Nanocrystals: Synthesis, Properties and Applications doc

[...]... energies, electron affinity (Ea ) and ionization potential (IP) are nonequivalent [59] The two energies differ to a smaller extent in a nanoparticle and are size-dependent Ea and IP are given by IP = W + αe2 R (1.8) Ea = W + βe2 R (1.9) with the constraint, α+β =1 (1.10) Here, R is the radius of the particle and α and β are constants The physical significance and the values of α and β have been a subject of... Electronic Properties Bulk metals possess a partially filled electronic band and their ability to conduct electrons is due to the availability of a continuum of energy levels above EF , the fermi level These levels can easily be populated by applying an 1.2 Properties of Nanocrystals 13 Fig 1.10 The temperature dependence of dc magnetization of (a) 3 nm and (b) 7 nm NiO nanoparticles under zero-field cooled and. .. instrumentation that have helped in fully characterizing nanomaterials Today, it is possible to prepare and study nanocrystals of metals, semiconductors and other substances by various means Advances in both experimental and theoretical methods have led to an understanding of the properties of nanocrystals 1.2 Properties of Nanocrystals Nanocrystals of materials are generally obtainable as sols Sols containing... It appears that the abundance of available oxidation states and the directional nature of the d- and f-orbitals (and to a limited extent, of the p-orbital) play a role in determining the shell that governs the property of a particular cluster A host of physical techniques has been used to follow phenomena such as the closure of the bandgap and the emergence of the metallic state from the cluster regime... of metals and semiconductors is obtained by scanning tunneling spectroscopy (STS) This technique provides the desired sensitivity and spatial resolution making it possible to carry out tunneling spectroscopic measurements on individual particles The various techniques and the region of the band structure probed by them are schematically illustrated in Fig 1.13 Nanoscale particles of metals and semiconductors... to a few tens of atoms For example, Landman and coworkers [57, 58] have carried out extensive computer simulations, on the structure and dynamics of alkanethiol-capped Au nanocrystals of different sizes Numerous methods have been devised to study the properties of larger clusters often borrowing from theories used to model the bulk Self-consistent Jellium model and local density approximation (a DFT... coordinated semiconductors Currently, experiments and theories go hand in hand in the study of small particles (∼1 nm) and as the methods develop, it is not difficult to visualize a time in the near future, where the same can be said for investigations on larger nanocrystals In a bulk metal, the energies required to add or remove an electron are equivalent and are called the work function (W ) In contrast,... twinned crystallites specially in the case of Au and Ag nanoparticles [34] Characterization by electron microscopy also has certain problems For example, the ligands are stripped from the clusters under the electron beam; the beam could also induce phase transitions and other dynamic events like quasi-melting and lattice reconstruction [35] The fact 1.2 Properties of Nanocrystals 9 Fig 1.7 A high resolution... of the surrounding medium, k = λ m , an and bn are Ricatti–Bessel functions that depend on the wavelength and the nanoparticle radius (R) For small particles, the scattering term and the higher order extinction terms are negligible The extinction coefficient is, therefore, given by, 3/2 24π 2 R3 m 2 Cext = , (1.17) λ ( 1 + 2 m )2 + 2 2 where 1 and 2 are the real and imaginary part of the frequency-dependent... Kreker and Kreibig [74, 75] have been instrumental in verifying the validity of Mie’s 1.2 Properties of Nanocrystals 21 Fig 1.16 Optical absorption spectra of gold nanoparticles with diameters of 22, 48, and 99 nm (reproduced with permission from [66]) theory for noble metal particles such as Au and Ag Qualitative estimates can however be easily made based on the observed plasmon resonance band Some . end of the book. Synthesis, Properties and Applications C.N.R. Rao G.U. Kulkarni 123 P.J. Thomas Properties and Applications Nanocrystals: Synthesis, With 113 Figures, 6 in Color and 5 Tables C.N.R Materials Editors: A. Planes, L. Ma ˜ nosa, and A. Saxena 80 Micro- and Macro -Properties of Solids Thermal, Mechanical and Dielectric Properties By D.B. Sirdeshmukh, L. Sirdeshmukh, and K.G. Subhadra 81 Metallopolymer. understanding and controlling the structure and properties of all important classes of materials. 78 Macromolecular Nanostructured Materials Editors: N. Ueyama and A. Harada 79 Magnetism and Structure in