EUROMAT 2013 - Tutorial on Helium Ion Microscopy

Helium Ion Microscopy – Extending the Frontiers of Nanotechnology

Giulio Lamedica

Assing SpA / Zeiss Microscopy

Nanofabrication

Why He ions for Imaging?

HeiM on Graphene

Summary

•

•

•

Orion NanoFab Technology•

Conclusions•

Introduction•

More Applications•

Nanofabrication


HeiM on Graphene

Summary

•

•

•

Orion NanoFAab technology•

Conclusions•

Introduction•


4

As the beam is raster scanned across the sample, secondary electrons are generated which are detected by ET Detector ….

Image Formation

HIM Image

BSPB

SE1 SE2

SE3

Pole piece

Resolution in CPM

BSP

Probe Size Interaction VolumeSE1/SE2)

Nanofabrication


HeiM on Graphene

Summary

•

•

•


Conclusions•

Introduction•


7

Superposition of the aberration discs

0 0.2 0.4 0.6 0.8 1 1.2 1.4

0

1

2

3

4

5

6

7

8

9

10

Resolution and Probe Size – Electron Beam

Probe Size:

35.0 iSS Cd Spherical aberration:

iCC U

UCd

Chromatic aberration:

idd

6.0Diffraction Error:

Demagnified source: gSo dMd

ai ai [mrad]

d p [n

m]

2222dCSgP ddddMd

10.04.2023

Carl Zeiss NTS, Peter Gnauck

1,00E-06

1,00E-04

1,00E-02

1,00E+00

1 10 100 1000

U [kV]

Wav

elen

gth

[n

m]

Resolution and Probe Size

He+

Ga+

e-

9

0 0.2 0.4 0.6 0.8 1 1.2 1.4

0

1

2

3

4

5

6

7

8

9

10

Resolution and Probe Size – Helium Ion Beam

Probe Size: 2222dCSgP ddddMd

35.0 iSS Cd Spherical aberration:

iCC U

UCd

Chromatic aberration:

idd

6.0Diffraction Error:

Demagnified source: gSo dMd

a

ai [mrad]d p

[nm

]

• The Helium Ion Microscope has a half angle (a/2) of 0.5mrad compared to a typical SEM of 5-10mrad

• The Helium Ion Microscope has a theoretical probe size of 0.2nm and a demonstrated probe size of 0.24nm (product specification <0.35nm)

No diffraction limitations (MHe/Me = 7289)

Helium ions are more particle-like in nature due to higher mass (compared to electrons)

1

Key Attributes of Helium Ion Microscopy

10

He ions have extremely little diffraction effects

Imaging of small aperture with He ions

Imaging of small aperture with He ions

Diffraction limited image

No diffraction limitations

Electron Beam

He ion beamWavelength ~ 0.01 nm

Wavelength ~ 0.0001 nm

MHe/Me = 7289

80X smaller at all energies

221

1

2cm

eUeUm

h

He

He


11

Spot size = 0.8 nm

Electrons

Very high lateral resolution in images

Sub-nm probe size and very narrow interaction volume

2He ions

Silicon Sample30 nm

1 keV e-beam into Silicon: Image

suffers from large interaction

volume at the surface. Many

SE’s are really SE2.

30 keV Helium into Silicon:

Beam is well collimated

beyond the SE escape depth.

Recoil contribution is

negligible.

Spot size = 0.35 nm


12

Surface sensitive imaging

Secondary electrons get generated from within 3-5 nm of the sample surface

3Electrons He ions

Silicon Sample30 nm

1 keV e-beam into Silicon: Image

suffers from large interaction

volume at the surface. Many

SE’s are really SE2.





negligible.

Sec

on

dar

y el

ectr

on

es

cap

e d

epth

Volume from which SE’s are generated

Volume from which SE’s are generated

High SE yield means low ion doses can generate excellent images

Helium ions generate many secondary electrons per ion

4


13

Electrons He ions

Silicon Sample30 nm

He ions product 4-7 times as

many secondary electrons





negligible.


14

Electrons

5X-10X greater depth of focus in the images

Helium ion beam has 5X lower convergence angle than FESEM

5He ions

Silicon Sample30 nm

Convergence Angle = 0.020

a

Best Focus

Best Focus


15

Extremely easy to get high resolution images of insulating samples without complex preparation

Insulating samples are only positively charged under helium ion beam

6

The sample interaction volumes and the positive and negative charge distributions (+,-) arising from imaging with the SEM and with the HIM. SE1 are secondary electrons

created from the primary beam. SE2 are secondary electrons created from backscattered electrons (BSE)

0 nm

10 nm

300 nm

Helium @ 30 kVSEM @ 0.5 kV

-

SE2SE2

SE1

BSE

---

++++ +

+

SE1

SE1

+++ ++

--

-

- -

Bulk Charging

SurfaceCharging

Positive surface charging only -

easily neutralized by electron flood

gun!

Electrons He ions

Why Helium Ion Microscopy?

Very high lateral resolution in images

Sub-nm probe size and very narrow interaction volume

1

No diffraction limitations

Helium ions are more particle-like nature due to higher mass (compared to electrons)

2

Surface sensitive imaging

Secondary electrons get generated from within 3-5 nm of the sample surface

3

High SE yield means low ion doses can generate excellent images

Helium ions generate many secondary electrons per ion

4

5X-10X greater depth of focus in the images

Helium ion beam has 5X lower convergence angle than FESEM

5

16

Extremely easy to get high resolution images of insulating samples without complex preparation

Insulating samples are only positively charged under helium ion beam

6

Nanofabrication


HeiM on Graphene

Summary

•

•

•


Conclusions•

Introduction•


What is Ion Beam Milling?

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Schematic showing material being sputtered away by helium beam

Illustration from “Gas-assisted focused electron beam and ion beam processing and fabrication”, J. Vac. Sci. Technol. B 26(4), Jul/Aug 2008

Helium ion beam can remove material …

(1) … at a controlled rate(2) … with high fidelity(3) … from within 5 nm of beam impact point

Complex shapes and arrays of shapes can be milled using patterning engine.

APPLICATION AREAS

(4) Nanopore fabrication in thin films(5) Precision milling of thin films(6) Optical and magnetic metamaterial research

Ion beam milling utilizes the sputtering capability of ion beam to remove material

Why is Helium Ion Beam Suitable for Nanofabrication?

Remove material by sputtering

Helium ions are much more massive than electrons

1

Remove material at a controlled rate

Helium ions are less massive than gallium ions

2

Remove material locally

Helium ions sputter material from within 5 nm radius of beam impact point

3

Chemically enhanced etching and deposition at length scales not achievable with Gallium FIB

Helium ions can induce etching and deposition reactions at surface with precursor gases4

No proximity effect in helium ion beam lithography

Helium ions scattering profile in resists is narrow conical with low backscatter

5

High sensitivity, better contrast than e-beam lithography

Helium ions can expose resists in 5X smaller doses

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Ion Beam Milling Comparison between Helium and Gallium FIB

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1 10 20 30 100 nm

Ga FIBHe FIB

Helium FIB

Type of Ion Source Gas Field Ion Source

Minimum feature size

Spot size (30 kV)

Diameter of sputteredregion in gold (spot)

1 nm

0.35 nm

2.6 nm

Gallium FIB

Liquid Metal Ion Source

25 nm

5 nm

20 nm

Suitable for milling Small structures Large structures

Nanofabrication Examples …

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Graphene Photonics

DNA Sequencing

Nanopores

Lithography Nanopillars

Nanofabrication


HeiM on Graphene

Summary

•

•

•


Conclusions•

Introduction•


He Ion Beam MillingGraphene Research

Research Area

Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional

(2D) honeycomb lattice, and is a basic building block for graphitic materials. It has

extraordinary properties:

(1) Electronic (2) Optical (3) Thermal (4)

Mechanical

2010 Nobel Prize in Physics awarded for groundbreaking experiments with

graphene

ResearchApplications

Nanoribbons

Transistors

Optical modulators

Integrated circuit

Transparent electrodes

Ultracapacitor

Chemical and electrical sensors

Structure

Helium Ion MicroscopyImaging of Graphene

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Material Science

Challenge How do you see graphene CVD growth?

Zeiss Solution Helium Ion Microscopy: highly surface sensitive imaging

The grain boundaries of

the graphene can be

identified as ridges on the

surface.

CVD grown graphene

monolayer on copper.

Sample Courtesy: University of Houston

Research


Material Science

Challenge How do you see quality of Graphene trasferred on Silicon ?

Zeiss Solution Helium Ion Microscopy: highly surface sensitive imaging

Research

University of Bielefeld (D)


Graphene Machining for Quantum Confinement

The bandgap in a graphene

ribbon increases as the

ribbon width decreases

In order to increase bandgap

above room temperature

thermal energy (25 meV),

confinement of ribbon to less

than 20 nm is desired.

M. Han, B. Özyilmaz , Y. Zhang., P Kim, Phys; Phys. Rev. Lett. 98 (2007) 206805

Graphene nanoribbons bandgaps can be modulated

Current Solutions

• Lithographic patterning has been applied, but resist deposition and then removal can alter graphene electronic properties.

• Ga FIB milling produces too much damage to be useful (image)

• E-beam bond damage, followed by chemical etch, cannot produce sufficiently sharp feature edges.

• Need: low damage, precise, method that does not touch graphene intended for pattern.

Gierak et al., Microscopy Today (2009)

FOV 500 nm

1.86 E18 1.99 E18

* All units in Ions/cm2

2.39 E18

2.13 E18

2.53 E18

2.93 E18

2.26 E18

2.63 E18 2.79 E185-6 nm width

Direct Patterning of Graphene:5 nm Features

Graphene created by the exfoliation method (1-3 layers thick)

Created on SiO2 over cylindrical holes on surface.

Ion milling carried out on the suspended area.

FOV 100 nm

2.79 E18

Dr. Dan Pickard, National University of Singapore

4.8 E18

2.9 E18

4.8 E18

Dose (ions/cm2)

5nm width

10nm width

20nm width

VerticalFOV 700nm

Direct Patterning of Graphene:Ribbon Width Control

• Pattern generator (Nabity ) used to define milling structures

• External control of column

• 700 nm vertical field of view

• Milling proceeded simultaneously down both sides of ribbon to maintain strength


10nm wide ribbon3.5 microns long

20nm wide ribbon3 microns long

Direct Patterning of Graphene

• 20 nm and 10 nm wide suspended ribbons

• 4 µm field of view

• Aspect ratio up to 350X

FOV 4 µm


• Graphene layer (could be multiple layers) on SiO2 substrate

• Goal: creation of a quadrupole quantum dots structure

• 4 dots, with 4 electrodes to control the occupancy of dots

• Created by bitmap imported into Orion patterning interface

• 10 nm gaps have been created

• Next required step: pattern electrodes to the device for electrical testing (using beam chemistry!)

Graphene Milling on a Substrate

Creation of features with high machining precision

Graphene on SiO2

Courtesy of Stuart Boden, University of Southampton

Graphene Nanoribbons

Why Helium Ion Milling over other methods?

• Fast

• Non-destructive

• Contamination free

• Extends limitations (down to 5-6 nm width)

• Capable of complex geometries

• External control of column

Nanofabrication


HeiM on Graphene

Summary

•

•

•


Conclusions•

Introduction•

More Applications…•

Carbon Nanotubes – Large Depth of Focus

200nm

Research Single walled Carbon nanotubes on Si-Ge catalyst imaged with a 70° tilt

Challenge study of the growth dynamics that progress parallel to the substrate in this case

Zeiss Solutionlong depth of focus allows the CNT attachment to the catalyst to be imaged deep into the background Contrast for low atomic weight material at high resolution

Sample courtesy Prof. H.N.Rutt, Univ. of Southampton

Helium Ion MicroscopyCarbon Nanotubes

Research CNT with Sn and Pd nanoparticles

Challenge How do you evaluate nanoparticle distribution?

Zeiss Solution Helium Ion Microscopy: Topographical and Material contrast

Nanowires – Strong Materials Contrast

100nm

Sample courtesy Princeton University

Research Nanowires in the beginning of growth phase Catalyst array in substrate

Challenge Study the dynamics of the growth in this system with greater detail

Zeiss SolutionStrong material contrast clearly delineates the nanowires but without saturation of the image

Helium Ion MicroscopySAM Modification

Research Nitro-biphenyl-thiol (NBPT) self-assembled monolayer on gold, Electron beam patterning via stencil mask converted terminal nitro group to amine

Challenge How to identify chemical changes?

Zeiss SolutionHelium Ion Microscopy: Topographical and Material contrast possible studies of this chemical lithography which otherwise requires AFM, which has throughput limitations

Helium Ion MicroscopyImaging of Uncoated Polymers

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200 nm 200 nm

SEM HIM

Research Bioengineering (PLLA/hydroxyapatite composites for large bone defect healing)

Challenge How do you visualize biomineral growth on sensitive polymer surfaces?

Zeiss Solution Helium Ion Microscopy: damage –free imaging

Hydroxyapatite

crystal on PLLA

Charging and

sample damage

Research Material Science

Challenge How do you visualize at high magnification low weight materials ?

Zeiss Solution HeIM: Good contrast for low weight materials @ over 1MX (0.29 nm res)

Helium Ion MicroscopyCarbon Black

Helium Ion MicroscopyImaging of Inner Ear Tectorial Membrane

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Bioscience

Challenge How do you see the complex morphology of tissue nanostructures?

Zeiss Solution Helium Ion Microscopy: charge neutralization technology allows clear view

Sample Courtesy: NIH

Research

Ion Beam MillingMetamaterial Research

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Research Area

Metamaterials are engineered materials with properties that are not found in natural

materials. Also known as “left-handed” media, “Negative refractive index” media

Metamaterials gain their properties from structure rather than composition, using

small periodic (1D, 2D or 3D) inclusions (holes, lines, space etc.) in bulk material to

create effective macroscopic property.

Electromagnetic WavesVisible lightInfraredTerahertzMicrowavesRadiowaves

ResearchApplications

Terahertz materials

Photonic materials

Plasmonic materials

Metamaterial antennas

Nonlinear materials

Metamaterial absorber

Superlens

Cloaking devices

Working Principle

The objective is to create a “structured” metamaterial that will exhibit desired properties when electromagnetic waves interact with respect to(1) Propagation (3) Absorption(2) Transmission (4) Reflection

Metamaterial


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TraditionalMethods

Lithography

Layer by Layer or Self-assembly based methods

Zeiss Ion Beam Milling

Solution

Drawbacks Multi-step – have to rely on success of multiple steps

Tedious – numerous iteration of process development steps

Structure is big enough to make with Ga FIB

20 nm Gold (evaporated)5 nm ITOGlass Substrate

Zeiss Ga FIB Solution: Array fabricated in 20 minutes

Source: “Focused-Ion-Beam Nanofabrication of Near-Infrared Magnetic Metamaterials”, Adv. Mater. 2005, 17, 2547–2549


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Going Smaller By making the shapes in the array smaller, one can modulate the frequency

response of the metamaterial.

Example: As array element is made smaller, transmission of shorter wavelengths is suppressed.

Long wavelengths blocked

Medium wavelengths blocked

Shortwavelengths blocked

How does one makesmaller

structures?

Helium Ion Beam Milling, (Neon Ion Beam Milling)

Ion Beam MillingComplex Shapes for Plasmonics

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Research Area Plasmonics, Photonics, Sensors

ChallengeHow does one make small enough structure in metal film that will exhibit plasmon-

enhanced transmission at desired wavelength?

Zeiss Solution Helium Ion Beam Milling

Theory: Fractal shapes

enhance plasmon-

assisted transmission*

*Source: “Fractal extensions of near-field aperture shapes for enhanced transmission and resolution”, Optics Express, 2005, 13, 636-647** Courtesy: Dan Pickard, NUS

First fractal iteration based on Hilbert Curve

Second Fractal iteration based on Hilbert Curve

50 nm

Helium ion

beam milling

can make

complex

structures Au Al Ag

**

Ion Beam MillingTechnology Comparison • Ga FIB vs. Helium Ion Beam

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1 10 20 30 100 nm

Ga FIBHe FIB

* Courtesy: Dan Pickard, NUS

What is Ion Beam Induced Etching?

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Schematic showing material being etched away by He beam in the

presence of precursor gas molecules


When an etch gas (such as XeF2) adsorbs on a surface,

enhanced etching/material removal will occur if the

surface is scanned by helium ion beam.

APPLICATION AREAS

(1) Photomask repair

(2) Removal of excessive amounts of material

Material removal in the scanned region

He+

Ion Beam Induced EtchingPhotomask Repair

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Area Photomasks for lithography

Challenge How do you increase throughput in EUV photomask repair?

Zeiss Solution Helium Ion Beam Induced Etching

TaN Absorber Layer

No XeF2 XeF2 Present

TaN Absorber Layer

12 nm wide lines at 25 nm

pitch

Etching speed significantly

enhanced by XeF2 precursor

Same exposure conditions

(areal dose / scan repeats etc.)

Introduce XeF2

100 nm

Source: Diederik Maas, TNO

What is Ion Beam Induced Deposition?

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Schematic showing material being deposited by He beam in the presence of

precursor gas molecules


When a deposition precursor gas adsorbs on a surface,

material will be deposited if the surface is scanned by

helium ion beam.

APPLICATION AREAS

(1) Deposition of conductive lines and pads

(2) Failure analysis of integrated chips

Material deposition in the scanned region

He+

Ion Beam Induced DepositionApplication • Vertical Nanopillars

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Area AFM probes tips, Hard mask for lithography

Challenge How does one create vertical nanopillars?

Zeiss Solution Helium Ion Beam Induced Deposition

Platinum Nanopillars

(a) At low currents

(b) Blow-up of the

enclosed pillar, the

yellow ellipse is the

estimated pillar

bottom

(c) At high currents

Source: Nanotechnology 21 (2010) 455302 (7pp)

What is Ion Beam Lithography?

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When resists such as HSQ and PMMA are

exposed to ion beams, their solubility

changes and can be used for patterning.

Just like electron beams, ion beams can be used for lithography

He+

He+

Develop

Develop

Ion Beam LithographySub-10 nm Lithography

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Research Area

There is an interest in making smaller and smaller lines at a tighter pitch using

lithography to keep up with Moore’s law.

State-of-the-artE-Beam Litho Best results : 6 nm lines at 12 nm pitch

Half-pitch = 5 nmDose = 4000 e-/nm




Source: Karl Berggren, MIT

Reaching limits of EBL ….

Ion Beam LithographySub-10 nm Lithography

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Ion Beam LithographyNeon Beam Lithography

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Nanofabrication


HeiM on Graphene

Summary

•

•

•

Orion NanoFab Technology•

Conclusions•

Introduction•


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Orion Plus

He – Ne Gas Field Ion Source (GFIS)Single column – dual source concept

Probe Size; Probe Current:

He – 0.5 nm; 0.1 - 5 pA

Ne – 1.9 nm; 0.1 - 2.5 pA

Accelerating Voltage

• 10 – 35 kV

Switching time between gases

~1 min

ETDetector

Electron Flood Gun

Sample

SE

Helium + Neon

Target Specs.

Higher sputter yield (30% greater than helium)

Shallower penetration depth

Higher SE yield compared to He - 3X faster resist exposure than He

Improved deposit quality – Metal deposit resistivity equivalent to Ga

Neon Beam Benefits

High resolution imaging using He combined with

High fidelity nanostructuring using Ne

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9/20/2012 Page 60

Carl Zeiss NTS LLC , Bernhard Goetze

Cryogenic Cooling

Gas InletHigh Voltage

High Speed Camera

Phosphor Screen

Gas Field Ion Source

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The Technology Behind It

Individual atoms are stripped away from the source until an atomic pyramid is created with just three atoms at the very end of the source tip – a configuration called the trimer.

Once the trimer is formed, the tip is maintained under high vacuum and cryogenic temperatures with helium or neon gas flowing over it.

The helium or neon atoms are attracted to the energized tip where they are ionized.

With ionization happening in the vicinity of a single atom, the resulting ion beam appears to be emanating from a region that is less than an angstrom in size.

FIM tip created via chemical etching

ALIS tip formed with additional reshaping

3 atom shelf called the “trimer” created through field evaporation

Single atom selected to form the final probe

Results in a sub-angstrom virtual source with high brightness (4x109 A/(cm2 sr)) and low energy spread (<1eV)

The Atomic Level Ion Source

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ORION NanoFab– The Column

9/20/2012

Bulk Milling with Ga

Multi-ion Beam Machining in ORION NanoFab

Intermediate Milling with NeFinal Milling with He

Sample: Gold film on Glass substrate

Ga Milling

He Milling

Ne Milling

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Nanofabrication


HeiM on Graphene

Summary

•

•

•


Conclusions•

Introduction•


The ORION NanoFab Platform

• Configurable architecture to address specific imaging and nanofabrication applications.

• High Resolution Imaging on insulating samples – ideal for life science and polymer imaging applications.

• 3D Nanofabrication of sub-10nm structures.

• Precise Machining with He/Ne beams and Rapid Prototyping with Ga beam – only platform offering unique combination of three different ion beams.

Sample

Helium + Neon

Ga XRE

Stereocilia

9/20/2012 67

Carl Zeiss NTS LLC , Bernhard Goetze

200 nm

HIM: Unsurpassed Resolution 0,24nm

Carbon Nanotubes (Provided by Prof. Brendan Griffin Univ. W. Australia)

CNT

HIM: Low Damaging Effect

MEMS

HIM: High Depth of Field

Collagene

HIM: Effective Charge Compensation

(Provided by Prof. Brendan Griffin Univ. W. Australia)

CNTHIM: Surface Details

9/20/2012 72Carl Zeiss NTS LLC , Bernhard Goetze

Collecting Duct

HIM: High Resolution and Elevated Surface Details

500nm

Catalyst: Pd on ZnO nanowires

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HIM: High Depth of Field

Bacteria

9/20/2012 74Carl Zeiss NTS LLC , Bernhard Goetze

200 nm

HIM: Minimal Sample Preparation

HIM: Nanofabricaation with Ga ions

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TEM lamella S/C

200nm

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Al bump su Silicio

HIM: Nanofabricaation with Neon ions

100nm

~4nm gap

TEM Image

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Plasmonic Devices

HIM: Nanofabricaation with He ions

Bulk Milling with Ga

Multi-ion Beam Machining in ORION NanoFab

Intermediate Milling with NeFinal Milling with He

Sample: Gold film on Glass substrate

Ga Milling

He Milling

Ne Milling

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HIM: Nanofabricaation with Multiple Beam

Plasmonic Devices

EUROMAT 2013 - Tutorial on Helium Ion Microscopy

Technology

Transcript of EUROMAT 2013 - Tutorial on Helium Ion Microscopy