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IN SITU SECOND-HARMONIC GENERATION CIRCULAR DICHROISM WITH SUBMONOLAYER SENSITIVTIY
摘要： In this work, we present an experimental setup for the in situ and ex situ study of the optical activity of samples, which can be prepared under ultra-high vacuum (UHV) conditions by second-harmonic generation circular dichroism (SHG-CD) over a broad spectral range. The use of a racemic mixture as a qualified reference for the anisotropy factor is described and, as an example, the chiroptical properties of 1.5 μm thick (multilayers) as well as sub-monolayer thin films of the R- and S-enantiomer of 1,1'-Bi-2-naphthol (BINOL) evaporated onto BK7 substrates were investigated.
关键词： Submonolayer sensitivity,Second-harmonic generation circular dichroism,Circular-linear dichroism
更新于2025-09-23 15:21:01
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Optical Properties of Plasmonic Nanoantennas Based on Arrays of Interacting V-Shaped Structures in the Mid-IR Range
摘要： Polarization-selected IR transmission, IR re?ection, and IR absorption spectra of arrays of V -shaped gold structures are experimentally studied for various structure periods. To form a local region of the enhanced electromagnetic ?eld in subwavelength nanogaps, arrays with unit cells consisting of two V -shaped structures, facing each other by acute angles with gaps of 0, 50, 100 nm were also used. The results of comparison of spectral data with measurements of dimensional parameters using atomic-force microscopy and scanning electron microscopy are presented. The possibility of using the fabricated structures to achieve the e?ect of surface-enhanced IR absorption by quantum dots is shown.
关键词： linear dichroism,plasmon nanoantennas,surface-enhanced IR spectroscopy
更新于2025-09-16 10:30:52
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Optical properties of helical edge channels in zinc-blende-type topological insulators: Selection rules, circular and linear dichroism, circular and linear photocurrents
摘要： We develop a theory of electron-photon interaction for helical edge channels in two-dimensional topological insulators based on zinc-blende-type quantum wells. It is shown that the lack of space inversion symmetry in such structures enables the electro-dipole optical transitions between the spin branches of the topological edge states. Further, we demonstrate the linear and circular dichroism associated with the edge states and the generation of edge photocurrents controlled by radiation polarization.
关键词： circular dichroism,edge photocurrents,topological insulators,electron-photon interaction,linear dichroism,helical edge channels
更新于2025-09-09 09:28:46
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Electric-field modulation of linear dichroism and Faraday rotation in few-layer phosphorene
摘要： Electro-optical modulators, which use an electric voltage (or an electric field) to modulate a beam of light, are essential elements in present-day telecommunication devices. Using a self-consistent tight-binding approach combined with the standard Kubo formula, we show that the optical conductivity and the linear dichroism of few-layer phosphorene can be modulated by a perpendicular electric field. We find that the field-induced charge screening plays a significant role in modulating the optical conductivity and the linear dichroism. Distinct absorption peaks are induced in the conductivity spectrum due to the strong quantum confinement along the out-of-plane direction and to the field-induced forbidden-to-allowed transitions. The field modulation of the linear dichroism becomes more pronounced with increasing number of phosphorene layers. We also show that the Faraday rotation is present in few-layer phosphorene even in the absence of an external magnetic field. This optical Hall effect is induced by the reduced lattice symmetry of few-layer phosphorene. The Faraday rotation is greatly influenced by the field-induced charge screening and is strongly dependent on the strength of perpendicular electric field and on the number of phosphorene layers.
关键词： electric field modulation,linear dichroism,optical conductivity,Faraday rotation,electro-optical modulators,few-layer phosphorene
更新于2025-09-09 09:28:46
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Inverted orbital polarization in strained correlated oxide films
摘要： Manipulating the orbital occupation of valence electrons via epitaxial strain in an effort to induce new functional properties requires considerations of how changes in the local bonding environment affect the band structure at the Fermi level. Using synchrotron radiation to measure the x-ray linear dichroism of epitaxially strained films of the correlated oxide CaFeO3, we demonstrate that the orbital polarization of the Fe valence electrons is opposite from conventional understanding. Although the energetic ordering of the Fe 3d orbitals is confirmed by multiplet ligand field theory analysis to be consistent with previously reported strain-induced behavior, we find that the nominally higher energy orbital is more populated than the lower. We ascribe this inverted orbital polarization to an anisotropic bandwidth response to strain in a compound with nearly filled bands. These findings provide an important counterexample to the traditional understanding of strain-induced orbital polarization and reveal a method to engineer otherwise unachievable orbital occupations in correlated oxides.
关键词： x-ray linear dichroism,epitaxial strain,CaFeO3,correlated oxides,orbital polarization
更新于2025-09-09 09:28:46
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Electronic states of dibenzo-p–dioxin. A synchrotron radiation linear dichroism Investigation
摘要： The UV absorbance bands of dibenzo-p-dioxin (dibenzo-1,4-dioxin, DD) are investigated by synchrotron radiation linear dichroism (SRLD) spectroscopy on molecular samples aligned in stretched polyethylene. The investigation covers the range 58000–30000 cm–1 (170–330 nm), thereby providing new information on the transitions of DD in the vacuum UV region. The observed polarization data enable experimental symmetry assignments of the observed transitions, leading to revision of previously published assignments by Ljubi? and Sablji? (J. Phys. Chem. A 109 (2005) 8209-8217). In general, the experimental spectra are well predicted by the results of quantum chemical calculations using time-dependent density functional theory (TD–DFT). The observed absorbance in the region 58000–55000 cm–1 (170–180 nm) in the vacuum UV is almost entirely short-axis polarized, in pleasing agreement with the predicted spectrum.
关键词： Dibenzo-p-dioxin,Near and vacuum UV,Stretched polyethylene,Polarization directions,Time-dependent density functional theory (TD-DFT),Synchrotron radiation,Linear dichroism (LD)
更新于2025-09-09 09:28:46