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R-SoXS, P-SoXS, IM-SoX, R-SoXR What does all that mean?So = SoftSoft matter and soft X-raysREXS 20116/16/2011Harald AdeDepartment of Physics, North Carolina State UniversityHonorary “co-author”: Jeff Kortright, LBNLThanks to organizers for inviting meResearch supported by: DOE Office of Science, Basic Energy Science, Division of Materials Science and Engineering, National Science Foundation


Soft x-rays

 Advanced Light Source


Beamlines we use are 5 3 2 2 stxm 6 3 2 soxr 7 3 3 waxs 11 0 1 2 soxs 11 0 2 1 stxm
Beamlines we use are: 5.3.2.2 (STXM), 6,3.2 (SoXR), 7.3.3. (WAXS), 11.0.1.2 (SoXS), 11.0.2.1 (STXM)

Hongping at 7.3.3. (SAXS/WAXS)

Cheng and Hongping at 11.0.1.2. (R-SoXS)

Brian at 5.3.2.2 STXM

11.0.2.1 STXM

Our energy range is lower than what you have seen so far at this conference

3


Structure morphology determination in real space absorption x ray microscopy

scattering vector q (WAXS), 11.0.1.2 (SoXS), 11.0.2.1 (STXM) (mm-1)

scattering vector q (mm-1)

Small Angle Scattering/RSoXS

Coherence length larger than domains,

but smaller than illuminated area

Structure/morphology Determination in Reciprocal Space: Resonant X-ray Scattering

40

information

about domain

statistics

20

0

-20

-40

-40

-20

0

20

40

Structure/morphology Determination in Real Space: Absorption X-ray Microscopy

Best for NEXAFS

Relatively slow

Low damage

Figure courtesy of/after J. Stohr


Goals of presentation
Goals of presentation (WAXS), 11.0.1.2 (SoXS), 11.0.2.1 (STXM)

  • Convey the power of carbon K-edge R-SoXS

    • Focus on organic devices

  • Provide understanding of some of the underlying physics of the tools

    • “gear heads” tutorial light

      • This will be short, you are already experts

  • Turn a few of you into (more frequent?) soft X-ray users

    • Impossible task?

       study organics at the carbon (or nitrogen and oxygen) edge

       great potential and opportunity to develop a new user community


Highlights roadmap
Highlights/roadmap (WAXS), 11.0.1.2 (SoXS), 11.0.2.1 (STXM)

C. Wang, T. Araki, H. Ade Appl. Phys. Lett. 87, 214109 (2005)

G. E. Mitchell, et al., Appl. Phys. Lett. 89, 044101 (2006);

T. Araki et al. Appl. Phys. Lett. 89, 124106 (2006)

  • Feasibility is established

     Development of a new facility at the ALS dedicated to R-SoXS

    H. Yang, et al. AdvFunct Mater. 20, 4209 (2010)

  • X-ray reflectivity coupled to device data and MC simulations shows that interface structure in PFB/F8BT bilayers contributes 50% to the poor performance.

     Non-equilibrium, sharp interfaces are best

    S. Swaraj et al., Nano Letters 10, 6863 (2010)

  • Scattering and microscopy shows that domains in all-polymer blends are too large or too impure

    Need better control. Use of block copolymers!?


Highlights roadmap ii work in progress

282.4 eV, calculations (WAXS), 11.0.1.2 (SoXS), 11.0.2.1 (STXM)

Si

Si

Highlights/roadmap-II: work in progress

X-ray reflectivity on organic TFT devices:

  • N2200/dielectric

  • pBTTT/dielectric

    Polarization dependent Soft X-ray Scattering

    (P-SoXS)

  • Unique contrast mechanism. How can it be exploited?

    Index matched Soft X-ray scattering

    (IM-SoXS)

  • Turn top surface “off”

  • Diffuse scatting from buried polymer interface

  • Eliot Gann will give a talk in ~1.5 hours


Soft X-rays: (WAXS), 11.0.1.2 (SoXS), 11.0.2.1 (STXM)Unique interaction with organic materials Scattering factorsand optical constants of C,N, and O

Assumed density of 1 g/cm3

Complex index of refraction:

n=1-δ+iβ

“Natural” scattering contrast:

Assumed density of 1 g/cm3

  • Quantitative absorption microscopy:

  • Beer’s Law: I=I0e-μρt

  •  20-200 nm thick samples


Near Edge X-ray Absorption Fine Structure (NEXAFS) Spectroscopy

“Resonant effects” are more than just elemental

Unsaturation C=O

Unoccupied Molecular Orbital

e-

Unsaturation C=C

C 1s edge ~ 290 eV

N 1s edge ~ 405 eV

O 1s edge ~ 540 eV

hn

Photon energy


MDI polyurea Spectroscopy

PBMA

MDI polyurethane

PMMA

TDI polyurea

TDI polyurethane

Nylon-6

PEO

PS

EPR

PBrS

PP

SAN

PE

Spectroscopy = selective contrast

Dhez, Ade, and Urquhart

J. Electron Spectrosc. 128, 85 (2003)

vectra

PC

PAR

Kevlar™

Data: Stony Brook STXM at NSLS

PBT

PNI

PET

Fingerpt.ppt 8 May 1998


Resonant scattering reflectivity r soxs r soxr contrast is almost as good as selective deuteration

PS Spectroscopy

N

P2VP

PMMA

Resonant Scattering/ReflectivityR-SoXS/R-SoXR(contrast is almost as good as selective deuteration)

Absorption (NEXAFS)

Scattering factors f’ and f” (optical const. δ and β, respectively) show strong energy dependence

Neutron community use different terminology: complex scattering length

Dispersion

R or I  (Δδ2+Δβ2)

  • “Bond specific” scattering!

  • Substantial potential as complementary tool!


Soft x ray resonant reflectivity ps pmma bilayer

NC SpectroscopySTATEUniversity

air

PS

PMMA

Si

Ade Research Group (Polymer Physics/X-ray Characterization Techniques)

Soft X-ray Resonant ReflectivityPS/PMMA bilayer

Complementary Tool to Neutrons and hard X-rays

C. Wang, T. Araki, H. Ade

Appl. Phys. Lett. 87, 214109 (2005)

  • Observed strong photon energy dependence

Potential: Diffuse scattering from interfaces

Data: Araki, BL6.3.2. ALS, Berkeley


air Spectroscopy

PS

PMMA

Si

Reflectivity:

If we had perfect data (simulations)

PS 50nm/PMMA 200nm


Interpretation of reflectivity data

Momentum transfer: Spectroscopy

PS

PMMA

Si

Interpretation of Reflectivity Data


NC SpectroscopySTATEUniversity

(Figure courtesy J. Stubbs UNH)

280.0 eV

280.0 eV

285.2 eV

285.2 eV

288.4 eV

288.4 eV

320.0 eV

320.0 eV

qR=4.5

q=0.39

qR=7.73

q=0.68

qR=10.9

q=0.95

Scattering Intensity [a.u]

R=115 nm

q (1/nm)

Ade Research Group (Polymer Physics/X-ray Characterization Techniques)

PMMA/P(BA-co-S)

P(MA-b-MMA) / PS

J.M. Stubbs,

D.C. Sundberg Polymer 46 (2005) 1125

Different process and composition

  • Fuzzy TEM

  • modified core/shell structure?

  • Phase less separated?

  • Where really is the PS?

Idealized, “consensus” particle

“PS”

“PS”

“PS”-”shell”

200 nm

150 nm

Scattering Intensity [a.u]

100 nm

  • “PS” about same size than PMMA/acrylate!

  • Scattering indicates PS is slightly more in center of nanoparticle relative to PMMA/P(BA-co-S)

q (1/nm)

  • “PS” effective radius larger than PMMA “radius”

T. Araki et al. Appl. Phys. Lett. 89, 124106 (2006)


Organic Electronics: SpectroscopyAn interesting area of applications and characterization needsContext: Energy Security/Independence, Global Warming

Flexible organic light emitting diodes (OLED)

(from Sony)

organic photovoltaics (OPV)

(from Nicole Cappello, Gatech)

organic thin film transistors,

(from www. livescience.com.)


PCBM Spectroscopy

P3HT

Critical Factors in Organic Photovoltaic Devices:Morphology, interfaces, domain purity, and energy levels

Bulk heterojunction devices

Need lateral structure ~10 nm in size

Light

“Organic Photovoltaics: Materials, Device Physics, and Manufacturing Technologies”, Wiley-VCH (August 25, 2008)

  • What makes fullerene-based devices so successful?

  • What are the primary shortcomings of polymer-polymer devices and can they be overcome?

  • What role can soft x-ray characterization methods play?

    • Morphology (including crystallinity): scattering and microscopy

    • Interfaces: scattering and reflectivity

    • Purity: quantitative compositional microscopy and scattering


Morphology polymer polymer blend devices
Morphology SpectroscopyPolymer:Polymer blend devices


Donor Spectroscopy

1:1 PFB:F8BT blend all-polymer solar cell model system 140 nm cast from chloroform  smallest domains to date140 °C yields max in efficiency, but PCE still <2%

Lateral composition maps from x-ray microscopy

Acceptor

NEXAFS contrast

  • Effective resolution < film thickness

    • Need 3D resolution, i.e. tomography

    • or scattering

C. R. McNeill et al. Nanotechnology 19, 424015 (2008)


Transmission geometry Spectroscopy

Channeltron

Sample

q

q

X-rays

Resonant Soft X-ray Scattering (R-SoXS) of PFB:F8BT blendHigh enough scattering contrast for transmission experiment

S. Swaraj,C. Wang, H Yan, B Watts,J. Lüning, C. R. McNeill, and H. Ade, Nano Letters 10, 6863 (2010)


Domain size analysis with R-SoXS Spectroscopy1:1 PFB:F8BT blends cast from chloroform

Pair distribution function P(r)

R-SoXS

284.7 eV

Small domains disappear at 200 ºC

Small domains get more pure

~7 nm feature

Average domain much larger than exciton diffusion length and/or too impure

 poor efficiency (partially) explained

Good S/R and Information content to 1 nm-1

S. Swaraj,C. Wang, H Yan, B Watts,J. Lüning, C. R. McNeill, and H. Ade, Nano Letters 10, 6863 (2010)


Another all polymer blend p3ht f8tbt initial data analysis
Another all-polymer blend: P3HT:F8TBT SpectroscopyInitial data/analysis

PCE=1.8% at 140 °C

McNeill APL 90, 193506 (2007)

 Unfavorable large range of domain size once annealed


Organic thin film transistors interfaces in plane organization
Organic Thin Film Transistors SpectroscopyInterfacesIn-plane organization


Interfaces in otfts dielectric n2200
Interfaces in OTFTs: Spectroscopydielectric/N2200

We are in the process to measure buried interface structure of N2200 with different dielectric polymers

 Relate this to device performance

Interface with PMMA is exceptionally sharp:

Initial fit ~0.5 nm

PS is less sharp:

Initial fit ~0.8 nm)

Cytop even less sharp:

Initial fit ~1,0 nm

 Correlated to turn-on voltage

PMMA/N2200

285.8 eV

PS/N2200

284.1 eV

cytop/N2200

688 eV

H. Yan, Z. Gu, H. Ade (NCSU), C.R. McNeill. T. Schuettfort (Cambridge)


Polarization in STXM and Scattering SpectroscopyAnother interesting and unique contrast mechanism probing domain size and domain correlation in TFT applications


Polarization contrast in stxm and scattering

Specific molecular orbitals are probed via x-ray photons at resonant energies

Absorption enhanced if photon polarization is parallel to transition dipole moment

Polarization contrast in STXM and Scattering

Collins et al. (2011).


Scattering is sensitive to quasi domain size of pentacene p soxs proof of principle

390 eV resonant energies

285.4 eV

Scattering is sensitive to quasi-domain size of pentaceneP-SoXS proof of principle

293eV

  • Use scattering when domains are too small for STXM

  • Or scattering too weak in TEM

500nm


Transmission p soxs from pbttt pmma tfts i q q 2

As-cast resonant energies

Transmission P-SoXS from PBTTT/PMMA TFTs: I(q)·q2

  • Non-Resonant scattering sensitive to mass-thickness

    • Similar to scattering using hard x-rays

  • Resonant scattering profiles completely different, showing definite trend

    • Clear trend of both feature size and feature contrast

Annealed

Thickness/roughness/density

Domain correlations

Non-Resonant

250 eV

Resonant

285.4 eV

780nm

600nm

480nm

max~150nm

Feature Size ~ Position of Max

Collins, Yan, Gann, Cochran, Chabinyc, Wang, McNeil, Ade (2011).


Device mobility is directly related to domain size
Device mobility is directly related to domain size resonant energies

  • saturation mobilities correlate exponentially to quasi-domain size

    • Corr. Coef = 0.992

Collins, Yan, Gann, Cochran, Chabinyc, Wang, McNeil, Ade (2011).


~150 nm thick, annealed at 180C resonant energies

P-SoXS signal from P3HT:F8TBT blends

STXM image at 285.4 eV

Not sure yet what this all means,

 Better real space method would be really helpful

Collins, Yan, Gann, Cochran, Chabinyc, Wang, McNeil, Ade (2011).


Utility of soft x rays
Utility of Soft X-rays resonant energies

  • Lots of great science possible (It’s also fun!)

  • R-SoXS, P-SoXS has the potential to reach a large, new community

    • Need more facilities,

      • particularly one in Europe

    • Better analysis tools


R-SoXS, R-SoXR, P-SoXS, IM-SoXS resonant energiesWhat do the acronyms mean?So = SoftSoft matter and soft X-raysR-SoXS: Resonant Soft X-ray ScatteringR-SoXR: Resonant Soft X-ray ReflectivityP-SoXS: Polarization dependent R-SoXSIM-SoXS: Index Matched SoXS

SoXS rhymes with


Thank you for your attention resonant energiesThanks to members of my group:B. Collins, S. Swaraj (now Soleil), H. Yan, E. Gann, J. Seokand C. McNeill, N. Greenham, I. Hwang (Cambridge), C. Wang (ALS), M. Chabinyc, and J. Cochran (UCSB)

Financial support: DOE Office of Science, Basic Energy Science, Division of Materials Science and Engineering

Contract: DE-FG02-98ER45737

Cheng and Hongping at the ALS


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