Influence of 20 MeV electron irradiation on the optical properties and phase composition of SiOx thin films

Abstract

Homogeneous films from SiO1.3 (250 nm thick) were deposited on crystalline Si substrates by thermal evaporation of silicon monoxide. A part of the films was further annealed at 700 °C to grow amorphous Si (a-Si) nanoclusters in an oxide matrix, thus producing composite a-Si-SiO1.8 films. Homogeneous as well as composite films were irradiated by 20-MeV electrons at fluences of 7.2 × 1014 and 1.44 × 1015 el/cm2. The film thicknesses and optical constants were explored by spectroscopic ellipsometry. The development of the phase composition of the films caused by the electron-beam irradiation was studied by transmission electron microscopy. The ellipsometric and electron microscopy results have shown that the SiOx films are optically homogeneous and the electron irradiation with a fluence of 7.2 × 1014 el/cm2 has led to small changes in the optical constants and the formation of very small a-Si nanoclusters. The irradiation of the a-Si-SiOx composite films caused a decrease in the effective refractive index and, at the same time, an increase in the refractive index of the oxide matrix. Irradiation induced increase in the optical band gap and decrease in the absorption coefficient of the thermally grown amorphous Si nanoclusters have also been observed. The obtained results are discussed in terms of the formation of small amorphous silicon nanoclusters in the homogeneous layers and electron irradiation induced reduction in the nanocluster size in the composite films. The conclusion for the nanoparticle size reduction is supported by infrared transmittance results.

Cryo-ePDF: Overcoming Electron Beam Damage to Study the Local Atomic Structure of Amorphous ALD Aluminum Oxide Thin Films within a TEM

“…However, one key practical barrier to the use of ePDF to examine ALD-grown materials is the potential for damage to the sample caused by electron beam exposure. , We note that although beam damage has been found to be significant in inorganic materials, − previous work using ePDF to study inorganic materials has largely neglected beam damage effects. , Beam damage alters the material structure from its original state and limits the relevance of ePDF results. Electron beam damage arises because of the reaction of electrons in the electron beam with the sample and can manifest as radiolysis, knock-on beam damage, and/or crystallization.…”

Towards quantitative treatment of electron pair distribution function

“…A very impressive application of ePDF was recently published (Hristova-Vasileva et al, 2018) which demonstrated the phase separation in amorphous non-stoichiometric Si-O layers. The electron radiation-induced transformation resulted in the formation of amorphous Si clusters encapsulated within an amorphous SiO 1.8 matrix.…”

Electron and Neutron Beam Irradiation Effects in Homogeneous and Nanostructured Oxides

“…As described above ( Figures 4 and 5 ), phase separation and silicon nanocluster formation take place upon irradiation of homogeneous SiO x films with high-energy electrons and neutrons. Experiments on the effect of high-energy electron and neutron irradiation of a(c)-Si-SiO x composite films containing thermally grown amorphous (a-Si) or crystalline (c-Si) Si nanoparticles have revealed 22 a radiation-induced decrease of the a-Si nanoparticle size, which is illustrated in Figure 6 ; the irradiation-induced nanocluster formation is also shown in the figure. The nanoparticle size decrease has been concluded on the basis of the observation of a decrease in the effective refractive index of the composite films ( Figure 7 ).…”

“…10,11,19 The effect of 20 MeV electron beam irradiation on the phase separation and Si nanocluster formation in homogeneous SiO 1.2 and SiO 1.3 films has been investigated at fluences of 2.4 × 10 14 , 7.2 × 10 14 , 1.44 × 10 15 , and 3.6 × 10 15 electrons/cm 2 . 22,23 The irradiation at fluence of 7.2 × 10 14 electrons/cm 2 has led to small changes in the optical constants and the formation of very small amorphous Si (a-Si) nanoclusters. The normalized pair distributions measured for the non-irradiated and irradiated SiO x samples are shown in Figure 4.…”