Fabrication of Chemical Vapor Deposition (CVD) Setup & Preparation of Copper Oxide (CuO) -CdX (X= Se, S) Nanoparticles Decorated Core-Shell Heterostructure

Abstract

The goal of this project is to fabricate a low cost chemical vapor deposition (CVD) setup and synthesize hybrid nanomaterials i.e. copper oxide (CuO)-CdX (X=Se, S) nanoparticles decorated core-shell heterostructure. The synthesized hybrid nanomaterials have been fabricated
into a device (photodetector) for the measurement of current-voltage characteristics in dark and under UV illumination. Furthermore, the growth model for the formation of core-shell heterostructure has also been discussed in this project.
Chapter-I narrates about the fundamentals of materials, nanomaterials and hybrid nanomaterials. In this chapter, the importance, properties, application of nanomaterials have been outlined. Moreover, the properties and morphology and corresponding application are highlydependent on the synthesis methods. Chemical vapor deposition (CVD) technique is found be one of versatile among all other preparation methods. The motivation by addressing the challenges have been discussed thoroughly.
Chapter-II describes the fabrication of a low cost CVD setup. For the fabrication of CVD setup, a three-zone horizontal furnace, reaction tube, a rotary van pump and three mass flow meters have been procured. A liquid precursor handling system and a reaction chamber which has fitted with two couplings have been designed. All these subcomponents have been assembled and integrated into a single unit CVD setup.
Chapter-III discusses about the detailed experimental procedure for the synthesis of CuO nanowires-CdX (X=Se, S) nanoparticles decorated core-shell heterostructure. For the synthesis of CuO-CdX (X= Se, S) heterostructure nanomaterials, CuO nanowires have been synthesizedfirst by using thermal oxidation of Cu foil in air at 5000C for 5 hours. These CuO nanowires grown on cu foils have been used for the synthesis of heterostructure by using the fabricated CVD. All these materials i.e. CuO nanowires, CuO-CdSe & CuO-CdS heterostructure have been
characterized by field emission electron microscopy (FESEM) attached with energy dispersive spectroscopy (EDS), x-ray diffraction (XRD), transmission electron microscopy (TEM) attached with high resolution TEM (HRTEM) and selected area diffraction pattern (SAED), RAMAN spectroscopy & UV-Vis spectroscopy. Moreover, these materials have been fabricated intoa photodetector for the measurement of current-voltage characteristics in dark and under UV illumination.
Chapter-IV describes the detailed material characterization of CuO-CdSe heterostructure
nanomaterials. The FESEM image of CuO nanowires reveals the formation CuO nanowires
stretching out of the surface. The surface of CuO nanowires is very much smooth and impurity
free. Formation of beaded like structures of CdSe is found to be attached intermittently on the surface of CuO nanowires. The presence of Cd, Se elements in the materials has been confirmed by EDS. However, the formation of these bead structure is well confirmed TEM along with the formation of core-shell heterostructure. XRD, HRTEM, SAED pattern confirms the crystalline
nature of the materials. Raman spectroscopy further confirms the presence of CdSe in the CVD synthesized materials. Using UV-Vis spectroscopy measurement the band gap is found to be ~2.2eV for CuO nanowires and 3.96eV for CuO-CdSe heterostructure.
Chapter-V discusses about the material characterization of CuO-CdS nanomaterials.
From FESEM image, the rough surface of CuO-CdS is found by FESEM observation which is attributed to the deposition of CdS nanoparticles thoroughly on to the surface of CuO nanowires during preparation of CuO-CdS core-shell structure by CVD process. The presence of Cd, S elements in the materials has been confirmed by EDS. The formation of core-shell heterostructure has been well verified by TEM. The crystalline natures of the materials have been confirmed by XRD, HRTEM, and SAED pattern. Raman spectroscopy further confirms the presence of CdS in the CVD synthesized materials. The band gap is found to be ~3.73eV for CuO-CdS heterostructure as measured by UV-Vis spectroscopy.
Chapter-VI discusses about some general trends in growth mechanism of hybrid nanomaterials and a probable growth mechanism of the present research work has been suggested as deduced from experimental characterization. The probable growth mechanism for CuO-CdSe is found to be gas phase adsorption, whereas surface diffusion and gas phaseadsorption growth mechanism for CuO-CdS has been suggested. However, the exact growth mechanism is yet to be established that needs further investigation in detail. Furthermore, the current-voltage characteristics of the fabricated photodetector have been measured by Keithley source meter 2400. The measured current for the CuO is 1.4μA at bias voltage 3 Volt. Similarly, the dark current measured for the CuO-CdSe is 11 μA. However, the current increased to 33μA under UV illumination at the biasing 3V. For CuO-CdS, the current is found to be 10.8μA and increased to 23.8 under UV illumination at the biasing 5V. The increase in photocurrent attribute because of the effective charge separation in electron-hole in the heterojunction, which has been discussed thoroughly in the chapter by using band diagram.