bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion-Beam-Induced Damaging and Dynamic Annealing Processes in Silicon
Authors: Short K.T. , Chivers D.J. , Elliman R.G. , Liu J. , Pogany A.P. , Wagenfeld H. , Williams J.S.
Published: March 2011

We have employed high resolution ion channeling and TEM methods to investigate the damage production and dynamic annealing processes which take place in (100) silicon bombarded at elevated temperatures. Two important observations have arisen from our results i) We have observed an amorphisation process for Sb-implanted silicon at 250°C which is more akin to amorphisation processes in metals, whereby the impurity (Sb) appears to influence the stability of amorphous zones associated with individual ion tracks. ii) We have demonstrated that previously amorphised layers in silicon can be recrystallised through a solid phase epitaxial process by subsequent bombardment with He+, Ar+ and Sb+ ions at substrate temperatures of 300–400°C, which are significantly below normal thermal regrowth temperatures of >500°C.
Characterization of N-Type Layers Formed in Si by Ion Implantation of Hydrogen
Authors: Wilson S. R. , Paulson W. M. , Krolikowski W. F. , Fathy D. , Gressett J. D. , Hamdi A. H. , Mcdaniel F. D.
Published: March 2011

Silicon wafers have been implanted with H+ (90 keV) to doses of 5.0E15/ cm2 and 2.OE16/cm2. The wafers were annealed in nitrogen at temperatures between 450 and 700°C for times between 10 and 60 min. The electrically active carrier profiles were measured by capacitance voltage and spreading resistance techniques. The residual damage was measured by TEM and RBS. The electrical measurements were essentially the same in both FZ and CZ silicon implying that oxygen is not playing a role in the donor formation which was observed. The donor concentration peaks near the projected range of the hydrogen after annealing at temperatures between 450–500°C. As reported previously 1000 H+ ions generate 1 donor in the implant peak. In addition, the donor concentration between the surface and Rp has increased more than a factor of 10 above the background concentration after a 450°C 10 min anneal. Anneals of 550°C for 30 min or more annihilates essentially all of the donors. The RBS results show small amounts of damage for the 5.0E15/cm2 implant dose but considerable crystal damage with a dose of 2.0E16/cm2, even after a 500°C, 30 min anneal. Cross-sectional TEM analysis of 500°C annealed samples showed a large number of small loops at depths corresonding to the depth of the peak electrical carrier concentration. The donors are directly correlated to the implant damage and resultant defects. SIMS data shows little diffusion for anneals of 500°C or less but after 550°C, 30 min the peak H concentration decreases by approximately a factor of 10.
Ion Mixing Processes
Authors: Nicolet Marc-A. , Banwell T. C. , Paine B. M.
Published: March 2011

We consider ion mixing in the low temperature regime, where it is insensitive to temperature. Mixing of most thin markers is Gaussian, independent of irradiation flux, and varies linearly with fluence. However, the mixing in some media varies widely between markers of similar mass and appears to correlate with thermal diffusion constants. In bilayer systems, the profile of long-range mixing is exponential, and the number of mixed atoms scales linearly with fluence. This can be modeled successfully with simple collisional theory. Short range mixing scales with the square root of the fluence, but again shows strong correlations with known bulk chemical properties. We conclude that chemical driving forces and low energy transport mechanisms such as interstitial migration play major roles in ion mixing, even at low temperatures.
Spatial Correlation Interpretation of Effects of As+ Implantation on the Raman Spectra of GaAs
Authors: Aspnes D.E. , Tiong K.K. , Amirtharaj P.M. , Pollak F.H.
Published: March 2011

The red shift and asymmetric broadening of the LO phonon mode of ion-implanted GaAs are both described quantitatively by a spatial correlation model based on a damage-induced relaxation of the momentum selection rule previously used by Richter, Wang, and Ley to describe similar effects in microcrystalline Si. The success of the model for a qualitatively different disorder microstructure suggests it may be possible to evaluate average sizes of crystallographically perfect regions in semiconductors from the phonon lineshapes of their Raman spectra.
Effects of Double-Implant on the Epitaxial Growth of Amorphous Silicon
Authors: Chen L.J. , Nieh C.W.
Published: March 2011

Investigation has been made on the effects of double implant of BF2+−As+, BF2+−P+, B+−As+ and B+−P+ on the thermal annealing behaviors of silicon. For specimens with As+ or P+ as the major dopants, the annealing behaviors were similar to those singly implanted with As+ or P+. For samples with BF2+ or B+ as the major impurities, drastic changes in annealing characteristics were found in comparison with BF2+ or B+ single implant specimens. High density twins, including primary twins on all four {111{ planes and twelve types of secondary twins were observed in BF2+−As+ and BF2+−P+ double implant samples.
Stoichiometric Disturbance in InP Measured During Ion Implantation Process
Authors: Haberland D. , Harde P. , Nelkowski H. , Schlaak W.
Published: March 2011

To measure the sputtered ions during implantation a specially designed UHV-target chamber with a SIMS apparatus was set up. Quantitative analysis are possible with an Auger spectrometer. Disturbances in the stoichiometry in InP are measured during implantation of Sn. The enrichment of the doped surface of InP with the lighter component phoshorus will be discussed in consideration of preferential sputtering and recoil effects during implantation. Measured depth profiles of Sn in InP will be compared with calculated distributions on condition that sputtering takes place. The sputtering yield of InP bombarded by 120 keV Sn+ is 17±5.
Anisotropic Transport of Impurities in Ion Mixing
Authors: Matteson S. , Keenan J.A. , Pinizzotto R.F.
Published: March 2011

Experimental investigations of the redistribution of a thin (1nm) Sn marker layer lying between two thicker dissimilar layers (Ge and Si) during 360 keV As ion irradiation are reported. Several permutations of layer arrangements were tested, i.e. Si/Sn/Ge, Ge/Sn/Si, Si/Sn/Si and Ge/Sn/Ge. It was also found that in the dissimilar “diffusion” couples, the Sn drifts in the Ge rich direction, regardless of whether the Ge is on the surface side or the substrate side of the marker. This phenomemon of anisotropic transport is interpreted as a drift induced by a gradient in the “diffusion” coefficient. The radiation resistance of concentrated alloys is discussed in the light of this phenomenon.
Magnetic Properties of Iron Implanted Polymers and Graphite
Authors: Koon N. C. , Weber D. , Pehrsson P. , Schindler A. I.
Published: March 2011

We have measured the magnetic properties of highly oriented pyrolytic graphite (HOPG), polyethylene (PE), and polyvinylidine fluoride (PVF2), implanted with fluences of 25 keV iron atoms ranging from 1016 to 1017 atoms/cm2 . The lowest fluence specimens were paramagnetic down to 2 K, with evidence for clusters of only a few spins, while the highest fluence specimens were clearly ferromagnetic, with magnetization curves resembling those of a set of randomly oriented soft magnetic planes. The critical fluence for formation of a ferromagnetic state appears to be between 1 and 3 × 1016 atoms/cm2 at 25 keV. Theseresults can be qualitatively understood based on the critical density for percolation of near neighbor exchange interactions.
Magnetoreflection in Ion-Implanted Graphite
Authors: Mcneil L.E , Elman B.S. , Dresselhaus M.S , Dresselhaus G. , Venkatesan T.
Published: March 2011

The use of a hot stage (T ∼ 600°C) for ion implantation into graphite permits the introduction of foreign species into the host material while eliminating most of the lattice damage associated with ion implantation at room temperature. This permits the use of the magnetoreflection technique for examination of changes in the electronic band structure induced by implantation Samples of graphite implanted with 31P and 11B at various energies and fluences are examined, and the in-plane and c-axis disorder are characterized using Raman spectroscopy and Rutherford Backscattering Spectrometer (RBS) techniques. Implantation-induced changes in the electronic band structure are interpreted in terms of the Slonczewski-Weiss- McClure band model. Small changes are found relative to the band parameters that describe pristine graphite.
Modifying Polycrystalline Films Through Ion Channelling
Authors: Iverson R. B. , Reif R.
Published: March 2011

A novel low-temperature process to enhance the grain size of a polycrystalline film on an amorphous substrate has been previously reported. In this process, ion implantation is used to selectively anorphize the film, and undamaged grains act as seed crystals in a subsequent low-temperature anneal. In this work, a 120 nm polycrystalline silicon film was implanted from three angles with phosphorous at 150°K. The total dose was l.0×l015/cm2 . Transmission electron micrographs after a partial anneal (700°C for 30 minutes) indicate that some crystallites survived implantation due to ion channelling in the (111) plane. After a 60 minute anneal at 700°C, 7 μm grains were observed.
Thin Polymeric Films Produced by Ion Implantation from Frozen Organic Molecules
Authors: Calcagno L. , Sheng K. L. , Foti G.
Published: March 2011

The synthesis of polymeric films under ion bombardment of frozen benzene has been investigated for the dependence of the thickness on the fluence and beam energy of keV proton and argon ions. Chemical analyses have been performed to characterize the films.
Effects of Nitrogen and Helium Ion Implantation on Uniaxial Tensile Properties of 316 SS Foils
Authors: Spitznagel J. A. , Hall B. O. , Doyle N. J. , Jayram Raman , Wallace R. W. , Townsend J. R. , Miller M.
Published: March 2011

Implantation of nitrogen into steels is known to affect surface sensitive mechanical properties. Tensile properties of thin foils implanted with either nitrogen or helium at 300 K have been measured. Fluences greater than 1 × 1016 ions/cm2 raise the yield stress and fracture stress and reduce the plastic strain to failure. Both nitrogen and helium give comparable stress-strain responses for equal average concentrations of implanted ions. The mechanical response is discussed in terms of plastic flow of laminated structures and hardening mechanisms. Initial results of atom probe field ion microscopy examinations of nitrogen implanted Fe-15 wt.% Cr-12 wt.% Ni alloy are described.
Industrial Applications of Ion Implantation
Authors: Hirvoney J.K.
Published: March 2011

The use of ion implantation for non-semiconductor applications has evolved steadily over the last decade. To date, industrial trials of this technology have been mainly directed at the wear reduction of steel and cobalt-cemented tungsten carbide tools by high dose nitrogen implantation. However, several other surface sensitive properties of metals such as fatigue, aqueous corrosion, and oxidation, have benefitted from either i)direct ion implantation of various ion species, ii)the use of ion beams to “intermix” a deposited thin film on steel or titanium alloy substrates, or iii)the deposition of material in conjunction with simultaneous ion bombardment.

This paper will concentrate on applications that have experienced the most industrial trials, mainly high dose nitrogen implantation for reducing wear, but will present the features of the other ion beam based techniques that will make them appear particularly promising for future commercial utilization.
Friction and Wear Behavior of a Cobalt-Based Alloy Implanted with Ti or N
Authors: Dillich S. A. , Bolster R. N. , Singer I. L.
Published: March 2011

Dry sliding friction tests and relative abrasive wear measurements were used to investigate the effects of ion implantation on the tribology of a centrifugally cast Co-Cr-W-C alloy. Titanium implantation was found to significantly reduce the friction and wear of the alloy. Auger spectroscopy showed that vacuum carburization of the surface occurred during Ti implantation. Similar Ti and C profiles were seen in both carbide and (Co-rich) matrix phases. The abrasive wear resistance of the alloy decreased as a result of N-implantation. Nitrogen implantation did not reduce the friction during dry sliding, however, a change in the wear mode was observed.
The Mechanical Properties of Si+ and Pb+ Implanted Al
Authors: Madakson P.B.
Published: March 2011

Commercially pure Al was implanted with 300 keV Si+ and 200 keV Pb+ to doses of between l011 and 1017 ions/cm2. Changes in friction, wear, oxidation and hardness were investigated. Silicon increased the hardness and wear resistance of Al and significantly decreased friction and the oxidation of the implanted surface. These changes were observed to be almost proportional to the implanted dose. The implantation of Pb+ resulted in a linear increase in hardness and a decrease in surface oxidation with dose. Friction decreased and wear resistance increased but the changes were not dose dependent. The implantation of Si+ did not significantly alter the distribution of impurities, such as Fe and Cu within the Al matrix, but Pb+ resulted in a diffusion of Fe to the implanted surface. Formation of precipitates was observed and the improvements in the surface properties studied are considered to result from precipitation hardening, which involves the impediment of dislocation movement by the precipitates during plastic deformation of the implanted Al.
Wear Behavior of Flat and Graded Profile Boron-Implanted Beryllium
Authors: Kumar K. , Newborn H. , Kant R.
Published: March 2011

Pin-on-disk tests were performed for comparative friction and wear behavior on flat and graded profile boron implanted beryllium samples. Peak, intended boron concentrations of 10, 20, 30 and 40 atom percent were investigated. Auger Electron Spectroscopy was used to determine the boron concentration as a function of depth. Preliminary work was performed to study the effects of (1) a low temperature (450°C, 1–1/2 hours) heat treatment of the implanted specimens and (2) a change in the pin material. All of the boron implanted beryllium samples showed significant improvement versus unimplanted beryllium and an anodized beryllium surface. Graded samples showed comparable friction coefficients but inferior wear resistance with respect to the flat profile samples.
Enhancement of Ferrous Alloy Surface Mechanical Properties by Nitrogen Implantation
Authors: Pollock John T.A. , Kenny Michael J. , Paterson Peter J.K.
Published: March 2011

Clarification of the relationship between nitrogen profiles and wear behaviour has been sought by studying nitrogen implanted mild steel. Implant energy and dose were in the ranges 25 – 65 keV and 0.9 − 3 × 1017 1ions cm−2, respectively. Wear characteristics were measured with a ball-on-disc system followed by interferometric
analysis. Nitrogen distributions before and after wear were determined by Auger electron spectroscopy and Rutherford backscattering methods, and compared with wear track profiles. On balance, the data offers qualified support for nitrogen migration at low loads, although nitrogen was not detected for wear depths >2 times the implant depth. Observations of wear on the abrader ball-bearing surface and the role of oxygen in the wear process are reported.
Wear Behavior and Structural Characterization of a Nitrogen Implanted Ti6Al4V Alloy at Different Temperatures
Authors: Martinella R. , Chevallard G. , Tosello C.
Published: March 2011

Mechanically polished Ti6Al4V samples were implanted with 100 key nitrogen ions to a fluence of 5.1017 ions/cm2 at two different bulk tenneratures: 370°C and 470°C. Wear tests were carried out with a reciprocating slidina tribotester. Structural modifications and wear morphologies were studied by TEM and SEM. 370°C implanted sample showed the same wear behavior as unimplanted ones, while 470°C implanted sample showed better wear resistance because of a TiN hardened layer. Correlations- between microstructural modifications, wear behavior and mechanisms are reported: results agree with the delamination theory. Comparison with ion- and gas-nitrided samples are presented.
Ion Beams and Catalysis
Authors: Cairns J.A.
Published: March 2011

Ion beam techniques have found increasing application in recent years to a wide variety of disciplines. It is the purpose of this paper to explore their potential in the field of catalysis, concentrating exclusively on solid heterogeneous catalysts. An initial description of the internal structure and external physical form of some typical catalysts is followed by an assessment of the use of ion beams for the preparation and interrogation of both “real” and model catalysts. These techniques are then compared to some of the modern tools used in current catalysis research. It emerges that ion beams can indeed be used to advantage in certain applications, such as detecting light elements selectively; measuring interaction effects between metals and supports in model systems; highlighting surface relaxation effects in metal single crystals; and even, in special circumstances, in synthesising catalysts.
Corrosion behavior of Ni+ -Ion Irradiated NiTi Alloys
Authors: Wang R. , Brimhall J. L.
Published: March 2011

Corrosion behavior of Ni+ -irradiated NiTi alloys was studied in chloride solutions, together with unirradiated NiTi material with different surface conditions. Ion irradiation with either 2.5 or 5 MeV Ni+ ions transformed the NiTi surface into an amorphous layer up to 1.5 micrometers thick. Studies of corrosion potential vs. time and polarization behavior indicated a small enhancement of the passivation for the Ni+-irradiated NiTi over the unirradiated NiTi. The unirradiated NiTi with a mechanically polished, coarse surface was susceptible to pitting and crevice corrosion attack in 1 N HCl solution. The homogeneous amorphous structure in the irradiated alloy retarded this type of localized corrosion.
Effect of N-Implantation on the Corrosive-Wear Properties of Surgical Ti-6Al-4V Alloy
Authors: Williams J. M. , Beardsley G.M. , Buchanan R. A. , Bacon R. K.
Published: March 2011

The effects of N-ion implantation on the corrosive-wear properties of Ti-6Al-4V, an alloy used for construction of the femoral component of artificial hip joints in humans, were tested. In corrosive-wear tests designed to simulate pertinent hip-joint parameters, electrochemical corrosion currents were measured for cylindrical samples in saline electrolyte in an arrangement which allowed the samples to be rotated between loaded polyethylene pads simultaneously with the current measurement. To further quantify material removal, Zr markers were ion-implanted into some samples so that, by use of Rutherford backscattering, material removal could be detected by changes in position of the marker relative to the surface. Corrosion currents were greatly reduced by implantation of approximately 20 at. % N, but even implantation of the Zr markers also reduced corrosion currents. The marker experiments confirmed the low rate of material removal for the implanted samples.
Enhancement of Uranium Oxidation Resistance by Molybdenum Implantation
Authors: Kaufmann E. N. , Musket R. G. , Colmenares C.A. , Appleton B. R.
Published: March 2011

Initial studies of the oxidation resistance imparted to uranium metal through the implantation of Mo ions have shown that a significantly increased resistance can be achievedfor doses of 5 ×1016/cm2. No enhancement of oxidation resistance was found for doses below 1 ×1016/cm2. We report results of weight-gain measurements, ion-beam analysis, and x-ray diffraction, as well as observations of the way in which the protective implanted layer fails at long exposure times.
Modification of the Hydriding of Uranium using Ion Implantation
Authors: Musket R. G. , Robinson-Weis G. , Patterson R. G.
Published: March 2011

The hydriding of depleted uranium at 76 Torr hydrogen and 130°C has been significantly reduced by implantation of oxygen ions. The high-dose implanted specimens had incubation times for the initiation of the reaction after exposure to hydrogen that exceeded those of the non-implanted specimens by more than a factor of eight. Furthermore, the nonimplanted specimens consumed enough hydrogen to cause macroscopic flaking of essentially the entire surface in times much less than the incubation time for the high-dose implanted specimens. In contrast, the ion-implanted specimens reacted only at isolated spots with the major fraction of the surface area unaffected by the hydrogen exposure.
Sol-Gel Synthesis of YBa2Cu3O7-& Using Yttrium, Barium and Copper Polyether Alkoxide Precursors
Authors: Page Catherine J. , Houk Carol S. , Burgoine Gary A.
Published: March 2011

Homogeneous solutions of yttrium, barium and copper 2-(2-methoxy)-ethoxyethoxides in 2-(2-methoxy)ethoxyethanol of appropriate lY:2Ba:3Cu stoichiometry have been prepared and used in sol-gel synthesis of YBa2Cu3O7-δ. To our knowledge, this is the first report of the preparation of a homogeneous solution of yttrium, barium and copper homoleptic alkoxides dissolved only in the parent alcohol. These solutions provide an excellent starting point for sol-gel synthesis of YBa2Cu3O7-° since the metals are mixed on the molecular scale, and because the solutions are stable with no possibility of ligand exchange to give insoluble products. Hydrolysis and careful heat treatment of gels produced from these solutions yield nearly pure tetragonal YBa2Cu3O7-δ at temperatures as low as 725°C. The preparation of these solutions and their characterization by small-angle x-ray scattering measurements and TEM are reported, as well as preliminary data pertaining to their use in the sol-gel synthesis of YBa2Cu3O7-δ.
From Ceramics to Superconductors: Rapid Materials Synthesis by Solid-State Metathesis Reactions
Authors: Treece Randolph E. , Gillan Edward G. , Jacubinas Richard M. , Wiley John B. , Kaner Richard B.
Published: March 2011

The preparation of materials from gas and liquid phase precursor reactions is well documented. However, solid-state precursor routes have remained largely unexplored. This synthetic void led us to develop rapid (< 2 s), solid-state metathesis (exchange) reactions with a very broad range of synthetic applications. An example is the self-propagating reaction:

where the Nal is simply washed away with water. Analogous reactions allow the preparation of carbides, suicides, chalcogenides (O, S, Se, and Te), and pnictides (N, P, As, and Sb), of main-group, transition-, and rare-earth metals. These methods can also be exploited to produce mixed-metal and mixed-nonmetal solid solutions.

To gain insight into some of the mechanistic factors involved in these reactions, such as initiation, nucleation, and propagation, we have employed a variety of physical characterization methods. This paper will review the range of materials accessible by our synthetic approaches, as well as the control of product crystallinity, phase, and homogeneity through the optimization of reaction conditions.
Characterizations of Sol-Gel Cordierite Precursors
Authors: Chen Yun Fa , Hadigui Saïd El , Vilminot Serge
Published: March 2011

Cordierite powders were prepared using silicon ethoxide, Mg(NO3).2.6H2O and Al (OBu)2etac (etac = ethylacetoacetate) and conditions of hydrolysis have been checked in order pure a cordierite to be obtained. D.T.A. measurements reveal a stepwise crystallization process with intermediate formation of metastable μ cordierite. Infrared studies allow to follow the evolution of the Si-O-Al network with temperature.
Synthesis of New Compounds by Ion-Exchange Reactions
Authors: Villafuerte-Castrejón M. E. , Aragón-Piña A.
Published: March 2011

Ion-exchange reactions, particularly with molten salts, are a convenient low temperature route to prepare new materials. Six different complex oxides (KTaO3, K2Ti4O4, NaAlSiO4, Na2Si2O5,ß-NaAlO2and K2Ge4O9) were reacted with different salts (NaCI, KC1, Na2SO4, NaNO3, LiCl and LiNO3) by the ion exchange route with molten salts. In this work, new phases and substitution reactions are reported.
Comparative Study of the Sol-Gel and Metallo-Organic Decomposition (MOD) Processes for the Preparation of Inorganic Materials
Authors: Paz-Pujalt Gustavo R. , Nie W. , Lurin C.
Published: March 2011

Sol-Gel processing and Metallo-Organic Decomposition are contrasted from the thermodynamics and chemical reactivity points of view. Differences and similarities on precursor requirements, processing characteristics, processing intermediates, and product formation pathways are outlined. Some specific examples are presented and their reaction thermodynamics are compared. Some conclusions regarding thermo-dynamic versus kinetic control are drawn from these examples.
Rheology of Zirconia-Alumina Gelcasting Slurries
Authors: Bleier A. , Omatete O. O. , Westmoreland C. G.
Published: March 2011

The rheology of zirconia-alumina composite slurries for gelcasting was studied in order to maximize the solids loading. The viscosity and yield stress were controlled by adjusting the pH. This approach allows the solids loading to be maximized for the gelcasting of near-net-shape composites. A strong correspondence exists among the rheological behavior, the surface charge on the particles, colloidal stability, and the maximum solids loading. The best pH conditions for gelcasting composites depends on the specific binary composition.
Novel Precipitation Route to Silica Grain
Authors: Simms Barbara , Gallo Tom
Published: March 2011

We describe a novel precipitation route to silica grain that lies in the interface between sol-gel and Stöber-type silica. The use of acetic acid as a catalyst for TEOS hydrolysis provides access to a precipitation window in which partially hydrolyzed TEOS and TEOS monomer, when reacted with aqueous ammonia, combine to form pumice-like silica particles in up to 90% yield as SlO2. Precipitated particles exhibit narrow particle size distributions that may be controlled for average particle sizes from 50µ to 400 µ. SEM micrographs show that the particles are agglomerates of small particles, which is consistent with the high degree of observed macroporosity.
Stability of Aqueous Suspensions of High Surface area Zirconia Powders in the Presence of Polyacrylic Acid Polyelectrolyte
Authors: Boutz Michel M. R. , Olde Scholtenhuis R. J. M. , Winnubst A. J. A. , Burggraaf A. A. J.
Published: March 2011

In this paper results of efforts to prepare stable aqueous suspensions of high surface area (> 100 m2 /gr) yttria stabilized tetragonal zirconia powders are presented using a low molecular weight ammonium polyacrylic acid deflocculant. Zetapotentials, viscosities, agglomerate sizes and sedimentation volumes have been measured to find the optimum pH and deflocculant concentration. It has been found that the optimum pH-value coincides with the pH at which the polyacrylic acid is fully dissociated. Using deflocculant concentrations below the optimum value leads to a highly unstable system, while concentrations above the optimum value influence the stability in a much weaker way.
Production of Sols from Aggregated Titania Precipitates
Authors: Bartlett John. R , Woolfrey James L.
Published: March 2011

Titania and titania/zirconia sols, with solids loadings exceeding 1000 g dm3, have been prepared on a 10 kg scale by chemical methods involving the hydrolysis of an appropriate mixture of alkoxides, followed by peptisation with dilute nitric acid. The rate of peptisation of the hydrolysates was determined by static light-scattering and photon-correlation spectroscopy, enabling the hydrodynamic radius, the radius of gyration and the fractal dimension of colloidal species to be monitored as a function of peptisation time.

The peptisation kinetics were influenced by a range of factors including the initial solids loading, the acid concentration, the reaction temperature and the age of the alkoxide hydrolysate. Hydrolysate peptisation is first order with respect to concentration of acid and exhibited a non-integer reaction rate order (complex mechanism) with respect to solids concentration. Sols produced from freshly-precipitated hydrolysate peptised at a faster rate than aged precipitates but slowly re-aggregated after peptising, yielding “equilibrium” aggregate sizes often exceeding 100 nm. This effect was not observed in sols produced from aged hydrolysate. These differences are interpreted using DLVO theory.
Studies on the Formation of Tin(IY) Oxygen Compounds by Sol-Gel-Process
Authors: Reuter H. , Kremser M. , Schröder D. , Jansen M.
Published: March 2011

Solutions of Sn(OR)4 and R'Sn(OR)3 with different amounts of alkali and alkaline earth metal alkoxides, MI(OR) and MII(OR)2 respectively, have been prepared. Slow evaporation of the solvent resulted in the crystallization of mixed metal alkoxide compounds. Solid state structures have been determined for two examples: K3H[Sn(O/Pr)6]2 and Na2[iPrSn(OiPr)5]·5iPrOH. Solutions as well as solids have been hydrolyzed by moisture. The thermal behaviour of the resulting amorphous powders was investigated by TG, DTA and XRD up to 1000°C in argon atmosphere. The structural evolution during the solid state step mainly depends on the nature and amount of the mono- and bivalent cations. The different influence of both parameters is described.
Electrical and Optical Properties of Sol-Gel Processed Pb(Zr,Ti)o3 Films
Authors: Ramamurthi S. D. , Swartz S. L. , Marken K. R. , Busch J. R. , Wood Battelle V. E.
Published: March 2011

Lead-zirconate-titanate, Pb(Zr0.53Ti0.47)O3, films were produced by the sol-gel method from alkoxide and acetate precursors in a 2-methoxyethanol solvent system. The PZT films were deposited on platinized silicon and single-crystal SrTiO3 substrates for electrical and optical characterization, respectively. The processing parameters, especially excess PbO content and annealing conditions, were shown to have a significant effects on the properties of PZT films. Epitaxial PZT films deposited on SrTiO3 waveguided over 10 mm distances with propagation losses as low as 5.9 dB/cm at 783 nm and a linear electro-optic effect was also demonstrated.
Sol-Gel Multilayers Applied by A Meniscus Coating Process
Authors: Britten Jerald A. , Thomas Ian M.
Published: March 2011

We describe a meniscus coating method to produce high-laser damage threshold, silica/alumina sol-gel multilayer reflectors on 30+ cm substrates for laser-fusion applications. This process involves forcing a small suspension flow through a porous applicator tube, forming a falling film on the tube. A substrate contacts this film to form a meniscus. Motion of the substrate relative to the applicator entrains a thin film on the substrate, which leaves behind a porous, optical quality film upon solvent evaporation. We develop a solution for the entrained film thickness as a function of geometry, flow and fluid properties by an analysis similar to that of the classical dip-coating problem. This solution is compared with experimental measurements. Also, preliminary results of multilayer coating experiments with a prototype coater are presented, which focus on coating uniformity and laser damage threshold (LDT).
Phase Transformations in Sol-Gel Yag Films
Authors: Hay R. S.
Published: March 2011

Diphasic yttrium-aluminum garnet (YAG) sols were gelled across TEM grids to make films. The films were heat-treated up to 300 hours between 800°C to 1150°C. Microstructure and phase evolution were observed by TEM. YAG fraction and grain size, matrix phases and grain size, nuclei/area, and film thickness were measured. Yttrium-aluminum monoclinic and transition alumina appeared at 800°C. YAG nucleated between 800°C and 950°C. Above 850°C nudeation was site-saturated. Final nuclei density averaged 0.3/μm3. Between 850°C and 1000°C YAG growth had ∼t1/2 dependence and Q ∼ 280 kJ/mole. Below 850°C nudeation was continuous and growth had ∼t0.85 dependence. Above 1000°C YAG growth had ∼t1/4 dependence and the matrix grains coarsened with ∼t1/4 dependence. Unreacted areas were more abundant in thinner films because the nuclei/area and reaction rate decreased. YAG growth was often accompanied by formation of 20 – 100 nm subgrains. Above 1100°C there was some readion to YAG by a different process.
Crystalline Thin and/or Thick Film of Perovskite-Type Oxides by Hydrothermal Electrochemical Techniques
Authors: Yoshimura Masahiro
Published: March 2011

Well crystallized polycrystalline perovskite-type oxide thin and/or thick films were prepared at sufficiently low temperatures by newly developed “hydrothermal electrochemical techniques” where metals were electrochemically oxidized and reacted with some components in hydrothermal solutions. BaTiO3 films 70 to 300 nm thick were formed in Ba(OH)2 solution at 100–200°C under saturation vapor pressure on the Ti substrate and Ti deposited glass substrates. The electrical current enhanced to thicken their films. SrTiO3, BaFeO3 and LiNbO3 films were also prepared.
Mechanics of Gels
Authors: Scherer George W.
Published: March 2011

The response of wet gels to applied stresses is discussed, with emphasis on the role of flow of the pore liquid. Even when the network of the gel is purely elastic, the gel exhibits time-dependent behavior that resembles viscoelasticity, which results from fluid flow. The permeability of the gel can be determined from measurement of this time-dependence. Fluid flow also influences the thermal expansion behavior of gels, and can cause severe stresses to develop during supercritical drying, if the autoclave is heated too rapidly.
Pore Structure Evolution of Silica Gel during Aging/ drying: Effect of Surface Tension
Authors: Deshpande Ravindra , Smith Douglas M. , Jeffrey Brinker C.
Published: March 2011

Two-step acid/base (B2) and acid/acid (A2) catalyzed silica gels have been aged in ethanol or water baths followed by various aprotic solvents with a range of surface tensions. The physical and chemical structures of xerogels dried from these aprotic solvents were studied by a series of techniques (nitrogen adsorption, elemental analysis, TGA, SAXS)and compared to the corresponding structures of low temperature (CO2) and high temperature (ethanol) aerogels. The aprotic solvents help to isolate the effects of pore fluid surface tension during drying since they do not react with the gel surface. B2 xerogels showed a linear decrease in surface area with increasing surface tension. Pore volume and pore size followed a similar trend. Micropore analysis on A2 xerogels showed an increase in micropore volume and surface area with increase in surface tension, whereas total surface area and pore volume showed an opposite trend. Thus, by varying surface tension and aging, one is able to independently control surface area, pore volume, and pore size.
Interpretation of Aerogel Shrinkage During Drying.
Authors: Rangarajan Bharath , Lira Carl T.
Published: March 2011

A variety of silica aerogels have been prepared by the hydrolysis of TEOS, and dried using supercritical CO2. The shrinkage which occurs during the drying process is dependent on the gel formulation and the extent of aging of the gels in their pore liquor. Such aging normally results in an increased density, modulus and pore size of wet gels. Upon drying the corresponding aerogels show the opposite behavior for modulus and density, which decrease with the extent of aging. Both drying and aging shrinkage were not observed for base-catalyzed gels, and were very small for HF-catalyzed gels. The use of formamide resulted in reduced drying shrinkage and a slightly larger amount of syneresis. Drying shrinkage is associated with the presence of micropores. Shrinkage during drying has been observed using a high pressure view cell and it was found that most of the shrinkage occurred during depressurization. An explanation consistent with the above is proposed.
Tailoring of Transition Metal Alkoxides Via complexation For The Synthesis of Hybrid Organic-Inorganic Sols and Gels
Authors: Sanchez C. , In M. , Toledano P. , Griesmar P.
Published: March 2011

The chemical control of hydrolysis-condensation reactions of transition metal alkoxides can be performed through the modification of the transition metal coordination sphere by using strong complexing ligands (SCL). Complexing organic groups can be bonded to the transition metal oxide network in two different ways, as network modifiers or network formers. Different illustrations of the role of complexing ligands on Ti(IV) and Zr(IV) alkoxides are presented. As a network modifier, SCL act as termination agents for condensation reactions allowing a control of particle growth. The complexing ligands being located at the periphery of the oxo core open many opportunities for colloid surface protection. SCL carrying organofunctional groups which exhibit non linear optical (NLO) properties have also been used as probes to study sol-gel transformations. SCL functionalized with organic polymerizable functions act as network formers. Hybrid organic-inorganic copolymers intimately interpenetrated on a nanometer size scale were synthesized from zirconium oxo polymers chemically bonded to polymeric methacrylate chains via a complexing function.
Characterization of Microporous Silica Gels Prepared from Modified Silicon Alkoxides
Authors: Fahrenholtz W. G. , Smith D. M.
Published: March 2011

Organically modified silica gels were prepared from mixtures of TEOS and methyl-substituted silicon alkoxides. The pore structure of dried gels was investigated in order to determine the effect of the organic additions on gel structure. For base catalyzed gels, surface area, pore volume, and skeletal density all showed dramatic decreases at high methyl contents. The surface area dropped by nearly three orders of magnitude, from over 800 m2/g for normal silica gels to less than 1 m2/g for gels containing over 60 mole percent modified alkoxide. The pore structure of acid catalyzed gels showed less dependence on composition. The nature of the surface of both acid and base catalyzed gels varied with modified alkoxide content. Higher organic contents produced materials that were more hydrophobic. In addition, the mechanical strength of acid catalyzed gels dropped in direct proportion to methyl content.
Processing of SiC-Based Fibres from Polycarbosilane
Authors: Kalyvas Vasilios , Ko J. C. , East G. C. , Mcintyre J. E. , Rand B. , Riley F. L.
Published: March 2011

A commercial polycarbosilane, thermolysis product of polysilastyrene, was spun into fibres. The self-curing character of the polymer permitted both oxidative and thermal curing of the precursor fibres. Pyrolysis of the latter produced ceramic fibres in high yields, which were fully characterised. Optimum tensile strength was attained after heat treatment at 1100°C. Oxidative reactions and crystallisation caused strength degradation above this temperature.
Alkynyl Substituted Carboranes as Precursors to Boron Carbide Thin Films, Fibers and Composites
Authors: Johnson Stephen E. , Yang Xiaoguang , Hawthorne M. F. , Thorne Kevin J. , Zheng Haixing , Mackenzie John D.
Published: March 2011

The use of alkynyl substituted derivatives of o-carborane as precursors to boron containing ceramics is described. These compounds undergo a thermally or photochemically induced polymerization to afford cross linked polyakynyl-o-carborane derivatives. The increase in molecular weight should allow for increased Tg's and the retention of modelled polymer preforms. In this report, these modification reactions are described. In addition, the retention of molded polymer preforms were analyzed after UV exposure and inert atmosphere pyrolysis.
Polymer Precursors for Aluminum Nitride Ceramics
Authors: Jensen James A.
Published: March 2011

The aluminum imine complexes [RCH=NAlR'2]2 undergo thermal condensation polymerization to yield alazane [poly(alkylaminoalane)] polymers. The aluminum imine complexes are prepared in quantitative yield by reduction of nitriles, such as acetonitrile and benzonitrile, with alkylaluminum hydride reagents. These alazane polymers are thermoplastic, soluble in aprotic solvents, and display low moisture and oxygen sensitivity. The alazanes convert to aluminum nitride ceramics in non-oxidizing atmospheres above 500°C.
Computation, Visualization, and Chemistry of Electric Field-Enhanced Production of Ceramic Precursor Powders
Authors: Harris Michael T. , Sisson Warren G. , Basaran Osman A.
Published: March 2011

The stability of a liquid emanating from a nozzle is profoundly affected by an electric field. This electric-field induced instability is used here to form ceramic precursor powders having well-controlled particle-size distribution and morphology. Moreover, a hybrid boundary element/finite element method is used to determine the shapes and stability of a drop hanging from a nozzle. The efficiency of two different electrode configurations is considered: in one configuration, the nozzle is attached to the top plate of a parallel-plate capacitor and in the other, the nozzle is surrounded by a concentric cylindrical electrode. The computational results show that such pendant drops lose stability at turning points with respect to field strength. The experimental and computational results reported here are of importance not only in the development of electrodispersion apparatus, but in fields as diverse as capillarity and separations.
Synthesis of Barium Titanate by a Basic pH Pechini Process
Authors: Kumar Suresh , Messing Gary L.
Published: March 2011

Barium titanate powders and thin films have been processed by the conventional acid pH Pechini process and a modified basic pH Pechini process. Higher pH of the starting solution resulted in significantly finer grains in the sintered thin films. It is proposed that the microstructure refinement is due to the precipitates, formed only in the basic pH solution and resin.
Formation of Highly Dispersed Metal Carbides, M2C (M=Mo, W) via Chemical Reduction Methods
Authors: Zeng Dongshui , Hampden-Smith M.J. , Datye A.
Published: March 2011

A new reduction method for the preparation of the molybdenum halides MoCl3(THF)3 and MoCl4(THF)2 in high yield and with high purity directly from MoCl5 is described. The preparation of pure starting materials is crucial to the success of the subsequent chemical reduction. Reduction of MoCl3(THF)3, MoCl4(THF)2 or WCl4 in THF with LiBEt3H at room temperature did not.result in formation of Mo and W as anticipated but instead resulted in formation of nanophase M2CM = Mo and W binary metal carbides. These species were characterized by SEM, TEM, energy dispersive spectroscopy, electron diffraction, elemental analysis, thermogravimetric analysis and X-ray diffraction techniques. These techniques showed the black solids were crystalline and comprised 1–2 nm sized crystallites Which could be grown by heating to higher temperatures (450 – 500°C). The solids isolated from these experiments could be redispersed in THF to form colloidal black solutions.
Formation of Highly Dispersed Rhodium Particles by Chemical and Photochemical Reduction
Authors: Duan Zhibang , Hampden-Smith M.J. , Datye A. , Nigrey P.J. , Quintana C. , Sylwester A.P.
Published: March 2011

Nanometer-sized metal particles have been prepared by chemical and photochemical reduction of homogeneous solutions of metal-organic rhodium(I) compounds. Reduction of [(COD)RhCl]2 with LiBEt3H in THF resulted in the formation of solutions containing crystalline, mono-dispersed Rh particles with average sizes of 2–4nm as determined by TEM and SAXS. The species [(COD)RhH]4 was isolated during the formation of the Rh colloids but was found not to be an intermediate in the reduction of Rh(I) to Rh(0). The catalytic activity of these highly dispersed metals towards pyrene hydrogenation has been investigated. Photochemical reduction of [(ethylene)2Rh(OEt)]2 at room temperature also resulted in formation of Rh as shown by TEM, EDS, ED and X-ray diffraction.
Cobalt Clusters on a Giant Graphite Lattice
Authors: Xhie J. , Sattler K. , Ge M. , Venkateswaran N.
Published: March 2011

Using a scanning tunneling microscope in UHV we have observed anomalous superstructures on highly oriented pyrolytic graphite. We found such structures on three different samples, with hexagonal symmetry in each case but with different lattice constants of 1.7 nm, 3.8 nm and 6.6 nm. These giant lattices can be explained by assuming that the top layer of graphite is slightly rotated. This produces a hexagonal modulation of the electron state density in the first layer. Lattice points in the giant lattice are characterized by high local density of states at the Fermi level. We find that adsorbed cobalt particles occupy the top sites of the giant lattice.
Luminescence of Direct and Indirect Gap Quantum Semiconductor Crystallites
Authors: Brus L. E.
Published: March 2011

Semiconductor crystallites (“quantum dots”) small with respect to the bulk exciton Bohr diameter show a three dimensional electronic quantum size effect. Their internal excited electronic states are discrete and shifted to higher energy than the bulk band gap[1,2].
Electronic Structure of Pd doped InP
Authors: Khowash P. K.
Published: March 2011

The electronic structure of metal impurities in III-V semiconductors are interesting because of their ability to create deep centers. We use a spin unrestricted self-consistent local density theory in a cluster model to calculate the charge distributions, one electron energy spectra and the density of states for pure InP and Pd doped InP, substituted at the In site. The pure semiconductor gap is calculated to be 1.44 eV in excellent agreement with the experimental value of 1.41 eV. A small magnetic moment of 0.561μB appears on the Pd site. The impurity introduces a levels of t2 character at 0.01 and 0.04 eV above the valence band edge.
Use of Calixarene Host Molecules to Stabilize Quantum-confined Cadmium Sulfide Formation
Authors: Chandler Robin R. , Coffer Jeffery L. , Gutsche C. David , Alam Iftikhar , Yang Hong , Pinizzotto Russell F.
Published: March 2011

We describe here the use of calixarenes, methylene (-CH2-) linked phenolic macrocyclic molecules, to stabilize the formation of quantum-confined (Q-) CdS clusters. Specifically, we focus on the use of an amino-derivatized calixarene, para-[(dimethylamino)- methyl]calix[6]arene, to stabilize Q-CdS clusters which have been characterized by High Resolution TEM (HREM), as well as absorption and emission spectroscopies. Under typical preparative conditions, an average particle diameter of 36 Å is obtained. HREM, in combination with Selected Area Diffraction (SAD), confirms the structure of the clusters as zinc blende CdS. Spectroscopic studies using absorption and emission methods indicate that both particle size and cluster photophysics are sensitive to the ratio of CdS to calixarene.