overlayer

Overlayer is a term used in multiple disciplines to describe a layer that lies atop another layer or substrate. In materials science and surface science, an overlayer refers to a thin film or coating deposited onto a base material, typically with a different chemical composition, structure, or properties. Overlayers can be metals, oxides, semiconductors, or organic films, and they are often employed to modify surface characteristics such as corrosion resistance, optical or electronic behavior, catalytic activity, adhesion, or wear properties. Common deposition methods include physical vapor deposition, chemical vapor deposition, sputtering, and atomic layer deposition. Characterization techniques frequently used for overlayers include X-ray photoelectron spectroscopy, ellipsometry, transmission electron microscopy, atomic force microscopy, and Raman spectroscopy. In device and processing contexts, the overlayer can serve as a passivation layer, barrier layer, adhesive layer, or functional coating in microelectronics, optics, and sensors. The properties and performance of an overlayer are strongly influenced by the interface with the substrate, including phenomena such as interdiffusion, strain, and chemical reactions that can occur during processing.

In geology and stratigraphy, an overlayer denotes the upper part of a stratified sequence that rests above an underlying layer or boundary. It records more recent deposition or tectonic events and is used to interpret the geological history of a region. The term is often contrasted with the underlayer or basement. In both contexts, an overlayer is essentially a layer added on top of another material, with important implications for the system’s overall properties and behavior.