Weiterentwicklungen am gepulsten Positronenstrahl und ausgewählte Anwendungen an Membranpolymeren

Im Rahmen dieser Arbeit wurde der gepulste Positronenstrahl und die zugehörige Ansteuerungselektronik weiterentwickelt, so dass jetzt auch moderne Polymere mit großen freien Volumen untersucht werden können. Diese sind besonders für die Membrantechnologie entscheidend, da sie meist über herausragende Separationseigenschaften verfügen. Einige dieser Systeme wurden zusätzlich in dieser Arbeit untersucht

Annealing behavior of open spaces in AlON films studied by monoenergetic positron beams

The impact of nitridation on open spaces in thin AlONx films deposited by a reactive sputtering technique was studied by using monoenergetic positron beams. For AlONx films with x = 0%–15%, positrons were found to annihilate from trapped states in open spaces, which coexist intrinsically in an amorphous structure with three different sizes. Nitrogen incorporation into the Al2O3 film increased the size of the open spaces, and their density increased as the post-deposition annealing temperature increased. The effect of nitrogen incorporation, however, diminished at x = 25%. The observed change in the network structure was associated with the formation of a stable amorphous structure, which we could relate to the electrical properties of AlONx/SiO2/Si gate stacks

Vacancy-type defects in Al2O3/GaN structure probed by monoenergetic positron beams

Defects in the Al2O3(25 nm)/GaN structure were probed by using monoenergetic positron beams. Al2O3 films were deposited on GaN by atomic layer deposition at 300 °C. Temperature treatment above 800 °C leads to the introduction of vacancy-type defects in GaN due to outdiffusion of atoms from GaN into Al2O3. The width of the damaged region was determined to be 40–50 nm from the Al2O3/GaN interface, and some of the vacancies were identified to act as electron trapping centers. In the Al2O3 film before and after annealing treatment at 300–900 °C, open spaces with three different sizes were found to coexist. The density of medium-sized open spaces started to decrease above 800 °C, which was associated with the interaction between GaN and Al2O3. Effects of the electron trapping/detrapping processes of interface states on the flat band voltage and the defects in GaN were also discussed

Correlation of Gas Permeability in a Metal-Organic Framework MIL-101(Cr)–Polysulfone Mixed-Matrix Membrane with Free Volume Measurements by Positron Annihilation Lifetime Spectroscopy (PALS)

Hydrothermally stable particles of the metal-organic framework MIL-101(Cr) were incorporated into a polysulfone (PSF) matrix to produce mixed-matrix or composite membranes with excellent dispersion of MIL-101 particles and good adhesion within the polymer matrix. Pure gas (O2, N2, CO2 and CH4) permeation tests showed a significant increase of gas permeabilities of the mixed-matrix membranes without any loss in selectivity. Positron annihilation lifetime spectroscopy (PALS) indicated that the increased gas permeability is due to the free volume in the PSF polymer and the added large free volume inside the MIL-101 particles. The trend of the gas transport properties of the composite membranes could be reproduced by a Maxwell model

Gold nanoparticle superlattices: structure and cavities studied by GISAXS and PALS

In this study the sizes of cavities formed within the ligand matrix of gold nanoparticle superlattices were probed using positron annihilation lifetime spectroscopy

Free volume in PEP-silica nanocomposites with varying molecular weight

The influence of confinement in polymer-nanocomposites on free volume and glass transition of the polymer chains was studied. The molecular weight (Mw) of poly(ethylene-alt-propylene) (PEP) was varied from 3k to 200k and so the end-to end distance of the chains at fixed diameter (∼15 nm) and concentration (15%) of the silica nanoparticles increased. Thus the topological confinement increases with increasing Mw. Using hydrophobic PEP and particles functionalized with short organic molecules, we can rule out contributions of permanent adsorption of the chains. DSC showed no change in glass transition temperature. The decrease in the specific heat capacity could be explained by a simple mixing rule. By positron annihilation lifetime spectroscopy, taking properly into account contributions of the silica particles, we rule out an influence of the geometrical confinement on the free volume in the PEP nanocomposites studied here

Controlled positioning of MOFs and their role in interfacially polymerized thin-film nanocomposites

status: publishe

Controlled positioning of MOFs and their role in interfacially polymerized thin-film nanocomposites

status: publishe