Pierce Maguire, DS Fox, Q Wang, Y Zhou, H Zhang maguirpi@tcd.ie Ne + - PowerPoint PPT Presentation

Pierce Maguire, DS Fox, Q Wang, Y Zhou, H Zhang maguirpi@tcd.ie Ne + , He + and Ga + Irradiation for Nanometre Tuning of 2D Materials Photonics & Nanofabrication Group, Trinity College Dublin

Introduction • Ions used for many decades (nuclear materials etc.) • Ions used with high resolution (GFIS/ GIM , LMIS, FIM)

Introduction • Tuning 2D materials using a variety of ion species, all at 30 kV Crystal structure Chemical composition Geometry

Microscopy of Perfectly Flat Materials Looking up internet memes, the only time I “work” with animals Imaging and Fabrication! 14/09/2015 Pierce Maguire-TCD

Motivation-Why tune 2D Materials? Graphene Molybdenum Disulphide • One example, opening a • Edge structure, vastly bandgap: different properties Ferromagnetic and Non-magnetic and half-metallic semiconducting Ataca et al., Phys. Chem. 115(10): 3934-3941 , 2011 Wang et al., Phys. Rev. Lett. 100, 206803, 2008 Liu et al., Nat. Comms. , 4:1776, 2014 Abbas et al., ACS Nano , 8 (2): 1538 – 1546, 2014 14/09/2015 Pierce Maguire-TCD

How do we tune 2D Materials? Crystal Structure, Stoichiometry, Geometry • Localised • Not Localised – Electron Beam – Classic Ion Irradiation Irradiation (TEM) • Well understood, some metallic contaminant • Powerful, but low issues, many energies throughput & expensive – Plasma Irradiation – Lithography • Versatile, can use with • Good res. and lithography throughput, can introduce – Synthesis residue • Resolution still less than • Varying source materials some ions, proximity effect All have compromises in throughput, tuning type and resolution 14/09/2015 Pierce Maguire-TCD

Outline MoS 2 Graphene Materials He + Ne + Ga + Beams 0.4 nm 2-5 nm 2-5 nm ~5-30 keV Raman EDX Measure 14/09/2015 Pierce Maguire-TCD

He + /Ne + Microscopes V. N. Tondare, J. Vac. Sci. Technol. A, SRIM: 30 keV ions in MgO with 4 nm MoS 2 Vol 23, No. 6, p.1498-1507 (2005). 14/09/2015 Pierce Maguire-TCD

MoS 2 samples Freestanding • Liquid exfoliated MoS 2 on TEM grid • Locating suitable flakes, 20 kV SEM • (a) InLens for surface detail and (b) InLens STEM images for thickness contrast Substrate • MBE deposited Mo, sulfurized on MgO STEM 14/09/2015 Pierce Maguire-TCD

Graphene samples • CVD graphene • Transferred to 280-300 nm SiO 2 on Si • On-substrate & freestanding (holes) – 2 μ m diameter – 10 μ m depth 14/09/2015 Pierce Maguire-TCD

Structural Modification • 5 × 5 𝜈 m squares in 3 × 3 arrays with various doses 1E13 to 1E17 for He + ~ × 50-100 mill rate of He + 1E11 to 1E15 for Ne + 14/09/2015 Pierce Maguire-TCD

Characterising Structure Amorphisation of few layer MoS 2 at high doses of He + Observed in TEM but Raman used more systematically (633 nm) Non-irradiated peak positions agree with literature (MoS 2 spectrum pictured here) 14/09/2015 Pierce Maguire-TCD

Characterising MoS 2 Structure • A 1g • E 1 2g o o In-plane vibration Out-of-plane vibration o o FWHM increase suggests FWHM increase suggests defects in-plane defects are o FWHM decrease may suggest introduced thinning Plane Cheng et al. RSC Adv. , 2012, 2 , 7798-7802 14/09/2015 Pierce Maguire-TCD

Structure: He + , Ne + , & MoS 2 14/09/2015 Pierce Maguire-TCD

Characterising Graphene Structure Raman spectrum features: • G peak at ∼ 1580 cm −1 (G’/ • 2D peak at ∼ 2700 cm − 1 2D) G • D peak at ∼ 1350 nm − 1 in defective graphene (air) D • Low defect density regime- I D /I G proportional to the defect density • We use FWHM G due to broad range of doses L. G. Cançado, Nano Lett. , 2011 , 11 (8), pp 3190 – 3196 14/09/2015 Pierce Maguire-TCD

Structure: He + , Ne + , Ga + & Graphene NOT SAME LASER λ • Cannot compare Ga + results directly just yet P. Maguire, in preparation Fox et al., Nanotechnology, 335702, 24 (2013) Y. Zhou et al., J. Chem. Phys., 133, 234703 (2010) 14/09/2015 Pierce Maguire-TCD

Stoichiometry: MoS 2 Preferential sputtering of sulphur atoms was observed as in literature with broad beam Argon ions (3keV Argon ions) S.P. Kaye et al., Thin Solid Films, 228, H C Feng and J M Chen, J. Phys. C: 252-256, 1993 Solid State Phys. 7 L75 1974 14/09/2015 Pierce Maguire-TCD

Stoichiometry: MoS 2 We irradiate freestanding sample and then characterise with EDX (in Titan STEM @300 keV) 14/09/2015 Pierce Maguire-TCD

Stoichiometry: He + and MoS 2 EDX Atomic %: Preferential sputtering of sulphur atoms was observed as in previous work with Argon ions. 14/09/2015 Pierce Maguire-TCD

Electrical characterisation 14/09/2015 Pierce Maguire-TCD

Nanostructure Fabrication • Milled nanoscale features with He + probe of different sizes (varied defocus) and imaged with Transmission Electron Microscope (TEM ) Probe sizes: ~13nm ~6nm ~1.5 nm 14/09/2015 Pierce Maguire-TCD

He + /Ne + Microscopes Nanoribbons fabricated with 30 keV He + ~10 nm ~5 nm ~1 nm 14/09/2015 Pierce Maguire-TCD

Fabrication Resolution • Liquid Metal Ion Source Ga + Graphene – Ga + resolution ~5 nm • Gas Field Ion Source (energy Y Zhang et al, Nanotechnology spread x10 smaller) 25 (2014) 135301 – He + resolution ~0.35 nm – Ne + resolution ~5 nm Ne + He + MoS 2 MoS 2 (When we try to Fox et al., Nano pretend Ne + Lett. , 2015 , 15 (8), behaves like He + !) pp 5307 – 5313 14/09/2015 Pierce Maguire-TCD

Summary Graphene MoS 2 Ion Beam He + Ne + Ga + He + Ne + Ga + Substrate On Off On Off On Off On Off On Off On Off EDX 0 0 0 0 0 0 0 H 0 H 0 N Raman P P H H P N H 0 H 0 N 0 P - P reviously Reported H -Reported H ere N-N ot yet done 0 -presently considered irrelevant or unrealisable due to experimental conditions e.g. high resolution EDX is not possible on-substrate. 14/09/2015 Pierce Maguire-TCD

Conclusion • Using direct write ion strategies we can precisely alter 2D materials with nanoscale precision • These techniques have distinct advantages in scalability & resolution – Structural defects introduced & characterised in Raman , TEM & electrically – Stoichiometry tuning, at high doses, preferential removal of sulphur observed – Nanostructure fabrication improved by quantifying the probe size effect , minimising damage extension – Sub-10 nm ribbons fabricated 14/09/2015 Pierce Maguire-TCD

Acknowledgements Get in touch: maguirpi@tcd.ie, hozhang@tcd.ie Thanks for your attention! • Prof. Zhang & Group • Qianjin Wang • AML & Collaborators, Nanjing University CRANN & AMBER • School of Physics

Results – Milling of MoS 2 flakes 200 nm 100 nm 1 nm 20 nm Danny Fox – Trinity College Dublin

Nanostructure fabrication Damage extension confined to ~ 1nm of milled edge Transition from crystalline to amorphous - For ribbons ~ 5nm and smaller Danny Fox – Trinity College Dublin 29

Other materials (a) (b) (c) 2 nm 2 nm 10 nm Mn 2 O 3 TiO 2