Oscillations of the absorbance of PbS nanocrystals grown in situ in Langmuir-Blodgett films of lead stearate

Oscillations of the absorbance of PbS nanocrystals point to the high uniformity of their sizes at the stage of «normal» growth in the matrix. The size quantization energies of the ground and the first excited states of an electron-hole pair are analyzed within the effective mass approximation. It is found that the mean radius of PbS nanocrystals is $r\approx1.7\,$nm and the potential barrier height at the contact between the semiconductor and the matrix is $V_e\approx4.5\,$eV. It is suggested that the finite barrier height is due to the action of electric fields of $\sim10^7\,$ V/m in the contact regions upon breaking the polar symmetry of the dipole arrangement of matrix molecules with respect to the surfaces of growing planar nanocrystals.