Volume 4, Issue 6 - Special issue: Interfaces in hybrid materials and nanocomposites for nanoscience and nanotechnology / Issue editor: Marie-Hélène Delville

By structuring matter at the nano level using highly versatile nanotechnology approaches and apparatus, multifunctionalities with manifestation of enhanced and/or novel useful properties could be attained. The challenges in nanoengineering are the ability to tune the nano-object characteristics (size, distribution, composition, and surface chemistry) and to have a good control on the possible synergy created at the interfaces, especially in the case of complex multifunctional materials. Surface nanoengineering goes hand in hand with the creation of interfaces between nano-objects – either inorganic or hybrid ones – and a closer look in this direction is essential. The present review aims at presenting the possibilities of surface nanoengineering by versatile approaches, namely supercritical fluids processes. Two main routes of nanostructuration, each containing three concepts, will be discussed: supercritical fluid chemical deposition performed in batch mode and continuous supercritical fluid synthesis. Both approaches can be used to access interesting materials with desired properties, with the choice of process depending on what the readers are pursuing.

Precipitation of nanoparticles from a supersaturated solid solution is important in understanding and controlling the formation of nanostructure, and as a result, many physical properties of materials, such as conductivity, mechanical, thermoelectric, and magnetic behavior of materials. In each case, the precipitation state, including size, density, chemical composition, spatial distribution, particle morphology, and volume fraction, of nanoparticles can all influence the properties of interest. In an effort to design nano/microstructures in steels, mainly for automotive applications, it is important to be able to describe the time evolution of the precipitation state, including both the nucleation and the growth processes. The present review is thus concerned with the homogenous precipitation of carbo-nitride nanoparticles in α-ferrite. The interfacial process, the time evolution of both carbon and nitrogen into precipitates, and the effects of supersaturation and spatial distribution are discussed and clarified. The involved mechanisms are discussed from a theoretical point of view; some major results are illustrated from newly developed experimental methods, and their relevance to topics of current interest is examined. At last, some major outstanding issues have been identified and avenues for further research suggested.

Emergence of two-dimensional (2D) materials with atomic-layer structures, such as graphene and MoS 2 , which have excellent physical properties, provides the opportunity of substituting silicon-based micro/nanoelectronics. An important issue before large-scale applications is the heat dissipation performance of these materials, especially when they are supported on a substrate, as in most scenarios. Thermal transport across the atomic-layer interface is essential to the heat dissipation of 2D materials due to the extremely large contact area with the substrate, when compared with their atomic-scale cross-sections. Therefore, the understanding of the interfacial thermal transport is important, but the characterization is very challenging due to the limitations for temperature/thermal probing of these atomic-layer structures. In this review, widely used characterization techniques for experimental characterization as well as their results are presented. Emphasis is placed on the Raman-based technology for nm and sub-nm temperature differential characterization. Then, we present physical understanding through theoretical analysis and molecular dynamics. A few representative works about the molecular dynamics studies, including our studies on the size effect and rectification phenomenon of the graphene-Si interfaces are presented. Challenges as well as opportunities in the thermal transport study of atomic-layer structures are discussed. Though many works have been reported, there is still much room in both the development of experimental techniques as well as atomic-scale simulations for a clearer understanding of the physical fundamentals of thermal transport across the atomic-layer interfaces, considering the remarkable complexity of physical/chemical conditions at the interface.

This article is a critical review on layered hybrid organic-inorganic functional structures. We specially discuss a series of results concerning the design of magnetic and multiproperty systems derived from hybridization of layered transition metal hydroxides. A series of hybrid materials showing original magnetic properties are reviewed, which were prepared by functionalization of layered simple hydroxides (LSH) of the general formula M 2 (OH) 3 A (M=Co, Cu, Ni, Zn, … and A=NO 3 - , OAc - , alkylcarboxylates, peptides, metal complexes…). To make the point on this vast family of hybrid compounds, we present first the work investigating the mechanism of interaction and the structural factors influencing the magnetic properties of hybrid materials based on LSH. Then, we detail how even more complex anions can be immobilized and grafted into the interlamellar space giving rise to new functionalities. These systems are very good models for understanding the correlations between the structure of hybrid systems and the physical properties brought by the inorganic host and by the molecular moieties grafted onto the inorganic metal network. The interface between the organic and inorganic components, i.e. chemical bonding, charge density, or local pressure, is essential for the control of the properties of multifunctional hybrid systems. Some conclusions are drawn on the future of this approach, useful for developing new two-dimensional functional systems.

The explosive growth of nanotechnology has brought challenging innovations in the synthesis of multifunctional nano-objects able to revolutionize the field of diagnosis and therapy in medicine. Furthermore, one important input of today’s nanotechnology in biology is that their design will also allow real progress to achieve temporal and spatial site local therapy and imaging. Such a breakthrough is made possible by the development of multifunctional biocompatible nanosystems resulting from cutting-edge researches based on pluridisciplinary approaches. Among the challenges are the design of the organic coating and its grafting at the surface of NPs while preserving the properties of both NPs and molecules. The molecules should ensure the colloidal stability of NPs in physiological media, their biocompatibility and biodistribution, and may bear functions to couple bioactive groups. This paper aims at providing challenges in functionalization of iron oxide nanoparticles for biomedical applications.

Magnetic particles of optimized nanoscale dimensions can be utilized as building blocks to generate colloidal nanocrystal assemblies with controlled size, well-defined morphology, and tailored properties. Recent advances in the state-of-the-art surfactant-assisted approaches for the directed aggregation of inorganic nanocrystals into cluster-like entities are discussed, and the synthesis parameters that determine their geometrical arrangement are highlighted. This review pays attention to the enhanced physical properties of iron oxide nanoclusters, while it also points to their emerging collective magnetic response. The current progress in experiment and theory for evaluating the strength and the role of intra- and inter-cluster interactions is analyzed in view of the spatial arrangement of the component nanocrystals. Numerous approaches have been proposed for the critical role of dipole-dipole and exchange interactions in establishing the nature of the nanoclusters’ cooperative magnetic behavior (be it ferromagnetic or spin-glass like). Finally, we point out why the purposeful engineering of the nanoclusters’ magnetic characteristics, including their surface functionality, may facilitate their use in diverse technological sectors ranging from nanomedicine and photonics to catalysis.