Scanning Tunnelling Microscope

• What is the full name of STM?

  Scanning Tunnelling Microscope

  
• What significant advances occurred by the 1980s?

  Research technology and physics on atomic scale
• What is the resolution capability of an STM?

  0.001 nm apart
• What can an STM produce images of?

  Individual rows of atoms
• How is the probe of an STM designed?

  With a very fine tip, a few atoms across

  
• What equipment moves the probe in an STM?

  Piezoelectric transducers
• How small are the increments of movement for the probe?

  0.001 nm
• What maintains the probe's position relative to the sample?

  Constant potential difference
• What happens when the probe is close to the sample surface?

  Electrons tunnel to the tip

  
• What does the tunnelling current indicate?

  Distance between the tip and the surface
• What occurs when the tip reaches a raised atom?

  Tunnelling current increases
• What occurs when the tip reaches a dip in the surface?

  Tunnelling current decreases
• How is a surface map produced in STM?

  By changes in tunnelling current

  
• What are the two modes of STM operation?

  Constant height and constant current
• What happens in constant height mode?

  Tip does not move vertically while scanning
• How does tunnelling current behave in constant height mode?

  It varies with changes in surface height
• What happens in constant current mode?

  Tip moves to keep current constant
• What is the effect of maintaining a constant current?

  The gap size remains the same
• What is quantum tunnelling a result of?

  Wave-like behaviour of particles
• What acts as a barrier for electrons in STM?

  The gap between the surface and the tip
• What happens to the amplitude of electrons' matter-wave at the barrier?

  It decreases due to the barrier
• When does tunnelling occur?

  If the barrier is weak enough
• What does the current passing from sample to probe indicate?

  It is sensitive to gap distance changes
• What is necessary for a general understanding of quantum tunnelling?

  A basic grasp of quantisation processes
• What does the term "quantum" refer to?

  Processes resulting from quantisation