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Colloidal synthesis of metal oxide nanocrystals and thin films
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A main driving force behind the recent years’ immense interest in nanoscience and nanotechnology is the possibility of achieving new material properties and functionalities within, e.g., material physics, biomedicine, sensor technology, chemical catalysis, energy storing systems, and so on. New (theoretical) possibilities represent, in turn, a challenging task for chemists and physicists. An important feature of the present nanoscience surge is its strongly interdisciplinary character, which is reflected in the present work.

In this thesis, nanocrystals and thin films of magnetic and ferroelectric metal oxides, e.g. RE2O3 (RE = Y, Gd, Dy), GdFeO3, Gd3Fe5O12, Na0.5K0.5NbO3, have been prepared by colloidal and sol-gel methods. The sizes of the nanocrystals were in the range 3-15 nm and different carboxylic acids, e.g. oleic or citric acid, were chemisorbed onto the surface of the nanoparticles. From FT-IR measurements it is concluded that the bonding to the surface takes place via the carboxylate group in a bidentate or bridging fashion, with some preference for the latter coordination mode. The magnetic properties of nanocrystalline Gd2O3 and GdFeO3 were measured, both with respect to magnetic resonance relaxivity and magnetic susceptibility. Both types of materials exhibit promising relaxivity properties, and may have the potential for use as positive contrast enhancing agents in magnetic resonance imaging (MRI). The nanocrystalline samples were also characterised by transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and quantum chemical calculations.

Thin films of Na0.5K0.5NbO3, GdFeO3 and Gd3Fe5O12 were prepared by sol-gel methods and characterized by x-ray powder diffraction (XRPD) and scanning electron microscopy (SEM). Under appropriate synthesis conditions, rather pure phase materials could be obtained with grain sizes ranging from 50 to 300 nm. Magnetic measurements in the temperature range 2-350 K indicated that the magnetization of the perovskite phase GdFeO3 can be described as the sum of two contributing terms. One term (mainly) due to the spontaneous magnetic ordering of the iron containing sublattice, and the other a susceptibility term, attributable to the paramagnetic gadolinium sublattice. The two terms yield the relationship M(T)=M0(T)+χ(T)*H for the magnetization. The garnet phase Gd3Fe5O12 is ferrimagnetic and showed a compensation temperature Tcomp ≈ 295 K.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi , 2008.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1182
Keyword [en]
nanoparticles, synthesis, contrast agents, functionalization, thin films
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-11831ISBN: 978-91-7393-899-0 (print)OAI: oai:DiVA.org:liu-11831DiVA: diva2:18250
Public defence
2008-06-10, Planck, Fysikhuset, Campus Valla, Linköpings Universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2008-05-21 Created: 2008-05-21 Last updated: 2009-05-15
List of papers
1. Synthesis and characterisation of Gd2O3 nanocrystals functionalised by organic acids
Open this publication in new window or tab >>Synthesis and characterisation of Gd2O3 nanocrystals functionalised by organic acids
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2005 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 288, no 1, 140-148 p.Article in journal (Refereed) Published
Abstract [en]

Nanocrystals of Gd2O3 have been prepared by various methods, using, e.g., trioctylphosphine oxide (TOPO), diethylene glycol (DEG) or glycine. The crystalline particles were of sizes 5 to 15 nm. Different carboxylic acids, e.g., oleic acid or citric acid, were adsorbed onto the surface of the particles made with DEG. IR measurements show that the molecules coordinate to the Gd2O3 surface via the carboxylate group in a bidentate or bridging manner. The organic-acid/particle complexes were characterised by XRPD, TEM, FTIR, Raman, and XPS.

Keyword
Nanocrystals; Synthesis; Functionalisation; IR; XPS
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13295 (URN)10.1016/j.jcis.2005.02.089 (DOI)000229861600019 ()
Available from: 2008-05-21 Created: 2008-05-21 Last updated: 2017-12-13
2. Surface interactions between Y2O3 nanocrystals and organic molecules—an experimental and quantum-chemical study
Open this publication in new window or tab >>Surface interactions between Y2O3 nanocrystals and organic molecules—an experimental and quantum-chemical study
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2005 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 592, no 1-3, 124-140 p.Article in journal (Refereed) Published
Abstract [en]

The surface interactions between Y2O3 nanocrystals and the organic molecules formic acid, diethylene glycol (DEG), and tetramethoxy silane (TMOS), have been studied experimentally and by quantum chemical calculations with the intent to elucidate the chemisorption characteristics such as adsorbate vibrational spectra and adsorption structures. Nanocrystal synthesis was performed by a colloidal method based on polyols and by a rapid combustion method. The products were experimentally characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS).

In the quantum chemical calculations, the B3LYP hybrid density functional ab initio method was used to study the chemisorption of formic acid, DEG and TMOS at the surface of Y12O18 clusters. From a comparison of calculated and experimental vibrational spectra, the binding mode for formic acid on Y2O3 was inferred to be of bridge or bidentate type. The XPS and FT-IR experiments showed that DEG is chemisorbed on the particle surface. The experimental IR spectra of DEG chemisorbed on Y2O3 were consistent with an adsorption mode where the hydroxyl groups are deprotonated according to the quantum-chemical computations. The adsorption energy is of the order of 370 kJ mol−1 for formic acid, 550 kJ mol−1 for DEG, and 60 kJ mol−1 for TMOS, according to the quantum chemical calculations.

Keyword
Ab initio quantum chemical methods and calculations; X-ray photoelectron spectroscopy; Chemisorption; Yttrium; Alcohols; Carboxylic acid; Silane
National Category
Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-13296 (URN)10.1016/j.susc.2005.07.027 (DOI)000232461700015 ()
Available from: 2008-05-21 Created: 2008-05-21 Last updated: 2017-12-13Bibliographically approved
3. Polyethylene glycol-cover ultra-small Gd2O3 nanoparticles for positive contras at 1.5 T magnetic resonance clinical scanning
Open this publication in new window or tab >>Polyethylene glycol-cover ultra-small Gd2O3 nanoparticles for positive contras at 1.5 T magnetic resonance clinical scanning
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2007 (English)In: Nanotechnology, ISSN 0957-4484, Vol. 18, no 39, 395501- p.Article in journal (Refereed) Published
Abstract [en]

The size distribution and magnetic properties of ultra-small gadolinium oxide crystals (US-Gd2O3) were studied, and the impact of polyethylene glycol capping on the relaxivity constants (r1, r2) and signal intensity with this contrast agent was investigated. Size distribution and magnetic properties of US-Gd2O3 nanocrystals were measured with a TEM and PPMS magnetometer. For relaxation studies, diethylene glycol (DEG)-capped US-Gd2O3 nanocrystals were reacted with PEG-silane (MW 5000). Suspensions were adequately dialyzed in water to eliminate traces of Gd3+ and surfactants. The particle hydrodynamic radius was measured with dynamic light scattering (DLS) and the proton relaxation times were measured with a 1.5 T MRI scanner. Parallel studies were performed with DEG–Gd2O3 and PEG-silane–SPGO (Gd2O3,< 40 nm diameter). The small and narrow size distribution of US-Gd2O3 was confirmed with TEM (~3 nm) and DLS. PEG-silane–US-Gd2O3 relaxation parameters were twice as high as for Gd–DTPA and the r2/r1 ratio was 1.4. PEG-silane–SPGO gave low r1 relaxivities and high r2/r1 ratios, less compatible with positive contrast agent requirements. Higher r1 were obtained with PEG-silane in comparison to DEG–Gd2O3. Treatment of DEG–US-Gd2O3 with PEG-silane provides enhanced relaxivity while preventing aggregation of the oxide cores. This study confirms that PEG-covered Gd2O3 nanoparticles can be used for positively contrasted MR applications requiring stability, biocompatible coatings and nanocrystal functionalization.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13297 (URN)10.1088/0957-4484/18/39/395501 (DOI)000249283300006 ()
Available from: 2008-05-21 Created: 2008-05-21 Last updated: 2015-12-17
4. Colloidal synthesis and characterization of ultrasmall perovskite GdFeO3 nanocrystals
Open this publication in new window or tab >>Colloidal synthesis and characterization of ultrasmall perovskite GdFeO3 nanocrystals
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2008 (English)In: Nanotechnology, ISSN 0957-4484, Vol. 19, no 8, 085608- p.Article in journal (Refereed) Published
Abstract [en]

Synthesis of very small (about 4 nm) perovskite structured gadolinium orthoferrite nanoparticles (GdFeO3) was performed by the polyol method. The material shows promising relaxivity properties and potential as a contrast agent in magnetic resonance imaging. The perovskite nanoparticles were characterized by x-ray diffraction, transmission electron microscopy, energy dispersive x-ray spectroscopy, Fourier transform infrared spectroscopy, magnetic resonance, and magnetization measurements. Upon heating in air at 800 °C for 3 h the size of the crystals increased to about 40 nm. The crystalline structure of the heat treated compound is in good agreement with perovskite GdFeO3 as the primary product. Contributions from various secondary phases were also identified, including one hitherto unknown phase with the suggested composition 'Gd3FeO6' and isostructural with Gd3GaO6. The novel 'Gd3FeO6' phase appears to be kinetically stabilized in the nano state.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13298 (URN)10.1088/0957-4484/19/8/085608 (DOI)000252967400014 ()
Available from: 2008-05-21 Created: 2008-05-21 Last updated: 2015-10-09
5. Sol–gel synthesis and characterization of Na0.5K0.5NbO3 thin films
Open this publication in new window or tab >>Sol–gel synthesis and characterization of Na0.5K0.5NbO3 thin films
2005 (English)In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 281, no 2-4, 468-474 p.Article in journal (Refereed) Published
Abstract [en]

Thin films of the perovskite structured Na0.5K0.5NbO3 (NKN) have been synthesized with three different sol–gel methods, viz. the alkoxide method, a modified Pechini method and a somewhat novel oxalate method, based on 2-methoxy ethanol as solvent with oxalic acid and ethylene glycol as chelating ligand and stabilizer. Only one method (the modified Pechini method) gave pure NKN phase while the other two methods gave extra peaks in the X-ray diffraction patterns, indicating that other, unidentified, phases were present. SEM images revealed grain sizes ranging from 100 to 300 nm.

Keyword
Characterization; Chemical solution deposition processes; Niobates; Dielectric materials
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13299 (URN)10.1016/j.jcrysgro.2005.04.044 (DOI)000231011600038 ()
Available from: 2008-05-21 Created: 2008-05-21 Last updated: 2017-12-13
6. Sol-gel synthesis and characterization of polycrystalline GdFeO3 and Gd3Fe5O12 thin films
Open this publication in new window or tab >>Sol-gel synthesis and characterization of polycrystalline GdFeO3 and Gd3Fe5O12 thin films
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2009 (English)In: Journal of Sol-Gel Science and Technology, ISSN 0928-0707, E-ISSN 1573-4846, Vol. 49, no 2, 253-259 p.Article in journal (Refereed) Published
Abstract [en]

Thin films of the perovskite and garnet structured gadolinium ferrites GdFeO3 and Gd3Fe5O12 have been synthesized by a sol-gel method, based on stoichiometric mixtures of acetyl acetone chelated Gd3+ and Fe3+ dissolved in 2-methoxy ethanol. After spin coating onto Si wafers, and heating in air at 700 degrees C for 20 h, neatly grown essentially single phase films were obtained. From X-ray photoelectron spectroscopy an iron deficiency is observed in the uppermost layer of both films, implying that the crystallites preferably end in planes rich in Gd and O but not in Fe. The films were also characterized by X-ray powder diffraction, scanning electron microscopy, infrared spectroscopy, and magnetic measurements.

Keyword
Thin film, Gadolinium iron oxides, Sol-gel synthesis, Magnetic properties, XPS
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-16962 (URN)10.1007/s10971-008-1859-0 (DOI)
Available from: 2009-02-28 Created: 2009-02-27 Last updated: 2017-12-13

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