Physical Sciences and Mathematics Commons^™

Saturable Absorption Of Free-Electron Laser Radiation By Graphite Near The Carbon K-Edge, Lars Hoffmann, Sasawat Jamnuch, Craig P. Schwartz, Tobias Helk, Sumana L. Raj, Hikaru Mizuno, Riccardo Mincigrucci, Laura Foglia, Emiliano Principi, Shervin Fatehi

Chemistry Faculty Publications and Presentations

The interaction of intense light with matter gives rise to competing nonlinear responses that can dynamically change material properties. Prominent examples are saturable absorption (SA) and two-photon absorption (TPA), which dynamically increase and decrease the transmission of a sample depending on pulse intensity, respectively. The availability of intense soft X-ray pulses from free-electron lasers (FELs) has led to observations of SA and TPA in separate experiments, leaving open questions about the possible interplay between and relative strength of the two phenomena. Here, we systematically study both phenomena in one experiment by exposing graphite films to soft X-ray FEL pulses of …

Investigation On The Synthesis, Application And Structural Features Of Heteroaryl 1,2-Diketones, Robert J. Wehrle, Alexander Rosen, Thu Vu Nguyen, Kalyn Koons, Eric Jump, Mason Bullard, Natalie Wehrle, Adam Stockfish, Patrick M. Hare, Abdurrahman Atesin, Tülay A. Ateşin, Lili Ma

Chemistry Faculty Publications and Presentations

A set of unsymmetrical heteroaryl 1,2-diketones were synthesized by a heteroarylation/oxidation sequence with up to 65% isolated yields. Palladium catalyst XPhos Pd G4 and SeO2 were the key reagents used in this methodology, and microwave irradiation was utilized to facilitate an efficient and ecofriendly process. The application of heteroaryl 1,2-diketones is demonstrated through the synthesis of an unsymmetrical 2-phenyl-3-(pyridin-3-yl)quinoxaline (5a) from 1-phenyl-2-(pyridin-3-yl)ethane-1,2-dione (4a). The lowest energy conformations of 4a and 5a were located using Density Functional Theory (DFT) at the M06-2X/def2-TZVP level of theory. Two lowest energy conformations of 4a differ with respect to the position of the N atom …

Band-Gap Tuning In Acceptor-Donor-Acceptor Boron Difluoride Formazanates, Francis L. Buguis, Michael Anghel, Joe B. Gilroy, Jasveer S. Dhindsa

Chemistry Publications

π-Conjugated molecules with acceptor-donor-acceptor (A-D-A) electronic structures are an important class of materials due to their tunable optoelectronic properties and applications in, for example, organic light-emitting diodes, nonlinear optical devices, and organic solar cells. The frontier molecular orbital energies, and thus band gaps, of these materials can be tuned by varying the donor and acceptor traits and π-electron counts of the structural components. Herein, we report the synthesis and characterization of a series of A-D-A compounds consisting of BF₂ formazanates as electron acceptors bridged by a variety of π-conjugated donors. The results, which are supported by DFT calculations, demonstrate …

Hierarchical Plasmon Resonances In Fractal Structures, Isobel C. Bicket, Edson P. Bellido, Danielle M. Mcrae, Francois Lagugne-Labarthet, Gianluigi A. Botton

Chemistry Publications

An equilateral triangular prism is used as the fundamental building block to con- struct additive Sierpinski fractals, enabling new surface plasmon resonances (SPR) in the first three generations of Sierpinski triangles, as well as topological intermediaries between generations. The modes are characterized using electron energy loss spectroscopy accompanied by eigenmode calculations and optical finite-difference time domain simulations. The complex fractal geometries present a predictable hierarchy of new resonances, each arising from the previous generational building blocks used to construct the fractal. Intermediate structures break the polarization degeneracy of the equilateral fractals while maintaining a rich multiband spectral response. Engineering defects …

Tools For Prescreening The Most Active Sites On Ir And Rh Clusters Toward C−H Bond Cleavage Of Ethane: Nbo Charges And Wiberg Bond Indexes, Yingbin Ge, Anna Le, Gregory J. Marquino, Phuc Q. Nguyen, Kollin Trujillo, Morgan Schimelfenig, Ashley Noble

All Faculty Scholarship for the College of the Sciences

B3LYP calculations were carried out to study the insertion of iridium (Ir) and rhodium (Rh) clusters into a C−H bond of ethane, which is often the ratelimiting step of the catalytic cycle of oxidative dehydrogenation of ethane. Our previous research on Ir catalysis correlates the diffusivity of the lowest unoccupied molecular orbital of the Ir clusters and the relative activities of the various catalytic sites. The drawback of this research is that the molecular orbital visualization is qualitative rather than quantitative. Therefore, in this study on C−H bond activation by the Ir and Rh clusters, we conducted analyses of natural …

Carving Plasmon Modes In Silver Sierpiński Fractals, Isobel C. Bicket, Edson P. Bellido, Danielle M. Mcrae, Francois Lagugne-Labarthet, Gianluigi A. Botton

Chemistry Publications

The surface plasmon resonance (SPR) modes of the first three generations of a Sierpiński fractal triangle are investigated using electron energy loss spectroscopy (EELS) complemented with finite difference time domain simulations. The Sierpiński fractal geometry is created in a subtractive manner, by carving triangular apertures into the triangular prism of the previous fractal generation. The ability of the fractal antenna to efficiently utilize space in coupling to long wavelength excitations is confirmed on the single nanostructure level via redshifting of the primary dipole mode as the fractal generation is increased. Through application of the Babinet principle, it is demonstrated that …

Heat And Work, The First Law Of Thermodynamics From The Boltzmann Pov, Carl W. David

Chemistry Education Materials

The First Law of Thermodynamics is discussed in terms of the Boltzmann distribution.

Nano To Global: Small Structures And Their Impact On Energy Markets, Kurt W. Kolasinski

Sustainability Research & Practice Seminar Presentations

No abstract provided.

Preventing Crossover In Redox Flow Batteries Through Active Material Oligomerization, Susan A. Odom

Chemistry Faculty Publications

No abstract provided.

Size And Site Dependence Of The Catalytic Activity Of Iridium Clusters Towards Ethane Dehydrogenation, Yingbin Ge, Hao Jiang, Russell Kato, Prasuna Gummagatta

All Faculty Scholarship for the College of the Sciences

This research focuses on optimizing transition metal nanocatalyst immobilization and activity to enhance ethane dehydrogenation. Ethane dehydrogenation, catalyzed by thermally stable Ir_n (n = 8, 12, 18) atomic clusters that exhibit a cuboid structure, was studied using the B3LYP method with triple-ζ basis sets. Relativistic effects and dispersion corrections were included in the calculations. In the dehydrogenation reaction Ir_n + C₂H₆ → H−Ir_n−C₂H₅ → (H)₂−Ir_n−C₂H₄, the first H-elimination is the rate-limiting step, primarily because the reaction releases sufficient heat to facilitate …

Characterization Of S-Swcnt/Pf-Pd Dispersions And Networks, Tamara N. El-Hayek Ms., Jeffrey Blackburn, Andrew Ferguson, Tammy Pheuphong

STAR Program Research Presentations

Single-Walled Carbon Nanotubes (SWCNTs) are being investigated for their use in a wide variety of renewable energy applications. Their unique physical properties contribute to desirable traits such as a high carrier mobility, strong optical absorption and tunable electronic band gap. Unfortunately, due to variability in certain parameters, SWCNTs are limited in their application. The major drawback is that SWCNTs are variable in size and type and typical synthetic methods are not selective. As a result, selective methods must be developed in order to sort these tubes and extract those which are desirable for a particular application. Though there are several …

Multiple-Time Step Ab Initio Molecular Dynamics Based On Two-Electron Integral Screening, Shervin Fatehi, Ryan P. Steele

Chemistry Faculty Publications and Presentations

A multiple-timestep ab initio molecular dynamics scheme based on varying the two-electron integral screening method used in Hartree–Fock or density functional theory calculations is presented. Although screening is motivated by numerical considerations, it is also related to separations in the length- and timescales characterizing forces in a molecular system: Loose thresholds are sufficient to describe fast motions over short distances, while tight thresholds may be employed for larger length scales and longer times, leading to a practical acceleration of ab initio molecular dynamics simulations. Standard screening approaches can lead, however, to significant discontinuities in (and inconsistencies between) the energy and …

Observation Of Ground-State Two-Neutron Decay, M Thoennessen, Z Kholey, A Spyrou, E Lunderberg, Paul A. Deyoung, H Attanayake, T Baumann, D Bazin, B A. Brown, G Christian, D Divaratne, S M. Grimes, A Haagsma, J E. Finck, N Frank, B Luther, S Mosby, T Nagi, Graham F. Peaslee, W A. Peters, A Schiller, J K. Smith, J Snyder, M Strongman, A Volya

Faculty Publications

Neutron decay spectroscopy has become a successful tool to explore nuclear properties of nuclei with the largest neutron-to-proton ratios. Resonances in nuclei located beyond the neutron dripline are accessible by kinematic reconstruction of the decay products. The development of two-neutron detection capabilities of the Modular Neutron Array (MoNA) at NSCL has opened up the possibility to search for unbound nuclei which decay by the emission of two neutrons. Specifically, this exotic decay mode was observed in¹⁶Be and ²⁶O.

A Highly Efficient Tio2-Xcx Nano-Heterojunction Photocatalyst For Visible-Light Induced Antibacterial Applications, Vinodkumar Etacheri, Michael Seery, Stephen Hinder, Georg Michlits, Suresh Pillai

Articles

Visible-light-induced antibacterial activity of carbon-doped anatase-brookite titania nano-heterojunction photocatalysts are reported for the first time. These heterostructures were prepared using a novel low temperature (100 °C) non-hydrothermal low power microwave (300 W) assisted method. Formation of interband C 2p states was found to be responsible for the band gap narrowing of the carbon doped heterojunctions. The most active photocatalyst obtained after 60 minutes of microwave irradiation exhibits a 2-fold higher visible-light induced photocatalytic activity in contrast to the standard commercial photocatalyst Evonik-Degussa P-25. Staphylococcus aureus inactivation rate constant for carbon-doped nano-heterojunctions and the standard photocatalyst was 0.0023 and -0.0081 min …

A Review On The Visible Light Active Titanium Dioxide Photocatalysts For Environmental Applications, Miguel Pelaez, Nicholas Nolan, Suresh Pillai, Michael Seery, Polycarpos Falaras, Athanassios G. Kontos, Patrick S.M. Dunlop, Jeremy W.J. Hamiltone, J. Anthony Byrne, Kevin O’Shea, Mohammad H. Entezari, Dionysios D. Dionysiou

Articles

Development of visible light active (VLA) titania photocatalysts

Fujishima and Honda (1972) demonstrated the potential of titanium dioxide (TiO 2) semiconductor mate-rials to split water into hydrogen and oxygen in a photo-electrochemical cell. Their work triggered the development of semiconductor photocatalysis for a wide range of environmental and energy applica-tions. One of the most significant scientific and commercial advances to date has been the development of visible light active (VLA) TiO2 photocatalytic materials. In this review, a background on TiO2 struc-ture, properties and electronic properties in photocatalysis is presented. The development of different strategies to modify TiO2 for the utilization …

Reduction Of Benzylidene Dibenzo[ A, D ]Cycloheptenes: Over-Reduction Of Antiaromatic Dianions To Aromatic Tetraanions, Blakely Tresca, Macdonald Higbee, Nancy S. Mills

Chemistry Faculty Research

The antiaromaticity of a series of dianions of p-substituted benzylidene dibenzo[a,d]cycloheptenes was examined through calculated measures of antiaromaticity. The nucleus-independent chemical shifts (NICS) and magnetic susceptibility exaltation both showed substantial antiaromatic character in the benzannulated tropylium anion. When the antiaromaticity was normalized for the area of the ring, these tropylium anions were shown to be among the most antiaromatic anions in the chemical literature. Attempts to make the dianion through reduction with lithium or potassium gave the tetraanion as the only species observable in the (1)H NMR spectrum. Quench of the reaction mixture with trimethylsilyl chloride or D(2)O confirmed the …

Nona-Arginine Facilitates Delivery Of Quantum Dots Into Cells Via Multiple Pathways, Yi Xu, Betty Revon Liu, Han Jung Lee, Katie Shannon, Jeffrey G. Winiarz, Tien-Chun Wang, Huey-Jenn Chiang, Yue-Wern Huang

Biological Sciences Faculty Research & Creative Works

Semiconductor quantum dots (QDs) have recently been used to deliver and monitor biomolecules, such as drugs and proteins. However, QDs alone have a low efficiency of transport across the plasma membrane. In order to increase the efficiency, we used synthetic nona-arginine (SR9), a cell-penetrating peptide, to facilitate uptake. We found that SR9 increased the cellular uptake of QDs in a noncovalent binding manner between QDs and SR9. Further, we investigated mechanisms of QD/SR9 cellular internalization. Low temperature and metabolic inhibitors markedly inhibited the uptake of QD/SR9, indicating that internalization is an energy-dependent process. Results from both the pathway inhibitors and …

Enhanced Oxygen Activation Over Supported Bimetallic Au-Ni Catalysts, Bert D. Chandler, Cormac G. Long, John D. Gilbertson, Christopher J. Pursell, G. Vijayaraghavan, K. J. Stevenson

Chemistry Faculty Research

New bimetallic Ni-Au supported nanoparticle catalysts were prepared by using dendrimer templated nanoparticles. Amine-terminated generation 5 polyamidoamine (PAMAM) dendrimers were anchored to a commercial silica with a siloxane linked anhydride. The dendrimer was then alkylated and used to template Ni-Au nanoparticles, which were subsequently extracted into organic solution as thiol monolayer protected clusters (MPCs). Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) indicated bimetallic nanoparticles of about 2 nm in size. Nanoparticles were deposited onto P-25 TiO2, and the capping thiol ligands were removed under flowing H2. DRIFTS infrared spectra of adsorbed CO showed only Au on the catalyst …

Highly Visible Light Active Tio2-Xnx Heterojunction Photocatalysts, Vinodkumar Etacheri, Michael Seery, Steven Hinder, Suresh Pillai

Articles

Nitrogen doped anatase-rutile heterojunctions are successfully synthesized through an ethylene-diaminetetraacetic acid (EDTA) modified sol-gel process.An FT-IR study of EDTA modified TiO2 gel confirms the existence of an ionic intermediate (as indicated by a Δν value of 233 cm-1).Differential scanning calorimetry (DSC), X-ray diffraction (XRD), and Raman spectroscopy are employed to study the phase evolution, phase purity, and crystallite size of samples. Formations of O-Ti-N and N-Ti-N bonds in calcined samples are confirmed using XPS and FT-IR spectro- scopy. AllEDTAmodified samples show significantly higher visible light photocatalytic activity than the unmodified sample. The most active nitrogen doped heterojunction obtained at 400C …

Universal Scaling Of Nonequilibrium Transport In The Kondo Regime Of Single Molecule Devices, G D. Scott, Z K. Keane, Jacob W. Ciszek, J M. Tour, D Natelson

Chemistry: Faculty Publications and Other Works

Scaling laws and universality are often associated with systems exhibiting emergent phenomena possessing a characteristic energy scale. We report nonequilibrium transport measurements on two different types of single molecule transistor devices in the Kondo regime. The conductance at low bias and temperature adheres to a scaling function characterized by two parameters. This result, analogous to that reported recently in semiconductor dots with Kondo temperatures two orders of magnitude lower, demonstrates the universality of this scaling form. We compare the extracted values of the scaling coefficients to previous experimental and theoretical results.

Preparation And Characterization Of 3 Nm Magnetic Niau Nanoparticles, Bethany J. Auten, B. P. Hahn, G. Vijayaraghavan, K. J. Stevenson, Bert D. Chandler

Chemistry Faculty Research

Using PAMAM dendrimers as nanoparticle templates, a synthetic route to prepare 3 nm magnetic NiAu nanoparticles was developed. Aqueous solutions of hydroxyl-terminated generation 5 PAMAM dendrimers in 25 mM NaClO₄ were shown to bind aqueous Ni^II. Coreduction of Ni^II and Au^III salts yielded bimetallic dendrimer stabilized nanoparticles, which were extracted into toluene with decanethiol. Characterization of the resulting monolayer protected clusters (MPCs) with transmission electron microscopy and UV–visible, atomic absorption, and X-ray photoelectron spectroscopies suggested that the MPCs had substantial surface enrichment in Au. Superconducting quantum interference device (SQUID) measurements at 5 K show the …

Silver Doped Titanium Dioxide Nanomaterials For Enhanced Visible Light Photocatalysis, Michael Seery, Reena George, Suresh Pillai, Patrick Floris

Articles

This paper presents a systematic study on two different preparation methods for titanium dioxide with silver. The silver can be incorporated by irradiating the reaction mixture during preparation to reduce silver ion to silver metal or by direct calcination of the sol–gel material to decompose silver nitrate to silver. Of the two methods, we found the latter produces a more effective photocatalytic material (6–50% improvement in catalytic efficiency), which is attributed to the fact that the silver is homogeneously dispersed throughout the material. The efficiency of the materials were examined using a Q-Sun solar simulator (visible light) and in Dublin …

Kondo Resonances And Anomalous Gate Dependence In The Electrical Conductivity Of Single-Molecule Transistors, L H. Yu, Z K. Keane, Jacob W. Ciszek, L Cheng, J M. Tour, T Baruah, M R. Pederson, D Natelson

Chemistry: Faculty Publications and Other Works

We report Kondo resonances in the conduction of single-molecule transistors based on transition metal coordination complexes. We find Kondo temperatures in excess of 50 K, comparable to those in purely metallic systems. The observed gate dependence of the Kondo temperature is inconsistent with observations in semiconductor quantum dots and a simple single-dot-level model. We discuss possible explanations of this effect, in light of electronic structure calculations.

Analysis Of The Potential Energy Surface Of Ar–Nh3, G. Chalasinski, S. M. Cybulski, M. M. Szczesniak, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

The combination of supermolecular Møller–Plesset treatment with the perturbation theory of intermolecular forces is applied in the analysis of the potential energy surface of Ar–NH₃. Anisotropy of the self‐consistent field (SCF) potential is determined by the first‐order exchange repulsion. Second‐order dispersion energy, the dominating attractive contribution, is anisotropic in the reciprocal sense to the first‐order exchange, i.e., minima in one nearly coincide with maxima in the other. The estimated second‐order correlation correction to the exchange effect is nearly as large as a half ΔE^SCF in the minimum and has a ‘‘smoothing’’ effect on the anisotropy of …

The Potential Energy Surface Of (Nh3)2, Z. Latajka, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

Ab initio calculations at the SCF and correlated levels are carried out to characterize the potential energy surface of the NH₃ dimer. The two basis sets used are 4‐31G∗ and a larger one containing two sets of d‐functions on N centers, 6‐31G∗∗ (1p, 2d). The only minimum occurring on the surface is a cyclic C_2h structure in which the two H‐bonding protons are displaced 42° from the N‐‐N axis. The surface contains a very shallow valley along the direction leading from this geometry to a single linear H bond although …

Studies Of Dispersion Energy In Hydrogen‐Bonded Systems. H2o–Hoh, H2o–Hf, H3n–Hf, Hf–Hf, M. M. Szczesniak, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

Dispersion energy is calculated in the systems H₂O–HOH, H₂O–HF, H₃N–HF, and HF–HF as a function of the intermolecular separation using a variety of methods. M≂ller–Plesset perturbation theory to second and third orders is applied in conjunction with polarized basis sets of 6‐311G∗∗ type and with an extended basis set including a second set of polarization functions (DZ+2P). These results are compared to a multipole expansion of the dispersion energy, based on the Unsöld approximation, carried out to the inverse tenth power of the intermolecular distance. Pairwise evaluation is also carried out using both atom–atom …