Piezoresistive sensors for force mapping of hip-prostheses

The success of artificial prosthetic replacements depends on the fixation of the artificial prosthetic component after being implanted in the thighbone. The materials for fixation are subject to mechanical stresses, which originate permanent deformations, incipient cracks and even fatigue fractures. This work shows the possibility of monitoring the mechanical stress over time in prosthesis. In this way, highly sensitive silicon thin-film piezoresistive sensors were developed attached to prosthesis and their results compared with commercial strain gauge sensors. Mechanical stress-strain experiments were performed in compressive mode, during 10,000 cycles. Experimental data was acquired at mechanical vibration frequencies of 0.5 Hz, 1 Hz and 5 Hz, and sent to a computer by means of a wireless link. The results show that there is a decrease in sensitivity of the thin-film silicon piezoresistive sensors when they are attached to the prosthesis, but this decrease does not compromise its monitoring performance. The sensitivity, compared to that of commercial strain gauges, is much larger due to their higher gauge factors (-23.5), when compared to the GFs of commercial sensors (2).

Thermal characterization of copolymers obtained by radiation grafting of styrene onto poly(tetrafluoroethyleneperfluoropropylvinylether) substrates: thermal decomposition, melting behavior and low-temperature transitions

Differential scanning calorimetric (DSC) and thermogravimetric analysis (TGA) have been used to study the thermal decomposition, the melting behavior and low-temperature transitions of copolymers obtained by radiation-induced grafting of styrene onto poly (tetrafluoroethylene- perfluoropropylvinylether) (PFA) substrates. PFA with different contents of perfluoropropylvinylether (PPVE) as a comonomer have been investigated. A two step degradation pattern was observed from TGA thermograms of all the grafted copolymers, which was attributed to degradation of PSTY followed by the degradation of the PFA backbone at higher temperature. One broad melting peak can be identified for all copolymers, which has two components in the samples with higher PPVE content. The melting peak, crystal-crystal transition and the degree of crystallinity of the grafted copolymers increases with radiation grafting up to 50 kGy, followed by a decrease at higher doses. No such decrease was observed in the ungrafted PFA samples after irradiation. This indicated that the changes in the heats of transitions and crystallinity at low doses are due to the radiation effects on the microstructure of PFA (chain scission), whereas at higher doses the grafted PSTY is the driving force behind these changes. (C) 2001 Elsevier Science Ltd. All rights reserved.

Atomic structure of the nanocrystalline Si particles appearing in nanostructured Si thin films produced in low-temperature radiofrequency plasmas

Nanostructured Si thin films, also referred as polymorphous, were grown by plasma-enhanced chemical vapor deposition. The term "polymorphous" is used to define silicon material that consists of a two-phase mixture of amorphous and ordered Si. The plasma conditions were set to obtain Si thin films from the simultaneous deposition of radical and ordered nanoparticles. Here, a careful analysis by electron transmission microscopy and electron diffraction is reported with the aim to clarify the specific atomic structure of the nanocrystalline particles embedded in the films. Whatever the plasma conditions, the electron diffraction images always revealed the existence of a well-defined crystalline structure different from the diamondlike structure of Si. The formation of nanocrystallinelike films at low temperature is discussed. A Si face-cubic-centered structure is demonstrated here in nanocrystalline particles produced in low-pressure silane plasma at room temperature.

Photo-induced electron trapping in indirect bandgap AlxGa1-xAs : Si at low temperature

A variation of photoconductivity excitation with wavelength is applied to Si-doped Al0.56Ga0.44As (indirect bandgap material) for a wide range of temperature. The lower the temperature the lower the photocurrent below 70 K. In the range 13-30 K there is a decrease in the photoconductivity spectrum slightly above the bandgap transition energy, followed by another increase in the conductivity. We interpret these results in the light of existing models and confirm the trapping by the X-valley effective mass state. which is responsible for attenuation of persistent photoconductivity below 70 K. A DX0 intermediate state which has non-negligible lifetime is proposed as responsible for the decrease in the photoconductivity with about 561 nm of wavelength of exciting light, in the investigated 13-30 g range.

Regioregular improvement on the oxidative polymerization of poly-3-octylthiophenes by slow addition of oxidant at low temperature

Many pathways can be used to synthesize polythiophenes derivatives. The polycondensation reactions performed with organometallics are preferred since they lead to regioregular polymers (with high content of heat-to-tail coupling) which have enhanced conductivity and luminescence. However, these pathways have several steps; the reactants are highly moisture sensitive and expensive. On the other hand, the oxidative polymerization using FeCl3 is a one-pot reaction that requires less moisture sensitive reactants with lower cost, although the most common reaction conditions lead to polymers with low regioregularity. Here, we report that by changing the reaction conditions, such as FeCl3 addition rate and reaction temperature, poly-3-octylthiophenes with different the regioregularities can be obtained, reaching about 80% of heat-to-tail coupling. Different molar mass distributions and polydispersivities were obtained. The preliminary results suggest that the oxidative polymerization process could be improved to yield polythiophenes with higher regioregularity degree and narrower molar mass distributions by just setting some reaction conditions. We also verified that it is possible to solvent extract part of the lower regioregular fraction of the polymer further improving the regioregularity degree. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Low-temperature deposition of silicon oxide and silicon nitride by reactive magnetron sputtering

In this study, oxide and nitride films were deposited at room temperature through the reaction of silicon Sputtered by argon and oxygen ions or argon and nitrogen ions at 250 and 350 W with 0.67 Pa pressure. It was observed that for both thin films the deposition rates increase with the applied RF power and decrease with the increase of the gas concentration. The Si/O and Si/N ratio were obtained through RBS analyses and for silicon oxide the values changed from 0.42 to 0.57 and for silicon nitride the Values changed from 0.4 to 1.03. The dielectric constants were calculated through capacitance-voltage curves with the silicon oxide values varying from 2.4 to 5.5, and silicon nitride values varying from 6.2 to 6.7, which are good options for microelectronic dielectrics. (c) 2008 Elsevier Ltd. All rights reserved.

A low-temperature insulating phase at v=1.5 for 2D holes in high-mobility SiSi1-xGex heterostructures with Landau level degeneracy

Magneto-transport measurements of the 2D hole system (2DHS) in p-type Si-Si1-xGex heterostructures identify the integer quantum Hall effect (IQHE) at dominantly odd-integer filling factors v and two low-temperature insulating phases (IPs) at v = 1.5 and v less than or similar to 0.5, with re-entrance to the quantum Hall effect at v = 1. The temperature dependence, current-voltage characteristics, and tilted field and illumination responses of the IP at v = 1.5 indicate that the important physics is associated with an energy degeneracy of adjacent Landau levels of opposite spin, which provides a basis for consideration of an intrinsic, many-body origin.

Application of low temperature thermochronology to understanding cooling and exhumation in the Central Swiss Alps

THESIS ABSTRACT : Low-temperature thermochronology relies on application of radioisotopic systems whose closure temperatures are below temperatures at which the dated phases are formed. In that sense, the results are interpreted as "cooling ages" in contrast to "formation ages". Owing to the low closure-temperatures, it is possible to reconstruct exhumation and cooling paths of rocks during their residence at shallow levels of the crust, i.e. within first ~10 km of depth. Processes occurring at these shallow depths such as final exhumation, faulting and relief formation are fundamental for evolution of the mountain belts. This thesis aims at reconstructing the tectono-thermal history of the Aar massif in the Central Swiss Alps by means of zircon (U-Th)/He, apatite (U-Th)/He and apatite fission track thermochronology. The strategy involved acquisition of a large number of samples from a wide range of elevations in the deeply incised L��tschen valley and a nearby NEAT tunnel. This unique location allowed to precisely constrain timing, amount and mechanisms of exhumation of the main orographic feature of the Central Alps, evaluate the role of topography on the thermochronological record and test the impact of hydrothermal activity. Samples were collected from altitudes ranging between 650 and 3930 m and were grouped into five vertical profiles on the surface and one horizontal in the tunnel. Where possible, all three radiometric systems were applied to each sample. Zircon (U-Th)/He ages range from 5.1 to 9.4 Ma and are generally positively correlated with altitude. Age-elevation plots reveal a distinct break in slope, which translates into exhumation rate increasing from ~0.4 to ~3 km/Ma at 6 Ma. This acceleration is independently confirmed by increased cooling rates on the order of 100��C/Ma constrained on the basis of age differences between the zircon (U-Th)/He and the remaining systems. Apatite fission track data also plot on a steep age-elevation curve indicating rapid exhumation until the end of the Miocene. The 6 Ma event is interpreted as reflecting tectonically driven uplift of the Aar massif. The late Miocene timing implies that the increase of precipitation in the Pliocene did not trigger rapid exhumation in the Aar massif. The Messinian salinity crisis in the Mediterranean could not directly intensify erosion of the Aar but associated erosional output from the entire Alps may have tapered the orogenic wedge and caused reactivation of thrusting in the Aar massif. The high exhumation rates in the Messinian were followed by a decrease to ~1.3 km/Ma as evidenced by ~8 km of exhumation during last 6 Ma. The slowing of exhumation is also apparent from apatite (U-Th)1He age-elevation data in the northern part of the L��tschen valley where they plot on a ~0.5km/Ma line and range from 2.4 to 6.4 Ma However, from the apatite (U-Th)/He and fission track data from the NEAT tunnel, there is an indication of a perturbation of the record. The apatite ages are youngest under the axis of the valley, in contrast to an expected pattern where they would be youngest in the deepest sections of the tunnel due to heat advection into ridges. The valley however, developed in relatively soft schists while the ridges are built of solid granitoids. In line with hydrological observations from the tunnel, we suggest that the relatively permeable rocks under the valley floor, served as conduits of geothermal fluids that caused reheating leading to partial Helium loss and fission track annealing in apatites. In consequence, apatite ages from the lowermost samples are too young and the calculated exhumation rates may underestimate true values. This study demonstrated that high-density sampling is indispensable to provide meaningful thermochronological data in the Alpine setting. The multi-system approach allows verifying plausibility of the data and highlighting sources of perturbation. R��SUM�� DE TH��SE : La thermochronologie de basse temp��rature d��pend de l'utilisation de syst��mes radiom��triques dont la temp��rature de fermeture est nettement inf��rieure �� la temp��rature de cristallisation du min��ral. Les r��sultats obtenus sont par cons��quent interpr��t��s comme des ��ges de refroidissement qui diff��rent des ��ges de formation obtenus par le biais d'autres syst��mes de datation. Gr��ce aux temp��ratures de refroidissement basses, il est ais�� de reconstruire les chemins de refroidissement et d'exhumation des roches lors de leur r��sidence dans la croute superficielle (jusqu'�� 10 km). Les processus qui entrent en jeu �� ces faibles profondeurs tels que l'exhumation finale, la fracturation et le faillage ainsi que la formation du relief sont fondamentaux dans l'��volution des cha��nes de montagne. Ces derni��res ann��es, il est devenu clair que l'enregistrement thermochronologique dans les orog��nes peut ��tre influenc�� par le relief et r��initialis�� par l'advection de la chaleur li��e �� la circulation de fluides g��othermaux apr��s le refroidissement initial. L'objectif de cette th��se est de reconstruire l'histoire tectono-thermique du massif de l'Aar dans les Alpes suisses Centrales �� l'aide de trois thermochronom��tres; (U-Th)/He sur zircon, (U-Th)/He sur apatite et les traces de fission sur apatite. Afin d'atteindre cet objectif, nous avons r��colt�� un grand nombre d'��chantillons provenant de diff��rentes altitudes dans la vall��e fortement incis��e de L��tschental ainsi que du tunnel de NEAT. Cette strat��gie d'��chantillonnage nous a permis de contraindre de mani��re pr��cise la chronologie, les quantit��s et les m��canismes d'exhumation de cette zone des Alpes Centrales, d'��valuer le r��le de la topographie sur l'enregistrement thermochronologique et de tester l'impact de l'hydrothermalisme sur les g��ochronom��tres. Les ��chantillons ont ��t�� pr��lev��s �� des altitudes comprises entre 650 et 3930m selon 5 profils verticaux en surface et un dans le tunnel. Quand cela �� ��t�� possible, les trois syst��mes radiom��triques ont ��t�� appliqu��s aux ��chantillons. Les ��ges (U-Th)\He obtenus sur zircons sont compris entre 5.l et 9.4 Ma et sont corr��l��s de mani��re positive avec l'altitude. Les graphiques repr��sentant l'��ge et l'��l��vation montrent une nette rupture de la pente qui traduisent un accroissement de la vitesse d'exhumation de 0.4 �� 3 km\Ma il y a 6 Ma. Cette acc��l��ration de l'exhumation est confirm��e par les vitesses de refroidissement de l'ordre de 100��C\Ma obtenus �� partir des diff��rents ��ges sur zircons et �� partir des autres syst��mes g��ochronologiques. Les donn��es obtenues par traces de fission sur apatite nous indiquent ��galement une exhumation rapide jusqu'�� la fin du Mioc��ne. Nous interpr��tons cet ��v��nement �� 6 Ma comme ��tant li�� �� l'uplift tectonique du massif de l'Aar. Le fait que cet ��v��nement soit tardi-mioc��ne implique qu'une augmentation des pr��cipitations au Plioc��ne n'a pas engendr�� cette exhumation rapide du massif de l'Aar. La crise Messinienne de la mer m��diterran��e n'a pas pu avoir une incidence directe sur l'��rosion du massif de l'Aar mais l'��rosion associ��e �� ce ph��nom��ne �� pu r��duire le coin orog��nique alpin et causer la r��activation des chevauchements du massif de l'Aar. L'exhumation rapide Mioc��ne a ��t�� suivie pas une diminution des taux d'exhumation lors des derniers 6 Ma (jusqu'�� 1.3 km\Ma). Cependant, les ��ges (U-Th)\He sur apatite ainsi que les traces de fission sur apatite des ��chantillons du tunnel enregistrent une perturbation de l'enregistrement d��crit ci-dessus. Les ��ges obtenus sur les apatites sont sensiblement plus jeunes sous l'axe de la vall��e en comparaison du profil d'��ges attendus. En effet, on attendrait des ��ges plus jeunes sous les parties les plus profondes du tunnel �� cause de l'advection de la chaleur dans les flancs de la vall��e. La vall��e est creus��e dans des schistes alors que les flancs de celle-ci sont constitu��s de granito��des plus durs. En accord avec les observations hydrologiques du tunnel, nous sugg��rons que la perm��abilit�� ��lev��e des roches sous l'axe de la vall��e �� permi l'infiltration de fluides g��othermaux qui a g��n��r�� un r��chauffement des roches. Ce r��chauffement aurait donc induit une perte d'H��lium et un recuit des traces de fission dans les apatites. Ceci r��sulterait en un rajeunissement des ��ges apatite et en une sous-estimation des vitesses d'exhumation sous l'axe de la vall��e. Cette ��tude �� servi �� d��montrer la n��cessit�� d'un ��chantillonnage fin et pr��cis afin d'apporter des donn��es thermochronologiques de qualit�� dans le contexte alpin. Cette approche multi-syst��me nous a permi de contr��ler la pertinence des donn��es acquises ainsi que d'identifier les sources possibles d'erreurs lors d'��tudes thermochronologiques. R��SUM�� LARGE PUBLIC Lors d'une orogen��se, les roches subissent un cycle comprenant une subduction, de la d��formation, du m��tamorphisme et, finalement, un retour �� la surface (ou exhumation). L'exhumation r��sulte de la d��formation au sein de la zone de collision, menant �� un raccourcissement et un apaissessement de l'��difice rocheux, qui se traduit par une remont��e des roches, cr��ation d'une topographie et ��rosion. Puisque l'��rosion agit comme un racloir sur la partie sup��rieure de l'��difice, des tentatives de corr��lation entre les ��pisodes d'exhumation rapide et les p��riodes d'��rosion intensive, dues aux changements climatiques, ont ��t�� effectu��es. La connaissance de la chronologie et du lieu pr��cis est d'une importance capitale pour une quelconque reconstruction de l'��volution d'une cha��ne de montagne. Ces crit��res sont donn��s par un retra��age des changements de la temp��rature de la roche en fonction du temps, nous donnant le taux de refroidissement. L'instant auquel les roches ont refroidit, passant une certaine temp��rature, est contraint par l'application de techniques de datation par radiom��trie. Ces m��thodes reposent sur la d��sint��gration des isotopes radiog��niques, tels que l'uranium et le potassium, tous deux abondants dans les roches de la cro��te terrestre. Les produits de cette d��sint��gration ne sont pas retenus dans les min��raux h��tes jusqu'au moment du refroidissement de la roche sous une temp��rature appel��e 'de fermeture' , sp��cifique �� chaque syst��me de datation. Par exemple, la d��sint��gration radioactive des atomes d'uranium et de thorium produit des atomes d'h��lium qui s'��chappent d'un cristal de zircon �� des temp��ratures sup��rieures �� 200��C. En mesurant la teneur en uranium-parent, l'h��lium accumul�� et en connaissant le taux de d��sint��gration, il est possible de calculer �� quel moment la roche ��chantillonn��e est pass��e sous la temp��rature de 200��C. Si le gradient g��othermal est connu, les temp��ratures de fermeture peuvent ��tre converties en profondeurs actuelles (p. ex. 200��C ≈ 7km), et le taux de refroidissement en taux d'exhumation. De plus, en datant par syst��me radiom��trique des ��chantillons espac��s verticalement, il est possible de contraindre directement le taux d'exhumation de la section ��chantillonn��e en observant les diff��rences d'��ges entre des ��chantillons voisins. Dans les Alpes suisses, le massif de l'Aar forme une structure orographique majeure. Avec des altitudes sup��rieures �� 4000m et un relief spectaculaire de plus de 2000m, le massif domine la partie centrale de la cha��ne de montagne. Les roches aujourd'hui expos��es �� la surface ont ��t�� enfouies �� plus de 10 km de profond il y a 20 Ma, mais la topographie actuelle du massif de l'Aar semble surtout s'��tre d��velopp��e par un soul��vement actif depuis quelques millions d'ann��es, c'est-��-dire depuis le N��og��ne sup��rieur. Cette p��riode comprend un changement climatique soudain ayant touch�� l'Europe il y a environ 5 Ma et qui a occasionn�� de fortes pr��cipitations, entra��nant certainement une augmentation de l'��rosion et acc��l��rant l'exhumation des Alpes. Dans cette ��tude, nous avons employ�� le syst��me de datation (U-TH)/He sur zircon, dont la temp��rature de fermeture de 200��C est suffisamment basse pour caract��riser l'exhumation du N��og��ne sup. /Plioc��ne. Les ��chantillons proviennent du L��tschental et du tunnel ferroviaire le plus profond du monde (NEAT) situ�� dans la partie ouest du massif de l'Aar. Consid��r��s dans l'ensemble, ces ��chantillons se r��partissent sur un d��nivel�� de 3000m et des ��ges de 5.1 �� 9.4 Ma. Les ��chantillons d'altitude sup��rieure (et donc plus vieux) documentent un taux d'exhumation de 0.4 km/Ma jusqu'�� il y a 6 Ma, alors que les ��chantillons situ��s les plus bas ont des ��ges similaires allant de 6 �� 5.4 Ma, donnant un taux jusqu'�� 3km /Ma. Ces donn��es montrent une acc��l��ration dramatique de l'exhumation du massif de l'Aar il y a 6 Ma. L'exhumation mioc��ne sup. du massif pr��date donc le changement climatique Plioc��ne. Cependant, lors de la crise de salinit�� d'il y a 6-5.3 Ma (Messinien), le niveau de la mer M��diterran��e est descendu de 3km. Un tel abaissement de la surface d'��rosion peut avoir acc��l��r�� l'exhumation des Alpes, mais le bassin sud alpin ��tait trop loin du massif de l'Aar pour influencer son ��rosion. Nous arrivons �� la conclusion que la datation (U-Th)/He permet de contraindre pr��cis��ment la chronologie et l'exhumation du massif de l'Aar. Concernant la dualit�� tectonique-��rosion, nous sugg��rons que, dans le cas du massif de l'Aar, la tectonique pr��domine.

Study of post-deposition contamination in low-temperature deposited polysilicon films

The presence of hydrogen in polysilicon films obtained at low temperatures by hot-wire CVD and the post-deposition oxidation by air-exposure of the films are studied in this paper. The experimental results from several characterization techniques (infrared spectroscopy, X-ray photoelectron spectroscopy, secondary ion mass spectrometry and wavelength dispersive spectroscopy) showed that hydrogen and oxygen are homogeneously distributed at grain boundaries throughout the depth of the films. Hydrogen is introduced during the growth process and its concentration is higher in samples deposited at lower temperatures. Oxygen diffuses along the grain boundaries and binds to silicon atoms, mainly in Si 2O groups.

Amorphous silicon thin film solar cells deposited entirely by Hot-Wire Chemical Vapour Deposition at low temperature (<150 ��C)

Amorphous silicon n-i-p solar cells have been fabricated entirely by Hot-Wire Chemical Vapour Deposition (HW-CVD) at low process temperature < 150 ��C. A textured-Ag/ZnO back reflector deposited on Corning 1737F by rf magnetron sputtering was used as the substrate. Doped layers with very good conductivity and a very less defective intrinsic a-Si:H layer were used for the cell fabrication. A double n-layer (��c-Si:H/a-Si:H) and ��c-Si:H p-layer were used for the cell. In this paper, we report the characterization of these layers and the integration of these layers in a solar cell fabricated at low temperature. An initial efficiency of 4.62% has been achieved for the n-i-p cell deposited at temperatures below 150 ��C over glass/Ag/ZnO textured back reflector.

Electronic transport in low temperature nanocrystalline silicon thin-film transistors obtained by Hot-Wire CVD

Hydrogenated nanocrystalline silicon (nc-Si:H) obtained by hot-wire chemical vapour deposition (HWCVD) at low substrate temperature (150 ��C) has been incorporated as the active layer in bottom-gate thin-film transistors (TFTs). These devices were electrically characterised by measuring in vacuum the output and transfer characteristics for different temperatures. The field-effect mobility showed a thermally activated behaviour which could be attributed to carrier trapping at the band tails, as in hydrogenated amorphous silicon (a-Si:H), and potential barriers for the electronic transport. Trapped charge at the interfaces of the columns, which are typical in nc-Si:H, would account for these barriers. By using the Levinson technique, the quality of the material at the column boundaries could be studied. Finally, these results were interpreted according to the particular microstructure of nc-Si:H.

Top-gate microcrystalline silicon TFTs processed at low temperature (<200��C)

N-type as well P-type top-gate microcrystalline silicon thin film transistors (TFTs) are fabricated on glass substrates at a maximum temperature of 200 ��C. The active layer is an undoped ��c-Si film, 200 nm thick, deposited by Hot-Wire Chemical Vapor. The drain and source regions are highly phosphorus (N-type TFTs) or boron (P-type TFTs)-doped ��c-films deposited by HW-CVD. The gate insulator is a silicon dioxide film deposited by RF sputtering. Al-SiO 2-N type c-Si structures using this insulator present low flat-band voltage,-0.2 V, and low density of states at the interface D it=6.4��10 10 eV -1 cm -2. High field effect mobility, 25 cm 2/V s for electrons and 1.1 cm 2/V s for holes, is obtained. These values are very high, particularly the hole mobility that was never reached previously.

Poly-Si���������xGex Film Growth for Ni Germanosilicided Metal Gate

Scaling down of the CMOS technology requires thinner gate dielectric to maintain high performance. However, due to the depletion of poly-Si gate, it is difficult to reduce the gate thickness further especially for sub-65 nm CMOS generation. Fully silicidation metal gate (FUSI) is one of the most promising solutions. Furthermore, FUSI metal gate reduces gate-line sheet resistance, prevents boron penetration to channels, and has good process compatibility with high-k gate dielectric. Poly-SiGe gate technology is another solution because of its enhancement of boron activation and compatibility with the conventional CMOS process. Combination of these two technologies for the formation of fully germanosilicided metal gate makes the approach very attractive. In this paper, the deposition of undoped Poly-Si���������xGex (0 < x < 30% ) films onto SiO��� in a low pressure chemical vapor deposition (LPCVD) system is described. Detailed growth conditions and the characterization of the grown films are presented.

Low-temperature sol-gel preparation of ordered nanoparticles of tungsten carbide/oxide

Tungsten carbide/oxide particles have been prepared by the gel precipitation of tungstic acid in the presence of an organic gelling agent [10% ammonium poly(acrylic acid) in water, supplied by Ciba Specialty Chemicals]. The feed solution; a homogeneous mixture of sodium tungstate and ammonium poly(acrylic acid) in water, was dropped from a 1-mm jet into hydrochloric acid saturated hexanol/concentrated hydrochloric acid to give particles of a mixture of tungstic acid and poly(acrylic acid), which, after drying in air at 100 degrees C and heating to 900 degrees C in argon for 2 h, followed by heating in carbon dioxide for a further 2 h and cooling, gives a mixture of WO, WC, and a trace of NaxWO3, with the carbon for the formation of WC being provided by the thermal carbonization of poly(acrylic acid). The pyrolyzed product is friable and easily broken down in a pestle and mortar to a fine powder or by ultrasonics, in water, to form a stable colloid. The temperature of carbide formation by this process is significantly lower (900 degrees C) than that reported for the commercial preparation of tungsten carbide, typically > 1400 degrees C. In addition, the need for prolonged grinding of the constituents is obviated because the reacting moieties are already in intimate contact on a molecular basis. X-ray diffraction, particle sizing, transmission electron microscopy, surface area, and pore size distribution studies have been carried out, and possible uses are suggested. A flow diagram for the process is described.

Structural and electrical properties of SrBi2Nb2O9 thin films prepared by chemical aqueous solution at low temperature

SrBi2Nb2O9 (SBN) thin films were prepared by the polymeric precursors method and deposited by dip coating onto Pt/Ti/SiO2/Si(100) substrates. The dip-coated films were specular and crack-free and crystallized during firing at 700 degrees C. Microstructure and morphological evaluation were followed by grazing incident X-ray diffraction (GIXRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The films exhibited somewhat porous grain structure with rounded grains of about 100 nm. For the electrical measurements, gold electrodes of 300 mu m in diameter were sputter deposited on the top surface, forming a metal-ferroelectric-metal (MFM) configuration. The remanent polarization (P-r) and coercive field (E-c) were 5.6 mu C/cm(2) and 100 kV/cm, respectively. (C) 1999 Elsevier B.V. B.V. All rights reserved.