R. E. Tallman

Anomalous pressure behavior of ZnSe Raman spectrum

The effects of pressure on the 1- and 2-phonon Raman spectrum of 68Zn76Se are investigated at 295, 125, and 11 K. At 295 K, the TO(Γ) line-width exhibits an anomalous 10-fold broadening in the pressure range 10.5–13 GPa, prior to the B1 phase transition. Other spectral features remain reasonably sharp. At 125 and 11 K the TO(Γ) anomaly is not seen. After the phase transition, a broadband is also seen in the TO(Γ) region for a wide range of downstroke pressures. Two explanations are considered: strong anharmonic coupling between TO(Γ) and (TO2–TA1)(X,K) difference modes, and structure or local bonding changes within the ZnSe lattice. First principles calculations of the 1- and 2-phonon density of states as a function of pressure are carried out and used to test the effect of the TO(Γ)→(TO 2–TA 1)(X,K) decay process. The results cannot rule out contributions from additional anharmonic channels and/or structural disorder effects.

Phonons and Phonon‐Mixing in ZnSe Isotopic Crystals, Pressure‐cycled Domains, and Nanorods

Pressure‐Raman spectra are compared for bulk crystalline 68Zn76Se and ZnSe nanorods. The broadening of TO(Γ) and LO(Γ) is explained by multiphonon mixing and the position of a gap in the 2‐phonon DOS. Nucleation of the phase transition in 68Zn76Se leads to striking similarities in the Raman spectra of retrieved bulk and nanorod samples.

Optical Phonon Modes of InP/II‐VI core‐shell Nanoparticles: a Raman and Infrared Study

Crystalline nanoparticles having ∼ 3nm diameter InP cores surrounded by different II‐VI cladding layers have been synthesized by colloidal chemistry. We report studies of the confined optical phonons in InP/ZnSe core‐shell nanocrystals by Raman scattering and far‐infrared (FIR) spectroscopy as a function or temperature. Based on comparison with a dielectric continuum model, the observed features are assigned to the surface optical (SO) modes of the InP core, and to the optical and SO modes of the ZnSe shell. Reasonable agreement is obtained between the Raman and FIR results, as well as with the calculations. Strong temperature dependent resonance Raman effects are observed.