Showing papers on "Nanosphere lithography published in 2010"

Ordered Nanowire Array Blue/Near-UV Light Emitting Diodes

Abstract: [∗] S. Xu , C. Xu , Y. Liu , Y. F. Hu , R. S. Yang , Q. Yang , Prof. Z. L. Wang School of Materials Science and Engineering Georgia Institute of Technology Atlanta, Georgia, 30332–0245 (USA) E-mail: zlwang@gatech.edu J. H. Ryou , H. J. Kim , Z. Lochner , S. Choi , Prof. R. Dupuis School of Electrical and Computer Engineering Georgia Institute of Technology Atlanta, Georgia, 30332–0245 (USA) ZnO-based light emitting diodes (LEDs) have been considered as a potential candidate for the next generation of blue/ near-UV light sources, [ 1 ] due to a direct wide bandgap energy of 3.37 eV, a large exciton binding energy of 60 meV at room temperature, and several other manufacturing advantages of ZnO. [ 2 ] While the pursuit of stable and reproducible p-ZnO is still undergoing, [ 3,4 ] heterojunctions of n-ZnO and p-GaN are employed as an alternative approach in this regard by considering the similar crystallographic and electronic properties of ZnO and GaN. [ 5–7 ] Compared with the thin fi lm/thin fi lm LEDs, [ 5,6 , 8 ] which may suffer from the total internal refl ection, n-ZnO nanowire/p-GaN thin fi lm heterostructures are utilized in order to increase the extraction effi ciency of the LEDs by virtue of the waveguiding properties of the nanowires. [ 9–11 ] But in all of these cases, the n-ZnO nanowires are randomly distributed on the substrate, which largely limits their applications in high performance optoelectronic devices. Here in this work, we demonstrate the capability of controlling the spatial distribution of the blue/near-UV LEDs composed of position controlled arrays of n-ZnO nanowires on a p-GaN thin fi lm substrate. The device was fabricated by a conjunction of low temperature wet chemical methods and electron beam lithography (EBL). The EBL could be replaced by other more convenient patterning techniques, such as photolithography and nanosphere lithography, rendering our technique low cost and capable of scaling up easily. Under forward bias, each single nanowire is a light emitter. By Gaussian deconvolution of the emission spectrum, the origins of the blue/nearUV emission are assigned particularly to three distinct electronhole recombination processes. By virtue of the nanowire/thin fi lm heterostructures, these LEDs give an external quantum effi ciency of 2.5%. This approach has great potential applications in high resolution electronic display, optical interconnect, and high density data storage. The design of the LED is shown in Figure 1a . Ordered ZnO nanowire arrays were grown on p-GaN (Figure 1 b–d), [ 12–14 ]

Particle Lithography from Colloidal Self-Assembly at Liquid−Liquid Interfaces

Abstract: Particle lithography has been extensively used as a robust and cost-effective method to produce large-area, close-packed arrays of nanometer scale features. Many technological applications, including biosensing, require instead non-close-packed patterns in order to avoid cross-talk between the features. We present a simple, scalable, single-step particle lithography process that employs colloidal self-assembly at liquid-liquid interfaces (SALI) to fabricate regular, open particle lithography masks, where the size of the features (40 to 500 nm) and their separation can be independently controlled between 3 and 10 particle diameters. Finally we show how the process can be practically employed to produce diverse biosensing structures.

Nanohole arrays in chemical analysis: manufacturing methods and applications

Abstract: Since the last decade, nanohole arrays have emerged from an interesting optical phenomenon to the development of applications in photophysical studies, photovoltaics and as a sensing template for chemical and biological analyses. Numerous methodologies have been designed to manufacture nanohole arrays, including the use of focus ion beam milling, soft-imprint lithography, colloidal lithography and, more recently, modified nanosphere lithography (NSL). With NSL or colloidal lithography, the experimental conditions control the density of the nanosphere mask and, thus, the aspect of the nanohole arrays. Low surface coverage of the nanosphere mask produces disordered nanoholes. Ordered nanohole arrays are obtained with a densely packed nanosphere mask in combination with electrochemical deposition of the metal, glancing angle deposition (GLAD) or etching of the nanospheres prior to metal deposition. A review of these methodologies is presented here with an emphasis on the optical properties of nanoholes interesting in analytical chemistry. In particular, applications of these novel plasmonic materials will be demonstrated as substrates for a localized surface plasmon resonance (LSPR), Surface Plasmon Resonance (SPR), surface enhanced Raman spectroscopy (SERS), and in electrochemistry with nano-patterned electrodes.

Facile Fabrication of Two-Dimensionally Ordered Macroporous Silver Thin Films and Their Application in Molecular Sensing

Abstract: Large-area, freestanding, two-dimensionally ordered macroporous (2DOM) Ag thin films with adjustable periodic spacings and good mechanical robustness were fabricated via nanosphere lithography at the solution surface (NSLSS) combined with interfacial reactions. The obtained 2DOM Ag thin films exhibited typical properties of plasmonic crystals with well-resolved reflectivity dips and vivid colors. The facile NSLSS method enabled the 2DOM Ag thin films to be readily transferred to arbitrary substrates to realize application as thin film sensors. Their application as both a surface plasmon resonance (SPR) sensor and a surface-enhanced Raman scattering (SERS) sensor in the detection of both small molecules and biological macromolecules were explored. As SERS substrates for the detection of 4-aminothiopheno) (4-ATP) molecules, the 2DOM Ag thin films showed enhancement factors as high as the 10 7 order, which made them a promising sensor for the detection of trace amount of analyte adsorbed on the surface. As SPR sensors, the 2DOM Ag thin films modified with a self-assembled monolayer of recognizing molecules as binding sites showed remarkable shift in the reflectivity dips responsive to the chemical environments. When used for the specific detection of avidin molecules, the 2DOM Ag thin film biosensors exhibited excellent performance with low detection limit (≈700 pM) and broad working range (100 pM-200 nM), indicating that they may be a promising candidate for high-performance biosensors.

Tuning plasmonic interaction between gold nanorings and a gold film for surface enhanced Raman scattering

Abstract: We investigate the plasmonic properties of gold nanorings in close proximity to a gold film. The rings have been fabricated using nanosphere lithography and are optimized to boost their near-infrared surface enhanced Raman scattering (SERS) effects. A SERS enhancement factor as large as 1.4×107 has been achieved by tuning the separation between the gold nanorings and the gold film. In addition, we have numerically and experimentally demonstrated an enhanced tunability of the plasmon resonance wavelength and a narrowing of the plasmon linewidth for increasing ring-film interaction.

Nanosphere Lithography at the Gas/Liquid Interface: A General Approach toward Free-Standing High-Quality Nanonets

Abstract: A general nanosphere lithography (NSL) approach toward facile fabrication of free-standing, large-area, high-quality nanonets was developed, which was based on a floating colloidal crystal monolayer (CCM) mask at the gas/liquid interface for materials deposition via interfacial reactions. The hole size, spacing, and thickness of the highly ordered nanonets, which showed interesting photonic properties, can be readily adjusted. This NSL approach at the gas/liquid interface can be easily extended to fabricate large-area ordered nanonets of various metal sulfides, metals as well as inorganic minerals. Furthermore, a variety of ordered gold nanoarrays with unusual patterns were produced by using nanonet bilayers as unique deposition masks, suggesting that the obtained transferable, high-quality nanonets can function as versatile lithographic masks to generate novel nanopatterns.

Fabrication of centimeter-sized single-domain two-dimensional colloidal crystals in a wedge-shaped cell under capillary forces.

Abstract: Self-assembly of colloidal spheres confined within cells of different shapes formed with two slides under capillary forces are studied. It is found that by controlling the shape of the cell the curvature of the drying front can result in a significant effect on the self-organization process. A curved drying front formed within parallel slides is always associated with growth of colloidal crystal structures with a high density of disorder. We demonstrate that single-domain two-dimensional colloidal crystals with centimeter size can be grown under capillary forces under a straight drying front formed in a wedge-shaped cell. These findings are demonstrated by laser diffraction, microscopy imaging methods and off-normal optical transmission measurements. The present growth method should be of importance in expanding colloidal crystal applications in angle-resolved nanosphere lithography, as well as in preparation of high-quality quasi-three-dimensional plasmonic crystals.

Optical Properties of Au, Ag, and Bimetallic Au on Ag Nanohole Arrays

Abstract: A systematic study of the optical properties and analytical response is reported for gold and silver nanohole arrays with different hole diameters with a fixed periodicity of 450 nm. Nanosphere lithography in combination with oxygen plasma etching has been used to fabricate the nanohole arrays. The plasmonic response of nanohole arrays is characterized in transmission spectroscopy (λ = 500−1000 nm spectral region), which varied with the metal composition and diameter of the nanoholes. The sensitivity to bulk refractive index (in nm/RIU) and the full width at half-maximum (FWHM) were measured for each plasmonic mode to compare the biosensing potential of the various nanohole arrays. A sensitivity of nearly 400 nm/RIU was observed and was maximal with the plasmonic band at λ = 554 nm for Ag nanohole arrays with the smallest hole diameter of 120 nm. Generally, the ratio of the full height (transmission intensity) and FWHM is constant for various hole diameters with Au nanohole arrays, whereas it improves for...

Size-related third-order optical nonlinearities of Au nanoparticle arrays.

Abstract: We report a systematic study of the size-related nonlinear optical properties of triangular Au particles. The triangular Au nanoparticle arrays of four sizes (37 nm, 70 nm, 140 nm and 190 nm) were fabricated on quartz substrates using nanosphere lithography. By performing the Z-scan method with femtosecond laser (800 nm, 50 fs), the optical nonlinearities of Au nanoparticle arrays were determined. The results showed a size-related competition between two mechanisms of ground-state bleaching and two-photon absorption. As the size increased, the nonlinear absorption changed from two-photon absorption to saturated absorption, while the nonlinear refraction changed from self-defocusing to self-focusing. These size-tunable nonlinearities make it possible to optimize the one- and two-photon figures of merit, W and T, for all-optical switching.

Directional photofluidization lithography for nanoarchitectures with controlled shapes and sizes.

Abstract: Highly ordered metallic nanostructures have attracted an increasing interest in nanoscale electronics, photonics, and spectroscopic imaging. However, methods typically used for fabricating metallic nanostructures, such as direct writing and template-based nanolithography, have low throughput and are, moreover, limited to specific fabricated shapes such as holes, lines, and prisms, respectively. Herein, we demonstrate directional photofluidization lithography (DPL) as a new method to address the aforementioned problems of current nanolithography. The key idea of DPL is the use of photoreconfigurable polymer arrays to be molded in metallic nanostructures instead of conventional colloids or cross-linked polymer arrays. The photoreconfiguration of polymers by directional photofluidization allows unprecedented control over the sizes and shapes of metallic nanostructures. Besides the capability for precise control of structural features, DPL ensures scalable, parallel, and cost-effective processing, highly compatible with high-throughput fabrication. Therefore, DPL can expand not only the potential for specific metallic nanostructure applications but also large-scale innovative nanolithography.

High performance InGaN/GaN nanorod light emitting diode arrays fabricated by nanosphere lithography and chemical mechanical polishing processes.

Abstract: We fabricated InGaN/GaN nanorod light emitting diode (LED) arrays using nanosphere lithography for nanorod formation, PECVD (plasma enhanced chemical vapor deposition) grown SiO2 layer for sidewall passivation, and chemical mechanical polishing for uniform nanorod contact. The nano-device demonstrates a reverse current 4.77nA at −5V, an ideality factor 7.35, and an optical output intensity 6807mW/cm2 at the injection current density 32A/cm2 (20mA). Moreover, the investigation of the droop effect for such a nanorod LED array reveals that junction heating is responsible for the sharp decrease at the low current.

Preparation of Nanoscale Ag Semishell Array with Tunable Interparticle Distance and Its Application in Surface-Enhanced Raman Scattering

Abstract: Nanoscale Ag semishell arrays with controlled size and tunable interparticle distance were prepared by combining nanosphere lithography with reactive ion etching. First, a large-area ordered monolayer of polystyrene (PS) nanospheres was deposited on glass substrates using the Langmuir−Blodgett (LB) technique. The PS spheres with different diameters were employed in LB procedures. Second, the monolayers of PS spheres were etched to control the diameter and tune the interparticle distance. Finally, a Ag layer was evaporated on the etched PS templates. Ag films with periodical nanostructures were obtained and can be used as surface-enhanced Raman scattering (SERS) substrates. These substrates exhibited homogeneity and good enhancement ability. SERS enhancement factor (EF) was represented on the order of 104−105. The correlation between nanoscale morphology and SERS activity of the substrates was investigated. When the size of Ag-semishell was fixed, the EF value decreased with the increase of interparitcle d...

Reusable Localized Surface Plasmon Sensors Based on Ultrastable Nanostructures

Abstract: Nanoparticle arrays created by nanosphere lithography are widely used in sensing applications since their localized surface plasmon resonances are extremely sensitive to changes in the local dielectric environment. A major drawback for any biologically oriented sensing application of conventionally produced particle arrays is the lack of stability of the nanoparticles in aqueous media and buffer solutions. Here, a robust and reusable nanoscale sensing platform based on localized surface plasmon resonances of gold nanoparticles embedded in a silicon dioxide matrix is presented. The architecture exhibits extremely high stability in aqueous environments and can be regenerated several times by simple mechanical cleaning of the surface. The platforms surface is ultraflat by design, thus making it an ideal substrate for any bio-oriented sensing application.

Controlling SERS intensity by tuning the size and height of a silver nanoparticle array

Abstract: It is demonstrated that the surface-enhanced Raman scattering (SERS) intensity of R6G molecules adsorbed on a Ag nanoparticle array can be controlled by tuning the size and height of the nanoparticles. A firm Ag nanoparticle array was fabricated on glass substrate by using nanosphere lithography (NSL) combined with reactive ion etching (RIE). Different sizes of Ag nanoparticles were fabricated with seed polystyrene nanospheres ranging from 430 nm to 820 nm in diameter. By depositing different thicknesses of Ag film and lifting off nanospheres from the surface of the substrate, the height of the Ag nanoparticles can be tuned. It is observed that the SERS enhancement factor will increase when the size of the Ag nanoparticles decreases and the deposition thickness of the Ag film increases. An enhancement factor as high as 2×106 can be achieved when the size of the polystyrene nanospheres is 430 nm in diameter and the height of the Ag nanoparticles is 96 nm. By using a confocal Raman mapping technique, we also demonstrate that the intensity of Raman scattering is enhanced due to the local surface plasmon resonance (LSPR) occurring in the Ag nanoparticle array.

Improved optical transmission and current matching of a triple-junction solar cell utilizing sub-wavelength structures.

Abstract: Sub-wavelength antireflective structures are fabricated on a silicon nitride passivation layer of a Ga0.5In0.5P/GaAs/Ge triple-junction solar cell using polystyrene nanosphere lithography followed by anisotropic etching. The fabricated structures enhance optical transmission in the ultraviolet wavelength range, compared to a conventional single-layer antireflective coating (ARC). The transmission improvement contributes to an enhanced photocurrent, which is also verified by the external quantum efficiency characterization of the fabricated solar cells. Under one-sun illumination, the short-circuit current of a cell with sub-wavelength structures is enhanced by 46.1% and 3.4% due to much improved optical transmission and current matching, compared to cells without an ARC and with a conventional SiNx ARC, respectively. Further optimizations of the sub-wavelength structures including the periodicity and etching depth are conducted by performing comprehensive calculations based on a rigorous couple-wave analysis method.

Correlation and Characterization of Three-Dimensional Morphologically Dependent Localized Surface Plasmon Resonance Spectra of Single Silver Nanoparticles Using Dark-Field Optical Microscopy and Spectroscopy and Atomic Force Microscopy

Abstract: We have developed a new and effective methodology to correlate optical and atomic force microscopy (AFM) images of single Ag nanoparticles (NPs), allowing us to study three-dimensional (3D) morphologically dependent localized surface plasmon resonance (LSPR) spectra of individual Ag NPs We fabricated arrays of distinctive microwindows on glass coverslips using a photolithography method, and created well-isolated individual Ag NPs with a wide variety of shapes and morphologies on the glass coverslips using a modified nanosphere lithography (NSL) method Using distinctive geometries of microwindows, we located individual Ag NPs of interest in their optical and AFM images, enabling us to correlate and characterize the LSPR spectra and 3D morphologies of the same single NPs using dark-field optical microscopy and spectroscopy (DFOMS) and AFM, respectively We found that LSPR spectra of single Ag NPs, with nearly equal volume [(86 ± 04) × 103 nm3], cross-section [(22 ± 02) × 102 nm3], and height (396 ± 3

Nanoscale resistive switching and filamentary conduction in NiO thin films

Abstract: We fabricate regular arrays of nanoelectrodes on NiO thin films via nanosphere lithography and directly probe the nanoscale resistive switching using a conductive atomic force microscope. The unipolar resistive switching is consistent with the conducting filament formation/rupture mechanism, and the switching power is as low as 10−9 W. We find that only about half of devices are switchable, and the Monte Carlo simulation suggests strong correlations between the switching reliability, the electrode size, and the filament dimension and density.

Surface-Enhanced Raman Spectroscopy Amplification with Film over Etched Nanospheres

Abstract: Polymer nanosphere lithography (NSL) masks were etched in oxygen plasma prior to metal deposition, which tunes the localized surface plasmon resonance (LSPR) and the interparticle distance resulting in greater Raman amplification than conventional film over nanosphere (FON). Various nanosphere masks were investigated, using nanosphere sizes of 220, 360, 450, 520, and 650 nm etched from 0 (conventional FON) to 10 min. Thereby, the film over etched nanospheres (FOEN) amplifies by up to a factor of 4 the Raman response of 4-nitrobenzenethiol (4-NBT) on Ag as compared to unetched FON. The LSPR response of FOEN and SEM analysis of the gap distance revealed that the optimal amplification results from a combination of tuning the gap (a gap/diameter of less than 1 improves the Raman response), matching the laser excitation wavelength (633 and 785 nm both investigated), and an increasing roughness of FOEN. Metal multilayers of Ag and Au were also deposited to investigate the effect on the Raman and LSPR response. ...

Polymeric nanopillar arrays for cell traction force measurements.

Abstract: This paper reports the development of a novel force measurement device based on polymeric nanopillar arrays. The device was fabricated by a process combining nanosphere lithography, oxygen plasma treatment, deep etching and nano-molding. Well-ordered polymeric nanopillar arrays with various diameters and aspect ratios were fabricated and used as cell culture substrates. Cell traction forces were measured by the deflection of the nanopillars. Since the location of the nanopillars can be monitored at all times, this device allows for the measurement of the evolution of adhesion forces over time.

ZnO nanowire arrays – Pattern generation, growth and applications

Abstract: ZnO nanowires and related materials are in the focus of attention for electronic, optical or sensor applications. However, size, position and arrangement control are essential conditions for the development of future nanowire based devices. Various kinds of template methods including nanosphere lithography and UV laser interference lithography are powerful tools for the preparation of the starting metal catalyst arrays and will be demonstrated and discussed. However, only if the growth mechanism and its guiding parameters are understood in detail, the template will force a pattern arranged growth of nanowires. The paper gives an overview of the various kinds of growth modes for vertical arranged nanowires. Specific experimental conditions establishing the VS or the VLS growth are discussed. In addition, insight is given why the patterning is not all the time conserved and how to overcome these obstacles. In the second part different kinds of applications are summarized. Electronic properties are discussed based on metal-semiconductor-metal devices. The influence of a core-shell nanowire structure on the optical properties is demonstrated. In addition, a simple approach for ZnO nanowire based gas sensors is discussed and shown. As a last example, the transfer of Al 2 O 3 coated nanowires into spinel tubes is reported.

Localized surface plasmon resonance biosensing with large area of gold nanoholes fabricated by nanosphere lithography.

Abstract: Localized surface plasmon resonance (LSPR) has been extensively studied as potential chemical and biological sensing platform due to its high sensitivity to local refractive index change induced by molecule adsorbate. Previous experiments have demonstrated the LSPR generated by gold nanoholes and its biosensing. Here, we realize large uniform area of nanoholes on scale of cm2 on glass substrate by nanosphere lithography which is essential for mass production. The morphology of the nanoholes is characterized using scanning electron microscope and atomic force microscope. The LSPR sensitivity of the nanoholes to local refractive index is measured to be 36 nm/RIU. However, the chip has demonstrated high sensitivity and specificity in biosensing: bovine serum albumin adsorption is detected with LSPR peak redshift of 27 nm, and biotin-streptavidin immunoassay renders a LSPR redshift of 11 nm. This work forms a foundation toward the cost-effective, high-throughput, reliable and robust chip-based LSPR biosensor.

Controlled photochemical particle growth in two-dimensional ordered metal nanoparticle arrays

Abstract: We report on a universal technique which allows us to precisely manipulate the diameter of metal nanoparticles in two-dimensional particle arrays. The approach is demonstrated here for hexagonally ordered gold nanoparticle arrays fabricated by means of diblock copolymer micelle lithography (BCML). The particles are used as nucleation centers in seed-mediated photochemical metal deposition, whereby the particle diameter increases. Repeatedly combining photochemical growth with thermal annealing steps additionally facilitates controlling the shape of the particles.

Inexpensive and fast wafer-scale fabrication of nanohole arrays in thin gold films for plasmonics

Abstract: In this paper, a fast and inexpensive wafer-scale process for the fabrication of arrays of nanoscale holes in thin gold films for plasmonics is shown. The process combines nanosphere lithography using spin-coated polystyrene beads with a sputter-etching process. This allows the batch fabrication of several 1000 microm(2) large hole arrays in 200 nm thick gold films without the use of an adhesion layer for the gold film. The hole size and lattice period can be tuned independently with this method. This allows tuning of the optical properties of the hole arrays for the desired application. An example application, refractive index sensing, is demonstrated.

Optical properties and immunoassay applications of noble metal nanoparticles

Abstract: Noble metal, especially gold (Au) and silver (Ag) nanoparticles exhibit unique and tunable optical properties on account of their surface plasmon resonance (SPR). In this paper, we mainly discussed the theory background of the enhanced optical properties of noble metal nanoparticles. Mie theory, transfer matrix method, discrete dipole approximation (DDA) method, and finite-difference time domain (FDTD) method applied brute-force computational methods for different nanoparticles optical properties. Some important nanostructure fabrication technologies such as nanosphere lithography (NSL) and focused ion beam (FIB) are also introduced in this paper. Moreover, these fabricated nanostructures are used in the plasmonic sensing fields. The binding signal between the antibody and antigen, amyloid-derived diffusible ligands (ADDLs)-potential Alzheimer's disease (AD) biomarkers, and staphylococcal enterotixn B (SEB) in nano-Moore per liter (nM) concentration level are detected by our designed nanobiosensor. They have many potential applications in the biosensor, environment protection, food security, and medicine safety for health, and so forth, fields.

Hydrogenated amorphous silicon solar cell on glass substrate patterned by hexagonal nanocylinder array

Abstract: The hydrogenated amorphous silicon thin film solar cell fabricated on the glass substrate patterned by hexagonal nanocylinder array prepared by self-assembled SiO2 nanoparticles and nanosphere lithography was investigated. It is demonstrated that the short-circuit current of the patterned solar cell with 65 nm depth nanocylinder increases from 12.3 to 14.4 mA/cm2, and the efficiency increases from 5.18% to 6.59% as compared to the flat solar cell. These phenomena suggest that both effective light trapping and localized surface plasmon lead to significant improvement of light absorption in amorphous silicon solar cells.