The combined effects of strain and phonon confinement are seen to explain why the Raman peak near 464 cm Ϫ1 in CeO 2Ϫy nanoparticles shifts to progressively lower energies and the lineshape of this feature gets progressively broader and asymmetric ͑on the low-energy side͒ as the particle size gets smaller. The increasing lattice constant measured for decreasing particle size explains this Raman shift well. The linewidth change is fairly well explained by the inhomogenous strain broadening associated with the small dispersion in particle size and by phonon confinement. The spectra are also likely to be directly affected by the presence of oxygen vacancies. Comparison of the temperature dependence of the Raman lineshape in the nanoparticles and the bulk shows that phonon coupling is no faster in the nanoparticles, so size-dependent phonon coupling does not contribute to the large nanoparticle peak red shifts and broadening at room temperature. Irreversible thermally induced changes are observed in the Raman peak position of the nanoparticles.

Control of nanocrystal surface defects for efficient charge extraction in polymer-ZnO photovoltaic systems J. Appl. Phys. 112, 066103 (2012) Experimental surface-enhanced Raman scattering response of two-dimensional finite arrays of gold nanopatches Appl. Phys. Lett. 101, 111606 (2012) Nano-hillock formation in diamond-like carbon induced by swift heavy projectiles in the electronic stopping regime: Experiments and atomistic simulations Appl. Phys. Lett. 101, 113115 (2012) Mass transport and thermal stability of TiN/Al2O3/InGaAs nanofilms

An ensemble of emitters can behave significantly different from its individual constituents when interacting coherently via a common light field. After excitation, collective coupling gives rise to an intriguing many-body quantum phenomenon, resulting in short, intense bursts of light: so-called superfluorescence 1 . Because it requires a fine balance of interaction between the emitters and their decoupling from the environment, together with close identity of the individual emitters, superfluorescence has thus far been observed only in a limited number of systems, such as atomic and molecular gases 2 and semiconductor crystals 37 , and could not be harnessed for applications. For colloidal nanocrystals, however, which are of increasing relevance in a number of opto-electronic applications 8 , the generation of superfluorescent light was precluded by inhomogeneous emission broadening, low oscillator strength, and fast exciton dephasing. Using caesium lead halide (CsPbX3, X = Cl, Br) perovskite nanocrystals 912 that are self-organized into highly ordered threedimensional superlattices 13,14 allows us to observe key signatures of superfluorescence: red-shifted emission with more than ten-fold accelerated radiative decay, extension of the first-order coherence time by more than a factor of four,