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With the miniaturization of a solid, quantum and interface effects become increasingly important. As a result, the band structure of a nanometric semiconductor changes: the band gap expands, the core level shifts, the bandwidth revises, and the sublevel separation within a band increases. Unfortunately, such a thorough change goes beyond the scope of currently available models such as the ‘quantum confinement’ theory. A consistent understanding of the factors dominating the band-structure change is highly desirable. Here we present a new approach for the size-induced unusual change by adding the effect of surface-coordination deficiency-induced bond contraction to the convention of an extended solid of which the Hamiltonian contains the intraatomic trapping interaction and the interatomic binding interaction. Agreement between modelling predictions and the observed size dependency in the photoluminescence of Si oxides and some nanometric III–V and II–VI semiconductors, and in the core-level shift of Cu–O nanosolids has been reached. Results indicate that the spontaneous contraction of chemical bonds at a surface and the rise in the surface-to-volume ratio with reducing particle size are responsible for the unusual change of the band structure of a nanosolid.

Snapback behaviour, with well-defined conduction states involved, has been observed in the ramped-current current-voltage (I-V) characteristics of ultra-thin silicon dioxide films after the occurrence of hard breakdown. The comparison of the snapback behaviour with the switching behaviour observed in the ramped-voltage measurement shows that the two behaviours are similar, suggesting that they can be explained by the same mechanism. The I-V relationship of each conduction state involved in either the snapback or the switching behaviours was found to follow a power law. These observations are consistent with the percolation model, and they can be easily explained in terms of the on/off of conductive percolation paths due to detrapping/trapping or neutral trap generation at certain SiO2 lattice sites (strategic positions) during the measurements.

Deeper insight is presented into the origin of the dielectric suppression and its effect on the photoabsorption of nanometric semiconductors. Consistency between modelling predictions and experimental observations reveals that the dielectric suppression originates from the enhancement of the crystal field due to surface bond contraction and the rise of the surface-to-volume ratio with decreasing particle size. The suppression of the dielectric function will lead to a blue shift in photoabsorption edges, which may find application in microelectronic and photonic devices of nanometre scales.

This work reports that the optimum diamond grain size can be controlled by adjusting the flow rate of Ar/H2 in the reaction chamber through orthogonal optimization. The dielectric properties of the diamond films were investigated using an RCL (resistance-capacitance-inductance) meter. It was found that (i) the dominating factors in controlling the grain size are in the following order: Ar/H2 gas ratio, gas total pressure, plasma power and substrate temperature; (ii) increasing the Ar gas fraction reduces the grain size of synthetic diamond films; and (iii) reducing the grain size lowers the dielectric constant. The grain size effect on the dielectric behaviour can be explained by the change of the crystal field caused by surface bond contraction of the nanosized particles.

Measurements using TGA, SEM, Raman spectroscopy and XRD reveal that diamond oxidizes at around 750 K through oxygen impinging into the densely packed {111} planes throughout the course of the reaction. It is also found that diamond graphitizes under vacuum at about 1100 K without orientation preference, which also occurs under an Ar inert gas environment. The intriguing oxidation behaviour of diamond indicates that oxidation occurs with selectivity of the bonding environment. It is explained that the diamond {111} plane is more favourable than the {220} surface for the oxide tetrahedron formation, and that the oxide bond formation produces loosely bonded dipoles on the surface that are eroded away during the process of oxidation.

The sintered rhombohedral PbTi0.1 Zr0.9 O3 (PZT) ceramics with doped CeO2 were prepared and investigated by means of XRD, SEM, EDX, and dielectric property measurement. It is found that a 0.4% CeO2 doping has two major effects on the growth dynamics and electric properties of the PZT materials. First, the grain size, morphology flatness and growth rate are enhanced by four to eight times. Second, the Curie temperature of the PZT is lowered by about 40 °C as compared to the undoped PZT samples. It is also found that the cerium is richer at the grain boundaries and precipitates in a glass-like phase that fills the gap between grain boundary. A possible mechanism for the driving force is discussed.

It has long been a puzzle regarding the atomistic origin of the thermally driven elastic softening of a solid specimen since the pioneering works of Anderson in 1966 and Watchman in 1961. Here we present an analytical solution developed from the perspective of the local bond average. It is shown that the thermally driven elastic softening of crystals can be directly related to the geometric and energetic response of the representative bonds or their average of the given specimen to the temperature variation. Reproduction of the experimental results of Ag, Au, MgO, Mg2SO4, Al2O3, KCl, Si, Ge and diamond crystals has been realized giving rise to information on the mean atomic cohesive energy without involving any hypothetical parameters used in classical thermodynamics or in continuum mechanics.