6,359 research outputs found
Single Gate P-N Junctions in Graphene-Ferroelectric Devices
Graphene's linear dispersion relation and the attendant implications for
bipolar electronics applications have motivated a range of experimental efforts
aimed at producing p-n junctions in graphene. Here we report electrical
transport measurements of graphene p-n junctions formed via simple
modifications to a PbZrTiO substrate, combined with a
self-assembled layer of ambient environmental dopants. We show that the
substrate configuration controls the local doping region, and that the p-n
junction behavior can be controlled with a single gate. Finally, we show that
the ferroelectric substrate induces a hysteresis in the environmental doping
which can be utilized to activate and deactivate the doping, yielding an
`on-demand' p-n junction in graphene controlled by a single, universal
backgate
Pyroelectric thin films - Past, present, and future
Pyroelectrics are a material class that undergoes a change in polarization as the temperature of the system is varied. This effect can be utilized for applications ranging from thermal imaging and sensing to waste-heat energy conversion to thermally driven electron emission. Here, we review recent advances in the study and utilization of thin-film pyroelectrics. Leveraging advances in modeling, synthesis, and characterization has provided a pathway forward in one of the more poorly developed subfields of ferroelectricity. We introduce the complex physical phenomena of pyroelectricity, briefly explore the history of work in this space, and highlight not only new advances in the direct measurement of such effects but also how our ability to control thin-film materials is changing our understanding of this response. Finally, we discuss recent advances in thin-film pyroelectric devices and introduce a number of potentially new directions the field may follow in the coming years
Pressurizing Field-Effect Transistors of Few-Layer MoS2 in a Diamond Anvil Cell
Hydrostatic pressure applied using diamond anvil cells (DAC) has been widely
explored to modulate physical properties of materials by tuning their lattice
degree of freedom. Independently, electrical field is able to tune the
electronic degree of freedom of functional materials via, for example, the
field-effect transistor (FET) configuration. Combining these two orthogonal
approaches would allow discovery of new physical properties and phases going
beyond the known phase space. Such experiments are, however, technically
challenging and have not been demonstrated. Herein, we report a feasible
strategy to prepare and measure FETs in a DAC by lithographically patterning
the nanodevices onto the diamond culet. Multiple-terminal FETs were fabricated
in the DAC using few-layer MoS2 and BN as the channel semiconductor and
dielectric layer, respectively. It is found that the mobility, conductance,
carrier concentration, and contact conductance of MoS2 can all be significantly
enhanced with pressure. We expect that the approach could enable unprecedented
ways to explore new phases and properties of materials under coupled
mechano-electrostatic modulation.Comment: 15 pages, 5 figure
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Light-Induced Currents at Domain Walls in Multiferroic BiFeO3.
Multiferroic BiFeO3 (BFO) films with spontaneously formed periodic stripe domains can generate above-gap open circuit voltages under visible light illumination; nevertheless the underlying mechanism behind this intriguing optoelectronic response has not been understood to date. Here, we make contact-free measurements of light-induced currents in epitaxial BFO films via detecting terahertz radiation emanated by these currents, enabling a direct probe of the intrinsic charge separation mechanisms along with quantitative measurements of the current amplitudes and their directions. In the periodic stripe samples, we find that the net photocurrent is dominated by the charge separation across the domain walls, whereas in the monodomain samples the photovoltaic response arises from a bulk shift current associated with the non-centrosymmetry of the crystal. The peak current amplitude driven by the charge separation at the domain walls is found to be 2 orders of magnitude higher than the bulk shift current response, indicating the prominent role of domain walls acting as nanoscale junctions to efficiently separate photogenerated charges in the stripe domain BFO films. These findings show that domain-wall-engineered BFO thin films offer exciting prospects for ferroelectric-based optoelectronics, as well as bias-free strong terahertz emitters
Temperature and thickness evolution and epitaxial breakdown in highly-strained BiFeO3 thin films
We present the temperature- and thickness-dependent structural and
morphological evolution of strain induced transformations in highly-strained
epitaxial BiFeO3 films deposited on LaAlO3 (001) substrates. Using
high-resolution X-ray diffraction and temperature-dependent
scanning-probe-based studies we observe a complex temperature- and
thickness-dependent evolution of phases in this system. A thickness-dependent
transformation from a single monoclinically distorted tetragonal-like phase to
a complex mixed-phase structure in films with thicknesses up to ~200 nm is the
consequence of a strain-induced spinodal instability in the BiFeO3/LaAlO3
system. Additionally, a breakdown of this strain-stabilized metastable
mixed-phase structure to non-epitaxial microcrystals of the parent rhombohedral
structure of BiFeO3 is observed to occur at a critical thickness of ~300 nm. We
further propose a mechanism for this abrupt breakdown that provides insight
into the competing nature of the phases in this system.Comment: 7 figure
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Phase Coexistence of Ferroelectric Vortices and Classical a1/a2 Domains in PbTiO3/SrTiO3 Superlattices.
Pseudo-Goldstone Boson Effects in Top-Antitop Productions at High Energy Hadron Colliders and Testing Technicolor Models
We study the top quark pair production process p+p(anti-p)-->top+antitop in
various kinds of technicolor (TC) models at the Fermilab Tevatron Run II and
the CERN LHC. The s-channel neutral pseudo-Goldstone bosons (PGB's) contribute
dominately to the production amplitudes from its coupling to the gluons through
the triangle loops of techniquarks and the top quark. Cross sections in
different TC models with s-channel PGB contributions are calculated. It is
shown that the PGB effects can be experimentally tested and different TC models
under consideration can be distinguished at the LHC. Therefore, the
p+p-->top+antitop process at the LHC provides feasible tests of the TC models.Comment: 10 pages in RevTex and 4 PS-files for the figures. Paramemter range
is changed, and some references are added. Version for publication in Phys.
Rev.
Giant Superelastic Piezoelectricity in Flexible Ferroelectric Membranes
Mechanical displacement in commonly used piezoelectric materials is typically
restricted to linear or biaxial in nature and to a few percent of the material
dimensions. Here, we show that free-standing BaTiO membranes exhibit
non-conventional electromechanical coupling. Under an external electric field,
these superelastic membranes undergo controllable and reversible
'sushi-rolling-like' 180 folding-unfolding cycles. This crease-free
folding is mediated by charged ferroelectric domains, leading to a giant > 3.8
and 4.6 m displacements for a 30-nm thick membrane at room temperature and
60C, respectively. Further increasing the electric field above the
coercive value changes the fold curvature, hence augmenting the effective
piezoresponse. Finally, it is found that the membranes fold with increasing
temperature followed by complete immobility of the membrane above the Curie
temperature, allowing us to model the ferroelectric-domain origin of the
effect
Quarkonium Wave Functions at the Origin
We tabulate values of the radial Schr\"{o}dinger wave function or its first
nonvanishing derivative at zero quark-antiquark separation, for ,
, and levels that lie below, or just above, flavor
threshold. These quantities are essential inputs for evaluating production
cross sections for quarkonium states.Comment: 9 pages, RevTeX, no figure
Towards understanding interactions between Sustainable Development Goals: the role of environment–human linkages
Only 10 years remain to achieve all Sustainable Development Goals (SDGs) globally, so there is a growing need to increase the effectiveness and efficiency of action by targeting multiple SDGs. The SDGs were conceived as an ‘indivisible whole’, but interactions between SDGs need to be better understood. Several previous assessments have begun to explore interactions including synergies and possible conflicts between the SDGs, and differ widely in their conclusions. Although some highlight the role of the more environmentally-focused SDGs in underpinning sustainable development, none specifically focuses on environment-human linkages. Assessing interactions between SDGs, and the influence of environment on them, can make an important contribution to informing decisions in 2020 and beyond.
Here, we review previous assessments of interactions among SDGs, apply an influence matrix to assess pairwise interactions between all SDGs, and show how viewing these from the perspective of environment-human linkages can influence the outcome.
Environment, and environment-human linkages, influence most interactions between SDGs. Our action-focused assessment enables decision makers to focus environmental management to have the greatest impacts, and to identify opportunities to build on synergies and reduce trade-offs between particular SDGs. It may enable sectoral decision makers to seek support from environment managers for achieving their goals.
We explore cross-cutting issues and the relevance and potential application of our approach in supporting decision making for progress to achieve the SDGs
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