Andrzej Bernasik

Surface segregation in yttria-stabilized zirconia by means of angle resolved X-ray photoelectron spectroscopy

Surface segregation of cations in undoped and titanium-doped yttria-stabilized zirconia was studied in air in the temperature range from 800 to 1400°C. Surface composition and distribution of the elements across the surface layer was examined using angle resolved X-ray photoelectron spectroscopy. The annealing procedure induced a silicon-rich surface layer of low zirconium concentration. The yttrium concentration only slightly increased at the surface. Enrichment factor of titanium in the titanium-doped yttria-stabilized zirconia was found to be higher than that of yttrium. No significant correlation between segregation of other cations was found.

Device performance of APFO-3/PCBM solar cells with controlled morphology

Polymer/fullerene solar cells with three different device structures: A) diffuse bilayer, B) spontaneously formed multilayer, and C) vertically homogenous thin films, are fabricated. The photocurrent/voltage performance is compared and it is found that the self-stratified structure (B) yields the highest energy conversion efficiency.

XPS studies of nitrogen-containing conjugated polymers–palladium systems

Polyaniline (PANI) and polypyrrole doped with chloride ions (PPyCl) have been treated with PdCl 2 solutions in HCl of various concentrations. Basing on the results of XPS studies it is shown that the differences in the redox and basic properties of both polymers lead to different mechanisms of their interactions with palladium ions present in the PdCl 2 solutions studied. Thus, in the PdCl 2 solutions of low acidity in which [PdCl 2 (H 2 O) 2 ] predominates, both polymers are oxidized with simultaneous reduction of a part of Pd 2+ to Pd 0 . In the PdCl 2 solutions of high acidity in which [PdCl 4 ] 2 is the major complex, reduction of Pd 2 does not occur. Owing to stronger basic properties of PANI than those of PPyCl, palladium is incorporated into the former polymer as anionic chlorocomplexes via protonation reaction. In the case of PPyCl the situation is more complex. Detailed analysis of the possible surface reactions taking place in the PPyCl Pd systems studied is given in the paper.

Electrical properties of Cr- and Nb-doped TiO2 thin films

The series of thin films of solid solutions of TiO2+xCr2O3 (0 < x < 0.013) and TiO2+yNb2O5 (0 < y < 0.05) were deposited on fused silica by means of reactive RF co-sputtering. The obtained films remain in the amorphous state up to 673 K. Annealing at 1173 K produces a well-developed rutile structure while formation of the anatase structure has not been observed. The high temperature electrical properties such as electrical conductivity, thermopower and work function were investigated within the wide range of oxygen activity (10-10–105 Pa). The effect of both Cr and Nb concentrations and film thickness on the measured parameters was studied. A mechanism for the incorporation of dopants (Cr and Nb) and defect model has been proposed. The influence of both intrinsic and extrinsic defects on the electrical properties has been discussed. The distribution of main elements (Ti, Si, O) as well as impurities were determined by the SIMS method.

XPS study of the cBN–TiC system

Sintered cubic boron nitride is widely used in various industrial applications because of its extreme wear and corrosion resistance, thermal and electrical properties. In order to obtain composite materials with these optimal properties it is important to elucidate whether chemical reactions occur at boron nitride/bonding phase interfaces. Some of these systems were then subjected to physical and thermal alteration This paper summarizes theoretical and experimental studies on the cBN–TiC 1:1 molar ratio. From theoretical calculations it follows that TiC reacts with boron nitride forming two new phases, TiB2 and TiN. Experimentally CBN–TiC composites were prepared by hot pressing, and the samples were subsequently heat treated. The samples were characterized after heat treatment using transmission electron microscopy and X-ray diffraction.

Selective protein adsorption on polymer patterns formed by self-organization and soft lithography.

Thin films, with both isotropic and ordered patterns of polymer domains, are used as substrates to study selective adsorption of two proteins (concanavalin A and lentil lectin) and to test reconstruction of polymer patterns by these proteins. Integral geometry approach is used to compare quantitatively fluorescence micrographs of protein patches with AFM images of original isotropic patterns, formed during blend casting of polystyrene/poly(methyl methacrylate) and PS/poly(ethylene oxide). Preferential adsorption of both lectins to PMMA phase domains, enhanced for PS/PMMA interfaces is concluded. In turn, protein binding to PS phase regions of PS/PEO blends is highly selective. Ordered protein grouping is obtained as a result of selective adsorption to alternating stripes of polystyrene (partly brominated to enable identification) and cross-linked PEO, prepared with solvent-assisted micromolding applied to PBrS/PEO bilayers. Biological activity test, performed with concanavalin A, confirms preserved functionality of a complementary protein, carboxypeptidase Y, adsorbed to polymer patterns.

Spectroscopic and microscopic characterization of biosensor surfaces with protein/amino-organosilane/silicon structure.

Composition and structure of biorecognition protein layers created on silicon substrates modified with amino-organosilanes determine the sensitivity and specificity of silicon based biosensing devices. In the present work, diverse spectroscopic and microscopic methods were applied to characterize model biosensor surfaces, formed on Si(3)N(4) or SiO(2) by modification with (3-aminopropyl)triethoxysilane, coating with rabbit gamma-globulins (IgGs) through physical adsorption, blocking with bovine serum albumin (BSA) and specific binding of an anti-rabbit IgG antibody. In addition, silanized substrates with directly adsorbed BSA or anti-rabbit IgG antibody were examined as reference surfaces. The protein/amino-organosilane/silicon structure of all surfaces was confirmed by X-ray photoelectron spectroscopy. Homogeneity of protein coverage was verified with near-field scanning optical microscope, working in reflection and fluorescence mode. Surface coverage with proteins was determined with angle-resolved XPS using a previously established bilayer approach. Inner structure of protein layers was examined with atomic force microscopy. Vertical arrangement of carbon functional groups was revealed by high resolution ARXPS. Combined spectroscopic and microscopic data reveal the complex character of interactions with the immobilized IgG molecules during blocking with BSA and immunoreaction with anti-IgG antibody. Within experimental error, neither surface coverage nor lateral structural scales of protein layer (provided by Fourier and auto-correlation analysis of topographic and phase images) increase during blocking procedure. On the other hand, coverage and all structural measures rise considerably after immunoreaction. In addition, it was found that polar functional groups orient towards substrate for all protein layers, independently of coverage, prior to and after both blocking and specific binding.

Protein adsorption and covalent bonding to silicon nitride surfaces modified with organo-silanes: comparison using AFM, angle-resolved XPS and multivariate ToF-SIMS analysis.

Organo-silanes provide a suitable interface between the silicon-based transducers of various biosensing devices and the sensing proteins, immobilized through physical adsorption, as for (3-aminopropyl)triethoxysilane (APTES), or covalent binding, e.g. via protein amine groups to (3-glycidoxypropyl)trimethoxysilane (GOPS) modified surface. Immobilization of rabbit gamma globulins (RgG) to silicon nitride surfaces, modified either with APTES or GOPS, was examined as a function of incubation time using atomic force microscopy (AFM), angle-resolved X-ray photoelectron spectroscopy (ARXPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). Multivariate technique of principal component analysis was applied to ToF-SIMS spectra in order to enhance sensitivity of immobilized RgG detection. Principal component regression shows a linear relationship with surface density determined rigorously from ARXPS following an organic bilayer approach, allowing for protein coverage quantification by ToF-SIMS. Taking it overall the surface immobilized amount of RgG is higher and develops faster on the surfaces silanized with APTES rather than with GOPS. Similar, although less distinct, difference is observed between the two surface types concerning the temporal evolution of average AFM height. The average height of protein overlayer correlates well with ARXPS and ToF-SIMS data expressed in terms of protein surface density. However, determined linear regression coefficients are distinctively higher for the surfaces modified with epoxy- rather than amino-silane, suggesting different surface density and conformation of the proteins immobilized through to covalent binding and physical adsorption.

Ordering domains of spin cast blends of conjugated and dielectric polymers on surfaces patterned by soft- and photo-lithography

Spin casting polymer blends of conjugated and dielectric macromolecules onto chemically patterned metal and oxidized silicon surfaces might provide a simple method to fabricate polymer-based circuitries that can be integrated with conventional electronics. Such solution-processing of the blend components offers simultaneous deposition and pattern-directed alignment of the phase separated polymer domains. The alignment is driven by self-organization guided by preferential surface segregation. Here we demonstrate that the laterally arranged domain structures in spin cast films of the conjugated poly(3-alkylthiophenes) (P3ATs): P3BT, P3DDT and regioregular R-P3HT, blended with dielectric polystyrene (PS), can be ordered by three different surface templates. The templates are formed by a patterned self-assembled monolayer (SAM), micro-contact printed on the surface of interest, i.e. hexadecanethiols on gold (for alignment of P3DDT/PS blend) and octadecyltrichlorosilanes on oxidized silicon (for R-P3HT/PS). Additionally gold lines are micro-patterned on SiO2 with photo-lithography (for P3BT/PS mixture). The forces driving pattern-directed self-organization of the polymers are discussed based on complementary studies of preferential surface segregation, observed for blend films spin cast on homogeneous surfaces that correspond to the different regions of the surface templates.

PDMS substrate stiffness affects the morphology and growth profiles of cancerous prostate and melanoma cells.

A deep understanding of the interaction between cancerous cells and surfaces is particularly important for the design of lab-on-chip devices involving the use of polydimethylsiloxane (PDMS). In our studies, the effect of PDMS substrate stiffness on mechanical properties of cancerous cells was investigated in conditions where the PDMS substrate is not covered with any of extracellular matrix proteins. Two human prostate cancer (Du145 and PC-3) and two melanoma (WM115 and WM266-4) cell lines were cultured on two groups of PDMS substrates that were characterized by distinct stiffness, i.e. 0.75 ± 0.06 MPa and 2.92 ± 0.12 MPa. The results showed the strong effect on cellular behavior and morphology. The detailed analysis of chemical and physical properties of substrates revealed that cellular behavior occurs only due to substrate elasticity.