An x-ray tube includes a target on which electrons impinge to form a diverging x-ray beam. The target has a surface formed from first and second target materials, each tailored to emit a respective x-ray energy profile. A first x-ray optic may be provided for directing the beam toward the sample spot, the first x-ray optic monochromating the diverging x-ray beam to a first energy from the energy emitted by the first target material; and a second x-ray optic may be provided, for directing the beam toward the sample spot, the second x-ray optic monochromating the diverging x-ray beam to a second energy from the energy emitted by the second target material. Fluorescence from the sample spot induced by the first and second monochromated energies is used to measure the concentration of at least one element in the sample, or separately measure elements in a coating and underlying substrate.