-

Calculation of structural and optical properties of silicon quantum dots: tuneable absorption energy and negative electron affinity

-

Ruhan Thirayathorn, Pairot Moontragoon, Vittaya Amornkitbamrung, Santi Meansiri3, Zoran Ikonic

-

The structural and optical properties of hydrogen-terminated silicon quantum dots

were investigated by using the Gaussian 09 program. The models of silicon quantum dots

assume that the silicon atoms are covalently bonded in diamond crystal structure, with

quantum dot diameters varying from 0.8 to 1.6 nanometers. The bonds of silicon atoms at

the surface were terminated by hydrogen atoms. The calculations of optimized structures

and ground state electronic properties for the quantum dots have been performed using

Hartree-Fock with 6-31G* basis set, and the exited states were then calculated by using

time-dependent density functional theory (TDDFT) with (B3LYP) hybrid functional. The

results show that the hydrogen-terminated silicon quantum dots have tuneable absorption

energy, depending on particle size, and the larger particles have lower absorption energy.

The calculated UV-VIS spectrum results show that with the quantum dots diameter changing

from 0.8 nm to 1 nm to 1.2 nm the absorption peak moves from 5.23 eV (238 nm) to 4.68

eV (264 nm) to 4.03 eV (308 nm). Moreover, the hydrogen-capped silicon nanocrystals

also show negative electron affinity (NEA).

-

Optoelectronics; Colloidal silicon quantum dots; Negative electron affinity.