The Effect of Annealing on the Size and Morphology of Palladium Nanopaticles

Palladium(Pd) nanoparticles are produced by variety of methods. In this research, at first Pd nanoparticles were produced by electron beam coating method and then morphology of Pd nanoparticles were studied. Obtained coating can be used as active layer in hydrogen and hydrogen compounds sensors or in hydrogen storage applications. The characterization of the Pd film has been performed by various techniques such as XRD and SEM. The texture and morphology of the materials has been investigated by Atomic Force Microscopy(AFM). Results of different analyses on the Pd films show that the increasing of annealing temperature could increase the Pd nanoparticles size.


Introduction
In recent years, there has been enormously wide-spread interest in nano-materials and their size-dependent properties. It is well known that metal particles of nanometer size have unique characteristics that differ fro m those of individual atoms and bulk materials [1]. Thin films of metal nanoparticles have been receiving increasing attention because of the optical, electronic and catalytic properties of such materials [2,3].
Thin films of pallad iu m(Pd ) and its alloys are used in a variety of technologically important applications including catalysis, gas sensors, and hydrogen permselective membrane [4][5][6][7]. In case of nanoporous coating based on palladium nanostructures high efficiency of adsorption /desorption processes and reactivity of Pd toward hydrogen allo w for applications of such coatings in hydrogen detectors [8]. It is well known that the optical properties of noble metals are improved by obtaining them in nanosized particulate films with a reference to specific applications [9]. Nanostructured palladiu m particles, because of their high activities toward o xygen reduction reactions, have attracted much attention in recent years as cathode catalysts for fuel cell applications [10]. Moreover, considerable effort has been focused on the synthesis of palladiu m nanoparrticles [11][12][13]. Special techniques are needed to synthesize materials with particle size in the nanometer range. Morphology of such materials are studied by SEM and AFM [14]. In thispaper, thin film palladiu m on glass/silicon substrate is de posited by the electron beam coating method. The films are subsequently reduced to form nanoparticulat palladiu m film by increasing temperature.

Experiments
Primary material used in this survey, palladiu m(99/95% pure) was bought fro m goodfello w Co. The Pd films were prepared by electron beam coating method on glass substrates. These substrates were cleaned with ultrasonic apparatus prior to deposition.
Then samples were exposed temperature. The temperatures of annealing process were 450℃, 550℃ and 650℃. The structure characterizat ions of the thin films were obtained by X-ray diffraction. The Pd nanoparticles formed and the fine structure of the Pd was observed by using SEM and AFM.  The particle average size was calculated using the Debye-Scherer formu la,

Results and Discussion
, where λ is the x-ray wavelength( 1.5406A  ), θ is the Bragg diffract ion angle and B is the peak width at half-ma ximu m. Mean crystallite size was obtained by measuring the broadening of the {004} diffraction peak and applying the x-powder software. The average crystallite size were: 3n m, 6n m and 19n m for the sample in 450℃, 550℃ and 650℃ respectively.
The obtained structure and topography of coating were studied by SEM and AFM. Fig.2 shows the scanning electron micrographs for thin films pallad iu m in difference annealing temperature. Present SEM images show a grain structure for Pd films, and the size of grains were higher with increasing of annealing temperature. The part icles fo rmed showed sizes of 44n m, 53n m and 286n m for 450℃, 550℃ and 650℃ respectively. These results are in agreement with XRD results. Fig. 3 shows topography of two dimansions and three dimansions annealed films in temperatures 450℃, 550℃ and 650℃. The Ato mic Force M icroscopy(AFM) images confirmed results previous experimental that with temperature increasing increases crystal structure.

Conclusions
In summary, Pd coating was obtained by electron beam on glass substrates. XRD results show that this film has amorphous structure at roo m temperature. Also, XRD patterns show that crystal grains are forming with the annealing and with increasing temperature, increase grains size. AFM and SEM results confirm it.