DomDocument não acrescentou o atributo xmlns na tag NFe

$infeNFe_id = "NFe11101284613439000180550010000004881093997017";
$cUF = 11;
$cNF = "09399701";
$natOp = "VENDA NO ESTADO MERC.ADQ.TERCEIROS";
$indPag = "0";
$mod = 55;
$serie = "1";
$nNF = "488";
$dEmi = "2010-12-02";
$dSaiEnt = "2010-12-02";
$hSaiEnt = "17:04:25";
$tpNF = "1";
$cMunFG = "1100205";
$tpImp = "1";
$tpEmis = "1";
$cDV = "7";
$tpAmb = "2";
$finNFe = "1";
$procEmi = "0";
$verProc = "1.0.0.0";
$CNPJ = "84613439000180";
$xNome = "MicroLine Software";
$xFant = "MicroLine Software";
$xLgr = "Av. Rafael Vaz e Silva";
$nro = "003091";
$xBairro = "LIBERDADE";
$cMun = "1100205";
$xMun = "PORTO VELHO";
$UF = "RO";
$CEP = "78904120";
$cPais = "1058";
$xPais = "BRASIL";
$fone = "6933213610";
$IE = "00000000415138";
$IM = "999911111";
$CNAE = "4645101";
$CRT = "1";

 $dom = new DomDocument("1.0", "UTF-8");

 $dom->preserveWhiteSpaces = false;
 $dom->formatOutput = false;

 //NFEPROC
 $nfeProc = $dom->createElement('nfeProc');
 $nfeProc->setAttribute("versao", "2.00");
 $nfeProc->setAttribute("xmlns", "http://www.portalfiscal.inf.br/nfe");

 //NFE
 $nfe = $dom->createElement("NFe");
 $nfe->setAttribute("xmlns", "http://www.portalfiscal.inf.br/nfe");

 //INFNFE
 $infNFe = $dom->createElement("infNFe");
 $infNFe->setAttribute("versao", "2.00");
 $infNFe->setAttribute("Id", $infeNFe_id);

 //IDE
 $ide = $dom->createElement("ide");
 $ide->appendChild($dom->createElement("cUF",$cUF));
 $ide->appendChild($dom->createElement("cNF",$cNF));
 $ide->appendChild($dom->createElement("natOp",$natOp));
 $ide->appendChild($dom->createElement("indPag",$indPag));
 $ide->appendChild($dom->createElement("mod",$mod));
 $ide->appendChild($dom->createElement("serie",$serie));
 $ide->appendChild($dom->createElement("nNF",$nNF));
 $ide->appendChild($dom->createElement("dEmi",$dEmi));
 $ide->appendChild($dom->createElement("dSaiEnt",$dSaiEnt));
 $ide->appendChild($dom->createElement("hSaiEnt",$hSaiEnt));
 $ide->appendChild($dom->createElement("tpNF",$tpNF));
 $ide->appendChild($dom->createElement("cMunFG",$cMunFG));
 $ide->appendChild($dom->createElement("tpImp",$tpImp));
 $ide->appendChild($dom->createElement("tpEmis",$tpEmis));
 $ide->appendChild($dom->createElement("cDV",$cDV));
 $ide->appendChild($dom->createElement("tpAmb",$tpAmb));
 $ide->appendChild($dom->createElement("finNFe",$finNFe));
 $ide->appendChild($dom->createElement("procEmi",$procEmi));
 $ide->appendChild($dom->createElement("verProc",$verProc));

 //EMIT
 $emit = $dom->createElement("emit");
 $emit->appendChild($dom->createElement("CNPJ", $CNPJ));
 $emit->appendChild($dom->createElement("xNome", $xNome));
 $emit->appendChild($dom->createElement("xFant", $xFant));
 $emit->appendChild($dom->createElement("IE", $IE));
 $emit->appendChild($dom->createElement("IM", $IM));
 $emit->appendChild($dom->createElement("CNAE", $CNAE));
 $emit->appendChild($dom->createElement("CRT", $CRT));

 //ENDEREMIT
 $enderEmit = $dom->createElement("enderEmit");
 $enderEmit->appendChild($dom->createElement("xLgr", $xLgr));
 $enderEmit->appendChild($dom->createElement("nro", $nro));
 $enderEmit->appendChild($dom->createElement("xBairro", $xBairro));
 $enderEmit->appendChild($dom->createElement("cMun", $cMun));
 $enderEmit->appendChild($dom->createElement("xMun", $xMun));
 $enderEmit->appendChild($dom->createElement("UF", $UF));
 $enderEmit->appendChild($dom->createElement("CEP", $CEP));
 $enderEmit->appendChild($dom->createElement("cPais", $cPais));
 $enderEmit->appendChild($dom->createElement("xPais", $xPais));
 $enderEmit->appendChild($dom->createElement("fone", $fone));

 $emit->appendChild($enderEmit);
 $infNFe->appendChild($ide);
 $infNFe->appendChild($emit);
 $nfe->appendChild($infNFe);
 $nfeProc->appendChild($nfe);
 $dom->appendChild($nfeProc);

 $dom->saveXML();
 $dom->save("teste.xml");
Na <NFe>, não esta criando o atributo xmlns. Atualmente está assim:

 

<NFe>

O certo seria:

<NFe xmlns="http://www.portalfiscal.inf.br/nfe">

Pq o atributo xmlns não está na NFe ?