New inorganic nanomaterials for low-voltage transistor applications

Alharthi, Fahad Ahmed A.

Abstract

This research aims to synthesise and characterise solution-processable high-k dielectric nanorods, which are potentially suitable for use as the dielectric layer in low-voltage Organic Field-Effect Transistor (OFET) applications. Oleic acid-stabilised titanium dioxide nanorods (TiO₂-OA), metal-doped anatase titanium oxide (TiO₂-OA-M; M=Nb, In, or Nb/In) nanorods, rutile titanium oxide nanorods (TiO₂) and barium titanium oxide nanorods (BaTiO₃) have been prepared and investigated.

Solution processable oleic acid-stabilised titanium dioxide nanorods (TiO₂-OA) have been prepared by hydrolysis of titanium (IV) tetraisopropoxide (TTIP) with oleic acid (OA) as surfactant in the presence of trimethylamine N-oxide (TMAO). Furthermore, a series of ligand exchange reactions were carried out to replace the oleic acid bonded on the surface of TiO₂-OA with diethyl 2-phenylethyl phosphonate (DEPPNA), octadecylphosphonic acid (ODPA) or octylphosphonic acid (OPA). The ligand exchange rate was characterised by a combination of 31P liquid NMR, ICP, CHN, and FT-IR. The solubility of the ligand-exchanged products in chlorobenzene was also investigated.

A novel method based on the co-hydrolysis of titanium (IV) tetraisopropoxide (TTIP) and niobium or/and indium isopropoxide or ethoxide has been investigated to prepare solution-processable, oleic acid- stabilised, niobium- and indium-doped, anatase TiO₂ nanorods (TiO₂-OA-M; M = Nb, In or Nb/In). The effect of niobium and indium precursors, the molar ratio of Nb or In precursors/TTIP and reaction time on the composition, structure and morphology of the Nb or In doped TiO₂ products have been investigated by a combination of XPS, XRD, ICP, CHN, FT-IR and TEM. Furthermore, a series of ligand exchange reactions were carried out to replace the oleic acid, which is bonded on the surface of TiO₂-OA-M, with diethyl 2-phenylethyl phosphonate (DEPPNA) or octadecylphosphonic acid (ODPA). The solubility of the products in chlorobenzene was also investigated.

Rutile titanium dioxide nanorods with different sizes were prepared by three different approaches. In the first approach，hair-like rutile nanorods TiO₂ were prepared by simple hydrolysis of a TiOCl₂ solution at low temperature (50, 70 and 90 °C). In the second approach, rutile nanorods TiO₂ with a length of 150-200 nm and a width of 25-40 nm were prepared by using a hydrothermal treatment of TiOCl₂ at 220 °C. In the third approach, rutile nanorods TiO₂ with length of 80 nm and diameter of 20 nm were prepared by using an hydrothermal reaction of TiOCl₂ in the presence of 3-hydroxytyramine hydrogen chloride, [(HO)₂C₆H₃CH₂CH₂NH₂·HCl] at 150°C. In order to improve the solubility of the obtained rutile titanium dioxide nanorods in organic solvents, different surface-modification methods have been investigated to coat the surface of the rutile titanium dioxide nanorods with various organic ligands. In the first method, a modification of the TiO₂ nanorods with oleic acid (OA) in chlorobenzene was investigated. In the second method, a two-stage treatment of TiO₂ nanorods in an acidic medium was studied, using a selection of oleic acid (OA), diethyl 2-phenylethyl phosphonate (DEPPNA), octylphosphonic acid (OPA) and decylphosphonic acid (ODPA) as ligands. In the third method, wet TiO₂ nanorods before dry was directly modified with a range of oleic acid and amines, e.g., octylamine, dodecylamine and hexadecylamine, as ligands. All the products were characterized by a combination of XRD, ICP, CHN, FT-IR and TEM.

The preparation of barium titanium oxide nanorods (BaTiO₃) has been investigated by different approaches. In the first approach, a hydrothermal reaction was carried out to convert the titanium dioxide nanorods prepared in the first and third parts in this research into BaTiO₃ nanorods. The effect of the molar ratio of Ba/Ti, the reaction pH, reaction time and temperature on the composition, structure and morphology of the products were fully investigated. In the second approach, a hydrothermal reaction using a single source Ba/Ti precursor, i.e., barium titanium ethylhexano-isoproxide BaTi(O₂CC₇H₁₅)(OC₃H₇)₅, was carried out to prepare barium titanium oxide nanorods. In the third approach, barium titanium oxide nanorods were prepared by using a hydrothermal reaction between barium chloride (BaCl₂) and titanium oxy chloride (TiOCl₂) in the presence of ethylene glycol as surfactant. All the products have been characterised by a combination of XRD, ICP, CHN, FT-IR and TEM.

Citation

Alharthi, F. A. A. (2016). New inorganic nanomaterials for low-voltage transistor applications. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4220679

• Thesis Type: Thesis
• Deposit Date: Oct 2, 2018
• Publicly Available Date: Feb 23, 2023
• Keywords: Chemistry
• Public URL: https://hull-repository.worktribe.com/output/4220679
• Additional Information: Department of Chemistry, The University of Hull
• Award Date: May 1, 2016