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Formation of nanoparticles by laser-activated processes
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Chemistry, Department of Materials Chemistry.
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. , p. 66
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 855
Keywords [en]
Inorganic chemistry, nanoparticles, laser-assisted CVD, laser ablation, emission spectroscopy, size-distribution
Keywords [sv]
Oorganisk kemi
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-3454ISBN: 91-554-5664-2 (print)OAI: oai:DiVA.org:uu-3454DiVA, id: diva2:162886
Public defence
2003-06-03, Häggsalen, The Ångström Laboratory, Uppsala, 10:15
Opponent
Supervisors
Available from: 2003-05-13 Created: 2003-05-13Bibliographically approved
List of papers
1. Light emission from tungsten nanoparticles during laser-assisted chemical vapor deposition of tungsten
Open this publication in new window or tab >>Light emission from tungsten nanoparticles during laser-assisted chemical vapor deposition of tungsten
2001 In: J. Appl. Phys., Vol. 89, p. 3967-Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-90504 (URN)
Available from: 2003-05-13 Created: 2003-05-13Bibliographically approved
2. Analysis of thermal radiation from laser-heated gasphase tungsten nanoparticles
Open this publication in new window or tab >>Analysis of thermal radiation from laser-heated gasphase tungsten nanoparticles
In: J. Chem. Phys.Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-90505 (URN)
Available from: 2003-05-13 Created: 2003-05-13Bibliographically approved
3. Size-Distribution and Emission Spectroscopy of W Nanoparticles Generated byLaser-Assisted CVD for Different WF6/H2/Ar Mixtures
Open this publication in new window or tab >>Size-Distribution and Emission Spectroscopy of W Nanoparticles Generated byLaser-Assisted CVD for Different WF6/H2/Ar Mixtures
2003 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 107, no 42, p. 11615-11621Article in journal (Refereed) Published
Abstract [en]

Tungsten nanoparticles were produced by ArF excimer laser-assisted chemical vapor deposition fromWF6/H2/Ar gas mixtures. Subsequent pulses excited the gas-phase particles, allowing optical emissionspectroscopy to monitor the intensity of the emitted radiation and temperature of the laser-heated particles.A systematic study on size-distributions of the deposited particles, determined by electron microscopy, inconnection with emission spectroscopy and rate of deposition measurements is presented, with respect todifferent partial pressures of the reactants. The rates of deposition of W nanoparticle films were determinedby X-ray fluorescence spectroscopy. In addition, the intensity of the scattered 193 nm laser line was alsomonitored as the partial pressure of H2 was varied.

National Category
Engineering and Technology Natural Sciences
Identifiers
urn:nbn:se:uu:diva-90506 (URN)10.1021/jp0343077 (DOI)
Available from: 2003-05-13 Created: 2003-05-13 Last updated: 2017-12-14Bibliographically approved
4. Characterization and modeling of evaporation of laser-heated, LCVD generated tungsten nanoparticles
Open this publication in new window or tab >>Characterization and modeling of evaporation of laser-heated, LCVD generated tungsten nanoparticles
In: J. Appl. Phys.Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-90507 (URN)
Available from: 2003-05-13 Created: 2003-05-13Bibliographically approved
5. In-situ monitoring and characterization of Nanoparticles During W Ablation in N2 Atmosphere
Open this publication in new window or tab >>In-situ monitoring and characterization of Nanoparticles During W Ablation in N2 Atmosphere
Show others...
2003 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 94, no 3, p. 2011-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].

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-90508 (URN)10.1063/1.1587253 (DOI)
Available from: 2003-05-13 Created: 2003-05-13 Last updated: 2017-12-14Bibliographically approved
6. Early stage of material removal during ArF excimer laser ablation of graphite
Open this publication in new window or tab >>Early stage of material removal during ArF excimer laser ablation of graphite
In: Appl. Phys. AArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-90509 (URN)
Available from: 2003-05-13 Created: 2003-05-13Bibliographically approved
7. Monitoring nanoparticle formation during laser ablation of graphite in atmospheric pressure ambient
Open this publication in new window or tab >>Monitoring nanoparticle formation during laser ablation of graphite in atmospheric pressure ambient
In: Appl. Phys. AArticle in journal (Refereed) Submitted
Identifiers
urn:nbn:se:uu:diva-90510 (URN)
Available from: 2003-05-13 Created: 2003-05-13Bibliographically approved

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