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CNST Group Seminars: 2013



CNST Electron Physics Group Seminar

ON-WAFER BAND-STOP FILTER USING BA HEXAGONAL FERRITE THIN FILMS ON A PT TEMPLATE

Ian Harward
University of Colorado, Colorado Springs

Friday, December 20, 2013, 10:30AM, Rm. H107C, Bldg. 217

E/M waves in the 30-300 GHz frequency range, or "millimeter waves," are used in a wide range of military and civilian applications. These include military and weather radar systems, automotive collision avoidance radar, airport body scanners, local area networks, and offer promise for several short-range wireless communications applications. One obstacle to the increased deployment of mm wave technology, however, is the lack of advances in magnetic structures which operate at those frequencies. It was therefore the aim of this work to utilize the M-type barium hexagonal ferrite (BaM) in a millimeter wave device. This ferrite material was chosen due to its high magnetic anisotropy, which boosts its ferromagnetic resonance frequency into the mm wave frequency range. I will discuss the development of a new thin film growth technique, metallo-organic decomposition (MOD), for the ferrite on a Pt template (on a Si wafer), as well as some important properties of the resulting films. Finally, an on-wafer band-stop filter based on this technology is demonstrated. Special mention of the vector network analyzer-based FMR system for characterizing the magnetic properties of the thin ferrite films will also be made.

For further information please contact Robert McMichael, 301-975-5121, robert.mcmichael@nist.gov.




CNST Nanofabrication Research Group Seminar

BOWTIE NANOANTENNAS FOR PLASMONIC NANOTWEEZERS AND ENHANCED OPTICAL MAGNETISM

Brian J. Roxworthy
University of Illinois at Urbana-Champaign

Monday, December 16, 2013, 1:30PM, Rm. H107, Bldg. 217

Optical trapping techniques are ubiquitous in modern science and optical forces have been employed to make substantial advancements in the biological sciences, colloidal physics, and micro/nano electro-mechanical systems (MEMS/NEMS). However, conventional optical tweezers based on high-numerical aperture (NA) focusing are fundamentally constrained by the diffraction limit, which places and upper bound on achievable optical forces for a given input power. This is particularly problematic for handling both fragile biological species that are easily damaged and nanometer-sized objects which have small polarizabilities. Recently, however, plasmonic optical tweezers based on metallic nanoparticles have emerged as a promising approach to circumvent this issue. These plasmonic "nanotweezers" exhibit remarkable sub-diffraction field confinement and enhancement, which produce greatly amplified optical forces in the near-field. Additionally, optical absorption in plasmonic nanostructures results in significant heat generation that induces local fluid convection currents. To this point, these effects have been generally regarded as deleterious to plasmonic nanotweezer performance. In this talk, I will discuss the trapping performance and underlying physics of plasmonic nanotweezers based on arrays of gold bowtie nanoantennas (BNAs). When illuminated off-resonance, the BNAs produce optical trapping efficiencies 15-20x that of a conventional optical tweezer with input power densities 1-2 orders of magnitude lower than the expected biological damage threshold. Further, the combination of optical and thermally-induced forces increases overall trap strength and produces phase-like behavior in trapped colloidal particles. These phases are characterized using plasmonic trapping "phase diagrams" that can be used to engineer specific trapping tasks including dexterous, single-particle manipulation, trapping and manipulation of self-assembled particle clusters, and particle sorting. Optical forces are further enhanced using femtosecond-pulsed illumination of the BNAs, which augments the trap stiffness to 2x that of nanotweezers employing continuous-wave illumination. The femtosecond nanotweezers exhibit a threshold power above which dielectric and metallic nanoparticles spontaneously fuse to the BNA surface, likely due to a Van der Waals effect. This fusing behavior inspired the design of a capped-BNA structure which produces simultaneous enhancement of electric and magnetic fields up to 30000x and 3000x, respectively. The large magnetic field enhancement is among the highest values reported to date and will find use in novel data storage applications, metamaterial research, nonlinear magnetics, low-loss plasmon propagation, and may lead to future optical manipulation modalities exploiting the magnetic vector of light.

For further information please contact Vladimir Aksyuk, 301-975-2867, vladimir.aksyuk@nist.gov.


CNST Energy Research Group Seminar

NOVEL ELECTRONIC AND MAGNETIC BEHAVIOR IN COMPLEX OXIDE HETEROSTRUCTURES

Steve May
Drexel University

Wednesday, December 4, 2013, 1:30 PM, Rm H107, Bldg 217

Scientific interest in ABO3 perovskite oxides remains intense due to the wide range of physical behavior present in these materials. Recent advances in thin film deposition techniques, such as molecular beam epitaxy (MBE), have made it possible to synthesize high quality perovskite heterostructures, material architectures that have enabled conventional semiconductor-based devices. In order to realize devices based on complex oxides, strategies to design and control the unique electronic and magnetic functionalities present in these materials must be developed, for instance by taking advantage of epitaxial constraints or interfacial phenomena enabled in heterostructures. This talk will describe activities in MBE-based synthesis and characterization of perovskite films and superlattices, and will highlight our efforts exploring electronic phase transitions in the La1-xSrxFeO3 system and novel magnetic behavior in (La,Eu)1-xSrxMnO3 manganites induced by controlling rotations and distortions of the corner-connected MnO6 octahedra.

For further information please contact Fred Sharifi, 301-975-4633, fred.sharifi@nist.gov.


CNST Nanofabrication Research Group Seminar

CELLULAR FORCES AND MECHANICAL COUPLING USING MICROENGINEERED DEVICES

Craig Copeland
Johns Hopkins University

Monday, November 25, 2013, 10:30AM Rm. H107, Bldg. 217

The biological response of cells to mechanical forces is integral to both normal cell function and the progression of many diseases, such as hypertensive vascular wall thickening, and cardiac fibrosis. Physical cues experienced by cells arise from internally generated contractile forces, as well as from external sources of force and strain in the local environment. In recent years, a wide range of microfabricated devices have opened new approaches to study the mechanics of individual cells. I will describe a set of experiments that use arrays of flexible micron-scale poly(dimethylsiloxane) (PDMS) cantilevers (posts) to probe the behavior of cell-generated contractile forces under varying chemical and mechanical conditions. The cells' forces bend the posts, which are individually tracked through microscopy and image analysis, yielding a dynamic, micron-scale map of the cells' mechanical activity. I have applied these techniques to the study of force generation by cardiac fibroblasts to elucidate mechanical coupling between these cells and the myocytes responsible for the heart's pumping action that may contribute to certain types of cardiac arrhythmia. I will discuss an enhanced version of the micropost array that enables the application of controlled global stretch to cells, and will present results on the combined active and viscoelastic response of arterial smooth muscle cells under driven conditions. Micropatterning of the post array surface can be used to facilitate cell-cell interactions while measuring intercellular forces between cells in a pair configuration. I will describe experiments performed on these constructs that include global stretch application and local chemical stimulation via micropipette fluid flow.

For further information please contact Samuel Stavis, 301-975-2844, samuel.stavis@nist.gov.


CNST Energy Research Group Seminar

THE GOLD STORY OF HOLEY GRAPHENE

James Radich
University of Notre Dame

Thursday, November 21, 10:30 AM, Rm H107, Bldg 217

Reduced graphene oxide (RGO) is finding use as a 2-D carbon support structure for the development of new nanomaterial electrode architectures. Utilizing chemically-exfoliated graphene oxide (GO) as precursor in wet-chemical syntheses enables excellent nanomaterial loading onto the high surface area support. This approach to composite electrode synthesis is amenable to practical implementation of graphene in energy storage devices such as lithium ion batteries and electrochemical capacitors since both the GO starting material and the nanomaterial precursors can be dispersed in water or other polar solvents. In this talk I will first describe the origin of the enhancements offered to energy storage electrodes through the use of RGO. By modeling the electrochemical response of an RGO-MnO2 electrode used in a lithium half-cell construct, the role of RGO is elucidated. A key discovery is the significant improvement of diffusion characteristics of lithium ions to the electroactive material anchored on the RGO surface. Next, I will show how this discovery set the stage for the development of Holey Graphene. In particular, through the use of gold nanoparticles and hydroxyl radicals, the RGO surface can be selectively etched to generate a porous graphene structure that remains dispersed in water for further processing toward energy storage composites. Finally, this new synthesis displays significant potential toward fine tuning the porosity, wrinkling, and level of oxidation in the final Holey Graphene material.

For further information please contact Veronika Szalai, 301-975-3792, veronika.szalai@nist.gov.


CNST NanoFabrication Research Group Seminar

DYNAMIC SELF-ASSEMBLY OF A DNA TETRAHEDRON

John P. Sadowski
Harvard University

Monday, November 18, 2013, 10:30AM – 11:30AM, Rm H107, Bldg 217

Kinetically-controlled isothermal growth is fundamental to biological development, yet it remains challenging to rationally design molecular systems that self-assemble isothermally into complex geometries via prescribed self-assembly and disassembly pathways. By exploiting the programmable chemistry of base pairing, sophisticated spatial and temporal control have been demonstrated in DNA self-assembly, but largely as separate pursuits. By integrating temporal with spatial control, my colleagues and I have demonstrated the dynamic self-assembly of a DNA tetrahedron, where a prescriptive molecular program orchestrates the kinetic pathways by which DNA molecules isothermally self-assemble into a well-defined three-dimensional wireframe geometry. In this reaction, nine DNA reactants initially co-exist in a metastable state, but upon catalysis by a DNA initiator molecule, navigate 24 individually characterizable intermediate states through prescribed hybridization pathways, organized both in series and in parallel, to arrive at the tetrahedral final product. In contrast to previous work on dynamic DNA nanotechnology, this developmental program coordinates growth of ringed substructures into a three-dimensional wireframe superstructure, taking a step towards the goal of kinetically controlled isothermal growth of complex three-dimensional geometries. I will also discuss the development of computational tools to perform sequence design for this class of structures.

For further information please contact J. Alex Liddle, 301-975-6050, james.liddle@nist.gov.


CNST Electron Physics Group Seminar

TRANSITION METAL OXIDES FOR BEYOND-CMOS ELECTRONIC

Sieu D. Ha
Harvard University

Friday, November 15, 2013, 10:30 AM, Rm H107, Bldg 217

There is presently tremendous need for new electronic materials and devices to meet growing demands in computational complexity. These needs have arisen from the plateau of Moore’s Law scaling benefits in conjunction with proliferating consumer electronics. Transition metal oxides are emerging as a candidate class of materials both for enhancing the performance of current electronic platforms and for extending the possibilities of electronics into new computational paradigms. For example, oxide devices known as resistive switches or memristive systems have been shown to exhibit circuit behavior that closely resembles the strengthening/weakening of synaptic connections between neurons that occurs in animal brains. Such analogous behavior has strong implications for future electronics that leverage the advantages that neuronal computation has over prevailing computer architectures. These include contextual processing, massively parallel computation, and fault tolerance. In this talk, I review modes of computation and describe how transition metal oxides may be used in new brain-inspired, neuromorphic electronics. I discuss the current limitations facing resistive switching technologies and what fundamental research is necessary to advance the field. Lastly, I detail my current research on growth, materials physics, and device fabrication of the correlated oxide material SmNiO3, which has an insulator-to-metal phase transition above room temperature and may have application in next-generation transistor-like devices.

For further information please contact Jabez McClelland, 301-975-3721, jabez.mcclelland@nist.gov.


CNST Energy Research Group Seminar

3D NANOSTRUCTURES FOR MULTIFUNCTIONAL PLASMONICS 

Francesco De Angelis
Nanostructure's Department  

Thursday, November 14, 2013, 10:30AM, Rm. H107, Bldg. 217  

The development of new fabrication methods together with innovative device conception is one of the main reasons for the strong and fast growth of nanoplasmonics in the last decade. These two aspects are strongly related and they stimulate each other in conceiving creative and unprecedented functions. In the last years we introduced different 3D nanostructures and devices for managing the electromagnetic field at the nanoscale. In the first part of the talk we will revise our recent results concerning the combination of 3D plasmonic nanodevices, Raman Spectroscopy, and Superhydrophobic surfaces which enable the investigation of surfaces with nanoscale spatial resolution or liquid sample highly diluted (attomolar concentration). In the second part, we will present a novel fabrication approach able to realize 3D hollow plasmonic nanostructures that are tunable in size, shape, and layout. The presented architectures offer new and unconventional properties such as the realization of 3D plasmonic hollow nanocavities with high electric field confinement and enhancement, finely structured extinction profiles, broad band optical absorption, extraordinary optical transmission, strong radial scattering and well defined radiation pattern. The fabrication process intrinsically promotes a straightforward integration of Plasmonics with Microfluidics, and Electronics, whereas the 3D nature of the proposed architectures overcomes intrinsic difficulties related to the 2D methods, passing from the surface to a volume concept in a wide range of multidisciplinary applications. Some possible applications in Neuroscience and Biology will be shown.  

For further information please contact Andrea Centrone, 301-975-8225, andrea.centrone@nist.gov.


CNST Electron Physics Group Seminar

THE REALIZATION OF A NEW BAND GAP ENGINEERED PHOTOFERROELECTRIC PHOTOVOLTAIC DEVICE WITH HIGH PHOTOCURRENT

Steven Bennett
Northeastern University

Friday, November 1, 2013, 10:30 AM, Rm H107, Bldg 217

In solar photovoltaics the conversion of light energy into electrical energy involves two fundamental steps. The first is the effective generation of charge carriers and the second is the presence of an electric field gradient to carry that charge and create a photocurrent. Traditional semiconductor photovoltaics utilize the electric field from a p-n junction to separate the light-generated charge carriers from their counter-part holes. However, the low electric fields present in these devices result in charge carrier loss due to electron-hole recombination. By increasing this electric field we can decrease the probability of electron-hole recombination; essentially increasing the effective photocurrent. This is where the promise of the ferroelectric photovoltaic effect lies (photoferroelectrics). Currently, the state of the art in photoferroelectrics shows that a high open circuit photovoltage is achievable through the use of epitaxial bismuth ferrite (BFO) thin films. However, its bandgap is comparatively large (2.35eV) giving it a low optical absorption efficiency, and therefore a low photocurrent.
In this talk, I will present a proof-of-concept demonstration of a novel approach towards enhancing the photocurrent from photoferroelectric BFO. The idea is to incorporate a bandgap engineered, discontinuous nano-granular thin film ferrite, (CdxMn(1-x)Fe2O4 [CMFO]), with BFO in a homoepitaxial heterostructure. The result is a photovoltaic device that has a spontaneous electric polarization and high photocurrent without the need for a p-n junction. An order of magnitude increase, and record photocurrent, was measured by incorporation of this discontinuous CMFO layer. The giant photocurrent enhancement can be explained by the overall increase in photo-induced charge carriers originating from the added narrow bandgap CMFO. Furthermore, the magnetic characteristics of both layers could lend to the possibility of tuning the absorption of the device by use of an external applied magnetic field.

For further information please contact Bob McMichael, 301-975-5121, robert.mcmichael@nist.gov.


CNST Nanofabrication Research Group Seminar

STRUCTURAL DNA NANOTECHNOLOGY FOR NANOPHOTONIC APPLICATIONS

Anirban Samanta
Arizona State University

Monday, October 28, 2013, 10:30 AM, Rm H107, Bldg 217

One of the central goal of nanotechnology is to control motion and organize matter with nanometer precession. DNA is a remarkable material to serve that purpose. In the past decade it has been proved that DNA, in building programmable nano patterns, holds great promise. Construction of DNA origami, a discrete nano structure, by folding a long scaffold strand with numerous short staple strands is very exciting. It is an excellent platform to put together hetero elements, for example nano particles or proteins that can explore a functional side of DNA nanotechnology. DNA origami provides precise control over the orientation and position of integrated elements. Metallic nanoparticles for example gold and silver, have been successfully organized on DNA scaffold in the past. On the contrary, reports of quantum dot self-assembly on DNA nanostructures are scarce. Functionalization of quantum dots has several difficulties due to the reduced stability of thiol-based conjugation, along with salt incompatibility, and thus requires more unconventional approaches. Recently we have developed a simple yet reliable strategy to synthesize DNA functionalized CdTe and "magic"-CdTe-core/thick-CdS-shell, ZnSe/ZnS, ZnSe/CdS, ZnCdSSe/ZnS QDs with emission wavelengths ranging from UV-visible to near infrared and subsequently demonstrate their organization by DNA origami nanostructures which could have great potential for biophotonic application. Furthermore, increasing knowledge of the functionalization of nanoparticles with oligonucleotides encourages the use of DNA nanostructures as ‘motherboards’ for many potential applications. Combining plasmonic nanostructures, semiconductors and proteins or fluorescent dye in complex networks leads to the concept of molecular circuits, where photons and chemical and electrical potential can be interconverted.

For further information please contact J. Alex Liddle, 301-975-6050, james.liddle@nist.gov.


CNST Nanofabrication Research Group Seminar

DESIGN, CHARACTERIZATION AND FUNCTIONALIZATION OF DNA MATERIALS

Daniel Schiffels
University of California, Santa Barbara

Tuesday, October 22, 2013, 10:30 AM, Rm H107, Bldg 217

The inherent programmability of DNA affords the design of self-assembling nanoscale objects with high precision. Since the 1970s, synthetic DNA of specifically "programmed" sequences have been used in vitro for the self-assembly of increasingly complex DNA objects. Prominent examples include DNA nanotubes (DNA-NT) made from DNA "tiles", a nanoscale world map, a Trojan horse and a nanoflask made by the DNA "origami" technique.
Here we study the mechanical properties of DNA nanostructures using both fluorescence video microscopy and electron microscopy. As a simple model system, we measure the thermal bending and twisting fluctuations of a set of DNA-NT of defined circumference between five and ten DNA double helices. Based on the well-studied mechanics of B-form double stranded DNA, described by the worm-like-chain model, we derive an elasticity model for multi -helix tubes. The model shows good agreement with experiments and reveals that DNA cross-overs contribute significantly to DNA-NT deformations.
We exploit DNA-NT micron-scale stiffness to additionally investigate DNA-NT dye interactions. We directly visualize DNA-NT deformations as function of both the position and density of covalently attached Cy3 molecules to specific sites on the DNA-NT. We further characterize the orientation of Cy3’s dipole axis with respect to the DNA axis by fluorescence polarization microscopy and find that, on average, dipoles are aligned on DNA-NTs with an angle of approx. 60° to the DNA axis.

For further information please contact J. Alex Liddle, 301-975-6050, james.liddle@nist.gov.


CNST Electron Physics Group Seminar

TUNNEL-DIODE RESONATOR AND NUCLEAR MAGNETIC RESONANCE STUDIES OF LOW-DIMENSIONAL MAGNETIC SYSTEMS

Steven Yeninas
Iowa State University, U.S. Department of Energy's Ames Laboratory

Thursday, October 21, 2013, 10:30 AM in Rm H107, Bldg 217

Oscillators have long served as versatile transducers for measuring an array of physical properties, including thermal expansion, surface impedance, and magnetic and electric susceptibilities. Two unique methods operating in the radio frequency, tunnel-diode resonator (TDR) and nuclear magnetic resonance (NMR), are extremely powerful tools for investigating electron spin correlations in novel low-dimensional magnetic and superconducting systems. TDR measurements investigate the bulk dynamic magnetic susceptibility by detecting frequency shifts of a self-resonating LC circuit driven by a tunnel-diode, capable of better than ppb precision. NMR examines local static and dynamic magnetic properties of materials by studying the hyperfine structure of specific nuclei arising from internally generated fields. This talk will introduce the principles of TDR and NMR, and demonstrate their use as spectroscopic probes for studying magnetic properties for two different classes of magnetic materials with implications in energy generation, energy storage, and spintronics applications.

For further information please contact Bob McMichael, 301-975-5121, Robert.Mcmichael@nist.gov.


CNST Nanofabrication Research Group Seminar

A SYMPHONY OF SYMMETRY: DESIGNED CRYSTALLINE DNA LATTICES

Nam Q. Nguyen
New York University

Monday September 30, 2013, 10:30 AM, Rm H107, Bldg 217

The physiochemical properties of deoxyribonucleic acid (DNA) have been exploited to assemble highly structured and well-ordered materials using hybridization and stably branched junctions. The self-assembly of designed periodic three-dimensional crystalline lattices has been the apex in the exploitation of DNA in structural DNA nanotechnology. The tensegrity triangle motif forms a rhombohedral crystalline lattice via sticky ended cohesion with four-arm branched junctions at the three vertices of the triangle. We have verified that the formation of the motif and of the crystals themselves is a result of covalent linkages at the vertices as well as interactions at the level of secondary structure. Here, methods to further increase the resolution limit of the diffracting system are discussed with other covalent modifications to the crystalline lattice.

For further information please contact J. Alex Liddle, 301-975-6050, james.liddle@nist.gov.


CNST Nanofabrication Operations Group Seminar

FAST 3D IMAGING USING MULTI‐FOCUS MICROSCOPY

Sara Abrahamsson
Howard Hughes Medical Institute

Wednesday, September 18, 2013, 2:00PM, Rm H107, Bldg 217

We have designed a diffractive optical element which, when placed in the Fourier plane of an optical imaging system, modifies the system to form an instant 3D image in the form of a simultaneously formed focal stack of 2D images. The element (Multi‐Focus Grating, MFG) is a binary phase‐only grating which splits up the original image into nine images, and focus shifts these images. We have also designed a chromatic correction module which, over a given wavelength spectrum, corrects the chromatic dispersion inherent in any diffracting element. These components have been appended to a high resolution wide‐field microscope to enable fast 3D imaging limited only by the signal strength and/or the readout speed of the acquisition camera. This Multi-Focus microscope was used for real time wide field imaging of dynamic three dimensional processes in live cells, such as tracking of single molecules and subcellular structures. We show its advantages for 3D super resolution imaging using PALM and STORM techniques. In order to further improve our Multi‐Focus Microscope (MFM) we are working with NIST to produce a new MFG with improved light efficiency.

For further information please contact: Vincent Luciani, 301-975-2886, Vincent.Luciani@nist.gov or Liya Yu, 301-975-4590, liya.yu@nist.gov.


CNST Nanofabrication Research Group Seminar

NANOARCHITECTURES FOR BATTERIES BEYOND LITHIUM

Sanja Tepavcevic
University of Chicago

Thursday August 1, 2013, 1:30 PM, Rm H107, Bldg 217

Rechargeable battery systems with different transporting ions will bring substantial relief and expansion of the existing energy storage market, which is primarily based on Li-ion technology. Sodium-based batteries are attractive alternative due to the abundance of sodium and enhanced operation stability while magnesium batteries with divalent nature of Mg-ion are expected to achieve substantially greater energy density. Due to shorter electron and ion diffusion path length, nanostructured electrode materials are one of the most attractive strategies to dramatically enhance battery performance. To achieve fast mass transport and high power density, unique hierarchical nanoarchitectures such as nanotubes and nanoribbons have been investigated and will be presented. We found that size matching of the transporting ions and host atoms (e.g. Li+ in TiO2) enable the use of the high density packed crystalline nanoscale materials as electrodes reaching theoretical capacity, highest rate capability, improved cycling life, and safety. On the other hand, our approach to achieving larger size ion/multiple charge intercalation is to use nanoscale materials that have adjustable d spacing and two-dimensional layered structure that can accommodate large volume/charge changes. Most of the known conventional battery materials start out as highly crystalline and pulverize to an amorphous state upon cycling: their predetermined crystalline structures often undergo phase transitions upon intercalation of transporting ions. These phase transitions cause swelling of the electrode materials resulting in local atomic rearrangements, limited diffusion of ions, and ultimately capacity degradation. We will present how contraintuitively starting from amorphous, low-crystalline materials we were able to create interconnected nanoporous electrodes that undergo self-organization upon repeated cycling. Amorphous TiO2 nanotubes convert into cubic titania, while open frame bilayered V2O5 structure adopts long range order upon intercalation of transporting ions. Both of these structures naturally choose and optimize their crystalline structure in order to achieve fast cycling (high power), high permeability (energy density) and mechanical resistance to cycling (stability).

For further information please contact James Alexander Liddle, 301-975-6050, james.liddle@nist.gov.


CNST Energy Research Group Seminar

NARROW GRAPHENE NANORIBBONS: TOP-DOWN VS. BOTTOM-UP APPROACHES

Alexander Sinitskii
University of Nebraska-Lincoln

Tuesday July 23, 2013, 2:00 PM, Rm H107, Bldg 217

Graphene, a two-dimensional carbon allotrope, is often considered as a complement or even replacement for silicon in many electronics applications. However, the absence of an electronic bandgap in graphene prevents its use in logic devices. According to the theoretical studies, a bandgap compared to that in silicon (1.1 eV) could be found in narrow graphene nanoribbons (GNRs) that have atomically precise armchair edges and widths less than 2 nm. Different top-down approaches, such as a combination of electron-beam lithography and dry etching, sonochemical method, nanowire lithography, and unzipping of carbon nanotubes, typically yield ribbons with widths > 10 nm and have a limited control over the edge structure in GNRs. Several recent studies have also focused on the development of bottom-up chemical approaches for narrow GNRs. Most of these methods are based on a polymerization of pre-synthesized molecular precursors followed by a cyclodehydrogenation. The reported bottom-up techniques could yield narrow atomically-engineered GNRs that are currently unachievable by any top-down approach, stimulating further research and development of new synthetic methods for GNRs. However, several problems still need to be solved, such as a limited length of synthetic GNRs, their poor solubility, difficulties with their precise placement on dielectric substrates for device fabrication, etc. In this seminar I will review recent efforts to synthesize GNRs with an emphasis on a comparative analysis of top-down and bottom-up approaches. I will also discuss a new bottom-up approach for gram quantities of narrow GNRs that was recently developed in my lab. These GNRs are less than 2 nm wide and have atomically precise armchair edges; they could be conveniently deposited from solution on any substrate, such as Si/SiO2, mica and Au(111), for further studies. The GNRs were characterized by different techniques, including NMR, UV-vis-NIR and Raman spectroscopy, XPS, EDX, PES/IPS, SEM, AFM and STM. These data suggest that GNRs obtained by this novel synthetic approach could be promising for field-effect transistors with high on-off ratios, as well as other applications, including coatings, composites and photovoltaic devices.

For further information please contact Andrei Kolmakov, 301-975-4724, andrei.kolmakov@nist.gov.


CNST Energy Research Group Seminar

SPECTROSCOPY OF CORRELATED NANOWIRES

Nick Bronn
University of Illinois, Urbana-Champaign

Thursday July 11, 2013, 11:00 AM, Rm H107, Bldg 217

The electronic properties of low-dimensional systems have attracted much attention for both fundamental science and potential use in technological applications. In this talk I will discuss studies of carbon nanotubes and mixed-valence manganite nanowires using two electron transport spectroscopic techniques. First, I will demonstrate how nonequilibrium tunneling spectroscopy with multiple superconducting probes allows for the measurement of the spatial dependence of electron interactions in carbon nanotubes, and can be used to distinguish whether those interactions are elastic or inelastic. Next, the observation of random telegraph noise in LSMO nanowires at low temperature will be shown to be consistent with fluctuations between domains arising from different orderings of the charge, spin, and lattice degrees of freedom.

For further information please contact Andrei Kolmakov, 301-975-4724, andrei.kolmakov@nist.gov.


CNST Energy Research Group Seminar

OPPORTUNITIES AND CHALLENGES FOR REVERSIBLY STORING ELECTRICAL ENERGY IN CHEMICAL BONDS: AGING IN LI-ION BATTERIES AND CAPACITY LIMITATIONS IN LI/O2 BATTERIES

Paul Albertus
Robert Bosch Research and Technology Center

Monday May 13, 2013, 10:30 AM, Rm H107, Bldg 217

Electrochemical energy storage has a crucial role to play in 21st century energy systems. The past several years have seen the introduction of Li-ion technology to transportation markets, and there is also surging interest in stationary energy storage as the fraction of intermittent renewables on the grid increases. This presentation will contain results from two projects investigating battery physics and chemistry: the first project was an exploration of the electrochemical and chemical changes that took place in a set of Li-ion cells during aging, and second project was a combined experimental and modeling study that identified the limitations to the capacity achieved by Li/O2 cells. By focusing on both a current state-of-the-art battery (Li-ion) as well as a research battery (Li/O2), the presentation aims to demonstrate some of the opportunities and challenges for electrochemical energy storage.

For further information please contact Paul Haney, 301-975-4025, paul.haney@nist.gov.


CNST Energy Research Group Seminar

THE IMPACT OF METALLIC IMPURITIES ON MINORITY CARRIER LIFETIME IN HIGH PURITY N-TYPE SILICON SOLAR CELL

Yohan Yoon
North Carolina State University

Friday, May 10, 2013 10:30 AM, Rm H107, Bldg 217

Typically n-type silicon has a higher minority carrier lifetime than p-type silicon with similar levels of contamination. That is because n-type silicon is more tolerant to metallic impurities, especially Fe. Also, it has no serious issues in relation to lifetime degradation, such as FeB pairs and light-induced degradation (LID). However, surface passivation of the p+ region in p+n solar cells is much more problematic than the n+p case where silicon nitride provides very effective passivation of the cell. Al2O3 passivation layer has been suggested for B-doped emitters. With this surface passivation layer, a 23.2% conversion efficiency has been achieved. After this discovery, n type silicon is now being seriously considered for photovoltaics. The major contribution of this study is to provide new electrical data relating to metallic impurities in n-type silicon, e.g. activation energy, capture cross sections. The injection-dependent lifetimes of intentionally metal contaminated n-type CZ silicon wafers were investigated using resonant-coupled photoconductance decay (RCPCD) and the quasi-steady-state photoconductance technique (QSSPC). Finally, a direct correlation between minority carrier lifetime/cell efficiency and the concentration of specific electrically active metallic impurities was established using deep level transient spectroscopy (DLTS).

For further information please contact Nikolai Zhitenev, 301-975-6039, nikolai.zhitenev@nist.gov.


CNST Nanofabrication Research Group Seminar

THREADING THE NEEDLE: SOLID-STATE NANOPORES FOR BIOMOLECULE DETECTION AND CHARACTERIZATION

Dr. Adam Hall
University of North Carolina at Greensboro

Monday, April 29, 2013, 10:30 AM, Rm. H107, Bldg H107

Solid-state nanopores represent an exciting young technology for molecular detection. Here, a nanometer-scale aperture is fabricated in a thin solid-state membrane and used as a portal through which individual molecules can be threaded one at a time. By monitoring the electronic signature of each translocation event, characteristics of the individual molecules that pass can be ascertained. In this talk, I will give an introduction to the system and then discuss several recent results, including detection of local protein structure along DNA molecules and direct force measurements performed with a combination optical tweezer-nanopore instrument. I will also describe a new fabrication technique that we have developed that uses a focused helium ion beam to make these devices quickly and at high resolution.

For further information please contact Alex Liddle, 301-975-6050, james.liddle@nist.gov.


CNST Nanofabrication Research Group Seminar

WEAR AND FAILURE OF GRAPHENE MONOLAYERS AT THE NANO-SCALE

Emil Sandoz-Rosado
Columbia University

Tuesday, April 23, 2013, 10:30 AM, Rm. H107, Bldg H107

Graphene is the strongest material measured and also has been shown to be gas-impermeable and chemically and thermally stable, making it an excellent candidate as a nanoscale tribological coating for N/MEMS, electrical contacts, and data storage. However, the wear and failure mechanisms of graphene under sliding load are not fully understood. Graphene’s resistance to wear will ultimately determine its suitability as a protective coating, thus it is imperative to study its tribological behavior. This study examines the velocity-dependent friction and wear behavior of CVD-grown monolayer graphene that has been transferred to an SiO2 substrate. Wear of the graphene monolayer was quantified by ex situ Raman spectroscopy mapping. It was found that friction and wear of monolayer graphene increased dramatically as sliding velocity of a 1.2µm radius diamond tip decreased. Frictional contribution by the bunching of graphene on the sliding front of a tip, known as the "puckering effect", was present at high speeds and over sliding distances as large as 100 µm, but diminished at lower speeds as the graphene was catastrophically damaged. Interestingly, the puckering effect in graphene caused higher friction at faster velocities than bare SiO2, indicating that the tribological benefits of graphene will have to be exploited with good membrane-substrate adhesion, slower sliding speeds, or a higher number of graphene layers to reduce the friction contribution of the puckering effect.

For further information please contact Rachel Cannara, 301-975-4258, rachel.cannara@nist.gov.


CNST Nanofabrication Research Group Seminar

HIGH RESOLUTION OPTICAL DNA MAPPING

Murat Baday
University of Illinois at Urbana-Champaign

Wednesday, April 10, 2013, 10:30 AM, Rm. H107, Bldg H107

Many types of diseases including cancer and autism are associated with copy-number variations in the genome. Most of these variations could not be identified with existing sequencing and optical DNA mapping methods. We have developed Multi-color Super-resolution technique, with potential for high throughput and low cost, which can allow us to recognize more of these variations. Our technique has made 10–fold improvement in the resolution of optical DNA mapping. Using a 180 kb BAC clone as a model system, we resolved dense patterns from 108 fluorescent labels of two different colors representing two different sequence-motifs. Overall, a detailed DNA map with 100 bp resolution was achieved, which has the potential to reveal detailed information about genetic variance and to facilitate medical diagnosis of genetic disease.

For further information please contact Samuel Stavis, 301-975-2844, samuel.stavis@nist.gov.


CNST Electron Physics Group Seminar

NANOTECHNOLOGY: DOES IT HAVE TO BE COMPLICATED?

Lyubov Belova
Royal Institute of Technology, Stockholm, Sweden

Monday, April 8, 2013, 10:30 AM, Rm H107, Bldg 217

With the development of nanoscience and methods of design and fabrication of nanomaterials the availability of inexpensive easy to use tools capable of large area patterning of nanoscale materials and structures is becoming increasingly important. InkJet technology has been developing rapidly over the last decade for high-resolution photo printing and has now expanded into patterning of functional materials, closing the gap from nano- to micro- to macro- scales. Piezoelectrically driven InkJets operate at room temperature in ambient conditions and thus are compatible with a wide variety of materials from ceramic and magnetic nanoparticles to carbon nanotubes, proteins and even live cells. A variety of substrates from paper to glass and plastics can be used. Some of our recent developments are related to direct patterning of oxides (e.g. ZnO, MgO) for electronics, optics and magneto-optic components. One of the targeted applications is UV sensing. In the second half of the talk I will describe the other end of the line of the nanotechnology tools: FIB / SEM based combined systems for ultra-high resolution microscopy, 3D tomography and nanoprototyping and how one can apply them both for direct fabrication of complex three-dimensional nano- and micro-structures and getting insight into the big world of small things, merging physics, chemistry and life sciences.

For further information please contact Robert McMichael, 301-975-5121, robert.mcmichael@nist.gov.


CNST Electron Physics Group Seminar

PROBING SUPEREXCHANGE COUPLING IN ATOMICALLY FABRICATED D-METAL COMPLEXES

Benjamin Bryant
Delft University of Technology

Friday, March 22, 2013, 3:30 PM, Rm H107, Bldg 217

Magnetic coupling between transition metal atoms that are linked through ligand p-orbitals relies on the virtual exchange of electrons between neighboring sites. According to the well-known Goodenough-Kanamori rules, the resulting superexchange interaction can be either antiferromagnetic or ferromagnetic, due to a combination of inter-atomic electron hopping (kinetic exchange) and intra-atomic Coulomb exchange. By using low temperature scanning tunneling microscopy, Fe atoms may be positioned in a copper nitride surface lattice with atomic precision, and their spin states characterized by inelastic tunnelling spectroscopy. In this way, we can construct, atom-by-atom, spin structures with different geometries, and probe their superexchange properties. By building structures with either zero, one or two 90 degree corners in the exchange path, we were able to test the Goodenough-Kanamori rules at the atomic scale. Further, we identify strongly anisotropic spin coupling between the Fe atoms. Our experiments reveal novel insights into complex superexchange coupling, that are of importance in the fields of molecular magnetism and strongly correlated transition metal oxides.

For further information please contact Joseph Stroscio, 301-975-3716, joseph.stroscio@nist.gov.


CNST Nanofabrication Research Group Seminar

SUPERCONDUCTING MICRORESONATORS FOR PHOTON DETECTION

Omid Noroozian
National Institute of Standards and Technology, Boulder, CO

Friday, March 1, 2013, 10:30 AM, Rm. H107, Bldg H107

Superconducting microresonators are relatively simple devices produced by depositing a single layer of superconducting thin film on a dielectric substrate and patterning with standard lithographic techniques. These devices have seen a growing number of applications in the last decade triggered by the demonstration of high-quality factor transmission-line resonators for photon detection. Some of these applications include microwave kinetic inductance detectors (MKID) for astrophysics from gamma rays to far-infrared waves, dark matter search experiments, multiplexed readout of bolometers and transition edge sensors (TES), microwave parametric amplifiers, quantum circuits for qubit readout, and coupling to nanomechanical systems.
In the first part of this talk I will present my work on MKIDs for use in astronomical instruments such as the Multiwavelength Submillemeter Kinetic Inductance Camera (MUSIC) and the Cornel-Caltech Atacama Telescope (CCAT). Various aspects of the detectors will be discussed including resonator design strategies for reduced frequency jitter noise caused by dielectrics, high density packing of lumped-element resonators for next generation large array focal plane telescopes (>10K pixels), resonator crosstalk and design methods for its reduction in large arrays, and ultra-high quality factor resonators made from titanium nitride (TiN) for direct absorption and detection of far-infrared photons.
In the second part I will present my recent work at NIST Boulder on using superconducting resonators coupled to SQUIDs for readout of an array of gamma-ray TESs in the frequency domain. The latest results indicate that this readout system can perform spectroscopy with energy resolutions of ~ 55 eV around 100 keV, very similar to state-of-the-art calorimeters. This technique takes simultaneous advantage of the excellent sensitivity of TESs and the multiplexing power of microresonators, promising easy and scalable readout of large arrays of detectors.

For further information please contact Kartik Srinivasan, 301-975-5938, kartik.srinivasan@nist.gov.


CNST Electron Physics Group Seminar

MAGNETIC DOMAIN-WALL MOTION AND COMPETING ANISOTROPIES IN EPITAXIAL EXCHANGE-BIASED THIN FILMS AND PATTERNED STRUCTURES

Wei Zhang
University of Washington

Tuesday, February 19, 2013, 10:30 AM, Rm. H107, Bldg. 217

Magnetic reversals in modern magnetic thin-film devices critically depend on the magnetic anisotropies, which may have different origins, i.e., magnetocrystalline, shape or interface. For example, the unidirectional exchange anisotropy (exchange bias) is of great technological importance due to its applications in magnetic storage devices. Competing anisotropies in epitaxial heterostructures usually induce complex magnetization reversal behaviors. We have achieved independent control of different magnetic anisotropies by controlled sample fabrications, and studied their competing effects on the domain-wall type reversals. I will talk about the quantitative model we developed on the domain-wall motion in thin-film heterostructures and also show the large-area fabrication of epitaxial nanostructure arrays using nanoimprint lithography. The results here may provide insight for future domain-wall devices such as the domain-wall racetrack memory.

For further information please contact Robert McMichael, 301-975-5212, robert.mcmichael@nist.gov.


CNST Nanofabrication Research Group Seminar

NOVEL APPLICATIONS OF NANOTECHNOLOGY FOR NEXT GENERATION BIOMEDICAL SENSING

Maurice Cheung
McGill University

Tuesday, February 12, 2013, 10:30 AM, Rm H107, Bldg 217

Nanotechnology has many biomedical applications ranging from over-the-counter hand held pregnancy tests to state-of-the-art super-resolution microscopes. Three specific applications of nanotechnology in sensing will be presented. (1) Optical filtering by a porous silicon thin film fabricated by a novel dry-etch technique for in an integrated sensing system. (2) The enhancement of signal and sensitivity of a ruthenium doped oxygen sensitive sol-gel sensor using gold nanoparticles. (3) Optical genomic mapping of lambda phage DNA by a chemically induced nanofluidic slitlike channel. Their implications in biomedical sensing, specifically in low-cost point-of-care diagnostics, continuous medical monitoring and cancer research will also be discussed.

For further information please contact Samuel Stavis, 301-975-2844, samuel.stavis@nist.gov.


CNST Nanofabrication Research Group Seminar

ADVANCED NANOMATERIALS-BASED MANUFACTURING PLATFORM FOR PRINTED SENSORS, ELECTRONICS, ENERGY AND MATERIAL APPLICATIONS

Ahmed Busnaina
Northeastern University

Friday, January 18, 2013, 10:30 AM, Rm. C103-C106, Bldg 215

The NSF Center for High-rate Nanomanufacturing (CHN) has developed a novel reconfigurable manufacturing technology platform that operates at ambient temperature and pressure, is water-based, material-independent and low energy, and requires small capital investment. It has been used to make structures and devices across length scales. The center has developed templates with nanoscale features to assemble and print structures down to 10 nm in a short time and over a large area. Recently, a rapid and scalable manufacturing process for 3D nanoscale features was developed to fabricate interconnects and plasmonic devices using nanoparticles. Nonvolatile memory switches using CNTs or molecules assembled at wafer level is one application. Another application is a new biosensor chip (0.02 mm2) capable of simultaneously detecting multiple biomarkers. The biosensor can be in vitro or in vivo with a detection limit that is 200 times lower than current technology. The center also developed several CNT and MoS2 based electronic devices. The center develops the fundamental science and engineering necessary to manufacture a wide array of applications ranging from electronics, energy, sensors and materials to biotechnology. A directed assembly-based nanomanufacturing factory could be built for as low as $50 million, a fraction of today’s cost, making nanotechnology accessible to millions of new innovators and entrepreneurs and unleashing a wave of creativity in the same way as the advent of the PC did for computing.

For further information please contact J. Alex Liddle, 301-975-6050, james.liddle@nist.gov.


CNST Electron Physics Group Seminar

QUANTUM MEASUREMENT IN LIVING CELLS

Thursday, January 17, 2013, 1:30PM, Rm. H107 Bldg. 217

Robert Scholten
The University of Melbourne

"Quantum technology" normally conjures thoughts of computation and communication, but also has exciting potential applications in new ways of measuring and imaging at the nanometer scale, particularly for biological systems. The NV defect centre in diamond is an especially promising single spin system for quantum measurements in biology. We have demonstrated optically detected magnetic resonance (ODMR), Rabi cycling and spin-echo of individual fluorescent nanodiamond NV centres inside living human HeLa cells. Variations in the decoherence rates linked to changes in the local environment inside the cells offer a new non-destructive imaging modality for intracellular biology. But even classical imaging is a vexing problem at the atomic scale, where there is demand for new advances, for example to determine the structure of bio-molecules. We have developed a new source of high-coherence electron bunches based on photoionisation of laser-cooled atoms. With laser control of the cold atom cloud, we can shape the electron bunches, and because the electrons are so cold, they retain their shape during propagation. While labeled by colleagues as "the world’s most expensive TV", it offers the control needed to generate ultra-high-brightness bunches for coherent diffractive imaging at nanometer and femtosecond resolution.

For further information please contact Jabez McClelland, 301-975-3721, jabez.mcclelland@nist.gov.


CNST Energy Research Group Seminar

IMPROVED ELECTRODE ARCHITECTURES FOR HIGH ENERGY DENSITY AND LONG LIFE LITHIUM-ION BATTERIES

Stephen J. Harris
LBNL

Monday January 14, 2013, 10:30 AM, Rm H107, Bldg H107

A long-term goal of DOE is the development of batteries that could power a commercially successful all-electric vehicle, probably requiring a range near 200 miles (at least double that of a Nissan Leaf). In order to achieve higher energy densities, current research focuses on new electrode chemistries with higher capacities and higher voltages (volumetric energy density = charge capacity ? voltage ? mass density) that could provide a >50% increase in energy density—still insufficient for a 200 mile range. (Volumetric energy density is more critical to auto companies than gravimetric energy density.) Improvement in the mass density term has been stymied because low electrode porosities always seem to lead to high tortuosities and low power densities. We note, however, that the inverse relationship between porosity and tortuosity applies only to electrodes with random microstructures, which inevitably have large local inhomogeneities. At the same time, failure in materials almost always begins at local inhomogeneities. Yet, current analyses of lithium-ion batteries are based on a porous electrode model that assumes a homogeneous mixture of flawless, isotropic particles. Our work suggests that variability in local microstructure and in internal particle morphology plays a critical role in reducing both performance and durability of Li-ion batteries. Following this reasoning, we are developing a new approach for electrode architectures. We suggest that with designed (i.e., non-random) microstructures and particles, we can create electrodes with a high density of active material, to maximize capacity; a low tortuosity, to maximize power; and improved uniformity (no weak spots), to maximize battery life.

For further information please contact Nikolai Zhitenev, 301-975-6039, nikolai.zhitenev@nist.gov.


CNST Energy Research Group Seminar

DIP PEN NANOLITHOGRAPHY: A BENCH-TOP NANOFABRICATION METHOD

Saju Nettikadan
Director of Applications Development: Nanoink

Thursday January 10, 2013, 10:30 AM, Rm H107, Bldg H107

Dip Pen Nanolithography is a direct write, tip based lithography technique. Operating under ambient conditions, DPN allows the deposition of a wide range of organic, inorganic, and biological molecules as well as polymers, gels and nanoparticle solutions. The material is coated onto the sharp tip and then transferred to the substrate when the tip contacts a surface. The rate of material transfer is influenced by the environmental conditions (temperature and humidity), surface chemistry, contact time, and the material being transferred. Applications of this technology range through physics, chemistry, materials and life sciences. In this presentation, we will discuss application of DPN for: 1. Top-down fabrication of diffraction gratings, spit ring resonators and graphene nanoribbons 2. Bottom-up fabrication of metallic nanoclusters, templates for CNT, single virus particles and proteins 3. Fabrication of biomolecular arrays for applications in cell biology, biosensor development and miniaturized protein biomarker assays.

For further information please contact Andrea Centrone, 301-975-8225, andrea.centrone@nist.gov.


CNST Electron Physics Group Seminar

TRANSPORT IN DIRAC SYSTEMS

Qiuzi Li, University of Maryland Research Assistant

Thursday January 3, 2013, 10:30 AM, Rm H107, Bldg H107

Graphene and 2D surface states of three-dimensional topological insulators (3DTIs) are of great fundamental interest and have potential applications in disruptive novel technologies. In order to study the novel phenomena in these systems, it is essential to understand their electron transport properties and in particular the main factors limiting their transport mobility. In this talk, I will present our theoretical works on the transport properties of both graphene and the 2D surfaces of 3DTIs, and discuss the similarity and difference between them. Relevant experiments will also be discussed.

For further information please contact Mark Stiles, 301-975-3745, mark.stiles@nist.gov.

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