Atomic absorption spectroscopy system for flux monitoring and atomic-layer control of molecular beam epitaxial growth of BiSrCaCuO

Abstract

Atomic absorption spectroscopy (AAS) system for accurate and in situ atomic-flux-monitoring during molecular beam epitaxial growth is reported in detail. Hollow cathode lamps are used as light sources. They emit the light with inherent spectral lines of the elements to be measured. A turret system with multiple hollow cathode lamps and line pass filters is equipped, which is suited in particular for atomic layer-by-layer growth. The intensities of the transmitted light on both conditions in the presence and absence of atomic beam flux are measured. An analytic expression for in situ calculating the beam flux rate using these measured quantities is discussed. A method for determining an unknown constant included in this expression is described. This uses the inductively coupled plasma spectroscopy technique to estimate the amount of atoms impinging on the substrate. Within the range of BiSrCaCuO growth conditions, the AAS measurements are not influenced by changing either the substrate temperature or the condition of ozone that is oxidizing agent. The resolution of the flux measurement is better than 1011 cm−2 s−1 for Sr and Ca, 1012 cm−2 s−1 for Cu, 1014 cm−2 s−1 for Bi. This AAS system is applied to a real-time flux control of an atomic layer-by-layer growth of BiSrCaCuO.