Transition metal dichalcogenide graded alloy monolayers by chemical vapor deposition and comparison to 2D Ising model.

In this work, a chemical vapor deposition (CVD) method was developed for the synthesis of transition metal dichalcogenide alloy monolayers, with a composition gradient in the radial direction. The composition gradient was achieved by controlling the substrate cooling rate during the CVD growth. The two types of alloys, namely, WS2(1-x)Se2x and MoS2(1-x)Se2x, were found to exhibit an opposite composition gradient. This is attributed to their different cohesive energies. A two-dimensional Ising model is used to explain the growth mechanism, where two ends of the composition were modeled as a magnetically ordered phase and a paramagnetic phase. The composition as a function of substrate temperature is then represented by the thermal magnetization curve.

Ag-carried CMC/functional copolymer/ODA-Mt wLED-treated NC and their responses to brain cancer cells.

The subject of this work is synthesis and characterization of novel multifunctional nanocomposite (8/2A-NC) consisting (1) carboxymethyl cellulose (CMC) as a matrix biopolymer and poly (maleic acid-alt-acrylic acid) as a reactive synthetic partner matrix polymer; (2) octadecyl amine montmorillonite (ODA-MMT) reactive organoclay provide intercalated silicate layers structures and aqueous colloidal dispersing medium, and MMT as carriers and targeting agents for anticancer agents in drug delivery systems, respectively. ODA as a intercalated surfactant finely dispersed 8/2A NC and its compatibility with matrix polymers via the interfacial polarization (complexing) and functionalization of matrix polymers by amine (ODA) and carboxylic acids from both the CMC and copolymer; (3) silver nanoparticles (AgNPs) as in-situ generated onto matrix polymers with unique nano-size and morphology parameters was synthesized. Important material science and bioengineering aspects of these investigations included (a) novel approach in synthetic pathways; (b) effects of physical and chemical structural rearrangements; (c) effects of Light Emitting Dioda (LED)-treatment on the FT-IR spectra, XRD reflection parameters, SEM-TEM morphology and nano-size and diameter distribution of AgNPs onto matrix polymers; (d) positive effect of LED-treatment of 8/2A nanocomposite and its response to the MIAPaCa-2 and U87 human brain cancer cell lines were evaluated. Novel 8/2A-NC multifunctional drug consisting unique positive, intercalating and encapsulated core-shell morphology structures, nano-size (5.6 nm) and narrow diameter distribution (94%) of AgNPs onto matrix polymers [silver NPs (0.25%) in 8/2A NC (25%)] with highest volume of contact area compared with used cancer micro-cells show lowest cell viability as an excellent anticancer platform. 8/2A-NC is a novel multifunctional drug with intercalating and encapsulated core-shell morphology structures consisting of positively charged, non-randomly distributed AgNPs with a large contact area and low diameters (5-6 nm). The anticancer properties of (This factor is not conformed experimentally in work) this drug can be explained by the following structural factors: 8/2A-NC contains a combination of active sites from protonated hydroxyl, carboxyl and amine groups; Ag+-cations and ODA-MMT with high physical and chemical surface areas. We suggest this material be further explored for anti-cancer testing.

Flat metallic surface gratings with sub-10 nm gaps controlled by atomic-layer deposition.

Atomic layer lithography is a recently reported new technology to fabricate deep-subwavelength features down to 1-2 nm, based on combinations of electron beam lithography (EBL) and atomic layer deposition (ALD). However, the patterning area is relatively small as limited by EBL, and the fabrication yield is not very high due to technical challenges. Here we report an improved procedure to fabricate flat metallic surfaces with sub-10 nm features based on ALD processes. To demonstrate the scalability of the new manufacturing method, we combine the ALD process with large area optical interference patterning, which is particularly promising for the development of practical applications for nanoelectronics and nanophotonics with extremely strong confinement of electromagnetic fields.

Statistically background-free, phase-preserving parametric up-conversion with faint light.

We demonstrate up-conversion with no statistically significant background photons and a dynamic range of 15 decades. Near-infrared 920 nm photons were converted into the visible at 577 nm using periodically poled lithium niobate waveguides pumped by a 1550 nm laser. In addition to achieving statistically noiseless frequency up-conversion, we report a high degree of phase preservation (with fringe visibilities ≥ 0.97) at the single-photon level using an up-converting Mach-Zehnder interferometer. This background-free process opens a path to single-photon detection with no intrinsic dark count. Combined with a demonstrated photon-number preserving property of an up-converter, this work demonstrates the feasibility of noiseless frequency up-conversion of entangled photon pairs.

Femtosecond nonlinear ultrasonics in gold probed with ultrashort surface plasmons.

Fundamental interactions induced by lattice vibrations on ultrafast time scales have become increasingly important for modern nanoscience and technology. Experimental access to the physical properties of acoustic phonons in the terahertz-frequency range and over the entire Brillouin zone is crucial for understanding electric and thermal transport in solids and their compounds. Here we report on the generation and nonlinear propagation of giant (1 per cent) acoustic strain pulses in hybrid gold/cobalt bilayer structures probed with ultrafast surface plasmon interferometry. This new technique allows for unambiguous characterization of arbitrary ultrafast acoustic transients. The giant acoustic pulses experience substantial nonlinear reshaping after a propagation distance of only 100 nm in a crystalline gold layer. Excellent agreement with the Korteveg-de Vries model points to future quantitative nonlinear femtosecond terahertz-ultrasonics at the nano-scale in metals at room temperature.

Dynamics of nonclassical light from a single solid-state quantum emitter.

We measure the dynamics of a nonclassical optical field using two-time second-order correlations in conjunction with pulsed excitation. The technique quantifies single-photon purity and coherence during the excitation-decay cycle of an emitter, illustrated here using a quantum dot. We observe that for certain pump wavelengths, photons detected early in the cycle have reduced single-photon purity and coherence compared to those detected later. A model indicates that the single-photon purity dynamics are due to exciton recapture after initial emission and within the same pulse cycle.

Optical properties of red emitting self-assembled InP/(Al0.20Ga0.80)0.51In0.49P quantum dot based micropillars.

Using focused ion beam etching techniques, micropillar cavities were fabricated from a high reflective AlAs/AlGaAs distributed Bragg reflector planar cavity containing self-assembled InP quantum dots in (Al(0.20)Ga(0.80))(0.51)In(0.49)P barrier layers. The mode spectra of pillars with different diameters were investigated using micro-photoluminescence, showing excellent agreement with theory. Quality factors of the pillar cavities up to 3650 were observed. Furthermore, for a microcavity pillar with 1.26 mum diameter, single-photon emission is demonstrated by performing photon correlation measurements under pulsed excitation.

Femtosecond surface plasmon interferometry.

We demonstrate femtosecond plasmonic interferometry with a novel geometry. The plasmonic microinterferometer consists of a tilted slit-groove pair. This arrangement allows for (i) interferometric measurements at a single wavelength with a single microinterferometer and (ii) unambiguous discrimination between changes in real and imaginary parts of the metal dielectric function. The performance is demonstrated by monitoring the sub-picosecond dynamics of hot electrons in gold.

Colloidal ZnO quantum dots in ultraviolet pillar microcavities.

Three dimensional light confinement and distinct pillar microcavity modes in the ultraviolet have been observed in pillar resonators with embedded colloidal ZnO quantum dots fabricated by focused ion beam milling. Results from a waveguide model for the mode patterns and their spectral positions are in excellent agreement with the experimental data.

Colloidal quantum dots in all-dielectric high-Q pillar microcavities.

We have fabricated all-dielectric high-Q optical pillar resonators with embedded colloidal CdSe/ZnS quantum dots or rods as light emitters by focused ion beam milling. Three-dimensional light confinement and distinct pillar microcavity modes are observed. Results from a waveguide model for the mode patterns and their spectral positions are in excellent agreement with the experimental data. Cavities with elliptical cross sections show higher quality factors in the short axis direction than do circular resonators of the same cross-sectional area.