Noel Smith

Oregon Physics(aka ‘Just above California’ Physics)

n.smith@oregon-physics.com

Bio-Chemistry with Ion Beams

• Oregon Physics

• Creating an Energetic Ion Beam and Focusing it

• Ion Beam Interactions with Solid Biomaterials

• Applications in Biochemical Material Analysis

• Ion Sources Developed for Biochemical Imaging

Outline

Oregon Physics• Small Commercial Company Developing:

• High Brightness Plasma Ion Sources (O2+, O-, Xe+, He+, Ne+, Ar+, H+, N2

+…)

• Ion and Electron Optics

For material science studies

• Chronology– Started Oregon Physics in ‘07 to commercialize ICP technology developed at the ANU. – Hyperion fully released in ‘10 , Hyperion II in ’13– Growing number of developments underway and products being released

Creating an Ion Beam• Create a Source of Ions

• Gas ionized by energetic electron beam (Electron Impact Source, EIS)• Gas field ionization source (Gas Field Ionization Source, GFIS)• Ions Created in the Plasma Phase (Plasma Ion Source)

+10

kV

0kV

High Brightness Source of IonsHigh Current Density and Low Thermal Ion Energy

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+ ++

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+

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+

++ +

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+

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+10kV

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vthermal

vextraction

Extracted ion current

radius of emissive surface

Focusing a Divergent Beam

Object Image

10keV Xe+

Electrostatic Lens (cylindrically symmetric)

0V 6.5kV 0V

Einzel Lens

fiPrinciple Plane

Object distance, U Image distance, V

Oregon Physics

• Focusing a Divergent Beam of Ions

Magnification, M=V/U=o/I

Lateral Magnification = 2/3Angular Magnification = 3/2

U V

Ion Extraction From a Plasma

ii

eBi E

E

M

Tkqn

0

max 6.0 <0.045eV

>1x1013cm-

3

Virtual Sourcedv~5-50m

Div

erge

nce

Ang

le

Radial Position

A Focused Ion Beam

ML1 x ML3 . x ML4 = Mtotal

o

i

FIELD DEFINING APERTURE

ANGLE DEFINING APERTURE

Balancing Source Image and Aberrations for Best Spot Size

Ion Optics (Cs(M), Cc(M))

Focused Beam (d, I)

Source of Ions (dv, I’,DE,E)

Final spot Gaussian Chromatic Spherical

dv, - virtual source diameter (m) I’ - Angular Intensity (A/sr)DE - Energy Spread (eV)E - Beam Energy (eV)d – image of the source (m)I – beam current (A)i – convergence angle (rad.)

Energy NormalizedSource Brightness

br = I’/(πE(dv/2)2)

dv

i

4

Optimized Focused Ion Beam

For a given beam divergence angle, the optimum balance of Gaussian demagnification and optical aberrations give the smallest focused beam

Ion Source

Extraction Electrode

Condenser Lens

Variable Beam Defining Aperture

Mass Filter

Mass Selection ApertureBeam Blanking Faraday Cup

Beam Scanning and Stigmation (Octupole)

Objective Lens

Sample

Ion Beam Optics

Plasma FIB Applications

Micro Machining

© Copyright 2011 Oregon Physics LLC

Splat Interface Analysis

ARL - Nickel Alloy Stencils for fracture analysis.(20mins, 300nA Xe+)

Energetic Ion Interactions With Solid Materials

Ion Beams for High Resolution Material Analysis(Atomic scale archeological dig)

Chemical Analysis from Sputtered Ions

• Chemical Image Resolution Determined by Ion Beam Focus.

(silicon segregated to ceramic grain boundary, Hillion et al, Cameca)

• Detection sensitivity heavily influenced by ion beam species.• Reactive ion beams favor increased sputtered ion yields

• Positive ion yield increases 100-1000x for many species with electronegative ion beams (eg oxygen).

• Parts-per-billion (ppb) detection limits.

• To liberate high molecular weight secondary ions, cluster ion beams are required.• eg Buckyballs (C60)• However, no ion yield enhancement.

Courtesy of Prof Garrison et al, Penn. State, USA

Snap Shots of Cluster (C60)and Atomic Bombardment

Tt=29 ps

Z. Potswana, Garrison et al, J. Phys. Chem. B, 108, 7831-7838, 2004

15keV C60+ and Ga+ into Ag<111>

•Single monomer ion produces lots of damage and little sputtering•Cluster produces 15x more sputtering and less residual amorphous material

Cluster beams: • Dramatically enhance the

yield of high mass molecular ions.

• Allow for measurements of the depth distribution of molecules.

Reactive atomic beams: • Dramatically enhance the yield

of low mass ions, for sub-ppm trace element imaging at high image resolution.

Atomic ion beam

Cluster ion beam (C60)

Environmental contaminants

- Rice sequesters arsenic .- Major source of As in our diets.- Threshold levels not well known for

arsenic to be a carcinogen.

Arsenic distribution in rice roots (Moore 2011)

Silicon at cell wall, but insufficient resolution to resolve arsenic distribution in cell.

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Primary Objective ‘Sub-cellular Chemical Imaging’

Primary Objective ‘Sub-cellular Chemical Imaging’

Symbiotic Organisms

- Reef building coral hosts photo-synthesizing algae.

- Studies to determine how algae assimilates nitrogen from seawater enriched with ammonium.

- Fundamental processes not understood.

- Algae immersed in 15N tagged NH3 - Timed immersion, then sample prep. and analysis.- 15N rich algae cells

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Primary Objective ‘Sub-cellular Chemical Imaging’

Molecular Imaging of Biological Tissues• C60 is very useful spectral data• Poor spatial resolution• Much brighter ion source needed for

sub- cellular imaging.

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Phosphocholine • Found in all cell membranes • Related to lipid production in cell walls • Energy storage and essential nutrient affecting immune response.

Cholesterol •Found in cell membranes•Related to cell membranepermeability and fluidity.

(Hillion et al 2007)

Simplest and most flexible method

• Thermionic electrons.• Independent control of mean electron

energy.• Low ion density and difficult to

maintain low energy spread (5-20eV)• Ions accelerated into filament• Ion density ~1x108-1x1010 ions cm-3

• br ~5-50 Am-2sr-1V-1 for argon

Broad pressure and mean electron energy range,suitable for ionizing clusters.

e-

e-e-

C60

C60+

C60

C60

C60

C60C60

C60

C60+

GRID(Beam Voltage)

EXTRACTOR(-kV’s w.r.t. grid)

FILAMENT(0 to -100V w.r.t. grid)

Ion Sources for Biochemical Imaging

40keV C60+ beam. >1000nm resolution.

Surface Analysis Ion BeamsDuoplasmatron (Trace Level Elemental SIMS)

eeee e e eeee e ++ ++ +

+

+

~ -30V

~ -500V

Long, Coathe and Drummond – Cambridge Univ – ‘60-’95

• Cold cathode – good for oxygen plasma

• High Plasma density (ni =1011-1013 cm-3)

• High brightness ~40-1000 Am-2sr-1V-1

• High energy spread 10-15eV• Continuous cathode erosion

15keV O- beam. 200nm resolution.

i

ir T

n

Inductive Power TransferTime varying current in an external coil creates a time varying B field, which induces an azimuthal E field.

xE=-B/t

Induction E field accelerates electrons to ionize resident gas.

(no=1x1012cm-3)

~9GHz

~18MHz

O-, SF6- C60

- for SIMS imaging of geological and biological materials

PLASMA

Plasma Chamberwith low loss tangent

Faraday Shield High Azimuthal Impedance

Extractor Electrode

Pole Gap~200 Gauss

Magnetic PolesTransverse B

RF Antenna

Ion-Ion plasma (depleted of hot electrons)

Extracting Negative Ions (High Res. SIMS Imaging)

© Copyright 2011 Oregon Physics LLC

Oxygen PlasmaO- formed primarily by dissociative electron attachment.O2 + e− → O + O−

O- Ion Source Parameters

© Copyright 2011 Oregon Physics LLC

O- Ion Beam with ICP Ion Source

Significant Resolution Enhancement Achieved with Inductive Plasmas

- No constraints from electrode erosion- Brightness 10x higher than DC plasma sources (eg duoplasmatron).- Latest data showing <50nm resolution (35nm reported), as opposed

200nm.

Strong Requirement for 10nm Resolution (Bio, semi, nuclear, metals ..)

- Significantly more work required to:- Understand negative ion extraction- Increase plasma density, while maintaining thermal ion energy.

C60 Ion Beams with ICP Ion Source ??

TODAY C60+

Brightness (Am-2sr-1V-1) ~0.1

Energy Spread (eV) ~10eV

Imaging Resolution (nm) 1000

Lifetime ~500 hours

40keV Electron Impact (Filament) Source Aiming for 40keV, 1pA, 100nm spot

TARGET C60+

Brightness (Am-2sr-1V-1) ~50

Energy Spread (eV) ~2eV

Imaging Resolution (nm) 100

Lifetime >500 hours

C60+ ion Densities of ~1x1011 cm-3 required.

• Electronegativity of C is too great for pure C60 plasma

• Use electropositive carrier gas (eg xenon)

• Internal vibration energy of C60 needs to be kept <44eV to prevent fragmentation

• Main constraint is that the x-section for fragmentation and ionization are similar at <20eV

C60 Ion Beams with ICP Ion Source ??

C60 Ion Beams with ICP Ion Source ??

C60 Oven

C60 effuses into plasma chamber

C60 transfer tube

ICP Xe/C60 Ion Beam

16O+

12C+

Xenon isotopes

>99% xenon isotopesAlmost 0.1% C60

+

Summary

- Low pressure ICP’s are proving to be significant for focused ion beam applications.

- Lots of exciting research to be done.

- Significant commercial applications in biology, semiconductors, metallurgy, nuclear sciences, manufacturing etc…