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Ahn S.,University of California at Berkeley | Hwang D.J.,State University of New York at Stony Brook | Park H.K.,AppliFlex LLC | Grigoropoulos C.P.,University of California at Berkeley
Applied Physics A: Materials Science and Processing | Year: 2012

The rear contact solar cell concept has been implemented to increase the solar cell efficiency. Practically, it necessitates rapid fabrication of a large number of via holes to form low-loss current paths. It is not a trivial task to drill a number of microscopic holes through a typical Si wafer of ̃200 μm thickness at reasonable processing throughput and yield. In this research, a femtosecond laser is employed to drill via holes in both crystalline silicon (c-Si) and multicrystalline silicon (mc-Si) thin wafers of ̃170 μm thickness with various laser parameters such as number of laser shots and pulse energy. Since a significantly high pulse energy compared to ablation threshold is mainly applied, aiming to achieve a rapid drilling process, the femtosecond laser beam is subjected to complex non-linear characteristics. Therefore, the relative placement of the sample with respect to the laser focal position is also rigorously examined. While the non-linear effect at high pulse energy regime is complex, it also facilitates the drilling process in terms of achieving high-aspect ratio, for example, by extending the effective depth of focus by non-linear effect. Cross-sectional morphological analysis in conjunction with on-line emission and shadowgraph imaging are carried out in order to elucidate the drilling mechanism. © Springer-Verlag 2012. Source

Park H.K.,AppliFlex LLC | Schriver K.E.,Vanderbilt University | Haglund Jr. R.F.,Vanderbilt University
Applied Physics A: Materials Science and Processing | Year: 2011

Polymers find a number of potentially useful applications in optoelectronic devices. These include both active layers, such as light-emitting polymers and hole-transport layers, and passive layers, such as polymer barrier coatings and light-management films. This paper reports the experimental results for polymer films deposited by resonant infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) and resonant infrared pulsed laser deposition (RIR-PLD) for commercial optoelectronic device applications. In particular, light-management films, such as anti-reflection coatings, require refractive-index engineering of a material. However, refractive indices of polymers fall within a relatively narrow range, leading to major efforts to develop both low- and high-refractive-index polymers. Polymer nanocomposites can expand the range of refractive indices by incorporating low- or high-refractive-index nanoscale materials. RIR-MAPLE is an excellent technique for depositing polymer-nanocomposite films in multilayer structures, which are essential to light-management coatings. In this paper, we report our efforts to engineer the refractive index of a barrier polymer by combining RIR-MAPLE of nanomaterials (for example, high refractive-index TiO 2 nanoparticles) and RIR-PLD of host polymer. In addition, we report on the properties of organic and polymer films deposited by RIR-MAPLE and/or RIR-PLD, such as Alq 3 [tris(8-hydroxyquinoline) aluminum] and PEDOT:PSS [poly(3,4- ethylenedioxythiophene): poly(styrenesulfonate)]. Finally, the challenges and potential for commercializing RIR-MAPLE/PLD, such as industrial scale-up issues, are discussed. © 2011 Springer-Verlag. Source

Lee D.,University of California at Berkeley | Pan H.,University of California at Berkeley | Ko S.H.,Korea Advanced Institute of Science and Technology | Park H.K.,AppliFlex LLC | And 2 more authors.
Applied Physics A: Materials Science and Processing | Year: 2012

A solution-processable, high-concentration transparent ZnO nanoparticle (NP) solution was successfully synthesized in a new process. A highly transparent ZnO thin film was fabricated by spin coating without vacuum deposition. Subsequent ultra-short-pulsed laser annealing at room temperature was performed to change the film properties without using a blanket high temperature heating process. Although the as-deposited NP thin film was not electrically conductive, laser annealing imparted a large conductivity increase and furthermore enabled selective annealing to write conductive patterns directly on the NP thin film without a photolithographic process. Conductivity enhancement could be obtained by altering the laser annealing parameters. Parametric studies including the sheet resistance and optical transmittance of the annealed ZnO NP thin film were conducted for various laser powers, scanning speeds and background gas conditions. The lowest resistivity from laser-annealed ZnO thin film was about 4.75×10 -2 Ω∈cm, exhibiting a factor of 10 5 higher conductivity than the previously reported furnace-annealed ZnO NP film and is even comparable to that of vacuum-deposited, impurity-doped ZnO films within a factor of 10. The process developed in this work was applied to the fabrication of a thin film transistor (TFT) device that showed enhanced performance compared with furnace-annealed devices. A ZnO TFT performance test revealed that by just changing the laser parameters, the solution-deposited ZnO thin film can also perform as a semiconductor, demonstrating that laser annealing offers tunability of ZnO thin film properties for both transparent conductors and semiconductors. © 2012 Springer-Verlag. Source

Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 99.99K | Year: 2010

Electron microscopy and micro-characterization capabilities are important in the materials and biological sciences and are used in numerous research projects. Achieving a fundamental under

Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase II | Award Amount: 999.81K | Year: 2011

Advanced electron microscopy and micro-characterization capabilities are critical for research in the materials and biological sciences and in particular for the development of nanotechnology to answer the growing needs to protect our environment, increase energy efficiency and develop clean energy sources. Achieving a fundamental understanding of materials nucleation and growth phenomena at the nanoscale is critical for nanotechnology and necessitates an experimental environment in which the important atomistic processes can be studied as they are occurring. The proposed innovation is based on a revolutionary, yet practical method for simultaneous nanoscale imaging of nanofabrication processes by integrating tip-based pulsed laser radiation sources within a transmission electron microscope. Nanoscale confinement of radiation fields of enhanced intensity underneath a tip-based probe enables a wide range of materials modification processes that open up an entirely new avenue for the definition and processing of nanostructures, while at the same time allowing for direct in-situ observation of the fundamental processes. During our Phase I project, we demonstrated delivery of a laser beam in optical near-field to a sample inside a transmission electron microscope for an in-situ imaging of a material undergoing nano-scale melting and recrystallization. This new capability remarkably enabled observation of the conversion of amorphous nanodomain precursors to single nanocrystals. The prototype in-situ probe holder developed during the Phase I project combines (a) photonic (laser) excitation in nanoscale, (b) in-situ transmission electron microscope imaging, and (c) simultaneous optical spectroscopic characterization of material properties. In this Phase II project, we will develop this prototype into a viable commercial product, a modular attachment kit to standard electron microscope instruments, to provide researchers in all aspects of science and technology with a powerful research tool to push the frontiers of science. This will be accomplished with systematic experiments to determine the optimal optical probe and detector configurations and the design and assembly of a prototype. Furthermore, the prototype will be tested in the real scientific studies of in-situ characterization of nanowire growth and the synthesis of nanostructures. The proposed product will enable a widespread adoption of unique facility for the in-situ nanoscale observation of laser material modification and nanomaterials growth processes. This entirely new capability will have a profound impact to the fields of materials science, nanofabrication, and the adoption of nanotechnology into marketplace.

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