Supramolecular approach to new inkjet printing inks

Electronically complementary, low molecular weight polymers that self-assemble through tunable π−π stacking interactions to form extended supramolecular polymer networks have been developed for inkjet printing applications and successfully deposited using three different printing techniques. Sequential overprinting of the complementary components results in supramolecular network formation through complexation of π-electron rich pyrenyl or perylenyl chain-ends in one component with π-electron deficient naphthalene diimide residues in a chain-folding polyimide. The complementary π−π stacked polymer blends generate strongly colored materials as a result of charge-transfer absorption bands in the visible spectrum, potentially negating the need for pigments or dyes in the ink formulation. Indeed, the final color of the deposited material can be tailored by varying the end-groups of the π-electron rich polymer component. Piezoelectric printing techniques were employed in a proof of concept study to allow characterization of the materials deposited, and a thermal inkjet printer adapted with imaging software enabled in situ analysis of the ink drops as they formed and of their physical properties. Finally, continuous inkjet printing allowed greater volumes of material to be deposited, on a variety of different substrate surfaces, and demonstrated the utility and versatility of this novel type of ink for industrial applications

Laser-assisted chemical liquid-phase deposition of metals for micro- and optoelectronics

Abstract The demands toward the development of simple and cost-effective fabrication methods of metallic structures with high lateral resolution on different substrates - applied in many fields of technology, such as in microelectronics, optoelectronics, micromechanics as well as in sensor and actuator applications - gave the idea to perform this research. Due to its simplicity, laser-assisted chemical liquid-phase deposition (LCLD) has been investigated and applied for the metallization of surfaces having practical importance (Si, GaAs, SiO2, Si3N4, etc.) since the beginning of the 80s. By the invention of novel substrates (polyimide, porous silicon), it was adequate to work out new precursors or just adopt old ones and optimise LCLD in order to fabricate metallic micro-patterns upon these materials for various purposes. According to the motivations mentioned above, LCLD was utilized for the fabrication of palladium (Pd) micro-patterns on polyimide (PI), polyimide/copper flexible printed circuit boards (PCBs), fused silica (SiO2) and silicon (Si). The selective metallization of porous silicon (PS) has been carried out with nickel (Ni). Depending on the types of lasers, either the focusing (Ar+ laser beam) or diaphragm projection (KrF and XeCl excimer laser pulses) method was employed. In the course of the work, various precursors of the corresponding metals have been investigated and utilized. In the beginning, the pyrolytic decomposition of palladium-amine complex ions ([Pd(NH3)4]2+) on PI by a scanned and focused Ar+ laser beam was optimised and discussed. Thick (up to several micrometers) and narrow (~ 10 μm) Pd conductor lines with electrical conductivity close to that of the bulk were obtained. In the continuation of these investigations, the precursor was developed further. [Pd(NH3)4]2+ was mixed with the solution of formaldehyde (HCOH) in order to induce the reduction of the metal complex ions. To our knowledge, we were the first - so far - who applied this solution and described the reaction. With the proper choice of the laser parameters, thin Pd films as catalyst layers for electroless copper plating were deposited utilizing Ar+ and excimer lasers as well. The chemically plated copper deposits - upon the obtained Pd film - have excellent electrical and good mechanical properties. In the second part of the thesis, three practical applications (metallization of via holes drilled in PI/Cu flexible PCBs, end-mirror fabrication on single-mode optical fibers, and carbon nanotube growth on Pd activated Si and Si/SiO2 substrates) of Pd LCLD were realized. The previously presented [Pd(NH3)4]2+ and [Pd(NH3)4]2+/HCOH precursors were employed for creating the catalyst Pd layers for the carbon nanotube chemical vapor-phase deposition and for the autocatalytic electroless chemical copper plating, respectively. Finally, a simple novel method was introduced for the area-selective metallization of PS. Since the surface of PS reduces spontaneously most metals from their aqueous solutions, it is difficult to realize localized metal deposition from liquid-phase precursors on it. We proposed the application of a stable Ni plating bath from which the metal deposits only when the PS is irradiated with photons having wavelength shorter than 689 nm, thus making possible an area-selective laser-assisted metal deposition. The deposited metal structures and patterns were analysed by field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectrometer (EDS), by the milling and imaging modes of a focused ion beam system (FIB), optical microscopy, profilometry, resistance, and by reflectance measurements

CNT-based catalysts for H2 production by ethanol reforming

Hydrogen production by steam reforming of ethanol (SRE) was studied using steam to ethanol ratio of 3 1 between the temperature range of 150-450 degrees C over metal and metal oxide nanoparticle catalysts (Ni, Co, Pt and Rh) supported on carbon nanotubes (CNTs) and compared to a commercial catalyst (Ni/Al2O3) The aim was to find out the suitability of CNTs supports with metal nanoparticles for the SRE reactions at low temperatures The idea to develop CNT based catalysts that have high selectivity for H-2 is one of the driving forces for this study The catalytic performance was evaluated in terms of ethanol conversion product gas composition hydrogen yield and selectivity to hydrogen The Co/CNT and Ni/CNT catalysts were found to have the highest activity and selectivity towards hydrogen formation among the catalysts studied Almost complete ethanol conversion is achieved over the Ni/CNT catalyst at 400 °C The highest hydrogen yield of 2 5 is however obtained over the Co/CNT catalyst at 450 °C The formation of CO and CH4 was very low over the Co/CNT catalyst compared to all the other tested catalysts The Pt and Rh CNT based catalysts were found to have low activity and selectivity in the SRE reaction Hydrogen production via steam reforming of ethanol at low temperatures using especially Co/CNT catalyst has thus potential in the future in e.g. the fuel cell applications

On-chip integrated vertically aligned carbon nanotube based super- and pseudocapacitors

Abstract On-chip energy storage and management will have transformative impacts in developing advanced electronic platforms with built-in energy needs for operation of integrated circuits driving a microprocessor. Though success in growing stand-alone energy storage elements such as electrochemical capacitors (super and pseusocapacitors) on a variety of substrates is a promising step towards this direction. In this work, on-chip energy storage is demonstrated using architectures of highly aligned vertical carbon nanotubes (CNTs) acting as supercapacitors, capable of providing large device capacitances. The efficiency of these structures is further increased by incorporating electrochemically active nanoparticles such as MnOx to form pseudocapacitive architectures thus enhancing device capacitance areal specific capacitance of 37 mF/cm². The demonstrated on-chip integration is up and down-scalable, compatible with standard CMOS processes, and offers lightweight energy storage what is vital for portable and autonomous device operation with numerous advantages as compared to electronics built from discrete components