Mean particle size=0.94*Lambda/(FWHM*cos(theta)

A material having 4 valance electrons is called semiconductor.

On a substrate made of e.g., sapphire single crystal is formed an Al underlayer having FWHM X-ray rocking curve value of 90 seconds or below. A buffer layer is formed on the AlN underlayer and has a composition of AlpGaqIn1−p−qN (0≦p≦1, 0≦y≦q). A GaN-based semiconductor layer group is formed on the buffer layer.

Hope this helps!!

Radio telescopes are much larger than optical telescopes because of wavelength.

Earth's atmosphere has two major "windows" where it is transparent to photons:

300 nm - 800 nm: optical wavelength window (approximate)

30 mm - 30 m: radio wavelength window (approximate)

Even the shortest-wavelengths used by radio telescopes at around 30 mm are still thousands of times longer than the longest wavelengths used by optical telescopes.

The wavelength has 2 effects on the size of a telescope:

* The angular resolution (in order to distinguish 2 nearby stars, FWHM) depends on the wavelength/aperture ratio. Radio-frequency photons require a wider aperture to focus than visible-light-frequency photons, so radio telescopes *must* be larger to get a reasonable resolution.

* A telescope typically requires the collecting area to be aligned within 1/10 of the wavelength it is designed for. Because it is almost impossible to get all the parts of a sufficiently large telescope aligned to within 80 nm, radio telescopes *can* be built much larger.