Submicron Particle Analysis

Differentiation of colloidal Solutions and Nanostructures

Using the theory of Mie the size of nanoparticles and their spatial distribution can be derived from a microscope spectrum, although the individual nanoparticles are below the optical resolution of a light microscope.

Determination of Size and Concentration of Nanoparticles from UV-VIS Spectra

In recent times, metallic nanoparticles have attracted substantial attention due to their interaction with visible light and unique optical-electronics properties. For example gold nanoparticles with different sizes have specific absorption spectra. When the diameters of monodisperse gold nanoparticles are ~30 nm, they show a blue-green light absorption, i.e. the red light is reflected yielding a rich “ruby red” color. Increasing the particles diameter shifts the absorption into the longer wavelengths range. Blue light is reflected yielding solutions with a pale blue or purple color. As particle size continues to increase absorption wavelengths move into the IR portion of the spectrum and most visible wavelengths are reflected, giving the nanoparticles clear or translucent color.

This example demonstrates the advantage of high-resolution microscope spectroscopy. The sample can be characterized directly under the microscope without much effort, and does not require any additional preparation in contrast to an electron microscope.

Silver colloidal solution in light microscope

Interference pattern of a semi-transparent diamond like carbon (DLC) layer recorded in NIR range (Blue: fitted curve. Red: measured curve.)

Silver colloidal solution in electron microscope

Using a mathematic algorithm (developed by W. Theiss Hard- and Software) the layer thickness is calculated