Ion beam induced modification and nanostructures formation in thin SiC/Pd films on c-Si substrate

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Abstract

Ion beam induced modification of thin metallic films is an emerging approach to grow metallic nanoparticles controllably. Modification of thin solid films is helpful in fabricating arrays of nanoscale particles for electronic and photonic devices and for the catalyzed synthesis of nanotubes and nanowires. In this work, the modification and nanostructures formation over the surface of SiC/Pd thin films of 15 and 45 nm thicknesses, grown on crystalline Silicon (c-Si) substrate by electron beam deposition, upon ion irradiation, have been investigated by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Rutherford backscattering spectrometry (RBS), Fourier Transform Infrared Spectroscopy (FTIR) and Raman spectroscopy. The SiC/Pd bilayer films were irradiated with 100 keV Ar+ ions at fluences of 1 × 1015 and 5 × 1015 ions/cm2 at room temperature. The surface morphology from SEM analysis showed the formation of nanoparticles that were interconnected after irradiation. The RBS and EDS results confirmed the presence of Pd, C, O and Si. While the Raman spectrum of the pristine sample displayed only a sharp peak at 520 cm−1 characteristic to c-Si substrate, the spectra of the irradiated sample red-shifted to lower wavenumbers indicating the appearance of Si nanocrystals.. Hence, ion beam irradiation is a promising method for the fabrication of SiC nanostructures on c-Si substrate.

Introduction

Ion beams have been used for the synthesis and modification of materials over the past decades. Ion beams with energies in the keV range have been used for surface modification through ion implantation. Thus, ion beam modification of materials uses energetic ions with a broad range of energies for modification of electrical, optical, structural and chemical properties of materials [1]. Recently, it has been shown that ion beams can cause surface modification of metal films on non-reactive substrates which can lead to a patterned surface [2], [3], [4]. The growth of metallic nanoparticles from thin films offers the possibility of scientific insight into novel processes [5] and advantages in development due to the adaptation of existing thin film technology. SiC is known for its outstanding properties such as wide band gap, high-temperature stability and high thermal conductivity, radiation hardness and chemical inertness [6], [7]. These properties make SiC a material of choice for applications in semiconductor devices which are operated in extreme conditions of temperature, power and irradiation [8]. Several methods have been employed to synthesize SiC nanostructures, such as sol–gel [9], atomic layer deposition (ALD) [10], chemical vapour deposition (CVD) [11], and electron beam evaporation [12]. Among these techniques, ion beam irradiation with beams in the tens to hundreds of keV range has been utilized to induce modification of metal thin films in order to grow nanostructures at room temperature [13], [14]. Lee et al. [15] have observed some intermixing of palladium films with silicon after implanting with phosphorus ions. Moreover, van der Weg et al. [16] have noted interdiffusion of Pd/Si after implanting with Ar+ ions. They observed no bubbles after implantation with Ar at high ion fluence whereas He bubbles were noted after implantation at the same ion fluence. There is a lot of literature on the effects of ion beam irradiation of metal thin films on substrates [15], [17], [18]. To our knowledge, there has been no or little focus on the effect of ion beam modification of a thin metal layer sandwiched between a thin semiconductor film and the substrate. In this work, ion beam modification and nanostructures formation in SiC/Pd thin films stacks of 15 and 45 nm thicknesses, grown on crystalline Silicon (c-Si) substrate by electron beam deposition, upon ion irradiation have been investigated by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Rutherford backscattering spectrometry (RBS) and Raman spectroscopy.

Section snippets

Experimental details

Pd metal catalysts of about 5 nm thickness were deposited on c-Si (1 0 0) substrates by electron beam evaporation. Then, SiC thin films of thicknesses 10 and 40 nm were deposited in situ on the Pd/Si (1 0 0) layered structure. Prior to the deposition, the substrates were cleaned in an ultrasonic bath using acetone, methanol and deionized water in sequence for the duration of 10 min for each step in order to remove dirt and contamination. The native oxide layer on the Si substrate was removed by

Surface morphology characterization

The SEM micrographs of pristine and ion irradiated SiC/Pd layer stacks on c-Si substrate are presented in Fig. 1. The pristine samples in Fig. 1(a) and (d) show smooth surfaces with small grains. Fig. 1(b) shows the formation of nanoparticles dispersed throughout the surface. As ion fluence increases to 5 × 1015 ions/cm2, a formation of isolated and interconnected nanoparticles was observed with a small fraction of surface area coverage as shown in Fig. 1(c). When the thickness of the SiC layer

Conclusions

Nanostructures formation over the surface of thin SiC/Pd films on c-Si substrate by ion beam induced modification with 100 keV Ar+ ions at room temperature has been successfully achieved. SEM studies showed the formation of interconnected grains dispersed throughout the surface of irradiated films at ion fluences of 1 × 1015 and 5 × 1015 ions/cm2. The SiC thin film thickness was found to be an important parameter on the formation of SiC nanoparticles. SEM images showed that the formation of

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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