Low-Loss Impedance-Matched Optical Metamaterials with Zero-Phase Delay

Metamaterials have dramatically expanded the range of available optical properties, enabling an array of new devices such as superlenses, perfect absorbers, and ultrafast switches. Most research has focused on demonstrating negative- and high-index metamaterials at terahertz and optical wavelengths. However, far less emphasis has been placed on low-loss near-zero-index metamaterials that exhibit unique properties including quasi-infinite phase velocity and infinite wavelength. Here, we experimentally demonstrate a free-standing metallodielectric fishnet nanostructure that has polarization-insensitive, zero-index properties with nearly ideal transmission at 1.55 μm. This goal was achieved by optimizing the metamaterial geometry to allow both its effective permittivity and permeability to approach zero together, which simultaneously produces a zero index and matched impedance to free space. The ability to design and fabricate low-loss, near-zero-index optical metamaterials is essential for new devices such as beam collimators, zero-phase delay lines, and transformation optics lenses

Controlling Disorder by Electric-Field-Directed Reconfiguration of Nanowires To Tune Random Lasing

Top-down fabrication is commonly used to provide positioning control of optical structures; yet, it places stringent limitations on component materials, and oftentimes, dynamic reconfigurability is challenging to realize. Here, we present a reconfigurable nanoparticle platform that can integrate heterogeneous particle assembly of different shapes, sizes, and chemical compositions. We demonstrate dynamic control of disorder in this platform and use it to tune random laser emission characteristics for a suspension of titanium dioxide nanowires in a dye solution. Using an alternating current electric field, we control the nanowire orientation to dynamically engineer the collective scattering of the sample. Our theoretical model indicates that a change of up to 22% in scattering coefficient can be achieved for the experimentally determined nanowire length distribution upon alignment. Dependence of light confinement on anisotropic particle alignment provides a means to reversibly tune random laser characteristics; a nearly 20-fold increase in lasing intensity was observed with aligned particle orientation. We illustrate the generality of the approach by demonstrating enhanced lasing for aligned nanowires of other materials including gold, mixed gold/dielectric, and vanadium oxide

Controlling Disorder by Electric-Field-Directed Reconfiguration of Nanowires To Tune Random Lasing

Top-down fabrication is commonly used to provide positioning control of optical structures; yet, it places stringent limitations on component materials, and oftentimes, dynamic reconfigurability is challenging to realize. Here, we present a reconfigurable nanoparticle platform that can integrate heterogeneous particle assembly of different shapes, sizes, and chemical compositions. We demonstrate dynamic control of disorder in this platform and use it to tune random laser emission characteristics for a suspension of titanium dioxide nanowires in a dye solution. Using an alternating current electric field, we control the nanowire orientation to dynamically engineer the collective scattering of the sample. Our theoretical model indicates that a change of up to 22% in scattering coefficient can be achieved for the experimentally determined nanowire length distribution upon alignment. Dependence of light confinement on anisotropic particle alignment provides a means to reversibly tune random laser characteristics; a nearly 20-fold increase in lasing intensity was observed with aligned particle orientation. We illustrate the generality of the approach by demonstrating enhanced lasing for aligned nanowires of other materials including gold, mixed gold/dielectric, and vanadium oxide

Regression analysis correlations between 25(OH)D2 and 25(OH)D3 serum concentrations and age, creatinine, PTH and 25(OH)D2/25(OH)D3 values.

<p>Regression analysis correlations between 25(OH)D2 and 25(OH)D3 serum concentrations and age, creatinine, PTH and 25(OH)D2/25(OH)D3 values.</p

Univariate analyses of correlations between 25(OH)D2 as well as 25(OH)D3 serum concentrations and subgroups.

§<p>indicates containing sub-groups, which are marked with a, b and c. Different letter marks indicate significant differences between the subgroups, same letters indicate no significant differences between the same marked subgroups.</p

Univariate analysis of correlations between subgroups and their total serum 25(OH)D concentrations.

§<p>indicates containing sub-groups, which are marked with a, b and c. Different letter marks indicate significant differences between the subgroups, same letters indicate no significant differences between the same marked subgroups.</p

Multivariate analysis of factors that affect 25(OH)D2 and 25(OH)D3 serum concentrations.

<p>Multivariate analysis of factors that affect 25(OH)D2 and 25(OH)D3 serum concentrations.</p

The distribution of serum creatinine and parathyroid hormone in gender, age and seasons.

§<p>indicates containing sub-groups, which are marked with a, b and c. Different letter marks indicate significant differences between the subgroups, same letters indicate no significant differences between the same marked subgroups.</p

Synthesis of Large-Area Highly Crystalline Monolayer Molybdenum Disulfide with Tunable Grain Size in a H₂ Atmosphere

Large-area and highly crystalline monolayer molybdenum disulfide (MoS₂) with a tunable grain size was synthesized in a H₂ atmosphere. The influence of introduced H₂ on MoS₂ growth and grain size, as well as the corresponding mechanism, was tentatively explored by controlling the H₂ flow rate. The as-grown monolayer MoS₂ displays excellent uniformity and high crystallinity evidenced by Raman and high-resolution transmission electron microscopy. The Raman results also give an indication that the quality of the monolayer MoS₂ synthesized in a H₂ atmosphere is comparable to that synthesized by using seed or mechanical exfoliation. In addition, the electronic properties and dielectric inhomogeneity of MoS₂ monolayers were also detected <i>in situ</i> via scanning microwave microscopy, with measurements on impedance and differential capacitance (d<i>C</i>/d<i>V</i>). Back-gated field-effect transistors based on highly crystalline monolayer MoS₂ shows a field-effect mobility of ∼13.07 cm² V^–1 s^–1 and an <i>I</i>_on/<i>I</i>_off ratio of ∼1.1 × 10⁷, indicating that the synthesis of large-area and high-quality monolayer MoS₂ with H₂ is a viable method for electronic and optoelectronic applications