Nanowire/nanotube memristor devices provide great potential for random-access high-density resist... more Nanowire/nanotube memristor devices provide great potential for random-access high-density resistance storage. However, fabricating high-quality and stable memristors is still challenging. This paper reports multileveled resistance states of tellurium (Te) nanotube based on the clean-room free femtosecond laser nano-joining method. The temperature for the entire fabrication process was maintained below 190 °C. A femtosecond laser joining technique was used to form nanowire memristor units with enhanced properties. Femtosecond (fs) laser-irradiated silver-tellurium nanotube-silver structures resulted in plasmonic-enhanced optical joining with minimal local thermal effects. This produced a junction between the Te nanotube and the silver film substrate with enhanced electrical contacts. Noticeable changes in memristor behavior were observed after fs laser irradiation. Capacitor-coupled multilevel memristor behavior was observed. Compared to previous metal oxide nanowire-based memristor...
Engineering nanoinks and photonic manufacturing for printable electronics
We have developed various nanoinks, including silver nanowires, silver nanoplates, Cu-Ag core-she... more We have developed various nanoinks, including silver nanowires, silver nanoplates, Cu-Ag core-shell nanoparticles, graphene oxide and graphene. Gram level nanoplates are successfully synthesized through a polymer controlled hydrothermal growth. Core-shell structures are synthesized through a microwave-assisted reduction and galvanic metal displacement. Graphene is fabricated through laser reduced graphene oxide. We show that these inks are enabling for direct writing on various substrates. Also, we displayed high viscous nanopastes can be developed by further concentration of these inks and metallic nanopastes can be used for low temperature packaging of flexible electronics and power electronics operating at high temperatures. For curing printed nanoinks and nanopastes, we compared three kinds of methods: thermal sintering, photonic sintering with flash light and athermal sintering with ultrafast fiber laser irradiation. It is possible to build 3D structures by combining ink printi...
for serving on my dissertation committee. I want to thank Dr. Zhili Feng for his advice and suppo... more for serving on my dissertation committee. I want to thank Dr. Zhili Feng for his advice and support during my graduate school career. Thanks to my fellow group members Yongchao Yu, Suhong Zhang, and Lingyue Zhang for their assistance and support. I also want to thank Dr. Ruozhou Li, Chaoli Ma, and Ying Ma for their direct support in different stages of my research. I want to thank all of my friends at the University of Tennessee and in Knoxville for their friendship, support, and prayers. I want to thank my family and my future wife, Emily Starnes, for their love, support, and prayers.
Colossal Photon Bunching Driven by Phonon Recombination Dynamics
Conference on Lasers and Electro-Optics, 2018
We report photon bunching g(2) (0) « 49 due to phonon sidebands in spectrally filtered cathodolum... more We report photon bunching g(2) (0) « 49 due to phonon sidebands in spectrally filtered cathodoluminescence from NV centers in diamond. The result is consistent with fast, phonon-mediated recombination dynamics, and supported by a stochastic model.
Colossal Bunching in Nanodiamond Cathodoluminescence
Frontiers in Optics 2017, 2017
Photon bunching with g(2)(0)>30 was observed in cathodoluminescence from nanodiamond particles... more Photon bunching with g(2)(0)>30 was observed in cathodoluminescence from nanodiamond particles evanescently coupled to Ag surface-plasmon polaritons. Comparisons with the photon bunching of isolated diamond nanoparticles point to Ag-plasmon-mediated decoherence processes.
Transient Liquid Phase Bonding of Inconel 718 With Ni and BNi-2 Nano-Braze Materials
Volume 2: Processes; Materials, 2019
Ni nanoparticles were successfully used to join Inconel 718 via transient liquid phase (TLP) bond... more Ni nanoparticles were successfully used to join Inconel 718 via transient liquid phase (TLP) bonding in a vacuum environment. Ni nanoparticles of 20 nm, 29 nm, and 41 nm in diameter were synthesized by controlling the reducing agent injection rate and joined at up to 1050 °C and heating rate 5–15 °C/min. Based on the Gibbs-Thomson equation and surface melting models, joining using Ni nanoparticles occurs due to competing solid-state sintering and surface melting processes. It was found that faster heating rate; higher maximum bonding temperature, and larger particle size resulted in higher bonding strength. Using a faster heating rate suppresses the amount of solid-state particle-particle sintering that occurs at lower temperatures, where particle-Inconel 718 joining is less active. The suppression of particle-particle sintering as a function of particle diameter is also discussed. The maximum bonding strength achieved is 243 MPa. The fracture surface for Ni nanoparticle-bonded join...
Preparation of Thick Ni/Al Reactive Multilayer Films and Prospective Use for Self-Powered Brazing of Ti-6Al-4V
Volume 2: Materials; Joint MSEC-NAMRC-Manufacturing USA, 2018
In this study we demonstrate a new method for depositing thick reactive multilayer films (RMFs) (... more In this study we demonstrate a new method for depositing thick reactive multilayer films (RMFs) (thickness > 14 μm) by using Ti interlayer integration and substrate preheating during fabrication. These two adjustments are designed to alleviate internal planar stresses that cause delamination between deposited layers and peeling off the substrate. Decreasing the distance between Ti interlayers helps to eliminate delamination between deposited layers. Through high speed camera measurements, the reaction propagation speed of an RMF sample with preheating is 42% slower than the same RMF that was not preheated, indicating a slower heat release rate. The preliminary experiments on brazing Ti-6Al-4V coated with BAlSi-4 brazing material revealed dendritic structure branching out from the RMF surface into the brazing material. The dendrite structures most likely form because of rapid melting and solidification of the brazing material. However, this rapid melting and solidification cycle d...
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
With the ever-increasing demand for power sources of high energy density and stability for emerge... more With the ever-increasing demand for power sources of high energy density and stability for emergent electrical vehicles and portable electronic devices, rechargeable batteries (such as lithium-ion batteries, fuel batteries, and metal–air batteries) have attracted extensive interests. Among the emerging battery technologies, metal–air batteries (MABs) are under intense research and development focus due to their high theoretical energy density and high level of safety. Although significant progress has been achieved in improving battery performance in the past decade, there are still numerous technical challenges to overcome for commercialization. Herein, this mini-review summarizes major issues vital to MABs, including progress on packaging and crucial manufacturing technologies for cathode, anode, and electrolyte. Future trends and prospects of advanced MABs by additive manufacturing and nanoengineering are also discussed.
Fe-based ceramic nanocomposite membranes fabricated via e-spinning and vacuum filtration for Cd i... more Fe-based ceramic nanocomposite membranes fabricated via e-spinning and vacuum filtration for Cd ions removal, (2019), doi: 2+
In this study, we demonstrate the successful brazing and superior mechanical performance of laser... more In this study, we demonstrate the successful brazing and superior mechanical performance of laser brazed Inconel® 718 using a Ni-Mn-Fe-Co-Cu high entropy alloy
Ag nanomaterials have been investigated as a filler material for brazing Inconel 718 well below t... more Ag nanomaterials have been investigated as a filler material for brazing Inconel 718 well below the bulk melting temperature of Ag using both vacuum and laser brazing. However, Ag nanoparticles and Ag nanowires exhibit different bonding strengths. In this study, we focus on different diffusion and wetting behaviors of two kinds of nanopastes. At 550°C, the areal coverage of the nanopaste decreases as a result of shrinkage in the nanopaste. The shrinkage is followed by rapid wetting and spreading on the Inconel 718 surface. A deeper investigation to the diffusion behavior of Ag nanoparticle and Ag nanowire pastes during laser brazing provides a clear correlation between the diffusion distance and the bonding strength. The diffusion of the base material into the Ag joint is shown to result in a concentration Bhump^near the Ag-Inconel 718 interface of different base material elements which is likely caused by a difference in diffusivity of Ag and the Inconel 718 constituent elements. Ag NW joints were found to have a thicker diffusion zone, but also exhibit some Nb/Mo segregation when brazed using 300-W laser power. This may lead in different metallurgic bonding.
This study investigated the characteristics and strength of the dissimilar joints between carbon ... more This study investigated the characteristics and strength of the dissimilar joints between carbon fiber reinforced plastic (CFRP) epoxy composites and aluminum alloys using two different heating methods, Ni/Al reactive multilayer films (RMF) and a low power continuous wave diode laser. To enhance the adhesion, the top resin layer of the CFRP and the surface of the aluminum alloy were patterned by femtosecond laser. Polycarbonate (PC) was used as a filler material during the joining processes. ANSYS simulation was applied to elucidate the thermal kinetics of the self-propagation reaction and the thermal profile, and evaluate the possibility of joining CFRP to aluminum using Ni/Al RMFs. The SEM image of the cross-section shows that melted PC flowed into the CFRP–aluminum alloy interface, suggesting strong mechanical bonding. A tensile strength of 9.5 MPa was reached using Ni/Al multilayers as heat sources, which provides a new way for joining CFRPs and aluminum alloys in space or under...
Self-powered brazing of Ti-6Al-4V was performed using Ni/Al reactive multilayer films (RMFs) as s... more Self-powered brazing of Ti-6Al-4V was performed using Ni/Al reactive multilayer films (RMFs) as self-propagated heat resources. BAlSi-4 was first coated on Ti-6Al-4V by plasma welding, then alternating layers of Ni and Al were successfully deposited on BAlSi-4 up to 32.9 µm thick with e-beam deposition. The joint microstructure was investigated and the AlNi and Ni 5 Al 3 phases were identified in the RMF. The cause for the two phases was determined to be differences in the diffusivity of Ni and Al, ultrafast brazing time, and faster cooling at the interface between brazing filler metal and the RMF. The maximum temperature of 683 • C was reached in the brazed joint, with a total RMF thickness of 135 µm, which is more than sufficient to melt the BAlSi-4 brazing material. The maximum bonding strength obtained was 10.6 MPa, with a self-power brazing procedure conducted in a minute. It is possible to further improve the bonding strength by using more ductile RMFs and/or modifying the bonding interface configuration.
We have successfully fabricated α-Fe O oxidizers with different shapes, including nanoparticles (... more We have successfully fabricated α-Fe O oxidizers with different shapes, including nanoparticles (NPs, diameter: ~22.1 nm), nanorods 2 3 (NRs, length: 385.3 nm) and nanowires (NWs). For the Al/Fe O NPs thermite reaction, as the nominal weight ratio for Al/Fe O (NPs) 2 3 2 3 reaches 2.5:1, the fastest combustion velocity (2.03 m/s), the largest instant plume propagation speed (10.71 m/s) as well as the maximum heat release (~9.46 kJ/g) can be achieved. However, with the same nominal weight ratio, the average combustion velocity and the instant plume speed of Al/Fe O (NRs) and Al/Fe nitrilotriacetic acid precusors NWs (FeNTA,) nanothermite are only about 0.16 m/s and 4.96 2 3 m/s, and 0.098 m/s and 3.28 m/s, respectively. This is probably due to the shape difference that renders different contact configurations between nano-fuel and nano-oxidizer. In addition, an incomplete calcination of FeNTA is also responsible for such a low combustion velocity. The reaction products were further identified by SEM and XRD analysis. Accordingly, the reaction mechanisms for the examined nanothermites were mainly controlled by the oxygen transfer dynamics.
Nanoscale control over the second-order photon correlation function g (2) (τ) is critical to emer... more Nanoscale control over the second-order photon correlation function g (2) (τ) is critical to emerging research in nonlinear nanophotonics and integrated quantum information science. Here we report on quasiparticle control of photon bunching with g (2) (0) > 45 in the cathodoluminescence of nanodiamond nitrogen vacancy (NV 0) centers excited by a converged electron beam in an aberrationcorrected scanning transmission electron microscope. Plasmon-mediated NV 0 cathodoluminescence exhibits a 16-fold increase in luminescence intensity correlated with a threefold reduction in photon bunching compared with that of uncoupled NV 0 centers. This effect is ascribed to the excitation of single temporally uncorrelated NV 0 centers by single surface plasmon polaritons. Spectrally resolved Hanbury Brown-Twiss interferometry is employed to demonstrate that the bunching is mediated by the NV 0 phonon sidebands, while no observable bunching is detected at the zero-phonon line. The data are consistent with fast phonon-mediated recombination dynamics, a conclusion substantiated by agreement between Bayesian regression and Monte-Carlo models of superthermal NV 0 luminescence.
Ag nanopastes composed of Ag nanoparticles or Ag nanowires and Cu-Ag nanopastes with Cu-Ag coresh... more Ag nanopastes composed of Ag nanoparticles or Ag nanowires and Cu-Ag nanopastes with Cu-Ag coreshell nanowires are used as a new brazing material for Inconel ® 718. Ag nanoparticles or Ag nanowires are further added to the core-shell paste to adjust to a eutectic composition. Microstructural analysis of the brazed joints was carried out with EDS and XRD. High bonding strength (>100 MPa) was obtained with both Ag and Cu-Ag nanopastes. It was concluded that the Cu-Ag nanopastes form stronger braze joints than the BAg-8 brazing alloy as a result of Hall-Petch strengthening. It has also been concluded that the addition Ag nanoparticles or Ag nanowires to the Cu-Ag core-shell nanowire paste have a significant impact on the bonding strength and fracture of the Cu-Ag joints.
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