bluuebunny/crossref_metadata_2025 huggingface dataset:
The Interfacial States between Metal/Oxide and the RRAM - Part II
Authors: Pan Wei , Evans David Russell
Published: April 2011

Switching resistance of a metal/oxide/metal structure (Pt/PrxCa1-xMnO3/Pt) upon the stimulation of electric pulse has triggered vast research interests and activities for next generation resistive RAM application. Continued from an earlier paper [1] that studied the mechanism of switching resistance, this paper extends to the switching endurance discussion using admittance spectra. Experimental data indicated that there exist interfacial dipoles (or states) at metal/oxide interfaces. Switching resistance comes from the change of interfacial dipoles. However, those interfacial dipoles are all meta-stable indicating the problem of long term switching endurance. We have tested many metal/PCMO contact combinations and characterized those contacts with basic memory criteria: bit separation, data retention, switch endurance, switching speed, and readout limitations. Among them, TiN/PCMO showed large bit separation, excellent data retention, and fast switching speed, but failed long term switching endurance test. Furthermore, the poor switch endurance is discussed using energy-well diagram. Therefore, a material system providing bi-stable states with reasonably large free energy separations is a must for this type of RRAM application. These energy levels can come from either structure or electrochemical potential differences at the metal/oxide interfaces.
Porphyrin Assembly with Fullerenes for Photovoltaic Applications
Authors: Sagawa Takashi , Yoshikawa Osamu , Jintoku Hirokuni , Takafuji Makoto , Ihara Hirotaka , Yoshikawa Susumu
Published: April 2011

Morphologically controllable thin-films of a zinc-containing tetraphenylporphyrin (ZnTPP) combined with an L-glutamide lipid has been fabricated and complexation of ZnTPP with fullerene was examined for organic thin-film solar cells, which gave 3 times enhancement of solar energy-to-electricity conversion efficiency through chlorobenzene-annealing in comparison with the conversion efficiency of untreated one.
Thin Film Encapsulated Transparent Organic Light Emitting Diodes
Authors: Tanase Cristina , van de Weijer Peter , Lifka Herbert , Rietjens Gerard
Published: April 2011

Highly transparent OLEDs are very attractive for lighting and light beautification applications. While the transparent anode is based on transparent ITO, the transparent cathode is based on a 3-layer approach: (semi)transparent electron injection layer that is a low work function metal, electrically transparent conductor used in order to limit the voltage drop across the OLED area, and overcoat to tune the optical properties without influencing the electrical properties. Transparent encapsulation based on thin film technology is used in order to protect devices from ambient exposure. Using this approach large area (50 cm2) transparent organic light-emitting device having 75% transparency in the off state is demonstrated. The efficiency of the transparent OLED is comparable with that of bottom emission OLED. It is demonstrated that by tuning the thickness and optical properties of both the cathode and the encapsulation the amount of light emitted through the anode and the cathode can be varied while the total amount of light emitted by the OLED remains the same. Moreover device optimization based on optical thin film calculations has been performed such that no angular dependence of emitted light is present both on anode and cathode side.
Influence of Cyclodextrin in the Synthesis of Magnetite
Authors: Cobos Cruz L. A. , Martínez Perez C. A. , Martínez Villafañe A , Matutes Aquino J. A. , Farias Macilla J. R. , García Casillas P. E.
Published: April 2011

Cyclodextrin (CD) has been studied intensively due to its ability to form inclusion complexes with a variety of guest molecules in the solid state. A few studies have paid attention to the use of CD to facilitate the synthesis of inorganic nanoparticles. In this work the synthesis of magnetite (M) is made in the presence of CD. The particle size of the inorganic material is controlled by the presence of CD, in which spherical particles of few nanometers are grown. The synthesis of Fe3O4 (M) in the presence of α-cyclodextrin (α-CD) and β-cyclodextrin (βCD) is described. The formation of an M-CD complex is studied in both cases by Fourier transform infrared spectroscopy (FT-IR) in order to elucidate the chemical bonding of the complex. The morphology and size of the particles are determined by Field Emission Scanning Electron Microscopy (FESEM) and software. X-ray diffraction (XRD) is used to confirm the formation of magnetite.
Glass-Ceramics of the Wollastonite - Tricalcium Phosphate-Silica System
Authors: López-Cuevas Jorge , Pech-Canul Martín I. , Rendón-Angeles Juan C. , Rodríguez-Galicia José L. , Gutiérrez-Chavarría Carlos A.
Published: April 2011

Glass-ceramics based on hypo-eutectic (GC1) and hyper-eutectic (GC2) compositions of the Wollastonite (W, CaSiO3) - Tricalcium Phosphate [TCP, Ca3(PO4)2] binary system, which are saturated with SiO2 during the glass melting stage, are synthesized by the petrurgic method, using cooling rates of 0.5, 1 or 2°C/h. All synthesized materials are subjected to in vitro bioactivity tests using Kokubo's Simulated Body Fluid (SBF). Primary a-Cristobalite is formed in all cases. Metastable Apatite [Ap, Ca10(PO4)6O] and W phases are additionally formed, in general, in the GC1 glass-ceramics, as well as in the GC2 material obtained at a cooling rate of 0.5°C/h. However, at faster cooling rates, TCP is formed instead of Ap phase in the latter composition. During the bioactivity tests, a hydroxyapatite [HAp, Ca10(PO4)6(OH)2]-like surface layer is formed in all materials. It is proposed that GC2 glass-ceramics cooled at a rate of 1°C/h have the potential to show good in vivo osseointegration properties.
Aem Investigation of Tetrahedrally Coordinated TI4+ in Nickel-Titanate Spinel
Authors: Anderson Ian M. , Bentley Jim , Carter C. Barry
Published: April 2011

The stoichiometry and site distribution of metastable nickel-titanate spinel has been studied with AEM. The results of EDXS and EELS agree that the metastable spinel is nonstoichiometric and titanium-deficient relative to its hypothetical endmember composition, “Ni2TiO4”. The titanium deficiency has been determined by EELS to be Δ = 0.025 ± 0.005. Channeling-enhanced microanalysis and ELNES studies indicate that the Ti4+ and Ni2+ cations are in tetrahedral and octahedral coordination, respectively, so that the metastable spinel has the normal cation distribution: Til−Δ[Ni2(1+Δ)]O4. This result is consistent with neutron powder-diffraction studies and SiO2-solubility measurements of similar equilibrated and quenched spinel-containing specimens. Metastable nickel-titanate spinel therefore contrasts with stable stoichiometric spinels which tend to the inverse cation distribution, Me[MeTi]O4.
Imaging Single Nacreous Tablets with the Atomic Force Microscope
Authors: Giles R. , Manne S. , Zaremba C.M. , Belcher A. , Mann S. , Morse D.E. , Stucky G.D. , Hansma P.K.
Published: April 2011

After describing some recent developments in atomic force microscopy (AFM), a specific application to the study of shell ultrastructure is examined in detail. By embedding bleached nacreous tablets in epoxy and imaging them with the atomic force microscope (AFM) during in situ dissolution, it was possible to visualize the topography of both the top faces of the tablets and the impressions in epoxy made by the bottom faces of the tablets. This epoxy imprint reproduced tablet features down to the 10 nm scale. Using this technique it should be possible to measure correspondence between topographic features on the proximal and distal faces of tablets, which is necessary to form a three-dimensional picture of the nacreous region. In addition to these dissolution experiments, growth experiments (in modified sea water) on bleached, embedded tablets indicated that aragonite grows on a tablet as asperities oriented along the c axis, normal to the tablet surface. No change was seen on the surface of the epoxy, which confirmed that the crystals were growing on the tablet surface, not spontaneously nucleating out of solution.
Experimental and Simulated Scanning Tunneling Microscopy of the Cleaved Rb1/3WO3 (0001) Surface
Authors: Lu Weier , Rohrer Gregory S.
Published: April 2011

Atomic-scale resolution scanning tunneling microscope (STM) images of cleaved (0001) surfaces of the hexagonal tungsten bronze, Rbl/3WO3, show two distinct contrast patterns. We have interpreted these images using simulated constant current STM topographs. These simulations are constructed based on calculations of the tunnel current as a function of the lateral and vertical position above the surface. By calculating simulated images for the limiting cases of different termination layers, different tip sizes, and different electronic structures, it is possible to systematically explore the important parameters and choose a model that most closely matches the experimental observations. In this case, we conclude that two distinct termination layers have been imaged, a W-O terminated surface and a Rb-O terminated surface. Also, we have found that the O atoms on the W-O surface relax to new positions nearer the 6-fold axis of rotational symmetry. Some of the advantages and disadvantages of this model are discussed.
The Role of Hydrogen in Current-Induced Degradation of GaAs/AlGaAs Heterojunction Bipolar Transistors
Authors: Ren F. , Abernathy C. R. , Chu S. N. G. , Lothian J. R. , Pearton S. J.
Published: April 2011

Carbon-doped base GaAs/AlGaAs HBTs display current-induced decreases in dc gain which are correlated with the amount of hydrogen incorporated in the base layer during growth by Metalorganic Molecular Beam Epitaxy (MOMBE). During device operation, minority carrier injection induced debonding of hydrogen from neutral C-H complexes leads to an increase in effective base doping level and therefore to a decrease in gain. Post-growth in-situ or ex-situ annealing eliminates this effect by breaking up the C-H complexes. Properly designed HBTs are stable even for very high collector current densities (105 A · cm−2)
W/Si1-xGex Schottky Barrier: Effect of Stress and Composition
Authors: Meyer F. , Aubry V. , Warren P. , Dutartre D.
Published: April 2011

The Schottky barrier height of W on Si1-xGex/ Si has been investigated as a function of composition and strain retained in the alloy for a given composition. The barrier height to ntype films does not vary significantly while that to p-type films follows the same trends than the band gap: it decreases with x and the strain. These results suggest that the Fermi level at the interface is pinned relative to the conduction band.
Comparing the Structure and Behavior of Point Defects in Silicon Oxynitride Gate Dielectrics formed by NH3-Nitridation and N2O-Growth/Nitridation
Authors: Yount J. T. , Lenahan P. M. , Saks N. S. , Brown G. A.
Published: April 2011

In this work, an electron spin resonance study of NH3-nitrided, N2O-nitrided, and N2O-grown oxides yields information relating the process history, point defect structure, and electrical behavior. NH3-nitridation is responsible for the introduction of bridging nitrogen centers, high capture cross section neutral electron traps, while N2O-processed dielectrics never exhibit these defects. In addition, structural changes at the interface due to nitridation result in observable differences in the interfacial defects.
The Microstructure and Electromigration behaviour of Al-0.35%Pd Interconnects
Authors: Elliott L.J. , Paine D.C. , Rose J.H.
Published: April 2011

Al-Pd alloys have shown promise for improved IC interconnect manufacturability and reliability. However, there has been little detailed evaluation of microstructure and conductor failure reported for this material. Microstructure and electromigration behaviour of Al-0.35%Pd unpassivated interconnect was studied on films deposited at 250°C or 450°C and patterned into test structures of varying width. Samples were electrically stressed to failure at l×106A/cm2 or 2×106A/cm2. At 450°C, AlPdx precipitates form while at 250°C, palladium remains in solution and a larger grain size is obtained. Slit voids were found in 1μm and 3μm wide lines, though only in the finer lines were the failures transgranular. A very large increase in lifetime of 1μm wide lines with a decrease in current density from 2×106A/cm2 to l×106A/cm2 suggests a critical current effect due to grain boundary clusters in the these lines.
Predicting and Comparing Electromigration Failure for Different Test Structures
Authors: Brown D.D. , Korhonen M.A. , Børgesen P. , Li C.-Y.
Published: April 2011

Electromigration and stress migration are important reliability concerns in the semiconductor industry. Relative and absolute assessments of lifetimes generally rely on the accelerated testing of ‘standard’ test structures. However, the sensitivity to various important electromigration phenomena is found to depend strongly on the type of test structure. Two common structures for electromigration testing are (i) a long line with large pads at either end and (ii) a more realistic interconnect line with W-studs at the line end. The effects of (a) different flux divergences at the line end, (b) interfacial diffusion, and (c) Cu-depletion generally result in different lifetimes for the two types of test structures under the same testing conditions. In this paper, we compare void growth rates and mean times to failure for both types of test structure taking these effects into account. Our results are used to explain differences in MTF values reported in the literature for different test structures.
Reliability Study of Plasma Etching Damage in ULSI Process
Authors: Li Xiao-Yu , Hsu Jen-Tai , Aum Paul , Bissessur Vivek , Chan David , Viswanathan C.R.
Published: April 2011

Plasma etching can cause damage in gate oxide during ULSI processing. The damage in the oxide is believed to arise through a high field induced stress current. However, there is another type of damage which is due to ion and photon bombardment on the edge of poly-Si gate during the plasma etching. These two damage mechanisms impose different reliability problems. One is hot-carrier(HC) stress and the other is Fowler-Nordheim(F-N) stress. MOS devices with special test structures to assess plasma process damage were fabricated using 0.35 μm CMOS technology. The devices with different poly gate antennas and etching through different poly-Si gate etching conditions were studied using SEM and various electrical techniques. It was found that oxide charging damaged device is more susceptible to F-N type of stress while ion and photon bombardment damaged device is more susceptible to HC type of stress.
The Formation Mechanism and Removal Methods of Metal Pillar by Plasma Etch
Authors: Kim Eungsoo , Yun Dong-Won , Jeong Chang-Bum , Han Sang-Kug , Lim Soon-Kwon , Choi Kyu-Hyun
Published: April 2011

During the plasma etching of Al-Si-Cu alloy used as a metal interconnection, it is generally reported that the metal pillar (or conical residue) affecting the degradation of device yield is formed by the micromasking effect of copper compound. However, it is stilldisputed with the formation mechanism and composition of the micromasking material. Moreover, the elimination method of the metal pillar is not well known.

According to previous reports, it is argued that the micromasking material consists of Cu agglomerates, A12Cu, or CuC1, and the formation mechanism of the micromasking is due to byproduct during plasma etching or reaction product during metal depositionor etching. However, using scanning electron microscopy (SEM), energy dispersive of x-ray (EDX), and high resolution Auger spectroscopy (HRAES), it is newly found that the micromasking consists of three layered structure, that is copper aluminum oxide, A12Cu, and Cu agglomerates. These results are quite different from previous reports. In addition, the removal methods of the metal pillar are suggested, which are high power dry etch process and multilayered metal deposition.
Effect of Phosphorus-Doped Polysilicon Anneal on Thin Oxide Reliability as Probed with X-Ray Damage Characterization
Authors: Nachman R. , Cerrina F.
Published: April 2011

In this paper we address the degradation of oxide reliability after annealing the phosphorusdoped polysilicon of MOS structures. The oxide reliability was studied in terms of X-ray radiation sensitivity as well as breakdown characteristics.

We found that annealing the polysilicon increased the radiation sensitivity of the gate oxide. We believe that this increase is a result of the phosphorus out-diffusion from the polysilicon into the oxide and a result of the creation of phosphorus related traps in the oxide bulk. We also found that the oxide charge to breakdown (Qbd) degradation correlates well with the density of the phosphorus in the oxide.
A Review of Orientation-Microstructure-Property Relationships for PZT / Metal or Metal-Oxide Layered Heterostructures
Authors: Auciello Orlando , Shareef H. N. Al , Gifford K. D. , Lichtenwalner D. J. , Dat R. , Bellur K. R. , Kingon A. I. , Ramesh R.
Published: April 2011

Studies performed by our group on orientation-microstructure-property relationships of Pb(ZrxTil1-x)O3 (PZT) / metal or metal-oxide layered heterostructure are reviewed. The work discussed is related to the synthesis and characterization of ferroelectric PZT and conductive Pt, RuO2, and Lao.5Sr0.5CoO3 layers and their integration into heterostructure capacitors suitable for non-volatile memories. The main objective of our research was to determine the influence of deposition techniques and their related parameters and layer processing on the orientation, microstructure, and properties of PZT-based capacitors, with the goal of controlling electrical properties such as polarization fatigue, retention, and imprint effects, in order to produce commercial non-volatile ferroelectric memories. The work discussed relates to the synthesis of films by ion beam sputter-deposition (IBSD), and pulsed laser ablation deposition (PLAD), where the heterostructures are grown in-situ without exposing the interfaces to uncontrollable atmospheric conditions. Comparisons are presented between orientation and microstructural characteristics and properties of PZT heterostructure capacitors produced by IBSD and PLAD and those synthesized by the sol-gel technique. The work reviewed indicates that substrate and template layers (at the ferroelectric/bottom electrode interface) and/or bottom electrode material type contribute to the control of orientation and/or microstructure, and properties of PZT-based capacitors.
Response Surface for CMOS Self-Aligned Titanium Silicide Process
Authors: Nanda A. K. , Meester S. , Wilkins C. W.
Published: April 2011

Sputtered deposited titanium films on silicon substrates were used to study the effects of first rapid thermal anneal temperature, duration of anneal time and thickness of the titanium films for TiSi2 formation. A central composite, coupled with a cross design was used to analyze response surface. Empirical models were developed and contour plots were generated to describe the outcome of the first anneal. A window of operation to control the process of titanium silicide formation was recommended. Response surface analysis of data revealed an operating window of ±10° C for RTA1 for stable TiSi2 formation. Within this window of operation, the within wafer uniformity was found to be at its minimum. Anneal time was found to have minimum effect on the variability although sheet resistance decreases monotonically with increasing anneal time. Thickness of titanium films were found to be very critical in determining final TiSi2 thickness as determined by RBS and/or XRF techniques.
The Insertion of Single-Wafer Integrated Thermal/CVD Technology in Front-End and Back-End of the Line Processing; Lessons Learned
Authors: Kermani Ahmad , Omstead Tom , Moslehi Mehrdad , Spence Paul , Winters William
Published: April 2011

The insertion of single-wafer thermal and CVD technologies into the front- and back-end of the line processing starts with study of the integrated circuits manufacturing and device performance requirements. Relying upon the lessons learned and using the concurrent engineering approach, next generation processing equipment design architecture is then defined. In order to meet the process performance, throughput, and cost of ownership requirements of semiconductor IC manufacturing as defined in the SIA road map, heavy emphasis must be put on sensor fusion and model-based process control. In the existing semiconductor IC manufacturing equipment, process control is usually accomplished by control of equipment settings, qualification wafer runs and ex-situ measurements of the various wafer properties, as well as design architecture for stable equipment performance. The conventional approach, however, suffers from slow drifts of various equipment state parameters such as infrared absorbing quartz media causing thermal memory effects, or deposition of films on the reactor walls causing variation in the optical characteristics of the reactor as well as chemical and particle memory effects. Using model-based real-time control in conjunction with implementation of various in-situ and ex-situ sensors, these effects can be well monitored and controlled. This paper is to discuss various production related issues with single-wafer thermal and CVD technologies.
Oxide Removal on Silicon by Rapid Thermal Processing Using SiH2CI2 and H2
Authors: Ren X. , Öztürk M. C. , Harris G. , Batchelor D. , Maher D.M.
Published: April 2011

In this paper, we report in-situ oxygen removal on Si using SiH2Cl2 and H2 in a high vacuum rapid thermal chemical vapor deposition reactor. The system consists of a main process chamber and a load-lock with base pressures of ∼ 1×10−7 Torr and 1×10−5 Torr respectively. The experiments were conducted in the temperature range of 750°C to 865 °C, and SiH2Cl2/H2 flow ratios of 1% to 7%. For comparison, samples were also prepared with only H2 prebaking in the same temperature and pressure range as well as with no in-situ cleaning. With no in-situ cleaning, the oxygen content was found to decrease at higher temperatures suggesting partial oxygen removal during early stages of growth. The results indicate a strong temperature dependence for the H2 clean with an increased effectiveness at higher temperatures which is believed to be due to temperature dependence of oxygen desorption from Si. In the temperature range studied, the SiH2Cl2 clean was found to be effective at 750°C. An additional oxygen removal mechanism appears to be introduced by the addition of SiH2Cl2. Using this approach, at 750°C, the peak oxygen concentration can be reduced to 4×1018 cm−3 whereas the H2 anneal at the same temperature results in a concentration of 6×1018 cm−3. At higher temperatures, the oxide can be removed in pure H2 just as efficiently or desorbed during initial stages of growth. The results show that the efficiency of the process increases as more SiH2 Cl2 is added to the system up to a critical pressure. However, if the SiH2Cl2 partial pressure is above this critical value, Si deposition can occur on the Si surface yielding an optimum partial pressure which is a function of temperature. The results indicate that the use of a small amount of SiH2Cl2 as a cleaning agent may provide a low temperature pre-epi clean.
Rapid Thermal Processing of Shallow Junctions Using Epitaxial CoSi2 as a Doping Source
Authors: Jones Erin C. , Ogawa Shinichi , Ameika Paul , Dass M. Lawrence A. , Fraser David B. , Chu Paul , Cheung Nathan W.
Published: April 2011

The electrical properties of shallow P+/N junctions formed by boron outdiffusion from polycrystalline and epitaxial CoSi2 contacts are discussed. The CoSi2 contacts are grown on (100) Si from a sputtered metal layer by rapid thermal annealing (RTA) at 900°C in forming gas. The epitaxial CoSi2 (epi-CoSi2) is made from layers of 15 nm Co / 2 nm Ti, and the polycrystalline material (poly-CoSi2) is made from a 15 nm Co layer with no Ti. Dopant is introduced by ion implantation into the silicide and the P+/N junctions are formed by a second RTA step. Junctions are found to have total leakage current densities as low as 4 nA/cm2 for poly-CoSi2 and 12 nA/cm2 for epi-CoSi2 at -5V and metallurgical junction depths of 60 nm beyond silicide/Si interface after 700-800°C annealing.
The Growth and In-Situ Doping of SiGe/Si Strained Heterostructures by RTP/VLP-CVD
Authors: Gu Shulin , Zheng Youdou , Zhang Rong , Wang Ronghua , Han Ping , Huang Xiaodong , Zhong Peixing , Hu Liqun , Zhu Shunmin , Chen J.N.
Published: April 2011

SiH4 and GeH4 Deposition and In-Situ Doping of SiGe/Si Strained Heterostructures by Rapid Thermal Process Very Low Pressure Chemical Vapor Deposition method have been studied in this paper. Ge incorporation rate increases to a maximum value and then decreases as temperature increases, the growth rate of SiGe alloy reaches its maximum value and then decreases as Ge composition increases. Ge incorporation also enhances Si deposition rate in SiGe alloy. The Boron and Phosphorus doping would change thegrowth rate of SiGe layers and the sharp doping interfaces in SiGe/Si heterostructures have been obtained.
Waste Minimization In Semiconductor Processing
Authors: Hardwick Steven J. , Mailloux Joanne C.
Published: April 2011

The US semiconductor industry uses 5–7 thousand pounds of arsine annually. Fifty to eighty percent of the arsine used becomes a waste product, which requires abatement. Traditional methods of abatement are reviewed with an emphasis on dry chemical scrubbing. A variety of dry chemical scrubbing materials were evaluated for arsine capacity, using activated carbon as the baseline for comparison. A proprietary mixed oxide composition, employing copper oxide as the active ingredient was identified as having high capacity and efficiency. Disposal and possible reclamation options are discussed.
Structure/Reactivity Studies Of Nd2O3/MgO AND MgO/Nd2O3 Catalysts Used In Methane Coupling
Authors: Burrows A. , Kiely C. J. , Devenish R. W. , Hargreaves J. S. , Hutchings G. J. , Joyner R. W. , Sinev M. Y.
Published: April 2011

Using High Resolution Electron Microscopy, we have investigated the structure/function relationships of the Nd2O3/MgO and MgO/Nd2O3 catalyst systems which are active in the oxidative coupling of methane. In both cases catalytic performance was found to depend critically on the morphology of Nd2O3. We demonstrate that high selectivities are associated with a thin disordered film of neodymia on the MgO surface for the Nd2O3/MgO system whilst for the reverse catalyst, the dominant morphology is a highly disordered cubic form of Nd2O3.
Decomposition Of Co2 To Carbon By H2-Activated Ni(II)- And Co(II)-Bearing Ferrites At 300°C
Authors: Kodama Tatsuya , Sano Taizo , Chang Shig-Ger , Tsuji Masamichi , Tamaura Yutaka
Published: April 2011

The reactivity of the H2-activated Ni(II)- and Co(II)-bearing ferrites with different levels of metal substitution have been studied for CO2 → C decomposition in comparison with that of the H2-activated magnetite. Ni 2+ and Co2+ have been substituted for Fe2+ or Fe3+ in magnetite with the spinel-type structure up to 14 % and 26 % of the mole ratio of Ni2+ and Co2 + to the total Fe content respectively. The reactivity of the Ni(II)- and Co(II)-bearing ferrite increased with the level of metal substitution. Especially, the Ni(II) substitution significantly facilitated the CO2 → C decomposition in a batch system. The rates of H2-activation (reduction) and CO2-decomposition (oxidation) for N(II)-bearing ferrite were studied by a thermogravimeteric analysis. The rates of both H2-activation and CO2-decomposition were much improved in the Ni(II)-bearing ferrite with the Ni(II)/Fetoul mole ratio of 14%. It is considered that the reduced Ni(II) ions which were formed on the surface of the ferrite is very active to facilitate both dissociation reactions of 1) H2 → 2 Hads and 2) CO2→ Cads + 2Oads,. From the change in the lattice constant of the Ni(II)-bearing ferrite during the H2-activation and CO2-decomposition, the oxygens in CO2 were considered to be incorporated into the oxygen deficient spinel lattice of the oxygen deficient Ni(II)-bearing ferrite which had been formed by the H2-activation.
In-Situ Microstructure Characterization of Sintering of
Controlled Porosity Materials
Authors: Kerch Helen M. , Burdette Harold E. , Gerhardt Rosario , Krueger Susan , Allen Andrew J. , Long Gabrielle G.
Published: April 2011

The isothermal sintering behavior of a colloidal gel with a
well-characterized pore structure was studied using a newly commissioned
in-situ small-angle neutron scattering furnace. The apparatus enables
small-angle scattering measurements to be performed on monolithic samples
during heat treatment in an oxidizing, reducing, or neutral environment at
temperatures up to 1700°C. In-situ, quantitative measurements of the pore
size evolution within a gel possessing a bimodal pore size distribution is
discussed. Also reported is the in-situ measurement of the gel's surface
area evolution which is an important microstructural parameter in
understanding the sintering behavior of highly porous materials.
Homogeneity in the Polyether Alkoxide Sol‐Gel Synthesis of
YBa2Cu3O7-δ
Authors: Houk Carol S. , Burgoine Gary A. , Page Catherine J.
Published: April 2011

We have investigated the homogeneity of sol‐gel derived YBa2Cu307‐s from the
solution phase to the final product using transmission electron microscopy
(TEM), x‐ray diffraction (XRD), and Energy Dispersive X‐ray (EDX) lateral
mapping techniques. The starting solutions contain stoichiometric amounts of
the metal 2‐(2‐methoxyethoxy)ethoxide components in
2‐(2‐methoxyethoxy)ethanol and appear to be homogeneous by TEM with a
uniform distribution of particles having an average size of less than 40 â.
Through elemental mapping we see elemental segregation in the high
temperature (950 °C) products, which are orthorhombic by XRD. In elemental
maps of gel samples fired to 700 °C, which are tetragonal by XRD, we also
see elemental inhomogeneity within particles and phase zoning in maps of
products from finely ground gels. A comparison of elemental maps and x‐ray
diffraction patterns of the products from gel processing and conventional
solid state processing is made.
Reorientational Motion and Phase Transitions of Cyclohexane in
Restricted Geometries
Authors: Zerda T. W. , Shao Yong
Published: April 2011

Rotational motion of cyclohexane in the liquid and the solid plastic phase
is studied using Raman light scattering. The results are compared with
molecular dynamics simulations run for model pores of diameters similar to
those used in the experiment. The presence of the surface layer and its
effect on the relaxation times is discussed. The temperature of the
solid-solid phase transition is determined from the analysis of the
ν21 band shape. It is shown that the depression of the cubic
to monoclinic phase transition depends on the pore diameter and is different
for modified and unmodified surfaces. It is suggested that molecules near
the pore walls form the amorphous structure and only molecules near the
center of the pore form crystallographic structure.
Plasma Enhanced Chemical Vapor Deposition of Silicon Sulfide and
Phosphorus Sulfide thin Films
Authors: Shibao R.K. , Srdanov V.I. , Hay M. , Eckert H.
Published: April 2011

Amorphous SiSx:H (x ∼ 2) films have been synthesized from H2S and
SiH4 precursors using a remote plasma enhanced chemical vapor deposition
apparatus. Structural studies by solid state nuclear magnetic resonance
(NMR) and Raman scattering reveal that the atomic environments in these
materials are similar to those observed in melt-quenched silicon sulfide
glasses, and are characterized by corner- and edge-shared SiS4/2
tetrahedra. Compared to these glasses, however, the films show consistently
higher fractions of corner-sharing S1S4/2 tetrahedra. The ratio
of corner- to edge sharing tetrahedra and the Si:S ratio can be influenced
by the H2S/S1H4 flow rate ratio during deposition.
Thus, PECVD opens up wider opportunities for structural tailoring of
amorphous silicon sulfide materials than currently possible by means of the
melt-quenching method. Preliminary data for the PECVD synthesis of
phosphorus sulfide is also presented.
High Yield Polycarbosilane Precursors to Stoichiometric SiC.
Synthesis, Pyrolysis and Application
Authors: Interrante Leonard. V. , Whitmarsh C.W. , Sherwood W. , Wu H.-J. , Lewis R. , Maciel G.
Published: April 2011

The synthesis and properties of two polycarbosilanes that have essentially a
“SiH2CH2” composition is described. One of these
polymers is a highly branched hydridopolycarbosilane (HPCS) derived from
Grignard coupling of CI3SiCH2CI followed by
LiAIH4 reduction. This synthesis is amenable to large scale
production and we are exploring applications of HPCS as a source of SiC
coatings and its allyl-derivative, AHPCS, as a matrix source for SiC- and
C-fiber-reinforced composites. These polymers thermoset on heating at
200-400 °C (or at 100 °C with a catalyst) and give near stoichiometric SiC
with low O content in ca. 80% yield on pyrolysis to 1000 °C. The second
method involves ring-opening polymerization of
1,1,3,3-tetrachlorodisilacyclobutane and yields a high molecular weight,
linear polymer that can be reduced to
[SiH2CH2]n (PSE), the monosilicon analog
of polyethylene. In contrast to high density polyethylene which melts at 135
°C, PSE is a liquid at room temperature which crystallizes at ca. 5 °C. On
pyrolysis to 1000 °C, PSE gives stoichiometric, nanocrystalline, SiC in
virtually quantitative yield. The polymer-to-ceramic conversion was examined
for PSE by using TGA, mass spec, solid state NMR, and IR methods yielding
information regarding the cross-linking and structural evolution processes.
The results of these studies of the polymer-to-ceramic conversion process
and our efforts to employ the AHPCS polymer as a source of SiC matrices are
described.
Polymeric Precursors for Yttria
Authors: Apblett Allen W. , Cannon Steven M. , Georgieva Galina D. , Long Jay C. , Raygoza-Maceda Isabel , Reinhardt Larry E.
Published: April 2011

Polymers that can be easily processed into fibers, films, or bodies are
excellent precursors for ceramics with useful morphologies. The ideal
preceramic polymer not only has proper physical properties (e.g. solubility
or fusibility) for processibility but also decomposes at low temperature
with high ceramic yield. One possibility for such precursors for yttria are
yttrium oxycarboxylates. The preparation of such polymers from YOC1 has been
investigated and several compounds with useful physical properties have been
discovered. These include a methanol-soluble yttrium oxycarboxylate,
(CH3OCH2CH2OCH2CO2YO)n
a liquid yttrium tricarboxylate,
(CH3OCH2CH2OCH2CO2)3Y,
and a method for preparing very concentrated yttrium mixed acetate and
formate sols.
Development of Acidity on Sol-Gel Prepared
TiO2-SiO2 Catalysts
Authors: Calvino J.J. , Cauqui M.A. , Gatica J.M. , Perez J.A. , Rodriguez-Izquierdo J.M.
Published: April 2011

Three different TiO2-SiO2 gels (Xerogel, Carbogel and
Aerogel) are more active acid catalysts than other reference samples used
here. As deduced from FTIR, XRD and XANES studies, the structural properties
of these gels are quite different to each other, thus revealing the strong
influence of the drying treatment. It is found that the degree of Si-O-Ti
linking and the surface acidity follows the same trend (X 〉 C 〉 A). We
conclude that supercritical drying at 600 K and 190 bars can induce Ti
leaching followed by redeposition in the narrower pores of the gel. These
effects modify both the textural and surface chemical properties of the
resulting material.
A New Route for The Synthesis of Reduced Transition Metal Oxides
Using Borohydrides
Authors: Manthiram A. , Zhu Y. T. , Dananjay A.
Published: April 2011

Reduction of aqueous solutions of tungstates, molybdates or vanadates by
aqueous alkali metal borohydrides at ambient‐temperature results in a
formation of dark colored gel. The gel is amorphous to X‐ray diffraction and
crystallizes sharply at around 300‐500 °C to yield reduced transition metal
oxides such as the oxide bronzes, NaxMyOz,
or the binary oxides, MO2 (M = V, Mo or W). The nature and
composition of the products formed are strongly influenced by the reaction
conditions such as the reaction pH as well as the concentration and amount
of the reagents. Experimental procedures to obtain the different phases are
presented. This novel low‐temperature approach has a potential to access new
metastable phases.
A Molecular Orbital Model of Gel-Silica Ir
Spectra
Authors: Chia Taipau , West Jon K. , Hench Larry L.
Published: April 2011

The infrared vibrational modes of sol-gel derived optical silica monoliths
depend upon thermal treatments and chemical environments, as shown by
Fourier transform infrared spectroscopy (FTIR). A semi-empirical quantum
mechanical theory (PM-3 in MOPAC 6.1) is used to analyze the structural
changes responsible for the spectral shifts. Optimized structures of
2-member, 3-, 4-, 5- and 6-member rings of SiO2 are calculated.
The force constants for the molecular bonds in the rings are obtained and
converted to the associated vibrational spectra for the rings. The peak
position of the asymmetric transverse optical (AS1TO) mode of the
rings shifts from 1070 cm−1 for 2-member rings to 1100
cm−1 for 3-member rings, 1150 cnr1 for 4-member
rings, 1140 cm−1 for 5-member and 1120 cm−1 for
6-member rings. The IR data show a 38 cm”1 shift of the
AS1TO mode as the gel-silica density changes from 1.1 g/cc to
2.2 g/cc. Thus, the intensification and shift of the AS1TO mode
in the gel-silica to higher wave-numbers corresponds to a change in the
distribution to larger silicate size rings.
Gelation Point In Borosilicate Sols From Rheological
Experiments
Authors: Surapanani Srinivas , Mullins Michael E. , Morrison Faith , Cornilsen Bahne C.
Published: April 2011

Dynamic oscillatory experiments are used to monitor the gelation of the
borosilicate systems prepared through the sol-gel process from metal
alkoxides. The rheological experiments show that tan δ = G”/G’ is
independent of frequency at the gel point in agreement with the results of
others on organic gelling systems. The dynamic moduli at the gel point
followed power-law behavior with respect to frequency. The power-law
exponent is found to be ∼0.70. The apparent fractal dimension, dp, of the
network cluster at the gel point is determined. The dF values for
the samples ranged from 2.5 to 3.8 depending on the final structure of the
evolved products at the gel point. The large values (dF > 3)
exclude a simple geometric interpretation of the results. The effect of
processing parameters, such as composition of reactants and temperature, on
the resulting microstructures near the gel point is discussed.
Pillaring of Layered Double Hydroxides With Cage-Like
Polysilicates: a Possible New Class of Base Catalysts or Catalyst
Precursors
Authors: Fyfe Colin A. , Fu Guoyi , Grondey Hiltrud
Published: April 2011

Pillaring of highly basic layered double hydroxides
(MgnAl(OH)2n+2Cl, n=2–5) with octameric
polysilicate (Si8O208-) has been achieved via a direct ion exchange route.
Experimental Studies On Diffusion Of Liquids In Porous
Glass
Authors: Shao Yong , Koone Neil , Zerda T. W.
Published: April 2011

Diffusion coefficients of water and cyclohexane in porous sol-gel glass of
average pore diameter 2.9 nm were obtained using a radioactive tracer
technique. This information was applied to calibrate the membrane in the
diaphragm cell which was subsequently used to measure the diffusion
coefficients for cyclohexane, acetone, toluene, acetonitrile, and
chloroform. Results for cyclohexane were compared with computer simulation
of molecular motion of cyclohexane in a model cylindrical pore of diameter
2.9 nm. Translational motion of polar liquids inside the pores was found to
be faster than that of neutral, not wetting solvents.
Synthesis, Structure and Magnetic Properties of Some New
Metal(II) Phosphonates: Layered
Fe(C2H5PO3).H2O,
α-Cu(C2H5PO3) and
Co(t-C4H9PO3).H2O, Tubular
β-Cu(CH3PO3)
Authors: Bujoli Bruno , Le Bedeau J. , Payen C. , Palvadeau P. , Rouxel J.
Published: April 2011

Fe(II)C2H5PO3. H2O has been prepared via
prolonged reaction between iron oxychloride and ethylphosphonic acid in
acetone, in a sealed tube. The lamellar structure is very similar to that of
previously reported divalent metal phosphonates M(II)(RPO3).
H2O (M= Mg, Mn, Ni, Zn). The compound shows sign of 2D
antiferromagnetic correlations above the Néel temperature Tn=24K
and a weak ferromagnetic behavior is observed below TN. We also
report on the preparation methods and the crystal structures of two new
anhydrous copper phosphonates
a-Cu(II)(C2H5PO3), and
β-Cu(II)(CH3PO3) which exhibits an original tubular
three-dimensional structure. The reactivity of bulky phosphonic acids is
also described, with the case of
Co(II)(t-C4H9PO3).H2O.
Cross-Condensation Reactions in an Organically Modified Silica
Sol-Gel
Authors: Prabakar S. , Assink R. A. , Raman N. K. , Brinker C. J.
Published: April 2011

High resolution 29Si NMR has been used to study the extent of
cross condensation taking place in a hybrid organic/inorganic sol-gel
system. Tetraethoxysilane (TEOS) and methyltriethoxysilane (MTEOS) sol-gels
were chosen for this purpose. The sols were prepared by acid catalyzed
hydrolysis of TEOS and MTEOS with a H2O/Si ratio of 0.3.
29Si NMR shows signals due to both self-condensation and
cross-condensation between TEOS and MTEOS. Resonance assignments were made
by comparing the positions and intensities of peaks in the spectra of single
and multicomponent systems. It was found that, within experimental error,
the self- and cross-condensation rates are equal and that extensive
molecular level mixing takes place during the early stages of the
reaction.
Pore Morphology Study of Silica Aerogels
Authors: Hua D.W. , Anderson J. , Hæreid S. , Smith D.M. , Beaucage G.
Published: April 2011

Silica aerogels have numerous properties which suggest applications such as
ultra high efficiency thermal insulation. These properties relate directly
to the aerogel's pore size distribution. The micro and meso pore size ranges
can be investigated by normal small angle x-ray scattering and possibly,
nitrogen adsorption. However, the measurement of larger pores (> 250 Å)
is more difficult. Due to their limited mechanical strength, mercury
porosimetry and nitrogen condensation can disrupt the gel structure and
electron microscopy provides only limited large scale structure information.
The use of small angle light scattering techniques seems to have promise,
the only hurdle is that aerogels exhibit significant multiple scattering.
This can be avoided if one observes the gels in the wet stage since the
structure of the aerogel should be very similar to the wet gel (as the
result of supercritical drying). Thus, if one can match the refractive
index, the morphology can be probed. The combination of certain alcoholic
solvents fit this index matching criteria. Preliminary results for the gel
network (micron range) and primary particle structure (nanometer) are
reported by using small angle light scattering and ultra-small angle x-ray
scattering. The effects on structure over the length scale range of <1 nm
to >5 μπι under different conditions (precursors, pH, etc.) are
presented. The change in structure of an aerogel during isostatic compaction
to 228 MPa (to simulate drying from wetting solvents) are also
discussed.
Effects of Deposition Temperature and Thermal Treatment on the Structure of C60 and C70 Films
Authors: Rusakova I. , Hamed A. , Hor P.H.
Published: April 2011

C60 and C70 polycrystalline thin films, prepared by sublimation of powders onto carbon holey film substrates held at temperatures Ts of 40 and 200 °C, were investigated at room temperature using conventional and high resolution TEM. A strong dependence of grain size on Ts is observed. We obtain a mean grain size ˜25 nm for both C60 and C70 films when using Ts = 40 °C, but this size is ˜250 nm for C60 and ˜130 nm for C70 when using Ts = 200 °C. In all cases, however, an fc.c. structure with a high density of planar defecTs, twins and stacking faulTs, is observed. When a C60 film grown at Ts = 40 °C was annealed for several hours at only about 250 °C in vacuum, recrystallization took place, with grains as large as 250 nm now being present in the film. A condition to observe this recrystallization seems to be that the powder used to grow the film must be dried for long enough periods of time to minimize the amount of solvent residues.
Plasmons in C60, Carbon Onions and Carbon Tubes
Authors: Östling Daniel , RosÉn Arne , Apell Peter , Mukhopadhyay Gautam
Published: April 2011

After the discovery of the C60 molecule a lot of attention has been given to its optical and collective properties. The latest development in fullerene related research was the synthesis of coaxial carbon sheets called carbon or nano tubes and also spherical concentric graphitic shells called carbon onions. With a model describing the collective dynamics of electrons we may gain insight in the physics of the collective resonances. Based on a simple equation of motion for the induced density in a carbon particle we demonstrate the existence of a rich spectrum of collective resonances for both carbon onions and carbon tubes.
Improved Second Harmonic Generation from Langmuir-Blodgett Films of an Azacrown Ether Fullerene Derivative
Authors: Leigh David A. , Wade Frances , King Terry A. , West David , Bahra Gurmit S.
Published: April 2011

The amphiphilic fullerene derivative (1-aza-18-crown-6)-hydrofullerene-60 (C60-1A18C6, 1) exhibits improved Langmuir and Langmuir-Blodgett (LB) film forming properties and the resulting LB films exhibit a nonlinear second order susceptibility, X(2)pp of 3.2 pm/V, the highest yet reported for a fullerene or fullerene derivative.
Quantitative In Situ Growth Measurements of Chlorine-Activated Homoepitaxial Diamond Cvd
Authors: Pan Chenyu , Margrave John L. , Hauge Robert H.
Published: April 2011

In situ quantitative studies of the effects of substrate temperature, methane and chlorine flow rates on homoepitaxial diamond growth rates on (110) surfaces in a chlorine-activated diamond CVD reactor have been carried out using a Fizeau interferometer. The temperature dependence of diamond growth rates was found to display three distinct growth activation energies, ranging from 9±2 kcal/mol in the substrate temperature of 750-950°C, to 3.2±0.2 kcal/mol in the temperature range of 300-650°C, followed by 1.2±0.2 kcal/mol in the temperature range of 102-250°C. Atomic hydrogen is believed to be the dominant activating species in the highest temperature range, and atomic chlorine is believed to be the dominant species in the lower temperature regions. Studies of the methane flow effect on diamond growth rates revealed a linearity, indicating that the diamond growth rate was of the first order in methane flows. Diamond growth rates were also found to increase linearly with the chlorine flow. At high chlorine flow rates, however, an accelerated diamond growth rate was observed. Discussion is given to explain the observed results.
Strain and Impurity Content of Synthetic Diamond Crystals
Authors: Mccormick T. L. , Jackson W. E. , Nemanich R.J.
Published: April 2011

Samples of diamond crystals produced under various high pressure, high temperature conditions were studied using both micro photoluminescence and Raman spectroscopy. The 0.3 - 0.6 mm sized samples exhibited various levels of inclusion content, impurity content and strain. Photoluminescence studies revealed the presence of nitrogen in three forms. The 1.945 eV, 2.15 eV and 2.46 eV zero phonon lines and their associated sidebands were detected. The ratios between forms of impurities and their integrated intensities varied between samples. Variations in the distribution of the nitrogen forms were seen between regions of high and low strain birefringence patterns.