Resonant Terahertz Detection Using Graphene Plasmons

Plasmons, collective oscillations of electron systems, can efficiently couple light and electric current, and thus can be used to create sub-wavelength photodetectors, radiation mixers, and on-chip spectrometers. Despite considerable effort, it has proven challenging to implement plasmonic devices operating at terahertz frequencies. The material capable to meet this challenge is graphene as it supports long-lived electrically-tunable plasmons. Here we demonstrate plasmon-assisted resonant detection of terahertz radiation by antenna-coupled graphene transistors that act as both plasmonic Fabry-Perot cavities and rectifying elements. By varying the plasmon velocity using gate voltage, we tune our detectors between multiple resonant modes and exploit this functionality to measure plasmon wavelength and lifetime in bilayer graphene as well as to probe collective modes in its moir\'e minibands. Our devices offer a convenient tool for further plasmonic research that is often exceedingly difficult under non-ambient conditions (e.g. cryogenic temperatures and strong magnetic fields) and promise a viable route for various photonic applications.Comment: 19 pages, 12 figure

СТРУКТУРА И МАГНИТНЫЕ СВОЙСТВА ПОРОШКА ГЕКСАФЕРРИТА СТРОНЦИЯ ПОСЛЕ ИЗМЕЛЬЧЕНИЯ В ВОДЕ И ТОЛУОЛЕ С ПОСЛЕДУЮЩИМ ОТЖИГОМ

oai:oai.mateltech.elpub.ru:article/107Structural changes of strontium hexaferrite powders after milling in water and toluene and after subsequent annealing were studied using X-ray diffraction, Scanning Electron Microscopy and Laser diffraction. Also magnetic properties changes were studied. The coarse-grain powder milling leads to an abrupt decrease of its particles size and the average crystallite size as well as an increase of SrFe12O19 phase lattice microstrains. Saturation magnetization and remanence decrease after milling in both media. At the same time coercive force of milled powders changes insignificantly with increasing milling time. The subsequent annealing allowed us to increase the magnetic properties of the powder. The annealed powders are characterized by the following magnetic properties: µ0Нci = 0,42¸0,49 T, µ 0Ir = 0,23¸0,24 T, (BH)max = 8-9,6 kJ/m3.Методами рентгеноструктурного анализа, растровой электронной микроскопии и лазерной дифракции исследованы структурные изменения в порошке гексаферрита стронция при измельчении в воде и толуоле, а также при последующем отжиге. Кроме того, изучено изменение магнитных свойств порошка. Установлено, что измельчение крупнозернистого порошка гексаферрита стронция приводит к значительному уменьшению размера частиц порошка, снижению размера областей когерентного рассеяния и увеличению микродеформации решетки фазы SrFe12O19. Обнаружено, что остаточная намагниченность и намагниченность насыщения при измельчении в обеих средах уменьшаются, а коэрцитивная сила меняется мало с увеличением продолжительности измельчения. В результате последующего отжига магнитные свойства порошка гексаферрита стронция резко увеличиваются, что обусловлено формированием нанокристаллической структуры. Для отожженных порошков характерны следующие свойства: µ0Нci = 0,42 µ 0,49 Тл, μоIr = 0,23 µ 0,24 Тл, (BH)max = 8,0 µ 9,6 МДж/м3. Показано, что магнитные свойства отожженных порошков зависят от среды и длительности процесса измельчения

Primer Extension Mutagenesis Powered by Selective Rolling Circle Amplification

Primer extension mutagenesis is a popular tool to create libraries for in vitro evolution experiments. Here we describe a further improvement of the method described by T.A. Kunkel using uracil-containing single-stranded DNA as the template for the primer extension by additional uracil-DNA glycosylase treatment and rolling circle amplification (RCA) steps. It is shown that removal of uracil bases from the template leads to selective amplification of the nascently synthesized circular DNA strand carrying the desired mutations by phi29 DNA polymerase. Selective RCA (sRCA) of the DNA heteroduplex formed in Kunkel's mutagenesis increases the mutagenesis efficiency from 50% close to 100% and the number of transformants 300-fold without notable diversity bias. We also observed that both the mutated and the wild-type DNA were present in at least one third of the cells transformed directly with Kunkel's heteroduplex. In contrast, the cells transformed with sRCA product contained only mutated DNA. In sRCA, the complex cell-based selection for the mutant strand is replaced with the more controllable enzyme-based selection and less DNA is needed for library creation. Construction of a gene library of ten billion members is demonstrated with the described method with 240 nanograms of DNA as starting material