Industrial-Scale Production of High-Quality Graphene Sheets by Millstone Grinders

Graphene exhibits a variety of unprecedented innate properties and has sparked great interest in both fundamental science and regarding prospective commercial applications. To meet the ever-increasing demand for high-quality graphene sheets, an industrial-scale, reliable, environmental-friendly, low-cost production process is required. However, large-scale production high quality graphene remains elusive. Here we demonstrate a scalable mechanical cleavage method for large-quantity production of high quality large-area and few-layer graphene sheets by introducing a millstone grinding process. The average thickness of the graphene sheets is around 5 nm. This procedure is simpler than the state-of-the-art methods that allows for scalable preparation of graphene dispersion in hundreds of litres by mechanical cleavage of graphite, and the yield is 30-40%. The size of the prepared graphene sheets can be tuneable from few micrometres to tens of micrometres by varying the dimension of raw graphite, which is larger than that produced by the state-of-the-art methods. Moreover, comparing to conductive agents, the conductivity of wafers containing graphene can be increased by one order of magnitude, suggesting a high potential of the prepared graphene sheets for the application as conductive agent in lithium battery cathodes. This allows the requirements of different sizes graphene sheets for industry applications in different fields.

Recent Advances and the Prospect of Graphene-Based Dye Sensitize Solar Cell and their Application on a Different Electrode: A critical review

: The investigation of a dye-sensitized solar cell (DSSC) as a potential alternative material to conventional silicon-based solar cells has attracted remarkable attention. These stances on graphene established optical properties (excellent transparency, conductance in near-infrared and visible light spectrums) and thermochemical stability as reported in the literature. However, graphene synthesis methods suitable for industrial-scale production and their practical application are still the concerns of the researcher in the related field. The single, few, and adhesive layer mechanical cleavage graphene methods are not yet pragmatic, as these methods will restrict the chance for scaling up. These limitations and inadequate reviews of graphene developments impelled us to compile the advances in graphene synthesis, properties, recent applications, and future directions. The mechanical exfoliation synthesis technique reported delivering quality graphene films sized from about 5 to 10 Graphene-TiO2 hybridization found to possess efficiency acclivity as high as 39%. This work provides graphene advances and limitations that can guide researchers in photovoltaic or optical modulation devices.

Laser Processing of Transparent Wafers with a AlGaN/GaN Heterostructures and High-Electron Mobility Devices on a Backside

Sapphire and silicon carbide substrates are used for growth of the III-N group heterostructures to obtain the electronic devices for high power and high frequency applications. Laser micromachining of deep channels in the frontside of the transparent wafers followed by mechanical cleavage along the ablated trench is a useful method for partitioning of such substrates after the development of the electronics on a backside. However, in some cases damage to the component performance occurs. Therefore, the influence of various parameters of the laser processing, such as fluence in the spot size, substrate thickness, orientation, and the polarization of focused laser beam, to the formation of damage zones at both sides of the transparent substrate with thin coatings when ablating the trenches from one side was investigated. The vicinity effect of the ablated trenches on the performance of the electronics was also evaluated, confirming the laser micromachining suitability for the dicing of transparent wafers with high accuracy and flexibility.

Robust quantum point contact operation of narrow graphene constrictions patterned by AFM cleavage lithography

Detecting conductance quantization in graphene nanostructures turned out more challenging than expected. The observation of well-defined conductance plateaus through graphene nanoconstrictions so far has only been accessible in the highest quality suspended or h-BN encapsulated devices. However, reaching low conductance quanta in zero magnetic field, is a delicate task even with such ultra-high mobility devices. Here, we demonstrate a simple AFM-based nanopatterning technique for defining graphene constrictions with high precision (down to 10 nm width) and reduced edge-roughness (+/−1 nm). The patterning process is based on the in-plane mechanical cleavage of graphene by the AFM tip, along its high symmetry crystallographic directions. As-defined, narrow graphene constrictions with improved edge quality enable an unprecedentedly robust QPC operation, allowing the observation of conductance quantization even on standard SiO2/Si substrates, down to low conductance quanta. Conductance plateaus, were observed at n × e2/h, evenly spaced by 2 × e2/h (corresponding to n = 3, 5, 7, 9, 11) in the absence of an external magnetic field, while spaced by e2/h (n = 1, 2, 3, 4, 5, 6) in 8 T magnetic field.

Layer-engineered large-area exfoliation of graphene

The competition between quality and productivity has been a major issue for large-scale applications of two-dimensional materials (2DMs). Until now, the top-down mechanical cleavage method has guaranteed pure perfect 2DMs, but it has been considered a poor option in terms of manufacturing. Here, we present a layer-engineered exfoliation technique for graphene that not only allows us to obtain large-size graphene, up to a millimeter size, but also allows selective thickness control. A thin metal film evaporated on graphite induces tensile stress such that spalling occurs, resulting in exfoliation of graphene, where the number of exfoliated layers is adjusted by using different metal films. Detailed spectroscopy and electron transport measurement analysis greatly support our proposed spalling mechanism and fine quality of exfoliated graphene. Our layer-engineered exfoliation technique can pave the way for the development of a manufacturing-scale process for graphene and other 2DMs in electronics and optoelectronics.

Features of realization of process of peeling of a nut shell between a plate and a spherical insert

The profitability of walnut cultivation and processing was investigated in the paper, both on small farms and large agricultural enterprises. The demand for walnuts in Ukraine and abroad was investigated. Theoretical studies of the dynamics of nut crop growth in the territory of our country were conducted. The tendency to increase domestic production of walnuts in the future is established. Among the most important areas of the organization of the process of purification of this raw material is noted the process of chopping (crushing) of its shell. Applying a constructive implementation of a vibrating machine «GMK-350» for the process of mechanical cleavage of the shell of a walnut were carried out studies of the influence of the working body (plate and spherical insert) on the technological and energy parameters of the process taking into account the quality of the processed product (the integrity of the core). The article analyzes the process of shelling of walnuts between the plate and the spherical insert. Graphical correlations between the size of the shell deformation and the dynamics of change of the driving force of change at different nut humidity and shell thickness are analyzed. The scheme of driving forces in the area of contact between the nut and the ring is drawn up and analyzed. The graphical dependences of the maximum crushing force on the bevel of the rings according to different shell thickness are presented; variations of the maximum crushing force depending on the humidity of the nuts for different thicknesses of the nut shell. It is established that, theoretically, the coefficient of friction increases as the angle of inclination of the ring increases. It is established that the crushing force of a walnut shell depends less on the friction coefficient and more on the contact surface.

Computational exploration of two-dimensional silicon diarsenide and germanium arsenide for photovoltaic applications

The properties of bulk compounds required to be suitable for photovoltaic applications, such as excellent visible light absorption, favorable exciton formation, and charge separation are equally essential for two-dimensional (2D) materials. Here, we systematically study 2D group IV–V compounds such as SiAs2 and GeAs2 with regard to their structural, electronic and optical properties using density functional theory (DFT), hybrid functional and Bethe–Salpeter equation (BSE) approaches. We find that the exfoliation of single-layer SiAs2 and GeAs2 is highly feasible and in principle could be carried out experimentally by mechanical cleavage due to the dynamic stability of the compounds, which is inferred by analyzing their vibrational normal mode. SiAs2 and GeAs2 monolayers possess a bandgap of 1.91 and 1.64 eV, respectively, which is excellent for sunlight harvesting, while the exciton binding energy is found to be 0.25 and 0.14 eV, respectively. Furthermore, band-gap tuning is also possible by application of tensile strain. Our results highlight a new family of 2D materials with great potential for solar cell applications.