In The Name of AllahIn The Name of Allah

Scanning Tunneling Scanning Tunneling MicroscopeMicroscope

Pooria GillPooria GillPhD of Nanobiotechnology

pooriagill@yahoo.com

Image from an STMImage from an STM

Iron atoms on the surface of Cu(111)

MicroscopyMicroscopy

Optical Microscopy

Scanning Electron Microscopy

Scanning Probe Microscopy

Scanning Probe MicroscopeScanning Probe Microscope

Atomic Force Microscope (AFM)

Electrostatic Force Microscope (EFM)

Magnetic Force Microscope (MFM)

Scanning Tunneling Microscope (STM)

Near-field Scanning Optical Microscope

(SNOM)

HistoryHistoryThe 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

The STM is an electron microscope thatuses a single atom tip to attain atomic resolution.

Scanning Tunneling Microscope (STM)Scanning Tunneling Microscope (STM)

SPM SPM SystemsSystems

Piezoelectric Scanner

General OverviewGeneral Overview

An extremely fine conducting probe is heldabout 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 keepthe signal constant and maintain the distance.

This enables it to follow even the smallestdetails of the surface it is scanning.

The TipThe Tip

As we will see later, is very important that thetip of the probe be a single atom.

Tungsten is commonly used because you can useElectro-chemical etching techniques to createvery sharp tips like the one above.

Quantum TunnelingQuantum 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.

NoteNote

•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 PiezoelectricityConverse PiezoelectricityPiezoelectricity 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.

The tip

PizosElectric Field

Advantages of Scanning Probe MicroscopyAdvantages of Scanning Probe Microscopy

•The resolution of the microscopes The resolution of the microscopes •Create small structures nanolithography Create small structures nanolithography •Do not require a partial vacuumDo not require a partial vacuum

Disadvantages of Scanning Probe MicroscopyDisadvantages of Scanning Probe Microscopy

•The detailed shape of the scanning tipThe detailed shape of the scanning tip•Slower in acquiring imagesSlower in acquiring images•The maximum image sizeThe maximum image size

Scanning ModesScanning Modes

STM Constant Current Mode

STM Constant Height Mode

System ComponentsSystem Components

Mechanical PartsMechanical PartsElectronics PartsElectronics PartsComputer + softwareComputer + software

Needle replacementNeedle replacement

Needle typeNeedle typePlatinum-iridium (PtIr)Platinum-iridium (PtIr)Tungsten tips Tungsten tips GoldGold

Needle preparationElectrochemical etchingElectrochemical etchingMechanical shearingMechanical shearing

System Software ExecutionSystem Software Execution

Sample preparationSample preparation

ZnO Nanoparticles around 6.5-8nm

www.natsyco.com

Gold Nano crystals 6-14nm www.natsyco.com

Gold

Nan

o crystals 6-14nm

Gold Nano crystals 6-14nm www.natsyco.com

CalibrationCalibration

Etching of atoms and molecules from the surface of gold (100x100nm) by our STM system

(a step for Nanorobotics)

Atomic resolution of graphiteAtomic resolution of graphite4x4x 0.2nm

Atomic resolution of graphiteAtomic resolution of graphite

ReferencesReferences1. 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 AttentionsThanks for your Attentions