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Introduction of Graphene
Published in Abhay Kumar Singh, Tien-Chien Jen, Chalcogenide, 2021
Abhay Kumar Singh, Tien-Chien Jen
The physical properties of polycrystalline materials depend on the size and distribution of grains as well as atomic structure of the grain boundaries. Graphene grain boundaries are more significant due to their ability to govern the electronic properties. The introduction of a point defect can lead to the injection of charge into the whole electronic system. Therefore, grain boundaries as lines of reconstructed point defects may have the same impact on a larger scale. Experimentally, it has been confirmed that grain boundaries composed of a pentagon and octagons that may act as conducting metallic wires [101]. Such line defects may raise the localized electronic states in a transverse direction; it may also extend along the line [101]. It can also enhance the conductivity along the line and open up the possibility of the fabrication of all-carbon electronic devices [101]. According to the theoretical description, grain boundaries can impede electronic transport; therefore, all recurrence of the grain boundaries may be divided into two distinct classes [99]. For example, one may have very high transmission probabilities (~ 0.8) of low-energy charge carriers across the grain boundary, while, the other may completely come from the reflection of charge carriers in a rather broad energy range (up to ~1 eV) [99]. The transport characterizations of the isolated individual grain boundary have confirmed their higher electrical resistance. However, the increase of resistance may vary across different grain boundaries [103].
Distance Measures for Quantifying the Differences in Microstructures
Published in Jeffrey P. Simmons, Lawrence F. Drummy, Charles A. Bouman, Marc De Graef, Statistical Methods for Materials Science, 2019
Both grain size and shape largely influence the mechanical properties of polycrystalline materials [1143]. Including size in theoretical models is relatively easy and not uncommon; however, including morphology is much more difficult. This is because of the rather complex and difficult to describe shapes that exist in polycrystalline materials. Determining and quantifying the differences between the morphology of grains in a polycrystalline material is the main goal of this section. Two measures of shape morphology, the affine moment invariant Ω¯3 and the shape quotient Q (see Section 17.2) will be used to generate distributions representing the grain shape in the set of microstructures SIN100.
Diamond Morphology
Published in Mark A. Prelas, Galina Popovici, Louis K. Bigelow, Handbook of Industrial Diamonds and Diamond Films, 2018
The properties of diamond single crystals depend on the crystal orientation, and the defects and impurities incorporated in the crystal. The properties of polycrystalline materials are not only dependent on the orientation, form, structure, impurities and defects of the individual crystals (often referred to as grains or crystallites) but also the material at or between the individual crystal boundaries. Whether the diamond product grown is a single crystal or is polycrystalline, once the material is grown “What you have is what you get” or more to the point “The structures that you can grow are all that you can get.” Heat treatments, mechanical deformation or other ordinary materials processing methods cannot be used in any practical way to significantly alter the bulk structure or properties of the material. This means that if you want to control or engineer the properties of diamond you must control the growth processii
A micropolar continuum model of diffusion creep
Published in Philosophical Magazine, 2021
At high temperatures, solid polycrystalline materials can deform by diffusion creep, where defects within the crystalline lattice move by diffusion. At scales much larger than the grain scale the material behaves as if it were a Newtonian viscous fluid, with an effective shear viscosity which depends on the grain size [1–4]. At the microscale individual grains can be considered as rigid bodies, which interact by the plating out or removal of material at grain boundaries, leading to a macroscale strain. Rigid bodies have both translational (velocity) and rotational (angular velocity) degrees of freedom to describe their motion. However, when a material is treated as a Newtonian viscous fluid at the macroscale, the microscale rotational degrees of freedom are lost, as the classical Cauchy continuum is based on point particles with only translational degrees of freedom.
Investigation of hydrogen effect on phosphorus-doped polysilicon thin films
Published in Surface Engineering, 2020
Meryem Mekhalfa, Beddiaf Zaidi, Bouzid Hadjoudja, Baghdadi Chouial, Allaoua Chibani
Polycrystalline silicon is among the materials that have a very important part in the industry, particularly for the manufacture of electronic components, integrated circuits and solar cells [1–6]. However, this material is characterised by a low photovoltaic efficiency in comparison with mono-crystalline silicon, due to the presence of grain boundaries. These boundaries increase sensibly the series resistance which leads to the decrease of the photovoltaic performances of the devices whose improvement and properties control are required [7–10]. The low efficiency of photovoltaic solar cells based on polycrystalline silicon films is mainly due to the electronic activity of the grain boundaries, because of the high density of recombination centres which lead to the attenuation of the minority carriers collection process. Generally, the polycrystalline silicon thin films contain a large number of grain boundaries which play a dual role as trapping centres of carriers and potential barriers for minority carriers’ passage, thus limiting the photovoltaic efficiency [11]. To improve the electronic quality of these thin films, several operations were used: doping, heat treatments and passivation by hydrogen [12–15]. In this paper, we investigated the effect of hydrogen on phosphorus doped polysilicon thin films.
Local stress analysis of partial dislocation interactions with symmetrical-tilt grain boundaries containing E-structural units
Published in Philosophical Magazine, 2018
Sivasakthya Mohan, Ruizhi Li, Huck Beng Chew
The plastic deformability of a crystalline metal is controlled by the glide of dislocations along preferred slip-systems [1–5]. In a polycrystalline metal, the numerous grain boundaries act as barriers for dislocation slip. As the grain size decreases, the density of grain boundaries increases, which strengthens the metal [6–8]. Studies have shown that the strength of conventional polycrystalline metals follows a Hall–Petch dependence on the inverse square-root of the grain size [9,10]. This relationship is well explained by dislocation pile-up at the grain boundary, where a critical pile-up length of half the grain size is required to generate a critical stress for transmission into the adjacent grain. At finer nanometre grain sizes, however, the material behaviour deviates from the Hall–Petch relationship, since strengthening is now controlled by the interaction of single dislocations with the grain boundary [1,11–16].