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Concept
Substrate (chemistry)
Summary
In chemistry, the term substrate is highly context-dependent. Broadly speaking, it can refer either to a chemical species being observed in a chemical reaction, or to a surface on which other chemical reactions or microscopy are performed.
In the former sense, a reagent is added to the substrate to generate a product through a chemical reaction. The term is used in a similar sense in synthetic and organic chemistry, where the substrate is the chemical of interest that is being modified. In biochemistry, an enzyme substrate is the material upon which an enzyme acts. When referring to Le Chatelier's principle, the substrate is the reagent whose concentration is changed.
Spontaneous reaction
Where S is substrate and P is product.
Catalysed reaction
Where S is substrate, P is product and C is catalyst.
In the latter sense, it may refer to a surface on which other chemical reactions are performed or play a supporting role in a variety of spectroscopic and microscopic techniques, as discussed in the first few subsections below.
In three of the most common nano-scale microscopy techniques, atomic force microscopy (AFM), scanning tunneling microscopy (STM), and transmission electron microscopy (TEM), a substrate is required for sample mounting. Substrates are often thin and relatively free of chemical features or defects. Typically silver, gold, or silicon wafers are used due to their ease of manufacturing and lack of interference in the microscopy data. Samples are deposited onto the substrate in fine layers where it can act as a solid support of reliable thickness and malleability. Smoothness of the substrate is especially important for these types of microscopy because they are sensitive to very small changes in sample height.
Various other substrates are used in specific cases to accommodate a wide variety of samples. Thermally-insulating substrates are required for AFM of graphite flakes for instance, and conductive substrates are required for TEM. In some contexts, the word substrate can be used to refer to the sample itself, rather than the solid support on which it is placed.
Official source
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