Gas-Induced Confinement-Deconfinement Interplay in Organic-Inorganic Hybrid Perovskite Thin Film Results in Systematic Band Modulation.

Gas-induced growth of organic-inorganic hybrid perovskites, especially methylammonium lead iodide (MAPbI3), has shown interesting properties and applications in the area of optoelectronics. In this report, we introduce a method of gas-induced band gap engineering of thin films of MAPbI3 due to systematic dimensional confinement-deconfinement along the crystallographic c axis of growing MAPbI3. Interestingly, such a restricted growth phenomenon was observed when the hexylammonium lead iodide (two-dimensional hybrid perovskite) film was exposed to methylamine gas instead of the conventional PbI2 film-methylamine gas precursor pair. Hexylamine, formed due to the cation exchange reaction, interacts selectively with the Pb centers of growing MAPbI3 crystals, and this induces an enormous restriction in the growth of MAPbI3 along the crystallographic c direction, leading to a unique sheet-type MAPbI3 film having a much higher band gap (2.18 eV) compared to conventional bulk MAPbI3. However, careful control of exposure timing gradually evaporates the hexylamine, leading to systematic dimensional deconfinement, enabling modulation of the band gap from 2.18 to 1.69 eV. An interplay of adsorption and desorption of hexylamine is also utilized for generating patterns of two different fluorescent hybrid perovskite materials in a single pixel. This new mechanistic investigation highlighting gas-induced interplay of dimensional confinement-deconfinement associated with band gap tuning provides smooth thin films, which can be used to develop optoelectronic devices.

Single-mode light guiding in diamond waveguides directly written by a focused proton beam.

Ion-implanted waveguides were directly written in bulk single-crystal diamond by scanning a focused 2 MeV proton beam. By controlling the fluence and the lateral size of the proton beam, a bright and near-circular single-mode profile was observed. Propagation loss and effective refractive index of the guided mode were measured by the Fabry-Pérot technique, confirming single-mode guiding. Micro-Raman maps of the waveguides were used to visualize damage profiles and defect distributions induced by the proton beam. The demonstration of single-mode light guiding in our waveguides shows that direct proton beam writing is a promising tool in the rapid manufacture of integrated optical circuits in bulk diamond.

Molecular Organization Induced Anisotropic Properties of Perylene - Silica Hybrid Nanoparticles.

Optically active silica nanoparticles are interesting owing to high stability and easy accessibility. Unlike previous reports on dye loaded silica particles, here we address an important question on how optical properties are dependent on the aggregation-induced segregation of perylene molecules inside and outside the silica nanoparticles. Three differentially functionalized fluorescent perylene - silica hybrid nanoparticles are prepared from appropriate ratios of perylene derivatives and tetraethyl orthosilicate (TEOS) and investigated the structure property correlation (P-ST, P-NP and P-SF). The particles differ from each other on the distribution, organization and intermolecular interaction of perylene inside or outside the silica matrix. Structure and morphology of all hybrid nanoparticles were characterized using a range of techniques such as electron microscope, optical spectroscopic measurements and thermal analysis. The organizations of perylene in three different silica nanoparticles were explored using steady-state fluorescence, fluorescence anisotropy, lifetime measurements and solid state polarized spectroscopic studies. The interactions and changes in optical properties of the silica nanoparticles in presence of different amines were tested and quantified both in solution and in vapor phase using fluorescence quenching studies. The synthesized materials can be regenerated after washing with water and reused for sensing of amines.

Magnetic annihilation of the dark mode in a strongly coupled bright-dark terahertz metamaterial.

Dark mode in metamaterials has become a vital component in determining the merit of the Fano type of interference in the system. Its strength dictates the enhancement and suppression in the amplitude and Q-factors of resulting resonance features. In this work, we experimentally probe the effect of strong near-field coupling on the strength of the dark mode in a concentrically aligned bright resonator and a dark split ring resonator (SRR) system exhibiting the classical analog of the electromagnetically induced transparency effect. An enhanced strong magnetic field between the bright-dark resonators destructively interferes with the inherent magnetic field of the dark mode to completely annihilate its effect in the coupled system. Moreover, the observed annihilation effect in the dark mode has a direct consequence on the disappearance of the SRR effect in the proposed system, wherein under the strong magnetic interactions, the LC resonance feature of the split ring resonator becomes invisible to the incident terahertz wave.

High-resolution 3D imaging and quantification of gold nanoparticles in a whole cell using scanning transmission ion microscopy.

Increasing interest in the use of nanoparticles (NPs) to elucidate the function of nanometer-sized assemblies of macromolecules and organelles within cells, and to develop biomedical applications such as drug delivery, labeling, diagnostic sensing, and heat treatment of cancer cells has prompted investigations into novel techniques that can image NPs within whole cells and tissue at high resolution. Using fast ions focused to nanodimensions, we show that gold NPs (AuNPs) inside whole cells can be imaged at high resolution, and the precise location of the particles and the number of particles can be quantified. High-resolution density information of the cell can be generated using scanning transmission ion microscopy, enhanced contrast for AuNPs can be achieved using forward scattering transmission ion microscopy, and depth information can be generated from elastically backscattered ions (Rutherford backscattering spectrometry). These techniques and associated instrumentation are at an early stage of technical development, but we believe there are no physical constraints that will prevent whole-cell three-dimensional imaging at <10 nm resolution.

Proton beam writing of Nd:GGG crystals as new waveguide laser sources.

Focused proton beam writing has been utilized to fabricate optical channel waveguides in Nd:GGG crystals. The 1 MeV proton beam irradiation creates a local modified region with positive refractive index changes at the end of the proton trajectory, in which the channel waveguide could confine the light field in a symmetric way. Room-temperature laser emission has been achieved at 1063.7 nm, with absorbed pump power of 61 mW (at 808 nm). The obtained slope efficiency of the Nd:GGG waveguide laser system is as high as 66%, which is, to our best knowledge, the highest value for integrated lasers from ion beam processed channel waveguide systems.

Thermal optimization and erasing of Nd:YAG proton beam written waveguides.

We report on how the optical and structural properties of Nd:YAG proton beam written waveguides are modified when they experienced annealing treatments from 50 °C to 950 °C. The microstructural changes caused in the vicinity of the nuclear damage region were found to be stable up to 700 °C, so that higher annealing temperatures lead to a complete waveguide erasing. Before this "erasing" temperature, the partial thermal-induced defect recombination reduces the propagation losses, reaching its minimum value (below 1 dB/cm) after a 400 °C thermal annealing.