Quantum dots (QDs) are small nanometer-sized (<10 nm) pure or composite materials with excellent novel properties, thus making them interesting and emerging candidates for new and exceptional ...applications in biomaterials research fields. As emerging members of QDs, carbon (especially, carbon QDs and graphene QDs) and semiconducting QDs have attracted greater attention owing to their excellent properties, unique size, versatile surface, and biocompatibility with nanotechnology. In this work, a comprehensive overview on the possibilities and achievements in the field of carbon and semiconducting QDs obtained by only microwave (MW)-assisted for biomedical purposes is provided. This specific literature review provides knowledge about MW-assisted synthesis and some selected bioapplication of carbon and semiconducting QDs. Currently, the MW-assisted fabrication of QDs represents a growing research field in nanomaterial research. MW-assisted approach for QD synthesis has been studied in details as this approach has several advantages such as uniform distribution of energy inside the reaction vessel, shorter reaction times, environmentally friendly and energy-saving technique, high reproducibility, and excellent control over experimental parameters. Also, a comprehensive overview is provided in this review, which contains the possibilities and achievements using MW-assisted heating approaches. This article updates the latest synthesis progress as well as applications and also comments all the challenges and perspective in this emerging research area.
•This review article provides knowledge about microwave-assisted synthesis and some selected bio applications.•Microwave-assisted heating is a simple, fast and inexpensive process to produce large quantity of quantum dots.•MW-assisted synthesis approach provides QDs formation in various media.•MW-assisted approach provides uniform distribution of energy, shorter reaction times and high reproducibility.
Defects induced by liquid-phase exfoliation of graphite using sonication were studied. It was shown that localized impact by cavitation shock waves can produce bulk ripplocations and various types of ...dislocations in graphite nanoplatelets. Formation of ripples is more pronounced in large aspect (length/width) ratio platelets or nanobelts. Quasi-periodical ripple systems were observed in many nanobelts after sonication. Mechanism of formation of ripples and dislocations during sonication was proposed. Surprisingly, fast high-temperature processing was found to anneal most of defects. This is consistent with our observations that defects associated with ripplocations are strongly localized and thus can be fast annealed.
Highly aligned CaCu3Ti4O12 nanorod arrays were grown on Si/SiO2/Ti/Pt substrates by radio-frequency sputtering at a low deposition temperature of 300 °C and room temperature. Structural and ...morphological studies have shown that the nanostructures have a polycrystalline nature and are oriented perpendicular to the substrate. The high density of grain boundaries in the nanorods is responsible for the nonlinear current behavior observed in these arrays. The current−voltage (I−V) characteristics observed in nanorods were attributed to the resistive memory phenomenon. The electrical resistance of microcapacitors composed of CaCu3Ti4O12 nanorods could be reversibly switched between two stable resistance states by varying the applied electric field. In order to explain this switching mechanism, a model based on the increase/decrease of electrical conduction controlled by grain boundary polarization has been proposed.
Tin oxide (SnO) powders were obtained by the microwave-assisted hydrothermal synthesis technique using SnCl
2·2H
2O as a precursor. By changing the hydrothermal processing time, temperature, the type ...of mineralizing agent (NaOH, KOH or NH
4OH) and its concentration, SnO crystals having different sizes and morphologies could be achieved. The powders were characterized by X-ray diffraction (X-ray), Field Emission Scanning Electron Microscopy (FE-SEM), High Resolution Transmission Electron Microscopy (HR-TEM) and Selected Area Electron Diffraction (SAED). The results showed that plate-like form is the characteristic morphology of growth and the TEM analyses indicate the growth direction as (200).
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•Method for contacts improvement between carbon nanostructures and metal electrodes.•Gradual increase of the contact area during sample heating by focused laser beam.•Higher ...temperatures achieved for graphene flakes as compared to carbon nanotubes.•Temperatures achieved in the first stage of annealing up to 2000K for graphene flakes.•Areas of metal/graphene contacts increased up to 20times as a result of annealing.
A new approach for electrical and thermal improvement of contacts between carbon nanostructures (multi-wall carbon nanotubes – MWCNTs and multi-layer graphene – MLG) and metal electrodes by localized laser heating is presented. The nanostructures were deposited over electrodes using the dielectrophoresis (DEP) technique. A focused laser beam was used for direct heating the samples in ambient atmosphere. The Raman spectroscopy was used to determine the process temperature by observations of the graphitic G-line downshift. In the laser annealing experiments, the G-line position was found first to downshift linearly with laser power indicating gradual heating of the sample proportional to the absorbed power. However, with increasing power the shift was found to saturate at levels that depend on the metal and the contact area. This saturation was attributed to gradual increase of the contact area and improvement of the thermal contacts between the nanostructures and metal electrode that can occur during sample heating. The maximum sample temperature in the beginning of the annealing process was always higher for MLG samples, due to smaller area of contact established between rigid multi-layer graphene and initially rough metal surface. The final result is the increased heat losses to the electrodes and, subsequently, the reduction of the samples temperature.
The main advantage of this method, when compared with traditional and rapid thermal annealing, is that the thermal treatment is localized in a small pre-determined region, allowing individually controlled annealing process.
We report the design and fabrication of microreactors and sensors based on metal nanoparticle-decorated carbon nanotubes. Titanium adhesion layers and gold films were sputtered onto Si/SiO2 ...substrates for obtaining the electrical contacts. The gold layers were electrochemically thickened until 1 μ m and the electrodes were patterned using photolithography and wet chemical etching. Before the dielectrophoretic deposition of the nanotubes, a gap 1 μ m wide and 5 μ m deep was milled in the middle of the metallic line by focused ion beam, allowing the fabrication of sensors based on suspended nanotubes bridging the electrodes. Subsequently, the sputtering technique was used for decorating the nanotubes with metallic nanoparticles. In order to test the as-obtained sensors, microreactors (100 μ L volume) were machined from a single Kovar piece, being equipped with electrical connections and 1/4′′ Swagelok-compatible gas inlet and outlets for controlling the atmosphere in the testing chamber. The sensors, electrically connected to the contact pins by wire-bonding, were tested in the 10−5 to 10−2 W working power interval using oxygen as target gas. The small chamber volume allowed the measurement of fast characteristic times (response/recovery), with the sensors showing good sensitivity.
The laser ablation method was used for depositing porous nanocrystalline indium–tin oxide thin films for gas sensing applications. Samples were prepared at different pressures using three gases (O
2, ...0.8N
2:0.2O
2, N
2) and heat-treated in the same atmosphere used for the ablation process. X-ray diffraction results show that the films are not oriented and the grain sizes are in the range between 15 and 40 nm. The grains are round shaped for all samples and the porosity of the films increases with the deposition pressure. The degree of sintering after heat treatment increases for lower oxygen concentrations, generating fractures on the surface of the samples. Film thicknesses are in the range of 1 μm for all gases as determined from scanning electron microscopy cross-sections. Electrical resistance varies between 36.3 Ω for the film made at 10 Pa pressure in N
2 until 9.35
×
10
7 Ω for the film made at 100 Pa in O
2.
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