Wilhelm Conrad Röntgen discovered X-rays on November 8, 1895, at the University of Wurzburg in Germany. X-rays are still called Röntgenstrahlen in Europe. Röntgen used electrons to bombard inert gas in tubes, and discovered that nearby photographic plates had been exposed by some sort of unknown ("X") radiation. He demonstrated that X-rays travel in straight lines and are very penetrative, traversing all materials to varying degrees. He received the first Nobel Prize in Physics in 1901 for his discovery, donating the prize money (then about $40,000) to the University of Wurzburg.

German physicist Wilhelm Conrad Röntgen (1845-1923).

Cartoon from Einstein Simplified: Cartoons on Science by Sidney Harris, 1989, Rutgers University Press, New Brunswick NJ, USA

The production of "characteristic" X-rays by electron bombardment of pure elements was first observed in 1909 by Charles G. Barkla and C.A. Sadler. However, the physical origin of X-rays was not clear. Barkla received the Nobel Prize in 1917.

C.G. Barkla (1877-1944).

The diffraction of X-rays by a systematic crystal was first confirmed by Max von Laue, a junior colleague of Rontgen, and his associates W. Friedrich and E.P. Knipping at the University of Munich in 1912. Von Laue got the Nobel Prize in 1914. Von Laue sent a copy of the paper reporting the results to William Henry Bragg, whose son, William Lawrence Bragg confirmed and extended von Laue's work.

Max von Laue (1879-1960)

In 1913, W.L. Bragg observed the first X-ray spectrum, examining the L lines produced from platinum using an NaCl crystal. W.L. Bragg confirmed that X-rays produced ionization and also could be diffracted by a regular crystal: the wave-particle duality. The older Bragg developed an X-ray detector that when coupled with the younger Bragg’s diffracting crystal is the basis of all X-ray spectrometry. The Braggs received the Nobel Prize in 1915 for their work.

W.H Bragg (1862-1942) and W.L. Bragg (1890-1971) on Swedish postage stamp.

In 1913, Henry G.J. Moseley at the University of Manchester in England discovered the systematic relationship between the atomic number of an element and the energy of the X-rays produced from it (Moseley's Law):

Two years later, at age 27, Moseley was was killed on the Gallipoli Peninsula on 10 August 1915.

H.G.J. Moseley (1887-1915)

Electron microprobe analysis was preceded by development the closely related analytical technique of X-ray fluorescence spectrometry. This technique was first proposed by Georg von Hevesy in 1923 and applied by other workers in the following few years. Von Hevesy discovered Hf in 1923 after noticing a gap at Z=79. This work earned him the 1943 Nobel prize in Chemistry.

Georg Charles von Hevesy (1885-1966)