Crystallized TiO2 film growth on unheated substrates by pulse-powered magnetron sputtering

Crystallized TiO₂ films were successfully grown in situ without heating by bipolar-pulse sputtering method at high deposition rates (∼40 nm/min). The optical emission study of the sputtering plasma during growth revealed that the “pulse geometry” had a great influence on the electron/ion temperature of the plasma. It was revealed that the crystallization and the accompanying enhancement in the photocatalytic activity were not caused by the “temperature effect” but caused by the “plasma effect”.     

Automated nondestructive assay of UF6 cylinders: Detector characterization and initial measurements

International Atomic Energy Agency (IAEA) inspectors currently perform periodic inspections at uranium enrichment plants to verify UF6 cylinder enrichment declarations. Measurements are typically performed with handheld high-resolution sensors on a sampling of cylinders taken to be representative of the facility's entire cylinder inventory. These measurements are time-consuming and assay only a small fraction of the total cylinder volume. An automated nondestructive assay system capable of providing enrichment measurements over the full volume of the cylinder could improve upon current verification practices in terms of manpower and assay accuracy. Pacific Northwest National Laboratory is developing an Integrated Cylinder Verification System (ICVS) intended for this purpose and has developed a field prototype of the nondestructive assay (NDA) components of an ICVS. The nondestructive assay methods would combine the “traditional” enrichment-meter signature (i.e. 186-keV emission from U-235) as well as “nontraditional” high-energy photon signatures derived from neutrons produced primarily by F-19(α,n) reactions. This paper describes the design, calibration and characterization of the NaI(Tl) and LaBr3(Ce) spectrometers utilized in the field prototype. An overview of a recent field measurement campaign is then provided, supported by example gamma-ray pulse-height spectra collected on cylinders of known enrichment.     

Influence of substrate doping on the surface chemistry and morphology of Copper Phthalocyanine ultra thin films on Si (111) substrates

16 nm thick Copper Phthalocyanine (CuPc) films were deposited at room temperature in Ultra High Vacuum onto “n” and “p” type doped Si(111) substrates covered with a native SiO₂ overlayer. Atomic Force Microscopy indicates that the two substrates are both atomically flat (0.15 nm root mean square roughness). Angle dependent X-ray photoemission spectroscopy shows that the thickness of the native SiO₂ over-layer is 0.8 nm (both for the “n” and “p” type Si substrate). Despite the identity of the substrate roughness, of the SiO₂ thickness, and of the CuPc film growth conditions, the organic films (made out of crystallites in the α-phase, as checked with X-ray Diffraction) grown on the “p” and “n” type substrate show clearly different morphological features (determined with Atomic Force Microscopy and Scanning Electron Microscopy measurements). While the CuPc film on “p” Si(111) shows a compact network of densely packed crystallites with sizes (along the substrate plane) ranging from 50 to 100 nm, the CuPc film on “n” Si(111) shows a slightly more open network of larger crystallites (with 75-150 nm size range). Accordingly, the CuPc film roughness is 0.67 nm and 1.15 nm for the “p” and “n” type substrate respectively. Due to the increased surface to volume effects (lower crystallite size) affecting the CuPc film on “p” Si(111), this film exhibits stronger interaction with oxygen and water vapor of the ambient air, as determined by photoemission spectroscopy experiments performed on samples as grown “in situ” and after prolonged (1 year) exposure to air.     

Reducing air-pollution: A new argument for getting drivers to abide by the speed limit?

Speeding is one of the main factors of car crash-risk, but it also contributes to increasing air-pollution. In two studies we attempted to lead drivers to abide by speed limits using “reducing air-pollution” as a new argument. We presented prevention messages that highlighted the role of speeding in increasing “crash-risk”, “air-pollution”, or both (Studies 1 and 2). The messages were also positively or negatively framed (Study 2). Given that women are more concerned with environmental issues than are men, we expected the following hypotheses to be validated for women. The message with the “air-pollution” argument was expected to be evaluated more positively than the “crash-risk” message (H1). The “air-pollution” and “crash-risk and air-pollution” messages were expected to be more effective than the “crash-risk” message on the behavioral intention to observe speed limits (H2a) and on the perceived efficacy of speed-limit observance in reducing air-pollution (H2b; Studies 1 and 2). Furthermore, positive framing was expected to be more effective than negative framing (H3), and presenting a message to be more effective than presenting no message (H4; Study 2).Broadly, our results argue in favor of our hypotheses. However in Study 2, the effects of message framing did not allow us to conclude that negative or positive framing was superior. All in all, messages with the “air-pollution” argument were more effective at leading drivers to observe speed limits. Thus, environmental protection may be a fruitful route to explore for increasing road safety.     

A population-based study of inpatients admitted due to suffocation in Taiwan during 2005–2007

The objective of this study was to analyze the epidemiology and factors associated with prognoses (inpatient fatality) of patients hospitalized due to suffocation. Data from 2005 to 2007 were sourced from the Taiwanese National Health Insurance Research Database. Suffocation was defined as E911–E915 according to the ICD-9-CM classification. In total, 4062 hospitalizations occurred in Taiwan due to suffocation from 2005 to 2007, with an inpatient fatality rate of 6.5%. Among hospitalizations due to suffocation, “foreign body unintentionally entering other orifice”, “food causing obstruction”, and “other object causing obstruction” accounted for 58.4%, 17.9%, and 11.0%, respectively. There were more cases of male inpatients than female patients; in terms of age, infants under 1 year old and the elderly aged 65 and over had the highest rates of hospitalization. Factors associated with inpatient fatality included “age”, “cardiac arrest”, “received surgery or procedure”, “acute respiratory failure”, “anoxic brain damage”, and “foreign body in larynx”. Infants and the elderly were high-risk groups for hospitalization as a result of suffocation; the dominant cause among inpatient fatality was “food causing obstruction”, which accounted for 22.2% of cases. Medical institutions should focus on the factors associated with inpatient fatality to improve prognoses and decrease the fatality rates of inpatients.     

Magnetic field enhances the graphitized structure and field emission effect of carbon nanotubes

This study uses a low temperature thermal chemical vapor deposition with an applied external magnetic field to grow carbon nanotubes (CNTs) on Ni/Ag-printed glass substrates. A mixture of C₂H₂ and H₂ gas was used for the growth of the CNTs. A Ni catalyst layer was deposited on the Ag-printed glass substrate by pulse electroplating. Scanning electron micrographs as well as the presence of two sharp peaks at 1320 cm⁻¹ (D band) and 1590 cm⁻¹ (G band) in the Raman spectra indicate that the graphitized structure of CNTs synthesized under a magnetic field has higher quality (i.e., a D-band to G-band intensity ratio of 0.303) than CNTs synthesized without a magnetic field. Transmission electron micrographs show a fine Ni catalyst at the tip of the tube for CNTs synthesized under a magnetic field, exhibiting a CNT “tip-growth” model. The synthesis of CNTs in the presence of a magnetic field also generates better field emission properties and better lighting morphology than without a magnetic field.     

Knowledge sharing over the network

This paper addresses an overview of “knowledge management” from business management/social science perspectives and information technology perspectives, including ongoing research of “knowledge sharing approach towards information retrieval”. We usually use various knowledge when facing practical problems, and transfer it to others for re-use. Such features are investigated for long-time period, and some are characterized and understood by terms such as “SECI model”, “the wisdom of crowds”, “knowledge-centric” and so forth. Information technology provides several functionalities to enhance knowledge management methodology from usable computer system points of views. Through research on knowledge sharing, some hints are provided this research area.     

Rethinking the role that the “step” in the load-displacement curves can play in measurement of fracture toughness for hard coatings

The “step” in the load-displacement curves during nanoindentation of hard coatings has been regarded as a representation of the energy dissipated during fracture of the coating thus is used in measuring the fracture toughness of this coating. This paper scrutinizes the “step” and finds that the “step” is a gap artificially bridged up with a straight line and that the “step” size corresponds with the thickness of the coating in testing. It is realized that the gap is formed due to loss of contact of the indenter with the sample. Upon catastrophic fracture of the coating, the indenter undergoes a freefall of a distance about the thickness of the coating. The size of such a “step” has no logic relationship with the energy dissipation that fractures the coating before the freefall of the indenter takes place.     

Predictions and detection of the “accommodation” forces on Janus particles subjected to directed radiation in a rarefied gas

The results of theoretical and experimental study of so-called “accommodation” forces acting on particles with artificial asymmetry of surface properties in rarefied gas in the directed radiation field are presented. The gas-kinetic theory of phenomenon in the free-molecular regime for some different types of boundary conditions of gas-surface interactions is developed. The theory predicts appearance of the unusual force caused by the difference of the normal momentum accommodation coefficients on hemispheres of considered model Janus particle. The measurements conducted by the experimental technique with macroparticles have confirmed the existence of the accommodation forces affecting a particle together with the forces of radiometric photophoresis. The experimental results for the system “steel particle-helium” are in good agreement with theoretical predictions, and the ratio of the “accommodation” forces to the photophoretic force does not exceed 3%. The estimations show that the “accommodation” forces can be comparable in some cases with the radiometric photophoretic forces for micron-sized particles in stratosphere, but do not exceed the gravity force. The action of “accommodation” forces, in our opinion, is not capable to provide effective vertical transport of aerosol particles against gravity at stratospheric altitudes.     

Magnetron sputtering - Milestones of 30 years

Since the introduction of the planar magnetron by J.S. Chapin in 1974 magnetron sputtering has become the most important technology for the deposition of thin films. Today it has conquered all industrial branches needing high-quality coatings for realization of new or improvement of existing products. The magnetron cathode combines the advantages of economic deposition even on large areas and the ability to coat very temperature sensitive plastic substrates. Main problems like poor target material utilization of the planar magnetron or process instabilities during deposition of highly insulating films have been solved by many innovations during the past 30 years. Novel films with even better quality seem to be possible with “High Power Impulse Magnetron Sputtering (HiPIMS)”. New attempts to increase sputter yield and thus film growth rate are “Sputter Yield Amplification (SYA)” or sputtering from hot targets. This paper gives a brief review on important milestones of the past three decades and outlines some ongoing developments.     

Photocatalytic TiO2 films deposited by reactive magnetron sputtering with unipolar pulsing and plasma emission control systems

TiO₂ films with thickness of about 500 nm were deposited on unheated non-alkali glass substrates by reactive magnetron sputtering using one Ti metal target with unipolar pulsed powering of 50 kHz and the plasma emission feedback system (PCU). In order to keep the very high deposition rate, the depositions were carried out in the “transition region” between the metallic and the reactive (oxide) sputter mode where the target surface was metallic and oxidized, respectively. Stable deposition was successfully carried out in the whole “transition region” with PCU at total gas pressure of 3.0 Pa. All the as-deposited films deposited in the “transition region” showed amorphous structure, which performed very low photocatalytic activity. After the post-annealing in air at higher than 300 °C, all the films crystallized to anatase polycrystalline structure. They performed both photoinduced decomposition of acetaldehyde and photoinduced hydrophilicity under UV light illumination. The highest deposition rate in this study to deposit the photocatalytic TiO₂ films in the “transition region” was 90 nm/min, which was over twenty times higher than that for conventional sputter deposition processes.     

Linear field emission cathode with ZnO grown in aqueous solutions

A new type of linear field emission cathode with ZnO nanostructure grown on nickel wires was prepared by hydrothermal approach. The obtained ZnO nanotapers were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicated that the ZnO nanotapers with sharp tips were high quality single crystals, and grow along (002) direction. The field emission properties were investigated by ZnO nanotapers on nickel wire as the cathode in the centre of a cylindrical ITO anode. The field enhancement factor β was about 2.23 × 10⁴ cm⁻¹, which improved greatly for the cylindrical configuration and sharp geometry of the ZnO nanotapers tip.     

The influence of substrate morphology on the growth of thin silicon films: A GISAXS study

Thin Si films, with thickness between 100 and 300 nm, were deposited by PECVD (Plasma Enhanced Chemical Vapour Deposition) in silane gas (SiH₄) highly diluted by hydrogen. The degree of dilution and the discharge power were varied in order to obtain different crystalline to amorphous fractions in the films. Two types of substrates were used. The first one was amorphous and relatively flat while the second one was polycrystalline with a roughness of a few tens of nanometers. The crystal fraction in the deposited samples, as estimated by Raman spectroscopy, varied between 0 and 40%, and the individual crystal size was between 2 and 8 nm. The larger individual crystals are usually present in those samples with the highest crystal fraction. The sample density, estimated upon the spectral distribution of the dielectric function in the infra red, was 15-25% less than the density of crystalline silicon. The GISAXS pattern of all of the examined samples indicated the presence of not-spherical-like “particles” in the “bulk” of the thin films, with an average “particle” size between 1.5 and 4 nm. These “particles” are most probably voids and their shape indicates columnar growth. By applying the GISAXS technique on samples deposited on different substrates, the borderline deposition conditions between “transport limited growth” and “growth dominantly influenced by plasma surface reactions” was estimated.     

French validation of a new version of the Driver Behavior Questionnaire (DBQ) for drivers of all ages and level of experiences

The purpose of this study was to validate a new version of the Driver Behavior Questionnaire (DBQ) on a sample of French drivers in order to gain a better understanding of different driver behaviors, by differentiating two types of violations (aggressive and ordinary), three types of errors (dangerous, inattention and inexperience) and by taking positive behaviors into account. 525 drivers (205 men and 320 women), between 18 and 79 years of age, filled in a questionnaire on line including the 41 items in the new version of the DBQ and information relative to their mobility and their accident history. Exploratory factor analysis confirmed a six-factor structure: “dangerous errors”, “inattention errors”, “inexperience errors”, “ordinary violations”, “aggressive violations” and “positive behaviors”. A revised version with 23 items of the new version of the DBQ was produced by selecting the items that loaded most strongly on the six factors. The results also showed the link between demographic variables (age and gender), mobility (kilometers driven weekly), the DBQ scores and the involvement in an accident in the previous five years. This study permitted to validate a more detailed version of the “Driving Behavior Questionnaire” among French drivers of all age and all level of experience.     

From mono- to polytopic interactions via hydrogen bonds — Capacitive sensor studies

Supra molecular materials can be generated via hydrogen bonding between monomers. This leads either to “monotopic” molecules as well as self-assemblies of a restricted number of complementary components as “di-” or “polytopic” molecules with more than one functional unit. The latter structures grow spontaneously by self organization and in principle consist of repeatedly branched chain molecules analogous to dendrimers. When disturbing these aggregates by analyte molecules (e.g. volatile organic compounds), the supra molecular structures break down leading to a pronounced change in dielectric behavior that is detectable with inter digital capacitors. “Monotopic”-materials show linear behavior with increasing analyte concentration whereas “polytopic” molecules lead to properties resembling a threshold sensor.     

Selection and experimental evaluation of low-cost porous materials for regenerator applications in thermoacoustic engines

This paper aims at evaluating three selected low-cost porous materials from the point of view of their suitability as regenerator materials in the design of thermoacoustic travelling-wave engines. The materials tested include: a cellular ceramic substrate with regular square channels; steel “scourers”; and stainless steel “wool”. Comparisons are made against a widely used regenerator material: stainless steel woven wire mesh screen. For meaningful comparisons, the materials are selected to have similar hydraulic radii. One set of regenerators was designed around the hydraulic radius of 200 μm. This included the ceramic substrate, steel “scourers”, stainless steel “wool” and stacked wire screens (as a reference). This set was complemented by steel “scourers” and stacked wire screens (as a reference) with hydraulic radii of 120 μm. Therefore six regenerators were produced to carry out the testing. Initial tests were made in a steady air flow to estimate their relative pressure drop due to viscous dissipation. Subsequently, they were installed in a looped-tube travelling-wave thermoacoustic engine to test their relative performance. Testing included the onset temperature difference, the maximum pressure amplitude generated and the acoustic power output as a function of mean pressure between 0 and 10 bar above atmospheric. It appears that the performance of regenerators made out of “scourers” and steel “wool” is much worse than their mesh-screen counterparts of the same hydraulic radius. However cellular ceramics may offer an alternative to traditional regenerator materials to reduce the overall system costs. Detailed discussions are provided.     

Electrochemical properties of facile emulsified LiV3O8 materials

LiV₃O₈ cathode materials are post-treated by a special emulsion method (termed “EM”) and then calcinated at different temperatures. The experimental results show that the structure of these oxides is different from LiV₃O₈ prepared by the solid-state reaction (acronym “STATE”) route, although their starting materials are identical. The EM product prepared at 500 °C exhibits a better electrochemical behavior than its counterpart prepared by traditional methods (STATE) or by EM at other temperatures. Its initial discharge capacity is 305 mAh g⁻¹, and it still maintains 250.2 mAh g⁻¹ after 100 cycles at 0.2 C at the voltage range of 1.8–4.0 V vs. Li/Li⁺.     

Thermionic emission from electron traps

Electron emission from traps filled by previous irradiation (exoelectron emission) is described in terms of thermionic emission from a surface layer of definite depth (isolated box model). From the kinetic equations a “thermionic range” is derived which is a common measure for the increasing temperature promoting the emission and the rejecting surface potential. Relative to the emission depth the emission efficiency is formulated which separates regions of strong and weak emission. The energy levels of the traps are readily computed in the case of strong emission. A check on F-centres in LiF confirms the theoretical model.