Optical properties of CdS/PVA nanocomposite films synthesized using the gamma-irradiation-induced method

Monodispersed spherical CdS nanoparticles embedded into polyvinyl alcohol (PVA) films are synthesized by using an in-situ gamma-irradiation-induced method. The formation mechanism of CdS nanoparticles capped by two united cells of PVA is purposed by means of surrounding the CdS nanoparticles with OH bonds of the PVA chain. CdS nanoparticles are found to possess an unusual orthorhombic structure in monoclinic crystalline PVA. The polymer matrix affords protection from agglomeration and controls the particle size. It is found that the distribution of the prepared nanoparticles increases and a narrower size distribution is observed when the gamma radiation is varied from 10 to 50 kGy. While the average size of the nanoparticles is found to be less affected by the variation of the gamma radiation doses. The size range of the synthesized nanoparticles is 14±1 nm. The optical absorption spectra of synthesized CdS nanoparticles in a polymer matrix reveal the blue shift in the band gap energy with respect to CdS bulk materials owing to quantum confinement effect. The photoluminescence study of nanocomposite films shows the green emission arising from the crystalline defects

Third-order nonlinear optical properties of silver nanoparticles mediated by chitosan

Silver nanoparticles in chitosan medium were prepared by the chemical reduction method. Silver nitrate and hydrazine were used as the precursor and reducing agent in the present of chitosan as a natural host polymer. The samples are characterized by UV–visible spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The measurements of nonlinear optical properties were defined by Z-scan technique using green CW laser beam operated at 532 nm wavelengths. Thermal effect has a dominant role in the overall material nonlinearity with CW laser. It is shown that the synthesized samples have a negative nonlinear refractive index

Optical Nonlinear Refractive Index of Laser-Ablated Gold Nanoparticles Graphene Oxide Composite

Gold nanoparticles were prepared in graphene oxide using laser ablation technique. The ablation times were varied from 10 to 40 minutes, and the particle size was decreased from 16.55 nm to 5.18 nm in spherical shape. The nanoparticles were capped with carboxyl and the hydroxyl groups were obtained from Fourier transform infrared spectroscopy. Furthermore, the UVvisible peak shifted with decreasing of nanoparticles size, appearing from 528 nm to 510 nm. The Z-scan technique was used to measure the nonlinear refractive indices of graphene oxide with different concentrations and a gold nanoparticle graphene oxide nanocomposite. Consequently, the optical nonlinear refractive indices of graphene oxide and gold nanoparticle graphene oxide nanocomposite were shifted from 1.63 × 10 −9 cm 2 /W to 4.1 × 10 −9 cm 2 /W and from 1.85 × 10 −9 cm 2 /W to 5.8 × 10 −9 cm 2 /W, respectively

Nanoscale characterization of ZnO, PbTiO3, CH3NH3PbI3 and thin film growth of Cu2OSeO3

Scanning probe microscopy (SPM) is a method to image and measure on the nanometre and atomic scale which has enabled significant progress in science and engineering. In this thesis this technique was used to study the electrical and piezoelectric properties of different materials. Materials were chosen based on their potential applications in science and technology. Each chapter in this dissertation is allocated to a specific material.ZnO with different structures has seen widespread research interest because of piezoelectricity properties that are used in a wide range of applications. In this dissertation the response of ZnO nano and microstructure platelets in dark and under laser illumination was studied using c-AFM. The results show that the grain boundaries in ZnO platelets are sensitive to light with energy below the band gap. This is due to the defect levels at grain boundaries and photoexcited carriers. The piezoelectric response of ZnO nano and microstructure platelets was studied by the PFM technique. Application of electrical field alters the piezoresponse in individual grains. These observations suggest new pathways for using conducting ZnO in optoelectronics devices which rely on grain and grain boundary engineering.Electrical conduction at domain walls of PbTiO3 (PTO) single crystals was also studied in this dissertation. PTO is a well-known ferroelectric material that has considerable ferroelectric and piezoelectric properties. It has applications in electrical devices like piezoelectric transducers and up to now studies are only focussed on piezoelectric domains for this material. Here, the study is focus on domain wall conductivity conducted by conductive atomic force microscopy (c-AFM). Naturally occurring 180° domains exhibit current flow along the delineating domain wall. The domain wall current flow shows Schottky-like rectifying behaviour.The nanoscale effects of photochemically-active additives on grain boundaries in CH3NH3PbI3 solar cells was studied. Scanning probe microscopy under light illumination, in particular Kelvin probe force microscopy, was applied to study the surface potential changes under laser light illumination. The recently found improvement in efficiency of BQ added solar cells can be clearly seen in vanishing contact potential differences at grain boundaries under illumination, rendering the material more uniform in solar cell operating conditions. Our findings shed light onto halide perovskite materials and functional additive design for improved solar cell performance.IIn addition to SPM measurements on ZnO and PTO, the growth of Cu2OSeO3 thin films is also discussed in this dissertation. The focus was to study the magnetic skyrmion systems in this material. The insulator Cu2OSeO3 has gained interest because of the possibility of electrical control of magnetism in insulator materials, which is energetically more efficient in comparison to metallic systems. Thin films were grown by the pulsed laser deposition (PLD) technique on MgO and NdGaO3 substrates. The grown thin films were characterized by XRD and AFM. The formation of skyrmions was confirmed by small angle neutron scatterin

Open photoacoustic cell configuration applied to the thermal characterization of liquid CdS nanocomposites

CdS nanofluids were prepared by the gamma-radiation method at different radiation doses. The samples were characterized by UV–Vis spectroscopy and transmission electron microscopy. The open cell photoacoustic technique was used to measure the thermal effusivity of the CdS nanocomposites. In this technique a He–Ne laser was used as the excitation source and was operated at 632.8 nm with an output power of 70 mW. The precision and accuracy of this technique were initially established by measuring the thermal effusivity of distilled water and ethylene glycol. The thermal-effusivity values of these two samples were found to be close to the values reported in the literature. The thermal effusivity of CdS nanofluids decreased from (0.453 to 0.268) W⋅S1/2⋅cm−2⋅K−1 with increased dosage of gamma radiation

Structural,optical and thermal properties of PVA/CdS nanocomposites synthesized by radiolytic method

Monodispersed spherical CdS nanoparticles stabilized in PVA solution were synthesized by the gamma radiolytic method and found the average particle size increased from 12 to 13 nm with the increment of dose from 10 to 40 kGy. The XRD results show that it has crystalline planes of cubic structure with crystal lattice parameter of 5.832 Å. The optical reflectance revealed a band-edge of CdS nanoparticles at about 475 nm and the reflectance wavelength red shifted with increasing dose due to increasing particle size. The thermal conductivity of CdS/PVA nanocomposites measured by the transient hot wire method that revealed a decrement of the thermal conductivity with an increase of dose caused by effect of radiation on crystallinity of the polymer structure

Optical Nonlinear Refractive Index of Laser-Ablated Gold Nanoparticles Graphene Oxide Composite

Gold nanoparticles were prepared in graphene oxide using laser ablation technique. The ablation times were varied from 10 to 40 minutes, and the particle size was decreased from 16.55 nm to 5.18 nm in spherical shape. The nanoparticles were capped with carboxyl and the hydroxyl groups were obtained from Fourier transform infrared spectroscopy. Furthermore, the UV-visible peak shifted with decreasing of nanoparticles size, appearing from 528 nm to 510 nm. The Z-scan technique was used to measure the nonlinear refractive indices of graphene oxide with different concentrations and a gold nanoparticle graphene oxide nanocomposite. Consequently, the optical nonlinear refractive indices of graphene oxide and gold nanoparticle graphene oxide nanocomposite were shifted from 1.63×10-9 cm2/W to 4.1×10-9 cm2/W and from 1.85×10-9 cm2/W to 5.8×10-9 cm2/W, respectively