Browsing by Subject "Thin films--Surfaces."

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Open Access
Atomic layer deposition of metal oxide thin films and nanostructures
(2013) Dönmez, İnci
With the continuing scaling down of microelectronic integrated circuits and increasing need for three-dimensional stacking of functional layers, novel or improved growth techniques are required to deposit thin films with high conformality and atomic level thickness control. As being different from other thin film deposition techniques, atomic layer deposition (ALD) is based on selflimiting surface reactions. The self-limiting film growth mechanism of ALD ensures excellent conformality and large area uniformity of deposited films. Additionally, film thickness can be accurately controlled by the number of sequential surface reactions. Gallium oxide (Ga2O3) thin films were deposited by plasma-enhanced ALD (PEALD) using trimethylgallium as the gallium precursor and oxygen plasma as the oxidant. A wide ALD temperature window was observed from 100 to 400 °C, where the deposition rate was constant at ~0.53 Å/cycle. The deposition parameters, composition, crystallinity, surface morphology, optical and electrical properties were studied for as-deposited and annealed Ga2O3 films. In order to investigate the electrical properties of the deposited films, metal-oxide-semiconductor capacitor structures were fabricated for a variety of film thicknesses and annealing temperatures. Ga2O3 films exhibited decent dielectric properties after crystallization upon annealing. Dielectric constant was increased with film thickness and decreased slightly with increasing annealing temperature. As an additional PEALD experiment, deposition parameters of In2O3 thin films were studied as well, using the precursors of cyclopentadienyl indium and O2 plasma. Initial results of this experiment effort are also presented. Accurate thickness control, along with high uniformity and conformality offered by ALD makes this technique quite promising for the deposition of conformal coatings on nanostructures. This thesis also deals with the synthesis of metal oxide nanotubes using organic nanofiber templates. Combination of electrospinning and ALD processes provided an opportunity to precisely control both diameter and wall thickness of the synthesized nanotubes. As a proof-ofconcept, hafnia (HfO2) nanotubes were synthesized using three-step approach: (i) preparation of the nylon 6,6 nanofiber template by electrospinning, (ii) conformal deposition of HfO2 on the electrospun polymer template via ALD using the precursors of tetrakis(dimethylamido)hafnium and water at 200 °C, and (iii) removal of the organic template by calculation to obtain freestanding HfO2 nanotubes (hollow nanofibers). When the same deposition procedure was applied on nanofibers with different average fiber diameters, thinner HfO2 wall thicknesses were obtained for the templates having smaller diameters due to insufficient exposure of precursor molecules to saturate their extremely large surface area. Thus, “exposure mode” was applied to obtain the desired wall thickness while coating high-surface area nanofibers. We present the experimental efforts including film deposition parameters, structural, elemental, and morphological properties of HfO2 nanotubes.
Open Access
Preparation and characterization of ultra thin films containing silver-copper nanoalloys using layer-by-layer deposition technique for antibacterial applications
(2012) Camcı, Merve Taner
The main objective of this master thesis is to explore the preparation, characterization and antibacterial applications of Layer-by-Layer (LbL) assembled ultra thin films containing AgCu nanoalloys. Within this purpose, first part of the research mainly focused on the preparation of Ag nanoparticles and AgCu nanoalloys in order to prevent the oxidation of copper to copper oxide and the formation of polyelectrolyte-AgCu nanoalloy films by Layerby-Layer assembly. Accordingly, Ag nanoparticles and AgCu nanoalloys were synthesized by the chemical reduction of silver and copper salts in aqueous solution with the help of strong reducing agents sodium borohydride or hydrazine hydrate in the presence of complexing agent and stabilizer, then ultra thin polyelectrolyte layers containing pre-prepared AgCu nanoalloys were constructed by Layer-by-Layer deposition technique in different combinations. Also the stability of these nano sized binary alloys in solution phase were prolonged in the presence of third metal zinc as a sacrificial anode. In the second part of the study, characterization of LbL assembled ultra thin polyelectrolyte and metal nanoparticle thin films using Optical (UV-visible) and X-ray Photoelectron Spectroscopy (XPS) was studied. In order to get further information on the optical response of single and bimetallic nanoparticles, Ag nanoparticle and AgCu nanoalloy incorporated ultra thin polyelectrolyte films were investigated by optical spectroscopy. In addition the LbL films were analyzed by Static XPS to extract atomic level chemical information due to elemental and chemical state analysis. In order to get further understanding at the molecular level, samples were analyzed under external bias application by Dynamic XPS and it was shown that Ag and Cu respond in the same way to applying external electrical stimuli when both are in the same environment as a result of alloy formation, as reflected by the same shifts in Ag3d and Cu2p binding energy positions. Lastly, in the third part of the study detailed antibacterial analysis of synthesized monometallic and multimetallic nanoparticle solutions and the organized ultra thin polyelectrolyte layers containing Ag and AgCu nanoclusters against Escherichia coli strain was performed. These approaches enabled us to show the better antibacterial behavior of AgCu nanoalloys as a result of successful synthesis of AgCu nanoalloy without any copper oxide formation as the end product.
Open Access
Preparation and characterization of ultra-thin films containing Au and Ag nanoparticles using layer-by-layer deposition technique
(2009) Cönger, Can Pınar
The main objective of this thesis is to investigate the layer-by-layer deposited polyelectrolyte and polyelectrolyte/metal nanoparticle films by using X-ray Photoelectron (XPS) and Optical Spectroscopy (UV-Vis). Within this purpose, in the first part of the study, layer-by-layer deposited single and oppositely charged bilayered films are investigated by XPS. To extract additional information in the molecular level, the samples are analyzed while applying an external voltage bias. It is shown that applying external electrical stimuli to a single polyelectrolyte layer coated Si/SiO2 system responds to the change in the polarity by molecular rearrangements, evidenced by the changes only in the intensity of the corresponding –N + (1s) peak. In the second part of the study, metal nanoparticle (Au and/or Ag) incorporated polyelectrolyte films are investigated by optical spectroscopy. Within this frame, multilayer gold and silver nanaoparticle/polyelectrolyte films are prepared both separately and in bimetallic form. In order to get further understanding about the optical responses of single type of metal nanoparticle incorporated systems, several experimental approaches are followed. These approaches also enable us to control and manipulate the optical properties of these compact structures. The last part focuses on incorporation of metallic ions into layer-by-layer assembled polyelectrolyte matrices through ion-exchange method. It is shown that metal ions can be incorporated and subsequently reduced within this polymer matrix by UV or X-ray irradiation and can also form nanoparticles.