Advanced colloidal lithography for sub-100 nm lift-off structures

We report on the fabrication of hexagonally ordered, sub-wavelength hole arrays (SWHA) by colloidal lithography combined with reactive ion etching and a lift-off process, and their characterization with scanning electron microscopy and ellipsometry.     

Fabrication of high-quality colloidal crystal films by vertical deposition method integrated with a piezoelectric actuator

In recent years the self-assembling of monodispersed colloidal spheres has gained much attention due to their potentials in many fields. Though many self-assembling methods have been put forward, the existence of many defects in colloidal crystals is still an open question restricting the dimensions of ordered domains and the performance thereof in many applications. In this paper we introduced a modified vertical deposition method to improve film quality of colloidal crystal films. A piezoelectric actuator was integrated with the conventional vertical deposition method, which excited the substrate vibrating along the vertical direction. The vibratory amplitude and frequency of the actuator could be controlled by the driving voltage. Our experimental observations indicated that, grown at proper driving parameters, frequency of 300 Hz and vibratory amplitude of 310 nm in our current observations, film quality could be greatly improved with less defects. The mechanism was also briefly illuminated.     

Self-assembly of colloidal crystals from polystyrene emulsion at elevated temperature by dip-drawing method

The self-assembly of colloidal crystal arrays from polystyrene (PS) sphere emulsion at elevated temperature by dip-drawing method was investigated. The dependence of effective sphere transfer in the meniscus of emulsion on temperature was discussed. The results show that the assembled arrays formed at 50 °C have fewer defects than those at room temperature. The elevated emulsion temperature during the ordered arrangement of colloidal crystals causes quicker solvent evaporation, hence quicker sphere transfer. However, exceeding solvent flux and crystal growth induced by over high temperatures result in more fracture lines displayed in arrays. At 50 °C, the effective sphere transfer by the solvent flux to the array edge can also be enhanced by increasing the PS volume fraction of emulsion, which obviously reduces fracture lines on the surface of multilayer.     

Directed growth of colloidal crystals on a hydrophobic polymer film by using hydrophilic traps

Deposition of colloidal crystal films onto a hydrophobic surface using capillary force-induced self-assembly is difficult to achieve because of wetting problems of the aqueous colloids with the substrate. We present here a method to overcome this problem. By introducing a hydrophilic trench around the hydrophobic polymer, uniform crystalline colloidal films can be deposited onto the surface of the polymer, provided a sufficient volume of suspension is used. The hydrophilic area around the polymer acts like an artificial trap that can help pin the colloidal suspension on the surface of the hydrophobic polymer surface and direct the self-assembly of colloidal spheres, which is the key to fabricate a uniform colloidal crystal film on the polymer surface.     

Durability of nitrided fluorocarbon polymer films for nanoimprint lithography

Hydrophobic fluorocarbon polymer films have been used as anti-sticking and releasing coatings for templates in nano-imprint lithography, but have poor durability against repeated high pressure pressing processes. The addition of nitrogen into fluorocarbon-based gas plasma can provide nitrided fluorocarbon polymer films, as confirmed by Fourier-transform infrared spectroscopy. Fluorocarbon and nitrided fluorocarbon films have almost the same 110.0° contact angle with water drops. The nitrided fluorocarbon films are harder and significantly enhance durability as anti-sticking layers. Durability enhancement has been confirmed by fabricating replicas with silicon templates using nitrided fluorocarbon anti-sticking layers.     

Colloidal lithography and Metal-Organic Chemical Vapor Deposition process integration to fabricate ZnO nanohole arrays

A complete set up of optimal process conditions for an effective colloidal lithography/catalyst assisted MOCVD process integration is presented. It mainly focuses on the determination of the deposition temperature threshold for ZnO Metal-Organic Chemical Vapour Deposition (MOCVD) as well as the concentration of metal-organic silver (Ag) catalyst. Indeed, the optimization of such process parameters allows to tailor the ZnO film morphology in order to make the colloidal lithography/catalyst assisted MOCVD approach a valuable bottom up method to fabricate bi-dimensional ordered ZnO nanohole arrays.     

Distributed feedback leaky laser emission from dye doped gel-glass dispersed liquid crystal thin film patterned by soft lithography

Gel-glass dispersed liquid crystal (GDLC) thin films doped with organic laser dye Rhodamine 6G (R6G) were prepared via a sol-gel procedure of tetraethyl orthosilicate (TEOS) and ethyl triethoxisilane (ETES). As characterized by scanning electronic microscope (SEM), surface-relief structures were successfully patterned on lower refractive index GDLC thin films by soft lithographic technology, which support distributed feedback (DFB) laser emission based on leaky mode propagation. The performance of the DFB laser emission was investigated and the spectral narrowing of the emitted radiation and the fine structure pattern were found to be controlled by the doping concentration of liquid crystal (LC) 4-cyano-4′-pentylbiphenyl (5CB). We also showed the synchronous excitation of a DFB lasing with random lasing mediated by light scattering inside the same GDLC leaky waveguide.     

High-speed fabrication of 3-dimensional colloidal photonic crystal films by slide coating of polymer microspheres with continuous feeding of colloidal suspension

A simple, yet rapid fabrication method for large area colloidal crystal film is demonstrated. Aqueous colloidal dispersion sandwiched between a hydrophobic top cell and a hydrophilic bottom substrate formed a flat meniscus at the drying front, from which high quality colloidal crystal films were obtained within 20 min due to the strong capillary force exerted by accelerated water evaporation aided by hot air blowing. Continuous supply of the suspension enabled the fabrication of the colloidal crystal over large area (> 4 cm²) without significant loss of colloids.     

A comparison between bottom contact and top contact all organic field effect transistors assembled by soft lithography

All-organic Field Effect Transistors (FETs) on plastic were fabricated by means of an innovative, simple and inexpensive technique. A thin Mylar® foil acts both as substrate and gate dielectric. We used pentacene, deposited by thermal sublimation, as semiconducting layer while contacts were fabricated with poly(ethylene-dioxythiophene)/polystyrene sulfonate (PEDOT/PSS) by means of soft lithography. On the opposite side of the foil a thin PEDOT/PSS film, acting as gate electrode, was spin coated. It is worth noting that this technique allows the realization of bottom contact and top contact devices on the same substrate and with the same semiconducting layer. Furthermore, assisted by Scanning Probe Microscopy investigations, we investigated how the device structure influences its electrical properties in terms of hole mobility, Series Contact Resistance and parasitic capacitance effects. The comparison between top-contact and bottom-contact devices shows interesting marked differences that can be mainly attributed to a different quality of PEDOT/PSS-semiconductor interface. The flexibility of the obtained structure and the easy scalability of the technological process open the way for economic production of high-resolution organic devices.     

Novel use of polymer brushes in colloidal lithography to overcome lateral capillary force

A general method has been developed for transferring interfacially trapped, submonolayer hexagonal arrays of silica particles for nano- and mesoscopic surface patterning. Poly(n-butyl acrylate) and poly(n-butyl acrylate-random-N,N-diethylaminoethyl acrylate) brushes were grafted on the substrates via the "graft-from" method using atom transfer radical polymerization. The polymer brush served as an adhesive promoter between the particles and the substrate and proved to be effective for locking the particles in the hexagonal lattice against the lateral capillary force arising from a thin layer of water attached to the surface of the substrate. Several parameters that influence preservation of the order of the particle arrays were examined. These include brush thickness, brush composition, interparticle distance, and particle diameter.     

Three-dimensional films of photoluminescent polyoxometalates fabricated by a colloidal crystal template

Three-dimensional ordered thin films based on 12-phosphotungstic acid (PW₁₂O₄₀/SiO₂) and lanthanide-substituted phosphotungstate (Eu(PW₁₁O₃₉)₂/SiO₂, Gd(PW₁₁O₃₉)₂/SiO₂ and Eu(P₂W₁₇O₆₁)₂/SiO₂) were constructed by an inverse opal method, using polystyrene colloidal crystal as a template. The samples were characterized by elemental analysis, XRD, IR spectra, UV–vis diffuse reflectance spectra (DR-UV–Vis) and SEM techniques. These thin films show well-defined lamellar array with inverse opal structure, and lanthanide polyoxometalate thin films exhibit photoluminescent properties.     

Broadband transmission masks, gratings and filters for extreme ultraviolet and soft X-ray lithography

Lithography and patterning on a nanometre scale with extreme ultraviolet (EUV) and soft X-ray radiation allow creation of high resolution, high density patterns independent of a substrate type. To realize the full potential of this method, especially for EUV proximity printing and interference lithography, a reliable technology for manufacturing of the transmission masks and gratings should be available. In this paper we present a development of broadband amplitude transmission masks and gratings for extreme ultraviolet and soft X-ray lithography based on free-standing niobium membranes. In comparison with a standard silicon nitride based technology the transmission masks demonstrate high contrast not only for in-band EUV (13.5 nm) radiation but also for wavelengths below Si L-absorption edge (12.4 nm).The masks and filters with free standing areas up to 1000 × 1000 μm² and 100 nm to 300 nm membrane thicknesses are shown. Electron beam structuring of an absorber layer with dense line and dot patterns with sub-50 nm structures is demonstrated. Diffractive and filtering properties of obtained structures are examined with EUV radiation from a gas discharge plasma source.     

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。     

A route to fabricate nanocontacts by X-ray lithography for the realization of single electron transistors and highly sensitive biosensors

The fabrication of single electron transistors and/or highly sensitive biosensors is still a challenging task on account of the tight control required to get proper shapes and size of the electrodes. The nanosized tips and the separation of a few nanometers between electrode pairs are critical features. Conventional lithography is not suited to obtain these features because of the resolution limits, so that previous alternative approaches have involved the use of electron beam lithography, focused ion beam lithography or scanning probe nanolithography. The novel approach presented in this letter is the exploitation of X-ray lithography in the Elettra synchrotron to fabricate arrays of nanocontacts spaced a few nanometers, devoted to the design of a new class of nanodevices based on nanoparticles and/or single molecules, including single electron transistors and highly sensitive biosensors. The method to fabricate such devices is illustrated and discussed. Experimental details of the fabrication process are given and preliminary results are presented through SEM and AFM images. It is worth noting that this paper presents a viable method to produce nanocontacts by using the X-ray lithography by synchrotron radiation source, that has not yet been reported together with experimental, though preliminary, data.     

Microfabricated PLGA scaffolds: a comparative study for application to tissue engineering

A variety of techniques for the manufacture of biodegradable, three-dimensional scaffolds for tissue engineering have been developed in recent years. In this study, we report and compare two simple methods for fabricating poly( -lactide-co-glycolide) (PLGA) scaffolds with feature sizes of 10–200 μm, which have been developed in our laboratories.

The first technique is based on the use of a microsyringe that makes use of a computer-controlled, three-axis micropositioner, which allows the control of motor speeds and position. A PLGA solution is drawn from the needle of the syringe by the application of a constant pressure of 10–300 mm Hg resulting in controlled polymer deposition of 10–600 μm in diameter. The second technique is based on “soft lithographic” approaches that utilizes a Poly(dimethylsiloxane) (PDMS) mold. The polymer solution is cast on the mold under vacuum. Polymer concentration, solvent composition, and casting conditions influence the integrity and the lateral resolution of the resulting scaffold. Both techniques allow the possibility of constructing three-dimensional architectures that permit the study of cell behaviour in an environment similar to that in vivo, and may provide tools for the construction of engineered tissue.     

Fabrication of large-area and high-quality colloidal crystal films on nanocrystalline porous substrates by a room temperature floating self-assembly method

When colloidal crystal films are deposited onto nanocrystalline porous substrates by the commonly used colloidal crystallization method of vertical deposition self-assembly, the colloidal crystal tends to be poorly adhered to the porous film. Herein, we present a fabrication of large-area, three-dimensional (3D) colloidal crystal thin films on nanocrystalline porous substrates by a room temperature floating self-assembly method that has recently been developed for colloidal crystal deposition. Firstly, colloidal suspensions were prepared by dispersing monodisperse colloidal microspheres at high volume fraction in a mixture of ethanol and water. At room temperature, these suspensions were spread onto nanocrystalline porous TiO₂ films. The colloidal particles assembled into 3D ordered structures at the air−liquid interface of the suspensions as a result of rapid evaporation of the solvents. After the solvents (water and ethanol) had evaporated completely, the colloidal crystals were directly deposited on the nanocrystalline porous TiO₂ films. Scanning electron microscopy images and normal-incidence transmission spectra of the samples showed that the colloidal crystal films deposited on the nanocrystalline porous TiO₂ substrates by this method had very high crystalline quality. In addition, the effect of the degree of surface roughness of the nanocrystalline porous substrate on the crystalline quality of the colloidal crystals has been studied.     

Combinatorial optimization of a molecular glass photoresist system for electron beam lithography

Electron beam lithography is a powerful technique for the production of nanostructures but pattern quality depends on numerous interacting process variables. Orthogonal gradients of resist composition, baking temperatures, and development time as well as dose variations inside writing fields are used to prepare ternary combinatorial libraries for an efficient stepwise optimization of a molecular glass negative tone resist system.     

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.     

Size-dependent self-assembly of submicron/nano beads-protein conjugates for construction of a protein nanoarray

A protein nanoarray is created when submicro and nano beads, varying in their size and each conjugated with different proteins, self-assemble to specific locations depending on the diameter matching the surface electron beam patterns created. Protein binding is confirmed from the fluorescence attenuation of the beads upon antigen–antibody binding on the bead surface. This method, called size-dependent self-assembly, allows control of the location of each type of bead, and thus, control of the location of multiple proteins. It provides fast multi-component patterning with a high binding resolution, which can be detected using a fluorescent light microscope. This method is developed to be a simple stand-alone tool for analysis of protein interactions. In addition, it has the potential to be used in conjunction with other protein analysis methods, such as enzyme-linked immunosorbent assay (ELISA) and atomic force microscopy (AFM).