C. V. Raman | EPFL Graph Search

Sir Chandrasekhara Venkata Raman (ˈrɑːmən; 7 November 1888 21 November 1970) was an Indian physicist known for his work in the field of light scattering. Using a spectrograph that he developed, he and his student K. S. Krishnan discovered that when light traverses a transparent material, the deflected light changes its wavelength and frequency. This phenomenon, a hitherto unknown type of scattering of light, which they called "modified scattering" was subsequently termed the Raman effect or Raman scattering. Raman received the 1930 Nobel Prize in Physics for the discovery and was the first Asian to receive a Nobel Prize in any branch of science. Born to Tamil Brahmin parents, Raman was a precocious child, completing his secondary and higher secondary education from St Aloysius' Anglo-Indian High School at the age of 11 and 13, respectively. He topped the bachelor's degree examination of the University of Madras with honours in physics from Presidency College at age 16. His first

Carbon nanotubes functionalized with dye molecules and metal nanoparticles

Tilman Assmus

Single-walled carbon nanotubes are highly interesting quasi one-dimensional nanostructures. They possess a multitude of fascinating optical, mechanical and electrical properties, which can be even further expanded through appropriate functionalization strategies. This thesis covers a number of functionalization strategies and their effects on the nanotube's optical and electrical properties. The first part deals with the functionalization of carbon nanotubes with dye molecules and the characterization of the functionalized system. Both covalent and noncovalent approaches were investigated with the goal of modifying the nanotubes' photoelectrical properties. Upon excitation with light of the appropriate wavelength, a clear electrical response could be observed on some functionalized individual nanotubes. Depending on the attached dye molecule, the conductivity change is either induced by a light-induced conformational change or by a charge transfer between the nanotube and the excited dye molecule. The perspectives of constructing an optoelectronic nanoswitch based on these effects are discussed. The second part of the thesis addresses carbon nanotubes functionalized by a low density of electrodeposited gold nanoparticles with sizes in the range between 10 and 100nm. In this case, the functionalization is targeted on amplifying the nanotube's Raman response (SERS effect). The novel sample preparation technique developed in this thesis allowed for an investigation of SERS on the level of individual molecule / nanoparticle hybrids. The optical emission spectra of the nanotube-nanoparticle hybrid structure disclosed Raman peaks associated with the nanotubes, which are superimposed on a broad luminescence background originating from the metal particles. Wavelength dependent experiments revealed maximum Raman intensity when both the nanotube and the metal particle are in optical resonance. In well-prepared samples the Raman signals collected over isolated particles exhibited an intensity enhancement by at least one order of magnitude, as compared to bare sections on the same tube, without appreciably interfering with polarization dependent Raman measurements.

EPFL2008

Raman imaging through multimode sapphire fiber

Sunan Deng, Georgia Konstantinou, Damien Claude-Marie Loterie, Christophe Moser, Demetri Psaltis

We report on a sapphire fiber Raman imaging probe's use for challenging applications where access is severely restricted. Small-dimension Raman probes have been developed previously for various clinical applications because they show great capability for diagnosing disease states in bodily fluids, cells, and tissues. However, applications of these sub-millimeter diameter Raman probes were constrained by two factors: first, it is difficult to incorporate filters and focusing optics at such small scale; second, the weak Raman signal is often obscured by strong background noise from the fiber probe material, especially the most commonly used silica, which has a strong broad background noise in low wavenumbers (

OPTICAL SOC AMER2019

Raman spectra of disordered oxides from first principles

Paolo Umari

This thesis is devoted to the study of Raman scattering from first-principles. We develop two different methods to calculate Raman spectra of large model structures. The first method concerns the extension of the perturbative variational approach for the calculation of dielectric tensors to the case of ultrasoft pseudopotentials, allowing a significant improvement in the size of the affordable systems. The second method permits to treat finite electric fields in Car-Parrinello molecular dynamics simulations with periodic boundary conditions. Applied to the calculation of Raman spectra, this approach, in the case of large systems, gives a further significant reduction of the computational effort required to obtain Raman spectra. The methods we develop in the first part of the thesis are then applied to the study of vitreous silica and vitreous boron oxide. By applying our perturbative approach, we obtain the Raman spectrum for a model structure of vitreous silica. The accurate description of the Raman couplings allows us to derive an estimate from the experimental spectrum for the concentration of oxygen atoms in three- and four-membered rings. Finally, we apply the finite field method to calculate the Raman spectrum of a large model structure of vitreous boron oxide. By investigating the contributions to the Raman spectrum from vibrations of different symmetry, we can extract from the experimental spectrum an estimate for the concentration of boron atoms belonging to three-membered rings.

EPFL2003

Carbon nanotubes functionalized with dye molecules and metal nanoparticles

Tilman Assmus

EPFL2008