Eigenstate

Otherwise, in the case of pure physisorption, adatoms and very small adclusters would not be observed with the STM because the probability for the sharp eigenstates of the adparticles to lie within the 10 meV energy window ( given by the bias voltage ) would be considerably small.

In all quantum theories, basis vectors (which are typically eigenstates) are abstractions of the unit basis vectors along the 3D axes. A general state is a vector sum of certain amounts of each basis vector state.