ODP.NET

I wish to make a backup, with host copy operation (using ASP.NET) but got problems with double backslash \\ occuring in my OracleCommand, got always exception "Invalid SQL", here's my command (.txt only as example):

OracleCommand oraCmdCopy = new OracleCommand(String.Format("host copy {0} {1}", @"D:\a.txt", @"F:\b.txt"), oraConn);

I've put a watch there's always:
D:\\a.txt
F:\\b.txt

I've tried with String.Replace(@"\\",@"\")...

but there is no positive result..

Can anyone tell me how to handle that situation?
[Oracle accepts D:\a.txt, but not D:/a.txt, tried that also...] is this double backslash a problem or should I use something else, not OracleCommand to execute that statement.

Thanks