Scanning Atomic Absorption Spectroscopy Monitor for MBE Growth of Superlattices

We report the construction of an atomic absorption spectroscopy (AAS) flux monitor capable of sequentially monitoring different elements through a single fiber optical pathway to control epitaxial growth of superlattices and other artificially structured materials. This capability is integrated into a 4-channel (i.e., 4 fiber optical pathways) AAS monitor system and thus makes it possible to control in realtime codeposition of up to 4 elements and sequential deposition of more elements, including superlattices of 2 or more complex compounds, e.g., 2 ternary Heusler alloys. The AAS monitor works by transmitting light emitted by the same atomic species being deposited and measuring the absorbance of the light passing through the vapor, which has been calibrated and converted to atomic flux. Split mode fiber optics is used to combine the light beams from multiple atomic sources into one beam as it enters the vacuum chamber, while the absorbance is measured sequentially using a stepper motor driven monochromator via phase sensitive detection. The sensitivity and fidelity of the system is tested, including the comparison between the results from the new "scanning" version with multiple sources through one fiber optical pathway and those from the single source-single channel monitor.