Abstract: Nanosciences and nanotechnology (NST) constitute currently a major research field all over the world. NST deal with the study of phenomena and manipulation of materials at atomic, molecular and macromolecular scales, where properties differ significantly from those at the larger scale. The properties of materials can be different at the nanoscale for two main reasons : size and quantum effects. Effects negligible at the macroscopic level become important at the nanometer scale, and vice versa. Scaling laws are described in order to understand some differences. Moreover, geometric arguments are necessary to understand the origin of some physical and chemical properties of nanosystems. On the other hand, quantum effects can begin to dominate the behaviour of matter at the nanoscale – particularly at the lower end – affecting the optical, electrical and magnetic behaviour of materials. The characteristic dimensions for which the properties change from the “macro-“ to the “nano-“ regimes are discussed.
Abstract: Shrinking the size of a solid down to nanometer scale is indeed fascinating, which makes all the otherwise constant physical quantities to be tunable such as the Young’s modulus, dielectric constant, melting point, etc. The variation of size also generates novel properties that can hardly be seen in the bulk such as the conductor-insulator and nonmagnetic-magnetic transition of noble metals at the nanoscale. Although the physics of materials at the nanoscale has been extensively investigated, the laws governing the energetic and dynamic behavior of electrons at such a scale and their consequences on the tunable physical properties of nanostructures have not been well understood [C. Q. Sun, Prog Solid State Chem 35, 1-159 (2007); Prog Mater Sci 54, 179-307 (2009)]. The objective of the contribution is to update the recent progress in dealing with the coordination-resolved energetic and dynamic behavior of bonds in the low-dimensional systems with consideration of the joint effect of temperature and pressure. It is shown that the broken-bond-induced local strain and the associated charge and energy quantum trapping at the defect sites perturbs the atomic cohesive energy, electroaffinity, the Hamiltonian and the associated properties of entities ranging from point defects, surfaces, nanocavities and nanostructures. Application of the theories to observations has led to consistent understanding of the behavior of nanometer-sized materials and the interdependence of these entities as well as the means of determining the bond energy through the temperature-dependent measurements.
Abstract: Nanoparticle research disciplines—chemical synthesis, applied physics and devices based on their physical-chemical properties, and computational physics—have been very active fields for the last 15 years or so, because of the potential and current applications in medicine, catalysis, energy storage, environment and electronics applications. This wide spectrum of disciplines and their applications keep metallic nanoparticles as one of the most promising nanostructures and their research as one of the cornerstones of nanotechnology. In this contribution we present a comprehensive and extended geometrical description for the most common shapes and structures for metallic nanoparticles, as well as experimental results for these geometries with some variations given by truncations.
Abstract: The description of different effects observed in nature by only one general equation is the “Holy Grail” for all physicists. This goal has been achieved for characteristic temperatures through a top-down approach (studying size effects from macroscopic laws) and is presented in this chapter. Here, we show the general equation based on the surface area to volume ratio of nanostructures and statistics (Fermi-Dirac or Bose-Einstein) followed by the particles involved in the investigated phenomena. From the distinction between fermions and bosons, so-called particles which follow a Fermi-Dirac or a Bose-Einstein statistics respectively, this equation indicates the universal behaviour of size and shape effects on different material properties like melting, ferromagnetism, vibration and superconduction. The same shape parameter used in this universal equation can be used to determine the melting enthalpy, the phase diagrams of alloys, the energy bandgap and also the creep behavior of nanomaterials. Theoretical predictions show satisfactory agreement with experimental data taken from literature.
Abstract: Compared to information on nanocrystals, that on amorphous nanosolids is on the whole much less organized. On the other hand, growth of structural data in recent years on the latter, that deal with the range of atomic order (short range order and beyond), coordinations of core and surface atoms and similar aspects in amorphous nanoparticles through computer simulation and other techniques, has been very impressive. Similar generation of information is also true for physical phenomena like crystallization and melting. Finally, interesting properties revealed through experimentations point toward important applications. The present article makes a brief survey of these areas and attempts at reaching certain conclusions mostly specific for amorphous nanostructures with respect to the crystalline counterparts. The article analyzes the structural data to try and explain different properties of amorphous nanosolids and also their position in the applications scenario.
Abstract: The present chapter deals with the difficult task of giving a brief survey of the synthetic routes employed to prepare materials with characteristic features on the nanometer scale. Definitions and general concepts regarding nanostructured and nanometer-sized materials are shortly tackled in the introductory part, which is followed by an overview of the most important approaches developed to synthesize such materials. No attempt is made to create a comprehensive and detailed synopsis of the experimental methods currently available. Rather, attention is focused on a selected number of general methodologies, the choice of which can be usually motivated by a mix of historical perspective, scientific significance and technological potential. So-called “top-down” approaches are discussed first, whereas the second part of the chapter is devoted to “bottom-up” ones. The former group includes mechanical processing, melt quenching, and de-vitrification methods. Sonochemistry, pulsed laser ablation, wet chemical synthesis, sol-gel processing, microwave processing, spray pyrolysis, flame synthesis, inert gas condensation, vapor deposition, and vapor-liquid-solid growth form instead the latter group.
Abstract: An extension of the classic thermodynamic theory to nanometer scale has generated a new interdisciplinary theory - nanothermodynamics. It is the critical tool for the investigation of the size-dependent physicochemical properties in nanocrystals. A simple and unified nanothermodynamic model for the melting temperature of nanocrystals has been established based on Lindemann’s criterion for the melting, Mott’s expression for the vibrational melting entropy, and Shi’s model for the size dependence of the melting point. The developed model has been extensively verified in calculating a variety of size- and dimensionality-dependent phase transition functions of nanocrystals. In this work, such a model was extended to explain the underlying mechanism behind the bandgap energy enhancement and Raman red shifts in semiconductor nanocrystals by (1) investigating the crystal size r, dimensionality d, and constituent stoichiometry x dependences of bandgap energies Eg in semiconductor quantum dots (QDs) and quantum wires (QWs); and (2) revealing the origin of size effect on the Raman red shifts in low dimensional semiconductors by considering the thermal vibration of atoms. For Eg, it is found that: (1) Eg increases with a decreasing r for groups IV, III-V and II-VI semiconductors and the quantum confinement effect is pronounced when r becomes comparable to the exciton radius; (2) the ratio of Eg(r, d)QWs/Eg(r, d)QDs is size-dependent, where Eg(r, d) denotes the change in bandgap energy; (3) the crystallographic structure (i.e. zinc-blende and wurtzite) effect on Eg of III-V and II-VI semiconductor nanocrystals is limited; and (4) for both bulk and nanosized III-V and II-VI semiconductor alloys, the composition effects on Eg are substantial, having a common nonlinear (bowing) relationship. For the Raman red shifts, the lower limit of vibrational frequency was obtained by matching the calculation results of the shifts with the experimental data of Si, InP, CdSe, CdS0.65Se0.35, ZnO, CeO2, as well as SnO2 nanocrystals. It shows that: (1) the Raman frequency (r) decreases as r decreases in both narrow and wide bandgap semiconductors; (2) with the same r, the sequence of size effects on (r) from strong to weak is nanoparticles, nanowires, and thin films; and (3) the Raman red shift is caused by the size-induced phonon confinement effect and surface relaxation. These results are consistent with experimental findings and may provide new insights into the size, dimensionality, and composition effects on the optical properties of semiconductors as well as fundamental understanding of high-performance nanostructural semiconductors towards their applications in optoelectronic devices.
Abstract: This paper reviews size effects in nanocrystalline metals and alloys made by electroforming, a particular form of electrodeposition. The main size effects in these fully dense, three-dimensional nanomaterials come from grain size reduction to less than 5 nm and down towards the limit of the amorphous structure. Details will be given on the synthesis of such materials and their microstructural characteristics including reduced crystal size and intercrystalline defect density. Properties which show either weak or strong grain size dependence will be discussed and compared with the structure-sensitivity of various properties in conventional polycrystalline materials.
Abstract: An extension of the classical thermodynamics to nanometer scale has been conducted to elucidate information regarding size dependence of phase transition functions and binary phase diagrams. The theoretical basis of the extension is Lindemanns criterion for solid melting, Motts expression for vibrational melting entropy, and Shis model for size dependent melting temperature. These models are combined into a unified one without adjustable parameters for melting temperatures of nanocrystals. It is shown that the melting temperature of nanocrystals may drop or rise depending on interface conditions and dimensions. The model has been extended and applied to size dependences of melting enthalpy, melting entropy, atomic cohesive energy. Moreover, the above modeling has been utilized to determine the size-dependent continuous binary solution phase diagrams. These thermodynamic approachs have extended the capability of the classical thermodynamics to the thermodynamic phenomena in the nanometer regime.