Electronic and spectroscopic properties of GeC superlattice nanocrystals: A first-principle study using diamondoid structures

• GeC superlattice nanocrystals diamondoids structure.
• Vibrational spectra, reduced masses, force constants.
• UV–Vis and NMR spectroscopy, NBO analysis.
• Size-dependent UV–Vis, NMR, NBO, Raman, IR.

Germanium carbide superlattices are used as building blocks to investigate GeC nanocrystal properties using diamondoid structures. Convergence of electronic and vibrational properties of GeC diamondoids to GeC bulk limits is observed using density functional theory. Energy gap, HOMO and LUMO vary according to confinement theory with shape fluctuations. Ge–C force constants reach 2.67 mDyne/Å which is close to that of silicon. Ge–Ge vibrations embodied inside GeC superlattice vibrations at 305.6 cm−1 are observed with reduced masses 33.77 amu and force constant 1.91 mDyne/Å which are nearly the values of pure bulk Ge. Bulk longitudinal optical (LO) vibrational mode of GeC at 812 cm−1 is reached within 6 GeC diamondoid cages. LO mode is confined to the range 603–812 cm−1 in moving from molecular, nano to bulk. Radial breathing mode (RBM) varies from 603 cm−1 to bulk 0 cm−1 limit. Size variation of UV–Vis and 1H NMR spectra of GeC diamondoids is analyzed. Present work results show that all the investigated spectroscopic tools are sensitive to nanocrystals size. Natural bond orbital (NBO) population analysis shows present compound deviation from ideal sp3 bonding to Ge(4s0.814p1.315p0.02) C(2s1.262p4.643p0.01) near the center of the present largest investigated GeC nanocrystal.