Problem with columns width

Hi, im working with the server side editor. All works great, now im tring to set the columns width. I read all the dcumentation, and nothing works for me. I try with

$('#example').dataTable( {
  "columnDefs": [
    { "width": "20%", "targets": 0 }
  ]
} );

or with "autoWidth": false.

I only want to give some columns a fixed width.

Heres is my code

  $('#example').DataTable( {
    
    "columnDefs": 
    [
    { "searchable": false, "targets": [6,0] },
    ],
  
  "footerCallback": function( thead, data, start, end, display ) {
    $(thead).find('th').eq(0).css({"background-color":"#C8ECA9"})
  },
         "footerCallback": function( tfoot, data, start, end, display ) {
    $(tfoot).find('th').eq(0).html("");
    $(tfoot).find('th').eq(1).html("");
    $(tfoot).find('th').eq(2).html("");
    $(tfoot).find('th').eq(3).html("");
    $(tfoot).find('th').eq(4).html("");
    $(tfoot).find('th').eq(5).html("");
    $(tfoot).find('th').eq(6).html("");
    $(tfoot).find('th').eq(7).html("");
  },
        
         responsive: true,
        "pageLength": 30,
        "processing": true,
        
        dom: "Tfrtip",
        ajax: {
            url: "examples/php/staff.php",
            type: "POST"
        },
        serverSide: true,
        columns: [
            { data: null, defaultContent: '', orderable: false, class:"center" },
            { data: "empresa", "width": "40%"  },
            { data: "nombre" },
            { data: "direccion", "width": "40%" },
            { data: "localidad" },
            { data: "tel" },
            { data: "mail", "searchable": false },
            { data: "nombre2" },
            { data: "codp" },
            { data: "provincia" },
            { data: "web" },
            { data: "cel" },
            { data: "rubro" },
            { data: "cuit" },
            { data: "notas" },
            
            
        ],order: [ 1, 'asc' ],
        tableTools: {
            sRowSelect: "os",
            sRowSelector: 'td:first-child',
            sSwfPath: "TableTools/swf/copy_csv_xls_pdf.swf",
            aButtons: [
                { sExtends: "editor_create", editor: editor },
                { sExtends: "editor_edit",   editor: editor },
                { sExtends: "editor_remove", editor: editor },
                {
                    sExtends: "collection",
                    sButtonText: "Exportar",
                    sButtonClass: "save-collection hidden-xs",
                    aButtons: [ 'copy', 'csv', 'xls', 'pdf' ]
                },
                {
                    sExtends: "print",
                    sButtonText: "Imprimir",
                    sButtonClass: "hidden-xs",
                    sInfo: "Presiones la tecla 'Escape' para salir"
                    
                    },
            ]
        },
        
    } );
} );

Thanks