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Scanning tunneling microscope by joshna.pptx

The scanning tunneling microscope (STM) allows for atomic-level examination of surfaces. It works by using an electrical probe tip that scans over a sample surface at a constant distance. Electrons tunnel through the vacuum between the tip and surface, producing a current that depends on their distance. The basic STM components include a piezoelectric tube, fine tip, tunneling current amplifier, and data processing unit. By maintaining a constant current as the tip scans, the device can map a sample's topography at the nanoscale with 3D resolution. STMs are used for integrated circuit fabrication, biomedical research, and material science studies.

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SCANNING TUNNELING MICROSCOPE
DEFINITION • An electron microscope that works by using an electrical probe tip which scans over the surface of a sample at a constant spacing is known as scanning tunneling microscope. STM allows for a 3D picture of the surface to be created
PRINCIPLE Tunnelling effect is the principle behind scanning tunneling microscope. When a voltage difference is applied between a conducting tip and a surface close to it, electrons can tunnel through the vacuum between the tip and the surface, causing a tunneling current. The current that results depends upon the distance between probe tip and sample surface.
CONSTRUCTION The basic components of STM are • Piezoelectric tube with the tip and electrodes capable of moving in X,Y,Z direction. • Fine needle tip made of tungsten for scanning the sample surface. • Tunneling current amplifier • Distance Control Unit and Scanning Unit • Data Processing and Display Unit
WORKING • Circuit is switched ON and necessary biasing voltage is given to the probe tip. • Due to biasing, the electrons will tunnel across the gap, and therefore produces a small electric current called tunnelling current. • The current produced is amplified and measured in the computer. • It is found that the current increases (or) decreases based on the distance (d) between the tip and the sample. • The current in the circuit should be monitored in such a way that it should be maintained constant. • Therefore, for maintaining the constant current distance (d) between the tip and the sample should be continuously adjusted whenever the tip move over the surface of the sample. • The height fluctuations (d) between the tip and the sample are recorded and as a resultant map of „bumps‟ is obtained in the computer. • Similarly the tip will scan the sample atom by atom and line by line and the topographyof the sample is recorded in the display unit.
ADVANTAGES DISADVANTAGES • Examine surfaces at an atomic level. • Give 3D profile of a surface. • Latest technique used in Research laboratories for scanning the materials. • Operate in temperatures from zero kelvin to few hundred degree Celsius. • Magnification is upto nano-scale • Even a very small sound (or) vibrations will disturb the measurement setup. • It should be kept in vacuum, as even a single dust particle may damage the tip of the probe. • Cost is high. • More Complexity
APPLICATIONS • It is used to produce integrated circuits • It is used in biomedical devices • Used in Research labs • Used in material science studies for both bump and flat surfaces
DEFINITION • An electron microscope- electrical probe tip- scans over the surface of a sample at a constant spacing -STM - 3D picture of the surface
PRINCIPLE Tunnelling effect When a voltage difference is applied between a conducting tip and a surface close to it, electrons can tunnel through the vacuum between the tip and the surface, causing a tunneling current. The current that results depends upon the distance between probe tip and sample surface.
CONSTRUCTION The basic components of STM are • Piezoelectric tube • Fine needle tip • Tunneling current amplifier • Distance Control Unit and Scanning Unit • Data Processing and Display Unit
WORKING
ADVANTAGES DISADVANTAGES • Examine surfaces at an atomic level. • Give 3D profile of a surface. • Latest technique used in Research laboratories for scanning the materials. • Operate in temperatures from zero kelvin to few hundred degree Celsius. • Magnification is upto nano-scale • Even a very small sound (or) vibrations will disturb the measurement setup. • It should be kept in vacuum, as even a single dust particle may damage the tip of the probe. • Cost is high. • More Complexity
APPLICATIONS • To produce IC • In biomedical devices • In Research labs • In material science studies
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