Microcontact Printing Of Self-assembled Monolayers Research Articles

Inkjet and microcontact printing of functional materials on foil for the fabrication of pixel-like capacitive vapor microsensors

The work presented demonstrates the utilization of micro-contact printing of self-assembled monolayers (SAMs) of gold nanoparticles (NPs) to pattern the porous thin metallic film composing the top electrode of an ultra-fast capacitive relative humidity sensor based on miniaturized parallel-plates electrodes. The rest of the device, which occupies an area of only 0.0314mm2, is fabricated by inkjet printing stacked individual drops of functional materials, namely gold NPs for the bottom electrode and a polymeric humidity sensing layer, on a polymeric foil. Compared to other printing methods, the use of microcontact printing to pattern the top electrode enables the additive transfer of a solvent-free metallic layer that does not interact chemically with the sensing layer, permitting the thinning of the latter without risk of short-circuits between electrodes, and broadening the range of usable sensing materials for detection of other gases. Thinning the sensing layer yields to ultra-fast response devices with high values of capacitance and sensitivity per surface area. The fabrication process is compatible with low heat-resistant polymeric substrates and scalable to large-area and large-scale fabrication, foreseeing the development of low-cost vapor sensing sheets with high space–time resolution, where every sensor would correspond to a pixel of a large array.

Anomalous uniform domain in a twisted nematic cell constructed from micropatterned surfaces

We have discovered an optically uniform type of domain that occurs in twisted nematic (TN) cells that are constructed from substrates chemically patterned with stripes via microcontact printing of self-assembled monolayers; such domains do not occur in TN cells constructed from uniform substrates. In such a cell, the azimuthal anchoring at the substrates is due to the elastic anisotropy of the liquid crystal rather than the conventional rubbing mechanism. A model is presented that predicts the relative stability of the twisted and anomalous states as a function of the material and design parameters.

Engineering the Microstructure of Organic Energetic Materials

The initiation sensitivity is highly dependent on void structures within an energetic material. It is technically feasible to modify the initiation sensitivity by lithographically defining the size and distribution of included voids on the micro- and nanoscale. We proposed a method to pattern organic energetic materials using microcontact printing of self-assembled monolayers. Pentaerythritol tetranitrate is spin-coated from solution as films onto patterned self-assembled monolayers. Images are presented for arbitrary patterns created based on the surface chemistry and concentration of the energetic material.

Microcontact printing of self-assembled monolayers to pattern the light-emission of polymeric light-emitting diodes

By patterning a self-assembled monolayer (SAM) of thiolated molecules with opposing dipole moments on a gold anode of a polymer light-emitting diode (PLED), the charge injection and, therefore, the light-emission of the device can be controlled with a micrometer-scale resolution. Gold surfaces were modified with SAMs based on alkanethiols and perfluorinated alkanethiols, applied by microcontact printing, and their work functions have been measured. The molecules form a chemisorbed monolayer of only ∼1.5 nm on the gold surface, thereby locally changing the work function of the metal. Kelvin probe measurements show that the local work function can be tuned from 4.3 to 5.5 eV, which implies that this anode can be used as a hole blocking electrode or as a hole injecting electrode, respectively, in PLEDs based on poly(p-phenylene vinylene) (PPV) derivatives. By microcontact printing of SAMs with opposing dipole moments, the work function was locally modified and the charge injection in the PLED could be controlled down to the micrometer length scale. Consequently, the local light-emission exhibits a high contrast. Microcontact printing of SAMs is a simple and inexpensive method to pattern, with micrometer resolution, the light-emission for low-end applications like static displays.

Submicron-scale manipulation of phase separation in organic solar cells

This paper describes a method for controlling the submicron-scale phase separation of poly(3-hexylthiophene) and (6,6)-phenyl-C61-butyric acid methyl ester in organic solar cells. Using microcontact printing of self-assembled monolayers on the device buffer layer to divide the surface into two regimes having different surface energies, an interdigitated structure aligned vertical to the substrate surface is achieved after spontaneous surface-directed phase separation. The power conversion efficiency increases upon decreasing the grating spacing, reaching 2.47%. The hole mobility increased as a consequence of improved polymer chain ordering, resulting in higher device efficiency, while smaller pattern sizes were used.

Micro- and Nano-Patterned Substrates to Manipulate Cell Adhesion

Cell adhesion to material surfaces regulates host responses to implanted biomaterials and the performance of cell arrays and biotechnological cell culture supports. Therefore, the engineering of substrates that control cell adhesive interactions is critical to the development of bio-interactive interfaces and biotechnological culture supports. We describe the application of advanced fabrication techniques to engineer substrates with well defined chemistry and topography to manipulate cell adhesive interactions. Microcontact printing of self-assembled monolayers and hot embossing imprint lithography approaches were integrated to manipulate focal adhesion assembly, cell adhesion, and cellular spreading and alignment. These micro- and nanopatterned substrates provide useful tools for the analyses of structure-function relationships in adhesive interactions.

Organic selective-area patterning method for microlens array fabrication

Refractive microlens arrays (MLAs) are widely used in many electro-optical devices due to their high performance and low optical loss. To fabricate a microlens array effectively, we have proposed a novel fabrication method based on a selective-area patterning method. The surface properties of glass substrates were defined as either hydrophilic or hydrophobic regions by microcontact printing of self-assembled monolayers (SAMs). Consequently, the microlens arrays were self-organized on the hydrophilic regions after the lens materials were nozzle-spread followed by UV curing. As a result, we have demonstrated microlenses with 50, 75, and 100 μm footprints, and f numbers as low as 5.4. The focused spot size of the 50 μm lens was 9.82 μm, which is near the diffraction limit. The optical measurement shows excellent light collecting efficiency of a microlens array, which is suitable for many electro-optical applications. Furthermore, all fabrication steps can be accomplished in ambient environment and at room temperature. It is anticipated that the present proposed method has great potential for mass production.

Gas sensing properties of ZnO thin films prepared by microcontact printing

In situ patterned zinc oxide (ZnO) thin films were prepared by precipitation of Zn(NO 3) 2/urea aqueous solution and by microcontact printing of self-assembled monolayers (SAMs) on Al/SiO 2/Si substrates. The visible precipitation of Zn(OH) 2 from the urea containing Zn(NO 3) 2 solution was enhanced by increasing the reaction temperature and the amount of urea. The optimized condition for the ZnO thin films was found to be the Zn(NO 3) 2/urea ratio of 1/8, the precipitation temperature of 80 °C, the precipitation time of 1 h and the annealing temperature of 600 °C, respectively. SAMs are formed by exposing Al/SiO 2/Si to solutions comprising of hydrophobic octadecylphosphonic acid (OPA) in tetrahydrofuran and hydrophilic 2-carboxylethylphosphonic acid (CPA) in ethanol. The ZnO thin film was then patterned with the heat treatment of Zn(OH) 2 precipitated on the surface of hydrophilic CPA. The ZnO gas sensor was exposed to different concentrations of C 3H 8 (5000 ppm), CO (250 ppm) and NO (1000 ppm) at elevated temperatures to evaluate the gas sensitivity of ZnO sensors. The optimum operating temperatures of C 3H 8, CO and NO gases showing the highest gas sensitivity were determined to be 350, 400 and 200 °C, respectively.

Electrochemical Patterning of Copper Using Microcontact Printing

This paper demonstrates that micropatterns of copper films can be fabricated by selective electrochemical etching of copper using microcontact printing of self-assembled monolayers (SAMs). The elastomeric stamps which have microstructures on their surfaces are made out of polydimethylsiloxane and then are inked with a solution of an alkanethiol in ethanol. SAMs of alkanethiol are patterned on the copper films by contacting stamps with the substrates. The patterned substrates are etched electrochemically in an electrolyte. SAMs of alkanethiol act as an electrochemical barrier leading to selective etching of copper films. Microstructures of copper with dimensions as small as 1.5 μm have been produced using this procedure. This method shows the capability of fabricating simple structures on a scale comparable to UV photolithography which produces printed circuits of copper for the semiconductor industry. © 2004 The Electrochemical Society. All rights reserved.

Concentration dependence in microcontact printing of self-assembled monolayers (SAMs) of alkanethiols

This communication discusses the electrochemical assessment of self-assembled monolayers (SAMs) formed via microcontact printing with various concentrations of 1-hexadecanethiol (HDT) ink. At concentrations above 20 mM, the printed SAMs are shown to have very similar qualities to those formed from solution using much longer preparation procedures.

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.

Creating Microstructures of Luminescent Organic Thin Films Using Layer-by-Layer Assembly

Ultrathin film devices is one of the aims for the layer-by-layer assembly of charged species. These authors have used microcontact printing of self-assembled monolayers to pattern a ruthenium-based luminescent dye system on a surface (see the optical micrograph shown in the Figure). Hydrogen bonding and hydrophobic interactions are revealed to be critical to the selectivity of this process.

Versatile patterning process for semiconductors based on microcontact printing

A new patterning process based on the microcontact printing of self-assembled monolayers on gold is presented. The method is readily adapted to processes utilising standard optical or electron beam resists, and is fully compatible with industrial semiconductor fabrication technology. The process can also be applied to surfaces which exhibit extreme nonplanarity such as sharp edges of mesas or etch grooves.

Micropatterned surfaces for control of cell shape, position, and function.

The control of cell position and function is a fundamental focus in the development of applications ranging from cellular biosensors to tissue engineering. Using microcontact printing of self-assembled monolayers (SAMs) of alkanethiolates on gold, we manufactured substrates that contained micrometer-scale islands of extracellular matrix (ECM) separated by nonadhesive regions such that the pattern of islands determined the distribution and position of bovine and human endothelial cells. In addition, the size and geometry of the islands were shown to control cell shape. Traditional approaches to modulate cell shape, either by attaching suspended cells to microbeads of different sizes or by plating cells on substrates coated with different densities of ECM, suggested that cell shape may play an important role in control of apoptosis as well as growth. Data are presented which show how micropatterned substrates were used to definitively test this hypothesis. Progressively restricting bovine and human endothelial cell extension by culturing cells on smaller and smaller micropatterned adhesive islands regulated a transition from growth to apoptosis on a single continuum of cell spreading, thus confirming the central role of cell shape in cell function. The micropatterning technology is therefore essential not only for construction of biosurface devices but also for the investigation of the fundamental biology of cell-ECM interactions.

Microcontact printing of self-assembled monolayers: applications in microfabrication

This paper describes applications in microfabrication using patterned self-assembled monolayers (SAMs) formed by microcontact printing. Microcontact printing is a flexible new technique that forms patterned SAMs with regions terminated by different chemical functionalities (and thus different physical and chemical properties), in patterns with dimensions. Patterns of SAM are formed using an alkanethiol as an `ink', and printing the alkanethiol on a metal support with elastomeric `stamp'. We fabricate the stamp by moulding a silicone elastomer using a master prepared by optical or x-ray microlithography or by other techniques. SAMs of long-chain alkanethiolates on gold and other metals can act as nanometer resists by protecting the supporting metal from corrosion by appropriately formulated etchants: the fabrication of microstructures of gold and silicon demonstrates the utility of patterned SAMs (formed by ) as nm resists. Patterned SAMs formed by can also control the wettability of a surface on the scale. The organization of liquids in patterned arrays with dimensions, and the patterned deposition of microcrystals and microcrystal arrays illustrate the use of controlled wettability for microfabrication.

Patterning of dielectric oxide thin layers by microcontact printing of self-assembled monolayers

This communication describes a technique used to pattern oxide thin layers using microcontact printing (μCP) and sol-gel deposition. The technique involves μCP of self-assembled monolayers (SAM's) of alkylsiloxane on various substrates (SiO2/Si, sapphire, ITO, and glass), followed by deposition of oxide thin layers from sol-gel precursors. Delamination of oxide layers from SAM-derivatized regions allows selective deposition of crystalline dielectric oxide layers on underivatized regions. To demonstrate the viability of this technique for integrated microelectronics and optics applications, patterned (Pb,La)TiO3 (PLT) and LiNbO3 layers were deposited on sapphire, silicon, and indium tin oxide (ITO) substrates. Use of lattice-matched substrates allows lithography-free deposition of patterned heteroepitaxial oxide layers. Strip waveguides of heteroepitaxial LiNbO3 with 4 μm lateral dimensions were fabricated on sapphire. Dielectric measurements for patterned PLT thin layers on ITO are also reported.