An energy contamination detection apparatus includes a membrane and a charge collection plate disposed at a distance from the membrane. The membrane is configured to receive an ion beam and allow a portion of the ion beam having energy levels above a desired energy level to pass therethrough toward the charge collection plate and absorb or reflect portions of the ion beam having energy levels at or below the desired energy level. A voltage source is electrically coupled to the charge collection plate for providing a bias voltage to the charge collection plate. A detection circuit is coupled to the charge collection plate and is configured to detect energy contamination based on an amount of charge collected on the charge collection plate.