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Graphene oxide (GO)/MnO2 nanocomposites were synthesized by adding KMnO4 in a solution of water and ethanol (3:1), containing 10 mg of GO. Brown precipitates were obtained after a continuous stirring for 1 hr. The precipitates were then washed with deionized water (DI) water and dried to obtain the MnO2-GO nanocomposites. Pure MnO2 was also synthesized using the same method without GO for the comparison. X-ray diffraction pattern confirm δ-MnO2 type of MnO2 with birnessite type MnO2 structure. The TEM images show the average diameter of MnO2 nanorods as 15 nm. Electrochemical characterizations were carried out in an aqueous solution of 3M KOH. Charge-discharge studies were carried out between 1A/g to 20 A/g current range. The MnO2-GO nanocomposites showed improved electrochemical performances. The capacitance of MnO2 and MnO2-GO electrodes was found to be as 300 F/g, and 350 F/g, respectively at a current of 0.5 A/g.
Ordered carbon nanotube (CNT) growth by deposition of nanoparticle catalysts using dip pen nanolithography (DPN) is presented. DPN is a direct write, tip based lithography technique capable of multi-component deposition of a wide range of materials with nanometer precision. A NanoInk NLP 2000 is used to pattern different catalytic nanoparticle solutions on various substrates. To generate a uniform pattern of nanoparticle clusters, various conditions need to be considered. These parameters include: the humidity in the vessel, temperature, and tip-surface dwell time. By patterning different nanoparticle solutions next to each other, identical growth conditions can be compared for different catalysts in a streamlined analysis process. Fe, Ni, and Co nanoparticle solutions patterned on silicon, mica, and graphite substrates serve as nucleation sites for CNT growth. The CNTs were synthesized by a chemical vapor deposition (CVD) reaction. Each nanoparticle patterned substrate is placed in a tube furnace held at 725°C during CNT growth. The carbon source used in the growth chamber is toluene. The toluene is injected at a rate of 5 mL/hr. Growth is observed for Fe and Ni nanoparticle patterns, but is lacking for the Co patterns. The results of these reactions provide important information regarding efficient and highly reproducible mechanisms for CNT growth.
Collaborative student research takes place in educational settings where the teacher directs the laboratory (traditional class) or allows the students to research a topic (non-traditional class). This study examines the role of collaborative student research in two separate settings: in high school (grades 9-12) and in college undergraduate institutions. These experiences include college level Research Experiences for Undergraduates (REU) and high school level Authentic Science Research (ASR) programs. These programs promote collaboration among student peers, teachers, professors, graduate students, post-docs, community members, and industry experts. Benefits of these collaborative student research programs may include development of skills aligned with educational standards such as Common Core State Standards and the Next Generation Science Standards. This study examines the short and long-term outcome of student engagement in collaborative student research experiences, and offers new insight regarding the impact that these unique experiences have on 21st century skill development. Students in this study have participated in non-traditional, research-based experiences ranging from 8 weeks to 4 years. Pre-post and retrospective student survey data was examined qualitatively and quantitatively to better understand the role in which collaborative student research experiences play in the formation of 21st century skills. Results of the study support the notion that collaborative student research experiences offer students meaningful interdisciplinary benefits, and these experiences are more than just a means of recruiting students into science, technology, engineering and math (STEM) fields.
Nanoparticles are of interest in many applications since their decreased size may give them properties that are very different from bulk material. Often nanoparticle properties such as size (diameter) and size distribution are evaluated using transmission electron microscopy (TEM). These parameters, size and size distribution, can be more easily obtained from digitized TEM images by mapping particle signal to black and background pixel to white in a process known as thresholding then performing an algorithm known as a particle analysis. The goal of this study was to compare the ability of several popular thresholding algorithms to segment TEM images. Performance of the thresholding algorithms was evaluated through qualitative and quantitative measures. Results show that the choice of a thresholding algorithm will strongly affect the results obtained from particle analysis.
In this study, Si1-xGexO2 was produced by hydrothermal oxidation of Si1-xGex alloys at temperatures of 450–500°C and pressures of 30–40 MPa. The resulting Si1-xGexO2 samples were annealed in forming gas (85/15:N2/H2) and the precipitation and growth of Ge crystallites as a function of oxidation and annealing conditions were investigated using FTIR, Raman spectroscopy, XPS, AFM and high resolution SEM. The particle size distribution through the oxide thickness is accounted for by consideration of the incorporation of hydroxyl groups in the amorphous oxide network and their effect on the rate of diffusion of Ge in the amorphous structure during H2 annealing.
Single crystal films of n-type 3C-SiC were hydrothermally processed at pressures ranging from 10 to 70 MPa at 550°C. To study the effects of initial thin film microstructure on hydrothermal processing, two different samples of CVD-grown SiC were studied: one, 200 nm thick, contained low angle boundaries and a high density of planar defects; the other, 3500 nm thick, was planar and contained relatively few defects. Raman Spectroscopy, X-Ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were used to study the chemistry and microstructure of the SiC material both before and after hydrothermal treatment. This study reveals that low temperature (T=550°C) oxidation of single crystal epitaxial SiC is possible but that the resulting oxide film microstructure is strongly dependent on the initial film microstructure and oxidation is greatly enhanced along low angle grain boundaries and on planar defects.
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