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

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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

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SLIDE 1

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

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SLIDE 2

Introduction

  • Ions used for many decades (nuclear

materials etc.)

  • Ions used with high resolution (GFIS/GIM,

LMIS, FIM)

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SLIDE 3

Introduction

  • Tuning 2D materials using a variety of ion

species, all at 30 kV Crystal structure Chemical composition Geometry

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SLIDE 4

Microscopy of Perfectly Flat Materials

14/09/2015 Pierce Maguire-TCD

Looking up internet memes, the only time I “work” with animals Imaging and Fabrication!

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SLIDE 5

Motivation-Why tune 2D Materials?

Graphene

  • One example, opening a

bandgap: Molybdenum Disulphide

  • Edge structure, vastly

different properties

14/09/2015 Pierce Maguire-TCD Wang et al., Phys. Rev. Lett. 100, 206803, 2008

Ferromagnetic and half-metallic Non-magnetic and semiconducting

Ataca et al., Phys. Chem. 115(10): 3934-3941, 2011 Liu et al., Nat. Comms., 4:1776, 2014 Abbas et al., ACS Nano, 8 (2): 1538–1546, 2014

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SLIDE 6

How do we tune 2D Materials?

  • Localised

– Electron Beam Irradiation (TEM)

  • Powerful, but low

throughput & expensive

– Lithography

  • Good res. and

throughput, can introduce residue

  • Resolution still less than

some ions, proximity effect

  • Not Localised

– Classic Ion Irradiation

  • Well understood, some

metallic contaminant issues, many energies

– Plasma Irradiation

  • Versatile, can use with

lithography

– Synthesis

  • Varying source materials

All have compromises in throughput, tuning type and resolution

Crystal Structure, Stoichiometry, Geometry

14/09/2015 Pierce Maguire-TCD

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SLIDE 7

Ga+ 2-5 nm Beams ~5-30 keV He+ 0.4 nm Ne+ 2-5 nm MoS2 Graphene Materials Raman EDX Measure

Outline

14/09/2015 Pierce Maguire-TCD

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SLIDE 8

He+/Ne+ Microscopes

SRIM: 30 keV ions in MgO with 4 nm MoS2

  • V. N. Tondare, J. Vac. Sci. Technol. A,

Vol 23, No. 6, p.1498-1507 (2005). 14/09/2015 Pierce Maguire-TCD

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SLIDE 9

MoS2 samples

Freestanding

  • Liquid exfoliated MoS2 on TEM grid
  • Locating suitable flakes, 20 kV SEM
  • (a) InLens for surface detail and (b)

STEM images for thickness contrast Substrate

  • MBE deposited Mo, sulfurized on

MgO

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InLens STEM

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SLIDE 10

Graphene samples

  • CVD graphene
  • Transferred to 280-300

nm SiO2 on Si

  • On-substrate &

freestanding (holes)

– 2 μm diameter – 10 μm depth

14/09/2015 Pierce Maguire-TCD

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SLIDE 11

Structural Modification

  • 5 × 5 𝜈m squares in 3 × 3 arrays with various doses

1E13 to 1E17 for He+ 1E11 to 1E15 for Ne+ ~ × 50-100 mill rate of He+

14/09/2015 Pierce Maguire-TCD

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SLIDE 12

Characterising Structure

Observed in TEM but Raman used more systematically (633 nm) Non-irradiated peak positions agree with literature (MoS2 spectrum pictured here) Amorphisation of few layer MoS2 at high doses of He+

14/09/2015 Pierce Maguire-TCD

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SLIDE 13

Characterising MoS2 Structure

  • A1g
  • Out-of-plane vibration
  • FWHM increase suggests

defects

  • FWHM decrease may suggest

thinning

  • E1

2g

  • In-plane vibration
  • FWHM increase suggests

in-plane defects are introduced

Cheng et al. RSC Adv., 2012,2, 7798-7802

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Plane

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SLIDE 14

Structure: He+, Ne+, & MoS2

14/09/2015 Pierce Maguire-TCD

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SLIDE 15

Characterising Graphene Structure

14/09/2015 Pierce Maguire-TCD

Raman spectrum features:

  • G peak at ∼1580 cm−1
  • 2D peak at ∼2700 cm−1
  • D peak at ∼1350 nm−1 in

defective graphene

  • Low defect density regime-

ID/IG 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 D G (air) (G’/ 2D)

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SLIDE 16

Structure: He+, Ne+, Ga+ & Graphene

  • 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

NOT SAME LASER λ

  • Cannot compare

Ga+ results directly just yet

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SLIDE 17

Stoichiometry: MoS2

Preferential sputtering of sulphur atoms was observed as in literature with broad beam Argon ions

S.P. Kaye et al., Thin Solid Films, 228, 252-256, 1993 H C Feng and J M Chen, J. Phys. C: Solid State Phys. 7 L75 1974 (3keV Argon ions)

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SLIDE 18

Stoichiometry: MoS2

We irradiate freestanding sample and then characterise with EDX (in Titan STEM @300 keV)

14/09/2015 Pierce Maguire-TCD

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SLIDE 19

Stoichiometry: He+ and MoS2

EDX Atomic %: Preferential sputtering of sulphur atoms was

  • bserved as in previous work with Argon ions.

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SLIDE 20

Electrical characterisation

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SLIDE 21

Probe sizes: ~13nm ~6nm ~1.5 nm

  • Milled nanoscale features with He+ probe of different sizes

(varied defocus) and imaged with Transmission Electron Microscope (TEM)

Nanostructure Fabrication

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SLIDE 22

He+/Ne+ Microscopes

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Nanoribbons fabricated with 30 keV He+ ~10 nm ~5 nm ~1 nm

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SLIDE 23

Fabrication Resolution

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  • Liquid Metal Ion Source

– Ga+ resolution ~5 nm

  • Gas Field Ion Source (energy

spread x10 smaller)

– He+ resolution ~0.35 nm – Ne+ resolution ~5 nm

Ga+ Graphene Y Zhang et al, Nanotechnology 25 (2014) 135301 He+ MoS2 Fox et al., Nano Lett., 2015, 15 (8), pp 5307–5313 Ne+ MoS2 (When we try to pretend Ne+ behaves like He+!)

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SLIDE 24

P-Previously Reported H-Reported Here N-Not yet done 0-presently considered irrelevant or unrealisable due to experimental conditions e.g. high resolution EDX is not possible on-substrate.

Summary

Graphene MoS2 Ion Beam He+ Ne+ Ga+ He+ Ne+ Ga+ Substrate On Off On Off On Off On Off On Off On Off EDX H H N Raman P P H H P N H H N

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SLIDE 25

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

  • f 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

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SLIDE 26
  • Prof. Zhang & Group
  • AML & Collaborators,

CRANN & AMBER

  • School of Physics

Acknowledgements

  • Qianjin Wang

Nanjing University

Get in touch: maguirpi@tcd.ie, hozhang@tcd.ie Thanks for your attention!

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SLIDE 27

Results – Milling of MoS2 flakes

200 nm 100 nm 20 nm 1 nm

Danny Fox – Trinity College Dublin

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SLIDE 28

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

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SLIDE 29

Other materials

(b) (a) (c)

2 nm 2 nm 10 nm Mn2O3 TiO2