Volume 7, Issue 5

A numerical model is suggested and validated for simulating frictional forces between two samples. The model employs knowledge of surface topographies and values of surface properties provided in the relevant literature and can be applied to contact between complex surfaces. It employs the Lennard-Jones molecular force theory and applies it to a surface segmented into cuboids, which represent separate springs in a Winkler layer. In order to model a contact of two rough surfaces, their asperities are merged into one surface that is put into contact with a perfectly flat surface. Validation, done by atomic force microscopy (AFM), shows that the model can be applied for contacts of rigid samples in the elastic regime of forces.

Thermal silver plating method by means of nanosilver-based paint could be an alternative to electrochemical processes. Electrochemical silver layering on aluminium is typically achieved with an intermediate layer, which provides very good adhesion of the layer to the aluminium surface but increases the resistance of the whole junction system. In the method of silver plating promoted by the authors, the intermediate layer is eliminated. The layer of silver paint was applied directly on the aluminium surface by spraying using aerograph. Procured silver layers, according to ISO 2409, prove proper adhesion to aluminium. The value of contact resistance with a pressure of 300 N cm −2 and current load of 200 A is 0.03 μΩ mm −2 , which is comparable to the contact resistance of layers generated by electrochemical means. This new method decreases the level of toxic waste emission and therefore is less harmful for the natural environment. It is also cheaper and simpler than the electrochemical process. An additional advantage is the possibility of silver plating of the chosen surfaces with various shapes.

If we wish to integrate modern science such as nanotechnology into the school science curriculum, we need to find the natural insertion point of modern science with the science, technology, engineering and math curriculum. However, integrating nanoscale science and technology (NST) essential concepts into the middle school science curriculum is challenging. The current study was designed to identify the insertion points of the eight NST essential concepts in the middle school science and technology curriculum. Middle school science and technology teachers underwent a course that included all eight NST essential concepts, aiming to help them understand the NST essential concepts in depth. Then, they were asked to identify a natural insertion point in the existing science and technology curriculum for each of the NST essential concepts. To support research validation, two different groups of teachers participated in two sequential stages of the study (the identification stage and the validation stage). The teachers in the identification stage identified the insertion points of all eight NST essential concepts in the subjects of the science and technology curriculum, which reflects the relevance of the NST concepts from the teachers’ perspective in terms of pedagogical level. The majority of the identified insertion points were validated in the second stage. Forty-two insertion points of the NST essential concepts were suggested to be integrated in middle school science and technology curriculum. All the insertion points that were suggested in the identification stage were confirmed in the validation stage. Another 11 new insertion points were added at the validation stage. The connections to the different scientific subjects in the curriculum are as follows: 19 insertion points were suggested by the teachers in the chemistry part of the chemistry curriculum, 12 in the life science, four in the physics-energy, and seven in technology-systems and products. The results present the opportunity to expose middle school students to contemporary science using the existing science and technology curriculum. The study serves as an example of integrating NST concepts into a middle school science curriculum in Israel, but it can be applied in other science curricula worldwide, taking into consideration the topics included in each curriculum.

Photodetectors (PDs) have great potential in applications of imaging, telecommunication, and biological sensing. In this article, state-of-the-art achievements on typical low-dimensional nanostructured PDs and hybrid PDs are reviewed. In the 2D nanostructured PDs part, 2D transition metal dichalcogenides have a natural gap, which promise high sensitivity of photodetection. Graphene and black phosphorus can also stand for 2D nanostructured PDs due to their broadband absorption and tunable direct bandgap, respectively. In the 1D nanostructured PDs part, owing to its high photoconductive characteristic, ZnO nanowire film is a promising material for ultraviolet PDs. Carbon nanotubes show potential in infrared (IR) detection due to its unique physical properties. In the 0D nanostructured PDs part, lead sulfide has a small bandgap and large Bohr exciton radius, which collectively give it a wide spectral tunability in the IR. In the hybrid PDs part, electrical and chemical doping is applied to combine different nanomaterials to realize PDs with high performance. In each part, the present situation and major challenges are overviewed. Then, the evolutions of the methods to overcome these challenges and the tremendous research breakthroughs are demonstrated. At last, future directions that could improve the performance of PDs are discussed.

The semi-conducting material zinc is one of the essential trace elements for humans, is a co-factor of more than 300 enzymes, and plays an important role in maintaining vital cellular functions. Deficiency of zinc may lead to cancer initiation; however, a high concentration also has toxic effects that might be life threatening. The toxicity can be addressed by the disequilibrium of zinc-mediated proteins and oxidative stress that produce nascent oxygen, hydroxyl radicals, and other reactive oxygen species. Zinc-based nanoparticles (NPs) are among the most important and multifunctional compounds. Zinc oxide (ZnO) NPs exhibit attractive antimicrobial and photocatalytic properties due to the smaller particle size and increased particle surface reactivity. Further, these are more biocompatible compared to other metallic NPs, easily synthesizable, and have high selectivity, enhanced cytotoxicity, and are a promising anticancer agent. However, some of the pertinent concerns regarding nano-zinc still needs to be clarified. Current research also demonstrates their usage in wastewater treatment, textile, medicine, etc. This review covers the importance of zinc for living systems and its NPs, with more emphasis on ZnO NPs. A comprehensive overview of ZnO NPs, their synthesis, characterization techniques, crystal structure, properties, and brief industrial applications are presented.

As memristor-simulating synaptic devices have become available in recent years, the optimization on non-linearity degree (NL, related to adjacent conductance values) is unignorable in the promotion of the learning accuracy of systems. Importantly, based on the theoretical support of the Mott theory and the three partial differential equations, and the model of conductive filaments (CFs), we analyzed and summarized the optimization schemes on the physical structure and the extra stimulus signal from the internal factor and external influence, two aspects, respectively. It is worth noting that we divided the extra stimulus signals into two categories, the combined pulse signal and the feedback pulse signal. The former has an internal logical optimized phenomenon, and the composition of only two parts in each cycle leads to a simple peripheral circuit. The latter can obtain an almost linear NL curve in software stimulation because of its feature in real-time adjustment of signals, but it is complex in hardware implementation. In consideration of space and energy consumption, achieving memristor with different resistive switching (RS) layers can be another optimization scheme. Special attention should be paid to the weaker NL, which could improve learning accuracy at the system level only when the value of other non-ideal properties such as the on/off ratio is within a certain range.