Lithographic Patterning Method Research Articles

A magnetic assembly approach to chiral superstructures

Colloidal assembly into chiral superstructures is usually accomplished with templating or lithographic patterning methods that are only applicable to materials with specific compositions and morphologies over narrow size ranges. Here, chiral superstructures can be rapidly formed by magnetically assembling materials of any chemical compositions at all scales, from molecules to nano- and microstructures. We show that a quadrupole field chirality is generated by permanent magnets caused by consistent field rotation in space. Applying the chiral field to magnetic nanoparticles produces long-range chiral superstructures controlled by field strength at the samples and orientation of the magnets. Transferring the chirality to any achiral molecules is enabled by incorporating guest molecules such as metals, polymers, oxides, semiconductors, dyes, and fluorophores into the magnetic nanostructures.

CsPbBr3 nanocrystals plasmonic distributed Bragg reflector waveguide laser

The recent development of perovskite-based lasers showcased the outstanding optical properties of the material such as high absorption coefficient and high quantum yield. The lasers were demonstrated in the form of nanowires and nanoplates, which are difficult to be integrated on a chip in the form of high-density arrays due to the difficulties in positioning them on the chip. The solution to this problem should be to use the well-known lithography process in the fabrication process of the lasers. In this work, we demonstrate several perovskite-based plasmonic lasers that were fabricated by using the lithographic in-mold patterning method that relies on the electron beam lithography process. The lasers utilized CsPbBr3 perovskite nanocrystals as the gain material and plasmonic distributed Bragg reflector grating structure as the optical feedback provider to achieve a low lasing threshold of 42.5 μJ/cm2 with a linewidth of 0.6 nm (FWHM) at room temperature. The use of the lithographic process in the fabrication of the lasers makes it possible to fabricate and integrate them on a chip in a relatively high-density manner, so that they can be used extensively in quantum optics and on-chip integrated photonics applications.

Hot Electron Extraction Enabled By Single-Crystal Metal Films and Nanostructures

In contrast to conventional photovoltaic devices which rely on bulk semiconductor material absorption and separation of electron-hole pairs, surface plasmon-based solar energy harvesting employs rectifying metal/dielectric interfaces to capture light and separate charges. Here, we describe the requirements for efficient hot electron extraction in plasmonic photovoltaic devices and demonstrate a new scalable and environmentally friendly electroless deposition method for single-crystal epitaxial noble metals films and nanostructures. The method produces ultra-smooth, low loss, single-crystal noble metal films ideal for subtractive patterning of nanostructures through ion beam milling, and high definition, sub-wavelength single crystal nanostructures through lithographic patterning methods. We describe the nucleation and growth of these metal films and nanostructures in the absence and presence of anionic shape-control agents and examine the role of specific anions in determining the resulting film and nanostructure morphologies via scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). These effects have been exploited to yield large area patterned, and shape-controlled nanoarrays of single crystal metal nanostructures for plasmonic and metamaterial applications. These approaches offer new and cost effective routes to achieve crystalline, shape-controlled surface nanostructure to enable efficient hot electron extraction for energy harvesting and catalysis applications and new noble metal alloys for improved electrocatalysis.

Plasmonic Photovoltaics Enabled By Single-Crystal Metal Films and Nanostructures

In contrast to conventional photovoltaic devices which rely on bulk semiconductor material absorption and separation of electron-hole pairs, surface plasmon-based solar energy harvesting employs rectifying metal/dielectric interfaces to capture light and separate charges. Here, we describe the requirements for efficient hot electron extraction in plasmonic photovoltaic devices and demonstrate a new scalable and environmentally friendly electroless deposition method for single crystal epitaxial noble metals films and nanostructures. The method produces ultra-smooth, low loss, single-crystal noble metal films ideal for subtractive patterning of nanostructures through ion beam milling, and high definition, sub-wavelength single crystal nanostructures through lithographic patterning methods. We describe the nucleation and growth of these metal films and nanostructures in the absence and presence of anionic shape-control agents and examine the role of specific anions in determining the resulting film and nanostructure morphologies via scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). These effects have been exploited to yield large area patterned, and shape-controlled nanoarrays of single crystal metal nanostructures for plasmonic and metamaterial applications. These approaches offer new and cost effective routes to achieve crystalline, shape-controlled surface nanostructure to enable efficient hot electron extraction for energy harvesting applications.

Microneedle Patterning of 3D Nonplanar Surfaces on Implantable Medical Devices Using Soft Lithography.

Micropatterning is often used to engineer the surface properties of objects because it allows the enhancement or modification of specific functionalities without modification of the bulk material properties. Microneedle arrays have been explored in the past for drug delivery and enhancement of tissue anchoring; however, conventional methods are primarily limited to thick, planar substrates. Here, we demonstrate a method for the fabrication of microneedle arrays on thin flexible polyurethane substrates. These thin-film microneedle arrays can be used to fabricate balloons and other inflatable objects. In addition, these thin-filmed microneedles can be transferred, using thermal forming processes, to more complex 3D objects on which it would otherwise be difficult to directly pattern microneedles. This function is especially useful for medical devices, which require effective tissue anchorage but are a challenging target for micropatterning due to their 3D nonplanar shape, large size, and the complexity of the required micropatterns. Ultrathin flexible thermoplastic polyurethane microneedle arrays were fabricated from a polydimethylsiloxane (PDMS) mold. The technique was applied onto the nonplanar surface of rapidly prototyped soft robotic implantable polyurethane devices. We found that a microneedle-patterned surface can increase the anchorage of the device to a tissue by more than twofold. In summary, our soft lithographic patterning method can rapidly and inexpensively generate thin-film microneedle surfaces that can be used to produce balloons or enhance the properties of other 3D objects and devices.

Advanced colloidal lithography: From patterning to applications

This article presents a comprehensive review about the current research activities on colloidal lithography, a highly efficient technology for fabricating large-area patterned functional nanostructures. Three aspects are elaborated: i) self-assembly of monolayer of colloidal crystals (MCCs) and their modifications; ii) lithographic patterning methods, including deposition and patterning of functional materials and pattern transfer onto the underlying substrates; iii) promising applications, especially in the optical and photonic-related fields in the past several years. Finally, perspectives on the current challenges and future trends in this area are given. The present review intends to inspire more ingenious designs and exciting research in colloidal lithography for advanced nanofabrication.

Highly transparent and flexible NO2 gas sensor film based on MoS2/rGO composites using soft lithographic patterning

The MoS2/GO hybrid composite thin film is prepared by a facile solution mixing process. To reduce the composite film spin-coated on a SiO2 (300 nm)/Si substrate, thermal annealing at 600 °C for 1 h in a N2 atmosphere is used. The thermally reduced GO (rGO) composite film is subjected to line patterning through a soft lithographic patterning method, and the patterned MoS2/rGO composite thin film is re-transferred onto a PET film from the Si substrate. The patterned MoS2/rGO composite thin film has a thickness of about 10 nm and the transmittance of the patterned MoS2/rGO composite thin film on the PET substrate is 93%. The NO2 gas sensor device is fabricated and its basic characteristics are systematically investigated. The patterned MoS2/rGO composite thin film gas sensor has a sensitivity at least four times higher than the pure rGO thin film gas sensor. In addition, the characteristics of the sensor device are also maintained at a bending radius of 14 mm. This transparent and flexible patterned MoS2/rGO composite thin film can be used as a highly sensitive gas sensor that will detect a concentration as low as 0.15 ppm of harmful gases such as NO2.

Fabrication of Flexible Optoelectronic Devices Based on MoS2/Graphene Hybrid Patterns By a Soft Lithographic Patterning Method

In this presentation, cross-stacking MoS2/graphene hybrid patterns for the application to advanced flexible opto-electronic devices have been performed by the soft-lithographic patterning method. Well-defined MoS2/graphene hybrid pattern was produced simply by a soft lithographic patterning technique without any defects. In-depth exploration for the optical properties of diverse cross-stacking photodetectors based on MoS2/graphene patterns was also implemented. Furthermore, cross-stacking MoS2/graphene based on the woven structure was transferred onto a flexible polyethylene terephthalate (PET) substrate for the analysis of mechanical properties of devices. Eventually, this method should pave the way for practical applications of transparent and flexible nano-electronic devices based on 2D materials.

Nano-Protrusive Gold Nanoparticle-Hybridized Polymer Thin Film as a Sensitive, Multipatternable, and Antifouling Biosensor Platform.

Hybrid films consisting of anisotropic octahedral gold nanoparticles (AuNPs) and polymers had their surfaces functionalized and were immobilized on surface plasmon resonance (SPR) sensors for biomolecule detection. Specifically, carboxylated octahedral AuNPs (C-Oh-AuNPs) and poly(allylamine hydrochloride) (PAH) were assembled as ultrathin films by using a layer-by-layer process. The ionic strength generated from the functional groups of C-Oh-AuNP and PAH influenced the composition, its surface morphology, and the reactivity of the film toward further chemical reactions such as the synthesis of spherical AuNPs (S-AuNPs). We were thus able to control the size and the structure of the C-Oh-AuNP and S-AuNPs converted to nano-raspberry-shaped particles. This hierarchical AuNP hybrid film exhibits much more sensitive and stable detection of biomolecules than regular flat chip systems, and this result may be due to the SPR of the AuNP at its surface being able to markedly enhance the local optical field of the chip. The micropatterning of the hybrid coating was also studied by using a soft lithographic patterning method. We, in particular, worked on creating multiplex patterns having different combinations of shapes and fluorescent colors. We expect our hybrid coating system with multicode biomolecular arrays to be used as a powerful platform for biosensor applications.

Fabrication of flexible optoelectronic devices based on MoS2/graphene hybrid patterns by a soft lithographic patterning method

A cross-stacking MoS2/graphene hybrid patterns for the application to advanced flexible opto-electronic devices have been demonstrated by soft-lithographic patterning method. Well-defined MoS2/graphene hybrid pattern was fabricated simply by a soft lithographic patterning technique. In-depth exploration for the optical properties of diverse cross-stacking photodetectors based on MoS2/graphene patterns was carried out. In addition, cross-stacking MoS2/graphene was demonstrated onto a flexible polyethylene terephthalate (PET) substrate for the analysis of physical properties of devices. Substantially, this method should pave the way for realistic applications of transparent and flexible nano-electronic devices based on 2D materials.

Fabrication of graphene-based flexible devices utilizing a soft lithographic patterning method

There has been considerable interest in soft lithographic patterning processing of large scale graphene sheets due to the low cost and simplicity of the patterning process along with the exceptional electrical or physical properties of graphene. These properties include an extremely high carrier mobility and excellent mechanical strength. Recently, a study has reported that single layer graphene grown via chemical vapor deposition (CVD) was patterned and transferred to a target surface by controlling the surface energy of the polydimethylsiloxane (PDMS) stamp. However, applications are limited because of the challenge of CVD-graphene functionalization for devices such as chemical or bio-sensors. In addition, graphene-based layers patterned with a micron scale width on the surface of biocompatible silk fibroin thin films, which are not suitable for conventional CMOS processes such as the patterning or etching of substrates, have yet to be reported. Herein, we developed a soft lithographic patterning process via surface energy modification for advanced graphene-based flexible devices such as transistors or chemical sensors. Using this approach, the surface of a relief-patterned elastomeric stamp was functionalized with hydrophilic dimethylsulfoxide molecules to enhance the surface energy of the stamp and to remove the graphene-based layer from the initial substrate and transfer it to a target surface. As a proof of concept using this soft lithographic patterning technique, we demonstrated a simple and efficient chemical sensor consisting of reduced graphene oxide and a metallic nanoparticle composite. A flexible graphene-based device on a biocompatible silk fibroin substrate, which is attachable to an arbitrary target surface, was also successfully fabricated. Briefly, a soft lithographic patterning process via surface energy modification was developed for advanced graphene-based flexible devices such as transistors or chemical sensors and attachable devices on a biocompatible silk fibroin substrate. Significantly, this soft lithographic patterning technique enables us to demonstrate a simple and efficient chemical sensor based on reduced graphene oxide (rGO), a metallic nanoparticle composite, and an attachable graphene-based device on a silk fibroin thin film.

Orthogonal patterning of multiple biomolecules using an organic fluorinated resist and imprint lithography.

The ability to spatially deposit multiple biomolecules onto a single surface with high-resolution while retaining biomolecule stability and integrity is critical to the development of micro- and nanoscale biodevices. While conventional lithographic patterning methods are attractive for this application, they typically require the use of UV exposure and/or harsh solvents and imaging materials, which may be damaging to fragile biomolecules. Here, we report the development of a new patterning process based on a fluorinated patterning material that is soluble in hydrofluoroether solvents, which we show to be benign to biomolecules, including proteins and DNA. We demonstrate the implementation of these materials into an orthogonal processing system for patterning multibiomolecule arrays by imprint lithography at room temperature. We further showcase this method's capacity for fabricating patterns of receptor-specific ligands for fundamental cell studies.

Opportunities with Fabric Composites as Unique Flexible Substrates

Flexible substrates enable new capabilities in applications ranging from electronics to biomedical devices. To provide a new platform for these applications, we investigate a composite material consisting of rigid fiber fabrics impregnated with soft elastomers, offering the ability to create load bearing, yet flexible substrates. We demonstrate an integrated and facile one-step imprint lithographic patterning method on a number of fabrics and resins. Furthermore, the bending and tensile properties were examined to compare the composites to other flexible materials such as PET and cellulose paper. Carbon fiber composites possess a higher tensile modulus than PET while retaining almost an order of magnitude lower bending modulus. Fabric composites can also have anisotropic mechanical properties not observed in homogeneous materials. Finally, we provide a discussion of these anisotropic mechanical responses and their potential use in flexible applications.

Suspended sub-50 nm vanadium dioxide membrane transistors: fabrication and ionic liquid gating studies

We demonstrate a robust lithographic patterning method to fabricate self-supported sub-50 nm VO(2) membranes that undergo a phase transition. Utilizing such self-supported membranes, we directly observed a shift in the metal-insulator transition temperature arising from stress relaxation and consistent opening of the hysteresis. Electric double layer transistors were then fabricated with the membranes and compared to thin film devices. The ionic liquid allowed reversible modulation of channel resistance and distinguishing bulk processes from the surface effects. From the shift in the metal-insulator transition temperature, the carrier density doped through electrolyte gating is estimated to be 1 × 10(20) cm(-3). Hydrogen annealing studies showed little difference in resistivity between the film and the membrane indicating rapid diffusion of hydrogen in the vanadium oxide rutile lattice consistent with previous observations. The ability to fabricate electrically-wired, suspended VO(2) ultra-thin membranes creates new opportunities to study mesoscopic size effects on phase transitions and may also be of interest in sensor devices.

마이크로미터 크기의 유기 전계 효과 트랜지스터 제작

본 연구에서는 기존 실리콘 반도체 기술 기반의 포토 및 이빔 리소그래피 공정을 통하여 유기 반도체 소자를 패터닝하였다. P3HT나 PEDOT 등의 유기 반도체는 용매에 녹기 때문에 MIMIC (micro-molding in capillaries)이나 inkjet printing 기술을 이용하여 마이크로미터 크기의 소자 제작이 가능하였으나, 펜타신은 용매에 녹지 않기 때문에 매우 복잡한 방법으로 마이크로미터크기의 소자를 제작하여왔다. 그러나, 본 연구에서는 원자층 증착 방법으로 증착한 산화 알루미늄막을 펜타신의 보호층으로 이용하여 기존의 포토 및 이빔 리소그래피 방법으로 마이크로미터크기의 펜타신 소자를 제작하였으며 그 전기 특성을 확인하였다.

Photolithographic patterning of subwavelength top emitting colloidal quantum dot based inorganic light emitting diodes on silicon

The combination of lithographic patterning and nanostamping methods makes it possible to accurately define diffraction-limited multicolor (wavelengths 560–620 nm) light sources on a silicon substrate. We demonstrate a postprocessing technique that utilizes standard photolithography process to pattern the cathode of top emitting diode. Correlation of electroluminescence, photoluminescence, and atomic force microscopy topography showed that the emission region is well defined through the robust multiscale patterning techniques, with the fineness of the emitting area mainly limited by the point spread function of the observing microscope.

Spontaneous dewetting-induced residue-free patterning at room temperature

A lithographic patterning method is presented that is based on dewetting induced by sequential molding under an applied pressure. Because of spontaneous dewetting taking place, the window to be opened is free from any residue and the surface exposure is instantaneously assured. This residue-free patterning can be accomplished without any heating process and surface treatment, irrespective of pattern duty ratio. The residue-free patterning is made possible with the use of a rigiflex mold and a roller that is used to bring about pressure-induced thinning leading to spontaneous dewetting. A necessary condition for the method is that the spreading coefficient of spin-coated liquid be negative. The exposed surface can be utilized as a sacrificial layer for etching of underlying layer and/or thin film deposition in a fabrication of electronic and biological devices.

Non-destructive patterning of conducting-polymer devices using subtractive photolithography

We demonstrate a non-destructive, high-throughput, and high-resolution lithographic patterning method to fabricate organic-semiconductor devices based on UV lithography with the standard equipment of well-established silicon technology. The method is applied to fabricate poly(3-hexylthiophene) (P3HT)-based organic thin-film transistors (OTFTs) with high yield. Patterns with features down to 2 pm are reproducibly demonstrated. We show that a few modifications in the processing steps are necessary in order to spin-coat photoresist onto P3HT films and to completely remove P3HT residues on the substrates that have been treated with a self-assembled monolayer. Compared with OTFTs whose P3HT channels are not patterned, the on/off ratio of the patterned devices is improved by over four orders of magnitude from about 70 to 106, because of the dramatically reduced gate leakage current. The extracted carrier mobility is not only virtually unchanged after the lithography processes, but also as high as 0.027 cm(2)/V s. Both the on/off ratio and the mobility are among the best reported values in P3HT-based OTFTs fabricated and measured in ambient conditions. (c) 2006 Elsevier B.V. All rights reserved.

Engineering Silicon Oxide Surfaces Using Self‐Assembled Monolayers

AbstractFor Abstract see ChemInform Abstract in Full Text.

Engineering Silicon Oxide Surfaces Using Self‐Assembled Monolayers

Although a molecular monolayer is only a few nanometers thick it can completely change the properties of a surface. Molecular monolayers can be readily prepared using the Langmuir-Blodgett methodology or by chemisorption on metal and oxide surfaces. This Review focuses on the use of chemisorbed self-assembled monolayers (SAMs) as a platform for the functionalization of silicon oxide surfaces. The controlled organization of molecules and molecular assemblies on silicon oxide will have a prominent place in "bottom-up" nanofabrication, which could revolutionize fields such as nanoelectronics and biotechnology in the near future. In recent years, self-assembled monolayers on silicon oxide have reached a high level of sophistication and have been combined with various lithographic patterning methods to develop new nanofabrication protocols and biological arrays. Nanoscale control over surface properties is of paramount importance to advance from 2D patterning to 3D fabrication.