Biomedical Engineering Reference
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itself. Heteroepitaxy is the formation of a compound on a different
compound or element and is much more prevalent. The principle
of ALE is to grow the deposit one atomic layer at a time [9]. EC-ALE
uses UPD for the surface-limited reactions in an ALE cycle [10].
Surface-limited reactions are developed for the deposition of each
component element in a cycle to directly form a compound via layer-
by-layer growth, avoiding 3D nucleations. With cycle, a compound
monolayer is formed, and the deposit thickness is controlled by
the number of cycles. In an EC-ALE process, each reactant has its
own solution and deposition potential, and there are generally rinse
solutions as well. In synthesis of CdTe, for example, atomic layers of
tellurium and cadmium are alternatively electrodeposited to build
up a thin layer of CdTe [11,12]. The necessary atomic level control
over the electrodeposition of these two elements is obtained by
depositing both elements using UPD. The thickness of the CdTe layer
prepared by EC-ALE can be specified by controlling the number of
Cd and Te layers that are deposited.
Transmission electron micrograph (TEM) of a CdTe deposit
formed using 200 cycle of CdTe via EC-ALE [13]. Reproduced by kind
permission from the publisher.
Figure 1.1
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