High-pressure apparatus for dielectric measurements in high frequency

The present article describes an experimental apparatus for the measurement of low-loss dielectric material under conditions of high pressures (maximum pressure 1500 bars) and high frequencies (1-15 MHz.) The measurements of these losses are based on the classical method of the Q-meter with a general Radio type 1690-A sample holder, located in a high-pressure bomb. All the manual operations made on the holder during the measurements are controlled by dc motors. The first results have shown that the dielectric losses of polyethylene (PE) vary with the pressure. This apparatus will later be used in the measurement of the dielectric losses of the insulating materials used for submarine telecommunication cables.     

Partial-transfer absorption imaging: A versatile technique for optimal imaging of ultracold gases

Partial-transfer absorption imaging is a tool that enables optimal imaging of atomic clouds for a wide range of optical depths. In contrast to standard absorption imaging, the technique can be minimally destructive and can be used to obtain multiple successive images of the same sample. The technique involves transferring a small fraction of the sample from an initial internal atomic state to an auxiliary state and subsequently imaging that fraction absorptively on a cycling transition. The atoms remaining in the initial state are essentially unaffected. We demonstrate the technique, discuss its applicability, and compare its performance as a minimally destructive technique to that of phase-contrast imaging.     

An apparatus for immersing trapped ions into an ultracold gas of neutral atoms

We describe a hybrid vacuum system in which a single ion or a well-defined small number of trapped ions (in our case Ba(+) or Rb(+)) can be immersed into a cloud of ultracold neutral atoms (in our case Rb). This apparatus allows for the study of collisions and interactions between atoms and ions in the ultracold regime. Our setup is a combination of a Bose-Einstein condensation apparatus and a linear Paul trap. The main design feature of the apparatus is to first separate the production locations for the ion and the ultracold atoms and then to bring the two species together. This scheme has advantages in terms of stability and available access to the region where the atom-ion collision experiments are carried out. The ion and the atoms are brought together using a moving one-dimensional optical lattice transport which vertically lifts the atomic sample over a distance of 30 cm from its production chamber into the center of the Paul trap in another chamber. We present techniques to detect and control the relative position between the ion and the atom cloud.     

Comparison of friction measurements using the atomic force microscope and the surface forces apparatus: the issue of scale

Results are presented of lateral force measurements using the atomic force microscope (AFM) and the surface forces apparatus (SFA). Two different probes are used in the AFM measurements; a sharp silicon nitride tip (radius R20 nm) and a glass ball (R15 m). The lateral force is measured between the (silicon nitride or glass) probe and a mica surface which has been coated by a thin lubricant film. In the SFA, a thin lubricant film separates two molecularly smooth mica surfaces (R1 cm) which are slid relative to each other. Perfluoropolyether (PFPE) and polydimethylsiloxane (PDMS) were used as the lubricant films. In the SFA where the contact diameter is largest, the PFPE film shows much lower friction than PDMS. As the size of the probe decreases, the difference in the measured friction decreases. For sharp AFM tips, no clear distinction between the tribological properties of the films can be made. Hence, the measured coefficient of friction varies according to the length scale probed, at least for small dimensions.     

Oxidation kinetics of a silicon surface in a plasma of oxygen with inert gases

The plasma oxidation of a silicon surface in an inductive plasma generation reactor were studied using spectroscopic ellipsometry and atomic emission spectroscopy. The effect of inert gases on the formation kinetics of ultrathin SiO₂ films is discussed. The effect of intense oxidation of Si in the plasma formed by nominally pure helium was found. It is suggested that this effect is due to the photostimulated acceleration of the reaction at the silicon-oxide interface by the intrinsic optical emission from the helium plasma.     

FEM analysis of the vibrational motion of oblique piezoelectric microcantilever in the vicinity of a sample surface in liquid

This article examines an oblique Microcantilever (MC) with an extended piezoelectric layer in liquid. The study of hydrodynamic force in MC which has been floated in viscous fluid is considered as paramount importance. To model the Vibrational motion, the Hamilton's principle has been used. For this purpose, the Vibrational motion equation has been modeled by considering the continuous beam based on the Euler–Bernoulli beam theory in liquid. Furthermore, using the Galerkin method and the Newmark algorithm, the differential equations of the MC has been solved. In this modeling, the inter-atomic forces between the MC tip and the sample surface have been considered in addition to the hydrodynamic and squeeze forces. The simulation results illustrate a reduction in the sensitivity of the vibrational motion under the effect of the squeeze force during the angularization of the MC. Moreover, the results illustrate that by reducing the MC distance from the sample surface, the Vibration amplitude decreases due to the increase in the fluid squeeze force. At the end, it has been shown that the time delay in sample surface topography in liquid substantially decreases in comparison with the air.     

Preparation of mica surfaces for enhanced resolution and cleanliness in the surface forces apparatus

We describe a simple technique for preparing arbitrarily thin mica substrates of unparalleled purity for use in the surface forces apparatus (SFA). Relatively thick mica samples (4–8 μm) are prepared in the conventional way, coated with a sputter deposited layer of silver, and attached (silver side down) to cylindrical lenses with a thick coat of thermosetting epoxy. These surfaces are then placed in a glovebox with the cell of the SFA where they are cleaved once again with a piece of tape, and then mounted and sealed in the SFA for immediate use. With this technique, the surfaces are never exposed to laboratory air, they are insensitive to asperities in the glue/silica support, and may be made arbitrarily thin by removing more mica until the desired thickness is achieved. We find that adhesion between two surfaces cleaved in this manner (∼300 mJ/m²) is significantly larger than for mica prepared in the conventional way (∼200 mJ/m²), and consistent with the adhesion measured in direct cleavage experiments. This suggests a cause for discrepancies in the measured adhesion which have appeared in the literature. This revised version was published online in July 2006 with corrections to the Cover Date.     

A novel method for improving surface finish of stereolithography apparatus

Stereolithography apparatus (SLA) is one of the most famous and versatile additive manufacturing techniques and has been widely used in many industrial fields. However, the surface quality of SLA parts is unsatisfactory for the precise parts due to stair stepping caused by the layered manufacturing process. In this study, the stair stepping of SLA parts was relieved by ultrahigh pressure atomizing coating with the polyethylene wax emulsion using a group of optimum coating parameters. The experimental results showed that polyethylene wax film with the thickness less than 0.1 mm bonded to the SLA parts adequately and the surface roughness of the SLA parts can be significantly reduced; the Ra of SLA parts was decreased to less than 2.5 μm. This method can be applied to improve both the outer surface and the inner surface of complex SLA parts with good dimensional accuracy and no damage to SLA parts, implying potential for fabrication of precise components. Expected advantages of this method include economical, operator-friendly, and time-saving for the manufacturers.     

Pulsed wire discharge apparatus for mass production of copper nanopowders

A pulsed wire discharge (PWD) apparatus for the mass production of nanopowders has been developed. The apparatus has a continuous wire feeder, which is operated in synchronization with a discharging circuit. The apparatus is designed for operation at a maximum repetition rate of 1.4 Hz at a stored energy of 160 J. In the present study, Cu nanopowder was synthesized using the PWD apparatus and the performance of the apparatus was examined. Cu nanopowder of 2.0 g quantity was prepared in N(2) gas at 100 kPa for 90 s. The particle size distribution of the Cu nanopowder was analyzed by transmission electron microscopy and the mean surface diameter was determined to be 65 nm. The ratio of the production mass of the powder to input energy was 362 g/kW h.     

Effects of geometrical dimensions and liquid properties on frequency response of resonating microcantilevers in the vicinity of a surface

Frequency response of an atomic force microscopy cantilever immersed in liquid near a surface strongly depends on the hydrodynamic forces specially the squeezed film damping, mechanical properties of the liquid including the dynamic viscosity and the density and the geometrical dimensions of the cantilever. For a slightly inclined magnetically oscillated cantilever with the approximate hydrodynamic forces acting on it, the analytical solution of the equation of motion has already been acquired. In this paper, the effects of geometrical dimensions of the cantilever on the resonance frequency, the motion amplitude and the quality factor are observed and then any increase in the kinematic viscosity of the liquid is studied through the simulation of the oscillatory motion of the cantilever. The acquired amplitude–frequency curves indicate that with an appropriate proportion between the cantilever dimensions, it is possible to optimize the quality factor for extremely small tip-sample separations. Also, if the thickness is increased and the width is reduced with the cross section area being held constant, the resonance will occur at higher frequency and the quality factor will be enhanced. Adding glycerol to water will result in the reduction of resonance frequency of the cantilever near the surface due to the viscous friction and squeezed film damping. Consequently the quality factor is decreased as a result of viscosity increase in the simulations.     

The determination of the thickness of a layer of intensive deformations in the vicinity of the friction surface in metal forming processes

A classic theoretical solution is used to estimate the value of the deformation rate intensity factor during the course of the extrusion of a bar. The experiment was performed on samples of brass. A law of the variation of the thickness of a layer of intensive deformations near the friction surface was determined. The obtained relationship is analyzed and its generalizations are proposed.     

Development of dielectric barrier discharge plasma processing apparatus for mass spectrometry and thin film deposition

Cost effective and a very simple dielectric barrier discharge plasma processing apparatus for thin film deposition and mass spectroscopic analysis of organic gas mixture has been described. The interesting features of the apparatus are the construction of the dielectric electrodes made of aluminum oxide or alumina (Al(2)O(3)) and glass and the generation of high ignition voltage from the spark plug transformer taken from car. Metal capacitor is introduced in between ground and oscilloscope to measure the executing power during the discharge and the average electron density in the plasma region. The organic polymer films have been deposited on Si (100) substrate using several organic gas compositions. The experimental setup provides a unique drainage system from the reaction chamber controlled by a membrane pump to suck out and remove the poisonous gases or residuals (cyanogens, H-CN, CH(x)NH(2), etc.) which have been produced during the discharge of CH(4)N(2) mixture.     

萃取浓缩火焰原子吸收分光光度法与石墨炉原子吸收分光光度法测定地表水中总铜的对比研究

作者分别采用萃取浓缩火焰原子吸收分光光度法(浓缩20倍)和石墨炉原子吸收分光光度法测定标准样品和地表水中的总铜,并进行了对比分析。结果表明,两种方法都具有较高的准确度和精密度,无显著性差异。     

Microbeam X-ray lithography apparatus for direct production of deep LIGA structures

A microbeam X-ray lithography apparatus, a new device for the direct production of microstructures in thick layers of X-ray resists, in particular, for the fabrication of X-ray lithography masks, was developed on the basis at the LIGA station of the VEPP-3 storage ring of the Siberian Center of Synchrotron and Terahertz Radiation. A microstructure pattern with given arbitrary topology was produced directly in a SU-8 negative resist layer up to 1 mm thick on a substrate moved in a vector mode using a collimated beam of synchrotron radiation with a special software. The design of the device and its technological capabilities and limitations are described. Examples of the fabricated microstructures with a high aspect ratio and X-ray lithography masks are presented.     

High-temperature and high-pressure pulsed synthesis apparatus for supercritical production of nanoparticles

In materials science continuous flow supercritical fluid reactors are widely used for highly controlled synthesis of nanoparticles. The major limitation of continuous flow reactors is that the inherent distribution of residence times leads to broadening of the corresponding size distribution of the nanoparticles, and in addition it is not possible to carry out synthesis with very short or very long reaction times. Here, we report a new synthesis concept that we call pulsed synthesis, which removes the limitations of flow synthesis at the expense of a more complex reactor design and extensive computer control. Another limitation of flow synthesis is that it is largely a black box, where limited direct information is available of the specific chemical reactions taking place, the particle nucleation, the particle growth, etc. Such information is commonly obtained from in situ synchrotron and neutron scattering studies, but transfer of information from in situ studies with static reactors to laboratory flow reactor conditions is highly non-trivial. The new pulse reactor provides superior heating rates, arbitrary residence times with narrow distribution limited only by the pulse duration, and the ability of using the same reactor both for nanoparticle production and in situ synchrotron studies; thus eliminating the need for transfer of in situ information to laboratory reactor designs.     

A ground-based radio frequency inductively coupled plasma apparatus for atomic oxygen simulation in low Earth orbit

A radio frequency (rf) inductively coupled plasma apparatus has been developed to simulate the atomic oxygen environment encountered in low Earth orbit (LEO). Basing on the novel design, the apparatus can achieve stable, long lasting operation, pure and high density oxygen plasma beam. Furthermore, the effective atomic oxygen flux can be regulated. The equivalent effective atomic oxygen flux may reach (2.289-2.984) x 10(16) at.cm(2) s at an oxygen pressure of 1.5 Pa and rf power of 400 W. The equivalent atomic oxygen flux is about 100 times than that in the LEO environment. The mass loss measured from the polyimide sample changes linearly with the exposure time, while the density of the eroded holes becomes smaller. The erosion mechanism of the polymeric materials by atomic oxygen is complex and involves initial reactions at the gas-surface interface as well as steady-state material removal.