Semiconductor Electronic Label-Free Assay for Predictive Toxicology.

While animal experimentations have spearheaded numerous breakthroughs in biomedicine, they also have spawned many logistical concerns in providing toxicity screening for copious new materials. Their prioritization is premised on performing cellular-level screening in vitro. Among the screening assays, secretomic assay with high sensitivity, analytical throughput, and simplicity is of prime importance. Here, we build on the over 3-decade-long progress on transistor biosensing and develop the holistic assay platform and procedure called semiconductor electronic label-free assay (SELFA). We demonstrate that SELFA, which incorporates an amplifying nanowire field-effect transistor biosensor, is able to offer superior sensitivity, similar selectivity, and shorter turnaround time compared to standard enzyme-linked immunosorbent assay (ELISA). We deploy SELFA secretomics to predict the inflammatory potential of eleven engineered nanomaterials in vitro, and validate the results with confocal microscopy in vitro and confirmatory animal experiment in vivo. This work provides a foundation for high-sensitivity label-free assay utility in predictive toxicology

Characterization of Thermo-Mechanical Damage in Tin and Sintered Nano-Silver Solders

abstract: Increasing density of microelectronic packages, results in an increase in thermal and mechanical stresses within the various layers of the package. To accommodate the high-performance demands, the materials used in the electronic package would also require improvement. Specifically, the damage that often occurs in solders that function as die-attachment and thermal interfaces need to be addressed. This work evaluates and characterizes thermo-mechanical damage in two material systems – Electroplated Tin and Sintered Nano-Silver solder. Tin plated electrical contacts are prone to formation of single crystalline tin whiskers which can cause short circuiting. A mechanistic model of their formation, evolution and microstructural influence is still not fully understood. In this work, growth of mechanically induced tin whiskers/hillocks is studied using in situ Nano-indentation and Electron Backscatter Diffraction (EBSD). Electroplated tin was indented and monitored in vacuum to study growth of hillocks without the influence of atmosphere. Thermal aging was done to study the effect of intermetallic compounds. Grain orientation of the hillocks and the plastically deformed region surrounding the indent was studied using Focused Ion Beam (FIB) lift-out technique. In addition, micropillars were milled on the surface of electroplated Sn using FIB to evaluate the yield strength and its relation to Sn grain size. High operating temperature power electronics use wide band-gap semiconductor devices (Silicon Carbide/Gallium Nitride). The operating temperature of these devices can exceed 250oC, preventing use of traditional Sn-solders as Thermal Interface materials (TIM). At high temperature, the thermomechanical stresses can severely degrade the reliability and life of the device. In this light, new non-destructive approach is needed to understand the damage mechanism when subjected to reliability tests such as thermal cycling. In this work, sintered nano-Silver was identified as a promising high temperature TIM. Sintered nano-Silver samples were fabricated and their shear strength was evaluated. Thermal cycling tests were conducted and damage evolution was characterized using a lab scale 3D X-ray system to periodically assess changes in the microstructure such as cracks, voids, and porosity in the TIM layer. The evolution of microstructure and the effect of cycling temperature during thermal cycling are discussed.Dissertation/ThesisDoctoral Dissertation Materials Science and Engineering 201

Synthesis, characterization and application of ZnO nanomaterials

In this thesis, high temperature vapor deposition method has been extensively used to synthesize nanomaterials. One of the as-synthesized nanostructures is superlattice-structured nanohelix, which is made of two types of alternating and periodically distributed long crystal strips. The manipulation of the nanohelix showed super-elasticity and special fracture mechanism. The other widely studied nanomaterial is vertically aligned ZnO nanowire array, which is epitaxially grown on GaN and SiC substrates. Several manipulation methods such as e-beam lithography (EBL), dielectrophoresis, and in situ direct manipulation, have been developed, so that the mechanical and electrical properties of a single nanowire can be characterized, which provide essential references for fabricating bridged nanowire based devices. Specifically, an improved atomic force microscope (AFM) based method has been developed to accurately measure the elastic modulus of bridged ZnO nanowires. Bridged nanostructure is an extremely important configuration in planar MEMS/NEMS devices and this new approach provides insights to the importance of boundary conditions. Novel physical and statistical models have been firstly developed to obtain better estimate of elastic modulus. For electrical properties of bridged nanowires, it is found that the direct contact of ZnO nanowire and Au electrodes displays a back-to-back Schottky behavior. Self-assembled monolayer (SAM) can improve the mechanical contact and increase the conductance. These devices with Schottky contacts show much better UV sensing performance than the ones with Ohmic contacts. Barrier height change is believed to play an important role in a lot of sensors. A thermionic emission-diffusion model is deduced to successfully explain the current change in a strain sensor. This thesis clearly exhibits the unique properties of ZnO nanomaterials and provides deeper understanding to methodologies as well as the phenomena. With further exploration, ZnO nanomaterials should be able to better understood and utilized, and come close to the next step of commercialization.Ph.D.Committee Chair: Wang, Zhong Lin; Committee Member: Gall, Kenneth A.; Committee Member: Snyder, Robert L.; Committee Member: Wong, Ching-Ping; Committee Member: Wu, C.F. Jef

Sensors for product characterization and quality of specialty crops—A review

This review covers developments in non-invasive techniques for quality analysis and inspection of specialty crops, mainly fresh fruits and vegetables, over the past decade up to the year 2010. Presented and discussed in this review are advanced sensing technologies including computer vision, spectroscopy, X-rays, magnetic resonance, mechanical contact, chemical sensing, wireless sensor networks and radiofrequency identification sensors. The current status of different sensing systems is described in the context of commercial application. The review also discusses future research needs and potentials of these sensing technologies. Emphases are placed on those technologies that have been proven effective or have shown great potential for agro-food applications. Despite significant progress in the development of non-invasive techniques for quality assessment of fruits and vegetables, the pace for adoption of these technologies by the specialty crop industry has been slow

Real-Time, Selective Detection of Heavy Metal Ions in Water Using 2d Nanomaterials-based Field-effect Transistors

Excessive intake of heavy metals damages the central nervous system and causes brain and blood disorders in mammals. Heavy metal contamination is commonly associated with exposure to mercury, lead, arsenic, and cadmium (arsenic is a metalloid, but classified as a heavy metal). Traditional methods to detect heavy metal ions include graphite furnace atomic absorption spectroscopy (GFAAS), inductively-coupled plasma optical emission spectroscopy (ICP-OES), and inductively-coupled plasma mass spectroscopy (ICP-MS). Recently, many new methods have been proposed to detect heavy metal ions, including atomic absorption spectrometry, fluorescent sensors, colorimetric sensors, electrochemical sensors, X-ray absorption fine structure spectroscopy, ultrasensitive dynamic light scatting assays, and ion selective electrodes. Although significant progress has been made, there are still some critical issues to be addressed, e.g., lack of portability, the need for well-trained personnel, highly expensive and complex instruments, long response time (tens of minutes or even longer), and the possibility of introducing additional contamination. Therefore, it is highly desirable to develop a real-time, low-cost, portable, user-friendly analytical platform for rapid inline analysis of mercury, lead and other heavy metal ions. This dissertation research aims to investigate field-effect transistor (FET) sensors based on two-dimensional (2D) nanomaterials with specific probe-functionalized gold (Au) nanoparticles (NPs). The fundamental mechanism of the FET platform is to use a 2D nanomaterial as the conducting channel to transport charge carriers (electrons or holes). Upon the capture of target analytes, the charge carrier concentration and/or mobility changes correspondingly with a signal of current change within the channel. As a result, the FET characteristic changes upon the introduction of the heavy metal ion solution, varies with the metal concentration, and takes only a few seconds to respond. Control experiments are performed to verify the selectivity of the 2D nanomaterial/Au NP hybrid sensor to specific targets. The rapid, selective, sensitive, and stable detection performance indicates the promise of 2D nanomaterial/Au NP hybrid sensors for heavy metal ion detection in an aqueous solution. This research is accomplished through several steps: First, various heavy metal ion contaminants, their damage, and the conventional detection methods are reviewed; Second, the FET-based plaform and its working mechanism are explored; Third, the understanding of various 2D nanomaterials, their unique properties pertinent to electronic sensing, and their selection to realize real-time, selective, and sensitive detection of heavy metal ions is carried out; Finally, improvement of stability, sensitivity and lifetime of FET sensors is investigated. In this thesis work, sensitive and selective FET-based 2D nanomaterial/Au NP hybrid sensors for Pb2+, Hg2+, As(III), and As(V) have been demonstrated. The 2D nanomaterials include reduced graphene oxide (rGO), molybdenum disulfide (MoS2), and black phosphorus (BP). The hybrid structure consists of a nanomaterial film, homogeneously dispersed Au NPs, and specific probes. The detection is enabled by recording the electrical conductance of the device through monitoring the change in the drain current of the 2D nanomaterial sheets. The platform offers a promising route for real-time (1-2 seconds), high-performance and low-cost detection of heavy metal ions. The lower detection limit can reach the order of µg/L (parts-per-billion or ppb). The sensor also shows high selectivity against other co-existing metal ions. To improve the sensitivity of the nanomaterial-based electronic sensor, theoretical analysis on the sensing mechanism has been carried out, together with experimental validation. Theoretical analysis indicates that sensitivity-related factors are semiconducting properties of nanomaterials (e.g., carrier mobility, band gap), number of probes, and adsorption capacity of Au NPs. Experimental results suggest that a higher sensitivity for sensors can be realized by forming hybrid structures with thinner 2D conducting materials with a larger band gap and a higher carrier mobility, increasing the areal density of anchoring sites on the sensor surface, and enhancing the adsorption of detection probes. Investigation into the stability of the nanomaterial-based electronic sensor includes the binding strength between the nanomaterial and electrodes, stability of the nanomaterials in ambient environment and water, the detachment of Au NPs, the lifetime and diffusion of probes, and the overall stability of the sensor platform. Subsequently, strategies to improve the stability of the nanomaterial-based FET sensor have been proposed. Finally, the FET sensor has been used for the accurate prediction of arsenic ions in lake water and integrated into a practical flowing water system for continuous detection of lead ions. The rapid, selective, sensitive, and stable detection performance of the FET sensor for various heavy metal ions in water suggests a promising future for in-situ detection of contamination events. The thesis study provides a scientific foundation to engineer FET sensors with enhanced performance. An attempt has been made to practically develop the FET platform into standalone sensors and to integrate the sensor into flowing water equipment for heavy metal ion detection. The thesis results thus contribute to the future application of FET sensors for monitoring water contamination and mitigating the public health risk

Characterization of Transient Heating in Power Electronic Devices and its Implications for Die Attached Reliability

Military and commercial interest in the use of power electronics for applications requiring extreme operating conditions and/or placement in extreme environments is driving research to identify and develop packaging technologies that can withstand these conditions. Specifically, there is an interest in the development of packaging technology than can function reliably under transient high power loading conditions. This thesis addresses the unique packaging considerations required for this type of application, with a focus on the implications on the durability of the die attach layer. Simulations of the thermal conditions experienced at the die attach layer for different power pulse magnitudes and durations are presented. A test apparatus and experimental test plan for studying the reliability of die attach materials under high power transient loading is discussed. Studies conducted to validate the test apparatus and characterize die attach reliability are described along with recommendations for further investigation of the reliability issues associated with high power, transient loading conditions

Ti-6Al-4V β Phase Selective Dissolution: In Vitro Mechanism and Prediction

Retrieval studies document Ti-6Al-4V β phase dissolution within total hip replacement systems. A gap persists in our mechanistic understanding and existing standards fail to reproduce this damage. This thesis aims to (1) elucidate the Ti-6Al-4V selective dissolution mechanism as functions of solution chemistry, electrode potential and temperature; (2) investigate the effects of adverse electrochemical conditions on additively manufactured (AM) titanium alloys and (3) apply machine learning to predict the Ti-6Al-4V dissolution state. We hypothesized that (1) cathodic activation and inflammatory species (H2O2) would degrade the Ti-6Al-4V oxide, promoting dissolution; (2) AM Ti-6Al-4V selective dissolution would occur and (3) near field electrochemical impedance spectra (nEIS) would distinguish between dissolved and polished Ti-6Al-4V, allowing for deep neural network prediction. First, we show a combinatorial effect of cathodic activation and inflammatory species, degrading the oxide film’s polarization resistance (Rp) by a factor of 105 Ωcm2 (p = 0.000) and inducing selective dissolution. Next, we establish a potential range (-0.3 V to –1 V) where inflammatory species, cathodic activation and increasing solution temperatures (24 oC to 55 oC) synergistically affect the oxide film. Then, we evaluate the effect of solution temperature on the dissolution rate, documenting a logarithmic dependence. In our second aim, we show decreased AM Ti-6Al-4V Rp when compared with AM Ti-29Nb-21Zr in H2O2. AM Ti-6Al-4V oxide degradation preceded pit nucleation in the β phase. Finally, in our third aim, we identified gaps in the application of artificial intelligence to metallic biomaterial corrosion. With an input of nEIS spectra, a deep neural network predicted the surface dissolution state with 96% accuracy. In total, these results support the inclusion of inflammatory species and cathodic activation in pre-clinical titanium devices and biomaterial testing

Microscopy and Analysis

Microscopes represent tools of the utmost importance for a wide range of disciplines. Without them, it would have been impossible to stand where we stand today in terms of understanding the structure and functions of organelles and cells, tissue composition and metabolism, or the causes behind various pathologies and their progression. Our knowledge on basic and advanced materials is also intimately intertwined to the realm of microscopy, and progress in key fields of micro- and nanotechnologies critically depends on high-resolution imaging systems. This volume includes a series of chapters that address highly significant scientific subjects from diverse areas of microscopy and analysis. Authoritative voices in their fields present in this volume their work or review recent trends, concepts, and applications, in a manner that is accessible to a broad readership audience from both within and outside their specialist area