Multilayer molybdenite flakes are semiconductors with an indirect bandgap. In contrast, monolayer flakes have a direct gap.  In the early years of the 20th century, molybdenite was used in some of the first crude semiconductor diodes, called cat's whisker detectors, which served as a demodulator in early crystal radios.    Monolayer molybdenite shows good charge carrier mobility and can be used to create small or low-voltage transistors.  The transistors can detect and emit light and may have future use in optoelectronics.