Magento 2 – Get Post Data in Checkout Success Observer

I have added custom field on checkout page.

I want to get all the post data, in Checkout success observer,

Here is my observer code

<?php
/** 
 Author : Disha
 **/
 namespace Neo\OrderComment\Observer;

 use Magento\Framework\Event\ObserverInterface;
 use Magento\Framework\App\RequestInterface;

 class Orderneo implements \Magento\Framework\Event\ObserverInterface
 {
    /** @var \Psr\Log\LoggerInterface **/
    protected $_logger;
    /** @var \Magento\Sales\Model\Order\Status\HistoryFactory **/
    protected $_historyFactory;
    /** @var \Magento\Sales\Model\OrderFactory **/
    protected $_orderFactory;
    /**
     * @param \Psr\Log\LoggerInterface
     * @param \Magento\Sales\Model\Order\Status\HistoryFactory
     * @param \Magento\Sales\Model\OrderFactory
     **/
    public function __construct(
        \Psr\Log\LoggerInterface $logger,
        \Magento\Sales\Model\Order\Status\HistoryFactory $historyFactory,
        \Magento\Sales\Model\OrderFactory $orderFactory){
        $this->_logger = $logger;
        $this->_historyFactory = $historyFactory;
        $this->_orderFactory = $orderFactory;
    }
    /**
     * Add order comment, to the last placed order
     * @param \Magento\Framework\Event\Observer
     **/
    public function execute(\Magento\Framework\Event\Observer $observer)
    {   
        // Get order id, of last placed order
        $orderIds = $observer->getEvent()->getOrderIds();
        foreach($orderIds as $orderId){
            $order = $this->_orderFactory->create()->load($orderId);
        }
        echo "<pre>"; print_r($this->getRequest()->getPost());
        exit;
    }
}

But I am getting this error, as unknown method getRequest(),

Fatal error:  Uncaught Error: Call to undefined method Neo\OrderComment\Observer\Orderneo::getRequest() in /var/www/html/magento2/app/code/Neo/OrderComment/Observer/Orderneo.php:42
Stack trace:
#0 /var/www/html/magento2/vendor/magento/framework/Event/Invoker/InvokerDefault.php(73): Neo\OrderComment\Observer\Orderneo->execute(Object(Magento\Framework\Event\Observer))
#1 /var/www/html/magento2/vendor/magento/framework/Event/Invoker/InvokerDefault.php(61): Magento\Framework\Event\Invoker\InvokerDefault->_callObserverMethod(Object(Neo\OrderComment\Observer\Orderneo), Object(Magento\Framework\Event\Observer))
#2 /var/www/html/magento2/vendor/magento/framework/Event/Manager.php(66): Magento\Framework\Event\Invoker\InvokerDefault->dispatch(Array, Object(Magento\Framework\Event\Observer))
#3 /var/www/html/magento2/var/generation/Magento/Framework/Event/Manager/Proxy.php(95): Magento\Framework\Event\Manager->dispatch('checkout_onepag...', Array)
#4 /var/www/html/magento2/vendor/magento/module-checkout/Controller/Onepage/Success.php in /var/www/html/magento2/app/code/Neo/OrderComment/Observer/Orderneo.php on line 42