Plasma-induced formation of Ag nanodots for ultra-high-enhancement surface-enhanced Raman scattering substrates

We report here plasma-induced formation of Ag nanostructures for surface-enhanced Raman scattering (SERS) applications. An array of uniform Ag patterned structures of 150 nm diameter was first fabricated on a silicon substrate with imprint lithography; then the substrate was further treated with an oxygen plasma to fracture the patterned structures into clusters of smaller, interconnected, closely packed Ag nanoparticles (20-60 nm) and redeposited Ag nanodots ( approximately 10 nm) between the clusters. The substrate thus formed had a uniform ultrahigh SERS enhancement factor (1010) over the entire substrate for 4-mercaptophenol molecules. By comparison, Au patterned structures fabricated with the same method did not undergo such a morphological change after the plasma treatment and showed no enhancement of Raman scattering.     

Top-down approaches to the formation of silica nanoparticle patterns

This article reports a simple, versatile approach to the fabrication of lithographically defined mesoscopic colloidal silica nanoparticle patterns over large areas using spin-coating, interferometric lithography, and reactive-ion etching. One-dimensional nanoparticle films (bands) and 2D discs, diamonds, and holes with sub-micrometer periodicity, high quality, and excellent uniformity were successfully fabricated over large areas. The well-defined shape and period of the patterned nanoparticle film were controlled in the interferometric lithography step, while the thickness of nanoparticle film was easily tuned in the spin-coating step. This approach can extend to other deposition methods such as convective self-assembly, electrostatic self-assembly, and other materials such as metallic and ferromagnetic nanoparticles. We have also been able to generate sparse, random, isolated particle patterns, using a combination of interferometric lithography and layer-by-layer deposition as an extension of this approach to another deposition method, and to generate disc nanoparticle patterns using colloidal lithography as an extension of this approach to another lithography technique. These patterned films will find important applications in the fields of material growth, biosensors, and catalysis, as well as serving as building blocks for further fabrication.     

Self-chemical ionization of diethylzinc

The self-chemical ionization of diethylzinc is examined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and semiempirical molecular orbital calculations. Electron impact of diethylzinc neutral produces the radical cation, C(4)H(15)Zn(+) (m/z x 122), which reacts further with the neutral (C(2)H(5))(2)Zn to give the following product ions: Zn(+) (m/z x 64), C(2)H(5)Zn(+) (m/z x 93), C(4)H(9)Zn(+) (m/z x 121), C(4)H(11)Zn(2)(+) (m/z x 187), and C(6)H(15)Zn(2)(+) (m/z x 215). To determine the structure and pathways for production of these ions, monoisotopic (12)C(4)H(15)(64)Zn(+), (64)Zn(+) and (12)C(2)H(5)(64)Zn(+) were individually isolated and reacted with the neutral background. We also performed semiempirical molecular orbital calculations (ZINDO/1). The molecular orbital calculations and experimental data are consistent in predicting that the ethyl group on the diethylzinc cation carries the positive charge. Copyright 1999 John Wiley & Sons, Ltd.     

High transmission nanowire contact arrays with subwavelength spacing

We demonstrate high optical transmission in solar cell contacts based on nanowire arrays with subwavelength spacing. The photocurrent results obtained from fabricated devices are compared with numerical simulations. The proposed contact design leads to optical losses significantly smaller than the fraction of the top surface taken up by the metallic contact (<10% vs. 36%). The resulting sheet resistance of the contact is 46.7 Ω/square, comparing favourably with transparent conductive oxides.

     

怀孕期头发中一些元素含量的变化趋势

用同步辐射激发X射线荧光分析,对11个产妇怀孕期间头发内一些元素含量的变化趋势进行了测量,在各自对比的基础上,得到了一些结果。     

Quantum Hall ferromagnetism in the presence of tunable disorder

In this Letter, we report our recent experimental results on the energy gap of the ν=1 quantum Hall state (Δ(ν=1)) in a quantum antidot array sample, where the effective disorder potential can be tuned continuously. Δ(ν=1) is nearly constant at small effective disorders, and collapses at a critical disorder. Moreover, in the weak disorder regime, Δ(ν=1) shows a B(total)(1/2) dependence in tilted magnetic field measurements, while in the strong disorder regime, Δ(ν=1) is linear in B(total), where B(total) is the total magnetic field at ν=1. We discuss our results within several models involving the quantum Hall ferromagnetic ground state and its interplay with sample disorder.     

Using bicellar mixtures to form supported and suspended lipid bilayers on silicon chips

Bicellar mixtures, planar lipid bilayer assemblies comprising long- and short-chain phosphatidylcholine lipids in suspension, were used to form supported lipid bilayers on flat silicon substrate and on nanotextured silicon substrates containing arrays of parallel troughs (170 nm wide, 380 nm deep, and 300 nm apart). Confocal fluorescence and atomic force microscopies were used to characterize the resulting lipid bilayer. Formation of a continuous biphasic undulating lipid bilayer membrane, where the crests and troughs corresponded to supported and suspended lipid bilayer regions, is demonstrated. The use of interferometric lithography to fabricate nanotexured substrates provides an advantage over other nanotextured substrates such as nanoporous alumina by offering flexibility in designing different geometries for suspending lipid bilayers.     

Imaging interferometric lithography: approaching the resolution limits of optics

The resolution limits of conventional optical lithography reflect the low-pass spatial-frequency [numerical aperture (NA) /lambda] filter characteristics of the imaging system. Imaging interferometric lithography extends the resolution of optical lithography to the spatial-frequency limits of optics (2/lambda) . Off-axis illumination downshifts the high-frequency components of the mask pattern. An interferometric beam at the wafer upshifts these frequency components back to their original spatial frequencies following the lens. 2x reduction imaging interferometric lithography experiments demonstrate a continuous frequency coverage up to ~3N.A./lambda with a consequent threefold resolution enhancement.     

Experimental demonstration of near-infrared negative-index metamaterials

Metal-based negative refractive-index materials have been extensively studied in the microwave region. However, negative-index metamaterials have not been realized at near-IR or visible frequencies due to difficulties of fabrication and to the generally poor optical properties of metals at these wavelengths. In this Letter, we report the first fabrication and experimental verification of a transversely structured metal-dielectric-metal multilayer exhibiting a negative refractive index around 2 microm. Both the amplitude and the phase of the transmission and reflection were measured experimentally, and are in good agreement with a rigorous coupled wave analysis.