Quantitative analysis of valence electron energy‐loss spectra of aluminium nitride

Dorneich,; French, None; Müllejans,; Loughin,; Rühle,

doi:10.1046/j.1365-2818.1998.00370.x

Cited by 64 publications

(45 citation statements)

References 27 publications

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“…26 Subsequently the spectra were corrected for multiple scattering events by Fourier-logarithmic deconvolution 40 and were scaled for constant relative thickness. 31 For energies below 3.0 eV, i.e., close to the optical band gap energy of SrTiO 3 ͑3.2 eV, 41 3.1 eV Refs.…”

Section: Discussionmentioning

confidence: 99%

Graded interface models for more accurate determination of van der Waals–London dispersion interactions across grain boundaries

et al. 2006

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Attractive van der Waals-London dispersion interactions between two half crystals arise from local physical property gradients within the interface layer separating the crystals. Hamaker coefficients and London dispersion energies were quantitatively determined for Σ5 and near-Σ13 grain boundaries in SrTiO 3 by analysis of spatially resolved valence electron energy-loss spectroscopy (VEELS) data. From the experimental data, local complex dielectric functions were determined, from which optical properties can be locally analyzed. Both local electronic structures and optical properties revealed gradients within the grain boundary cores of both investigated interfaces. The results show that even in the presence of atomically structured grain boundary cores with widths of less than 1 nm, optical properties have to be represented with gradual changes across the grain boundary structures to quantitatively reproduce accurate van der Waals-London dispersion interactions. London dispersion energies of the order of 10% of the apparent interface energies of SrTiO 3 were observed, demonstrating their significance in the grain boundary formation process. The application of different models to represent optical property gradients shows that long-range van der Waals-London dispersion interactions scale significantly with local, i.e., atomic length scale property variations. Attractive van der Waals-London dispersion interactions between two half crystals arise from local physical property gradients within the interface layer separating the crystals. Hamaker coefficients and London dispersion energies were quantitatively determined for ⌺5 and near-͚13 grain boundaries in SrTiO 3 by analysis of spatially resolved valence electron energy-loss spectroscopy ͑VEELS͒ data. From the experimental data, local complex dielectric functions were determined, from which optical properties can be locally analyzed. Both local electronic structures and optical properties revealed gradients within the grain boundary cores of both investigated interfaces. The results show that even in the presence of atomically structured grain boundary cores with widths of less than 1 nm, optical properties have to be represented with gradual changes across the grain boundary structures to quantitatively reproduce accurate van der Waals-London dispersion interactions. London dispersion energies of the order of 10% of the apparent interface energies of SrTiO 3 were observed, demonstrating their significance in the grain boundary formation process. The application of different models to represent optical property gradients shows that long-range van der Waals-London dispersion interactions scale significantly with local, i.e., atomic length scale property variations. Disciplines Engineering | Materials Science and Engineering Comments

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Section: Discussionmentioning

confidence: 99%

Graded interface models for more accurate determination of van der Waals–London dispersion interactions across grain boundaries

et al. 2006

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“…SSD spectra are obtained from experimental spectra by deconvolution of elastic phonon and multiple scattering effects. This is achieved by fitting the experimental zero-loss peak with a multiparameter asymmetric function 10 followed by Fourier-log deconvolution proposed by Johnson and Spence 11 and computed by Egerton. 12 The convergence angular effects are corrected using Egerton's CONCOR software.…”

Section: Methodsmentioning

confidence: 99%

Crystal structure and band gap determination of HfO2 thin films

Cheynet¹,

Pokrant²,

Tichelaar³

et al. 2007

Journal of Applied Physics

150

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Valence electron energy loss spectroscopy ͑VEELS͒ and high resolution transmission electron microscopy ͑HRTEM͒ are performed on three different HfO 2 thin films grown on Si ͑001͒ by chemical vapor deposition ͑CVD͒ or atomic layer deposition ͑ALD͒. For each sample the band gap ͑E g ͒ is determined by low-loss EELS analysis. The E g values are then correlated with the crystal structure and the chemical properties of the films obtained by HRTEM images and VEELS line scans, respectively. They are discussed in comparison to both experimental and theoretical results published in literature. The HfO 2 ALD film capped with poly-Si exhibits the largest band gap ͑E g = 5.9± 0.5 eV͒, as a consequence of its nanocrystallized orthorhombic structure. The large grains with a monoclinic structure formed in the HfO 2 ALD film capped with Ge and the carbon contamination induced by the precursors in the HfO 2 CVD film capped with Al 2 O 3 are identified to be the main features responsible for lower band gap values ͑E g = 5.25± 0.5 and 4.3± 0.5 eV respectively͒.

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“…The methods of VEELS have been discussed in detail. 24,73,74 The experimentally determined ELF is first corrected for multiple scattering effects using Fourier logarithm deconvolution, then the ELF is scaled through application of the index sum rule shown in Eq. (16), where P represents the Cauchy principal part of the integral.…”

Section: ϫ3mentioning

confidence: 99%

Origins and Applications of London Dispersion Forces and Hamaker Constants in Ceramics

French

2000

Journal of the American Ceramic Society

263

100

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The London dispersion forces, along with the Debye and Keesom forces, constitute the long-range van der Waals forces. London's and Hamaker's work on the point-to-point dispersion interaction and Lifshitz's development of the continuum theory of dispersion are the foundations of our understanding of dispersion forces. Dispersion forces are present for all materials and are intrinsically related to the optical properties and the underlying interband electronic structures of materials. The force law scaling constant of the dispersion force, known as the Hamaker constant, can be determined from spectral or parametric optical properties of materials, combined with knowledge of the configuration of the materials. With recent access to new experimental and ab initio tools for determination of optical properties of materials, dispersion force research has new opportunities for detailed studies. Opportunities include development of improved index approximations and parametric representations of the optical properties for estimation of Hamaker constants. Expanded databases of London dispersion spectra of materials will permit accurate estimation of both nonretarded and retarded dispersion forces in complex configurations. Development of solutions for generalized multilayer configurations of materials are needed for the treatment of more-complex problems, such as graded interfaces. Dispersion forces can play a critical role in materials applications. Typically, they are a component with other forces in a force balance, and it is this balance that dictates the resulting behavior. The ubiquitous nature of the London dispersion forces makes them a factor in a wide spectrum of problems; they have been in evidence since the pioneering work of Young and Laplace on wetting, contact angles, and surface energies. Additional applications include the interparticle forces that can be measured by direct techniques, such as atomic force microscopy. London dispersion forces are important in both adhesion and in sintering, where the detailed shape at the crack tip and at the sintering neck can be controlled by the dispersion forces. Dispersion forces have an important role in the properties of numerous ceramics that contain intergranular films, and here the opportunity exists for the development of an integrated understanding of intergranular films that encompasses dispersion forces, segregation, multilayer adsorption, and structure. The intrinsic length scale at which there is a transition from the continuum perspective (dispersion forces) to the atomistic perspective (encompassing interatomic bonds) is critical in many materials problems, and the relationship of dispersion forces and intergranular films may represent an important opportunity to probe this topic. Am. Ceram. Soc., 83 [9] 2117-46 (2000 Centennial FeatureThe London dispersion force is retarded at large separations, where the transit time of the electromagnetic interaction must be considered explicitly. Novel phenomena, such as equilibrium surficial films and bimodal wettin...

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Quantitative analysis of valence electron energy‐loss spectra of aluminium nitride

Cited by 64 publications

References 27 publications

Graded interface models for more accurate determination of van der Waals–London dispersion interactions across grain boundaries

Graded interface models for more accurate determination of van der Waals–London dispersion interactions across grain boundaries

Crystal structure and band gap determination of HfO2 thin films

Origins and Applications of London Dispersion Forces and Hamaker Constants in Ceramics

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