text: This property describes why electrons form patterns in LEED.
full_question: This property describes why electrons form patterns in LEED. In the debate resolved by this concept, Poisson argued that one side must be false since otherwise a small spot would be present, and that spot was later shown to exist by Arago. Electrons following Bragg's law after being fired at a nickel crystal provided evidence for this phenomenon in the Davisson-Germer experiment. An equation describing this phenomenon sets a certain value equal to Planck's constant over the momentum. This property is the subject of the de Broglie hypothesis. For 10 points, name this concept that resolved a debate over the nature of light by treating it as having two natures. 
first_sentence: This property describes why electrons form patterns in LEED.
raw_answer: wave-particle duality [or de Broglie until it is read; accept answers along the lines of "matter has wave nature" or "waves have particle nature"]