Site-specific stamping of graphene micro-patterns over large areas using flexible stamps

Site-specific stamping has the potential of becoming a low-cost, high-throughput method for depositing specific-shaped graphene micro-patterns over large areas on a wide variety of substrates. The use of an approach involving flexible stamps presented here represents an important advance towards reaching that potential. This approach entails lithographic creation (dry etching) of high-quality micro-pillar arrays of highly oriented pyrolytic graphite (HOPG) over large areas. This is followed by embedding the micro-pillar arrays in polydimethylsiloxane (PDMS), and detaching them from the HOPG base. This results in flexible stamps containing embedded HOPG micro-pillar arrays with freshly cleaved stamping surfaces. The flexible HOPG/PDMS stamps are then brought into contact with substrate surfaces to site-specifically stamp graphene or few-layer graphene (FLG) arrays over large areas. The freshly cleaved nature of the micro-pillar surfaces in the flexible stamps, the low elastic modulus of the flexible stamps and the elimination of sidewall deposits on the micro-pillars allow for more uniform stamping, relative to the use of stiff HOPG stamps from earlier studies. This approach has the potential to expand the substrate choice for graphene or FLG stamping to include curved and/or flexible substrates that could have an impact on the burgeoning field of flexible/stretchable electronics.     

Controllable and Facile Fabrication of Gold Nanostructures for Selective Metal‐Assisted Etching of Silicon

A method with the combination of organic‐vapor‐assisted polymer swelling and nanotransfer printing (nTP) is used to manufacture desirable patterns consisting of gold nano‐clusters on silicon wafers for Au‐assisted etching of silicon. This method remarkably benefits to the size control and regional selection of the deposited Au. By tuning the thickness of the Au films deposited on the polydimethylsiloxane (PDMS) stamps, along with the swelling of PDMS stamps in acetone atmosphere, the Au films are cracked into diverse nanostructures. These nanostructures are covalently transferred onto silicon substrates in a large scale and enable to accelerate the chemical etching of silicon. The etched areas are composed of porous structures which can be readily distinguished from the surroundings on optical microscope. PDMS stamps and the Au clusters provide the control over the feature of the etched areas and the porous silicon, respectively. The silicon surfaces with patterned porous features offer a platform for exploiting new functional templates, for example, they present a diversity of antireflective and fluorescent performance.     

Nanofabrication of polymer surfaces utilizing colloidal lithography and ion etching

In this paper, we utilize colloidal lithography based on electrostatic self-assembly of polystyrene colloidal particles onto a polymer surface as a nanoscale mask. The pattern is then transferred to the surface by ion beam etching. Each particle acts as an individual mask, resulting in an array of identical structure. Ion beam exposure etches away the unmasked surface between the particles, so the particle mask pattern can be transferred into the polymer surface. This method allows to nanofabricate bulk polymeric surfaces with systematic variation in relief, structure sizes, and aspect ratios. It is a fast, simple, and reliable method to fabricated different polymeric surfaces even on large area samples (>1 cm/sup 2/). The structural variation is achieved by use of different conditions during the self-assembly of the mask (e.g., different particles sizes) or different ion etching conditions during the pattern transfer (e.g., ion energy, ion flux, ion incident angle, etching time, gas environment).     

Efficient methods of nanoimprint stamp cleaning based on imprint self-cleaning effect

Nanoimprint lithography (NIL) is a nonconventional lithographic technique that promises low-cost, high-throughput patterning of structures with sub-10 nm resolution. Contamination of nanoimprint stamps is one of the key obstacles to industrialize the NIL technology. Here, we report two efficient approaches for removal of typical contamination of particles and residual resist from stamps: thermal and ultraviolet (UV) imprinting cleaning-both based on the self-cleaning effect of imprinting process. The contaminated stamps were imprinted onto polymer substrates and after demolding, they were treated with an organic solvent. The images of the stamp before and after the cleaning processes show that the two cleaning approaches can effectively remove contamination from stamps without destroying the stamp structures. The contact angles of the stamp before and after the cleaning processes indicate that the cleaning methods do not significantly degrade the anti-sticking layer. The cleaning processes reported in this work could also be used for substrate cleaning.     

Soft lithographic printing of patterns of stretched DNA and DNA/electronic polymer wires by surface-energy modification and transfer

Aligned and stretched lambda DNA is directed to specific locations on solid substrates. Surface-energy modification of glass substrates by using patterned polydimethylsiloxane (PDMS) stamps is used to direct DNA onto the surface-energy-modified micrometer-scale pattern through molecular combing. As an alternative, patterned and nonpatterned PDMS stamps modified with polymethylmethacrylate (PMMA) are utilized to direct the stretched DNA to the desired location and the results are compared. The DNA is elongated through molecular combing on the stamp and transfer printed onto the surfaces. PMMA-modified stamps show a more defined length of the stretched DNA, as compared to bare PDMS stamps. A combination of these two methods is also demonstrated. As an application example, transfer printing of DNA decorated with a semiconducting conjugated polyelectrolyte is shown. The resulting patterned localization of stretched DNA can be utilized for functional nanodevice structures, as well as for biological applications.     

Neuronal networks in vitro: formation and organization on biofunctionalized surfaces

Receptor-mediated recognition of substrate molecules is a prerequisite for nerve cells in order to find their target structures in vivo and leads to formation of neuronal connections and networks. In order to study these mechanisms under in vitro conditions, we cultured embryonic hippocampal neurons or neuronal cell lines, SH-SY5Y and PCC7-PCC7-Mz1, onto biofunctionalized surfaces. Micropatterning on polymer surfaces, glass- and silicone-oxide-based chip materials was performed in a micrometer range by microcontact printing using polydimethylsiloxane (PDMS) stamps. Hippocampal neurons were found to form networks on chip surfaces under serum-free conditions and remained functional for more than a week. Human neuroblastoma cells SH-SY5Y as well as PCC7-Mz1 stem cells were found to follow microcontact printed pattern on polystyrene surfaces. Both cell lines showed neuronal marker expression and were cultured for up to 7 days with serum containing culture medium. Widths of 3–5 µm of coating lines were found to enhance single cell spreading along the pattern. The techniques described in this study may be useful in promoting nerve cell regeneration and organization following transection due to trauma or surgery. The neuronal alignment and network formation in vitro may furthermore serve as a model system in the field of biosensors. © 1999 Kluwer Academic Publishers     

Adsorption of a cholesteric liquid crystal polyester on silver nanoparticles studied by surface-enhanced Raman scattering and micro Raman spectroscopy

A Raman study of the adsorption of thermotropic cholesteric liquid crystal polyester PTOBDME ([C(34)H(36)O(8)](n)) on Ag surfaces is presented in this work. The affinity and adsorption mechanism of this polymer was tested on Ag metal colloids and on Ag films obtained by direct immobilization of the colloidal nanoparticles. We have first studied the structure of PTOBDME suspended in several solvents in order to identify the Raman bands used as structural markers. The adsorption of the polymer leads to a deep conformational change involving both the main chain and the aliphatic side chain. The interaction of polymers like PTOBDME with metals could be interesting in the formation of functionalized surfaces, providing them with specific physicochemical properties with possible applications in recognition phenomena, which can be easily characterized by Raman spectroscopy.     

玻璃基底上的蛋白质微接触压印图型化

研究了一种将胶原Ⅰ型蛋白通过微接触压印技术图型化于玻璃基底表面的方法.采用标准光刻工艺制备印章母版,并运用反应离子刻蚀设备对印章表面进行氧等离子体处理,以期改善印章表面亲水性能.将涂敷了胶原Ⅰ型蛋白,并经返潮处理的印章以50 g/cm^2大小的力与玻璃表面接触10 s,得到蛋白质微图型.结果表明,采用反应离子刻蚀技术能显著改善聚二甲基硅氧烷（PDMS）印章表面的亲水性.表面亲水性得到改善的PDMS印章,在经过湿盒返潮后,再进行微接触压印得到的蛋白质微图型其质量得到显著提高.     

Molecular interactions at biointerfaces: a study of lipid adsorption

The study of the behaviour of biointerfaces is of great interest because it enables us to gain a much better understanding of the interactions between different biological compounds. Superficial processes are strongly dependent on such interactions. In the present work, we have focused our attention on the adsorption of a cationic lipid onto different colloidal polymer systems. Subsequently, the coadsorption of this lipid and an immunoprotein (F(ab') ₂) was performed trying to achieve stable latex particles. The aim was to obtain a structured interface similar to that of a simple biological membrane. Mainly, we have placed emphasis on the study of interaction forces that govern lipid adsorption when we change the dielectric constant in the medium. In order to obtain homogeneous aqueous lipid solutions some ethanol was added to samples. The adsorption isotherms were carried out at different experimental conditions, changing the ethanol contents and the pH of the environment. Moreover, the electrokinetic behaviour and the colloidal stability of these biocomplexes were studied, and both yielded highly compatible results. The adsorption of lipid onto polymeric sorbents is an irreversible process that takes place rapidly. The preferential interaction between the lipid and polymeric surfaces is electrostatic. Only in those samples with low alcohol concentration, hydrophobic forces take place weakly. Lipid-surface interactions are influenced by the nature of buffer ions. The colloidal stability of the systems decreases as the amount of the adsorbed lipid is higher. Sequential coadsorption experiments showed that the lipid molecules adhere both to the polymer surface and to the previously adsorbed immunoprotein.     

Guiding the Dewetting of Thin Polymer Films by Colloidal Imprinting

Micropatterned surfaces are important in many biomedical and bioengineering applications, such as the development of biosensors. An approach for the creation of ordered surface patterns, fabricated combining colloidal crystals, consisting of ordered layers of micrometric particles, with dewetting of bilayers of thin polymer films is introduced. The produced patterns are both topographical and chemical in nature, consisting of ordered arrays of microscale holes imprinted in a polymer film, with tunable size. The spontaneous dewetting of the polymer film enables this tunability, with a maximum sevenfold increase in lateral size of the holes and sixfold increase in depth from imprinting to coalescence with neighboring holes. Polymer dewetting and layer inversion are seen to compete during the annealing of the polymer bilayers, and the optimal conditions for hole growth are identified. An in‐depth investigation highlights the effects of UV‐ozone treatment on the long‐range ordering of the colloidal crystals and on preventing the dewetting of the imprinted bilayers. Ordered patterns of different size and depth are produced over large areas by tuning of the colloidal crystal assembly, UV surface treatment and dewetting conditions. Potential applications of the micropatterns produced in the present work include microarrays for single cell studies and biosensors.     

Improvement of transmittance by fabricating broadband subwavelength anti-reflection structures for polycarbonate

We report on how to increase transmittance of a 0.2 mm thick polycarbonate (PC) film by periodic subwavelength anti-reflection structures in the visible spectral range. Subwavelength anti-reflection structures like moth-eyes are fabricated into the polycarbonate substrate itself by thermal nano-imprinting lithography (TH-NIL), which uses silicon stamps that have periodic structures such as gratings (lines and spaces) and pillared dots, and are fabricated by laser interference lithography (LIL) and transformer coupled plasma etching. To increase transmittance of a polycarbonate film, we control the periods and shapes of patterns, the number of patterned surfaces, and the overlapping direction of patterns that are fabricated into its surfaces. As a result of this, we show that average transmittance improves as the pattern period gets shorter and as both surfaces of the film are patterned. We also show that the spectrum range gets larger as the pattern period gets shorter and is determined by the longer pattern period in the case of designing a film to have different pattern period on its surfaces. The maximum average transmittance of a polycarbonate film increases up to approximately 6% compared to a bare sample in the 470-800 nm spectral range.     

Fabrication of elliptical nanorings with highly tunable and multiple plasmonic resonances

Herein, a new and facile patterning method is demonstrated for the scalable fabrication of gold elliptical rings (ERs) in a controlled manner over large areas. In this method, well-ordered hexagonally arrayed polystyrene (PS) rings, fabricated by colloidal lithography, were used as masters to generate poly(dimethylsiloxane) (PDMS) stamps with circular apertures. The stamps were then stretched and utilized as molds for creating elliptical PS rings by a capillary filling process. Through subsequent reactive ion etching and chemical wet-etching, the elliptical PS rings could be readily transferred into an underlying gold film, leading to the formation of gold ERs. Since the aspect ratio (AR) of the elliptical PS rings could be controlled by varying the applied strain during the capillary filling process, gold ERs with different ARs could be fabricated in a scalable manner. The optical properties of the gold ERs were characterized by UV-vis/NIR and IR extinction measurements. The ERs exhibited only odd modes of polarization-dependent plasmonic resonances at normal incidence. The experiments and corresponding theoretical studies illustrated that all resonant modes could be tuned across a broad spectral range from the visible to the mid infrared (550-4700 nm) by simply varying the AR of the ERs. Moreover, the experimental data were confirmed by COMSOL simulations.     

Ultra‐Smooth,Chemically Functional Silica Surfaces for Surface Interaction Measurements and Optical/Interferometry‐Based Techniques

The study of interfacial phenomena is central to a range of chemical, physical, optical, and electromagnetic systems such as surface imaging, polymer interactions, friction/wear, and ion‐transport in batteries. Studying intermolecular forces and processes of interfaces at the sub‐nano scale has proven difficult due to limitations in surface preparation methods. Here, we describe a method for fabricating reflective, deformable composite layers that expose an ultra‐smooth silica (SiO₂) surface (RMS roughness < 0.4 nm) with interferometric applications. The robust design allows for cleaning and reusing the same surfaces for over a week of continuous experimentation without degradation. The electric double‐layer forces measured using the composite surfaces are within 10% of the theoretically predicted values. We also demonstrate that standard chemisorption and physisorption procedures on silica can be applied to chemically modify the surfaces; as a demonstration of this, the composite surfaces are successfully modified with octadecyltrichlorosilane (OTS) to study their hydrophobic interactions in water using a surface force apparatus (SFA). These composite surfaces provide a basis for the preparation of a variety of new surfaces, and should be particularly beneficial for the SFA and colloidal probe methods that employ optical/interferometric and electrochemical techniques, enabling characterization of previously unattainable surface and interfacial phenomena.

     

Diffusion of self-assembled monolayers of thiols on the gold surfaces covered with polydimethylsiloxane stamps

Thiols can diffuse and form self-assembled monolayers (SAMs) on the gold surfaces covered with polydimethylsiloxane (PDMS) stamps. For the first time, with cells as the indicator of how far alkanethiols had diffused to form SAM, we studied the growth dynamics of SAMs of HS(CH₂)₁₁(OCH₂CH₂)₃OH (EG₃) and HS(CH₂)₁₁(OCH₂CH₂)₆OH (EG₆) on the gold surfaces covered with PDMS stamps. The growth of SAMs is well described by one-dimensional diffusion from a line source of concentration, with surface diffusion coefficient of 193.4 ± 19.2 μm²/min (EG₃) and 95.8 ± 18.9 μm²/min (EG₆).     

Fabrication of silicon/polymer composite nanopost arrays and their sensing applications

A novel technique is reported for fabricating silicon/polymer composite nanopost arrays by combining colloidal lithography and surface-initiated atom-transfer radical polymerization. The composite nanopost arrays possess a core/shell nanoarchitecture, with shells of poly(2-hydroxyethyl methacrylate) and cores of silicon nanoposts. The polymer brush possesses quasi-3D homogeneous nanoarchitectures due to the controllable polymerization process using the surface-initiated atom-transfer radical polymerization technique. The composite nanopost arrays are durable due to the particular nanoarchitectures. The backbone templates of the composites are silicon nanopost arrays directly etched from silicon substrates, and the polymer shell is covalently grafted from the arrays. The composite nanopost arrays exhibit vivid colors. Moreover, the colors of the composite nanopost arrays can be tuned from green to red by changing the thickness of fi lm. Specifically, the composite nanopost arrays can be used as sensors to rapidly detect water vapors with high stability and reproducibility. Many different functional surfaces could be prepared through this technique using other functional monomers.     

Broadband optical antireflection enhancement by integrating antireflective nanoislands with silicon nanoconical-frustum arrays

Based on conventional colloidal nanosphere lithography, we experimentally demonstrate novel graded-index nanostructures for broadband optical antireflection enhancement including the near-ultraviolet (NUV) region by integrating residual polystyrene antireflective (AR) nanoislands coating arrays with silicon nano-conical-frustum arrays. This is a feasible optimized integration method of two major approaches for antireflective surfaces: quarter-wavelength AR coating and biomimetic moth's eye structure.     

Morphology-controllable fabrication of ordered platinum nanoshells with reduced symmetry

This paper presents a novel method for fabricating an ordered array of metallic nanoshells with a controllable shape by a combination of a porous polymer template and a nanocrystal-seeded electroless plating technique. The morphology of hollow particles has a strong dependence on the seed-deposition time onto the surfaces of the original colloidal template. Using this method, ordered Pt nanobowls (bowl-shaped shells) and, alternatively, nanocups (cup-shaped shells) are prepared. These materials show some intriguing properties: (i) reduced symmetry of the building blocks; (ii) a well-ordered structure; and (iii) a high ratio of surface area to volume, all of which are useful in many areas such as catalysts, sensors, and photonic crystals.     

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.     

Polymer-assisted fabrication of gold nanoring arrays

In this paper,we report a new strategy for the fabrication of gold nanoring arrays via colloidal lithography and polymer-assisted self-assembly of gold nanoparticles (Au NPs).First,multi-segmented polymer nanorod arrays were fabricated via colloidal lithography.They were then used as templates for Au NP adsorption,which resulted in nanoparticles on the poly(4-vinyl pyridine) (P4VP) segments.Continuous gold nanorings were formed after electroless deposition of gold.The diameter,quantity,and spacing of the gold nanorings could be tuned.Three dimensional coaxial gold nanorings with varying diameters could be fabricated on a polymer nanorod by modifying the etch parameters.The nanorings exhibited optical plasmonic resonances at theoretically predicted wavelengths.In addition,the polymer-assisted gold nanorings were released from the substrate to generate a high yield of free-standing nanorings.This simple,versatile method was also used to prepare nanorings from other metals such as palladium.     

Manufacture of colloidal polymer ellipsoids for anisotropic conducting nano-composites

This project aimed to make anisotropic conducting nano-composites based on a segregated system of 20 nm gold particles and deformed polyethylene spheres of colloidal size. Two methods for achieving the deformation of the colloidal polyethylene spheres were attempted, namely to exploit the elongational flow field at the entrance to a capillary and alternatively to make cast films of a water soluble polymer containing the colloidal particles and draw them in the solid state. In the latter method, sections of film were elongated at an elevated temperature using a tensile testing machine. The drawn films were dissolved in water and the deformed particles were extracted and concentrated by ultracentrifugation. This method was successful in producing ellipsoids of a prescribed aspect ratio. Further successful deformation was carried out using PMMA particles and monodisperse polystyrene particles. Polystyrene spheres containing 20 nm diameter magnetite particles could not be deformed using this process. A range of experimental techniques were exploited to characterise the ellipsoidal particles, including transmission electron microscopy and photocorrelation spectroscopy. Subsequent addition of metal oxide particles to the polymer ellipsoids resulted in some success in that a small number of 20 nm diameter magnetite particles was observed to be attached to the surfaces of the much larger (1 m) polystyrene ellipsoids. The mechanism of attachment has not yet been elucidated but this has significant potential for future composite device production.