Femtosecond laser patterning, synthesis, defect formation, and structural modification of atomic layered materials
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Introduction The electronic and mechanical properties of two-dimensional (2D) materials have showed potential to overcome the drawbacks of conventional electronics in moving toward mechanically flexible/stretchable applications for lightweight, portable, and conformable products such as flexible displays, solar cells and batteries, and wearable health patches.1 In spite of the very good properties of graphene, the zero-energy bandgap in its electronic structure makes it unsuitable for switching devices in electronics. Recently, 2D layered semiconductors, in particular, the series of transition-metal dichalcogenides (TMDCs) such as MoS2 and WSe2, have shown reliable performance as novel semiconductor materials that can provide mechanical flexibility and high mobility.2 While the potential of 2D layered materials is exciting, major roadblocks will have to be resolved for successful transition to commercial applications by developing reliable technologies for the controlled fabrication of high-performance devices (e.g., gate width of ∼10 nm for TMDC-based field-effect transistors with high ON-OFF current ratios,3 reliable means to control the number of TMDC layers for bandgap tuning,4
on-demand tuning of electronic properties by defect engineering,5 and maskless patterning of 2D layered materials). Ultrafast lasers offer unique processing routes that take advantage of distinct interaction mechanisms with 2D materials to enable extremely localized energy deposition. Both thermal and non-thermal mechanisms can contribute to the processing of layered materials, depending on the amount of energy absorbed.6 For femtosecond laser processing of graphite, time-of-flight measurements have confirmed that femtosecond laser-driven Coulomb explosion (i.e., ionization assisted non-thermal ablation mechanism) is responsible for atomic-scale material removal from graphite, suppressing subsequent thermal material ejection.7,8 It is also noted that atomic-scale material removal from layered materials by ultrafast lasers is frequently coupled with chemical reactions such as oxidation or burning, as in the case of graphene.9 It is believed that such a disturbance can lead to non-thermal bond breaking and even stochastic extraction of atoms from layered materials. The reduced in-plane thermal conductivity tends to accelerate the process thus partly contributing to high spatial confinement of the process.9
Jae-Hyuck Yoo, Lawrence Livermore National Laboratory, USA; [email protected] Eunpa Kim, Samsung Electronics, South Korea; [email protected] David J. Hwang, Department of Mechanical Engineering, State University of New York at Stony Brook, USA; [email protected] doi:10.1557/mrs.2016.248
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MRShttp:/www.cambridge.org/core. BULLETIN • VOLUME 41 • DECEMBER 2016 • of www.mrs.org/bulletin © 2016 Materials Research Society Downloaded from University Leeds, on 15 Dec 2016 at 07:48:35, subject to the Cambridge Core terms of use, available at http:/www.cambridge.org/core/terms. http://dx.doi.org/10.1557/mrs.2016.248
FEMTOSECOND LASER PA
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