Leonard Matisen

Blocking properties of gold electrodes modified with 4-nitrophenyl and 4-decylphenyl groups

The electrochemical properties of Au electrodes grafted with 4-nitrophenyl and 4-decylphenyl groups have been studied. The electrografting of gold electrode surface with aryl groups was carried out by electroreduction of the corresponding diazonium salts in acetonitrile. The nitrophenyl film growth on gold was examined by atomic force microscopy, electrochemical quartz crystal microbalance and X-ray photoelectron spectroscopy. These measurements showed that a multilayer film of nitrophenyl groups was formed. Cyclic voltammetry was used to study the blocking properties of aryl-modified gold electrodes towards the Fe(CN)63−/4− redox system. The reduction of oxygen was strongly suppressed on these electrodes as evidenced by the rotating disc electrode results.

Electrochemical Modification of Gold Electrodes with Azobenzene Derivatives by Diazonium Reduction

An electrochemical study of Au electrodes electrografted with azobenzene (AB), Fast Garnet GBC (GBC) and Fast Black K (FBK) diazonium compounds is presented. Electrochemical quartz crystal microbalance, ellipsometry and atomic force microscopy investigations reveal the formation of multilayer films. The elemental composition of the aryl layers is examined by X-ray photoelectron spectroscopy. The electrochemical measurements reveal a quasi-reversible voltammogram of the Fe(CN)6 (3-/4-) redox couple on bare Au and a sigmoidal shape for the GBC- and FBK-modified Au electrodes, thus demonstrating that electron transfer is blocked due to the surface modification. The electrografted AB layer results in strongest inhibition of the Fe(CN)6 (3-/4-) response compared with other aryl layers. The same tendencies are observed for oxygen reduction; however, the blocking effect is not as strong as in the Fe(CN)6 (3-/4-) redox system. The electrochemical impedance spectroscopy measurements allowed the calculation of low charge-transfer rates to the Fe(CN)6 (3-) probe for the GBC- and FBK-modified Au electrodes in relation to bare Au. From these measurements it can be concluded that the FBK film is less compact or presents more pinholes than the electrografted GBC layer.

Atomic layer deposition of aluminum oxide films on graphene

Seed-layer approach was studied to initiate atomic layer deposition (ALD) of Al2O3 films on graphene. Low-temperature ALD and electron beam evaporation (EBE) were applied for seed-layer preparation before deposition of the dielectric at 200 °C using trimethyl-aluminum and water or ozone as precursors. To characterize nucleation of the films and possible influence of the ALD processes on the quality of graphene, properties of graphene and Al2O3 films were investigated by Raman spectroscopy, X-ray fluorescence and X-ray photoelectron spectroscopy methods. The results suggest that seed layer formation by low-temperature ALD was more efficient in the O3-based process than in the H2O-based one while EBE seed layer provided fastest growth of Al2O3 together with minimum incubation period.

Pt coated Cr2O3 thin films for resistive gas sensors

The resistive response of atomic layer deposited thin epitaxial α-Cr2O3(0 0 1) films, to H2 and CO in air, was studied. The films were covered with Pt nanoislands formed by electron-beam evaporation of a sub-monolayer amount of the material. The gas measurements were performed at 250°C and 450°C. These temperatures led to different proportion of chemical states, Pt2+ and Pt4+, to which the Pt oxidized. The modification was ascertained by the X-ray photoelectron spectroscopy method. As a result of the modification, the response was fast at 250°C, but slowed at 450°C. A disadvantageous abundance of Pt4+ arising at 450°C in air could be diminished by high-vacuum annealing thus restoring the response properties of the system at 250°C.

Electrochemical properties of gold and glassy carbon electrodes electrografted with an anthraquinone diazonium compound using the rotating disc electrode method

In this paper, gold and glassy carbon (GC) electrodes were electrochemically grafted with anthraquinone (AQ) groups derived from Fast Red AL salt via electrochemical reduction of AQ diazonium cations. For the first time, the electrografting was performed by combining the cyclic voltammetry (CV) or potential step method with the rotating disc electrode (RDE) technique in order to prepare thick films of AQ on Au and GC electrodes. For comparison purposes, a CV or potential step method without the RDE was also used. The attachment of thick AQ films to the Au electrode surface was confirmed by X-ray photoelectron spectroscopy and atomic force microscopy. The highest surface concentration value (ΓAQ) of AQ on the Au and GC electrodes (ca. 2.1 × 10−8 and 1.8 × 10−8 mol cm−2, respectively) was obtained by employing the combination of CV and RDE methods during the electrografting procedure. The oxygen reduction reaction results revealed that the electrochemical behaviour of AQ-modified Au electrodes does not depend on the ΓAQ value similar to the GC electrodes modified with thick AQ films. However, some differences were observed when the blocking effect of thick AQ films on Au and GC electrodes towards the ferri/ferrocyanide redox probe was studied.

Formation of nickel oxide nanostructures on TiO2

A new method to prepare catalytic NiO templates for growing carbon nanotubes is described. The method utilizes sol-gel chemical reactions in formation of NiO containing nanostructures on TiO2 surfaces. The structures are studied using X-ray photoelectron spectroscopy and atomic force microscopy methods.

Oxygen Reduction on Catalysts Prepared by Pyrolysis of Electrospun Styrene–Acrylonitrile Copolymer and Multi-walled Carbon Nanotube Composite Fibres

For the first time, the oxygen reduction reaction (ORR) is studied on pyrolysed electrospun multi-walled carbon nanotube (MWCNT) and styrene–acrylonitrile (SAN) composite fibre catalysts in alkaline medium. Scanning electron microscopy images revealed that the prepared catalysts mainly consist of MWCNTs, while nitrogen doping of the catalysts is confirmed by X-ray photoelectron spectroscopy. This indicates that SAN can be used as a nitrogen precursor. The ORR studies carried out by rotating disc electrode (RDE) and rotating ring-disc electrode (RRDE) methods showed that the prepared catalysts were considerably more active towards the ORR than the pristine MWCNTs.Graphical Abstract