Xiao-Lan Zhong

Copper Can Still Be Epitaxially Deposited on Palladium Nanocrystals To Generate Core-Shell Nanocubes Despite Their Large Lattice Mismatch

Here we report the synthesis of Pd@Cu core-shell nanocubes via epitaxial growth, where the lattice mismatch is 7.1%. The synthesis involved the use of Pd seeds with different shapes (including cubes, cuboctahedra, and octahedra) for the epitaxial growth of Cu shells. Different from the conventional growth mode, Cu atoms initially nucleated only on a few of the many faces of a Pd seed, onto which more Cu atoms were continuously added to generate Cu blocks. Later, the Cu atoms also started to nucleate and grow on other faces of the Pd seed until the entire surface of the seed was covered by a Cu shell. As a result, the Pd seed was rarely located in the center of each core-shell structure. The final product took a cubic shape enclosed by {100} facets regardless of the type of Pd seeds used because of the selective capping of Cu(100) surface by hexadecylamine. The edge lengths of the Pd@Cu nanocubes could be tuned from 50 to 100 nm by varying the amount of Pd seeds while keeping the amount of CuCl(2) precursor.

Linear and passive silicon optical isolator

On-chip optical isolation plays a key role in optical communications and computing based on silicon integrated photonic structures and has attracted great attentions for long years. Recently there have appeared hot controversies upon whether isolation of light can be realized via linear and passive photonic structures. Here we demonstrate optical isolation of infrared light in purely linear and passive silicon photonic structures. Both numerical simulations and experimental measurements show that the round-trip transmissivity of in-plane infrared light across a silicon photonic crystal slab heterojunction diode could be two orders of magnitudes smaller than the forward transmissivity at around 1,550 nm with a bandwidth of about 50 nm, indicating good performance of optical isolation. The occurrence of in-plane light isolation is attributed to the information dissipation due to off-plane and side-way scattering and selective modal conversion in the multiple-channel structure and has no conflict with the reciprocal principle.

High Surface‐Enhanced Raman Scattering Performance of Individual Gold Nanoflowers and Their Application in Live Cell Imaging

Molecular imaging techniques based on surface-enhanced Raman scattering (SERS) face a lack of reproducibility and reliability, thus hampering its practical application. Flower-like gold nanoparticles have strong SERS enhancement performance due to having plenty of hot-spots on their surfaces, and this enhancement is not dependent on the aggregation of the particles. These features make this kind of particle an ideal SERS substrate to improve the reproducibility in SERS imaging. Here, the SERS properties of individual flower-like gold nanoparticles are systematically investigated. The measurements reveal that the enhancement of a single gold nanoparticle is independent of the polarization of the excitation laser with an enhancement factor as high as 10(8) . After capping with Raman signal molecules and folic acid, the gold nanoflowers show strong Raman signal in the living cells, excellent targeting properties, and a high signal-to-noise ratio for SERS imaging.

Investigation of Size‐Dependent Plasmonic and Catalytic Properties of Metallic Nanocrystals Enabled by Size Control with HCl Oxidative Etching

Particle size is one important parameter of nanocrystals that need to be tightly controlled, owing to its versatility for tailoring the properties and functions of nanocrystals towards various applications. In this article, oxidative etching by hydrogen chloride is employed as a tool to control the size of metallic nanocrystals. As a result of the size control, investigations into the size-dependent plasmonic and catalytic properties of metallic nanocrystals can be investigated. Given that the shape can be kept consistent when tuning the particle size in this system, it enables the systematic investigation of size-dependent properties free of the influence of other factors such as shape effect.

The Role of Etching in the Formation of Ag Nanoplates with Straight, Curved and Wavy Edges and Comparison of Their SERS Properties

We investigate the role of etching in the formation of Ag nanoplates with different morphologies. By examining the reduction of AgNO3 with poly(vinyl pyrrolidone) in an aqueous solution under a hydrothermal condition, we confirm that etching plays an essential role in promoting the growth of Ag triangular nanoplates with straight edges at the expense of multiple twinned particles via Ostwald ripening. Once all the multiple twinned particles are gone, etching will continue at the corners of nanoplates, leading to the formation of enneahedral nanoplates with curved edges. When the nanoplates with straight edges are transferred into ethanol and subjected to a solvothermal treatment, we obtain nanoplates with wavy edges and sharp corners due to etching on the edges. A comparison study indicates that, at the same particle concentration, Ag nanoplates with wavy edges embraces a SERS enhancement factor at least 6 and 13 times stronger than those with straight and curved edges, respectively. The results from finite difference time domain calculations support our experimental observation that the sharp features on nanoplates with wavy edges are the most active sites for SERS.

Seed‐Mediated Synthesis of Single‐Crystal Gold Nanospheres with Controlled Diameters in the Range 5–30 nm and their Self‐Assembly upon Dilution

Single-crystal gold nanospheres with controlled diameters in the range 5-30 nm were synthesized by using a facile approach that was based on successive seed-mediated growth. The key to the success of this synthesis was the use of hexadecyltrimethylammonium chloride (CTAC) as a capping agent and a large excess of ascorbic acid as a reductant to ensure fast reduction and, thus, single crystallinity and a spherical shape of the resultant nanoparticles. The diameters of the gold nanospheres could be readily controlled by varying the amount of seeds that were introduced into the reaction system. The gold nanospheres could be produced with uniform diameters of up to 30 nm; thus, their localized surface plasmon resonance properties could be directly compared with the results that were obtained from theoretical calculations. Interestingly, we also found that these gold nanospheres self-assembled into dimers, larger aggregates, and wavy nanowires when they were collected by centrifugation, dispersed in deionized water, and then diluted to different volumes with deionized water.

Au@Pd core–shell nanocubes with finely-controlled sizes

We report a facile method for the synthesis of highly uniform Au@Pd core–shell nanocubes with finely- and well-controlled sizes by seed-mediated growth. Using single-crystal seeds of Au spheres with a uniform size, we could reproducibly obtain Au@Pd core–shell nanocubes with a narrow size distribution ( 98%). Moreover, the size of the Au@Pd core–shell nanocubes could be finely and readily tuned in a controllable fashion from 11.4 to 41.1 nm in edge length by varying the concentration of Na2PdCl4, the amount of seeds, or both. We have also investigated the localized surface plasmon resonance properties of Au@Pd core–shell nanocubes as a function of Pd shell thickness.

Fabrication of semiconductor-polymer compound nonlinear photonic crystal slab with highly uniform infiltration based on nano-imprint lithography technique

We present a versatile technique based on nano-imprint lithography to fabricate high-quality semiconductor-polymer compound nonlinear photonic crystal (NPC) slabs. The approach allows one to infiltrate uniformly polystyrene materials that possess large Kerr nonlinearity and ultrafast nonlinear response into the cylindrical air holes with diameter of hundred nanometers that are perforated in silicon membranes. Both the structural characterization via the cross-sectional scanning electron microscopy images and the optical characterization via the transmission spectrum measurement undoubtedly show that the fabricated compound NPC samples have uniform and dense polymer infiltration and are of high quality in optical properties. The compound NPC samples exhibit sharp transmission band edges and nondegraded high quality factor of microcavities compared with those in the bare silicon PC. The versatile method can be expanded to make general semiconductor-polymer hybrid optical nanostructures, and thus it may pave the way for reliable and efficient fabrication of ultrafast and ultralow power all-optical tunable integrated photonic devices and circuits.

All-analytical semiclassical theory of spaser performance in a plasmonic nanocavity

Experimental approaches to manipulating light-matter interaction at the nanoscale level have quickly advanced in recent years, leading to the use of surface plasmon amplification by stimulated emission of radiation (spaser) in plasmonic nanocavities. Yet, a well-understood analytical theory to quantitatively explain certain characteristics of the spaser system has still been lacking and is greatly needed. Here, we develop an all-analytical semiclassical theory to investigate the energy exchange between active materials and fields and the spaser performance in a plasmonic nanocavity. The theory incorporates the four-level atomic rate equations in association with the classical oscillator model for active materials and Maxwells equations for fields, thus allowing one to uncover the relationship between the characteristics of the spaser (the output power, saturation, and threshold) and the nanocavity parameters (quality factor, mode volume, loss, and spontaneous emission efficiency), atomic parameters (number density, linewidth, and resonant frequency), and external parameters (pumping rate). The semiclassical theory has been employed to analyze previous spaser experiments and shows that using a single gold nanoparticle plasmonic nanocavity to ignite the spaser is very difficult due to its high threshold. The theory can be commonly used in understanding and designing all novel microlaser, nanolaser, and spaser systems.

Robust synthesis of gold rhombic dodecahedra with well-controlled sizes and their optical properties

Through the seed-mediated growth method in N,N-dimethylformamide (DMF)–water medium using trisodium citrate and poly(vinyl pyrrolidone) (PVP) as stabilizer, Au rhombic dodecahedra with a narrow size distribution ( 90%) could be reproducibly synthesized thanks to the robust formation of rhombic dodecahedra by DMF–water medium and surface stabilization by trisodium citrate. Moreover, the edge lengths of these Au rhombic dodecahedra could be readily controlled from 19 to 67 nm by varying the amount of seeds, concentration of HAuCl4, or both, and thus the localized surface plasmon resonance peak positions of the Au rhombic dodecahedra could be continuously tuned from 532 to 655 nm.