Nanofabrication of Plasmonic Devices in

the Helium Ion Microscope

Advanced Materials

Characterization Workshop

UIUC

7 June, 2012

Larry Scipioni

Carl Zeiss Microscopy

•Stanford University, Stanford, CA

•Carl Zeiss Microscopy

•Argonne National Labs

•INA, Zaragoza, Spain

Content

•Nano-Apertures

•The helium ion micrscope (HIM)

•Nano-Atennae

1. Nano-Apertures

Optics with diffraction limit

Spot size ~ λ/2 ~ 150 nm

@ λ = 257 nm

1X demagnification system

with negligible aberration

D. S. Pickard et al., JVST. B. (2003)

Motivation: Multiple E-beam Lithography

Increase production throughput with multiple beams

Motivation – Nanoscale Photoelectron

Sources

1. Focus light to the near-field with a nanophotonic structure:

C-aperture with sub-100 nm dimensions

2. Near-field locally excites photoelectrons in a photocathode

(CsBr)

3. Extract photoelectrons with a negative bias voltage

This unit can be

duplicated in an array

for multiple beam sources

(not to scale)

C-Aperture Properties

< 100 nm

1. Small gap/ridge

-- small radiation source

2. Sharp edges

-- good charge concentrationSmall spot requires:

+-

Induced surface current

concentrates charges at the ridge

2.2 α

ααα

α

C-Aperture – Resonance Conditions

Target : 20 nm spot

→ try α = 20 nm

λ=257 nm

(CsBr has a strong

absorption at 257 nm)

J. A. Matteo et al., Appl. Phys. Lett. (2004)

experiments

FDTD

simulations α=40n

m

α=55n

m

T

Aperture Size, α (nm)

Reso

nan

t W

avele

ng

th, λ

(nm

)

Tra

nsm

issio

n (

ct.

/sec.)

Wavelength (nm)

Al80nmAl90nm

Al100nm

simulation

experiment

α=40nm

α=55nm

experiment

Fabrication – Conventional FIB Milling

J. B. Leen et al., Opt. Lett. (2008)

FDTD Simulation,

with λ = 980 nm incidence

Through Membrane Milling

(experiment)

Fabrication – Conventional FIB Milling

J. B. Leen et al., Opt. Lett. (2008)

Through Membrane Milling

(FDTD simulation)

Direct Metal Milling

(experiment)

Direct Metal Milling

(FDTD Simulation)

(With λ=980 nm incidence)

Ga FIB: Ion Milling Dynamics

TRIM simulation

30keV Ga+

Point beam

Au substrate

1000 ions incoming

-120

-70

-20

30

80

-120 -70 -20 30 80Z, n

m

Y, nm

SRIM, All Sputtered Atoms

-10

-8

-6

-4

-2

0

2

4

6

8

10

-10 -5 0 5 10Z, n

m

Y, nm

SRIM, Sputtered Atoms Near Ga+ Impact Point

Nanometer-Precision Machining with Helium Ions

“As particle reflection coefficients increase with decreasing energy (and are quite

high for light Ions), reflective scattering (a) collisions near the target surface

contribute increasingly to sputtering.”*

Is sputtering more localized?

*Behrisch and Eckstein, Sputtering by Particle

Bombardment, Topics in Applied Physics 110, Springer-

Verlag GmbH, Heidelberg, 2007.

2. First Commercial Helium Ion Microscope: Orion

ALIS – Atomic Level Ion Source

Provides a high brightness source

capable of sub-nanometer imaging

resolution

Sub-nanometer Probe Size

Asbestos fiber (crocidolite) and carbon

membrane

200nm field of view

35keV beam

Resolution: 0.21 nm

Excellent surface detail as well

Localization of Sputtered Atoms

TRIM simulation

30keV He+

Point beam

Au substrate

1000 ions incoming

SRIM, All Sputtered Atoms

-120

-100

-80

-60

-40

-20

0

20

40

60

80

-60 -40 -20 0 20 40 60 80 100 120

Y, nm

Z, n

m

SRIM, Sputtered Atoms Near He+ Impact Point

-10

-8

-6

-4

-2

0

2

4

6

8

10

-10 -8 -6 -4 -2 0 2 4 6 8 10

Y, nm

Z, n

m

100nm

50nm 40nm 30nm 20nm 10nm

He-ion vs. Ga-ion

Helium Ion FIB Gallium Ion FIB

100nm

100nm

100nm100nm

Direct Metal Milling Through Membrane

Milling

Material: 40 nm thick aluminum (imaged from HIM) Material: gold (imaged from SEM)

80 100 120 1400

50

100

150

200

X (nm)

Ima

ge

In

ten

sity (

arb

. u

nit)

50 nm

Results

Three neighboring C-apertures,

HIM machined

Image of emission spots

Profiles of photo-current (down

the beam, no focusing)

Simulations indicate beam size

at source should be 22 nm

• Needs to be verified

0

20

40

60

80

100

120

140

160

180

x 1

0^4

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

eV

0.65 eV 1.28 eV 1.71 eV 1.82 eV 2.07 eV 2.31 eV

Line width: 10 nm

STEM image

EELS spectrum

from whole

structure

Higher Order Fractal Apertures

Daniel Pickard, NUS

3. Plasmon Coupling in Nano-antennae

Localized surface plasmons (LSP’s) are electron density

oscillations, which are concentrated on the exterior of

nanostructured materials (NSM).

.

Electron Energy Loss Spectrum

Surface and

Bulk Plasmons

Elastic Beam

~ 1.65 - 3.1 eV

750 - 400nm IR UV

Goal

100 nm thick single crystal Au membrane

Ga ion beams introduce significant damage to thin films. The

resulting stress causes films to buckle. Milled feature size limited

to ~ 50+ nm

Fabrication with Gallium FIB

He Ion Milling: Low Lateral Damage

Nestor Zaluzec, ANL

4 nm

We were able to visualize and measure coupling of the low

energy loss surface plasmons modes ( 0.8 - 3 eV ) of

coupled nanostructures.

1.65 - 3.1 eV <-> 750 - 400nm

Plasmons Observed: STEM-EELS

Conclusions

•Use new beam technology to make newer

beam sources

•Helium-ion FIB uniquely able to mill sub-20

nm C-apertures.

•Photoelectron emission with good

brightness measured

Acknowledgements

Stanford University

Prof. Piero A. Pianetta

Richard C. Tiberio, Paul Rissman, James Conway

Paul C. Hansen and Yin Yuen (Hesselink Lab)

Carl Zeiss, NTS

Chuong Huynh, David Ferranti, Bill Thompson

Funding Support:

DARPA grant TXFEL 1138606-1

Argonne National Labs and INA

Nestor J. Zaluzec, Dean J.Miller, Jon M. Hiller, and Raul Arenal