Atomic Force Microscopy Study

Atomic Force Microscopy (AFM) :

The atomic force microscope probes the surface of a pattern with a sharp tip, a couple of microns long and often less than 100Å in diameter. The tip is found at the free end of a cantilever that is 100 to 200µm long. Forces between the tip and the pattern surface cause the cantilever to curve, or deflect. A detector calculates the cantilever deviation as the tip is scanned over the pattern, or the patternn is scanned under the tip. The measured cantilever deflections let a computer to create a map of surface topography. AFMs can be used to study insulators and semiconductors as well as electrical conductors. Atomic Force Microscopy operates in several modes. [8]

a. Contact Mode AFM:

Measures topography by

Scanning Tunneling Microscopy (STM) :

The scanning tunneling microscope is the father of complete SPM's. The STM was the first tool to form exact space images of surfaces with atomic resolution.

STM's use a edged, conducting tip with a bias voltage affected between the tip and the sample. When the tip is carried within about 10 angstrom of the specimen, electrons from the specimen begin to “ tunnel ” through the 10 angstrom gap into the tip or vice versa, depending upon the sign of the bias voltage. (See Figure 12.) The resulting tunneling current varies with tip to sample spacing, and it is the signal used to create an STM image. For tunneling to take place, either the sample and the tip must be conductors or semiconductors. Unlike AFM’s, STM’s can't figure insulating

Comparison Among Different SPM

TYPE PROPERTIES USED FOR SCANNING RESOLUTION USED FOR

Scanning Tunneling Microscopy (STM) Tunneling Current betwen sample and probe

Vertical Resolution <1 Å

**Lateral Resolution ̴ 10 Å #Conductors,insulators,semiconductor

#Liquid layers,liquid crystals and solids surfaces.

Magnetic Force Microscopy (MFM)

Magnetic force

Vertical Resolution ̴ 1 Å

**Lateral Resolution ̴ 100 Å #Magnetic Material

Scanning Capacitance Microscopy (SCM)

Capacitance developed in the presence of tip near sample surface

Vertical Resolution ̴ 1 Å

**Lateral Resolution ̴ 5000 Å #Conductors

#Solids

Table1: Comparison Scanning Tunneling Microscopy(STM) , Atomic Force Microscopy(AFM), Magnetic Force Microscopy(MFM), Scanning Capacitance Microscopy(SCM).**Lateral Resolution depends upon the resolution of mechanical XYZ stage.

The Application Areas Of