248 research outputs found
Etching of silicon in alkaline solutions: a critical look at the {111} minimum
Anisotropic wet-chemical etching of silicon in alkaline solutions is a key technology in the fabrication of sensors and actuators. In this technology, etching through masks is used for fast and reproducible shaping of micromechanical structures. The etch rates Image depend mainly on composition and temperature of the etchant. In a plot of etch rate versus orientation, there is always a deep, cusped minimum for the {1 1 1} orientations. We have investigated the height of the {1 1 1} etch-rate minimum, as well as the etching mechanisms that determine it. We found that in situations where masks are involved, the height of the {1 1 1} minimum can be influenced by nucleation at a silicon/mask-junction. A junction which influences etch or growth rates in this way can be recognized as a velocity source, a mathematical concept developed by us that is also applicable to dislocations and grain boundaries. The activity of a velocity source depends on the angle between the relevant {1 1 1} plane and the mask, and can thus have different values at opposite {1 1 1} sides of a thin wall etched in a micromechanical structure. This observation explains the little understood spread in published data on etch rate of {1 1 1} and the anisotropy factor (often defined as Imag
Simulation of anisotropic wet-chemical etching using a physical model
We present a method to describe the orientation dependence of the etch rate of silicon, or any other single crystalline material, in anisotropic etching solutions by analytical functions. The parameters in these functions have a simple physical meaning. Crystals have a small number of atomically smooth faces, which etch (and grow) slowly as a consequence of the removal (or addition) of atoms by rows and layers. However, smooth faces have a roughening transition (well known in statistical physics); at increasing temperature they become rougher, and accordingly the etch and growth rates increase. Consequently, the basic physical parameters of our functions are the roughness of the smooth faces and the velocity of steps on these faces. This small set of parameters describes the etch rate in the two-dimensional space of orientations (on the unit sphere). We have applied our method to the practical case of etch rate functions for silicon crystals in KOH solutions. The maximum deviation between experimental data and simulation using only nine physically meaningful parameters is less than 5% of the maximum etch rate. This method, which in this study is used to describe anisotropic etching of silicon, can easily be adjusted to describe the growth or etching process of any crysta
Observation of magnetoelectric behavior at room temperature in Pb(Fe1-xTix)O3
The coexistence of ferroelectric and ferromagnetic properties at room
temperature is very rarely observed. We have been successful in converting
ferroelectric PbTiO3 into a magnetoelectric material by partly substituting Fe
at the Ti site. The Pb(Fe1-xTix)O3 system exhibits ferroelectric and
ferromagnetic ordering at room temperature. Even more remarkably, our results
demonstrate a coupling between the two order parameters. Hence it could be a
futuristic material to provide cost effective and simple path for designing
novel electromagnetic devices.Comment: Total 14 pages of text and figure
Magnetic and microwave properties of (Ni,Co)Fe2O4-ferroelectric and (La,Ca,Sr)MnO3-ferroelectric multilayer structures
Structural, magnetic and ferromagnetic resonance characterization studies
have been performed on lay-ered ferromagnetic-ferroelectric oxides that show
strong magnetoelectric coupling. The samples contained thick films of ferrites
or substituted lanthanum manganites for the ferromagnetic phase and lead
zirconate titanate for the ferroelectric phase, and were sintered high
temperatures. Results indicate defect free ferrites, but deterioration of
manganite parameters due to diffusion at the interface and accounts for poor
magnetoelectric coupling in manganite-PZT samples
Magnetoelectric Effect in Ni-PZT-Ni Cylindrical Layered Composite Synthesized by Electro-deposition
The magnetoelectric (ME) coupling of cylindrical trilayered composite was
studied in this paper. The Ni-lead zirconate titanate (PZT)-Ni trilayered
cylindrical composite was synthesized by electro-deposition. The maximum ME
voltage coefficient of cylindrical ME composite is 35V/cm Oe, about three times
higher than that of the plate trilayered composite with the same raw materials
and magnetostrictive- piezoelectric phase thickness ratio. The high ME voltage
coefficient of cylindrical composite owes to the self-bound effect of circle.
Moreover, the resulting complex condition can induce a double peak in the field
dependence of ME coefficient.Comment: 11 pages, 5 figure
Investigation of biferroic properties in La0.6Sr0.4MnO3/0.7 Pb(Mg1/3Nb2/3)O3 0.3 PbTiO3 epitaxial bilayered heterostructures
Epitaxial bilayered thin films consisting of La0.6Sr0.4MnO3 (LSMO) and 0.7
Pb(Mg1/3Nb2/3)O3 0.3 PbTiO3 (PMN-PT) layers of relatively different thicknesses
were fabricated on LaNiO3 coated LaAlO3 (100) single crystal substrates by
pulsed laser ablation technique. Ferroelectric and ferromagnetic
characteristics of these heterostructures confirmed their biferroic nature. The
magnetization and ferroelectric polarization of the bilayered heterostructures
were enhanced with increasing PMN-PT layer thickness owing to the effect of
lattice strain. Dielectric properties of these heterostructures studied over a
wide range of temperature under different magnetic field strength suggested a
possible role of elastic strain mediated magnetoelectric coupling behind the
observed magneto-dielectric effect in addition to the influence of
rearrangement of the interfacial charge carriers under an applied magnetic
field
Giant Magnetoelastic Effects in BaTiO3-based Extrinsic Multiferroic Hybrids
Extrinsic multiferroic hybrid structures consisting of ferromagnetic and
ferroelectric layers elastically coupled to each other are promising due to
their robust magnetoelectric effects even at room temperature. For a
quantitative analysis of these magnetoelectric effects, a detailed knowledge of
the piezoelectric and magnetoelastic behavior of both constituents as well as
their mutual elastic coupling is mandatory. We here report on a theoretical and
experimental study of the magnetic behavior of BaTiO3-based extrinsic
multiferroic structures. An excellent agreement between molecular dynamics
simulations and the experiments was found for Fe50Co50/BaTiO3 and Ni/BaTiO3
hybrid structures. This demonstrates that the magnetic behavior of extrinsic
multiferroic hybrid structures can be determined by means of ab-initio
calculations, allowing for the design of novel multiferroic hybrids
Tailoring of ferromagnetic Pr0.85Ca0.15MnO3/ferroelectric Ba0.6Sr0.4TiO3 superlattices for multiferroic properties
Superlattices composed of ferromagnetic Pr0.85Ca0.15MnO3 and ferroelectric
Ba0.6Sr0.4TiO3 layers were fabricated on (100) SrTiO3 substrates by a
pulsed-laser deposition method. The capacitance and resistive parts of the
samples were analyzed from the complex impedance measurements, performed on the
samples using a special experimental set-up. The superlattice with larger
ferroelectric thickness shows unique characteristics which are not present in
the parent ferromagnetic thin film. The superlattice show both ferromagnetic
and ferroelectric transitions which is an evidence for the coexistence of both
the properties. The high magnetoresistance (40 % at 80K) shown by the
superlattice can be attributed to the coupling between ferromagnetic and
ferroelectric layers, i.e, to the magnetoelectric effect.Comment: To be published in App. Phys. Let
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