1,094 research outputs found
Effect of manganese doping on the size effect of lead zirconate titanate thin films and the extrinsic nature of dead layers
We have investigated the size effect in lead zirconate titanate (PZT) thin
films with a range of manganese (Mn) doping concentrations. We found that the
size effect in the conventional Pt/PZT/Pt thin-film capacitors could be
systematically reduced and almost completely eliminated by increasing Mn doping
concentration. The interfacial layer at the electrode-film interface appears to
disappear almost entirely for the PZT films with 2% Mn doping levels, confirmed
by the fits using the conventional in-series capacitor model. Our work
indicates that the size effect in ferroelectrics is extrinsic in nature,
supporting the work by Saad et al. Other implications of our results have also
been discussed. By comparing a variety of experimental studies in the
literature we propose a scenario that the dead layer between PZT (or barium
strontium titanate, BST) and metal electrodes such as Pt and Au might have a
defective pyrochlore/fluorite structure (possibly with a small portion of
ferroelectric perovskite phase).Comment: 21 pages, 6 figure
Voltage-controlled electron tunnelling from a single self-assembled quantum dot embedded in a two-dimensional-electron-gas-based photovoltaic cell
We perform high-resolution photocurrent (PC) spectroscopy to investigate
resonantly the neutral exciton ground-state (X0) in a single InAs/GaAs
self-assembled quantum dot (QD) embedded in the intrinsic region of an
n-i-Schottky photodiode based on a two-dimensional electron gas (2DEG), which
was formed from a Si delta-doped GaAs layer. Using such a device, a single-QD
PC spectrum of X0 is measured by sweeping the bias-dependent X0 transition
energy through that of a fixed narrow-bandwidth laser via the quantum-confined
Stark effect (QCSE). By repeating such a measurement for a series of laser
energies, a precise relationship between the X0 transition energy and bias
voltage is then obtained. Taking into account power broadening of the X0
absorption peak, this allows for high-resolution measurements of the X0
homogeneous linewidth and, hence, the electron tunnelling rate. The electron
tunnelling rate is measured as a function of the vertical electric field and
described accurately by a theoretical model, yielding information about the
electron confinement energy and QD height. We demonstrate that our devices can
operate as 2DEG-based QD photovoltaic cells and conclude by proposing two
optical spintronic devices that are now feasible.Comment: 34 pages, 11 figure
A combined finite element-Langevin dynamics (FEM-LD) approach for analyzing the mechanical response of bio-polymer networks
postprin
Strain Modulated Electronic Properties of Ge Nanowires - A First Principles Study
We used density-functional theory based first principles simulations to study
the effects of uniaxial strain and quantum confinement on the electronic
properties of germanium nanowires along the [110] direction, such as the energy
gap and the effective masses of the electron and hole. The diameters of the
nanowires being studied are up to 50 {\AA}. As shown in our calculations, the
Ge [110] nanowires possess a direct band gap, in contrast to the nature of an
indirect band gap in bulk. We discovered that the band gap and the effective
masses of charge carries can be modulated by applying uniaxial strain to the
nanowires. These strain modulations are size-dependent. For a smaller wire (~
12 {\AA}), the band gap is almost a linear function of strain; compressive
strain increases the gap while tensile strain reduces the gap. For a larger
wire (20 {\AA} - 50 {\AA}), the variation of the band gap with respect to
strain shows nearly parabolic behavior: compressive strain beyond -1% also
reduces the gap. In addition, our studies showed that strain affects effective
masses of the electron and hole very differently. The effective mass of the
hole increases with a tensile strain while the effective mass of the electron
increases with a compressive strain. Our results suggested both strain and size
can be used to tune the band structures of nanowires, which may help in design
of future nano-electronic devices. We also discussed our results by applying
the tight-binding model.Comment: 1 table, 8 figure
Diffusion of Mn interstitials in (Ga,Mn)As epitaxial layers
Magnetic properties of thin (Ga,Mn)As layers improve during annealing by
out-diffusion of interstitial Mn ions to a free surface. Out-diffused Mn atoms
participate in the growth of a Mn-rich surface layer and a saturation of this
layer causes an inhibition of the out-diffusion. We combine high-resolution
x-ray diffraction with x-ray absorption spectroscopy and a numerical solution
of the diffusion problem for the study of the out-diffusion of Mn interstitials
during a sequence of annealing steps. Our data demonstrate that the
out-diffusion of the interstitials is substantially affected by the internal
electric field caused by an inhomogeneous distribution of charges in the
(Ga,Mn)As layer.Comment: 11 pages, 5 figure
Electrical conduction of silicon oxide containing silicon quantum dots
Current-voltage measurements have been made at room temperature on a Si-rich
silicon oxide film deposited via Electron-Cyclotron Resonance Plasma Enhanced
Chemical Vapor Deposition (ECR-PECVD) and annealed at 750 - 1000C. The
thickness of oxide between Si quantum dots embedded in the film increases with
the increase of annealing temperature. This leads to the decrease of current
density as the annealing temperature is increased. Assuming the Fowler-Nordheim
tunneling mechanism in large electric fields, we obtain an effective barrier
height of 0.7 0.1 eV for an electron tunnelling
through an oxide layer between Si quantum dots. The Frenkel-Poole effect can
also be used to adequately explain the electrical conduction of the film under
the influence of large electric fields. We suggest that at room temperature Si
quantum dots can be regarded as traps that capture and emit electrons by means
of tunneling.Comment: 14 pages, 5 figures, submitted to J. Phys. Conden. Mat
Comparison of chemical profiles and effectiveness between Erxian decoction and mixtures of decoctions of its individual herbs : a novel approach for identification of the standard chemicals
Acknowledgements This study was partially supported by grants from the Seed Funding Programme for Basic Research (Project Number 201211159146 and 201411159213), the University of Hong Kong. We thank Mr Keith Wong and Ms Cindy Lee for their technical assistances.Peer reviewedPublisher PD
Ultrafast Optical Excitation of a Persistent Surface-State Population in the Topological Insulator Bi2Se3
Using femtosecond time- and angle- resolved photoemission spectroscopy, we
investigated the nonequilibrium dynamics of the topological insulator Bi2Se3.
We studied p-type Bi2Se3, in which the metallic Dirac surface state and bulk
conduction bands are unoccupied. Optical excitation leads to a meta-stable
population at the bulk conduction band edge, which feeds a nonequilibrium
population of the surface state persisting for >10ps. This unusually long-lived
population of a metallic Dirac surface state with spin texture may present a
channel in which to drive transient spin-polarized currents
Effect of Nenas honey supplementation on the oxidative status of undergraduate students
Honey is a dietary antioxidant as it contains phenolic compounds, such as flavonoids and phenolic acids. Antioxidants are non-nutritive, biologically active ingredients in food that reduce oxidative stress. The antioxidant content in each type of honey varies depending on its source. This study was aimed to determine the effect of Nenas honey supplementation on the oxidative status of a group of healthy medical students. They were divided into two groups; control (n=10) and supplemented (n=13), where 1 tablespoon of Nenas honey was given each day. Blood sampling was done at baseline, 1st and 2nd month of the study for determination of DNA damage and antioxidant enzyme activities, such as superoxide dismutase (SOD), glutathione peroxidise (GPx), and catalase (CAT). Results showed that Nenas honey increased the level of DNA damage at the 1st month but reduced it significantly at the 2nd month as compared to control. GPx and CAT activities also decreased significantly with honey supplementation throughout the study, though no changes were observed in SOD activity. Fasting glucose levels remained within the normal range with honey supplementation. In conclusion, Nenas honey decreases oxidative stress which leads to a reduction of antioxidant enzyme activities in the body
Very large magnetoresistance in lateral ferromagnetic (Ga,Mn)As wires with nanoconstrictions
We have fabricated (Ga,Mn)As nanostructures in which domain walls can be
pinned by sub-10 nm constrictions. Controlled by shape anisotropy, we can
switch the regions on either side of the constriction to either parallel or
antiparallel magnetization. All samples exhibit a positive magnetoresistance,
consistent with domain-wall trapping. For metallic samples we find a
magnetoresistance up to 8%, which can be understood from spin accumulation. In
samples where, due to depletion at the constriction, a tunnel barrier is
formed, we observe a magnetoresistance of up to 2000 %.Comment: 4 pages, 3 figures, submited to Phys. Rev. Let
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