The role of transition radiation in cathodoluminescence imaging and spectroscopy of thin-foils

Mendis, Budhika G.; Howkins, Ashley; Stowe, David; Major, Jonathan D.; Durose, K.

doi:10.1016/j.ultramic.2016.05.002

Cited by 10 publications

(15 citation statements)

References 35 publications

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“…Figure 3 shows such effects in the radiation spectra, which should be readily observable by using angle-resolved measurements of TR of double-layer graphene in TEM. 47,49,50 In this figure, the angular distribution of the joint spectral density of radiation emitted from two graphene layers, θ ω ̅ ̅ ( , ) , is plotted as a function of the angle θ relative to the direction of motion of the external electron, for several values of the radiation frequency ω ̅ . Results are shown using reduced units for the spectral density with normalization factor = e c / c 2 , for two interlayer distances, (a) d̅ = 0.1 and (b) d̅ = 1.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…46−48 In particular, angle-resolved measurements of CL can be used within TEM experiments to distinguish between transition radiation (TR) and incoherent CL in the form of, for example, luminescence from various materials. 49,50 In addition, a number of experiments have been carried out using different energetic electron sources to generate electromagnetic radiation from graphene, 51−53 increasing the interest in studying the coupling between moving electrons, plasmons, and radiation fields. In that context, electron beam irradiation of graphene has been recently explored for its prospects to fill in technological gap regarding the lack of radiation sources at THz frequencies.…”

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confidence: 99%

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Energy Losses and Transition Radiation in Multilayer Graphene Traversed by a Fast Charged Particle

Akbari¹,

Mišković²,

Seguí

et al. 2017

ACS Photonics

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We present a fully relativistic formulation of the energy loss of a charged particle traversing a number of graphene layers and apply it to the case of two spatially separated layers probed by an energetic electron. We focus on the THz frequency range, using a Drude model to describe the conductivity of graphene and allowing for different doping density in each layer. We distinguish two types of contributions to the electron energy loss: the energy deposited in graphene layers in the form of electronic excitations (Ohm losses), which include the excitation of Dirac plasmon polaritons (DPP), and the energy that is emitted in the form of transition radiation. We study in detail the contribution of each layer to the ohmic losses and analyze the directional decomposition of the radiation emitted in the half-spaces defined by the graphene planes. By increasing the interlayer distance and changing the relative doping densities in graphene layers, we find surprisingly strong asymmetries in both the directional and layer-wise decompositions with respect to the direction of motion of the external electron. A modal decomposition is also performed in the limit of vanishing damping in graphene, exposing quite intricate roles of bonding and antibonding hybridization between DPPs in ohmic losses.

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Section: ■ Results and Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Energy Losses and Transition Radiation in Multilayer Graphene Traversed by a Fast Charged Particle

Akbari¹,

Mišković²,

Seguí

et al. 2017

ACS Photonics

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“…where the exponent was found to vary in the range 1.0-1.12 for n-type and 1.0-1.8 for p-type materials. In a more recent example, on undoped polycrystalline CdTe solar cell materials, Mendis et al [37] determined values ranging from 1.29 to 1.46. Quick examination of Eqn.…”

Section: Factors Affecting the CL Signalmentioning

confidence: 99%

A Review and Perspective on Cathodoluminescence Analysis of Halide Perovskites

Guthrey

Moseley

2020

Advanced Energy Materials

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Halide perovskite solar cells have achieved a certified efficiency of 25.2%, surpassing CdTe and CIGS, which have long been regarded as the most-efficient thin-film photovoltaic materials. As this exciting class of materials continues to mature, researchers will require characterization techniques capable of exposing the interplay between structure, chemistry, and optoelectronic properties to inform processing strategies and increase both device efficiencies and long-term stability. Cathodoluminescence microscopy is an ideal technique to provide such information due to the high spatial resolution and robust optical information acquired. Here, the current body of work related to cathodoluminescence analysis of halide perovskite materials for optoelectronic applications is surveyed. This review demonstrates how cathodoluminescence can monitor degradation due to environmental stressors, phase segregation resulting from material processing, and other halide perovskite-centric material issues. A persistent concern associated with e-beam-based analysis of halide perovskites is what effect the electron beam has on the material properties being probed.Addressing this, a detailed discussion is provided on the origin of the cathodoluminescence signal and a review of studies focused on revealing changes in the properties of halide perovskites resulting from This article is protected by copyright. All rights reserved. e-beam excitation. Finally, a perspective on future opportunities to expand the role of cathodoluminescence analysis for halide perovskites is provided.

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“…Cathodoluminescence measurements on thin foils in the TEM have the potential to help address both of these issues, because the electron beam-sample interaction volume is much smaller, enabling higher resolution imaging, and because the resulting images can be directly correlated to high resolution TEM micrographs of material microstructure and TEM-EDX maps of material composition. Despite this promise, and the availability of commercial TEM-CL holders, the technique has not been successfully applied to solar cell characterisation because of problems with low signal [3].…”

Section: Motivation and Summarymentioning

confidence: 99%