Stamping Technique Research Articles

Pollen-imprinted polyurethanes for QCM allergen sensors

Molecularly imprinted polymers for detecting plant pollen were designed as artificial recognition materials for quartz crystal microbalances in the gaseous phase. Imprints of birch (diameter, 25 mum) and nettle (diameter, 15 mum) pollen can be generated by polydimethylsiloxane stamping technique as proven by atomic force microscopy. If pollen grains are able to access the cavities and thus are incorporated, the resulting sensors display Sauerbrey-like negative frequency shifts. Non-Sauerbrey behaviour can be observed as soon as pollen is prevented from entering the selective hollows: this results in grain mobility on the electrode surface leading to frequency increases. Access to the cavities is determined by the diameter ratio between pollen grains and imprints as can be revealed during cross-selectivity measurements of nettle and birch pollen imprinted layers. When the amount of pollen grains on the electrode surface exceeds the number of available imprints, the excess particles move freely, resulting in positive, non-Sauerbrey frequency shifts.

Patterning of HeLa Cells on a Microfabricated Au-Coated ITO Substrate

HeLa cells were patterned on a microfabricated Au-coated ITO substrate. Part of the Au film was dissolved by the electrochemical wet stamping technique, and the substrate was then immersed in a thiol-terminated methoxy-poly(ethylene glycol) (mPEG-SH) solution for further modification. Self-assembled monolayers (SAMs) on the gold island can form cell- and protein-resistant regions on the substrate, and living HeLa cells can adhere to the exposed ITO surface. Single cell patterns could be achieved when the size of a microstructure unit matched that of the cell. The fluorescence experiments further proved that living HeLa cells prefer to attach to the ITO substrate rather than the mPEG-SH-modified gold islands.

Fabrication of multilayer organic solar cells through a stamping technique

In this article, we demonstrate a simple and reliable stamping technique for fabricating multi-layer solar cells. A poly(di-methylsilane) (PDMS) stamp is used for transferring the active layers onto the substrate. An intermediate solvent treatment is introduced to temporarily modify the PDMS surface; therefore, the polymer film can be uniformly formed on top of the PDMS surface. This method is involves non-contaminative and non-invasive processes, therefore it can avoid possible degradation or contamination of the polymer film and the PDMS stamp can be reused. Devices realized through this stamping technique both by direct and inverted structures exhibited power conversion efficiencies of 3.2 and 2.83% respectively.

Mechanism of Reactive Wetting and Direct Visual Determination of the Kinetics of Self-Assembled Monolayer Formation

Reactive wetting (RW) of alkane thiols and disulfides on gold is studied experimentally using the wet stamping technique. Theoretical description based on Langevin dynamics is developed to explain the experimental results and to clarify the physical processes underlying RW. In this description, thermal fluctuations of the three-phase contact line combine with the surface reaction to gradually build a low-energy self-assembled monolayer (SAM) onto which the front propagates. The results of the model match the experiments and allow determination of the kinetic rate constants of SAM formation.

Single Molecular Stamping of a Sub-10-nm Colloidal Quantum Dot Array

We introduce a nanoscale stamping technique of sub-10-nm colloidal quantum dot (QD) arrays to highly localized areas of three-dimensional nanostructures using a quartz tuning fork employed as the stamp pad (the "Nano Stamp"). CdSe/ZnS core-shell nanoparticles with diameters of 9.8 nm were deposited on microfabricated silicon probe tips. The number of transferred QDs, which ranged from several thousands down to single molecular order (less than 10), was precisely controlled by adjusting the stamping depths and angles. The stamping areas were varied from 1.2 microm x 1.2 microm down to 30 nm x 30 nm. Using the Nano Stamp, QDs can be transferred to a variety of protruding nanostructures. The amount of particles transferred to the tip was assessed by fluorescence intensity measurements, and the number of particles was estimated by direct transmission electron microscopy (TEM) observation. Correlation between the fluorescence intensity and the observed stamping depth and the approaching angle of the tip was found, demonstrating the efficacy of our Nano Stamp technique.

On-Chip, Cell-Based Microarray Immunofluorescence Assay for High-Throughput Analysis of Target Proteins

We have developed an immunofluorescence-based assay for high-throughput analysis of target proteins on a three-dimensional cellular microarray platform. This process integrates the use of three-dimensional cellular microarrays, which should better mimic the cellular microenvironment, with sensitive immunofluorescence detection and provides quantitative information on cell function. To demonstrate this assay platform, we examined the accumulation of the alpha subunit of the hypoxia-inducible factor (HIF-1alpha) after chemical stimulation of human pancreatic tumor cells encapsulated in 3D alginate spots in volumes as low as 60 nL. We also tested the effect of the known dysregulator of HIF-1alpha, 2-methoxyestradiol (2ME2), on the levels of HIF-1alpha using a dual microarray stamping technique. This chip-based in situ Western immunoassay protocol was able to provide quantitative information on cell function, namely, the cellular response to hypoxia mimicking conditions and the reduction of HIF-1alpha levels after cell treatment with 2ME2. This system is the first to enable high-content screening of cellular protein levels on a 3D human cell microarray platform.

Organic thin film transistors and polymer light-emitting diodes patterned by polymer inking and stamping

To fully realize the advantages of organic flexible electronics, patterning is very important. In this paper we show that a purely additive patterning technique, termed polymer inking and stamping, can be used to pattern conductive polymer PEDOT and fabricate sub-micron channel length organic thin film transistors. In addition, we applied the technique to transfer a stack of metal/conjugated polymer in one step and fabricated working polymer light-emitting devices. Based on the polymer inking and stamping technique, a roll-to-roll printing for high throughput fabrication has been demonstrated. We investigated and explained the mechanism of this process based on the interfacial energy consideration and by using the finite element analysis. This technique can be further extended to transfer more complex stacked layer structures, which may benefit the research on patterning on flexible substrates.

Catalytic combustion as a synthesis tool for micropatterned carbon materials

Abstract There is an extensive literature on the catalysis of carbon combustion by finely divided metals. Under some conditions a high degree of catalytic enhancement is observed, and the accelerated carbon consumption occurs in the immediate vicinity of the catalyst particle. These observations suggest that catalytic combustion could be used as a tool for shape control or micropattern formation in carbon materials, in which molecular oxygen serves as a “dry” etchant acting selectively on catalyst particles positioned by controlled metal deposition. This study uses carbon thin films and liquid-phase catalyst deposition as a model material and reaction system for a proof-of-principle demonstration of this new concept. A polydimethylsiloxane stamping technique is used to transfer metal chloride solutions onto carbon thin films in the form of ordered droplet microarrays that dry to produce catalytic micropatches. Controlled combustion at 400 °C selectively etches the carbon in the catalyst-doped regions to reveal the underlying quartz substrate in a predefined circle micropattern. This study focuses on catalyst selection, drying behavior, pattern resolution, feature fidelity, and etchant selectivity ratio, and the results are used to discuss the further potential for catalytic combustion synthesis and shape control.

Particle Assembly on Patterned Surfaces Bearing Circular (Dots) and Rectangular (Stripes) Surface Features

Irreversible and localized adsorption of spherical particles on surface features of various shapes (collectors) was studied using the random sequential adsorption (RSA) model. Collectors in the form of dots and rectangles were considered, including the two limiting cases of squares and stripes. Numerical simulation of the Monte Carlo type enabled one to determine particle configurations, average coverage of particles, and the distribution for various collector length to particle size ratios L = L/d and collector width to particle size ratios B = b/d. It was predicted that particle coverage under the jamming state was highly nonuniform, exhibiting a maximum at the center and at the periphery of the collectors. The averaged number of particles Np adsorbed at the jamming state was also determined as a function of the L and B parameters, as well as the averaged number of particles per unit length in the case of stripes. It was revealed that Np was the highest for the circular and square collectors (for a fixed value of L). On the other hand, for L > 5, our numerical results could be well approximated by the analytical expressions Np = thetainfinityL2 for circles, Np = 4thetainfinityL2/pi for squares, Np = 4thetainfinityBL/pi for rectangles, and Np = 4thetainfinityB/pi for stripes (per unit length). It was demonstrated that the theoretical results are in agreement with experimental data obtained for latex particles adsorbing on patterned surfaces obtained by a polymer-on-polymer stamping technique of gold covered silicon and on photolitographically patterned silane layers on silica.

Contact Printing Beyond Surface Roughness: Liquid Supramolecular Nanostamping

Liquid supramolecular nanostamping (LiSuNS) is an efficient stamping technique that replicates various DNA features with no need of solid surface contact. LiSuNS is based on the specific interaction of complementary DNA strands. An original pattern composed of multiple DNA strands on a rough surface can be copied onto a liquid prepolymer that is subsequently hardened, leading to a solid surface that displays the mirror image of the master used.

Irreversible Adsorption of Particles on Surface Features of a Circular and Rectangular Shape

The irreversible adsorption of spherical particles on surface features of various shapes (collectors) was studied using the Random Sequential Adsorption (RSA) model. Collectors in the form of circles and rectangles were considered, including the limiting cases of squares. Numerical simulation of the Monte Carlo type enabled the particle configurations to be determined, together with their density distribution (coverage) and the saturation coverage for various collectors to particle size ratio L̅ = L/2a and collector width to particle size ratio b̅ = b/2a. An unexpected feature found in these calculations was that the local coverage distribution of adsorbed particles was highly non-uniform, exhibiting a maximum at the centre and at the periphery of these collectors. The main finding of these calculations was the averaged number of particles <Np> adsorbed at the saturation state on collectors as a function of the L̅ and b̅ parameters. It was revealed that <Np> was highest for the square collector (for a fixed value of L̅). For L̅ > 5, our numerical results could be well approximated by the analytical expression <Np> = Θ∞ L̅2 for circles, <Np> = 4Θ∞ L̅2π for squares and <Np> = Θ∞ b̅L̅2/π for rectangles. It was demonstrated that the theoretical results are in an agreement with experimental data obtained for latex particles adsorbed onto patterned surfaces obtained by a polymer-on-polymer stamping technique for gold-covered silicon and on photolithographically-patterned silane layers on silica.

Micropatterning metal electrode of organic light emitting devices using rapid polydimethylsiloxane lift-off

The authors demonstrate a subtractive stamping technique for patterning metal electrodes of organic light emitting devices. Patterning is achieved by placing a relief patterned polydimethylsiloxane stamp in contact with a planar metal electrode film and subsequently peeling off the stamp. A fast peel rate increases the weak adhesion energy of the stamp to the metal so that no surface treatment, pressure, or temperature control is necessary to lift-off the metal film in contact with the stamp. Patterning is dependent on metal film thickness, geometry of the features, and peel direction of stamp release. The minimum feature size patterned is 13μm wide stripes within <1μm in-plane edge roughness and 0.1μm height transition region of the patterned edge.

Electrical Readouts of Single and Few Molecule Systems in Metal-Molecule-Metal Device Structures

Electrical conduction through molecular junctions are measured in different local environments through two test beds that are ideal for single/few molecule and molecular monolayer systems. A technique has been developed to realize Au films with approximately 1.5 A surface roughness comparable to the best available techniques and suitable for formation of patterned device structures. The technique utilizes room temperature e-beam evaporated Au films over oxidized Si substrates silanized with (3-mercaptopropyl)trimethoxysilane (MPTMS). The lateral (single/few molecule) and vertical (many molecules) device structures are both enabled by the process for realizing ultraflat Au layer. Lateral metal-molecule-metal (M-M-M) device structures are fabricated by forming pairs of Au electrodes with nanometer separation (nano-gap) through an electromigration-induced break-junction (EIBJ) technique at room temperature and conductivity measurements are carried out for dithiol functionalized single molecules. We have used the flat Au layer (using the current technique) as the bottom contact in vertical M-M-M device structures. Here, molecular self-assembly are formed on the Au surface, and patterned (20 x 20 microm2) top Au contacts were successfully transferred on to the device using a stamping technique (where the Au is deposited on a polydimethylsiloxane (PDMS) pad and following a physical contact on the thiolated Au layer). The single molecular property of XYL, a highly conductive molecule and many molecular property of HS-C9-SH, an insulating molecule in its molecular monolayer form are measured. Observation of enhanced conduction following molecular deposition, and comparison of conductance-voltage characteristics to those predicted theoretically, confirms the success of trapping single/few molecules in the nano-gap. The observed approximately 10(2) less conductance through the molecular monolayer of HS-C9-SH compared to the estimation of a linear sum of single molecule conductances over large area indicate that either all the molecules are not in physical contact with the top stamping electrode or electrode-molecule coupling has a less broadening in presence of it own environment or both.

Particle Assembly on Surface Features (Patterned Surfaces)

Irreversible adsorption (deposition) of spherical particles on surface features of various shapes (collectors) was studied using the random sequential adsorption (RSA) model. The collectors in the form of linear line segments, semicircles, and circles were considered. Numerical simulation of the Monte Carlo type enabled one to determine particle configurations, the jamming coverage, and the end to end length of particle monolayers for various collector length (L) to particle size (d) ratio L = L/d. It was revealed that the jamming coverage for linear collectors Theta'(infinity) increases for L > 2 according to a linear dependence with respect to 1/L. For 2 > L > 1, a parabolic dependence of Theta'(infinity) on 1/L was predicted, characterized by the maximum value of Theta'(infinity) = 1.125 for L = 4/3. These dependencies allowed one to formulate an equation determining the length of nanostructures on surfaces if the averaged number of adsorbed particles is known. It was also predicted that the end to end length of the monolayer on a linear collector <L(e)>/L increased linearly with 1/L for L > 2. For 2 > L > 1 the dependence of <L(e)>/L on L was approximated by a polynomial expression, exhibiting a maximum of <L(e)>/L = 1.17 for L = 1.45. In the case of circular collectors, the jamming coverage was found to be substantially smaller for the same value of 1/L. It was demonstrated that the theoretical results are in agreement with our preliminary experimental data obtained for latex particles adsorbing on polyelectrolyte modified mica and on patterned surfaces obtained by a polymer-on-polymer stamping technique of gold covered silicon (Zheng et al. Langmuir 2002, 18, 4505).

Platinum-plated nanoporous gold: An efficient, low Pt loading electrocatalyst for PEM fuel cells

Platinum-plated nanoporous gold leaf (Pt-NPGL) is made by coating a conformal, atomically thin skin of platinum over the high surface area pores of a thin membrane of nanoporous gold. Because Pt loading in Pt-NPGL can be controlled down to 0.01 mg cm −2 using only simple benchtop chemistry, the material holds promise as a low Pt loading, carbon-free electrocatalyst. Here, we report successful use of Pt-NPGL as a catalyst in proton exchange membrane (PEM) fuel cells. Stable and high performance Pt-NPGL/Nafion membrane electrode assemblies (MEAs) were made using a stamping technique. The performance of Pt-NPGL MEAs is comparable to conventional carbon-supported nanoparticles-based MEAs with much higher loading, generating an output power density of up to 4.5 kW g −1 Pt in our non-optimized test configuration. Correlations between the performance of Pt-NPGL MEAs, the electrochemically accessible surface area, and material microstructure are discussed. Our success in using Pt-NPGL as a fuel cell catalyst suggests that creating precious metals skins over nanoporous metal supports is a viable strategy for designing new catalysts for PEM fuel cells. This promising approach allows tailoring catalytic activity by engineering precious metal/substrate interactions, employs materials with dual functionality acting both as current collector and catalyst, and may avoid the sintering problems plaguing conventional nanoparticle-based catalysts.

Localized Chemical Wave Emission and Mode Switching in a Patterned Excitable Medium

Chemical waves are initiated from complex geometries in the excitable Belosouv-Zhabotinsky medium using a wet stamping technique. Because of the coupling between the system's chemical kinetics and geometry, waves are emitted only from selected locations. By varying the nature of the wave-triggering reagent (here formaldehyde or methanol), it is possible to switch between two spatially distinct modes of wave emission. The system's dynamics is studied numerically, and the results of modeling agree with experimental observations.

Application of electromagnetic-assisted stamping (EMAS) technique in incremental sheet metal forming

The application of high velocity electromagnetic-assisted stamping (EMAS) technique in incremental sheet metal forming has been proposed. EMAS whose principle is based on Lorenz force is a hybrid forming process that uses both quasi-static conventional stamping technique and electromagnetic forming actuators built into sharp corners and other difficult-to-form contours to form metals. The recent push to use more artificial intelligent (AI) aluminum alloys in automobile and aircraft industries as a result of increasing demand for fuel efficient cars and aircrafts, large size vehicle panels, improved formability limit of materials and weight reduction have placed EMAS as one of the best high velocity forming technique. It is believed that the end result of this vision will lead to more cost effective land and aerospace vehicles.

Isolated, sealed nanofluidic channels formed by combinatorial-mould nanoimprintlithography

We present a new approach for fabricating isolated, sealed, high-density nanofluidic channelarrays using combinatorial-mould nanoimprint lithography. This method provides adirected stamping technique for fabricating micro- to nanoscale channel arrays from thesimple combination of two grating moulds of the proper geometry. In this method, a thinpolymer film is cast on a silicon grating mould and subsequently embossed with a secondgrating mould. The film, after it is patterned on both sides, is then stamped onto asubstrate and etched with oxygen plasma to remove the suspended residue layer and isolatethe nanochannels. We have successfully fabricated arrays of high-density nanochannels onsilicon and indium tin oxide glass (ITO glass) with well-controlled dimensions(i.e. 250 nm square, in cross-section). Placing a nanochannel array in contact with anaqueous fluorescein solution fills the channels by capillary action, and the integrityof the seal formed by the nanochannel enclosures was verified by observing asignificant contrast in the photobleaching rate under fluorescence microscopy.

Micron-scale organic thin film transistors with conducting polymer electrodes patterned by polymer inking and stamping

We report organic thin film transistors (OTFTs) with conductive polymer poly (3,4-ethylenedioxythiophene)/poly(4-styrenesulphonate) (PEDOT) electrodes that are fabricated by a simple polymer inking and stamping technique. An OTFT channel length of 2μm has been achieved. This patterning technique is a purely additive process, which does not affect the functionality of the conductive polymers, and is fully compatible for patterning on a flexible substrate. Electrical characteristics of top contact (TC) pentacene TFTs with PEDOT electrodes is superior to those with gold electrodes due to a lower carrier injection barrier. Extracted contact resistance shows that the channel length of TC OTFTs can be further reduced to increase the drain current.

Stamping with high information density

Supramolecular NanoStamping (SuNS) is a newly developed stamping technique that enables the transfer of spatial together with chemical information from a master containing DNA features to a secondary substrate. Here we discuss the importance and implications of a stamping technique with high information density.