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High-Resolution Electron Energy Loss Spectroscopy
Published in Arthur T. Hubbard, The Handbook of Surface Imaging and Visualization, 2022
In this article our intent is to provide an overview of HREELS, especially for the reader unfamiliar with the technique who wishes to gain a quick grasp of the applications and limitations of the method. For the interested reader, more in-depth reviews are given in Ibach and Mills1 and Ho2 as well as in the references for each section. In Section 2 an introduction to the experimental apparatus is given, highlighting common features of modem spectrometers. In Section 3 we outline the main features of HREELS theory with emphasis on the interpretation of adsorbate spectra. Finally, in Section 4 we examine modem applications of the technique, placing special emphasis on applications of broad technical importance, such as catalysts, silicon technology, metal oxides, and polymers. Many important areas, such as surface phonon dispersion studies, have been omitted in the interest of brevity.
Radiative Effects in Translucent Solids, Windows, and Coatings
Published in John R. Howell, M. Pinar Mengüç, Kyle Daun, Robert Siegel, Thermal Radiation Heat Transfer, 2020
John R. Howell, M. Pinar Mengüç, Kyle Daun, Robert Siegel
For ordinary behavior at an interface as in Figure 17.9, some of the radiation in medium 1 traveling toward region 2 will undergo total internal reflection at the interface when n1 > n2, as discussed in Section 17.5.2. For ordinary radiative behavior, this occurs when the incidence angle θ1 is equal to or larger than the angle for total reflection, θ1 ≥ sin−1(n2/n1). When region 2 in Figure 17.9 is sufficiently thin, however, electromagnetic theory predicts that, even for an intensity incident at θ1 greater than sin−1(n2/n1), total internal reflection does not occur. Rather, part of the incident intensity propagates across the thin region 2 and enters medium 3. This effect is the essence of radiation tunneling, as discussed in Chapter 16. This tunneling stems from the surface due to electron or lattice vibrations. They are called either surface plasmon polaritons (SPP, for electrons) or surface phonon polaritons (SPhP, for phonons). The effect has been verified experimentally (Xu et al. 1994) and has been used in producing photon scanning tunneling microscopes and near-field optical thermometers that can have subwavelength resolution (Goodson and Ashegi 1997). Details about recent developments are given in Chapter 16.
Simultaneously Evaporated Al-Doped Zn Films for Optoelectronic Applications
Published in Devrim Balköse, Ana Cristina Faria Ribeiro, A. K. Haghi, Suresh C. Ameta, Tanmoy Chakraborty, Chemical Science and Engineering Technology, 2019
Yasir Beeran Pottathara, Obey Koshy, M.A. Khadar
The detected intense Raman peaks at 99 and 437 cm−1 are allotted to the E2 (low) and E2 (high) optical phonon modes, respectively, reported for bulk ZnO.19 The typical hexagonal wurtzite phase of ZnO was observed at 437 cm−1 for all samples, and its presence indicates the good crystal quality consistent with GI-XRD observations. Besides the weak and broad band observed at ∼334 cm−1 in the AZO film, samples may be attributed to Raman second-order scattering usually originating from zone boundary phonon E2 (M) in the Brillouin zone.20 In nanostructured materials, a large fraction of atoms resides at grain boundaries, and as a result, surface optical phonons become observable with measurable intensity. One of the characteristic features of surface modes is that they appear in between the TO and LO modes. The surface phonon mode peak intensity should become weaker as the size of the grain increases. From the GI-XRD results, it is understood that the grain size of the AZO films declines with the increase in Al concentration. In addition to E2 modes, weak Al (LO) mode is observed ∼581 cm−1 with shifting to higher wavenumber can be accredited to the alteration of ZnO6 octahedra and this kind of shifting of the Raman bands to higher wavenumbers is due to the nanocrystalline nature of the film samples.
Surface and Constriction Engineering of Nanoparticle Based Structures Towards Ultra-Low Thermal Conductivity as Prospective Thermoelectric Materials
Published in Nanoscale and Microscale Thermophysical Engineering, 2023
Pasan Henadeera, Nalaka Samaraweera, Chathura Ranasinghe, Anusha Wijewardane
Another technique shown to be capable of disrupting the phonon transport in nanostructures such as nanowires is the removal of shell atoms. The roughness caused by randomly removing a limited number of atoms from the surface causes the surface phonon modes to scatter thus reducing the of the structure. Because of this, the ability to utilize such methods to further inhibit the thermal transfer across 5 nm diameter 60% constriction NPC structures is evaluated within the current study. The selection of atoms demarcated as the total shell atoms are visualized in Figure 11 using blue spheres while red spheres indicate the internal atoms of the structure. Thus, the removed atoms are maintained as a fraction of the shell atoms.
Effect of surface phonon scattering on thermal stress around small-scale elliptic holes in a thermoelectric material
Published in Journal of Thermal Stresses, 2021
Kun Song, Deshun Yin, Peter Schiavone
In contrast to the case of a composite considered at the macroscale, the incorporation of surface/interface energy in smaller scale models of deformation means that the stress field suffers a jump across the surface/interface of an embedded inhomogeneity. With this in mind, Wang et al. [11] investigated the stress field induced by surface tension around an arbitrarily shaped nanosized hole using complex variable techniques, while Song et al. [12] studied the effect of surface elasticity on the thermal stress distribution around a circular nano-hole. Since the stresses in thermoelectric materials are induced mainly by thermal expansion, surface phonon scattering is another dominant factor affecting the stress distribution at these smaller scales. Ghazanfarian and Abbassi [13] indicated that surface phonon scattering generally leads to a temperature jump on the surface of micro- and nano-scale composites and subsequently presented a boundary condition to simulate this temperature jump. Based on this idea, Song et al. [14] proposed an interface condition to simulate the temperature jump on the interface between an embedded nano-scale inhomogeneity and its surrounding elastic matrix and used this condition to study electric and heat conduction in a thermoelectric material containing a circular nano-inhomogeneity. However, the specific effect of surface phonon scattering on the thermal stress in thermoelectric composites remains largely unreported in the literature.
Mechanical testing of two-dimensional materials: a brief review
Published in International Journal of Smart and Nano Materials, 2020
Karrar K. Al-Quraishi, Qing He, Wesley Kauppila, Min Wang, Yingchao Yang
Phonon dispersion measurement can be used to characterize the mechanical properties of graphene through high-resolution electron energy loss spectroscopy (HREELS), which is a powerful tool to investigate surface phonon dispersion, surface structure, and monitor epitaxial growth. HREELS deals with small energy losses in the range of 10−3 eV to 1 eV. The main advantages of HREELS include high surface sensitivity, excellent resolution in both energy and momentum domains, and wide energy and momentum windows. In graphene, there are two types of phonons: lattice vibrations in the plane of the sheet giving rise to transverse and longitudinal acoustic and optical branches, and lattice vibrations out of the plane of the layer which give rise to the so-called flexural phonons [223]. The acoustic phonons of graphene can provide information on its elastic properties. The sound velocities of the transverse acoustic and longitudinal acoustic branches could be used to calculate the in-plane stiffness and the shear modulus of 2D materials.