Problem with setting accesskay to a button in silverlight application

Question

Dear All,

            I am working with silverlight 3.0

i have a problem in setting Accesskey to a button Control. there is a property in button control.I tried to set that but it seems not working. 

AutomationProperties.AccessKey="S"

Can anybody have the idea to set the access key?

its better to get the solution in xaml file.

Thanks in Advance