46 research outputs found
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Graphene integrated optical biosensor for detection of breast cancer cell media
No full textIn situ monitoring of the etching of thin silicon oxide films in diluted NH4F by IR ellipsometry
No full textInfrared spectroscopic ellipsometry IRSE was applied for monitoring of the etching process of electrochemically formed silicon oxides 11.5 nm and 3.8 nm in diluted NH4F solution. Quantitative evaluations of ellipsometric spectra deliver the time dependent thicknesses of the oxide films during the etch process and therefore their etch rates. From interpretation of IRSE spectra it is concluded that no longitudinal optical phonon LO of the silicon oxide stretching vibration is contributing to the IR absorption of electrochemically prepared silicon oxide film
Fiber optic lossy mode resonance sensors for chemical sensing
No full textThis work presents the fabrication and characterization of a fiber optic gas sensor utilizing Lossy Mode Resonances (LMR) achieved with a nanoscale polyphenylene oxide (PPO) coating. The PPO coating is applied to the cladding removed region of a multi-mode silica fiber, simultaneously serving as both the LMR support layer and the sensing material. The PPOcoated LMR sensor is exposed to various concentrations of ammonia as a case study. The sensor demonstrates a high sensitivity of 0.25 nm/ppm within the ammonia concentration range of 2.5 to 37.5 ppm. These results highlight the potential of this PPO-based fiber optic sensor for efficient and sensitive detection of hazardous compounds in different settings, ranging from medical to industrial
Surface enhanced infrared absorption Infrared ellipsometry of Au evaporated ultrathin organic films
No full textThe presented Infrared IR ellipsometric study proves the high potential of this method for quantitative interpretation of the SEIRA Surface Enhanced Infrared Absorption effect in infrared spectra on base of optical layer models incorporating effective medium theory. The IR ellipsometric measurements of gold capped ultrathin nitrobenzene NB films on Si 111 show different line shapes compared to those of the non modified thin NB films. Additionally a strong enhancement of the amplitudes of vibrational bands due to the SEIRA effect is observed. In comparison to vibrational bands of the film without gold on top an enhancement factor of about 5 7 is determined for the stretching vibrations of the NO2 head group of the NB molecules. Experimental results are compared to optical simulations for the NB film with and without gold islands. The observed band shapes can be explained qualitatively by optical simulations for a 3 nm thick NB film with a volume fraction of gold which is close to the percolation border of the film. For simulation of the pure NB film a simple optical layer calculation was used, whereas for Au evaporated films a Bruggeman model for ellipsoids with an effective medium shell was use
Studies of electrochemically grafted thin organic layers on inorganic surfaces with infrared spectroscopic ellipsometry
No full textIn this contribution we present IR spectroscopic ellipsometry IRSE measurements of electrochemically grafted organic films down to monolayer thickness. Formation of organic layers of 4 methoxybenzene anisole on TiO2, Au and Si 111 surfaces was confirmed from observation of respective absorption bands in the ellipsometric spectra. Orientation of molecules in a thin film on Au surface and in a thick film grafted on a TiO2 substrate is discussed. For silicon substrates, oxidation was found to be a main side reaction and could be investigated by inspection of the silicon oxide related bands in the IRSE spectra. The presented results outline the high potential of IRSE for technologically relevant studies of interfacial structures and thin film propertie
Electronic and surface properties during the etch back of anodic oxides on Si 111 surfaces in 40 NH4F solution
No full textAn etch back procedure of anodically oxidized Si 111 surfaces was investigated by photoluminescence, photo voltage, atomic force microscopy and infrared spectroscopic ellipsometry. The first step was the preparation of an H terminated Si surface in diluted HF solution. The second step was the formation of an anodic oxide layer at different potentials in 40 NH4F solution followed by an oxide etching in the same solution leading to an H passivated Si surface. The in situ monitoring of the photoluminescence intensity and photo voltage amplitude allows the investigation of interface recombination and surface charging at the different steps of preparation. The experimental results are discussed with respect to oxide thickness, surface roughness and interface defect concentratio
