Nano-particle and nano-phase network structure in feco thin film using plasma focus

Abstract

Summary form only given. In the present investigation we have used plasma focus, as a thin film deposition source, in two different ways: (a) in a conventional way, by replacing the usually used copper anode with a FeCo fitted anode and then depositing the ablated FeCo plasma, the one ablated by the hot plasma and energetic electron beam, on Si substrate placed up the anode axis, the distance between FeCo sample and Si substrate is 25 cm, and (b) by the ablation of FeCo target disc, in a specially designed chamber attached to the lower end of plasma focus device, with the use of extracted electron beam. The DPF device was operated different shots at a charging voltage of 12 kV with hydrogen as the filling gas at a pressure of 12 mbar. The deposited films have been analyzed for their structure, surface morphology, magnetic characteristics and stoichiometry using X-ray diffractometer (XRD), field emission scanning electron microscope (FSEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscope (TEM), and vibrating sample magnetometry (VSM). When the conventional way is used, the samples with 30 shots or less show a uniform FeCo thin film. The agglomerates with size of 100 nm are composed of smaller grains of the size approximately about 20-30 nm. When the number of focus shots was increased, a different surface morphology is observed. The surface of the sample has a complex distribution of nano-wire like network on the top of a carpet like background. When the number of the shots is further increased, much denser network structure is observed. The EDX of the samples show that the deposited films are stoichiometric and when the number of focus shots is more than 50, FeCo thin film is so thick that silicon peaks disappear from the EDX spectra. The XRD and EDX also show the partial oxidation of the deposited FeCo thin films. The magnetism was observed to increase with the increase in the number of focus shots, the coercivity ranged from 170-240 Oe, which shows that the materials are intermediate magnetic materials. TEM shows different particles or agglomerates have different crystal planes, and amorphous in between. When electrons were used as the source for ablation, smaller particles were found on the surface of the deposited film and network structures were not observed. The magnetism with the similar coercivity is also smaller compared with the samples deposited using the same number focus shots for the conventional way. The XRD and EDX also show the crystal characteristics of the deposited samples