bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced thermal Properties and Gas Barrier Property of PMMA Nanocomposites with Layered Silicate via Soap-Free Emulsion Polymerization
Authors: Cheng Hsiu-Yu , Jang Guang-Way William
Published: April 2011

Polymer/SWN nanocomposites were synthesized in the soap-free emulsion polymerization of methyl methacrylate (MMA) using 2-hydroxylethyl methacrylate (HEMA). The SWN in the polymer/SWN nanocomposites was individually dispersed in water, and these are adsorbed on the surface of monomer droplets. Polymer/SWN nanocomposites were obtained by adding an aqueous dispersion of layered silicate to the polymer emulsion. X-ray diffraction (XRD) and FT-IR spectra were utilized to characterize the structures of the nanocomposites. The degree of dispersion of these nanocomposites was investigated by transmission electron microscopy (TEM). Furthermore, the thermal and mechanical properties of polymer/SWN nanocomposites were determined using thermogravimetric analysis (TGA), differential scanning calorimeter (DSC) and dynamic mechanical analysis (DMA). The increased tanδ of the obtained nanocomposites is caused by the fine dispersion of SWN particles into the polymer matri
A Self-Contained, Nano-Gap Biomolecule Impedance Sensor with Fluidic Control System
Authors: Liang Huinan , Nam Wook Jun , Fonash Stephen J
Published: April 2011

A sub-50 nm biomolecular direct electrical-detection structure integrated with micro- and nano-fluidic systems has been constructed. These devices are composed of integrated microfluidic channels in PDMS and nanofluidic channels in silicon oxide. These in turn are all integrated with a nano-gap sensing structure which has metallic electrodes. The microfluidic channel in PDMS provides access to the nanofluidic channel feeding the nano-gap sensing structure. We provide a demonstration of the bio-molecular sensing capabilities of our device by using the carboxyl-amino group interaction and a nano-gap structure with gold electrodes. First, probe molecules with amino groups are infused through the fluidic system to the nano-gap and are self-assembled onto the gold electrodes via thiolate bonding. Then target molecules with terminating carboxyl groups are infused to bind with the probe molecules. Impedance changes are measured electrically at each infusing and binding step using an Agilent 4284A impedance analyzer thereby detecting the appearance of each molecule type as it passes through the system. We are able to detect about 15% impedance changes with the carboxyl-amino binding occurrence.
Development of Double-cantilever Infrared Focal Plane Arrays: Fabrication and Post-process Curvature Modification
Authors: Huang Shusen , Lin I-Kuan , Tao Hu , Zhang Xin
Published: April 2011

Uncooled double-cantilever microbolometers have the potential of reaching a noise-equivalent temperature difference (NETD) approaching the theoretical limit and thus have gained increasing interest. Each pixel of the device consists of two overlapping bimaterial cantilevers that deflect in opposite directions as their temperature rises due to the absorption of incident infrared radiation. This paper reports recent progress in the development of these double-cantilever focal plane arrays (FPAs), including fabrication and post-process curvature modification.
Nanopatterned Hydrogel Probes for Rapid Detection of Staphylococcus aureus
Authors: Saaem Ishtiaq , Kreiswirth Barry , Libera Matthew
Published: April 2011

We studied the use of nanopatterned hydrogels as a possible foundation for medical devices for the detection ofStaphylococcus Aureus. Nanopatterned hydrogels, approximately 200 nm in diameter, were created by locally crosslinking dry amine-terminated poly(ethylene glycol) [PEG] (6000 Da) thin films using a focused electron beam. These gels then had a dry height of 50 nm and a swell ratio of about five. They were patterned into arrays with approximately 500 nm inter-gel spacing. These arrayed gels were functionalized with Immunoglobulin G [IgG], a biomolecule that binds Protein A. We are interested in seeing whether these arrayed gels can be used for bacterial capture and subsequent detection. We show, using an assay that binds IgG to Protein A expressingStaphylococcus Aureus[S.Aureus], that nanopatterned hydrogels can indeed be used as probes for detection. We further show that the specificity of our assay by using a knockout variant ofS.Aureusthat doesn't express Protein A as a negative control.
Properties of Ferromagnetic GaGdN
Authors: Hite J. K. , Davies R. P. , Frazier R. M. , Thaler G. T. , Abernathy C. R. , Pearton S. J. , Zavada J. M.
Published: April 2011

Single phase GaGdN and GaGdN:Si films were grown on sapphire substrates. The undoped films were highly resistive films but became conductive with the addition of Si. SQUID magnetometry indicated room temperature ferromagnetism in both types of materials. Structural defects had a strong influence on the magnetic ordering of the material, as seen in a drastic reduction of magnetic moment with degrading crystalline quality. Magnetization of the co-doped film increased with Si content, reaching levels higher than that of the undoped material. Gd-doped AlN films grown in a similar fashion also displayed Curie temperatures above room temperature.
Growth and characterization of semi-polar (11-22) GaN with in-situ SiNx interlayers
Authors: Hollander Jonathan , McAleese Clifford , Kappers Menno , Humphreys Colin
Published: April 2011

Semi-polar (1122) GaN films were grown on (1100) m-plane sapphire substrates. Growth demonstrated surface striations aligned perpendicular to the in-plane GaN m-axis. SiNx interlayers were incorporated into the as-grown films with the purpose of decreasing the density of defects in the material. Inclusion of interlayers increased the characteristic length of surface striations and feature size. X-ray rocking curves widths are shown to be correlated to specific threading dislocation geometry. Skew-symmetric omega scan peak broadening suggests a decrease in the proportion of screw-type dislocations to edge-type dislocations with increasing number of interlayers.
Titanium Nitride Epitaxy on Tungsten (100) by Sublimation Crystal Growth
Authors: Mercurio Lisa , Edgar James H. , Du Li , Kenik E. A.
Published: April 2011

Titanium nitride crystals were grown from titanium nitride powder on tungsten by the sublimation-recondensation technique. The bright golden TiN crystals displayed a variety of shapes including cubes, truncated tetrahedrons, truncated octahedrons, and tetrahedrons bounded by (111) and (100) crystal planes. The TiN crystals formed regular, repeated patterns within individual W grains that suggested epitaxy. X-ray diffraction and electron backscattering diffraction revealed that the tungsten foil was highly textured with a preferred foil normal of (100) and confirmed that the TiN particles deposited epitaxially with the orientation TiN(100)‖W(100) and TiN[100]‖W[110], that is, the unit cells of the TiN crystals were rotated 45° with respect to the tungsten. Because of its larger coefficient of thermal expansion compared to W, upon cooling from the growth temperature, the TiN crystals were under in-plane tensile strain, causing many of the TiN crystals to crack.
The Structural and Optical Properties of Self-assembled InGaN/GaN Quantum Dots Grown by Molecular Beam Epitaxy
Authors: Smeeton Tim Michael , Sénès Mathieu , Smith Katherine L , Hooper Stewart E , Heffernan Jon
Published: April 2011

The structural and optical properties of InGaN quantum dots grown by plasma-assisted molecular beam epitaxy (MBE) have been characterised using atomic force microscopy, high-resolution transmission electron microscopy (TEM), Z-contrast scanning TEM, micro-photoluminescence (PL), temperature dependent PL and time-resolved PL. The uncapped InGaN nano-islands have densities of ∼1.5 × 1011 cm−2, heights of (1.7 ± 1.0) nm and diameters of (10 ± 4) nm. These parameters are not substantially changed during overgrowth of a GaN cap and the resulting quantum dots have a composition of In0.15Ga0.85N. The observation of narrow luminescence peaks in micro-PL measurements proves light emission from discrete energy states and the optical properties indicate strong confinement of carriers in the quantum dots and an unusually weak impact of piezoelectric field effects.
Electronic Properties and Stability of Artificial In-N Molecules
Authors: Pozhar Liudmila A , Mitchel William C
Published: April 2011

In the work reported here the Hartree-Fock (HF), restricted open shell HF (ROHF), and multiconfiguration self-consistent field (CI/CASSCF/MCSCF) methods are used to predict electronic properties of several artificial molecules of InAsN and indium nitride whose structure and composition have been derived from those of the corresponding symmetry elements of the zincblende and wurtzite bulk lattices. Both quantum-confined and “vacuum” clusters (whose geometry has been optimized without any spatial constraints applied to the atomic positions) were studied focusing on the electronic energy level structure, direct optical transition energy (OTE), and charge and spin distributions. The obtained results indicate that inclusion of “impurity” atoms (such as As atoms) may enhance stability of both vacuum and confined pyramidal In-N molecules and provide for manipulations of the OTE in a wide range of its values. The CI/CASSCF/MCSCF OTEs of the studied wurtzite-based clusters may also vary in a wide range, from 1.7440 eV for the smallest pre-designed prismatic molecule In6N6 to 6.9780 eV for its almost perfect prismatic “vacuum” counterpart. These evaluations closely correlate with experimental data available in literature.
Design and Optimization of GaN-based Semiconductor Saturable Absorber Mirror Operating at Around 415 nm
Authors: Lin Fen , Xiang Ning , Wang Xin Cai , Arokiaraj Jesudoss , Liu Wei , Liu Hong Fei , Chua Soo Jin
Published: April 2011

A broadband GaN-based semiconductor saturable absorber mirror (SESAM) with a dielectric SiO2/Si3N4 distributed Bragg reflector (DBR) operating at wavelength around 415 nm was fabricated. Serious oscillation fringes due to the light interference were observed in the SESAM's reflectance spectrum. Such oscillation in reflectivity can impede the function of the saturable absorber. Simulations showed that by removing the sapphire substrate and thinning the GaN buffer layer, oscillation fringes could be significantly reduced. Experiments were carried out and the results agreed well with the simulation prediction.
Ultrathin AlN/GaN Heterojunctions by MBE for THz Applications
Authors: Cao Yu , Jena Debdeep
Published: April 2011

High electron mobility transistor (NEMT) based on AlN/GaN can be the source to generate terahertz (THz) radiation. The basic requirements are that a) the electron density in the 2DEG should be large enough for ensuring that the electron-electron scattering mean-free path is much shorter than the distance between the contacts to ensure a viscous, fluid-like flow, and b) the mobility should be high enough such that the possible plasma modes are not strongly damped. To show AlN/GaN HEMT is a qualified candidate for THz generation, we have calculated the plasma frequency for the two-dimensional electron gas (2DEG) in the GaN channel and compared it with other material, such as Si, GaAs and InAs. 3nm AlN has been grown on the GaN substrate by Nitrogen-source radio-frequency molecular-beam expitaxy (RFMBE). The growth temperature has been optimized and found to be 730C. Results from Hall measurement show the electron charge is ∼2.5*1013 cm−2 with the mobility of 530 cm2/Vs (room temperature) and 860 cm2/Vs (77K). A series AlN samples have been grown and studied by AFM, which shows the critical thickness of AlN on GaN is between 4nm and 5nm.
Electrical Detection of Deoxyribonucleic Acid Hybridization With AlGaN/GaN High Electron Mobility Transistors
Authors: Kang ByoungSam , Pearton S. J. , Chen J. J. , Ren F. , Johnson J. W. , Therrien R. J. , Rajagopal P. , Roberts J. C. , Piner E. L. , Linthicum K. J.
Published: April 2011

Au-gated AlGaN/GaN High Electron Mobility Transistor (HEMT) structures were functionalized in the gate region with label free 3′-thiol modified oligonucleotides. This serves as a binding layer to the AlGaN surface for hybridization of matched target Deoxyribonucleic Acid (DNA). X-ray photoelectron spectroscopy (XPS) shows that immobilization of thiol modified DNA covalently bonded with gold on the gated region. Hybridization between probe DNA and matched or mismatched target DNA on the Au-gated HEMT was detected by electrical measurements. The HEMT drain-source current showed a clear decrease of 115 μA as this matched target DNA was introduced to the probe DNA on the surface, showing the promise of the DNA sequence detection approach for biological sensing.
Investigation of Electrical Properties in Si Ion Implanted GaN Layer as A Function of Dose and Energy
Authors: Satoh Masataka , Saitoh T , Nomoto K , Nakamura T
Published: April 2011

The sheet resistance and sheet carrier concentration for Si ion implanted GaN have been investigated as a function of Si ion dosages and ion's energy using van der Pauw method and Hall effect measurement. Si ion implanted GaN is annealed at 1200 °C for 10 sec in N2 gas flow with 50 nm-thick SiNx cap layer to avoid dissociation of GaN. For Si ion energy of 30 keV, the sheet resistance is decreased from 103 to 56 ohm/sq. for the dose ranging from 1 × 1014 to 2 × 1015/cm2. For the Si dose larger than 2 × 1015/cm2, the sheet carrier concentration is saturated around 1 ×s 1015/cm2. Si ion implanted GaN with energy of 50, 80, and 120 keV at a dose of 2 × 1015/cm2 also reveal the sheet carrier concentration of about 1 × 1015/cm2 with the decrease of electron mobility. It is suggested that the implanted Si donors are strongly compensated by the residual implantation-induced defects.
Electron-Beam-Induced Dissociation of Boron-Deuterium Pairs in Diamond
Authors: Barjon Julien , Chevallier Jacques , Jomard François , Baron Céline , Deneuville Alain
Published: April 2011

The diffusion of deuterium in boron-doped homoepitaxial diamond films leads to the passivation of boron acceptors via the formation of B-D pairs. In this letter, the stability of these complexes is investigated under the stress of a low-energy (10keV) electron-beam irradiation at low temperature (∼100K). The dissociation of the complexes is evidenced by cathodoluminescence spectroscopy and is shown to result in the reactivation of most acceptors. The dissociation yield per incident electron is found to be strongly dependent on the e-beam current, which suggests a dissociation involving a vibrational excitation of the complexes by hot electrons.
The Mechanism for Ultrananocrystalline Diamond Growth: Experimental and Theoretical Studies
Authors: May Paul William , Mankelevich Yuri A.
Published: April 2011

Ar/CH4/H2 gas mixtures have been used to deposit microcrystalline diamond, nanocrystalline diamond and ultrananocrystalline diamond films using hot filament chemical vapor deposition. A 3-dimensional computer model was used to calculate the gas phase composition for the experimental conditions at all positions within the reactor. Using the experimental and calculated data, we show that the observed film morphology, growth rate, and across-sample uniformity can be rationalized using a model based on competition between H atoms, CH3 radicals and other C1 radical species reacting with dangling bonds on the surface. Proposed formulae for growth rate and average crystal size are tested on both our own and published experimental data for Ar/CH4/H2 and conventional 1%CH4/H2 mixtures, respectively.
DNA Bonding to CVD Diamond Probed by Scanning Electron-, Fluorescence-, and Atomic force- Microscopy
Authors: Nebel Christoph E. , Uetsuka Hiroshi , Rezek Buhuslav , Shin Dongchan , Tokuda Norio , Nakamura Takako
Published: April 2011

Double stranded desoxyribonucleic acid (ds-DNA) layers, bonded to hydrogen terminated polycrystalline diamond, are characterized by scanning electron (SEM), fluorescence (FM), and atomic force microscopy (AFM). DNA grafting has been achieved using photochemical bonding of ω-unsaturated 10-amino-dec-1-ene molecules. SEM detects local variations of electron affinities on polycrystalline diamond, revealing distinct grain structures. FM applied on fluorescence labeled ds-DNA show laterally varying intensities of typically 20 %, which resembles also grain structure as detected by SEM. Contact and tapping mode AFM characterization reveal a tilted DNA bonding to diamond, dense layer formation which gives rise to smoothening of surface properties. The lateral density variation of DNA is attributed to local variations of the photo-electron emission efficiency which affects the photochemical attachment chemistry of amine linker molecules to diamond.
Synthetic diamond devices for radiotherapy applications: Passive and active dosimetry
Authors: Descamps Caroline , Tromson Dominique , Mer Christine , Nesladek Milos , Bergonzo Philippe
Published: April 2011

For all its remarkable properties, diamond is well known as an interesting material for radiation detection and more particularly for medical uses. Natural diamond use for detection application is limited because of its high cost and the severe gem selection needed to fabricate reproducible and reliable devices. The recent progress of the chemical vapour deposition (CVD) technique offers new possibilities in the fabrication of ionisation chambers as well as thermoluminescent dosimeters for the particular field of radiotherapy. This paper presents the use of CVD diamond for both applications.

For the use of diamond for TL applications, the purpose of this study was to control the trapping levels in the material with deliberate incorporation of impurities in CVD diamond film during the growth.

For ionisation chamber fabrication, the aim was to purposely incorporate defects (with nitrogen incorporation) in the material in order to better understand the modification of the charge transport during irradiation. The first results obtained when the device is used to monitor the beam fluency of a medical accelerator facility are presented here.

For both applications, several preliminary dosimetric parameters were probed and namely the reproducibility of the response, the linearity of the signal with the dose, and for TL dosimeters, both the optical and thermal fadings were carefully studied. Results are extremely encouraging and lead to interesting prospects for the use of diamond for dosimetry.
Low Temperature Aqueous Polymeric Precursor Processing of ZnO:Er Using a Glycerol Chelating Agent
Authors: Choppali Uma , Gorman Brian P
Published: April 2011

Erbium doped ZnO (ZnO:Er) is considered to be a suitable candidate for fabrication of the current injection optical devices. Although ZnO: Er thin films have been synthesized previously by pulsed laser deposition, we present low – temperature processed ZnO:Er thin films from polymeric precursors. In this work, we study the effect of variation of Er doping concentration on the structural and electrical properties of the synthesized films. ZnO nanoparticles of varied Er doping concentration, derived from the prepared polymeric solution, has been spin – coated onto surface modified substrates, and annealed at different temperatures. The effect of Er doping concentration on film grain size and strain was analyzed using X-ray diffraction. XRD data reveals that doping of Er ions reduces compressive strain considerably in the films. It is speculated that the presence of larger Er cations in ZnO cause tensile stress, which neutralizes the inherent compressive stress, observed in undoped ZnO, significantly decreasing and hence, making the films stress free. Crystallite size of ZnO:Er thin films, annealed at 600°C, was calculated to be approximately 12 nm using Scherrer's equation. The surface morphology of the thin films was characterized by both SEM and AFM. Electrical resistivity of the films, annealed at 450oC, was calculated to be 290 Ω-m for 5 at wt% and 125 Ω-m for 10 at wt% ZnO:Er films.
A Comparison of the Mechanical Properties and the Impact of Contact Induced Damage in a- and c- Axis ZnO Single Crystals
Authors: Coleman Victoria A. , Bradby J E , Jagadish C , Phillips M R
Published: April 2011

Nanoindentation studies were conducted on a-axis oriented ZnO single crystals. The mechanical properties and deformation mechanisms were monitored and compared to previously determined data from c-axis material. Hardness and modulus values reveal that a-axis ZnO is significantly softer than c-axis material (measured hardness of 2 ± 0.2 GPa) and behaves much more plastically. Additionally, the influence of contact induced damage upon the defect structure of a-axis material was also examined using cathodoluminescence spectroscopy and monochromatic imaging to monitor the luminescence from indent sites. Deformation directly under the indent site enhanced the occurrence of red defect luminescence, and was attributed to a native defect in ZnO that has a higher formation energy than the defects responsible for the green and yellow visible defect bands, which were present in the ZnO during growth and were found to cluster to the indent site during annealing.
Acceptors in ZnO Studied by Photoluminescence
Authors: Reshchikov Michael A , Garbus James , Lopez Gabriel , Ruchala Monica , Nemeth Bill , Nause Jeff
Published: April 2011

We studied photoluminescence from melt-grown ZnO crystals annealed in air ambient at different temperatures. Along with intense and sharp excitonic lines, we observed several broad bands presumably related to deep acceptors. Two luminescence bands peaking at 1.95 and 2.15 eV at 10 K were studied in detail at different temperatures. The 1.95 eV band has been attributed to transitions from shallow donors to yet unidentified deep acceptor. Very slow non-exponential decay of this band at low temperatures supports such an assumption.
Interface and Luminescence Properties of Pulsed Laser Deposited MgxZn1-xO/ZnO Quantum Wells with Strong Confinement
Authors: Heitsch Susanne , Zimmermann Gregor , Müller Alexander , Lenzner Jörg , Hochmuth Holger , Benndorf Gabriele , Lorenz Michael , Grundmann Marius
Published: April 2011

MgxZn1-xO/ZnO/MgxZn1-xO quantum wells (QWs) (0.12 ≤ x ≤ 0.15) have been grown on a-plane sapphire substrates by pulsed laser deposition. The nominal ZnO well layer thickness lies between 1.2 nm and 6 nm. Atomic force microscopy (AFM) investigations at ZnO/MgxZn1−xO heterostructures show the film-like structure of the ZnO layers. Their root mean square surface roughness of ∼ 0.5 nm gives information about the interface roughness in the QWs. AFM results from the MgxZn1−xO barrier layers show the same surface structure and roughness. We confirmed the lateral homogeneity of the Mg distribution in the MgxZn1−xO barrier layers by scanning cathodoluminescence measurements. The QWs show a bright and laterally homogeneous luminescence, suggesting good crystalline quality of the ZnO wells. The measured QW photoluminescence energies agree well with calculated values and display the presence of the quantum-confined Stark effect. As a result of quantum confinement a high-energy shift of the ZnO excitonic photoluminescence of 222 meV is observed in the thinnest QW.
Raman Scattering Characterization of Implanted ZnO
Authors: Alarcon-Llado Esther , Cusco Ramon , Artus Luis , Gonzalez-Diaz German , Martil Ignacio , Jimenez Juan , Wang Buguo , Callahan Michael
Published: April 2011

In this work we investigate the lattice damage induced in ZnO implanted with potential group V acceptors by means of Raman scattering. ZnO samples were implanted with N and P to high doses and Raman spectra were obtained prior and after rapid thermal annealing (RTA). Characteristic disorder-activated modes are observed in the spectra that can be used to assess the degree of lattice damage. ZnO samples were also implanted with native Zn+ and O+ ions under similar conditions to study specific effects of implantation with N+ and P+. As revealed by the intensity of disorder-activated bands, the implantation induced lattice damage is considerably higher for Zn+ than for the lighter O+ ion. In samples implanted with N+ additional Raman peaks emerge that are not observed either in the samples implanted with the native Zn+ and O+ ions or in the samples implanted with P+, thus pointing to a local vibrational mode of N or a N complex as the origin of these modes. Disorder-activated features are fully removed by RTA, indicating a high degree of lattice recovery by RTA even for the heavily damaged ZnO samples implanted with Zn+.
Fabrication OF ZnO and ZnMgO Thin Films and UV Photodetectors by Mist Chemical Vapor Deposition Method
Authors: Kawaharamura Toshiyuki , Kawaharamura Toshiyuki , Nishinaka Hiroyuki , Fujita Shizuo
Published: April 2011

Deposition of Zn1-xMgxO thin films on glass substrates has been investigated by the simple and cost-effective mist CVD technique. A water solution of zinc acetate and magnesium acetate was used as the source of Zn and Mg. The solution was ultrasonically atomized, and the aerosols hence formed were supplied by the N2 carrier gas to the substrates. The band gap energy of ZnMgO was successfully controlled from 3.25 eV (ZnO) to 3.75 eV with the concentration ratio [Mg]/([Zn]+[Mg]) in the solution. The transparency in the visible region was higher than 90% and the surface RMS roughness was 7.5 nm (an example for ZnO) despite the polycrystalline structure; they are satisfactory for the optical applications. A UV photodetctor with interdigital electrode structure on the ZnMgO surface was fabricated, where the photoresponsivity of 2.6 A/W at 350 nm and the lowest detectable power of about 1 μW were obtained. Although these values are satisfactory for the simple UV detection but the existence of deep defects is deteriorating the dynamic response of the detector device.
Optical and Electrical Properties of Gallium-Doped Mg15Zn85O Thin Films
Authors: Wei Wei , Bhosle Vikram , Jin Chunming , Narayan Roger J
Published: April 2011

Ga-doped Mg0.15Zn0.85O thin films have been grown on fused silica substrates at 350°C with four different gallium concentration values using pulsed laser deposition. X-ray diffraction results indicate that these films were textured with c-plane parallel to the substrate surface. The bandgap of the films were determined based on the absorption measurements. The bandgaps of the Ga-doped thin films shifted to higher energy with respect to that of the unalloyed Mg0.15Zn0.85O thin film due to the band filling effect of electron distribution in the conduction band. Resistivity of the films was measured with four-point probe at temperatures from 295 K to 15 K. The activation energy of the gallium dopants was extracted by fitting the temperature dependent curve of resistivity.
Modification of Blinking Statistics in Solid State Quantum Dot/Conjugated Organic Polymer Composite Nanostructures
Authors: Hammer Nathan I , Early Kevin T , Odoi Michael Y , Tangirala Ravisubhash , Sill Kevin , Emrick Todd , Barnes Michael D
Published: April 2011

Fluorescence intermittency, or “blinking” in quantum dot systems has been the subject of great interest since the first observation of this phenomenon nearly 10 years ago. The stability of quantum dot fluorescence emission is especially important in the context of photovoltaic, optoelectronic, and biological applications, where device performance, or the ability to track labeled particles, is affected adversely by fluorescence intermittency. Single-molecule spectroscopy combined with atomic force microscopy measurements reveal that CdSe quantum dots functionalized with oligo(phenylene vinylene), OPV, ligands exhibit modified optical properties such as suppression of blinking when compared to conventional TOPO covered or ZnS-capped CdSe quantum dots. The blinking suppression is shown to be highly sensitive to the degree of ligand coverage on the quantum dot surface and this effect is interpreted as resulting from charge transport from photoexcited OPV into vacant trap sites on the quantum dot surface. This direct surface derivatization of quantum dots with organic ligands also enables a “tunable” quantum dot surface that allows dispersion of quantum dots in a variety of polymer supported thin films without phase segregation. This facilitates straightforward inclusion of these new hybrid materials into solid state formats and suggests exciting new applications of composite quantum dot/organic systems in optoelectronic systems.
Enhanced Luminescence Efficiency from Hydrogel Microbead Encapsulated Quantum Dots
Authors: Neogi Arup , Ghosh Santaneel , Li Jianyou , Cai Tong , Hu Zhibing
Published: April 2011

In this paper, a novel quantum dot (QD) based nanomaterial system is presented for efficient FRET analysis. The quantum dots have been embedded in hydrogel microspheres based on poly(N-isopropylacrylamide) (PNIPAM) a thermoresponsive polymer that undergoes a volume phase transition across the low critical solution (LCST). The optical properties of the quantum dots entrapped within the gel microspheres has been modified due to change in refractive index, volume density of the surrounding hydrogel medium. The QDs encapsulated in the PNIPAM microspheres showed 100–200 % enhancement in the PL efficiency as the microgels shrank at the temperature above the LCST temperature of the gel.
Elastic Energy Relaxation in Buried Quantum Dots
Authors: Chaldyshev Vladimir V , Kolesnikova Anna L. , Romanov Alexei E.
Published: April 2011

We theoretically analyze three models, which correspond to three different ways of the elastic energy relaxation in buried quantum dots. The first model considers formation of a pair of prismatic dislocation loops. One of them lies on dot/matrix interface, whereas the other is a satellite and locates in the adjacent matrix. The second model also includes the satellite loop and differs from the first one by non-local reduction of the dot plastic distortion. The origin of the satellite loop is the materials conservation requirement. The third model considers the case when this requirement is violated and only the misfit dislocation loop is formed. We determine the critical radii of the dots and loops, as well as the dependence of the satellite loop size on the dot size. The model calculation are compared to the relevant experimental data.
Controlling Lateral Ordering of InGaAs Quantum Dots with Arsenic Background
Authors: Marega Euclydes , Waar Ziad Abu , Hussein Mohammad , Salamo Gregory
Published: April 2011

We present in this work a method to control lateral ordering of In0.4Ga0.6As quantum dots (QDs) using the surface anisotropic and the growth environment. We have shown experimentally that using As2 molecules instead of As4 as a background flux is promising to control the diffusion of adatoms in away to make it possible to control the ordering of In0.4Ga0.6As QDs together with the GaAs surface properties specially for GaAs (100) surfaces. For GaAs (n11)B surfaces the As4 provides a better two dimension ordering than the As2 environment. Our results are consistent with reported experimental and theoretical studies on surface structure and diffusion mechanism over GaAs surface.
Nano-Graphitization in Amorphous Carbon Films via Electron Beam Irradiation and the Iron Implantation
Authors: Aizawa Tatsuhiko , Iwamura Eiji
Published: April 2011

Nano-graphitization from amorphous carbon state is assisted by the electron beam irradiation. An inter-columnar region in the amorphous carbon films with low atomic and electron densities is controlled to have a graphitic structure with relatively low dose electron beam irradiation. This amorphous carbon ? beam interaction generates a new type of carbon hybrids where amorphous carbon phase columns are sustained by the graphitic inter-columnar network. This hybrid film has an exotic mechanical and tribologic response: extraordinary reversible deformability up to 8 – 10 % normal strain, high wearing resistance and low friction at high normal pressure. A combination of iron implantation with this electron irradiation provides us the other nano-graphitization process. An amorphous carbon film including the implanted iron atoms is chemically modified to have a columnar graphitic structure by the electron beam irradiation. In this post-implantation electron beam irradiation, the basic graphitic units with 1-2 nm in size are controlled to align vertically along the film thickness. This type of nano-graphitization has a strong dependency on the iron doses before electron beam irradiation. The above two types of nano-graphitization provides us a new tool to explore the functionalized structural thin films in application.
Room-Temperature Nanoimprint Lithography
Authors: Matsui Ken-Ichiro , Matsui Shinji
Published: April 2011

Room-temperature nanoimprint lithography (RT-NIL) using spin-coated hydrogen silsesquioxane (HSQ) resin as the replication material was developed. HSQ pattern with 50 nm linewidth was successfully obtained by the RT-NIL. Postbaking temperature dependence of a HSQ imprinted depth on a mold linewidth was investigated. HSQ imprinted depth had a dependence on the mold linewidth. This revealed that the RT-NIL is suitable for the linewidths of below 1 mm. Furthermore, we have also developed a new imprinting technique that uses liquid-phase hydrogen silsesquioxane (HSQ) as an alternative to the spin-coated HSQ resin. The liquid-phase HSQ imprint technique enabled fabrication of various HSQ patterns with a wide range of linewidths from 25 nm to 300 mm. Arbitrary patterns, including both submicron and greater than 100 micron patterns, were simultaneously replicated with a one-step imprint process, something very difficult to accomplish with spin-coated HSQ. Moreover, after imprinting, the residual HSQ layer in the compressed area was less than 10 nm thick.
Nanostructural Evolution in Non-epitaxial Growth of Thin Films
Authors: Hu Minghui , Noda Suguru , Komiyama Hiroshi
Published: April 2011

The initial growth of non-epitaxial thin films was studied and discussed using the concept that thermodynamics controls the unit-structure within the surface diffusion length of deposits, whereas kinetics controls the ensemble-structure on a large scale. Three basic topics, growth mode (island shape), crystalline (island inner) structure, time-dependent properties of island ensemble (island size, distance, and density), are summarized based on the investigation of thin film growth of metals on TiO2, Cu on SiO2 and Ti/SiO2. This study provides fundamental understanding of structural control during thin film growth, and further can be applied to various advanced devices for electronics, photonics, catalysis, and energy applications.
Process Integration of Composite High-k Tunneling Dielectric for Nanocrystal Based Carbon Nanotube Memory
Authors: Ganguly Udayan , Hou Tuo-Hung , Kan Edwin Chihchuan
Published: April 2011

Recently, metal nanocrystal based carbon nanotube memory has been demonstrated with sub-5V low bias programming, single electron sensitivity but poor room temperature retention. The process integration of an ultra-thin tunnel dielectric is essential for lateral, vertical scaling and reliable room temperature operation. Low defect density and conformal deposition on the nanotube are required to enhance the performance as a tunnel barrier. Additionally, Au contamination in the CNT decreases the on/off current ratio in the CNTFETs by substantially increasing the off current. Consequently, the dielectric should function as a good diffusion barrier for Au in the nanocrystals. We have explored composite tunneling dielectric film with SiO2 seed layer for conformal high-k deposition to demonstrate minimal Au contamination and improved retention. Room temperature retention of better than three days has been observed.
A Nanodamascene Process to be used as a Building Block for Nanodevices
Authors: Dubuc Christian , Beauvais Jacques , Drouin Dominique
Published: April 2011

We report a single-electron transistor concept and its related process enabling the fabrication of ultrasmall junction capacitance. The method utilizes a nanodamascene approach where trenches in silicon oxide are covered with a filling material and planarized with chemical mechanical polishing. Single-electron transistors fabricated with this approach were characterized up to 433 K and demonstrated that the nanodamascene process has high resolution, is relatively simple and is highly scalable.
Fabrication of Tin Loaded Resorcinol Formaldehyde Aerogel Spheres for Extreme Ultraviolet Source Emission
Authors: Paguio Reny R , Nikroo Abbas , Frederick Chris A , Hund Jared F , Thi Mary
Published: April 2011

Low density Sn doped resorcinol formaldehyde aerogels were fabricated for extreme ultraviolet (EUV) source emission lithography experiments (EUVL). EUVL is a candidate to succeed conventional optical lithography. EUVL requires a reliable emission (13.5 nm) source. One type of source is a laser-produced plasma. Several laser-plasma source materials have been considered such as lithium, xenon and tin. Tin is considered ideal because it has a high conversion effeciency. However, solid tin targets create a large quantity of debris which can damage the optics of the laser system. As a solution to this problem, we minimized the amount of tin by dispersing it in a low density resorcinol formaldehyde (R/F) matrix. These targets were fabricated into small spheres using the microencapsulation method. Initial experimental results show that these targets yield a similar intensity in the EUV regime when compred to a full density Sn target.
Tin Oxide Based Transparent Ferromagnetic Semiconductor Thin Films by Spray Pyrolysis
Authors: Kashyap Subhash Chand , Gopinadhan Kalon , Chaudhary Sujeet , Pandya Dinesh K.
Published: April 2011

Cobalt- and manganese-incorporated SnO2 thin films exhibiting room temperature ferromagnetism have been prepared by spray pyrolysis technique. Analysis of structural, magnetic and electrical properties of Sn1−xCoxO2−δ thin films indicates that the origin of ferromagnetism, seen for x<0.125, lies in the polarization of free carriers, leading to the necessary exchange interaction. The films exhibit a Curie temperature > 500K. The XRD study indicates that Sn1−xCoxO2−δ films with x<0.125 is single phasic with no evidence of any Co clusters or magnetic oxides, which supports the intrinsic nature of the ferromagnetism. The electrical transport studies indicate that extra electrons are generated on Co-incorporation in the SnO2 lattice. In the case of Sn1−xMnxO2·δ films, ferromagnetism is observed in a narrow range of manganese (0.075≤x≤0.10) with an associated increase in carrier concentration. The detailed analysis of various properties suggests that Mn-ions have been incorporated in the SnO2 lattice, and there is absence of any Mn-clusters, Mn-related secondary phases.
AC-Susceptibility Measurements of the Superparamagnetic Relaxation in Systems of Ni1−xZnxFe2O4 Nanoparticles
Authors: Adair Antony , Galindo Jose T. Elizalde , Botez Cristian , Flores Verónica Corral , Baques Dario Bueno , Cobas Luis Fuentes , Matutes-Aquino José A.
Published: April 2011

We have investigated the effect of Zn-doping on the superparamagnetic relaxation of nanosized nickel ferrite particles. Our temperature-resolved AC-susceptibility data demonstrate that the relaxation of these systems is well described by an Arrhenius-type law, behavior which allows a precise determination of the effective energy barrier to magnetization reversal, Ueff. We observe that the Zn-content dependence of Ueff exhibits a pronounced maximum when half on the magnetic Ni2+ ions are replaced by nonmagnetic Zn2+. The average blocking temperature (measured at a given frequency) shows a similar behavior. The observed increase of Ueff is attributed to an enhanced magnetic anisotropy induced by the crossover between two magnetocrystalline regimes. Our findings demonstrate the ability to control the superparamagnetic relaxation of ferrimagnetic spinel nanoparticles through chemical manipulations.
Thermo-optical Properties of Nanoparticles and Nanoparticle Complexes Embedded in Ice: Characterization of Heat Generation and Actuation of Larger-scale Effects
Authors: Richardson Hugh H. , Hickman Zachary N. , Thomas Alyssa C. , Kordesch Martin E. , Govorov Alexander O.
Published: April 2011

We have investigated the thermo-optical properties of gold NPs embedded in an ice matrix [1]. Resonant laser light of relatively weak intensity is able to melt ice with embedded Au NPs, whereas even a very intense laser beam does not melt ice alone. This comes from strong absorption in Au NPs in the regime of plasmon resonance. By recording time-resolved Raman signals, we observe the melting process and determine the threshold melting power , where is the background temperature. We also observe relatively large scattering in the threshold laser intensity that leads to melting of the ice because of the mesoscopic nature of the sample. We can understand this observation using the TEM images of NPs, showing that geometry of NP complexes varies greatly. In our recent theoretical paper we showed that the local temperature inside and around a NP complex depends strongly on its geometry, and this leads to large scattering for the measured as a function of the reduced temperature, for different complexes [2].

We recently discovered that NPs immobilized on glass surfaces can be characterized by single particle spectroscopy. Single and small NP clusters can be discriminated using the integrated intensity of the plasmon emission band. A cluster of four gold NPs has ∼ 4 times the intensity of a single gold NP. When the NPs are aggregated into a cluster then broadening of the intensity profile plot is not observed Gold NPs that are not clustered together but are found within the excitation volume will lead to a broadening of a cross sectional slice. We will use these principles to determine the amount of heat generation from single and clustered gold NPs.

[1] H. H. Richardson, Z. N. Hickman, A. O. Govorov, A. C. Thomas, W. Zhang, M. E. Kordesch, Nano Lett. (2006); DOI: 10.1021/nl060105l.

[2] A. O. Govorov, H. H. Richardson, W. Zhang, and T. Skeini, Nanoscale Res. Lett. 1, 100101 (2005).
Influence Of Cation Vacancies on the Ferroelectric Properties of SBT Doped with Praseodymium
Authors: Mata Jorge , Durán Alejandro , Martínez Eduardo , Siqueiros Jesus
Published: April 2011

Dielectric and ferroelectric properties were studied in Sr0.85−yPr0.15VyBi2Ti2O9 polycrystalline samples where cation vacancies were induced. DRX characterization shows that the Aurivillius structure can accept 10% of induced vacancies without precipitation of second phases. Thermoelectric analysis and ferroelectric hysteresis measurements show that the vacancies modify the transition temperature Tc and slightly the polarization values. From the ε-T curves it was observed that the polarization magnitude and Tc are affected as a consequence of the induced vacancies. A broad peak at Tc, typical of the diffuse phase transition behavior of this material was also observed. Furthermore, the induced vacancies in praseodymium-modified SBT produce an increased on Tc from ∼180 to ∼240 °C, these facts show that induced vacancies in the structure are a tuning mechanism for the dielectric and ferroelectric properties.
Dielectric Permittivity Enhancement in PZT by Light Doping with Gd
Authors: Portelles Jorge J. , Almodovar Nelson S , Fuentes Juan , Martinez Eduardo , Raymond Oscar , Heiras Jesus L , Siqueiros Jesus M
Published: April 2011

PbZr0.53Ti0.4703 doped with 0.6% at. of Gd2O3 has been produced following the traditional solid state reaction technique. The ferro-paraelectric transition temperature is reduced from 386 °C to 352 °C. Remnant polarization and coercive field measurements were made from the hysteresis loops obtained at 23 °C and at different applied electric fields up to a maximum of 17 kV/cm. Piezoelectric performance was studied in the 4 Hz to 4 MHz frequency range at 25 °C and the radial electromechanical coupling factor was determined. A detailed electrical conductivity study in the 30-450 °C temperature range is performed in a wide frequency interval. The different participating transport mechanisms are elucidated and the corresponding activation energies were determined by fitting the experimental data. In particular, in the 30 to 300 °C temperature interval, the ac conductivity follows Jonscher universal relaxation law.
Brillouin and Raman Scattering Studies on the Relaxor Ferroelectric 0.71Pb(Ni1/3Nb2/3)O3-0.29PbTiO3 Single Crystal
Authors: Tsukada Shinya , Ike Yuji , Kano Jun , Wang Ruiping , Shimojo Yoshiro , Sekiya Tadashi , Kojima Seiji
Published: April 2011

Brillouin and Raman spectra of a 0.71Pb(Ni1/3Nb2/3)O3-0.29PbTiO3 single crystal were measured in two light scattering geometries to elucidate the origins of central peaks that is related to the dynamics of the polar nanoregions. Two Lorentzian-type central peaks exist in the Brillouin spectra. The shape and the full width at half maximum of the broader peak in Brillouin spectra are almost same as that observed in Raman spectra. This indicates that two relaxations occur in the polar nanoregions. These two processes might be originated from the different switching directions of polarization.
Advanced Thermal Interface Materials
Authors: Zhang Yimin , Xiao Allison , McVey Jeff
Published: April 2011

Thermal interface materials (TIMs) are used to dissipate thermal energy from a heat-generating device to a heat sink via conduction. The growing power density of the electronic device demands next-generation high thermal conductivity and/or low thermal resistance TIMs. This paper discusses the current state-of-art TIM solutions, particularly fusible particles for improved thermal conductivity. The paper will address the benefits and limitations of this approach, and describe a system with unique filler morphology. Thermal resistance and diffusivity/conductivity characterization techniques are also discussed.
Smart Lead-Free Solders via Shape-Memory Alloy Reinforcement
Authors: Dutta Indranath , Majumdar Bhaskar S. , chen Tiandan , Chung Koh Choon , Ye Bing
Published: April 2011

Microelectronic solder joints are exposed to aggressive thermo-mechanical cycling (TMC) during service, resulting in strain localization near solder / bond-pad interfaces, which eventually leads to low-cycle fatigue (LCF) failure of the joint. In order to mitigate these strain concentrations and thereby improve LCF life, a ‘smart solder’ reinforced with a martensitic NiTi based shape memory alloy (SMA) is being developed. This paper presents an overview of processing, characterization and modeling of these composite solders, and articulates the role of NiTi particles on strain evolution in composite solders. Based on finite element modeling and experiments on model single fiber composites, it is shown that NiTi pariculate reinforcements can reduce inelastic strain levels in the solder via shape recovery associated with the B19′→B2 transformation. In situ TMC studies in the SEM, in conjunction with strain analysis via digital image correlation, show evidence of reverse deformation in the solder commensurate with the NiTi phase transformation, demonstrating the conceptual viability of the smart solder approach. Details of processing and joint formation, and the resultant microstructures of smart solder are discussed. Finally, results of TMC experiments on monolithic solder and NiTi/solder composite joints are reported, highlighting the beneficial effect of shape-memory transformation in reducing inelastic strain range, and hence enhancing the LCF life, of solders.