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In-situ monitoring and characterization of Nanoparticles During W Ablation in N2 Atmosphere
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
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2003 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 94, no 3, 2011- p.Article in journal (Refereed) Published
Abstract [en]

ABSTRACT Nanoparticles were generated by pulsed laser ablation of tungsten in a N[sub 2] ambient at atmospheric pressure. Size distributions and concentrations were monitored in situ versus laser fluence, repetition rate, and ablated spot size, by a differential mobility analyzer and a particle counter. The multishot ablation threshold was determined to be ∼6 J/cm² for the laser used (ArF excimer, δ = 193 nm). Mostly small, nonlognormally, distributed particles (<20 nm in diameter) were generated below the ablation threshold (Φ[sub th]), and the relative concentration of larger particulates (>20 nm in diameter) increased above Φ[sub th]. Modeling of the temperature and ablated depth dependence on fluence showed that the formation of clusters below Φ[sub th] could not be assigned to a thermal process, but are connected to particle condensation from a photochemically desorbed thin layer. X-ray diffraction and x-ray photoelectron spectroscopy analysis performed on polydisperse nanoparticles revealed an amorphous phase of the particles, and the elemental composition was found to be WN[sub 0.3].

Place, publisher, year, edition, pages
2003. Vol. 94, no 3, 2011- p.
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-90508DOI: 10.1063/1.1587253OAI: oai:DiVA.org:uu-90508DiVA: diva2:162883
Available from: 2003-05-13 Created: 2003-05-13 Last updated: 2013-06-14Bibliographically approved
In thesis
1. Formation of nanoparticles by laser-activated processes
Open this publication in new window or tab >>Formation of nanoparticles by laser-activated processes
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Due to the small dimensions, nanoparticles and materials consisting of nano-sized building blocks exhibit unique — mostly superior — properties, well differing from their bulk counterpart. Most of the novel properties of nanoparticles (and nanomaterials) are size-dependent, while the majority of the common gasphase methods used for generation of nanopowders result in different, usually wide, size-dispersions. Further understanding of the fundamental processes leading to particle formation is therefore required, leading to better control of size and distribution of the nanoparticles, thus allowing engineering of the desired properties for both nanoparticles and nanomaterials.

In this present thesis, nanoparticles were produced by two different gasphase techniques activated by lasers, namely laser chemical vapor deposition (LCVD) and pulsed laser ablation (PLA). Optical emission spectroscopy (OES) was performed on thermal (blackbody-like) radiation originating from laser-excited particles during LCVD and coupled to measured size-distributions. In-situ monitoring of size-distributions by a differential mobility analyzer (DMA) was employed during PLA. In addition, deposited nanoparticles were characterized by a variety of standard techniques.

Different cooling mechanisms of the laser-excited gasphase particles were identified based on temperature and emitted intensity data extracted from OES measurements. The strong evaporation at elevated temperatures also allowed direct size manipulation of the particles. By monitoring the intensity of the emitted thermal radiation and the scattered laser line, strong indications about the so called coagulation limit, where a broadening of the size-distribution occurred, was obtained. The DMA monitoring, supported by modeling, gave information about different mechanisms (thermal and photochemical) of the ablation process, and particle condensation well below the ablation threshold was also found.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2003. 66 p.
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 855
Inorganic chemistry, nanoparticles, laser-assisted CVD, laser ablation, emission spectroscopy, size-distribution, Oorganisk kemi
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
urn:nbn:se:uu:diva-3454 (URN)91-554-5664-2 (ISBN)
Public defence
2003-06-03, Häggsalen, The Ångström Laboratory, Uppsala, 10:15
Available from: 2003-05-13 Created: 2003-05-13Bibliographically approved

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