AFM: 6 Must Know Measurements

Dalia Yablon SurfaceChar LLC [email protected] AFM - Principles of operation

piezo AFM can measure many other useful surface properties Mechanical Tapping mode lateral (LFM) Magnetic 10nm lateral resolution force modulation (FMM) magnetic force (MFM) <1nm vertical resolution contact resonance (CR-FM) Flexible environments torsional resonance (TRM) Optical Near field Raman (NSOM-Raman) (fluid, air, temp) pulsed force (PFM) shear force modulation Near field IR Force Other Electrical molecular pulling Kelvin force (KFM) lithography Electrostatic force (EFM) manipulation Piezo force (also PFM!) thermal microscopy (SThm) Conducting AFM (C-AFM) 3-D nanoprinting Scanning capacitance (SCM) Must know measurements with AFM

• Topography – 3 dimensional maps • Mechanical contrast: Mapping with materials contrast • Mechanical properties: Nanoscale adhesion and modulus • Electrical properties: Mapping with electrical contrast • Magnetic properties: Mapping with magnetic contrast • Optical: Chemical information Topography – 3 dimensional maps

• Most common measurement • AFM provides true measurement of z (height) • (in contrast to electron/optical microscopy) • Enables measurements like roughness analysis • Topography is the backbone of all AFM imaging measurements • Feedback is on the z piezo to provide topography • Any other imaging mechanism contrast (mechanical, electrical, magnetic) are all collected simultaneously with the topography Materials contrast imaging: Phase imaging

Tapping mode!

– Drive base of cantilever with a sinewave generator – Phase lag between cantilever drive and response – Response is due to complicated material response including elastic and viscoelastic properties – Key method to discriminate materials, though not well understood

drive response

D amplitude

f Differentiating materials via phase imaging

Df Df Phase lag image Solution-cast triblock copolymer film (equilibrated)

f

100 nm From G. Haugstad ABA block copolymer, solvent-vapor annealed: poly (styrene-isobutylene-styrene) or SIBS (styrene cylinders standing or lying down)

Relatively bright regions: glassy phase of triblock copolymer → less dissipative Stiffness, adhesion, viscosity,…can give dissipation Topography

Component #3 Phase

Component Component Component #5 #4 #1 and #2 Single point mechanical measurements: Force curve/force spectroscopy

Modulus

Adhesion Force curves on impact copolymer Create force maps…

Height Adhesion Forcemaps on cells

Adhesion

Data from nanosurf

Epithelial cells Adhesion force (nN) Elastic modulus

background

Elastic modulus (kPa) Elastic modulus

Fibroblast cells Data from Asylum Research (online image gallery) Kelvin probe microscopy

• Maps surface potential • What can it measure? – Trapped charge, spontaneous polarization, work function variation, potential difference

• Requires cantilevers with electrically conductive coating • Two passes – First pass: topography with typical piezo actuation/tapping mode – Second pass: AC electrical bias plus a DC bias to vibrate the tip [cantilever driven electrically] Electrical properties: surface potential (Kelvin probe force microscopy KPFM)

Graphene

Copper foil

BN Image courtesy of Asylum Research Magnetic Properties (Magnetic force microscopy – MFM)

Topography MFM

10um 10um

Data and image courtesy of ParkAFM AFM-IR

• Adds chemical information to the AFM topography

Courtesy of Neaspec

• Combine AFM + IR – Apertureless scattering method

– Photothermal method

Courtesy of Anasys Instruments AFM-IR: Nanoscale spatial resolution for thin film

Topography Nano-FTIR Absorption

3.8nm max

0nm 1730 cm-1 min 200 nm ON Resonance High-resolution PMMA/PS diblock thin films (period: 50nm) 2.3nm max

-1 0nm 1650 cm min OFF 100 nm Resonance Data courtesy of Neaspec Summary

• Topography – 3 dimensional maps • Mechanical contrast: Phase imaging • Mechanical properties: Force spectroscopy • Electrical properties: Kelvin probe microscopy • Magnetic properties: Magnetic force microscopy • Optical: AFM-IR • Nanoscale Resolution • Environmental flexibility

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