Two photon photopolymerization (2PP) is a new and modern method in solid freeform fabrication. 2PP allows the fabrication of sub-micron structures from a photopolymerizable resin. By the use of near-infrared (NIR) lasers it is possible to produce 3D structures with a spatial feature resolution as good as 200 nm. This technique can be used in polymer-based photonic and micro-electromechanical systems (MEMS), for 3D optical data storage or for the inscription of optical waveguides based on a local refractive index change upon laser exposure. Since the 2PP only takes place inside the focus of the laser beam, complex 3D-structures can be in-scri-bed into a suitable matrix material.

In the presented work, 2PP is used to write optical waveguides into a prefabricated mechanically flexible polydimethylsiloxane matrix. The waveguides were structured by selectively irradiating a polymer network, which was swollen by a monomer mixture. The monomer was polymerized by two photon photopolymerization and the uncured monomer was removed by evaporation at elevated temperatures. This treatment led to a local change in refractive index in the order of Δn = 0.02, which was significantly above the industrial requirement of Δn = 0.003. The measured optical losses were around 2.3dB/cm. Since all unreacted monomers were removed by eva-po-ration, the final waveguide was stable up to temperatures of more than 200°C.

In a second approach highly porous sol-gel materials (based on tetramethoxysilane (TMOS) as precursor and the surfactant cetylpyridinium chloride monohydrate as structural temp-late) were utilized as matrix materials. The precursor was organically modified with poly(ethylene glycol) spacers in order to increase the toughness and thus facilitate the fabrication of transparent porous monoliths and flexible films. The pores of the sol-gel-derived matrix were filled with acrylate-based monomers of high refractive index and after selective irradiation using 2PP waveguides (Δn = 0.015) could be written into the material.

We investigate a method for non-contact patterning of molten polymer nanofilms based on thermocapillary modulation. Imposed thermal distributions along the surface of the film generate spatial gradients in surface tension. The resulting interfacial stresses are used to shape and mold nanofilms into 3D structures, which rapidly solidify when cooled to room temperature. Finite element simulations of the evolution of molten shapes illustrate how this technique can be used to fabricate features of different heights and separation distances in a single process step. These results provide useful guidelines for controlling proximity effects during evolution of adjacent structures.

We have developed manufacturable approaches to form single, vertically aligned carbon nanotubes, where the tubes are centered precisely, and placed within a few hundred nm of 1-1.5 m deep trenches. These wafer-scale approaches were enabled by chemically amplified resists and inductively coupled Cryo-etchers for forming the 3D nanoscale architectures. The tube growth was performed using dc plasma-enhanced chemical vapor deposition (PECVD), and the materials used for the pre-fabricated 3D architectures were chemically and structurally compatible with the high temperature (700 C) PECVD synthesis of our tubes, in an ammonia and acetylene ambient. Tube characteristics were also engineered to some extent, by adjusting growth parameters, such as Ni catalyst thickness, pressure and plasma power during growth. Such scalable, high throughput top-down fabrication techniques, combined with bottom-up tube synthesis, should accelerate the development of PECVD tubes for applications such as interconnects, nano-electromechanical (NEMS), sensors or 3D electronics in general.

The development of new optimized photoinitiators for the two-photon induced photopolymerization (TPIP) is essential in order to obtain high resolutions in this solid freeform fabrication process. Herein, we present the syntheses and characterizations of a series of efficient photoinitiators, comprising of a cross conjugated D-π-A-π-D system. The different donor- and acceptor functionalities of the investigated photoinitiators as well as the synthesis of targeted derivatives containing double and triple bonds in the conjugated backbone allowed the evaluation of structure-activity relationships. The basic photophysical properties as well as the activity and ideal processing window under TPIP conditions were investigated for each initiator and compared with typical commercially available one-photon initiator and with two highly potential initiators well known from literature. These tests figured out that the new chromophores are highly potential even at concentrations down to 0.05 wt%.

Organic light emitting material direct writing is demonstrated based on nanomaterial enabled laser transfer. Through utilization of proper nanoparticle size and type, and the laser wavelength choice, a single laser pulse could transfer well defined and arbitrarily shaped tris-(8-hydroxyquinoline)Al patterns ranging from several microns to millimeter size. The unique properties of nanomaterials allow laser induced forward transfer at low laser energy (0.05 J/cm2) while maintaining good fluorescence. The technique may be well suited for the mass production of temperature sensitive organic light emitting devices.

The combined effects of melting temperature depression, lower conductive heat transfer loss, strong absorption of the incident laser beam, and relatively weak bonding between nanoparticles during laser irradiation result in the transfer of patterns with very sharp edges at relatively lower laser energy than commonly used, thus inducing minimal damage to the target organic light emitting diode material with no evidence of cracks. This technique can be applied to a broad range of laser wavelengths with proper selection of nanoparticle size and size distribution, as well as the material type. Additionally, nanomaterial enabled laser transfer may be particularly advantageous for the mass production of temperature sensitive devices.

Single-chamber micro solid oxide fuel cells (SC-μSOFCs) with coplanar electrodes were fabricated using a robotically controlled direct-write microfabrication approach. Viscoelastic, gel-based inks were employed to create homogeneous electrodes of controlled width and interelectrode distance as well as uniform cross-sectional thickness. Electrode powders, NiO-YSZ (yttria-stabilized zirconia) for the anode and (La0.8Sr0.2)0.98MnO3-YSZ for the cathode, were first dispersed with a cationic polyethyleneimine solution. Polyacrylic acid was added to induce a fluid-to-gel transition. The rheology of the fabricated inks was characterized. The inks were then extruded through cylindrical micronozzles and deposited onto YSZ electrolyte substrates using a robotic deposition apparatus. Thickness and width of the sintered electrodes were close to the diameter of the extrusion nozzle. The improved shape retention of the deposited electrodes also enabled the fabrication of continuous electrodes with square cross-section. The cathode adhered very well to the electrolyte during sintering. However, the mismatch between the thermal expansion coefficient of anode and electrolyte seems to cause detaching and breaking of the anode so that electrochemical characterization of the fabricated cells was not yet possible.

This proceeding discusses recent progress on engineered fluidic surface-tension-directed self-assembly involving liquid solder. The process is applied to the assembly of discrete inorganic semiconductor device components at different length scales producing electrically interconnected devices and systems. Prior results include assembly with unique angular orientation and contact pad registration, parallel packaging, and the programmable assembly of various types of light emitting diodes. Recent progress on the scaling of the minimal die size from 300 to 30 μm is discussed which required the development of a new delivery system to concentrate and effectively introduce the components to solder-based receptors. Specifically, components are pre-oriented at a liquid-air or liquid-liquid interface and transferred onto the solder based receptors using a dynamic contact angle with a dipping process. Recent applications include the tiling of curved and 3D surfaces with single crystal semiconductors including the formation of flexible 3D solar cells.

A theoretical study of resolution in nanoimprint lithography (NIL) has been carried out using molecular dynamics (MD) simulation. We have performed a MD simulation for glass NIL, monitored the friction force during entire NIL process and evaluated the deformed shapes of glass patterns after the mold releasing. The resolution in NIL is governed by the maximum tensile stress acting on the glass, which is induced by the friction force during the mold releasing. Based on the distribution of average number density of atoms in the molded glass, the ultimate resolution in the glass NIL has been proved to be 0.4 nm.

We demostrate an advanced precision cutting tool using a 349 nm nanosecond-pulsed UV laser micromachining setup. After expansion and collimation, the laser beam is directed vertically and focused with a high performance triplet lens. With an Al mirror inserted in the path of the convergent beam, the beam can be focused on a horizontal machining plane at any desired tilting angles. Microstructures of a wide range of geometries on hard materials can be formed using this custom machining method. Conventional linear and rotary machining on sapphire materials have been demonstrated.

We have grown tree-like vertically-aligned carbon nanotubes (CNTs) on silicon substrate, suitable for highly sensitive interdigital capacitive sensors. As an application, we present a sensitive pressure sensor with branched CNTs as its capacitance plates.

After realization of the interdigital structure, the growth of CNTs has been achieved through direct-current plasma enhanced chemical vapor deposition (DC-PECVD) method. A sequential growth and hydrogenation has led to the formation of multiple branched structures of nanotubes. The growth of tree-like CNTs on the interdigitally patterned substrate results in a high overlap between adjacent fingers and consequently a significant response to mechanical variations of the membrane as a result of the applied pressure.