In The Name of Allah In The Name of Allah Scanning Tunneling Microscope Pooria Gill PhD of Nanobiotechnology

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 BinningHeinrich Rohrer

The STM is an electron microscope that uses a single atom tip to attain atomic resolution. Scanning Tunneling Microscope (STM)

SPM Systems 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 Classically, when an object hits a potential that it doesn’t have enough energy to pass, it will never go though that potential wall, it always bounces back. In English, if you throw a ball at a wall, it will bounce back at you. Classical Wave Function For Finite Square Well Potential Where E<V

Quantum Tunneling In quantum mechanics when a particle hits a potential that it doesn’t have enough energy to pass, when inside the square well, the wave function dies off exponentially. If the well is short enough, there will be a noticeable probability of finding the particle on the other side. Quantum Wave Function For Finite Square Well Potential Where E<V

Quantum Tunneling The finite square well potential is a good approximation for looking at electrons on conducting slabs with a gap between them.

Quantum Tunneling More graphs of tunneling: An electron tunneling from atom to atom: n(r) is the probability of finding an electron V(r) is the potential

Quantum Tunneling Now looking more in depth at the case of tunneling from one metal to another. E F represents the Fermi energy. Creating a voltage drop between the two metals allows current. Tip Sample

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.

Small Movements To get the distance between the tip and the sample down to a couple of Angstroms where the tunneling current is at a measurable level, STMs use feedback servo loops and converse piezoelectricity.

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. The tip Pizos Electric Field

Advantages of Scanning Probe Microscopy The resolution of the microscopesThe resolution of the microscopes Create small structures nanolithographyCreate small structures nanolithography Do not require a partial vacuumDo 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 Scanning Modes STM Constant Current Mode

STM Constant Height Mode

System Components System Components Mechanical Parts Electronics Parts Computer + software

Needle replacement Needle replacement Needle type Platinum-iridium (PtIr) Tungsten tips Gold Needle preparation Electrochemical etching Mechanical shearing

System Software Execution

Sample preparation Sample preparation

ZnO Nanoparticles around 6.5-8nm

Gold Nano crystals 6-14nmwww.natsyco.com

Gold Nano crystals 6-14nm

Gold Nano crystals 6-14nmwww.natsyco.com

Calibration

IgM Russia System

IgM Single Molecule

The state of the art 3D image of a single antibody protein IgM on the surface scanned by NAMA-STM

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

What SONY claims? Is it true? Answer is yes, SONY says true Normal CDSony Fabricated CD

The above images of DVD surface ( 4500 x 4500 nm) scanned from different directions show the Stability and reproducibility of NAMA-STM

References 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), 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– 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, D. P. ALLISON. Immobilization of DNA for scanning probe microscopy, Proc. Nadl. Acad. Sci. USA, Vol. 89, pp , November Hiroyuki Tanaka. Visualization of the Detailed Structure of Plasmid DNA, J. Phys. Chem. B , 112, 16788– Hiroyuki Tanaka. High-resolution scanning tunneling microscopy imaging of DNA molecules on Cu(111) surfaces, Surface Science 432 (1999) L611–L Handbook of microscopy for nanotechnology / edited by Nan Yao. Zhong Lin Wang Kluwer Academic Publishers. 9. Scanning probe microscopes : applications in science and technology / K.S. Birdi by CRC Press LLC. 10. SCANNING PROBE MICROSCOPY, 2007 Springer Science+Business Media, LLC.

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