Scanning Tunneling Microscopy lecture-2

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

Servos
Servos are small in the in the devices with a shaft that can be in the precisely in the controlled with electrical in the signals.
Servos are in the used all the time in radio in the controlled in the cars, in the puppets, and in the robots.
 
Converse Piezoelectricity
Piezoelectricity is the ability of certain in the crystals to in the produce a voltage when in the subjected in the mechanical in the stress.
When you apply an electric in the field to a piezoelectric in the crystal, the crystal in the distorts. This is known as converse in the piezoelectricity. In the distortions of a piezo in the usually on the order of micrometers in the , which is in the scale in the needed to keep in the tip of the STM a couple in the Angstroms from in the surface.
Problems and Solutions

  •  in the Bringing the tip close to the surface and in the scanning in the surface.
  • Feedback Servo Loops
  •  in the Keeping in the tip close to the surface.
  • Converse Piezoelectricity
  • Creating in the very fine tip.
  • Electro-chemical etching
  • a Forces in the between tip and in the sample.
  • Negligible in most cases
  • A Mechanical in the vibrations and in the noise.
  • Soft suspension of the microscope within an ultra high vacuum chamber (10-11 Torr)
  •  in the Thermal length in the fluctuations of the sample and in the especially the tip.
  • Very low temperatures

Vibration-Isolation

See by diagram
The original in the STM design had the tunnel in the unit with in the permanent in the magnets levitated on a in the superconducting lead in the bowl. They used 20 L of liquid in the helium per 2 hour.
Uses of STM
Measuring in the high precision in the optical components and in the disk drive in the surface in the roughness of machined or ground in the surfaces is a common in the use for STM.

in the Below is a trace of an individual in the turn mark on a diamond- in the turned aluminum in the substrate to be used for in the subsequent magnetic in the film deposition for a high in the capacity hard in the drive.
By measuring in the variations in current, in the voltage, tip/surface in the separation, and their in the derivatives, the electronic in the properties of different in the materials can be studied.
One such in the element in the studied was the bucky ball (C60). When you in the press down on a bucky in the ball by 1/10th nm, it lowers in the resistance of the bucky in the ball by 152 times.
Different STM Ideas
You could in the decide not to use in the piezoelectricity to keep in the distance between 2time  the tip and the surface in the equal at all times, in the  and instead use the current in the measurements to determine in the surface of a in the sample.

Pros:

  • You can scan in the much faster.

Cons:

  • The surface in the must not have in the cavities more than a few in the Angstroms deep (an in the atom or 2 in the ) because of in the tunneling.

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