Session SM3: Nanoscience

Application of Carbon Nanotubes as Working Electrodes for Cyclic Voltammetry {\&} Impedance Spectroscopy

Research conducted focuses on applications of Multi Walled Carbon Nanotubes (MWCNTs) serving as working electrodes for cyclic voltammetry (CV) and impedance spectroscopy. Expectations of increased electrochemical properties of the working electrodes were confirmed and the analysis of CNTs electrical properties was obtained. Conditions for the MWCNTs are as follows: after acidic functionalization, MWCNTs bonded with N-hydroxysuccinimide, and MWCNTs bonded with the AChE protein. Iron cyanide was chosen as the optimal analyte solution. Concentration of MWCNTs on the working electrode was also investigated. With CV an increase in capacitance, sensitivity, and sensibility was noticed. When compared to the unmodified graphite carbon electrode the modified electrode yielded lower resistivity, and higher capacitance. When compared to NHS and the AChE protein, the functionalized CNTs yielded a higher capacitance, increased sensitivity and sensibility with decrease in surface roughness. Through FTIR analysis the presence of increased carboxyl groups, enzymes, and N-hydroxysuccinimide on the walls of the MWCNTs was confirmed. In conclusion the addition of MWCNTs improved the electrodes sensitivity and sensibility for CV.   

Insights into the Structure of MoS$_{2}$ Nanotubes as revealed by aberration corrected STEM

Transition metal chalcogenides like MoS$_{2}$ or WS$_{2}$ are quasi-two dimensional (2D) compounds. Similar to carbon, transitional metal chalcogenides also form close caged structures known as inorganic fullerenes (IF) and nanotubes (INTs). We have sought to use probe aberration corrected electron microscopy for elucidating some important features and aspects of MoS$_{2}$ nanotubes. Thus we have synthesized MoS$_{2}$ nanotubes, and during the course the analysis we have observed some important features, namely, unusual facetted caps and curvatures in these nanotubes. Aberration-corrected scanning transmission electron microscopy (STEM) along with simulated STEM images has been carried out to understand better the structure of the nanotubes. Further details involving the nature of the nanotubes, as well as the structure and bonding of the Mo-S in the nanotubes have been investigated, and our results have revealed various interesting aspects for the first time to our knowledge.   

Voltage induced by domain wall motion in a ferromagnetic nanowire

We study current-induced domain-wall motion in a narrow ferromagnetic wire. We obtain an analytic expression for the voltage variation caused by the domain wall motion. Our finding shows that above critical current, the voltage will be periodic as the tilt angle of domain wall. Furthermore, we propose several possible measurements of the voltage to determine the parameters, which describe the motion of domain wall.   

Evolution of Structure and Energy Stability of Ag Nanoparticles

Nanotechnology is a leading interdisciplinary science that is emerging as a distinctive field of research. Its advances and applications will result in technical capabilities that will allow the development of novel nanomaterials with applications that will revolutionize the industry in many areas. In this work we present the structural evolution and energy stability results for silver nanoparticles from the small (1-2 nm) to the big (50 nm) size ranges. We have found that the appearances of structural lattice defects are important factors that influence the growth process. A simple assembly model for a path transformation for silver nanoparticles is presented and compared with experimental evidence.   

The Dyakonov-Perel spin dynamics in the strong spin-orbit coupling regime

We study the spin evolution in a high-mobility two dimensional electron gas (2DEG) with generic spin-orbit interactions (SOI). A fully understanding of the D'yakonov-Perel's (DP) mechanism is presented by using the microscopic linear response theory from the diffusive to the ballistic regime. We derive a set of spin dynamical equations which capture the characters of the purely exponential and damped oscillatory spin evolution modes in the different spin-orbit coupling (SOC) regime. It is shown that the oscillatory spin dynamics appear when the electron life time is larger than the half of the spin precession time due to the SOI. We also proposed a way to measure the SOC strength and the electron life time from the spin oscillatory mode.   

Internal and External Radiative Decay Engineering of Rare Earth Doped Nanocrystalline Sesquioxides

Rare earth (RE) based sesquioxide structures (RE2O3), when doped judiciously with trivalent RE ions, are not susceptible to photobleaching and offer many sharp electronic transitions with excited state lifetimes on the order of milliseconds. Additionally, internal lattice engineering of the host offers several distinct crystal phases which may be synthesized easily by tuning the host RE. Similarly, the proximity of noble metals to trivalent rare earth ions has shown promise as a sensitizer that greatly enhances the photoluminescence of the rare earth ion. More recently, results have been reported for gold coated silica dielectric nanoparticles which have been modeled extensively and shown to act as a nano-antenna, enhancing the electric field inside the dielectric core. This short range antenna effect offers radiative decay engineering at the external level. Here, we report the internal and external radiative decay engineering of several rare earth doped sesquioxide and metallic hetero-nanostructures and discuss the nanoscale physics of these systems.   

Synthesis and Modification of Selected Rare Earth Nanoparticles

The goal of this research is to develop multifunctional nanomaterials for biological applications. The rare earth based nanoparticles (RENPs) have a potential to offer multiple modalities, which can be utilized in more comprehensive imaging of biological tissues. The specific goal was to modify the RENPs with clusters of transition metals in order to enhance their luminescence signal. The luminescent system based on the Er$^{3+}$:Y$_{2}$O$_{3}$ nanoparticles (NPs) was selected for the present studies. Several synthetic approaches were investigated in order to control the size and shape. The precipitation from homogenous solution using the urea decomposition yielded perfectly spherical Er$^{3+}$:Y$_{2}$O$_{3}$ with narrow size distribution and particle diameter of approximately 250 nm. The synthesis of Er$^{3+}$:Y$_{2}$O$_{3}$ using the microemulsion precipitation resulted in the irregularly shaped NPs with the average diameter of approximately 100 nm. The Er$^{3+}$:Y$_{2}$O$_{3}$ NPs surrounded by chitosan shell were modified with gold clusters in order to enhance their luminescence by metallic surface plasmon resonance. The luminescence of such [Er$^{3+}$:Y$_{2}$O$_{3}$][Chitosan-Au] hybrid NPs was investigated as a function of the gold content in the chitosan shell.   

The Growth and Characterization of PbTe/CdTe at Texas State University

The new Materials Science, Engineering, and Commercialization program at Texas State University (MSEC) has developed a state-of-the-art nine-chamber molecular-beam epitaxy (MBE) growth chamber for semiconductor growth, consisting of II-VI, III-V, and IV-VI compounds. We present the results of heteroepitaxial PbTe/CdTe growth doped with Tl that was characterized through a variety of techniques, including variable-field Hall measurement and quantitative mobility spectrum analysis. We report on the need for consideration of the anisotropy of the conduction and valence bands during analysis. By producing then analyzing these structures, MSEC can work to improve devices such as photodiodes and thermo-electrics for a wide variety of applications.   

Structure of MoS$_{2}$ Plates as Revealed by High Resolution Electron Microscopic Techniques

Molybdenum disulfide (MoS$_{2})$ is a compound found in nature as molybdenite, natural MoS$_{2}$ has a hexagonal crystal form. MoS$_{2}$ is a compound very useful for its properties; it is used as lubricant, catalyst in hydrodesulfuration, in hydrogen fuel storage, etc. Currently, researchers are synthesizing MoS$_{2}$ with new shapes and MoS$_{2}$ nanoparticles. In this work MoS$_{2}$ nanohexagonal plates were synthesized at different temperatures and characterized with XRD, SEM, Raman spectroscopy and HRTEM. This compound has a plate size of 20--30 nm as revealed by SEM, with HRTEM was possible to measure the interatomic distance of Mo--Mo, which was 2.8 {\AA}. This compound is intended to be used as catalyst in fuel hydrodesulfuration.   

Crystallization of Germanium for Use in Low-Cost Solar Cells

Solar cells with a Germanium substrate can reach 40{\%} efficiency on earth with the aid of solar concentrators; however, Ge is expensive, meaning that these high-efficiency cells are feasible only for extreme applications such as outer-orbit missions. The purpose of this research is to determine if annealing Ge thin films may be a possible, low-cost alternative to slicing large, thick wafers of Ge for solar cells. Samples of Ge were deposited on transmission electron microscope (TEM) grids through vacuum evaporation, annealed at various temperatures and lengths of time in a tube furnace, and then analyzed through the TEM to test the annealed thin films. This tests the ease of crystallization in Ge, and if the size of the grains is reasonable. It was found that the Ge crystallized at relatively cost-effective temperatures, specifically temperatures over 400 C with moderate grain sizes reaching 7$\mu $m. Experiments to evaluate whether grains of the size obtained can support a photovoltaic layer will be conducted in later research.   

Synthesis, Morphology, and Optical Characterization of Nanocrystalline Er$^{3+}$:Y$_{2}$O$_{3}$

We describe a methodology to synthesize trivalent erbium doped yttrium oxide (Er$^{3+}$:Y$_{2}$O$_{3})$ nanoparticles having an average diameter of about 25 nm. The room-temperature absorption spectrum obtained between 400 and 900 nm wavelength range and the fluorescence spectra of the Er$^{3+}$ (4$f^{11}) \quad ^{2}H$(2)$_{11/2 }+^{4}S_{3/2} \quad \to \quad ^{4}I_{15/2}$ and $^{4}F_{9/2} \quad \to \quad ^{4}I_{15/2}$ transitions were analyzed in detail. The lifetimes for the $^{2}H$(2)$_{11/2}+^{4}S_{3/2}$ and $^{4}F_{9/2}$ metastable states have been measured and investigated the effect of Er$^{3+}$ concentrations and particle size on the emission intensity and decay times. The detailed structural and optical analyses suggest that the nanoparticles of Er$^{3+}$:Y$_{2}$O$_{3}$ have potential applications in diverse fields of photonics including laser systems and optical communication devices.