2 things: 1) fzero is designed to find a single zero at a time. You will need to loop through each value for x0 and record the zero the fzero found for that starting point. Something like:
for i = 1:length(x0)
z(i) = fzero(fun, x0(i));
end
2) exp is a function that expects 1 input, if you want to calculate e^(-.2x) you can write:
exp(-.2*x)
