High-Resolution and Quantitative AFM Mapping of The Mechanical - - PowerPoint PPT Presentation

Sergei Magonov1, Marko Surtchev1 , Sergey Belikov1, Ivan Malovichko2 and Stas Leesment2

1NT-MDT Development Inc., Tempe AZ USA 2NT-MDT, Zelenograd-Moscow, Russia

High-Resolution and Quantitative AFM Mapping of The Mechanical Properties of Polymers

Outline

1. Studies of Local Mechanical Properties in AFM 2. Quantitative Nanomechanical (QNM) Experiments in HybriD™ Mode 3. QNM of Neat Polymer Samples 4. QNM of Polymer Blends 5. High-Resolution QNM Mapping 6. Conclusions

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AFM Operator & Operating Procedures Loading & Aligning a Probe

Single probe and multi-probe cartridge; manual and automatic alignment

Loading of a Sample

Manual and automatic loading

Engagement of a Probe

Manual and automatic engagement; soft approach algorithm

Measurements’ Routines

Studies at variable tip-forces; automated and non-attended multi-site and multi-probe experiments Oscillatory Resonance Mode: Amplitude Modulation Oscillatory Non-Resonance Mode: Contact Mode Hybrid Mode

AFM Modes

LDPE

Amplitude-vs-Distance Curve Deflection-vs-Distance Curve Deflection-vs-Distance Curve

PVAC

DMT: Eel=2.9 GPa Eel=2.3 GPa O-P:

Currently HybriD Mode is most

• ptimal for Quantitative

Nanomechanical Studies and High-Resolution Mapping of Elastic Modulus and Adhesion

E, GPa E, GPa

Deflection-vs-time Curve

• Max. Deformation-vs-Amplitude Max. Force-vs-Amplitude

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Studies of Local Mechanical Properties in AFM

Studies of Local Mechanical Properties in AFM

Phase 200 nm Height 90 nm

Contact Mode

Height 7 nm

HybriD Mode Amplitude Modulation Mode

Dodecanol Adsorbate on MoS2

Comparison of Tip-Sample Forces in Different AFM Modes All three modes complement each other in the nanoscale characterization of materials. The contact mode is most suitable for lateral force imaging and piezoresponse studies. The amplitude modulation is superior for operation at low forces and for multi- frequency approaches in studies of local electric properties.

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Quantitative Nanomechanical Study in HybriD Mode

On-Line and Off-Line Analysis of Force-versus-Time or Force-versus-Deformation Cures Fit of the Force-vs-Time “Inverted Parabola” Curve

• r Part of It to Find Average Elastic Modulus and

Work of Adhesion (I. Malovichko, NT-MDT) Point-by-Point Calculation of Elastic Modulus and Work of Adhesion from Region of Interest of Force- versus-Deformation Curve (S. Belikov, NT-MDT) Elastic modulus and Work of Adhesion Maps are collected as the arrays up to 1024×1024 size. On-line and off-line analysis can be performed using Hertz, DMT and JKR models. 5 of 21

QNM Study in HybriD Mode: Experimental Details

Experimental: Si probes with stiffness of k = 25 N/m and 28 N/m and a nominal tip radius of 10 nm were applied. Force range was in the 5 nN - 100 nN range Scan rate was in the 0.4 - 1.0 Hz range Oscillation amplitude: 20 nm at 1. 5 kHz; for soft samples - up to 100 nm at 1.5 kHz. Typical Map density 512 x 512 Saving Force Curve (Force Volume) - optional

Finding of Probe Spring Constant and Optical Sensitivity

Inverse optical sensitivity (IOS) can be obtained from Dvt & DvZ curves in the HybriD and contact modes.

Samples:

• 1. Neat polymers in blocks: Polycarbonate (PC),

Low-density polyethylene (LDPE), octene- branched polyethylene with density 0.87 g/cm3 (PE87)

• 2. Polymer blends as films with thickness above

100 nm: Polystyrene-PS with LDPE (PS|LDPE), PS with poly(methyl methacrylate) (PS/PMMA), PS with high-density polyethylene (PS|HDPE), PS with poly(butadiene) (PS/PBd), PS with poly(vinyl acetate) (PS/PVAC), syndiotactic PS with poly(vinyledene fluoride) (sPS/PVDF)

• 3. Films of block copolymers (PS-b-PMMA, PS-b-

PBd-b-PS) and blocks of semicrystalline HDPE and linear low-density polyethylene (LLDPE)

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 

wR h R E h P  2 3 4

2 / 3

 



R a h R a E kD P

r 2 3

, 3 4   

Error Propagation in QNM Analysis of Force Curves

Hertz: DMT:

r

E k a dh dD 2 

 

1 / 1

1 





dZ dD dh dD

x x y     1 1 x x y   1

x = DvZ; y = Dvh

k aE aE x

r r

  2 2

E, Pa 10M 50M 0.1G 0.5G 1G 3G 5G 10G 20G 30G 40G k, N/m 710m 2.1 3.3 9.6 15.2 31.6 44.5 70.5 111.7 146.6 177.6 Table 1. Probes with Minimal k (N/m) for Material with Modulus E (Pa) & Error Propagation of 2

0.005˚C

Silver Nanoparticles on Mica: Scans (512×512) with 1 Hz rate

• Temperature

stability better than 0.01C

• Thermal drift lower

than 0.2 nm/min 7 of 21

Thermal, Acoustic, Vibration Enclosure

Elastic modulus Deformation 1 mm Height 1 mm

Fvt FvZ

Elastic Modulus Work of Adhesion Deformation 1 mm 1 mm

QNM of Neat Polymers: Polycarbonate Block

20 nN 30 nN 60 nN 20 nN 30 nN 60 nN 60 nN 20 nN 30 nN 60 nN 20 nN 30 nN 60 nN 60 nN

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QNM of Neat Polymers: Low-Density PE Block

Height Elastic Modulus 1 mm 1 mm Work of Adhesion Deformation

20 nN 30 nN 60 nN 20 nN 30 nN 60 nN

1 mm 1 mm

20 nN 30 nN 60 nN 20 nN 30 nN 60 nN

Fvt FvZ

60 nN 60 nN

Elastic modulus Deformation

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QNM of Neat Polymers: Octene-PE 0.87 Block

Height Elastic Modulus 1 mm 1 mm Work of Adhesion Deformation 1 mm 1 mm

20 nN 30 nN 60 nN 20 nN 30 nN 60 nN 20 nN 30 nN 60 nN

Deformation

Fvt FvZ

60 nN 60 nN 20 nN 30 nN 60 nN

Elastic Modulus

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QNM of Polymer Blends: PS/PBd

Height 1.5 mm Height 5 mm Height 1.5 mm Phase Elastic Modulus Elastic Modulus 1.5 mm 1.5 mm 1.5 mm Elastic Modulus, 6 nN Elastic Modulus, 20 nN

6 nN 20 nN

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QNM of Polymer Blends: PS/LDPE

Height 5 mm Height 5 mm 5 mm 2 mm 2 mm 2 mm Elastic Modulus Elastic Modulus Deformation Deformation Deformation Deformation Elastic Modulus Elastic Modulus

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QNM of Polymer Blends: PS/HDPE

Height Elastic Modulus Deformation 2 mm 2 mm 2 mm Height Elastic Modulus Height Phase 7 mm 7 mm 7 mm 7 mm Deformation Elastic Modulus

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QNM of Polymer Blends: PS/PMMA

Height 20 mm Height 2 mm Map of PMMA Raman Band Height 2 mm 2 mm 2 mm Elastic Modulus Elastic Modulus 20 mm Elastic Modulus Elastic Modulus

30 nN 80 nN

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QNM of Polymer Blends: PS/PVAC

Height Height Elastic Modulus Height Elastic Modulus 7 mm 7 mm 2 mm 2 mm 2 mm Elastic Modulus Elastic Modulus

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QNM of Polymer Blends: sPS/PVDF

Height Elastic Modulus Deformation Work of Adhesion Deformation Elastic Modulus 6 mm 6 mm 6 mm 6 mm

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High-Resolution QNM of Polymers: HDPE

Height Height Elastic Modulus Elastic Modulus Height Height Work of Adhesion 3 mm 1 mm 1 mm 400 nm 400 nm 400 nm

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High-Resolution QNM of Polymers: LLDPE

Height 1 mm Height 1 mm Height 3 mm Phase 1 mm Elastic Modulus 1 mm Elastic Modulus

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High-Resolution QNM of Polymers: PS-b-PB-b-PS

Elastic Modulus Height Elastic Modulus Height Elastic Modulus Height Deformation Work of Adhesion 1 mm 150 nm 150 nm 150 nm 400 nm 400 nm 400 nm

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High-Resolution QNM of Polymers: PS-b-PMMA

1 mm 1 mm 1 mm 1 mm 400 nm 400 nm 400 nm Height Elastic Modulus Height Elastic Modulus Height Elastic Modulus Elastic Modulus Elastic Modulus

6 nN 25 nN

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Conclusions

QNM measurements of polymer samples in HybriD mode verified the value of quantitative mapping of elastic modulus for characterization of polymers and, particularly, for compositional mapping of heterogeneous materials. High spatial resolution of modulus mapping approaching 10 nm was demonstrated

• n lamellar structures of semicrystalline polymers and block copolymers.

These results provide a solid background for studies of mechanical properties of polymers at interfaces and in other confined geometries. A combination with local electric and spectroscopic methods will make such studies even more comprehensive. In our next HybriD mode applications we will address the viscoelastic behavior of polymers.