Jin-Kyun Lee

Generation of intense pulsed ion beams

An electrostatic vacuum triode is described in which it is possible to efficiently produce intense ion beams in the energy range around 100 keV for short times (∼50 nsec). In experiments to date, results have shown excellent agreement with predicted behavior. Equivalent proton currents of almost 500 A have been obtained at a peak energy in excess of 100 keV. The triode can easily be adapted to existing electron beam facilities.

Detection of Transmitter Release from Single Living Cells Using Conducting Polymer Microelectrodes

The advent of organic electronics has made available a host of materials and devices with unique properties for interfacing with biology.1–2 One example is the use of conducting polymer coatings on metal electrodes that are implanted in the central nervous system and interface electrically with neurons, providing stimulation and recording the neurons electrical activity.3–5 Coating a metal electrode with a conducting polymer has been shown to lower the electrical impedance and decrease the mechanical properties mismatch at the interface with tissue, with beneficial effects on the lifetime of the implant.3, 6 Conducting polymers can also be functionalized with biomolecules that stimulate neural growth and minimize the immune response to the implant.3–5, 7 Other examples are organic electronic ion pumps,8 and ion transistors,9 which are recently invented devices capable of precise delivery of neurotransmitters to neurons. These devices were recently implanted in the ear of a guinea pig and were shown to control its hearing.10 Conducting polymers such as poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS), a material that has been shown to be biocompatible with a variety of different cells,1 have been used for these applications. These examples highlight the main advantages that organic electronic materials bring to the interface with biology, including their “soft” nature, which offers better mechanical compatibility with tissue than traditional electronic materials, and natural compatibility with mechanically flexible substrates, which paves the way for the development of implants that better conform to the non-planar shape of organs. Finally, the ability of organics to transport ionic in addition to electronic charge creates the opportunity to interface with electrically active cells in novel ways, as the work on ion pumps indicates.

Acid-sensitive semiperfluoroalkyl resorcinarene: an imaging material for organic electronics.

An acid-sensitive semiperfluoroalkyl resorcinarene was synthesized, and its lithographic properties were evaluated. Its solubility in segregated hydrofluoroether solvents enables the patterning of delicate organic electronic materials.

High-Performance Electron-Transporting Polymers Derived from a Heteroaryl Bis(trifluoroborate)

In this communication, we report that dipotassium aryl bis(trifluoroborate)s make stable and easy-to-purify yet reactive monomers under Suzuki polycondensation reactions. A bis(trifluoroborate) of 2-alkylbenzotriazole was prepared successfully and copolymerized with dibromobenzothiadiazole in the presence of a Pd catalyst and LiOH, yielding high molecular weight conjugated polymers. This polymer (P1) composed of all electron-accepting units shows excellent electron-transport properties (μ(e) = 0.02 cm(2) V(-1) s(-1)), which proves the value of the aryl bis(trifluoroborate) monomers and suggests that many other types of semiconducting polymers that could not be accessed previously can be synthesized using this approach.

Orthogonal processing: A new strategy for organic electronics

The concept of chemical orthogonality has long been practiced in the field of inorganic semiconductor fabrication, where it is necessary to deposit and remove a layer of photoresist without damaging the underlying layers. However, these processes involving light sensitive polymers often damage organic materials, preventing the use of photolithography to pattern organic electronic devices. In this article we show that new photoresist materials that are orthogonal to organics allow the fabrication of complex devices, such as hybrid organic/inorganic circuitry and full-colour organic displays. The examples demonstrate that properly designed photoresists enable the fabrication of organic electronic devices using existing infrastructure.

Role of Solvent Dielectric Properties on Charge Transfer from PbS Nanocrystals to Molecules

Transfer of photoexcited charge from PbS nanocrystals to ligand molecules is investigated in different solvents. We find that the charge transfer rate increases dramatically with solvent dielectric constant. This trend is accounted for by a modified Marcus theory that incorporates only static dielectric effects. The choice of solvent allows significant control of the charge transfer process. As an important example, we find that PbS nanocrystals dispersed in water exhibit charge transfer rates 1000 times higher than the same nanocrystals in organic solvent. Rapid charge extraction will be important to efficient nanocrystal-based photovoltaic and photodetector devices.

Advances in the efficient generation of intense pulsed proton beams

Recent studies on the space−charge−limited reflex vacuum triode pulsed ion accelerator show a marked improvement in the output parameters and efficiency of the device. In the current machine, a 50−nsec pulse of 130−keV protons of 6000 A is produced at a current density of 20 A/cm2. Energies up to 300 keV have been investigated. The troide efficiency, defined as proton energy output versus total energy input, has been raised from 10 to 42% by the addition of magnetic fields that prevent anomalous electron loss in the fringing fields at the edges of the electrodes. Time−of−flight measurements confirmed the peak energies. The beam was measured to have about a 10 ° half−angle of spread. The results obtained indicate that the accelerator may be scaled to the ranges of parameters currently achieved by pulsed electron accelerators.

Charge-Transport Anisotropy in a Uniaxially Aligned Diketopyrrolopyrrole-Based Copolymer.

Aligned films of a semiconducting DPP‐based copolymer exhibit highly anisotropic charge transport with a band‐like temperature dependence along the alignment direction and hole mobilities of up to 6.7 cm2 V−1 s−1. X‐ray diffraction measurements reveal an exceptional degree of in‐plane alignment, high crystallinity, and a dominant face‐on orientation of the polymer backbones. The surprising charge‐transport properties are interpreted in a tie‐chain model consistent with anisotropic activation energies.

Dry photolithographic patterning process for organic electronic devices using supercritical carbon dioxide as a solvent

The particular challenge of micropatterning organic materials has stimulated numerous approaches for making effective and repeatable patterned structures with fine features. Among all the micropatterning techniques photolithography, being the preferred method for the inorganic semiconductor industry, did not create much impact due to its incompatibility with the majority of organic electronic materials. Here we introduce a novel, chemically benign approach to dry photolithographic patterning of organic materials using super-critical carbon dioxide (scCO2) as a green developing solvent. We illustrate the possible applications of the new technique by patterning conducting polymers and light emitting polymers for organic light emitting diodes.

Orthogonal Processing and Patterning Enabled by Highly Fluorinated Light‐Emitting Polymers

a m i p p f o d f a p m o s t Solution processing of organic electronic materials is a highly attractive processing option for many applications, particularly organic light emitting diodes (OLEDs) for display and solidstate lighting. It is a low cost approach with no limitations with regard to substrate size. While highly effi cient full color displays are rather straightforward to fabricate via vacuum-assisted shadow mask deposition of organic small molecules, it is challenging to achieve solution-processed full color displays due to the limitations imposed by compatibility issues among active light-emitting components and other chemicals and solvents used in the device patterning process. Much work has been done on the patterning of organic electronic materials, which has been summarized in the review by Menard et al. [ 1 ] However, many of the novel patterning techniques described in the review, such as inkjet printing and screen printing, suffer from the disadvantages of low resolution and low throughput. As such, photolithography is still the ideal technique for patterning of organic light-emitting materials, since it has good resolution, high-throughput, easy scalability to large substrates, good registration between multiple layers and is very well established in the semiconductor industry. However, the standard organic and polar solvents used in the processing of photosensitive materials can damage the organic light-emitting materials used as active layers. Many approaches have been proposed to overcome this problem. Several groups [ 2–6 ] have demonstrated light-emitting polymers with side-groups that can be cross-linked under light activation to produce insoluble polymer networks in desired areas, hence they can be directly patterned in a way similar to standard photoresist materials. Huang et al. [ 7 ] showed that inserting a photocurable interlayer