Fabrication of nano patterns on various substrates using nanosphere lithography technique

This paper presents a procedure for fabricating large-area, size-tunable, metal arrays with a periodically different shape using Nanosphere Lithography (NSL). This technique has attracted considerable interest because of its important applications as diffraction devices, chemical and optical data recording. Their ordered arrays can be used for anti-reflection surfaces, bio-sensors and nanopatterning masks. Two different types of patterns, honeycomb and hexagonal patterns, could be fabricated on various substrates with different procedures. All steps for making different patterns employed a PS (polystyrene) monolayer by spin coating. Honeycomb patterns were fabricated by spin coating a PS monolayer on a glass substrate and depositing a metal followed by removal of the monolayer, whereas the hexagonal pattern was produced by the transfer of a gold deposited monolayer onto a GaN substrate using the same process. These processes allow simple and excellent control of the size and shape of the patterns. All experimental results on structure characterization and determination of the nanoparticle metrics were accomplished by atomic force microscopy and field emission-scanning electronic microscopy.     

Fabrication of large number density platinum nanowire arrays by size reduction lithography and nanoimprint lithography

Large number density Pt nanowires with typical dimensions of 12 microm x 20 nm x 5 nm (length x width x height) are fabricated on planar oxide supports. First sub-20 nm single crystalline silicon nanowires are fabricated by size reduction lithography, and then the Si nanowire pattern is replicated to produce a large number of Pt nanowires by nanoimprint lithography. The width and height of the Pt nanowires are uniform and are controlled with nanometer precision. The nanowire number density is 4 x 10(4) cm(-1), resulting in a Pt surface area larger than 2 cm(2) on a 5 x 5 cm(2) oxide substrate. Bimodal nanowires with different width have been generated by using a Pt shadow deposition technique. Using this technique, alternating 10 and 19 nm wide nanowires are produced.     

Fabrication of stacked-ring netted tubular constructs via 3D template electrohydrodynamic printing

Electrohydrodynamic (EHD) printing is an emerging additive manufacturing process which provides several opportunities for advanced fiber patterning and alignment. In this study, stacked-ring netted tubular constructs were printed using controlled EHD fiber deposition. To achieve this, a modified EHD system was developed which integrated air and heating moduli, in addition to a 3D cylindrical collector. The impact of additional peripheral components was evident through enhanced solidification of as-formed polycaprolactone (PCL) polymer fiber prints, which further enabled fabrication of stacked PCL fiber rings. Subsequently, stacked-ring netted tubular constructs (via x-axis deposition manipulation) were fabricated. Electric field simulations were used to elucidate construct formation mechanism. The modified printing system provides much needed control on fiber deposition and solidification, enabling integration of essential bio-interface features and morphologies (e.g., tissue structure and surface mimicry) for advanced 3D biomaterial engineering.     

Investigating the suitability of electrohydrodynamic lithography for the fabrication of cell substrates

We have investigated the feasibility of using electrohydrodynamic lithography (EHDL) to produce large lateral areas of patterned polymer substrates for use in biomedical applications. Half centimetered squared regions of uninterrupted patterning were obtained and characterised by profilometry and microscopy. The patterning was found to be elliptical in shape and was composed of concentric bands of distinct patterns centred on initial, randomly located nucleation sites. The size of the patterned area was limited by the degree to which the inter-electrode gap could be kept perfectly parallel, with a difference in height of just 15 nm influencing the patterning. Such sensitivity meant that issues such as the stiffness of the electrodes were important. Hierarchical patterning was achieved by combining EHDL with fracture-induced structuring. The substrates fabricated using EHDL were demonstrated to be viable for cell culture in vitro using fibroblast (3T3) and muscle (C2C12) cell lines.     

Fabrication of 3D copper oxide structure by holographic lithography for photoelectrochemical electrodes

We fabricated three-dimensional copper oxide structure by holographic lithography and electroless deposition. A five-beam interference pattern defined a woodpile structure of SU-8. The surface modification of SU-8 structure was achieved by multilayer coating of polyelectrolyte, which is critical for activating the surface for the reduction of copper. Copper was deposited onto the surface of the structure by electroless deposition, and subsequent calcinations removed the SU-8 structure and simultaneously oxidized the copper into copper oxide. The porous copper oxide structure was used as a photoelectrochemical electrode. Because of the highly porous structure, our structure showed higher photocurrent efficiency.     

Fabrication of multiplex quasi-three-dimensional grids of one-dimensional nanostructures via stepwise colloidal lithography

By using O2-plasma etched monolayers of hexagonally close-packed latex spheres as masks for metal vapor deposition, we successfully demonstrate a stepwise colloidal lithography to stepwise grow highly ordered multiplex quasi-three-dimensional grids of metallic one-dimensional nanostructures, e.g., nanowires and nanorods. The success of the present approach is centered at manipulation of the incidence angle of metal vapor beams with respect to the normal direction of colloidal masks and particularly the azimuth angle phi of the projection of the vapor beam incidence on the masks with respect to the vector from one sphere to the nearest neighbors. Stepwise deposition of different metals by regularly varying phi allows consecutively stacking of 1D nanostructures into multiplex quasi-3D grids. This stepwise angle-resolved colloidal lithography should provide a significant nanochemical complement of conventional lithographic techniques, enabling us to easily fabricate sophisticated 3D nanostructures with defined vertical and lateral heterogeneity.     

Fabrication of silicon nanowire for detecting p-amyloid (1-42) by nanoimprint lithography

Ultraviolet nanoimprint lithography (UV-NIL) is a high volume and cost-effective patterning technique with sub-10 nm resolution. It has great potential as a candidate for next generation lithography. Using UV-NIL, nanowire patterns were successfully fabricated on a four-inch silicon-on-insulator (SOI) wafer under moderate conditions. The fabricated nanowire patterns were characterized by FE-SEM. Its electrical properties were confirmed by semiconductor parameter analysis. Monoclonal antibodies against beta-amyloid (1-42) were immobilized on the silicon nanowire using a chemical linker. Using this fabricated silicon nanowire device, beta-amyloid (1-42) levels of 1 pM to 100 nM were successfully determined from conductance versus time characteristics. Consequently, the nanopatterned SOI nanowire device can be applied to bioplatforms for the detection of proteins.     

Fabrication of 3D functionalized microstructure via scanning probe lithography and self-assembly methods

A type of 2-dimensional planar pattern with spatial resolution can be easily produced using scanning probe lithography (SPL). However, it has not been used successfully for fabricating 3-dimensional (3D) structures due to the low aspect ratio of the resulting structure. Herein, we describe a method for fabricating a 3D functionalized structure via a combination of SPL and self-assembly techniques. In this study, a 3D structure was established on a Si surface with a passivated monolayer via SPL. The patterned layer was modified using a omega-functionalized organosilane. Lateral force microscopy (LFM) was applied to discriminate the chemical functionalities and gold nanoparticles were also used to clearly identify the modified layer.     

Nanoimprinting lithography of a two-layer phase mask for three-dimensional photonic structure holographic fabrications via single exposure

We report a combined holographic and nanoimprinting lithography technique to produce three-dimensional woodpile photonic crystal templates through only one single exposure. The interference lithography process uses an integratable diffractive optical element for large throughout 3D pattern manufacturing. The diffractive optical element consists of two layers of phase grating separated by an intermediate layer, fabricated by repeated nanoimprinting lithography, followed by an SU8 photoresist bonding technique. Grating periods, relative orientation, diffraction angle, and efficiency, as well as layer to layer phase delay, are well designed during manufacturing. By thermally optimizing the thickness of the intermediate layer, this paper demonstrates the fabrication of interconnected 3D photonic structures with arbitrary symmetry through a single laser exposure. The two-layer phase mask approach enables a CMOS-compatible monolithic integration of 3D photonic structures with other integrated optical elements and waveguides.     

Fabrication of moth eye structures via charged nanoparticle lithography with size and density control

We have developed and demonstrated an effective method for fabricating the moth eye structures formed by charged nanoparticle lithography (cNPL). We attached high-density gold nanoparticles (Au NPs) to GaN without aggregation by making the surface of Au NPs negatively charged and GaN positively charged. Au NPs were effectively used as an etching mask, and the moth eye structures of GaN were formed by inductively coupled plasma reactive ion etching. The moth eye structures with various sizes and densities were fabricated by the cNPL, and the moth eye structures reduced the reflectance. The cNPL, as a simple technique with size and density control, will provide high potential to optical device applications.     

Fabrication of large area hexagonal boron nitride thin films for bendable capacitors

Highly reliable and bendable dielectrics are desired in flexible or bendable electronic devices for future applications. Hexagonal boron nitride （h-BN） can be used as bendable dielectric due to its wide band gap. Here, we fabricate high quality h-BN films with controllable thickness by a low pressure chemical vapor deposition method. We demonstrate a parallel-plate capacitor using h-BN film as the dielectric. The h-BN capacitors are reliable with a high breakdown field strength of -9.0 MV/cm. Tunneling current across the h-BN film is inversely exponential to the thickness of dielectric, which makes the capacitance drop significantly. The h-BN capacitor shows a best specific capacitance of 6.8 F/cm^2, which is one order of magnitude higher than the calculated value.     

Synthesis of biocompatible, mesoporous Fe(3)O(4) nano/microspheres with large surface area for magnetic resonance imaging and therapeutic applications

This article reports the fabrication of mesoporous Fe(3)O(4) nano/microspheres with a high surface area value (163 m(2)/g, Brunauer-Emmett-Teller) and demonstrates their use for drug loading, release, and magnetic resonance imaging (MRI). These monodispersed, mesoporous Fe(3)O(4) nano/microspheres with controllable average sizes ranging from 50 to 200 nm were synthesized using a Fe(3)O(4)/poly(acrylic acid) hybrid sphere template and subsequent silica shell formation and removal. We found that the SiO(2) coating is a crucial step for the successful synthesis of uniform mesoporous Fe(3)O(4) nano/microspheres. The as-synthesized mesoporous Fe(3)O(4) nanospheres show a high magnetic saturation value (M(s) = 48.6 emu/g) and could be used as MRI contrast agents (r(2) = 36.3 s(-1) mM(-1)). Trypan blue exclusion and MTT assay (see Supporting Information ) cytotoxicity analyses of the nanospheres based on HepG2 and MDCK cells showed that the products were biocompatible, with a lower toxicity than lipofectamine (positive control). Hydrophilic ibuprofen and hydrophobic zinc(II) phthalocyanine drug loading into mesoporous Fe(3)O(4) nanospheres and selected release experiments were successfully achieved. The potential use of mesoporous Fe(3)O(4) nanospheres in biomedical applications, in light of the nano/microspheres' efficient drug loading and release, MRI, and low cytotoxicity, has been demonstrated. It is envisaged that mesoporous Fe(3)O(4) nanospheres can be used as drug carriers and MRI contrast agents for the reticuloendothelial system; they can also be delivered locally, such as via a selective catheter.     

Fabrication of alignment structures for a fiber resonator by use of deep-ultraviolet lithography

We present a novel method to mount and align an optical-fiber-based resonator on the flat surface of an atom chip with ultrahigh precision. The structures for mounting a pair of fibers, which constitute the fiber resonator, are produced by a spin-coated SU-8 photoresist technique by use of deep-UV lithography. The design and production of the SU-8 structures are discussed. From the measured finesses we calculate the coupling loss of the SU-8 structures acting as a kind of fiber splice to be smaller than 0.013 dB.     

Fabrication of hemispherical nano structure on a curved Al surface using low-temperature and high-voltage anodizing method

A simple method of fabricating hemispherical nanostructures on a curved aluminum rod surface was presented. In conventional methods of fabricating nanopatterns on a curved aluminum surface, mechanical or chemical processes have been widely used for the lens technologies. Such processes are not only expensive with long processing times, however, but they also involve local fabrication and are limited in the dimension size. In this paper, a method of fabricating hemispherical nanostructures on a curved aluminum surface is suggested for a functional three-dimensional (3D) master using a low-temperature and high-voltage (LTHV) anodizing method. By reducing the aluminum reaction rate under a low-temperature environment, the reaction current density can be remarkably reduced even though a high voltage was induced. Using the LTHV anodizing method, the hemispherical pattern size can be easily controlled with respect to voltage variations. The sizes of the hemispherical nanopatterns were about 150-300 nm. Using the LTHV anodizing process, hemispherical nanostructures can be obtained on a curved aluminum surface with controllable pattern sizes of 150-300 nm without defects such as burring from Joule's heat, micro-scratches, and cracks. A curved 3D hemispherical nanostructure may be used as a master in the roll-to-roll process.     

Fabrication and application of polyimide plastic molds for nanoimprint lithography

In this work, we have developed low-cost, high modulus, flexible, and UV transparent polyimide plastic molds for nanoimprint lithography (NIL). Different structures of poly(amic acids) (PAA) and polyimides (PI) have been synthesized. By casting the PAA or PI solutions on a silicon master, flexible but still rigid plastic molds can be produced. The advantages of the PI molds are: (1) high glass-transition temperatures (Tg) up to 310 degrees C, (2) high thermal stability over 500 degrees C, (3) high tensile modulus, and (4) UV transparency for use in UV-NIL. Various micrometer and nanometer scale patterns could be obtained from the PI molds on a large area (4 inch wafer). The imprinting results showed that the PI molds could be faithfully used for both hot embossing NIL and UV-NIL.     

有机太阳能电池ITO电极的光刻制备法及其研究

目前有机太阳能电池是光电行业研究的热点之一。通常该器件以ITO为阳极，通过真空蒸镀的方法制作。在对器件进行测试时，ITO电极的设计制作，有利于器件的保护。用光刻技术进行ITO电极的制作，可以得到非常精细的结果。重点阐述了利用光刻方法制作优良ITO电极的注意点，包括表面清洗、曝光控制、显影控制和腐蚀工艺，其中由于不同ITO玻璃的导电层厚度、各成分含量不同，所以腐蚀工艺的研究是重点中的重点。提供了对生成光刻ITO电极的质量进行准确评价的一种简便方法。     

Fabrication of fluorine-doped diamond-like carbon stamps for UV nanoimprint lithography

Two fluorine-doped diamond-like carbon (F-DLC) stamps with sub-100 nm line patterns were fabricated using a direct etching method. These were applied successfully to ultraviolet (UV) nanoimprint lithography without requiring an anti-adhesion layer coating. Tests were performed to determine the optimum fluorine concentration for the F-DLC stamps. The ideal stamp material consisted of 25?at.% F-DLC with a contact angle of 85°, UV transmittance of 16.4-26.8%, and hardness of 4.5?GPa. The O(2) plasma etch rate of the DLC was increased considerably by the fluorine doping, making it comparable to the etch rate of polymethyl methacrylate (PMMA). Thus, only PMMA was used as the etch mask in the fabrication of the stamps.     

Fabrication of large area nanoprism arrays and their application for surface enhanced Raman spectroscopy

This work demonstrates the fabrication of metallic nanoprism (triangular nanostructure) arrays using a low-cost and high-throughput process. In the method, the triangular structure is defined by the shadow of a pyramid during angle evaporation of a metal etching mask. The pyramids were created by nanoimprint lithography in polymethylmethacrylate (PMMA) using a mould having an inverse-pyramid-shaped hole array formed by KOH wet etching of silicon. Silver and gold nanoprism arrays with a period of 200?nm and an edge length of 100?nm have been fabricated and used as effective substrates for surface enhanced Raman spectroscopy (SERS) detection of rhodamine 6G (R6G) molecules. Numerical calculations confirmed the great enhancement of electric field near the sharp nanoprism corners, as well as the detrimental effect of the chromium adhesion layer on localized surface plasmon resonance. The current method can also be used to fabricate non-equilateral nanoprism and three-dimensional (3D) nanopyramid arrays, and it can be readily extended to other metals.