ICMCTF2016 Session F1-2: Nanomaterials and Nanofabrication

Despite being one of the best characterized materials known to mankind, silicon continues being actively investigated for a variety of applications. Silicon is abundant, inexpensive and non-toxic. This is a highly desirable combination of properties, especially for application that demand large-scale utilization. This talk will focus on the use of silicon nanostructures for the solution of energy-related issues. We focus on silicon nanoparticles produced via a continuous-flow non-thermal plasma reactor. This technique enables the rapid conversion of the silicon-containing precursor (silane or silicon tetrachloride) into <10 nm nanoparticles with a precise control over their structure (amorphous vs. crystalline). In addition, non-thermal plasmas are well-known to impart a unipolar charge distribution onto particles dispersed within their volume. This allows producing nanoparticles with a narrow size distribution. We take advantage of the properties of plasma-produced nanoparticles for the development of structures tailored towards (a) waste heat recovery and (b) electrochemical energy storage. For waste heat recovery, it is important to develop bulk materials with precise control over their nanostructure (i.e. grain size distribution). We have used hot-pressing to sinter plasma-produced silicon nanocrystals into bulk nanostructured silicon, and we have characterized their electrical and thermal transport properties. The narrow size distribution of the nanoparticles translated into a narrow size distribution of grains after sintering. We have found that the thermoelectric figure of merit ZT reaches a value of 0.3 for samples with grain sizes below 150 nm, and that ZT has a weak dependence over grain size in this regime. We will discuss the implications of these results for the development of silicon-based bulk nanostructured materials, focusing in particular on the competing effects of grain boundary scattering on phonon and charge transport. Small plasma-produced silicon nanoparticles are also ideal for the development of silicon-based anodes for lithium ion batteries. We have developed a simple wet-coating technique which is based on the addition of a polymer to an ink formulation containing silicon nanoparticle. After coating and annealing at 600°C, the polymer decomposition leads to the formation of an amorphous carbon matrix with silicon nanoparticles dispersed within it. This structure achieves a reversible capacity of 1000 mAh/gram, and most notably it shows a stable performance for more than 200 charge-discharge cycles at a rate of 0.1C. Strategies for additional improvements will be discussed.

Recently, there has been a growing interest in materials that can present high-functionalities. The design of coatings for environmental surfaces is a diverse challenge to the engineers and scientist in the manufacturing industry. The environmental surfaces are not only exposed to abrasion and wear caused by daily contact with humans, but also to aggressive cleaning procedures. Developing a surface treatment that can provide sufficient stability and antibacterial properties simultaneously will be beneficial as a value-added process for manufacturing industries. The use of plasma processes to functionalize surfaces is growing at a tremendous rate in all fields of science and technology. Among the different types of plasma, only the non-thermal (e.g., the cold) plasma can be used for surface engineering of heat sensitive polymeric textile substrates to functionalize textiles. In this work, an amorphous carbon thin film has been deposited on a cotton fabric to control the surface texture and chemistry. The potential to use amorphous carbon thin film lies in the fact that the films properties can be tailored by changing the plasma parameters.

The morphological evolutions of surfaces were investigated by low vacuum scanning electron microscopy (LV-SEM) and atomic force microscopy (AFM). Chemical states of surfaces were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy. The wettability of the test surfaces were also measured using static water contact angle (WCA). XPS graphs of samples after plasma treatments revealed that the surfaces were completely covered by amorous carbon, with no presence of nitrogen. The WCA measurements of test fabrics displayed a significant increase in hydrophobicity, with a contact angle of nanocoated cotton samples around 145º. The results clearly show the feasibility of low-temperature plasma deposition process to modify the surface of fabric towards tuning the wetting behavior and antibacterial properties.

In recent eras, the enhancement of mechanical properties of polymeric materials by the addition of different kinds of nanofillers has become an interesting area of research. The resultant composite properties are affected by several factors including the type, size and shape of filler, aspect ratio of filler particles, and dispersion in matrix polymer . There are three methods by which nanofillers are added and dispersed in the polymer matrix. These three methods include: direct mixing of polymer and nanoparticles, in situ polymerization in presence of nanoparticles, and simultaneous in situ polymerization and nanoparticles formation. The current study is based on direct mixing of nanoparticles into polymer matrix

Epoxy resin which is one of the most common polymer matrixes due to its wide applications in various industries such as adhesives, coatings, composite materials and construction, has been considered for improving its properties using reinforcing Nano fillers. The incorporation of relatively low percentages of nanoparticles in epoxy coating system, bring dramatic improvements in mechanical properties, thermal stability and adhesion of epoxy resin.

The purpose of this work is to investigate the effect of inorganic nanoparticles on mechanical, thermal and morphological properties of epoxy/Polyamid coating system, and comparing the obtained results with that of unreinforced coating. The nanocomposite coatings are formulated by incorporation of various types of nanoparticles (ZrO₂, ZnO, SiO₂, and Fe₂O₃) with 2 wt. % loading for each type of nanostructure. Direct incorporation technique has been used for the dispersion of nanostructure into epoxy matrix via high speed mechanical stirring and ultrasonication.

The results revealed that the incorporation of such a small amount of these nanoparticles brings significant changes to mechanical properties, with SiO₂ reinforced sample been superior in both mechanical and thermal properties. Although Fe₂O₃ and ZnO₂ increased the mechanical properties of the coating, in comparison to the unreinforced coating sample; however they reduced the thermal stability and the glass transition temperature (Tg) of the coating. The hardness and elastic modulus increased 71 and 26 % with epoxy/SiO₂ compared to unreinforced epoxy coating. Thermal analysis shows that thermal stability increases with the epoxy/SiO₂ and epoxy/ZrO₂ while it decreases with epoxy/ZnO and epoxy/Fe₂O₃ compositions

Concentric metal-semiconductor solid Zn/ZnO nanospheres and hollow semiconducting ZnO nanoballoons synthesized from metallic solid Zn nanospheres by a unique thermal radiation method. The chemical properties, crystalline structures, and photoluminescence mechanisms for the metallic solid Zn nanospheres, semiconducting hollow ZnO nanoballoons, and metal-semiconductor concentric solid Zn/ZnO nanospheres are presented. We show that metallic solid Zn nanospheres, semiconducting hollow ZnO nanoballoons, and metal-semiconductor concentric solid Zn/ZnO nanospheres has distinct PL emission mechanisms. The PL emissions of the metallic solid Zn nanospheres are mainly dependent on the electron transitions between the Fermi level (E_F) and the 3d band, where as those of the semiconducting hollow ZnO nanoballoons are assigned to the near band edge (NBE) and deep level electron transitions. The PL emissions of the concentric solid metal-semiconductor Zn/ZnO nanospheres are associated to the electron transitions across the metal-semiconductor junction, from the E_Fto the valence and 3d bands, and from the interface states to the valence band. All three nanostructures have good and effective visible-light emissions at room temperature, so they all are potential candidates for use in optoelectronic nanodevices, such as light-emitting diodes (LEDs) and laser diodes (LDs).