Synthesis of embedded Si nano-particles using swift heavy ions and its optical properties
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Synthesis of embedded Si nano-particles using swift heavy ions and its optical properties
P. K. Sahoo1, D. P. Mahapatra2, and D. Kanjilal3 1
School of Physical Sciences, National Institute of Science Education and Research (NISER),
Bhubaneswar-751005, India 2
Institute of Physics, Sachivalaya Marg, Bhubaneswar – 751 005, India
3
Inter-University Accelerator Centre, New Delhi 110 067, India
ABSTRACT Embedded Si nano-particles of average size around 5nm were synthesized in an amorphous Si matrix by two stage ion implantation processes. It has been observed that amorphous Si (a-Si) layers were recrystallized using 50 MeV Au ions with enhanced regrowth rate with activation energy in the range of 0.29 eV. During the crystallization process Si nanocrystals were formed in the a-Si layers due to sudden quenching of the molten tracks created by MeV Au ions. The recrystalizations were confirmed by Rutherford backscattering spectrometry-Channeling (RBSC) technique. The structural modification and nanocluster creation that emerged during recrystallization process was observed in high-resolution transmission electron microscopy and photoluminescence (PL) spectroscopy. The PL emission was observed over a broad band of 2.8 – 3.4 eV and centered at 3.25 eV. The Si nano-crystal formation can be explain by a mechanism combining the melting within the ion tracks by thermal spike process and the subsequent recrystallization nucleated from the crystalline sides at the interface. INTRODUCTION The light emission in the UV and visible range from various Si nanostructures in silicon-based materials has been a subject of considerable research and technological interest in the last decades [1-6]. Scientifically, there has been a desire to understand the nature of light emission from an indirect-band-gap material such as Si particularly, at nanometer dimensions. In addition to nano-dimensions another approach to tune the emission energy is through isoelectronic impurity doping of rare-earth ions such as Er+ into the crystalline Si (c-Si) lattice [2]. This leads to emission in the near-infrared spectral region, but to date have only met with limited success in terms of high quantum efficiency at room temperature. More recently however, there has been a lot of studies on electrochemically etched c-Si, known as porous silicon (PSi) [4], due to its intense room-temperature PL in the visible spectral region, and the easy fabrication process. This work has spawned research on silicon nanoparticles [5], films of nanocrystalline Si (nc-Si) embedded in SiO2 [6], c-Si remnants in the SiO2 [7], recrystallization of amorphous silicon [8] and Si ion implantation into fused silica [9], among many others. The origin of luminescence in nc-Si has been extensively investigated and is still a matter of debate. Many of the experimental results have been explained in the framework of a quantum confinement model [6]. The emission from the nanocrystals would not only be due to electron–hole recombination inside the nanoclusters, but would also be related to s
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