Tuning structural, electrical, linear, and nonlinear optical properties of cadmium zinc telluride quantum dot thin films

Quantum dots of Cd0.18Zn0.14Te0.68 thin films of various thicknesses are deposited on a glass substrate using inert gas condensation and characterized using many techniques. Structural analysis confirms the cubic polymorph of the thin films. The particle size increased from 5.7 to 10.35 nm as the film thickness increased from 10 to 100 nm. Bandgap calculations show two direct allowed transitions, one of which is 1.8 eV for different thicknesses. The other transition changes from the ultra-violet region (3.7 eV) for 10 nm thickness to yellow (2 eV) for 100 nm thickness, depending on the particle size. This result suggests that this material is suitable for use in multiple absorption layers of the same material rather than multilayers of different materials in tandem solar cells. The optical linear and nonlinear parameters highly depend on the particle size. Electrical conductivity shows intrinsic conduction with low activation energies from ambient temperature to 336 K

Erratum to: Study of the structural, electrical and optical properties of Ge-Pb-Te nanocrystals

This erratum corrects a mistake happened in Figure 1 in the article. In the recent version Figure 1 is incorrect, we need to exchange it with the correct figure attached with this erratum

Study of the structural, electrical and optical properties of Ge-Pb-Te nanocrystals

Nanocrystals of Pb37.5Ge12.5Te50 with average size 24 nm are prepared using direct solid state reactions of pure elements in vacuum. The obtained Pb37.5Ge12.5Te50 nanocrystal alloy was used as a starting material for preparing thin films by inert gas condensation (IGC) technique. The obtained thin films show a nanocrystalline structure. Particle size of thin film increases from 4.3 to 6.9 nm with increasing film thickness from 10 to 60 nm. Optical studies for thin films revealed a direct allowed electronic transition. The values of optical band gap Eopg decreased from 2.26 to 1.63 eV with increasing film thickness from 10 to 60 nm and inversely proportional to particle size. The electrical conductivity of nanocrystalline thin films was enhanced by a factor of 1000 times with increasing film thickness from 10 to 60 nm. The reduction of electrical conductivity during cooling cycle for 46 and 60 nm film thicknesses can be explained by the so-called core-shell model. The growth of crystal during heating process causes an increase in thin film resistance during cooling which reduces the probability of the presence of current paths within thin film

Tuning Paramagnetic effect of Co-Doped CdS diluted magnetic semiconductor quantum dots

Diluted magnetic semiconductor quantum dots (DMS-QDs) are known for their outstanding optical and magnetic properties. II–VI DMS-QDs, in particular, are interesting for spintronics, nonvolatile memory, and magneto-optical devices. Therefore, studying the optical and magnetic properties of different II-VI semiconductors doped with transition metal atoms is of great importance. Tuning II-VI QDs optical properties can be mastered by changing the QDs particle size and/or structure. However tuning the magnetic properties of DMS-QDs is still within trial and error verification, although it is crucial in targeting different applications in spintronics. We hereby demonstrate, the ability to tune the paramagnetic effect of homogeneous Co-doped CdS QDs following a co-precipitation synthesis route with different Co2+ concentrations. The structural, optical and magnetic properties have been comprehensively studied. The dopant cobalt atoms concentration and chemical-configuration were precisely tracked by x-ray photoemission spectroscopy. Excitingly, the different Co-concentrations of 2, 5 and 10% significantly improve the magnetic properties of the CdS QDs, which exhibit a paramagnetic concentration-dependent effect. With 10% of Co atoms, we were able to achieve ~ 200 x 10(-6) molar susceptibility, that is, the same value to that of pure CoS. Thus we could obtain the highest possible paramagnetic effect in the CdS semiconducting matrix exhibiting 2.76 eV band gap, i.e. in the visible range. This efficacious result encourages the use of the present method in preparing DMS-QDs materials targeting various spintronics applications.AE and IM are acknowledging the funding provided by the joint Russian Egyptian STDF project no. 13756. AE is also grateful also for the general administration of Missions at the Ministry of High Education in Egypt for funding the mission trip to Centro de Fisica de Materiales on 2016. CR and EO are grateful for funding from the Spanish Ministry of Economy and Competitiveness (grant MAT2016-78293-C6-5-R, including FEDER funds), the Basque Government (grant IT-1255-19) and the Interreg POCTEFA V-A Spain–France–Andorra Program (EFA 194/16/TNSI) partly financed by ERDF funds.Peer reviewe

Preparation and characterization of Ge-Ni-Te nanocomposite

NixGe50–xTe50 with x = 2, 4, 6, 8, 10, 15 and 20 at% ternary nanocomposite prepared using multistage solid-state direct reaction. Nanocrystalline nature was studied by X-ray powder diffraction, results reviled that, the main phase is rhombohedral GeTe polymorph, and the second major phase is hexagonal Ni3GeTe2. The calculated average crystallite size of the whole constituents in prepared samples is within the range of 47.3-83.8 nm. Optical properties evaluated from diffuse reflection measurements and the calculated bandgap of all samples are nonmonotonically changes with Ni content from 1.45 to 1.62 eV with the direct allowed transition

Harvesting multiple optical energies using ZnPc/CdS-QDs hybrid organic/inorganic semiconductors

The substitution of inorganic-based electronics by organic semiconducting materials is a current trend in science and technology for its economic and environmental benefits, but it is hardly progressing. The reason thereof is the lack of improved efficiency, which affects the organic semiconductors performance in many devices when compared with their inorganic-based counterparts. A recent peculiar idea of using heterostructures consisting of both organic and inorganic materials has become an auspicious solution. To this end, the ability to synthesize hybrid organic/inorganic semiconductors targeting different applications is of utmost importance. We hereby present a successful simple route to synthesize a stable homogenous hybrid organic/inorganic system consisting of zinc phthalocyanine (ZnPc) oligomers as the organic base, and Cadmium sulfide quantum dots (CdS QDs) as the inorganic part. The structural and optical characterizations of the prepared samples demonstrate new optical absorption transitions for the hybrids in the red region belonging to the ZnPc molecules, besides the original blue band absorption of the CdS QDs. This is combined with a reduced radiative emission of the whole system. Thus, the hybrid materials are capable of harvesting multiple frequencies within the visible spectra more efficiently than pure QDs, while relaxing non-radiatively rather than by emitting electrons or heat. These qualities favor the use of these hybrids as solar cell or thermal-power active materials.AE and IM are acknowledging the funding provided by the joint Russian Egyptian STDF Project No. 13756. AE is also grateful for the general administration of Missions at the Ministry of High Education in Egypt for funding the mission trip to Centro de Fisica de Materiales on 2016. CR and EO are grateful for funding from the Spanish Ministry of Economy and Competitiveness (Grant MAT2016-78293-C6-5-R, including FEDER funds) and the Interreg POCTEFA V-A Spain–France–Andorra Program (EFA 194/16/TNSI) partly fnanced by ERDF funds

Biomimetic Mineralization of Tooth Enamel Using Nanocrystalline Hydroxyapatite under Various Dental Surface Pretreatment Conditions

In this report, we demonstrated the formation of a biomimetic mineralizing layer obtained on the surface of dental enamel (biotemplate) using bioinspired nanocrystalline carbonate-substituted calcium hydroxyapatite (ncHAp), whose physical and chemical properties are closest to the natural apatite dental matrix, together with a complex of polyfunctional organic and polar amino acids. Using a set of structural, spectroscopy, and advanced microscopy techniques, we confirmed the formation of a nanosized ncHAp-based mineralized layer, as well as studying its chemical, substructural, and morphological features by means of various methods for the pretreatment of dental enamel. The pretreatment of a biotemplate in an alkaline solution of Ca(OH)2 and an amino acid booster, together with the executed subsequent mineralization with ncHAp, led to the formation of a mineralized layer with homogeneous micromorphology and the preferential orientation of the ncHAp nanocrystals. It was shown that the homogeneous crystallization of hydroxyapatite on the biotemplate surface and binding of individual nanocrystals and agglomerates into a single complex by an amino acid booster resulted in an increase (~15%) in the nanohardness value in the enamel rods area, compared to that of healthy natural enamel. Obtaining a similar hierarchy and cleavage characteristics as natural enamel in the mineralized layer, taking into account the micromorphological features of dental tissue, is an urgent problem for future research