| 1. |
- Feng, Jicheng, et al.
(författare)
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General Approach to the Evolution of Singlet Nanoparticles from a Rapidly Quenched Point Source
- 2016
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:1, s. 621-630
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Tidskriftsartikel (refereegranskat)abstract
- Among the numerous point vapor sources, microsecond-pulsed spark ablation at atmospheric pressure is a versatile and environmentally friendly method for producing ultrapure inorganic nanoparticles ranging from singlets having sizes smaller than 1 nm to larger agglomerated structures. Due to its fast quenching and extremely high supersaturation, coagulational growth already begins at the atomic scale at room temperature. On the basis of this knowledge, we develop a simple semiempirical yet versatile model for predicting the size distribution of singlet particles as a function of the process conditions. The model assumes that a plume of a turbulent aerosol flow flares out from a concentrated point source, eventually reaching the walls of the confinement where a fraction of the particles is deposited. Despite the complexity of the entire process, the concentration and size evolution of particles can be adequately described by a first-order differential equation accounting for coagulation, turbulent dilution, and diffusional deposition to the walls. The model provides a simple and practical tool that can generally be used to design and control point vapor source reactors for the synthesis of singlets with tunable sizes starting from that of single atoms.
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| 2. |
- Giamarelou, Maria, et al.
(författare)
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Indirect evidence of the composition of nucleation mode atmospheric particles in the high Arctic
- 2016
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Ingår i: Journal of Geophysical Research - Atmospheres. - 2169-897X .- 2169-8996. ; 121:2, s. 965-975
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Tidskriftsartikel (refereegranskat)abstract
- Previous long-term observations have shown that nanoparticle formation events are common in the summer-time high Arctic and linked to local photochemical activity. However, current knowledge is limited with respect to the chemical precursors of resulting nanoparticles and the compounds involved in their subsequent growth. Here we report case-study measurements during new particle formation (NPF) events of the particle size distribution (diameter>7nm) and for the first time the volatility of monodisperse particles having diameter 40nm, providing indirect information about their composition. Volatility measurements provide indirect evidence that a predominant fraction of the 12nm particle population is ammoniated sulfates in the summertime high Arctic. Our observations further suggest that the majority of the sub-40nm particle population during NPF events does not exist in the form of sulfuric acid but rather as partly or fully neutralized ammoniated sulfates.
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| 3. |
- Petallidou, Klito C., et al.
(författare)
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Tuning atomic-scale mixing of nanoparticles produced by atmospheric-pressure spark ablation
- 2023
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Ingår i: Nanoscale Advances. - 2516-0230. ; 5:24, s. 6880-6886
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Tidskriftsartikel (refereegranskat)abstract
- Nanoparticles (NPs) mixed at the atomic scale have been synthesized by atmospheric-pressure spark ablation using pairs of Pd and Hf electrodes. Gravimetric analysis of the electrodes showed that the fraction of each material in the resulting mixed NPs can be varied from ca. 15-85 at% to 85-15 at% by employing different combinations of electrode polarities and thicknesses. These results were also qualitatively corroborated by microscopy and elemental analysis of the produced NPs. When using pairs of electrodes having the same diameter, the material from the one at negative polarity was represented at a substantially higher fraction in the mixed NPs regardless of whether a pair of thin or thick electrodes were employed. This can be attributed to the higher ablation rate of the electrodes at the negative polarity, as already known from earlier experiments. When using electrodes of different diameters, the fraction of the element from the thinner electrode was always higher. This is because thinner electrodes are ablated more effectively due to, at least in part, the increased importance of the associated heat losses compared to its thicker counterpart. In those cases, the polarity of the electrodes had a significantly smaller effect. Overall, our results demonstrate, for the first time, that spark ablation can be used to control atomic scale mixing and thus produce alloyed NPs with compositions that can be tuned to a good extent by simply using different combinations of electrode diameters and polarities. This expands the capabilities of the technique for producing mixed nanoparticle building blocks of well-defined composition that are highly desired for a wide range of applications.
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| 4. |
- Valenti, Marco, et al.
(författare)
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Hot Carrier Generation and Extraction of Plasmonic Alloy Nanoparticles
- 2017
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Ingår i: ACS Photonics. - : AMER CHEMICAL SOC. - 2330-4022. ; 4:5, s. 1146-1152
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Tidskriftsartikel (refereegranskat)abstract
- The conversion of light to electrical and chemical energy has the potential to provide meaningful advances to many aspects of daily life, including the production of energy, water purification, and optical sensing. Recently, plasmonic nanoparticles (PNPs) have been increasingly used in artificial photosynthesis (e.g., water splitting) devices in order to extend the visible light utilization of semiconductors to light energies below their band gap. These nanoparticles absorb light and produce hot electrons and holes that can drive artificial photosynthesis reactions. For n-type semiconductor photoanodes decorated with PNPs, hot charge carriers are separated by a process called hot electron injection (HEI), where hot electrons with sufficient energy are transferred to the conduction band of the semiconductor. An important parameter that affects the HEI efficiency is the nanoparticle composition, since the hot electron energy is sensitive to the electronic band structure of the metal. Alloy PNPs are of particular importance for semiconductor/PNPs composites, because by changing the alloy composition their absorption spectra can be tuned to accurately extend the light absorption of the semiconductor. This work experimentally compares the HEI efficiency from Ag, Au, and Ag/Au alloy nanoparticles to TiO2 photoanodes for the photoproduction of hydrogen. Alloy PNPs not only exhibit tunable absorption but can also improve the stability and electronic and catalytic properties of the pure metal PNPs. In this work, we find that the Ag/Au alloy PNPs extend the stability of Ag in water to larger applied potentials while, at the same time, increasing the interband threshold energy of Au. This increasing of the interband energy of Au suppresses the visible-light induced interband excitations, favoring intraband excitations that result in higher hot electron energies and HEI efficiencies.
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| 5. |
- Valenti, Marco, et al.
(författare)
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The Role of Size and Dimerization of Decorating Plasmonic Silver Nanoparticles on the Photoelectrochemical Solar Water Splitting Performance of BiVO4 Photoanodes
- 2016
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Ingår i: ChemNanoMat. - Weinheim : WILEY-V C H VERLAG GMBH. - 2199-692X. ; 2:7, s. 739-747
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Tidskriftsartikel (refereegranskat)abstract
- Ag nanoparticles (NPs) are deposited on BiVO4 photoanodes to study their effect on the photoelectrochemical (PEC) water splitting performance of the semiconductor. 15 nm light-absorbing NPs and 65 nm light scattering NPs were studied separately to compare their light trapping ability for enhancing the semiconductors absorption through light concentration and light scattering, respectively. The 15 nm NPs enhanced the BiVO4 external quantum efficiency throughout the semiconductors absorption range (e.g.,approximate to 2.5 fold at lambda=400 nm). However, when a hole scavenger was added to the electrolyte, no enhancement was ob-served upon NP deposition, indicating that the NPs only facilitate the injection of holes from the semiconductor surface to the electrolyte but do not enhance its absorption. On the other hand, the 65 nm scattering NPs not only facilitated hole injection to the electrolyte, but also enhanced the absorption of the semiconductor (by approximate to 6%) through light scattering. Such a dual effect, i.e., of enhancing both the surface properties and the absorption of the semiconductor, makes light scattering Ag NPs an ideal decoration for PEC water splitting photoelectrodes.
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