bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of Resorcinol Formaldehyde Aerogel Using Photo-Acid Generators for Inertial Confinement Fusion Experiments
Authors: Saito K.M. , Paguio R.R. , Hund J.F. , Jimenez R. M. 
Published: September 2011

ABSTRACTTraditionally, the synthesis of resorcinol formaldehyde (R/F) aerogels consists of a 2-step (base/acid catalysis) polycondensation reaction. Since the acid catalyst in the reaction controls the gelation time, the replacement of the acid catalyst with a non-ionic photo-acid generator decreased the gelation time from hours, down to a few minutes at room temperature using a UV light source. The reaction rate was not only fast, but the liquid precursor was stable for several hours prior to UV exposure. After drying, the resulting aerogel porosity was characterized by scanning electron microscopy (SEM) and confirmed the internal structure of the aerogel was similar to the original R/F pore structures. This paper will discuss the modifications made to the traditional R/F formulation, as well as the benefits of a fast gelation time for aerogel casting applications such as thin films, cylinders, and solid and hollow microspheres.
Nonadiabatic Chemical-to-Electrical Energy Conversion in Catalytic Schottky Junction Nanostructures
Authors: Karpov Eduard G. , Mohan Jyotsna 
Published: September 2011

ABSTRACTNonadiabatic energy dissipation by electron subsystem of nanostructured solids unveil interesting opportunities for the solid-state energy conversion and sensor applications. We found that planar Pd/n-SiC, Pt/n-GaP and Pd/n-GaP Schottky structures with nanometer thickness metallization demonstrates a nonadiabatic channel for the conversion into electricity the energy of a catalytic hydrogen-to-water oxidation process on the metal layer surface. The observed abovethermal current greatly complements the usual thermionic emission current, and its magnitude is linearly proportional to the rate of formation and desorption of product water molecules from the nanostructure surface. The possibilities and advantages of utilizing the nonadiabatic functionality in a novel class of chemical-to-electrical energy conversion devices are discussed. The technology has a potential for a very high volumetric energy density due to the intrinsically planar device architecture.
Ferromagnetism in lightly Gd doped GaN: The role of defects
Authors: Mishra J. K. , Dhar S. , Khaderabad M. A. , Brandt O. 
Published: September 2011

ABSTRACTGd:GaN layers grown with different Gd concentrations by molecular beam epitaxy (MBE) are studied using photoconductivity and photo-thermoelectric power spectroscopy. Our study reveals that the incorporation of Gd produces a large concentration of acceptor-like defects in the GaN lattice. The defect band is found to be located ~450meV above the valence band. Moreover, the concentration of defects is found to increase with the Gd concentration. The effect of annealing on the structural and the magnetic properties of GaN implanted with Gd is also investigated. A clear correlation between the saturation magnetization and the defect density is observed in implanted samples. The colossal magnetic moment per Gd ion and the ferromagnetism observed in this material is explained in terms of the formation of giant defect cluster around each Gd ion.
Structural, Magnetic and Electronic Properties of Dilute MnScN(001) Grown by RF Nitrogen Plasma Molecular Beam Epitaxy
Authors: Constantin Costel , Wang Kangkang , Chinchore Abhijit , Chia Han-Jong , Markert John , Smith Arthur R. 
Published: September 2011

ABSTRACTThe structural, magnetic, and electronic properties of dilute Mn-doped scandium nitride thin films grown by radio frequency N-plasma molecular beam epitaxy are explored. The results indicate a small magnetization extending up to as high as 350K. There is a slight dependence on the manganese concentration, with the lower Mn concentration showing a larger saturation magnetization.
Synthesis of New Flexible Aerogels from Di- and Trifunctional Organosilanes
Authors: Hayase Gen , Kanamori Kazuyoshi , Nakanishi Kazuki , Hanada Teiichi 
Published: September 2011

ABSTRACTRecent years, although silica aerogels are expected to be the promising material for energy savings, the lack of mechanical strength prevents from commercial applications such as to low-density thermal insulators. To improve mechanical properties, methyltrimethoxysilane (MTMS) and dimethyldimethoxysilane (DMDMS) are used in this study as the co-precursor of aerogels because the network becomes flexible due to the relatively low cross-linking density and to the unreacted methyl groups. Because of the strong hydrophobicity of MTMS/DMDMS-derived condensates, phase separation occurs in aqueous sol and must be suppressed to obtain uniform and monolithic gel. We employed surfactant n-hexadecyltrimethylammonium chloride (CTAC) in starting compositions to control phase separation during a 2-step acid/base sol-gel reaction. By changing the starting composition, various microstructures of pores are obtained. In the uniaxial compression test, the aerogel showed high flexibility and spring-back to the original shape after removing the stress.
Low temperature CVD growth of graphene nano-flakes directly on high K dielectrics
Authors: Rümmeli Mark H. , Bachmatiuk Alicja , Dianat Arezoo , Scott Andrew , Börrnert Felix , Ibrahim Imad , Zhang Shasha , Borowiak-Palen Ewa , Cuniberti Gianaurelio , Büchner Bernd 
Published: September 2011

ABSTRACTThe potential of MgO and ZrO2 as catalytically active substrates for graphene formation via thermal CVD is explored. Experimental observations show the growth of single and multi-layer graphene nano-flakes over MgO and ZrO2 at low temperatures. The graphene nano-flakes are found to anchor at step sites. Ab initio calculations indicate step sites are crucial to adsorb and crack acetylene.
Metal-catalyzed graphitization in Ni-C alloys and amorphous-C/Ni bilayers
Authors: Saenger Katherine L. , Lavoie Christian , Carruthers Roy , Bol Ageeth A. , Mcardle Timothy J. , Chu Jack O. , Tsang James C. , Grill Alfred 
Published: September 2011

ABSTRACTMetal-catalyzed graphitization from vapor phase sources of carbon is now an established technique for producing few-layer graphene, a candidate material of interest for post-silicon electronics. Here we describe two alternative metal-catalyzed graphene formation processes utilizing solid phase sources of carbon. In the first, carbon is introduced as part of a cosputtered Ni-C alloy; in the second, carbon is introduced as one of the layers in an amorphous carbon (a-C)/Ni bilayer stack. We examine the quality and characteristics of the resulting graphene as a function of starting film thicknesses, Ni-C alloy composition or a-C deposition method (physical or chemical vapor deposition), and annealing conditions. We then discuss some of the competing processes playing a role in graphitic carbon formation and review recent evidence showing that the graphitic carbon in the a-C/Ni system initially forms by a metal-induced crystallization mechanism (analogous to what is seen with Al-induced crystallization of amorphous Si) rather than by the dissolution-upon-heating/precipitation-upon-cooling mechanism seen when graphene is grown by metal-catalyzed chemical vapor deposition methods.
On the Formation of Carbon Nanotube Serpentines: Insights from Multi-Million Atom Molecular Dynamics Simulation
Authors: Machado Leonardo D. , Legoas Sergio B. , Soares Jaqueline S. , Shadmi Nitzan , Jorio Ado , Joselevich Ernesto , Galvao Douglas S. 
Published: September 2011

ABSTRACTIn this work we present preliminary results from molecular dynamics simulations for carbon nanotubes serpentine dynamics formation. These S-like nanostructures consist of a series of parallel and straight nanotube segments connected by alternating U-turn shaped curves. Nanotube serpentines were experimentally synthesized and reported in recent years, but up to now no atomistic simulations have been carried out to address the dynamics of formation of these structures. We have carried out fully atomistic molecular dynamics simulations in the framework of classical mechanics with a standard molecular force field. Multi-million atoms structures formed by stepped substrates with a carbon nanotube (about 1 micron in length) placed on top of them have been considered in our simulations. A force is applied to the upper part of the tube during a short period of time and then turned off and the system set free to evolve in time. Our results showed that these conditions are sufficient to form robust serpentines and validate the general features of the ‘falling spaghetti mechanism’ previously proposed to explain their formation.
Curvature-induced Symmetry Lowering and Anomalous Dispersion of Phonons in Single-Walled Carbon Nanotubes
Authors: Reppert Jason , Podila Ramakrishna , Li Nan , Loebick Codruta Z. , Stuart Steven J. , Pfefferle Lisa D. , Rao Apparao M. 
Published: September 2011

ABSTRACTHere we report rich and new resonant Raman spectral features for several sub-nanometer diameter single wall carbon nanotubes (sub-nm SWNTs) samples grown using chemical vapor deposition technique operating at different temperatures. We find that the high curvature in sub-nm SWNTs leads to (i) an unusual S-like dispersion of the G‑band frequency due to perturbations caused by the strong electron-phonon coupling, and (ii) an activation of diameter-selective intermediate frequency modes that are as intense as the radial breathing modes (RBMs). Furthermore, an analytical approach which includes the effects of curvature into the overlap integral and the energy gap between the van Hove singularities is discussed. Lastly, we show that the phonon spectra for sub-nm SWNTs obtained from the molecular dynamic simulations which employs a curvature-dependent force field concur with our experimental observations.
Properties Modeling of Low-Dimensional Carbon Nanostructures
Authors: Basteev Andrew , Bazyma Leonid , Ugryumov Mykhaylo , Chernishov Yuriy , Slepicheva Margarita 
Published: September 2011

ABSTRACTThe modeling of single wall carbon nanotubes properties (length, diameter, chirality, defective wall structure) influence on sorption capability at different thermodynamic conditions (T= 80-273 К; P = 2-12 MPa) is presented in this work. The applied simulation procedure is the molecular dynamics as well the new event-driven simulation algorithm has been used. In the frameworks of this event-driven simulation algorithm the modeling of structure formation for carbon nanotubes have been done with different chirality and with wall defects presence. The analysis of obtained results and their comparison with published experimental and theoretical results are performed.
Effect of Sidewall Fluorination on the Mechanical Properties of Catalytically Grown Multi-Wall Carbon Nanotubes
Authors: Ganesan Yogeeswaran , Peng Cheng , Ci Lijie , Khabashesku Valery , Ajayan Pulickel M. , Lou Jun 
Published: September 2011

ABSTRACTWe report on the usage of a simple microfabricateddevice, that works in conjunction with a quantitative nanoindenter inside a scanning electron microscope (SEM), for the in situ quantitative tensile testing of individual sidewall fluorinated multi-wall carbon nanotubes (MWNTs). The stress vs. strain curves and the tensile strength values for five fluorinated specimens have been presented and compared to those of pristine MWNT specimens (data reported earlier). The fluorinated specimens were found to deform and fail in a brittle fashion similar to pristine MWNTs. However, sidewall fluorination was found to have considerably degraded the mechanical properties (tensile strength and load bearing capacity) of the MWNTs.
Dynamics of Graphene Nanodrums
Authors: Brunetto Gustavo , Legoas Sergio B. , Coluci Vitor R. , Lucena Liacir S. , Galvao Douglas S. 
Published: September 2011

ABSTRACTRecently, it was proposed that graphene sheets deposited on silicon oxide can act as impermeable atomic membranes to standard gases, such as helium, argon, and nitrogen. It is assumed that graphene membrane is clamped over the surface due only to van der Waals forces. The leakage mechanism can be experimentally addressed only indirectly. In this work we have carried out molecular dynamics simulations to study this problem. We have considered nano-containers composed of a chamber of silicon oxide filled with gas and sealed by single and multi-layer graphene membranes. The obtained results are in good qualitative agreement with the experimental data. We observed that the graphene membranes remain attached to the substrate for pressure values up to two times the largest value experimentally investigated. We did not observe any gas leakage through the membrane/substrate interface until the critical limit is reached and then a sudden membrane detachment occurs.
Characterizing the effect of uniaxial strain on the surface roughness of Si nanowire MEMS-based microstructures
Authors: Escobedo-Cousin E. , Olsen S.H. , Pardoen T. , Bhaskar U. , Raskin J.-P. 
Published: September 2011

ABSTRACTThis work addresses the paucity of roughness measurements by reporting on roughness parameters in uniaxial strained Si beams relevant for state of the art MOSFETs, nanowire and MEMS devices, with varying degrees of strain. Roughness is characterized by high resolution AFM and strain is characterized by Raman spectroscopy. Microstructures comprising a silicon nitride actuator are used to induce a wide range of stress levels in Si beams. The microstructures also allow the comparison of surface evolution in the strain direction (along the Si beam) compared with the unstrained direction (across the Si beam). A gradual reduction in rms roughness amplitude and increase in roughness correlation length in the direction of the applied stress are found for increasing values of strain. In contrast, surface roughness in the direction perpendicular to the applied stress remained largely unchanged from the unstrained initial state.
Improving PZT Thin Film Texture Through Pt Metallization and Seed Layers
Authors: Sanchez L.M. , Potrepka D.M. , Fox G.R. , Takeuchi I. , Polcawich R.G. 
Published: September 2011

ABSTRACTLeveraging past research activities in orientation control of lead zirconate titanate (PZT) thin films [1,2], this work attempts to optimize those research results using the fabrication equipment at the U.S. Army Research Laboratory so as to achieve a high degree of {001}- texture and improved piezoelectric properties. Initial experiments examined the influence of Ti/Pt and TiO2/Pt thins films used as the base-electrode for chemical solution deposition PZT thin film growth. In all cases, the starting silicon substrates used a 500 nm thermally grown silicon dioxide. The Pt films were sputter deposited onto highly textured titanium dioxide films grown by a thermal oxidation process of a sputtered Ti film [3]. The second objective targeted was to achieve highly {001}-textured PZT using a seed layer of PbTiO3 (PT). A comparative study was performed between Ti/Pt and TiO2/Pt bottom electrodes. The results indicate that the use of a highly oriented TiO2 led to highly {111}-textured Pt, which in turn improved both the PT and PZT orientations. Both PZT (52/48) and (45/55) thin films with and without PT seed layers were deposited and examined via x-ray diffraction methods (XRD) as a function of annealing temperature. As expected, the PT seed layer provides significant improvement in the PZT {001}-texture while suppressing the {111}-texture of the PZT. Improvements in the Lotgering factor (f) were observed upon comparison of the original Ti/Pt/PZT process (f=0.66) with samples using the PT seed layer as a template, Ti/Pt/PT/PZT (f=0.87), and with films deposited onto the improved Pt electrodes, TiO2/Pt/PT/PZT (f=0.96).
Mechanical and Material Characterization of Bilayer Microcantilever-based IR detectors
Authors: Lin I-Kuan , Du Ping , Zhang Yanhang , Zhang Xin 
Published: September 2011

ABSTRACTInfrared radiation (IR) detection and imaging are of great importance to a variety of military and civilian applications. Microcantilever-based IR detectors have recently gained a lot of interest because of their potential to achieve extremely low noise equivalent temperature difference (NETD) while maintaining low cost to make them affordable to more applications. However, the curvature induced by residual strain mismatch within the microcantilever severely decreases the device performance. To meet performance and reliability requirement, it is important to fully understand the deformation of IR detectors. Therefore, the purpose of this study is threefold: (1) to develop an engineering approach to flatten IR detectors, (2) to model and predict the elastic deformation of IR detectors using finite element analysis (FEA), and (3) to study the inelastic deformation during isothermal holding.
Investigation and Study of a Transparent and Translucent Facade System, with a Minimum Thickness, a Free Form Design, and a High Thermal Insulation Value to be used in to Architectural Development
Authors: Alonso Luis A. , Lauret Benito , Alonso Fernando 
Published: September 2011

ABSTRACTThis article examines, from the energy viewpoint, a new lightweight, slim, high energy efficient, light-transmitting envelope system, providing for seamless, free-form designs for use in architectural projects. The research was based on envelope components already existing on the market, especially components implemented with granular silica aerogel insulation, as this is the most effective translucent thermal insulation there is today. The tests run on these materials revealed that there is not one that has all the features required of the new envelope model, although some do have properties that could be exploited to generate this envelope, namely, the vacuum chamber of vacuum insulated panels (VIP), the monolithic aerogel used as insulation in some prototypes, and reinforced polyester barriers. By combining these three design components — the high-performance thermal insulation of the vacuum chamber combined with monolithic silica aerogel insulation, the free-form design potential provided by materials like reinforced polyester and epoxy resins—, we have been able to define and test a new, variable geometry, energy-saving envelope system.
Sub-Micron Feature Patterning of Thermoplastics using Multi-Scale BMG Tooling
Authors: Stratton Dermot J. , Byrne Cormac , Mulcahy James , Browne David J. 
Published: September 2011

ABSTRACTOne potential application for Bulk Metallic Glasses (BMGs) is in dies with micro- and nano-sized features. Three basic characteristic sets inherent to BMGs make them ideal materials for micro/nano-tooling applications: (1) excellent compressive strength, wear and corrosion resistance; (2) amorphous structure which presents no microstructural length scale limitation to cutting and forming operations; (3) the presence of a glass transition temperature above which they can be easily formed. There are many potential applications for multi-scale BMG tooling, including in production of microfluidic and other precision biomedical devices. In the current work, discs were cut from 5 mm diameter cylindrical specimens of Zr44Cu40Al8Ag8 BMG produced via arc melting and casting into water-cooled copper molds. The cylindrical specimens were then thermoplastically formed into thin coin-like disc samples. The thin disc-shaped plates were then ground and polished to create a smooth flat surface. Sub-micron-sized features were patterned into the plates via a focused ion beam. We demonstrated that such feature sizes are not achievable in conventional crystalline metallic tool materials. The patterned BMG tools were then set in a compression press where the platen temperature was precisely controlled and a series of load-controlled embossing trials were carried out in which the features of the BMG tooling were replicated in poly(methyl methacrylate) (PMMA) sheet. An exercise in mapping out the size limitation of such a multi-scale embossing operation is reported.
Digital Pulsed Force Mode AFM and Confocal Raman Microscopy in Drug-Eluting Coatings Research
Authors: Haugstad G. , Wormuth K. 
Published: September 2011

ABSTRACTControlled release of amorphous drug from a polymer matrix depends intimately upon the degree of mixing of drug and polymer, the susceptibility of the drug to crystallization, and the ability of the drug to dissolve and diffuse through water-swollen polymer. Characterization methods ideally would follow these processes on the molecular level in situ and in real time. We move closer to this ideal state of characterization through application of two imaging methods: digital pulsed force mode atomic force microscopy (D-PFM AFM) and confocal Raman microscopy (CRM). We examine model spin-coated films ~1 μm thick containing the drug dexamethasone dispersed in poly(n-alkyl methacrylate) homopolymer and blend coatings. We report aqueous-immersion studies of surface and subsurface structural changes due to drug elution over time frames ranging from very fast (a few minutes) to slow (tens of hours).
Circular AFM Mode: A New AFM Mode for Investigating Surface Properties
Authors: Noel Olivier , Mazeran Pierre-Emmanuel , Nasrallah Hussein 
Published: September 2011

ABSTRACTFor the first time, a new AFM mode is presented that simultaneously allows the measuring of adhesion and friction forces at different constant and continuous sliding velocities. Our methodology consists of implementing a circular relative displacement of the contact to reach a constant sliding velocity, with no stop periods. Some of the main advantages of performing a circular displacement is that continuous and high sliding velocities (more than 1 mm/s) can be reached compared to the low sliding velocities (up to 10 μm/s) available when using commercial AFM. Also, a stationary state is reached when doing measurements. Moreover, the circular mode can be coupled with the classical operating mode, for instance, force spectrum. Main applications of this circular mode are related to metrological measurements in physics that require high speed displacements. As an example, we report the evolution of friction and adhesive forces measured in air at different high sliding velocities.
Scanning Probe Microscopy with Diamond Tip in Tribo-nanolithography
Authors: Lysenko Oleg , Grushko Vladimir , Mitskevich Evgeni , Mamalis Athanasios 
Published: September 2011

ABSTRACTThe results obtained by direct nano-patterning demonstrate the potential of the SPM-based techniques that include surface scratching to create 3D nanostructures. Such techniques became known as tribo-nanolithography and have prospects of being successfully implemented in the future nanofabrication industry. An important obstacle to this, however, is the effect of wear at the nanometer scale which is critical to the stability of tribo-nanolithoraphic processes. Such stability is achievable via in-depth theoretical and experimental studies of friction at the nanoscale along with the development of pioneering equipment. Our work presents the results of experimental fabrication of nanostructures formed by nanoscratching with the use of the multifunctional scanning tunneling microscopy previously developed by the authors. The authors attempted scratching the silicon surface by using a boron-doped diamond tip. This operation was undertaken in the same direction sequentially with the tip sliding a side of the groove by one of the tip’s facets and the consequent surface scanning. Although not being applicable to non-conductive surfaces, the proposed technique has significant advantages. One advantage is related to the high stiffness of the tunneling probe as compared to the stiffness of the AFM cantilever. High stiffness and perpendicularity of the tip to the surface during surface processing eliminates bending beam effects on the typical AFM and ensures machining effectiveness. Purposely synthesized boron-doped single-crystal diamonds were used as a tip material. The results of experimental fabrication of nanostructures formed by nanoscratching with the use of the multifunctional scanning probe are demonstrated and discussed.