This note reports on an example of depth analysis by plasma profiling time of flight mass spectrometry of rare earth doped materials: codoped Eu and TbZnO thin layers developed for making white LEDs.
REE (Rare Earth Elements) unique electronic, optical, luminescent, and magnetic properties have made them attractive for a variety of applications. Recently, considerable research activity is being carried out on rare earth (RE) doped materials for photonics. Among these materials, the optical properties of ZnO studied extensively for various applications in the photoelectrochemical cells, diluted magnetic semiconductors (DMS), field effect transistors, and photoluminescence devices may be tailored by RE doping for wide range electroluminescent devices (white LEDs).
For rapid optimization of thin film deposition processes, direct analysis techniques (with no sample preparation) are highly in demand. Plasma Profiling Time of Flight Mass Spectrometry (PP-TOFMSTM) provides direct measurement of the chemical composition of materials as a function of depth, with nanometre resolution and the capability to measure both thin and thick layers. It consists in a pulsed radio frequency glow discharge plasma source fed with pure Ar and created under a pulsed RF potential coupled to a time of flight mass spectrometer (TOFMS).
The key strength of PP-TOFMS is to record a full and continuous spectrum over a flaxible mass range at any depth point (sampling as low as sub-nanometer/point). In addition the high mass range benefits from low background, which makes PP-TOFMS high mass sensitive. As a result, PP-TOFMS is well suited for measuring REE composition distribution in thin films.
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