streaming replication trigger file

Hi all,

I am a bit confused regarding streaming replication.

I have two server: A and B.
I set up replication successfully.
But when the master A goes down, B are not acting as master.

My recovery.conf as follows:

standby_mode = 'on'
primary_conninfo = 'host=10.0.0.91 port=5432 user=postgres'
trigger_file = 'C:\\pg\\stopreplication\\standby.txt' 
restore_command = 'copy \pg\\wal_archive_91\\%f %p' 

When I manually create the C:\\pg\\stopreplication\\standby.txt' file, then it is working. That is, B is becoming the master.
So, my question is, how this trigger file should be created so that B will become master automatically as soon as A goes down?