Wojciech Lisowski

ADSORPTION OF HYDROGEN ON EVAPORATED COBALT FILMS

Hydrogen adsorption on evaporated Co films has been studied by means of measurements of the surface potential changes that occur during this process, and analysis of the desorption spectrum of hydrogen. It has been observed that hydrogen adsorbed at 78 K on Co films exists in three forms with essentially different electrical properties: atomic, electronegatively polarized β− form; atomic, electropositively polarized β+ form and reversibly adsorbed, molecular, positively polarized α form. The β− form is not homogeneous from the point of view of the bond energy with the metal surface and consists of the states βs− and β− characterized by activation energy of desorption 10.0 and 18.8 kcal/mol H2 correspondingly. The Activation energy of desorption of the β+ form is low, i.e. 2.1 kcalmol H2.

Studies on the possibility of determination of surface area of palladium films by means of adsorption of hydrogen or oxygen and reciprocal titration of these gases

Abstract The kinetics of surface potential changes in palladium films was studied in order to investigate the possibility of determining surface areas of these films by means of adsorption of oxygen or hydrogen and by titration of preadsorbed oxygen with hydrogen or preadsorbed hydrogen with oxygen at 348–370 K. It was found that the incorporation of oxygen in the bulk of palladium films and the occurrence of unreactive forms of the adsorbate in the case of titration of preadsorbed hydrogen with oxygen as well as desorption of hydrogen during the evacuation of the apparatus complicate the problem to such an extent that the volumetric method alone is inadequate. This method can be used for the determination of the surface area of palladium films only when combined with a determination of the kinetics of surface potential changes or some other method which makes it possible to follow the behaviour of the adsorbate on the surface of the metal.

Effect of plasma electrolytic oxidation in the solutions containing Ca, P, Si, Na on the properties of titanium†

The surface layers were formed on titanium by plasma electrolytic oxidation (PEO) in the solutions which contain various amounts of Na(2)SiO(3)x5H(2)O, Na(3)PO(4) x12H(2)O and Ca(CH(3)COO)(2) xH(2)O. The layers were characterized using a scanning electron microscope (SEM) coupled with an energy dispersive spectrometer (EDS) and an X-ray diffractometer (XRD). The titanium/oxide surface layer interface was analyzed by X-ray photoelectron spectroscopy (XPS). The adhesive strength of the oxide layers was evaluated by the scratch-test. The bioactivity of the surface was determined by soaking in a simulated body fluid (SBF) for 7 and 30 days. The corrosion resistance was determined by electrochemical methods after 13, 181, and 733 h exposure in SBF at a temperature of 37°C. The oxide layers obtained were rough and porous and enriched with Ca, P, Si, and Na and their properties depended on the concentration of the components of the electrolyte. The results of the electrochemical examinations, after a 13 h exposure in SBF, show that the surface modification by PEO improves the corrosion resistance of titanium and it is not degraded after a long-term exposure in SBF. The electrochemical impedance spectroscopy (EIS) results indicate that the surface layers have a complex structure.

Characterization of titanium hydride film after long-term air interaction: SEM, ARXPS and AES depth profile studies

Thin titanium hydride (TiHy) films are compared with thin titanium films after analysis using a combination of scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and angle-resolved x-ray photoelectron spectroscopy (ARXPS). The TiHy films were prepared under ultrahigh vacuum conditions by precisely controlled hydrogen sorption at 298 K on Ti films evaporated onto a glass substrate. Analysis was performed in separate systems after long-term exposure of the films to air. Scanning electron microscopy analysis revealed a grain structure of the TiHy film, with a smaller grain size than the Ti film. Both the surface and bulk regions have been analysed in terms of their chemical composition and elemental distribution. Titanium dioxide was found to be the main chemical compound forming a contamination layer on both the TiHy and Ti film surfaces. Also, significant concentrations of carbon monoxide and hydrocarbon as well as small amounts of nitrogen and titanium carbide were detected. The thickness of the contaminated titanium oxide layer on the TiHy and Ti films was found to be ~13 and~20 nm, respectively. Long-term air interaction with the TiHy film leads to bulk penetration of oxygen but not to complete TiHy decomposition.

Hydrophilic polycarbonate for generation of oil in water emulsions in microfluidic devices

This report details the method for rendering hydrophilic surfaces of microchannels fabricated in polycarbonate (PC). We characterize the wetting properties and stability of the hydrophilic character of two coatings--one formed by a layer of poly(allylamine) (PAH*) and the second including an additional layer of poly(styrene-sulfonate) (PSS). This second (PC-PAH/PSS) coating yields highly hydrophilic surface that is stable against weeks of exposure to various fluids including organic oils. This coating allows for stable generation of oil-in-water emulsions of hydrocarbon, silicone and fluorinated oils without the use of surfactants and over days of continuous use.

KINETICS AND THERMODYNAMICS OF HYDROGEN INTERACTION WITH THIN COBALT FILMS

Abstract The kinetics and thermodynamics of hydrogen adsorption on thin cobalt films at 195, 273 and 298 K have been studied by means of sticking probability measurements, thermal desorption mass spectrometry (TDMS) and examination of adsorption isotherms. The dissociative adsorption occurs with a high initial sticking coefficient ( S 0 close to unity) at all temperatures. The behaviour of the sticking probability S as a function of hydrogen coverage θ has been analyzed. Two TDMS peaks were detected when hydrogen adsorption was carried out at 195 K. The isosteric heat of adsorption remains constant at 286 K up to θ ≈ 0.5 and then decreases indicating the arising of a new adsorbed state of hydrogen at θ > 0.5. A detailed analysis of the adsorption entropy for T ≈ 286 K has been performed.

Early diagnosis of fungal infections using piezomicrogravimetric and electric chemosensors based on polymers molecularly imprinted with d-arabitol

An elevated concentration of d-arabitol in urine, especially compared to that of l-arabitol or creatinine, is indicative of a fungal infection. For that purpose, we devised, fabricated, and tested chemical sensors determining d-arabitol. These chemosensors comprised the quartz crystal resonator (QCR) or extended-gate field-effect transistor (EG-FET) transducers integrated with molecularly imprinted polymer (MIP) film recognition units. To this end, we successfully applied a covalent approach to molecular imprinting, which involved formation of weak reversible covalent bonds between vicinal hydroxyl groups of arabitol and boronic acid substituents of the bithiophene functional monomer used. The MIP films were synthesized and simultaneously deposited on gold electrodes of quartz crystal resonators (Au-QCRs) or Au-glass slides by oxidative potentiodynamic electropolymerization. With the QCR and EG-FET chemosensors, the d-arabitol concentration was determined under flow-injection analysis and stagnant-solution binding conditions, respectively. Selectivity with respect to common interferences, and l-arabitol in particular, of the devised chemosensors was superior. Limits of detection and linear dynamic concentration ranges of the QCR and EG-FET chemosensors were 0.15 mM and 0.15 to 1.25 mM as well as 0.12 mM and 0.12 to 1.00 mM, respectively, being lower than the d-arabitol concentrations in urine of patients with invasive candidiasis (>220 μM). Therefore, the devised chemosensors are suitable for early diagnosis of fungal infections caused by Candida sp. yeasts.

Characterization of titanium hydride films covered by nanoscale evaporated Au layers: ToF-SIMS, XPS and AES depth profile analysis

Thin titanium hydride (TiHy) films, covered by ultrathin gold layers, have been compared with the corresponding titanium films after analysis using a combination of time-of-flight SIMS (ToF-SIMS), XPS and AES. The TiHy layers were prepared under UHV conditions by precisely controlled hydrogen sorption at 298 K on Ti film evaporated onto a glass substrate. Both Ti and TiHy films were then covered in situ by a nanoscale Au layer. Analyses were performed in separate systems after long-term exposure of the films to air. The thin gold layers covering the Ti and TiHy surfaces prevent any extensive air interaction with both films, allowing characterization of the bulk Ti and TiHy layers ex situ, even after a long-term application in air. The chemical nature of the TiHy layers has been analysed after sputtering of the Au top layer. The high-mass-resolution positive-ion ToF-SIMS spectra disclosed only one peak at mass 49 (49Ti+) for the Ti and two peaks at mass 49 (49Ti+ and 48TiH+) for the TiHy film, reflecting a difference in hydrogen concentration. Analysis of the features of the Ti Auger spectra during the sputter profile measurements allows the TiHy to be distinguished and characterized in the bulk region of the Au/TiHy layer. Besides TiHy, TiO and TiOH were detected by XPS to be the main chemical compounds in the interface region of the Au/TiHy film.

High-temperature interaction of nitrogen with thin iron films: Thermal desorption kinetics studies combined with microstructure analysis of Fe–N films

The interaction of nitrogen with thin iron films at 673 K has been studied by means of thermal desorption mass spectrometry (TDMS) and a combination of scanning electron microscopy and transmission electron microscopy. TDMS spectra indicate the coexistence of atomic and molecular states of nitrogen adsorbed at 673 K and at a nitrogen pressure of 0.75 Pa. The origin of the molecular state is discussed as an intermediate state towards dissociative adsorption of nitrogen. Reconstruction of the polycrystalline iron film occurs as a result of both nitrogen interaction at 673 K and thermal desorption by heating the sample substrate to 950 K. The Fe grains become finer and the Fe film surface shows an increase in roughness upon interaction with nitrogen at 673 K. TDMS heating involves annealing of the Fe film and decomposition of the “surface nitrides.” The bulk structure of the Fe film is affected by the nitrogen-induced reconstruction of its topmost surface region.

Kinetics of hydrogen adsorption and desorption on thin platinum films

Abstract The nature of hydrogen adsorption on thin platinum films at 78, 195, 273 and 298 K has been studied by means of sticking probability measurements and thermal desorption mass spectrometry (TDMS). A high value of the initial sticking coefficient (S0 ≈ 0.95) was found at all temperatures. The behaviour of the sticking probability S as a function of hydrogen coverage θ has been analyzed. Three TDMS peaks of hydrogen were detected on Pt films when the adsorption was carried out at 195 K. The TDMS analysis carried out for hydrogen adsorbed at 78 K, revealed the existence of a molecular form of hydrogen deposit.