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The hybrid organic-inorganic perovskites (HOIPs) have attracted much attention recently due to their preeminent efficiency in solar cells. According to the difference on the crystalline structure, the HOIPs could be classified into layered and non-layered perovskites. Very recently, it has been realized that the non-layered HOIPs with common-vertex structure possess even better opto-electrical performance. Yet the carrier recombination mechanism in perovskite remains not very clear, and a clear understanding of this mechanism is essential to pinpoint the working mechanism of photovoltaic and electroluminescent materials. Here we report the optical studies on the hybrid perovskite crystalline nano-sheet of CH3NH3PbBr3 with common-vertex structure. It is shown that the non-layered perovskite crystalline nanosheets possess the exciton binding energy about two orders of magnitude smaller than that of the layered perovskite and the colloidal nanoplates, which is beneficial for the designing of the high-efficiency photovoltaic devices. By measuring the temperature-dependent photoluminescence (PL) spectra, the excitation-power-variant PL spectra, and the time-resolved PL spectra, we identify that both the free-carrier and the localized exciton recombination channels may coexist in the crystallites. Further, for the thin crystallite (∼60 nm), the free-carrier recombination channel dominates; whereas when the thickness increases beyond 200 nm, the localized exciton recombination channel plays the major role. We suggest these results are helpful to improve further the photovoltaic and electroluminescent performances of perovskite devices.

We report here the electrodeposition of periodically structured single-crystalline zinc branches from an ultrathin aqueous electrolyte layer of ZnSO4. The main trunk and side branches of electrodeposits are regularly angled, and each branch is made of periodic bead-like structures. Layered morphology has been observed on each bead. During electrodeposition, spontaneous oscillation of electric current occurs when constant voltage is applied across the electrodes, and the oscillation leads to periodic patterns on deposit branches. According to electron diffraction of transmission electron microscopy (TEM), the whole branch of electrodeposits has the same crystallographic orientation despite the fact that the branch looks like an assembly of beads. We interpret this unique growth behavior to the epitaxial nucleation in the transport-limited growth system. Copyright © 2006 John Wiley & Sons, Ltd.

By combining the advantages of both a metallic metamaterial and a dielectric interlayer, we demonstrate the general mechanism to construct the dispersion-free metastructure, in which the intrinsic dispersion of the metallic structures is perfectly cancelled out by the thickness-dependent dispersion of the dielectric spacing layer. As examples to apply this concept, a broadband quarter-wave plate and a half-wave plate are demonstrated. By selecting the structural parameters, the polarization state of light can be freely tuned across a broad frequency range, and all of the polarization states on the Poincaré sphere can be realized dispersion free.

In this article we report our experimental observations that the repeated polytypism of wurtzite (WZ) and zinc-blende (ZB) phases induced by the fluctuation of the density of stacking faults can lead to the self-organized formation of ZnO hierarchical nanostructures characterized by a hexagonal central trunk decorated with thin blades. The blades epitaxially nucleate on the ZB stripes assisted by the reentrant corners at the ZB-WZ interfaces. Consequently, the blades keep a fixed angle with respect to the central trunk and resemble two sets of mutually intercalated propellers, each set possessing its own threefold rotational symmetry and being rotated for 60${}^{\ensuremath{\circ}}$ with respect to each other. We also study the optical properties of such novel structures, and show through numerical simulations that the blades provide the essential boundary conditions to establish the resonant electromagnetic responses in the hierarchical nanostructures.

Using the analytical solution of hydrodynamic equations, energy level populations of the plasma dominated by He-like Mg ions are obtained by solving the rate equations numerically for a short pulsed pumping laser. Variations of gain coefficient for the lasing transition 1s3d-1s4f of MgXI ( λ=154 A ) versus time and space are calculated. Also, the influence of pumping laser pulse duration on gain coefficient is discussed.

We report here a unique in-plane self-templating electrochemical growth of arrays of copper nanopearl chains from an ultrathin layer of CuSO4 electrolyte. Scanning electron microscopy indicates that the electrodeposit filaments form equally spaced bundles, which consist of long, straight, pearl-chain-like copper filaments with corrugated periodic structure. The bundle separation can be tuned by changing the applied electric current in electrodeposition. Experiments show that the periodic morphology on the nanopearl chain corresponds to the periodic distribution of copper and cuprous oxide. The mechanism for the bundle formation is discussed.

In this paper, we report the long-range ordering effect observed in the electro-crystallization of Zn and ZnO from an ultrathin aqueous electrolyte layer of ZnSO4 . The deposition branches are regularly angled, covered with random-looking, scalelike crystalline platelets of ZnO. Although the orientation of each crystalline platelet of ZnO appears random, transmission electron microscopy shows that they essentially possess the same crystallographic orientation as the single-crystalline zinc electrodeposit underneath. Based on the experimental observations, we suggest that this unique long-range ordering effect results from an epitaxial nucleation effect in electrocrystallization.