In-situ monitoring for CVD processes

Aiming towards process control of industrial high yield/high volume CVD reactors, the potential of optical sensors as a monitoring tool has been explored. The sensors selected are based on both Fourier transform infrared spectroscopy (FTIR) and tunable diode laser spectroscopy (NIR-DLS). The former has the advantage of wide spectral capability, and well established databases. NIR-DLS spectroscopy has potentially high sensitivity, laser spatial resolution, and the benefits of comparatively easier integration capabilities-including optical fibre compatibility. The proposed technical approach for process control is characterised by a 'chemistry based' feedback system with in-situ optical data as input information. The selected optical sensors continuously analyze the gas phase near the surface of the growing layer. The spectroscopic data has been correlated with process performance and layer properties which, in turn establish data basis for process control. The new process control approach is currently being verified on different industrialised CVD coaters. One of the selected applications deals with the deposition of SnO2 layers on glass based on the oxidation of (CH3)2SnCl2, which is used in high volume production for low-E glazing

Neandertal and Denisovan DNA from Pleistocene sediments.

Although a rich record of Pleistocene human-associated archaeological assemblages exists, the scarcity of hominin fossils often impedes the understanding of which hominins occupied a site. Using targeted enrichment of mitochondrial DNA we show that cave sediments represent a rich source of ancient mammalian DNA that often includes traces of hominin DNA, even at sites and in layers where no hominin remains have been discovered. By automation-assisted screening of numerous sediment samples we detect Neandertal DNA in eight archaeological layers from four caves in Eurasia. In Denisova Cave we retrieved Denisovan DNA in a Middle Pleistocene layer near the bottom of the stratigraphy. Our work opens the possibility to detect the presence of hominin groups at sites and in areas where no skeletal remains are found

Biotransformation of lanthanum by Aspergillus niger

Lanthanum is an important rare earth element and has many applications in modern electronics and catalyst manufacturing. However, there exist several obstacles in the recovery and cycling of this element due to a low average grade in exploitable deposits and low recovery rates by energy-intensive extraction procedures. In this work, a novel method to transform and recover La has been proposed using the geoactive properties of Aspergillus niger. La-containing crystals were formed and collected after A. niger was grown on Czapek-Dox agar medium amended with LaCl 3. Energy-dispersive X-ray analysis (EDXA) showed the crystals contained C, O, and La; scanning electron microscopy revealed that the crystals were of a tabular structure with terraced surfaces. X-ray diffraction identified the mineral phase of the sample as La 2(C 2O 4) 3·10H 2O. Thermogravimetric analysis transformed the oxalate crystals into La 2O 3 with the kinetics of thermal decomposition corresponding well with theoretical calculations. Geochemical modelling further confirmed that the crystals were lanthanum decahydrate and identified optimal conditions for their precipitation. To quantify crystal production, biomass-free fungal culture supernatants were used to precipitate La. The results showed that the precipitated lanthanum decahydrate achieved optimal yields when the concentration of La was above 15 mM and that 100% La was removed from the system at 5 mM La. Our findings provide a new aspect in the biotransformation and biorecovery of rare earth elements from solution using biomass-free fungal culture systems. </p

A method for checking homogeneity of subsurface regions by variable angle ATR: Experiments on polymers vs. optical modelling

The subsurface structure of many technically applied materials is characterised by alterations of the composition (swelling or surface reactions on polymers, leaching of glasses etc.). The same situation holds for coated materials where graded layers are more or less typical with the gradient strongly influencing the materials properties. The attenuated total reflection (ATR) spectroscopy is a powerful tool for analysing such surface regions. Because of problems with optical contact the ATR method is difficult to handle in practise. Based on variable angle ATR - FTIR spectroscopy a straightforward method has been established which can detect compositional inhomogeneities in subsurface regions or across layers. The method works as follows: (i) making ATR measurements at two different angles of incidence without changing sample, (ii) normalising the ATR absorbance spectra by using an appropriate band of the substrate as an internal standard, (iii) making difference spectra of the normali sed spectra. In the case of a homogeneous material the difference spectrum virtually vanishes whereas in the case of an inhomogeneous surface region the difference spectrum reflects the compositional gradient. Clearly, the method is only applicable to samples and ATR configurations where the penetration depth for both angles of incidence is higher than layer thickness. Furtheron, the substrate band used as an internal standard must be within the linear absorbance range and should exhibit a low structural sensitivity. The method has been tested at polyamid -12 foils: (a) coated by methacrylate layers, (b) plasma treated, and (c ) leached by a surface treatment with solvents. More detailed results are presented. The experimental findings have been supported by spectra modelling. Based on an optical multilayer model the ATR spectra of a homogeneous polymer and of the same material with a slightly altered surface layer have been calculated for different angles of incidence and the two pola risations. By applying steps (ii) to (iii) the experimental results are confirmed. In conclusion, the test method show some significant advantages in comparison with common ATR handling techniques: The method can be applied on one test specimen, there is no need for any reference material. The measurements are carried out by only changing the angle of incidence, without any additional sample preparation or optical re-adjustments

FTIR investigations and modelling. Application to carbon fibre composites

The application of specular reflectance FTIR spectroscopy for the investigation of carbon fiber reinforced epoxy composites is discussed. The use of the general 4 x 4 matrix algorithm allows to determine the dielectric functions of the sample parallel and perpendicular to the optical axis. The parallel component shows a Drude like spectral behaviour of the carbon fiber, and the perpendicular component is mainly determined by the polyme

Laser based coating and modification of carbon fibres: Application of industrial lasers to manufacturing of composite materials

For high temperature applications of fibre reinforced ceramic composites, the adhesion, and chemical reactions at the fibre-matrix interface, has to be engineered by coating the fibres. Based on a technological 5 kW cw-CO2 laser, an atmospheric pressure laser assisted CVD process has been established performing a continuous high rate coating of carbon fibre rovings. Layers of pyrolytic carbon have been deposited from CH4 with a rate of 0.6 μm/s, which enhances the tensile strength and Weibull modulus of fibres. The design of the LCVD reactor and the optimization of its operational conditions are supported by computational fluid dynamics techniques. The gas flow dynamics, concentration of species and heat tranfer in the reaction chamber have been calculated. Within the symmetrical chamber a flow regime is established with a free standing laminar gas flow around the fibre tape which shields the reaction zone against purge gases. The diffusion limited deposition rate of this configuration is estimated. The influence of laser irradiation on mechanical properties and structure of the carbon fibres have been checked by tensile (bundle) testing, SEM/EDX, XRD and Raman spectroscopy. The detected changes indicate a complex dependence on irradiation time, laser power and gaseous ambient

FTIR based process control for industrial reactors

Aiming to process control of industrial high yield / high volume CVD reactors, the potential of Fourier transform infrared spectroscopy (FTIR) has been checked as a monitoring tool. Tin oxide deposition on glass by oxidation of dimethyl tin dichlorid in a cold-wall thermal CVD reactor was selected as test case. Four different FTIR monitoring modes have been evaluated and found feasible : transmission, (gas) emission, reflection and surface emission. The most detailed information of the composition of the gas atmosphere in the deposition zone is derived from the transmission and (gas) emission measurements. The emission mode is best suited for high temperature CVD reactors, needs only low effort for optical adaptation of the monitoring system but higher effort in data treatment for process control. Information on both gas composition and surface layer are derived from the reflection and the surface emission modes. Depending on the polarization state of the surface emission, spectra contain information either on the sample surface only or on the reacting gas phase, too