bluuebunny/crossref_metadata_2025 huggingface dataset:
Recent Progress on GaN HEMTs
Authors: Nakajima Shigeru , Tateno Yasunori , Sano Seigo
Published: February 2009

This paper is overviewed the recent progress on GaN HEMTs. High power, high frequency and high efficiency performance are reported. In addition, the results about long-term reliabilities and good manufacturability demonstrate that GaN HEMTs are ready for mass production.
Optimization of GaN Barriers During the Growth of InGaN/GaN Quantum Wells at Low Temperature
Authors: Kasarla Kalyan R , Chiang Wenyu , Rahimi Ronak , Korakakis D.
Published: February 2009

InGaN/GaN MQWs are grown on c-plane sapphire substrates using a low pressure metal organic vapor phase epitaxy (MOVPE) system. Trimethylgallium (TMGa), Triethylgallium (TEGa), Trimethylindium (TMIn) and ammonia were used as precursors for Ga, In and N, respectively and the growths were carried out at low temperature. Structural properties of grown MQWs are characterized using atomic force microscopy (AFM), and scanning electron microscope (SEM) and x-ray diffraction technique (XRD) is used to calculate the Indium incorporation in these MQWs. Surface morphologies over large areas of InGaN/GaN MQWs are observed using the tapping mode AFM; results indicate the surface roughness depends on the barrier thickness. Density of V- defects, effect of barrier width on the surface morphology and also on V-defect density will be presented and discussed.
Fabrication and Electrical Properties of Metal/Double-Insulator/Metal Diode
Authors: Choi Kwang Nam , Park Jun Woo , Lee Hosun , Chung Kwan Soo
Published: February 2009

We have fabricated two metal/double insulator/metal diodes using a sputtering system and atomic layer deposition. Here, we show metal/double insulator/metal diode applied as a switch element. The diode exhibits good rectifying characteristics at room temperature. We used the electrode material with Pt and insulators were HfO2/ZrO2 and NiO/ZnO each. The devices were fabricated using the lithographic system and top electrode sizes were 30 µm x 30 µ;m. The double insulator diode produces an enhanced nonlinearity by incorporating two adjacent oxides instead of the single oxide layer of the MIM diode. In the double insulator diode the mode of tunneling under positive applied biases can be made different from that under negative applied biases resulting in improved asymmetry.
Optimization of Samarium Oxide Deposition on Gallium Arsenide
Authors: Stewart Anthony Duane , Scheuermann Andrew G , Gerger Andy P , Gila Brent P , Abernathy Cammy R , Pearton Stephen J
Published: February 2009

Samarium oxide (Sm2O3) and samarium gallium oxide (SmxGa1-x)2O3 have been proposed as candidate dielectric materials for the development of gallium arsenide (GaAs) Metal Oxide Semiconductor Field Effect Transistor (MOSFET) technology. Growth of thin (20nm-50nm) Sm2O3 and (SmxGa1-x)2O3 layers on GaAs substrates via plasma-assisted molecular beam epitaxy (MBE) has been performed using a range of growth temperatures and samarium cell temperatures. X-ray photoelectron spectroscopy (XPS) of the deposited films showed evidence of unbonded Sm metal in the films which decreased with decreasing Sm cell temperature, but was relatively independent of substrate temperature. Stoichiometry of the oxide was found to be independent of substrate temperature, but increased in oxygen to metal ratio as the Sm cell temperature was decreased. Decreasing the Sm cell temperature also suppressed the formation of the monoclinic phase and promoted the growth of the cubic phase. Films grown at higher (500şC) temperature showed the presence of a crystalline interface, but relatively high surface roughness and the presence of multiple crystalline phases. Current-voltage analysis of one hundred micron diameter MOS diodes showed breakdown fields at 1 mA/cm2 of up to 4.35 MV/cm. Breakdown field was found to decrease with increasing Sm unbonded metal content in the films. The effect of stoichiometry and phase distribution on the interface state density (Dit) and capacitance-voltage behavior of MOS diodes was also investigated.
Formation of Doping Profiles in Float Zone Silicon by Helium Implantation and Plasma Hydrogenation
Authors: Job Reinhart , Niedernostheide Franz-Josef , Schulze Hans-Joachim , Schulze Holger
Published: February 2009

By means of two-point-probe Spreading Resistance (SR) analyses, the formation and evolution of hydrogen-related and vacancy-related donor and acceptor states were studied in helium implanted and subsequently hydrogen plasma-treated n-type Float-Zone (FZ) silicon wafers. He-implantation was carried out at 3.75 MeV, applying fluences of 1×1014 cm-2 and 2×1013 cm-2. After 15-min post-implantation H-plasma exposures at substrate temperatures between 350 °C and 500 °C, distinct surplus doping profiles were observed in the subsurface layers of the treated FZ Si samples down to about 20 μm depth. Enhanced donor concentrations could be observed as well acceptor-like states, at least partially compensating for the initial n-type doping, so that even buried p-type layers can be created under appropriate process conditions. The nature of the defect complexes that were responsible for the observed doping profiles in the subsurface layer of the studied samples will be discussed.
Search For New Piezoelectrics
Authors: Ganesh Panchapakesan , Cohen Ronald
Published: February 2009

Recent first principles simulations using density functional theory and novel low temperature x-ray diffraction experiments show the existence of a high pressure morphtotropic phase boundary (MPB) in pure PbTiO3. In this paper we apply chemical pressure by substituting smaller atoms in the ABO3 ‘A’ and ‘B’ sites. We find that the ground state of layered PbSnTiO3 (PSnT) is Pmm2, and for rocksalt SnGeTiO3 and PbGeTiO3 is R3m. The polarization of PbSnTiO3 is large (1.13,0,0)C/m2 and is due to the large Born effective charge of the small ‘Sn’ atom. We estimate the d33 for PSnT to be about 2400 pC/N, which is as large as that of currently used relaxor ferroelectrics.
Enhanced 1.54 μm Luminescence in Er-doped ZnO Nanoparticle Films via Indirect Excitation
Authors: Pan Zhengda , Morgan S. H. , Ueda A. , Aga R. , Xu H. Y. , Hark S. K. , Mu R.
Published: February 2009

Photoluminescence (PL) of Er-doped ZnO nanoparticle films was studied. The films were fabricated using e-beam evaporation. The films were subsequently annealed at 700 °C in air for an hour. The atomic force microscopy (AFM) image revealed nano-sized ZnO particles. PL was measured at two excitation wavelengths, 325 and 514.5 nm. The 325 nm is used for exciting the ZnO host semiconductor and 514.5 nm is used for directly exciting Er3+ ions in the ZnO films. Er3+ luminescence was observed from the annealed film using either indirect (325 nm) or direct (514.5 nm) excitations. It has been found that the indirect excitation is about 40 times more efficient than the direct excitation in producing 1.54 μm PL. With indirect excitation, the Er3+ luminescence observed is attributed to energy transfer from ZnO host to the Er3+ ions doped. Energy transfer from e-h pairs resulting from ZnO host excitation may provide efficient routes for exciting Er3+ ions inside nano-crystalline particles of the films.
Three-Dimensional Integration Technology for Advanced Focal Planes
Authors: Keast Craig Lewis , Aull Brian , Burns James , Chen Chenson , Knecht Jeff , Tyrrell Brian , Warner Keith , Wheeler Bruce , Suntharaligam Vyshi , Wyatt Peter , Yost Donna
Published: February 2009

We have developed a three-dimensional (3D) circuit integration technology that exploits the advantages of silicon-on-insulator (SOI) technology to enable wafer-level stacking and micrometer-scale electrical interconnection of fully fabricated circuit wafers. This paper describes the 3D technology and discusses some of the advanced focal plane arrays that have been built using it.
Statistical Analysis of the Influence of Thinning Processes on the Strength of Silicon
Authors: Yang Yu , Cotrin Teixeira Ricardo , Roussel Philippe , Swinnen Bart , Verlinden Bert , De Wolf Ingrid
Published: February 2009

Wafer thinning, one of the key enabling techniques for 3D integration, is widely studied due to its impact on Si breakage strength. However, most studies only focused on the average strength, without checking the failure mechanisms. This may result in misleading conclusions and the mechanism of breakage is still ambiguous.
In this paper, the mechanical strength of wafers that were thinned using different methods [rough grinding(RG), fine grinding(FE), plasma etching(PE), chemical mechanical polishing(CMP)] was evaluated statistically and through failure analysis. The results provide the industry guidance on their wafer thinning strategy.
Si wafers were thinned down to 300μm by different thinning techniques: only RG; RG+FG; RG+FG+10μm CMP and RG+FG+10μm PE. Next the samples were diced into strips and the strength was tested using a 4-point bending test.
The breakage strength of the dies was plotted in Weibull graphs and on wafer maps. Both RG and PE samples showed a strong bimodal distribution. On the other hand, both FG and CMP wafers showed a monomodal behaviour. This observation was unexpected and until now never reported in literature.
The RG wafer has large surface grooves and is the weakest one, as expected. The bimodal distribution of the strength of RG-dies could be related to the direction of the grinding marks on the surface (along width or length of the Si strips). There is a direct correlation with the position of the dies on the wafer and the bimodal distribution. Samples with lines perpendicular to the tensile stress (along the width of the strips) are more vulnerable than the rest. The fracture on these samples propagates vertically from the ground surface, along the {110} plane. The others are stronger and break along the {111} plane.
FG improves both the surface roughness and the strength compared to RG. The Weibull curve, with a monomodal behavior, shifts to a higher breakage strength, indicating that the effect of the grooves on the breakage strength is removed by FG.
After CMP, the strength raises 17% compared to FG-Si due to the removal of surface roughness. Similarly, PE increases the average strength by 15% from FG. However, the Weibull plot shows that after PE, there is again a bimodal failure distribution. The weaker one falls on top of the FG distribution and the stronger one mixes up with the CMP. This indicates that although a large fraction of these samples have a similar strength as CMP, but some parts still have defects, probably local roughness related, that serve as easy initiation of fracture.
This study shows that the orientation of the grinding marks plays an important role in determining the fracture plane and thus the strength. FG can efficiently remove this effect. We also showed for the first time that even after PE there is a bimodal strength distribution. Part of the dies has the same strength as the ones after CMP, but part of the population still has a lower strength.
Characterization of texture and microstructure of electrodeposited Ni layers
Authors: Noda Homuro , Shibata Akinobu , Sone Masato , Ishiyama Chiemi , Higo Yakichi
Published: February 2009

The texture and microstructure of electrodeposited Ni layers formed in an additive-free Watt's bath were investigated. The microstructure of the electrodeposited Ni layer consists of fine columnar grains extending along the growth direction. The major texture components of electrodeposited Ni layers on Ni-P substrate were (112) and (110) fibers. On the other hand, electrodeposited Ni layers on Cu substrate had a strong (110) fiber texture. In the vicinity of the interface between the electrodeposited Ni layer and the Cu substrate, obvious epitaxial regions were not observed. Many twins parallel to the growth direction were observed in the electrodeposited Ni layer. It is suggested that grains with a twin relationship grew preferentially during the electrodeposition reaction.
The National Nuclear Laboratory and Collaborative University Research in the UK
Authors: Fairhall Graham A.
Published: February 2009

The UK has recently established its first National Nuclear Laboratory (NNL). This has been formed out of the Nexia Solutions organisation, formally the Research and Technology subsidiary of BNFL. Over the next year the NNL will develop so that it can fulfil its mission, which will include the development and maintenance of key skills and undertaking strategic R&D programmes both in the UK and in international collaborations.
A key role of the NNL will be to enhance its interactions with universities to facilitate skills transfer into the nuclear industry as well as support its R&D programmes. Over the past decade the NNL and its predecessor has already established close relationships with leading universities in the UK including Sheffield, Manchester, Leeds and Imperial College London. One of the key objectives of the NNL has been to work in an integrated way with university researchers with programmes spanning fundamental research through to applied R&D.
This paper describes the future plans for working with universities as the NNL develops, building on the success to date.
Joint R&D research programmes already cover many important areas for the nuclear industry. This includes support for the UK Pu disposition programme where R&D at the Immobilisation Science Laboratory, Sheffield has included investigating a range of ceramic and glass wasteforms which has allowed a number of ceramic wasteforms to be down selected for detailed evaluation. Cementation research has included understanding wasteform performance, for example long-term durability. This has involved work on determining free water and the implications for immobilisation of reactive wastes.
Other work involving the NNL and Universities, in particular at Leeds and Manchester, has considered the characteristics and behaviour of intermediate and high level waste sludges. This has included determining the chemical speciation of actinides and fission products, and physical properties of active and simulated sludges using experimental and modelling techniques.
A significant programme on environmental work has been undertaken by the NNL. In research applicable to low level waste disposal and contaminated land reactive transport modelling is utilised to apply experimental and field based research in environmental geochemistry and radiochemistry undertaken by university collaborators. This paper will describe a number of examples of R&D carried out by NNL in association with its university partners.
Calcium Phosphate: A Potential Host for Halide Contaminated Plutonium Wastes
Authors: Metcalfe Brian L. , Donald Ian W. , Fong Shirley K. , Gerrard Lee A. , Strachan Denis M. , Scheele Randall D
Published: February 2009

The presence of significant quantities of fluoride and chloride in four types of legacy wastes from plutonium pyrochemical reprocessing required the development of a new wasteform which could adequately immobilize the halides in addition to the Pu and Am. Using a simulant chloride-based waste (Type I waste) and Sm as the surrogate for the Pu3+ and Am3+ present in the waste, AWE developed a process which utilised Ca3(PO4)2 as the host material. The waste was successfully incorporated into two crystalline phases, chlorapatite, [Ca5(PO4)3Cl], and spodiosite, [Ca2(PO4)Cl]. Radioactive studies performed at PNNL with 239Pu and 241Am confirmed the process. A slightly modified version of the process in which CaHPO4 was used as the host was successful in immobilizing a more complex multi-cation oxide–based waste (Type II) which contained significant concentrations of Cl and F in addition to 239Pu and 241Am. This waste resulted in the formation of cation-doped whitlockite, Ca3-xMgx(PO4)2, β-calcium phosphate, β-Ca2P2O7 and chlor-fluorapatite rather than the chlorapatite and spodiosite formed with Type I waste.
Hybrid Membranes Based on Aromatic Polymer Blends for Fuel Cell Applications
Authors: de Bonis Catia , D'Epifanio Alessandra , Mecheri Barbara , Di Vona Maria Luisa , Trombetta Marcella , Traversa Enrico , Licoccia Silvia
Published: February 2009

Blend membranes based on sulfonated polyetheretherketone (SPEEK) and containing 5 wt.% of silylated and sulfonated polyphenylsulfone (SiSPPSU) were prepared and characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR/FTIR) and by electrochemical impedance spectroscopy (EIS). Tests in a direct methanol fuel cell station were also performed.
The experimental results demonstrated that the presence of hybrid polymer SiSPPSU allowed to increase the proton conductivity of electrolyte and to improve its performance under fuel cell operating conditions. Due to its satisfactory properties, SPEEK/ SiSPPSU blend membrane has a potential use in DMFCs operating at intermediate temperatures.
Forging of Steam Turbine Blades with an Fe3Al-based Alloy
Authors: Janschek Peter , Bauer-Partenheimer Knut , Krein Ronny , Hanus Pavel , Palm M.
Published: February 2009

The forging capabilities of two high-strength Fe3Al-based alloys have been evaluated. Based on these results one alloy has been used for forging steam turbine blades. Blades of about 600 mm length were successfully forged by a standard procedure otherwise employed for forging of 9-12 wt.% Cr steels. The forged steam turbine blades showed very good form filling, no pores and smooth surfaces. The blades were finished by cutting and grinding by standard procedures. The microstructure consists out of a Fe3Al matrix with additional Laves phase which predominantly precipitated on grain boundaries. The large Fe3Al grains in the cast precursors did only partially recrystallise during forging. This may be partially due to pinning of the grain boundaries by Laves phase precipitates. Cracks may form at those grain boundaries which are decorated with these brittle precipitates.
On the Effect of Strain Rate and Temperature on the Yield Strength Anomaly in L21-structured Fe2AlMn
Authors: Wittmann Markus W. , Chang Janelle M. , Liao Yifeng , Baker Ian
Published: February 2009

The effects of strain rate and temperature on the yield strength of near-stoichiometric Fe2AlMn single crystals were investigated. In the temperature range 600-800K the yield stress increased with increasing temperature, a response commonly referred to as a yield strength anomaly. No strain rate sensitivity was observed below 750K, but at higher temperatures the yield stress increased with increasing strain rate. Possible mechanisms to explaining the effects of temperature and strain rate are discussed.
Intermetallic Compounds in Co-base Alloys–Phase Stability and Application to Superalloys
Authors: Ishida Kiyohito
Published: February 2009

The phase stability of intermetallic compounds of Co3X has been discussed with a focus on the γ' phase of Co3Al, Co3W and Co3(Al, W) with the L12 structure. The critical temperatures of the γ' phase of Co3Al, Co3W and Co3(Al, W) compounds are estimated to be about 870 , 980 and 1076 , respectively. The effect of alloying elements on the Co-Al-W -base alloys was found to be very similar to that of Ni-base superalloys, where Ti, Ta, Nb and V are the γ' stabilizing elements, while Mn, Fe and Cr are the γ' forming elements. The mechanical properties of Co-Al-W-base alloys were also found to be similar to those of Ni-base alloys. In particular, the flow strengths of Co-Al-W-base alloys at temperatures above 800 were comparable or higher than those of Ni-base superalloys, which implies that the Co-base superalloys strengthened by the γ' phase have great potential as a new type of high-temperature alloys.
Mechanical Testing and Material Modeling of Thermoplastics: Polycarbonate, Polypropylene and Acrylonitrile-Butadiene-Styrene
Authors: Bouvard Jean-Luc , Brown Hayley , Marin Esteban , Wang Paul , Horstemeyer Mark
Published: February 2009

The work presents some results of an ongoing research program aimed at building a material database and material models for specific types of polymers. Results for three thermoplastics are the focus of the present article: polycarbonate, polypropylene, and acrylonitrile-butadiene-styrene. Uniaxial compression / tension tests at room temperature and different strain rates have been performed to characterize their mechanical response. A rate-dependent material model has been developed and implemented in a finite element code to predict such mechanical behavior. The model predictions have shown good agreement with the tests results.
A Molecular Dynamics Study of the Rotational Dynamics and Polymerization of C60 in C60-Cubane Crystals
Authors: Coluci Vitor , Sato Fernando , Braga Scheila F. , Skaf Munir S. , Galvao Douglas S
Published: February 2009

Recently, heteromolecular crystals of fullerene C60 and cubane (C8H8) have been synthesized. For some temperatures the C60 molecules are free to rotate whereas cubanes behave like a static bearing in a so-called rotor-stator phases. In this work we report classical and tight-binding molecular dynamics simulations in order to investigate the rotor-stator dynamics and polymerization processes. Our results show that, for 200 K and 400 K, cubane molecules remain basically fixed, presenting only thermal vibrations within the timescale of our simulations, while C60 fullerenes show rotational motions. Fullerenes perform “free” rotational motions at short times (< 1 ps), small amplitude hindered rotational motions (librations) at intermediate times, and rotational diffusive dynamics at long times (> 10 ps). Random copolymerization among cubanes and fullerenes were observed when temperature is increased, leading to the formation of a disordered structure.
Statistics of Internal Elastic Fields and Dislocation Density Tensor in Deformed FCC Crystals
Authors: Deng Jie , El-Azab Anter , Larson B.C.
Published: February 2009

The statistics of internal elastic fields and dislocation density tensor associated with arbitrary 3D dislocation distributions have been modeled using probability density function and pair correlations. Numerical results for these quantities have been obtained for dislocation structures generated by the method of dislocation dynamics simulation.
Nanomechanical study of synthesis of metallic core-shell clusters via coalescence
Authors: Shintani K. , Mizuno S.
Published: February 2009

Morphological evolution of two metallic clusters of different elements at coalescence is investigated using molecular-dynamics (MD) simulation. All the pair combinations of the elements Ni, Cu, Au, Ag, Pt, and Pd are considered. The final structures of united bimetallic clusters are classified into three categories: epitaxial, core-shell, and alloyed. Which type of structure appears via coalescence depends on the size and temperature of clusters, which can be summarized in an observed structure map.
Simulation of Initial Growth Process of Pt Clusters on Carbon Materials – First-Principles Calculations
Authors: Okazaki-Maeda Kazuyuki , Yamakawa Shunsuke , Morikawa Yoshitada , Hyodo Shiaki , Akita Tomoki , Maeda Yasushi , Tanaka Shingo , Kohyama Masanori
Published: February 2009

First-principles calculations have been applied to investigate the interactions between Ptn (n=1˜13) clusters and a graphene sheet to model the Pt/C fuel-cell catalytic electrode. For the small clustesr (n<7), planar configurations vertically adsorbed on graphene (V-2D) are more stable than the three-dimensional (3D) configurations. For the large clusters (n>7), the 3D clusters are more stable than the V-2D clusters. In order to investigate the effects of defects and dopants in a graphene sheet, the interactions between the Pt13 cluster and the graphene sheet with an atomic vacancy and an dopant atom, such as boron and nitrogen atoms have been examined. For the atomic vacancy, the Pt atom is directly adsorbed on the C atom vacant site. For the Pt13 cluster adsorbed on the graphene sheet doped with the B or N atoms, the Pt atom is not directly adsorbed on the impurity atoms. The adsorption of the Pt13 cluster above the vacancy of the graphene sheet is more stable that that on the doped graphene sheet in the present calculations.
Micromechanics-based conversion of CT data into anisotropic elasticity tensors, applied to FE simulations of a mandible
Authors: Hellmich Christian , Kober Cornelia , Erdmann Bodo
Published: February 2009

Computer Tomographic (CT) image data have become a standard basis for structural analyses of bony organs. In this context, regression functions between stiffness components and Hounsfields units (HU) from Computer Tomography, related to X-ray attenuation coefficients, are widely used for the definition of the (actually inhomogeneous and anisotropic) material behavior inside the organ. Herein, we suggest to derive the functional dependence of the fully orthotropic stiffness tensors on the Hounsfield units from the physical information contained in the X-ray attenuation coefficients: (i) Based on voxel average rules for the X-ray attenuation coefficients, we assign to each voxel the volume fraction occupied by water (marrow) and that occupied by solid bone matrix. (ii) By means of a continuum micromechanics representation for bone, which is based on voxel-invariant (species and whole bone-specific) stiffness properties of solid bone matrix and of water, we convert the aforementioned volume fractions into voxel-specific orthotropic stiffness tensor components. The micromechanics model, in combination with the average rule for X-ray attenuation coefficients, predicts a quasi-linear relationship between axial Young's modulus and HU, and highly nonlinear relationships for both circumferential and radial Young's moduli as well as for the shear moduli in all principal material directions. Corresponding whole-organ Finite Element analyses of a partially dentulous human mandible characterized by atrophy of the alveolar ridge show that volumetric strain concentrations/peaks within the organ are decreased when considering material anisotropy, and increased when considering material inhomogeneity.
Structural Characterization of Iron in Human Spleen
Authors: Kopani Martin , Miglierini Marcel , Lancok Adriana , Jurecka Stanislav , Dekan Julius , Melnik Milan , Sisovsky Vladimir , Mikula Milan , Manka Jan , Skratek Martin , Danihel Ludovit , Jakubovsky Jan
Published: February 2009

Iron is essential element for fundamental cell functions, catalyst for chemical reaction. Iron can be found in human body mainly in the form of ferritin - 5Fe2O3.9H2O.

57Fe Mössbauer spectrometry, X4ray powder diffraction, (XRD), X4ray fluorescence (XRF), scanning and transmission electron microscopy (TEM) were carried out for investigation of iron oxide particles in human spleens with diagnosis of hemosiderosis, hereditary spherocytosis, and reference sample.

Room temperature Mössbauer spectra of all investigated samples exhibit doublet4like features identified as Fe(III) predominantly in ferrihydrite and haem environments within the tissue. Low temperature Mössbauer effect measurements at 77 K revealed, however, no changes in the magnetic ordering of the investigated samples. A contribution of ferromagnetically split sextets is clearly seen for all investigated samples measured at 5K. Their occurrence indicates that part of the sample is magnetically ordered, i.e. below the blocking temperature of a superparamagnetic behaviour. The ratio of relative contents of doublet to sextet components suggests differences in the size of ferritin cores in the investigated samples. The hemosiderosis sample exhibits the largest ferritin core which, in turn, stores the highest amount of Fe and thus triggers this disease.

Additional structural characterization is obtained from powder XRD and XRF measurements. XRF results show presence of different chemical elements such as iron, sulphur, phosporus, chlorine, zinc, chromium, and bromine. TEM investigation reveals iron accumulation in macrophages of the human spleen. The size of the particles is around 5 μm.

The amount of chemical elements and pH in surrounding environments can influence iron oxidation status and may cause transformation of biogenic to abiogenic (toxic) character of ferritin.
Detection Limits of Captured Protein on the BioCD
Authors: Barden Chad , Zhao Ming , Wang Xuefeng , Nolte David D.
Published: February 2009

The BioCD is a spinning biochip that uses quadrature laser interferometry to detect captured protein on the disc surface. We describe the detection limits of protein binding on this optical biosensor. The fundamental metrology limit is 1 picometer for a single 100-micron diameter spot. Under assay conditions for prostate specific antigen, we can detect 25 pg/ml at 10 assays per disc.
Effects of Device Architecture on the Performance of Organic Thin Film Transistors
Authors: Zhou Xiaojing , Mutkins Karyn E. , Elkington Daniel , Sirois Kathleen , Belcher Warwick , Dastoor Paul Christopher
Published: February 2009

The impact of device dimension and architecture on the device performance of an all–solution fabrication organic thin film transistor (OTFT) has been investigated. The saturation drain current is inversely proportional to the channel length, indicating that a characteristic of field–effect like transistor has been obtained. In contrast, the drain current is independent of the thickness of polyvinylphenol (PVP) dielectric layer and a large leakage current is observed at the gate electrode indicating that the device also shows electrochemical transistor characteristics. Although separate conductance measurements of a single poly(3–hexylthiophene) (P3HT) layer and a P3HT/PVP layer reveal that the conductance is proportional to the thickness of the layer, the maximum achieved drain current in the fabricated OTFT is inversely proportional to the P3HT thickness. Using this data, an interface of P3HT/PVP or a maximum P3HT thickness for a working transistor of approximately 160 ± 16 nm can be extracted. The mechanism of operation of these devices is discussed.
Resonant Fatigue Testing of Cantilever Specimens Prepared from Thin Films
Authors: Kwak Kwangsik , Otsu Masaaki , Takashima Kazuki
Published: February 2009

Fatigue properties of thin film materials are extremely important to design durable and reliable microelectromechanical systems (MEMS) devices. However, it is rather difficult to apply conventional fatigue testing method of bulk materials to thin films. Therefore, a fatigue testing method fitted to thin film materials is required. In this investigation, we have developed a fatigue testing method that uses a resonance of cantilever type specimen prepared from thin films. Cantilever beam specimens with dimensions of 1(W) × 3(L) × 0.01(t) mm3 were prepared from Ni-P amorphous alloy thin films and gold foils. In addition, cantilever beam specimens with dimension of 3(L) × 0.3(W) × 0.005(t) mm3 were also prepared from single crystalline silicon thin films. These specimens were fixed to a holder that is connected to an golddio speaker used as an actuator, and were resonated in bending mode. In order to check the validity of this testing method, Young's moduli of these specimens were measured from resonant frequencies. The average Young's modulus of Ni-P was 108 GPa and that of gold foil specimen was 63 GPa, and these values were comparable with those measured by other techniques. This indicates that the resonance occurred theoretically-predicted manner and this testing method is valid for measuring the fatigue properties of thin films. Resonant fatigue tests were carried out for these specimens by changing amplitude range of resonance, and S-N curves were successfully obtained.
Thermal Bubble Nucleation in Nanochannels: Simulations and Strategies for Nanobubble Nucleation and Sensing
Authors: Sridhar Manoj , Xu Dongyan , Hmelo Anthony B. , Li Deyu , Feldman Leonard C.
Published: February 2009

Progress in the state of the art of nanofabrication now allows devices that may enable the experimental sensing of bubble nucleation in nanochannels, and the direct measurement of the bubble nucleation rate in nanoconfined water and other fluids. In this paper we report on two aspects in achieving this goal: 1) new molecular dynamics simulations of nanobubble formation in nanoconfined argon and water model systems and 2) an ultrasensitive nanofluidic device architecture potentially able to detect individual nanobubble nucleation events.
Functionalized Magnetic Nanoparticles for Selective Targeting of Cells
Authors: Tremel Wolfgang , Shukoor Mohammed Ibrahim , Natalio Filipe , Tahir Muhammad Nawaz , Wiens Matthias , Schladt Thomas , Barz Matthias , Theato Patrick , Schröder Heinz Christoph , Müller Werner
Published: February 2009

MnO nanoparticles were conjugated to single stranded DNA (ssDNA), Cytosin-phosphatidyl-Guanosin oligonucleotide (CpG ODN) to detect and activate Toll-like (TLR9) receptors in cells and to follow nanoparticle cellular trafficking by different means of imaging while at the same time serving as a drug carrier system. By virtue of their magnetic properties these nanoparticles may serve as vehicles for the transport of target molecules into cells, while the fluorescent target ligand allows optical detection simultaneously.x
Influence of carbon nanotube grafting on chemo-electrical properties of Conductive Polymer nanoComposites
Authors: Castro Mickaël , Lu Jianbo , Kumar Bijandra , Bruzaud Stéphane , Feller Jean-François
Published: February 2009

New unique abilities towards solvents' vapor of electrically Conductive Polymer nanoComposites (CPCs) have made it a subject, holding the attention of research groups. The direct conversion from chemical information into an electrical signal can take advantage of existing low power microelectronics and sensing technology such as detection of toxic vapor; environmental monitoring in chemical industry and quality control in food processing, beverage and perfume industry. Conductive Polymer nanoComposite (CPC) is a heterogeneous system consisting of insulated polymer matrices and conductive nanofillers. In this paper we have investigated a new route for CNT grafting via ring opening polymerization of e-caprolactone. The influence of this treatment on chemo-electrical properties of the so-called CPC based sensor was investigated in this work.
Multifunctional Elastomer Nanocomposites based on EPDM and Carbon Nanotubes
Authors: Ciselli Paola , Lu Lan , Busfield James JC , Peijs Ton
Published: February 2009

Elastomeric composites based on Ethylene-Propylene-Diene-Monomer (EPDM) filled with multi-wall carbon nanotubes (MWNTs) have been prepared, showing improved mechanical properties as compared to the pure EPDM matrix. The results have been discussed using the Guth model. The main focus of the study was on the electrical behavior of the nanocomposites, in view of possible sensor applications. A linear relation has been found between conductivity and deformations up to 10% strain, which means that such materials could be used for applications such as strain or pressure sensors. Cyclic experiments were conducted to establish whether the linear relation was reversible, which is an important requirement for sensor materials.
Direct-Write Fabrication of Polymer Nanocomposite Fibers
Authors: Berry Scott M. , Pabba Santosh , Cambron Scott D. , Cohn Robert W. , Keynton Robert S.
Published: February 2009

The unique properties of carbon-nanotube (CNT)-doped polymers have generated several promising applications including gas sensors, high-strength/light-weight materials, and electromagnetic interference shielding. The ability to process CNT-doped materials into complex architectures may enable further advancement of these devices. We have developed a direct-write technique for processing CNT-doped poly(methyl methacrylate) (PMMA) into 3D arrays of precisely-positioned fibers with micro- and sub-microscale diameters. In this method, a programmable micromanipulator-controlled syringe was loaded with solvated CNT/PMMA and utilized to draw an array of freely-suspended solution filaments on a substrate in a “connect-the-dots” fashion. As the filaments are drawn, they are thinned by surface tension-driven necking as they dry and form solid fibers. The degree of thinning can be controlled by varying the viscosity of the solution, which acts to resist the necking while the volatile solvent evaporates and solidification occurs. Multiple fibers were drawn to investigate the effects of several factors on fiber diameter and process yield. These variables included fiber length (4, 8, and 18 mm), fiber drawing velocity (5 and 20 mm/s), polymer concentration in solution (22 and 24% by wt.), and CNT concentration in solution (0, 0.5, 1, and 1.5% by wt.), with the latter two of these variables strongly influencing solution viscosity. Measurement of the fibers via scanning electron microscopy (SEM) revealed several trends: Fiber diameter was not influenced by CNT concentration, but increased with increasing PMMA concentration (P<0.001), increasing drawing rate (P<0.01), and decreasing fiber length (P<0.001), with fiber diameter ranging from 538 nm to >100 μm. Furthermore, fiber yield exceeded 75% for all tested solutions except for the lowest viscosity CNT-doped solution (24% PMMA/0.5% CNT, η=50.1 Pa*s), which experienced capillary breakup prior to solidification. The conductivities of direct-write PMMA/CNT fibers ranged from <10-7to 0.15 S/m, with shorter fibers having higher conductivities (P<10.005). Also, fibers drawn from solutions with 1.0% CNTs had higher conductivities that those drawn from solutions with 0.5% or 1.5% CNTs (P<0.01). This nonlinear trend was further investigated by cleaving fibers in liquid nitrogen and imaging their cross-sections with an SEM. This analysis illustrated that the CNTs, which were functionalized to remain dispersed in the solvent, tended to randomly aggregate within the polymer-fiber matrix, particularly for fibers drawn from solutions containing 1.5% CNTs. In conclusion, CNT/PMMA fibers were successfully drawn with the direct-write technique and CNT doping had no significant influence on fiber diameter or yield compared with fibers drawn from PMMA homopolymer. However, the CNTs were found to strongly aggregate when drawn from solutions loaded at high concentrations (1.5%), thereby hindering electrical transport.
Matrix Formation Leading to Catalyst Free Growth of GaN Nanowires
Authors: Halpern Joshua B. , Harris Gary L. , He Maoqi , Zhou Piezhen , Cheek Christina E.
Published: February 2009

Catalyst-free vapor-solid GaN nanowire growth occurs when ammonia flows over Ga first forming a GaN matrix, the top layer of which is composed of hexagonal platelets. Multiphase nanowire growth occurs at nanoscale nucleation sites on the GaN platelets. Lower layers of the matrix are Ga rich, upper ones are stoichiometrically GaN. Gallium for later stages of growth is sourced from the decomposition of GaN particles and Ga rich GaN. Growth temperature exerts a strong influence on nucleation site formation. Scanning electron microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) was used to characterize the matrix.
Effect of Metal - Silicon Nanowire Contacts on the Performance of Accumulation Metal Oxide Semiconductor Field Effect Transistor
Authors: Garg Pranav , Hong Yi , Iqbal Md. Mash-Hud , Fonash Stephen J.
Published: February 2009

Recently, we have experimentally demonstrated a very simply structured unipolar accumulation-type metal oxide semiconductor field effect transistor (AMOSFET) using grow-in-place silicon nanowires. The AMOSFET consists of a single doping type nanowire, metal source and drain contacts which are separated by a partially gated region. Despite its simple configuration, it is capable of high performance thereby offering the potential of a low manufacturing-cost transistor. Since the quality of the metal/semiconductor ohmic source and drain contacts impacts AMOSFET performance, we repot here on initial exploration of contact variations and of the impact of thermal process history. With process optimization, current on/off ratios of 106 and subthreshold swings of 70 mV/dec have been achieved with these simple devices
Growth and Characterization of p-n Junction Core-Shell GaAs Nanowires on Carbon Nanotube Composite Films
Authors: Mohseni Parsian , Lawson Gregor , Adronov Alex , LaPierre Ray
Published: February 2009

Thin films composed of poly(ethylene imine)-functionalized single-walled carbon nanotubes (CNTs) were formed through a vacuum filtration process and decorated with Au nanoparticles, roughly 40 nm in diameter. The Au nanoparticles, on the surface of the CNT fabric, accommodated the growth of GaAs nanowires (NWs), according to the vapour-liquid-solid (VLS) mechanism, in a gas-source molecular beam epitaxy (GS-MBE) system. Structural analysis indicated that the nanowires, up to 2.5 μm in length, were not preferentially oriented at specific angles with respect to the substrate surface. The NWs grew in the energetically favored [0001] direction of the wurtzite lattice while stacking faults, characterized as zincblende insertions, were observed along their lengths. Micro-photoluminescence spectroscopy demonstrated bulk-type optical behaviour. Current-voltage behaviour of the core-shell pn-junction heterostructured NWs exhibited asymmetric rectification. Thus, the potential for the incorporation of such hybrid NW/CNT architectures into an emerging class of flexible opto-electronic devices is demonstrated.
Silver nanowires: synthesis, characterization and optical properties
Authors: Barnakov Yuri A. , Li Heng , Zhu Guohua , Mayy Mohammed , Robinson Erik J. , Bonner Carl , Noginov Mikhail A.
Published: February 2009

We describe electrochemical synthesis of a bulk metamaterial, consisting of silver nanowires in Porous Anodic Alumina membrane and its characterization. We have found that the quality of the synthesized metamaterial depends on the metal used as a working electrode at the optimal conditions of the electroplating process. The dissolution of the thin layer of working electrode is occurred during the electrochemical reaction. It suggests an important role of interfacial phenomena taking place between the working electrode and the sample holder.
The Strength of Gold Nanowires and Nanoporous Gold
Authors: Dou Rui , Derby Brian
Published: February 2009

We have measured the yield strength of gold nanowires with diameters in the range from 30 to 70 nm fabricated by electro-deposition into porous alumina templates. All nanowire sizes showed yield strengths much greater than polycrystalline gold with the 30 nm specimens having a yield strength of 1.4 GPa. We found no significant work hardening at plastic strains up to 30%. The strength of the nanowires as a function of wire diameter follows the same trend as has been found for the compression strength of larger gold pillars reported in the literature. TEM observations of deformed wires are consistent with mechanisms of dislocation induced deformation. The strength of nanoporous gold nanowires measured by uniaxial compression test is also reported here. Although two different mechanisms are thought to operate in gold nanowires and nanoporous gold respectively, their strengths show very similar dependence on wire or ligament diameter. However the nanoporous material shows significant strain hardening.
Modifying the Pore Size of Resorcinol Formaldehyde Aerogels for Fabrication of Hollow Spheres for Direct Drive ICF Experiments
Authors: Paguio Reny , Federick Chris A. , Ilavsky Jan , Hund Jared F. , Nikroo Abbas , Thi Mary A.
Published: February 2009

This work investigates an alternative way to modify the pore size of a 100 mg/cc resorcinol formaldehyde (R/F) aerogel without any significant change to the aerogel target density. This was successfully accomplished by an addition of hydrophilic polymer additive [Poly Vinyl Alcohol (PVA) or Poly Acrylic Acid (PAA)] to the R/F precursor solution which acts as an impurity in the reaction. The polymer can modify the cross linking or aggregation of the primary particles which can change the structure formation of the aerogel, thus changing the pore size. This paper will discuss this process modification and the fabrication of hollow, large pore R/F aerogel spheres that are used for direct drive inertial confinement fusion (ICF) cryogenic ice layering experiments at the University of Rochester Laboratory for Laser Energetics (LLE). The aerogels were characterized using scanning electron microscopy (SEM), nitrogen gas adsorption, and ultra small angle x-ray scattering (USAXS).
Neutron Studies of the Iron-based Family of High Tc Magnetic Superconductors
Authors: Lynn Jeffrey W.
Published: February 2009

We briefly review recent neutron scattering investigations carried out at the NIST Center for Neutron Research on the crystal structures, magnetic structures, and spin dynamics of the iron-based ROFe(As,P) (R=La, Ce, Pr, Nd), and (Ba,Sr,Ca)Fe2As2 systems. All the undoped materials exhibit universal behavior, where a tetragonal-to-orthorhombic structural transition occurs between ˜100−220 K, below which the systems become antiferromagnets. The magnetic structure within the a-b plane consists of chains of parallel Fe spins that are coupled antiferromagnetically in the orthogonal direction, with an ordered moment typically less than one Bohr magneton. Hence these are itinerant electron magnets, with a spin structure that is consistent with Fermi-surface nesting and a spin wave bandwidth ˜200 meV. The rare-earth moments order antiferromagnetically at low T like ‘conventional’ magnetic-superconductors. With doping, the structural and magnetic transitions are suppressed in favor of superconductivity, with superconducting transition temperatures up to 56 K, while the Ce crystal field linewidths are affected when superconductivity sets in. The application of pressure in CaFe2As2 transforms the system from a magnetically ordered orthorhombic material to a ‘collapsed’ non-magnetic tetragonal system which is superconducting at lower T when anisotropic pressure is applied. Fe1+xTe shows a transition from a monoclinic to orthorhombic low T structure with increasing x, and a crossover from commensurate to incommensurate magnetic order. Se doping suppresses the magnetic order, while incommensurate magnetic scattering is observed in the superconducting regime.
Synthesis of layered double hydroxides in W/O micro-emulsion: Influence of method of preparation on the physico-chemical and adsorption characteristics
Authors: Mandal Sujata , Deshpande Aniruddha S. , Harle Arti S. , Mayadevi S.
Published: February 2009

Zn/Al layered double hydroxide was synthesized in micro-emulsion system with the oil phase comprising of cyclohexane + TX100 (surfactant) + n-hexanol (co-surfactant). Aqueous NaOH solution was used as the precipitating agent. The XRD pattern showed Zincite as the primary and hydrotalcite as the secondary phase. The d003 diffraction peak corresponded to interlayer hydroxide ion. There was no interlayer NO3- ion. The synthesized LDH showed much higher BET surface area (116.3 m2/g) than similar LDH synthesized by conventional co-precipitation technique (4.2 m2/g). Well defined flaky nano-crystals having an average dimension of 5-20 nm were observed by HRTEM.
Structural Transformation and Mechanical Properties of Cold Sprayed Nickel Coatings after Annealing
Authors: Zou Yu , Rezaeian Ahmad , Szpunar Jerzy , Irissou Eric , Yue Stephen
Published: February 2009

Cold spray is a relatively new coating technology in which coatings can be produced by powdered particles under large plastic deformation without significant heating. In this paper, nickel coatings were fabricated by cold spray process followed by heat treatment in inert gas. Structural transformation of both as-sprayed and annealed coatings was investigated by Electron Backscattering Diffraction (EBSD) in a FEG-SEM. The results show that after cold spraying sub-micron grains and subgrains with high crystal strain appear in the particle bond interface, but not shown in the center of particles. Microstructure was transformed to be uniform and stresses were released after annealing in 400°C for one hour. And ductility and formability were significantly improved due to recovery and recrystallization. Continuous recrystallization after large strain deformation could occur after cold spraying followed by annealing.