Mykhailo Ya. Valakh

A spectroscopic and photochemical study of Ag+-, Cu2+-, Hg2+-, and Bi3+-doped CdxZn1−xS nanoparticles

A combination of stationary and time-resolved absorption and photoluminescence spectroscopy with flash and steady-state photolysis of Ag(+), Cu(2+), Hg(2+), or Bi(3+)-doped Cd(x)Zn(1-)(x)S nanoparticles was used to assess the nature of the doping influence upon the optical properties of Cd(x)Zn(1-x)S nanoparticles. The relationships between the type and the concentration of a dopant and the dynamics of the photoinduced processes in the doped nanoparticles are derived and discussed. A correlation is found between the magnitude of doping-induced changes in the intensity and decay dynamics of the deep trap photoluminescence and an enhancement of the transient bleaching recovery and acceleration of the photocorrosive degradation of the doped Cd(x)Zn(1-x)S NPs compared to the undoped ones. The impact of the dopant upon the intensity of the luminescence and microsecond transient bleaching bands was found to grow substantially from Ag(+) to Cu(2+), Hg(2+) and Bi(3+). The same trend was found to hold for the acceleration of the steady-state photochemical corrosion of doped Cd(x)Zn(1-x)S nanoparticles. The differences among the effect of the dopant ions studied were interpreted in terms of the depth and charge of surface states created by Cd(2+) (Zn(2+)) substitution by a dopant.

Phonon Spectra of Small Colloidal II-VI Semiconductor Nanocrystals

Resonant Raman spectroscopy has been employed to explore the first- and higher-order phonon spectra of several kinds of II-VI nanocrystals (NCs), with the aim of better understanding of the nature of phonon modes and forming a unified view onto the vibrational spectrum of semiconductor NCs. Particularly, besides the previously discussed TO, SO, LO, and 2LO modes, the combinational modes of TO

Study of acoustical phonon modes in superlattices with SiGe QDs

Multilayers with SiGe nanoislands (QDs) grown in a broad temperature range are studied using Raman spectroscopy, HRXRD and compared with similar multilayers without islands. As the growth temperature increases, Si content in the islands increases, partially relieving strain. These structural transformations manifest themselves in both the intensity and frequency of the low‐frequency Raman peaks. Due to composition‐ and strain‐induced changes in the island band structure, excitation conditions come out of resonance, reducing Raman peak intensity. We have shown that at the interpretation of the Raman scattering by folded acoustic phonons for structures with nanoislands the real morphology of the island layer should be considered. The observed series of the low‐frequency Raman peaks, for the multilayered structures with the number of QD layers below ten, is due to the acoustic phonon modes within the islands. The enhancement of the scattering intensity due to resonance of the excitation light with the elect...