Physical Sciences and Mathematics Commons^™

Photoluminescence Switching In Quantum Dots Connected With Fluorinated And Hydrogenated Photochromic Molecules, Ephraiem S. Sarabamoun, Jonathan M. Bietsch, Pramod Aryal, Amelia G. Reid, Maurice Curran, Grayson Johnson, Esther H. R. Tsai, Charles W. Machan, Guijun Wang, Joshua J. Choi

Chemistry & Biochemistry Faculty Publications

We investigate switching of photoluminescence (PL) from PbS quantum dots (QDs) crosslinked with two different types of photochromic diarylethene molecules, 4,4'-(1-cyclopentene-1,2-diyl)bis[5-methyl-2-thiophenecarboxylic acid] (1H) and 4,4'-(1-perfluorocyclopentene-1,2-diyl)bis[5-methyl-2-thiophenecarboxylic acid] (2F). Our results show that the QDs crosslinked with the hydrogenated molecule (1H) exhibit a greater amount of switching in photoluminescence intensity compared to QDs crosslinked with the fluorinated molecule (2F). With a combination of differential pulse voltammetry and density functional theory, we attribute the different amount of PL switching to the different energy levels between 1H and 2F molecules which result in different potential barrier …

Synthesis And Characterization Of Hydroxy-Functionalized Copper Indium Disulfide Quantum Dots, Julia Schexnayder

WWU Honors College Senior Projects

Quantum dots offer tunable electronic and optical properties due to the quantum confinement effect, making them desirable for various applications. However, their native hydrophobic form requires surface chemistry modification for certain applications. This research explores the method of ligand exchange using 11-mercapto-1-undecanol for improving the stability of copper indium disulfide (CIS) quantum dot (QD) nanoparticles in polar environments. The effects of this ligand exchange on QD chemical composition, optical properties, hydroxy-reactivity, and hydrodynamic radius are characterized. Analysis of characterization results indicates successful surface modification through hydroxyfunctionalization, as confirmed by 1H-NMR and IR spectroscopy. The desired optical properties of the QDs …

Perspectives On Determinism In Quantum Mechanics: Born, Bohm, And The “Quantal Newtonian” Laws, Viraht Sahni

Publications and Research

Quantum mechanics has a deterministic Schrödinger equation for the wave function. The Göttingen–Copenhagen statistical interpretation is based on the Born Rule that interprets the wave function as a “probability amplitude.” A precept of this interpretation is the lack of determinism in quantum mechanics. The Bohm interpretation is that the wave function is a source of a field experienced by the electrons, thereby attributing determinism to quantum theory. In this paper, we present a new perspective on such determinism. The ideas are based on the equations of motion or “Quantal Newtonian” Laws obeyed by each electron. These Laws, derived from …

Perspectives On Determinism In Quantum Mechanics: Born, Bohm, And The 'Quantal Newtonian' Laws, Viraht Sahni

Publications and Research

Quantum mechanics has a deterministic Schrödinger equation for the wave function. The Göttingen-Copenhagen statistical interpretation is based on the Born Rule that interprets the wave function as a ‘probability amplitude’. A precept of this interpretation is the lack of determinism in quantum mechanics. The Bohm interpretation is that the wave function is a source of a field experienced by the electrons, thereby attributing determinism to quantum theory. In this paper we present a new perspective on such determinism. The ideas are based on the equations of motion or ‘Quantal Newtonian’ Laws obeyed by each electron. These Laws, derived from the …

Single-Photon Generation From Self-Assembled Gaas/Inalas(111)A Quantum Dots With Ultrasmall Fine-Structure Splitting, Christopher F. Schuck, Robert Boutelle, Kevin Silverman, Galan Moody, Paul J. Simmonds

Physics Faculty Publications and Presentations

We present a novel semiconductor single-photon source based on tensile-strained (111)-oriented GaAs/InAlAs quantum dots (QDs) exhibiting ultrasmall exciton fine-structure splitting (FSS) of ≤ 8 µeV. Using low-temperature micro-photoluminescence spectroscopy, we identify the biexciton-exciton radiative cascade from individual QDs, which, combined with small FSS, indicates these self-assembled GaAs(111) QDs are excellent candidates for polarization-entangled photon-pair generation.

Diffuse Spectra Model Of Photoluminescence In Carbon Quantum Dots, S. E. Kumekov, N. K. Saitova, Karen S. Martirosyan

Physics and Astronomy Faculty Publications and Presentations

The attractive aspect of excitation related to fluorescence nature in carbon quantum dots (CQD) has guided to several assumptions correlated with clusters size distribution, shapes as well as presence of different emissive states. In this study, a dimer–excimer model of photoluminescence (PL) in CQD describing discrete multiple electronic states for the excitation-dependent emission is described. The functional dependence of the characteristic width of the diffuse spectra of PL on the size of a quantum dots are calculated. The effective width of PL spectrum can be tuned from 0.1 to 1 eV.

Strain-Driven Quantum Dot Self-Assembly By Molecular Beam Epitaxy, Kathryn E. Sautter, Kevin D. Vallejo, Paul J. Simmonds

Physics Faculty Publications and Presentations

Research into self-assembled semiconductor quantum dots (QDs) has helped advance numerous optoelectronic applications, ranging from solid-state lighting to photodetectors. By carefully controlling molecular beam epitaxy (MBE) growth parameters, we can readily tune QD light absorption and emission properties to access a broad portion of the electromagnetic spectrum. Although this field is now sufficiently mature that QDs are found in consumer electronics, research efforts continue to expand into new areas. By manipulating MBE growth conditions and exploring new combinations of materials, substrate orientations, and the sign of strain, a wealth of opportunities exist for synthesizing novel QD nanostructures with hitherto unavailable …

Gold/Qds-Embedded-Ceria Nanoparticles: Optical Fluorescence Enhancement As A Quenching Sensor, Nader Shehata, Effat Samir, Ishac Kandas

Electrical & Computer Engineering Faculty Publications

This work focuses on improving the fluorescence intensity of cerium oxide (ceria) nanoparticles (NPs) through added plasmonic nanostructures. Ceria nanoparticles are fluorescent nanostructures which can emit visible fluorescence emissions under violet excitation. Here, we investigated different added plasmonic nanostructures, such as gold nanoparticles (Au NPs) and Cadmium sulfide/selenide quantum dots (CdS/CdSe QDs), to check the enhancement of fluorescence intensity emissions caused by ceria NPs. Different plasmonic resonances of both aforementioned nanostructures have been selected to develop optical coupling with both fluorescence excitation and emission wavelengths of ceria. In addition, different additions whether in-situ or post-synthesis have been investigated. We found …

Interactions Of (My) 6 (M = Zn, Cd; Y = O, S, Se) Quantum Dots With N-Bases, Mariusz Michalczyk, Wiktor Zierkiewicz, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

(MY)₆ clusters, with M = Zn and Cd and Y = O, S, Se, form double-layer drum-like structures containing M–Y covalent bonds. The positive regions near the M atoms attract the N atom of both NH₃ and NMe₃ so as to form a noncovalent M···N bond. This bond is quite strong, with interaction energies exceeding 35 kcal/mol. The bond strength diminishes with reduced electronegativity of the Y atom (O > S > Se) and is stronger for M = Zn than for Cd. Trimethylation of the base enhances the bond strength. The interaction is dominated by the electrostatic component …

Study Of The Kinetic Energy Densities Of Electrons As Applied To Quantum Dots In A Magnetic Field, Marlina Slamet, Viraht Sahni

Publications and Research

There are three expressions for the kinetic energy density t(r) expressed in terms of its quantal source, the single‐particle density matrix: t_A(r), the integrand of the kinetic energy expectation value; t_B(r), the trace of the kinetic energy tensor; t_C(r), a virial form in terms of the 'classical' kinetic field. These kinetic energy densities are studied by application to 'artificial atoms' or quantum dots in a magnetic field in a ground and excited singlet state. A comparison with the densities for natural atoms and molecules in their ground state is made. The near nucleus …

Three-Dimensional Carbon Nanotube Yarn Based Solid State Solar Cells With Multiple Sensitizers Exhibit High Energy Conversion Efficiency, Glenn Grissom, Jared Jaksik, Monica Mcentee, Erin M. Durke, Sayeeda Tj Aishee, Margaret Cua, Okenwa Okoli, Ahmed Touhami, H. Justin Moore, M. Jasim Uddin

Chemistry Faculty Publications and Presentations

Fiber-type dye sensitized solar cells that are non-metallic, flexible, and thread-like in structure have many potential military and functional textile applications. With the use of quantum dots (QD), exciton transfer facilitators (Phenyl-C61-butyric acid methyl ester-PCBM) and Poly(3-hexylthiophene-2,5-diyl-P3HT), and careful preparation of the TiO2 oxide layer deposited on the carbon fiber working electrode, an optimized efficiency of 7.6% was obtained. Carbon nanotube yarn (CNTY) was used to prepare both the working and counter electrodes of the fabricated cells. TiCl4 annealing of the TiO2 layer was carried out and the resulting oxide layer morphology was found to be very uniform. The quantum …

Kinetic Effects In 2d And 3d Quantum Dots: Comparison Between High And Low Electron Correlation Regimes, Marlina Slamet, Viraht Sahni

Publications and Research

Kinetic related ground state properties of a two-electron 2D quantum dot in a magnetic field and a 3D quantum dot (Hooke's atom) are compared in the Wigner high (HEC) and low (LEC) electron correlation regimes. The HEC regime corresponds to low densities sufficient for the creation of a Wigner molecule. The LEC regime densities are similar to those of natural atoms and molecules. The results are determined employing exact closed-form analytical solutions of the Schrödinger-Pauli and Schrödinger equations, respectively. The properties studied are the local and nonlocal quantal sources of the density and the single particle density matrix; the kinetic …

Quantum Dot Growth On (111) And (110) Surfaces Using Tensile-Strained Self-Assembly, Paul J. Simmonds

Physics Faculty Publications and Presentations

The self-assembly of epitaxial quantum dots on (001) surfaces, driven by compressive strain, is a widely used tool in semiconductor optoelectronics. In contrast, the growth of quantum dots on (111) and (110) surfaces has historically been a significant challenge. In most cases the strain relaxes rapidly via dislocation nucleation and glide before quantum dots can form. In this paper, we discuss a method for the reliable and controllable self-assembly of quantum dots on both (111) and (110) surfaces, where tensile strain is now the driving force. By showing that tensile-strained self-assembly is applicable to several material systems, we demonstrate the …

Schrödinger, 3, David Peak

Schrodinger

The 3D infinite square well: quantum dots, wells, and wires

In the preceding discussion of the Schrödinger Equation the particle of interest was assumed to be “moving in the x -direction.” Of course, it is not possible for a particle to be moving in one spatial direction only. If that were true, according to the HUP it could be anywhere in the y - and z -directions and therefore be undetectable with finite volume detectors. Now, we consider the more realistic case of motion in all three spatial directions. For this purpose, we start with the 3D infinite square well. …

Importance Of The Inter-Electrode Distance For The Electrochemical Synthesis Of Magnetite Nanoparticles: Synthesis, Characterization, Computational Modelling, And Cytotoxicity, Seyedeh Maryamdokht Taimoory, John F. Trant, Abbas Rahdar, Mousa Aliahmad, Fardin Sadeghfar, Mahmoud Hashemzaei

Chemistry and Biochemistry Publications

Magnetite (Fe3O4) nanoparticles, are promising inorganic nanomaterials for future biomedical applications due to their low toxicity and unique magnetic properties. However, the synthesis of these particles can often be expensive, energy intensive, and non-scalable, requiring the addition of surfactants to stabilize the material to control the particle size and avoid agglomeration. We wish to report a simple, green, surfactant-free electrochemical synthesis of these materials using a closed aqueous system at ambient temperature. Particle diameter, between 19 and 33 nm, was controlled by simply modifying the distance between the electrodes. These magnetite nanoparticles were then fully characterized using both spectroscopy and …

Quantum Dot Band Gap Measurements, John Ryan Peterson

Student Works

This presentation was given during the summer of 2016 as part of the BYU REU program funded by the NSF. Here I give a brief explanation of our quantum dot synthesis as well as explain the use of absorption spectroscopy to measure indirect band gap energies of semiconductors. Our experimental setup is shown and recent improvements are explained. We report indirect band gaps of quantum dots containing varying amounts of cobalt oxide and manganese oxide and synthesized in the protein ferritin. The data show that the band gap can be tuned arbitrarily in a certain range by varying the concentrations …

Direct Band Gap Measurements, John Ryan Peterson

Student Works

This presentation was given during the summer of 2016 as part of the BYU REU program funded by the NSF. Here I give a brief explanation of our quantum dot synthesis and then explain the mechanism of photoluminsecence used to measure indirect band gap energies of semiconductors. Our experimental setup is shown. Direct band gaps of lead sulfide quantum dots synthesized in ferritin are reported. The data show that the band gap can be tuned arbitrarily in a certain range by varying the concentrations of the reactants. We compare stability of quantum dots in ferritin to quantum dots synthesized without …

Quantum Dot Band Gap Investigations, John Ryan Peterson

Student Works

Improving solar panel efficiency has become increasingly important as the world searches for cheap renewable energy. Recent developments in the industry have focused on multi-layer cells, some of which use semiconducting dyes to absorb light in place of crystalline solids. In this paper, I characterize various dyes recently synthesized for use in solar panels. These dyes contain semiconducting nanoparticles enclosed primarily by the protein ferritin to limit particle size. The band gaps were measured using either optical absorption spectroscopy or measuring the photoluminescence spectrum, depending on the type of semiconductor. The results indicate that both manganese oxide and lead sulfide …

Hybrid Type-I Inas/Gaas And Type-Ii Gasb/Gaas Quantum Dot Structure With Enhanced Photoluminescence, Hai-Ming Ji, Baolai Liang, Paul J. Simmonds, Bor-Chau Juang, Tao Yang, Robert J. Young, Diana L. Huffaker

Physics Faculty Publications and Presentations

We investigate the photoluminescence (PL) properties of a hybrid type-I InAs/GaAs and type-II GaSb/GaAs quantum dot (QD) structure grown in a GaAs matrix by molecular beam epitaxy. This hybrid QD structure exhibits more intense PL with a broader spectral range, compared with control samples that contain only InAs or GaSb QDs. This enhanced PL performance is attributed to additional electron and hole injection from the type-I InAs QDs into the adjacent type-II GaSb QDs. We confirm this mechanism using time-resolved and power-dependent PL.These hybrid QD structures show potential for high efficiency QD solar cell applications.

Strain-Driven Growth Of Gaas(111) Quantum Dots With Low Fine Structure Splitting, Paul J. Simmonds

Physics Faculty Publications and Presentations

Symmetric quantum dots (QDs) on (111)-oriented surfaces are promising candidates for generating polarization-entangled photons due to their low excitonic fine structure splitting(FSS). However, (111) QDs are difficult to grow. The conventional use of compressive strain to drive QD self-assembly fails to form 3D nanostructures on (111) surfaces. Instead, we demonstrate that (111) QDs self-assemble under tensile strain by growing GaAs QDs on an InP(111)A substrate. Tensile GaAs self-assembly produces a low density of QDs with a symmetric triangular morphology. Coherent, tensile QDs are observed without dislocations, and the QDs luminescence at room temperature. Single QD measurements reveal low FSS with …

Hetero-Junctions Of Boron Nitride And Carbon Nanotubes: Synthesis And Characterization, Yoke Khin Yap

Department of Physics Publications

Hetero-junctions of boron nitride nanotubes (BNNTs) and carbon nanotubes (CNTs) are expected to have appealing new properties that are not available from pure BNNTs and CNTs. Theoretical studies indicate that BNNT/CNT junctions could be multifunctional and applicable as memory, spintronic, electronic, and photonics devices with tunable band structures. This will lead to energy and material efficient multifunctional devices that will be beneficial to the society. However, experimental realization of BNNT/CNT junctions was hindered by the absent of a common growth technique for BNNTs and CNTs. In fact, the synthesis of BNNTs was very challenging and may involve high temperatures (up …

Carrier Capture Dynamics Of Single Ingaas/Gaas Quantum-Dot Layers, K. N. Chauhan, D. Mark Riffe, E. A. Everett, D. J. Kim, H. Yang, F. K. Shen

All Physics Faculty Publications

Using 800 nm, 25-fs pulses from a mode locked Ti:Al₂O₃ laser, we have measured the ultrafast opticalreflectivity of MBE-grown, single-layer In_0.4Ga_0.6As/GaAs quantum-dot (QD) samples. The QDs are formed via two-stage Stranski-Krastanov growth: following initial InGaAs deposition at a relatively low temperature, self assembly of the QDs occurs during a subsequent higher temperature anneal. The capture times for free carriers excited in the surrounding GaAs (barrier layer) are as short as 140 fs, indicating capture efficiencies for the InGaAs quantum layer approaching 1. The capture rates are positively correlated with initial InGaAs thickness and …

Pump Dependence Of The Dynamics Of Quantum Dot Based Waveguide Absorbers, T. Piwonski, Jaroslaw Pulka, Guillaume Huyet, Et. Al.

Physical Sciences Publications

The nonlinear two stage recovery of quantum dot based reverse-biased waveguide absorbers is investigated experimentally and analytically as a function of the initial ground state occupation probability of the dot. The latter is controlled experimentally by the pump pulse power. The slow stage of the recovery is exponential and its basic timescale is independent of pump power. The fast stage of the recovery is a logistic function which we analyze in detail. The relative strength of slow to fast components is highlighted and the importance of higher order absorption processes at the highest pump level is demonstrated.

Mixed State Effects In Waveguide Electro-Absorbers Based On Quantum Dots, T. Piwonski, Jaroslaw Pulka, Guillaume Huyet, Et. Al.

Physical Sciences Publications

Multi-pulse heterodyne pump-probe measurements are used to investigate the reverse bias dynamics of InAs/GaAs quantum dots in a waveguide structure. Using a femtosecond pulse, we simultaneously populate high energy ground states and low energy excited states and measure the resulting gain and phase dynamics over the bandwidth of the pulse. We identify a ∼5 ps timescale in the phase dynamics which can be associated with low energy ground states outside the pulse bandwidth and may provide an explanation for the deterioration of monolithic mode locked laser performance at high reverse voltages.

Induced Absorption Dynamics In Quantum Dot Based Waveguide Electroabsorbers, T. Piwonski, Jaroslaw Pulka, Guillaume Huyet, Et. Al.

Physical Sciences Publications

Two-color pump-probe measurements are used to study the carrier dynamics of InAs/GaAs quantum dots in a waveguide structure under reverse bias conditions. For the case of initially populating the ground state (GS), we find relaxation dynamics that include both absorptive and bleaching components in the excited state (ES) wavelength range. We reproduce the main features of this induced absorption dynamics using a simple model with an additional term for induced absorption at the ES due to carriers injected at the GS. The induced absorption dynamics includes multiple recovery timescales which can be attributed to phonon-assisted processes of GS/ES interaction.

Refractive Index Dynamics Of Quantum Dot Based Waveguide Electroabsorbers, T. Piwonski, Jaroslaw Pulka, Guillaume Huyet, Et. Al.

Physical Sciences Publications

The refractive index dynamics of InAs/GaAs quantum dot based waveguide absorbers is studied using heterodyne pump-probe measurements. Absorption reduction due to the pump can be accompanied by either positive or negative refractive index changes depending on the wavelength used. This change in sign of the phase amplitude coupling can be understood by considering the atomlike nature of the quantum dot transitions involved.

Recovery Time Scales In A Reversed-Biased Quantum Dot Absorber, T. Piwonski, Gillian Madden, Jaroslaw Pulka, Guillaume Huyet, Et. Al.

Physical Sciences Publications

The nonlinear recovery of quantum dot based reverse-biased waveguide absorbers is investigated both experimentally and analytically. We show that the recovery dynamics consists of a fast initial layer followed by a relatively slow decay. The fast recovery stage is completely determined by the intradot properties, while the slow stage depends on the escape from the dot to the wetting layer.

The Fast Recovery Dynamics Of A Quantum Dot Semiconductor Optical Amplifier, T. Piwonski, Guillaume Huyet, Et. Al.

Physical Sciences Publications

We consider a rate equation model of a quantum dot semiconductor optical amplifier that takes into account carrier capture, escape, and Pauli blocking processes. We evaluate possible differences between phonon-assisted or Auger processes being dominant for recovery. An analytical solution which corresponds to phonon-assisted interaction is then used to accurately fit experimental recovery curves and allows an estimation of both the carrier capture and escape rates.

Spectroscopic Imaging Of Quantum Dot Cellular Interactions, Lorenzo Salford

Masters

Quantum dots (QDs) are a diverse class of engineered nanomaterials that have great potential for use as agents in imaging, diagnostics and drug-delivery because of their intense and photostable fluorescence. Advances in the field of nanotoxicology, however, have recently identified potential risks and hazards associated with exposure to QDs. The main purpose of this research is to investigate the capabilities of a synergistic range of different techniques, including cytotoxicity assays, confocal microscopy and vibrational spectroscopy, to probe their interaction with Biological systems. With the combination of these techniques it is hoped to understand the mechanisms of the interaction of QDs …

Intradot Dynamics Of Inas Quantum Dot Based Electroabsorbers, T. Piwonski, Jaroslaw Pulka, Gillian Madden, Guillaume Huyet, Et. Al.

Physical Sciences Publications

The carrier relaxation and escape dynamics of InAs/GaAs quantum dot waveguide absorbers is studied using heterodyne pump-probe measurements. Under reverse bias conditions, we reveal differences in intradot relaxation dynamics, related to the initial population of the dots’ ground or excited states. These differences can be attributed to phonon-assisted or Auger processes being dominant for initially populated ground or excited states, respectively.