Per Hanarp

Control of nanoparticle film structure for colloidal lithography

Colloidal lithography utilises nanoparticles’ ability to self-organise on surfaces, which make them suitable as lithographic masks for the production of nano sized surface features. Adsorption under the influence of electrostatic particle–particle interactions results in ordered structures with the particles separated an average distance described by the random sequential adsorption model (RSA). Large areas (cm2) with a high density of nanoparticles can be covered, which is very useful for application areas like biosensors, biomaterials and catalysis, where large numbers of nano sized features are often required. Feature size, shape and spacing can be systematically varied. In this work methods to control the deposition of films consisting of polystyrene particles on flat oxidised titanium surfaces for particle sizes between 20 and 500 nm and coverages of 0–0.45 are demonstrated and discussed. Experimental difficulties encountered were aggregation of particles at high coverage/large particles and a low coverage limit at low ionic strengths. Experimental solutions to overcome these limitations, maintaining the fast parallel processing advantage of colloidal lithography, are presented. They include heating to stabilize initial (i.e. after adsorption) particle arrangements, use of spacer silica particles, and plasma etching to reduce particle sizes.

Coherent imaging of nanoscale plasmon patterns with a carbon nanotube optical probe

We introduce a carbon nanotube as optical near-field probe and apply it to visualize the plasmon fields of metal nanostructures in both amplitude and phase at 30 nm resolution. With 91 nm Au disks designed for fundamental plasmon resonance, we observe the antiphase optical fields near two pole regions that are evidence of dipolar oscillation, in good agreement with theoretical field patterns. This opens the door to phase-sensitively map optical propagation and storage in photonic crystals and nanooptic resonators or circuits, in particular to verify coherent control of plasmon polaritons.

Nanostructured model biomaterial surfaces prepared by colloidal lithography

Adsorption of 110 nm negatively charged polystyrene particles on positively charged titanium surfaces was studied for the purpose of making surfaces with controlled nanotopography. Surfaces with 9–26 % saturation coverages of evenly spaced particles were produced by varying the salt concentration in the particle solution (0.01–1 mM NaCl). This is a quick and relatively simple method to make uniform nanostructures over large surface areas (~cm2). The produced surfaces are used for in vitro cell studies of how sub-micrometre topography influences cell adhesion and function.

Corrosion Induced Degradation of Pt/C Model Electrodes Measured with Electrochemical Quartz Crystal Microbalance

Degradation of fuel cell model electrodes during accelerated aging was studied using electrochemical quartz crystal microbalance with dissipation monitoring. The model electrodes, consisting of Pt particles (5 nm) on planar carbon and Pt-only and carbon-only films, were prepared by thermal evaporation onto uncoated quartz crystal sensors. The characterization of electrode composition and morphology was performed by X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, and atomic force microscopy. The experiments were conducted in a flow cell with 0.5 M H(2)SO(4) at room temperature and up to 70 degrees C by repeated cycling between 0.02 and 1.4 V(RHE) (where RHE is reversible hydrogen electrode) at 50 mV s(-1). During cyclic corrosion, the Pt-only sample loses mass equivalent to 0.6% of a monolayer per cycle in a process that is not temperature-dependent. The experiments with the Pt particle layer on a carbon electrode show a mass loss that is almost 2 times larger than the Pt-only sample and exhibits an Arrhenius type of temperature dependence. The results suggest that the presence of Pt catalyzes carbon corrosion with an apparent activation energy of 0.33 eV. In all measurements, the carbon-only sample loses much less mass than the other samples.

Patterning colloidal monolayer films using microcontact particle stripping

We combined the basic component of microcontact printing (μCP), the use of an elastomeric stamp to transfer a pattern, with colloidal lithography, a parallel technique to obtain arrays of nanostructures at surfaces. This novel method, entitled microcontact particle stripping (μCPS), uses a stamp to selectively remove the pre-adsorbed particles located in the contact regions, leaving the particles in the non-contact regions unaffected. The particles, in the nanopatterned regions, can further be used as a lithographic mask.

Stability of Nanostructured Pt/Glassy Carbon Electrodes Prepared by Colloidal Lithography

The stability of nanostructured Pt/glassy carbon (GC) model electrodes upon exposure to a realistic electrochemical/electrocatalytic reaction environment (continuous reaction, continuous electrolyt ...

Nanostructured, Glassy-Carbon-Supported Pt/GC Electrodes: The Presence of Secondary Pt Nanostructures and How to Avoid Them

Nanostructured, glassy carbon GC supported Pt/GC electrodes, with Pt nanostructures nanodisks of controlled size 100–140 nm in diameter and separation homogeneously distributed on a planar GC substrate, were recently shown to be interesting model systems for electrocatalytic reaction studies M. Gustavsson, H. Fredriksson, B. Kasemo, Z. Jusys, C. Jun, and R. J. Behm, J. Electroanal. Chem., 568, 371 2004. We present here electron microscopy and electrochemical measurements which reveal that the fabrication of these nanostructured electrodes via colloidal lithography, in addition to the intended nanodisks, results in a dilute layer of much smaller Pt nanoparticles diameter 5n m on the GC surface in the areas between the Pt nanodisks. We further demonstrate that by using the developed, related method of hole-mask colloidal lithography HCLH. Fredriksson, Y. Alaverdyan, A. Dmitriev, C. Langhammer, D. S. Sutherland, M. Zach, and B. Kasemo, Adv. Mater. (Weinheim, Ger.), 19, 4297 2007, similar electrodes can be prepared which are free from these Pt nanoparticles. The effect of the additional small Pt nanoparticles on the electrochemical and electrocatalytic properties of these nanostructured electrodes, which is significant and can become dominant at low densities of the Pt nanodisks, is illustrated and discussed. These results leave HCL the preferred method for the fabrication of nanostructured Pt/GC electrodes, in particular, of low-density Pt/GC electrodes.

Tunable optical excitations in gold nanorings

The optical response of gold nanorings is measured and analyzed theoretically. Compared to gold disks, nanorings exhibit a red-shifted surface plasmon that can be tuned by varying the ratio between ring thickness arid radius.