Relativistic effects in electron-energy-loss-spectroscopy observations of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">S</mml:mi><mml:mi mathvariant="normal">i</mml:mi><mml:mo>/</mml:mo><mml:mi mathvariant="normal">S</mml:mi><mml:mi mathvariant="normal">i</mml:mi><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>interface plasmon peak

Moreau, Philippe; Brun, Nathalie; Walsh, Caroline; Colliex, C.; Howie, A.

doi:10.1103/physrevb.56.6774

Cited by 102 publications

(67 citation statements)

References 24 publications

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“…Our computations on interface plasmons in semiconductors highlight a sensitivity to interface diffuseness which should be more easily detectable. Relativistic corrections, which we have ignored, are however more likely to be significant in this situation [17] than would be expected for bulk plasmon excitation in metals.…”

Section: Discussionmentioning

confidence: 97%

“…The usual circular objective aperture, imposing an axial cut-off q a , axially limits the Fourier range of loss probability as a function of x to values of q x < [q 1/2 . Within the restrictions of classical excitation theory, this effect can be modelled by a further Fourier transform of our data [17]. Another option, already explored as a route to higher spatial resolution in valence EELS [18], is to work with a spectrometer collection aperture displaced in the q y direction to select only high values of q with less need for non-local corrections but at the expense of reduced signal strength.…”

Section: Discussionmentioning

confidence: 99%

“…In accordance with the above discussion, the peak shift is much more pronounced for small values of q y . For these free electron situations, the delocalization parameter [qλ(x, ω)] −2 employed in equation (17) and evaluated at the peak frequency ω = ω p (x) takes the form…”

Section: Free Electron Interfacesmentioning

confidence: 99%

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Plasmon excitations at diffuse interfaces

Howie

Abajo

Rivacoba

2008

J. Phys.: Condens. Matter

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Energy losses experienced by a fast electron probe moving through a dielectric medium have been studied both numerically and analytically, where the response function varies continuously with position in one transverse direction. The frequent assumption that the loss spectrum should exhibit a peak determined by the plasmon energy in a homogeneous medium with the composition found locally at the probe position can be incorrect. In free electron systems, inhomogeneous effects can cause spectral shape changes as well as peak shifts. Computations for diffuse interfaces between semiconductors with differing band gaps are also reported. Prospects for improved spatial resolution in valence loss spectroscopy at higher momentum transfer are discussed.

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

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Plasmon excitations at diffuse interfaces

Howie

Abajo

Rivacoba

2008

J. Phys.: Condens. Matter

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“…We use the classical dielectric approach 10 to calculate the energy loss of the relativistic electron, as a function of its position across the well, for a sandwich interface. 11 Dielectric functions derived from the low energyloss spectra of the well and barrier test layers were input in a dedicated program. 12 Before comparing with the experimental results, the calculated positions of the plasmon energies across a well are convoluted with our estimated spatial resolution ͑ϳ0.7 nm͒.…”

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confidence: 99%

Subnanometer-resolved measurement of the tunneling effective mass using bulk plasmons

Stolojan

Moreau

Goringe

et al. 2006

Applied Physics Letters

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Superlattices are periodic structures where the constituents alternate between low-and high-bandgap materials; the resulting quantum confinement tailors the resulting device properties and increases their operating speed. Amorphous carbon is an excellent candidate for both the well and barrier layers of the superlattices, leading to a fast and reliable device manufacturing process. We show theoretically and experimentally that, using low energy-loss spatially resolved spectroscopy, we can characterize the component layers of a superlattice. We measure quantum confinement of the electron wave function in the superlattice's wells and calculate the effective tunneling mass for amorphous carbon superlattices as m * = 0.067m e . This effective mass makes diamondlike carbon films as feasible candidate for electronic devices. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2188593͔ Diamond-like carbon films have optical band gaps from 1.2-4.0 eV controllable through the deposition parameters, such as the plasma power. 1 They are an attractive option for the semiconductor industry due to the inexpensive, fast and reliable manufacturing method. When the deposition parameter is varied cyclically during deposition, we obtain a bandgap modulation in an essentially homogenous material system, 2,3 leading to higher device speeds and controllable electronic properties. The confining potential of a band-gapmodulated artificial structure on the electron wave function leads to the quantization of the particle momentum and energy, controlled by the well's width and depth and the number of alternating barrier and well layers. 4,5 This can lead to the tailoring of devices for specific applications, such as frequency generators for the mobile phone industry. The design and testing of manufacturing processes for superlattices require not only the ability to characterize the morphology of the individual layers, but also their individual electronic properties. This places electron energy loss spectroscopy ͑EELS͒ in a transmission electron microscope ͑TEM͒ in the unique position of providing all this information. Here, we use an alternative method of acquiring spectral information on a subnanometer scale, and then set the theoretical basis for interpreting the measured collective excitation on the subnanometer scale. We then extract the tunneling effective mass by modeling the changes measured in the collective excitations using the "particle-in-a-box" quantum confinement model.In an electron microscope, it is possible to image the barrier and well layers constituent of a superlattice, even when their respective physical properties are very similar, at large defoci ͓Fig. 1͑a͔͒. 6 Energy loss spectroscopic profiling provides spatially resolved energy-loss spectra across linear features, under parallel illumination. 7 This method utilizes the manner in which a Gatan imaging filter forms images and energy-loss spectra, by collecting two-dimensional data sets with one axis, the energy loss and the other axis the spatial dimension norma...

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“…This means that the final result is not a superposition of the surface excitation to the bulk excitation but a replacement. We modelled the energy loss of the relativstic electron using the classical dielectric approach (Garcia-Molina 1985) for a sandwich interface (Turowski 1994, Moreau 1997, using dedicated software (Walsh 1992). This was done using the dielectric functions extracted from the energy loss spectra of barrier and well test layers grown under identical conditions as the superlattices.…”

Section: Spatial Resolutionmentioning

confidence: 99%

Quantum effects in band gap-modulated amorphous carbon superlattices

Stolojan

Moreau

Goringe

et al.

Springer Proceedings in Physics

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Diamond-like carbon (DLC) films, with their controllable optical band gaps from 1-4eV, have promised much as electronic semiconducting materials for many years. Particularly, hydrogenated amorphous carbon films (a-C:H) have attracted interest in their possible use in light emitting diodes, flat panel displays and solar cells. Photoemission in these films can be explained by the electron-hole recombination at sp 2 -bonded carbon clusters, enhanced by the quantumconfinement of the rigid sp 3 -matrix. The speed of such devices can be improved by constructing homogenous carbon superlattices from alternate high and low band-gap a-C:H layers. Here, we measure directly the electronic properties across superlattices, using Energy Loss Spectroscopic Profiling (ELSP) in a Transmission Electron Microscope (TEM). By analysing the valence losses across the layers, we characterise the electronic structure of the films. By modelling the influence of the interface collective modes of oscillation (interface plasmons), we show that the measured changes in the bulk plasmon energies of the wells are due to quantum confinement and predicted using the 'particle-in-a-box' model. These a-C superlattice structures have the potential of introducing a highly versatile novel large area amorphous semiconductor that is carbon based and deposited at room temperature.

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Relativistic effects in electron-energy-loss-spectroscopy observations of theSi/SiO2interface plasmon peak

Cited by 102 publications

References 24 publications

Plasmon excitations at diffuse interfaces

Plasmon excitations at diffuse interfaces

Subnanometer-resolved measurement of the tunneling effective mass using bulk plasmons

Quantum effects in band gap-modulated amorphous carbon superlattices

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