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Carbon nanomaterials have caught tremendous attention in the last few decades due to their unique physical and chemical properties. Tremendous effort has been made to develop new synthesis techniques for carbon nanomaterials and investigate their properties for different applications. In this work, carbon nanospheres (CNSs), carbon foams (CF), and single-walled

Carbon nanomaterials have caught tremendous attention in the last few decades due to their unique physical and chemical properties. Tremendous effort has been made to develop new synthesis techniques for carbon nanomaterials and investigate their properties for different applications. In this work, carbon nanospheres (CNSs), carbon foams (CF), and single-walled carbon nanotubes (SWNTs) were studied for various applications, including water treatment, energy storage, actuators, and sensors.

A facile spray pyrolysis synthesis technique was developed to synthesize individual CNSs with specific surface area (SSA) up to 1106 m2/g. The hollow CNSs showed adsorption of up to 300 mg rhodamine B dye per gram carbon, which is more than 15 times higher than that observed for conventional carbon black. They were also evaluated as adsorbents for removal of arsenate and selenate from water and displayed good binding to both species, outperforming commercial activated carbons for arsenate removal in pH > 8. When evaluated as supercapacitor electrode materials, specific capacitances of up to 112 F/g at a current density of 0.1 A/g were observed. When used as Li-ion battery anode materials, the CNSs achieved a discharge capacity of 270 mAh/g at a current density of 372 mA/g (1C), which is 4-fold higher than that of commercial graphite anode.

Carbon foams were synthesized using direct pyrolysis and had SSA up to 2340 m2/g. When used as supercapacitor electrode materials, a specific capacitance up to 280 F/g was achieved at current density of 0.1 A/g and remained as high as 207 F/g, even at a high current density of 10 A/g.

A printed walking robot was made from common plastic films and coatings of SWNTs. The solid-state thermal bimorph actuators were multifunctional energy transducers powered by heat, light, or electricity. The actuators were also investigated for photo/thermal detection. Electrochemical actuators based on MnO2 were also studied for potential underwater applications.

SWNTs were also used to fabricate printable electrodes for trace Cr(VI) detection, which displayed sensitivity up to 500 nA/ppb for Cr(VI). The limit of detection was shown to be as low as 5 ppb. A flow detection system based on CNT/printed electrodes was also demonstrated.
ContributorsWang, Chengwei, Ph.D (Author) / Chan, Candace K. (Thesis advisor) / Tongay, Sefaattin (Committee member) / Wang, Qing Hua (Committee member) / Seo, Dong (Committee member) / Arizona State University (Publisher)
Created2015
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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

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
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Description
There has been a surge in two-dimensional (2D) materials field since the discovery of graphene in 2004. Recently, a new class of layered atomically thin materials that exhibit in-plane structural anisotropy, such as black phosphorous, transition metal trichalcogenides and rhenium dichalcogenides (ReS2), have attracted great attention. The reduced symmetry in

There has been a surge in two-dimensional (2D) materials field since the discovery of graphene in 2004. Recently, a new class of layered atomically thin materials that exhibit in-plane structural anisotropy, such as black phosphorous, transition metal trichalcogenides and rhenium dichalcogenides (ReS2), have attracted great attention. The reduced symmetry in these novel 2D materials gives rise to highly anisotropic physical properties that enable unique applications in next-gen electronics and optoelectronics. For example, higher carrier mobility along one preferential crystal direction for anisotropic field effect transistors and anisotropic photon absorption for polarization-sensitive photodetectors.

This dissertation endeavors to address two key challenges towards practical application of anisotropic materials. One is the scalable production of high quality 2D anisotropic thin films, and the other is the controllability over anisotropy present in synthesized crystals. The investigation is focused primarily on rhenium disulfide because of its chemical similarity to conventional 2D transition metal dichalcogenides and yet anisotropic nature. Carefully designed vapor phase deposition has been demonstrated effective for batch synthesis of high quality ReS2 monolayer. Heteroepitaxial growth proves to be a feasible route for controlling anisotropic directions. Scanning/transmission electron microscopy and angle-resolved Raman spectroscopy have been extensively applied to reveal the structure-property relationship in synthesized 2D anisotropic layers and their heterostructures.
ContributorsChen, Bin, 1968- (Author) / Tongay, Sefaattin (Thesis advisor) / Bertoni, Mariana (Committee member) / Chang, Lan-Yun (Committee member) / Arizona State University (Publisher)
Created2018
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Description
Layer structured two dimensional (2D) semiconductors have gained much interest due to their intriguing optical and electronic properties induced by the unique van der Waals bonding between layers. The extraordinary success for graphene and transition metal dichalcogenides (TMDCs) has triggered a constant search for novel 2D semiconductors beyond them. Gallium

Layer structured two dimensional (2D) semiconductors have gained much interest due to their intriguing optical and electronic properties induced by the unique van der Waals bonding between layers. The extraordinary success for graphene and transition metal dichalcogenides (TMDCs) has triggered a constant search for novel 2D semiconductors beyond them. Gallium chalcogenides, belonging to the group III-VI compounds, are a new class of 2D semiconductors that carry a variety of interesting properties including wide spectrum coverage of their bandgaps and thus are promising candidates for next generation electronic and optoelectronic devices. Pushing these materials toward applications requires more controllable synthesis methods and facile routes for engineering their properties on demand.

In this dissertation, vapor phase transport is used to synthesize layer structured gallium chalcogenide nanomaterials with highly controlled structure, morphology and properties, with particular emphasis on GaSe, GaTe and GaSeTe alloys. Multiple routes are used to manipulate the physical properties of these materials including strain engineering, defect engineering and phase engineering. First, 2D GaSe with controlled morphologies is synthesized on Si(111) substrates and the bandgap is significantly reduced from 2 eV to 1.7 eV due to lateral tensile strain. By applying vertical compressive strain using a diamond anvil cell, the band gap can be further reduced to 1.4 eV. Next, pseudo-1D GaTe nanomaterials with a monoclinic structure are synthesized on various substrates. The product exhibits highly anisotropic atomic structure and properties characterized by high-resolution transmission electron microscopy and angle resolved Raman and photoluminescence (PL) spectroscopy. Multiple sharp PL emissions below the bandgap are found due to defects localized at the edges and grain boundaries. Finally, layer structured GaSe1-xTex alloys across the full composition range are synthesized on GaAs(111) substrates. Results show that GaAs(111) substrate plays an essential role in stabilizing the metastable single-phase alloys within the miscibility gaps. A hexagonal to monoclinic phase crossover is observed as the Te content increases. The phase crossover features coexistence of both phases and isotropic to anisotropic structural transition.

Overall, this work provides insights into the controlled synthesis of gallium chalcogenides and opens up new opportunities towards optoelectronic applications that require tunable material properties.
ContributorsCai, Hui, Ph.D (Author) / Tongay, Sefaattin (Thesis advisor) / Dwyer, Christian (Committee member) / Zhuang, Houlong (Committee member) / Arizona State University (Publisher)
Created2018
Description
The study of the mechanical behavior of nanocrystalline metals using microelectromechanical systems (MEMS) devices lies at the intersection of nanotechnology, mechanical engineering and material science. The extremely small grains that make up nanocrystalline metals lead to higher strength but lower ductility as compared to bulk metals. Effects of strain-rate dependence

The study of the mechanical behavior of nanocrystalline metals using microelectromechanical systems (MEMS) devices lies at the intersection of nanotechnology, mechanical engineering and material science. The extremely small grains that make up nanocrystalline metals lead to higher strength but lower ductility as compared to bulk metals. Effects of strain-rate dependence on the mechanical behavior of nanocrystalline metals are explored. Knowing the strain rate dependence of mechanical properties would enable optimization of material selection for different applications and lead to lighter structural components and enhanced sustainability.
ContributorsHall, Andrea Paulette (Author) / Rajagopalan, Jagannathan (Thesis director) / Liao, Yabin (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2014-05
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Description
Solid-state lithium-ion batteries are a major area of research due to their increased safety characteristics over conventional liquid electrolyte batteries. Lithium lanthanum zirconate (LLZO) is a promising garnet-type ceramic for use as a solid-state electrolyte due to its high ionic conductivity. The material exists in two dierent phases, one that

Solid-state lithium-ion batteries are a major area of research due to their increased safety characteristics over conventional liquid electrolyte batteries. Lithium lanthanum zirconate (LLZO) is a promising garnet-type ceramic for use as a solid-state electrolyte due to its high ionic conductivity. The material exists in two dierent phases, one that is cubic in structure and one that is tetragonal. One potential synthesis method that results in LLZO in the more useful, cubic phase, is electrospinning, where a mat of nanowires is spun and then calcined into LLZO. A phase containing lanthanum zirconate (LZO) and amorphous lithium occursas an intermediate during the calcination process. LZO has been shown to be a sintering aid for LLZO, allowing for lower sintering temperatures. Here it is shown the eects of internal LZO on the sintered pellets. This is done by varying the 700C calcination time to transform diering amounts of LZO and LLZO in electrospun nanowires, and then using the same sintering parameters for each sample. X-ray diraction was used to get structural and compositional analysis of both the calcined powders and sintered pellets. Pellets formed from wires calcined at 1 hour or longer contained only LLZO even if the calcined powder had only undergone the rst phase transformation. The relative density of the pellet with no initial LLZO of 61.0% was higher than that of the pellet with no LZO, which had a relative density of 57.7%. This allows for the same, or slightly higher, quality material to be synthesized with a shorter amount of processing time.
ContributorsLondon, Nathan Harry (Author) / Chan, Candace (Thesis director) / Tongay, Sefaattin (Committee member) / Department of Physics (Contributor) / Materials Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2017-05
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Description
This thesis presents systematic studies on angle dependent Raman and Photoluminescence (PL) of a new class of layered materials, Transition Metal Trichalcogenides (TMTCs), which are made up of layers possessing anisotropic structure within the van-der-Waals plane. The crystal structure of individual layer of MX3 compounds consists of aligned nanowire like

This thesis presents systematic studies on angle dependent Raman and Photoluminescence (PL) of a new class of layered materials, Transition Metal Trichalcogenides (TMTCs), which are made up of layers possessing anisotropic structure within the van-der-Waals plane. The crystal structure of individual layer of MX3 compounds consists of aligned nanowire like 1D chains running along the b-axis direction. The work focuses on the growth of two members of this family - ZrS3 and TiS3 - through Chemical Vapor Transport Method (CVT), with consequent angle dependent Raman and PL studies which highlight their in-plane optically anisotropic properties. Results highlight that the optical properties of few-layer flakes are highly anisotropic as evidenced by large PL intensity variation with polarization direction (in ZrS3) and an intense variation in Raman intensity with variation in polarization direction (in both ZrS3 and TiS3).

Results suggest that light is efficiently absorbed when E-field of the polarized incident excitation laser is polarized along the chain (b-axis). It is greatly attenuated and absorption is reduced when field is polarized perpendicular to the length of 1D-like chains, as wavelength of the exciting light is much longer than the width of each 1D chain. Observed PL variation with respect to the azimuthal flake angle is similar to what has been previously observed in 1D materials like nanowires. However, in TMTCs, since the 1D chains interact with each other, it gives rise to a unique linear dichroism response that falls between 2D and 1D like behavior. These results not only mark the very first demonstration of high PL polarization anisotropy in 2D systems, but also provide a novel insight into how interaction between adjacent 1D-like chains and the 2D nature of each layer influences the overall optical anisotropy of Quasi-1D materials. The presented results are anticipated to have impact in technologies involving polarized detection, near-field imaging, communication systems, and bio-applications relying on the generation and detection of polarized light.
ContributorsPant, Anupum (Author) / Tongay, Sefaattin (Thesis advisor) / Alford, Terry Lynn (Committee member) / He, Ximin (Committee member) / Arizona State University (Publisher)
Created2016
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Description
A new class of layered materials called the transition metal trichalcogenides (TMTCs) exhibit strong anisotropic properties due to their quasi-1D nature. These 2D materials are composed of chain-like structures which are weakly bound to form planar sheets with highly directional properties. The vibrational properties of three materials from the TMTC

A new class of layered materials called the transition metal trichalcogenides (TMTCs) exhibit strong anisotropic properties due to their quasi-1D nature. These 2D materials are composed of chain-like structures which are weakly bound to form planar sheets with highly directional properties. The vibrational properties of three materials from the TMTC family, specifically TiS3, ZrS3, and HfS3, are relatively unknown and studies performed in this work elucidates the origin of their Raman characteristics. The crystals were synthesized through chemical vapor transport prior to mechanical exfoliation onto Si/SiO¬2 substrates. XRD, AFM, and Raman spectroscopy were used to determine the crystallinity, thickness, and chemical signature of the exfoliated crystals. Vibrational modes and anisotropic polarization are investigated through density functional theory calculations and angle-resolved Raman spectroscopy. Particular Raman modes are explored in order to correlate select peaks to the b-axis crystalline direction. Mode III vibrations for TiS3, ZrS3, and HfS3 are shared between each material and serves as a unique identifier of the crystalline orientation in MX3 materials. Similar angle-resolved Raman studies were conducted on the novel Nb0.5Ti0.5S3 alloy material grown through chemical vapor transport. Results show that the anisotropy direction is more difficult to determine due to the randomization of quasi-1D chains caused by defects that are common in 2D alloys. This work provides a fundamental understanding of the vibrational properties of various TMTC materials which is needed to realize applications in direction dependent polarization and linear dichroism.
ContributorsKong, Wilson (Author) / Tongay, Sefaattin (Thesis advisor) / Wang, Liping (Committee member) / Green, Matthew (Committee member) / Arizona State University (Publisher)
Created2017
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Description
Microplastics are emerging to be major problem when it comes to water pollution and they pose a great threat to marine life. These materials have the potential to affect a wide range of human population since humans are the major consumers of marine organisms. Microplastics are less than 5 mm

Microplastics are emerging to be major problem when it comes to water pollution and they pose a great threat to marine life. These materials have the potential to affect a wide range of human population since humans are the major consumers of marine organisms. Microplastics are less than 5 mm in diameter, and can escape from traditional wastewater treatment plant (WWTP) processes and end up in our water sources. Due to their small size, they have a large surface area and can react with chlorine, which it encounters in the final stages of WWTP. After the microplastics accumulate in various bodies of water, they are exposed to sunlight, which contains oxidative ultraviolet (UV) light. Since the microplastics are exposed to oxidants during and after the treatment, there is a strong chance that they will undergo chemical and/or physical changes. The WWTP conditions were replicated in the lab by varying the concentrations of chlorine from 70 to 100 mg/L in increments of 10 mg/L and incubating the samples in chlorine baths for 1–9 days. The chlorinated samples were tested for any structural changes using Raman spectroscopy. High density polyethylene (HDPE), polystyrene (PS), and polypropylene (PP) were treated in chlorine baths and observed for Raman intensity variations, Raman peak shifts, and the formation of new peaks over different exposure times. HDPE responded with a lot of oxidation peaks and shifts of peaks after just one day. For the degradation of semi-crystalline polymers, there was a reduction in crystallinity, as verified by thermal analysis. There was a decrease in the enthalpy of melting as well as the melting temperature with an increase in the exposure time or chlorine concentration, which pointed at the degradation of plastics and bond cleavages. To test the plastic response to

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UV, the samples were exposed to sunlight for up to 210 days and analyzed under Raman spectroscopy. Overall the physical and chemical changes with the polymers are evident and makes a way for the wastewater treatment plant to take necessary steps to capture the microplastics to avoid the release of any kind of degraded microplastics that could affect marine life and the environment.
ContributorsKelkar, Varun (Author) / Green, Matthew D (Thesis advisor) / Tongay, Sefaattin (Committee member) / Halden, Rolf U. (Committee member) / Arizona State University (Publisher)
Created2017
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Description
Thin film solar cells are based on polycrystalline materials that contain a high concentration of intrinsic and extrinsic defects. Improving the device efficiency in such systems relies on understanding the nature of defects - whether they are positive, negative, or neutral in their influence - and their sources in order

Thin film solar cells are based on polycrystalline materials that contain a high concentration of intrinsic and extrinsic defects. Improving the device efficiency in such systems relies on understanding the nature of defects - whether they are positive, negative, or neutral in their influence - and their sources in order to engineer optimized absorbers. Oftentimes, these are studied individually, as characterization techniques are limited in their ability to directly relate material properties in individual layers to their impact on the actual device performance. Expanding the tools available for increased understanding of materials and devices has been critical for reducing the translation time of laboratory-scale research to changes in commercial module manufacturing lines. The use of synchrotron X-ray fluorescence (XRF) paired with X-ray beam induced current and voltage (XBIC, XBIV respectively) has proven to be an effective technique for understanding the impact of material composition and inhomogeneity on solar cell device functioning. The combination of large penetration depth, small spot size, and high flux allows for the measurement of entire solar cell stacks with high spatial resolution and chemical sensitivity. In this work, I combine correlative XRF/XBIC/XBIV with other characterization approaches across varying length scales, such as micro-Raman spectroscopy and photoluminescence, to understand how composition influences device performance in thin films. The work described here is broken into three sections. Firstly, understanding the influence of KF post-deposition treatment (PDT) and the use of Ag-alloying to reduce defect density in the Ga-free material system, CuInSe2 (CIS). Next, applying a similar characterization workflow to industrially relevant Ga-containing Cu(In1-xGax)Se2 (CIGS) modules with Ag and KF-PDT. The influence of light soaking and dark heat exposure on the modules are also studied in detail. Results show that Ag used with KF-PDT in CIS causes undesirable cation ordering at the CdS interface and affects the device through increased potential fluctuations. The results also demonstrate the importance of tuning the concentration of KF-PDT used when intended to be used in Ag-alloyed devices. Commercially-processed modules with optimized Ag and KF concentrations are shown to have the device performance instead be dominated by variations in the CIGS composition itself. In particular, changes in Cu and Se concentrations are found to be most influential on the device response to accelerated stressors such as dark heat exposure and light soaking. In the final chapter, simulations of nano-scale XBIC and XBIV are done to contribute to the understanding of these measurements.
ContributorsNietzold, Tara (Author) / Bertoni, Mariana I. (Thesis advisor) / Holt, Martin (Committee member) / Shafarman, William N. (Committee member) / Tongay, Sefaattin (Committee member) / Arizona State University (Publisher)
Created2021