Raman spectroscopy of oxygenated amorphous CdTe films

Abstract

Oxygenated CdTe films prepared by r.f. sputtering have been shown to have band gap energies between 1.48 and 3.35 eV, depending on the amount of oxygen incorporated in the CdTe matrix. Samples with oxygen concentrations above 7 at.% are amorphous, whereas those with oxygen concentrations below 7 at.% are polycrystalline, as determined by x-ray and Raman measurements. The Raman spectra of the polycrystalline samples show that there is ca. 4 at.% Te in the form of inclusions under high pressure, which is relatively easy to detect owing to the enhanced Raman cross-section of Te. The Raman spectra of the amorphous samples is dominated by a single broad band at 159 cm-'. The fact that tellurates in general show a similar band, in spite of their different vibrational density of states, indicates that it corresponds to Te-Te bonds in the amorphous matrix.

Overcoming the exciton binding energy in two-dimensional perovskite nanoplatelets by attachment of conjugated organic chromophores

“…We are convinced that the most direct proof of the attachment of the PDIs to the perovskite NPLs is shown by our TA measurements photoexciting the PDI (510 nm excitation) as described below in this work. Attempts to show the attachment by nuclear magnetic resonance (NMR) measurements are far from conclusive in this case (and in many cases in literature 40,41 ) because there is always a certain fraction of the PDIs (or ligands, such as oleic acid) in solution. Moreover, the binding-equilibrium conditions in the type of solvent (deuterated chloroform) required for NMR measurements are different than in hexane.…”

Surface-mediated structural transformation in CdTe nanoparticles dispersed in SiO2 thin films

“…During the conversion of CdTe to CdTeO 3 , O occupies Te sites and Te displaces Cd into interstitial positions. 14 The structural differences between cubic CdTe nanoparticle core (aϭbϭcϭ6.481 Å) and monoclinic CdTeO 3 surface layer (aϭ6.41 Å, bϭ7.23 Å, and cϭ7.642 Å) the presence of stress and to a large concentration of stacking faults. Low value of stacking fault formation energy ͑31-34 erg/nm 2 ͒ in CdTe strongly favors this.…”

Post-Synthesis Crystallinity Tailoring of Water-Soluble Polymer Encapsulated CdTe Nanoparticles using Rapid Thermal Annealing

“…These three peaks correspond to the Te A1 mode at ~127 cm -1 , the Te E mode at ~141 cm -1 , and the CdTe LO mode at ~165 cm -1 [9][10][11]. Due to the modes' finite width and hence overlapping frequencies, there could also be a portion of the Te E peak contributed by the CdTe TO phonon mode which is located at ~140 cm -1 .…”

“…Due to the modes' finite width and hence overlapping frequencies, there could also be a portion of the Te E peak contributed by the CdTe TO phonon mode which is located at ~140 cm -1 . The presence of the two Te peaks have been attributed to Te inclusions within the center of the crystal or surface defects along the boundaries of the material [9][10][11]. It is difficult to quantify from the Raman measurements the amount of Te inclusions or defects, due to the fact that Te crystals exhibit a relatively high Raman scattering signal in comparison to CdTe as a result of unequal Raman cross-sections [10,12].…”

“…The presence of the two Te peaks have been attributed to Te inclusions within the center of the crystal or surface defects along the boundaries of the material [9][10][11]. It is difficult to quantify from the Raman measurements the amount of Te inclusions or defects, due to the fact that Te crystals exhibit a relatively high Raman scattering signal in comparison to CdTe as a result of unequal Raman cross-sections [10,12]. Following a baseline correction and peakfitting routine, Gaussian-Laurentzian peaks were fitted to the Raman spectra for analysis.…”