Nanoscale 3D Molecular Imaging by Extreme Ultraviolet Laser … · Nanoscale 3D Molecular Imaging...

PhD preliminary exam

Nanoscale 3D Molecular Imaging by Extreme

Ultraviolet Laser Ablation Mass Spectrometry

Ilya Kuznetsov

Electrical and Computer Engineering Department

May 8th, 2015

Nanoscale imaging mass spectrometer – a logical step

in the development of the EUV field at CSU

Oct. 1994 - demonstration

of Table-top 46.9 nm laser

Dec. 1999 – spherical

mirror metal ablation

Jan. 2005 – spherical

mirror polymer ablation

May. 2005 – demonstration

of compact 46.9 nm laser

Jun. 2006 – van der Waals

clusters mass spectra

Dec. 2006 – polymer

ablation with zone plate

Jul. 2008 – optical spectra of 46.9 nm

ablated materials with spherical mirror

2

D. Crick +

C. Menoni =

The Concept

Extreme ultraviolet (EUV) laser pulses possess unique

properties for chemical probing

46.9 nm pulses can be focused to ≤100

nm diameter spots

26.4 eV energy per photon is enough to

ionize any atom or molecule

1012 photons (10 µJ) per pulse are ample

for single shot ablation and detection

>1 Hz repetition rate is suitable for imaging

3

Working with EUV light is complex

≤10-3 torr vacuum requirement to reduce attenuation

Special optics designed for 46.9 nm use only:

grazing incidence mirrors - ~70% for gold at 10° grazing angle

multilayer mirrors - Sc/Si, ~40% reflectivity at normal incidence

diffraction optics - free standing Fresnel zone plate (ZP) lenses

2.13 mm focal distance

10% efficiency

<200 nm thick

4

Composition (chemical) imaging is essential analytical

technique in many fields

Composition Imaging - a visual representation of complex solid

chemistry by scanning it with probing beam.

Materials science

Forensic science

Microbiology

Pharmacy

Medicine

←membrane systems

↖intracellular areas ↗therapeutic agent

5

Time-of-flight (TOF) mass spectrometry imaging allows

multi-component detection at high speed

6

M1

H+

H H

M1 H+

M2 H+

M1+

H

H

H H

H+

Field-free region

increase mass-

separation

detector

Accelerating potential (~ kV)

Focused ion beam - secondary ion mass spectrometry (SIMS)

Focused photon beam - laser ablation/desorption (MALDI)

sam

ple

y

x

Ep ~ qe*Z*U Ek ~ m*V2

m/Z

Secondary ion mass spectrometry (SIMS) – a

competing method for imaging small molecules

7

Static limit: ion dose density <1013 cm-2

Spatial resolution: 0.1-10 µm

Depth resolution <10 nm

Mass resolution ≤104

ion

bunch

SIMS cannot perform high resolution 3D imaging

8

m

Δm

↑ length of pulse → ↑ spatial resolution → ↓ depth resolution → ↓ mass resolution

Primary

ion beam

configuration

Δt2 ~ Δm0.5

Secondary

ions bunch

Δt1

Matrix assisted laser desorption and ionization (MALDI)

method dramatically extends the mass range of SIMS

9

UV-absorbing matrix has to be

applied to maintain ionization

analyte matrix

Microscope image Selected ion distribution

Spatial resolution limited by matrix effects and wavelength

Depth resolution limited by slice thickness

UV-laser created plasma is hotter than that of EUV,

which reduces analytical capabilities

10

𝑛𝑒𝑐 =𝜖𝑜𝑚𝑒

2

𝑒2𝜆2 =

1021

(𝜆[𝜇𝑚])2[𝑐𝑚−3]

Distance

Electron

density

nec =1.5*1022

(=266 nm)

So

lid

=266 m

= 46.9 mm

nec

nec =5*1023

(=46,9 nm)

Ablation is induced by direct solid

photoabsorption

EUV-created plasma stays cold because

of negligible inverse bremsstrahlung

800 nm, 120 ps 46.9 nm, 1.5 ns M. Berrill et al, JOSA B/Vol. 25, No. 7, 2008

This presentation describes the state of development

of the imaging nanoprobe

1. Design considerations

11

2. Instrument characterization

3. Experimental results 4. Future work

ø120 nm

Ground grid

PD

Zone plate lens allows for narrow focusing and

efficient ion extraction

12

y

x

~3% area ratio

Collimated beam reduces losses at the zone plate

13

Interaction chamber

~50% of initial light intensity

Time-of-flight tube provides higher mass resolution in

reflectron mode

14

EUV vacuum photodetectors allow for the calibration

and monitoring of pulse energy

Gold-coated photoemission

detector for calibration

15

Residual gas photoionization

in-line detector for monitoring

Variable pressure gas cell attenuates the laser when

needed for imaging with higher resolution

16

Capillary lifetimes

T = 1.4e-0.014p R² = 0.9778

0.0

0.2

0.4

0.6

0.8

1.0

25 75 125 175 225 275T

p, mtorr

no filter

0.2 um Al

0.4 um Al

Expon. (no filter)

Expon. (0.2 um Al)

EUV TOF mass spectrometer in the laboratory

17


18



ø120 nm

Mass resolution of 1000 is enough to measure masses

with ~0.1 a.m.u. (Da) accuracy within few kDa range

19

Au3+

Au5+

Au+

Au2+

m

Δm

Spectrum of aminoacid Alanine is comparable to that

of SIMS and better than MALDI with no matrix

20

A distinct peak from the smallest

~50 zL single shot ablation crater

I. Kuznetsov et al, Nature Communications, 2015

Molecular sensitivity to aminoacid Alanine of 0.01 amol

is 40× better than that of SIMS

21

ALANINE EUV TOF

(First results)

SIMS TOF

# of primary particles (dose) 3.9 106 4.1 108

# of secondary ions at 90 m/z 80 1.76 106

Area probed (µm2) 4.5 10-2 2.25 104

Depth probed (µm) 3.5 10-3 2 10-3

Volume probed (aL) 0.05 4.5 104

Sensitivity (amol) 0.01 0.4

Ion yield, normalized to

probed volume (L-1)

4 1014 8.5 1010

Level of fragmentation 1.1 1

10 keV Bi+ at 45° into C


Depth resolution of better than 70 nm is achieved on

inorganic multilayers

22

Hf and HfO peaks follow the

natural isotopic abundance

35 nm per shot

70 nm per shot

Depth resolution of 20 nm is achieved on organic

multilayers

23

Nile

Red

Ala

nin

e

ITO

Sample

EUVL

Nile Red Alanine ITO

20 nm

Substrate


~75 nm spatial resolution was measured on

photoresist edge

24 I. Kuznetsov et al, Nature Communications, 2015


25



ø120 nm

Bukminsterfullerene (C60) spectrum shows formation of

giant stable fullerenes with mass up to ~3 kDa

26

Ionization energies: 7.6 eV, 11.4 eV…

Surface plasmon resonance near 22 eV

C2 separation in mass spectrum above 720 Da

Parent antibiotic molecules are observed in single shot

spectra

27

290.32 g/mol

331.35 g/mol

[M+H]+

[M+H]+

Switching between positive and negative ion extraction

modes allow for parent molecular ion detection

28

Nile Red 318.37 g/mol

Soda-lime glass SiO2, 60.08 g/mol

(~74% wt)

+

impurities:

Na2O

CaO

K2O

MgO

Our first 2D image of high resolution

29

ITO

trench

120 nm

of resist

Before experiment After experiment

40×40 shots with

250 nm step

↓

10×10 µm

area

One shot per spot

Ablation crater size:

400 nm FWHM

50 nm depth

2D complimentary image of near 100 nm resolution

30

ITO composition image has low contrast due

to presence of resist peak near Indium

Mass spectrometry image of resist by 4

characteristic peaks has 140 nm resolution

75 nm demonstrated

3D image of heterogeneous sample precisely reveals

the intrinsic volumetric organization

31

1

2

3

4

Sh

ot

#

Gold pillar, imbedded into resist

on top of ITO-coated glass

3D composition image of the M.Smegmatis correlates

in size with its microscopic image

32

Image of the bacterium with 300×300×80 µm2 voxel size

Image by differential

interference microscopy

70 m/z 81 m/z


33



ø120 nm

MALDI spectrum of Vitamin B12 with no matrix is very

similar to EUV TOF

34

EUV TOF spectrum Heaviest vitamin: 1355.37 Da

Corrin Ring: 306.4 Da

Dimetylbenzimidazole (DMB): 146.08 Da

Post-ablation soft ionization provides valuable insight

into higher mass neutral species

L. Takahashi et al, Imaging with Mass Spectrometry: a Secondary Ion and VUV-Photoionization Study

of Ion-Sputtered Atoms and Clusters from GaAs and Au, J. Phys. Chem. A 2009, 113, 4035-4044

35

VUV light from a pulsed gas discharge lamp offers a

simple and affordable alternative for EUV TOF

Ionization and extraction scheme

36

System overview

← Extraction pulse using a Pockel’s cell driver

Neutral species Ions EUV laser

Accurate ionization and extraction timing is needed

Lamp design

37

≤10.4 eV

Optical spectral measurements show the density of 1+ ions

to be ~5% of the neutrals

Atomic transitions for argon

38

Lamp’s optical emission spectrum

Next steps will include increasing VUV production

efficiency and improving ion extraction mechanism

UV-graded fused silica ring

flash tube (+mirror)

39

Power supplies to produce

up to 100 A current

Build a stack of HV capacitors

to further increase current

Characterization

Other ways to increase the mass range

Using more intense light sources:

specialized VUV pulsers

second EUV pulse

non-EUV lasers

Fostering protonation:

water + cryocooling

gas “puff” near the sample

Ionization by electron attachment

40

With the availability of a higher mass range, compositional

mapping at the subcellular level becomes possible

41

Component % of

Total Cell

Weight

Approximate #

of Molecules /

Cell

# of

Different

Kinds

Water 70 4 x 1010 1

Inorganic Ions 1 2.5 x 108 20

Carbohydrates & Precursors 3 2 x 108 200

Amino Acids & Precursors 0.4 3 x 107 100

Proteins & Polypeptides 15 1 x 106 2000-3000

Nucleotides & Precursors 0.4 1.2 x 107 200

Lipids & Precursors 2 2.5 x 107 50

Other Small Molecules 0.2 1.5 x 107 250

Nucleic Acids - DNA 1 1 to 4 1

Nucleic Acids - RNA 6 5 x 105 1000

▼now

Without knowledge and effort from brilliant people…

Advisors: Carmen Menoni, Jorge Rocca

CSU professors and committee members: Dean Crick, Elliot and Barbara

Bernstein, Diego Krapf

Collaborating professors: Gregory Tallents, Libor Juha, Philippe Zeitoun,

Andrew Duffin, Debbie Crans, Olga Boltalina, Steven Strauss

Collaborating students: Valentin Aslanyan, Tomas Burian, Thai-Hoa Chung,

Donn Calkins, Estela Magallanes, Andrew Rossal

Internship students: Nengyun Zhang, Catalina Tome, Christopher Limberger,

Cornelius Oster, Nicolas Detrez, Yonas Tesfai, Jonas Boch

Graduate students and postdocs: Jorge Filevich, Feng Dong, Bryce

Schroeder, Gerald Gasper, Tyler Green

42

… and many more from the lab!

Summary: EUV TOF imaging nanoprobe is built and

characterized, further improvements are on the way

Sample utilization efficiency is greater than 1%

Molecular sensitivity is 0.01 amol and 40×

higher than that of SIMS

Parent molecular peaks detected in positive or

negative modes with single laser shot

Depth resolution of 20 nm is achieved on an

organic bilayer system and can be higher

Lateral resolution is better than 75 nm

43

ø120 nm

Post-ablation ionization will

open room for new insights

Thank you for your kind attention!

Nanoscale 3D Molecular Imaging by Extreme Ultraviolet Laser … · Nanoscale 3D Molecular Imaging...

Documents

Transcript of Nanoscale 3D Molecular Imaging by Extreme Ultraviolet Laser … · Nanoscale 3D Molecular Imaging...