Mass-Based Environmental Factor and Energy Assessment of Microwave-Assisted Synthesized Transition Metal Nanostructures

This paper describes mass-based energy phase-space projection of microwave-assisted synthesis of transition metals (zinc oxide, palladium, silver, platinum, and gold) nanostructures. The projection uses process energy budget (measured in kJ) on the horizontal axes and process density (measured in kJg−1) on the vertical axes. These two axes allow both mass usage efficiency (Environmental-Factor) and energy efficiency to be evaluated for a range of microwave applicator and metal synthesis. The metrics are allied to the: second, sixth and eleventh principle of the twelve principle of Green Chemistry. This analytical approach to microwave synthesis (widely considered as a useful Green Chemistry energy source) allows a quantified dynamic environmental quotient to be given to renewable plant-based biomass associated with the reduction of the metal precursors. Thus allowing a degree of quantification of claimed “eco-friendly” and “sustainable” synthesis with regard to waste production and energy usage.

Green Chemistry Allometry Test of Microwave-Assisted Synthesis of Transition Metal Nanostructures

Microwave irradiation is considered an important approach to Green Chemistry, because of its ability to rapidly increase the internal temperature of polar-organic compounds that lead to synthesis times of minutes rather than hours when compared to conventional thermal heating. This works describes a dual allometry test for the discrimination between the solvents and reagents used in the microwave-assisted synthesis of transition metal (zinc oxide, palladium silver, platinum, and gold) nanostructures. The test is performed in log-log process energy phase-space projection, where the synthesis data (kJ against kJ·mol-1) has a power-law signature. The test is shown to discriminate between recommended Green Chemistry, problematic Green Chemistry, and Green Chemistry hazardous solvents. Typically, recommended Green chemistry exhibits a broad y-axes distribution within an upper exponent = 1 and lower exponent = 0.5. Problematic Green Chemistry exhibits a y-axes narrower distribution with an upper exponent = 0.94 and lower exponent = 0.64. Non-Green Chemistry hazardous data exhibits a further narrowing of the y-axes distribution within upper exponent = 0.87 and lower exponent = 0.66. In all three cases, the y-axes is aligned to original database power-law signature. It is also shown that in the x-axes direction (process energy budget) the grouped order of magnitude decreases from four orders for recommended Green Chemistry solvent and reagent data, through two orders for non-Green Chemistry hazardous material and down to one order for problematic Green Chemistry.

Intrinsic luminescence from metal nanostructures and its applications

Intrinsic luminescence from metal nanostructures complements conventional scattering and absorption behaviors and has many interesting and unique features. This phenomenon has attracted considerable research attention in recent years because of its various potential applications. In this review, we discuss recent advances in this field, summarize potential applications for this type of luminescence, and compare theoretical models to describe the phenomena. On the basis of the excitation process, the characteristic features and corresponding applications are summarized briefly in three parts, namely, continuous-wave light, pulsed laser, and electron excitation. A universal physical mechanism likely operates in all these emission processes regardless of differences in the excitation processes; however, there remains some debate surrounding the details of the theoretical model. Further insight into these luminescence phenomena will not only provide a deeper fundamental understanding of plasmonic nanostructures but will also advance and extend their applications.

A Review on Metal Nanostructures: Preparation Methods and Their Potential Applications

Metal nanostructures have been of great research interest in recent years due to their physicochemical, plasmonic properties and potential applications. A lot of work has been done on the controlled synthesis of metal nanostructures for various applications. In this review, we try to focus on recent developments in synthesis and applications of metal nanostructures. Firstly, we summarized different preparation methods and then briefly explained their potential applications.

Chiral metal nanostructures:synthesis,properties and applications

Chirality,the property that an object cannot coincide with its mirror image arising from lack of mirror symmetry,is ubiquitous in nature at various length scales.The physical and chemical properties are strongly related to the nature of chiral complexes,playing a significant role in various fields such as photonics,biochemistry,medicine and catalysis.In particular,the recent flexible design of chiral metal nanostructures offers one platform for deeply understanding the origin of chirality and one roadmap for the precise construction of chiral nanomaterials directed by the applications.Herein,we summarize the different geometries and classical synthetic approaches to chiral noble metal nanomaterials.Moreover,chiroptical properties and potential applications of chiral metal nanostructures are discussed as well.Finally,the opportunities and challenges toward the synthesis and application of chiral metal nanostructures are proposed.

Photothermal ablation therapy for cancer based on metal nanostructures

Besides conventional surgery, radiation therapy, and chemotherapy, which all tend to have side-effects and damage normal tissues, new medical strategies, such as photothermal sensitization and photo-thermal ablation therapy (PTA) with near-IR laser light, have been explored for treating cancer. Much of the current excitement surrounding nanoscience is directly connected to the promise of new nanotechnology for cancer diagnosis and therapy. The basic principle behind PTA is that heat generated from light can be used to destroy cancer cells. Strong optical absorption and high efficiency of photothermal conversion at the cancer sites are critical to the success of PTA. Because of their unique optical properties, e.g., strong surface plasmon resonance (SPR) absorption, noble metal nanomaterials, such as gold and silver, have been found to significantly enhance photothermal conversion for PTA applications. Substantial effort has been made to develop metal nanostructures with optimal structural and photothermal properties. Ideal metal nanostructures should have strong and tunable SPR, be easy to deliver, have low toxicity, and be convenient for bioconjugation for actively targeting specific cancer cells. This review would highlight some gold nanostructures with various shapes and properties, including nanoparticles (NPs), nanorods (NRs), nanoshells, nanocages, and hollow nanospheres, which have been studied for PTA applications. Among these structures, hollow gold nanospheres (HGNs) exhibit arguably the best combined properties because of their small size (30―50 nm), spherical shape, and strong, narrow, and tunable SPR absorption.

Rational Design of Plasmonic Metal Nanostructures for Solar Energy Conversion

Plasmonic metal nanostructures,possessing unique surface plasmon resonance properties,show excellent capabilities for light trapping and coupling.On this basis,various plasmonic metal nanostructures offer extraordinary opportunities to promote the conversion efficiency of solar energy to electric energy,hydrogen energy or thermal energy,and so on.In this review article,we highlight a number of recent research achievements on the rational design of plasmonic metal nanostructures so as to maximize the utilization of the entire solar spectrum.Compared with single metal nanoparticles,multiplex(such as multicompositions,sizes,or shapes)nanoparticle structures emphasize advantages in broadening the absorption range and improving light-utilization efficiency.This review concludes with discussions regarding challenges in this research field and proposals of prospects for future directions.

Friction and Wear Behaviors of Nanostructured Metals

Nanostructured （ns） materials, i.e., polycrystalline materials with grain sizes in the nanometer regime （typically below 100 nm）, have drawn considerable attention in the past decades due to their unique properties such as high strength and hardness. Wear resistance of ns materials, one of the most important properties for engineering materials, has been extensively investigated in the past decades. Obvious differences have been identified in friction and wear behaviors Between the ns materials and their corresponding coarse-grained （cg） counterparts, consistently correlating with their unique structure characteristics and mechanical properties. On the other hand, the superior tribological properties of ns materials illustrate their potential applications under contact loads. The present overview will summarize the important progresses achieved on friction and wear behaviors of ns metallic materials, including ultrafine-grained （ufg） materials in recent years. Tribological properties and effects on friction and wear behaviors of ns materials will be discussed under different wear conditions including abrasive wear, sliding wear, and fretting wear. Their correlations with mechanical properties will be analyzed. Perspectives on development of this field will be highlighted as well.

2D and 3D orientation mapping in nanostructured metals: A review

Nanostructured metals possess various excellent properties and offer the potential for a wide range of applications.Improvements in the properties and performance of nanostructured metal components motivate a complete characterization of the microstructures and crystallographic orientations of nanostructured metals with nanoscale spatial resolution.Two well developed orientation mapping techniques for such characterization are electron backscatter diffraction(EBSD)in the scanning electron microscope and precession electron diffraction(PED)using diffraction spots in the transmission electron microscope.However,these methods can only characterize the structure in two dimensions.It is still a great challenge to characterize grains in three dimensions,i.e.from the interior of the nanostructured metals.Recently,three-dimensional orientation mapping in the transmission electron microscope(3 D-OMi TEM)was developed and further improvements of this technique are introduced in this paper.Utilization of these orientation mapping techniques for structural and orientational characterizations are demonstrated by examples of surface-deformed metals with gradient nanostructures,and a sputtered gold film of nano-islands containing nanograins.The merits and challenges of each of these techniques are discussed and suggestions for further developments are proposed.

Partial electrical potential distribution around nanospheres in metallic nanostructured films

In light of the nanostructured surface model, where half-spherical nanoparticles grow out symmetrically from a plane metallic film, the mathematical model for the partial electrical potential around nanospheres is developed when a uniform external electric field is applied. On the basis of these models, the three-dimensional spatial distribution of the partial electrical potential is obtained and given in the form of a curved surface using a numerical computation method. Our results show that the electrical potential distribution around the nanospheres exhibits an obvious geometrical symmetry. These results could serve as a reference for investigating many abnormal phenomena such as abnormal infrared effects, which are found when CO molecules are adsorbed on the surface of nanostructured transition metals.

Achieving high strength and high ductility in nanostructured metals: Experiment and modelling

Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Kowloon, Hong Kong, Chinagrains to a^1-martensite nanograins with bimodal grain size distribution for lower strain rates to nanotwins in the ultrafine/coarse grained austenite phase for higher strain rates. Meanwhile, we will further address the mechanism-based plastic models to describe the yield strength, strain hardening and ductility in nanostructured metals with bimodal grain size distribution and nanotwinned polycrystalline metals. The proposed theoretical models can comprehensively describe the plastic deformation in these two kinds of nanostructured metals and excellent agreement is achieved between the numerical and experimental results. These models can be utilized to optimize the strength and ductility in nanostructured metals by controlling the size and distribution of nanostructures.

Structural and Optical Properties and Emerging Applications of Metal Nanomaterials

Nanomaterials possess intriguing optical properties that depend sensitively on size, shape, and material content of the structures. Controlling such structural characteristics of the nanostructures allows the tailoring of their physical and chemical properties, e.g. optical, electronic, and catalytic, to achieve what is desired lot specific applications of interest. This review will cover the development of various shapes for silver and gold nanomaterials with emphasis on their relation to optical properties. Examples of various modern synthetic methods and characterization techniques are highlighted. The influence of the metal nanomaterial＇s shape and optical absorption on surface enhanced Raman scattering （SERS） and a final note on new emerging applications of metal nanostructures are also discussed.

Local electric field and configuration of CO molecules adsorbed on a nanostructured surface with nanocones

Based on the nanostructured surface model that the （platinum, Pt） nanocones grow out symmetrically from a plane substrate, the local electric field near the conical nanoparticle surface is computed and discussed. On the basis of these results, the adsorbed CO molecules are modelled as dipoles, and three kinds of interactions, i.e. interactions between dipoles and local electric field, between dipoles and dipoles, as well as between dipoles and nanostructured substrate, are taken into account. The spatial configuration of CO molecules adsorbed on the nanocone surface is then given by Monte-Carlo simulation. Our results show that the CO molecules adsorbed on the nanocone surface cause local agglomeration under the action of an external electric field, and this agglomeration becomes more compact with decreasing conical angle, which results in a stronger interaction among molecules. These results serve as a basis for explaining abnormal phenomena such as the abnormal infrared effect （AIRE）, which was found when CO molecules were adsorbed on the nanostructured transition-metal surface.

Analysis of phase shift of surface plasmon polaritons at metallic subwavelength hole arrays

We present the transmission spectra of light transmitting a metallic thin film perforated with differently shaped sub- wavelength hole arrays, which are calculated by a plane-wave-based transfer matrix method. We analyze the transmission peak positions and the phase-shift angles of different surface plasmon polariton （SPP） modes by using the microscopic theoretical model proposed by Haitao Liu and Philippe Lalanne [Liu Haitao, and Lalanne Philippe 2008 Nature 452 728], in which the phase shift properties of the SPPs scattered by the subwavelength hole arrays are considered. The results show that the transmission peak position and the minus phase shift angle of the SPP increase as the hole size increases. On the other hand, the effective dielectric constant of the metallic film can be deduced by the microscopic theoretical model.

Current Progress of Mechanical Properties of Metals with Nano-scale Twins

Focus on face-centered cubic （fcc） metals with nano-scale twins lamellar structure, this paper presents a brief overview of the recent progress made in improving mechanical properties, including strength, ductility, work hardening, strain rate sensitivities, and in mechanistically understanding the underling deformation mechanisms. Significant developments have been achieved in nano-twinned fcc metals with a combination of high strength and considerable ductility at the same time, enhanced work hardening ability and enhanced rate sensitivity. The findings elucidate the role of interactions between dislocations and twin boundaries （TBs） and their contribution to the origin of outstanding properties. The computer simulation analysis accounts for high plastic anisotropy and rate sensitivity anisotropy by treating TBs as internal interfaces and allowing special slip geometry arrangements that involve soft and hard modes of deformation. Parallel to the novel mechanical behaviors of the nano-twinned materials, the investigation and developments of nanocrystalline materials are also discussed in this overview for comparing the contribution of grain boundaries/TBs and grain size/twin lamellar spacing to the properties. The recent advances in the experimental and computational studies of plastic deformation of the fcc metals with nano-scale twin lamellar structures provide insights into the possible means of optimizing comprehensive mechanical properties through interfacial engineering.

Local field distribution and configuration of CO molecules adsorbed on the nanostructure platinum surface

This paper shows that the local electric field distribution near the nanostructure metallic surface is obtained by solving the Laplace equation, and furthermore, the configuration of CO molecules adsorbed on a Pt nanoparticle surface is obtained by using Monte Carlo simulation. It is found that the uneven local electric field distribution induced by the nanostructure surface can influence the configuration of carbon monoxide （CO） molecules by a force, which drags the adsorbates to the poles of the nanoparticles. This result, together with our results obtained before, may explain the experimental results that the nanostructure metallic surface can lead to abnormal phenomena such as anti-absorption infrared effects.

Electric potential distribution near nanocone arrays on metal substrates

Based on the nanostructured surface model,where conical nanoparticle arrays grow out symmetrically from a plane metal substrate,a theoretical model of the local electric potential near nanocones is built when a uniform external electric field is applied.In terms of this model,the electric potential distribution near the nanocone arrays is obtained and given by a curved surface using a numerical computation method.The computational results show that the electric potential distribution near the nanocone arrays exhibit an obvious geometrical symmetry.These results could serve as a basis for explaining many abnormal phenomena,such as the abnormal infrared effects（AIREs） which are found on nanostructured metal surfaces,as well as a reference for investigating the applications of nanomaterials,such as nanoelectrodes and nanosensors.

Recent process of plasma effect in organic solar cells

Due to the compromise between exciton diffusion length and light absorption, the active layer thickness of organic solar cells(OSCs) is limited. As we all know, embedding metal nanostructures into OSCs can improve the performance of OSCs by triggering surface plasma resonance, scattering, and other effect without increasing the physical thickness of light trapping layer. Besides, the plasma response and other roles will distinguish when metal nanostructures are embedded into different position of OSCs, which are equally important to the performance of OSCs. In this paper, the enhancement mechanisms of various metal nanostructures in different layers of OSCs are summarized from the electricity and optics aspects.This review also further highlights the progress of plasma effect and their working mechanism in OSCs,and it is expected to provide more perspective of plasma effect for performance enhancement of OSCs.

Recent Progress of Electrode Materials for Flexible Perovskite Solar Cells

Flexible perovskite solar cells(FPSCs) have attracted enormous interest in wearable and portable electronics due to their high power-per-weight and low cost. Flexible and efficient perovskite solar cells require the development of flexible electrodes compatible with the optoelectronic properties of perovskite. In this review, the recent progress of flexible electrodes used in FPSCs is comprehensively reviewed. The major features of flexible transparent electrodes, including transparent conductive oxides, conductive polymer, carbon nanomaterials and nanostructured metallic materials are systematically compared. And the corresponding modification strategies and device performance are summarized. Moreover, flexible opaque electrodes including metal films, opaque carbon materials and metal foils are critically assessed. Finally, the development directions and difficulties of flexible electrodes are given.

Morphology and electric potential-induced mechanical behavior of metallic porous nanostructures

Understanding mechanical behaviors influenced by electric potential and tribological contacts is important for verifying the robustness and reliability of applications based on metallic porous nanostructures in electrical stimulations.In this work,nickel-based metallic porous nanostructures were studied to characterize their mechanical properties and morphologically dependent contact areas during application of an electric potential using a nanoindenter.W e observed that the indentation moduli of nickel-based metallic porous nanostructures were altered by pore size and application of electric potential.In addition,the structural aspects of the surface morphology of nickel-based porous nanostructures had a critical effect on the determination of contact area.W e suggest that the relation between electric potential and the mechanical behaviors of metallic porous nanostructures can be crucial for building mechanically robust functional devices,which are influenced by electric potential.The morphological shape characteristics of metallic porous nanostructures can be alternative decisive factors for manipulation of tribological performance through regulation of contact area.