Question

Name the two most common types of SPMs.

(a) How do they differ?

(b) What are the advantages of each type?

(c) What are the major limitations of each type?

Short answer

A scanning tunneling microscope (STM) is a device that produces images of atoms on material surfaces. The STM is not an optical microscope; instead, it detects electrical forces using a probe that tapers down to a single atom in diameter.

Step-by-step solution

(a) Scanning Tunneling Microscope 

A scanning tunneling microscope (STM) uses an extremely tiny metallic tip to scan the sample surface in a raster pattern.

It is based on the quantum mechanical tunneling theory.

The tunneling current $\left(I_t\right)$controls the location of the tip above the surface.

$I_t=V{e}^{-Cd}$is the magnitude of the tunneling current, where V is the bias voltage, C is a constant, and d is the distance between the probe and the surface.

The sample surface is scanned in a raster pattern with the help of a flexible force-sensing cantilever stylus in an atomic force microscope (AFM).

The sensor in this microscope is in contact with the sample's surface.

(b) Advantage  of STM

The scanning tunneling microscope's (STM) advantage is that the tip never comes into contact with the sample's surface, ensuring that the sample's surface is never harmed or altered.

The atomic force microscope (AFM) has the advantage of allowing the sample surface to be either an electrical conductor or an insulator.

Limitation of STM 

The scanning tunneling microscope (STM) is limited by the need that the sample surface be an electrical conductor.

The sensor of an atomic force microscope (AFM) comes into contact with the sample surface, which might modify the properties of the sample surface.