You need to create the worksheet object in the same manner that you created the workbook.
Dim ExcelApp As Excel.Application
Dim ExcelWorkbook As Excel.Workbook
Dim ExcelSheet As Excel.Worksheet
Set ExcelApp = Excel.Application
Set ExcelWorkbook = ExcelApp.Workbooks.Add
Set ExcelSheet = ExcelWorkbook.Worksheets.Add
ExcelSheet.Name = "New_Sheet_Name " & CStr(Unique_ID)
Unique_ID: each sheet needs to be identified with a unique name.
Also assure that you dispose the objects or the Excel application will keep running after your program closes.
Set ExcelSheet = Nothing
Set ExcelWorkbook = Nothing
Set ExcelApp = Nothing