$(18$ pts$)$ This part concerns about scanning electrochemical microscopy. Please answer the

following questions:

$.$ Explain in feedback mode, what the positive feedback and negative feedback are

$.$ Sketch approach curves for each of the feedback mode in $1).$ Clearly label the axes to get full

credits.

$.$ Provide an example of the application of SECM, explain how it is used in this type of application.

$(12$ pts$)$ The images shown in the next page $($first half page$)$ were obtained with an AFM tip

modified with amine groups. Image $b$ is the topography of the surface and image $c$ is the chemical

force microscopic image. Explain the observations.

$(12$ pts$)1).$ In the Tafel plot shown next page $(2$nd half page$),$ which metal is more active for

hydrogen evolution? Why?

$.$ What is the slope of this Tafel plot $($one branch is enough$)$ if $=0\mathrm{.}5?$

$a$