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

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

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

Abdichtung fuer Fluid enthaltende Kammer

DE 102009048607 A1 UPAB: 20110425 NOVELTY - The sealing allows a chamber (1) to be formed in a housing (5) that comprises a gasket (6) and/or a film (7) that divides the chamber into two cavities. Channels (2-4) opened in a direction of the gasket or the film is formed in parts (5.1, 5.2) of the housing at a region around the chamber. The channels are provided on or in the gasket. Inert purging gas or fluid removed from a measuring cell is conducted through the channels in such a way that the purging gas or the fluid immediately flows along a surface of the gasket and/or of the film. USE - Sealing for determining permeation rate of a film or solid within a chamber (all claimed). Uses include but are not limited to determine permeation rate of a film or solid for selected molecules e.g. water, oxygen or methane, or atoms of substances and/or chemical elements or chemical compounds. ADVANTAGE - The inert purging gas or fluid removed from the measuring cell are conducted through the channels in such a way that the purging gas or the fluid immediately flows along the surface of the gasket and/or of the film, thus avoiding penetration of substances into the chamber, and hence providing a secure sealing of the chamber against external influences

Control of plasma process instabilities during thin silicon film deposition

Fourier transform infrared absorption spectroscopy (FTIR), optical emission spectroscopy (OES), self-bias voltage and plasma impedance controls were applied as in situ process diagnostics during the deposition of amorphous silicon thin-films. The diagnostic abilities of OES and FTIR are compared. The FTIR in-situ direct measurement of silane concentration in exhaust line is more precise than OES control. All in situ process diagnostics clearly indicates the inconsistency of plasma properties and therefore of deposition conditions. The drifts are comparable with the film deposition time. The FTIR measurement of reactant concentration in the process chamber evidence that the strong silane concentration drop (about 50%) in a plasma is the cause of the short-term drift of OES signals (SiH* emission), plasma impedance and self-bias voltage signals. The influences of the deposition chamber geometry and technological parameters on process drifts are considered. The decrease of the gas residence time in the reactor leads to a decrease of Initial Transient State phenomena. Finally, the improvement of solar cell performance based on thin silicon films is demonstrated when drifts are reduced. (C) 2009 Elsevier B.V. All rights reserved

Infrasorb: Optical detection of the heat of adsorption for high throughput adsorption screening of porous solids

The demand for fast screening methods in modern materials chemistry led to the development of a room temperature operated high-throughput tool for adsorption screening. Within five minutes a porosity screening of a large sample pool can be realized. Using a variety of different porous materials (activated carbons, porous polymers, metal-organic frameworks, zeolites) and the test gas n-butane, the reliability of the new instrument is shown. Furthermore, possible applications in the determination of n-butane capacities and BET surface areas are given as well as the application in synthesis or product control. The presented data exhibit high quality factors for the correlation of integrated signal intensity (heat of adsorption) and specific surface areas (above 0.97). As an example for the applicability of other gases that can be used with this tool, screening measurements using cyclohexane as test gas are also presented. The developed automated screening tool is an important step to overcome the bottle-neck between high-throughput syntheses technologies developed in the last decades and measurement of adsorption properties

Optisch-spektroskopische Bestimmung der Permeabilität von Ultrabarrierematerialien

Die Qualität und Haltbarkeit von Produkten (z.B. Lebensmittel, Pharmaerzeugnisse) werden im entscheidenden Maße von der Durchlässigkeit des Verpackungsmaterials gegenüber der umgebenden Atmosphäre bestimmt. Dabei spielt der Ausschluss von Feuchte und Sauerstoff aufgrund der Permeabilitätseigenschaften des Verpackungsmaterials die dominierende Rolle. Im Gegensatz zu den Permeationseigenschaften von herkömmlichen Verpackungsmaterialien stellen die transparenten und flexiblen Verkapselungen von organischen Halbleiterstrukturen, wie beispielsweise für LCD- und OLED- Displays, eine wesentlich größere Herausforderung dar. Für einen stabilen Langzeitbetrieb werden Wasserdampfdurchlässigkeiten von bis zu 10-6 g/(m2 d) gefordert, wobei für LCD-Systemen diese um mindestens zwei Größenordungen und bei OLEDs diese um mindestens 5 Größenordnungen unter denen von Standardverpackungen liegen. Zur Entwicklung, Optimierung und Qualitätskontrolle der entsprechenden Barriereschichtsysteme bzw. deren Herstellungsprozesse ist ein hochempfindliches Messsystem zur Bestimmung niedrigster Permeationsraten erforderlich, welches zudem eine möglichst einfache, schnelle und kostengünstige Messung der Permeationsrate ermöglicht. Ein auf Basis der Laserdiodenspektroskopie entwickeltes Permeationsmesssystem ermöglicht eine signifikante Verbesserung der Nachweisempfindlichkeit um bis zu zwei Größenordnungen im Vergleich zu derzeit kommerziell verfügbaren Messsystemen. Im Mittelpunkt der Entwicklungsarbeiten standen dabei Fragen zur Konditionierung des Messsystems, zum Erreichen stabiler Gleichgewichtszustände bei statischem und dynamischem Betrieb, bzw. zu den daraus abgeleiteten Messbedingungen und Auswertalgorithmen. Des Weiteren wird das Messsystem hinsichtlich Zuverlässigkeit der Messergebnisse und der Reproduzierbarkeit der für Ultrabarriereschichten kritischen Folieneinspannung diskutiert

Continuous coating of ceramic fibres by industrial-scale laser driven CVD: fibre modification and structure of interfaces

A laser induced chemical vapour deposition process (L-CVD) has been developed to treat and coat ceramic fibre bundles. This method is characterised by several advantages, among them high deposition rates and very short residence times of the fibres in the deposition chamber. Laser irradiation of SiC based fibres has been found to result in strong structural changes due to recrystallisation accompanied by evolving gaseous SiO and CO. The deposition of thin py-C layers shifts this thermal SiC fibre degradation process to significantly higher power densities, which results in coated fibres without degradation. With CH4 as precursor, layers of highly ordered pyrolytic graphite have been deposited on Nicalon fibres

FTIR monitoring of industrial scale CVD processes

Chemical vapour deposition (CVD) as well as infiltration (CVI) processes are key technologies in many industrial sectors, including extensive use in micro electronics, surface protection of components, for energy efficient optical coatings on glass for buildings and for manufacturing fibre reinforced ceramic composite materials. Gaseous precursors containing the elements to be deposited are pyrolysed at the heated substrate or, alternatively, by exciting the molecules with laser photons or by a plasma. Although the techniques are used on a technological scale, the underlying chemistry is not completely understood. The goal of the presentation is to improve CVD process control by a multipurpose, knowledge based feedback system for monitoring the CVD/CVI process with in-situ FTIR spectroscopic data as input information. In the presentation, three commonly used, and distinctly different, types of industrial CVD/CVI processes are taken as test cases: (i) a thermal high capacity CVI batch p rocess for manufacturing carbon fibre reinforced SiC composites for high temperature applications, (ii) a continuously driven CVD thermal process for coating float glass for energy protection, and (iii) a laser stimulated CVD process for continuously coating bundles of thin ceramic fibres (i) The CVI process operates near 1000oC, in the low pressure region and with CH3SiCl3 (MTS) as a SiC precursor. Using FTIR emission spectroscopy, several gaseous species have been detected including MTS, SiCl2, (SiCl3)n=1,2, SiCl4, HSiCl3, CH4, CH3Cl and HCl which, consequently, can be monitored simultaneously. (ii) The CVD process operates at atmospheric pressure. A model reactor has been developed for studying the concentration dependence of FTIR emission spectra. The measured spectra are compared with calculated spectra which have been derived by optical modelling of a multilayer based optical model. (iii) Based on an industrial 6kW cw-CO2- laser, a laser driven process currently runs in a prototy pe coater. Layers of graphitisised carbon and several ceramic materials (SiC, TiCxNy, TiB2, BN, etc.) have been deposited on carbon fibres and on SiC fibres. Depending on the selected precursor, the chemistry of the laser driven CVD process is characterised by photothermal reaction paths, typically in the temperature region 1300oC -2500oC and photolytical paths. The FTIR measurements have been carried out by rapid extraction of the gaseous reaction products and measurements in an optimised volume gas cell. As an example, the deposition of SiC layers from MTS results in the detection of HCl, HSiCl3, H2SiCl2, SiCl2, CH4, CO and C2H2