5 kv = 0.5 nm atomic resolution tem image ebpg (electron beam pattern generator) 100 kv = 0.12 nm

5 kV = 0.5 nm

Ato

mic

res

olut

ion

TE

M im

age

EBPG (Electron beam pattern generator)

100 kV = 0.12 nm

SNOM

To locate single molecules:Optical microscopy:-fluorescence (labeling)-particle tagging(-electron microscopy)

Piezoelectric (Voltage – Displacement)

Precise tip control is achieved with Piezoelectrics

Displacement accurate to ± .05 Å

PZT = (Pb,Zr)TiO3

Basic Principles of STM

Electrons tunnel between the tip and sample, a small current I is generated (10 pA to 1 nA).

I proportional to e-2κd, I decreases by a factor of 10 when d is increased by 1 Å.

d ~ 6 Å Bias voltage:mV – V range

Copper Surface

Silicon

Silicium-oppervlak met stappen

(Bron: Sandia Nat.Labs.)

Si(100)

Two Modes of Scanning

Constant Height Mode

Constant Current Mode

Usually, constant current mode is superior.

Instrumental Design Continued

TipsCut platinum – iridium wires

Tungsten wire electrochemically etched

Tungsten sharpened with ion milling

Best tips have a point a few hundred nm wide

Vibration Control

Coiled spring suspension with magnetic damping

Stacked metal plates with dampers between them

Interpreting STM Images

Hydrogen on Gadolinium

“Topography” model good for large scale images, but not for the atomic level.

Electron charge density model more accurate for atomic level images.

Best model requires complex quantum mechanical considerations

Atomic Force microscope(Scanning Force Microscope)

PiezoElectric

positioner

Feedbackelectronics

Laser diodeDeflection detector

Flexible cantilever

Probe tip

display

AFM Tip

y

z

l

L

ylL

z 3 l ~ 100m

L ~ 3 cm

z ~ 1000 y !!!

Detection: beam deflection

Optical lever amplification

Scanning modes

Constant height Constant force

Contact mode Tapping mode

High friction No friction forces

Resolution: scanning probe microscope

object tip geometry image

Tip convolution is not linear: results DO NOT add upResolution is depends on tip AND sample

Imaging and manipulationof Carbon nanotubes

Millipede 1024 tips