Towards Multi-Level Modeling of Self-Assembling Intelligent Micro-Systems

We investigate and model the dynamics of two-dimensional stochastic self-assembly of intelligent micro-systems with minimal requirements in terms of sensing, actuation, and control. A microscopic agent-based model accounts for spatiality and serves as a baseline for assessing the accuracy of models at higher abstraction level. Spatiality is relaxed in Monte Carlo simulations, which still capture the binding energy of each individual aggregate. Finally, we introduce a macroscopic model that only keeps track of the average number of aggregates in each energy state. This model is able to quantitatively and qualitatively predict the dynamics observed at lower, more detailed modeling levels. Since we investigate an idealized system, thus making very few assumptions about the exact nature of the final target system, our framework is potentially applicable to a large body of self-assembling agents ranging from functional micro-robots endowed with simple sensors and actuators to elementary microfabricated parts. In particular, we show how our suite of models at different abstraction levels can be used for optimizing both the design of the building blocks and the control of the stochastic process

Nanopatterned Self-Assembled Monolayers by Using Diblock Copolymer Micelles as Nanometer-Scale Adsorption and Etch Masks

Nanopatterned self-assembled monolayers (SAMs) are obtained from a simple, straight-forward procedure by using masks derived from monolayers of block copolymer micelles. The nanopatterned SAMs consist of regularly spaced circular hydrophilic areas with diams. of approx. 60 nm on a continuous hydrophopic background or vice versa. The surfaces are shown to be excellent tools for the prepn. of arrays of nanocrystal

Stenciled conducting bismuth nanowires

Stencil lithography is used here for the fabrication of bismuth nanowires using thermal evaporation. This technique provides good electrical contact resistance by having the nanowire structure and the contact pads deposited at the same time. It has also the advantage of modulating nanowires' height as a function of their width. As the evaporated material deposits on the stencil mask, the apertures shrink in size until they are fully clogged and no more material can pass through. Thus, the authors obtain variable-height (from 27 to 95 nm) nanowires in the same evaporation. Upon their morphological (scanning electron microscopy and atomic force microscopy) and electrical characterizations, the authors obtain their resistivity, which is independent of the nanowire size and is the lowest reported for physical vapor deposition of Bi nanowires (1.2×10−3 Omega cm), only an order of magnitude higher than that of bulk bismuth

Analysis of the blurring in stencil lithography

A quantitative analysis of the blurring and its dependence on the stencil-substrate gap and the deposition parameters in stencil lithography, a high resolution shadow mask technique, is presented. The blurring is manifested in two ways: first, the structure directly deposited on the substrate is larger than the stencil aperture due to geometrical factors, and second, a halo of material is formed surrounding the deposited structure presumably due to surface diffusion. The blurring is studied as a function of the gap using dedicated stencils that allow a controlled variation of the gap. Our results show a linear relationship between the gap and the blurring of the directly deposited structure. In our configuration, with a material source of ~5 mm and a source-substrate distance of 1 m, we extract that ~10 micrometers of gap enlarge the directly deposited structures by ~50 nm. The measured halo varies from 0.2 to 3 micrometers in width depending on the gap, the stencil aperture size and other deposition parameters. We also show that the blurring can be reduced by decreasing the nominal deposition thickness, the deposition rate and the substrate temperature

Organic Thin Film Transistors on Flexible Polyimide Substrates Fabricated by Full Wafer Stencil Lithography

This paper presents new results on miniaturized organic thin film transistors (TFT) fabricated on a spin coated polyimide (PI) film. Patterning steps, that are vital for the integrity and electrical performances of the organic TFT, were performed using resistless shadow-mask lithography with two high precision MEMS fabricated stencils, thus avoiding solvents and high temperature processes. Both pentacene and source-drain (S/D) electrodes were directly patterned through stencils with high accuracy on wafer scale. The TFT have been characterized before and after peeling the flexible PI film off the rigid surface, showing full transistor functionality in both cases

Characterization of Ferrofluid-Based Stimuli-Responsive Elastomers

Stimuli-responsive materials undergo physicochemical and/or structural changes when a specific actuation is applied. They are heterogeneous composites, consisting of a non-responsive matrix where functionality is provided by the filler. Surprisingly, the synthesis of polydimethylsiloxane (PDMS)-based stimuli-responsive elastomers (SRE) has seldomly been presented. Here, we present the structural, biological, optical, magnetic, and mechanical properties of several magnetic SRE (M-SRE) obtained by combining PDMS and isoparafin-based ferrofluid (FF). Independently of the FF concentration, results have shown a similar aggregation level, with the nanoparticles mostly isolated (>60%). In addition to the superparamagnetic behavior, the samples show no cytotoxicity except the sample with the highest FF concentration. Spectral response shows FF concentrations where both optical readout and magnetic actuation can simultaneously be used. The Young’s modulus increases with the FF concentration until the highest FF concentration is used. Our results demonstrate that PDMS can host up to 24.6% FF (corresponding to 2.8% weight of Fe3O4 nanoparticles concentration). Such M-SRE are used to define microsystems – also called soft microsystems due to the use of soft materials as main mechanical structures. In that scenario, a large displacement for relatively low magnetic fields (<0.3 T) is achieved. The herein presented M-SRE characterization can be used for a large number of disciplines where magnetic actuation can be combined with optical detection, mechanical elements, and biological sample

Reusability of nanostencils for the patterning of Aluminum nanostructures by selective wet etching

One of the major advantages of stencil lithography is the possibility to use stencils many times. However, when stencils contain nanoapertures, the clogging of the membranes limits the useful life time of the stencils. The clogging is due to the accumulation of material deposited inside the apertures of the stencil. Here, we report a study on the effect of the clogging on the life time of stencils after Al depositions through the stencils. Then we present a method to clean the stencils based on Al wet etching to eliminate the clogging. We show that this method allows the reusability of stencils for the repeatable depositions of Al nanostructures

Double-gate pentacene thin-film transistor with improved control in sub-threshold region

In this work double-gate pentacene TFT architecture is proposed and experimentally investigated. The devices are fabricated on a polyimide substrate based on a process that combines three levels of stencil lithography with standard photolithography. Similarly to the operation of a conventional double-gate silicon FET, the top-gate bias modulates the threshold voltage of the bottom-gate transistor and significantly improves the transistor sub-threshold swing and leakage current. Moreover, the double gate TFT shows good promise for the enhancement of I-ON/I-OFF, especially by the control of I-OFF in devices with poor top interfaces. (C) 2010 Elsevier Ltd. All rights reserved