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1. Electrostatic potential of a uniformly charged annulus

   https://doi.org/10.1088/1361-6404/ad2cf6  

   Ciftja, Orion; Bentley_Jr, Cleo L (March 2024, European Journal of Physics)

   Abstract The calculation of the electrostatic potential and/or electrostatic field due to a continuous distribution of charge is a well-covered topic in all calculus-based undergraduate physics courses. The most common approach is to consider bodies with uniform charge distribution and obtain the quantity of interest by integrating over the contributions from all the differential charges. The examples of a uniformly charged disk and ring are prominent in many physics textbooks since they illustrate well this technique at least for special points or directions of symmetry where the calculations are relatively simple. Surprisingly, the case of a uniformly charged annulus, namely, an annular disk, is largely absent from the literature. One might speculate that a uniformly charged annulus is not extremely interesting since after all, it is a uniformly charged disk with a central circular hole. However, we show in this work that the electrostatic potential created by a uniformly charged annulus has features that are much more interesting than one might have expected. A uniformly charged annulus interpolates between a uniformly charged disk and ring. However, the results of this work suggest that a uniformly charged annulus has such electrostatic features that may be essentially viewed as ring-like. The ring-like characteristics of the electrostatic potential of a uniformly charged annulus are evident as soon as a hole is present no matter how small the hole might be. The solution of this problem allows us to draw attention to the pedagogical aspects of this overlooked, but very interesting case study in electrostatics. In our opinion, the problem of a uniformly charged annulus and its electrostatic properties deserves to be treated at more depth in all calculus-based undergraduate physics courses covering electricity and magnetism. 

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2. Interaction Potential between a Uniformly Charged Square Nanoplate and Coplanar Nanowire

   https://doi.org/10.3390/nano13232988  

   Ciftja, Orion (December 2023, Nanomaterials)

   We study a structure consisting of two electrostatically interacting objects, a uniformly charged square nanoplate and a uniformly charged nanowire. A straightforward motivation behind this work is to introduce a model that allows a classical description of a finite two-dimensional quantum Hall system of few electrons when the Landau gauge is imposed. In this scenario, the uniformly charged square nanoplate would stand for the neutralizing background of the system while a uniformly charged nanowire would represent the resulting quantum striped state of the electrons. A second important feature of this model is that it also applies to hybrid charged nanoplate-nanowire systems in which the dominant interaction has electrostatic origin. An exact analytical expression for the electrostatic interaction potential between the uniformly charged square nanoplate and coplanar nanowire is obtained by using a special mathematical method adept for this geometry. It is found that the resulting interaction potential is finite, monotonic and slowly-varying for all locations of the nanowire inside the nanoplate. 

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3. Generating Focused 3D Perfect Vortex Beams By Plasmonic Metasurfaces

   https://doi.org/10.1002/adom.201701228  

   Zhang, Yuchao; Liu, Weiwei; Gao, Jie; Yang, Xiaodong (January 2018, Advanced Optical Materials)

   Abstract Perfect vortex (PV) beams possessing annular intensity profiles independent of topological charges promise significant advances in particle manipulation, fiber communication, and quantum optics. The PV beam is typically generated from the Fourier transformation of the Bessel–Gauss beam. However, the conventional method to produce PV beams requires a series of bulky optical components, which greatly increases the system complexity and also hinders the photonic device integration. Here, plasmonic metasurfaces made of rectangular‐hole nanoantennas as integrated beam converters are designed and demonstrated to generate focused 3D PV beams in a broad wavelength range, by combining the phase profiles of axicon, spiral phase plate, and Fourier transform lens simultaneously based on the Pancharatnam–Berry phase. It is demonstrated that the PV beam structures can be adjusted by varying several control parameters in the metasurface design. Moreover, multiple PV beams with arbitrary arrangement and topological charges are also produced. These results have the promising potential for enabling new types of compact optical devices for tailoring complex light beams and advancing metasurface‐based functional integrated photonic chips. 

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4. Stable surfactant monolayers at the electrochemical interfacial double layer across a wide potential range

   https://doi.org/10.1063/5.0246955  

   Wang, Chenglai; Yu, Chun-Chieh; Shi, Qiufan; Wu, Zishan; Zhang, Boxin; Cronin, Stephen B; Xiong, Wei (March 2025, Chemical Physics Reviews)

   Cetyltrimethylammonium bromide (CTAB) has been used to enhance the selectivity of CO2 electrochemical reduction. Traditionally, this selectivity was attributed to repulsion of water molecules due to a CTAB self-assembled monolayer, which forms under negative potential and disassembles at positive voltage due to electrostatic repulsions. In this report, using in operando interface sensitivity sum frequency generation spectroscopy, we investigated the self-assembly behavior of CTAB across a broad electrochemical potential range. We observed that CTAB molecules form a stable monolayer at the Stern layer over the entire potential scan, even when the electrodes are positively charged. Rather than disassembling, the CTAB molecules reorient themselves to balance the electrostatic interactions and the non-covalent hydrophobic effects, the latter being the primary driving force maintaining the monolayer at a positive potential. This finding contrasts the traditional view that CTAB monolayers are absent when the electrodes are positively charged, indicating a stable and ordered monolayer with respect to the electrostatic repulsions at liquid/electrode interfaces. The balance between non-covalent and electrostatic interactions offers a facile and reversible electrochemical method to control the local environment and dominating interactions at the Stern layer of the electrode surface, thus providing a means for engineering a micro-electrochemical environment. 

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5. Interaction energy of a pair of identical coplanar uniformly charged nanodisks

   https://doi.org/10.1063/1.5025336  

   Ciftja, Orion; Berry, Isaac (March 2018, AIP Advances)

   We consider a nanosystem consisting of two coplanar uniformly charged nanodisks that are coupled via Coulomb forces. Such a model represents a typical situation encountered in two-dimensional semiconductor quantum dot systems of electrons. We provide an exact integral expression for the interaction energy between the two coplanar nanodisks as a function of their separation distance. It is found that the difference between a standard Coulomb potential and the current one has features reminiscent of a Lennard-Jones interaction potential. The results derived can be useful to understand formation of clusters and/or aggregates in systems of coplanar charged nanodisks that contain electrons. 

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