Resonant excitation of coherent phonons in CdTe/sub 1-x/Se/sub x/ quantum dots

Abstract

The mechanisms for the generation of coherent phonons with ultrafast laser pulses are not well understood for absorbing media.' While the selection rules are usually consistent with those of stimulated Raman scattering,"2 a definitive identification of the generation process hinges on analyses of the dependence of the phonon amplitude on the central frequency and width of the pulses.' However, few resonant studies have been reported in the l i t e r a t~r e .~'~ Here, we describe experiments on CdTe,_,Se, quantum dots revealing a large resonant enhancement in the coherent phonon yield at laser energies in the vicinity of the fundamental gap.Pump-probe transmission experiments were performed at room temperature on a commercial 'sample (RG780, Schott Glass Technologies Inc.) J consisting of -2 nm-radius CdTe0.32Se0.6 nanocrystals embedded in a borosilicate matrix. We used a Tisapphire oscillator operating at a repetition rate of 82 MHz that produces pulses of width 45-50 fs in the 720-850 nm range and a balanced detector. The intensities of the pump and probe pulses were 20 and 5 mW. The respective polarizations were perpendicular to each

Raman Spectra of Quaternary CdS1−x−ySexTey Nanocrystals Embedded in Borosilicate Glass

“…Within recent decades, II-VI semiconductor nanocrystals, obtained by various techniques, have attracted continuous interest due to the size tunability of their optical properties, resulting in numerous applications [1][2][3][4]. Raman spectroscopy has proved to be a reliable tool for fast and nondestructive characterization of ternary II-VI nanocrystals, namely, the determination of their chemical composition for both one-mode and two-mode systems [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. In two-mode ternary systems (CdS 1−x Se x , CdSe 1−x Te x ), the nanocrystal composition is usually determined from the difference of frequencies of LO phonons corresponding to the two sublattices of the nanocrystal [5,10,[12][13][14]19] or from their intensity ratio [5,6].…”

Ultrafast Dynamics Evidence of High Temperature Superconductivity in Single Unit Cell FeSe onSrTiO3

“…To address whether phonon is the pairing glue and why a capping layer leads to the reduction of T c 11 , we investigate the effect of the capping layer. We prepared a separate sample of 10UC FeTe/STO, where we unambiguously generated and detected a coherent acoustic phonon mode 17,24,25 in the FeTe layer ( Fig. 4a) 26 , thus likely plays a more crucial role.…”

Coherent Acoustic Phonons in Colloidal Semiconductor Nanocrystal Superlattices

“…20 This technique was successfully used to study coherent phonons in various colloidal samples. 21−32 Most of these works were aimed at detecting the Lamb modes 33 phonon modes of individual metallic, 22−24 dielectric, 26,27,29 or semiconductor 21,25 nanoparticles. The frequencies, f L , of these modes are defined by the elastic parameters of an individual colloid and cover the range from several gigahertz (GHz) to several terahertz (THz) for micro-and nanoparticles with typical sizes between 10 −6 and 10 −9 m, respectively.…”