Composition mapping in InGaN by scanning transmission electron microscopy

Rosenauer, A.; Mehrtens, Thorsten; Müller, Knut; Gries, Katharina; Schowalter, Marco; Satyam, P.V.; Bley, Stephanie; Tessarek, Christian; Hommel, D.; Sebald, K.; Seyfried, Moritz; Gutowski, J.; Avramescu, Adrian; Engl, Karl; Lutgen, S.

doi:10.1016/j.ultramic.2011.04.009

Cited by 169 publications

(183 citation statements)

References 38 publications

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“…Neither of these is appropriate for the current case, where unresolved oxygen atoms lie close to the metal atoms; rather, we use intensities integrated over a Voronoi cell surrounding the atom column of interest. A Voronoi cell is an area bounded by the perpendicular bisectors of all vectors that link adjacent atom columns [40,[46][47][48]. The mean integrated intensity in a Voronoi cell is proportional to the scattering cross-section of the atom column, while retaining a useful degree of insensitivity to exact experimental conditions such as defocus and spatial incoherence [43].…”

Section: Introductionmentioning

confidence: 99%

Atomic structure study of the pyrochloreYb2Ti2O7and its relationship with low-temperature magnetic order

et al. 2017

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There has been great interest in the magnetic behavior of pyrochlore oxides with the general formula A 2 B 2 O 7 , in which rare-earth (A) and transition metal (B) cations are ordered on separate interpenetrating lattices of corner-sharing tetrahedra. Such materials exhibit behaviors including quantum spin-ice, (quantum) spin-liquid, and ordered magnetic ground states. Yb 2 Ti 2 O 7 lies on the boundary between a number of competing magnetic ground states. Features in the low-temperature specific heat capacity that vary in sharpness and temperature from sample to sample suggest that, in some cases, the magnetic moments order, while in others, the moments remain dynamic down to temperatures as low as ∼16 mK. In this paper, three different Yb 2 Ti 2 O 7 samples, all grown by the optical floating zone technique but exhibiting quite different heat capacity behavior, are studied by aberration-corrected scanning transmission microscopy (STEM). Atomic-scale energy-dispersive x-ray analysis shows that a crystal with no specific heat anomaly has substitution of Yb atoms on Ti sites (stuffing). We show that the detailed intensity distribution around the visible atomic columns in annular dark field STEM images is sensitive to the presence of nearby atoms of low atomic number (in this case oxygen) and find significant differences between the samples that correlate both with their magnetic behavior and measurements of Ti oxidation state using electron energy loss spectroscopy. These measurements support the view that the magnetic ground state of Yb 2 Ti 2 O 7 is extremely sensitive to disorder.

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Section: Introductionmentioning

confidence: 99%

Atomic structure study of the pyrochloreYb2Ti2O7and its relationship with low-temperature magnetic order

et al. 2017

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“…[12][13][14] The WL states are not considered in the FCI calculation, since they do not significantly influence the lower QD state transitions due to their rather large energy separation. Though it is known that also the shape and the size of the QDs may depend on the growth direction, 15 we assume the same QD geometry for the nonpolar growth direction (with the restriction that the modeling in the different crystal orientations requires a shift of the QD boundaries of about 10%) to focus on the effect of the built-in field orientation on the optical properties.…”

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confidence: 99%

Strong dipole coupling in nonpolar nitride quantum dots due to Coulomb effects

Schuh

Barthel

Marquardt

et al. 2012

Applied Physics Letters

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Optical properties of polar and nonpolar nitride quantum dots (QDs) are determined on the basis of a microscopic theory which combines a continuum elasticity approach to the polarization potential, a tight-binding model for the electronic energies and wavefunctions, and a many-body theory for the optical properties. For nonpolar nitride quantum dots, we find that optical absorption and emission spectra exhibit a weak ground-state oscillator strength in a single-particle calculation whereas the Coulomb configuration interaction strongly enhances the ground-state transitions. This finding sheds new light on existing discrepancies between previous theoretical and experimental results for these systems, as a weak ground state transition was predicted because of the spatial separation of the corresponding electron and hole state due to intrinsic fields whereas experimentally fast optical transitions have been observed.

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“…GaN materials are robust, with high thermal conductivity and high melting temperatures making them suitable for high current density devices such as SLEDs and semiconductor optical amplifiers. Indium gallium nitride (InGaN) QWs suffer from thickness variations [33], [34] and indium dislocation or clustering [35], [36] causing dot-like behavior [37], resulting in a density of states that lends itself to broad bandwidth applications. Additionally, strong polarization effects (both spontaneous and piezoelectric) result in large inbuilt fields that result in a forward bias significantly modifying the emission wavelength of the device.…”

Section: Theoretical Resolution Of Oct Systemsmentioning

confidence: 99%

Gallium Nitride Superluminescent Light Emitting Diodes for Optical Coherence Tomography Applications

Goldberg

Boldin

Andersson

et al. 2017

IEEE J. Select. Topics Quantum Electron.

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Abstract-Optical coherence tomography (OCT) exploits the coherent properties of light to permit noninvasive and in situ imaging of biological tissues. By expanding the range of OCT light sources from the traditional telecoms wavelengths to include ∼400 nm gallium nitride (GaN) based superluminescent light emitting diodes (SLEDs) subcellular axial and lateral resolution could be achieved, provided enhanced bandwidth is also achieved. Due to the focus on high-power applications for GaN SLEDs, there has been limited work on increasing the source bandwidth. In this paper, we demonstrate for the first time a ∼400 nm GaN SLED with >10 nm bandwidth employed within an OCT system, where an axial resolution of ∼7 µm is achieved. Bespoke GaN SLEDs suggest that <4 µm axial resolution imaging is imminent for short wavelength devices.Index Terms-Axial resolution, broad bandwidth, gallium nitride superluminescent light emitting diodes, optical coherence tomography.

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Composition mapping in InGaN by scanning transmission electron microscopy

Cited by 169 publications

References 38 publications

Atomic structure study of the pyrochloreYb2Ti2O7and its relationship with low-temperature magnetic order

Atomic structure study of the pyrochloreYb2Ti2O7and its relationship with low-temperature magnetic order

Strong dipole coupling in nonpolar nitride quantum dots due to Coulomb effects

Gallium Nitride Superluminescent Light Emitting Diodes for Optical Coherence Tomography Applications

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