Quantum phenomena of ZnSe nanocrystals prepared by electron beam evaporation technique

Abstract

Substrate temperature dependent optical and structural properties of Zinc selenide (ZnSe) thin films were studied. Films were grown onto glass substrate by electron beam evaporation technique in high vacuum (10-6 Torr) at various temperatures in range of room temperature (RT) to 300 °C. Microstrain and dislocation density were also found to vary between 0.69×10 -3 , 1.12×10 -3 , 3.59×1010 cm -2 and 9.49×1010 cm -2 . The lattice parameter value 'a' for these films was calculated and found to increase from 5.577 Å to 5.652 Å respectively. Scanning electron micrographs (SEM) showed that clusters are composed of spherical and needle like nanocrystals distributed uniformly over the surface whose c-axis is parallel to the surface of the film. This confirmed the mixture comprised cubic and hexagonal phases. A comparison of atomic force microscopy (AFM) images showed that the grain size increased from about 139 nm for the RT deposited ZnSe film to about 39 nm for the ZnSe film deposited at 300 °C. The binding energy of 54.4 eV is similar to the values obtained for other selenides. The Auger parameter for zinc was calculated from the experimental binding energies of the zinc (2p 3/2 ) XPS line and the LMM Auger line the reference values are 1042.49 eV -1020.19 eV for zinc. All the films were characterized optically by UV-vis-NIR spectrophotometer in photon wavelength range (300 nm -2000 nm). The optical transmittance and reflectance were utilized to compute the absorption coefficient, refractive index and band gap energy of the films. The bandgap value of RT and 100 oC deposited ZnSe films are 2.88 eV and 2.78 eV, which are found to be blue shifted by about 0.08 -0.18 eV from the bandgap value of 2.70 eV for the standard bulk material.

Selenium-transition metal supported on a mixture of reduced graphene oxide and silica template for water splitting

“…Moreover, the nanospheres of NiSe 2 tend to agglomerate in the absence of reduced graphene. In the case of CoSeO 3 /rGO-ST (c and d) and FeSe 2 /rGO-ST (e and f) the particles tended to be cubes this is in agreement with Kaviyarasu 56 who prepared cubic ZnSe and Balamuralitharan et al 57 who prepared MnSe 2 cubes. Abundant mesoporous structures are spreading all over the matrix, which increases the surface area (in agreement with TEM analysis).…”

“…61 As shown in FeSe 2 /rGO-ST, the characteristic oxidation state of Se − is assigned to binding energies of ∼54.53 and ∼56.6 eV. 62,63 Moreover, the atomic Se −2 corresponds to ∼53.84 eV and 57.37 eV in the case of NiSe/rGO-ST. 56 The high-resolution XPS spectra of Co2p, Fe 2p, and Ni 2p are also separately presented in Fig. 4(d and e), respectively.…”