D. Christofilos

Quantitative Determination of the Size Dependence of Surface Plasmon Resonance Damping in Single Ag@SiO2 Nanoparticles

The optical extinction spectra of single silver nanoparticles coated with a silica shell were investigated in the size range 10-50 nm. Measurements were performed using the spatial modulation spectroscopy technique which permits independent determination of both the size of the metal nanoparticle under study and the width of its localized surface plasmon resonance (LSPR). These parameters can thus be directly correlated at a single particle level for the first time. The results show a linear increase of the width of the LSPR with the inverse diameter in the small size regime (less than 25 nm). For these nanoparticles of well-controlled environment, this can be ascribed to quantum confinement of electrons or, classically, to increase of the electron surface scattering processes. The impact of this effect was measured quantitatively and compared to the predictions by theoretical models.

Time-resolved investigation of the vibrational dynamics of metal nanoparticles

Abstract Time resolved excitation and detection of the coherent vibrational motion of metal nanoparticles are discussed in the light of femtosecond pump-probe experiments performed in silver nanoparticles with radius ranging from 2.1 to 15.3 nm. Analysis of the phase of the observed sample absorption oscillations shows that coherent excitation is dominated by an indirect displacive mechanism due to subpicosecond heating of the lattice by fast electron-lattice energy transfer for large nanoparticles (R>10 nm). For smaller particles, the results suggest an additional contribution from direct coupling with the non-equilibrium electron gas. Both mechanisms, being related to an isotropic particle expansion, the fundamental radial mode is preferentially excited because of its better spatial matching with the excitation process. Optical control of the acoustic nanoparticles vibration is also demonstrated.

A high pressure Raman study of calcium molybdate

Abstract In this work we present a Raman study of CaMoO4 as a function of hydrostatic pressure up softening in the scheelite structure, while in the high pressure phases its slope becomes positive. The v1v3 stretching modes of the MoO2−4 group exhibit drastic changes in their pressure dependencies at both phase transitions. This behavior is connected with the increase in the coordination number of the Mo ion in the high pressure phases. These characteristics are compared with the high pressure behavior of other molybdates and tungstates.

Optical response of a single noble metal nanoparticle

The characterization of a single metal nanoobject by comparing its theoretical and experimental far-field spectra measured by a spatial modulation spectroscopy (SMS) technique is discussed in the case of gold and silver nanoparticles. Quantitative determination of the polarization dependent absorption cross-section spectrum of a single nanoparticle is shown to permit its optical identification, i.e., determination of its shape, size and orientation on a surface.

Environment effect on the acoustic vibration of metal nanoparticles

Abstract The impact of the environment on the frequency and damping of the breathing acoustic mode of noble metal nanoparticle is discussed using the model of isotropic homogeneous elastic spheres embedded in an elastic medium. The results are compared to the experimental investigations performed in glass embedded silver nanoparticles and gold colloids using a time-resolved pump–probe technique.

Pressure screening in the interior of primary shells in double-wall carbon nanotubes

The pressure response of double-wall carbon nanotubes has been investigated by means of Raman spectroscopy up to

Temperature and pressure dependence of Raman-active phonons of CaMoO4: an anharmonicity study

10\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}

Optical response of a single gold nanoparticle

. The intensity of the radial breathing modes of the outer tubes decreases rapidly but remain observable up to

High-pressure Raman study and lattice dynamical calculations for SrWO4

9\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}

Structural anisotropic properties of a-plane GaN epilayers grown on r-plane sapphire by molecular beam epitaxy

, exhibiting a behavior similar (but less pronounced) to that of single-wall carbon nanotubes, which undergo a shape distortion at higher pressures. In addition, the tangential band of the external tubes broadens and decreases in amplitude. The corresponding Raman features of the internal tubes appear to be considerably less sensitive to pressure. All findings lead to the conclusion that the outer tubes act as a protection shield for the inner tubes whereas the latter increase the structural stability of the outer tubes upon pressure application.