The 25th International Conference on Amorphous and Nano-crystalline Semiconductors
August 18–23, 2013 Toronto, Ontario Canada
New Nano-materials: Growth and Characterization III
Chair: Andrei Sazonov, University of Waterloo
Structural and Optical Properties of DLC Thin Films Deposited by PLD Technique
Department of Physics, Indian Institute of Technology Guwahati, Guwahati -781039, India
Diamond like carbon (DLC) thin films have potential applications as protective coating in magnetic storage disks, hard coating on the cutting tools, IR sensors and lenses, radiation detectors etc. Pulsed Laser deposition (PLD) is unique technique to produce such high quality DLC films almost free from hydrogen at room temperature (RT). The transition of film properties from diamond like to graphite like can be achieved simply by controlling the experimental conditions. In the present work, DLC thin films were deposited via pulsed laser ablation of graphite target using Q-switched Nd:YAG laser (532 nm, 10 Hz, 10 ns) at a base pressure of the order of ~10–5 mbar. The films were deposited on glass and silicon substrates by varying the temperature from RT to 700°C. The morphology was characterized by scanning electron microscope (SEM). The sp3 and sp2 bonds were analyzed by micro-Raman spectroscopy and Fourier transform infrared (FTIR) absorption spectroscopy. UV-Vis spectroscopy was used to estimate the optical band gap.
The Raman spectra of PLD deposited film at RT showed a broad band at 1545 cm–1, characteristic of DLC films. Raman D band (~1360 cm–1) and G band (~1570 cm–1), characteristic features of carbon materials were clearly observed at higher substrate temperature. The increase in the relative intensity of D band and shift of G band towards higher wavenumber at higher substrate temperature indicates the increase in ordering of sp2 clusters. The optical band gap were estimated by absorption spectra using Tauc plot. The band gap of DLC film deposited at RT was found to be 2.96 eV and decreased to 1.78 eV for film deposited at substrate temperature of 300°C. IR absorption increases with increase in substrate temperature due to sp2 clustering. A broad band in IR spectra was observed around 1250 cm–1, which is attributed to a stretching mode of mixed sp2-sp3 bonds. The broadness increases towards high frequency for DLC film deposited at 300°C due to vibration of sp2 bonds. For all DLC samples, very low intensity of IR spectra around 3000 cm–1 indicates that PLD deposited DLC films are nearly free from hydrogen.
Keywords: Nd:YAG, Fourier transform infrared, micro-Raman, pulsed laser deposition
Characterization of Mechanically Synthesized AgInSe2 Quantum Dots
Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, Pardubice, Studentska 573, Pardubice 532 10, Czech Republic
A quantum dot solar cell is an emerging field in solar cell research that uses quantum dots as the photovoltaic material. Quantum dots have band gaps that are tunable across a wide range of energy levels by changing the quantum dot size. The embedment of different sized dots within same layer encourages absorption of whole spectrum energy. Also other effects like very high surface to volume ratio, Quantum Transport make them attractive for future devices. AIS quantum dots (QDs) with tetragonally distorted phase have been prepared by mechanically alloying the synthsized bulk AIS powder at room temperature in a planetary ball mill under Ar. QDs are formed with range ~10 nm in size. These ball-milled QDs contain different shapes and the Rietveld analysis of x-ray powder diffraction data reveals their detailed structural features. High resolution transmission electron microscope (HRTEM) images also detect the presence of the tetragonal phase in ball-milled samples. The particle size of QDs and their distributions obtained from Rietveld analysis agree well with the observations of HRTEM images. Peak Broadening (FWHM) which is the main characteristics of decrease in size, is observed. XRD data reveals the downscaling of crystallite from 103 nm to 7 nm, also tetragonally distorted structure of the system was not disturbed by milling. The Raman analysis (1014 nm at room temperature) predicts bands at 167 cm–1 and 230 cm–1 (motion and oscillation between In and Se atoms) in all as synthesized and milled powders confirming again chalcopyrite type structure. The DSC study also reveals the phase evolution and crystallization kinetics. Bulk samples show endo melting peak at 134°C. Also one peak at 220°C may correspond to traces of Se slightly mixed with Indium. Cooling-crystallization complexity of the peak/peaks signifies crystallization from melt was heterogeneous nucleation and crystallization from multiple types of centers. Unlike this milled samples show two crystallization effects at approx. 135°C and 380°C. Optical properties investigated to find band edges and suggest it around 1.3 eV which is encouraging for photovoltaic applications. In this presentation the advances in chalcopyrite type solar cells and possibility of ball milled top down facile route for the syntheses of AIS Quantum dots and their properties will be discussed.
The Ministry of Education, Youth and Sports of the Czech Republic, Project CZ.1.07/2.3.00/30.0021 "Strengthening of Research and Development Teams at the University of Pardubice", financially supported this work.
Keywords: photovoltaic materials, quantum dots, top down approach
Synthetic Strategies for Shape Directing Nanomaterials: A Brief Review
1. Materials and Nanotechnology Research Laboratory, College of the North Atlantic, 1600 Nichols Adam Highway, Labrador City, NL A2V 0B8, Canada
2. Department of Chemistry, Wilfred Laurier University, Science Building, 75 University Ave. W., Waterloo ON N2L 3C5 Canada
Components of the next generation technologies such as the semiconductor nanocrystals (NCs) are going to be materials with nanometric dimensions with many useful applications in lasers, photovoltaics, light emitting diodes, and biological assays. Lead chalcogenides are of extensive interest among the semiconductor NCs due to their narrow band gap and large Bohr's radius. We present a brief review of studies on different areas related to surfactant, phospholipid/protein conjugated semiconductor nanoparticles ranging from their basic synthetic strategies of shape-directed morphologies to their applications in biodegradable materials and nanotoxicology. Phospholipids, especially anionic ones, and water soluble proteins show the significant shape-directing ability of both noble metal and semiconductor nanoparticles under different circumstances. Protein-nanoparticle composites exhibit the unique behavior of seeding, fibrillation, and self-association with possible relevance to amyloidosis or protein misfolding diseases and to the synthesis of biodegradable protein films with potential environmental impact. Surfactant assisted pathways are the simplest in view of the environmental concerns due to their good reproducibility and high yield. Results on surface activity of highly hydrophobic surfactants and platelike PbSe and CuSe nanoparticles will be presented. Lead selenide (PbSe) and copper selenide (CuSe) having core shell morphologies were synthesized in aqueous phase at a relatively mild temperature (85°C) in the presence of various cationic Gemini surfactants (12-2-12, 12-0-12, and 16-2-16) as capping/stabilizing agents. PbSe reactions produced predominantly plate like cubic morphologies along with long Se nanorods (NRs) as a reaction by product. CuSe particles were polyhedral thin plates with perforations. High resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), and X-ray diffraction (XRD) measurements were used to characterize the shape and structure of the particles. Infrared spectroscopic (FT-IR) studies suggested a strong affinity of cationic surfactant for NC surface which was the driving force for the monolayer formation in the form of a shell. Stronger interfacial adsorption of a surfactant with greater hydrophobicity controlled the morphology to produce platelike geometries. The size of PbSe and CuSe particles increased while the thickness decreased as the hydrophobicity of the surfactant increased in the order of 12-2-12 < 12-0-12 < 16-2-16.
Present research and future directions toward environmental impact, nanotoxicology, and protein misfolding diseases will be discussed (if time permits).
Keywords: nanotechnology, synthesis and applications, semiconductor nanoparticles
pH Dependence Study of Zinc Oxide Nanorods Grown on Indium Tin Oxide Coated Substrate
1. Department of Chemistry and Biochemistry, The University of Tulsa, Tulsa, OK, USA 74104
2. Department of Physics, The University of Tulsa, Tulsa, OK, USA 74104
Controlled growth of ZnO nanorods on various substrates is of great interest in photonic and electronic device applications. Also of interest is increasing the optical activity of zinc oxide nanorods in the visible spectrum. In this study, we report a pH dependence for the morphology and photoluminescence of aligned ZnO nanorods grown on an Indium Tin Oxide (ITO) coated glass substrate. The ZnO nanorods were grown by a hydrothermal technique using equimolar ratios of zinc (II) nitrate and hexamethylenetetramine in solution at 95°C. The pH of the reaction solution prior to oven heating was varied from pH 5 to pH 10.6. Surface properties of the ZnO nanorods on ITO substrates were studied using scanning electron microscopy and photoluminescence spectroscopy. We also compared the use of NaOH to adjust the pH with the use of NH4OH, the latter necessary at higher pH due to the relative insolubility of zinc. It was found that the size of the nanorods can vary two fold due to pH and the choice of base. Uniformity of coverage is also significantly dependent upon these variables and will be discussed as it relates to solubility and crystal growth. It was also found that the intensity of the photoluminescence in the visible range is pH dependent. For example, the intensity of luminescence at 550 nm for ZnO nanorods grown at pH 7 is ~250% of the corresponding emission for a sample prepared at pH 5.
Keywords: ZnO nanorods, chemical bath deposition, pH dependence, oxide semiconductors