Transmission electron microscope (TEM) makes the accelerating and gathering electron beam onto a very thin sample. The electrons collide with atoms in the sample and change the direction, then produce the three-dimensional angle scattering. The size of the scattering angle is related to the density and thickness of the sample, so the image can be formed in different light and shade. TEM is usually used to observe the morphology and dispersion of particles and measure the size of the particles.
From TEM photographs, we can see the particle size and dispersion of blue tungsten oxide.