Increment alphabet letter

Dim startExcelColumn As String = "A"
Dim lastExcelColumn As String = startExcelColumn

For Each col As DataColumn In dtExcel.Columns
If iCounter > 0 Then
lastExcelColumn = Chr(Asc(lastExcelColumn) + 1)
End If
iCounter += 1
Next


oWorkSheet.Range(startExcelColumn & "1", lastExcelColumn & "1").Font.Bold = True