Per Morgen

SiC nanocrystals as Pt catalyst supports for fuel cell applications

A robust catalyst support is pivotal to Proton Exchange Membrane Fuel Cells (PEMFCs) to overcome challenges such as catalyst support corrosion, low catalyst utilization and overall capital cost. SiC is a promising candidate material which could be applied as a catalyst support in PEMFCs. SiC nanocrystals are here synthesized using nano-porous carbon black (Vulcan® XC-72) as a template using two different reactions, which result in particle sizes in the ranges of 50–150 nm (SiC-SPR) and 25–35 nm (SiC-NS). Pt nano-catalysts of size 5–8 nm and 4–5 nm have successfully been uniformly deposited on the nanocrystals of SiC-SPR and SiC-NS by the polyol method. The SiC substrates are subjected to an acid treatment to introduce the surface groups, which help to anchor the Pt nano-catalysts. These SiC based catalysts have been found to have a higher electrochemical activity than commercially available Vulcan based catalysts (BASF & HISPEC). These promising results signal a new era of SiC based catalysts for fuel cell applications.

Growth of a stacked silicon nitride/silicon oxide dielectric on Si(100)

We have recently developed processes to grow ultrathin amorphous silicon oxide and amorphous silicon nitride layers on clean Si(111) and Si(100) surfaces exploring the self-limiting nature of the direct oxidation of Si with O2, and the self-limiting nature of the direct nitridation of Si with atomic N produced by microwave dissociation of N2, at processing temperatures around 500°C. In some of today’s microprocessor devices mixed dielectric systems are used as complementary metal oxide semiconductor gate dielectrics. We demonstrate the use of our processes to produce such systems in various structures, and with maximum control, by exposing oxide to N, or nitride to O2 at 500°C. In addition we produce a stacked layer, consisting of 7–8A of SiO2 on top of Si(100), with a layer of varying thickness of Si3N4 grown on top of this structure. The growth of Si3N4 occurs at room temperature in this process. Such structures or thermally postprocessed structures thereof should be further examined as potential stacke...

Oxygen reduction and methanol oxidation behaviour of SiC based Pt nanocatalysts for proton exchange membrane fuel cells

Research with proton exchange membrane fuel cells has demonstrated their potential as important providers of clean energy. The commercialization of this type of fuel cell needs a breakthrough in the electrocatalyst technology to reduce the relatively large amount of noble metal platinum used with the present carbon based substrates. We have recently examined suitably sized silicon carbide (SiC) particles as catalyst supports for fuel cells based on the stable chemical and mechanical properties of this material. In the present study, we have continued our work with studies of the oxygen reduction and methanol oxidation reactions of SiC supported catalysts and measured them against commercially available carbon based catalysts. The deconvolution of the hydrogen desorption signals in CV cycles shows a higher contribution of Pt (110) and Pt (111) peaks compared to Pt (100) for SiC based supports than for carbon based commercial catalysts, when HClO4 is used as an electrolyte. The Pt (110) and Pt (111) facets are shown to have higher electrochemical activities than Pt (100) facets. To the best of our knowledge, methanol oxidation studies and the comparison of peak deconvolutions of the H desorption region in CV cyclic studies are reported here for the first time for SiC based catalysts. The reaction kinetics for the oxygen reduction and for methanol oxidation with Pt/SiC are observed to be similar to the carbon based catalysts. The SiC based catalyst shows a higher specific surface activity than BASF (Pt/C) for methanol oxidation and oxygen reduction while the mass activity values are comparable.

Plasma assisted growth of ultrathin nitrides on Si surfaces under ultrahigh vacuum conditions

Plasma assisted nitridation of Si is a very useful and easily controlled process for the direct in-situ deposition of pure silicon-nitride films on Si under ultrahigh vacuum conditions. The plasma used in the present work is formed by microwave dissociation of nitrogen gas. Under these circumstances an additional activation barrier to the formation of nitride exists which can be overcome by isothermal processing at temperatures from 300 °C and up. Room temperature growth of ultrathin silicon-nitride films on top of different substrates is also found to be possible through the use of dispersed atomic Si layers which react with the microwave excited nitrogen plasma at room temperature. Studies are undertaken with the Si(111) and Si(100) surfaces and the results for these two surfaces are compared. The conditions for the growth of amorphous versus microcrystalline films are established with a critical temperature around 500-600°C.

Surface charging, discharging and chemical modification at a sliding contact

Electrostatic charging, discharging, and consequent surface modification induced by sliding dissimilar surfaces have been studied. The surface-charge related phenomena were monitored by using a home-built capacitive, non-contact electrical probe, and the surface chemistry was studied by X-ray photoelectron spectroscopy (XPS). The experiments were performed on the disk surface of a ball-on-rotating-disk apparatus; using a glass disk and a Teflon (polytetrafluoroethylene) ball arrangement, and a polyester disks and a diamondlike carbon (DLC) coated steel ball arrangement. The capacitive probe is designed to perform highly resolved measurements, which is sensitive to relative change in charge density on the probed surface. For glass and Teflon arrangement, electrical measurements show that the ball track acquires non-uniform charging. Here not only the increase in charge density, but interestingly, increase in number of highly charged regions on the ball track was resolved. Threefold increase in the number o...

Ultrasound Enhanced Plasma Treatment of Glass-Fibre-Reinforced Polyester in Atmospheric Pressure Air for Adhesion Improvement

A glass-fibre-reinforced polyester (GFRP) plate was treated with dielectric barrier discharge (DBD) at atmospheric pressure in air for adhesion improvement. The effects of ultrasonic irradiation using a high-power gas-jet generator during the treatment were investigated. The optical emission spectrum of the discharge remained almost unchanged by the ultrasonic irradiation, indicating that the bulk property of the discharge was not significantly influenced by the ultrasound. However, the ultrasonic irradiation during the plasma treatment suppressed occasional arcing in the DBD, preventing damage of the GFRP plates. The polar component of the surface energy of the polyester plate was 21 mJ/m2 before the treatment, increased markedly to 52 mJ/m2 after 2-s plasma treatment without ultrasonic irradiation, and further increased slightly after longer treatments. In addition, the polar component of the surface energy increased due to the simultaneous ultrasonic irradiation, indicating that the adhesive property would be further improved. This result shows a good agreement with surface characterization by X-ray photoelectron spectroscopy. Time-of-flight secondary ion mass spectrometry ion images show that nitrogen-containing functional groups were uniformly attached after the treatments. The roughness of the GFRP surfaces increased after the plasma treatment, but the ultrasonic irradiation did not enhance surface roughening.

Tuning surface plasmons in interconnected hemispherical Au shells

We present a new approach for making interconnected hemispherical shells by stripping Au from templates of anodized aluminum, where the metal thickness can be adjusted without affecting the outer radius of curvature, film roughness and the sharpness of the hemisphere contact areas. This provides increased understanding of the surface plasmon resonances (SPRs) observed for Film-On-Nanospheres (FONs) by decoupling these parameters, which are coupled in the case of FONs. Investigating the influence of the shell thicknesses on the spectral positions of SPRs for FONs involves a dielectric core with a fixed radius encased by a metal film with adjustable thickness. By performing linear reflection spectroscopy, we demonstrate a wide tunability of the SPR by tailoring the inner hemisphere diameter, while keeping the outer diameter fixed. Deposition of extra Au on top of thick, previously stripped hemispherical shells isolates optical response contributions from Au grain- and island-mediated roughness, and unsharpening contact areas in form of decreasing LSPR quality factor. Two-photon luminescence scanning optical microscopy of shells with different thicknesses, applying several different laser wavelengths, is exploited to map local electromagnetic hot spots and correlate the high field enhancements with the linear reflection spectroscopy measurements.

Ultrasound enhanced 50 Hz plasma treatment of glass-fiber-reinforced polyester at atmospheric pressure

Glass-fiber-reinforced polyester (GFRP) plates are treated using a 50 Hz dielectric barrier discharge at a peak-to-peak voltage of 30 kV in helium at atmospheric pressure with and without ultrasonic irradiation to study adhesion improvement. The ultrasonic waves at the fundamental frequency of around 30 kHz with the sound pressure level of approximately 155 dB were introduced vertically to the GFRP surface through a cylindrical waveguide. The polar component of the surface energy was almost unchanged after the plasma treatment without ultrasonic irradiation, but drastically increased approximately from 20 up to 80 mJ m−2 with ultrasonic irradiation. The plasma treatment with ultrasonic irradiation also introduced oxygen- and nitrogen-containing functional groups at the GFRP surface. These changes would improve the adhesion properties of the GFRP plates.

Two-photon luminescence microscopy of large-area gold nanostructures on templates of anodized aluminum

Using linear reflection spectroscopy and far-field two-photon luminescence (TPL) scanning optical microscopy, we characterize highly enhancing, large-area gold nanostructures formed on porous templates made by anodization of aluminum with either oxalic acid or phosphoric acid. These templates are formed by a newly developed, stepwise technique making use of protective top oxide layers facilitating continuously tunable interpore distances. The upper, porous alumina layers are subsequently removed and the remaining embossed barrier layer is used as template for the sputtered gold, where the density of gold particles covering the sample is adjusted by regulating the sputtering conditions. We observe spatially averaged field intensity enhancement (FE) factors of up to ~5.210(2) and bright spots in the TPL-images exhibiting maximum FE factors of up to approximately 1410(2) which is the largest estimated FE from any hitherto examined structures with our setup. We relate this large-area massive FE to constructive interference of surface plasmon (SP) polaritons scattered from the densely packed, randomly distributed gold particles and directly correlate this particle density with the strong and broad SP resonances as well as the magnitude of the FE factors. The average FE and the position of high enhancements in the TPL-images are dictated by the excitation wavelength, and the structures could evidently serve as versatile structures facilitating practical molecular sensing.

Tribological properties of sulfur-implanted steel

Abstract The tribological properties of a low-alloy steel surface treated by sulfur ion implantation (concentration range 1–30 at.%) have been tested under boundary lubrication conditions and compared with untreated steel. Pin-on-disc wear tests, carried out at constant load and speed, showed that sulfur implantation of the discs had a pronounced wear-reducing effect, leading to an up to three times longer sliding length before breakdown of the lubricating system (scuffing). Sulfur implantation (at high doses) amorphized the steel surface and led to the formation of nano-crystallites of the hexagonal FeS compound, which is supposed to have very beneficial lubricating properties. The transfer of a sulfur containing tribofilm to the pin counterface was observed at high sulfur doses and static load conditions. Under oscillating load conditions, the tribofilm transfer mechanism was apparently much less effective. The final state of the discs was characterized by very smooth, polished wear tracks, irrespective of implantation level. A significant fraction of the implanted sulfur remained in the wear tracks up to the critical friction coefficient.