Grain Sizes and Surface Roughness in Platinum and Gold Thin Films

Abstract

We have used silicon and glass as substrate for gold and platinum thin films deposition. The film thickness are between 40 and 440 nm for gold and between 26 and 220 nm for platinum. We have analyzed these samples by scanning tunneling microscopy and by X ray diffraction. The crystallographic and morphological grain sizes are discussed. In this work we have analyzed crystallographic and morphological grain sizes and surface roughness of platinum and gold thin films, as a function of the film thickness T. The growth dynamics of theses films have been studied in recent papers [1 – 8]. We verified that the grain sizes play a major role in the noise spatial correlation length. In growth dynamics morphological grain sizes are more relevant than the crystallographic ones. This occurs because the arriving particles that are being deposited on the film surface are exposed to the morphological grain profiles. The crystallographic grain sizes have been also measured, since it is a very important parameter to understand the film nanostructure. In addition, we give the surface film roughness as a function of the thickness T and also the specific preferential crystallographic orientation of the deposited films. 2. Materials and Methods We have used two kinds of substrate for the films deposition. The first one was monocrystalline silicon and the second one was ordinary glass microscope slide. The second substrate, being amorphous, allows us to verify if any preferential orientation for the films crystallography comes from the substrate epitaxy or not. The technique for films deposition was “Metal Plasma Immersion Ion Implantation and Deposition” (MePIIID) [9 – 12]. This technique is highly effective for producing high quality films, including metals, alloys, oxides, nitrides, carbides and diamond-like carbon. In this approach, plasma is formed from a vacuum arc plasma gun, and allowed to stream toward a substrate. The plasma gun has a cylindrical cathode made of the material that will be deposited on the substrate. The anode has also a cylindrical shape; the cathode is surrounded by a ceramic tube, isolating the cathode from the anode. A discharge initiates when the system is triggered, producing a plasma of the cathode material. A coil surrounding the anode, in series with the arc, focuses the plasma. A particle filter is located on the exit of the plasma gun, to remove the macroparticles produced with the plasma. This particle filter is basically a quarter-torus coil in series with the arc, producing a curved magnetic field to guide the plasma to the substrate, while the macroparticles travel in straight line due to their inertia. Finally, the substrate is located in front of the particle filter. The plasma gun operates in a repetitively pulsed mode. In this work, the parameters used for the platinum and gold depositions were: 200 A for the arc current, with 5 ms for arc duration and the frequency of the pulses was 1 Hz. The characterization techniques used for this work were scanning tunneling microscopy (STM) to measure the morphological grain size and surface roughness, and X ray diffraction do