Problem with leftButton on textField

I'm trying to put one image on texfield, but dont't run. What's the problem?

var emailImage = Titanium.UI.createButton({
                backgroundImage:'/images/login/Email_icon.png',
                width:'14dp',
                height:'15dp'
            });
 
            var txt_User = Titanium.UI.createTextField({
                width: "80%",
                color: "#222",
                paddingLeft: '5dp',
                hintText: 'Email Address',
                borderColor: "gray",
                borderRadius: 1,
                bubbleParent: false,
                font: {
                    fontSize: '12dp'
                },
                height: '40dp',
                top: '60dp',
                backgroundColor: '#ffffff',
                leftButton: emailImage,
                leftButtonPadding: '50dp',
                leftButtonMode: Titanium.UI.INPUT_BUTTONMODE_ALWAYS,
                keyboardType: Titanium.UI.KEYBOARD_DEFAULT,
                returnKeyType: Titanium.UI.RETURNKEY_DEFAULT,
                borderStyle: Titanium.UI.INPUT_BORDERSTYLE_LINE
            });