The invention relates to a nanofocus X-
ray tube 20 pwovided with a target 4 and a device used for calibrating an electronic beam 28 on the target 4. According to the invention, the target 4 has at least one of target units 22, 24, 26 made of target material for emitting x-
ray beam, and is composed by amicro-structuring process and a
nanostructure formed on a carrier unit 4 composed of a
carrier material, the
nanostructure has a
diameter less than 1 nm, wherein the target units 6, 22, 24, 26 only partly cover the carrier unit 4. When the X-
ray tube 20 is operated, the electronic beam is selected with a cross section large than the cross sections of the target units 6, 22, 24, 26, in this way, the electronic beam 28 can entirely always irradiate on the target units 6, 22, 24, 26 all the time. According to the invention, the
carrier material is
diamond or contains diamonds, diamonds are added for increase conductive performance.