Sebastian Dahle

Plasma-oxidation of Ge(100) surfaces using dielectric barrier discharge investigated by metastable induced electron spectroscopy, ultraviolet photoelectron spectroscopy, and x-ray photoelectron spectroscopy

The radical oxidation of Ge(100) applying a dielectric barrier discharge plasma was investigated using metastable induced electron spectroscopy, ultraviolet photoelectron spectroscopy, and x-ray photoelectron spectroscopy. The plasma treatments were performed in a pure oxygen atmosphere as well as under environmental conditions at room temperature. In both atmospheres GeO2 layers up to thicknesses of several nm were formed on the Ge(100) surface.

Chemical improvement of surfaces. Part 2: Permanent hydrophobization of wood by covalently bonded fluoroorganyl substituents

Abstract A recently developed esterification method in our laboratory was applied to permanent hydrophobization of wood surfaces. Specifically, the covalent attachment of fluoroorganyl substituents to wood hydroxy groups via benzotriazolyl-activated, substituted benzoic acids was in focus. Weight percent gain values from 10% to 28% were obtained on Scots pine (Pinus sylvestris) sapwood veneer chips. It proved feasible to lower the temperature for wood modification from 150°C to 120°C, or even to 70°C so that thermal decomposition of wood during modification can be neglected. The modified chips were analyzed by attenuated total reflection – infrared and X-ray photoelectron spectroscopy. Covalent attachment of the fluorobenzoic acids led to a very high, permanent hydrophobicity of the wood surface, documented by outstanding contact angles of up to 143°.

Characterisation of PMMA/ATH Layers Realised by Means of Atmospheric Pressure Plasma Powder Deposition

We report on the characteristics of aluminium trihydrate filled poly(methyl methacrylate) composite (PMMA/ATH) coatings realised by plasma deposition at atmospheric pressure. For this purpose, PMMA/ATH powder was fed to a plasma jet where the process and carrier gas was compressed air. The deposited coatings were investigated by X-ray photoelectron spectroscopy and water contact angle measurements. Further, the raw material was characterised before deposition. It was found that, with respect to the raw material, aluminium was uncovered in the course of the plasma deposition process which can be explained by plasma-induced etching of the PMMA matrix. As a result, the wettability of plasma-deposited PMMA/ATH was significantly increased. Even though a uniform coating film could not be realised as ascertained by confocal laser scanning microscopy, the deposited coatings feature notably enhanced characteristics which could be advantageous for further processing.

Efficient new process for the desulfurization of mixtures of air and hydrogen sulfide via a dielectric barrier discharge plasma

The efficient removal of hydrogen sulfide, H2S, from streams of H2S in air via a dielectric barrier discharge (DBD) plasma has been investigated using a quadrupole mass spectrometer. A suitable plasma device with a reservoir for storing sorbent powder of various kinds within the plasma region was constructed. Plasma treatments of gas streams with high concentrations of hydrogen sulfide in air yielded a removal of more than 98% of the initial hydrogen sulfide and a deposition of sulfur at the surface of the dielectric, while small amounts of sulfur dioxide were generated. The presence of calcium carbonate within the plasma region of the DBD device resulted in the removal of over 99% of the initial hydrogen sulfide content and the removal of 98% of the initial sulfur dioxide impurities from the gas mixture.

Chemical improvement of surfaces. Part 4: Significantly enhanced hydrophobicity of wood by covalent modification with p-silyl-functionalized benzoates

Abstract One aim of this work was the chemical modification of surfaces of Scots pine (Pinus sylvestris L.) sapwood veneer chips by covalently bonded substances for improved hydrophobicity. The durable attachment of organosilyl moieties to the surface was in focus. Several benzotriazolyl-activated p-silylated benzoic acid derivatives were applied to the esterification of OH groups at different temperatures and reaction times. The reactions resulted in weight percent gains from 8% to 43% and corresponding quantities of covalently bonded organomaterials of 0.3–2.1 mmol g-1 wood. The hydrophobicity was significantly increased as indicated by contact angles from 121° to 142°. All modified wood samples were analyzed by attenuated total reflection-infrared, contact angle measurements, and X-ray photoelectron spectroscopy.

DBD Plasma Treatment of Titanium in O2, N2 and Air

Dielectric Barrier Discharge plasma treatment of a titanium metal foil in oxygen, nitrogen and air under atmospheric conditions is investigated employing X-Ray Photoelectron Spectroscopy (XPS). We investigated three different reference samples and compare the results with a large number of studies on the XPS analysis of titanium compounds containing oxygen and nitrogen. The plasma treatment in all three different process gases leads to the formation of titanium dioxide films, while rather small nitrogen fractions are found after nitrogen and air plasma treatments. This finding is explained basing on plasma chemistry insight from the literature.

Silver nano particle formation on Ar plasma – treated cinnamyl alcohol

Metastable induced electron spectroscopy, ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy are employed to study the adsorption of silver on cinnamyl alcohol films prepared on Au(111) substrates by thermal evaporation. Additionally, the impact of an Ar atmosphere dielectric barrier discharge plasma applied to the cinnamyl alcohol film preliminary to the Ag adsorption is investigated. In both cases silver nano particles with an average diameter of 9 nm are formed. These particles do not interact chemically with the underlying cinnamyl alcohol film. We do not find any influence of the preliminary Ar plasma-treatment on the adsorption behavior at all.

Adsorption of silver on cellobiose and cellulose studied with MIES, UPS, XPS and AFM

Metastable induced electron spectroscopy, ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy as well as atomic force microscopy were employed to study the adsorption of silver on cellulose as well as its precursor cellobiose. The formation of silver nanoparticles encapsulated by the organic film previously found for the monomer glucose is well reproduced for the dimer cellobiose. For the polymer cellulose on the other hand, no nanoparticle formation is found even though the surface is covered with silver atoms. No significant chemical interaction is found in any of these cases.

Silicon Dioxide Coating of Titanium Dioxide Nanoparticles from Dielectric Barrier Discharge in a Gaseous Mixture of Silane and Nitrogen

AbstractThe coating of titanium dioxide nanoparticles with silicon dioxide has been carried out by dielectric barrier discharge (DBD) plasma treatments to enhance the thermostability of Titania for applications at high temperature processes. During the first coating processing step, a closed film of silicon nitride was produced via plasma treatment in a gaseous mixture of silane and nitrogen, while atmospheric surface contaminations got mainly removed. In the second processing step, the DBD plasma treatment in oxygen or air was used to convert the silicon nitride mainly into silicon dioxide. Remaining carbon impurities at the interfaces between titanium dioxide and silicon nitride after the nitrogen/silane plasma treatment were subsequently removed simultaneously. Atomic force microscopy and X-ray photoelectron spectroscopy were employed to study the DBD plasma treatments of the TiO2 nanoparticles.

Quadrupole mass spectroscopy of neon

isused to carry out the experiments. All measurements wereperformed at room temperature. Neon (Linde Gas, >99.999%) isoffered via backfilling the chamber using a bakeable leak valve.The gas line is evacuated and can be heated in order to ensurecleanness. A quadrupole mass spectrometer with electron impactionization and an electron multiplier (Balzers QMS 112 A) is usedto analyse the gas composition with an overall integration time of30s per data point. During measurements, the partial pressure ofthe analysed neon gas has been chosen to be about 100 timesas big as the total pressure of the residual gas. Additionally, aspectrum of the residual gas before neon dosage has beensubtracted from the neon spectrum. All peak positions have beencorrected according to the literature values of helium and oxygen.