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- Halim, Joseph, 1985-
(author)
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Synthesis and Characterization of 2D Nanocrystals and Thin Films of Transition Metal Carbides (MXenes)
- 2014
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Licentiate thesis (other academic/artistic)abstract
- Two dimensional (2D) materials have received growing interest because of their unique properties compared to their bulk counterparts. Graphene is the archetype 2D solid, but other materials beyond graphene, such as MoS2 and BN have become potential candidates for several applications. Recently, a new family of 2D materials of early transition metal carbides and carbonitrides (Ti2CTx, Ti3C2Tx, Ti3CNTx, Ta4C3Tx, and more), labelled MXenes, has been discovered, where T stands for the surface-terminating groups.Before the present work, MXenes had only been synthesized in the form of exfoliated and delaminated powders, which is not suitable for electronic applications. In this thesis, I demonstrate the synthesis of MXenes as epitaxial thin films, a more suitable form for electronic and photonic applications. Results show that 2D epitaxial Ti3C2Tx films - produced by HF and NH4HF2 etching of magnetron sputter-grown Ti3AlC2 - exhibit metallic conductive behaviour down to 100 K and are 90% transparent to light in the visible-infrared range. The results from this work may open the door for MXenes as potential candidates for transparent conductive electrodes as well as in electronic, photonic and sensing applications.MXenes have been shown to intercalate cations and molecules between their layers that in turn can alter the surface termination groups. There is therefore a need to study the surface chemistries of synthetized MXenes to be able to study the effect of intercalation as well as altering the surface termination groups on the electronic structure and chemical states of the elements present in MXene layers. X-ray Photoelectron Spectroscopy (XPS) in-depth characterization was used to investigate surface chemistries of Ti3C2Tx and Ti2CTx. This thesis includes the discussion of the effect of Ar+ sputtering and the number of layers on the surface chemistry of MXenes. This study serves as a baseline for chemical modification and tailoring of the surface chemistry groups to potential uses and applications.New MXene phases, Nb2CTx and V2CTx, are shown in this thesis to be produced from HF chemical etching of Nb2AlC and V2AlC powders. Characterization of the produced MXenes was carried out using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Transmission Electron Microscope (TEM) and XPS. Nb2CTx and V2CTx showed promising performance as electrodes for Li-ion batteries.In this thesis, electrochemical etching was used in an attempt to produce 2D metal carbides (MXene) from their ternary metal carbides, Ti3SiC2, Ti3AlC2 and Ti2AlC MAX phases. MAX phases in the form of highly dense bulk produced by Hot Isostatic Press. Several etching solutions were used such as HF, NaCl and HCl. Unlike the HF chemical etching of MAX phases, which results in MXenes, the electrochemical etching resulted in Carbide Derived Carbon (CDC). Here, I show the characterization of the produced CDC using several techniques such as XRD, TEM, Raman spectroscopy, and XPS. Electrochemical characterization was performed in the form of cyclic voltammetry, which sheds light on the etching mechanism.
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- Hu, Jiwen, 1986-, et al.
(author)
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Selective detections of Hg2+ and F- by using tailor-made fluorogenic probes
- 2018
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In: Sensors and actuators. B, Chemical. - : Elsevier. - 0925-4005 .- 1873-3077. ; 269, s. 368-376
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Journal article (peer-reviewed)abstract
- By ingeniously using a (imino)coumarin-precursor, three reactive fluorogenic probes of MP, FP, and FMP have been fabricated in a single facile synthetic route. MP and FP are able to respectively act as selective "turn-on" fluorescent probes for detecting Hg2+ and F- in buffer solution via specific analyte-induced reactions. Linear ranges for the detection of Hg2+ and F- are 0-10 mu M and 0-100 mu M with the limits of detection (LODs) of 4.0 x 10(-8) M and 1.14 x 10(-6) M (3 delta/slope), respectively. FMP is able to work as a molecular "AND" logic gate-based fluorogenic probe for monitoring the coexistence of Hg2+ and F- via a multistep reaction cascade. The analytes-induced sensing mechanisms have been determined by using high-performance liquid chromatography analysis (HPLC). In addition, three probes show negligible toxicity under the experimental conditions, and are successfully used for monitoring Hg2+ and F- in living cells with good cell permeability. The success of the work demonstrates that ingenious utility of specific analyte-induced reactions and conventional concepts on the appropriate molecular scaffold can definitely deliver tailor-made probes for various intended sensing purposes. (C) 2018 Published by Elsevier B.V.
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- Shu, Rui, et al.
(author)
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Microstructure and mechanical, electrical, and electrochemical properties of sputter-deposited multicomponent (TiNbZrTa)N-x coatings
- 2020
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In: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 389
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Journal article (peer-reviewed)abstract
- A series of (TiNbZrTa)Nx coatings with a thickness of similar to 1.1 mu m were deposited using reactive magnetron sputtering with segmented targets. The deposition temperature was varied from room temperature to 700 degrees C resulting in coatings with different microstructures. The coatings were characterized by electron microscopy, atomic force microscopy, compositional analysis, and X-ray diffraction. Effects of the deposition temperature on the electrical, mechanical and corrosion properties were studied with four-point probe, nanoindentation and potentiodynamic polarization measurements, respectively. X-ray photoelectron spectroscopy (XPS) analyses reveal a gradual change in the chemical state of all elements with increasing growth temperature from nitridic at room temperature to metallic at 700 degrees C. A NaCl-type structure with (001) preferred orientation was observed in the coating deposited at 400 degrees C, while an hcp structure was found for the coatings deposited above 400 degrees C. The resistivities of the TiNbZrTa nitride coatings were found to be around 200 mu Ocm. In 0.1 M H2SO4 aqueous solution, a corrosion current density of 2.8 x 10(-8) A/cm(2) and a passive behaviour up to 1.5 V vs. Ag/AgCl were found for the most corrosion resistant coating. The latter corrosion current is about two orders of magnitude lower than that found for a reference hyper-duplex stainless steel.
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