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Full-Text Articles in Physics

Force-Feedback High-Speed Atomic Force Microscope For Studying Large Biological Systems, Byung I. Kim, Ryan Boehm Dec 2012

Force-Feedback High-Speed Atomic Force Microscope For Studying Large Biological Systems, Byung I. Kim, Ryan Boehm

Physics Faculty Publications and Presentations

We designed and developed a high-speed atomic force microscope (HSAFM) utilizing a force-feedback scheme for imaging large biological samples. The system collects three simultaneous images: a deflection image, a topographic image, and a force image. We demonstrated that this force-feedback HSAFM is capable of acquiring large topographic images of Escherichia coli biofilms at approximately one frame per second in air. We discuss how the self-actuating cantilever and the piezo tube follow those larger biological topographic features during the HSAFM imaging process.


Engaging The Community Through An Undergraduate Biomedical Physics Course, Grace Van Ness, Ralf Widenhorn Dec 2012

Engaging The Community Through An Undergraduate Biomedical Physics Course, Grace Van Ness, Ralf Widenhorn

Physics Faculty Publications and Presentations

We report on the development of an undergraduate biomedical physics course at Portland State University, motivated by both student interest and the desire of the university?s Physics Department to provide an interdisciplinary intermediate-level physics course. The course was developed through the community engagement of physicians, clinical researchers, and basic science researchers. Class meetings were a combination of regular and guest lectures, hands-on exercises, web-based activities, class discussions, and a student poster information session for patrons at a local science museum. The course inspired students to engage in research projects in biomedical physics that enhance their understanding of science and ...


Effects Of Sn Doping On The Morphology And Properties Of Fe-Doped In2o3 Epitaxial Films, Tie Zhou, Lin Wei, Yanru Xie, Qinghao Li, Guoxiang Hu, Yanxue Chen, Shishen Yan, Guolei Liu, Liangmo Mei, Jun Jiao Nov 2012

Effects Of Sn Doping On The Morphology And Properties Of Fe-Doped In2o3 Epitaxial Films, Tie Zhou, Lin Wei, Yanru Xie, Qinghao Li, Guoxiang Hu, Yanxue Chen, Shishen Yan, Guolei Liu, Liangmo Mei, Jun Jiao

Physics Faculty Publications and Presentations

(Sn, Fe)-codoped In₂O₃ epitaxial films were deposited on (111)-oriented Y-stabilized ZrO₂ substrates by pulsed laser deposition with constant Fe concentration and different Sn concentrations. The influence of Sn concentration on the crystal structure and properties of Fe-doped In₂O₃ ferromagnetic semiconductor films has been investigated systematically. Experimental results indicate that Sn doping can effectively reduce the surface roughness and suppresses breakup of the films into separated islands. At the same time, the optical band gap increases and the electrical properties improve correspondingly. However, although the carrier density increases dramatically with the Sn doping, no obvious change of the ferromagnetism ...


Crystallography Open Database (Cod): An Open-Access Collection Of Crystal Structures And Platform For World-Wide Collaboration, Saulius Gražulis, Adriana Daškevič, Andrius Merkys, Daniel Chateigner, Luca Lutterotti, Miguel Quirós, Nadezhda R. Serebryanaya, Peter Moeck, Robert T. Downs, Armel Le Bail Nov 2012

Crystallography Open Database (Cod): An Open-Access Collection Of Crystal Structures And Platform For World-Wide Collaboration, Saulius Gražulis, Adriana Daškevič, Andrius Merkys, Daniel Chateigner, Luca Lutterotti, Miguel Quirós, Nadezhda R. Serebryanaya, Peter Moeck, Robert T. Downs, Armel Le Bail

Physics Faculty Publications and Presentations

Using an open-access distribution model, the Crystallography Open Database (COD, http://www.crystallography.net) collects all known 'small molecule / small to medium sized unit cell' crystal structures and makes them available freely on the Internet. As of today, the COD has aggregated ~150,000 structures, offering basic search capabilities and the possibility to download the whole database, or parts thereof using a variety of standard open communication protocols. A newly developed website provides capabilities for all registered users to deposit published and so far unpublished structures as personal communications or pre-publication depositions. Such a setup enables extension of the COD ...


Annealing Effect On Photovoltaic Performance Of Cdse Quantum-Dots-Sensitized Tio2 Nanorod Solar Cells, Yitan Li, Lin Wei, Ruizi Zhang, Yanxue Chen, Jun Jiao Oct 2012

Annealing Effect On Photovoltaic Performance Of Cdse Quantum-Dots-Sensitized Tio2 Nanorod Solar Cells, Yitan Li, Lin Wei, Ruizi Zhang, Yanxue Chen, Jun Jiao

Physics Faculty Publications and Presentations

Large area rutile TiO₂ nanorod arrays were grown on F:SnO₂ (FTO) conductive glass using a hydrothermal method at low temperature. CdSe quantum dots (QDs) were deposited onto single-crystalline TiO₂ nanorod arrays by a chemical bath deposition (CBD) method to make a photoelectrode. The solar cell was assembled using a CdSe-TiO₂ nanostructure as the photoanode and polysulfide solution as the electrolyte. The annealing effect on optical and photovoltaic properties of CdSe quantum-dotssensitized TiO₂ nanorod solar cells was studied systematically. A significant change of the morphology and a regular red shift of band gap of CdSe nanoparticles were observed after annealing ...


Dark Current Modeling With A Moving Depletion Edge, Justin Charles Dunlap, Morley M. Blouke, Erik Bodegom, Ralf Widenhorn Oct 2012

Dark Current Modeling With A Moving Depletion Edge, Justin Charles Dunlap, Morley M. Blouke, Erik Bodegom, Ralf Widenhorn

Physics Faculty Publications and Presentations

Within a pixel in a digital imager, generally either a chargecoupled device or complementary metal oxide semiconductor device, doping of the semiconductor substrate and application of gate voltages create a region free of mobile carriers called the depletion region. This region fills with charge after incoming photons or thermal energy raise the charges from the valence to the conduction energy band. As the signal charge fills the depletion region, the electric field generating the region is altered, and the size of the region is reduced. We present a model that describes how this dynamic depletion region, along with the location ...


Decay Rates Of A Molecule In The Vicinity Of A Spherical Surface Of An Isotropic Magnetodielectric Material, H. Y. Chung, P.T. Leung, D. P. Tsai Oct 2012

Decay Rates Of A Molecule In The Vicinity Of A Spherical Surface Of An Isotropic Magnetodielectric Material, H. Y. Chung, P.T. Leung, D. P. Tsai

Physics Faculty Publications and Presentations

A comprehensive study is presented on the decay rates of excited molecules in the vicinity of a magnetodielectric material of spherical geometry via electrodynamic modeling. Both the models based on a driven-damped harmonic oscillator and on energy transfers will be applied so that the total decay rates can be rigorously decomposed into the radiative and the nonradiative rates. Clarifications of the equivalence of these two models for arbitrary geometry will be provided. Different possible orientations and locations of the molecule are studied with the molecule being placed near a spherical particle or a cavity. Among other results, TE modes are ...


Controlled Spatial Switching And Routing Of Surface Plasmons In Designed Single-Crystalline Gold Nanostructures, Rolf Kӧnenkamp, Robert Campbell Word, Joseph Fitzgerald, Athavan Nadarajah, S. D. Saliba Oct 2012

Controlled Spatial Switching And Routing Of Surface Plasmons In Designed Single-Crystalline Gold Nanostructures, Rolf Kӧnenkamp, Robert Campbell Word, Joseph Fitzgerald, Athavan Nadarajah, S. D. Saliba

Physics Faculty Publications and Presentations

Electron emission microscopy is used to visualize plasmonic routing in gold nano-structures. We show that in single-crystalline gold structures reliable routing can be achieved with polarization switching. The routing is due to the polarization dependence of the photon-to-plasmon coupling, which controls the mode distribution in the plasmonic gold film. We use specifically designed, single-crystalline planar structures. In these structures, the plasmon propagation length is sufficiently large such that significant plasmon power can be delivered to the near-field region around the end tips of the router. Solid state devices based on internal electron excitation and emission processes appear feasible.


Open Structure Zno/Cdse Core/Shell Nanoneedle Arrays For Solar Cells, Yanxue Chen, Lin Wei, Guanghua Zhang, Jun Jiao Sep 2012

Open Structure Zno/Cdse Core/Shell Nanoneedle Arrays For Solar Cells, Yanxue Chen, Lin Wei, Guanghua Zhang, Jun Jiao

Physics Faculty Publications and Presentations

Open structure ZnO/CdSe core/shell nanoneedle arrays were prepared on a conducting glass (SnO2:F) substrate by solution deposition and electrochemical techniques. A uniform CdSe shell layer with a grain size of approximately several tens of nanometers was formed on the surface of ZnO nanoneedle cores after annealing at 400°C for 1.5 h. Fabricated solar cells based on these nanostructures exhibited a high short-circuit current density of about 10.5 mA/cm2 and an overall power conversion efficiency of 1.07% with solar illumination of 100 mW/cm2. Incident photo-to-current conversion efficiencies higher than 75% were also ...


Turbulent Concentration Diffusion In Multiphase Flow, John D. Ramshaw Sep 2012

Turbulent Concentration Diffusion In Multiphase Flow, John D. Ramshaw

Physics Faculty Publications and Presentations

In multifluid multiphase flow models, the velocity of each phase is determined by its own momentum equation, which is coupled to the other phases by pairwise interphase drag forces proportional to velocity differences. When the drag coefficients are large, the phase velocities become nearly equal and the relative motion of the phases becomes diffusional rather than inertial. The multifluid momentum equations then reduce to a single momentum equation for the mixture and a system of linear relations that determine the small residual velocity differences between the phases. We derive such diffusional relations in a very general form that applies to ...


Influence Of Solvent On The Chiral Resolution Of Organic Molecules On Au(111): Ec-Stm Study Of Biphenyl Dicarboxylic Acid On Au(111) In An Aqueous Environment, Byung I. Kim, Joey Hanson, Matthew Turner, Lauren Reeder Aug 2012

Influence Of Solvent On The Chiral Resolution Of Organic Molecules On Au(111): Ec-Stm Study Of Biphenyl Dicarboxylic Acid On Au(111) In An Aqueous Environment, Byung I. Kim, Joey Hanson, Matthew Turner, Lauren Reeder

Physics Faculty Publications and Presentations

Adsorption-induced chiral resolution of organic molecules is important due to its potential applications in stereo-selective catalysis. We studied the adsorption-induced chiral resolution using a model achiral molecule of 4,4′ biphenyl dicarboxylic acid (BPDA) on Au(111) in 0.1 M perchloric acid (HClO4) by electrochemical scanning tunneling microscopy (EC-STM). Our experimental data showed that the BPDA molecules formed island structures with distinctive preferred orientations at the length scale of the molecular size. The molecules did not show any orientational ordering above the length scale, indicating that chiral resolution was absent in the aqueous environment. Previously, the molecules were ...


Effects Of Long-Range Tip-Sample Interaction On Magnetic Force Imaging: A Comparative Study Between Bimorph Driven System And Electrostatic Force Modulation, Byung I. Kim May 2012

Effects Of Long-Range Tip-Sample Interaction On Magnetic Force Imaging: A Comparative Study Between Bimorph Driven System And Electrostatic Force Modulation, Byung I. Kim

Physics Faculty Publications and Presentations

Magnetic force microscopy (MFM) using electrostatic force modulation has been designed and developed to avoid the drawbacks of the bimorph driven system. The bimorph driven system has poor frequency response and overlap of the topographic features on magnetic structures of the MFM images. In the electrostatic force modulation system, the amplitude increases in the noncontact regime as the tip approaches due to the capacitive coupling between tip and sample. MFM using electrostatic force modulation has been applied to observe maze-like stripe domain structures on a CoCr film. The contrast mechanism and imaging stability of MFM using electrostatic force modulation are ...


Concentration Dependence Of Magnetic Moment In Ce1-XFeXO2, Geoffrey L. Beausoleil Ii, Aaron Thurber, S. S. Rao, Gordon A. Alanko, Charles Hanna, Alex Punnoose Apr 2012

Concentration Dependence Of Magnetic Moment In Ce1-XFeXO2, Geoffrey L. Beausoleil Ii, Aaron Thurber, S. S. Rao, Gordon A. Alanko, Charles Hanna, Alex Punnoose

Physics Faculty Publications and Presentations

In this study, we examined the impact of iron doping on the structural, chemical, and magnetic properties of ceria (Ce1-xFexO2). Samples were produced in triplicate through a coprecipitation approach in a forced hydrolysis synthesis that yielded consistently sized nanocrystals using three different cerium precursors: cerium chloride, cerium ammonium nitrate, and cerium nitrate. Particles were characterized by x ray diffraction (XRD), x ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) spectroscopy, and vibrating sample magnetometry (VSM). XPS and EPR data shows iron to be in the Fe3+ state and confirms the ...


Size, Surface Structure, And Doping Effects On Ferromagnetism In Sno2, Gordon A. Alanko, Aaron Thurber, Charles Hanna, Alex Punnoose Apr 2012

Size, Surface Structure, And Doping Effects On Ferromagnetism In Sno2, Gordon A. Alanko, Aaron Thurber, Charles Hanna, Alex Punnoose

Physics Faculty Publications and Presentations

The effects of crystallite size, surface structure, and dopants on the magnetic properties of semiconducting oxides are highly controversial. In this work, Fe:SnO2 nanoparticles were prepared by four wet-chemical methods, with Fe concentration varying from 0% to 20%. Analysis confirmed pure single-phase cassiterite with a crystallite size of 2.6 ± 0.1 nm that decreased with increasing. Fe% doped substitutionally as Fe3+. Pure SnO2 showed highly reproducible weak magnetization that varied significantly with synthesis method. Interestingly, doping SnO2 with Fe < 2.5% produced enhanced magnetic moments in all syntheses; the maximum of 1.6 × 10−4 µB/Fe ion at 0.1% Fe doping was much larger than the ...


Unusual Crystallite Growth And Modification Of Ferromagnetism Due To Aging In Pure And Doped Zno Nanoparticles, Aaron Thurber, Gordon A. Alanko, Geoffrey L. Beausoleil Ii, Kelsey Dodge, Charles Hanna, Alex Punnoose Apr 2012

Unusual Crystallite Growth And Modification Of Ferromagnetism Due To Aging In Pure And Doped Zno Nanoparticles, Aaron Thurber, Gordon A. Alanko, Geoffrey L. Beausoleil Ii, Kelsey Dodge, Charles Hanna, Alex Punnoose

Physics Faculty Publications and Presentations

We report the unusual growth of pure and Fe-doped ZnO nanoparticles prepared by forced hydrolysis and the weakening of ferromagnetism due to aging in ambient conditions. More than four dozen nanoparticle samples in the size range of 4–20 nm were studied over 1 to 4 years. The as-prepared samples had significant changes in their crystallite sizes and magnetization as they aged in ambient conditions. Detailed studies using x ray diffraction and transmission electron microscopy (TEM) demonstrated that the crystallite size increased by as much as 1.4 times. Lattice parameters and strain also showed interesting changes. Magnetometry studies of ...


De Novo Transcriptome Of Safflower And The Identification Of Putative Genes For Oleosin And The Biosynthesis Of Flavonoids, Haiyan Li, Yuanyuan Dong, Jing Yang, Xiuming Liu, Yanfang Wang, Na Yao, Lili Guan, Nan Wang, Jinyu Wu, Xiaokun Li Feb 2012

De Novo Transcriptome Of Safflower And The Identification Of Putative Genes For Oleosin And The Biosynthesis Of Flavonoids, Haiyan Li, Yuanyuan Dong, Jing Yang, Xiuming Liu, Yanfang Wang, Na Yao, Lili Guan, Nan Wang, Jinyu Wu, Xiaokun Li

Physics Faculty Publications and Presentations

Safflower (Carthamus tinctorius L.) is one of the most extensively used oil crops in the world. However, little is known about how its compounds are synthesized at the genetic level. In this study, Solexa-based deep sequencing on seed, leaf and petal of safflower produced a de novo transcriptome consisting of 153,769 unigenes. We annotated 82,916 of the unigenes with gene annotation and assigned functional terms and specific pathways to a subset of them. Metabolic pathway analysis revealed that 23 unigenes were predicted to be responsible for the biosynthesis of flavonoids and 8 were characterized as seed-specific oleosins. In ...


Limits On Large Extra Dimensions Based On Observations Of Neutron Stars With The Fermi-Lat, Jay Norris Feb 2012

Limits On Large Extra Dimensions Based On Observations Of Neutron Stars With The Fermi-Lat, Jay Norris

Physics Faculty Publications and Presentations

We present limits for the compactification scale in the theory of Large Extra Dimensions (LED) proposed by Arkani-Hamed, Dimopoulos, and Dvali. We use 11 months of data from the Fermi Large Area Telescope (Fermi-LAT) to set gamma ray flux limits for 6 gamma-ray faint neutron stars (NS). To set limits on LED we use the model of Hannestad and Raffelt (HR) that calculates the Kaluza-Klein (KK) graviton production in supernova cores and the large fraction subsequently gravitationally bound around the resulting NS. The predicted decay of the bound KK gravitons to γγ should contribute to the flux from NSs. Considering ...


Cantilever-Based Optical Interfacial Force Microscopy, Byung I. Kim Feb 2012

Cantilever-Based Optical Interfacial Force Microscopy, Byung I. Kim

Physics Faculty Publications and Presentations

Atomic force microscopy (AFM) is one of the most important tools that lead current nanoscience and nanotechnology in many diverse areas including physics, chemistry, material engineering, and nano-biology. The current AFM technique has been routinely applied to forced unbinding processes of biomolecular complexes such as antibody-antigen binding, ligand-receptor pairs, protein unfolding, DNA unbinding, and RNA unfolding studies (Butt et al., 2005; Fritz & Anselmetti, 1997; Schumakovitch et al., 2002). AFMs have also been applied to intermolecular friction studies (Carpick et al., 1997; Colchero et al., 1996; Fernandez-Torres et al., 2003; Goddenhenrich et al., 1994; Goertz et al., 2007; B.I. Kim et al ...


Dynamic Ccd Pixel Depletion Edge Model And The Effects On Dark Current Production, Justin Charles Dunlap, Morley M. Blouke, Erik Bodegom, Ralf Widenhorn Jan 2012

Dynamic Ccd Pixel Depletion Edge Model And The Effects On Dark Current Production, Justin Charles Dunlap, Morley M. Blouke, Erik Bodegom, Ralf Widenhorn

Physics Faculty Publications and Presentations

The depletion edge in Charge-Coupled Devices (CCD) pixels is dependent upon the amount of signal charge located within the depletion region. A model is presented that describes the movement of the depletion edge with increasing signal charge. This dynamic depletion edge is shown to have an effect on the amount of dark current produced by some pixels. Modeling the dark current behavior of pixels both with and without impurities over an entire imager demonstrates that this moving depletion edge has a significant effect on a subset of the pixels. Dark current collected by these pixels is shown to behave nonlinearly ...


Proton-Fountain Electric-Field-Assisted Nanolithography (Pen): Fabrication Of Polymer Nanostructures That Respond To Chemical And Electrical Stimuli. An Overview In The Context Of The Top-Down And Bottom-Up Approaches To Nanotechnology, Andres H. La Rosa, Mingdi Yan, Rodolfo Fernandez, Elia Zegarra Jan 2012

Proton-Fountain Electric-Field-Assisted Nanolithography (Pen): Fabrication Of Polymer Nanostructures That Respond To Chemical And Electrical Stimuli. An Overview In The Context Of The Top-Down And Bottom-Up Approaches To Nanotechnology, Andres H. La Rosa, Mingdi Yan, Rodolfo Fernandez, Elia Zegarra

Physics Faculty Publications and Presentations

The development of chemically functionalized materials, such that their physical properties can vary in response to external mechanical, chemical, or optical stimuli, offers potential applications in a wide range of fields, namely microfluidics, electronic memory devices, sensors and actuators. In particular, patterned structures built with stimuli-responsive polymer materials are attractive due to their inherent lower cost production and for building soft scaffolds that mimic closer natural bio-environments. In addition, harnessing the construction of patterns with nanoscale dimensions would not only a) allow building lab-on-a-chip devices that require minimal chemical reactants volumes, but also b) find applications in the area of ...