Lithographic Patterning Techniques Research Articles

Defined Transfer of Colloidal Particles by Electrochemical Microcontact Printing

AbstractSoft lithography, in particular microcontact printing (µCP), represents a well‐established and widespread class of lithographic patterning techniques. It is based on a directed deposition of molecules or colloidal particles by a transfer process with a micro‐structured stamp. A critical aspect of µCP is the adhesion cascade that enables the directed transfer of the objects. Here, the interfacial properties of a µCP‐stamp are tuned electrochemically to modify the adhesion cascade. During the printing process, the µCP‐stamp is submerged in an electrolyte solution and acted as a working electrode whose surface properties depended on the externally applied potential, thus enabling in situ rapid switching of its adhesion properties. As a proof of principle, defined particle patterns are selectively removed from a monolayer of colloidal particles. The adhesion at the particle/solid interface and the transfer mechanisms are determined by using the colloidal probe technique based on atomic force microscopy (AFM). In this case, a single particle is brought into contact with an electrode with the same surface chemistry as the µCP‐stamp. Hence, it became possible to determine the electrochemical potential ranges suitable to establish an adhesion cascade.

Shape control in 2D molecular nanosheets by tuning anisotropic intermolecular interactions and assembly kinetics

Since molecular materials often decompose upon exposure to radiation, lithographic patterning techniques established for inorganic materials are usually not applicable for the fabrication of organic nanostructures. Instead, molecular self-organisation must be utilised to achieve bottom-up growth of desired structures. Here, we demonstrate control over the mesoscopic shape of 2D molecular nanosheets without affecting their nanoscopic molecular packing motif, using molecules that do not form lateral covalent bonds. We show that anisotropic attractive Coulomb forces between partially fluorinated pentacenes lead to the growth of distinctly elongated nanosheets and that the direction of elongation differs between nanosheets that were grown and ones that were fabricated by partial desorption of a complete molecular monolayer. Using kinetic Monte Carlo simulations, we show that lateral intermolecular interactions alone are sufficient to rationalise the different kinetics of structure formation during nanosheet growth and desorption, without inclusion of interactions between the molecules and the supporting MoS2 substrate. By comparison of the behaviour of differently fluorinated molecules, experimentally and computationally, we can identify properties of molecules with regard to interactions and molecular packing motifs that are required for an effective utilisation of the observed effect.

Nanolithographic Fabrication Technologies for Network-Based Biocomputation Devices.

Network-based biocomputation (NBC) relies on accurate guiding of biological agents through nanofabricated channels produced by lithographic patterning techniques. Here, we report on the large-scale, wafer-level fabrication of optimized microfluidic channel networks (NBC networks) using electron-beam lithography as the central method. To confirm the functionality of these NBC networks, we solve an instance of a classical non-deterministic-polynomial-time complete ("NP-complete") problem, the subset-sum problem. The propagation of cytoskeletal filaments, e.g., molecular motor-propelled microtubules or actin filaments, relies on a combination of physical and chemical guiding along the channels of an NBC network. Therefore, the nanofabricated channels have to fulfill specific requirements with respect to the biochemical treatment as well as the geometrical confienement, with walls surrounding the floors where functional molecular motors attach. We show how the material stack used for the NBC network can be optimized so that the motor-proteins attach themselves in functional form only to the floor of the channels. Further optimizations in the nanolithographic fabrication processes greatly improve the smoothness of the channel walls and floors, while optimizations in motor-protein expression and purification improve the activity of the motor proteins, and therefore, the motility of the filaments. Together, these optimizations provide us with the opportunity to increase the reliability of our NBC devices. In the future, we expect that these nanolithographic fabrication technologies will enable production of large-scale NBC networks intended to solve substantially larger combinatorial problems that are currently outside the capabilities of conventional software-based solvers.

Integration of on-chip perovskite nanocrystal laser and long-range surface plasmon polariton waveguide with etching-free process.

Perovskite materials prepared in the form of solution-processed nanocrystals and used in top-down fabrication techniques are very attractive to develop low-cost and high-quality integrated optoelectronic circuits. Particularly, integrated miniaturized coherent light sources that can be connected to light-guiding structures on a chip are highly desired. To control light propagating on a small footprint with low-loss optical modes, long-range surface plasmon polariton (LRSPP) waveguides are employed. Herein, we demonstrate an on-chip fabricated photonic-plasmonic hybrid system consisting of a perovskite lasing structure coupled to an LRSPP waveguide achieving a low lasing threshold and a propagation length over 100 μm. Preventing perovskite material degradation and the formation of surface roughness of the laser cavity during fabrication is made possible by designing a fabrication technique without any etching step.

Self‐Healing Lithographic Patterning of Perovskite Nanocrystals for Large‐Area Single‐Mode Laser Array

AbstractLead halide perovskites exhibit extraordinary optoelectronic performances and are being considered as a promising medium for high‐quality photonic devices such as single‐mode lasers. However, for perovskite‐based single‐mode lasers to become practical, fabrication and integration on a chip via the standard top‐down lithography process are strongly desired. The chief bottleneck to achieving lithography of perovskites lies in their reactivity to chemicals used for lithography as illustrated by issues of instability, surface roughness, and internal defects with the fabricated structures. The realization of lithographic perovskite single‐mode lasers in large areas remains a challenge. In this work, a self‐healing lithographic patterning technique using perovskite CsPbBr3 nanocrystals is demonstrated to realize high‐quality and high‐crystallinity single‐mode laser arrays. The self‐healing process is compatible with the standard lithography process and greatly improves the quality of lithographic laser cavities. A single‐mode microdisk laser array is demonstrated with a low threshold of 3.8 µJ cm−2. Moreover, the control of the lasing wavelength is made possible over a range of up to 6.4 nm by precise fabrication of the laser cavities. This work presents a general and promising strategy for standard top‐down lithography fabrication of high‐quality perovskite devices and enables research on large‐area perovskite‐based integrated optoelectronic circuits.

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.

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.

Printing-Assisted Surface Modifications of Patterned Ultrafiltration Membranes.

Understanding and restricting microbial surface attachment will enhance wastewater treatment with membranes. We report a maskless lithographic patterning technique for the generation of patterned polymer coatings on ultrafiltration membranes. Polyethylene glycol, zwitterionic, or negatively charged hydrophilic polymer compositions in parallel- or perpendicular-striped patterns with respect to feed flow were evaluated using wastewater. Membrane fouling was dependent on the orientation and chemical composition of the coatings. Modifications reduced alpha diversity in the attached microbial community (Shannon indices decreased from 2.63 to 1.89) which nevertheless increased with filtration time. Sphingomonas species, which condition membrane surfaces and facilitate cellular adhesion, were depleted in all modified membranes. Microbial community structure was significantly different between control, different patterns, and different chemistries. This study broadens the tools for surface modification of membranes with polymer coatings and for understanding and optimization of antifouling surfaces.

Ferromagnetic resonance in a topographically modulated permalloy film

A major focus within the field of magnonics involves the manipulation and control of spin-wave modes. This is usually done by patterning continuous soft magnetic films. Here, we report on work in which we use topographic modifications of a continuous magnetic thin film, rather than lithographic patterning techniques, to modify the ferromagnetic resonance spectrum. To demonstrate this technique we have performed in-plane, broadband, ferromagnetic resonance studies on a 100-nm-thick permalloy film sputtered onto a colloidal crystal with individual sphere diameters of 200 nm. Effects resulting from the, ideally, sixfold-symmetric underlying colloidal crystal were studied as a function of the in-plane field angle through experiment and micromagnetic modeling. Experimentally, we find two primary modes; the ratio of the intensities of these two modes exhibits a sixfold dependence. Detailed micromagnetic modeling shows that both modes are quasiuniform and nodeless in the unit cell but that they reside in different demagnetized regions of the unit cell. Our results demonstrate that topographic modification of magnetic thin films opens additional directions for manipulating ferromagnetic resonant excitations.

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.

Topography-controlled alignment of DNA origami nanotubes on nanopatterned surfaces

The controlled positioning of DNA nanostructures on technologically relevant surfaces represents a major goal along the route toward the full-scale integration of DNA-based materials into nanoelectronic and sensor devices. Previous attempts to arrange DNA nanostructures into defined arrays mostly relied on top-down lithographic patterning techniques combined with chemical surface functionalization. Here we combine two bottom-up techniques for nanostructure fabrication, i.e., self-organized nanopattern formation and DNA origami self-assembly, in order to demonstrate the electrostatic self-alignment of DNA nanotubes on topographically patterned silicon surfaces. Self-organized nanoscale ripple patterns with periodicities ranging from 20 nm to 50 nm are fabricated by low-energy ion irradiation and serve as substrates for DNA origami adsorption. Electrostatic interactions with the charged surface oxide during adsorption direct the DNA origami nanotubes to the ripple valleys and align them parallel to the ripples. By optimizing the pattern dimensions and the Debye length of the adsorption buffer, we obtain an alignment yield of ∼70%. Since this novel and versatile approach does not rely on any chemical functionalization of the surface or the DNA nanotubes, it can be applied to virtually any substrate material and any top-down or bottom-up nanopatterning technique. This technique thus may enable the wafer-scale fabrication of ordered arrays of functional DNA-based nanowires.

Self‐Organization of Inkjet‐Printed Organic Semiconductor Films Prepared in Inkjet‐Etched Microwells

AbstractThe high‐precision deposition of highly crystalline organic semiconductors by inkjet printing is important for the production of printed organic transistors. Herein, a facile nonconventional lithographic patterning technique is developed for fabricating banks with microwell structures by inkjet printing solvent droplets onto a polymer layer, thereby locally dissolving the polymer to form microwells. The semiconductor ink is then inkjet‐printed into the microwells. In addition to confining the inkjet‐printed organic semiconductor droplets, the microwells provide a platform onto which organic semiconductor molecules crystallize during solvent evaporation. When printed onto the hydrophilic microwells, the inkjet‐printed 6,13‐bis(triisopropylsilylethynyl) pentacene (TIPS_PEN) molecules undergo self‐organization to form highly ordered crystalline structures as a result of contact line pinning at the top corner of the bank and the outward hydrodynamic flow within the drying droplet. By contrast, small crystallites form with relatively poor molecular ordering in the hydrophobic microwells as a result of depinning of the contact line along the walls of the microwells. Because pinning in the hydrophilic microwells occurred at the top corner of the bank, treating the surfaces of the dielectric layer with a hydrophobic organic layer does not disturb the formation of the highly ordered TIPS_PEN crystals. Transistors fabricated on the hydrophilic microwells and the hydrophobic dielectric layer exhibit the best electrical properties, which is explained by the solvent evaporation and crystallization characteristics of the organic semiconductor droplets in the microwell. These results indicate that this technique is suitable for patterning organic semiconductor deposits on large‐area flexible substrates for the direct‐write fabrication of high‐performance organic transistors.

Optically rewritable patterns of nuclear magnetization in gallium arsenide

The control of nuclear spin polarization is important to the design of materials and algorithms for spin-based quantum computing and spintronics. Towards that end, it would be convenient to control the sign and magnitude of nuclear polarization as a function of position within the host lattice. Here we show that, by exploiting different mechanisms for electron-nuclear interaction in the optical pumping process, we are able to control and image the sign of the nuclear polarization as a function of distance from an irradiated GaAs surface. This control is achieved using a crafted combination of light helicity, intensity and wavelength, and is further tuned via use of NMR pulse sequences. These results demonstrate all-optical creation of micron scale, rewritable patterns of positive and negative nuclear polarization in a bulk semiconductor without the need for ferromagnets, lithographic patterning techniques, or quantum-confined structures.

The Development of Anodic Aluminum Oxide Based Micro-channel Plate for Large-area Photo-detector

ABSTRACTAnodized Aluminum Oxide (AAO) based micro-channel plates (MCP) are fabricated in order to develop economical large-area photodetectors. Commercially available glass capillary array has a limitation to reach channel diameter below ~10 microns. However, smaller channel diameter is desired for better spatial and fast timing resolution. AAO based MCP is a good candidate to produce channel diameter less than 10 um by taking advantage of the nano-scale intrinsic pores during etching process. In this study, various channel diameters are fabricated with use of lithographic patterning techniques and wet etching; and characterized with optical, atomic force, and scanning electron microscopies. The channel diameter, channel length and related aspect ratio, as well as the open area are varied in order to maximize the MCP photon amplification.

Edge Transfer Lithography Using Alkanethiol Inks

Edge lithographic patterning techniques are based on the utilization of the edges of micrometer-sized template features for the reproduction of submicrometer structures. Edge transfer lithography (ETL) permits local surface modification in a single step by depositing self-assembled monolayers onto a metal substrate selectively along the feature edges of an elastomeric stamp. In this report two stamp designs are described that now allow for the use of alkanethiol inks in ETL and their use as etch resists to reproduce submicrometer structures in gold. Anisotropically modified stamps are shown to combine the potential for very high-resolution patterning with the versatility and simplicity of microcontact printing.

Enhanced molecular patterning via microdisplacement printing

Here we demonstrate the versatility of “microdisplacement printing,” a soft lithographic patterning technique that employs microcontact printing to replace pre-formed self-assembled monolayers (SAMs) selectively. We use molecules that are common in microcontact printing as well as low-molecular-weight molecules that cannot be patterned by traditional methods. Multiple component SAMs were fabricated by additional processing steps, extending microdisplacement printing to more complex patterns.

Masterless Soft Lithography: Patterning UV/Ozone−Induced Adhesion on Poly(dimethylsiloxane) Surfaces

A novel microreactor-based photomask capable of effecting high resolution, large area patterning of UV/ozone (UVO) treatments of poly(dimethylsiloxane) (PDMS) surfaces is described. This tool forms the basis of two new soft lithographic patterning techniques that significantly extend the design rules of decal transfer lithography (DTL). The first technique, photodefined cohesive mechanical failure, fuses the design rules of photolithography with the contact-based adhesive transfer of PDMS in DTL. In a second powerful variation, the UVO masks described in this work enable a masterless soft lithographic patterning process. This latter method, UVO-patterned adhesive transfer, allows the direct transfer of PDMS-based polymer microstructures from a slab of polymer to silicon and other material surfaces. Both methods exploit the improved process qualities that result from the use of a deuterium discharge lamp to affect the UVO treatment to pattern complex, large area PDMS patterns with limiting feature sizes extending well below 1 microm (> or = 0.3 microm). The use of these structures as resists is demonstrated for the patterning of metal thin films. A time-of-flight secondary ion mass spectroscopy study of the process provides new insights into the mechanisms that contribute to the chemistry responsible for the interfacial adhesion of DTL transfers.

Electroactive polymer patterns with metal incorporation on a polymeric substrate

AbstractElectroactive polymer patterns on a polymeric substrate were fabricated using either a UV lithographic approach or plasma polymerization method. For the lithographic patterning technique, photosensitive thin films comprising polyaniline (PANI) coatings on viologen‐grafted low‐density polyethylene (LDPE) substrates were first prepared. The composite film was subsequently exposed to UV irradiation through a mask. Under UV irradiation, reactions between PANI and viologen occurred, resulting in the conversion of the PANI to a doped state. The PANI micropatterns were developed by using N‐methylpyrrolidinone (NMP) to dissolve the soluble‐unexposed (and hence undoped) parts. The use of Ar plasma treatment of the composite film instead of UV irradiation was not successful in inducing the doping reaction between PANI and viologen. On the other hand, plasma polymerization was shown to be another convenient way for the selective surface deposition of aniline polymer on the surface of the LDPE substrate through a mask. The further incorporation of metal/metal ions in both the PANI‐viologen and plasma polymerized aniline system was successfully carried out on the micropatterns. Polym. Eng. Sci. 44:2061–2069, 2004. © 2004 Society of Plastics Engineers.

Fabrication of Pt−Si Schottky Diodes Using Soft Lithographic Patterning and Selective Chemical Vapor Deposition

This work demonstrates the feasibility of using soft lithographic patterning in conjunction with additive metallization to fabricate micron-scale electronic devices. Specifically, the fabrication of platinum/platinum silicide/silicon Schottky diodes is demonstrated using a unique combination of soft lithographic patterning and additive metallization techniques. The diode architecture provides a useful means through which to demonstrate the specific characteristics and general utility of this fabrication technique. A 30 × 10 array of micron-scale diode features was patterned on a silicon substrate using a polymeric film prepared by micromolding in capillaries (MIMIC), a soft lithographic patterning technique. Following etching to remove oxide from the substrate surface, metallization by selective platinum chemical vapor deposition (CVD) was used to form rectifying contacts to the substrate. The polymeric film successfully served both as an oxide etch resist before metallization and as a deposition-inhibiti...

Magnetic force microscopy of single-domain single-crystal iron particles with uniaxial surface anisotropy

Lithographic patterning techniques have been used to fabricate arrays of submicron particles from a [110] single-crystal iron thin film with a strong uniaxial surface anisotropy and with an easy axis of magnetization lying in the [001] direction (in the plane of the film). Magnetic force microscopy images indicate that these islands are single domain over a wide range of island shapes and sizes. The uniaxial surface anisotropy is stronger than the shape anisotropy for the island geometries used, so the easy axes of the islands all lie roughly in the [001] direction, regardless of the island shape. Magnetic force images were also taken as both the magnetic tip and sample were subjected to a gradually increasing externally applied field. This technique allows us to monitor the magnetization reversal of individual islands and provides a direct measure of their switching fields.