How to set column width when export datagrid to excel in wpf

Question

private void Export_Click(object sender, RoutedEventArgs e)

{

ExportToExcel();

}

private void ExportToExcel()

{

datagrid10.SelectAllCells();

datagrid10.ClipboardCopyMode = DataGridClipboardCopyMode.IncludeHeader;

ApplicationCommands.Copy.Execute(null, datagrid10);

String resultat = (string)Clipboard.GetData(DataFormats.CommaSeparatedValue);

String result = (string)Clipboard.GetData(DataFormats.Text);

datagrid10.UnselectAllCells();

System.IO.StreamWriter file = new System.IO.StreamWriter(@"C:\Users\Santhosh\Desktop\Exportdata.xls");

file.WriteLine(result.Replace(',', ' '));

file.Close();

MessageBox.Show(" Exporting DataBase to Excel file created", "Infromation", MessageBoxButton.OK, MessageBoxImage.Information);

}

This is my code 

 when i excute excel is created but in excel file columns are smaller and date format is in #### when i expand it then it will show correct date fromat.

How to set column width to excel sheet when i'm export.