Showing papers on "Nanosphere lithography published in 2005"
TL;DR: The use of nanosphere lithography for the fabrication of highly reproducible and robust SERS substrates is described and progress in applying SERS to the detection of chemical warfare agents and several biological molecules is described.
Abstract: The ability to control the size, shape, and material of a surface has reinvigorated the field of surface-enhanced Raman spectroscopy (SERS). Because excitation of the localized surface plasmon resonance of a nanostructured surface or nanoparticle lies at the heart of SERS, the ability to reliably control the surface characteristics has taken SERS from an interesting surface phenomenon to a rapidly developing analytical tool. This article first explains many fundamental features of SERS and then describes the use of nanosphere lithography for the fabrication of highly reproducible and robust SERS substrates. In particular, we review metal film over nanosphere surfaces as excellent candidates for several experiments that were once impossible with more primitive SERS substrates (e.g., metal island films). The article also describes progress in applying SERS to the detection of chemical warfare agents and several biological molecules.
2,986 citations
TL;DR: Three vibrational modes of benzenethiol are studied simultaneously on one substrate, and it is demonstrated that the smaller Raman shifted peak shows a maximum enhancement closer to the LSPR lambda(max) than that of a larger Raman shift peak, in agreement with the predictions of the electromagnetic enhancement mechanism of SERS.
Abstract: A detailed wavelength-scanned surface-enhanced Raman excitation spectroscopy (WS SERES) study of benzenethiol adsorbed on Ag nanoparticle arrays, fabricated by nanosphere lithography (NSL), is presented. These NSL-derived Ag nanoparticle array surfaces are both structurally well-characterized and extremely uniform in size. The WS SERES spectra are correlated, both spatially and spectrally, with the corresponding localized surface plasmon resonance (LSPR) spectra of the nanoparticle arrays. The surface-enhanced Raman scattering (SERS) spectra were measured in two excitation wavelength ranges: (1) 425−505 nm, and (2) 610−800 nm, as well as with the 532-nm line from a solid-state diode-pumped laser. The WS SERES spectra have line shapes similar to those of the LSPR spectra. The maximum SERS enhancement factor is shown to occur for excitation wavelengths that are blue-shifted with respect to the LSPR λmax of adsorbate-covered nanoparticle arrays. Three vibrational modes of benzenethiol (1575, 1081, and 1009 ...
906 citations
TL;DR: The efficient technique is shown to scale down the size of metallic nanoparticles from 200 to 30 nm, while preserving the original nanosphere spacing and order.
Abstract: The application of shadow nanosphere lithography for the preparation of large-area, two-dimensional, metallic nanostructures of different shape is described. Through changing the mask morphology by temperature processing and varying the evaporation conditions, particles with morphologies such as rings, rods, and dots have been produced. This process allows outstanding control of the size and morphology of the particles. The efficient technique is shown to scale down the size of metallic nanoparticles from 200 to 30 nm, while preserving the original nanosphere spacing and order. The 150-nm-diameter Fe rings produced by this method show ferromagnetic behavior, which was predicted by theoretical simulation. All the experimental results were confirmed by computer simulations, which also showed the possibility of creating periodic arrays of any other geometrical shape.
336 citations
TL;DR: It is demonstrated that the localized surface plasmon resonance (LSPR) nanosensor can detect Al(2)O(3) film growth with atomic spatial resolution normal to the nanoparticle surface with 10 times greater spatial resolution than that in the previous long-range distance-dependence study using multilayer self-assembled monolayer shells.
Abstract: Atomic layer deposition (ALD) is used to deposit 1−600 monolayers of Al2O3 on Ag nanotriangles fabricated by nanosphere lithography (NSL). Each monolayer of Al2O3 has a thickness of 1.1 A. It is demonstrated that the localized surface plasmon resonance (LSPR) nanosensor can detect Al2O3 film growth with atomic spatial resolution normal to the nanoparticle surface. This is approximately 10 times greater spatial resolution than that in our previous long-range distance-dependence study using multilayer self-assembled monolayer shells. The use of ALD enables the study of both the long- and short-range distance dependence of the LSPR nanosensor in a single unified experiment. Ag nanoparticles with fixed in-plane widths and decreasing heights yield larger sensing distances. X-ray photoelectron spectroscopy, variable angle spectroscopic ellipsometry, and quartz crystal microbalance measurements are used to study the growth mechanism. It is proposed that the growth of Al2O3 is initiated by the decomposition of tr...
296 citations
TL;DR: The growth of ordered arrays of vertically aligned silicon nanowires by molecular beam epitaxy using prepatterned arrays of gold droplets on Si(111) substrates is shown.
Abstract: Because of their importance in fundamental research and possible applications in nanotechnology and nanoelectronics, semiconductor nanowires have attracted much interest. In addition to the growth itself, the control of the size and location is an essential problem. Here we show the growth of ordered arrays of vertically aligned silicon nanowires by molecular beam epitaxy using prepatterned arrays of gold droplets on Si(111) substrates. The ordered arrays of gold particles were produced by nanosphere lithography.
266 citations
TL;DR: Two-dimensional ordered arrays of gold (Au) nanoparticles were fabricated using two different variants of the nanosphere lithography technique, using reactive ion etching to simultaneously reduce the dimension of the masking nanospheres and create arrays of nanopores on the substrate prior to the deposition of the Au films.
Abstract: Two-dimensional ordered arrays of gold (Au) nanoparticles were fabricated using two different variants of the nanosphere lithography technique. First, ordered arrays of polystyrene nanospheres on Si substrate were used as deposition masks through which gold films were deposited by electron beam evaporation. After the removal of the nanospheres, an array of triangular Au nanodisks was left on the Si substrate. After thermal annealing at increasing temperature, systematic shape transition of the nanostructures from original triangular Au nanodisks to rounded nanoparticles was observed. This approach allows us to systematically vary the size and morphology of the particles. In the second and novel technique, we made use of reactive ion etching to simultaneously reduce the dimension of the masking nanospheres and create arrays of nanopores on the substrate prior to the deposition of the Au films. These samples were subsequently annealed, which resulted in size-tunable and ordered Au nanoparticle arrays with t...
173 citations
TL;DR: An electrochemical method is developed to quantitatively modify and spectroscopically monitor the size and shape of Ag nanotriangles fabricated by nanosphere lithography on an indium tin oxide (ITO) electrode surface.
Abstract: An electrochemical method is developed to quantitatively modify and spectroscopically monitor the size and shape of Ag nanotriangles fabricated by nanosphere lithography (NSL) on an indium tin oxide (ITO) electrode surface. AFM and SEM results demonstrate that the preferential order of electrochemical oxidation for a nanotriangle is, surprisingly, bottom edges first, then triangular tips, then out-of-plane height.
172 citations
TL;DR: The figure shows an SEM image of the ordered quasi-one-dimensional parallel wires of silica spheres on a polymer-coated substrate.
Abstract: Ordered 2D non-close-packed sphere arrays with controllable lattice structures have been fabricated by using soft lithography based on the solvent-swelling and mechanical deformation behaviors of PDMS film. The figure shows an SEM image of the ordered quasi-one-dimensional parallel wires of silica spheres on a polymer-coated substrate.
168 citations
TL;DR: In this work, a detailed and systematic study of the plasmonic properties of a novel film over nanowell surface is investigated, resulting in an improvement in the figure of merit.
Abstract: In this work, a detailed and systematic study of the plasmonic properties of a novel film over nanowell surface is investigated. These nanostructures are fabricated using nanosphere lithography and reactive ion etching and structurally characterized by AFM and SEM. The resulting structures show remarkably narrow plasmon bands in reflectance spectra (as little as 0.10 eV) and greater sensitivity to external dielectric environment than has been seen in other nanoparticle systems, resulting in an improvement in the figure of merit (FOM = refractive index sensitivity (eV·RIU-1)/full width at half-maximum (eV)) for refractive index sensing. Theoretical modeling for the plasmon spectra of these nanostructures is done using discrete dipole approximation code under periodic boundary conditions. The modeling results match the measurements accurately in aspects of the variation of the plasmon line shape with altering internanowell distance and dielectric environment.
152 citations
TL;DR: In this paper, the authors describe the preparation of large-area, two-dimensional metallic structures using shadow nanosphere lithography, which allows for an encapsulation of the metallic structures, to prevent them from oxidation.
Abstract: In this letter we describe the preparation of large-area, two-dimensional metallic structures using shadow nanosphere lithography. By varying the position of the substrate with respect to the evaporation source during the sample preparation, we make morphologies such as cups, rods, and wires, that are not accessible by the standard nanosphere lithography. This technique also allows for an encapsulation of the metallic structures, to prevent them from oxidation. Morphologies predicted by our computer simulations have been subsequently confirmed experimentally.
139 citations
TL;DR: A novel method to produce solution-phase triangular silver nanoparticles is presented and Mie theory and the Discrete Dipole Approximation method have been used to model and interpret the optical properties of the released Ag nanoparticles.
Abstract: A novel method to produce solution-phase triangular silver nanoparticles is presented. Ag nanoparticles are prepared by nanosphere lithography and are subsequently released into solution. The resulting nanoparticles are asymmetrically functionalized to produce either single isolated nanoparticles or dimer pairs. The structural and optical properties of Ag nanoparticles have been characterized. Mie theory and the Discrete Dipole Approximation method (DDA) have been used to model and interpret the optical properties of the released Ag nanoparticles.
TL;DR: Using femtosecond transient spectroscopy, the optically detected laser-induced coherent phonon oscillation of monolayers of periodic arrays of prismatic-shaped silver and gold nanoparticles, assembled by using the technique of nanosphere lithography is studied.
Abstract: Using femtosecond transient spectroscopy, we studied the optically detected laser-induced coherent phonon oscillation of monolayers of periodic arrays of prismatic-shaped silver and gold nanoparticles, assembled by using the technique of nanosphere lithography. In this method, the same size of polystyrene sphere and the same vacuum conditions are used. Under these circumstances, the gold nanoprisms formed are found to have sharper tips than the corresponding silver nanoprisms. For both gold and silver nanoparticles, the surface plasmon absorption maximum is found to depend linearly on size. The coherent lattice oscillation periods are also found to depend linearly on size. However, although the observed dependence for the silver nanoparticle is found to follow the calculated dependence of a single particle on size (based on a one-dimensional standing wave model), the gold nanoparticle deviates from this model, and the deviation is found to increase with the size of the nanoparticles. This deviation can be explained by considering interparticle coupling. A simple interparticle lattice oscillating dipolar coupling model of the dimer is found to qualitatively account for both the sign and the size dependence of the deviation. The absence of this deviation in the silver nanoparticle arrays is blamed on the weak interparticle coupling due to their rounded tips and the possibility of oxidation of their surfaces.
TL;DR: In this paper, hexagonally patterned lysozyme nanoarrays have been assembled on silicon wafers by combining nanosphere lithography and surface silane chemistry using vapor and solution deposition processes.
Abstract: Hexagonally patterned lysozyme nanoarrays have been assembled on silicon wafers by combining nanosphere lithography and surface silane chemistry using vapor and solution deposition processes. The patterned protein regions extend over cm sized regions, and the size of each island is ∼120 nm for the solution-prepared template and ∼60 nm for the vapor-prepared template. Antibody test indicates that the patterned lysozyme maintains its bioactivity on the surface. This new approach offers a fast and reliable method to fabricate protein arrays over large areas with feature sizes comparable to scanning-probe based techniques.
01 Dec 2005
TL;DR: This work exploits the highly tunable nature of nanoparticle optical properties to establish the optimisation conditions of the SERS substrate and enables the development of SERS-based sensors for the detection of a Bacillus anthracis biomarker and glucose in a serum-protein matrix.
Abstract: In the 28 years since its discovery, surface-enhanced Raman scattering (SERS) has progressed from model system studies of pyridine on a roughened silver electrode to state-of-the-art surface science studies and real-world sensing applications. Each year, the number of SERS publications increases as nanoscale material design techniques advance and the importance of trace analyte detection increases. To achieve the lowest limits of detection, both the relationship between surface nanostructure and laser excitation wavelength and the analyte-surface binding chemistry must be carefully optimised. This work exploits the highly tunable nature of nanoparticle optical properties to establish the optimisation conditions. Two methods are used to study the optimised conditions of the SERS substrate: plasmon-sampled and wavelength-scanned surfaced Raman excitation spectroscopy (SERES). The SERS enhancement condition is optimised when the energy of the localised surface plasmon resonance of the nanostructures lies between the energy of the excitation wavelength and the energy of the vibration band of interest. These optimised conditions enabled the development of SERS-based sensors for the detection of a Bacillus anthracis biomarker and glucose in a serum-protein matrix.
TL;DR: In this paper, the authors present recent advances in the preparation of magnetic nanoparticle superstructures from ferrofluids and by nanosphere lithography, and discuss different successes of methods presented in this article to create magnetic nanoparticles.
Abstract: The aim of this microreview is to present recent advances in the preparation of magnetic nanoparticle superstructures from ferrofluids and by nanosphere lithography. Different successes of methods presented in this article to create magnetic nanoparticles will be discussed in view of different requirements of available assembling techniques. Theoretical aspects of nanoparticle assemblies and their assembled layer magnetic properties are not reviewed here. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
TL;DR: Frequency-scanned excitation profiles of coherent second harmonic generation (SHG) were measured for silver nanoparticle arrays prepared by nanosphere lithography to identify an enhancement of SH emission efficiency that peaks near approximately 650 nm for nanoparticles 50 nm in height.
Abstract: Frequency-scanned excitation profiles of coherent second harmonic generation (SHG) were measured for silver nanoparticle arrays prepared by nanosphere lithography. The frequency of the fundamental beam did not coincide with the localized surface plasmon resonance (LSPR) of the nanoparticles and was tuned so that the coherent second harmonic (SH) emission was in the region of the LSPR at 720−750 nm. The SH emission from the arrays was compared with a smooth silver film to identify an enhancement of SH emission efficiency that peaks near ∼650 nm for nanoparticles 50 nm in height. The polarization and orientation dependence of this enhancement suggests that it is related to a dipolar LSPR mode polarized normal to the plane of the substrate. Linear extinction spectra are dominated by in-plane dipoles and do not show this weak out-of-plane LSPR mode. The nanoparticle arrays are truncated tetrahedrons symmetrically oriented by nanosphere lithography to cancel SH from in-plane dipoles which allows observation of...
TL;DR: The formation of the tripodal nanoparticles is attributed to the inhomogeneous heating and lattice rearrangement of the as-deposited nanoparticles to a metastable state as mentioned in this paper.
Abstract: Prismatic gold nanoparticles in the periodic monolayer arrays prepared with nanosphere lithography technique can be reshaped with femtosecond laser pulses at different powers and wavelengths. As the power density of 400 nm femtosecond laser increases, the prismatic particle tips begin to round and the overall particle shape changes from a prism to a sphere with a tripodal intermediate. The formation of the tip-rounded nanoprisms is probably due to the dewetting properties of gold on quartz surface and the low melting temperature at the tips. The formation of the tripodal nanoparticles is attributed to the inhomogeneous heating and lattice rearrangement of the as-deposited nanoparticles to a metastable state, which is more stable than the prismatic shape but less stable than the spherical shape. With 800 nm femtosecond laser irradiation, only tip-rounded nanoprisms are observed and no spherical nanoparticles are formed at the laser powers used. This is most likely due to the blueshift of the plasmon absorp...
TL;DR: A new strategy for the fabrication of arrayed colloidal particles well-ordered nanometric holes of three or four fold symmetry by anisotropic reactive ion (plasma) etching of self-organized layers of colloidal spheres is developed.
Abstract: In summary, we have developed a new strategy for the fabrication of arrayed colloidal particles well-ordered nanometric holes of three or four fold symmetry by anisotropic reactive ion (plasma) etching of self-organized layers of colloidal spheres. We demonstrated that a mesoporous silica matrix with regular open windows could be used as a lithographic mask and the resulting arrangement of pores on a particle was dependent on the orientation of the colloidal particle stacking. A variety of organic and inorganic materials such as metals for metal−polymer composites, DNA and proteins, semiconducting and ceramic materials, and other polymers and small chemicals can be incorporated via chemical and physical attachment. Particles with patterned pores and composite particles by our nanomachining process can be used as novel functional materials in the field of electronics, photonics, and biotech areas.
TL;DR: In this article, it is shown that third harmonic Nd:YAG pulse laser irradiation (15 mJ/cm2 per pulse) leads to an evolution from the initial polycrystalline, triangular shaped particles to spherical single crystalline particles.
Abstract: Laser morphological manipulation has been performed on gold nanoparticles periodically arranged on solid supports by nanosphere lithography It is shown that third harmonic Nd:YAG pulse laser irradiation (15 mJ/cm2 per pulse) leads to an evolution from the initial polycrystalline, triangular shaped particles to spherical single crystalline particles These morphological changes are accompanied by a significant change in the optical absorption properties of the array This study demonstrates that laser irradiation is an excellent technique to control the properties of nanostructured materials on solid supports Further, it is suggested that the selected area treatment possible with the laser is a valuable new technique for designing functional nanomaterials for applications such as high-density data storage devices
TL;DR: In this article, a spring-block stick-slip model is introduced for simulating the phenomenon and the influence of several controllable parameters on the final structure is investigated.
TL;DR: In this article, a periodic array of vertically aligned isolated carbon nanofibers (CNFs) have been fabricated using self-assembled polystyrene spheres as shadow masks for catalyst-pattern formation.
Abstract: Periodic arrays of vertically aligned isolated carbon nanofibers (CNFs) have been fabricated using self-assembled polystyrene spheres as shadow masks for catalyst-pattern formation. Proper use of monolayer and bilayer masks, and judicial combination of angle-deposition technique with monolayer masks have allowed us to control the dot size and spacing of catalyst patterns. As long as the catalyst-dot size is not too large, isolated single CNF has grown from each catalyst dot. Combining nanosphere lithography with conventional photolithography, we have been able to realize patterned growth of CNF arrays on selected areas.
TL;DR: It is demonstrated that colloidal lithography with self-assembled monolayers of crosslinkable polymeric particles can be used to create hierarchical arrays of nanopores on substrates.
TL;DR: In this article, the deformation of soft polystyrene spheres is found to limit the usefulness of nanosphere lithography in high-density applications because of the eventual closure of the void areas between the self-assembled nanospheres which function as channels for material deposition.
Abstract: The deformation of 'soft' polystyrene spheres is found to limit the usefulness of nanosphere lithography in high-density applications because of the eventual closure of the void areas between the self-assembled nanospheres which function as channels for material deposition. We have used a plasma etching technique to reopen and enlarge these channels in the template in a controlled manner. This enables the controlled fabrication of a range of nanoarrays of very high density and variable sizes. The resulting shape of the nanodots produced can be understood by considering the etching-induced surface diffusion of the polystyrene in the plasma treatment.
TL;DR: In this paper, a large-area ordered 512nm pitch hole array, with vertical and smooth sidewalls, has been successfully formed on a GaAs substrate, indicating the potential application in photonic crystal devices of this method.
Abstract: Two-dimensional (2D) photonic crystal patterns have been fabricated by an improved nanosphere lithography method. By introducing an intermediary SiO2 layer between the self-assembled layer and the substrate, this method can be applied to a wide range of materials without much concern for their surface hydrophilicity. The controllability of the photonic crystal patterns has also been investigated. The air-filling factor of the photonic crystal patterns can be easily tailored by thinning the polymer nanospheres in inductively coupled O2 plasma with a controllable etch rate. Large-area ordered 512nm pitch hole array, with vertical and smooth sidewalls, has been successfully formed on a GaAs substrate, indicating the potential application in photonic crystal devices of this method.
TL;DR: In this paper, Nanosphere lithography was used to fabricate surface patterns on glass substrate using polystyrene (PS) colloidal microspheres and a carbon precursor, namely, sucrose solution, was infiltrated into the voids between the spheres.
Abstract: Nanosphere lithography was used to fabricate surface patterns on glass substrate. Polystyrene (PS) colloidal microspheres were first fabricated into an ordered monolayer/multilayers on the substrate via self-assembly process using a flow-controlled vertical deposition (FCVD) method. A carbon precursor, namely, sucrose solution, was infiltrated into the voids between the spheres. Carbonization of sucrose ended up with the formation of glassy carbons. Removal of the colloidal spheres left behind a surface pattern of thin carbon film. Depending on the template structures, the carbon patterns can be quadrangular or hexagonal in shape. A further step was taken to use the patterns as a template to grow silica spheres with a nonclose-packed structure.
TL;DR: A comparative analysis of the properties of two optical biosensor platforms encompasses a comprehensive set of non-specific binding studies demonstrate that the single transduction mechanism is due to the specific binding of ConA to the mannose-functionalized surface.
Abstract: This work encompasses a comparative analysis of the properties of two optical biosensor platforms: (1) the propagating surface plasmon resonance (SPR) sensor based on a planar, thin film gold surface and (2) the localized surface plasmon resonance (LSPR) sensor based on surface confined Ag nanoparticles fabricated by nanosphere lithography. The binding of Concanavalin A (ConA) to mannose-functionalized self-assembled monolayers (SAMs) is chosen to illustrate the similarities and the differences of these sensors. A comprehensive set of non-specific binding studies demonstrate that the single transduction mechanism is due to the specific binding of ConA to the mannose-functionalized surface. Finally, an elementary (2x1) multiplexed version of a LSPR carbohydrate sensing chip to probe the simultaneous binding of ConA to mannose and galactose-functionalized SAMs is also demonstrated.
TL;DR: In this paper, the authors present fabrication techniques for leveraging micro-and nanostructures on biodegradable polymers, such as replication molding, laser interference lithography, nanosphere lithography and block copolymer lithography.
Journal Article•
TL;DR: In this article, a 2D hexagonal array of uniformly sized nano-holes, whose average size can be potentially changed from 50 nm to 240 nm, was fabricated using the etched nanosphere lithography (NSL) method.
Abstract: A 2-dimensional hexagonal array of uniformly sized nano-holes, whose average size can be potentially changed from 50 nm to 240 nm, was fabricated using the etched nanosphere lithography (NSL) method. The conventional NSL method utilizing polystyrene beads (PS) coated on a Si substrate often suffers from a loss of uniformity during the etching of the PS beads. It was demonstrated that the uniformity of the hole size and position can be greatly improved by inserting a polyimide (PI) film between the Si substrate and the PS beads. A sufficiently thick (~40 run) PI film can act as a sacrificial layer, minimizing the rebound of the plasma during the reactive ion etching of the PS beads. Hence, the etching of the PS beads stabilized by the PI film can be used to determine the final desired size of the hole. The periodicity of the pattern can also be selected by changing the initial PS bead diameter.
TL;DR: In this paper, students explore the parallel fabrication technique known as nanosphere lithography to create patterns using small nylon spheres as a nanosphere mask and talcum powder as the material deposited through the mask to form desired particle patterns.
Abstract: In this Activity, students are introduced to the unique challenges of nanoscale fabrication. They will learn the general principles of serial and parallel nanofabrication techniques. Using a macroscale analogy, students explore the parallel fabrication technique known as nanosphere lithography to create patterns. The representation of the technique uses small nylon spheres as a nanosphere mask and talcum powder as the material deposited through the mask to form desired particle patterns.
TL;DR: In this article, large-area arrays of size-tunable Co nanomagnets have been fabricated using a methodology based on nanosphere lithography using a monolayer of latex spheres as an inverse mask for the formation of Co elements by electrodeposition.
Abstract: Large-area arrays of size-tunable Co nanomagnets have been fabricated using a methodology based on nanosphere lithography. The technique employs a monolayer of latex spheres as an inverse mask for the formation of Co elements by electrodeposition. By tuning the size of the spheres with reactive ion etching, magnetic elements of 310 and 240nm diameter have been obtained. Analysis of the arrays using high-field torque magnetometry and three-dimensional micromagnetic modeling clearly demonstrates a change in anisotropy as the diameter of the elements is reduced. More detailed investigation of the field dependence indicates the presence of magnetic vortices at low fields.