Metal-doped semiconductor nanoparticles and methods of synthesis thereof

The present invention generally relates to binary or higher order semiconductor nanoparticles doped with a metallic element, and thermoelectric compositions incorporating such nanoparticles. In one aspect, the present invention provides a thermoelectric composition comprising a plurality of nanoparticles each of which includes an alloy matrix formed of a Group IV element and Group VI element and a metallic dopant distributed within the matrix

Core-shell nanoparticle arrays double the strength of steel

Manipulating structure, defects and composition of a material at the atomic scale for enhancing its physical or mechanical properties is referred to as nanostructuring. Here, by combining advanced microscopy techniques, we unveil how formation of highly regular nano-arrays of nanoparticles doubles the strength of an Fe-based alloy, doped with Ti, Mo, and V, from 500 MPa to 1 GPa, upon prolonged heat treatment. The nanoparticles form at moving heterophase interfaces during cooling from the high-temperature face-centered cubic austenite to the body-centered cubic ferrite phase. We observe MoC and TiC nanoparticles at early precipitation stages as well as core-shell nanoparticles with a Ti-C rich core and a Mo-V rich shell at later precipitation stages. The core-shell structure hampers particle coarsening, enhancing the material's strength. Designing such highly organized metallic core-shell nanoparticle arrays provides a new pathway for developing a wide range of stable nano-architectured engineering metallic alloys with drastically enhanced properties. ?The Author(s) 2017.1116Ysciescopu

Methods for synthesis of semiconductor nanocrystals and thermoelectric compositions

The present invention provides methods for synthesis of IV VI nanostructures, and thermoelectric compositions formed of such structures. In one aspect, the method includes forming a solution of a Group IV reagent, a Group VI reagent and a surfactant. A reducing agent can be added to the solution, and the resultant solution can be maintained at an elevated temperature, e.g., in a range of about 20.degree. C. to about 360.degree. C., for a duration sufficient for generating nanoparticles as binary alloys of the IV VI elements

Bandgap engineering in semiconductor alloy nanomaterials with widely tunable compositions

Over the past decade, tremendous progress has been achieved in the development of nanoscale semiconductor materials with a wide range of bandgaps by alloying different individual semiconductors. These materials include traditional II-VI and III-V semiconductors and their alloys, inorganic and hybrid perovskites, and the newly emerging 2D materials. One important common feature of these materials is that their nanoscale dimensions result in a large tolerance to lattice mismatches within a monolithic structure of varying composition or between the substrate and target material, which enables us to achieve almost arbitrary control of the variation of the alloy composition. As a result, the bandgaps of these alloys can be widely tuned without the detrimental defects that are often unavoidable in bulk materials, which have a much more limited tolerance to lattice mismatches. This class of nanomaterials could have a far-reaching impact on a wide range of photonic applications, including tunable lasers, solid-state lighting, artificial photosynthesis and new solar cells

A general perspective of the characterization and quantification of nanoparticles: Imaging, spectroscopic, and separation techniques

This article gives an overview of the different techniques used to identify, characterize, and quantify engineered nanoparticles (ENPs). The state-of-the-art of the field is summarized, and the different characterization techniques have been grouped according to the information they can provide. In addition, some selected applications are highlighted for each technique. The classification of the techniques has been carried out according to the main physical and chemical properties of the nanoparticles such as morphology, size, polydispersity characteristics, structural information, and elemental composition. Microscopy techniques including optical, electron and X-ray microscopy, and separation techniques with and without hyphenated detection systems are discussed. For each of these groups, a brief description of the techniques, specific features, and concepts, as well as several examples, are described.Junta de Andalucía FQM-5974CEI-Biotic Granada CEI2013- MP-1

Mechanical Characterization of Cryomilled Al Powder Consolidated by High-Frequency Induction Heat Sintering

In the present investigation, an aluminum powder of 99.7% purity with particle size of ~45 µm was cryomilled for 7 hours. The produced powder as characterized by scanning, transmission electron microscopy, and X-ray diffraction gave a particle size of ~1 µm and grain (crystallite) size of 23±6 nm. This powder, after degassing process, was consolidated using high-frequency induction heat sintering (HFIHS) at various temperatures for short periods of time of 1 to 3 minutes. The present sintering conditions resulted in solid compact with nanoscale grain size (<100 nm) and high compact density. The mechanical properties of a sample sintered at 773 K for 3 minutes gave a compressive yield and ultimate strength of 270 and 390 MPa, respectively. The thermal stability of grain size nanostructured compacts is in agreement with the kinetics models based on the thermodynamics effects

Thermal Stability, Microstructures and Mechanical Properties of Nanostructured/Ultrafine Structured Cu-5vol.%Al₂O₃ Nanocomposites Fabricated by High Energy Mechanical Milling and Powder Compact Extrusion

Ultrafine structured metal matrix nanocomposites (MMNCs) have received much attention due to their attractive engineering applications and scientific interest. On the engineering aspect, ultrafine structured MMNCs have a higher room temperature strength and better high temperature performance due to grain boundary strengthening, nanoparticle strengthening and Zener pinning effects compared to their metal matrices. On the scientific aspect, there is the question of whether the linear superposition of basic strengthening mechanisms, which is applicable to conventional precipitation-hardened alloys, is still valid in evaluating the strength of ultrafine structured MMNCs. In general, there might be a synergistic effect among different strengthening mechanisms when the grain sizes of matrices of MMNCs are reduced down to the submicrometer range. In this thesis, a model system of Cu-5vol.%Al₂O₃ was selected to study with the aim of deepening and reinforcing the understanding of the microstructure/property relationship and contributions of various strengthening mechanisms to the overall strength of ultrafine structured MMNCs. Nanostructured Cu-5vol.%Al₂O₃ nanocomposite powder particles were produced by high energy mechanical milling (HEMM) of a powder mixture of Cu powder and Al₂O₃ nanopowder. The nanocomposite powders were then annealed at 300-600°C for up to 5 h. The powders had a high thermal stability at temperatures up to 600°C. After annealing at 600°C for 5 h, Cu nanograins in the microstructure of the nanocomposite powder particles only grew slightly and the microstructure of the Cu matrix of powder particles was still well within the nanostructure range. The activation energy for the grain growth of the Cu nanograins was determined to be 63.4 kJ/mol, which is much lower than that of coarse grained monolithic Cu and similar to that of nanocrystalline monolithic Cu, and suggests the grain growth behavior is controlled by grain boundary diffusion. The impressive thermal stability of the microstructure of the powder particles is mainly associated with the effect of Al₂O₃ nanoparticles on the grain growth through inhibiting the grain boundary diffusion. Ultrafine structured Cu-5vol.%Al₂O₃ nanocomposite samples were synthesized by powder compact extrusion at 750 and 900°C, and their microstructures and tensile properties were characterized. The microstructural characterization showed that there is no significant difference in the mean Cu grain sizes for both samples but the sample extruded at 900°C has far less Al₂O₃ nanoparticles in comparison to the sample extruded at 750°C. The tensile testing results exhibited that the 900°C extruded sample has a larger strength and higher ductility at fracture as compared to those of the 750°C extruded sample. This shows that the dissolution of Al₂O₃ nanoparticles in the Cu matrix takes place when the powder compact is heated and extruded at 900°C, and the dissolution of the Al₂O₃ nanoparticles leads to superior tensile properties of the sample extruded at 900°C. Further ultrafine structured Cu-5vol.%Al₂O₃ nanocomposite samples were prepared by extrusion of powder compacts of nanostructured Cu-5vol.%Al₂O₃ nanocomposite powder at temperatures ranging from 300 to 900°C. The experimental results showed that Cu grains and the sizes and volume fractions of Al₂O₃ nanoparticles of bulk ultrafine structured Cu-5vol.%Al₂O₃ nanocomposite samples increased with the increase of the extrusion temperature. The average sizes of Cu grains and Al₂O₃ nanoparticles and the volume fraction of Al₂O₃ nanoparticles of the extruded samples increased from 132 nm, 43 nm and 0.75% to 263 nm, 100 nm and 4%, respectively, as the extrusion temperature increased from 300 to 900°C. The increases in the sizes and volume fraction of the Al₂O₃ nanoparticles with the increase of the extrusion temperature were caused by the precipitation of Al₂O₃ nanoparticles during extrusion. The samples extruded at 400°C or lower fractured prematurely without yielding, while the samples extruded at T≥500°C fractured after yielding. The yield strengths and ultimate tensile strengths of such materials changed only slightly with the increase of the extrusion temperature and had values in the range 466-517 and 546-564 MPa. However, the tensile ductility of the extruded samples was proportional to the extrusion temperature and increased from 0.76 to 5.82% with increasing the extrusion temperature from 500 to 900°C. The slight decrease of yield strength and significant increase of the ductility of the consolidated sample with increasing extrusion temperature suggests that the level of interparticle atomic bonding in the consolidated samples increases with increased extrusion temperature. It is speculated that the fracture of the samples extruded at T ≤800°C is associated with the weak bonding of residual interparticle boundaries which have not been transformed into grain boundaries. When the extrusion temperature T ≥800°C, the area of the residual interparticle boundaries may be too small to play any major role in causing the fracture of the consolidated sample. Analysis of the contributions of different strengthening mechanisms demonstrates that grain boundary strengthening makes the largest contribution to the strength of the extruded samples relative to the nanoparticle strengthening and strain hardening and experimentally measured yield strength of the extruded samples can be predicted appropriately by the sum of Peierls stress, grain boundary strengthening, nanoparticle strengthening and strain hardening. The effect of annealing on an ultrafine structured Cu-5vol.%Al₂O₃ nanocomposite sample made by powder compact extrusion at 900°C was investigated by annealing for 1h at different temperatures in the range of 500-900°C. This revealed that Al₂O₃ nanoparticles provided excellent thermal stability to the ultrafine structured Cu-5vol.%Al₂O₃ nanocomposite sample. The microstructure and microhardness of the sample remained stable up to annealing at 800°C for 1 h. High resistance of Al₂O₃ nanoparticles to coarsening was responsible for this high thermal stability. The microhardness increase observed for the sample annealed at 700°C for 1 h came from the precipitation of small Al₂O₃ nanoparticles. On the other hand, the sudden drop in microhardness of the sample annealed at 900°C for 1 h was related to the coarsening of small Al₂O₃ nanoparticles and grain growth of the Cu matrix. This thesis concludes with suggestions for future work that would extend on from the findings presented here

Cryomilling as environmentally friendly synthesis route to prepare nanomaterials

The milling of materials at cryogenic temperature has gained importance both in academic as well as the industrial community in the last two decades, primarily because of significant advantages this technique as compared to milling at room temperature; environmental friendly nature, cost-effectiveness, rapid grain refinement, less contamination, and large scale production capability of various nanomaterials. Scientifically, milling at cryo-temperature exhibits several distinct material related phenomena; suppression of recovery and recrystallization, predominant fractures over cold welding, significantly low oxidation, and contamination, leading to rapid grain refinement. Cryomilling has extensively been used to obtain finer scale powder of spices for the preservation of aroma, medicines for effective dissolution, or amorphization. It has been considered an environmentally friendly process as it utilizes benign liquid nitrogen or argon without discharging any toxic entity to the environment, making the process attractive and sustainable. The present review is intended to provide various scientific as well as technological aspects of cryomilling, environmental impact, and future direction