195 research outputs found
Experimental demonstration of complete 180 degree reversal of magnetization in isolated Co-nanomagnets on a PMN-PT substrate with voltage generated strain
Rotating the magnetization of a shape anisotropic magnetostrictive nanomagnet
with voltage-generated stress/strain dissipates much less energy than most
other magnetization rotation schemes, but its application to writing bits in
non-volatile magnetic memory has been hindered by the fundamental inability of
stress/strain to rotate magnetization by full 180 degrees. Normally,
stress/strain can rotate the magnetization of a shape anisotropic elliptical
nanomagnet by only up to 90 degrees, resulting in incomplete magnetization
reversal. Recently, we predicted that applying uniaxial stress sequentially
along two different axes that are not collinear with the major or minor axis of
the elliptical nanomagnet will rotate the magnetization by full 180 degrees.
Here, we demonstrate this complete 180 degree rotation in elliptical
Co-nanomagnets (fabricated on a piezoelectric substrate) at room temperature.
The two stresses are generated by sequentially applying voltages to two pairs
of shorted electrodes placed on the substrate such that the line joining the
centers of the electrodes in one pair intersects the major axis of a nanomagnet
at ~+30 degrees and the line joining the centers of the electrodes in the other
pair intersects at ~ -30 degrees. A finite element analysis has been performed
to determine the stress distribution underneath the nanomagnets when one or
both pairs of electrodes are activated, and this has been approximately
incorporated into a micromagnetic simulation of magnetization dynamics to
confirm that the generated stress can produce the observed magnetization
rotations. This result portends an extremely energy-efficient non-volatile
"straintronic" memory technology predicated on writing bits in nanomagnets with
electrically generated stress
Multilevel ultrafast flexible nanoscale nonvolatile hybrid graphene oxide-titanium oxide memories
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Graphene oxide (GO) resistive memories offer the promise of low-cost environmentally sustainable fabrication, high mechanical flexibility and high optical transparency, making them ideally suited to future flexible and transparent electronics applications. However, the dimensional and temporal scalability of GO memories, i.e., how small they can be made and how fast they can be switched, is an area that has received scant attention. Moreover, a plethora of GO resistive switching characteristics and mechanisms has been reported in the literature, sometimes leading to a confusing and conflicting picture. Consequently, the potential for graphene oxide to deliver high-performance memories operating on nanometer length and nanosecond time scales is currently unknown. Here we address such shortcomings, presenting not only the smallest (50 nm), fastest (sub-5 ns), thinnest (8 nm) GO-based memory devices produced to date, but also demonstrate that our approach provides easily accessible multilevel (4-level, 2-bit per cell) storage capabilities along with excellent endurance and retention performance-all on both rigid and flexible substrates. Via comprehensive experimental characterizations backed-up by detailed atomistic simulations, we also show that the resistive switching mechanism in our Pt/GO/Ti/Pt devices is driven by redox reactions in the interfacial region between the top (Ti) electrode and the GO layer.This work was carried out under the auspices of the EU FP7
project CareRAMM. This project received funding from the
European Union Seventh Framework Programme (FP7/2007-
2013) under grant agreement no. 309980. The authors are
grateful for helpful discussions with all CareRAMM partners,
particularly Prof. Andrea Ferrari and Ms. Anna Ott at the
University of Cambridge, and Drs. Abu Sebastian and Wabe
Koelmans at IBM Research Zurich. We also gratefully
acknowledge the assistance of the National EPSRC XPS
User’s Service (NEXUS) at Newcastle University, U.K. (an
EPSRC Mid-Range Facility) in carrying out the XPS measurement
Lower and Upper Bound for the Pull-in Parameters of a Micro- or Nanocantilever Beam Immersed in Liquid Electrolytes
An analytical method is proposed to accurately estimate the pull-in parameters of a micro- or nanocantilever beam immersed in liquid electrolytes with a flexible support at one end. The system is actuated by electrochemical force, namely the sum of electric and osmotic forces, and is subject to Casimir or van der Waals forces according to the spacing between the two electrodes. The deflection of the beam is described by a fourth-order nonlinear boundary value problem that can be formulated by an equivalent nonlinear integral equation. At first, a priori upper and lower analytical estimates on the beam deflection are derived and then very accurate lower and upper bounds for the pull-in voltage and tip deflection are obtained. The analytical predictions are in excellent agreement with the numerical results provided by the shooting method. Finally, a simple closed-form relation is proposed for the pull-in voltage under the effect of bulk ion concentration
Classical and fluctuation-induced electromagnetic interactions in micronscale systems: designer bonding, antibonding, and Casimir forces
Whether intentionally introduced to exert control over particles and
macroscopic objects, such as for trapping or cooling, or whether arising from
the quantum and thermal fluctuations of charges in otherwise neutral bodies,
leading to unwanted stiction between nearby mechanical parts, electromagnetic
interactions play a fundamental role in many naturally occurring processes and
technologies. In this review, we survey recent progress in the understanding
and experimental observation of optomechanical and quantum-fluctuation forces.
Although both of these effects arise from exchange of electromagnetic momentum,
their dramatically different origins, involving either real or virtual photons,
lead to different physical manifestations and design principles. Specifically,
we describe recent predictions and measurements of attractive and repulsive
optomechanical forces, based on the bonding and antibonding interactions of
evanescent waves, as well as predictions of modified and even repulsive Casimir
forces between nanostructured bodies. Finally, we discuss the potential impact
and interplay of these forces in emerging experimental regimes of
micromechanical devices.Comment: Review to appear on the topical issue "Quantum and Hybrid Mechanical
Systems" in Annalen der Physi
Nanomechanical Resonators: Toward Atomic Scale
The quest for realizing and manipulating ever smaller man-made movable structures and dynamical machines has spurred tremendous endeavors, led to important discoveries, and inspired researchers to venture to new grounds. Scientific feats and technological milestones of miniaturization of mechanical structures have been widely accomplished by advances in machining and sculpturing ever shrinking features out of bulk materials such as silicon. With the flourishing multidisciplinary field of low-dimensional nanomaterials, including one-dimensional (1D) nanowires/nanotubes, and two-dimensional (2D) atomic layers such as graphene/phosphorene, growing interests and sustained efforts have been devoted to creating mechanical devices toward the ultimate limit of miniaturization— genuinely down to the molecular or even atomic scale. These ultrasmall movable structures, particularly nanomechanical resonators that exploit the vibratory motion in these 1D and 2D nano-to-atomic-scale structures, offer exceptional device-level attributes, such as ultralow mass, ultrawide frequency tuning range, broad dynamic range, and ultralow power consumption, thus holding strong promises for both fundamental studies and engineering applications. In this Review, we offer a comprehensive overview and summary of this vibrant field, present the state-of-the-art devices and evaluate their specifications and performance, outline important achievements, and postulate future directions for studying these miniscule yet intriguing molecular-scale machines
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