bluuebunny/crossref_metadata_2025 huggingface dataset:
Single-Step Microstructure Patterning in Titania-Doped Sol-Gel Glassy Thin Films with Electron Beams
Authors: Luo Xinshi , Zha Congji , Luther-Davies Barry
Published: April 2011

To achieve a simplified microstructure patterning process, patterning in thin films with a singlestep exposure to UV-light or E-beam process for fabrication of integrated optical waveguides and components is of great interest in optics, because the complicated structure developing stage by wet chemical or plasma etching is not required. In this paper, we describe our study on the microstructure patterning in TiO2-doped hybrid glassy polymer thin films by irradiating with focused E-beam. An anhydrous sol-gel process based on hydrolysis and condensation of metal alkoxides with boric acid under non-hydrous conditions was applied to homogeneously incorporating TiO2into silica network, and transparent glassy TiO2-doped thin films with varied TiO2concentrations (up to 40 mol%) were prepared by spin coating the hybrid polymer onto fused silica substrates and silicon wafers. The TiO2-doped hybrid material showed a low OH absorption, low optical losses at the telecommunication windows (<0.40 dB/cm at 1550 nm and <0.20 dB/cm at 1310 nm respectively), good thermo-optical linearity and good thermal stability up to 200 °C. Single-step direct surface patterning in the TiO2-doped hybrid glassy films with focused electron beams irradiation showed that fine structure with resolution at submicron level can be fabricated. As the process does not need a developing (etching) process, the profiles of the lines fabricated by the E-beam direct writing showed few distortion. The high precise patterning microstructure with submicron feature sizes in the TiO2-doped hybrid glassy thin films may provide potentials for applications to the fabrication of optical gratings.
New High-Dielectric-Constant Polymer-Ceramic Composites
Authors: Arbatti Milind , Shan Xiaobing , Cheng Z.-Y.
Published: April 2011

A ceramic-powder polymer composite, making use of a newly developed ceramics - CaCu3Ti4O12 (CCTO) - that has a giant dielectric constant as the filler, is developed. In this work, poly(vinylidene fluoride - trifluoroethylene) [P(VDF-TrFE)] 55/45 mol% copolymer was used as matrix. It is found that the wettability between the copolymer and CCTO is poor, which makes the solution cast composites have a poor uniformity. The uniformity and thus the dielectric constant of the composites can be significantly improved by using hot-press technology to form “sandwich” structure. It is also found that the thermal annealing process can improve the dielectric constant of the composite. The experimental data show that for the flexible composites the dielectric constant at 1 kHz can reach more than 300 at room temperature and more than 700 at ∼70 °C.
Hybrid materials for Optical Limiting
Authors: Örtenblad Marcus , Parola Stephane , Chaput Frédéric , Desroches Cédric , Sigala Catherine , Létoffé Jean Marie , Miele Philippe , Baldeck Patrice L. , Eliasson Bertil , Eriksson Anders , Lopes Cesar
Published: April 2011

Materials based on alkynyl platinum derivatives and thiacalixarenes were prepared through the sol-gel process The molecular species were grafted to the matrix (class II hybrid) in order to maximise the concentration and the stability of the final solid-state material Broadband optical limiting performance in the visible wavelength region was observed in the prepared materials Thermomechanical characterisation of the matrix is also discussed.
The Synthesis and Characterization of Energy-Conducting Polymers with Pendant Inorganic Chromophores
Authors: Alstrum-Acevedo James H. , DeSimone Joseph M. , Schauer C. K. , Papanikolas John M.
Published: April 2011

We are interested in the synthesis, characterization, and performance evaluation of functional nanoscale materials comprised of a polymeric scaffold with appended cationic transition-metal lumiphores. We have developed a methodology to prepare, spectroscopically characterize, and evaluate a series of organic copolymers functionalized with inorganic chromophores. Preparation of these hybrid systems first involves the synthesis of a linear AB diblock copolymeric scaffold in which A is polystyrene (PS) and B is poly(p-tert-butoxycarbonyloxystyrene) (PStBOC), using Reversible Addition-Fragmentation chain-Transfer (RAFT) radical polymerization. The PStBOC block (B) was converted into poly(4-hydroxystyrene) by acid hydrolysis of the t-BOC moieties, and Ru(II) trisbipyridyl complexes were covalently appended using standard ester coupling reagents. These lumiphores were selected due to their strong absorbance in the visible spectrum, chemical/photochemical stability, useful redox properties, and long-lived excited state lifetimes. Attachment of the cationic transition-metal chromophores to block B of these linear AB diblock copolymeric arrays is expected to promote solid-state self-assembly into nanoscale structures. The metal-loaded macromolecular assemblies were characterized spectroscopically and the determination of the solid-state morphology of films of these materials was investigated using Transmission Electron Microscopy (TEM).
Interlamellar Incorporation of Charged Polymer Nanobeads into Sodium Montmorillonite
Authors: Khvan Svetlana , Lee Sang-Soo , Kim Junkyung
Published: April 2011

Complete delamination of clay in polymer matrix has been strongly prohibited due to strong adhesion of guest polymer chains between hydrophilic clay as well as degradation and desorption of organic materials in the gallery at high temperature. Incorporation of charged nanosized polystyrene beads directly into the gallery of pristine clay through exfoliation-exchange mechanism has been proposed to overcome the drawbacks.

Synthesis of polymer nanobeads via emulsifier-free emulsion polymerization allowed to achieving formation of particles of appropriate particle size and surface charge density. Surface characterization, performed with XPS and ToF SIMS, has provided the results on the existence and the nature of the functional groups on the polymer particle surface, which have been found to be in a good compliance.

Morphology of polymer-incorporated clay was observed from TEM, FE-SEM images. Study on mechanism of incorporation via XRD, XPS, ToF-SIMS suggested that adsorption of polymer nanobeads through cationic exchange of intergallery cation of clay for onium ion at the surface of polymer nanobead not only improves compatibility of clay with polymer matrix, but, what is essential, dramatically promotes expansion of clay gallery.
Spontaneous Formation of Ridges on Patterned Mesas and Their Role in the Evolution of Step Arrays
Authors: Chang Kee-Chul , Blakely Jack M.
Published: April 2011

Mesa structures fabricated on Si(111) surfaces have been found experimentally to develop step arrays with large spacing of the order of a micron or more after annealing at temperatures where sublimation becomes important. Ridges around the edges initially develop during annealing and form barriers to step motion before eventually breaking down. This produces an array of steps of the same sign with a few wide terraces. Computer simulations using one dimensional Burton, Cabrera and Frank (BCF) theory including attachment-detachment rates and step-step repulsion for this configuration show that the terraces evolve under different dynamics depending on the terrace widths. For large terrace widths, sublimation dominates the step dynamics and the Ehrlich-Schwoebel effect is negligible. Sinusoidal terrace width distributions result in this case. The experimentally measured step distribution has such a sinusoidal shape suggesting that the step dynamics is sublimation dominated on the mesas after ridge breakdown.
Photo Etching of Polyimide Thin Film by TiO2 Micro Wire Prepared Using Phase Separation-Selective Leaching Method
Authors: Sone Y. , Nishio K. , Yasumori A.
Published: April 2011

TiO2 photocatalysts have a strong oxidation ability for organic compounds under UV irradiation. The surfaces of polyimide and polymethyl methacrylate (PMMA) were photocatalytically machined using a porous TiO2 wire prepared by phase separation and selective leaching with elongation. After UV irradiation, these surfaces were decomposed along the length of the TiO2 wire. Such surface decomposition depended on the irradiation angle of UV light and irradiation time. The machining rate of PMMA was higher than that of the polyimide.
Topography Evolution of Si (001) Substrate Fabricated by Ar+ Ion Beam Sputter Etching
Authors: Kim Hyung Seok , Suh Ju Hyung , Park Chan Gyung
Published: April 2011

Self-formed nanopatterns on Si (001) substrates fabricated by ion beam sputter etching were investigated by atomic force microscopy (AFM). The ion beam sputtering was performed with an Ar+ ion beam produced from a Kaufman type ion gun. In order to fabricate the periodic nanoscale patterns on Si surface, the effects of sputter parameters such as ion energy, flux, incident angle and etching time on surface morphology was investigated. As a result, nanometer scale ripples and 3-dimensioal nanodots were formed uniformly after ion beam sputtering. The surface morphology of Si was significantly dependent on incident angle and ion beam flux.
Fabrication of High Aspect Ratio Nanoscale Pit Using Carbon Nanotube Probe
Authors: Arima Norikazu , Matsumuro Akihito
Published: April 2011

We developed a method to fabricate nanoscale pits having high aspect ratio, using a scanning tunneling microscope with an attached carbon nanotube (CNT) probe. CNT probes used in this study were synthesized by the pulling method. The nanostructures were produced in Au thin film in an ambient pressure and room temperature. The results of our experiment show that a threshold value exists for the fabrication of the pits between 1 V and 2 V. The depth and diameter of the pit increased with the increase in the bias voltage and tunnel current, respectively. Consequently, a bias voltage of 3 V and tunnel current of 4 nA were found to be the optimum conditions for a high aspect ratio nanoscale pit fabrication. In changing the fabrication time at the optimum conditions, the depth of the pit increased with the increase in the fabrication time, with little change in the diameter of the pit. This demonstrates that CNT probes can be useful for fabricating nanoscale structures.
Controlled growth of nanowires using annealing and pulsed laser deposition
Authors: Park Hyun D. , Hogan Timothy P.
Published: April 2011

A new nanowire growth technique using annealing and pulsed laser deposition is described. The technique demonstrates the control in the precise nanowire growth temperature thereby yielding higher quality nanowires than obtained from simple annealing alone. InSb substrate and gold target were used to demonstrate the new technique. The results from the variation of gold deposits from 2.5 mins to 40 mins at the fixed growth temperature of 510 °C are discussed.
Nanopatterning of GaAs(110) vicinal surfaces by hydrogen-assisted MBE
Authors: Crespillo M. L. , Sacedón J. L. , Joyce B. A. , Tejedor P.
Published: April 2011

The effect of atomic hydrogen on the growth mode and surface morphology of GaAs(110) thin films grown by molecular beam epitaxy (H-MBE) has been studied for different kinetic regimes using atomic force microscopy (AFM). Growth in the Ga supply-limited regime after H-assisted oxide removal leads to the formation of multi-atomic step arrays by step bunching with a very uniform terrace size distribution in the 80 nm range. Growth under As-deficient conditions after H-assisted oxide removal induces a rapid self-organization of the GaAs(110) surface into a ridge pattern along the <001> tilt direction, which is broken down into a 3D mound morphology when H is also present during growth. A chacteristic nanofacetting of the surface with very straight <1–10> -type steps is observed at high temperatures regardless of atomic hydrogen being used during oxide desorption and/or epitaxial growth.
Photocatalysis of Columnar TiO2 Thin Films
Authors: Suzuki Motofumi , Kishimoto Kazuaki , Maekita Wataru , Nakajima Kaoru , Kimura Kenji
Published: April 2011

Photocatalysis of oblique columnar TiO2 thin films has been investigated as a function of thickness using photobleaching of methylene blue (MB). The degradation rate of MB depends on the thickness of the films, although no significant differences in the columnar morphology, crystallinity and optical absorption are found. The relation between the degradation rate and the thickness is well described by a simple model, in which the degradation rate at a certain depth is proportional to the intensity of ultra violet (UV) light. The photocatalytic active thickness is estimated at approximately 200 nm. Thus the interior surface of the oblique columnar TiO2 thin films works well as photocatalyst.
IN SITU Tem Study of Electron Beam Stimulated Organization of Three-Dimensional Void Superlattice in Caf2
Authors: Ding T. H. , Zhu S. , Wang L. M.
Published: April 2011

CaF2 is widely adopted as deep-UV window material and thin film optical coating. It has been known that ordered defect superlattices may form in electron irradiated CaF2.[1] However, the nature of the defects on the superlattice point (i.e., Ca colloids or voids) has not been certain and the self-organization mechanism has not been fully understood. In this study, single crystal CaF2 were irradiated under 200 keV electron beam at room temperature with in situ TEM observation of the dynamic process of defect ordering. The superlattice reached steady state after an electron dose of 1×1021e-/cm2 with void radius about 5 nm. Videos recorded during the in-situ observation reveal the dynamic self-organization process of the void superlattice. Coalescence was prevalent at the initial stages. Migration and preferential growth were dominant at the final stages of the superlattice formation. At a dose higher than 3×1021 e-/cm2 the superlattice structure was destroyed. These critical doses of void superlattice formation and deformation seem to be independent of dose rate. The anisotropic diffusivity of the migrating “molecules” may explain the superlattice formation.
Laser and particle beam irradiation effects in amorphous metals
Authors: Sorescu Monica
Published: April 2011

In view of the potential use of amorphous magnets as radiation-resistant materials, we performed a comparative study between laser and particle beam induced effects in amorphous alloy systems. We irradiated Fe81B13.5 Si3.5C2, Fe40Ni38Mo4B18, Fe66Co18B15Si1 and Fe72.6Cr22Al4.8Si0.3Y0.3 with pulsed laser radiation as well as with high (W=7 MeV) and low energy (W=30 and 50 keV) electrons and with 2.8 MeV alpha particles. The irradiation effects in these systems were investigated using several complementary techniques: transmission and conversion electron Mössbauer spectroscopy, magnetometry and electron microscopy. We were able to deduce details of the mechanism of magnetic texture formation and of the amorphous-to-crystalline phase transformations in the studied amorphous alloys.
Microstructure Development in High-Temperature Mo-Si-B Alloys
Authors: Sakidja R. , Perepezko J. H.
Published: April 2011

Mo-Si-B alloys are considered as potential high temperature structural materials due to their high melting points (above 2000°C) and excellent oxidation resistance attributed to their self-healing characteristics over an extended temperature range. In the current study, the effect of alloying additions to achieve lower weight density and microstructure stability has been examined. The critical factor to the alloying additions appears to be the stability of the high melting ternary-based T2 borosilicide phase.
Developing an Application for Refractory Open Cell Metal Foams in Jet Engines
Authors: Azzi Wassim E. , Roberts William L. , Rabiei Afsaneh
Published: April 2011

The thermodynamic efficiency of the Brayton cycle, upon which all gas turbines (aeropropulsion and power generation) are based on scales with the peak operating temperature. However, the peak temperature is limited by the turbine blades and the temperature they can withstand. The highest temperatures in the gas turbine occur in the combustor region but these temperatures are often too high for turbine blades. As a result, the combustion products must be diluted with relatively cooler air from the compressor to reduce the temperature to tolerable levels for the turbine blades. This research suggests placing a ring of high temperature open cell metal foam between the combustors and turbine sections of the jet engine to mix and average the difference in temperatures resulting from the cooling schemes in combustor cans. Temperature mixing effect was tested using a special setup with the application of an infrared camera and streams of hot and cold air passing through the foam. High speed flow pressure drop around Mach 1 (340 m/s) was done on the same foam samples to understand pressure drop in the compressible regime of air. Infrared imaging showed that open cell metal foams successfully mixed and averaged the difference in temperatures of the hot and cold gasses thus creating a more uniform temperature profile while pressure drop testing revealed that open cell metal foams result in minimal pressure drop at high flows especially when the increase in temperature in taken into consideration.
Nondestructive Damage Sensitivity and Reinforcing Effect of Functionalized Carbon Nanotube and Nanofiber/Epoxy Composites Using Electro-Micromechanical Techniques
Authors: Park Joung-Man , Jung Jin-Kyu , Kim Sung-Ju , Kim Dae-Sik , Lee Jae-Rock , Kim Tae-Wook
Published: April 2011

Nondestructive damage sensing and load transfer mechanisms of thermal treated carbon nanotube (CNT) and nanofiber (CNF)/epoxy composites were investigated using electro-micromechanical technique. Carbon black (CB) was used only for the comparison. Electro-micromechanical techniques were applied to obtain the fiber damage and stress transferring effect of carbon nanocomposites with their contents. Thermal treatment and temperature affected on apparent modulus and electrical properties on nanocomposites due to enhanced inherent properties of each CNMs. Coefficient of variation (COV) of volumetric electrical resistance can be used to obtain the dispersion degree indirectly for various CNMs. Dispersion and surface modification are very important parameters to obtain improved mechanical and electrical properties of CNMs for multifunctional applications. Further optimized functionalization and dispersion conditions will be investigated for the following work continuously.
Synthesis, Characterization, and Modeling of Nanotube Materials with Variable Stiffness Tethers
Authors: Frankland S. J. V. , Herzog M. N. , Odegard G. M. , Gates T. S. , Fay C. C.
Published: April 2011

Synthesis, mechanical testing, and modeling have been performed for a carbon nanotube material in which the nanotubes are functionalized with variable stiffness tethers (VST) capable of cross-linking the nanotubes. Tests using nanoindentation indicated a six-fold enhancement in the storage modulus when comparing the base material (the cross-linking agent with no nanotubes) to the composite (functionalized nanotube material) that contained 5.3 wt% of nanotubes. To understand how crosslinking the nanotubes may further alter the stiffness, a model of the system was constructed using nanotubes crosslinked with the VST. The model predicted that for a composite with 5 wt% nanotubes at random orientations, crosslinked with the VST, the bulk Young's modulus was reduced to 30% that of the non-crosslinked equivalent.
InAs Quantum Dot Development for Enhanced InGaAs Space Solar Cells
Authors: Raffaelle R. P. , Sinharoy Samar , William King C. , Bailey S. G.
Published: April 2011

The majority of high-efficiency space solar cells being produced today are based on multi-junction devices of lattice-matched III-V materials. An alternative which has been receiving an increasing amount of attention is the lattice mis-matched or metamorphic approach to multi-junction cell development. In the metamorphic triple junction cell under development by ERI and its partners, the InGaAs junction (bottom cell) of the three-cell stack is the current limiting entity, due to the current matching which must be maintained through the device. This limitation may be addressed through the incorporation of InAs quantum dot array into the depletion region of an InGaAs cell. The InAs quantum dots in the InGaAs cell will provide sub-gap absorption and thus improve its short circuit current. This cell could then be integrated into the three-cell stack to achieve a space solar cell whose efficiency exceeds current state-of-the-art standards. A theoretical estimate predicts that a InGaAlP(1.95eV)/InGaAsP(1.35 eV)/InGaAs(1.2 eV) triple junction cell incorporating quantum dots to improve the bottom cell current would have an efficiency exceeding 40%. In addition, theoretical estimates have demonstrated that the use of quantum dot structures may also hold other cell benefits such as improved temperature coefficients and better radiation tolerance, which are especially important for utilization in space. As a first step towards achieving that goal, we have initiated the development of InAs quantum dots on lattice-mismatched InGaAs (1.2 eV bandgap) grown epitaxially on GaAs by metallorganic vapor phase epitaxy (MOVPE). These quantum dots have been characterized via photoluminescence (PL) and atomic force microscopy (AFM). A correlation exists between the quantum dot size and resulting optical band structure and can be controlled via the synthesis parameters. Quantum dots were incorporated into prototype InGaAs devices. A comparison of the resulting photovoltaic efficiency under simulated 1 sun intensity and air mass zero (AM0) illumination and spectral response demonstrated that an improvement in the long-wavelength photoconversion efficiency was achieved through the incorporation of the InAs quantum dots.
Computer Simulation of Displacement Damage in Silicon Carbide
Authors: Devanathan R. , Gao F. , Weber W. J.
Published: April 2011

We have performed molecular dynamics simulation of displacement events on silicon and carbon sublattices in silicon carbide for displacement doses ranging from 0.005 to 0.5 displacements per atom. Our results indicate that the displacement threshold energy is about 21 eV for C and 35 eV for Si, and amorphization can occur by accumulation of displacement damage regardless of whether Si or C is displaced. In addition, we have simulated defect production in high-energy cascades as a function of the primary knock-on atom energy and observed features that are different from the case of damage accumulation in Si. These systematic studies shed light on the phenomenon of non-ionizing energy loss that is relevant to understanding space radiation effects in semiconductor devices.
Assessment of Shielding Material Performance for Deep Space Missions
Authors: Mansur L. K. , Frame B. J. , Gallego N. C. , Guetersloh S. B. , Johnson J. O. , Klett J. W. , Townsend L. W.
Published: April 2011

Radiation doses from galactic cosmic rays (GCR) are a significant issue for spacecraft crew exposures in deep space. We report initial work to evaluate a range of materials for GCR shielding. Earlier work has shown that conventional spacecraft materials, aluminum and higher atomic number structural alloys, provide relatively little shielding and, under certain conditions, may increase radiation risk. Materials containing high proportions of hydrogen and other low atomic mass nuclei provide improved GCR shielding. Polyethylene (PE) is generally considered a good performance benchmark shield material. However, PE shielding occupies volume and adds mass to the spacecraft. In this work we investigate several materials that are shown to provide shielding similar to PE, but which could furnish additional spacecraft functions, possibly eliminating the need for materials currently used for structural support or thermal management. Carbon forms that can incorporate a large mass of hydrogen, as well as polymers and polymer composites are being explored. Calculations of shielding effectiveness in GCR spectra have been carried out. Experiments to measure shielding properties recently have been completed at the NASA Space Radiation Laboratory (NSRL) located at Brookhaven National Laboratory (BNL) using high energy beans of O16. In this paper we report preliminary shielding results.
Raman Spectroscopy of Graphitic Foams
Authors: Barros Eduardo B. , Demir Nasser S. , Souza Filho Antonio G. , Filho Josué Medes , Jorio Ado , Dresselhaus Gene , Dresselhaus Mildred S.
Published: April 2011

To better understand the very high thermal conductivity to weight ratio of the graphitic foams recently developed at the Oak Ridge National Laboratory, a Raman spectroscopy study was performed. It was also shown that the Raman scattering can be useful for the characterization of the graphitic foam, being able to evaluate the quality of the samples with respect to the density and location of lattice defects.
Spectroscopic Investigations on the Effect of Proton Bombardment of Polyimide
Authors: Edwards David L , de Groh Kim K , Nehls Mary , Miller Sharon K , Banks Bruce , Stephens Chris , Artiaga Ramon , Benson Roberto , Balascuta S. , Zaleski Jeffrey M. , Chipara Mircea
Published: April 2011

The effect of the radiation component of the space environment on polyimide films is reviewed. Experimental data obtained by electron spin resonance and dynamical mechanical analysis proved that the ionizing radiation generates free radicals with a long lifetime through a dominant chain scission mechanism. The radiation-induced shift of the glass transition of polyimide towards lower values confirms the decrease of the average molecular mass of the polymer during irradiation. The importance of polyimide for space exploration is critically analyzed.
TEM Studies of Protective Al Coatings on Kapton H
Authors: Yang Judith C. , Xu Huiping , Li Long , Waters Deborah , Banks Bruce
Published: April 2011

Polymeric materials undergo rapid erosion when exposed to the harsh low-earth-orbit (LEO) environment. Coatings can reduce the erosion rate of polyimide Kapton from atomic oxygen (AO) attack. Specifically, we are investigating how thin Al coatings can protect Kapton. Protective Al layers with variations in layer thickness and growth conditions were deposited on Kapton H. The quality of these protective coatings were evaluated by mass loss measurement and compared to Kapton alone and the SiO2 coating, where dramatically decreased erosion rate was noted. To understand how these coatings protect Kapton as well as how the AO interacts with the coatings, we are investigating the microstructure of these coated materials by plane view and cross-sectional transmission electron microscopy (TEM) methods. To understand the AO degradation mechanism, we attempted to correlate the mass loss with growth conditions and microstructures. We noted a slight improvement in erosion resistance of the Al coating due to the presence of the dendrimer, but a major improvement when the Al coating is deposited under ultrahigh vacuum conditions.
New Materials on the Renaissance Artists' Palette
Authors: Berrie Barbara H. , Matthew Louisa C.
Published: April 2011

In the light of new documentary information regarding the range of materials available to sixteenth century artists, cross sections from paintings were re-examined using scanning electron microscopy - energy dispersive spectrometry. Among a variety of new materials, colored glassy pigments were found including diverse yellow glassy particles, specifically lead silicate and a glass colored by lead antimonate. These are the “yellow smalts” described in Renaissance writings on artists’ materials.
A Study of the Materials of Pontormo's “Portrait of Alessandro de' Medici”
Authors: Sutherland Ken , Price Beth A. , Passeri Irma , Tucker Mark
Published: April 2011

In studies of the materials of old master paintings, the characterization of thin and degraded layers often presents unusual challenges for routinely used methods of analysis. This paper discusses analyses performed as part of a study of the materials and techniques of Pontormo's “Portrait of Alessandro de’ Medici” (1534–5) carried out during a recent cleaning and restoration of the painting. Pontormo built up the portrait using a complex sequence of preparation, drawing and paint layers, the analysis of which was complicated further in some areas by the presence of degraded materials on the paint surface. The materials used for the various stages of preparation and painting were characterized by gas chromatography/mass spectrometry (GCMS), Fourier transform infrared microspectroscopy (FTIR) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). The focus of this paper will be the particular approaches taken to the characterization of the preparation layers and degraded surface materials.
Laser Cleaning of Fifteenth and Early Sixteenth Century A.D. Wax Votive Images from St. Peter's Cathedral, Exeter, England
Authors: Moreno Teresa
Published: April 2011

A rare collection of cast votive images (ex-votos) made of beeswax were found in the 1940s behind the cresting of a screen above the tomb of Bishop Edmund Lacey in the Cathedral Church of St. Peter in Exeter, England. Some of these fragmentary, aged and brittle waxes, dating to the late fifteenth to early sixteenth centuries A.D., served as the basis to further test the cleaning of dirt and accretions using a Q-switched Nd:YAG laser. Because of the low melting point of the wax, observations made of the effects on the wax substrate due to heat emitted from the laser were critical to establish the efficacy of the cleaning method. Preliminary optical microscopy was used to establish a typology of the waxes based on their condition, color, and nature of the weathering phenomena. Several techniques were used to characterize the waxes and the surface deposits, including gas chromatography-mass spectroscopy (GC-MS), energy-dispersive x-ray fluorescence (EDXRF) and scanning electron microscopy (SEM-EDS), in addition to simple tests of melting point and hardness that served to help understand the nature, condition and treatment of the waxes [1].
The Development of Ultra-cool Melt Adhesives for Mounting Resin-Coated (RC) Photographic Papers.
Authors: McGlinchey Chris , Yuan Bing
Published: April 2011

The development of an adhesive that is a hybrid between a pressure sensitive adhesive and a heat seal adhesive is described. The goal of this project, which is a joint collaboration between the Museum of Modern Art and the Polymer Research Institute, is to develop a preservation quality adhesive for application to RC print photographs. RC prints are clad in polyethylene, a low surface energy (LSE) polymer that requires special consideration when devising an adhesive to adhere to it. In arriving at a formula for this purpose research has focused on a combination of hydrocarbon-based polymers and low molecular weight oligomers. In addition, this work addresses other aspects such as activation conditions and joint design, factors critical to developing an adhesive that has the potential to satisfy the stringent criteria of a material acceptable to conservation applications.
Producing New Stone Consolidants for the Conservation of Monumental Stones
Authors: Mosquera María J. , de los Santos D.M. , Montes A.
Published: April 2011

A customary procedure in the protection of monumental buildings is the consolidation of decaying stone by the application of commercial products containing tetraethoxysilane (TEOS). These products polymerize within the porous structure of the decaying stone, significantly increasing the cohesion of the material. However, TEOS-based consolidants suffer practical drawbacks, such as cracking of the network during the drying phase, and significant blocking of the rock pores. These limitations are related to the growth of a dense microporous network of the xerogel inside the stone material, which is typical from TEOS sols. Therefore, the purpose of this work is to increase porosity of the product by including colloidal particles in the starting sol.

We prepared a colloid-polymer composite gel using TEOS and a commercial silica colloid. The percentage by weight of silica colloid particles to total silica was 54%. Ethanol and dibutyltindilaurate (DBLT) were chosen as solvent and catalyst, respectively. This catalyst promotes the gelation at a neutral pH, preventing stone decay related to acid or basic catalysis. We characterized the properties playing a key role in consolidation. Data were compared with those obtained using a popular commercial product: Tegovakon V 100 produced by Goldsmith.

In spite of the colloidal particle addition, sols exhibited viscosity values close to those of the commercial products, as a consequence of their dispersion in ethanol. A gelation time similar to that of commercial consolidants was maintained, whereas the contained sol was stable over a period of up to six months. Concerning textural parameters, the addition of colloid permitted to obtain a crack-free, mesoporous material structure. This generated a crack-free material whereas the gel from Tegovakon V 100 exhibited cracking.

We also evaluated the consolidant efficacy on a biocalcareous stone, one of the most common monumental building stone employed in the southwest of Spain. Three key parameters -penetration depth in the rock, mechanical properties and water vapour diffusivity- were measured. Stone permeation was similar to that from the commercial product. Notably, a significant improvement of compression strength of the stone was observed. Reduction in vapour diffusivity of the treated stone was slightly lower for our gel than for the commercial consolidant.
Estimation of Firing Temperature and Compositional Variability of Archaeological Pottery by Differential Scanning Calorimetry
Authors: Giordana A. , Peacock E. , McCarthy M. , Guilbeau K. , Jacobs P. , Seger J.D. , Ramsey W.G.
Published: April 2011

Digital Scanning Calorimetry (DSC), a thermal characterization technique, can be used to rapidly obtain a rough upper estimate of the firing temperature of archaeological pottery as well as an indication of its composition. The technique involves heating a small sample (10–20 mg) of ground ceramic above the vitrification temperature, cooling and reheating. The curves of the two heating cycles are then compared. The validity of the technique was evaluated by a blind test in which 35 tiles fired at different temperatures were analyzed without knowing their firing point, and by analysis of archaeological pottery samples assumed to be local or imported based upon stylistic criteria.
Ferromagnetism in Fe-doped β-Ga2O3 Prepared by a Solid State Reaction
Authors: Hojo Hajime , Fujita Koji , Tanaka Katsuhisa , Hirao Kazuyuki
Published: April 2011

Polycrystalline β-Ga2O3 doped with Fe3+, (Ga1−x Fex)2O3 (x=0.02, 0.05, 0.08 and 0.1), has been prepared by a solid-state reaction. Ferromagnetic ordering is observed at room temperature for samples prepared by β-Ga2O3 and Fe(NO3)3·9H2O and sintered at low temperatures below 900 °C, while the sintering at temperatures above 900 °C leads to the paramagnetic behavior. X-ray diffraction analysis for the samples sintered at 500 °C reveals that the single phase of β-Ga2O3 can be obtained up to x=0.08 without traces of secondary phase or other impurity. Magnetization as a function of temperature shows superparamagnetic or cluster spin-glass behavior, indicating that long-range ferromagnetic ordering does not exist in the present systems. It is suggested that the inhomogeneous distribution of Fe3+ is responsible for the ferromagnetic behavior.
Water-Dispersible FePt Nanoparticles Having ω-Mercapto-α-carboxylic Acid Ligands
Authors: Mabry Janis K. , Tackett Laura Beth , Bargaria Hitesh , Sun Xiangcheng , Ada Earl T. , Shamsuzzoha Mohammad , Sun Kai , Wang Lu-min , Johnson Duane T. , Nikles David E.
Published: April 2011

FePt nanoparticles, ∼ 2nm in diameter, were prepared by the polyol reduction of platinum(II) acetylacetonate and iron(III) acetylacetonate in the presence of oleyl amine and oleic acid surfactants. The particles were dispersed in hexane and the dispersion added to a solution of 11-mercaptoundecanoic acid in cyclohexanone. As the 11-mercaptoundecanoic acid ligands replaced the oleic acid ligands, the particles precipitated. The particles could be dispersed in basic water, made basic either with sodium hydroxide or ammonium hydroxide. X-ray photoelectron spectra showed a peak near 164 eV, sulfur (2p) confirming the presence of the thiol ligand. Similarly, the oleic acid ligands were replaced with either 3-mercaptopropionic acid or 16-mercaptohexadecanoic acid to give FePt particles that could be dispersed in water. Dispersions made with FePt nanoparticles having 11-mercaptoundeacnoic acid ligands and ammonium counter ions were dried on TEM grids to give highly ordered films consisting of close-packed arrays of FePt nanoparticles. When the counter ion was sodium, the particles tended to aggregate, instead of forming ordered arrays.
A Novel Fabrication Technique for Interacting Ferromagnetic-metal Nanoparticle Systems: Fine-tuning of Particle Diameter and Interparticle Spacing
Authors: Tomita Satoshi , Akamatsu Kensuke , Shinkai Hiroyuki , Ikeda Shingo , Nawafune Hidemi , Mitsumata Chiharu , Kashiwagi Takanari , Hagiwara Masayuki
Published: April 2011

Metallic Ni nanoparticles were embedded in polyimide (PI) films by applying a chemical surface modification technique. The technique consists of a simple alkali treatment of the PI films, an ion exchange reaction, and thermal annealing. The transmission electron microscopic studies showed that the initial alkali treatment time determined the diameter (d) of Ni nanoparticles formed by the annealing at 300 °C.With increasing the annealing time, the thickness of the composite layers containing Ni nanoparticles decreased while the d was almost constant. The shrinkage of the composite layer led to a decrease in the spacing (r) among Ni nanoparticles. The d and r can thus be fine-tuned independently. Electron magnetic resonance study clearly indicated that the tuning of d and r enable us to control the magnetic dipolar interaction in the Ni nanoparticle systems. The present technique opens a new way to realize tailor-made nanomagnetic structures.
Reliability of 4-Mbit Toggle MRAM
Authors: Åkerman Johan , Brown Philip , Butcher Brian , Dave Renu , DeHerrera Mark , Durlam Mark , Engel Brad , Fuchs Earl , Griswold Mark , Grynkewich Greg , Janesky Jason , Martin John , Nahas Joseph , Pietambaram Srinivas , Rizzo Nick , Slaughter Jon , Smith Ken , Sun Ji-Jun , Tehrani Saied
Published: April 2011

A 4Mb magnetoresistive random access memory (MRAM) with a novel magnetic free layer and toggle switching mode is presented. The new free layer uses a balanced synthetic-antiferromagnet trilayer structure and a novel write pulse sequence to provide robust switching performance with immunity from ½-select disturbs. This new mode greatly improves the switching performance of the MRAM as compared to conventional MRAM. The intrinsic reliability of the magnetoresistive tunnel junction (MTJ) and the metal interconnect system of MRAM are two other areas of great interest due to the new materials involved. Time dependent dielectric breakdown (TDDB) and resistance drift were the two main failure mechanisms identified for intrinsic memory bit reliability. Results indicated that a lifetime over 10 years is achievable under the operating conditions. Finally data retention is demonstrated over times that are orders of magnitude longer than 10 years.
Stress Hysteresis and Thermal-Mechanical Behavior of PECVD Silicon Nitride and Ebeam Aluminum Films for Microbolometer Applications
Authors: Huang Shusen , Zhang Xin
Published: April 2011

Uncooled cantilever-based microbolometer arrays received more attention recently due to high sensitivity and low cost. The central idea is built on the deflection of a bilayer SiNx/Al material upon the temperature change. The thermal-mechanical behavior of the bilayer is significant for the performance of the microbolometers. In this paper, we perform thermal cyclings to aluminum and SiNx films. The CTEs and the stress evolutions were measured using a curvature measurement system. The curvature profile of a SiNx/Al/Si component was predicted using an extension of Stoney's formula, well agreeing with the experimental results. This work demonstrates fundamental mechanics issues in bilayer SiNx/Al components, which have a great potential for the use in uncooled microbolometer applications.
Structural Evolution and Alignment of Cylinder-Forming PS-b-PEP Thin Films in Confinement Studied by Time-Lapse Atomic Force Microscopy
Authors: Zheng Qin , Lee Dong-Chan , Yu Luping , Sibener S. J.
Published: April 2011

We have utilized time-resolved high-temperature atomic force microscopy (AFM) to investigate the mechanism by which topographic templates induce alignment of cylinder-forming diblock copolymer thin films. By tracking the same sample spot during thermal annealing, we observed that the structural evolution and alignment of thin films in confinement involve an intermediate state with disordered morphology and the evolution and annihilation of disclination quadrupoles guided by the channel edges, which ultimately lead to the essentially perfect alignment of cylindrical microdomains.
Nano-scale Stress and Compositional Analysis of Epitaxial Si1-xGex/Si (100) Undulated Films
Authors: Wu Chi-Chin , Hull Robert
Published: April 2011

Spontaneous surface roughening, stress relaxation and composition re-distribution are coupled fundamental processes during the growth of strained epitaxial Si1-xGex / Si (100) alloy layers. In this work, we will present both modeling and experimental approaches to investigate the inter-relationships among these mechanisms. Stress distributions in undulated layers were calculated via the Finite Element Method by assuming a sinusoidal surface geometry. They were investigated as functions of undulation wavelength and amplitude between the trough and peak regions. For example, with a 50 nm layer of × = 0.3 having undulations of 250 nm wavelength and 40 nm amplitude, the compressive stress is twice as high in the trough regions than in the peak regions even without compositional redistribution. To explore compositional redistribution in response to these laterally varying strain fields, an experimental approach has been developed to determine local germanium concentrations for such undulated alloy layers. An etchant consisting of HNO3 (70 wt %): H2O: HF (0.5 wt %), 25: 35: 5, at 28 °C etches Si1-xGex / Si (100) alloy layers at a rate of several nanometers per minute. The etching rate increases linearly with increasing Ge concentration in the alloy layer. Such etching experiments can thus be applied to etch alloy layers with compositionally varying undulations on the free surface and utilized to quantify the local germanium concentrations. For an alloy layer with × = 0.3, the Ge concentration from this analysis is estimated to be about 20 % enhanced / depleted in the peak / trough regions, respectively.
Real-Time Coarsening Dynamics of Ge/Si(100) Nanostructures Using Elevated Temperature Scanning Tunneling Microscopy.
Authors: Mckay Michael R. , Drucker Jeff , Shumway John
Published: April 2011

Coarsening dynamics of Ge/Si(100) nanostructures were monitored using real-time, elevated temperature scanning tunneling microscopy. Gas-source molecular beam epitaxy from digermane at 0.2 ML / min onto Si(100) at temperatures near 500 °C produced mixed hut and pyramid cluster ensembles. The width of the most elongated rectangular-based hut clusters is always less than the side length of square-based pyramid clusters for island ensembles grown using these conditions. This suggests that pyramid elongation to form hut clusters occurred at early growth stages for some smaller clusters. Growth temperature annealing revealed that pyramid clusters are more stable than narrow hut clusters with larger volumes. These larger volume huts decay by reducing their length at constant width, finally becoming small pyramids. These pyramids, which are smaller than those which never elongated to form huts, are less stable and consequently dissolve. Atomistic elastic modeling confirms that hut clusters less efficiently store elastic energy than pyramid clusters which explains our observations. Large (> 1μm diameter), low chemical potential clusters deplete the surface of Ge adatoms as evidenced by the existence of denuded zones devoid of smaller clusters. These large clusters are responsible for the decrease in total island volume in the STM field of view during the anneal.
Stability Study of Highly Dispersed Au Clusters Produced on Defected TiO2 (110); Evidence from SEM and Olefin TPD
Authors: Yang Y. , McFarland E.
Published: April 2011

The stability of Au nanoclusters created at defect sites on TiO2(110) surfaces is under investigation. Using Ar ion sputtering, 0 - 10% of the surface area of ideal surfaces are modified with defects at a controlled defect density. Defected surfaces are also produced using controlled vacuum heating to 1300 K for 25 minutes. Identical exposures (< 1Å) of Au were evaporated on each surface and results of propylene temperature programmed desorption (TPD) heating cycles to < 700 K are compared with ideal control surfaces. Results support the model that Au deposited on a sputtered surface is immobilized at defect sites and the clusters so formed are stable with respect to sintering. As previously observed, with increased sputtering time there is a decrease in the cluster size and increased defect density. The desorption peak of propylene from the Au-TiO2 surface is used as an in situ probe of cluster size stability. By cyclically performing TPD to 700 K for longer times and additional cycles (or higher temperature), the sintering stability can be assessed. On the sputtered TiO2 (110) surface, evaporated gold clusters sinter with only ∼25% maintaining their initial size. On the unsputtered 1300 K annealed TiO2, Au is stable with respect to sintering for many cycles of 800 K heating. This phenomenon is attributed to both the surface stability and Au affinity for the thermal defects created on the surface. This work extends our previous investigations of Au cluster formation on defected TiO2 to their stability with respect to sintering.
The Geometry of Amorphous Silicon Effect on Metal Induced Lateral Crystallization Rate
Authors: Kim Y.-S. , Kim M.-S. , Joo S.-K.
Published: April 2011

In this study, we observed that the MILC behavior changed when the amorphous silicon active pattern width was changed abruptly and explain that phenomena with novel MILC mechanism model. The 10nm thick Ni layers were deposited on glass substrate that has various amorphous silicon patterns on it. Then we annealed the sample at 550 °C with RTA (rapid thermal annealing) machine and measured the crystallized length with optical microscope. The MILC rate was reduced dramatically and stopped for several hours (incubation time). After the incubation time, the MILC started again and the incubation time increased as the amorphous silicon pattern width difference getting larger. We can explain these phenomena with the tensile stress that was caused by volume shrinkage due to the phase transform from amorphous silicon to crystalline silicon.
Growth, crystal structure and stability of Ag-Ni/Cu films
Authors: Bdikin I. K. , Strukova G. K. , Strukov G.V. , Kedrov V.V. , Matveev D.V. , Zver'kov S. A. , Kholkin A. L.
Published: April 2011

AgxNi1−x (x=0.0–1.0) films were grown on Cu substrates by electrodeposition method. The films were found to be a nanocrystalline mixture of pure silver and nickel. The grain sizes were determined by X-ray diffraction and electron microscopy techniques. The minimal value was 3.3 nm for the alloy with 70 wt% Ni concentration. The stability of the grown films upon heating in air and in vacuum was examined. An increase in the grain size was found to begin at 150 °C.