Transcript STM Workshop 29-11-1391

In The Name of Allah
Scanning Tunneling Microscope
Pooria Gill
PhD of Nanobiotechnology
[email protected]
Image from an STM
Iron atoms on the surface of Cu(111)
Microscopy

Optical Microscopy

Scanning Electron Microscopy

Scanning Probe Microscopy
Scanning Probe Microscope

Atomic Force Microscope (AFM)

Electrostatic Force Microscope (EFM)

Magnetic Force Microscope (MFM)

Scanning Tunneling Microscope (STM)

Near-field Scanning Optical Microscope (SNOM)
History
The scanning tunneling microscope was developed
at IBM Zürich in 1981 by Gerd Binning and
Heinrich Rohrer who shared the Nobel Prize for
physics in 1986 because of the microscope.
Gerd Binning
Heinrich Rohrer
Scanning Tunneling Microscope (STM)
The STM is an electron microscope that
uses a single atom tip to attain atomic resolution.
SPM Systems
Piezoelectric Scanner
General Overview
An extremely fine conducting probe is held
about an atom’s diameter from the sample.
Electrons tunnel between the surface and the tip,
producing an electrical signal.
While it slowly scans across the surface,
the tip is raised and lowered in order to keep
the signal constant and maintain the distance.
This enables it to follow even the smallest
details of the surface it is scanning.
The Tip
As we will see later, is very important that the
tip of the probe be a single atom.
Tungsten is commonly used because you can use
Electro-chemical etching techniques to create
very sharp tips like the one above.
Quantum Tunneling
The second tip shown above is recessed by about
two atoms and thus carries about a million times
less current. That is why we want such a fine tip. If
we can get a single atom at the tip, the vast
majority of the current will run through it and thus
give us atomic resolution.
Note
•A STM does not measure nuclear position directly.
•Rather it measures the electron density clouds on the
surface of the sample.
•In some cases, the electron clouds represent the atom
locations pretty well, but not always.
Converse Piezoelectricity
Piezoelectricity is the ability of certain crystals to
produce a voltage when subjected to mechanical stress.
When you apply an electric field to a piezoelectric
crystal, the crystal distorts. This is known as converse
piezoelectricity. The distortions of a piezo is usually on
the order of micrometers, which is in the scale needed to
keep the tip of the STM a couple Angstroms from the
surface.
Electric Field
Pizos
The tip
Advantages of Scanning Probe Microscopy
•The resolution of the microscopes
•Create small structures nanolithography
•Do not require a partial vacuum
Disadvantages of Scanning Probe Microscopy
•The detailed shape of the scanning tip
•Slower in acquiring images
•The maximum image size
Scanning Modes

STM Constant
Current
Mode

STM Constant Height Mode

 System
Components
Mechanical Parts
Electronics Parts
Computer + software

 Needle
replacement
Needle type
Platinum-iridium (PtIr)
Tungsten tips
Gold
Needle preparation
Electrochemical etching
Mechanical shearing
System Software Execution
 Sample
preparation

ZnO Nanoparticles
around 6.5-8nm
www.natsyco.com

Gold Nano crystals 6-14nm
www.natsyco.com
Gold Nano crystals 6-14nm

Gold Nano crystals 6-14nm
www.natsyco.com
Calibration


Etching of atoms and
molecules from the surface
of gold (100x100nm) by
our STM system
(a step for Nanorobotics)
Atomic resolution of graphite

4x4x 0.2nm
Atomic resolution of graphite


References
1.
Pooria Gill, Bijan Ranjbar, Reza Saber. Scanning Tunneling Microscopy of Cauliflower-like DNA
Nanostructures Synthesized by Loop-mediated Isothermal Amplification. IET Nanobiotechnology
2011; 5 (1), 8-13.
2.
Reza Saber, Saeed Sarkar, Pooria Gill, Behzad Nazari, Faramarz Faridani. High Resolution Imaging
of IgG and IgM Molecules by Scanning Tunneling Microscopy in Air Condition. Scientia Iranica
(Transaction F: Nanotechnology) 2011; 18 (6), 1643–1646.
3.
M.Q. Li. Scanning probemicroscopy (STM=AFM) and applications in biology, Appl. Phys. A 68,
255–258 (1999).
4.
Errez Shapir et al., High-Resolution STM Imaging of Novel Single G4-DNA Molecules, J. Phys.
Chem. B, Vol. 112, No. 31, 2008.
5.
D. P. ALLISON. Immobilization of DNA for scanning probe microscopy, Proc. Nadl. Acad. Sci.
USA, Vol. 89, pp. 10129-10133, November 1992.
6.
Hiroyuki Tanaka. Visualization of the Detailed Structure of Plasmid DNA, J. Phys. Chem. B 16788
2008, 112, 16788–16792.
7.
Hiroyuki Tanaka. High-resolution scanning tunneling microscopy imaging of DNA molecules on
Cu(111) surfaces, Surface Science 432 (1999) L611–L616.
8.
Handbook of microscopy for nanotechnology / edited by Nan Yao. Zhong Lin Wang. 2005 Kluwer
Academic Publishers.
9.
Scanning probe microscopes : applications in science and technology / K.S. Birdi. 2003 by CRC
Press LLC.
10.
SCANNING PROBE MICROSCOPY, 2007 Springer Science+Business Media, LLC.
Thanks for your Attentions