NSOM Basics Quiz and Flashcards: Near-Field Scanning Optical Microscopy

Study Notes

Electron Microscopy

Electron beam is focused and the image is formed using magnetic lenses.
There are two common forms of electron microscopy: transmission electron microscopy (TEM) and scanning electron microscopy (SEM).
In SEM, the surface of the polymeric surface is scanned using an electron beam and the reflected or back scattered beam of electrons is collected and displayed on a cathode ray tube screen.
SEM provides an image that represents the surface contour of the scanned material.
Most polymer surfaces must be overlaid with a conductive coating in SEM, as the surface must be conductive.
Magnifications up to about 50,000 can be achieved using SEM.

Transmission Electron Microscopy (TEM)

TEM utilizes an image formed by an electron beam that passes through the sample.
This allows internal microstructures to be determined.
Structural details of materials can be observed on an atomic level by looking at contrasts in the image caused by various concentrations of different elements.
Very thin films are employed in TEM.
Under good conditions, magnifications up to one million are possible employing TEM.

Scanning Probe Microscopy (SPM)

SPM encompasses a group of surface detection techniques that include atomic force microscopy (AFM) and scanning tunneling microscopy (STM).
SPM techniques investigate only the outermost few atomic layers of the surface with nanometer resolutions and, at times, atomic-level resolution.
STM is generally used with electrically conductive materials and requires extremely low pressures less than 1 × 10–10 mbar.
AFM can be run under room conditions and does not require the use of electrically conductive material.

Scanning Tunneling Microscopy (STM)

STM experiments involve holding a metallic tip close (about 0.5–1 nm) to the surface.
A voltage is applied between the tip and sample surface, driving a tunneling current.
The conductive surface reconstructs the atomic positions via minimizing the surface free energy.
This gives topographic superstructures with specific electronic states, which are recorded as surface contours or images.

Near-Field Scanning Optical Microscopy (NSOM)

NSOM allows an extension of optical microscopy to near that of electron microscopy.
The central feature is the optical element that is similar to that employed in atomic force microscopy (AFM).
Light is directed through the probe tip onto the sample from just immediately above the sample surface.
The light emanating from the probe tip is smaller than the light’s wavelength and spreads out over the surface.
This results in the maximum influence occurring at the surface with little contribution from regions nearby.
The light is measured as absorption or fluorescence and collected and recorded electronically.
NSOM can be fitted onto a regular optical microscope or coupled with scanning probe microscopy (SPM).

Description

Learn about the principles of Near-field Scanning Optical Microscopy (NSOM), its capabilities, and its similarities with Atomic Force Microscopy (AFM). Discover how NSOM allows for high-resolution optical microscopy, extending its capabilities to near that of electron microscopy.