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Speaker:
Bamidele
Allimi
Advisor:
Bio: Dele
received his Bachelors (Engineering Physics) in 2000 from The Obafemi Awolowo
University, Ile-Ife, Nigeria. After working for two years with Deloitte and
Touche, Nigeria, he moved to Bowling Green State University, Ohio, USA where he
received his Masters degree (Physics) in 2005. He worked on the Photocurrrent
measurement of Gallium Arsenide deposited on Silicon by Pulsed Laser Deposition
(PLD) technique for his Masters thesis. Dele joined the Functional Materials
group as a PhD candidate in fall, 2005 and currently working on PLD of metal
insulator materials - V2O3 and ferromagnetic materials - CoFe2O3.
Topic: Growth
of V2O3 thin-films on sapphire substrates via pulsed laser deposition.
Abstract:
This
presentation is on the growth of V2O3 thin-films on sapphire substrates via
pulsed laser deposition (PLD). The films were characterized using X-ray
diffraction (XRD), X-ray photoemission spectroscopy (XPS), X-ray absorption fine
structure (XAFS) spectroscopy, and atomic force microscopy (AFM). XPS
measurements confirmed that the stoichiometry of the powder was conserved in the
films. XRD patterns together with XAFS measurements proved that V2O3 was
epitaxial on the a- sapphire substrate with epitaxial relation
(110)film//(110)substrate and the results were consistent with the epitaxy on
the c-plane substrate as well. A strain effect of substrates on the film is
discussed.
Speaker:
Ramesh Nath
Advisor:
Bio:
Ramesh
graduated from the National University of Singapore (NUS) with a Bachelor of
Science with Honours (Materials Science) in 2001. He then continued his Masters
in Science in NUS (Materials Science) where he graduated in 2003. His masters
thesis topic involves the in situ TEM observation of nickel silicide formation
on SiGe substrates. After graduation, he then continued in the area of in situ
TEM studying silicide and magnetic film growth as a research scientist. Ramesh
joined the UConn IMS Materials Science and Engineering program in the Fall
semester of 2004. He joined the NanoMeasurements Lab under the guidance of
Prof. Bryan Huey, studying the imaging of ferroelectric domains using Piezo
Force Microscopy (PFM). Since then, Ramesh has developed a novel method of High
Speed PFM, which allows the acquisition of data a higher rate, up till to 2
orders of magnitude or more, compared to conventional PFM.
Topic:
Dynamic
studies of ferroelectric domain switching using high speed piezoresponse force
microscopy
Abstract:
Dynamics of
ferroelectric domain switching are characterized in BiFeO3 thin films for
interfaces of varying orientation. Piezo Force Microscopy is commonly used for
such nanoscale domain studies, but practical limitations on imaging speeds limit
its application for dynamic studies. In this work a new method, high speed PFM (HSPFM),
is applied to investigate dynamic processes such as switching, charge
dissipation, and domain wall motion. Uniquely, measurements are performed with
high-speed PFM, allowing complete image acquisition with standard resolution
(256x256 pixels) in less than 3 seconds. The influence on domain switching of
interfaces of varying orientation is presented for BiFeO3 films grown on (100)
and (111) SrTiO3 substrates. Based on movies of hundreds of such images, domain
nucleation and growth of epitaxial BiFeO3 films are presented and exhibit a
profound asymmetry in domain switching mechanisms.
Speaker:
Chunguang
Tang
Advisor:
Bio:
BS:
University of Science and Technology Beijing, China (mainland)
Major in physical metallurgy
Worked for Xiangtan (pronounced as
Shiangtan) Iron Steel Co. for 5 years
MS: National University of Singapore,
Singapore
Major in materials science
Joined UConn in Aug. 2005 and now working with Prof. Ramprasad.
Topic: Diffusion
of O defects near Si:HfO2 interfaces: An ab initio investigation
Abstract:
Device
miniaturization in the microelectronic industry requires the replacement of SiO2
by high-permittivity materials such as HfO2 and ZrO2. While HfO2 and ZrO2 are
expected to be thermodynamically stable on Si, undesired interfacial phases such
as silicides, silicates and silica are known to form. In this work we
investigated the formation and migration energies of O defects in Si: HfO2
heterostructures by first principles modeling, and found that the segregation of
O defects provides a mechanism for such interfacial phase formation.
Speaker:
Shan Zhong
Advisor:
Bio:
Shan
Zhong received the B.Sc. degree in materials science and engineering from
Shanghai Jiao Tong University, Shanghai, China, and the M.Sc. degree in
metallurgy and materials engineering from University of Connecticut, Storrs, CT,
in 2003 and 2005, respectively. He is currently pursuing his Ph.D. degree in
materials science and engineering at the University of Connecticut, Storrs, CT.
His research interests include modeling and deposition of ferroelectric
superlattices, multilayers and multiferroic thin films. He is a member of the
American Physical Society and the Materials Research Society.
Topic: Ferroelectric
Multilayers and Heterostructures for High Performance Tunable Microwave Devices
Applications
Abstract:
Ferroelectric
multilayers and heterostructures have attracted a significant amount of
interests in the past decades due to their unique properties compared to their
homogenous counterparts. A number of peculiar phenomena, such as gigantic
dielectric permittivity, enhanced spontaneous polarizations, high dielectric
tunability, and special phase transformation characteristics, have been
discovered in various ferroelectric materials heterostructure systems. This
study is a theoretical and experimental effort to understand their potential
applications in high performance tunable microwave devices. A comprehensive
thermodynamic modeling, using Landau-Ginzburg-Devonshire formalism, theory of
elasticity, and principles of electrostatics will be developed to analyze the
interlayer coupling, interface effect, strain effect in ferroelectric
multilayers and heterostructures. The theoretical results will then be employed
to guide the fabrications of ferroelectric multilayers with high dielectric
tunability, low dielectric loss, and temperature insensitive dielectric
permittivity, which have potential applications in next generation tunable
microwave devices. With the guidance of theoretical analysis, multilayered
Ba1-xSrxTiO3 (BST) films were deposited on Pt coated Si substrates via
metalorganic solution deposition. The multilayer heterostructures consisted of
three distinct layers of ~220 nm nominal thickness with compositions
corresponding to BST 63/37, BST 78/22, and BST 88/12. At room temperature, the
heterostructure has a small-signal dielectric permittivity of 360 with a
dissipation factor of 0.012 and a dielectric tunability of 65% at 444 kV/cm.
These properties exhibited minimal dispersion as a function of temperature
ranging from 90 to -10oC.
Topics
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