Silicon nanocrystals optical properties

On the other hand, the nonlinear optical properties of nanometer-sized materials are also known to be different from the bulk, and such properties are strongly dependent on size and shape [11]. In 1992, Wang and Herron reported that the third-order nonlinear susceptibility, of silicon nanocrystals increased with decreasing size [12]. In contrast to silicon nanocrystals, of CdS nanocrystals decreased with decreasing size [ 13 ]. These results stimulated the investigation of the nonlinear optical properties of other semiconductor QDs. For the CdTe QDs that we are concentrating on, there have been few studies of nonresonant third-order nonlinear parameters. 

Prakash, G. V., Cazzanell, M., Gaburro, Z., Pavesi, L., lacona, F., Franzo, G. and Priolo, F. (2002) Nonlinear optical properties of silicon nanocrystals grown by plasma-enhanced chemical vapor deposition. /. Appl. Phys., 91, 4607 610. 

In a Si zero-dimensional system the strong quantum confinement can increase the optical infrared gap of bulk Si and consequently shift the optical transition energies towards the visible range [65,66]. This is the reason for which silicon nanocrystals (Si-NCs) with a passivated surface are used as the natural trial model for theoretical simulations on Si based light emitting materials, such as porous Si or Si nanocrystals dispersed in a matrix. In this section we present a comprehensive analysis of the structural, electronic and optical properties of Si-NCs as a function of size, symmetry and surface passivation. We will also point out the main changes induced... 

Porous silicon (por-Si) formed by electrochemical etching of (llO)-oriented p-type Si wafers is an example of novel nanostructured medium with controllable optical properties. It was found to exhibit the strong in-plane birefringence (up to 18 %) and free-carrier dichroism [1-5]. Both phenomena originate from the form anisotropy of Si nanocrystals and voids assembling the material [3-5]. Below, we report the analysis of the dichroism in por-Si on the basis of the generalized effective-medium approximation (EMA) [7] as well as prominent anisotropy of absorption by silicon-hydrogen surface bonds. 

Silicon nanoparticles (Si NPs) with sizes in the order of bulk exciton Bohr radius [1, 2] present interesting optical properties for fluorescent labeling in biological imaging applications with their potential nontoxicity [3-6], However, the origin of their photoluminescence has been subjected to intense debate for almost two decades. This debate has been focused on whether quantumatomic-scale defects at the surface of the nanocrystals are responsible for the light emission [7]. 

Wilcoxon JP, Samara GA, Provencio PN (1999) Optical and electronic properties of Si nanoclusters synthesized in inverse micelles. Phys Rev B 60 2704-2714 Wilson WL, Szajowski PF, Brus LE (1993) Quantum confinement in size-selected surface-oxidized silicon nanocrystals. Science 262 1242-1244... 

Ge M, Fang X, Rong J, Zhou C (2013) Review of porous silicon preparation and its application for lithium-ion battery anodes. Nanotechnology 24(422001) 1-10 Gelloz B (2010) Chapter 14 Silicon nanocrystals in porous silicon and their applications. In Pavesi L, Turan R (eds) Silicon nanocrystals. Wiley-VCH, Weinheim Golovan L, Timoshenko VY (2013) Nonlinear-optical properties of porous silicon nanostructures. J Nanoelectron Optoelectron 8(3) 223-239... 

Most of the semiempirical tight-binding methods for nanostructures are based on the parametrization of bulk systems. It consists of an iterative fitting procedure, performed on the tight-binding parameters, to match the bulk silicon band structure calculated using the most advanced techniques [21]. The as-calculated parameters are then applied to the study of the electronic properties of silicon nanostructures. When the nanostructures are well passivated, the surface is expected to play a minor role, and the main electronic and optical properties are determined by the nanocrystal core. 

---