custom alpha-data in surface plot

I am plotting multiple surfaces in one figure. Now I want to make the areas of the plot close to zero a transparency-gradient. For example

if z(i,j) >= 0 && z(i,j) <= 0.1
  transparancy(i,j) = 1-z(i,j)/0.1;
else
  transparancy(i,j) = 0;
end

I tried using the 'alpha' function and the colormap method but didn't succeed. Can anybody help me on my way?

Answer 1

[Walter Roberson]

Do not use the alpha function: use the AlphaData property of the surface object.

surf(z, 'AlphaData', transparancy)

[Björn]

I tried this but it doesn't change anything. Do you have another suggestion?