Electrochemical Growth and Characterization of ZnO Nanowires

ZnO semiconductor materials, especially nanostructured materials, have potential applications in large-area electronics, photonics and optoelectronics due to their unique electrical and optical properties. ZnO nanowires have advantages of high surface area to volume ratio, with the prospective for nanoscale control of doping the electrical properties for 1-D nanoelectronic devices. Many techniques have been tried to achieve high quality ZnO nanowires in large scale with low cost and simple fabrication. However, most of these techniques require high temperatures that exclude applications in flexible electronics. P-type conductivity is another impediment for fully realizing ZnO materials for electronic device application; and this limitation has prevented advances in optoelectronic and integrated circuit applications for ZnO. To overcome the problems, this study investigated the synthesis and doping of ZnO nanowires at low temperature through a rapid electrochemical deposition growth technique. Material properties were studied using scanning electron microscopy (SEM), photoluminescence spectroscopy (PL), Raman spectroscopy, X-ray diffraction (XRD), ultraviolet to visible (UV-Vis) transmission spectroscopy, and electrical current-voltage measurements. ZnO nanowire doping was investigated using Al for n-type doping and for p-type doping, Ag/Al (co-doping) and Li. Al and Ag have significant influences on ZnO nanowire structures, while Li was found to improve the nanowire structure quality. The mechanisms for electrochemical deposition were studied through characterization of the chemical reactions, interface science and semiconductor/solution interface. It was found that the low temperature grown nanowires had high oxygen vacancy condition induced donor defect states, while, incorporation of Li dopants contributed to trap states (deep acceptor states), rather than shallow acceptor states in the band gap. Shown by XRD and PL, oxygen assisted post-growth annealing was found to promote recrystallization of ZnO and elimination of oxygen vacancies for better crystal quality and photoluminescence emission. Cr, Al or Au metals were used as contacts to Li-doped ZnO nanowires to examine electrical properties of the doped nanowires, turning out high ideal factor were obtained because of the poor contact quality due to significant surface and interface states in ZnO nanowires. At last, mechanisms of surface states related tunneling current at the metal-semiconductor interface were discussed

Desipramine Pretreatment Improves Sympathetic Remodeling and Ventricular Fibrillation Threshold after Myocardial Ischemia

Abnormal increase in sympathetic nerve sprouting was responsible for the ventricular arrhythmogenesis after myocardial infarction. This study investigated whether the norepinephrine transporter inhibitor, desipramine, can modulate sympathetic remodeling and ventricular fibrillation threshold (VFT) after myocardial ischemia-reperfusion. Rats were administered desipramine (0.8 mg/kg, IV) before or after myocardial ischemia. VFT, infarct size, tyrosine hydroxylase (TH) and growth-associated protein 43 (GAP43)-positive nerve fibers were measured after one week. The VFT of preischemic treatment group was 11.0±2.65 V and significantly higher than that of control ischemic group (7.2±1.30 V, P<0.05). Infarct size in the preischemic treatment group (23.3±2.4%) was significantly lower than that in the control ischemic group (30.8±1.3%, P<0.05) and the delayed application group (27.1±2.6%, P<0.05). The density of TH and GAP43-positive nerve fibers in the control ischemic group was significantly higher than that in the other three groups (P<0.05). The density of nerve fibers improved after desipramine treatment. Moreover, there was a negative correlation between the VFT and both TH and GAP43-positive nerve fiber density in the infarct border zone (P<0.05). Desipramine treatment before acute myocardial ischemia can decrease infarct size, improve sympathetic remodeling, and increase VFT and electrical stability of ischemic hearts. Desipramine appears to cause myocardial ischemic preconditioning

Quantitative Carrier Transport in Quantum Dot Photovoltaic Solar Cells from Novel Photocarrier Radiometry and Lock-in Carrierography

Colloidal quantum dots (CQDs) are promising candidates for fabricating large-scale, low-cost, flexible, and lightweight photovoltaic solar cells. However, their power conversion efficiency is still insufficient for commercial applications, partly and significantly, due to the not-well-understood carrier transport mechanisms and the lack of effective characterization techniques. Addressing these issues, carrier transport kinetics in CQD systems were studied to develop high-frequency dynamic testing and/or large-area quantitative imaging techniques: photocarrier radiometry (PCR), and homodyne (HoLIC) and heterodyne (HeLIC) lock-in carrierographies. Based on the discrete carrier hopping transport in CQDs, various carrier drift-diffusion current-voltage (J-V) analytical models and new concepts including the imbalanced carrier mobilities, reversed Schottky barrier, and double-diode model were developed to quantitatively interpret carrier transport and J-V characteristics in CQD solar cells. The further quantitative study of carrier mobility, CQD bandgap energy, phonon-assisted carrier transport, and open-circuit voltage deficit revealed CQD solar cell efficiency optimization strategies. Applying these energy transport mechanisms, for the first time, an analytical PCR signal generation model for CQD systems was developed from a novel trap-state-mediated carrier hopping transport theory. Therefore, multiple carrier transport parameters including carrier hopping lifetime, diffusivity, and diffusion length were extracted to investigate carrier transport dependencies on temperature, quantum dot size, surface-passivation ligands, and carrier hopping activation energies. As an imaging extension of PCR, using a heterodyne method to overcome the limitations of camera frame rate and exposure time of even the state-of-the-art InGaAs cameras, the first camera-based HeLIC theoretical model for ultrahigh-frequency (up to 270 kHz) imaging of CQD solar cells was achieved. Therefore, quantitative imaging of carrier lifetime, diffusivity, and diffusion and drift lengths of CQD solar cells was accomplished to explore the influences of carrier transport and contact/CQD interface on CQD solar cells. Also, low-frequency HoLIC large-area imaging evaluated the sample homogeneity and quality, reflecting preliminary carrier lifetime distribution. The combination of the novel carrier discrete hopping transport mechanism, J-V models, PCR, and the lock-in carrierography techniques (HoLIC and HeLIC) shows great potential for quantitative carrier transport study of CQD solar cells and for fast, all-optical, contactless, large-area, and nondestructive characterization of commercial photovoltaic materials and devices.Ph.D.2018-06-19 00:00:0

Influence of substrate on electrical conductivity of isotropic conductive adhesive

Isotropic conductive adhesive (ICA) is widely used with different kinds of substrates in electronics packaging applications. Therefore it is necessary to understand the influence of electrical conductivity of ICA from substrate. In this work, we investigated the electrical resistivity of ICA on quartz, PCB and glass substrate. The experimental data showed that the in-plane electrical conductivity of ICA on PCB is almost twice that of the glass substrate, while the conductivity of ICA on quartz is also significantly greater than that of glass, under the same curing temperature and with the same bond line thickness (BLT) of ICA. This paper later concludes that thermal conductive adhesive (TCA) on substrate with higher thermal expansion coefficient (CTE) is likely to give better performance. Finally, Finite Element Modeling (FEM) and analysis shows that this phenomenon could be universal to ICA and TCA

Distribution and source of organic matter in surface sediment from the muddy deposit along the Zhejiang coast, East China Sea

To constrain organic matter compositions and origins, elemental (TOC, TN, C/N) and stable carbon (δC) and nitrogen isotope (δN) compositions are measured for surface sediments collected from muddy deposit along the Zhejiang coast, East China Sea. The results showed that the TOC, TN, C/N, δC, and δN were 0.19–0.67%, 0.03–0.09%, 6.76–9.22, − 23.43 to − 20.26‰ and 3.93–5.27‰ respectively. The δC values showed that the mixing inputs of terrigenous and marine organic matter generally dominated sedimentary organic matter in the west part, and the sedimentary organic matters were mainly influenced by the marine organic matter in the east part of the study area. A stable carbon isotope two end member mixing model estimates ~ 38% terrestrial -derived and ~ 62% marine-derived inputs to sedimentary organic matter. Microbial mineralization strongly controls δN values, and therefore cannot be used to identify the provenance of organic matter for the Zhenjiang coast

Ultrafast Nucleic Acid Detection Equipment with Silicon-Based Microfluidic Chip

Recently, infectious diseases, such as COVID-19, monkeypox, and Ebola, are plaguing human beings. Rapid and accurate diagnosis methods are required to preclude the spread of diseases. In this paper, an ultrafast polymerase chain reaction (PCR) equipment is designed to detect virus. The equipment consists of a silicon-based PCR chip, a thermocycling module, an optical detection module, and a control module. Silicon-based chip, with its thermal and fluid design, is used to improve detection efficiency. A thermoelectric cooler (TEC), together with a computer-controlled proportional&ndash;integral&ndash;derivative (PID) controller, is applied to accelerate the thermal cycle. A maximum of four samples can be tested simultaneously on the chip. Two kinds of fluorescent molecules can be detected by optical detection module. The equipment can detect viruses with 40 PCR amplification cycles in 5 min. The equipment is portable, easily operated, and low equipment cost, which shows great potential in epidemic prevention

Finite Element Analysis to the Constitutive Behavior of Sintered Silver Nanoparticles Under Nanoindentation

Finite element (FE) simulation is adopted as a fundamental tool to evaluate the mechanical reliability of packaging structures for electronic devices. Nevertheless, the determination of mechanical properties of sintered silver nanoparticles (AgNP) remains challenging as the traditional tensile test is difficult to be performed at a limited size. In the current study, spherical nanoindentation is utilized to measure the applied load-penetration depth responses of sintered AgNP reinforced by SiC microparticles at various weight ratios (0.0, 0.5, 1.0 and 1.5 wt.%). To describe the elasto-plastic behavior of this heterogeneous material, FE analysis is performed to simulate the indentation behavior and determine the parameters in the modified power-law model by fitting the average applied load-penetration depth responses. To overcome the uniqueness problem, the Young\u27s modulus is directly determined by continuous stiffness measurement technique and the proposed constitutive model can provide a reasonably accurate mechanical estimation of sintered AgNP. The effect of SiC content on sintered AgNP is discussed by correlating the morphology observed by scanning electron microscope (SEM) and the constitutive parameters obtained from the FE simulations

Evaluation of the quality grade of Congou black tea by the fusion of GC-E-Nose, E-tongue, and E-eye

In the present study, the comprehensive quality of Congou black tea (CBT) including aroma, taste, and liquid color was investigated by a combination of gas chromatography electronic nose (GC-E-Nose), electronic tongue (E-tongue), and electronic eye (E-eye). An excellent discrimination of different quality grades of CBT was accomplished through the fusion of GC-E-Nose, E-tongue, and E-eye combined with orthogonal partial least squares discriminant analysis, with parameters of R2Y = 0.803 and Q2 = 0.740. Moreover, the quantitative evaluation of CBT quality was successfully achieved by partial least squares regression analysis, with the absolute error within 1.39 point, and the relative error within 1.62%. Additionally, 12 key variables were screened out by stepwise multiple linear regression analysis, which significantly contributed to the comprehensive quality score of CBT. Our results suggest that the fusion of multiple intelligent sensory technologies offers great potential and practicability in the quality evaluation of black tea