The sub-micron hole array in sapphire produced by inductively-coupled plasma reactive ion etching

The sub-micron hole array in a sapphire substrate was fabricated by using nanosphere lithography (NSL) combined with inductively-coupled-plasma reactive ion etching (ICP-RIE) technique. Polystyrene nanospheres of about 600 nm diameter were self-assembled on c-plane sapphire substrates by the spin-coating method. The diameter of polystyrene nanosphere was modified by using oxygen plasma in ICP-RIE system. The size of nanosphere modified by oxygen plasma was varied from 550 to 450 nm with different etching times from 15 to 35 s. The chromium thin film of 100 nm thick was then deposited on the shrunk nanospheres on the substrate by electron-beam evaporation system. The honeycomb type chromium mask can be obtained on the sapphire substrate after the polystyrene nanospheres were removed. The substrate was further etched in two sets of chlorine/Argon and boron trichloride/Argon mixture gases at constant pressure of 50 mTorr in ICP-RIE processes. The 400 nm hole array in diameter can be successfully produced under suitable boron trichloride/Argon gas flow ratio.     

Extending nanosphere lithography for the fabrication of periodic arrays of subwavelength metallic nanoholes

In this work we extend the classical nanosphere lithography method to the fabrication of subwavelength metallic nanohole arrays. By combining the reactive ion etching of self-assembled films of polystyrene nanospheres with metal deposition, ordered arrays of nanoholes of different sizes were fabricated. These structures exhibit a well-defined optical response different from that of the regular triangular array and continuous metallic film.     

Surface texturing of GaAs using a nanosphere lithography technique for solar cell applications

In this study, we present novel methods to texture the surface of GaAs substrates using the nanosphere lithography (NSL) technique that is based on arrays of SiO₂ nanospheres. Closed-packed arrays of SiO₂ nanospheres were formed on a benzocyclobutene (BCB) layer, followed by embedding SiO₂ nanospheres into the BCB layer. To texture the GaAs surface, three patterns were fabricated by nanosphere lithography. First, a convex pattern from the shape of the nanospheres was produced on the surface of GaAs. Second, a concave shape was produced on the surface of GaAs by additional wet etching to remove SiO₂ nanospheres. These two methods were found to be effective in reducing the reflectance to a range of 400-800 nm. Finally, the arrays of SiO₂ nanospheres were transferred onto the GaAs by dry-etching using a mixture of Cl₂ and BCl₃ gases, resulting in arrays of GaAs nanorods. The dry-etched surface structure showed the lowest reflectance.     

Hollow hematite nanosphere/carbon nanotube composite: mass production and its high-rate lithium storage properties

Spray pyrolysis was used to produce hollow hematite (α-Fe(2)O(3)) nanosphere (HHNS)/carbon nanotube (CNT) composite on a large scale. The method offers simplicity, high productivity, versatility, low cost, and suitability for industry. The structure is composed of hollow nanospheres in a network of CNTs. The possible formation mechanism of hollow α-Fe(2)O(3) nanospheres is due to the rapid evaporation of water and the super-hydrophobicity of the CNT surface. The electrochemical tests show that the HHNS/CNT composite is a promising lithium storage material in terms of high capacity (～700 mAh g(-1)), good high-rate capability, and good cycle life (up to 150 cycles). The materials improve both lithium ion and electron transport, which are limiting factors on the high-rate capability of lithium-ion batteries. The production method can be easily adapted to produce a wide range of hollow metal oxide nanosphere/CNT composites.     

Periodic Large‐Area Metallic Split‐Ring Resonator Metamaterial Fabrication Based on Shadow Nanosphere Lithography

A fast and cheap, large‐area (>1 cm²), high‐coverage fabrication technique for periodic metallic split‐ring resonator metamaterials is presented, which allows control of inner‐ and outer‐ring diameters, gap angles, as well as thickness and periodicity. This method, based on shadow nanosphere lithography, uses tilted‐angle‐rotation thermal evaporation onto Langmuir–Blodgett‐type monolayers of close‐packed polystyrene nanospheres. Excellent agreement of the process parameters with a simplified model is demonstrated. Pronounced, tunable optical metamaterial resonances in the range of 100 THz are consistent with simulations.     

Preparation of hollow carbon nanospheres via explosive detonation

Hollow carbon nanospheres were prepared via a rapid detonation technique, by using negative-oxygen balance explosive trinitrotoluene and nickel powder as starting materials and inorganic acid as solvent. The carbon/metal nanocomposite particles precursor with core-shell structure was engendered firstly during detonation, and then the metal nickel core was dissolved through inorganic acid to attain the hollow carbon nanospheres. High-Resolution Transmission Electron Microscope, X-ray diffraction and Raman spectrum were used to characterize the precursor and the as-synthesized samples respectively. The results show that the external diameter of the hollow carbon nanospheres is 25-150 nm and the thickness of the wall is about 2-10 nm. The surface of hollow carbon nanosphere displays multilayer wall in structure with 0.35 nm space between the layers. Based on the experimental results, possible formation mechanism was also proposed.     

A study on the mechanical and electrical reliability of individual carbon nanotube field emission cathodes

Individual carbon nanotube (CNT) field emission characteristics present a number of advantages for potential applications in electron microscopy and electron beam lithography. Mechanical and electrical reliability of individual CNT cathodes, however, remains a challenge and thus device integration of these cathodes has been limited. In this work, we present an investigation into the reliability issues concerning individual CNT field emission cathodes. We also introduce and analyze the reliability of a novel individual CNT cathode. The cathode structure is composed of a multi-walled carbon nanotube (MWNT) attached by Joule heating to a nickel-coated Si microstructure. The junction of the CNT and the Si microstructure is mechanically and electrically robust to withstand the strong electric field conditions that are typical for field emission devices. An optimal Ni film coating of 25?nm on the Si microstructure is required for mechanical and electrical stability. Experimental current-voltage data for the new cathode structure definitively demonstrates carbon nanotube field emission. Additionally, we demonstrate that our new nanofabrication method is capable of producing sophisticated cathode structures that were previously not realizable, such as one consisting of two parallel MWNTs, with highly controlled CNT lengths with 40?nm accuracy and nanotube-to-nanotube separations of less than 10?μm.     

Fluorescence enhancement using silver nanotriangle arrays

We describe the fabrication of silver nanotriangle array using angle resolved nanosphere lithography and utilizing the same for enhancing fluorescence. The well established nanosphere lithography is modified by changing the angle of deposition between the nanosphere mask and the beam of silver being deposited resulting in nanotriangles of varying surface area and density. The 470 nm plasmon resonance wavelength of the substrate was determined using minimum reflectivity method which closely matches with excitation wavelength of the fluorophore. Ten times enhancement in fluorescence emission intensity is obtained from fluorescein isothiocyanate coated on top of silver nanotriangle array separated by a spacer layer of poly vinyl alcohol as compared to glass. The enhanced fluorescence emission is attributed to the increase in local field enhancement.     

Nano-patterning of an iCVD polymer, followed by covalent attachment of QDs

A novel method for processing sub-50 nm structures by using carbon nanotube (CNT) masks and integrating quantum dots (QDs) on patterned polymer substrates has been established. Poly(styrene-alt-maleic anhydride) (PSMa) was prepared by the initiated chemical vapor deposition (iCVD) method, an alternative to spin-on deposition. The sub-50 nm PSMa polymer patterns were prepared by low energy oxygen plasma etching by using CNTs as the masks. The water soluble, amine-functionalized QDs underwent the nucleophilic acyl substitution reaction with the PSMa containing anhydride functional groups. This integration method was designed to incorporate high performance QDs on inexpensive, lightweight flexible substrates.     

一种用于LSPR传感的纳米金属列阵制作方法

提出利用光刻定位自组装填充的方法制作纳米金属列阵．在平面基板上通过光刻手段制作具有列阵微区的定位模板,再利用单分散聚苯乙烯纳米球在微区里进行自组装,得到单层规则排布的纳米球结构;进一步沉积金属后,通过去牺牲层工艺去除球体,可得到呈六角形分布的纳米金属列阵结构;最后对获得的纳米金属列阵结构的形貌和光学性能进行分析,给出金属纳米列阵结构的电子显微镜照片和消光谱．     

Local-field enhancement of optical nonlinearities in the AGZO nano-triangle array

Enhancement of the third order optical nonlinearities in Ga and Al co-doped ZnO (AGZO) nano-triangle array was investigated by performing a Z-scan method with a femtosecond laser (800 nm, 40 fs). The AGZO nano-triangle array was fabricated on silica substrates by nanosphere lithography (NSL) method, showing a surface plasmon resonance (SPR) peak around 3 μm. The two photon absorption (TPA) coefficient and nonlinear refractive index of the AGZO nano-triangle array were determined to be 340 cm/GW and 3.22 × 10⁻² cm²/GW under an excitation intensity of 26 GW/cm². It shows a 3.4-fold enhancement of the nonlinear refraction in the AGZO array with respect to that in the AGZO film, which attributes to the local field enhancement effect. The finite-difference time-domain (FDTD) simulation was in agreement with the experimental results. It indicates that the AGZO nano-triangle arrays have potential applications for nonlinear optical devices like all-optical switching, optical limiting and other types of signal processing.     

A large-area nanoscale gold hemisphere pattern as a nanoelectrode array

Two-dimensional (2D) nanostructure patterns have extensive applications in photonic devices, nanoelectronics, electrochemical devices, biosensors, catalysts and high-density magnetic recording devices. It remains a challenge to develop low-cost, high-throughput, high-resolution techniques for the fabrication of large-area (wafer-scale) 2D nanostructure array patterns with controlled feature size, shape and pitch. The present work has demonstrated a low-cost, high-throughput, high-resolution approach for the fabrication of large-area, high-quality nanostructure array patterns by nanosphere lithography combined with electroplating. The gold hemisphere array pattern obtained is capable of functioning as a nanoelectrode array (NEA) in which the gold hemispheres act as individual electrodes that are separated with an insulating polypyrrole (PPY) film. Cyclic voltammetry measurement has shown a sigmoid-shaped voltammogram, which is characteristic of electrochemical characteristics of a nanoelectrode array. NEAs are expected to find extensive applications in fundamental electrochemistry studies and electrochemical devices.     

High-resolution nanosphere lithography (NSL) to fabricate highly-ordered ZnO nanorod arrays

Here we report our successful development of a high-resolution, low-cost, simple and convenient technique based on nanosphere lithography (NSL) to fabricate large-scale periodic gold nanoparticle pattern, which is the most common catalyst material in the synthesis of nanostructure and also a feature material for surface plasmon resonation (SPR) research. In order to improve lithography resolution by PS nanosphere self-assembling monolayer (SAM), we adapted the following steps in our fabrication strategy. The original continuous etching by oxygen plasma was replaced by multiple short treatments to avoid heating effect. In addition, direct oxidation was utilized to remove the nanospheres instead of the supersonic process. Using the obtained Au nanoparticle pattern, ZnO nanorod arrays with an average diameter of 50 nm were easily obtained by 600 nm PS nanospheres SAM, which was even smaller than the minimum size by utilizing 400 nm nanospheres SAM in the previous work. Thus, we succeeded in the fabrication of highly-ordered ZnO nanorod arrays with largely tunable diameter by this higher-resolution nanosphere lithography. We also present X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL) and Raman results of our as-grown samples, indicating great crystallization quality and optical property.     

Fabrication of monolayer of polymer/nanospheres hybrid at a water-air interface

A new type of polymer-assisted self-assembly of nanospheres at a water-air interface was uncovered. By adding merely 1-3 ppm of polyethylene oxide in the water, the polystyrene nanospheres, applicable to diameters ranging from 100 nm to 1 μm, were found to gradually move closer to each other and eventually form a close-packed structure confirmed from its diffraction pattern. As it turns out, polyethylene oxides are adsorbed onto the surface of polystyrene nanospheres, giving rise to the effective screening of coulomb repulsive force between nanospheres followed by the onset of polymer-bridging effect as demonstrated from the strong suppression of Brownian motion. The resulting monolayer of close-packed polymer/nanospheres hybrid at the water-air interface with area size more than 1 cm(2) are robust and can be transferred to a substrate of any kind without serious breaking due to surface tension tearing. Our finding may provide a further extension to the scope of nanosphere lithography technique.     

Simulation of the elastic response and the buckling modes of single-walled carbon nanotubes

The mechanical behavior of carbon nanotube (CNT) is one of the basic problems on the nanotube composite and nano machinery. Molecular dynamics is an effective way of investigating the behavior of nano structures. The compression deformation of single-walled carbon nanotubes (SWCNTs) is simulated, using the Tersoff–Brenner potential to describe the interactions of atoms in CNT. From the MD simulation for some SWCNTs whose diameters range from 0.5 nm to 1.7 nm and length ranges from 7 nm to 19 nm, respectively, we get the Young’s modulus from 1.25 TPa to 1.48 TPa. The Young’s modulus of CNT decreases as the radius of CNT increases. The Young’s modulus of zigzag CNT is higher than that of armchair CNT. The results also show that there are two different buckling modes for SWCNTs. The difference between the buckling behavior in macroscopic scale and that in nano scale is studied.     

Characterization of metal-modified and vertically-aligned carbon nanotube films for functionally enhanced gas sensor applications

Carbon nanotube (CNT) networked films have been grown by radiofrequency plasma enhanced chemical vapour deposition (RF-PECVD) technology onto low-cost alumina substrates, coated by nanosized Fe-catalyst for growing CNTs, to perform chemical detection of hazardous gases, at an operating sensor temperature in the range 25-150 °C. The morphology and structure of the CNT networks have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The carbon nanotubes were “forest-like” with ropes vertically-aligned to the substrate surface. A dense network of bundles of multiple tubes consisting of multi-walled carbon nanostructures appears with a maximum length of 7-10 μm and single-tube diameter varying in the range of 5-35 nm. Surface functionalizations of the vertically-aligned CNT networks with nominally 5 nm thick Pt-, Ru- and Ag-nanoclusters, prepared by magnetron sputtering, provide higher sensitivity for significantly enhanced gas detection of NO₂, H₂, ethanol and toluene up to a low limit of sub-ppm level. The measured electrical conductance of the functionalized CNTs upon exposures of a given oxidizing and reducing gas is modulated by a charge transfer model with p-type semiconducting characteristics. Functionalized CNT gas sensors exhibited better performances compared to unmodified CNTs, making them highly promising candidates for environmental air monitoring applications, at ppb-level of toxic gas detection.     

Improving mechanical and electrical properties of oriented polymer-free multi-walled carbon nanotube paper by spraying while winding

In this study, a new method is introduced for fabricating carbon nanotube (CNT) paper, in which the solvent is sprayed on the CNT sheet while it is wound on a rotating mandrel. As the solvent evaporated, the capillary force pulls CNT closer together, resulting in a CNT paper with a high degree of alignment and a high packing density. Three batches of multi-walled CNTs with different wall thicknesses, tube diameters and lengths are utilized for synthesizing highly oriented CNT papers. It is found that CNTs with smallest diameter of 8 nm form strongest CNT paper with a tensile strength of 563 MPa and a tensile modulus of 15 GPa, while that made with CNTs of 10 nm diameter shows the highest electrical conductivity of 5.5 × 10⁴ S/m.     

Large-scale submicron horizontally aligned single-walled carbon nanotube surface arrays on various substrates produced by a fluidic assembly method

Single-walled carbon nanotube (CNT) arrays have been assembled on various substrates over mm-scale surface areas by combining fluidic alignment with soft lithography (micropatterning in capillaries) techniques. The feature size of the nanotube patterns reaches down to submicrometre scale. To this end, tailored substrate surface modification and pre-alignment of chopped CNTs in suspension are highly critical.     

Enhanced light extraction efficiency for glass scintillator coupled with two-dimensional photonic crystal structure

In order to improve the light extraction efficiency for Tb³⁺-doped glass scintillator, we propose an effective approach by incorporating a two-dimensional photonic crystal structure: a periodic array of hexagonally close-packed polystyrene nanosphere monolayer onto glass surface. The in-plane vector for the light suffering total internal reflection is changed into light cone resulting light emission out of glass. The optimized diameter of polystyrene nanosphere is 500 nm and the maximum enhancement of extraction efficiency reaches 25%. The enhancement shows angular dependence from the far-filed distribution pattern.     

Experimental Reconstruction of Thermal Parameters in CNT Array Multilayer Structure

The thermal conductivities, thermal diffusivity, thermal anisotropy ratio, and thermal boundary resistance for the multilayered microstructure of a carbon nanotube (CNT) array are reconstructed experimentally using the 3ω method with two different width metal heaters. The thermal impedance in the frequency domain and sensitivity coefficients are introduced to simultaneously determine the multiple thermal parameters. The thermal conductivity at 295 K is 38 W · m⁻¹ · K⁻¹ along the nanotube growth direction, and two orders of magnitude lower in the direction perpendicular to the tubes with the anisotropy ratio as large as 86. Separation of the contact and CNT array resistances is realized through circuit modeling. The measured thermal boundary resistances of the CNT array/Si substrate and insulating diamond film interfaces are 3.1 m² · K · MW⁻¹ and 18.4 m² · K · MW⁻¹, respectively. The measured thermal boundary resistance between the heater and diamond film is 0.085 m² · K · MW⁻¹ using a reference sample without a CNT array. The thermal conductivity for a CNT array already exceeds those of phase-changing thermal interface materials used in microelectronics.