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

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

Hydrogen kinetics in a-Si:H and a-SiC:H thin films investigated by real-time ERD

Hydrogen effusion from hydrogenated amorphous silicon (a-Si:H) and amorphous silicon carbide (a-Si1 xCx:H) thin films during a temperature ramp between RT and 600 C was studied by in situ realtime elastic recoil detection analysis. Point to point contour maps show the hydrogen depth profile and its evolution with the ramped temperature. This paper proposes a diffusion limited evolution model to study H kinetic properties from total retained H contents recorded in a single ramp. In a compact a-Si:H layer where H predominantly effuses at high temperatures between 500 and 600 C, an activation energy value of 1.50 eV and a diffusion pre-factor of 0.41 10 4 cm2/s were obtained. Applied to an non-stoichiometric a-Si1 xCx:H film in the same range of temperature, the model led to reduced values of activation energy and diffusion prefactor of 0.33 eV and 0.59 10 11 cm2/s, respectively.National Research Foundation of South Africa (Grant specific unique reference number (UID) 85961).http://www.elsevier.com/locate/nimbhb201

Thermally Induced Nano-Structural and Optical Changes of nc-Si:H Deposited by Hot-Wire CVD

We report on the thermally induced changes of the nano-structural and optical properties of hydrogenated nanocrystalline silicon in the temperature range 200–700 °C. The as-deposited sample has a high crystalline volume fraction of 53% with an average crystallite size of ~3.9 nm, where 66% of the total hydrogen is bonded as ≡Si–H monohydrides on the nano-crystallite surface. A growth in the native crystallite size and crystalline volume fraction occurs at annealing temperatures ≥400 °C, where hydrogen is initially removed from the crystallite grain boundaries followed by its removal from the amorphous network. The nucleation of smaller nano-crystallites at higher temperatures accounts for the enhanced porous structure and the increase in the optical band gap and average gap

Synthesis of nanocrystalline silicon thin films using the increase of the deposition pressure in the hot-wire chemical vapour deposition technique

Nanostructured thin silicon-based films have been deposited using the hot-wire chemical vapour deposition (HWCVD) technique at the University of the Western Cape. A variety of techniques including optical and infrared spectroscopy, Raman scattering spectroscopy, X-rays diffraction (XRD) and transmission electron microscopy (TEM) have been used for characterisation of the films. The electrical measurements show that the films have good values of photoresponse, and the photocurrent remains stable after several hours of light soaking. This contribution will discuss the characteristics of the hydrogenated nanocrystalline silicon thin films deposited using increased process chamber pressure at a fixed hydrogen dilution ratio in monosilane gas

Thermal annealing of protocrystalline a-Si:H

It proves difficult to obtain a set of protocrystalline silicon materials with different characteristics from the same deposition chamber to study the exact nature of these transition region materials. Hot-wire deposited protocrystalline silicon was thus isochronically annealed at different temperatures to investigate the bonded hydrogen configurations and structural disorder. Modeling of optical reflection and transmission spectra with Scout® yielded the optical parameters and infrared spectroscopy confirms that bonded hydrogen remains in the material, with the exception of a longer anneal of six hours at 520 °C. Sub bandgap absorption as inferred from photothermal deflection spectroscopy was related to these characteristics

Investigation of the Thermal Stability of a Solar Absorber Processed through a Hydrothermal Technique

In this work, we study the thermal stability of a hydrothermally treated stainless steel (SS) selective solar absorber by annealing in air in a temperature range between 300 °C and 700 °C for a soaking time of 2 h. Thermal stability testing in the presence of air is critical if the vacuum is breached. Therefore, the SS was characterized by X-ray diffraction (XRD), mechanical, and optical techniques. The XRD analysis shows that the grain size of the as-treated absorber is 67 nm, whereas those of the annealed absorbers were found to be in the range between 66 and 38 nm. The phase of the as-treated and annealed SS was further identified by XRD as Fe2O3. The EDS result shows that the elemental components of the SS were C, Cr, Fe, and O. The strain (ε) and stress (σ) calculated for the as-treated absorber are 1.2 × 10−1 and −2.9 GPa, whereas the annealed absorbers are found in the range of 4.4 × 10−1 to 5.2 × 10−1 and −121.6 to −103.2 GPa, respectively, at 300–700 °C. The as-treated SS absorbers exhibit a good spectra selectivity of 0.938/0.431 = 2.176, which compares with 0.941/0.403 = 2.335 after being annealed at 300 °C and 0.884/0.179 = 4.939 after being annealed at 700 °C. These results indicate a small improvement in absorptivity (0.941) and emissivity (0.403) after annealing at 300 °C, followed by a significant decrease after annealing at 700 °C. The obtained analysis confirms that the annealed SS absorber exhibits excellent selectivity and is suitable to withstand any thermal condition (≤700 °C) in air. Thus, using a cost-effective approach as demonstrated in this study, the as-treated and annealed SS absorber could be used for photo-thermal conversion applications

Investigation of the Thermal Stability of a Solar Absorber Processed through a Hydrothermal Technique

In this work, we study the thermal stability of a hydrothermally treated stainless steel (SS) selective solar absorber by annealing in air in a temperature range between 300 °C and 700 °C for a soaking time of 2 h. Thermal stability testing in the presence of air is critical if the vacuum is breached. Therefore, the SS was characterized by X-ray diffraction (XRD), mechanical, and optical techniques. The XRD analysis shows that the grain size of the as-treated absorber is 67 nm, whereas those of the annealed absorbers were found to be in the range between 66 and 38 nm. The phase of the as-treated and annealed SS was further identified by XRD as Fe2O3. The EDS result shows that the elemental components of the SS were C, Cr, Fe, and O. The strain (ε) and stress (σ) calculated for the as-treated absorber are 1.2 × 10−1 and −2.9 GPa, whereas the annealed absorbers are found in the range of 4.4 × 10−1 to 5.2 × 10−1 and −121.6 to −103.2 GPa, respectively, at 300–700 °C. The as-treated SS absorbers exhibit a good spectra selectivity of 0.938/0.431 = 2.176, which compares with 0.941/0.403 = 2.335 after being annealed at 300 °C and 0.884/0.179 = 4.939 after being annealed at 700 °C. These results indicate a small improvement in absorptivity (0.941) and emissivity (0.403) after annealing at 300 °C, followed by a significant decrease after annealing at 700 °C. The obtained analysis confirms that the annealed SS absorber exhibits excellent selectivity and is suitable to withstand any thermal condition (≤700 °C) in air. Thus, using a cost-effective approach as demonstrated in this study, the as-treated and annealed SS absorber could be used for photo-thermal conversion applications

Employing the effective medium approximation to model the optical properties of crystallized a-Si:H obtained by MIC

Metal induced crystallization of hydrogenated amorphous silicon has been the subject of intense scrutiny in recent years. In this contribution we report on the metal-mediated-thermally induced changes of the structural and optical properties of hydrogenated amorphous silicon deposited by hot-wire CVD, where aluminium and nickel were used to induce crystallization. The metal-coated amorphous silicon was subjected to a thermal annealing regime of between 150 and 520°C. The structural measurements, obtained by Raman spectroscopy, show partial crystallization occurring at 350 °C. At the higher annealing temperatures of 450°C and 520°C complete crystallization occurs. Reflection and transmission measurements in the UV-visible range were then used to extract the optical properties. By adopting the effective medium approximation a single optical model could be constructed that could successfully model material that was in different structural phases, irrespective of metal contamination. Changes in the absorption of the material in various stages of transition were confirmed with a directly measured absorption technique, and the modelled absorption closely followed the same trends

The effect of surface oxidation on hydrogen absorption in Ti-6Al-4V alloy studied by elastic recoil detection (ERD), X-ray diffraction and nanohardness techniques

International audienceThe effect of naturally occurring oxide and oxidised layers formed by ion implantation and thermal oxidation on hydrogen absorption was investigated in Ti-6Al-4V alloy samples as a possible candidate for hydrogen storage. The samples were implanted with two different oxygen fluences (1.5 × 1017 and 3.0 × 1017 ions/cm2) at room temperature and 550 °C, and comparison was made with thermally oxidised samples at a temperature of 550 °C for 2 h. All samples were afterwards hydrogenated at 550 °C for 2 h. The elastic recoil detection analysis show that approx.14 at.% H was absorbed in as-received and thermally oxidised samples. The native oxide layer and the oxidised layer formed by thermal oxidation enhanced the absorption of hydrogen regardless of their different thickness and stoichiometry. The amount of hydrogen, however, was significantly lower in implanted samples, approx. 3–5 at.%, suggesting that oxygen ions implanted in alloy prevent hydrogen absorption. It was found that the average amount of absorbed hydrogen within the projected depth was reduced due to implantation of oxygen ions regardless of their fluences and implantation temperature. The hydrides were not determined in any of investigated samples while the surface hardness of all samples increases after hydrogenation although to different extent

Synthesis of nanocrystalline silicon thin films using the increase of the deposition pressure in the hot-wire chemical vapour deposition technique

Nanostructured thin silicon-based films have been deposited using the hot-wire chemical vapour deposition (HWCVD) technique at the University of the Western Cape. A variety of techniques including optical and infrared spectroscopy, Raman scattering spectroscopy, X-rays diffraction (XRD) and transmission electron microscopy (TEM) have been used for characterisation of the films. The electrical measurements show that the films have good values of photoresponse, and the photocurrent remains stable after several hours of light soaking. This contribution will discuss the characteristics of the hydrogenated nanocrystalline silicon thin films deposited using increased process chamber pressure at a fixed hydrogen dilution ratio in monosilane gas