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Full-Text Articles in Nanoscience and Nanotechnology

Toward Tailored Functionality Of Titania Nanotube Arrays: Interpretation Of The Magnetic-Structural Correlations, Pegah M. Hosseinpour, Eugen Panaitescu, Don Heiman, Latika Menon, Laura H. Lewis Dec 2013

Toward Tailored Functionality Of Titania Nanotube Arrays: Interpretation Of The Magnetic-Structural Correlations, Pegah M. Hosseinpour, Eugen Panaitescu, Don Heiman, Latika Menon, Laura H. Lewis

Latika Menon

Ordered arrays of titania nanotubes (NTs) are considered as good candidates for photocatalytic applications including water splitting. Considering that the functionality of these nanostructures is influenced by their morphology, electronic and the crystallographic structure, fundamental understanding of these properties and their possible correlations can clarify the approaches toward enhanced photocatalytic efficiency. In this work, ordered arrays of titania NTs are synthesized electrochemically and are subjected to isochronal annealing treatments in various atmospheres (oxygen-rich, oxygen-deficient and reducing) to modify their morphology, crystal and electronic structure. Upon characterization of these NTs, direct correlations are found between the annealing atmosphere and the corresponding ...


Vapor–Liquid–Solid Growth Of Serrated Gan Nanowires: Shape Selection Driven By Kinetic Frustration, Zheng Ma, Dillon Mcdowell, Eugen Panaitescu, Albert V. Davydov, Moneesh Upmanyu, Latika Menon Dec 2013

Vapor–Liquid–Solid Growth Of Serrated Gan Nanowires: Shape Selection Driven By Kinetic Frustration, Zheng Ma, Dillon Mcdowell, Eugen Panaitescu, Albert V. Davydov, Moneesh Upmanyu, Latika Menon

Latika Menon

Compound semiconducting nanowires are promising building blocks for several nanoelectronic devices yet the inability to reliably control their growth morphology is a major challenge. Here, we report the Au-catalyzed vapor–liquid–solid (VLS) growth of GaN nanowires with controlled growth direction, surface polarity and surface roughness. We develop a theoretical model that relates the growth form to the kinetic frustration induced by variations in the V(N)/III(Ga) ratio across the growing nanowire front. The model predictions are validated by the trends in the as-grown morphologies induced by systematic variations in the catalyst particle size and processing conditions. The ...


A Study Of Anodization Process During Pore Formation In Nanoporous Alumina Templates, Z. Wu, C. Richter, L. Menon Oct 2012

A Study Of Anodization Process During Pore Formation In Nanoporous Alumina Templates, Z. Wu, C. Richter, L. Menon

Latika Menon

We have carried out a systematic investigation of the anodization procedure in order to determine the exact chemical mechanism of the dissolution process responsible for pore formation in nanoporous alumina templates. We measured the anodization current as a function of time and compared it with the thickness of porous aluminum oxide layer obtained from cross-section scanning electron microscopy images. From this, we calculated the number of moles of electrons generated per mole of porous alumina grown. This analysis is consistent with a reaction mechanism in which aluminum is converted to aluminum oxide in addition with the direct transfer of aluminum ...


Size Dependence Of Energetic Properties In Nanowire-Based Energetic Materials, L. Menon, D. Aurongzeb, S. Patibandla, K. Bhargava Ram, C. Richter, A. Sacco Oct 2012

Size Dependence Of Energetic Properties In Nanowire-Based Energetic Materials, L. Menon, D. Aurongzeb, S. Patibandla, K. Bhargava Ram, C. Richter, A. Sacco

Latika Menon

We prepared nanowire-array-based thin film energetic nanocomposites based on Al–Fe₂O₃. The ignition properties as a function of wire dimensions and interwire spacing have been investigated. We show significant variations in ignition behavior, which we relate to the kinetic and heat transfer dynamics of the various configurations studied. Our results indicate the possibility for nanoscale control of reaction parameters such as flame temperature and burn rate in such composites for optimized configurations (optimum wire size, interwire spacing, film thickness, etc.).


Possible Room-Temperature Ferromagnetism In Hydrogenated Carbon Nanotubes, Adam Friedman, Hyunkyung Chun, Yung Joon Jung, Don Heiman, Evan Glaser, Latika Menon Oct 2012

Possible Room-Temperature Ferromagnetism In Hydrogenated Carbon Nanotubes, Adam Friedman, Hyunkyung Chun, Yung Joon Jung, Don Heiman, Evan Glaser, Latika Menon

Latika Menon

We find that ferromagnetism can be induced in carbon nanotubes (CNTs) by introducing hydrogen. Multiwalled CNTs grown inside porous alumina templates contain a large density of defects resulting in significant hydrogen uptake when annealed at high temperatures. This hydrogen incorporation produces H-complex and adatom magnetism which generates a sizable ferromagnetic moment and a Curie temperature near TC=1000  K. We studied the conditions for the incorporation of hydrogen, the temperature-dependent magnetic behavior, and the dependence of the ferromagnetism on the size of the nanotubes.


Optimal Parameters For Synthesis Of Magnetic Nanowires In Porous Alumina Templates: Electrodeposition Study, Adam L. Friedman, Latika Menon Oct 2012

Optimal Parameters For Synthesis Of Magnetic Nanowires In Porous Alumina Templates: Electrodeposition Study, Adam L. Friedman, Latika Menon

Latika Menon

We have carried out a systematic study of the electrodeposition process to understand the effect of varying three important quantities on the synthesis of nanowires inside porous alumina templates. We have electrodeposited iron nanowires inside porous alumina to determine the optimal settings of these variables to induce effective and efficient nanowire growth. First, we vary the pH of the electrolyte solution to show that pH has little effect on the deposition rate. Second, we vary the magnitude of the applied ac voltage to show that the deposition rate increases with increasing voltage. Finally, we vary the frequency of the applied ...


Negative Index Metamaterials Based On Metal-Dielectric Nanocomposites For Imaging Applications, L. Menon, W. T. Lu, A. L. Friedman, S. P. Bennett, D. Heiman, S. Sridhar Oct 2012

Negative Index Metamaterials Based On Metal-Dielectric Nanocomposites For Imaging Applications, L. Menon, W. T. Lu, A. L. Friedman, S. P. Bennett, D. Heiman, S. Sridhar

Latika Menon

Negative index metamaterials are demonstrated based on metal-dielectric nanocomposites prepared using a versatile bottom-up nanofabrication approach. The method involves the incorporation of vertically aligned metal nanowires such as Au and Ag inside dielectric aluminum oxide nanotemplates. Optical absorbance measurements show resonance peaks corresponding to the transverse and longitudinal surface plasmon modes. A quantitative model based on effective medium theory is in excellent agreement with experimental data, and points to specific composite configurations and wavelength regimes where such structures can have applications as negative refraction media for imaging.


Magnetic Properties Of Gamnas Nanodot Arrays Fabricated Using Porous Alumina Templates, S. P. Bennett, L. Menon, D. Heiman Oct 2012

Magnetic Properties Of Gamnas Nanodot Arrays Fabricated Using Porous Alumina Templates, S. P. Bennett, L. Menon, D. Heiman

Latika Menon

Ordered arrays of GaMnAs magnetic semiconductor nanodots have been fabricated using anodic porous alumina templates as etch masks. The magnetic behavior is studied for prepared arrays with 40 nm dot diameter, 15 nm dot thickness, and 80 nm periodicity. The disklike nanodots exhibit an easy axis for fields applied in the radial direction and a hard axis in the smaller direction. In the radial direction superparamagnetism is observed with a blocking temperature of 30 K. The fabrication technique is convenient for preparing nanodot arrays of compound semiconductors that cannot be formed by self-assembly techniques.


Super-Resolution Imaging Using A Three-Dimensional Metamaterials Nanolens, B. D. F. Casse, W. T. Lu, Y. J. Huang, E. Gultepe, L. Menon, S. Sridhar Oct 2012

Super-Resolution Imaging Using A Three-Dimensional Metamaterials Nanolens, B. D. F. Casse, W. T. Lu, Y. J. Huang, E. Gultepe, L. Menon, S. Sridhar

Latika Menon

Super-resolution imaging beyond Abbe's diffraction limit can be achieved by utilizing an optical medium or "metamaterial" that can either amplify or transport the decaying near-field evanescent waves that carry subwavelength features of objects. Earlier approaches at optical frequencies mostly utilized the amplification of evanescent waves in thin metallic films or metal-dielectric multilayers, but were restricted to very small thicknesses (⪡λ, wavelength) and accordingly short object-image distances, due to losses in the material. Here, we present an experimental demonstration of super-resolution imaging by a low-loss three-dimensional metamaterial nanolens consisting of aligned gold nanowires embedded in a porous alumina matrix. This ...


A Study Of Titania Nanotube Synthesis In Chloride-Ion-Containing Media, E. Panaitescu, C. Richter, L. Menon Oct 2012

A Study Of Titania Nanotube Synthesis In Chloride-Ion-Containing Media, E. Panaitescu, C. Richter, L. Menon

Latika Menon

We have completed a detailed experimental investigation into the recently discovered synthesis of titania nanotubes in chloride-ion-containing media. We show that the role of the chloride ions is catalytic and it has a strong effect in increasing the reactivity of the solution, while the nature of cations has no visible role. We have identified the critical parameters for optimal growth and fast production of nanotubes, and a basic growth mechanism for the tubes is proposed. This opens routes for significant improvements of the method toward uniformity and/or better overall yield, making it a viable alternative to the present established ...


Growth And Magnetic Properties Of Polycrystalline Self-Assembled Bifurcated Co Nanowires, Jesse Silverberg, Adam L. Friedman, Latika Menon Oct 2012

Growth And Magnetic Properties Of Polycrystalline Self-Assembled Bifurcated Co Nanowires, Jesse Silverberg, Adam L. Friedman, Latika Menon

Latika Menon

We use anodization of aluminum foil with variable applied anodization voltage to create an alumina template with bifurcated porous structures. The template is then used to electrodeposit Co, fabricating unique bifurcated Co nanowires. In order to better understand the crystal structure of our new material, we then report magnetic properties of these self-assembled bifurcated Co nanowires. Magnetic measurements of the bifurcated wires are studied as functions of branch/stem ratios, wire length, and temperature. The results are compared with those of straight Co nanowires of similar dimensions and thin film Co samples to find that a different crystal lattice structure ...


Investigation Of Electrical Transport In Hydrogenated Multiwalled Carbon Nanotubes, Adam Friedman, Hyunkyung Chun, Don Heiman, Yung Jung, Latika Menon Jun 2011

Investigation Of Electrical Transport In Hydrogenated Multiwalled Carbon Nanotubes, Adam Friedman, Hyunkyung Chun, Don Heiman, Yung Jung, Latika Menon

Latika Menon

Highly disordered multiwalled carbon nanotubes of large outer diameter (~60 nm) fabricated by means of chemical vapor deposition process inside porous alumina templates exhibit ferromagnetism when annealed in a H2/Ar atmosphere. In the presence of an applied magnetic field, there is a transition from positive to negative magnetoresistance. The transition may be explained in terms of the Bright model for ordered and disordered carbon structures. Additionally, temperature dependent electrical transport experiments exhibit a zero-bias anomaly at low temperature.


High-Throughput Assembly Of Nanoelements In Nanoporous Alumina Templates, Evin Gultepe, Dattatri K. Nagesha, Latika Menon, Ahmed A. Busnaina, Srinivas Sridhar Jun 2011

High-Throughput Assembly Of Nanoelements In Nanoporous Alumina Templates, Evin Gultepe, Dattatri K. Nagesha, Latika Menon, Ahmed A. Busnaina, Srinivas Sridhar

Latika Menon

The authors demonstrate a nanofabrication method utilizing nanoporous alumina templates which involves directed three dimensional assembly of nanoparticles inside the pores by means of an electrophoretic technique. In their demonstration, they have assembled polystyrene nanobeads with diameter of 50 nm inside nanopore arrays of height of 250 nm and diameter of 80 nm. Such a technique is particularly useful for large-scale, rapid assembly of nanoelements for potential device applications.