  We investigate the tunnel rates and energies of excited states of small
numbers of electrons in a quantum dot fabricated in a Si/SiGe heterostructure.
Tunnel rates for loading and unloading electrons are found to be strongly
energy dependent, and they vary significantly between different excited states.
We show that this phenomenon enables charge sensing measurements of the average
electron occupation that are analogous to Coulomb diamonds. Excited-state
energies can be read directly from the plot, and we develop a rate model that
enables a quantitative understanding of the relative sizes of different
electron tunnel rates.
