Growth, Characterizations, and Applications of Patterned Nanostructured Thin Film

A unique microreactor-assisted nanomaterial synthesis and printing process was studied for the fabrication of patterned metal oxide nanostructured thin films. The process uses a continuous flow microreactor to control and generate a reactive chemical flux that was transported to a patterned microfluidic channel. The microreactor-assisted nanomaterial synthesis process can generate reactive building blocks, ranging from molecules, clusters to nanoparticles with constant concentration and compositions. The reactive solution was then delivered to the substrate surface, guided by a patterned microchannel. The growth kinetics of the nanostructured ZnO on silicon wafers were studied by measuring the thickness of the film using the stylus profiler and scanning electron microscope under various growth conditions controlled by using the microreactor and the microchannel made of Polydimethylsiloxane. The process contains three zones, a mixing zone, a reactant generation zone, and a deposition zone. This process allows a separation of the homogeneous reaction in the solution and the heterogeneous reaction on the substrate surface, resulting in a well-controlled growth of the ZnO nanostructures on the substrate surface so that the growth mechanisms and kinetics can be studied. Different growth parameters, including flow rate, residence time, the temperature of the chemical solution and temperature of the substrate, are varied to study the growth kinetics. A key process parameter is the flow rate; a higher flow rate can result in faster growth of ZnO nanostructures. A lower flow rate will result in a longer residence time of the chemical solution within zone 2, which can lead to the homogenous formation of solid nanoparticles, thus reduce the concentration of reactive Zn(OH)₂ (aq). This finding is further supported by growth experiments carried out using reactors with two different reaction channel lengths within zone 2. Besides, the thickness of rectangular patterned ZnO nanostructured films show a saddle-shaped profile, which is thinner near the center. This thickness profile is a result of combined heat and mass transfer of the reactive solution within the patterned channel, as qualitatively supported by COMSOL simulations. By measuring the growth rates as a function of substrate temperatures, the activation energy of the rate constant is obtained at 22.65kJ/mol. This process not only provides better control to fabricate patterned metal oxide nanostructures but also offers the unique capability to study the growth mechanisms. The improved understandings were applied to demonstrate a novel, scalable process to fabricate ZnO nanostructures with multiscale 3D geometric shapes. In particular, the precursor solutions were firstly mixed and heated in a microreactor to control solution temperature and to generate reactive species. The reacting solution was then delivered to the substrate surface guided by a patterned PDMS channel with different designs, including the spiral pattern, the parallel pattern, and the split-and-recombine pattern. ZnO nanostructures with multiscale 3D geometric shapes were formed guided by the patterned channel. It is found that geometry is controlled by the channel geometry, flow rate, and substrate temperature. The stylus profiler measures film thickness, and the result shows that the unique characteristics of each pattern type. With the aid of the Comsol simulation, the parameters that control the growth are studied: in the spiral pattern, the consumption of the reactant can result in a thinner film as the solution flows through the channel. In the parallel-design pattern, the film thickness is determined by the flow rate of the solution in each channel in parallel. With the channel narrowed and the flow rate reduced, a thinner ZnO nanostructured film is obtained. In the split-and-recombine design pattern, the film growth rate is halved as the channel split and doubled as the channels re-combined. The temperature profile within the channel is another critical parameter of controlling the growth of ZnO nanostructures in all dimensions. This scalable process, aided with new understandings, will provide a unique capability to fabricate metal oxide nanostructures of controlled multiscale 3D geometric shapes. Besides ZnO, the microreactor-assisted nanomaterial synthesis and printing process was used to deposit patterned CuO and Cu₂(OH)₃NO₃ nanostructures on surface, including dense nanocrystalline CuO film, CuO nanorods, Cu₂(OH)₃NO₃ nanorods, and Cu₂(OH)₃NO₃ nanoplates using the same reactants, Cu(NO3)2 and Hexamethylenetetramine. The critical process parameter that controls the formation of different products is the concentration of the OH- in the solution, which can be controlled by the ratio of the reactants and the temperature of the microreactor. The high concentration of OH- leads to the formation of Cu(OH)₂, which is then converted to CuO on the heated substrate surface. In contrast, the low concentration of OH- leads to the formation of Cu₂(OH)₃NO₃. These results show the applicability of the microreactor-assisted nanomaterial synthesis and printing process to deposit metal oxide nanostructures with controlled structure and composition. The utility of microreactor-assisted nanomaterial synthesis and printing process was demonstrated via the fabrication of heterojunction ZnO/CuO bi-layer film. The bilayer film was built by depositing a patterned nanocrystalline CuO film on a gold-coated glass surface using the microreactor-assisted nanomaterial synthesis and printing process, followed by the deposition of ZnO nanostructured film with a smaller-size pattern using the same process. The heterojunction ZnO/CuO bi-layer film shows rectifying behavior; it allows currents to flow when forward biased and passes only low leakage currents with reverse bias; the p-n diode has a rectification ratio around 10⁴, which is comparable to the values among the best solution-processed p-n junction diodes. The results of this study demonstrate the capability of our microreactor-assisted nanomaterial synthesis and printing process to fabricate structured thin films for functional devices

Velocity distribution characteristics and parametric sensitivity analysis of liquid nitrogen jet

Liquid nitrogen is expected to be used as a jet medium in petroleum engineering because of its cryogenic and non-polluting characteristics. To identify the velocity distribution characteristics of liquid nitrogen jet, a computational fluid dynamics model was built by coupling the equations for nitrogen properties. The velocity and pressure distributions of liquid nitrogen jet were analyzed by comparing them with water jet ones. Meanwhile, the influences of relevant parameters on the centerline velocity distributions of liquid nitrogen jet were researched as well. The simulation results showed that the liquid nitrogen jet not only displayed higher velocity but also presented fewer kinetic energy losses than the water jet during jetting process. The nozzle outlet velocity of liquid nitrogen jet was increased by increasing the nozzle pressure drop, and was slightly influenced by confining pressure and nozzle diameter. In the external space of the nozzle, the attenuation amplitude of centerline velocity was decreased with the growth of nozzle diameter, and was slightly influenced by nozzle pressure drop and confining pressure. This study is expected to provide a theoretical guide for parametric design of liquid nitrogen jet

Study on the epidemiological burden of acute gastroenteritis in Heilongjiang Province

Objective The objective is to reveal the epidemiological burden and predictors of acute gastroenteritis in Heilongjiang Province. Methods A multi-stage stratified random sampling method was used to collect the incidence of acute gastroenteritis in the past 4 weeks. Results A total of 19 171 people were investigated. The monthly prevalence of acute gastroenteritis was 3.51% [95% confidence interval (95% CI): 3.25%-3.77%], the annual incidence rate was 37.24%, and the incidence rate was 0.466 times per person-year. The weighted monthly prevalence rate was 3.61%, the weighted annual incidence rate was 38.07%, and the weighted incidence rate was 0.479 times per person-year. It was estimated that the average annual incidence of acute gastroenteritis in this province was 14.423 million people per year, with a total of 18.147 million cases. Multivariate Logistic regression analysis showed that the nature of the residence, season, age, whether they had left their residence due to business or trips in the past 2 weeks, and the annual per capita income of the family were the influencing factors.58.66% of acute gastroenteritis cases were attributed to contaminated food. Conclusion Acute gastroenteritis in Heilongjiang Province had a heavy epidemiological burden and a high proportion of foodborne diseases, which should be paid more attention to

Velocity distribution characteristics and parametric sensitivity analysis of liquid nitrogen jet

Liquid nitrogen is expected to be used as a jet medium in petroleum engineering because of its cryogenic and non-polluting characteristics. To identify the velocity distribution characteristics of liquid nitrogen jet, a computational fluid dynamics model was built by coupling the equations for nitrogen properties. The velocity and pressure distributions of liquid nitrogen jet were analyzed by comparing them with water jet ones. Meanwhile, the influences of relevant parameters on the centerline velocity distributions of liquid nitrogen jet were researched as well. The simulation results showed that the liquid nitrogen jet not only displayed higher velocity but also presented fewer kinetic energy losses than the water jet during jetting process. The nozzle outlet velocity of liquid nitrogen jet was increased by increasing the nozzle pressure drop, and was slightly influenced by confining pressure and nozzle diameter. In the external space of the nozzle, the attenuation amplitude of centerline velocity was decreased with the growth of nozzle diameter, and was slightly influenced by nozzle pressure drop and confining pressure. This study is expected to provide a theoretical guide for parametric design of liquid nitrogen jet

Tuning Thermal Conductivity of Hybrid Perovskites through Halide Alloying

Tuning the thermal transport properties of hybrid halide perovskites is critical for their applications in optoelectronics, thermoelectrics, and photovoltaics. Here, we demonstrate an effective strategy to modulate the thermal transport property of hybrid perovskites by halide alloying. A highly tunable thermal conductivity of mixed-halide hybrid perovskites is achieved due to halide-alloying and structural distortion. Our experimental measurements show that the room temperature thermal conductivity of MAPb(BrxI1-x)3 (x = 0-1) can be largely modulated from 0.27 W/mK (x = 0.5) to 0.47 W/mK (x = 1). Molecular dynamics simulations further demonstrate that the thermal conductivity reduction of hybrid halide perovskites results from the suppression of the mean free paths of the low-frequency acoustic and optical phonons. It is found that halide alloying and the induced structural distortion can largely increase the scatterings of optical and acoustic phonons, respectively. The confined diffusion of MA+ cations in the octahedra cage is found to act as an additional thermal transport channel in hybrid perovskites and can contribute around 10-20% of the total thermal conductivity. Our findings provide a strategy for tailoring the thermal transport in hybrid halide perovskites which may largely benefit their related applications

Effects of unsaturated flow on Hillslope recession characteristics

Recession flow analysis is usually conducted to infer hydraulic parameters of hillslope aquifers. Various Boussinesq equation-based models, both linear and nonlinear, have been used to analyze the recession curves for sloping aquifers, with a focus on the long-time recession behavior. Based on a modified Boussinesq equation with capillarity incorporated, we demonstrate the significant effect of unsaturated flow on the recession curve, which result in three (instead of two) power law regimes with two transition points (instead of one) corresponding to the formation of a fully unsaturated zone at the adjacent area of the upslope boundary and across the whole domain, respectively. The results show that the power of the second and third recession regime is variable, depending on the slope angles, soil types, and hillslope geometries. The unsaturated flow effects also lead to the absence of drastic drop of (Formula presented.) at the transition between the first and second regime, which was predicted by previous numerical models but has not been observed in the field or laboratory experiments. These findings have important implications for recession flow analysis in studies of hillslope aquifers

Large-scale Generation of Patterned Bubble Arrays on Printed Bi-functional Boiling Surfaces

Bubble nucleation control, growth and departure dynamics is important in understanding boiling phenomena and enhancing nucleate boiling heat transfer performance. We report a novel bi-functional heterogeneous surface structure that is capable of tuning bubble nucleation, growth and departure dynamics. For the fabrication of the surface, hydrophobic polymer dot arrays are first printed on a substrate, followed by hydrophilic ZnO nanostructure deposition via microreactor-assisted nanomaterial deposition (MAND) processing. Wettability contrast between the hydrophobic polymer dot arrays and aqueous ZnO solution allows for the fabrication of heterogeneous surfaces with distinct wettability regions. Heterogeneous surfaces with various configurations were fabricated and their bubble dynamics were examined at elevated heat flux, revealing various nucleate boiling phenomena. In particular, aligned and patterned bubbles with a tunable departure frequency and diameter were demonstrated in a boiling experiment for the first time. Taking advantage of our fabrication method, a 6 inch wafer size heterogeneous surface was prepared. Pool boiling experiments were also performed to demonstrate a heat flux enhancement up to 3X at the same surface superheat using bi-functional surfaces, compared to a bare stainless steel surface.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Nature Publishing Group. The published article can be found at: http://www.nature.com/srep/. Supplementary Information and Movies S1-S5 are available online at: http://www.nature.com/articles/srep23760#s