Nanocrystals of CdSe in thin film matrix

Abstract

Nanocrystals of CdSe have been produced in an SiO x thin film matrix by thermal vacuum evaporation of SiO and CdSe. A new way of forming CdSe nanoclusters in the matrix has been used. The average size of the CdSe nanocrystals, between 2.4 nm and 6.0 nm, has been estimated from the (110) maximum in the x-ray diffraction spectra. Quantum size increase of the optical bandgap of the CdSe nanocrystals has been observed. A good coincidence between the average size of the nanocrystals calculated from the observed bandgap increase and x-ray diffraction measurement has been obtained. The substructure observed in the nanocrystal absorption can be related to relatively small nanocrystal size fluctuations around the average size.

Formation of CdSe nanoclusters in SiO thin films

“…The film thickness and deposition rate of both materials were controlled during deposition by two preliminary calibrated quartz monitors MIKI-FFV, whose quartz crystal heads were fixed above the respective source. In order to ensure the same composition of the SiO x matrix (x Ϸ 1.5 [10]) in all samples, the deposition rate of SiO x was kept constant (ϳ3.5 nm/s). The SiO x films were produced in a one-step procedure while the CdSe ones were deposited in a step-by-step manner.…”

“…Some as-prepared films were annealed in air at 670 K for 80 min. The X-ray diffraction studies performed have shown [10] that CdSe nanocrystals of hexagonal wurtzite structure were formed after annealing.…”

“…A size-induced increase in the optical band gap of CdSe nanocrystals and fine structure in their absorption spectra has been observed and related [10,11] to a relatively narrow nanocrystal size distribution. The technique employed for fabrication of those nanocrystals was based on the assumption that during the deposition of ultrathin films of thermally evaporated CdSe on a rough surface of another thin film, nanoclusters might be formed in the surface valleys.…”

“…This mechanism takes place on the smooth surface of a crystalline material but it cannot be used for nanocrystal growth on a rough surface. It has been shown [7][8][9][10] that, in this case a nonepitaxial self-organized nanocluster formation is possible. It occurs on the rough surface of amorphous thin films deposited by means of physical evaporation, sputtering or glow-discharge techniques.…”

“…In a previous work [10], we have reported the fabrication of CdSe nanoparticles in a thin film SiO x matrix by means of a multilayer deposition approach. A size-induced increase in the optical band gap of CdSe nanocrystals and fine structure in their absorption spectra has been observed and related [10,11] to a relatively narrow nanocrystal size distribution.…”