Scanning Probe Microscopy

Muhammad Khurram Farooqi (CIIT/FA11/MSPHY/006/LHR)Department of Physics CIIT Lahore

1Scanning Probe MicroscopySubmitted by

Report (Submitted to)Dr. Aamir RazzaqIntroduction 2Scanning Probe Microscopy

3Scanning Probe Microscopy(SPM) is a technique ofmicroscopywhich makes images of surfaces, using a physical probe that scans the sample. An image of the surface is obtained by mechanically dragging the probe on surface of the specimen, line by line. SPMs are used both as standard analysis tools and as high-level research instruments.Historical Background4SPM was founded with the invention of thescanning tunnelling microscopein 1981. In 1986, very soon after their first publications about the STM in 1981, the inventors of this marvellous instrument,GertBinnigand Heinrich Rohrer from the IBM Research Laboratory inRschlikon(Switzerland), were awarded the Nobel Prizein Physics. Nowadays,SPMscan be found in many academic and industrial physics, chemistry and biology laboratories. Components

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S.P.M Working7

Working8The STM works like a record playerThe principle of the STM is very simple.Can be compared best with that of an old-fashioned record player. Just like in a record player, the instrument uses a sharp needle, referred to as the tip, to interrogate the shape of the surface. Working9But in contrast with a normalrecord player, the STM tip does not touch the surface. A voltage is applied between the metallic tip and the specimen, typically between a fewmilliVolts(mV) anda few Volts (V).

Working10When the tip is far away from the surface, the current is zero. The STM operates at very small distances between the tip and the surface of only 0.5 to 1.0 nm, i.e. 2 to 4 atomic diameters. At these distances, the electrons can jump from the tip to the surface or vice versa. This jumping is a quantum mechanical process, known as tunneling.

Working11Hence the name of this microscope is tunneling microscope. The tunneling process is very difficult, which implies that the tunneling current is always very low.STMsusually operate at tunneling currents between a fewpicoAmperes(pA) and a fewnanoAmperes(nA).

SPM Environments

12Scanning probe microscopes can be operated in a variety of environments. But only four environments are described:Ultra-high vacuum (UHV),Ambient (air), Liquid, and electrochemical (EC).

1. Ultra-high Vacuum

13The first STMs were operated primarily in UHV to study atomically clean surfaces. STM applied to atomically clean surfaces allows characterization of structure, without the added complication of contamination that is always present in air. 2. Ambient(Air)

14The easiest, least expensive, and thus most popular environment for SPMs is ambient, or air. STM in air is difficult, since most surfaces develop a layer of oxides or other contaminants that interfere with the tunnelling current. A clean, fresh surface can be prepared by peeling away older surfaces. 3. Liquid

15Liquid cells for the SPM allow operation with the tip and the sample fully submerged in liquid, It has capability for imaging hydrated samples. A liquid environment is useful for a variety of SPM applications, including studies of biology, geologic systems, corrosion etc.

4. Electrochemical

16Like UHV, electrochemical cells provide a controlled environment for SPM operation.EC-SPMs consist of a cell, a potentiostat, and software. Applications of EC-SPM include real-space imaging of electronic and structural properties of electrodes.Key features includeAn instrument that is easy to use Has lower operating costs. Minimal training time is desirable in a multi-user facility. Finally, an instrument that is easy to run will be used moreand produce more results. 17KEY FEATURES OF SPMS

1. User Interface

SPMs are built upon operating systems that allow multi-tasking.

182. Optical Microscope

All SPMs include optical microscopes to help monitor.A good optical microscope speeds up our work. In optical microscope, the following features are present: optical image clarity useful magnification range zoom lens integrated video camera

19Applications

20One of the most versatile and at the same time also very complex SPM measurement technique is the optical nearfield microscopy (Scanning Nearfield Optical Microscope, SNOM or NSOM). This class of instruments are used for investigation of electromagnetic interactions (light) with a resolution below the wavelength of the used electromagnetic field. Applications21An STM can be used as a spectroscopy tool, probing the electronic properties of a material with atomic resolution.It is used to study the local electronic structure of the surface known as scanning tunnelling spectroscopy (STS).Innovation22If we have this instrument in our Lab then we can scan the surface if the Electroactive Conducting Polymers ECPs and quite easily fine out their properties such as ElectricalMechanicalSurface analysis etcTypes23Atomic Force Microscopy(AFM)Scanning Tunnelling Microscopy(STM)Near-Field Scanning Optical Microscopy(NSOM) Contact Atomic Force Microscopy(CAFM)Magnetic Force Microscopy(MFM)Lateral Force Microscopy(LFM), Electrostatic Force Microscopy(EFM), Scanning Capacitance Microscopy (SCM), Scanning Thermal Microscopy(STM) etc.

The End24Thanks