Diamond FED diodes

Final Paper    Final Paper

Final Presentation     Final Presention

Therapeutic Nanodevices: Drug Delivery

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December 18, 2008

Functionalized Nanomaterials for Medical Applications

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Biomimetic subwavelength antireflective gratings on GaAs

Chih-Hung Sun,

 

1 Brian J. Ho,1 Bin Jiang,2 and Peng Jiang1,*

OPTICS LETTERS / Vol. 33, No. 19 / October 1, 2008 p 2224-2226

Purpose of Study-

The authors developed a simple effective method in order to make a patterned surface that decreases the reflectivity of a surface.  In this manuscript they apply this method to GaAs wafers.

Methods-

Silica colloidal spheres are dispersed on a wafer using a simple spin-coating technique.  The size of the colloids can be controlled by varing the speed of the spin-coater.  In order to apply this method to GaAs surfaces, a single-layer reduction technique was employed.  Once the silica has  been deposited, a PDMS stamp is created.   Using the stamp as a mold, they are able create a template to form a patterned polymer film.

Key Findings-

• Subwavelength antireflective gratings can be easily formed on a variety of substrates.
• Silica colloids can be uniformily dispersed across a substrate, and be used to create a pattern template.

Photovoltaic cells fabricated by electrophoretic deposition of CdSe nanocrystals

Nathanael J. Smith, Kevin J. Emmett, and Sandra J. Rosenthal

Applied Physics Letters 93, 043504 2008

Purpose: To use Electrophoretic depsosition (EPD) to deposite CdSe nanocrystals onto TiO₂ for use in photovoltaic cells.

Methods: The CdSe nanocrystals were synthesized using a solution of CdO, trioctylphosphineoxide (TOPO), hexadecylamine, and dodecylphosphonic acid which was heated to 320 °C. The Se was injected via a Se in tributylphosphine solution. The nanocrystals were grown, isolated, and finally stored in hexanes. A voltage of 500V was established between the two electrodes and the electrodes were then placed in the solution of nanocrystals in hexanes. The nanocrystals were deposited onto a variety of materials including TiO₂, Indium/Tin Oxide, glass, and Si.

Key Findings:
1. The EPD was extremely sensitive to the preparation conditions of the nanocrystals. Although the same basic procedure was used, the minor differences that are inherent in the synthesis and isolation caused some nanocrystals to deposit while others did not at all.
2. Deposition stops once the population of either the negatively or positively charged nanocrystals is depleted. (In this case is was the negative species)
3. Unreacted precursors (esp. TOPO) cause the nanocrystals to favor staying in solution rather than forming films on the selected material.
4. Formation of films on the materials is complete after 1 minute.
5. More Cd is deposited on the negative electrode.
6. Nanocrystals do indeed play a role in the functioning of a photovoltaic cell, even though the efficiency of the CdSe nanocrystal cells is ~10^-6%

Entrapment of Photosystem I within Self-Assembled Films

“Entrapment of Photosystem I within Self-Assembled Films”

Helen A. Kincaid, Tom Niedringhaus, Madalina Ciobanu, David E. Cliffel, and G. Kane Jennings

Purpose

This paper discusses the ability to extract photosystem proteins from plants and incorporate them into devices that take advantage of the light harvesting ability of the proteins to generate electricity.  It focuses on the method of forming a SAM on the surface of a gold substrate and using this SAM to attach photosystem I in a patterned structure.  Alkanethiol SAMs with chain lengths longer than 12 carbons were shown to be too long and prevented charge transfer to the Au substrate.

Methods

Gold substrates were prepared using a silicon wafer that was cleaned and coated with evaporated chromium and gold layers.  SAMs were formed on the Au surface by immersion of the substrate in a 1 mM alkanethiol and ethanol solution.  The same process was done in a solution of PSI to get a thin layer of PSI on the SAM.  After finishing this process, the SAMs were backfilled with a long-chain alkanethiol in different solvents depending on the experiment.  Reflectance-Absorbance Infrared Spectroscopy (RAIRS), Spectroscopic Ellipsometry (SE), and Electrochemical Impedance Spectroscopy (EIS) were used to do electrochemistry on the resulting SAM/PSI covered substrate.

Key Findings

Backfilling the SAM is found to be essential in controlling the coverage of the PSI on the substrate.  Also time of exposure and concentration of the PSI solution are found to affect the type of coverage that the PSI will have on the SAM.  The choice of solvent (polarity) is involved in the quality of the backfilled SAM that is formed.  Polar solvents are found to be more effective than nonpolar solvents in getting a densely packed SAM.

Micro- and nanoscale characterization of hydrophobic and hydrophilic leaf surfaces

Bhushan B., Jung Y.C

Nanotechnology 17 (2006) 2758–2772

Purpose

 

Characterization of micro- and nanoscale topographic features of hydrophobic leaves, and analyze their roll in the superhydrophobic behavior. The study also makes a comparison of hydrophilic leaves with the purpose to understand the importance of low energy surface materials in the improvement of hydrophobic behavior.

Methods

 

Four type of leaves were studied: lotus and colocasia with hydrophobic characteristics and, fagus and magnolia with hydrophilic characteristics. Topographical characterization of the leaves was performed using SEM. Height of the micro and nano features was measured using optical profilometry and AFM in both modes, contact and tapping. Finally wetting properties were determined using a contact angle goniometer.

Key Findings

·         Comparison between hydrophobic and hydrophilic leaves revealed that the later have a thin wax film, which suggests that low energy constituents over this surfaces influence the hydrophobic behavior.

·         Combination of low surface energy materials and roughness are the responsible factors for superhydrophobic behavior.

·         Superhydrophobic behavior combines micro- and nanoscale roughness. However nanoscale roughness is the main responsible for the increase in the contact angle due to the increase of air pockets under the drops.

Novel Strategy for Diameter-Selective Separation and Functionalization of Single-Wall Carbon Nanotubes

By: R. M. Tromp, A. Afzali, M. Freitag, D. B. Mitzi, and Zh. Chen

Published in: Nano Lett. 2008, 8, 469-472

Purpose of Study

The electronic properties of carbon nanotubes (CNTs) are related to diameter and chirality. Chirality determines whether the CNT is semiconducting or metallic. Efforts to separate CNTs based on chirality and diameter have been met with varying degrees of success. The paper describes a diameter-selective method to separate CNTs.

Methods Used

Size matching between anchor molecules and the diameter of the carbon nanotube was used. This technique makes use of the arene-arene (π- π) interaction between condensed aromatic compounds and carbon nanotubes. This results in the formation of a host-guest pair. The anchor molecule used was C₂₆H₁₇NO₂. C₂₆H₁₇NO₂ has the shape of a folded ribbon with a folding angle of 126.5 °. The arms of the ribbons possess two conjugated carbon rings. These are expected to interact with the CNTs.

To determine the degree of interaction between the anchor and the CNT, the anchor was functionalized to make it soluble in toluene. A mixture of CNT, toluene and C₂₆H₁₇NO₂ was sonicated, then centrifuged. The Raman spectra of the liquid and solid portions were measured.

Key Findings

1. CNTs are insoluble in toluene. However in the presence of the functionalized anchor molecule some of the CNTs went into suspension.

2. Raman spectra of the solid and solution after centrifugation showed different peaks. The precipitate spectra showed peaks for CNTs about 1.6 nm in diameter. While the solution spectra showed peaks for CNTs with diameters of about 1.15 nm. This indicates that the anchor molecule interacted with CNTs with diameters smaller than 1.3 nm.

3. The separation of CNTs is sensitive to diameter but, not to the electronic characteristics of the nanotubes. So both metallic and semiconducting nanotubes below 1.3 nm in diameter were present in solution.

4. Carbon nanotube field effect transistors (CNTFETs) were prepared using larger diameter CNTs and mixed diameter (untreated) CNTs. CNTFETs with larger diameter nanotubes showed better performance over those made with untreated CNTs.

Simple Solid-Phase Synthesis of Hollow Graphitic Nanoparticles and their Application to Direct Methanol Fuel Cell Electrodes

Han, S; Yun, Y; Park, K-W; Sung, Y-E; Heon, T. Simple Solid-Phase Synthesis of Hollow Graphitic Nanoparticles and their Application to Direct Methanol Fuel Cell Electrodes. Advanced Materials 15 No. 22 (2003) 1922-1925.

Purpose of the study

To synthesize hollow low graphitic nanoparticles with high crystallinity for the purpose of being integrated into Direct Methanol Fuel Cell (DMFC) electrodes as a catalyst support.

Methods

The source of carbon used for the synthesis of these graphitic nanoparticles was a resorcinol-formaldehyde (RF) gel. This carbon precursor was homogenously mixed in aqueous solution with both cobalt and nickel metal salts. These salts served as the catalytic precursors. The mixture was heated under inert atmospheric conditions in order to generate a metal-carbon composite. This composite consisted of in-situ catalytic metal particles, amorphous carbon, and the desired graphitic nanoparticles. Both acid treatment and KMnO4 oxidation were employed (respectively) in order to remove the metal particle and amorphous carbon impurities and to produce the final product. The crystallinity and basic physical properties of the particles were verified using TEM, HRTEM, XRD, and Raman spectroscopy. To test the practical applications of these particles towards DMFC electrodes, an electrochemical study of a Pt-Ru (1:1) alloy catalyst (synthesized via borohydride reduction) supported on the hollow graphitic nanoparticles was conducted and the results compared to pre-existing catalyst supports.

Key findings

1. TEM images show that the graphitic particles exist in a relatively uniform size range of 30-40nm, with shell thicknesses of 5-8nm, while HRTEM showed that the outer shells of the particles were composed of various graphitic layers.
2. Electrochemical studies showed that the Pt-Ru catalyst supported on the hollow graphitic nanoparticles exhibited higher methanol oxidation, higher electrical conductivity, and a higher maximum power density than both the commercial E-TEK catalyst support and the Vulcan XC-72 catalyst support at 30C (~room temp.) and 60C.
3. In general, hollow graphitic nanoparticle catalyst supports were shown to exhibit superior performance when compared to commercial supports. The synthetic method for these particles uses a relatively cheap polymeric carbon precursor and could be adjusted for large scale production.

Glossary

- TEM: Transmission Electron Microscopy

- HRTEM: High Resolution Transmission Electron Microscopy

- XRD: X-ray diffraction

- KMnO4: potassium permanganate

Power generation with laterally packaged piezoelectric fine wires

Rusen Yang, Yong Qin, Liming Dai and Zhong Lin Wang

Nature Nanotechnology Advance online publication, 9 November 2008

Purpose of the Study

Demonstrate a flexible power generator based on cyclic stretching–releasing of a piezoelectric fine wire that has a number of advantages over generators based on vertically aligned nanowire arrays.

Methods

The generator was fabricated by bonding a ZnO piezoelectric fine wire (PFW) laterally on a Kapton polyimide film. Both ends of the PFW is fixed to electrodes. A current/voltage measurement meter was connected to two ends of the PFW without introducing any external power source in the circuit.

Key Findings

1.   When the substrate bends and stretches the wire, a tensile strain of 0.05–0.1% is induced in the wire, and forcing electrons to flow along an external circuit to charge the wire. And when the substrate is released, electrons flow back in the opposite direction.

2.    Periodically bending and releasing the PFW therefore generates an alternating current, which can be up to ~50 mV, and the energy conversion efficiency of the wire can be as high as 6.8%.

3.    Generators based on multiple PFWs can be integrated to raise the output voltage.

Important Definitions

1.    Piezoelectricity: Piezoelectricity is the ability of some materials to generate an electric potential in response to applied mechanical stress.

2.    Kapton: Kapton is a polyimide film developed by DuPont which can remain stable in a wide range of temperatures, from -269 °C to +400 °C (4 K-673 K).