Chemistry Reference
In-Depth Information
In addition to the electrochemical techniques, many
insitu
and
exsitu
surface analyti-
cal techniques are used in studies of silicon electrodes, such as ellipsometry for
determining thin surface film thickness,
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infrared spectroscopy for surface
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XPS
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for surface composition, SEM
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and STM
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for
surface morphology, TXRF for surface concentration of metals,
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and AFM for surface
morphology.
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One particularly important aspect in electrochemical measurements is surface
treatment (or surface preparation). The electrochemical behavior of silicon can be
strongly affected by surface treatment procedures.
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The most important goal
of surface preparation is to produce a chemically clean and physically homogeneous
surface that is reproducible and relatively stable so that representative and reproducible
results can be generated. Since silicon is usually covered with a native oxide of various
thicknesses and chemical compositions in the air or in aqueous solutions, most surface
treatments are designed to remove this initial surface oxide film. The most common
procedure used in surface treatment of a silicon electrode includes a dip of the elec-
trode in a HF solution. A very common treatment of silicon electrodes for electro-
chemical experiments employs concentrated HF solutions such as 48% HF at room
temperature with dipping time ranging from 10 to 60s.
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Also, addition of oxidizing
agents such as to the HF solutions is used to enhance the etching rate. The surface
after a dip in HF solutions is typically terminated with hydrogen (see Chapter 2 for
details). As will be seen in the rest of this topic, the surface condition resulting from
preparation by a specific cleaning solution may still vary to a wide extent due to the
many poorly controllable material and procedure factors.
adsorption,
