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EXPLORING THE NANOLANDSCAPEScanning Probe Microscopy

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IMAGE GALLERY

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The Nanoscale

• Atomic diameter ~ 0.3 nm = 3 Å

• Microelectronics interconnect ~ 0.25 µm– http://www.intel.com/technology//itj/q31998/articles/art_1.htm

• Red blood cell (5µm)

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Proximal Probes

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History

• Topografiner

• Tunneling through a controllable vacuum gap

• Scanning Tunneling Microscope

• Atomic Force Microscope (Scanning Force Microscope)

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Operation of a Scanning Probe Microscope

• Scanning with sub-Angstrom precision• Probe detection (e.g., current, force, position, …)• Electronics processing• Computer control• Image processing• Vibration isolation• Environmental control (e.g., vacuum, atmosphere,

fluid; temperature)

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Scanning Tunneling Microscope

Omicron

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Scanning Force Microscope

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Tunneling

• One-dimensional tunneling

• Density of electronic statesof sample and tip

2m1/ 2

2

I So 2

To 2

e 2d

So

= sample wavefunction

To

= tip wavefunction

= workfunction

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Forces

non-contact Distance

tip to sample separation

repulsive force

attractive force

contact

Force

Trace

Retrace

F k x

Typical:

k 0.3N / m

x = 10nm

F = 3nN

Contact vs. non-contact modes ...Forces to atto-newton (10-18 N) range ...

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Themes

• IMAGING

• INTERROGATING

• MANIPULATING

atoms and nanoscale objects

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IMAGING

ATOMS AND NANOSCALE OBJECTSATOMS AND NANOSCALE OBJECTS

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Large-scale Atomic-scale

Graphite4.2 nm 4.2 nm

STM

Gold Grating30 µm 30 µm

STMDiNardo

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Semiconductor Surfaces - Si(100)

Tilted dimer

SymmetricDimer

Unreconstructed

L) OccupiedR) Unoccupied

Hamers, 1986

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Temperature-dependent Reconstructions

• Low-temperature Si(100)-c(42) vs. (2 1)– Domain boundaries, p(2 2) regions

Wolkow, 1992

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Homoepitaxial Growth - Si(100)

Mo, 1988

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Fractional Images

• Probing atomic orbitals– Frequency-modulated

Atomic Force Microscopy

– Si tip / Si(111)-77

Si atom

Giessibl, 2000

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Metal Surfaces

Wahlström, 1998

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0.4 ML Ag/Cu(110)

c(102) model

a, b) 230230 nm2

c) 5.45.4 nm2

d) 3.83.8 nm2Sprunger, 1996

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Interfaces - Cross-sectional Imaging

Ohmori, 1999

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Molecular Adsorption - CO/Pt(111)

Pederson, 1996

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Coatings - Colloidal Latex Particles

VacancyRecoveryFaulted LayerInterstitial DefectLine DefectOrientation ChangeBrennan, 2000

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Coatings - Latexes

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Carbon Nanotubes

Odom, 1998

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Overlapping Nanotubes

Avouris, 1999

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Nanotube Shapes and Forces

Avouris, 1999

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Biological Macromolecules - Collagen

Brennan, 2000

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Biological Macromolecules - Fibronectin

Brennan, 1999

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INTERROGATING

ATOMS AND NANOSCALE OBJECTSATOMS AND NANOSCALE OBJECTS

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Visualizing the Tunnel JunctionSTM-TEM

Naitoh, 1996

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Scanning

Ohnishi, 1998

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Bias-dependent imaging ~ Graphite

DiNardo

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Bias-dependent imaging ~ GaAs(110)

• GaAs(110) (cleaved) surface

Feenstra, 1987

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Spectroscopy ~ on the Nanoscale

• Beam techniques average over surface species• SPM techniques measure density of states related

to the atom (or molecule) under the tip– electronic spectrum - measure dI/dV [or (dI/dV)/(I/V)]

Hamers, 1986

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Electronic SpectroscopyAtom by Atom

• Reconstructed Si(100)-21 surface– Dimers– Occupied electronic states of dimers (between atoms)

– Unoccupied electronic states of dimers (away from atoms)

Hamers, 1986

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Defects

• Atomic-sized defects– Al/Si(111)-√3√3 structure

– different electronic states

Hamers, 1988

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Chemical Reactivity

NH3 reacted with the Si(111)-77 surface

Wolkow, 1988

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Vibrational SpectroscopyMolecule by Molecule

Lauhon, 2000

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Chemical Reactions

Lauhon, 2000

Electron-induced dissociation product -pyridine on Cu(100) at 8K

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Surface DiffusionChasing Atoms with the Atom Tracker

Swartzentruber, 1996

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H-enhanced diffusion of Pt atoms

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Horch, 1999

an STM movie ...

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Electrostatic Force Microscopy (EFM)

• Application– Topography of integrated circuit

– Monitoring an active integrated circuit

Digital Instruments, www.di.com

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Scanning Capacitance Microscopy

Nakakura, 1999

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Magnetic Force Microscopy (MFM)

• Magnetic tip interaction with surface• Application: Disk drive

– Morphology

– Magnetic structure

Digital Instruments, www.di.com

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Scanning Chemical Microscopy

• Measure chemical interaction between the tip and sample

• Functionalize the tip with hydrophobic or hydrophilic species

• Scan over surface and measure adhesion force or friction force

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Carbon Nanotube Tips- Functionalization -

Wong, 1998

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Scanning Chemical Microscopy

Frisbee, 1994 / Wong, 1998

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Adhesion Forces

Wong, 1998

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Friction Force Microscopy

• Macroscopic friction forces

• Microscopic friction forces

Ffr N

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Polymer Thin Films

Nie, 1999

Polypropylene film(a) AFM + (b) FFM, (c) non-contact AFM

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nN Bond ForcesStrength of a Covalent Bond

Grandbois, 1999

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Ballistic Electron Emission Microscopy - BEEM

• Three-terminal setup• Probe potential barrier at interface between metal

and semiconductor• Electrons are forward-focused without scattering

(ballistic)

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BEEM

Bell, 2000

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MANIPULATING

ATOMS AND NANOSCALE OBJECTSATOMS AND NANOSCALE OBJECTS

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Moving Atoms

• Xe– Physisorbed noble gas - (low temperature)

• Fe– Quantum “Corrals”

Eigler, 1991 / Crommie, 1993

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Confined Electrons

• Reflections of free electron (waves) at boundaries

• Standing waves solutions

• One-dimensional free electron solution (infinite barrier)

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Quantum Corral

Crommie, 1993

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Forming Nanowires

Ohnishi, 1998

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Nanowire modeling

Okamoto, 1999

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Measuring Currents through One- and Two-atomic-row Nanowires

Ohnishi, 1998

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Nanoelectronics

• Nanoscale channels

• Nanoscale objects

• Currents - description based on quantum-mechanical transport

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Nanoscale patterning

• Desorption– H-terminated Si(100)

• Deposition– Fe(CO)5

Adams, 1996

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Nanotube Circuits

Avouris, 1999

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Nanotube FET

Martel, 1998 / Avouris, 1999

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Diamond-like Carbon Films

STM AFM

Mercer, 1996

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Protein-folding Forces

Rief, 1999

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Comparison of Force Curves

Rief, 1999

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Related Techniques

• Scanning Near-field Optical Microscopy

• Scanning Thermal Microscopy

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Some Acronyms ...

• STM• STS• AFM• TM-AFM• FFM, LFM• CFM