Alignment and characterization of carbon nanotubes of photolithographically patterned electrodes

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2004.Includes bibliographical references (p. 45-48).The goal of this work is to make an (n,m) assignment for individual suspended single wall carbon nanotubes (SWNTs) based on the measurements of their Raman Radial Breathing Modes and electron transition energies E[sub]ii based on Raman spectroscopy. The suspended SWNTs are grown on a photolithographically defined electrode pattern, which is designed so that suspended SWNTs are grown at known locations with known directions. The suspended SWNTs are then characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), and Raman spectroscopy. Finally, the information on the diameter distribution and the energy of the electronic transitions of the resonant suspended SWNTs obtained from Raman spectroscopy is compared to other published works to make (n,m) assignments of a number of suspended SWNTs.by Hyungbin Son.M.Eng

Laser-Heating Effect on Raman Spectra of Individual Suspended Single-Walled Carbon Nanotubes

We studied the Raman spectra of 21 individual suspended single-walled carbon nanotubes (SWNTs) using different excitation laser powers. The results indicate that the laser-heating effect is more significant for suspended SWNT than nanotubes sitting on a substrate. The spectral variations of these individual SWNTs induced by different laser power shed new light on the temperature dependence of Raman spectra and electronic properties of SWNTs. By analyzing the frequency downshift of each nanotube induced by increased laser power, the temperature coefficient of radial breathing mode (RBM) frequency ω RBM is supposed to be diameterand chirality-dependent, whereas that of the G-band frequency ω G + is not. The behaviors of full width at half-maximum (fwhm) and intensity ratio between anti-Stokes and Stokes spectra (I AS /I S ) of RBM with increasing laser power reflected the temperature increase and the consequent variation in the electronic density of states (DOS) of SWNT. The variation of resonance intensity with laser power showed interesting dependence on E ii > E laser or E ii < E laser , suggesting downshift of E ii with increased temperature, which offers the possibility of utilizing the optical/thermal response of SWNT to modulate the electronic property of nanotubes

Raman spectroscopy of SWNTs

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 71-76).A single wall carbon nanotube (SWNT) is a new form of carbon, whose atomic arrangement is equivalent to a graphene sheet rolled into a cylinder in a seamless way. The typical diameter of a SWNT ranges from 0.6 nm to several nm and the typical length ranges from tens of nm to several cm. Due to its small diameter and high aspect ratio, a SWNT has very unique electronic and vibrational properties. The goals of this thesis work are to design and construct a Raman instrument capable of obtaining signals from many different types of individual SWNTs, to develop methods and tools to collect, organize and analyze large amounts of Raman spectra from them, to use resonant Raman spectroscopy to characterize individual SWNTs, and to investigate how their electronic and vibrational properties change under various conditions, such as strain, or different substrate interactions. A high-efficiency widely-tunable Raman instrument is developed for the study of SWNTs. The environmental effects on the electronic and vibrational properties are investigated by suspended SWNTs. Using the high-efficiency Raman instrument, weak optical transitions of metallic SWNTs are found. The effect of strain on the vibrational mode frequencies of SWNTs are studied.by Hyungbin Son.Ph.D

EIT by nuclear magnetic resonance

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, June 2004.Includes bibliographical references (p. 65-66).Electromagnetically Induced Transparency (EIT) is a quantum nonlinear optical interference effect in which light at a certain frequency makes normally opaque atomic systems transparent to light at another frequency. Recent experiments in Atomic Molecular and Optical (AMO) physics demonstrated how the EIT effect can be used to store light pulses in an atomic system by coupling the light to the atomic system. One of the most elegant predictions of EIT theory is that the quantum phase of the dark state of the system remains unchanged even with a coupling between the dark state and another state. However, this has never been experimentally shown because of the lack of atomic systems that have long enough decoherence times and the difficulty of applying the complex pulse sequences needed to measure quantum phases in atomic systems. In this thesis, I use nuclear magnetic resonance techniques to implement the EIT effect and confirm this prediction, using Ramsey interferometry and visibility measurements to quantify the loss of quantum phase.by HyungBin Son.S.B

Categorizer: a tool to categorize genes into user-defined biological groups based on semantic similarity

Background. Communalities between large sets of genes obtained from high-throughput experiments are often identified by searching for enrichments of genes with the same Gene Ontology (GO) annotations. The GO analysis tools used for these enrichment analyses assume that GO terms are independent and the semantic distances between all parent–child terms are identical, which is not true in a biological sense. In addition these tools output lists of often redundant or too specific GO terms, which are difficult to interpret in the context of the biological question investigated by the user. Therefore, there is a demand for a robust and reliable method for gene categorization and enrichment analysis. Results We have developed Categorizer, a tool that classifies genes into user-defined groups (categories) and calculates p-values for the enrichment of the categories. Categorizer identifies the biologically best-fit category for each gene by taking advantage of a specialized semantic similarity measure for GO terms. We demonstrate that Categorizer provides improved categorization and enrichment results of genetic modifiers of Huntington’s disease compared to a classical GO Slim-based approach or categorizations using other semantic similarity measures. Conclusion Categorizer enables more accurate categorizations of genes than currently available methods. This new tool will help experimental and computational biologists analyzing genomic and proteomic data according to their specific needs in a more reliable manner.Biochemistry and Molecular Biology, Department ofMedicine, Faculty ofScience, Faculty ofOther UBCReviewedFacult

Electrophoretic Deposition of Aged and Charge Controlled Colloidal Copper Sulfide Nanoparticles

Colloidal nanoparticles (NPs) have been recently spotlighted as building blocks for various nanostructured devices. Their collective properties have been exhibited by arranging them on a substrate to form assembled NPs. In particular, electrophoretic deposition (EPD) is an emerging fabrication method for such nanostructured films. To maximize the benefits of this method, further studies are required to fully elucidate the key parameters that influence the NP deposition. Herein, two key parameters are examined, namely: (i) the aging of colloidal NPs and (ii) the charge formation by surface ligands. The aging of Cu2-xS NPs changes the charge states, thus leading to different NP deposition behaviors. The SEM images of NP films, dynamic light scattering, and zeta potential results demonstrated that the charge control and restoration of interparticle interactions for aged NPs were achieved via simple ligand engineering. The charge control of colloidal NPs was found to be more dominant than the influence of aging, which can alter the surface charges of the NPs. The present results thus reveal that the charge formation on the colloidal NPs, which depends on the surface ligands, is an important controllable parameter in EPD

Tuning of aluminum concentration distribution in high nickel cathode particles for lithium ion batteries

© 2019 This study focuses on a novel approach for the structural design of LiNi0.86Co0.12Al0.02O2 cathodes by tailoring the distribution of Al elements using milled-Al(OH)3. The distribution of Al in the cathode material is investigated using an electron probe micro analyzer. By controlling milled-Al(OH)3 addition time at 3 and 6 h, thickness of Al-rich layer is varied during co-precipitation process and following calcination with LiOH produces cathode materials with the variant Al distribution. Initial discharge capacities of the cathodes with the Al addition at 3 and 6 h are 202 and 195 mA h g−1 and the IE (initial efficiency) is 92.5 and 86.6%, respectively. The capacity retentions from the cycling test of the individual cathodes are as high as 96.7 and 92.6% at 50 cycles under 1 C rate, respectively. This advanced electrochemical performance is attributed to gradual increase of Al element from inner to outer in active material11sciescopu

Time Evolution Studies on Strain and Doping of Graphene Grown on a Copper Substrate Using Raman Spectroscopy

© 2019 American Chemical Society.The enhanced growth of Cu oxides underneath graphene grown on a Cu substrate has been of great interest to many groups. In this work, the strain and doping status of graphene, based on the gradual growth of Cu oxides from underneath, were systematically studied using time evolution Raman spectroscopy. The compressive strain to graphene, due to the thermal expansion coefficient difference between graphene and the Cu substrate, was almost released by the nonuniform Cu2O growth; however, slight tensile strain was exerted. This induced p-doping in the graphene with a carrier density up to 1.7 × 1013 cm-2 when it was exposed to air for up to 30 days. With longer exposure to ambient conditions (>1 year), we observed that graphene/Cu2O hybrid structures significantly slow down the oxidation compared to that using a bare Cu substrate. The thickness of the CuO layer on the bare Cu substrate was increased to approximately 270 nm. These findings were confirmed through white light interference measurements and scanning electron microscop