Metal-coated Substrates Research Articles

Imaging the Engineered Polarization States of Surface Plasmon Polaritons at Visible Wavelengths

We experimentally demonstrate and image the hybrid nature of surface plasmon polaritons (SPPs) at visible wavelengths excited in low aspect ratio 1D and 2D periodic plasmonic structures with periods nearly equal to the resonance wavelengths, fabricated on thin homogeneous metal-coated glass substrates. A thin homogeneous metal layer was sandwiched between the substrate and the periodic metal patterns to out-couple the SPPs as leakage radiation through the substrate. This resulted in the detection of SPP excitation as transmission peaks in a dark background, as opposed to transmission dips in a bright background in the structures without the metal layer reported earlier. Due to the periods being almost equal to the resonance wavelengths, the transmission peaks were not due to extraordinary transmission phenomenon, but because of the radiative leakage of wavelength selective SPPs excited on the surface. A cross-axis polarizer-analyzer was used in broadband leakage radiation microscopy to diminish the direct zeroth -order transmission and image the real and Fourier plane characteristics of the SPP transmission. The bright emission of different colors against a dark background corresponding to the transmission plasmonic resonances for different periods, in both real and Fourier plane revealed the hybrid nature of excited SPPs, when the polarizer was positioned at 45$^\circ$ with respect to the grating vector. The fabricated plasmonic substrates present interesting opportunities for imaging and sensing applications.

Growth of carbon nanowalls on metal-coated substrates via microwave plasma enhanced chemical vapor deposition.

In this study, we investigated the growth properties of carbon nanowalls (CNW) depending on the substrate types. We deposited metal films on Si substrates via RF magnetron sputtering with the use of four-inch W, Cu and Ni targets. A microwave plasma enhanced chemical vapor deposition (PECVD) system was used to grow CNWs on the metal-coated Si substrates using H2 and CH4 gases. The vertical and superficial conditions of the grown CNWs depending on the substrate types were characterized by field emission scanning electron microscopy (FE-SEM). Raman analysis was used to investigate the structural properties of the CNWs. Based on this experiment, it was found that the direct growth of CNW was possible on the metal layer with a thickness of more than 50 nm.

Reactive Metal Bonding of Carbon Nanotube Arrays for Thermal Interface Applications

Vertically aligned carbon nanotube (CNT) arrays can offer an attractive combination of high thermal conductance and mechanical compliance for thermal interface applications. These arrays require a reliable, thermally conductive bonding technique to enable integration into devices. This paper examines the use of a reactive metal bonding layer to attach and transfer CNT arrays to metal-coated substrates, and the thermal performance is compared with CNT arrays bonded with indium solder. Infrared microscopy is used to simultaneously measure the intrinsic thermal conductivity of the CNT array and the thermal boundary resistance of both the bonded and growth CNT interfaces over a range of applied compressive stresses. A coarse-grained molecular simulation is used to model the effects of compressive pressure on the CNT array thermal conductivity. Reactive metal bonding reduces the thermal boundary resistance to as low as 27 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> · K · W <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , which is more than an order of magnitude less than the nonbonded contact.

Laser-induced transfer of nanoparticles for gas-phase analysis

An experimental study of laser-induced forward transfer of nanoparticles from a metal-coated glass substrate is presented. Nanoparticles are efficiently removed from the substrates due to transient blister formation. A combination of mass spectrometry, atomic force microscopy studies of the irradiated substrates, and theoretical considerations of temperature distributions and stress in the films during irradiation serves to provide insight into the mechanisms involved.

Efficient unidirectional polarization-controlled excitation of surface plasmon polaritons

Efficient excitation of surface plasmon polaritons (SPPs) remains one of the most challenging issues in areas of plasmonics related to information communication technologies. In particular, combining high SPP excitation efficiency and acceptance of any polarization of incident light appeared to be impossible to attain due to the polarized nature of SPPs. Here we demonstrate plasmonic couplers that represent arrays of gap SPP resonators producing upon reflection two orthogonal phase gradients in respective linear polarizations of incident radiation. These couplers are thereby capable of efficiently converting incident radiation with arbitrary polarization into SPPs that propagate in orthogonal directions dictated by the phase gradients. Fabricated couplers operate at telecom wavelengths and feature the coupling efficiency of ∼25% for either of two linear polarizations of incident radiation and directivity of SPP excitation exceeding 100. We further demonstrate that an individual wavelength-sized unit cell, representing a meta-scatterer, can also be used for efficient and polarization sensitive SPP excitation in compact plasmonics circuits. Devices capable of converting light of any polarization into surface plasmon polaritons could aid the development of on-chip optical circuits. Anders Pors and co-workers from the University of Southern Denmark and the University of Burgundy in France have now fabricated such a ‘coupler’ from gradient metasurfaces — arrays of miniature gold patches on a thin dielectric layer covering a metal-coated glass substrate. Their device is compatible with wavelengths of light in the telecommunications window (around 1,500 nm) and does not require a specific polarization in order to excite plasmons. Furthermore, it allows the direction of plasmon propagation to be controlled by changing the polarization of the incident beam. Calculations indicate that the coupling efficiency could be as high as 40%, with a directivity of around 50:1.

PLD fabrication of ZnO nanostructures on metal-coated substrates

In this work, ZnO nanostructures were fabricated on metal (a metal alloy containing Fe, Cr, Mn and Ni) coated silicon substrates by applying pulsed laser deposition. The samples were prepared at substrate temperatures in the range of 550 – 650 °C, oxygen pressure of 5 Pa, and laser fluence ≤ 1 J cm−2 i.e., process parameters usually used for thin-film deposition. We found that the metal layer's role is substantial in the preparation of nanostructures, the morphology of the catalyst layer determines the growth of the ZnO nanowalls and the increase of the process temperature leads to nanorods formation on the nanowalls.

Enhancement of Fluorescent Labeling via a Composited Thin Film

Fluorescent labeling is the prevailing imaging technique in cell biological research. When statistical investigations on a large number of cells are involved, experimental study is required for both low magnification to get a reliable statistical population and high contrast to achieve accurate diagnosis on the nature of the cells’ perturbation. As microscope objectives of low magnification generally yield low collection efficiency, such studies are limited by the fluorescence signal weakness. To overcome this technological insufficiency, Le Moal et al. proposed a method based on metal-coated substrates that enhanced the fluorescence process and improved collection efficiency in fluorescence microscope observation and that could be directly used with a common microscope setup. In this paper, we use an Ag-Si3N4-Ag multilayer film coated on the substrate and numerically analyse the optical behavior of a fluorophore which was placed above the composited film coated on the substrate. The results shows that by using an Ag-Si3N4-Ag composited film the fluorescence imaging can be enhanced remarkably.

Fabrication of Deterministic Nanostructure Assemblies with Sub-nanometer Spacing Using a Nanoimprinting Transfer Technique

Deterministic patterning or assembly of nanoparticles often requires complex processes that are not easily incorporated into system architectures of arbitrary design. We have developed a technique to fabricate deterministic nanoparticle assemblies using simple and inexpensive nanoimprinting equipment and procedures. First, a metal film is evaporated onto flexible polymer pillars made by nanoimprinting. The resulting metal caps on top of the pillars can be pulled into assemblies of arbitrary design by collapsing the pillars in a well-controlled manner. The nanoparticle assemblies are then transferred from the pillars onto a new substrate via nanoimprinting with the aid of either cold welding or chemical bonding. Using this technique, a variety of patterned nanoparticle assemblies of Au and Ag with a critical dimension less than 2 nm were fabricated and transferred to silicon-, glass-, and metal-coated substrates. Separating the nanostructure assembly from the final architecture removes significant design constraints from devices incorporating nanoparticle assemblies. The application of this process as a technique for generating surface-enhanced Raman spectroscopy substrates is presented.

Nanocomposite Generators: Flexible Nanocomposite Generator Made of BaTiO3 Nanoparticles and Graphitic Carbons (Adv. Mater. 22/2012)

K. J. Lee and co-workers demonstrate the fabrication of a flexible nanocomposite generator using piezoelectric BaTiO3 nanoparticles and universal graphitic carbons (carbon nanotubes and reduced graphene oxide). The nanomaterials are dispersed in a matrix of polydimethyl-siloxane and spun onto a metal-coated plastic substrate. This method enables the production of self-powered energy-harvesting systems in a simple, low-cost, and large-scale manner, thus overcoming the limitations of previous nanogenerators. The resulting device is demonstrated on page 2999.

The effect of annealing temperature, residual O2 partial pressure, and ambient flow rate on the growth of SiO x nanowires

The active oxidation of a metal-coated Si substrate offers a convenient method to grow dense silica nanowire films directly on the substrate surface. In this study we investigate the effects of temperature and O2 partial pressure in combination with different flow rates of the purging annealing gas. The flow rate is shown to have a direct effect on the onset of active oxidation and on the concentration and flux of monoxide vapor produced. Thicker nanowires are observed for increasing flow rates, while nanowire heights tend to decrease as predicted from simple velocity profile calculations. These results support the notion that the thicknesses of the nanowire films are determined by a critical monoxide vapor concentration above the substrate surface that can be readily modified by the flow rate of the purging gas.

Nanostructured metallic foam electrodeposits on a nonconductive substrate

A way to prepare the nanostructured metallic foam (NMF) electrodeposits on nonconductive materials was suggested for the first time. This innovative process involves the electrochemical preparation of NMFs on a metal-coated nonconductive substrate and subsequent removal of the deliberately heat-treated dense layer around the NMF trunks, leaving self-supported NMFs on the nonconductive substrate. The creation of nanostructured (or nanoramified) nickel foams on alumina was demonstrated as an exemplary application of the fabrication process.

Assembly and Embedding of Nanoparticles in a Ni-Matrix

To create a new kind of surface suitable for tribological applications, a monolayer of nanoparticles was deposited on a metal-coated substrate. This was followed by embedding the nanoparticles in a metal matrix. For the deposition, SiO2 nanoparticles were used, succeed by an embedding by Ni electroplating. For the deposition, the SiO2 nanoparticles were attached to the surface using a linker of CO2H and SH. In this experiment, the linker connects the nanoparticles with an Au surface. To obtain an optimal linkage between the surface and nanoparticles, various deposition technologies like dip-coating, spin-coating, and electrophoresis were investigated. Afterwards, the SiO2 nanoparticles were embedded by electroplating. The results have shown that it is possible to create a surface with a defined roughness. Furthermore, the mechanical investigations indicate that the nanoparticles have an influence on the hardness of the developed layer.

FESEM studies of densely packed aligned nickel nanopillars on silicon substrate by electrochemical deposition through porous alumina membrane

Field Emission Scanning Electron Microscopic studies of the electrochemically grown highly oriented Ni nanopillars within the arrays of porous alumina membrane have been investigated. Both secondary electron emission and backscatter detection modes are applied to study the fabrication of free-standing Ni nanopillars on metal-coated silicon substrate. FESEM imaging clearly shows the growth of the nanopillars through the nanopores. Backscatter imaging depicts the compositional variations across the Ni/alumina/Ta/Si structure with clear contrasts at the metallic/non-metallic interfaces. The alumina membrane is also etched out to get free-standing Ni nanopillars and FESEM imaging verifies the growth of the vertically oriented nanopillars on Si substrate. These densely packed, highly ordered nanopillars have excellent magnetic, field-emission and sensing applications.

Field emission characterization of vertically oriented uniformly grown nickel nanorod arrays on metal-coated silicon substrate

Vertically oriented, densely packed Ni nanorod arrays have been fabricated on metal-coated Si substrate via cost-effective electrochemical technique. Directional growth of the nanorods is performed through the nanopores of anodic alumina membrane via electrodeposition process. Al2O3 membrane is removed at the final fabrication step by wet-etching process to get vertically-standing nanorods on Si wafer. Electron microscopic images depict the growth of highly ordered, uniformly grown Ni nanorods with diameter around 50 nm. These types of vertically aligned uniform nanorods supported by Si substrate have very good applications in sensors and field emission displays. Closer look of the electron microscopic images show very sharp tips, which provide large field enhancement and, therefore, are particularly suitable for field emission applications. Field emission studies of the nanorods are performed with standard diode configuration with sample as cathode and a stainless steel tip as anode under high vacuum. Field emission current as a function of applied field shows considerable electron emission with low threshold field around 5 V/μm. The field emission data are found to be well-fitted with linear Fowler–Nordheim plot, indicating the cold field emission mechanism in our samples. Calculation of the geometrical field enhancement factor (β) of the as-synthesized nanorod tip is found to be around 3690, which is sufficient to enhance the macroscopic field at the emitter tip and, hence, supplies the required barrier field (also called local field at the emitter-tip) to produce low-threshold cold field electron emission. Therefore, the cost-effective synthesis of vertically aligned Ni nanorods supported by Si substrate can be used as a field emission device for potential low power panel applications.

Hydrogel-based protein and oligonucleotide microchips on metal-coated surfaces: Enhancement of fluorescence and optimization of immunoassay

Manufacturing of hydrogel-based microchips on metal-coated substrates significantly enhances fluorescent signals upon binding of labeled target molecules. This observation holds true for both oligonucleotide and protein microchips. When Cy5 is used as fluorophore, this enhancement is 8–10-fold in hemispherical gel elements and 4–5-fold in flattened gel pads, as compared with similar microchips manufactured on uncoated glass slides. The effect also depends on the hydrophobicity of metal-coated substrate and on the presence of a layer of liquid over the gel pads. The extent of enhancement is insensitive to the nature of formed complexes and immobilized probes and remains linear within a wide range of fluorescence intensities. Manufacturing of gel-based protein microarrays on metal-coated substrates improves their sensitivity using the same incubation time for immunoassay. Sandwich immunoassay using these microchips allows shortening the incubation time without loss of sensitivity. Unlike microchips with probes immobilized directly on a surface, for which the plasmon mechanism is considered responsible for metal-enhanced fluorescence, the enhancement effect observed using hydrogel-based microchips on metal-coated substrates might be explained within the framework of geometric optics.

Simple Fabrication of a Convex Glass Mold for Microchip Electrophoresis

The conventional photolithography-chemical wet-etching method for preparing a convex mold usually uses a metal-coated glass or silicon-wafer substrate, and thus produces a waste solution containing heavy metal such as chromium. In this work, a simple photolithography-chemical wet-etching method using a slide glass without a coating of metal was proposed to fabricate a convex mold for preparing a PDMS (polydimethylsiloxane) microchip. A photoresist was directly coated on a cleaned slide glass, and was prebaked for 90 s. After covering with a photo-mask, the coated slide glass was illuminated with UV-visible light, followed by development with a developing reagent. Then, the slide glass was etched in a 1 M HF/1 M NH4F solution for a certain time. Finally, the etched slide glass was cleaned with acetone for removing the remaining photoresist. A PDMS microchip with a cross microchannel was prepared using the convex mold. The microchip was used for the electrophoresis of two fluorescent dyes and fluorescent labeled protein A. The experimental results showed that the simple method without using a metal-coated substrate could be used for convex molds for preparing microchips.

The Answer to the Challenging Question: Is there a Size Limit of Nanowires?

Our present analysis will focus on the S(V)LS mechanism. In the S(V)LS process, silicon nanowires are grown by heating the metal-coated silicon substrate at high temperature in an argon and hydrogen atmosphere. Here, we demonstrate the origin of the driving force needed for the metal supersaturation and calculate the binary phase diagrams of Au-Si nanosystems involved in the growth of nanowires. These new diagrams can be used for other purposes helping to improve the understanding of the physical properties of nanostructures. We also answer the challenging question that many researchers have addressed on whether a minimum size limit of silicon nanowires exists. The nanowire size limit has been evaluated on the basis of thermodynamics and using silicon nanowires obtained via the S(V)LS rather than the VLS mechanism. At 1100°C, the temperature commonly used for the growth of nanowires by the S(V)LS mechanism, it has been found that there is no minimum size limit of nanowires.

Chemical bath deposition of thin TiO 2-anatase films for dielectric applications

Titania thin films were prepared on bare Si and Pt/Ti/SiO 2/Si substrates by chemical bath deposition (CBD) from solutions of a titanium peroxo complex and subsequent calcinations at 350 and 700 °C, respectively. The CBD process allowed deposition on both uncoated and metal-coated Si substrates with the same deposition rate. Optimization of the annealing process yielded uniform and crack-free nanocrystalline anatase films. The influence of the film thickness, irradiation of visible light, measuring frequency, temperature and substrate on the dielectric properties will be discussed in the paper. Films with a final thickness of about 600 nm showed comparably high relative permittivity of 31.8 on silicon and of 52.7 on Pt/Ti/SiO 2/Si substrates, respectively. The present route provides anatase thin films with higher dielectric constants than classical sol–gel routes and is therefore a promising candidate for potential applications in large scale integration.

Fabrication of MgO whiskers on metal-coated substrates by heating MgB2 powders: Effects of Ag layer thickness

A thermal evaporation approach was developed to synthesize single-crystalline MgO whiskers on silver (Ag) layer-coated Si substrates. Magnesium diboride (MgB2) and oxygen (O2) were used as Mg and, O precursors, respectively. The synthetic process using a thinner Ag layer facilitated the growth of 1D whiskers, and the product mainly comprises film-like structures with thicker Ag layer thickness. X-ray diffraction and selected area electron diffraction pattern revealed that the whiskers were of a single-crystalline cubic structure of MgO. We also discuss the possible mechanism by which the thickness of the underlying Ag layer affects the resultant morphology of the MgO structures.

Synthesis of Aligned Carbon Nanotubes on Double-Sided Metallic Substrate by Chemical Vapor Deposition

Aligned multiwalled carbon nanotubes (MWCNTs) were grown on both sides of a metallic or metal-coated substrate by water-vapor-assisted chemical vapor deposition (CVD). Aligned CNT films with thicknesses ranging from 1 to >100 μm were obtained. By manipulating various operating factors, namely, the position of the substrate in the reactor, the amount of water vapor, the amount of catalyst, the reactor temperature, and the growth time, the morphology and thickness of these carbon nanotube films could be adjusted. This technique was used to fabricate a thermal interface material, made up of a thin copper foil covered with Cr−Au−MWCNT on both sides, that has a thermal resistance as low as 12 mm2 K/W.