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- All Subjects: Materials Science
- Language: English
Description
Due to the potential synergistic properties from combining inorganic and organic moieties, inorganic/organic hybrids materials have recently attracted great attention. These hybrids are critical components in coating and nanocomposite additive technologies and have potential for future application in catalysis, energy production or storage, environmental remediation, electronic, and sensing technologies. Most of these hybrids utilize low dimensional metal oxides as a key ingredient for the inorganic part. Generally, clay materials are used as inorganic components, however, the use of low dimensional transition metal oxides may provide additional properties not possible with clays. Despite their potential, few methods are known for the use of low dimensional transition metal oxides in the construction of inorganic/organic hybrid materials.Herein, new synthetic routes to produce hybrid materials from low dimensional early transition metal oxides are presented. Included in this thesis is a report on a destructive, chemical exfoliation method designed specifically to exploit the Brønsted acidity of hydrated early transition metal oxides. The method takes advantage of (1) the simple acid-base reaction principle applied to strong two-dimensional Brønsted solid acids and mildly basic, high-polarity organic solvents, (2) the electrostatic repulsion among exfoliated nanosheets, and (3) the high polarity of the organic solvent to stabilize the macroanionic metal oxide nanosheets in the solvent medium. This exfoliation route was applied to tungstite (WO3∙H2O) and vanadium phosphate hydrate (VOPO4∙H2O) to produce stable dispersions of metal oxide nanosheets. The nanosheets were then functionalized by adduct formation or silane surface modification. Both functionalization methods resulted in materials with unique properties, which demonstrates the versatility of the new exfoliation methods in preparing novel hybrid materials.
Further extension of the method to aqueous systems allowed discovery of a new synthetic method for electrically-conducting polyaniline-polyoxometalate hybrid materials. Namely, destructive dissolution of MoO2(HPO4)(H2O) in water produces protons and Strandberg-type phosphomolybdate clusters, and in the presence of aniline and an oxidizing agent, the clusters self-assemble with protonated anilines and selectively form polyaniline-phosphomolybdate hybrids on various types of surfaces through in situ oxidative chemical polymerization. New conductive nanocomposite materials were produced by selectively coating the surface of silica nanoparticles.
ContributorsCiota, David (Author) / Seo, Dong-Kyun (Thesis advisor) / Trovitch, Ryan (Committee member) / Birkel, Christina (Committee member) / Arizona State University (Publisher)
Created2022
Description
Since the discovery of graphene, two dimensional materials (2D materials) have become a focus of interest for material research due to their many unique physical properties embedded in their 2D structure. While they host many exciting potential applications, some of these 2D materials are subject to environmental instability issues induced by interaction between material and gas molecules in air, which poses a barrier to further application and manufacture. To overcome this, it is necessary to understand the origin of material instability and interaction with molecules commonly found in air, as well as developing a reproducible and manufacturing compatible method to post-process these materials to extend their lifetime. In this work, the very first investigation on environmental stability on Te containing anisotropic 2D materials such as GaTe and ZrTe3 is reported. Experimental results have demonstrated that freshly exfoliated GaTe quickly deteriorate in air, during which the Raman spectrum, surface morphology, and surface chemistry undergo drastic changes. Environmental Raman spectroscopy and XPS measurements demonstrate that H2O molecules in air interact strongly on the surface while O2, N2, and inert gases don't show any detrimental effects on GaTe surface. Moreover, the anisotropic properties of GaTe slowly disappear during the aging process. To prevent this gas/material interaction based surface transformation, diazonium based surface functionalization is adopted on these Te based 2D materials. Environmental Raman spectroscopy results demonstrate that the stability of functionalized Te based 2D materials exhibit much higher stability both in ambient and extreme conditions. Meanwhile, PL spectroscopy, angle resolved Raman spectroscopy, atomic force microscopy measurements confirm that many attractive physical properties of the material are not affected by surface functionalization. Overall, these findings unveil the degradation mechanism of Te based 2D materials as well as provide a way to significantly enhance their environmental stability through an inexpensive and reproducible surface chemical functionalization route.
ContributorsYang, Sijie (Author) / Tongay, Sefaattin (Thesis advisor) / Gould, Ian (Thesis advisor) / Trovitch, Ryan (Committee member) / Ghirlanda, Giovanna (Committee member) / Arizona State University (Publisher)
Created2017
Description
Sn-based group IV materials such as Ge1-xSnx and Ge1-x-ySixSny alloys have great potential for developing Complementary Metal Oxide Semiconductor (CMOS) compatible devices on Si because of their tunable band structure and lattice constants by controlling Si and/or Sn contents. Growth of Ge1-xSnx binaries through Molecular Beam Epitaxy (MBE) started in the early 1980s, producing Ge1-xSnx epilayers with Sn concentrations varying from 0 to 100%. A Chemical Vapor Deposition (CVD) method was developed in the early 2000s for growing Ge1-xSnx alloys of device quality, by utilizing various chemical precursors. This method dominated the growth of Ge1-xSnx alloys rapidly because of the great crystal quality of Ge1-xSnx achieved. As the first practical ternary alloy completely based on group IV elements, Ge1-x-ySixSny decouples bandgap and lattice constant, becoming a prospective CMOS compatible alloy. At the same time, Ge1-x-ySixSny ternary system could serve as a thermally robust alternative to Ge1-ySny binaries given that it becomes a direct semiconductor at a Sn concentration of 6%-10%. Ge1-x-ySixSny growths by CVD is summarized in this thesis. With the Si/Sn ratio kept at ~3.7, the ternary alloy system is lattice matched to Ge, resulting a tunable direct bandgap of 0.8-1.2 eV. With Sn content higher than Si content, the ternary alloy system could have an indirect-to-direct transition, as observed for Ge1-xSnx binaries. This thesis summarizes the development of Ge1-xSnx and Ge1-x-ySixSny alloys through MBE and CVD in recent decades and introduces an innovative direct injection method for synthesizing Ge1-x-ySixSny ternary alloys with Sn contents varying from 5% to 12% and Si contents kept at 1%-2%. Grown directly on Si (100) substrates in a Gas-phase Molecular Epitaxy (GSME) reactor, both intrinsic and n-type doped Ge1-x-ySixSny with P with thicknesses of 250-760 nm have been achieved by deploying gas precursors Ge4H10, Si4H10, SnD4 and P(SiH3)3 at the unprecedented low growth temperatures of 190-220 °C. Compressive strain is reduced and crystallinity of the Ge1-x-ySixSny epilayer is improved after rapid thermal annealing (RTA) treatments. High Resolution X-ray Diffraction (HR-XRD), Rutherford Backscattering Spectrometry (RBS), cross-sectional Transmission Electron Microscope (XTEM) and Atomic Force Microscope (AFM) have been combined to characterize the structural properties of the Ge1-x-ySixSny samples, indicating good crystallinity and flat surfaces.
ContributorsHu, Ding (Author) / Kouvetakis, John (Thesis advisor) / Menéndez, Jose (Committee member) / Trovitch, Ryan (Committee member) / Arizona State University (Publisher)
Created2019
Description
The work described in this thesis explores the synthesis of new semiconductors in the Si-Ge-Sn system for application in Si-photonics. Direct gap Ge1-ySny (y=0.12-0.16) alloys with enhanced light emission and absorption are pursued. Monocrystalline layers are grown on Si platforms via epitaxy-driven reactions between Sn- and Ge-hydrides using compositionally graded buffer layers that mitigate lattice mismatch between the epilayer and Si platforms. Prototype p-i-n structures are fabricated and are found to exhibit direct gap electroluminescence and tunable absorption edges between 2200 and 2700 nm indicating applications in LEDs and detectors. Additionally, a low pressure technique is described producing pseudomorphic Ge1-ySny alloys in the compositional range y=0.06-0.17. Synthesis of these materials is achieved at ultra-low temperatures resulting in nearly defect-free films that far exceed the critical thicknesses predicted by thermodynamic considerations, and provide a chemically driven route toward materials with properties typically associated with molecular beam epitaxy.
Silicon incorporation into Ge1-ySny yields a new class of Ge1-x-ySixSny (y>x) ternary alloys using reactions between Ge3H8, Si4H10, and SnD4. These materials contain small amounts of Si (x=0.05-0.08) and Sn contents of y=0.1-0.15. Photoluminescence studies indicate an intensity enhancement relative to materials with lower Sn contents (y=0.05-0.09). These materials may serve as thermally robust alternatives to Ge1-ySny for mid-infrared (IR) optoelectronic applications.
An extension of the above work is the discovery of a new class of Ge-like Group III-V-IV hybrids with compositions Ga(As1–xPx)Ge3 (x=0.01-0.90) and (GaP)yGe5–2y related to Ge1-x-ySixSny in structure and properties. These materials are prepared by chemical vapor deposition of reactive Ga-hydrides with P(GeH3)3 and As(GeH3)3 custom precursors as the sources of P, As, and Ge incorporating isolated GaAs and GaP donor-acceptor pairs into diamond-like Ge-based structures. Photoluminescence studies reveal bandgaps in the near-IR and large bowing of the optical behavior relative to linear interpolation of the III-V and Ge end members. Similar materials in the Al-Sb-B-P system are also prepared and characterized. The common theme of the above topics is the design and fabrication of new optoelectronic materials that can be fully compatible with Si-based technologies for expanding the optoelectronic capabilities of Ge into the mid-IR and beyond through compositional tuning of the diamond lattice.
Silicon incorporation into Ge1-ySny yields a new class of Ge1-x-ySixSny (y>x) ternary alloys using reactions between Ge3H8, Si4H10, and SnD4. These materials contain small amounts of Si (x=0.05-0.08) and Sn contents of y=0.1-0.15. Photoluminescence studies indicate an intensity enhancement relative to materials with lower Sn contents (y=0.05-0.09). These materials may serve as thermally robust alternatives to Ge1-ySny for mid-infrared (IR) optoelectronic applications.
An extension of the above work is the discovery of a new class of Ge-like Group III-V-IV hybrids with compositions Ga(As1–xPx)Ge3 (x=0.01-0.90) and (GaP)yGe5–2y related to Ge1-x-ySixSny in structure and properties. These materials are prepared by chemical vapor deposition of reactive Ga-hydrides with P(GeH3)3 and As(GeH3)3 custom precursors as the sources of P, As, and Ge incorporating isolated GaAs and GaP donor-acceptor pairs into diamond-like Ge-based structures. Photoluminescence studies reveal bandgaps in the near-IR and large bowing of the optical behavior relative to linear interpolation of the III-V and Ge end members. Similar materials in the Al-Sb-B-P system are also prepared and characterized. The common theme of the above topics is the design and fabrication of new optoelectronic materials that can be fully compatible with Si-based technologies for expanding the optoelectronic capabilities of Ge into the mid-IR and beyond through compositional tuning of the diamond lattice.
ContributorsWallace, Patrick Michael (Author) / Kouvetakis, John (Thesis advisor) / Menéndez, Jose (Committee member) / Trovitch, Ryan (Committee member) / Arizona State University (Publisher)
Created2018