| 1. |
- Cardenas, J. F., et al.
(författare)
-
Light induced selective heating of nanostructured pyrolitic graphite surfaces investigated by Raman scattering
- 2013
-
Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 415, s. 232-236
-
Tidskriftsartikel (refereegranskat)abstract
- Nanostructured surfaces of highly oriented pyrolytic graphite (HOPG) were characterized by Raman spectroscopy. The disc-shape nanostructures similar to 110 nm high and with two different diameters similar to 147 and 217 nm are prepared on HOPG using hole-mask colloidal lithography and oxygen reactive ion etching. Significant roughening of the HOPG surface is introduced by the nano-fabrication process, but the nano-disc structures preserves their crystalline structure. Resonant light absorption results in selective heating of nanostructures, although the surrounding medium remains relatively unaffected. Temperature differences of up to 350 K were measured under irradiation with similar to 11 mW/mu m(2). Further increase of the light intensity leads to combustion of structures.
|
|
| 2. |
|
|
| 3. |
- Edman Jönsson, Gustav, 1983, et al.
(författare)
-
Nanostructures for Enhanced Light Absorption in Solar Energy Devices
- 2011
-
Ingår i: International Journal of Photoenergy. - : Hindawi Limited. - 1687-529X .- 1110-662X. ; 2011
-
Tidskriftsartikel (refereegranskat)abstract
- The fascinating optical properties of nanostructured materials find important applications in a number of solar energy utilization schemes and devices. Nanotechnology provides methods for fabrication and use of structures and systems with size corresponding to the wavelength of visible light. This opens a wealth of possibilities to explore the new, often of resonance character, phenomena observed when the object size and the electromagnetic field periodicity (light wavelength lambda) match. Here we briefly review the effects and concepts of enhanced light absorption in nanostructures and illustrate them with specific examples from recent literature and from our studies. These include enhanced optical absorption of composite photocatalytically active TiO(2)/graphitic carbon films, systems with enhanced surface plasmon resonance, field-enhanced absorption in nanofabricated carbon structures with geometrical optical resonances and excitation of waveguiding modes in supported nanoparticle assembles. The case of Ag particles plasmon-mediated chemistry of NO on graphite surface is highlighted to illustrate the principle of plasmon-electron coupling in adsorbate systems.
|
|
| 4. |
- Fredriksson, Hans, 1974, et al.
(författare)
-
Hole-Mask Colloidal Lithography
- 2007
-
Ingår i: Advanced Materials. ; 19, s. 4297-4302
-
Tidskriftsartikel (refereegranskat)
|
|
| 5. |
- Fredriksson, Hans, 1974
(författare)
-
Nanostructured carbon materials prepared by hole-mask colloidal lithography
- 2007
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Research and development of nanofabrication methods can be motivated both formanufacturing of commercially available products like micro electronic componentsand for development of model systems for fundamental and applied science. Thefabrication process developed during this work, hole-mask colloidal lithography(HCL), is primarily oriented towards the latter two, specifically for research in thefields of catalysis, nanoparticle plasmons, and bio- and fundamental physics. Designof structured samples with precise control over size and shape of the nanostructuresare crucial components in all of these fields.The thesis describes the hole-mask colloidal lithography (HCL) technique, the generalprinciples of HCL and the technical and functional differences from standard colloidallithograpy (CL). The technique is illustrated with examples giving details on how tofabricate features with diameters from ~40 to 400 nm and with different shapes andmutual orientations. Some of the demonstrated geometries are discs, ellipses, cones,particle pairs and particles buried into a TiO2 surface.The nanostructuring of carbon materials using the HCL technique is described indetail. Nanostructured carbon surfaces are relevant as model systems to study theoptical properties of naturally occurring nanocarbon structures like aerosols andinterstellar dust. The applied fabrication process utilizes oxygen plasma to etch thepart of the carbon surfaces, not protected by the HCL mask. Analysis of the structuresize and shape resulting from the applied process parameters gives information aboutthe materials durability in reactive oxygen atmospheres, which is valuable forapplications where carbon materials are exposed to similar environments.The HCL technique is used to create etch-masks subsequently used to nanostructurecarbon surfaces via oxygen RIE. HOPG and GC surfaces are patterned in parallelusing identical fabrication processes. Careful characterization of the resulting size andshape of the carbon nanostructures, using SEM and AFM, revealed a significantdifference in response to oxygen plasma treatments for the two materials. On HOPGlateral etching under the etch mask is effectively suppressed thus resulting inpractically no undercut while GC is subject to severe etching under the masks. Theetch rate in the forward direction was found to be more than three times higher for GCthan HOPG (0.65 and 0.19 nm/s respectively). The HOPG nanostructuring processwas also followed with spectrophotometry, revealing decreased reflectance as a resultof the evolution of nanostructures. Part of the change in reflectance is due to thepresence of the etch mask, which consists of gold nanodiscs, but the major part isattributed to the carbon nanostructures.
|
|
| 6. |
- Fredriksson, Hans, 1974
(författare)
-
Nanostructures of Graphite and Amorphous Carbon - Fabrication and Properties
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nanoscience is a well-established research area, which concerns properties and fabrication of objects with typical dimensions on the 1-100 nanometer length scale. A central issue has been the development of techniques for fabrication and characterization of nanometer sized objects, which have contributed considerably to progress in both practical applications and fundamental research. Still, a standing challenge in nanofabrication is to further decrease the size limit and increase the precision in structure fabrication, with a simultaneous increase in reliability and cost-efficiency. Other goals are to facilitate fabrication of nanostructures in a variety of materials, with different geometries and spatial distributions. Examples of practical applications of nanofabrication are, electronic devices, nanoparticle reinforced composite materials, materials for extraction and storage of energy, sensors and biomedical applications. In this thesis, the development and application of a nanofabrication technique termed hole-mask colloidal lithography (HCL) is described. The technique is based on self-assembly of nanospheres in combination with spin coating and thin film evaporation to produce supported nanostructured masks for etch and/or deposition processes. HCL relies on a parallel process and uses relatively simple laboratory equipment. Therefore it is fast and cost-effective and can be used to structure large surface areas in a reasonable time. Furthermore, HCL is suited for fabrication of nanostructures with a variety of different shapes, with well-defined sizes and in a large variety of different materials. Demonstrated examples include discs, ellipses, bi-metallic particle pairs, cones and inverted ring structures in Au, Ag, Cr. Specifically, the use of HCL to fabricate nanostructures in three different carbon materials, highly oriented pyrolytic graphite (HOPG), glassy carbon (GC) and amorphous carbon, is described. Such nanostructured materials are relevant both in technical applications and in model studies of e.g. soot particles. The manufactured nanostrucutres have been characterized with respect to their geometrical, mechanical, and optical properties, using microscopy and spectroscopy techniques, and their reactivity towards oxidation has been explored. From studies of such samples, it is concluded that the etch rate in oxygen plasma is different for HOPG and GC, which influences the resulting size and shape of the nanostructures after the applied oxidation treatment. It is also shown that the atomic arrangement of the HOPG nanostructures is similar to that of the bulk material. Investigations of the optical properties reveal resonant absorption and scattering of light for nanostructures in all three materials, i.e. peak position, amplitude and width of the measured optical spectra are shown to correlate with the nanostructure sizes. This correlation is used to optically monitor oxidation, and the resulting decrease in volume, of carbon nanostructures under high temperature oxidation conditions and is proposed as a general sensing method to study oxidation/combustion of soot and other carbon nanostructures.
|
|
| 7. |
- Fredriksson, Hans, 1974, et al.
(författare)
-
Patterning of highly oriented pyrolytic graphite and glassy carbon surfaces by nanolithography and oxygen plasma etching
- 2009
-
Ingår i: Carbon. - 0008-6223. ; 47:5, s. 1335-1342
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a process for the fabrication of nanostructures on two types of carbon surfaces; glassy carbon (GC) and the basal surface of highly oriented pyrolytic graphite (HOPG). Using hole-mask colloidal lithography, etch masks with three different feature diameters were prepared on each of the two surface types. Oxygen reactive ion etching of different durations was then used to transfer the mask pattern onto the surfaces, yielding nanopillars with diameters ranging from not, vert, similar40 to 470 nm and heights between not, vert, similar30 and 430 nm. The structures were characterized using atomic force microscopy, scanning electron microscopy and optical spectrophotometry. Identical preparation schemes applied to the two materials yield nanostructures with remarkably different geometrical properties. In general GC structures are higher and narrower than HOPG structures prepared at the same plasma conditions. From the nanostructure dimensions and the corresponding etch times we have estimated etch rates in the forward and lateral directions to 0.19 and 0.015 nm/s for HOPG and 0.65 and 0.15 nm/s for GC. The different rates are attributed to different (an)isotropic etching behavior of the two materials in oxygen plasma. In addition, optical characterization reveals interesting changes in the surface reflectance as a result of the nanostructuring.
|
|
| 8. |
- Fredriksson, Hans, 1974, et al.
(författare)
-
Reduction of Cu-Promoted Fe Model Catalysts Studied by In Situ Indirect Nanoplasmonic Sensing and X-ray Photoelectron Spectroscopy
- 2015
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:8, s. 4085-4094
-
Tidskriftsartikel (refereegranskat)abstract
- The reduction of Cu-promoted Fe model catalysts was investigated using X-ray photoelectron spectroscopy (XPS) and indirect nanoplasmonic sensing (INPS). The catalysts were prepared by evaporation of 1 nm thick Fe particle films onto quartz wafers, followed by deposition of 0, 0.2, or 0.02 nm of Cu (i.e., 0, 2, or 19 wt %) as a promoter. For the XPS measurements, a reaction cell with in vacuo transfer to the measurement chamber was used. The catalysts were first oxidized at 400 degrees C in Ar/O-2, achieving fully oxidized Fe2O3 and CuO. Subsequently, the samples were heated to temperatures between 100 and 400 degrees C in pure H-2, and the resulting change in oxidation state was measured. Fe2O3 was found to be reduced to Fe3O4 at 225 degrees C and to a mixed state of FeO and metallic Fe at 275 degrees C. The corresponding temperatures for Cu-promoted Fe catalysts were 100 degrees C lower. In the absence of FeOx, Cu was reduced to metallic Cu, via Cu2O, at temperatures between 125 and 175 degrees C. In addition to the XPS measurements, INPS was used to obtain more detailed insight into the reduction process, both in pure H-2 and in wet H-2, containing 0.8 vol % H2O. These in situ experiments show that the presence of H2O increases the reduction temperature by 36 degrees C or more, depending on the amount of Cu promoter used, where the catalyst with the industrially relevant 2 wt % promoter material exhibits the smallest increase. The INPS measurements also demonstrate that increasing the amount of Cu promoter decreases the Fe2O3 reduction temperature, in both dry and wet H-2. Together, XPS and INPS offer a powerful combination for monitoring the oxidation state of flat model catalysts during pretreatments, an approach that can equally well be used during catalytic reaction conditions.
|
|
| 9. |
- Fredriksson, Hans, 1974, et al.
(författare)
-
Resonant optical absorption in graphite nanostructures
- 2009
-
Ingår i: Journal of Optics A: Pure and Applied Optics. - 1361-6617 .- 1464-4258. ; 11:11
-
Tidskriftsartikel (refereegranskat)abstract
- A systematic investigation of the correlation between optical absorption and the size of graphitenanostructures is presented. Five different samples with structure diameters ranging from ∼160to 330 nm and heights from ∼60 to 190 nm were prepared. The disk-like nanostructures wereetched out of the basal plane surface of highly oriented pyrolytic graphite, using hole-maskcolloidal lithography and oxygen reactive ion etching. Optical absorption spectra forwavelengths between 200 and 2500 nm were then measured. Furthermore, electrodynamicscalculations were conducted to model the optical properties of graphite nanostructures ofsimilar sizes. Both the experimental and the theoretical work revealed resonant absorptioncorrelated to the nanostructure diameters and heights. These absorption peaks are red-shifted,from the visible for the smallest structures to near infrared for the largest. Simultaneously, theintensity of the absorption peaks increases for increasing structure heights, while increasingdiameters results in decreased absorption.
|
|
| 10. |
|
|
