Biomedical Engineering Reference
In-Depth Information
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Figure 11.1
SEM images of NPG structures. (a) A 1 mm thick NPG sheet made by
dealloying a piece of 12-carat white gold leaf in nitric acid for 1 h; (b) Large pore NPG
sheet made by annealing sample (a) at 400 C for 8 h and i lled with silver; (c) Hierarchical
porous sheet (plan view) made by annealing the sample shown in (b) at 400 C for 4
h, and performing a second dealloying etch in nitric acid for 5 min; (d) Cross-section
micrograph of sample (c) [21]. (Reprinted with permission from [21].)
Up to now, dealloying as a useful and simple method has been exten-
sively used for preparation of NPG. Among the various alloys, research-
ers focused on gold-silver alloy [19, 23] because gold and silver can form
monophasic solid solution with any kind of composition, and possesses
enough standard electrode potential dif erence [23]. h is NPG preparation
method is convenient and easy to control. High specii c surface area and
uniform structure are other properties of the dealloying procedure. Since
the pore diameter can be controlled by tuning the corrosion process, this
method is appropriate for mass industrial productions.
11.2.2 Template-Assisted Method
h e template-assisted approach is another process for the preparation of
NPG i lms (NPGF) in which gold is i rst loaded on a prepared template,
and the template is then eliminated by physical or chemical methods [24].
Although the template-assisted technique is a time-consuming process, it
takes advantage of precise control over the size and structure of the NPGF.
Biological template [25], colloid crystal template [26], and porous alumina
[27] are paradigms which are used as the templates. For instance, a three-
dimensional gold i lm electrode has been fabricated by electrochemical
