Accurate measurement of atomic beam flux by pseudo-double-beam atomic absorption spectroscopy for growth of thin-film oxide superconductors

Abstract

We report the use of pseudo-double-beam atomic absorption spectroscopy to make very accurate (0.1%–1%) measurements of the beam flux from Knudsen effusion cells in a molecular beam epitaxy system. This system has been used to grow Bi–Sr–Ca–Cu–O–based superconducting thin films and heterostructures in an atomic-layer-by-layer fashion. The resulting material displays excellent crystallographic and transport properties. Atomic absorption measurement of beam fluxes may also be of benefit for other materials systems, such as InGaAs/InP.

Perspective: Oxide molecular-beam epitaxy rocks!

“…The use of atomic absorption spectroscopy for oxide MBE composition control has allowed fluxes to be measured with an accuracy of better than 1%. [68][69][70][71][72][73][74][75] In situ RHEED oscillations during the shuttered MBE growth of multicomponent oxides has also been shown to provide a means to accurately calibrate fluxes.…”

Crucible aperture: An effective way to reduce source oxidation in oxide molecular beam epitaxy process

“…But source oxidation problem leads to flux instability 2 , and maintaining stable fluxes in an oxygen environment for all elements is a challenging task [3][4] . In case of Ca and Sr, when exposed to strong oxidation condition, they tend to oxidize so much 2 that a real-time flux monitoring scheme such as atomic absorption spectroscopy (AA) [5][6] is required to control their fluxes better than 1%. As the number of component elements grows, such a real-time monitoring scheme becomes cumbersome to implement, and makes the complex-oxide growth very complicated.…”

Self-corrected sensors based on atomic absorption spectroscopy for atom flux measurements in molecular beam epitaxy

“…A double-beam setup is often adopted to compensate for long-term changes in the source intensity and detector sensitivity. Frequent baseline re-calibrations while blocking the atom beam can circumvent baseline stability issues, 9 but such steps can be difficult to implement and can interfere with deposition processes, especially automated ones. In one of the first commercially available AAbased flux sensors, a double-beam optical configuration was combined with the common optical path for automatic correction of transmission (COPACT) geometry, in which a xenon flash lamp was used as a reference.…”

“…3,12,13 Most of the existing AA-based flux sensor designs use a monochromator or bandpass filter (5 -10 nm window) with a wide slit or bandpass to select the wavelength of interest, and a photomultiplier tube (PMT) or a charge coupled device (CCD) for detection. 4,6,7,9 The disadvantages of using a wide slit or wide bandpass width are poor sensitivity due to the possibility of inclusion of multiple lines in the detected signal, and the presence of non-linearities in the calibration curves. 14,15 Many existing AA-based flux sensor designs utilize a normalization scheme in which the absorption is measured in relation to the total HCL output.…”

“…3,4 Optical flux sensors based on the atomic absorption (AA) principle have been developed and employed to monitor atom fluxes in the past. [4][5][6][7][8][9][10][11] By passing a light beam matched to the absorption energy of the element of interest through the atomic beam, one can detect the intensity attenuation resulting from resonant atomic absorption. The attenuation is proportional to the atom density within the irradiated volume, and can be used to calibrate the atom flux and determine the deposition rate.…”