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- Nugroho, Ferry, 1986, et al.
(författare)
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Topographically Flat Nanoplasmonic Sensor Chips for Biosensing and Materials Science
- 2017
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Ingår i: ACS Sensors. - : American Chemical Society (ACS). - 2379-3694. ; 2:1, s. 119-127
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Tidskriftsartikel (refereegranskat)abstract
- Nanoplasmonic sensors typically comprise arrangements of noble metal nanoparticles on a dielectric support. Thus they are intrinsically characterized by surface topography with corrugations at the 10–100 nm length scale. While irrelevant in some bio- and chemosensing applications, it is also to be expected that the surface topography significantly influences the interaction between solids, fluids, nanoparticles and (bio)molecules, and the nanoplasmonic sensor surface. To address this issue, we present a wafer-scale nanolithography-based fabrication approach for high-temperature compatible, chemically inert and topographically flat and laterally homogeneous nanoplasmonic sensor chips. We demonstrate their sensing performance on three different examples, for which we also carry out a direct comparison with a traditional nanoplasmonic sensor with representative surface corrugation. Specifically, we (i) quantify the film-thickness dependence of the glass transition temperature in poly(methyl metacrylate) thin films, (ii) characterize the adsorption and specific binding kinetics of the avidin – b-BSA protein system and (iii) analyze supported lipid bilayer formation on SiO2 surfaces.
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- Benavidez, A. D., et al.
(författare)
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Environmental Transmission Electron Microscopy Study of the Origins of Anomalous Particle Size Distributions in Supported Metal Catalysts
- 2012
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 2:11, s. 2349-2356
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Tidskriftsartikel (refereegranskat)abstract
- In this Environmental Transmission Electron Microscopy (ETEM) study we examined the growth patterns' of uniform distributions of nanoparticles (NPs) using model catalysts. Pt/SiO2 was heated at 550 degrees C in 560 Pa of O-2 while Pd/carbon was heated in vacuum at 500 degrees C and in 300 Pa of 5%H-2 in Argon at temperatures up to 600 degrees C. Individual NPs of Pd were tracked to determine the operative sintering mechanisms. We found anomalous growth Of NPs occurred during the early stages of catalyst sintering wherein some particles started to grow significantly larger than the mean, resulting in a broadening of the particle size distribution (PSD). The abundance of the larger particles did not fit the log normal distribution. We can rule out sample nonuniformity as a cause for the growth of these large particles, since images were recorded prior to heat treatments. The anomalous growth of these particles may help explain PSDs in heterogeneous catalysts which often show particles that are significantly larger than the mean, resulting in a long tail to the right. It has been suggested previously that particle migration and coalescence could be the likely cause for such broad size distributions. We did not detect any random migration of the NPs leading to coalescence. A directed migration process was seen to occur at elevated temperatures for Pd/carbon under H-2. This study shows that anomalous growth of NPs can occur under conditions where Ostwald ripening is the primary sintering mechanism.
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- Fredriksson, Hans, 1974, et al.
(författare)
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Reduction of Cu-Promoted Fe Model Catalysts Studied by In Situ Indirect Nanoplasmonic Sensing and X-ray Photoelectron Spectroscopy
- 2015
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:8, s. 4085-4094
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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.
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- Kelf, T. A., et al.
(författare)
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Ultrafast Vibrations of Gold Nanorings
- 2011
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 11:9, s. 3893-3898
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the vibrational modes of gold nanorings on a silica substrate with an ultrafast optical technique. By comparison with numerical simulations, we identify several resonances in the gigahertz range associated with axially symmetric deformations of the nanoring and substrate. We elucidate the corresponding mode shapes and find that the substrate plays an important role in determining the mode damping. This study demonstrates the need for a plasmonic nano-optics approach to understand the optical excitation and detection mechanisms for the vibrations of plasmonic nanostructures.
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- Langhammer, Christoph, 1978, et al.
(författare)
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Asymmetric Hysteresis in Nanoscopic Single-Metal Hydrides: Palladium Nanorings
- 2012
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:40, s. 21201-21207
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Tidskriftsartikel (refereegranskat)abstract
- Using direct nanoplasmonic sensing (DNPS), we have studied hydrogen sorption in Pd nanorings with a constant average inner diameter of 240 nm and varying wall thickness. As the main finding we observe an unusual feature above a critical wall thickness in the appearance of a double plateau in the hydrogenation coexistence curve, whereas a single plateau is seen during dehydrogenation for all wall thicknesses. This is the first experimental observation of asymmetric hysteresis in a single metal system. We explain this effect by structural defect-related sample heterogeneity and the interplay of strain-dependent hydrogenation thermodynamics and kinetics.
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