Filip Frederix

Aqueous Chemical Solution Deposition of Ferroelectric Thin Films

Thin films of various ferroelectric multimetal oxides such as (Bi 1 m x La x ) 4 Ti 3 O 12 (BLT), SrBi 2 Ta 2 O 9 (SBT) and PbZr 1 m x Ti x O 3 (PZT) have been prepared by an entirely aqueous chemical solution deposition (CSD) route. Two critical issues related with aqueous CSD have hereby been worked out: in spite of the high degree of hydrolysis of tetra- and pentavalent metal ions (Ti 4+ , Zr 4+ , Ta 5+ , ) we managed to prepare stable aqueous precursor solutions by chemical modification of these individual metals, avoiding phase segregation. Another problem related with aqueous CSD is the wetting of the substrate (both metallic and metal oxide) by the aqueous solution. The hydrophilicity of the substrates is optimized by a chemical treatment of the substrate surface. In this manner, the addition of wetting agents, hence possibly disturbing the gelation reactions, is avoided. In order to study the gelation, decomposition, crystalization and the morphology of the thin films, various characterization techniques ((cryo-)TEM, SEM, EDX, TGA-MS/FTIR, HT-DRIFT, HT-XRD, ) are used.

Nanopatterning of gold colloids for label-free biosensing

We present an approach for the controlled positioning of single gold colloids onto dot and line nanoarrays which have the potential to serve as label-free biosensor platforms. The separation between the high-resolution nanolithography step, extreme ultraviolet interference lithography, and the subsequent functionalization has many advantages, among them the independence of the linkage chemistry. The activation of the pre-patterned substrates is performed by transforming them into a surface of biotinylated nanopatches in a protein-resistant background. Complexes of streptavidin and single-stranded DNAs can then be selectively immobilized onto the biotinylated patches, which are embedded in an inert background. This approach enables the creation of single gold colloid dot and line arrays by directed self-assembly using the specificity of DNA hybridization.

Simultaneous atomic force microscope and quartz crystal microbalance measurements: Investigation of human plasma fibrinogen adsorption

We have combined the tapping-mode atomic force microscope (AFM) and quartz crystal microbalance (QCM) for simultaneous investigation of human plasma fibrinogen adsorption on a metallic surface using these two instruments. The AFM images show the surface changes with molecular resolution while the corresponding resonance frequency shift of the QCM provides quantitative adsorbed mass estimates over the whole sensing area. The combination of AFM with QCM allowing the simultaneous measurements with two techniques working at very different scales and probing different properties of the adsorbed layer provides quantitative and qualitative information that can distinguish different protein adsorption mechanisms.

Simultaneous AFM and QCM Measurements Methodology Validation Using Electrodeposition

We assess the validity and advantages of using a quartz crystal microbalance ~QCM! as the metallic-coated substrate used for atomic force microscopy ~AFM! measurements by studying two well-known electrochemical reactions, silver electrodeposition on gold and copper electrodeposition on gold. We compare the results provided by electrochemistry ~cyclic voltammetry!, QCM frequency, and damping variations as well as AFM topography, and analyze the advantages of combining the three methods in the same instrument. Comparison of the evolution of the frequency of the third and fifth QCM overtones allows identification of the type of interaction between the sensing electrode and its environment: a rigid layer when the frequency shift is proportional to the overtone number, viscous interaction when the frequency shift is proportional to the square root of the overtone number. This identification scheme leads to results confirmed by the QCM damping.

Investigation of protein adsorption with simultaneous measurements of atomic force microscope and quartz crystal microbalance

We have combined the tapping-mode atomic force microscope (AFM) and quartz crystal microbalance (QCM) for simultaneous investigation and characterization of protein adsorption on various metallic surfaces using these two instruments. The adsorption of proteins such as human plasma fibrinogen and anti-human immunoglobulin onto the metal or oxide/QCM surface were monitored using both methods at the same time when varying the concentration of proteins. The combination of AFM with QCM allowing the simultaneous measurements with two techniques working at very different scales and probing different properties of the adsorbed layer provides quantitative and qualitative information that can distinguish different protein adsorption behavior.

Development of microelectronic based biosensors

Biosensors offer the opportunity to sense the biological world providing valuable information for medical diagnostics, analytical chemistry, environmental monitoring and fundamental research. Convergence of engineered (bio)chemical surfaces with micro- and nano- systems promises tremendous advances and potential cost reductions in biotechnology. This paper introduces some key challenges facing biosensor development, focussing on opportunities that arise from microsystem platforms utilising novel materials and processes. Examples from our work are presented illustrating the implementation of acoustic wave sensors and novel FET-type sensors.