The transmission electron microscope is one that utilizes a high-energy electron beam that probes sample materials with a thickness less than 100 nanometers (nm). While some electrons are either absorbed or bounced of the material, others pass through it creating a magnified image as the one shown in the example. Current TEMs use digital cameras placed behind the material to capture and record images, magnifying images up to 30 million times. The TEM is the most popular microscope used the make images published in scientific journals on nanocrystals found in semiconductors.
The atomic force microscope (AFM) uses a small silicon tip as a probe to make images of sample material. While the probe move along the surface of the sample, the electrons of the atoms in the material begin to repel the electrons of the probe. The AFM then adjusts the height of the probe to keep the force of the sample constant. A mechanism records the movement of the probe and sends this information to a computer that will generate a three-dimensional image as shown in the slide. The image will show the exact topography of the surface.
A scanning tunneling microscope (STM) uses a wavelike property of electrons known as tunneling , which allows electrons emitted from a probe to penetrate, or tunnel into, the surface of the examined object. The electrons generate a tiny electric current that the STM measures. Similar to the atomic force microscope, the height of the probe in the STM is adjusted constantly to keep the current constant. In doing, so a detailed map of the material’ surface is produced as the example in this slide shows.
New solar cells are based on nanoparticles of semi conductors, nanofilms and nanotubes by embedding in a charge transfer medium. Films formed by sintering of nanometric particles of TiO2 (diameter 10-20 nm) combine high surface area, transparency, excellent stability and good electrical conductivity and are ideal for photovoltaic applications. Non porous oxide films are highly promising material for photovoltaic applications.