Karin Sahre

Ion-beam induced chemical and structural modification in polymers

In order to increase the sensitivity to moisture uptake of polyimide (PI) and polyethersulfone films applied in bimorphic humidity sensors 50, 130 and 180 keV boron ions with irradiation doses between 1013 and 1016 B+/cm2 were implanted. A complex investigation of the following features has been carried out: chemical changes in the surface regions by attenuated total reflection–FTIR spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS); optical properties by spectroscopic ellipsometry; hardness and elastic modulus by depth-sensing low-load indentation technique; conductivity of modified polymer films. It could be shown, that the partial destruction of chemical bonding under ion bombardment leads to the creation of new amorphous and graphite-like structures, which increase the surface film conductivity by several orders of magnitude, and enhances the sensitivity of these polymer films to moisture uptake. The ion-beam irradiation destroys the anisotropic features of the refractive index of PI layers leading to its isotropization. Radiation-induced changes in the layer structure result in an increase of the hardness and elastic modulus of the modified layers up to ten and six times, respectively. The hardness and refractive index depth profiles were determined. The detectable effective modification depth estimated from the depth profiles is 250–300 nm at an ion energy of 50 keV and 400–450 nm at an ion energy of 180 keV.

Palladium‐Catalyzed Chain‐Growth Polycondensation of AB‐type Monomers: High Catalyst Turnover and Polymerization Rates

Chain-growth catalyst-transfer polycondensations of AB-type monomers is a new and rapidly developing tool for the preparation of well-defined π-conjugated (semiconducting) polymers for various optoelectronic applications. Herein, we report the Pd/PtBu3-catalyzed Negishi chain-growth polycondensation of AB-type monomers, which proceeds with unprecedented TONs of above 100,000 and TOFs of up to 280 s(-1). In contrast, related AA/BB-type step-growth polycondensation proceeds with two orders of magnitude lower TONs and TOFs. A similar trend was observed in Suzuki-type polycondensation. The key impact of the intramolecular (vs. intermolecular) catalyst-transfer process on both polymerization kinetics and catalyst lifetime has been revealed.

Characterization of ion-beam modified polyimide layers

Thin chemically modified polyimide films are widely used as functional layers for new microelectronic sensors. Modification of the chemistry of these polymers can lead to different mechanical, optical and electrical properties. Ion implantation is a preferred method to modify polyimide structures. In this work the ion-induced changes of chemical structures of three polyimides were analyzed by attenuated total reflection. Fourier transform infrared spectroscopy (ATR-FTIR); X-ray photoelectron spectroscopy (XPS); Raman spectroscopy; and spectroscopic ellipsometry and atomic force microscopy (AFM). The results indicate that during the implantation process the imide structures were partly destroyed. Carbon-rich, graphite-similar and amorphous structures were formed in the surface-near area of the polyimide layers. The changes in molecular structures especially depend on the dose of implanted boron ions.

Swelling behavior of thin anisotropic polymer layers

The swelling of thin anisotropic aromatic polymer films in microelectronic devices and micromechanical systems can lead to significant reliability problems. Polymer swelling is caused by the reversible sorption of gas molecules such as water or volatile organic compounds in the polymer. In this paper, we investigate the relationship between the number of sorbed molecules and the resulting anisotropic volume expansion, with particular focus on in-plane-stress and out-of-plane expansion. Based on analytical and phenomenological studies of the polymer-gas interactions we have developed a model describing the microphysical mechanisms of sorption and swelling. The model is valid for a variety of gases and polymers, the chemical and structural properties of which are available in the literature or may be measured directly.

Influence of ion-beam induced chemical and structural modification in polymers on moisture uptake

Abstract Polyimide thin films are a promising material for microelectronics and aerospace applications. In particular, they are sensitive to moisture and gas uptake. This leads to film swelling which may be monitored by a corresponding change in piezoresistance caused by plate bending of a polymer–silicon double-layer or bimorphic sensor, respectively. However, the expansion of the polymer, induced by moisture or gas uptake, can usually be influenced by surface ion-beam modification. By this, the selectivity to a partial gas may be enhanced or decreased. In this work, the influence of ion-beam induced surface modification on both polymer structure and moisture uptake of polyimide and polyethersulfone is investigated. To modify the polymer layer surface boron ions were implanted with energies from 50 to 180 keV and irradiation doses between 1013 and 1016 B+/cm2. It could be shown that increase of irradiation dose leads partly to a destruction of the imide and aromatic groups. The aromatic structure is degraded by hydrogen abstraction. This corresponds to the creation of a new amorphous and graphite-like structure, which increases the modified surface film conductivity by several orders of magnitude, and which decreases the Freundlichs coefficient of the moisture-uptake behaviour.

Mechanical stress in micromachined components caused by humidity-induced in-plane expansion of thin polymer films

Thin polymer films have found widespread application in silicon-based microelectronic devices and micromechanical systems due to their unique material properties. When exposed to ambient humidity, polymers tend to expand due to the uptake of moisture in the film. In most microelectronic applications, this characteristic is rather undesirable due to associated reliability problems. We have investigated humidity-dependent mass uptake and expansion for a range of polymers at room temperature and have found that the isotherms are generally nonlinear. Based on the obtained relationships, the polymer process can be optimized in view of reduced mass uptake and reduced mechanical stress in the polymer. Results are given for polyimide P12540. Both mass uptake and swelling can be approximated by a linear humidity dependence with an error of about 10%. Based on these results, the empirical quantities swelling ratio and stress coupling factor are defined, and linearized sorption parameters are discussed.

Phosphorus-containing Polysulfones - A Comparative Study

A comparative study of the influence of 2-(10-oxo-10H-9-oxa-10λ 5-phosphaphenanthrene10-yl)-benzene-1,4-diol (DOPO-HQ) and 2-(2,8-dimethyl-10-oxo-10H-10λ 5-phenoxaphosphine-10-yl)benzene-1,4-diol (DPPO-HQ) on their ability to form polysulfones (PSU) with 4,4′ -difluorodiphenylsulfone (DFDPS) as well as the properties of the aromatic phosphorus-containing polysulfones (P-PSU) is reported. These properties are also compared to bisphenol A-based polysulfone. Both diols have the phosphorus unit as substituent and differ in the number of oxygen atoms within the environment of the phosphorus changing from DOPO-HQ (phosphinate structure, Ar2 OP(=O)) to DPPO-HQ (phosphine oxide structure, Ar3PO). The nucleophilic aromatic polycondensation was carried out successfully using both phosphorus-containing aromatic diols instead of bisphenol A and was followed by ATR-FTIR in-line monitoring. The use of DPPO-HQ decreased the number of side reactions and enhanced slightly the molecular weight. The thermal stability of DPPO-HQ-based PSU is slightly better than DOPO-HQ-based PSU. Thermal decomposition schemes for PSU and for both P-PSUs are proposed based on thermogravimetric analysis and Pyrolysis GC-MS results.

Facile synthesis of oligo(3-hexylthiophene)s conductive wires with charge-transfer functions

A series of fully conjugated oligo(3-hexylthiophene)s bearing different starting- and end-groups have been synthesized by means of externally initiated Kumada catalyst-transfer polymerization (KCTP) and Grignard Metathesis Polymerization (GRIM). These kinds of oligomers’ starting- and end-groups include tert-butyl protected thiols to be used for binding of oligomers to gold electrodes and tetracyanobutadiene-based donor–acceptor (DA) end-groups, such as dimethylaniline-tetracyanobutadiene (DMA-TCBD) and ferrocene-tetracyanobutadiene (Fc-TCBD), introduced to control the charge transport through the oligomers. The DMA-TCBD and Fc-TCBD end groups were incorporated by means of a Diederich-type click transformation of appropriately end-terminated oligo(3-hexylthiophene)s. The efficiency of the end-group functionalization was comprehensively assessed by NMR spectroscopy and MALDI-TOF spectrometry whereas the redox activities of the DA end-groups were examined by cyclic voltammetry. KCTP showed a much superior performance compared to GRIM in the introduction of a desirable end-group functionality. The thus-prepared conjugated oligomers are attractive materials for application in molecular electronics which will be explored in future studies.

Interactions of Nitroxide-Conjugated and Non-Conjugated Glycodendrimers with Normal and Cancer Cells and Biocompatibility Studies

Poly(propyleneimine) glycodendrimers fully modified with maltose units were administered to different cancer cell lines and their effect on cell viability was evaluated by using MTS assay and flow cytometry. The mechanism of dendrimer-cell interactions was investigated by the electron paramagnetic resonance (EPR) technique by using a new nitroxide-conjugated glycodendrimer. The nitroxide groups did not modify both the biological properties (cell viability and apoptosis degree) of the dendrimers in the presence of the cells and the dendrimer-cell interactions. Since this class of dendrimers is already known to be biocompatible for human healthy cells, noncancer cells such as human peripheral blood mononuclear cells (PBMCs) and macrophages were also treated with the glycodendrimer, and EPR spectra of the nitroxide-conjugated glycodendrimer were compared for cancer and noncancer cells. It was found that this dendrimer selectively affects the cell viability of tumor cells, while, surprisingly, PBMC proliferation is induced. Moreover, H-bond-active glycodendrimer-cell interactions were different for the different cancer cell lines and noncancer cells. The nitroxide-conjugated glycodendrimer was able to interact with the cell membrane and eventually cross it, getting in contact with cytosol antioxidants. This study helps to clarify the potential anticancer effect of this class of dendrimers opening to future applications of these macromolecules as new antitumor agents.

The chemical structure and stability of plasma-deposited thin hydrocarbon layers on polyethylene

AbThe surfaces of polyethylene (PE) films were modified by deposition of layers from acetylene/ethylene monomer gases in a low-pressure radio-frequency plasma. The chemical structure of the plasma-deposited layers and their long-term stability were studied by X-ray photoelectron spectroscopy (XPS), attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, and contact angle measurements. These studies have shown that the plasma-deposited layers consist mainly of amorphous, short-chain, functional CxHy structures with aryl units. As the reactive radical centers formed during the plasma process are susceptible to further reaction with atmospheric oxygen and water, the chemical stability of these layers was investigated. This stability is ensured over the long-term, although an increase in the number of functional groups is obtained over time. It was demonstrated that the post-reactions reach a state of equilibrium after a few weeks.