- #1
Ziggy12
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Homework Statement
Suppose the STM tip current is given by
[tex] i = aV e^{-A\phi^{1/2}s} [/tex]
a) Derive an expression for the fractional change in tip current as function of fractional change in tip spacing s.
b) If [tex]\phi = 4V[/tex] select a reasonable set of V values so that a 1Å increase in s will cause a factor of 10 decrease in i. (a and A are given)
Homework Equations
Given in problem
The Attempt at a Solution
It's probably very simple but I'm stuck. I'm simply using error formula to get that
[tex] \delta i = \frac{\partial i}{\partial s} \delta s = -A\phi^{1/2} \cdot i \cdot \delta s[/tex]
And then I move out i to the left side to get the fractional change in current.
But that doesn't seem correct. Because then I don't understand how I am supposed to solve b), since the fractional change is independent of V.
I tried other ways as well, but V seems to dissaperar out of the equation anytime I do that.
If anyone has a good idea on how to proceed, it would be welcome.
Thanks
// John[/B]