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Physical and electronic properties o...

Blagojevic, Vladimir.

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Physical and electronic properties of vanadium and titanium oxides nanocrystals.

紀錄類型:	書目-語言資料,印刷品 : Monograph/item
正題名/作者:	Physical and electronic properties of vanadium and titanium oxides nanocrystals./
作者:	Blagojevic, Vladimir.
面頁冊數:	92 p.
附註:	Adviser: Louis Brus.
Contained By:	Dissertation Abstracts International68-09B.
標題:	Chemistry, Inorganic. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3285045
ISBN:	9780549271130

Physical and electronic properties of vanadium and titanium oxides nanocrystals.
Blagojevic, Vladimir.

Physical and electronic properties of vanadium and titanium oxides nanocrystals. - 92 p.

Adviser: Louis Brus.

Thesis (Ph.D.)--Columbia University, 2007.

This thesis addresses the synthesis and physical properties of vanadium oxides nanocrystals, with particular focus on phase transitions, and the electronic properties of small titanium dioxide nanoclusters. The first part describes the synthesis of vanadium (III) oxide nanocrystals of different shapes and sizes. We achieved this through hydrothermal reduction of vanadyl hydroxide, using different ligands to control size and shape of resulting nanocrystals. The reaction exhibited a minimum required temperature, while reaction time was strongly dependent on ionic strength of the solution and the type of the surfactant, varying from 2 to 14 days.

ISBN: 9780549271130Subjects--Topical Terms:

517253
Chemistry, Inorganic.

Physical and electronic properties of vanadium and titanium oxides nanocrystals.
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035 $a (UMI)AAI3285045
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100 1 $a Blagojevic, Vladimir. $3 1279953
245 1 0 $a Physical and electronic properties of vanadium and titanium oxides nanocrystals.
300 $a 92 p.
500 $a Adviser: Louis Brus.
500 $a Source: Dissertation Abstracts International, Volume: 68-09, Section: B, page: 5941.
502 $a Thesis (Ph.D.)--Columbia University, 2007.
520 $a This thesis addresses the synthesis and physical properties of vanadium oxides nanocrystals, with particular focus on phase transitions, and the electronic properties of small titanium dioxide nanoclusters. The first part describes the synthesis of vanadium (III) oxide nanocrystals of different shapes and sizes. We achieved this through hydrothermal reduction of vanadyl hydroxide, using different ligands to control size and shape of resulting nanocrystals. The reaction exhibited a minimum required temperature, while reaction time was strongly dependent on ionic strength of the solution and the type of the surfactant, varying from 2 to 14 days.
520 $a We used V2O3 nanoparticles synthesized in this manner to observe a magnetic phase transition, which occurs at 150K in the bulk crystal. V2O3 makes a transition from paramagnetic to antiferromagnetic behavior on cooling, resulting in sharp drop in observed magnetic moment at the transition temperature. Initial SQUID measurement showed an inflection point around 150K, rather than sharp drop, in magnetic susceptibility of V2O3 nanoparticles, prompting us to use muon spin relaxation (muSR) to investigate the origin of the paramagnetic signal in our sample below the transition temperature. muSR allowed us to observe a change in volume of paramagnetic phase as the function of temperature, showing its continuous decrease with decreasing temperature, below 150K, and indicating a possible size dependence of the magnetic transition in V2O 3 nanoparticles.
520 $a Our search for a good way to synthesize long V2O3 nanorods and nanowires led us to discover a way to synthesize long VO 2 nanoribbons by way of hydrothermal recrystallization of VO2. While this reaction produces long nanoribbons with rectangular cross-section without any surfactant, at 210°C, we found that the best results are obtained by using 0.25% solution of 2-propanol in water. The nanowires produced this way have a cross-section 6-15nm high and 20-40nm wide, and they are single crystal. We found that the nanowires oxidized almost instantaneously, when exposed to air, creating, what appears to be, a self-passivating oxide layer on the surface. We were able to observe a phase transition, using differential scanning calorimetry, temperature dependent X-ray diffraction and Raman spectroscopy. Both DSC and TD-XRD showed a phase transition closely resembling that in the bulk crystal in the nanowire samples that have been exposed to air. Due to the fact that the Raman signal of these samples was dominated by the surface oxide, we conducted Raman experiments in inert and reducing atmosphere. These experiment showed much wider hysteresis of the phase transition than that of the bulk crystal and our own nanowire samples, with surface oxide layer. Our conclusion is that there is a strong possibility that the surface oxide layer suppressed the widening of the phase transition hysteresis.
520 $a Our original idea was to complement the experimental work on vanadium oxides with first principle calculations. As a precursor to calculations of VO2 nanoclusters, we started work on constructing TiO2 nanoclusters, because of their shared crystalline structure. This developed, over time, into a project on its own, where we tried to develop a good methodology to construct and calculate large anatase- and rutile-inspired TiO2 nanoclusters and correlate these results with the existing body of experimental and theoretical work relating to the dye-sensitized TiO2 solar cells. To achieve this, we conducted a series of tests, using small molecules and clusters containing titanium, of different basis sets, in order to find the best balance between the accuracy and the size of the calculations, choosing LACVP basis set. We conducted another series of calculations, using small clusters inspired by the local structures of anatase and rutile, in order to find a good way to construct large clusters, that would resemble anatase and rutile as close as possible. These calculations resulted in construction of anatase-inspired Ti21O70H54, and rutile-inspired Ti23O80H68 cluster. We proceeded to calculate their electronic structures and found that they are very similar to the electronic structures of anatase and rutile, respectively. We also found that the lowest unoccupied molecular orbital is localized in rutile-inspired, while it is delocalized in anatase-inspired cluster.
590 $a School code: 0054.
650 4 $a Chemistry, Inorganic. $3 517253
690 $a 0488
710 2 $a Columbia University. $3 571054
773 0 $t Dissertation Abstracts International $g 68-09B.
790 $a 0054
790 1 0 $a Brus, Louis, $e advisor
791 $a Ph.D.
792 $a 2007
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3285045