We determine Faraday rotations and measure the optical reflection and transmission from magneto-optical Cd1−xMnxTe crystals with various stoichiometric ratios. For wavelengths between 675 and ...1025 nm, we derive Verdet constants, optical loss coefficients, and the complex indices of reflection that are relevant measures to find suitable stoichiometric ratios of Cd1−xMnxTe for the realization of miniaturized optical isolators. By reflection and transmission measurements, we determine the stoichiometric ratios of several different Cd1−xMnxTe crystals and discuss the observed dependence of the optical properties on the stoichiometric ratio with respect to their use in optical isolators. Finally, we show the relevant figure of merit, i.e., the ratio of Verdet constants and optical loss coefficients for Cd1−xMnxTe crystals with Mn contents ranging from x = 0.14 to x = 0.50.
We present measurements of the D" Raman mode in graphene and carbon nanotubes at different laser excitation energies. The Raman mode around 1050-1150 cm super(-1) originates from a double-resonant ...scattering process of longitudinal acoustic (LA) phonons with defects. We investigate its dependence on laser excitation energy, on the number of graphene layers, and on the carbon nanotube diameter. We assign this Raman mode to so-called inner processes with resonant phonons mainly from the Gamma-K high-symmetry direction. The asymmetry of the D" mode is explained by additional contributions from phonons next to the Gamma-K line. Our results demonstrate the importance of inner contributions in the double-resonance scattering process and add a fast method to investigate acoustic phonons in graphene and carbon nanotubes by optical spectroscopy.
The line shape of the double-resonant 2D Raman mode in bilayer graphene is often considered to be characteristic for a certain laser excitation energy. Here, in a joint experimental and theoretical ...study, we analyze the dependence of the double-resonant Raman scattering processes in bilayer graphene on the electronic broadening parameter γ. We demonstrate that the ratio between symmetric and anti-symmetric scattering processes sensitively depends on the lifetime of the electronic states, explaining the experimentally observed variation of the complex 2D-mode line shape.
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We performed resonance Raman spectroscopy on HiPCO‐produced single‐walled carbon nanotubes in the spectral region of 846 and 1692cm−1, using laser excitation energies between 1.58 and 2.73eV. We ...observe a characteristic peak around 846cm−1 and its overtones around 1692cm−1. Especially the latter was controversially discussed in the past and has been assigned to a double‐resonant Raman process involving two oTO phonons. We demonstrate that both peaks slightly depend on the excitation laser energy by means of their shape, intensity, and peak position. Following the model proposed by Dobardžić et al., we relate both peaks to oTO Γ‐point phonons. As we analyze both, the first‐order band and its overtone simultaneously, we are able to provide a unified explanation of these low‐intensity Raman bands in carbon nanotubes.
Raman spectrum of an HiPCO‐produced buckypaper carbon nanotube sample at 2.33 eV laser energy. Both insets show a magnification of the oTO‐related first‐ and second‐order Raman bands, which we discuss in this article.
The reaction of neutral single-walled carbon nanotubes (SWCNTs) with diazonium salts proceeds with a high selectivity towards metallic carbon nanotube species; this reaction is well-understood and ...the mechanism has been elucidated. In the present joint theoretical and experimental study, we investigate the reaction of negatively charged SWCNTs - carbon nanotubides - with diazonium salts. Our density functional theory calculations predict a stronger binding of the aryl diazonium cations to charged metallic SWCNTs species and therefore lead to a preferential addend binding in the course of the reaction. The Raman resonance profile analysis on the reductive arylation of carbon nanotubides obtained by the solid state intercalation approach with potassium in varying concentrations confirms the predicted preferred functionalization of metallic carbon nanotubes. Furthermore, we were also able to show that the selectivity for metallic SWCNT species could be further increased when low potassium concentrations (K : C < 1 : 200) are used for an initial selective charging of the metallic species. Further insights into the nature of the bound addends were obtained by coupled thermogravimetric analysis of the functionalized samples.
We determine Faraday rotations and measure the optical reflection and transmission from magneto-optical Cd1−xMnxTe crystals with various stoichiometric ratios. For wavelengths between 675 and ...1025 nm, we derive Verdet constants, optical loss coefficients, and the complex indices of reflection that are relevant measures to find suitable stoichiometric ratios of Cd1−xMnxTe for the realization of miniaturized optical isolators. By reflection and transmission measurements, we determine the stoichiometric ratios of several different Cd1−xMnxTe crystals and discuss the observed dependence of the optical properties on the stoichiometric ratio with respect to their use in optical isolators. Finally, we show the relevant figure of merit, i.e., the ratio of Verdet constants and optical loss coefficients for Cd1−xMnxTe crystals with Mn contents ranging from x = 0.14 to x = 0.50.
The reaction of neutral single-walled carbon nanotubes (SWCNTs) with diazonium salts proceeds with a high selectivity towards metallic carbon nanotube species; this reaction is well-understood and ...the mechanism has been elucidated. In the present joint theoretical and experimental study, we investigate the reaction of negatively charged SWCNTs - carbon nanotubides - with diazonium salts. Our density functional theory calculations predict a stronger binding of the aryl diazonium cations to charged metallic SWCNTs species and therefore lead to a preferential addend binding in the course of the reaction. The Raman resonance profile analysis on the reductive arylation of carbon nanotubides obtained by the solid state intercalation approach with potassium in varying concentrations confirms the predicted preferred functionalization of metallic carbon nanotubes. Furthermore, we were also able to show that the selectivity for metallic SWCNT species could be further increased when low potassium concentrations (K : C < 1 : 200) are used for an initial selective charging of the metallic species. Further insights into the nature of the bound addends were obtained by coupled thermogravimetric analysis of the functionalized samples.
The reaction of negatively charged SWCNTs with diazonium salts was analyzed in a combined experimental and computational DFT study.
The reaction of negatively charged SWCNTs with diazonium salts was analyzed in a combined experimental and computational DFT study.
The reaction of neutral single-walled carbon nanotubes (SWCNTs) ...with diazonium salts proceeds with a high selectivity towards metallic carbon nanotube species; this reaction is well-understood and the mechanism has been elucidated. In the present joint theoretical and experimental study, we investigate the reaction of negatively charged SWCNTs – carbon nanotubides – with diazonium salts. Our density functional theory calculations predict a stronger binding of the aryl diazonium cations to charged metallic SWCNTs species and therefore lead to a preferential addend binding in the course of the reaction. The Raman resonance profile analysis on the reductive arylation of carbon nanotubides obtained by the solid state intercalation approach with potassium in varying concentrations confirms the predicted preferred functionalization of metallic carbon nanotubes. Furthermore, we were also able to show that the selectivity for metallic SWCNT species could be further increased when low potassium concentrations (K : C < 1 : 200) are used for an initial selective charging of the metallic species. Further insights into the nature of the bound addends were obtained by coupled thermogravimetric analysis of the functionalized samples.
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