| 1. |
- Schwind, Markus, 1983, et al.
(author)
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Diffraction from Arrays of Plasmonic Nanoparticles with Short-Range Lateral Order
- 2012
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In: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 6:11, s. 9455-9465
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Journal article (peer-reviewed)abstract
- We have measured the angular distribution of light scattered off 2D plasmonic Al nanoparticle ensembles. We created.. these samples with disk-like nanoparticles, 175 and 500 nm in diameter, respectively, using hole-mask colloidal lithography and electron beam lithography. The nanoparticle arrangements In the samples display the Short-range order (but no long-range order) characteristic for an ensemble formed by random sequential adsorption. As a consequence of this, the ensemble scattering patterns can be quantitatively well described by combining the single-particle scattering pattern with a static structure factor that carries information about the diffraction effects caused by the short-range order of the ensemble. We also performed sensing experiments in which we monitored changes in the angle-resolved scattering intensity for a fixed wavelength as a function of the thickness of an ultrathin SiO2 coating covering the Al nanoparticles. The data show that the angle and strength of the main diffraction peak vary linearly, with SiO2 coating thickness In the range 1.5-4.5 nm and suggest that measurements of the scattering profile could be a competitive alternative to traditional transmission measurements in terms of sensitivity.
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| 2. |
- Barth, Joachim, et al.
(author)
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Investigation of the thermoelectric properties of LiAlSi and LiAlGe
- 2010
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In: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 1543-186X .- 0361-5235. ; 39:9, s. 1856-1860
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Journal article (peer-reviewed)abstract
- The compounds LiAlSi and LiAlGe were synthesized and their thermoelectric properties and temperature stability were investigated. The samples were synthesized by arc melting of the constituent elements. For the determination of the structure type and the lattice parameter, x-ray powder diffraction was used. Both compounds were of the C1 b structure type. The stability of the compounds was investigated by differential thermal analysis and thermal gravimetry. The Seebeck coefficient and the electrical resistivity were determined in the temperature range from 2 K to 650 K. All compounds showed p-type behavior. The thermal conductivity was measured from 2 K to 400 K. The evaluation of the thermal conductivity yielded values as low as 2.4 W m -1 K -1 at 400 K for LiAlGe. The low values are ascribed to high mass fluctuation scattering and a possible rattling effect of the Li atoms.
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| 3. |
- Hosseinpour, Saman, et al.
(author)
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Integration of Quartz Crystal Microbalance with Vibrational Sum Frequency Spectroscopy-Quantification of the Initial Oxidation of Alkanethiol-Covered Copper
- 2012
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In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:46, s. 24549-24557
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Journal article (peer-reviewed)abstract
- We report the first integration of the interface sensitive technique vibrational sum frequency spectroscopy (VSFS) and the mass sensitive technique quartz crystal microbalance (QCM). VSFS-QCM has been applied in-situ to follow the formation of a thin Cu2O-like oxide on octadecanethiol-covered copper in dry air at ambient pressure conditions. We observed significant changes and an evolution of the VSF spectra caused by alterations in the electronic properties of the metal surface, and simultaneous shifts in the QCM resonance frequency due to a mass change during the formation of the oxide. QCM and VSFS exhibit a resolution corresponding to the formation of around 2% and 5% of an ideal monolayer of Cu2O, respectively. The successful integration of QCM increases the versatility of VSFS in numerous applications, where simultaneous in situ mass and spectroscopic information is desirable.
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| 4. |
- Langhammer, Christoph, 1978, et al.
(author)
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Localized Surface Plasmon Resonances in Aluminum Nanodisks
- 2008
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 8:5, s. 1461-1471
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Journal article (peer-reviewed)abstract
- The plasmonic properties of arrays of supported Al nanodisks, fabricated by hole-mask colloidal lithography (HCL), are analyzed for the disk diameter range 61-492 nm at a constant disk height of 20 nm. Strong and well-defined (UV-vis-NIR) localized surface plasmon resonances are found and experimentally characterized with respect to spectral peak positions, peak widths, total cross sections, and radiative and nonradiative decay channels. Theoretically, the plasmon excitations are described by electrostatic spheroid theory. Very good qualitative and quantitative agreement between model and experiment is found for all these observables by assuming a nanoparticle embedded in a few nanometer thick homogeneous (native) aluminum oxide shell. Other addressed aspects are: (i) the role of the strong interband transition in Al metal, located at 1.5 eV, for the plasmonic excitations of Al nanoparticles, (ii) the role of the native oxide layer, and (iii) the possibility of using the plasmon excitation as an ultrasensitive, remote, real-time probe for studies of oxidation/corrosion kinetics in metal nanoparticle systems. © 2008 American Chemical Society.
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| 5. |
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| 6. |
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| 7. |
- Schwind, Markus, 1983, et al.
(author)
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Combined in Situ Quartz Crystal Microbalance with Dissipation Monitoring, Indirect Nanoplasmonic Sensing, and Vibrational Sum Frequency Spectroscopic Monitoring of Alkanethiol-Protected Copper Corrosion
- 2013
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:23, s. 7151-7161
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Journal article (peer-reviewed)abstract
- In this study, we have applied three techniques to simultaneously and in situ study the initial stage of corrosion of copper protected by a self-assembled monolayer of octadecanethiol (ODT). We combined quartz crystal microbalance with dissipation monitoring (QCM-D), indirect nanoplasmonic sensing (INPS), and vibrational sum frequency spectroscopy (VSFS) and obtained complementary information about mass uptake and optical and spectroscopic changes taking place during the initial corrosion phase. All three techniques are very sensitive to the formation of a corrosion film (thickness in the range 0-0.41 nm) under mildly corrosive conditions (dry air, <0.5% relative humidity). The three techniques yield information about the viscoelasticity of the corrosion film (QCM-D), the homogeneity of the corrosion reaction on the surface (INPS), and the stability of the ODT. protection layer (VSFS). Furthermore, by also studying the corrosion process in humid air (ca. 70% relative humidity), we illustrate how the combination of these techniques can be used to differentiate between simultaneously occurring processes, such as water adsorption and corrosion product formation.
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| 8. |
- Schwind, Markus, 1983
(author)
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Kinetic Measurements Using Nanoplasmonic Sensing
- 2010
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Licentiate thesis (other academic/artistic)abstract
- In this thesis the nanoplasmonic sensing technique was used to study kinetics of (i) the oxidation of Al nanoparticles in air and water and (ii) the solid-liquid phase transition in Sn nanoparticles. The nanoplasmonic sensing technique detects changes of the localized surface plasmon resonance (LSPR) in metal nanoparticles.When light shines on metal nanoparticles, at some wavelength the conduction electrons oscillate in resonance with the light. This resonance is called LSPR. It depends on the electronic structure, size, and shape of the nanoparticle as well as the optical properties of its nanoenvironment.(i) LSPRs in Al nanoparticles were characterized in detail: Extinction, scattering, and absorption efficiencies were determined experimentally for several different nanodisk sizes in the UV-vis-NIR spectral range. The experimental values were shown to be in good agreement with calculations based on the modified long wavelength approximation (MLWA).The oxidation in air of these Al particles was followed for long time periods. The results showed that nanoplasmonic sensing has potential for oxidation studies of metallic nanoparticles. In a more elaborate study, using both the nanoplasmonic sensing technique and quartz crystal microbalance with dissipation monitoring (QCM-D), highly resolved oxidation kinetics were measured for oxidation in water. MLWA model calculations of the LSPR facilitated interpretation of the results. Oxidation of Al nanoparticles in water was found to proceed in several stages, as reported for bulk Al, forming presumably pseudoboehmite (Al2O3·H2O) in the process.(ii) LSPRs in solid and liquid Sn nanoparticles were studied in the temperature range 25-250◦C. Distinct changes of the LSPR features occur when the particles melt and freeze. A large hysteresis between the melting and freezing point is observed. Obviously, nucleation of the solid phase is hindered unless the temperatures is considerably below the melting point. Kinetic measurements of the freezing event at different constant temperatures were performed. Classical nucleation theory with modifications considering the finite nanoparticle dimensions accounts well for the observed behavior.
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| 9. |
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| 10. |
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| 11. |
- Schwind, Markus, 1983, et al.
(author)
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Localized and Propagating Plasmons in Metal Films with Nanoholes
- 2013
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 13:4, s. 1743-1750
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Journal article (peer-reviewed)abstract
- The occurrence of plasmon resonances in thin (similar to 20 nm) Al and Au films, perforated with nanoholes, was studied. In both metals, two 9 plasmon resonances were observed: (i) A surface plasmon polariton mode associated with a maximum in extinction and (ii) a localized resonance in the nanohole associated with a minimum in extinction. By varying the diameter of the nanoholes, the scaling of the peak positions of the plasmon resonances was determined as a function of hole diameter. In the large nanohole limit, the plasmon peak positions depend only on the nanohole diameter being independent of the material. On the other hand, for small nanoholes the plasmon peak positions are material and size dependent. In contrast to Al films where the localized plasmons can be excited from the near-IR to the UV, no plasmon resonances were observed for Au at energies above the interband threshold (2.4 eV). The interaction between a distinct interband transition in Al at 1.5 eV and the localized plasmon resonance is considered in detail. We observe for the first time experimentally a noncrossing behavior of the interband transition and the localized plasmon resonance. The energy (size) dependence of surface plasmon peak width, being a measure for the decay/damping of the latter, is very different for the two metals. This can be explained by considering the different decay mechanisms active in the two metals. Apart from these basic plasmonics results, we test the potential of using the shifts of the plasmon resonances in perforated Al films to follow the atmospheric oxidation/corrosion kinetics of Al. The results are quantified by model calculations. The obtained kinetic law for the oxide growth is in good agreement with a previous XPS study on plain Al films. This suggests that the nanohole-induced plasmon resonances can be a sensitive and simple measure for Al corrosion and metal corrosion in general.
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| 12. |
- Schwind, Markus, 1983, et al.
(author)
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LSPR study of the kinetics of the liquid-solid phase transition in Sn nanoparticles
- 2010
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In: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:3, s. 931-936
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Journal article (peer-reviewed)abstract
- Using the localized surface plasmon resonance as a probe in solid and liquid Sn nanoparticles of 107 nm diameter and 52 nm height, we have studied their kinetics of melting and freezing at temperature ramps and, for the first time, at fixed temperatures. During temperature ramps, the kinetics exhibit distinct hysteresis. The melting occurs near the bulk melting point while the freezing is observed at much lower temperatures so that the undercooling interval is similar to 130 K. The time scale of the freezing kinetics measured at different fixed temperatures rapidly decreases as the latter are lowered. All these findings have been quantitatively described by assuming the nucleation to occur on the edges of nanoparticles and employing the classical nucleation theory with the corresponding modifications.
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| 13. |
- Schwind, Markus, 1983, et al.
(author)
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Nanoplasmonic sensing and QCM-D as ultrasensitive complementary techniques for kinetic corrosion studies of aluminum nanoparticles
- 2011
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In: Applied Surface Science. - : Elsevier BV. - 0169-4332. ; 257:13, s. 5679-5687
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Journal article (peer-reviewed)abstract
- Corrosion (oxidation) kinetics of Al nanodisks, 262nm in diameter and 20nm in height, was measured in degassed Milli-Q water at 23 degrees C and neutral pH by quartz crystal microbalance with dissipation monitoring (QCM-D) and nanoplasmonic sensing. The former detects the changes of the resonance frequency and the damping of the oscillation of a piezoelectric quartz crystal resonator. The latter detects the changes of the localized surface plasmon resonance (LSPR) in the metallic part of the Al nanoparticle, caused both by the shrinking metallic core and the changes in the dielectric environment as the oxide grows. Highly resolved kinetic data were obtained which show different corrosion stages. The two techniques yield complementary information not obtainable with one technique alone. Two main corrosion mechanisms, namely homogeneous oxide growth and nanoparticle fragmentation and roughening, are distinguished. The time dependence of the corrosion kinetics, determined using QCM-D, is in agreement with weight gain studies of bulk Al found in literature. The nanoplasmonic sensing measurements are compared to analytical model calculations of LSPR shifts which yield an estimate for the increase of oxide thickness during homogeneous oxide growth. (C) 2011 Elsevier B. V. All rights reserved.
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| 14. |
- Schwind, Markus, 1983
(author)
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Nanoplasmonic Sensing for Materials Science
- 2013
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Doctoral thesis (other academic/artistic)abstract
- With the rising importance of nanoscience and nanotechnology, there is a need for new sensitive and easy-to-use characterization techniques able to follow processes at the nanoscale. In this thesis different aspects of nanoplasmonic sensing for studying materials science processes at the nanoscale are demonstrated and discussed for the following model systems: oxidation/corrosion of Al and Cu and the solid-liquid phase transition of Sn.Nanoplasmonic sensing relies on the excitation of localized surface plasmons (LSPR) in metal nanoparticles. The resonance details are very sensitive to optical property changes in/on the nanoparticles themselves or in their nano- scale neighborhood, e. g., surface oxidation/corrosion.The corrosion of Al and Cu nanoparticles and thin films was studied using nanoplasmonic sensing in various environments like dry and humid air and liquid water and (for Cu) with and without a corrosion inhibitor. Corrosion kinetics were measured with submonolayer sensitivity – even in the case of very slow corrosion, such as in mildly oxidizing environments and when the metal surface was protected by a corrosion inhibitor.The solid-liquid (melting-freezing) phase transition in Sn nanoparticles was investigated by nanoplasmonic sensing. The undercooling as well as the melting and freezing kinetics were measured and analyzed theoretically.In order to gain broad information about studied systems, it is often desirable to combine several techniques in situ, with the same sample. Nanoplasmonic sensing is very suitable for such combinations. Here, experimental integration was realized of nanoplasmonic sensing with quartz crystal microbal- ance with dissipation monitoring (QCM-D) and with vibrational sum frequency spectroscopy (VSFS).This thesis demonstrates that nanoplasmonic sensing is a highly sensitive, fast, easy-to-use, and versatile technique that can be used to monitor a variety of processes in materials science in situ and in real time.
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| 15. |
- Schwind, Markus, 1983, et al.
(author)
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Nanoplasmonic Sensing for Monitoring the Initial Stages of Atmospheric Corrosion of Cu Nanodisks and Thin Films
- 2013
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In: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 160:10, s. C487-C492
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Journal article (peer-reviewed)abstract
- Nanoplasmonic sensing as a powerful experimental technique for corrosion kinetics monitoring is demonstrated. Its versatility is illustrated by studies of initial corrosion carried out on model systems consisting of copper nanodisks and extended copper films in both dry (<0.5% relative humidity, RH) and humid (65 +/- 5% RH) air. Samples with and without a protective self-assembled monolayer of octadecanethiol (ODT) were studied. Thus, we studied four different corrosion situations. Two versions of the technique were employed, direct and indirect nanoplasmonic sensing (INPS). The former used disk-shaped nanoparticles as both sample structures and sensing particles, the latter used extended films as the sample, with the nanoplasmonic sensing particles embedded under the sample. Corrosion kinetics were recorded with high sensitivity and high temporal resolution (submonolayer detection limit; temporal resolution 1-2 seconds). In dry air, six times lower oxidation rates were observed for ODT-covered Cu compared to bare Cu, demonstrating the protection efficiency of the ODT as a corrosion inhibitor. In humid air, a higher oxidation rate was measured for both bare (2.4 times higher) and ODT-covered (1.7 times higher) samples, compared to the same samples exposed to the dry air environment. Oxidation occurred first after a short induction period during which water was adsorbed. For the Cu nanodisks (direct sensing) and Cu films (indirect sensing) studied here, very similar oxidation kinetics were observed.
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| 16. |
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| 17. |
- Zhdanov, Vladimir, 1952, et al.
(author)
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Overheating and undercooling during melting and crystallization of metal nanoparticles
- 2010
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In: Physica E: Low-Dimensional Systems and Nanostructures. - : Elsevier BV. - 1386-9477. ; 42:7, s. 1990-1994
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Journal article (peer-reviewed)abstract
- In analogy with macroscopic metal samples, crystallization of metal nanoparticles may occur appreciably below the thermodynamic melting temperature, Tm (this temperature depends on the particle size), while melting occurs at Tm. If the surface melting is suppressed, nanoparticles can be overheated during melting. We describe these effects by using the classical nucleation theory and assuming that the nucleation starts at the particle corners or edges. The corresponding undercooling or overheating temperature intervals are found to be about 0.1Tm for corners and 0.15Tm for edges. These values are, respectively, two and one and a half times smaller than that for macroscopic samples. Under certain conditions, crystallization and melting can be controlled by the propagation of the front of a new phase. The corresponding temperature interval is found to be very narrow (about 0.02Tm).
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