Scientific Highlights 2012



Laser-Induced Forward Transfer for the Fabrication of Devices

Abstract:
In conjunction with the increasing availability of cost-efficient laser units during the recent years, laser-based micromachining techniques have been developed as an indispensable industrial instrument of ‘‘tool-free’’ high-precision manufacturing techniques for the production of miniaturized devices made of nearly every type of materials. Laser cutting and drilling, as well as surface etching, have grown meanwhile to mature standard methods in laser micromachining applications where a well-defined laser beam is used to remove material by laser ablation. As an accurately triggerable nonmechanical tool, the ablating laser beam directly allows a subtractive direct-write engraving of precise microscopic structure patterns on surfaces, such as microchannels, grooves, and well arrays, as well as for security features. Therefore, laser direct-write (LDW) techniques imply originally a controlled material ablation to create a patterned surface with spatially resolved three-dimensional structures, and gained importance as an alternative to complementary photolithographic wet-etch processes. However, with more extended setups, LDW techniques can also be utilized to deposit laterally resolved micropatterns on surfaces, which allows, in a general sense, for the laser-assisted ‘‘printing’’ of materials.
Keywords: laser induced forward transfere; laser direct-write techniques; high-precision manufacturing; laser-assisted printing;

Facility: ENE, EMPA, LMX, Thin Films and Interfaces

Reference: M. Nagel, T. Lippert, Laser-induced forward transfer for the fabrication of decives, in Nanomaterials; Processing and Characterization with Lasers, Eds. H. Zeng, C. Guo, W. Cai, S. C. Singh, Wiley-Blackwell, John Wiley & Sons Publishers, Weinheim, pp. 255-316, 2012.

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Sequential printing by laser-induced forward transfer to fabricate a polymer light-emitting diode pixel

Abstract:
Patterned deposition of polymer light-emitting diode (PLED) pixels is a challenge for electronic display applications. PLEDs have additional problems requiring solvent orthogonality of different materials in adjacent layers. We present the fabrication of a PLED pixel by the sequential deposition of two different layers with laser-induced forward transfer (LIFT), a “dry” deposition technique. This novel use of LIFT has been compared to “normal” LIFT, where all the layers are transferred in a single step, and a conventional PLED fabrication process. For the sequential LIFT, a 50-nm film of an alcohol-soluble polyfluorene (PFN) is transferred onto a receiver with a transparent anode, before an aluminum cathode is transferred on top. Both steps use a triazene polymer dynamic release layer and are performed in a medium vacuum (1 mbar) across a 15 μm gap. The rough morphologies of the single-layer PFN pixels and the PLED device characteristics have been investigated and compared to both bilayer Al/PFN pixels fabricated by normal LIFT and conventionally fabricated devices. The functionality of the sequential LIFT pixels (0.003 cd/A, up to 200 mA/cm2, at 30−40 V) demonstrates the suitability of LIFT for sequential patterned printing of different thin-film layers.
Keywords: Laser induced forward transfere; Laser printing; sequential laser deposition; organic light emitting diodes; triazene polymer; PLED pixels; thin-films; patterned deposition: laser direct-write;

Facility: ENE, EMPA, LMX, Thin Films and Interfaces

Reference: J. R. H. Shaw-Stewart, T. Lippert, M. Nagel, F. A. Nüesch, A. Wokaun; Appl. Mater. & Interfaces 4, 3535 (2012)

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Tunable conductivity threshold at polar oxide interfaces

Abstract:
The physical mechanisms responsible for the formation of a two-dimensional electron gas at the interface between insulating SrTiO3 and LaAlO3 have remained a contentious subject since its discovery in 2004. Opinion is divided between an intrinsic mechanism involving the build-up of an internal electric potential due to the polar discontinuity at the interface between SrTiO3 and LaAlO3, and extrinsic mechanisms attributed to structural imperfections. Here we show that interface conductivity is also exhibited when the LaAlO3 layer is diluted with SrTiO3, and that the threshold thickness required to show conductivity scales inversely with the fraction of LaAlO3 in this solid solution, and thereby also with the layer's formal polarization. These results can be best described in terms of the intrinsic polar-catastrophe model, hence providing the most compelling evidence, to date, in favour of this mechanism.
Keywords: pulsed laser deposition; conducting interfaces; SrTiO3, LaAlO3; polar catastrophy;

Facility: ENE, SLS, LDM, U. Geneva, U. Liege, LMX, Thin Films and Interfaces

Reference: M. L. Reinle-Schmitt, C. Cancellieri, D. Li, D. Fontaine, M. Medarde, E. Pomjakushina, C.W. Schneider, S. Gariglio, Ph. Ghosez, J.-M. Triscone, P. R. Willmott, Nat. Commun. 3:932 (2012)

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Laser-Induced Forward Transfer for the Fabrication of Devices

Abstract:
X-ray near edge absorption spectroscopy was used to probe the electronic structure of multiferroic orthorhombic LuMnO3 polycrystalline samples and strained, twin-free orthorhombic (1–10) LuMnO3 films grown by pulsed laser deposition on (1–10) YAlO3 substrates. For all o-LuMnO3 samples x-ray near edge absorption spectroscopy spectra reveal that the pre-edge structure is influenced by the increase in MnO6 distortion as a result of the smaller Re-ion or film strain. Furthermore there is clear evidence of anisotropic Mn-O bonding and Mn orbital ordering along the c- and [110] direction. The experimental film and bulk data are in agreement with ab initio simulations.
Keywords: pulsed laser deposition; othrorhomic LuMnO3 thin films; multiferroics; X-ray near edge absorption spectroscopy; electronic structure; ab initio simulations; FEFF;

Facility: ENE, NUM, LDM, LNS, Thin Films and Interfaces

Reference: Y. Hu, C. N. Borca, E. Kleymenov, M. Nachtegaal, B. Delley, M. Janousch, A Dönni, M. Tachibana, H. Kitazawa, E. Takayama-Muromachi, M. Kenzelmann, C. Niedermayer, T. Lippert, A. Wokaun, C. W. Schneider, Appl. Phys. Lett. 100, 252901 (2012)

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Red-green-blue polymer light-emitting diode pixels printed by optimized laser-induced forward transfer

Abstract:
An optimized laser-induced forward transfer (LIFT) technique has been used to fabricate tri-color organic light-emitting diode (OLED) pixels. At reduced pressures, and with a defined donor-receiver gap, patterned depositions of polyfluorene-based OLED pixels have been achieved. OLED pixel functionality has been demonstrated and compared with devices made using conventional deposition techniques. In addition, improved functionality has been obtained by coating the cathode with an electron-injecting layer, a process not possible using conventional OLED fabrication techniques. The OLED pixels fabricated by LIFT reach efficiencies on the range of conventionally fabricated devices and even surpass them in the case of blue pixels.
Keywords: Laser induced forward transfere; Laser printing; sequential laser deposition; organic light emitting diodes; triazene polymer; PLED pixels; thin-films; patterned deposition: laser direct-write;

Facility: ENE, EMPA, LMX, Thin Films and Interfaces

Reference: J. Shaw-Stewart, T. Lippert, M. Nagel, F. Nüesch, A. Wokaun; Appl. Phys. Lett. 100, 203303 (2012)

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