Behind the Quantum Confinement and Surface Passivation of Nanoclusters

Abstract

A new model is presented to describe the quantum confinement and surface passivation effects of nanoclusters. The quantum well depth (ϕ) and the band gap width (Eg) of nanoclusters are independent concepts, because the ϕ depends on the surface electron density while the Eg is a function of the crystal field of the solid. The ϕ and Eg can be correlated with the joint physical and chemical effects, which are quite simple but have rarely been noticed. It is suggested that the bond contraction at the surface and the rise in the surface-to-volume ratio (γ), as well as the cluster interaction, enhance intrinsically the crystal field and hence the band gap Eg. Reaction with electronegative elements, such as oxygen and nitrogen, widens extrinsically the Eg by producing holes below the Fermi level [Appl. Phys. Lett.72, 1706 (1998)]. The formulation agrees well with experimental observations on the band gap enlargement by reducing particle size.

Oxidation electronics: bond–band–barrier correlation and its applications

“…Here we show that the PL frequency shift of Si oxide nanoparticles is determined by the joint effect of oxidation and surface-bond contraction-BOLS and BBB mechanism [382]. It is known that the frequency-shift of PL reflects the band-gap change of the system.…”

“…34(a). The possible errors in measurement may result from the accuracy of shapes and sizes of the particles that could lead to different p i values [382]. The fact that the c-axis lattice contracts more significantly than does the a-axis lattice may results from the anisotropy of the CN or from the bond strength in different directions.…”

“…Band-gap expansion and surface bond contraction are suggested to play major roles dictating the property changes of a solid. Importantly [382], all the detectable physical quantities relating to the cohesive energy or binding energy density will change with the dimension of a nanosolid of which the portion of surface atoms and the curvature of the surface vary with its dimension. Developments so far have led to the following advances in applications.…”

Size dependence of nanostructures: Impact of bond order deficiency

“…Property tunability also includes thermodynamics (critical temperatures for phase transitions such as liquidation, evaporation, and heat transport), lattice dynamics (optical and acoustic modes of lattice vibration), optics (photoemission and absorption) [13e15], electronics (work function, energy-level positions, electronephonon coupling) [16,17], magnetic (magnetization tailoring or enhancement) and dielectric performance. Surfaces passivated by electronegative additives such as C, N, and O, also affect the performance of the nanosolids [18]. A recent review [19] suggests that not only size-dependent phase transition but also chemical interaction between the core of the nanoparticle and its surfactant molecules are responsible for the observed X-ray absorption fine structure (XAFS) spectral changes, which can be explained when constructing detailed models of coreesurfactant interaction.…”

“…Considering an assembly composed of n particles of mean size K j and with each particle, there are N j atoms, the total binding energy, V(r, n, N j ) [18]:…”