bluuebunny/crossref_metadata_2025 huggingface dataset:
Injection of spin polarized electrons in InAs quantum dots
Authors: Russ Andreas , Yasar Mesut , Petrou Athos , Kioseoglou George , Li Connie , Hanbicki Aubrey , Jonker Berend , Korkusinski Marek , Hawrylak Pawel
Published: February 2010

We present the results of an electrical injection study of spin polarized electrons from ferromagnetic Fe contacts into electronic shells of self-assembled InAs quantum dots (QDs) incorporated in GaAs/AlGaAs spin LED structures. The circular polarization of the emitted light was measured as function of current and magnetic field. The polarization of the EL spectra exhibits strong maxima at energies that do not coincide with the electroluminescence (EL) intensity peaks. The magnetic field dependence of the polarization maxima is consistent with spin injection from the ferromagnetic Fe contacts. The experimental results are compared with calculated emission spectra from multi-exciton complexes (N = 2 and N = 6) as function of electron spin polarization. The energies of the EL features as well as their polarization characteristics are understood in terms of energy shifts due to exchange interactions between spin-down electrons occupying adjacent shells.
Optical Properties of Si Quantum Dots in Silica via an Implantation Mask
Authors: Barbagiovanni Eric G. , Goncharova Lyudmila V , Simpson Peter J , Armstrong Nathan
Published: February 2010

We studied photoluminescent properties and luminescent decay dynamics in Si quantum dots (QDs) produced by Si implantation in SiO2, and their modification by the application of an implantation mask. Silicon quantum dots were prepared by ion implantation, followed by high temperature annealing leading to nanocrystal nucleation and growth. The mask was prepared by spin-coating silica microspheres to achieve laterally-selective implantation, to control QD size and separation. Transmission electron microscopy (TEM) images were obtained to verify the diameter of the quantum dots. We observe a noticeable peak shift and narrowing in the photoluminescence spectra with the application of the implantation mask. Observed maxima in the photoluminescence spectra are compared with a quantum field theoretical model using an infinite confining 1D potential for Si quantum dots. We comment on the role of excitation transfer by observing a change in the dispersion exponent of the luminescent decay dynamics due to the mask.
Theromophotovoltaic Enhancement: 2D Photonic Crystals to Increase TPV Efficiencies
Authors: Shemelya Corey M. , Vandervelde Thomas E.
Published: February 2010

Here, we report on the enhancement of photon conversion by integration of photonic crystal (PhC) and surface plasmon (SP) structures into thermophotovoltaic (TPV) cells. PhCs consisting of rods of air are incorporated into the base of semiconductor TPV cells to increase the duration of thermal photon absorption, thus significantly enhancing quantum and conversion efficiencies (QE and CE, respectively). The potential of PhCs to augment the CE of TPV cells for most IR wavelengths makes it a widely useful technology. The ability to turn waste heat into usable energy will improve efficiency in a variety of electrical and electromechanical systems.
Surfaces Matter
Authors: Bruner Eric L.
Published: February 2010

Aculon, Inc. specializes in inventing and commercializing unique molecular-scale surface and interfacial coatings leveraging nanotechnology discoveries made at Princeton University. These coatings can be classified into three functional areas; non-stick, pro-stick/adhesion, and anti-corrosion.
The company has formulated coating solutions and processes for numerous markets including optical, display, electronics, consumer products and industrial coatings. These specialized coatings outperform all known alternatives in characteristics such as adhesion, stain resistance, and scratch resistance.
Fueling the company’s commercialization efforts are its proprietary Self-Assembled Monolayer of Phosphonates (SAMP) technology. The commercialization of SAMP treatments can be used for a variety of applications including imparting hydrophobicity, adhesion, or corrosion inhibition to numerous substrates.
For surface treatments to be effective, they must be mechanically and chemically stable under conditions experienced in the intended area of use. Aculon’s proprietary Self-Assembled Monolayer of Phosphonates methodology can impart any of these properties as desired to metals, metal oxides and even some polymer surfaces by drawing on its library of structurally tailored phosphonic acids.
The secret to the commercialization is covalent bonding, which creates a uniquely strong attachment between the SAMP and the substrate. Because the SAMP is one approximately 1.5 nm thick, it completely covers the material to which it is applied, and assures total surface coverage regardless of the type or texture of that material. The composition of the SAMP determines the properties that it imparts to its substrate.
In 1998, Professor Jeffery Schwartz of Princeton University discovered that well-ordered monolayers of phosphonates could be formed by self-assembly on a wide variety of oxide and oxide-terminated surfaces. At that time Professor Schwartz and his team also discovered that a simple dip process enabled SAMP formation on substrates of complex structures and geometries, as well as traditionally “unreactive” surfaces.
The research showed that SAMP adhesion to oxides was mechanically strong and resisted removal by hydrolysis and oxidation. It showed further that by using the dip method, SAMPs of a variety of molecular structures, including aliphatic, aromatic, and heteroaromatic, could be prepared.
Commercialization of SAMPs proves that such surface-bound phosphonates can dictate control of the surface properties of myriad substrates and that they can be implemented using well-known industrial techniques and conditions. These processes can be scaled to meet the needs of large or small facilities, and can be applied to surfaces of nearly any size or shape without special needs. Based on the needs of the producer, surface modification can be completed during the time of manufacturing or can be performed as a post-production step.
Bridging the Nano-gap: From Scientific Discovery to Real World Products
Authors: Dutta Partha Sarathi
Published: February 2010

Going from a small scale laboratory invention or discovery to a large scale application is not a trivial task and incorporating them into a product for a viable business is even more difficult. As technologies approach final products and applications, the number of criteria it must meet increases exponentially. Economics of the manufacturing process, environmental issues, intellectual property management, etc. needs to be assessed and monitored carefully. Bridging the gap from research to business not only needs multi-disciplinary understanding of the various aspects of the technology, but also how and what it could potentially enable or replace in current technologies and how to go about it through partnerships with global business entities. Especially with new materials, such as nano-scale materials, technology push needs to be rigorous and often the end results are uncertain. One needs to start from a large number of end user applications and narrow down to 1-2 high value-add or high volume opportunities. This process also requires constant development of the existing products to meet the exact needs for the high opportunity end markets. Timing for such efforts is crucial and the resources needed for such activities are often under-estimated by small start-up firms. Even for materials with well understood end products and established markets, significant market pull requires huge investments in product reliability demonstrations, cost of manufacturing, etc. Innovation, flexibility, change, educated risk, adaptability, focus and excellence are all key drivers and necessary ingredients for a successful and sustainable start-up venture. While scientific and engineering innovations are absolutely necessary, the metric for success for any business is revenue generation. Finding the right mechanisms for closing this gap (so-called the valley of death) is where the innovations of entrepreneurs lies. In this paper, I will share some of my personal learning experiences through the start-up company Applied Nanoworks Inc., (now Auterra Inc.).
Decreased lung carcinoma cell density on select polymer nanometer surface features for lung replacement therapies
Authors: Zhang Lijuan , chun Young Wook , Webster Thomas J
Published: February 2010

PLGA (poly-lactic-co-glycolic acid) has been widely used as a biomaterial in regenerative medicine due to its biocompatibility and biodegradability properties. Previous studies have shown that cells (such as bladder smooth muscle cells, chondrocytes, osteoblasts, and vascular smooth muscle cells) respond differently to nano-structured PLGA surfaces (such as those with surface features less than 100 nm in at least one dimension) compared to nano-smooth surfaces. The purpose of the present in vitro research was to prepare PLGA films with various nanometer surface features and determine, for the first time, whether lung cancer epithelial cells respond differently to such topographies. Poly(dimethylsiloxane) (PDMS) molds prepared by placing PDMS onto various polystyrene monolayers and two solution evaporation methods were used to create nanometer surface features on PLGA. The intended spherical surface nano-topographies on PLGA with RMS values of 2.23, 5.03, 5.42 and 36.90 nm were formed, while PLGA surfaces with RMS values of 0.62 and 2.23 nm were obtained by different solution evaporation methods. Most importantly, lung cancer epithelial cells adhered less on the PLGA surfaces with an RMS value of 0.62, 2.23 and 5.42 nm after 4 hours of culture compared to any other PLGA surface created here. After three days, PLGA surfaces with an RMS value of 0.62 nm had much lower cell density than any other sample. In this manner, PLGA with specific nanometer surface features may inhibit lung cancer cell density which may provide for an important biomaterial for the treatment of lung cancer for a wide range of applications (from drug delivery to regenerative medicine).
Observation of Uptake and Distribution of Quantum Dots in Plants
Authors: Wang Annie R. , Xu Hengyi , Dixon John , Aguilar Zoraida Pascual
Published: February 2010

Engineered nanoparticles that offer unique physical and chemical properties are rapidly flooding the market for commercial applications. The applications include, but are not limited to, cosmetic products, light emitting diodes, solid state display, drug delivery, disease diagnosis, nanoscale drug reformulations, MRI contrast agents, and new treatments. Predictions have indicated a dramatic increase in the market for nanotechnology and corresponding products to reach $1 trillion in 2012.
As a result of the predicted increase in the use of NPs as components of consumer product, the presence of engineered nanoparticles in the environment has sparked human health safety concerns. NPs may be introduced to organisms by inhalation, intravenous (usually purposefully), ingestion, or absorption through the skin. It is projected that the total production of NPs will reach 58,000 tons/year in 2011-2020 which assures human exposure to NPs at the workplace, in food and drinking water, and wearable consumer products. This paper addresses the QD distribution when plants are exposed to NPs. Mung beans were incubated with aqueous solutions of quantum dots and allowed to grow for 21 days. The seedlings were sectioned and observed under the microscope to establish the locations of NPs with respect to the roots, stem, and leaves.
Drug Deliverable, Self-assembled Rosette Nanotubes (RNTs) for Orthopedic Applications
Authors: Chen Yupeng , Song Shang , Fenniri Hicham , Webster Thomas J
Published: February 2010

Rosette nanotubes (RNTs) are novel, biomimetic, synthetic, self-assembled drug delivery agents. Because of base stacking and hydrophobic interactions, the RNT hollow-tube structure can be used for incorporating drugs. Another advantage of using RNTs is their ability to be injected and become solid at body temperatures for orthopedic applications without the use of any external stimuli (such as UV light or crosslinking agents). The nano-features of RNTs create a favorable, biologically-inspired, cellular environment. In this study, methods to incorporate dexamethasone (DEX, a bone growth promoting drug) into RNTs were investigated. The drug-loaded RNTs were characterized using Nuclear Magnetic Resonance (NMR), Diffusion Ordered Spectroscopy (DOSY) and Ultraviolet-visible Spectroscopy (UV-vis). Results showed that small molecular drugs with hydrophobic aromatic rings were incorporated into RNTs. Subsequent drug release experiments demonstrated that DEX was released from the RNTs and had a positive impact on osteoblast functions. Importantly, compared to other drug carriers, RNTs increased the total drug loading and was the highest when DEX was incorporated during the RNT self-assembly process. Thus, this study offered a novel drug delivery device that itself is bioactive and can be used to deliver a variety of drugs for various orthopedic applications.
Novel Anti-Cancer, Anti-Bacterial Coatings for Biomaterial Applications: Selenium Nanoclusters
Authors: Tran Phong Anh , Taylor Erik , Sarin Love , Hurt Robert H. , Webster Thomas J
Published: February 2010

Two common problems with implantation after cancerous tumor resection are cancer recurrence and bacteria infection at the implant site. Tumor resection surgery sometimes can not remove all the cancerous cells, thus, cancer can return after implantation. In addition, bacteria infection is one of the leading causes of implant failure. Therefore, it is desirable to have anti-cancer and anti-bacterial molecules which both rapidly (for anti-infection purposes) and continuously (for anti-cancer purposes) are available at the implant site following implantation. Therefore, the objective of the present in vitro study was to create a multi-functional coating for anti-cancer and anti-bacterial orthopedic implant applications. Elemental selenium was chosen as the biologically active agent in this effort because of its known chemopreventive and anti-bacterial properties. To achieve that objective, titanium (Ti), a conventional orthopedic implant material was coated with selenium (Se) nanoclusters. Different coating densities were achieved by varying Se concentration in the reaction mixture. Titanium substrates coated with Se nanoclusters were shown to enhance healthy osteoblast (bone-forming cell) and inhibit cancerous osteoblast proliferation in co-culture experiments. Functions of S. epidermidis (one of the leading bacteria that infect implants) were inhibited on Ti coated with Se-nanoclusters compared to uncoated materials. Thus, this study provided for the first time a coating material (selenium nanoclusters) to the biomaterials’ community to promote healthy bone cells’ functions, inhibit cancer growth and prevent bacteria infection.
Assessment of Nanomodified Endotracheal Tubes in a Bench Top Airway Model
Authors: Machado Mary C. , Chang Daniel , Webster Thomas J , Tarquinio Keiko M
Published: February 2010

Ventilator associated pneumonia (VAP) is a serious and costly clinical problem. Specifically, receiving mechanical ventilation over 24 hours increases the risk of VAP and is associated with high morbidity, mortality and medical costs. This complication is especially hard to diagnose in children because of non-specific clinical signs and lack of established diagnostic methods. Cost effective endotracheal tubes (ETTs) that are resistant to bacterial infection would be essential tools for the prevention of VAP. In addition to their bacterial resistance, ETT with magnetic nanoparticles could aid in the diagnosis of VAP allowing physicians to locate infections with greater accuracy. The objective of this study was twofold, first to develop strategies to decrease bacterial adhesion on nano-rough ETT and secondly to develop better methods to assessin vitrobacterial adhesion or biofilm formation on ETT. In preliminary tests, nanomodified polyvinyl chloride (PVC) ETTs has been shown to be effective at reducing bacterial colonization. This study also sought to evaluate the bacterial resistance of these ETTs more effectively by creating a bench top airway model, which can create a similar environment to the flow system that ETTs are exposed toin vivo. The airway model designed to test ETTs has two Plexiglas chambers representing the oropharynx and the lungs, a tube representing the trachea and finally an intricate pumping system to the oropharynx with bacteria flow and to the lung with simulated compliance and resistance. ETTs were connected to a ventilator and passing the oropharynx into the trachea and observed under the mechanical ventilation and continuous bacterial flow system. In addition, the study examined dual gas flow conditions and their effect on bacterial growth of ETT. In no less than three separate trials in the airway chamber, each ETT will be tested for its effectiveness at the reduction of bacterial growth within the airway by sampling from both lung and oropharynx chambers during continuous operation. Special attention will be given to the long-term effects on the ETT by including a study that lasts longer than ten days. Both the bacterial proliferation in the two chambers and on the ETT itself will be carefully analyzed. This specialized testing should yield valuable information on the efficacy of nanomodified ETT in airway conditions and will provide further evidence to determine if nanomodified ETTs are a valid solution to VAP.
Phosphorescent White OLEDs for Solid-state Lighting
Authors: Xia Sean , Levermore Peter , Adamovich Vadim , Lin Chun , Kwong Raymond C. , Weaver Michael S. , Brown Julie J.
Published: February 2010

White OLEDs (WOLEDTMs) fabricated using energy efficient phosphorescent OLED (PHOLEDTM) technology open up exciting new ways to develop efficient white lighting. WOLEDs have the potential to transform the lighting industry. In this presentation, phosphorescent WOLEDs with high conductivity transport layers will be discussed. White light can be generated by partial energy transfer from blue to green and red. Single WOLED stacks are demonstrated that match the Energy Star® lighting color criteria for 2700K and 3000K with high efficiency (˜80 lm/W) and high color rendering indices (˜80). Both devices had operational lifetimes (LT70%) over 30,000 hours measured from an initial luminance of 1,000 cd/m2. Different techniques to improve optical outcoupling will also be discussed.
An Improved Triple-Tandem Organic Solar Cell
Authors: Zhao Dewei , Sun Xiao Wei , Ke Lin , Tan Swee Tiam
Published: February 2010

We present an efficient polymer-small molecule triple-tandem organic solar cell (OSC), consisting of poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) bulk heterojunction as the first and second cells, and small molecules copper phthalocyanine (CuPc) and fullerene (C60) as the third cell on top. These sub-cells are connected by an intermediate layer of Al(1 nm)/MoO3(15 nm), which appears to be highly transparent, structurally smooth, and electrically functional. Compared to our previous all polymer triple-tandem organic solar cells (2.03%), this polymer-small molecule triple-tandem organic solar cell achieves an improved power conversion efficiency of 2.18% with a short-circuit current density (Jsc) = 3.02 mA/cm2, open-circuit voltage (Voc) = 1.51 V, and fill factor (FF) = 47.7% under simulated solar irradiation of 100 mW/cm2 (AM1.5G), which can be attributed to the increased photocurrent generation in the third cell since the third cell has the complementary absorption with two bottom cells despite a slightly reduced Voc.
Area-scaling of Organic Solar Cells and Integrated Modules
Authors: Choi Seungkeun , Potscavage William J , Kippelen Bernard
Published: February 2010

We report on the improved performance of large-area organic solar cells and modules by integrating metal grids directly with the indium tin oxide (ITO), thereby reducing the series resistance contribution from the ITO. Devices with different areas (0.1, 7, and 36.4 cm2) were prepared to study the area-dependency of the organic solar cells based on pentacene and C60 heterojunctions. Modules were prepared in which four individual cells (7 cm2) were connected in series and parallel. For the series connected modules, VOC scales linearly with the number of cells while parallel connected modules exhibited multiplied current density as expected.
UV-Vis. Spectroelectrochemical Study on Electron Blocking and Trapping Behaviors in Conducting Polymer Bilayers with Diphenylamine End Groups
Authors: Li Yunfeng , Tin Chin-Che , Cammarata Vince
Published: February 2010

Spectroelectrochemistry was used to study the electron trapping and rectifying behavior in several diphenylamine endgroup polymeric bilayers. Various combinations of the following monomers were pairwise sequentially electropolymerized onto ITO transparent electrodes: FD, DNTD, DPTD and Cl4DPTD. Poly(FD) is a p-type material while poly(DNTD), poly(DPTD) and poly(Cl4DPTD) are bipolar materials being both n-type and p-type. Bilayers of ITO|poly(FD)|poly (DNTD) or ITO|poly (FD)|poly (DPTD), block electrons from reducing the outer layer even at -1.0 V vs Ag/AgCl, yet holes effectively oxidize both layers. The LUMO differences between poly(DNTD) and poly(Cl4DPTD) or poly(DPTD) and poly(Cl4DPTD) provide a large enough electronic barrier that electron trapping can occur between these n-type materials. The visible spectra results imply that these polymers, poly(DPTD) or poly(Cl4DPTD) can be used as photovoltaic materials.
Hydrogen adsorption calculations in expanded graphite and amorphous carbons
Authors: Peng Lujian , Morris James Robert
Published: February 2010

This paper uses an efficient and accurate approach to estimate the hydrogen physical adsorption in various carbon structures. By comparing with previous Grand Canonical Monte Carlo (GCMC) and other methods on expanded graphite, the introduced method is shown to be accurate, but the calculation is much faster and more intuitive. Our preliminary results in amorphous carbons show high hydrogen uptake close to 0.8% at 300 K and moderate pressure.
In-situ TEM Observation for Reaction Mechanism in MgH2 Hydrogen Storage Material
Authors: Ono Akifumi , Isobe Shigehito , Wang Yongming , Hashimoto Naoyuki , Ohnuki Somei
Published: February 2010

In-situ observation on the catalytic effect of Nb2O5 in MgH2 was carried out by using transmission electron microscopy (TEM). We prepared two kinds of samples, because we tried to observe the reaction from two kinds of viewpoints. MgH2 catalyzed with 1 mol% of Nb2O5 was prepared for an overall viewpoint on the desorption process of MgH2 with catalyst by conventional TEM. The dehydrogenation of the 1 mol% sample started at 150 °C and Mg nano-size particles were formed. However, Nb2O5 was not confirmed in diffraction patterns and images, because it was highly dispersed by ball-milled. So MgH2 catalyzed with 10 mol% of Nb2O5 was prepared for local viewpoint to focus the boundary between the catalyst and the Mg phase by high voltage electron micro scope (HVEM). The sample mixed in mortar was prepared for this, because it was difficult to find the boundary in the sample ball-milled. The high resolution images of the 10 mol% sample revealed that the dehydrogenation started from the interface of MgH2 and Nb2O5. The result suggested that the dehydrogenation could proceed with hydrogen diffusion from MgH2 phase to the interface between Mg and Nb2O5.
In-situ TEM Observation for Reaction of LiH with NH3 by Means of Environmental Cell
Authors: Hirasawa Hiroko , Isobe Shigehito , Wang Yongming , Yamamoto Hikaru , Miyaoka Hiroki , Hashimoto Naoyuki , Ohnuki Somei , Ichikawa Takayuki , Kojima Yoshitsugu
Published: February 2010

In-situ observation of the reaction between light weight hydride LiH and NH3 gas was performed by means of TEM (Transmission Electron Microscopy) with an environmental cell. This environmental cell was designed for the observation of the gas-solid reaction under 0 ∼ 0.2 MPa gas atmosphere at 20 ∼ 150 °C. It has been confirmed a volume expansion and generation of LiNH2, that is the reaction between LiH and NH3. Moreover, it was revealed that LiNH2 was generated at the surface of LiH particle at first process of the reactions.
In-situ Kinetics Studies on Hydrogenation of Transition Metal (=Ti, Fe) Doped Mg Films
Authors: Tan Zhuopeng , Heilweil Edwin J. , Bendersky Leonid
Published: February 2010

In this paper we report on kinetics studies of the growth rates of a hydride phase during the metal-hydride phase transformation of Mg films doped with transition metals (=Ti, Fe). Infrared emission imaging of wedge-shaped thin films during hydrogen loading reveals different effects of Ti and Fe additives on Mg hydride growth rates. Compared to hydrogenation of pure Mg, Ti addition (atomic fraction 1.6 % and 2.3 %) does not increase the Mg hydride growth rate. However, this doping results in the formation of a thicker hydride layer residing on top of the films. The hydrogenation rate is increased by an order of magnitude for addition of atomic fraction 3.1 % of Fe and the thickness of Mg hydride layer is more than twice that of the hydride layer during hydrogenation of pure Mg. Results obtained here can be used to guide powder design for hydrogen storage applications.
Phase Transformation from Mg to MgH2 Studied by SEM Metallography
Authors: Montone Amelia , Aurora Annalisa , Mirabile Gattia Daniele , Vittori Antisari Marco
Published: February 2010

Metallographic information has been used to support the kinetic analysis and the relative experimental findings in the phase transformation from Mg to MgH2, by absorption of hydrogen gas. In particular the method provides detailed information on the role of localized features like catalyst particles and defects present in the sample, which is obtained from ball milled MgH2 enriched with 5wt% Fe. In this work we have compared the kinetics of the hydrogenation reaction carried out at two different temperatures while keeping constant the thermodynamic force driving the reaction. This last was achieved by carefully controlling the hydrogen gas pressure. Despite this fact, the sample microstructure shows a marked effect of the temperature on the nucleation mechanism. In particular we have noticed that the density of sites active for nucleation is higher at lower temperature.

Instant nucleation deduced by the kinetic analysis was confirmed by comparing the microstructure of samples at different reaction stages.
In-situ Raman study of the thermal decomposition of LiBH4
Authors: Reed Daniel , Book David
Published: February 2010

With relatively high gravimetric and volumetric hydrogen storage capacities, borohydrides have attracted interest as potential hydrogen storage media. Lithium borohydride has a maximum theoretical gravimetric hydrogen storage density of 18.4 wt%, and has been shown to be reversible when heated to 600°C in 350 bar hydrogen1. It is hoped that a greater understanding of the decomposition and reformation mechanisms, may lead to the development of LiBH4-based materials that can absorb and desorb hydrogen under less extreme conditions. However, these studies have proved a challenge: currently most in-situ investigations have used x-ray diffraction or neutron diffraction however these cannot readily give information on non-crystalline or liquid phases. The preparation of samples measured ex-situ via XRD, NMR2 and Raman3 have shown the reaction products and stable intermediates during the thermal decomposition, however, it is very difficult to detect short lived intermediate (or byproduct) species. Raman spectroscopy has the advantages that: materials with only short-range order can be analysed; and by focusing the laser on regions in a sample the reaction path can be monitored with changing temperature with a rapid scan rate.

After heating lithium borohydride through its phase change and melting point, shifts in peak position and peak width were observed, which agreed with other studies4. A sample was also heated to 500°C (under 1 bar Ar) to decompose the sample. A number of intermediates and reaction products have been predicted and observed ex situ. This work shows the in situ formation of lithium dodecaborane (Li2B12H12) and amorphous boron from liquid lithium borohydride. It is therefore possible to determine at what temperatures certain intermediates and products form.
Enhancement of TiO2 Photocatalytic Activity by N- Doping Using the Gas Phase Impregnation Method
Authors: Li Chennan , Srinivasan Sesha , Kislov Nikolai , Schmidt Mark , Stefanakos Lee , Goswami Yogi
Published: February 2010

This paper investigated an inexpensive way to improve the overall photocatalytic activity of TiO2 by N- doping using anhydrous ammonia as the nitrogen source. Doping amount could be further optimized by controlling the reaction time. Experiments showed that photocatalytic effect has one threshold concentration. Lower or higher reaction will decrease the photocatalytic efficiency. Experiments showed that the suitable reaction temperature should be lower than 650oC.
Environmental Friendly and Highly Regioselective Oxybromination in An Aqueous System Using SBA-15 Supported Sulfated Zirconia Catalyst
Authors: Ai-Jan Chen , Xiao-Rong Chen , Mou Chung-Yuan
Published: February 2010

Brominated aromatic compounds have been widely used in synthetic organic chemistry for themanufacturing of many bulk and fine chemicals. In contrast to direct bromination by toxic elemental bromine or HBr, we developed an environmentally friendly system for oxybromination using hydrogen peroxide and ammonium bromide in the aqueous phase under mild temperature and near neutral conditions over a SBA-15 supported sulfated zirconia (SZ) catalyst. The ready availability of the catalyst and the nearly neutral aqueous solution are the salutary features of this approach. Bromination of aromatics with electron-withdrawing group took place readily, and bromoproducts were produced in moderate to excellent yields. A good to excellent para-selectivity was observed. The SZ/SBA-15 catalyst may be re-used several times without substantial loss of activity.

We also studied the catalytic activity of SZ which were supported on mesoporous SBA-15 silica or mesoporous SZ. On bromination silica supported sulfated zirconia (SZ/SBA-15) showed much better catalytic ability for bromination then self-supported SZ (m-SZ). Furthermore, we found the catalytic activity of SZ decreased as the calcinations temperature increased. The good catalytic performance of the SZ/SBA-15 materials was attributed to the well dispersed of sulfate groups to give sulfated silica-zirconia of with (1) very good redox property and (2) high strength and high density of acid sites.
γ-Al2O3 Thin Films Catalyst Model Support Preparation on β-NiAl(110) Alloy
Authors: Zhang Zhongfan , Li Long , Shah Malay , Wen Jianguo , Yang Judith C
Published: February 2010

Low temperature oxidation of NiAl(110) alloy has been studied with surface characterization methods and cross-section TEM. Our work demonstrated thin and high quality single crystal γ-Al2O3(111) films have grown heteroepitaxially on NiAl(110) alloy. The orientation relationship of metal/oxide is NiAl(110) || γ-A12O3(111)and NiAl(211)∥γ-Al2O3(311) with very slight lattice mismatch. Al cation outward diffusion dominates during this low temperature oxidation confirmed by EELS mapping along interface.
Twisted Nanostructures of 2H-MoS2 Slabs
Authors: Ramos Manuel , Ferrer Domingo A. , José-Yacamán Miguel , Berhault Gilles , Torres Brenda , Chianelli Russell r.
Published: February 2010

In the last decades, HRTEM approach has been quite fruitful to study structural characteristics of layered transition metal sulfide (LTMS) catalytic materials since providing direct local information about the structural organization of this quite important class of catalysts at the nanoscale level. However, up to now, HRTEM observations of some common localized structural organization like honeycomb-like structures have remained unexplained. In the present study, a structural model corresponding to stacked 2H-MoS2 slabs twisted along their basal direction is proposed to explain honeycomb like-structures observed by HRTEM. This model is based on a comparison between experimental and simulated images of 2H-MoS2 catalysts promoted with cobalt. The resulting Density of States (DOS) of the twisted structure was then calculated.
Bimetallic Nanoparticles of PtCu and PtNi; Synthesis and CO Oxidation Catalysis
Authors: Yamamoto Takao A. , Nakagawa Takashi , Seino Satoshi , Nitani Hiroaki
Published: February 2010

Bimetallic nanoparticles of PtCu and PtNi supported on iron oxide particles were synthesized by a new method employing a 4.8-MeV electron beam as a trigger for reduction of their aqueous ions, and their CO oxidation catalysis was evaluated to find activities enhanced by the alloying. Sample materials of PtCu (PtNi) bimetallic grains supported on γ-Fe2O3 particles were synthesized by irradiating with the electron beam a glass vial containing precursors in an aqueous solution. The vial contains aqueous ions of platinum and copper (nickel) and γ-Fe2O3 particles of average size of 30 nm. The irradiation induces water radiolysis generating reducing species, such as hydrated electrons, and metallic nanograins are formed and stabilized on the support material. The irradiation was finished in several seconds without using any organic solvent and any surfactant. The average grain sizes observed with a TEM were around 3 nm in diameter. XRD patterns of PtCu samples exhibited the FCC structure with peak shifts obeying the Vegard’s law at low Cu concentrations. X-ray absorption spectra measured at edges of the constituent elements indicated that Pt is in the metallic state and coordinates certainly with Cu or Ni. Catalytic activity of CO oxidation of the material was evaluated by measuring residual CO contents in air in contact with the sample material by using a gas-chromatograph. The activities of the PtCu and PtNi samples were higher than that of monolithic Pt on γ-Fe2O3. The correlation between the atomic structure in these nanograins and their activities was investigated, which indicated that the random alloy enhances the activity. These bimetallic nanoparticles are expected as catalysts for preferential oxidation of CO in hydrogen gas fed to fuel cells.
Preparation of Platinum Nanoparticles Using Linear Polyethyleneimine as a Stabilizer by Liquid-phase Reduction Method
Authors: Imai Takanori , Abe Yoshimoto , Nishio Keishi , Tamura Ryuji , Shibata Hirobumi , Kineri Tohru , Gunji Takahiro
Published: February 2010

Platinum nanoparticles stabilized by linear polyethyleneimine were prepared by the liquid-phase reduction of chloroplatinic(IV) acid with sodium borohydride. The particle sizes were 3.26 nm and 1.76 nm when the molecular weights of linear polyethyleneimine were 25000 and 2150, respectively. These nanoparticles were well-dispersed in water in the range of pH 1-6. Branched polyethyleneimine also provided nanoparticles that dispersed in water in the range of pH 0-8. Linear poly(ethyleneimine-co-N-methylethyleneimine) gave nanoparticles that dispersed in water in the range of pH 0-10. The dispersibility of the nanoparticles decreased with increasing content of the N-methyl group.
Preparation of Pt Nanoparticles Dispersed in Mesoporous Silica
Authors: Chiba Yukitoshi , Shibata Hirobumi , Nagata Daichi , Gunji Takahiro , Tamura Ryuji , Kineri Tohru , Nishio Keishi
Published: February 2010

Platinum nanoparticles were dispersed in mesopores of mesoporous silica using a sol-gel process with a composite template consisting of an amphiphilic triblock copolymer (Pluronic P123 or F127) and a Pt-organic complex, which was prepared with K2Pt(II)Cl4 as a Pt source and 1,10-phenanthroline as a chelating agent. The obtained Pt-1,10-phenanthroline complex did not dissolve in any of several solvents, e.g., hexane, benzene, toluene, THF, H2O, CH3OH, and C2H5OH. However, when the Pt-1,10-phenanthroline complex was reacted with ethylenediamine it dissolved in many solvents. Platinum nanoparticles dispersed in mesoporous silica were obtained using a sol-gel process with a complex template consisting of Pt-1,10-phenanthroline-ethylenediamine, and an amphiphilic triblock copolymer (Pluronic P123 or F127). A sample dried at 353 K was bright yellow. When it was subsequently heat-treated at 823 K, it turned light gray. This change indicates that Pt nanoparticles can be obtained by heat-treatment at high temperature, because, to generate Pt nanoparticles, the organics chelated to Pt ions must be removed. Measurements from small-angle x-ray scattering show that mesoporous silica obtained using a complex template has a much more highly ordered pore structure than that obtained using only an amphiphilic triblock copolymer. It has both large pores (above 8 nm) and a large surface area (about 290 m2/g). Furthermore, results of a TEM investigation showed that Pt nanoparticles were generated only in mesopores of mesoporous silica.
Structural Properties of the Bimetallic Cluster Au12Ag6 on the NOx (x=1,2,3) Adsorption Processes
Authors: Molina Bertha , Castro Jorge , Soto Jorge , Yépez Enrique , Calles Alipio
Published: February 2010

It has been shown that Au and Ag nanoparticles present catalytic properties of pollutant gases, product of the hydrocarbons combustion processes, whose efficiency is strongly dependant on their size, morphology and supporting material. The activity of Ag subnanometric particles supported on alumina in the NOx reduction mechanism, for the reaction HC-SCR (Hydrocarbon Selective Catalytic Reaction) is a good example of these catalytic properties. It is also well established that both Au and Ag nanoparticles are oxygen poisoning resistant and that in certain reactions the bimetallic combination may be more efficient than their isolated parts. In this work we present a DFT calculation of the NOx (x =1, 2, 3) adsorption energies on the Au12Ag6 cluster surface. It is also discussed the possible synergetic effect of the different configurations, forming small Ag islands composed of one to five atoms, on the surface of the bimetallic cluster. The analysis was done using DFT in the ZORA approximation.
Transition Pathway Analysis of Homogeneous Dislocation Nucleation in a Perfect Silicon Crystal
Authors: Saeed Hasan Aftab , Izumi Satoshi , Hara Shotaro , Sakai Shinsuke
Published: February 2010

Transition pathway sampling was carried out for homogeneous dislocation nucleation in perfect crystal Si. The sampling algorithm employed was Nudged Elastic Band method. Results obtained were compared with corresponding results for Cu. The stress and activation barrier ranges were found to be much higher for Si than those reported for Cu. The results also showed that while for lower values of resolved shear stress the dislocation embryo approaches that of a perfect dislocation, for higher resolved shear stress values the embryo is far from perfect. That is, the shear displacement of most particles is considerably less than the Burger’s vector. This investigation also demonstrated for the first time that Athermal shear stress for homogeneous dislocation nucleation in Si does not exist, as the crystal undergoes twinning at such high stresses.
Interface Effects on the Mechanical Properties of Nanocrystalline Nanolaminates
Authors: Jankowski Alan F.
Published: February 2010

Nanocrystalline nanolaminate (ncnl) structures are widely used in the study of physical properties in order to engineer materials for a variety of industrial applications. Often, novel and interesting mechanical behaviours that are found in nanolaminate materials can be linked with two characteristic features of structure. These are the layer pair spacing and the grain size. For the case of nanolaminates synthesized by physical vapor deposition processes, the layer spacing corresponds with the repeating sequence of layer pairs and can be referred to as composition wavelength. The grain size is the average width of the tapered columnar structure along the growth direction. Since the mechanical properties of strength and hardness are known to functionally vary with the separation between dislocations in crystalline materials, both structural features can potentially contribute to the total interfacial area and the characteristic separation of interfaces that mitigate dislocation motion. In this investigation, the individual contribution of layer pair spacing and grain size to the total interfacial structure are each quantified in an assessment of strength and hardness. A model is proposed for the total interfacial area of the material volume under plastic deformation that can quantify the interfacial area contribution from the layer pairs and the grain size. It is anticipated that each structural feature can potentially dominate the plastic deformation of the nanolaminate as dependent upon the specific layer pair spacing, the grain size, and the extent of plastic deformation.
High-Throughput Optimization of Adhesion in Multilayers by Superlayer Gradient
Authors: Grachev Sergey Yu , Cuminatto Coraly , Søndergård Elin , Barthel Etienne
Published: February 2010

We used thickness gradients for high throughput optimization of adhesion in film stacks. The idea is based on the so-called superlayer test where a top layer under high compression exerts a load onto the lower interfaces and may cause delamination and buckling. Thus, on one hand, the thickness gradient of the superlayer results in the gradient of the load. On the other hand, the adhesion gradient can be realized by changing the thickness of an adhesion enhancer (or an adhesion reducer). When applied in two perpendicular directions (cross-gradient), the gradient of the superlayer in one direction and of the adhesion enhancer in the other, the plane of the sample represents a map where the line of delamination relates the interfacial toughness to the thickness of the enhancer.
In our tests we used Mo superlayers under compressive stress of the order of ˜1.5 GPa on a Si wafer with a native oxide. The adhesion reduction was observed with this methodology when Ag layer up to 10 nm thick was deposited onto the substrate prior to Mo deposition. The delamination occurred at Ag thicknesses starting from ˜6 nm. This thickness of Ag corresponds to the islands coalescence and formation of a continuous film which immediately results in adhesion reduction. The other test was performed with a step gradient of Ti enhancer placed under a 10 nm thick Ag layer in otherwise the same arrangement. A single test showed that 2.8 Å of Ti was sufficient to improve the adhesion between Ag and SiOx by several times.
Towards a Virtual Laboratory for Grain Boundaries and Dislocations
Authors: Echeverri Restrepo Sebastián , Thijsse Barend J.
Published: February 2010

In order to perform a systematic study of the interaction between grain boundaries (GBs) and dislocations using molecular dynamics (MD), several tools need to be available. A combination of computational geometry and MD was used to build the foundations of what we call a virtual laboratory. First, an algorithm to generate GBs on face-centered cubic bicrystals was developed. Two crystals with different orientations are placed together. Then, by applying “microscopic” rigid body translations along the GB plane to one of the crystals and removing overlapping atoms, a set of initial configurations is sampled and a minimum energy configuration is found. Second, to classify the geometry of the GBs a local symmetry type (LST) describing the angular environment of each atom is calculated. It is found that for a given relaxed GB the number of atoms with different LSTs is not very large and that it is possible to find unique geometrical patterns in each GB. For instance, the LSTs of two GBs having the same “macroscopic” configuration but different “microscopic” degrees of freedom can be dissimilar: the configurations with higher GB energy tend to have a higher number of atoms with different LSTs. Third, edge dislocations are introduced into the bicrystals. We see that full edge dislocations split into Shockley partials. Finally, by loading the bicrystals with tensile stresses the edge dislocations are put into motion. Various examples of dislocation-GB interactions in Cu are presented.
Effect of Surface Roughness on Determination of Creep Parameter using Impression Creep Technique
Authors: Yan Wuzhu , Zhao Bin , Yue Zhufeng
Published: February 2010

The indentation creep test, especially the impression creep, exhibits a magic appealing in the determination of creep properties of small structures in industry for its simplicity, efficiency and non-destruction merits. Most of previous researches of indentation or impression creep neglect the effect of surface roughness of materials, which plays a crucial role in extracting creep properties of materials. The FE results showed that the surface roughness has no effect on the determination of creep exponent when the punching stress is larger than 150MPa. However, under a smaller punching stress the stress exponent is decreased due to the “Tuner” effect of asperities. The conclusions drawn in the present study provide an important guidance on experiment results amendment for impression creep technique.
Characterization and Control of the Wettability of Conducting Polymer Thin Films
Authors: Chang Jean H. , Hunter Ian W
Published: February 2010

The wettability of electrochemically deposited conducting polymer films is highly dependent on several parameters including the deposition conditions, the dopant, and the roughness of the working electrode. To produce superhydrophobic surfaces, one must be able to control the micro and nanostructure of the film. In this study, a template-free method of producing superhydrophobic (water contact angle of 154°) polypyrrole films was demonstrated. The polypyrrole was doped with the low surface-energy heptadecafluorooctanesulfonic acid and had microstructures with nanometer-scale roughness. The microstructures served to increase the roughness of the film and amplify the hydrophobicity of the surface. It is also of interest to be able to dynamically adjust the wettability of a polypyrrole surface after deposition. Applications of this functionality include microfluidics, self-cleaning surfaces, liquid lenses, and smart textiles. By oxidizing or reducing a polypyrrole film, one can change the surface morphology as well as the chemical composition, and control the wettability of the surface. This study characterizes the electrochemically-induced changes in surface energy of polypyrrole. The relationship between applied voltage, charge transferred, surface roughness, and water contact angle was investigated. Upon reduction, the polypyrrole film was switched to a superhydrophilic state and the maximum change in contact angle was observed to be 154°. Surface wettability was found to be not fully reversible, with some hysteresis occurring after the first electrochemical cycle.