Lateral Size and Thickness Dependence in Ferroelectric Nanostructures Formed by Localized Domain Switching

Ferroelectric nanostructures can be formed by local switching of domains using techniques such as piezo-force microscopy (PFM). Understanding lateral size effects is important to determine the minimum feature size for writing ferroelectric nanostructures. To understand these lateral size effects, we use the time-dependent-Ginzburg-Landau equations to simulate localized switching of domains for a PFM type and parallel-plate capacitor configurations. Our investigations indicate that fringing electric fields lead to switching via 90 deg domain wedge nucleation for thicker films while at smaller thicknesses, the polarization switches directly by 180 deg rotations. The voltage required to switch the domain increases by decreasing the lateral size and at very small lateral sizes the coercive voltage becomes so large that it becomes virtually impossible to switch the domain. In all cases, the width of the switched region extends beyond the electrodes, due to fringing.Comment: 21 pages, 11 figure

Moral relativism and reasons for action

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Linguistics and Philosophy, 1999.Includes bibliographical references (p. [103]-105).There are many varieties of moral relativism. Appraiser relativism, according to which the proposition expressed by a moral sentence varies from context to context, is motivated by the thought that it provides the best explanation of the intractability of fundamental moral disagreements. In response, it is standardly objected that appraiser relativism runs afoul of our linguistic intuitions about when people are contradicting one another. In Chapter One, I expand upon this objection in three ways: (i) the problematic class of intuitions is larger than has previously been noticed; (ii) three strategies that have been offered to explain away those intuitions fail; and (iii) even if we grant that appraiser relativism is true, it still would not provide us with any explanation whatsoever of the intractability of the relevant disagreements. Agent relativism, according to which there are no universal moral requirements, is motivated by the thought that there are always reasons to comply with one's moral requirements, but that the desires to which such reasons would have to correspond are too capricious for there to be any universal moral requirements. In Chapter Two, I argue that the moral universalist is free to maintain either (i) that any fully rational, fully informed agent will have a desire that would be served by complying with what the moral universalist takes to be universal moral requirements, and so desires are not too capricious, or (ii) that a naturalistically acceptable account of reasons need not suppose that reasons are grounded in desires. Either way, the moral universalist is free to reject this motivation for agent relativism. If desires do not provide the basis for reasons for action, what does? In Chapter Three, I give an analysis of reasons for action based on the ways in which an action can be good or bad. I argue that the analysis is preferable to two other analyses, and that it provides a promising explanation of why there are always reasons for agents to comply with their moral requirements. I conclude, however, that the analysis relies on distinctions which, despite being intuitively plausible, remain in need of theoretical justification.by Robert Streiffer.Ph.D

The Ethics of Deliberate Exposure to SARS-CoV-2 to Induce Immunity

We explore the ethics of deliberately exposing consenting adults to SARS-CoV-2 to induce immunity to the virus (“DEI” for short). We explain what a responsible DEI program might look like. We explore a consequentialist argument for DEI according to which DEI is a viable harm-reduction strategy. Then we consider a non-consequentialist argument for DEI that draws on the moral significance of consent. Additionally, we consider arguments for the view that DEI is unethical on the grounds that, given that large-scale DEI would be highly likely to result in some severe illnesses and deaths, DEI amounts to a form of killing. Our thesis is that incorporating a DEI program alongside the status-quo “calibrate-the-curve” responses could have significant advantages at the early stages of pandemics. These potential advantages mean that, at a minimum, research into DEI would have been justified early in the COVID-19 pandemic, and that DEI programs should be explored as potential additions to our overall approach to emerging pandemics in the future

Stabilization of monodomain polarization in ultrathin PbTiO3 films

Using in situ high-resolution synchrotron x-ray scattering, the Curie temperature T-C has been determined for ultrathin c-axis epitaxial PbTiO3 films on conducting substrates (SrRuO3 on SrTiO3), with surfaces exposed to a controlled vapor environment. The suppression of T-C was relatively small, even for the thinnest film (1.2 nm). We observe that 180 degrees stripe domains do not form, indicating that the depolarizing field is compensated by free charge at both interfaces. This is confirmed by ab initio calculations that find polar ground states in the presence of ionic adsorbates.open15511

Domain Engineering for Enhanced Ferroelectric Properties of Epitaxial (001) BiFeO Thin Films

No Abstract.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/61869/1/817_ftp.pd

The origin of paramagnetic magnetization in field-cooled YBa2Cu3O7 films

Temperature dependences of the magnetic moment have been measured in YBa_2Cu_3O_{7-\delta} thin films over a wide magnetic field range (5 <= H <= 10^4 Oe). In these films a paramagnetic signal known as the paramagnetic Meissner effect has been observed. The experimental data in the films, which have strong pinning and high critical current densities (J_c ~ 2 \times 10^6 A/cm^2 at 77 K), are quantitatively shown to be highly consistent with the theoretical model proposed by Koshelev and Larkin [Phys. Rev. B 52, 13559 (1995)]. This finding indicates that the origin of the paramagnetic effect is ultimately associated with nucleation and inhomogeneous spatial redistribution of magnetic vortices in a sample which is cooled down in a magnetic field. It is also shown that the distribution of vortices is extremely sensitive to the interplay of film properties and the real experimental conditions of the measurements.Comment: RevTex, 8 figure