79 research outputs found
Atomic-scale compensation phenomena at polar interfaces
The interfacial screening charge that arises to compensate electric fields of
dielectric or ferroelectric thin films is now recognized as the most important
factor in determining the capacitance or polarization of ultrathin
ferroelectrics. Here we investigate using aberration-corrected electron
microscopy and density functional theory how interfaces cope with the need to
terminate ferroelectric polarization. In one case, we show evidence for ionic
screening, which has been predicted by theory but never observed. For a
ferroelectric film on an insulating substrate, we found that compensation can
be mediated by interfacial charge generated, for example, by oxygen vacancies.Comment: 3 figure
Models of Nation-Building via Systems of Differential Equations
Nation-building modeling is an important field of research given the increasing number of candidate nations and the limited resources available. A modeling methodology and a system of differential equations model are presented to investigate the dynamics of nation-building. The methodology is based upon parameter identification techniques applied to a system of differential equations, to evaluate nation-building operations. Data from Operation Iraqi Freedom (OIF) and Afghanistan are used to demonstrate the validity of different models as well as the comparison of models
Electron-beam induced emergence of mesoscopic ordering in layered MnPS
Ordered mesoscale structures in 2D materials induced by small misorientations
have opened pathways for a wide variety of novel electronic, ferroelectric, and
quantum phenomena. Until now, the only mechanism to induce this periodic
ordering was via mechanical rotations between the layers, with the periodicity
of the resulting moir\'e pattern being directly related to twist angle. Here we
report a fundamentally new mechanism for emergence of mesoscopic periodic
patterns in multilayer sulfur-containing metal phosphorous trichalcogenide,
MnPS, induced by the electron beam. The formation under the beam of
periodic hexagonal patterns with several characteristic length scales,
nucleation and transitions between the phases, and local dynamics are
demonstrated. The associated mechanisms are attributed to the relative
contraction of the layers caused by beam-induced sulphur vacancy formation with
subsequent ordering and lattice parameter change. As a result, the plasmonic
response of the system is locally altered, suggesting an element of control
over plasmon resonances by electron beam patterning. We pose that harnessing
this phenomenon provides both insight into fundamental physics of quantum
materials and opens a pathway towards device applications by enabling
controlled periodic potentials on the atomic scale.Comment: Electron microscopy data and analysis codes are freely available
here: https://github.com/kevinroccapriore/MnPS
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