form submit through jquery ajax - unable to get form values

See more:

jQuery

unable to get form data on server side

here is my form tag

<form id="JqAjaxForm" enctype="multipart/form-data" >
<input accept="doc/docx" type="file"  önchange="CopyMe(this, 'textfield');" style="display:none" id="tt" size="40" />
<br /><br />
<input
id="Text1"
type="text" />
<input id="btnsubmit" type="submit" value="SUBMIT" />
</form>

here is the script to submit form through ajax jquery

<script type="text/javascript">

$(function(){
$("#JqAjaxForm").submit(function(e){
e.preventDefault();

dataString = $("#tt").serialize();
alert(dataString)

$.ajax({
type: "POST",
url: "senddoc.aspx",
data: dataString,
dataType: "json",
success: function(data) {

if(data.email_check == "invalid"){
$("#message_ajax").html("<div class="errorMessage">Sorry " + data.name + ", " + data.email + " is NOT a valid e-mail address. Try again.</div>");
} else {
$("#message_ajax").html("<div class="successMessage">" + data.email + " is a valid e-mail address. Thank you, " + data.name + ".</div>");
}

}

});

});
});

</script>

at code behind if i use Request.Files("tt1")
it shows nothing

pls suggest