Tuning the lifetime of the surface plasmon upon sputtering

The lifetime of the surface plasmon in sputtered Ag ultrathin films on Cu(111) was investigated by high‐resolution electron energy loss spectroscopy measurements. The linewidth of the surface plasmon was found to follow a square‐root dependence on the fluence. Such finding allows the tuning of the lifetime of the plasmonic excitation upon sputtering and has general implications in plasmon‐based spectroscopies and in plasmon‐mediated processes across the films and at their surfaces. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Catalyst formation at various temperatures by hydrogen radical treatment and synthesis of silicon nanowires

Metal nanocrystals as catalyst from a metal oxide film were fabricated at various temperatures after hydrogen radical treatment and great quantities of silicon nanowires (SiNWs) were successfully synthesized using the hydrogen microwave afterglow deposition method. Indium (In) metal nanocrystals with size of about 12 nm were obtained from indium oxide film after hydrogen radical pre-treatment for 5 min at 400 °C and their quantity reached approximately 3 × 10¹⁰ cm⁻². Subsequently, a numerous SiNWs were grown with the crystal diffraction of (1 1 1), (2 2 0) and (3 1 1). The diameters of the SiNWs mainly ranged from 5 to 120 nm and their lengths extended to about 8.5 μm.     

GISAXS study of carbon nanotubes grown by CVD

We report a quantitative Grazing Incidence Small Angle X‐ray Scattering (GISAXS) study of a dense film of mutually oriented carbon nanotubes (CNTs) grown by a catalytically‐activated DC HF CCVD process after dispersion of metallic catalytic (Co) islands on SiO₂/Si(100) substrates. The GISAXS pattern analysis is expanded to non‐correlated surface science systems and is based on CNTs density, characteristic lengths, atomic Co dispersion throughout the CNTs and roughnesses of uncorrelated particles. The results are closely compared to SEM and TEM observations. The GISAXS patterns, even dominated by envelope features of disordered objects, provide significant complementary quantitative data about CNTs films. The results underline that cobalt continuously fills the nanotube in the course of the growth and that the CNTs experience a large tendency toward mutual alignment. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Purely quadratic dispersion of surface plasmon in Ag/Ni(111): the influence of electron confinement

Surface plasmon dispersion in nanoscale thin Ag films deposited onto the Ni(111) surface was investigated by angle‐resolved electron energy loss spectroscopy. We found that the dispersion curve contains only the quadratic term. The vanishing of the linear term was ascribed to the presence in the film of Ag 5sp‐related quantum well states. Screening effects enhanced by electron confinement in Ag quantum well states push the position of the centroid of the induced charge of the surface plasmon less inside the interface compared to other Ag systems, rendering null the linear coefficient of the dispersion curve. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Damping of the surface plasmon in clean and K-modified Ag thin films

The damping processes of electronic collective excitations of Ag/Ni(1 1 1) were studied by high-resolution electron energy spectroscopy. The FMHM of the Ag surface plasmon was reported as a function of Ag thickness, primary electron beam energy, Ag surface plasmon energy, and parallel momentum transfer. The broadening of the Ag surface plasmon was found to be related to 5sp–5sp transitions, for which a critical wave vector of 0.2 Å⁻¹ exists. Moreover, we provide a direct evidence of the occurrence of chemical interface damping in thin films, upon doping the Ag/Ni(1 1 1) system with K adatoms. The enhanced plasmon broadening in K/Ag/Ni(1 1 1) was ascribed to the existence of additional electron–hole decay channels at the K/Ag interface.     

Structural properties of GaAs nanostructures formed by a supply of intense As4 flux in droplet epitaxy

We investigated detailed structural properties of GaAs nanostructures formed by a supply of intense As₄ flux to Ga droplets. Scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (TEM) revealed that whisker-like nanostructures had formed on the truncated cone-shaped bases after crystallization. Moreover, electron energy loss spectroscopy in scanning transmission electron microscopy (STEM-EELS) revealed that elemental Ga atoms remained inside the nanostructures while outside, some had crystallized into GaAs. These findings suggest that crystallization started at the edges of the droplets and the GaAs grew upward along the periphery of the droplets until the droplets were completely covered with crystallized GaAs.     

Synthesis and catalytic activity of hybrid metal/silicon nanocomposites

In this Letter we demonstrate that hydrogen‐terminated porous silicon (PSi) layers and powders can serve as highly efficient reductive templates for noble metal salts. The reduction results in metal nanoparticle (NP) formation in the pores of PSi. Gold NP formation has been monitored in‐situ by measuring the plasmon resonance response. Pt NPs, formed in the PSi matrix, were investigated by transmission electron microscopy and energy‐dispersive X‐ray analysis. Furthermore, hybrid Pt/PSi nanocomposites exhibit a high catalytic activity for CO oxidation.

     

Inelastic mean free path, surface excitation parameter, and differential surface excitation parameter in Au for 300-3000 eV electrons

An analytical approach for simultaneously determining an inelastic mean free path (IMFP), a surface excitation parameter (SEP) and a differential SEP (DSEP) with absolute units was applied for the analysis of absolutely measured reflection electron energy loss spectra for Au. The IMFP, SEP and DSEP in Au for 300-3000 eV electrons are successfully obtained. The obtained DSEPs show a reasonable agreement with those theoretically calculated. The present SEPs were compared with those calculated by several empirical equations, revealing that the present SEPs are close to those calculated using the Oswald's equation. The IMFPs for Au determined by the present analysis were compared with those calculated by the TPP-2M predictive equation, revealing that the present IMFPs are in fairly good agreement with those calculated by the TPP-2M equation. The results confirmed that the present approach is effective for experimentally determining the SEP, DSEP, and IMFP for electrons in solids.     

In situ synthesis of mesoporous CdS nanoparticles in ternary cubic phase lyotropic liquid crystal

An in situ technique for the synthesis of CdS nanoparticles in a ternary lyotropic cubic phase liquid crystal has been carried out. The extremely viscous cubic phase liquid-crystal system consists of poly(oxyethylene)₁₀ nonyl phenol ether as non-ionic surfactant, octane as oil phase and an aqueous phase containing reactant ions (Cd²⁺ and S^2-). Thioacetamide (TAA) has been utilized as a source for slow release of sulfur in the in situ synthesis of CdS. Rheological results show that CdS nanoparticle growth did not disrupt the structure of the cubic phase liquid-crystal system. This indicates that homogenous synthesis of CdS in the liquid crystal had been achieved. The final products were characterized using X-ray photoelectron spectroscopy, thermal gravimetric analysis, transmission electron microscopy and UV-visible spectroscopy. It was found that the CdS nanoparticles formed have a mesoporous structure with a size dependent on the TAA decomposition aging time. Received: 29 March 2002 / Accepted: 4 September 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +603-8921/3257, E-mail: shahidan@pkrisc.cc.ukm.my     

Surface Plasmon Resonance and Field Enhancement of Au/Ag Alloyed Hollow Nanoshells

We investigate the nanostructure, surface plasmon resonance （SPR） absorption and nonlinear enhancement of Au/Ag alloyed hollow nanoshells prepared by the replacement reaction of Ag nanoparticles in a HAuCI4 aqueous solution. As the volume of HAuCl4 increases from OmL to 0.S mL, the SPR band of the Au/Ag alloyed nanoshells is tuned from 430nm to 780nm, and the third-order nonlinear optical susceptibility is enhanced nearly by an order of magnitude, which indicates a large enhancement of local field in the Au/Ag alloyed hollow nanoshells with hole defects.     

Ion beam sputter deposited W/Si multilayers: Influence of re-sputtering on the interface structure and structure modification at ultra short periods

X-ray multilayer mirrors of period ranging from 9.6 to 1.7 nm, deposited using ion beam sputtering, have been examined using grazing incidence X-ray reflectivity (GIXRR) and grazing incidence X-ray diffraction. Detailed analysis of GIXRR data revealed that significant amount of re-sputtering of Si layer takes place while W deposition is underway. Re-sputtering is mainly due to bombardment of high-energy neutrals getting reflected from the W target. Due to re-sputtering interface of the multilayer becomes asymmetric. This puts a major hindrance in avoiding the intermixing and achieving sharp interfaces at shorter periods. Maximum thickness of Si which gets lost due to re-sputtering during deposition is ∼0.8 nm. The shortest period multilayer estimated, that could be deposited without intermixing, was 2.7 nm. These results are of significance for developing low period W/Si multilayers.     

Influence of oxygen on the growth of carbon nanotubes by the SiC surface decomposition method

The influence of oxygen on the development of carbon nanotubes (CNTs) during the annealing process of the surface decomposition method on SiC(000−1) surfaces was investigated. In the case of annealing a SiC substrate under ultra-high vacuum conditions, carbon nanofibers (CNFs) form between the CNT layer and the substrate. However, CNTs form without CNFs by annealing the substrate in an oxygen atmosphere. The mean length of CNTs is longer than those formed without an oxygen atmosphere. From cross-sectional transmission electron microscopy images, it was found that oxygen plays an important role in CNT growth by the surface composition method.     

Silver nanoparticle supported on halloysite nanotubes catalyzed reduction of 4-nitrophenol (4-NP)

The silver nanoparticles with about 10 nm diameter were immobilized onto the halloysite nanotubes (HNTs) via the in situ reduction of AgNO₃ by polyol process. The silver nanoparticles supported halloysite nanotubes (Ag/HNTs), with Ag content of about 11%, were used for the catalyzed reduction of 4-nitrophenol (4-NP) with NaBH₄ in alkaline aqueous solutions. The effect of the reduction of 4-NP catalyzed by the catalysts in the presence of variable concentration NaBH₄ was investigated. It was found that the reduction rate increased with the increasing of the amounts of NaBH₄. And the larger amounts of NaBH₄ reduced the induction time.     

Selective suppression of extinction within the plasmon resonance of gold nanoparticles

We present extinction measurements on rectangular two-dimensional arrays of gold nanoparticles on a dielectric waveguide. The spectra exhibit spectrally narrow bands of suppressed extinction within the particle–plasmon resonance, resulting from destructive interference between the incident light field and the excited waveguide modes. The dependence of the spectral position of these high-transmission bands on different waveguide modes is investigated in detail. Received: 3 July 2001 / Published online: 10 October 2001     

The effects of hydrogen plasma pretreatment on the formation of vertically aligned carbon nanotubes

The effects of H₂ plasma pretreatment on the growth of vertically aligned carbon nanotubes (CNTs) by varying the flow rate of the precursor gas mixture during microwave plasma chemical vapor deposition (MPCVD) have been investigated in this study. Gas mixture of H₂ and CH₄ with a ratio of 9:1 was used as the precursor for synthesizing CNTs on Ni-coated TiN/Si(1 0 0) substrates. The structure and composition of Ni catalyst nanoparticles were investigated by using scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (XTEM). Results indicated that, by manipulating the morphology and density of the Ni catalyst nanoparticles via changing the flow rate of the precursor gas mixture, the vertically aligned CNTs could be effectively controlled. The Raman results also indicated that the intensity ratio of the G and D bands (I_D/I_G) is decreased with increasing gas flow rate. TEM results suggest H₂ plasma pretreatment can effectively reduce the amorphous carbon and carbonaceous particles and, thus, is playing a crucial role in modifying the obtained CNTs structures.     

Epitaxial TiC/SiC multilayers

Epitaxial TiC/SiC multilayers were grown by magnetron sputtering at a substrate temperature of 550 °C, where SiC is normally amorphous. The epitaxial TiC template induced growth of cubic SiC up to a thickness of ～2 nm. Thicker SiC layers result in a direct transition to growth of the metastable amorphous SiC followed by renucleation of nanocrystalline TiC layers.

     

Modified growth of Ge quantum dots using C2H4 mediation by ultra-high vacuum chemical vapor deposition

C₂H₄ mediations were used to modify the Stranski-Krastanow growth mode of Ge dots on Si(0 0 1) at 550 °C by ultra-high vacuum chemical vapor deposition. With appropriate C₂H₄-mediation to modify the Si surface, the elongated Ge hut clusters can be transformed to highly uniform Ge domes with a high Ge composition at the core. These C₂H₄-mediated Ge dots, almost bounded by {1 1 3} facets, have an average diameter and height of 55 and 9 nm, respectively. We propose two major mechanisms to depict the formation of these C₂H₄-mediated Ge dots: (i) an almost hydrogen-passivated Si surface to limit the nucleation sites for dot formation, and (ii) the incorporation of Ge atoms, repelled by the C-rich areas, into the existing Ge dots. This work provides a useful scheme to tune the topography of Ge dots in an UHV/CVD condition for possible optoelectronic applications.     

Optical oscillation modes of plasmon particles observed in direct space by phase-contrast near-field microscopy

Light distributions near resonant metal nanoparticles are recorded by a scattering-type scanning near-field optical microscope (s-SNOM), for the first time with a sub-particle-size resolution (<10 nm) and with simultaneous amplitude and phase contrast. The images depict the optical oscillation patterns of single plasmon particles. Examples are presented of particles excited in dominantly dipolar and quadrupolar modes, and also of closely spaced particles sustaining a gap mode. The gap mode can provide enhanced optical fields in nanometric spots for non-linear and single-molecule spectroscopy applications. Received: 20 June 2001 / Revised version: 3 August 2001 / Published online: 19 September 2001     

First-principles calculations of magnetic and electronic structures around surfaces and interfaces of magnetic multi-layered structure

Electronic and magnetic structures of ferromagnetic (FM)/non-magnetic (NM) and FM/antiferromagnetic (AF) bi-layer systems are calculated by the first principles approach. For the FM/NM system, we focus on the Co/Cu multi-layered structure whose interfacial layer is assumed to have a mixed composition of Co and Cu atoms, and show a possibility that Co atoms at the interface play a significant role as the spin-dependent scattering potentials. In the FM/AF system, we consider Fe or Co monolayer as FM layer and MnNi as AF layers. It is predicted that the Mn moments adjacent to FM layer are forced to align the FM moments, and those of under layer go gradually to anti-parallel alignment as in the bulk MnNi.     

High yield incorporation and washing properties of halides incorporated into single walled carbon nanotubes

We describe here the high yield filling (i.e. >50%) of single walled nanotubes (SWNTs) with a variety of halides, achieved according to various modified filling procedures. Both bundles and discrete SWNTs can be filled continuously up to lengths of several hundred nm, often with filling yields approaching 60–70% or better. In addition some high yield filled SWNTs were subjected to long-term washing in either boiling or room temperature. aqueous media, which does not remove the filling from the tubules, but enables effective removal of water-soluble extraneous materials . Received: 10 May 2002 / Accepted: 25 October 2002 / Published online: 10 March 2003 RID="*" ID="*"Corresponding author. Fax: +44-1865/272-690, E-mail: jeremy.sloan@chem.ox.ac.uk