Fabrication of a carbon-nanotube-based field-effect transistor by microcontact printing

The fabrication of a field-effect transistor with both channel material and source and drain electrodes made from carbon nanotubes (CNTs) through patterned deposition of CNT films by microcontact printing is described. Surfactant-dispersed single-walled CNTs are first separated into semiconducting and metallic fractions by gel filtration. The semiconducting and metallic CNTs are then sequentially transferred by dendrimer-coated polydimethylsiloxane stamps onto dendrimer-coated silicon wafers following a printing protocol optimized for this purpose. The resulting CNT micropatterns are visualized by atomic force microscopy. Semiconducting as well as metallic CNTs preserve their characteristic electronic properties within the transferred films. A device composed of a rather thick (ca. 5 nm) and densely patterned film of metallic CNTs cross-printed on top of a thinner (ca. 1.5 nm) and less dense film of semiconducting CNTs shows the typical properties of a field-effect transistor with the metallic CNT stripes as electrodes, the semiconductive CNT stripes as channel material, and the silicon substrate as gate electrode.     

Advances in single-molecule magnet surface patterning through microcontact printing

We present an implementation of strategies to deposit single-molecule magnets (SMMs) using microcontact printing microCP). We describe different approaches of microCP to print stripes of a sulfur-functionalized dodecamanganese (III, IV) cluster on gold surfaces. Comparison by atomic force microscopy profile analysis of the patterned structures confirms the formation of a chemically stable single layer of SMMs. Images based on chemical contrast, obtained by time-of-flight secondary ion mass spectrometry, confirm the patterned structure.     

Subwavelength surface-relief gratings fabricated by microcontact printing of self-assembled monolayers

We have designed and tested subwavelength diffractive optical elements consisting of surface-relief gratings made by microcontact printing of self-assembled monolayers. The first device is a beam deflector for 1.55-mum operation consisting of a surface-relief grating made up of eight pillars over one period (9.3 mum) of the grating. The widths of the pillars vary to approximate a linear phase profile within each grating period. The second device is a quarter-wave plate for 632.8-nm operation consisting of a subwavelength surface-relief grating with a 300-nm period and 58% duty cycle.     

Biomimetic micropatterning of silica by surface-initiated polymerization and microcontact printing

Micropatterns of silica on a gold substrate were generated by a biomimetic approach, namely, the biosilicification of silicic acids. The procedure consists of three simple steps: pattern generation of a polymerization initiator, (BrC(CH(3))(2)COO(CH(2))(11)S)(2), by microcontact printing; surface-initiated, atom-transfer radical polymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA) from the patterned area; and polycondensation of silicic acids. The tertiary amine-containing polymer, pDMAEMA, aided in the spatially controlled polycondensation of silicic acids on surfaces in the presence of phosphate ions, and micropatterns of silica on a gold substrate were successfully generated in combination with the technique of microcontact printing. The procedure could be extended to the controlled fabrication of silica patterns with any size, shape, or thickness.     

Pattern formation of cytochrome c by microcontact printing and dip-pen nanolithography

We report the results of fabricating micrometer and submicrometer-scale patterns of cytochrome c on gold surfaces. We used direct micro-contact printing (μCP) and indirect dip-pen nanolithography (DPN) for fabricating cytochrome c arrays. The protein dots were formed in diameters of 2 μm by μCP and of ∼200 nm by DPN, respectively. We analyzed the pattern size and height of protein arrays with atomic force microscopy (AFM). We expect that these methods will be potentially useful for developing small-scale biosensors and protein chip microarrays.     

Tip‐mould microcontact printing for functionalisation of optical microring resonator

We present an approach to functionalise optical microring resonators as hybridisation platforms, using tip‐mould reactive microcontact printing process. Derived from reactive microcontact printing using an ad hoc mould of polydimethylsiloxane (PDMS), the method functionalises single microring resonator with a target‐specific capture agent. The authors report the functionalisation of silicon nitride (SiN) 200μm diameter microring resonator with single‐strand DNA and the hybridisation detection of 100 nM target analyte, while concurrently monitoring not‐functionalised microring as a control sensor. Results show that the functionalisation approach permits to address single microring resonators with mutual distance lower than 100μm with high precision, enabling a better integration of multiple spotting zones on the chip concerning traditional functionalisation procedures.Inspec keywords: DNA, molecular biophysics, biosensors, microsensors, optical resonators, microcavities, soft lithography, polymers, silicon compounds, integrated optics, optical sensors, micro‐opticsOther keywords: tip‐mould reactive microcontact printing, optical microring resonator, hybridisation platforms, polydimethylsiloxane, PDMS, target‐specific capture agent, single‐strand DNA, hybridisation detection, multiple spotting zones, chip, size 200 mum, SiN     

Micropatterning of Ag and Au nanoparticles by microcontact printing and block copolymer micelles

Micropatterns of gold and silver nanoparticles were successfully obtained by combining microcontact printing and poly(2-vinylpyridine)-block-poly(cyclohexyl metharylate) (P2VP-b-PCHMA) diblock copolymer micelles with metal precursors. The metal ions were incorporated into poly(2-vinylpyridine) blocks and located into the core area of micelles. Then the metal-loaded micellar solutions were used as inks which were spin coated as thin layers onto polydimethylsiloxane stamps and transferred onto the substrates by stamping. Different morphologies of micellar aggregates were formed on the substrates depending on the stamp morphologies, and single layers of nanoparticles in the micropattern were obtained by the reducing process.     

Micropatterning of emitting layers by microcontact printing and application to organic light-emitting diodes

The microcontact printing (μCP) technique, which is a simple and low damage fabrication technique for thin films, was successfully applied to fabricate patterned emitting layers such as polyfluorene (PF). We fabricated micropatterns by transferring dried and uniform thin films, and observed strong electroluminescence (EL) from the fabricated organic light-emitting diodes (OLEDs) with the patterned emitting layers. The performance of the fabricated device was superior to that of a conventionally fabricated device. This demonstrates the well-controlled interfaces achieved by μCP. Furthermore, we succeeded in fabricating OLEDs with multiple emitting layers. These results show that this technique is promising for application to cost-effective, high luminance and multicolored OLED displays.     

Co-patterning chitosan and bovine serum albumin on an aldehyde-enriched glass substrate by microcontact printing

Chitosan and bovine serum albumin were co-patterned onto a glass substrate by microcontact printing technique. The process uses a microfabricated polydimethylsiloxane stamp to transfer chitosan on an aldehyde functionalized glass substrate, followed by adding a drop of albumin solution to the patterned side and holding for 30 min. After being washed with phosphate-buffered saline and cleaned by ultrasonic, the co-patterns of chitosan and albumin, each with their own micropatterns, were formed on the same surface. In this procedure, ultrasonic cleaning takes an important role to obtain clear patterns, whereas the printing/adding sequence has less influence. Moreover, patterns printed could give higher contrast than those assembled from solution. These co-patterns could find applications in cell localization and cell growth guidance.     

Controlling orientation of V(2)O(5) nanowires within micropatterns via microcontact printing combined with the gluing Langmuir-Blodgett technique

Previously, we suggested a facile method to transfer dioctadecyldimethylammonium bromide (DODAB)/V(2)O(5) nanowire hybrid patterns onto both hydrophobic and hydrophilic substrates via microcontact printing combined with the Langmuir-Blodgett (LB) technique (Park et al 2007 Nanotechnology 18 405301). Herein, we report on the delicate control of the orientation of V(2)O(5) nanowires within the micropatterns transferred via the gluing LB technique using a patterned polydimethylsilicate (PDMS) stamp. According to the orientation of the PDMS line patterns relative to the air-water interface, the aligned orientation of the nanowires, either parallel or perpendicular to the patterns, could be obtained and attributed to the moving direction of the water menisci formed between the PDMS stamp and water. In particular, addition of a small amount of ethanol in the subphase enhanced the dispersion of the DODAB at the air-water interface as well as the aggregation of V(2)O(5) nanowires, resulting in alignment of the V(2)O(5) nanowires via compression of the hybrid LB film by a barrier. Directional alignment of nanowires has potentially broad applications in the fabrication of aligned nanowire devices.     

Ambient ammonia production via electrocatalytic nitrite reduction catalyzed by a CoP nanoarray

Industrial-scale ammonia(NH₃)production mainly relies on the energy-intensive and environmentally unfriendly Haber-Bosch process.Such issue can be avoided by electrocatalytic N₂ reduction which however suffers from limited current efficiency and NH3 yield.Herein,we demonstrate ambient NH₃ production via electrochemical nitrite(NO₂^-)reduction catalyzed by a CoP nanoarray on titanium mesh(CoP NA/TM).When tested in 0.1 M PBS(pH=7)containing 500 ppm N0₂^-,such CoP NA/TM is capable of affording a large NH₃ yield of 2,260.7±51.5μg·h^-1·cm^-2 and a high Faradaic efficiency of 90.0±2.3%at-0.2 V vs.a reversible hydrogen electrode.Density functional theory calculations reveal that the potential-determining step for NO₂^-reduction over CoP(112)is*NO2→*NO₂H.     

Multiwalled carbon-nanotube-functionalized microelectrode arrays fabricated by microcontact printing: platform for studying chemical and electrical neuronal signaling

A facile method is proposed for the deposition of multiwalled carbon nanotube (MWCNT) layers onto microelectrode arrays by means of a microcontact printing technique, leading to the fabrication of MEAs characterized by well defined electrical and morphological properties. Using polydimethyl siloxane stamps, produced from different mold designs, a flexibility of printing is achieved that provides access to microscale, nanostructured electrodes. The thickness of MWCNT layers can be exactly predetermined by evaluating the concentration of the MWCNT solution employed in the process. The electrode morphology is further characterized using laser scanning and scanning electron microscopy. Next, by means of impedance spectroscopy analysis, the MWCNT-electrode contact resistance and MWCNT film resistance is measured, while electrochemical impedance spectroscopy is used to estimate the obtained electrode-electrolyte interface. Structural and electrochemical properties make these electrodes suitable for electrical stimulation and recording of neurons and electrochemical detection of dopamine. MWCNT-functionalized electrodes show the ability to detect micromolar amounts of dopamine with a sensitivity of 19 nA μm(-1) . In combination with their biosensing properties, preliminary electrophysiological measurements show that MWCNT microelectrodes have recording properties superior to those of commercial TiN microelectrodes when detecting neuronal electrical activity under long-term cell-culture conditions. MWCNT-functionalized microelectrode arrays fabricated by microcontact printing represent a versatile and multipurpose platform for cell-culture monitoring.     

Selective atomic layer deposition of metal oxide thin films on patterned self-assembled monolayers formed by microcontact printing

We demonstrate a selective atomic layer deposition of TiO2, ZrO2, and ZnO thin films on patterned alkylsiloxane self-assembled monolayers. Microcontact printing was done to prepare patterned monolayers of the alkylsiloxane on Si substrates. The patterned monolayers define and direct the selective deposition of the metal oxide thin films using atomic layer deposition. The selective atomic layer deposition is based on the fact that the metal oxide thin films are selectively deposited only on the regions exposing the silanol groups of the Si substrates because the regions covered with the alkylsiloxane monolayers do not have any functional group to react with precursors.     

Synthesis of flexible magnetic nanowires of permanently linked core-shell magnetic beads tethered to a glass surface patterned by microcontact printing

We have developed an efficient, one-step method to create magnetic nanowires consisting of permanently linked chains of magnetic beads of varying flexibility tethered to a patterned glass surface using simple amidation chemistry. The flexibility of the nanowire was governed by the molecular weight of the molecule used to covalently link the beads and its length by the height of the microchannel in which it was synthesized. The nanowire diameter was determined both by the bead size and by the number of beads adhering to each dot in the microstamped, patterned array. Longer nanowires can form loops attached at two points on the glass surface. Both single flexible chains and flexible loops can adopt different configurations (straight, hairpin, S-shaped, etc.) when subjected to magnetic fields, the configurations depending on the directions of these fields. Shorter, less flexible nanowires align with the field always and do not exhibit the more exotic configurations seen for long, flexible chains and loops. These magnetic nanowires can have potential use in microfluidic pumping and mixing processes and in microparticle manipulation.     

Interstitial elements created via metal 3D printing

3D printing of metals, such as laser powder bed fusion (LPBF) printing of stainless steels, often leads to elevated oxygen content in the alloy substrate relative to conventional processing routes. Here we show that the extremely rapid cooling rate (10⁶–10⁷ K/s) during LPBF processing of austenitic stainless steel can trap a considerable fraction of oxygen and other elements in the interstitial sites of the metal lattice, at concentrations far exceeding the room temperature solubilities. High resolution characterization and atomistic simulations with density functional theory reveal that oxygen and other elements exist in octahedral interstitial sites of the metal lattice and bond with their neighboring metal atoms. Our findings suggest that additive manufacturing can be a potential strategy of incorporating beneficial interstitial elements into a metal substrate. Given the well-known effect of interstitial elements in conventional alloys, significant improvement of the physicochemical properties of printed alloys is possible.