Laura L. Kosbar

N-type organic thin-film transistor with high field-effect mobility based on a N,N′-dialkyl-3,4,9,10-perylene tetracarboxylic diimide derivative

N,N′-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8H) thin films have been implemented into organic thin-film field-effect transistors. Mobilities up to 0.6 cm2 V−1 s−1 and current on/off ratios >105 were obtained. Linear regime mobilities were typically half of those measured in the saturation regime. X-ray studies in reflection mode suggest a spacing of ∼20 A for thin evaporated films of PTCDI-C8H, which is consistent with the value of ∼21±2 A obtained from our simulations when an interdigitated packing structure is assumed.

High-mobility ultrathin semiconducting films prepared by spin coating.

The ability to deposit and tailor reliable semiconducting films (with a particular recent emphasis on ultrathin systems) is indispensable for contemporary solid-state electronics. The search for thin-film semiconductors that provide simultaneously high carrier mobility and convenient solution-based deposition is also an important research direction, with the resulting expectations of new technologies (such as flexible or wearable computers, large-area high-resolution displays and electronic paper) and lower-cost device fabrication. Here we demonstrate a technique for spin coating ultrathin (∼50 Å), crystalline and continuous metal chalcogenide films, based on the low-temperature decomposition of highly soluble hydrazinium precursors. We fabricate thin-film field-effect transistors (TFTs) based on semiconducting SnS2-xSex films, which exhibit n-type transport, large current densities (>105 A cm-2) and mobilities greater than 10 cm2 V-1 s-1—an order of magnitude higher than previously reported values for spin-coated semiconductors. The spin-coating technique is expected to be applicable to a range of metal chalcogenides, particularly those based on main group metals, as well as for the fabrication of a variety of thin-film-based devices (for example, solar cells, thermoelectrics and memory devices).

Cleavable epoxy resins : design for disassembly of a thermoset

A series of cycloaliphatic diepoxides with cleavable acetal links were synthesized and characterized. These materials were shown to undergo thermosetting reactions with cyclic anhydride in very similar fashion to a commercial cycloaliphatic epoxide, but cured samples were easily dissolved in a variety of acid-containing solvent mixtures. Such materials can extend the utility of thermosetting epoxies by preserving their positive attributes while eliminating their well known intractability after curing. The latter property is particularly a problem for manufacturers designing products for disassembly at end of use in order to facilitate recycling.

Patterning organic–inorganic thin-film transistors using microcontact printed templates

We report the simple, low-cost, and parallel fabrication of patterned organic–inorganic thin-film transistors (TFTs) by microcontact printing a molecular template on the substrate surface prior to film deposition. We printed molecules with hydrophobic tail groups on the gate oxide surfaces of TFTs to chemically, differentiate the substrate surface and confine the self-assembly of thin films, deposited from solutions flooded across the entire surface, to the transistor channels. TFTs are fabricated with good device characteristics and no current leakage. This process is more general to the patterning of other solution-deposited thin-film materials.

Network morphology of polymer stabilized liquid crystals

Monomer solubility is identified as the primary factor determining network morphology in polymer stabilized cholesteric liquid crystal textures. Poorly soluble monomers form coarse structures composed of discrete, oblong grains, whereas soluble monomers yield smooth, continuous polymer networks. A crossover from smooth to grainy structure is observed as a function of monomer concentration. The grainy structure results from precipitation polymerization and the observed behavior is well described by the Flory–Huggins theory of polymer solubility.Monomer solubility is identified as the primary factor determining network morphology in polymer stabilized cholesteric liquid crystal textures. Poorly soluble monomers form coarse structures composed of discrete, oblong grains, whereas soluble monomers yield smooth, continuous polymer networks. A crossover from smooth to grainy structure is observed as a function of monomer concentration. The grainy structure results from precipitation polymerization and the observed behavior is well described by the Flory–Huggins theory of polymer solubility.

Introducing Biobased Materials into the Electronics Industry

Abstract: Lignin, a biopolymer formed in the cell walls of plants, is a by-product of paper manufacturing. In research at IBM, it was incorporated into a resin used in the fabrication of printed wiring boards (PWB) for the microelectronics industry. The resin had physical and electrical properties similar to those of current laminate resins. PWBs fabricated from the lignin-based resin passed most of the standard physical, electrical, and reliability tests for an “FR4”-grade laminate. A comparison of the lignin-based resin and current resins via life-cycle assessment indicated up to 40% lower energy consumption for the biobased resin. Large-scale manufacture of lignin-based resins would require an inexpensive source of lignin with low ionic contamination.

The Effect of Surface Preparation on the Structure and Electrical Transport in an Organic Semiconductor

Self-assembled monolayers (SAMs) with a variety of structures and terminal groups were evaluated as underlayers for pentacene deposition. It was found that the most critical factor in the formation of highly oriented thin film pentacene with large grain size was the geometric structure of the monolayer. Monolayers with terminal bonds parallel to the surface produce large pentacene grains with an angular rather than the dendridic structure normally observed on octadecyltrichlorosilane (OTS) coated substrates. The grain size, X-ray scattering, carrier mobility, and current on/off ratios are all improved with monolayers of the appropriate geometry.

Network Morphology and Switching Transitions in Polymer Stabilized Cholesteric Textures

Abstract We study the fundamental properties of polymer stabilized cholesteric texture (PSCT) liquid crystal cells by (1) characterizing the polymerization process within the liquid crystal medium and, (2) identifying the effects of the resulting polymer network on the switching transition of the cholesteric. We show that monomer solubility is the primary factor determining network morphology-poorly soluble monomers yield coarse structures composed of discrete particles, whereas soluble monomers yield smooth, highly interconnected networks. Following network formation, we use confocal microscopy to obtain in situ images of both the polymer network and the liquid crystal domain structure as the cells are switched between the planar and focal conic textures.

Biobased epoxy resins for computer components and printed wiring boards

Lignin, a by-product of paper manufacturing, has been used to develop a new series of resins for various computer components, particularly printed wiring boards (PWB). PWBs are commonly fabricated from epoxy/fiberglass laminates onto which electrical components are mounted. Replacement of the current petroleum derived phenolic epoxy resins with bio-based materials would reduce the environmental concerns with the fabrication, assembly, and disposal of PWBs. Resins used in PWBs must have a high glass transition temperature, low moisture absorption, high thermal stability, flame retardancy and good dielectric properties. Lignin is the only common phenolic-based biopolymer, thus it is naturally hydrophobic and has good thermal stability. Resin formulations which are lignin/epoxy copolymers (containing at least 50% lignin) exhibit acceptable physical and electrical properties for a wide range of applications, including PWBs. Laminates formed from lignin based resins can be processed in a similar fashion to current laminates, minimizing the financial considerations of converting to this resin system.

Organic-inorganic electronic devices based on hybrid perovskites

The organic-inorganic perovskites provide an ideal opportunity to combine useful properties in a hybrid composite that can be processed using simple solution or evaporation-based thin film techniques. Since these techniques are performed at ambient temperature, it is envisioned that the hybrid materials are likely to be compatible with a range of potential applications, including those that may require flexible plastic substrates. Besides the organic-inorganic thin film transistor (OITFT) and organic-inorganic light emitting diode (OILED) devices discussed in this article, organic-inorganic hybrids may also provide novel possibilities for thermoelectric, dielectric, photoconductive and magnetic applications. In each case, the possibilities afforded by the hybrid systems are only beginning to be considered.