bluuebunny/crossref_metadata_2025 huggingface dataset:
ZnO-based p-n Junctions with p-type ZnO by ZnTe Oxidation
Authors: Kaminska Eliana , Przezdziecka Ewa , Piotrowska Anna , Kossut Jacek , Dynowska Elzbieta , Dobrowolski Witold , Barcz Adam , Jakiela Rafal , Lusakowska Elzbieta , Ratajczak Jacek
Published: April 2011

The fabrication and properties of ZnO-based rectifying p-n and p-i-n junctions are reported. ZnO films with p-type conductivity were obtained by oxidation of ZnTe grown by MBE on GaAs substrate. Insulating and n-type ZnO films were deposited by magnetron sputtering. The processing of p-n junctions into device structures involved the formation of mesa geometry and preparation of ohmic contacts to p- and n-type regions.
Group I elements in ZnO
Authors: Meyer Bruno K. , Volbers N. , Zeuner A. , Lautenschläger S. , Sann J. , Hoffmann A. , Haboeck U.
Published: April 2011

Diffusion of Li, Na and K into single-crystal substrates of ZnO were performed. We compare the results with ZnO epitaxial films doped with the respective elements during growth. The diffused and in-situ doped layers were studied using mass spectroscopy, low temperature photoluminescence and Raman spectroscopy. Li and Na are known to produce deep acceptor centers which give rise to shallow donor to deep acceptor recombinations in the visible spectral region. We will demonstrate that also shallow acceptors are introduced having binding energies around 300 meV. A donor-acceptor pair recombination (zero phonon line at 3.05 eV) with LO phonon replica is observed analogous to the “edge” emission in other II-VI compounds.
Comparison of Lasing Characteristics of GaInNAs Quantum Dot Lasers and GaInNAs Quantum Well Lasers
Authors: Liu Chongyang Y. , Yoon Soon Fatt , Sun Zhongzhe Z.
Published: April 2011

Self-assembled GaInNAs/GaAsN single layer quantum dot (QD) lasers grown using solid source molecular beam epitaxy have been fabricated and characterized. Temperature-dependent measurements have been carried out on the GaInNAs QD lasers. High-temperature operation up to 65°C was demonstrated from an unbonded GaInNAs QD laser (50 × 1060 μm2), with high characteristic temperature (T0) of 79.4 K in the temperature range of 10-60°C. For comparison, temperature-dependent operation has also been studied on the GaInNAs single quantum well (SQW) lasers. Unlike the relation between the cavity length and T0 in GaInNAs SQW lasers, longer-cavity GaInNAs QD laser (50 × 1700 μm2) showed lower T0 of 65.1 K, which is presumably believed due to the nonuniformity of the GaInNAs QD layer.
Interdiffused SbN-based Quantum Well on GaAs for 1300-1550 nm Diode Lasers
Authors: Arif Ronald A. , Tansu Nelson
Published: April 2011

A new method to realize InGaAsSbN quantum well (QW) structures on GaAs substrate is presented. This approach combines the established growth technique of InGaAsN and InGaAsSb QWs by metal organic chemical vapor deposition (MOCVD), with a post-growth thermal interdiffusion to achieve high quality interdiffused InGaAsSbN QW for diode lasers emitting at 1300-1550-nm. In addition to presenting the optimized interdiffused SbN-based QW design at 1550-nm, strain-compensated interdiffused InGaAsSb-GaAsN QW structure is also presented. Preliminary experimental findings of N- and Sb-diffusivities in GaAs matrix show good agreement with theory, indicating the feasibility of realizing interdiffused InGaAsSbN QW.
High-speed high-quality epitaxial growth of N and B codoped 6H-SiC by closed sublimation method
Authors: Maeda Tomohiko , Nakamura Yoshihiro , Iwaya Motoaki , Kamiyama Satoshi , Amano Hiroshi , Akasaki Isamu , Furusho Tomoaki , Kinoshita Hiroyuki , Yoshimoto Masahiro
Published: April 2011

N and B codoped 6H-SiC epilayers were grown by the closed sublimation method, the growth rate of which was as high as 100 mm/h. Donor acceptor (DA) pair emission at different temperatures was investigated for two samples with different B concentrations. The integrated photon count obtained from the photoluminescence (PL) spectra of the sample having high B concentration increases with temperature. To estimate the internal quantum efficiency, we measured the PL integrated photon counts of GaN at 10 K as a reference. The integrated PL photon count of 6H-SiC DA-doped epilayer at 250 K is almost comparable to that of GaN at 10 K, which is thought to be almost 100% because of the freezing of the nonradiative recombination at low temperature. This result implies that the internal quantum efficiency of the 6H-SiC DA-doped epilayer exceeds 95%.
Polarity dependence of In-rich InGaN and InN/InGaN MQWs
Authors: Che Songbek , Shinada Takuro , Mizuno Tomoyasu , Ishitani Yoshihiro , Yoshikawa Akihiko
Published: April 2011

In-rich InGaN films (XIn>0.5) and InN/InGaN multi-quantum wells were grown on Ga- and N-polarity GaN templates by radio-frequency plasma-assisted molecular beam epitaxy. The In-polarity InGaN films grown at 450°C showed superior crystalline quality and smoother surface morphology compared to the N-polarity samples, which were grown at 500∼550°C. By using the In-polarity In0.7Ga0.3N as a barrier layer, the InN/InGaN multi-quantum wells were successfully fabricated on the III-element polarity GaN templates at 450°C. Fine periodic structures and strong photoluminescence emission around optical communication wavelength were obtained from the In-polarity MQWs. These results indicate that the In-polarity growth is preferred to obtain a high quality InGaN film and the InN/InGaN MQWs in spite of its lower growth temperature.
Temperature dependence of transport properties of InN films
Authors: Thakur J.S. , Naik R. , Naik Vaman M , Haddad D. , Auner G.W. , Lu H. , Schaff W.J.
Published: April 2011

The temperature dependence of Hall mobility, µ, and carrier density, Ne, for thin InN films grown by Molecular Beam Epitaxy and Plasma Source Molecular Beam Epitaxy have been investigated. For temperature up to 300 K, a large temperature-independent Ne is observed in films grown by the above two techniques. However, for higher temperatures, carrier density (Ne) increases with temperature. The characteristic behavior of the mobility for the films with low carrier density is different from that of the high carrier density film, particularly at low temperatures. The low carrier density film shows a peak ∼250 K in mobility as a function of temperature which is contrast to the temperature independent mobility observed for the high density film for T < 300 K. We have investigated theoretically the effect of concentration of donor, acceptor, and threading dislocations on the carrier mobility in these films. Various electron-scattering mechanisms for the mobility in these films have been discussed.
The mean inner potential of GaN measured from nanowires using off-axis electron holography
Authors: Wong Andrew See Weng , Ho Ghim Wei , Dunin-Borkowski Rafal E , Kasama Takeshi , Oliver Rachel A , Costa Pedro MFJ , Humphreys Colin John
Published: April 2011

The mean inner potentials of wurtzite GaN nanowires are measured using off-axis electron holography in the transmission electron microscope (TEM). The nanowires have a circular cross-section and are suspended across holes in a holey carbon film, resulting in an accurate knowledge of their thickness profiles and orientations. They are also free of the implantation and damage that is present in mechanically-polished ion-milled TEM specimens. The effect of a thin amorphous coating, which is present on the surfaces of the nanowires, on measurements of their mean inner potential is assessed. A value for the mean inner potential of GaN of (16.7 ± 0.3) V is obtained from these samples.
Electrical Characterization of Blue Light Emitting Diodes as a Function of Temperature
Authors: Madhu Murthy , Kamto Tegueu Alphonse Marie , Awaah Michael , Wang Dake , Park Minseo , Walker Frederick J. , Kumar Das Kalyan
Published: April 2011

Blue light emitting diodes (LEDs) based on an AlGaN/GaN/AlGaN double heterojunction structure were electrically characterized as a function of temperature. Current-voltage (I-V), capacitance-voltage (C-V) and reverse recovery storage time measurements were conducted at temperatures in the range between -8° and 75° C. Capacitance-voltage measurements as a function frequency (20 Hz – 1 MHz) and electroluminescence study at room temperature were also performed. It was observed that the diode turn-on voltage decreased with increasing temperature, however, reverse leakage currents monitored at -1, -5 and -10 V showed only a slight increase with increasing temperature. The concentration of deep states and their position in the bandgap, as extracted from logarithmic plots of the forward characteristics, were not influenced by the measurement temperature. Recombination lifetimes, as obtained from experimentally determined reverse recovery storage times, remained constant over the range of temperature considered. A higher value of diode capacitance was observed at low measurement frequencies (20 Hz – 1 kHz), gradually dropping to a lower value over a frequency range between (1 kHz – 100 kHz) and remained constant from 100 kHz to 1 MHz. A loss peak centered about 10 kHz was observed in the corresponding plot of gm/ω as a function of frequency, f. The position of the peak in the gm/ω - frequency (f) plot and dC/dω(for f in the range 1 kHz – 100 kHz ), yielded a concentration of deep-states of approximately 2.2 × 1015/cm3, located at 0.39 eV above the valence bandedge.
Reduction of Base Access Resistance in AlGaN/GaN Heterojunction Bipolar Transistors using GaInN Base Cap Layer and Selective Epitaxial Growth
Authors: Shah Jay M , Gessmann Thomas , Luo Hong , Xi Yangang , Chen Kaixuan , Kim Jong Kyu , Schubert E. Fred
Published: April 2011

One of the major challenges affecting the performance of Npn AlGaN/GaN heterojunction bipolar transistors (HBTs) is the high base access resistance, which is comprised of the base contact resistance and the base bulk resistance. A novel concept is proposed to reduce the base access resistance in Npn AlGaN/GaN HBTs by employing polarization-enhanced contacts and selective epitaxial growth of the base and emitter. In addition, this technique reduces the exposed base surface area, which results in a lower surface recombination current. Such a structure would enable better performance of AlGaN/GaN HBTs in terms of higher current gain and a lower offset voltage. Theoretical calculations on polarization-enhanced contacts predict p-type specific contact resistance lower than 10-5 Ωcm2. Experimental results using transmission line measurement (TLM) technique yield specific contact resistances of 5.6×10-4 Ωcm2 for polarization-enhanced p-type contacts and 7.8×10-2 Ωcm2 for conventional p-type contacts.
W2B based High Thermal Stability Ohmic Contacts to n-GaN
Authors: Khanna Rohit , Pearton S J , Kao C J , Kravchenko I I , Ren F , Chi G C , Dabiran A , Osinsky A
Published: April 2011

A novel metallization scheme for Ohmic contact (Ti/Al/ W2B /Ti/Au) to n-GaN using high temperature boride was studied using contact resistance, scanning electron microscopy and Auger Electron Spectroscopy measurements. A minimum contact resistance of 7×10-6 Ω.cm2 was achieved for W2B based scheme at an annealing temperature of 800 °C. Contact resistances were found to be essentially independent of measurement temperature, indicating that tunneling plays a dominant role in the current transport. The outdiffusion of Ti to the surface at temperatures of ∼500°C, and at 800°C the onset of intermixing of Al within the contact was found to occur. By 1000°C, the contact showed a reacted appearance and AES showed almost complete intermixing of the metallization. The reliability measurements for the contact resistance of W2B based contact showed excellent stability for extended periods at 200°C, which simulates the type of device operating temperature that might be expected for operation of GaN-based power electronic devices.
Highly p-Type a-GaN Grown on r-Plane Sapphire Substrate
Authors: Tsuchiya Yosuke , Okadome Yoshizane , Furukawa Hiroko , Honshio Akira , Miyake Yasuto , Kawashima Takeshi , Iwaya Motoaki , Kamiyama Satoshi , Amano Hiroshi , Akasaki Isamu
Published: April 2011

Mg-doped p-type a-plane GaN films were grown on unintentionally doped a-plane GaN templates by metalorganic vapor phase epitaxy (MOVPE). The Mg concentration in a-plane GaN increased with increasing Mg source gas flow rate. A maximum hole concentration of 2.0 × 1018 cm-3 with a hole mobility of 4.5 cm2/Vs and resistivity of 0.7 Ω·cm were achieved. The activation ratio was 5.0 × 10-2. It was found that a maximum hole concentration in p-type a-plane GaN was higher than that in p-type c-plane GaN. The activation energy of Mg acceptors in p-type a-plane GaN with the maximum hole concentration was found to be 118 meV by temperature-dependent Hall-effect measurement.
Structural analysis of ELO-GaN grown on sapphire using the x-ray micro-beam of an 8-GeV storage ring
Authors: Miyajima Takao , Takeda Shingo , Kurihara Hideaki , Watanabe Kyoko , Kato Madomi , Hara Nobuhide , Tsusaka Yoshiyuki , Matsui Junji , Kudo Yoshihiro , Tomiya Shigetaka , Goto Shu , Ikeda Masao , Narui Hironobu
Published: April 2011

We investigated the micrometer-scale structure of epitaxially laterally overgrown GaN (ELO-GaN) on a sapphire without a SiO2 mask using the 2×4 μm2 micro-beam x-ray of an 8-GeV storage ring. The GaN (0 0 0 12) rocking curve of a wing region had a sharp peak with a FWHM of 46 arcsec, while that of a seed region had several broad peaks. This peak-narrowing indicates that the density of threading dislocations (TD) is reduced and the grain size is extended in the wing region by the lateral growth. The observed grain size in the wing region was 10 μm × 5 μm. The mapping of the rocking curves shows that the wing regions hang down from the seed region at a tilting angle of 81.5 arcsec, although there is no SiO2 mask which is a cause of c-axis tilting in ELO-GaN. After comparing the results of ELO-GaN with and without coalescence, we conclude that the small c-axis tilting is caused by the compressive stress induced by the difference in the thermal expansion coefficient of the GaN and the sapphire substrate. Because a shrinkage of grain size was observed after the coalescence of the wing regions, it is thought the coalescence is one of the causes of the generation of the few threading dislocations in the wing regions. We believe that the reduction of the threading dislocations and the expansion of gain size in the wing regions are important for the further improvement of the device characteristics of GaN-based LDs grown on ELO-GaN.
Misfit dislocations in green-emitting InGaN/GaN quantum well structures
Authors: Costa Pedro MFJ , Datta Ranjan , Kappers Menno J , Vickers Mary E , Humphreys Colin J
Published: April 2011

Misfit dislocations (MDs) have been observed using transmission electron microscopy (TEM) in InGaN/GaN quantum well (MQW) structures grown under different metal-organic vapour phase epitaxy (MOVPE) regimes and with In-contents equal to or higher than 20%. These dislocations are even observed in a single quantum well 3 nm thick with an In-content of 22%. Conversely, no MDs were observed in QW structures with an In-content of 16%. The presence of MDs in the QW stack leads to strain relaxation which has been confirmed in the indium-rich structures by high resolution X-ray diffraction (HRXRD).
Life cycle analysis of mortars and its environmental impact
Authors: Moropoulou Antonia , Koroneos Christopher , Karoglou Maria , Aggelakopoulou Eleni , Bakolas Asterios , Dompros Aris
Published: April 2011

Over the years considerable research has been conducted on masonry mortars regarding their compatibility with under restoration structures. The environmental dimension of these materials may sometimes be a prohibitive factor in the selection of these materials. Life Cycle Assessment (LCA) is a tool that can be used to assess the environmental impact of the materials. LCA can be a very useful tool in the decision making for the selection of appropriate restoration structural material. In this work, a comparison between traditional type of mortars and modern ones (cement-based) is attempted. Two mortars of traditional type are investigated: with aerial lime binder, with aerial lime and artificial pozzolanic additive and one with cement binder. The LCA results indicate that the traditional types of mortars are more sustainable compared to cementbased mortars. For the impact assessment, the method used is Eco-indicator 95
The Application of Energetic SHS Reactions in the Synthesis of Multi-functional Bone Tissue Engineering and Drug Delivery Systems
Authors: Ayers Reed , Burkes Doug , Gottoli Guglielmo , Yi H.C. , Guigné Jaque , Moore John
Published: April 2011

The term combustion synthesis, or self-propagating high temperature synthesis (SHS), refers to an exothermic chemical reaction process that utilizes the heat generated by the exothermic reaction to ignite and sustain a propagating combustion wave through the reactants to produce the desired product(s). The products of combustion synthesis normally are extremely porous: typically 50 percent of theoretical density

Advantages of combustion synthesis over traditional processing routes, e.g., sintering, in the production of advanced materials such as ceramics, intermetallic compounds and composites include process economics, simplicity of operation, and low energy requirements. However, the high exothermicity and rapid combustion propagation rates necessitate a high degree of control of these reactions.

One research area being conducted in the Institute for Space Resources (ISR) at the Colorado School of Mines (CSM) is the application of combustion synthesis (SHS) to synthesize advanced, engineered porous multiphase/heterogeneous calcium phosphate (HCaP), NiTi, NiTi-TiC, TiB-Ti, TiC-Ti for bone tissue engineering and drug delivery systems. Such material systems require a complex combination of properties that can be truly classified as multi-functional materials. The range of properties includes: an overall porosity of 40-60% with a pore size of 200-500 μm; mechanical properties (compression strength and Young’s modulus) that match those of natural bone to avoid ‘stress shielding’; and a surface chemistry that is capable of facilitating bone growth and mineralization.

The paper will discuss the synthesis of porous multiphase/heterogeneous calcium phosphate (HCaP), NiTi, NiTi-TiC, TiB-Ti, TiC-Ti for bone tissue engineering and drug delivery systems.
Ultrafast Dynamics of Nanotechnology Energetic Materials
Authors: Yu Hyunung , Hambir Selezion A. , Dlott Dana D.
Published: April 2011

Our work involves understanding the chemical reaction dynamics of nanotechnology energetic materials on the time and length scales of individual molecules or nanoparticles. These types of measurements provide insights into fundamental mechanisms and make a close connection to modern atomistic simulation methods. We are especially interested in the relationships between performance and nanostructure. We have developed a number of diagnostic instruments in our laboratory that can be used to probe chemical reaction dynamics, reaction propagation over short length scales, and explosive performance. Some recent results on energetic materials containing Al nanoparticles and either nitrocellulose (NC) or Teflon oxidizers are presented.
Understanding and Tuning the Reactivity of Nano-Energetic Materials
Authors: Rai A. , Zhou L. , Prakash A. , McCormick A. , Zachariah M. R.
Published: April 2011

Mixtures of fuel and oxidizers with particle sizes in the nanometer range have been widely used for energy intensive applications like propellants and explosives. Nano- Al is invariably used as fuel, while a host of metal oxide nanoparticles are used as oxidizers. This article aims at understanding and tuning the reactivity of these nano-energetic materials. The first part of this article discusses the oxidative reactivity of aluminum nanoparticles as measured experimentally using single-particle mass-spectrometer (SPMS) and microscopy and then modeled. Experimental evidence suggests that outward diffusion of aluminum is an important phenomenon in the oxidation of aluminum nanoparticle. Also melting of the aluminum core is necessary for the reaction to take place vigorously. In the second part of the paper we discuss the formation of novel oxidizers. A super-reactive formulation of Al/KMnO4 has been developed which is shown to be orders of magnitude more reactive than the traditional formulations of Al/Fe2O3, Al/MoO3 and Al/CuO. We demonstrate the formation of novel composite oxidizers to tune the reactivity of the Al/Metal oxide system.
The Inelastic Neutron Scattering spectrum of 2,4-Dinitroimidazole and the Reproduction of Its Solid-State Features by Periodic DFT methods
Authors: Ciezak Jennifer , Trevino Samuel F.
Published: April 2011

The inelastic neutron scattering spectra of 2, 4 –Dinitroimidazole (24DNI) are presented from 25 to 1200 cm-1. Direct comparisons were made to the experimental spectra using solid-state calculation methods at the BLYP/dnd, BP/dnd, and PWC/dnd theory levels. Comparison of the observed and calculated INS spectra revealed that the BLYP/dnd calculations provide the best description of the experimental INS spectrum below 1000 cm-1. The PWC/dnd calculations were found to give the best vibrational agreement with the experimental frequencies above 1000 cm-1. In addition, the six experimental lattice vibrations were assigned. The first overtone of the lattice vibration with the highest vibrational energy is nearly degenerate with one of the fundamental vibrations, suggesting the possibility of a “doorway mode”.
Theoretical Chemical Characterization of Energetic Materials
Authors: Rice Betsy Mavity , Byrd Edward F. C.
Published: April 2011

Our research is focused on developing computational capabilities for the prediction of properties of energetic materials associated with performance and sensitivity. Additionally, we want to identify and characterize the dynamic processes that influence conversion of an energetic material to products upon initiation. We are attempting to achieve these goals through the use of standard atomistic simulation methods. In this paper various theoretical chemistry methods and applications to energetic materials will be described. Current capabilities in predicting structures, thermodynamic properties, and dynamic behavior of these materials will be demonstrated. These are presented to exemplify how information generated from atomistic simulations can be used in the design, development, and testing of new energetic materials. In addition to illustrating current capabilities, we will discuss limitations of the methodologies and needs for advancing the state of the art in this area.
Characterising the Response of Energetic materials and Polymer-Bonded Explosives (PBXs) to High-Rate Loading.
Authors: Proud William , Greenaway M.W. , Siviour C.R. , Czerski H. , Field J.E. , Porter D. , Gould P. , Church P.D. , Cullis I.G.
Published: April 2011

Polymer-bonded explosives (PBXs) are being increasingly used as energetic fillings and components in many systems. They are perceived as more chemically and mechanically stable than traditional fillings such as RDX/TNT. They are castable into predetermined shapes, machinable and can be used as structural components. However, along with all these undeniable advantages, as a class, these materials are now undergoing extensive characterisation to ensure they comply with both the legal and technical requirements in energetic systems.

It is well-known that polymers display non-linear behaviour and are much more complex than, for example, simple metal systems at any rate of strain. The understanding of PBX systems involves areas as diverse as polymer chemistry, chemical compatibility, mechanical properties, impact tests, and thermal stability. In this paper, aspects of energetic material response are outlined which are relevant to the understanding of PBX sensitivity.
Mechanical Properties of Biological Nanocomposite Nacre: Multiscale Modeling and Experiments on Nacre from Red Abalone
Authors: Ghosh Pijush , Verma Devendra , Mohanty Bedabibhas , Katti Kalpana S , Katti Dinesh R
Published: April 2011

Nacre, the inner iridescent layer of mollusks shell is a bio-nanocomposite with the mineral aragonite as a major constituent and 2-5% of organics mainly in the form of proteins. Our multiscale modeling and experimental studies reveal that the microstructure and the small weight percent of organics are the key parameters attributed to the extreme toughness of nacre. We report that the presence of platelet interlocks nacre have a significant role in the enhancement of mechanical properties. Molecular simulation study is conducted to understand the behavior of aragonite-organic interface. The mechanical behavior of organics and inorganics in presence of each other is described using steered molecular dynamics simulations. This provides some understanding on the deformation mechanisms of the protein present between the aragonite layers. Our nanoindentation results indicate that the elastic modulus and hardness of nacre decreases as it is exposed to a denaturing temperature for proteins. The changes in the organic inorganic interaction have been experimentally described using Fourier Transform Infrared Spectroscopy. This work gives insight into the contribution of the various factors existing at different length scales on the overall mechanical behavior of nacre.
Rheological and Morphological Characterization of Triblock Copolymer (PEO-PPO-PEO)-Clay Gel in Aqueous Solution
Authors: Jiang Jun , Li Chunhua , Rafailovich Miriam , Sokolov Jonathan
Published: April 2011

Thermal gelation and structure properties of high concentration triblock copolymer poly (ethylene oxide)99-poly(propylene oxide)69-poly(ethylene oxide)99 (Pluronic F127)-clay aqueous solutions were characterized by rheological measurements and scanning electron microscopy (SEM). The sol-gel transition temperature, as well as the viscosity of the F127 solution was found to depend both on the concentration of polymer and clay filler. In all cases, Pluronic F127 gels are pseudoplastic, showing the shear-thinning behavior. Above the gel transition, the viscosity of the solutions increased with increasing the clay concentration. The corresponding macrostructure of the gels was studied by lyophilizing thick samples and scanning them with a scanning electron microscope (SEM). A well-ordered network of porosity was observed as a function of polymer concentration and orientation.
A Model for Nonlinear Viscoelastic Mechanical Responses of Collagenous Soft Tissues
Authors: Oyen Michelle
Published: April 2011

Experimental observations of the time-dependent mechanical responses of collagenous tissues have demonstrated behavior that deviates from standard treatments of linear or quasi-linear viscoelasticity. In particular, time-dependent deformation can be strongly coupled to strain level, and strain-rate independence can be observed under monotonic loading, even for a tissue with dramatic stress relaxation. It was postulated that this nonlinearity is fundamentally associated with gradual recruitment of individual collagen fibrils during applied mechanical loading. Based on previously observed experimental results for the time-dependent response of collagenous soft tissues, a model is developed to describe the mechanical behavior of these tissues under uniaxial loading. Tissue stresses, under applied strain-controlled loading, are assumed to be a sum of elastic and viscoelastic stress contributions. The relative contributions of elastic and viscoelastic stresses is assumed to vary with strain level, leading to strain- and time-dependent mechanical behavior. The model formulation is examined under conditions of monotonic loading at varying constant strain rates and stress-relaxation at different applied strain levels. The model is compared with experimental data for a membranous biological soft tissue, the amniotic sac, and is found to agree well with experimental results. The limiting behavior of the novel model, at large strains relative to the collagen recruitment, is consistent with the quasi-linear viscoelastic approach.
Bio-mimetic study of novel materials for joint replacements
Authors: Ribeiro Rahul , Ganguly Poulomi , Darensbourg Donald , Usta Meitin , Ucisik A. Hikmet , Liang Hong
Published: April 2011

Polytrimethylene carbonate (PTMC) and poly ε-caprolactone are conventional biodegradable, biocompatible polymers. Their friction response against cartilage and surface attraction forces were studied toward using them as artificial cartilage materials. Their behavior was compared to that of natural cartilage and a conventional joint replacement material, ultrahigh molecular weight polyethylene. It was possible to polymerize these materials using a calcium based catalyst. Simulated body fluid (SBF) was used as lubricant between surfaces in the friction tests. It was found that higher surface attractive forces on a silicon tip AFM related to lower friction coefficients. This confirs the fact that hydrophilic surfaces enhance the effectiveness of boundary lubrication of simulated body fluid. PTMC and PTMC-ε-caprolactone co-polymer showed lower hydrophilicity and higher friction coefficients and need to be modified in order to bring them closer in behavior to natural cartilage.
Polypeptide-Solvent Interactions Measured by Single Molecule Force Spectroscopy
Authors: Valiaev Alexei , Lim Dong Woo , Chilkoti Ashutosh , Schmidler Scott , Zauscher Stefan
Published: April 2011

Stimulus-responsive biomolecules have attracted a large research interest because of their potential application in various areas such as drug delivery, actuators and sensing devices at the nanoscale. Using single-molecule force spectroscopy (SMFS) we studied elastin-like polypeptides (ELPs). These stimulus-responsive polypeptides undergo an inverse temperature transition, accompanied by a large conformational change, when the solvent quality is changed by increasing the temperature or by addition of salt. Understanding the relationship between peptide sequence and mechanisms of force generation can provide a route to engineer ELPs with desirable mechano-chemical properties. Here we studied the effect of solvent quality and type of guest residue on the mechanical properties of ELPs on the single-molecule level. We used a statistical approach to estimate polymer elasticity parameters from model fits to the data. With this approach we were able to resolve small changes in the Kuhn segment length distributions associated with different molecular architectures. We then show that these mechanical differences likely arise from differences in the hydrophobic hydration of sidegoups, in line with recent predictions from molecular dynamics simulations.
Biosynthesis and Electron Microscopy Characterization of Diatom Nanocomposites
Authors: Gutu Timothy , Jiao Jun , Jeffryes Clayton , Qin Tian , Chang Chih-hung , Rorrer Gregory L.
Published: April 2011

The fabrication of Si-Ge oxide composites in a two-stage photobioreactor cultivation process was systematically optimized by increasing the amount of germanium assimilated into the diatom cells. In this optimization process of the synthesis of Si-Ge oxides that maintain the original morphology of the diatoms, high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) both equipped with an energy dispersive X-ray spectrometer were extensively used to characterize the evaluation of the chemical composition and structural properties of the processed diatoms.
Controlled direct growth of vertical and highly-ordered ’carbon nanotube - silicon’ heterojunction array
Authors: Kuo Teng-Fang , Xu Jimmy
Published: April 2011

Carbon nanotubes (CNT) have been studied intensively for its unique electrical and mechanic properties and numerous applications. However, electronical integration of carbon nanotubes with silicon to form an electronically functional entity or device, though highly desirable, has remained a great challenge. Whereas vertical aligned bundles of nanotubes have been grown directly on silicon, the integration is mechanical, rather than electronical, in nature. In the present work, we report on Controlled growth of vertical and highly-ordered array of ’carbon nanotube silicon’ (CNS) heterojunction diodes of uniform diameter, length, and alignment. The as grown CNS heterojunction structure is not only electronically functional but also strongly rectifying with an on off ratio as high as five orders of magnitude in current voltage characteristics measured at room temperature. The controlled direct growth of the CNS hetero junction array of such high uniformity is enabled by the formation of a highly ordered nanopore array alumina matrix directly on the silicon, following a precisely controlled anodization of an aluminum thin film evaporated on silicon. Iterations of development and optimization of the anodization process conditions and real time monitoring and control of the anodization process were required for the formation and adhesion of the alumina growth matrix directly on silicon. Under carefully controlled and optimized conditions developed in this work, we are able to obtain an abrupt heterointerface between a terminal end of the carbon nanotube and the silicon substrate, without an intermediate barrier layer, as required for an electronically functional CNS hetero junction. The growth process is applicable to silicon doped in either type, enabling access to another critical parameter of the electronic function.
Protein Adsorption on the Surface Functionalized Planar Si
Authors: Tay Li-Lin , Rowell Nelson , Boukherroub Rabah , Lockwood David
Published: April 2011

The peak energy of photoluminescence (PL) from an undecylenic acid functionalized porous Si demonstrated a large PL red-shift (∼ 75 nm) during 2.5 hours of protein incubation in our previous work. [1] Here we present a similar in-situ PL study of surface functionalized planar Si (Si:COOH). The PL of Si:COOH exhibited a 5 nm red-shift in its peak frequency and an approximately 10% drop in its intensity after incubation in a protein solution. Vibrational spectroscopic characterization was carried out upon the Si:COOH sample for which we observed the PL red-shift. The infrared absorption spectra showed clear evidence of protein adsorption on Si:COOH. This correlation study between the PL peak energy and the vibrational spectrum provided strong evidence that the observed red-shift was due to the formation of semiconductor-protein (Si:COOH:BSA) complexes.
Laser-assisted chemical vapor deposition of carbon coated cobalt nanoparticles
Authors: Alm Oscar , Carlsson J.-O. , Boman M.
Published: April 2011

Carbon coated nanoparticles were synthesized by laser-assisted (ArF excimer laser, λ = 193 nm) chemical vapor deposition (LCVD). The particles were formed in the gas-phase by photolytic dissociation of cobaltocene in argon and the particles were deposited onto a silicon substrate. The particles were deposited at two different laser fluencies, 70 and 300 mJ/cm2.

Single crystalline spherical cobalt particles with a well-defined carbon shell were observed by transmission electron microscopy (TEM) for the highest fluence, 300 mJ/cm2. The metallic nucleus phase were identified as either β-Co or Co3O4. Polycrystalline particles were deposited at 70 mJ/cm2, these particles contained α-Co, β-Co, CoO and Co3O4. The particles deposited at 300 mJ/cm2were log-normally distributed and the total diameter had a mean geometric size of 25 nm while the nuclei had a mean diameter of 10 nm. X-ray photoelectron spectroscopy (XPS) measurements showed that the particles had a carbon content roughly ten times the amount of cobalt. Sputtering showed that both cobalt oxide and metallic cobalt was present. HRTEM micrographs of the particles revealed that only one phase was present in the whole nucleus, proving the nuclei were either oxide or metallic. Raman spectroscopy showed that that the carbon shell contained mostly amorphous carbon. Small domains of carbon of more graphitic character was embedded in the amorphous carbon shell in the 300 mJ/cm2sample.
Self-Assembly of Magnetic and Semiconductiong Nanoparticles on Modified Diblock Copolymer Templates
Authors: Yufa Nataliya A , Cisse Amadou L , Darling Seth B , Bader Sam D , Guyot-Sionnest Philippe , Sibener Steven J
Published: April 2011

Combining inorganic and organic components to create functional materials has been an active area of research in recent years. Inorganic components possess useful electric, photonic, or magnetic properties while organic components can self-assemble into a variety of morphologies on the nanoscale. We describe a novel approach for arraying nanoparticles using a modified diblock copolymer scaffold. Thin (30 nm) films of poly(styrene-block-methylmethacrylate) (PS-b-PMMA) copolymer were used as a substrate. Upon annealing, PS-b-PMMA forms lying-down cylinders of PMMA in a matrix of PS. These thin films were modified by exposure to ultraviolet light in vacuum which photochemically thinned the PMMA, creating a more highly corrugated surface. We find that colloidal superparamagnetic FePt nanodots and semiconducting CdSe nanodots deposited on this surface show a strong preference for the photochemically modified phase. This hierarchical self-assembly method may prove useful for many nanomaterials-based applications.
STM observation of formation process of carbon nanotube from 6H-SiC (000-1)
Authors: Maruyama Takahiro , Kawamura Yasuyuki , Bang Hyungjin , Fujita Naomi , Shiraiwa Tomoyuki , Tanioku Kenji , Hozumi Yoko , Naritsuka Shigeya , Kusunoki Michiko
Published: April 2011

Formation process of nanosized cap structures on a thermally treated 6H-SiC(000-1) substrate was investigated using atomic-resolution ultrahigh-vacuum scanning tunneling microscopy (UHV-STM). After formation of clusters of carobon particles 1-2 nanometer in diameter at 1150°C, these nanoparticles merged, forming nanosized cap structures. Hexagonal carbon networks, partly composed of pentagons, were clearly observed on the surface of the cap structures for a sample annealed above 1200°C. A model for the formation of carbon nanocaps on 6H-SiC(000-1) was proposed.
Ignition in Al-Fe2O3 Nanocomposites
Authors: Menon Latika , Bhargava Ram K. , Patibandla S. , Richter C. , Sacco A.
Published: April 2011

We demonstrated a novel approach to fabricate a self-assembled array of energetic nanocomposites which undergo an exothermic reaction at high temperature. The nanocomposites are a mixture of fuel and oxidizer materials where one of the components (fuel or oxidizer) is in the form of an array of nanowires embedded in the other component (oxidizer or fuel) which is in the form of a thin film. Our fabrication approach allows for a very high packing density of the nanocomposites, precise control of oxidizer-fuel sizes at the nanoscale level and intimate mechanical contact between oxidizer and fuel. Such nanocomposites will have important applications in novel energetic devices, for example MEMS-based fuzes, nanoexplosives and in applications requiring light-weight, single-use energy sources.
Sb surfactant-mediated epitaxy of Ge on Si(113) studied by AFM, SEM and GIXRD
Authors: Clausen Torben , Flege Jan-Ingo , Schmidt Thomas , Falta Jens
Published: April 2011

We have investigated the Sb surfactant-mediated growth of Ge on Si(113) over the temperature range from 500°C to 700°C. The surface morphology, film thickness, interface roughness and strain state of the films have been determined by the use of scanning electron microscopy, atomic force microscopy and grazing incidence x-ray diffraction. After growth at temperatures between 500°C and 600°C smooth Ge films have been observed, which show a partial strain relaxation. However, increasing the temperature to 700°C, a rough surface with a high density of three-dimensional islands has been found.
Nanoscale Assembly of Nanowires Templated by Microtubules
Authors: Zhou Jing , Luo Tzy-Jiun Mark , Gao Yan , Xue Mei , Lau Joseph , Hamasaki Toshikazu , Hu Evelyn , Wang Kang , Dunn Bruce
Published: April 2011

Conventional top-down lithographic processes approach their practical and theoretical limits at dimensional scales less than 100 nm. Alternative bottom-up methods are being investigated to build nanoscale architectures, including the use of biomolecules whose functional groups bind inorganic particles. In this study, the fabrication and alignment of microtubule-based nanowires are investigated. Microtubules (MT) are fibrous proteins found in nearly all eukaryotes. Our work was carried out using polymerized alpha- and beta-tubulins, which were cross-linked with glutaraldehyde to stabilize the protein structure. Ni coated microtubules were fabricated by reducing Ni2+ to Ni0 on Pd activated microtubule surface. Focus Ion Beam was used to write metal contacts on these Ni microtubule nanowires and DC conductivity values were measured. Au deposition on MT was performed by both electroless deposition and electrodeposition, by reducing HAuCl4 onto MT prebound with 2 nm Au colloids. Although most MTs exhibited discontinuous Au binding, a fraction of MTs were covered completely by Au. Preliminary electrical measurements for these materials are reported. Alignment of microtubules was also achieved by injecting MTs into microfluidic devices over amine-coated substrate surfaces. These biotemplating approaches are the first steps towards constructing more complicated 2D and 3D architectures.
Infrared Spectroscopic Characterization of Functional Monolayers on Silicon
Authors: Rowell Nelson , Tay Li-Lin , Baribeau Jean-Marc , Boukherroub Rabah , Lockwood David
Published: April 2011

Infrared vibrational spectroscopy in an attenuated total reflection geometry has been employed to investigate the presence of organic and inorganic thin layers on Si-wafer surfaces. Three different processes were compared for surface contaminant removal; microwave plasma, UV-ozone, and a piranha solution cleaning. The CH vibrations at 2928 and 2856 cm-1 characteristic of organic contaminants were monitored before and after each cleaning procedure to determine how well it removed surface contaminants. We found that native oxide removal from the Si surface should only be carried out after a cleaning essay. We observed that surface oxide removal exposed a hydrophobic bare Si surface, attracting organic molecules present in solution or the ambient. A large increase of the CH vibrational signature was observed for a Si wafer after an HF dip. A combination of plasma cleaning followed by UV-Ozone treatment was found the most effective one for Si wafer cleaning. We were able to evaluate the effectiveness of the cleaning methods, hydrogen surface passivation and oxide removal/regrowth.
Directed self assembly of nanocrystals within macroscopic to nanoscopic features
Authors: Stanley Scott K. , Coffee Shawn S. , Ekerdt John G.
Published: April 2011

This paper discusses a kinetically-driven patterning scheme to marry top-down and bottom-up assembly of nanoparticle arrays. We explain how Ge atoms interact with different dielectric surfaces to either etch the surface or to accumulate and self assemble into nanocrystals during chemical vapor deposition. By exploiting the different reactivity of these dielectrics, the accumulation of adatoms is controlled and thus subsequent self assembly of nanocrystals is controlled. Scanning electron microscopy and atomic force microscopy are used to determine particle densities. We have achieved dense (>1011 cm-2) arrays of self-assembled Ge nanocrystals within ∼100 µm sized features (defined by optical lithography) with no Ge deposition on the adjacent SiO2 sacrificial mask region. Electron beam lithography was used to pattern smaller (100 µm to 500 nm) features in which to direct the self assembly. As features shrink below 10 µm, nanoparticle nucleation within the feature is sharply affected. Finally, diblock copolymers are used to pattern 20 nm features to template self assembly of nanoparticles at a scale useful for device applications.
HRTEM and EELS Studies of GdSi2 Nanostructures Grown by Self-Assembly
Authors: Zhang Jiaming , Ye Gangfeng , Loloee R. , Crimp Martin A. , Nogami Jun
Published: April 2011

There has been considerable interest in the properties of rare earth metal nanostructures grown epitaxially on Si(001) surfaces. The questions arises as to what extent the nanometer scale lateral dimensions (width and thickness) affect the material properties. We compare thin film Gd silicide samples with Gd nanostructures grown on Si(001) using high resolution transmission electron microscopy (HRTEM). The nanostructures have the same orthorhombic crystal structure as the thicker silicide films. Electron energy loss spectroscopy measurements from metallic Gd and the thin film silicides are also shown as references for similar measurements on the nanostructures.
Structural and morphological variations of encapsulated metal oxides in single walled carbon nanotubes
Authors: Costa Pedro MFJ , Thamavaranukup Narun , Rutherford Thomas , Friedrichs Steffi , Sloan Jeremy , Green Malcolm
Published: April 2011

Single walled carbon nanotubes have been filled with a variety of metal oxides and the structural and morphological characteristics of the metal_oxide@SWNT composites studied. Advanced techniques of software aberrations correction for transmission electron microscopy were used for characterisation. This research shows that, despite their higher reactivity compared to salts such as halides, oxides can be encapsulated within SWNTs with some compounds attaining remarkable filling yields.
Assembly of Nanomaterials using Polymers and Biomaterials: Sensing and Electronic Applications
Authors: Lee Jaebeom , Kotov Nicholas A , Govorov Alexander O
Published: April 2011

The hybrid assembly of inorganic nanomaterials upon chemical and biological bonding has occupied attentions to yield manifold optical and electromagnetic properties. Nanomaterials that can be virtually conjugated with any other nanomaterials by ligand-receptor / antigen-antibody reactions, polymer tethering, and DNA hybridization are of importance for fundamental comprehension of electronic process in nano-scale regime as well as for development of advanced sensing and imaging devices. Semiconducting nanoparticles(NPs)/ nanowires(NWs) like CdTe that have compatibly narrow range of strong photoluminescence (PL) with broad range of absorbance band stand in the spotlight of imaging and sensing materials. Optical effects in noble metallic NPs such as Au and Ag have been worth noticing due to localized surface plasmons. These optical modes lead to highly localized electromagnetic fields outside the particles that take advantage of the development of novel system such as surface enhanced Raman spectroscopy (SERS) and highly compacted optoelectronic devices and sensors. In particular, it is known that metallic NPs has stronger plasmon field than the surface of bulky metals, leading to potent interactions to adjacent materials in secured conjugated superstructures that induce non-linear optical properties. In this report, we review on a novel biological / polymeric inspired hybrid superstructures between semiconducting CdTe nanowires and Au or Ag nanoparticles. This superstructure demonstrates remarkable optical effects i.e., PL en-hancement of NWs, sensing application for temperature and solvents stemming from SERS-like collective interactions of NPs and NWs., and light harvest from Förster resonance energy tra-nsfer (FRET).