Raman spectroscopy

About: Raman spectroscopy is a research topic. Over the lifetime, 122605 publications have been published within this topic receiving 2891083 citations. The topic is also known as: Raman Spectrum Analysis & spectrum Analysis, Raman.

Introduction: Infrared and Raman Spectroscopy

Abstract: This chapter introduces how both mid-infrared (mid-IR) and Raman spectroscopy provide characteristic fundamental vibrations that are employed for the elucidation of molecular structure. Mid-IR, near-IR, and Raman spectroscopy are part of vibrational spectroscopy. Raman spectroscopy is best at symmetric vibrations of nonpolar groups while IR spectroscopy is best at the asymmetric vibrations of polar groups. Infrared and Raman spectroscopy involve the study of the interaction of radiation with molecular vibrations but differ in the manner in which photon energy is transferred to the molecule by changing its vibrational state. IR spectroscopy measures transitions between molecular vibrational energy levels as a result of the absorption of mid-IR radiation. The IR and Raman vibrational bands are characterized by their frequency (energy), intensity, and band shape (environment of bonds). The frequencies of these molecular vibrations depend on the masses of the atoms, their geometric arrangement, and the strength of their chemical bonds. Two different approaches are used for the interpretation of vibrational spectroscopy and elucidation of molecular structure. The first approach is the use of group theory with mathematical calculations of the forms and frequencies of the molecular vibrations, and the second approach is the use of empirical characteristic frequencies for chemical functional groups. IR spectroscopy was the first structural spectroscopic technique widely used by organic chemists. An extensive user base resulted in a great increase in available IR interpretation tools and the eventual development of FT-IR instrumentation.

Raman amplifiers for telecommunications

Abstract: Raman amplifiers are being deployed in almost every new long-haul and ultralong-haul fiber-optic transmission systems, making them one of the first widely commercialized nonlinear optical devices in telecommunications. This paper reviews some of the technical reasons behind the wide-spread acceptance of Raman technology. Distributed Raman amplifiers improve the noise figure and reduce the nonlinear penalty of fiber systems, allowing for longer amplifier spans, higher bit rates, closer channel spacing, and operation near the zero-dispersion wavelength. Lumped or discrete Raman amplifiers are primarily used to increase the capacity of fiber-optic networks, opening up new wavelength windows for wavelength-division multiplexing such as the 1300 nm, 1400 nm, or short-wavelength S-band. As an example, using a cascade of S-band lumped amplifiers, a 20-channel, OC-192 system is shown that propagates over 867 km of standard, single-mode fiber. Raman amplifiers provide a simple single platform for long-haul and ultralong-haul amplifier needs and, therefore, should see a wide range of deployment in the next few years.

Semiconductor nanocrystals covalently bound to metal surfaces with self-assembled monolayers

Abstract: A method is described for attaching semiconductor nanocrystals to metal surfaces using self-assembled difunctional organic monolayers as bridge compounds. Three different techniques are presented. Two rely on the formation of self-assembled monolayers on gold and aluminum in which the exposed tail groups are thiols. When exposed to heptane solutions of cadmium-rich nanocrystals, these free thiols bind the cadmium and anchor it to the surface. The third technique attaches nanocrystals already coated with carboxylic acids to freshly cleaned aluminum. The nanocrystals, before deposition on the metals, were characterized by ultraviolet-visible spectroscopy, X-ray powder diffraction, resonance Raman scattering, transmission electron microscopy (TEM), and electron diffraction. Afterward, the nanocrystal films were characterized by resonance Raman scattering, Rutherford back scattering (RBS), contact angle measurements, and TEM. All techniques indicate the presence of quantum confined clusters on the metal surfaces with a coverage of approximately 0.5 monolayers. These samples represent the first step toward synthesis of an organized assembly of clusters as well as allow the first application of electron spectroscopies to be completed on this type of cluster. As an example of this, the first X-ray photoelectron spectra of semiconductor nanocrystals are presented. 51 refs., 17 figs.

Temperature-Dependent Raman Studies and Thermal Conductivity of Few-Layer MoS2

Abstract: We report on the temperature dependence of in-plane E2g and out-of-plane A1g Raman modes in high-quality few-layer MoS2 (FLMS) prepared using a high-temperature vapor-phase method. The materials obtained were investigated using transmission electron microscopy. The frequencies of these two phonon modes were found to vary linearly with temperature. The first-order temperature coefficients for E12g and A1g modes were found to be (1.32 and 1.23) × 10–2 cm–1/K, respectively. The thermal conductivity of the suspended FLMS at room temperature was estimated to be ∼52 W/mK.