Exciton diffusion in semiconducting single-wall carbon nanotubes studied by transient absorption microscopy

Spatiotemporal dynamics of excitons in isolated semiconducting single-walled carbon nanotubes are studied using transient absorption microscopy. Differential reflection and transmission of an 810-nm probe pulse after excitation by a 750-nm pump pulse are measured. We observe a bi-exponentially decaying signal with a fast time constant of 0.66 ps and a slower time constant of 2.8 ps. Both constants are independent of the pump fluence. By spatially and temporally resolving the differential reflection, we are able to observe a diffusion of excitons, and measure a diffusion coefficient of 200 cm2/s at room temperature and 300 cm2/s at lower temperatures of 10 K and 150 K.Comment: 6 pages, 4 figure

Characterization for the Development of the Hybrid Multi-Junction Silicon Germanium Solar Cell

Based on the previous development of the hybrid multi-junction silicon (HMJ-Si) solar cell, this work characterized the preceding design for the development of the hybrid multi-junction silicon germanium (HMJ-SiGe) solar cell. Seven focus areas were investigated: diffraction pattern generation, photon propagation, silicon diffusion processing, ohmic contacts, the distributed Bragg reflector (DBR), the Fresnel zone plate (FZP), and the germanium/germanium telluride (Ge/GeTe) pn-junction Diffraction patterns were theoretically examined, and contact grating design characterization for reflectance and transmittance properties was modeled using rigorous coupled wave analysis. An improved silicon diffusion process follower was developed, and theoretical study and experimental assessment were accomplished for appropriate ohmic contacts, the DBR, the FZP, and the Ge/GeTe pn-junction for incorporation into the HMJ-SiGe solar cell architecture. Results showed that minima locations are nonexistent, the ratio between the metal width and electrical contact spacing is vital, an interfacial layer is required for Fermi level de-pinning, the DBR can reject detrimental wavelengths, the FZP excessively prevents transmittance, and p-type GeTe can form a pn-junction on n-type germanium. With an average efficiency of 1.27%, the HMJ-SiGe solar cell demonstrated a capstone requirement of charging a capacitor to 2.5 VDC in 11 minutes to illuminate a light emitting diode

Synthesis and Characterization of Amide and Urea Receptor Systems for Anion and Metal Complexation and the Synthesis and Use of Block Copolymers for Optoelectronic Crystal Growth

The content of this dissertation is divided into two parts, as a result of projects from two research groups during the course of my research at the University of Kansas. The first five chapters detail my work with Dr. Bowman-James which has focused on host-guest chemistry ranging from ligand synthesis to anion and metal binding. I joined the Bowman-James group after my fourth year at KU and have been a member from 2015 to 2017. Ditopic pyrazine pincers or “duplex” pincers were synthesized and investigated for both their anion binding and their metal binding merit. Chapter 2 will investigate duplex hosts as anion binding hosts, the duplex receptors were synthesized with R group functionalizations that permit a range of solubilities in various solvents. Their anion binding capabilities will be discussed in comparison to their monotopic counterparts. The duplex pincers were also studied for transition metal binding capabilities which will be detailed in Chapter 5. Palladium complexes were made and characterized with the duplex pincers and some of the interesting features of these compounds will be discussed. Aside from the duplex hosts, urea macrocyclic receptors were also synthesized and characterized for their anion host capabilities, which will be discussed in Chapter 3. Variations in macrocycle size and urea components were explored and binding merit was determined on these receptor complexes. The final two chapter of this dissertation highlight one of my projects in the Ren group from my first year of graduate school in 2011 up through my fourth year in 2015. I joined the Bowman-James group after Dr. Ren moved to Temple University. Chapter 6 will include a review on the field of organic photovoltaic and optoelectronic devices. Chapter 7 will detail my work synthesizing block copolymers for use as compatibilizing agents for P3HT and C60 interfaces. These organic photovoltaic devices exhibited an interesting magnetoconductive behavior that can be observed at room temperature in these charge transfer systems

Is the tetraneutron a bound dineutron-dineutron molecule?

In light of a new experiment which claims a positive identification, we discuss the possible existence of the tetraneutron. We explore a novel model based on a dineutron-dineutron molecule. We show that this model is not able to explain the tetraneutron as a bound state, in agreement with other theoretical models already discussed in the literature.Comment: 9 pages, 3 figures, J. Phys. G, in pres

Quasi-experimental study with the undergraduate nursing program using simulation learning to reduce medication errors

Medication errors in the nursing practice are not only costly but may harm or kill a patient. The problem addressed in this study is the relationship that exists between the lack of medication administration skills taught to students in an undergraduate nursing program. The purpose of this quantitative quasi-experimental study with a two-group pretest-posttest design was to examine if the addition of medication-simulated learning was associated with improved medication administration knowledge compared to a traditional Pharmacology classroom setting

Ben and Jerry\u27s: When Subsidiaries Fight Back

Ben and Jerry’s is a world-leader in the premium ice cream market, having a very well-established brand known for high quality ice cream and unique flavors. Additionally, they are known for a large emphasis on economic and social equity, standing fast in their values and being very outspoken about their stances on prominent current events. After being acquired by Unilever, a global consumer goods company, Ben and Jerry’s came face to face with the reality that their company values will sometimes clash with their parent company’s after putting out a statement regarding the Israeli-Palestinian conflict that Unilever quickly denounced. While navigating this conflict that eventually resulted in a private settlement out of court, Ben and Jerry’s was forced to reconsider how to best maintain their own brand and mission, while simultaneously being a subsidiary

Utility of a needs assessment as an initial outreach tool : A case study of recovery planning for the threatened Oregon Coast Coho Salmon

Outreach is a key element in natural resource public participation processes in order to create an engaging, thoughtful, and productive environment for citizen involved decision-making. This project examined the utility of a needs assessment as an initial outreach tool within the context of the National Oceanic and Atmospheric Administration Fisheries (NOAA Fisheries) recovery planning for the Threatened Oregon Coast coho salmon (Oncorhynchus kisutch). I conducted an informational needs assessment of the Oregon watershed councils which reside within the area of the listed coho salmon evolutionarily significant unit. Through the use of the needs assessment, I was able to ascertain the informational needs of the watershed council coordinators regarding coho salmon topics, identify the resources coordinators use for this information, understand their usage of web sites, and learn their preferred mechanism of communication for recovery planning information. From collecting this information, I provide recommendations to NOAA Fisheries for increasing the efficiency and effectiveness of their recovery planning outreach strategies and discuss the utility of the needs assessment as a tool for outreach personnel

Exciton diffusion in semiconducting single-walled carbon nanotubes studied by transient absorption microscopy

This is the publisher's version, also available electronically from http://journals.aps.org/prb/abstract/10.1103/PhysRevB.86.205417.Spatiotemporal dynamics of excitons in isolated semiconducting single-walled carbon nanotubes are studied using transient absorption microscopy. Differential reflection and transmission of an 810-nm probe pulse after excitation by a 750-nm pump pulse are measured. We observe a biexponentially decaying signal with a fast time constant of 0.66 ps and a slower time constant of 2.8 ps. Both constants are independent of the pump fluence. By spatially and temporally resolving the differential reflection, we are able to observe a diffusion of excitons, and measure a diffusion coefficient of 200±10 cm2/s at room temperature and 300±10 cm2/s at lower temperatures of 10 K and 150 K