inserting unicode data from c# form to oracle 11g?

Question

when i want to insert some unicode data from c# form to oracle 11g EX ... in oracle the data like this '????????' but when i want to insert unicode data from oracle command it does not have any problem.
insert into depts values (8,'?????')
it does not have a problem (oracle sql command) but in c# i use

com.CommandText = "insert into DEPTS values('"+dept_cod_txt.Text+"','"+dept_name_txt.Text+"')"; com.ExecuteNonQuery();