Lithography with metastable atoms
A standing wave of laser light can pattern a beam of metastable atoms (green). Away from the regions close to the zero intensity, the light excites the atoms to a highly energetic level from which they rapidly decay into the ground state. The ground-state atoms (red) are simply reflected from the surface. The metastable atoms that reach the surface deposit their energy in the resist and cause residual hydrocarbons to adhere permanently to the substrate.