phi) 200 mm aspherical mirror to (lambda) /100 rms WFE for the purpose of a telescope demonstrator which both structure and mirrors are made from sintered Silicon Carbide. This outstanding performance has been achieved through a coordinated R and D program with the Insitut fuer Oberflaechen Modifizierung for the mastering of all the figuring aspects of any sintered Silicon Carbide telescope mirrors based on Ion Beam Figuring.