Rough Vacuum Research Articles

Flexible WO3 based electrochromic displays using proton conducting solid electrolytes

AbstractAll solid‐state flexible electrochromic displays were fabricated based on WO3 films deposited below 50 °C by heating a hot wire in a rough vacuum of the order of 1 Torr. Indium Tin Oxide (ITO) covered polyethylene tetraphthalate (PET) substrates and gel‐like organic electrolytes were used. These proton conductive electrolytes were based on poly(methyl methacrylate) (PMMA) into which a strong Brönsted phosphododecatungstic acid (H3PW12O40‐POM) was added at various concentrations. Transmittance measurements were recorded and it was found that all displays exhibited an intense, reversible electrochromic effect. The coloring voltage was found to depend strongly on the content in solids of the electrolyte, the POM's concentration and the basicity of the polymeric matrix. For devices polarized by voltage pulses it was found that the response time was of the order of 500 ms; coloration and bleaching times were comparable. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Toluene removal from nonionic surfactant coacervate phase solutions by vacuum stripping

Cloud point extraction (CPE) has been demonstrated to remove volatile aromatic pollutants from wastewater by using a nonionic surfactant as a separating agent. To make this process economically feasible, the surfactant in the concentrated or coacervate phase containing most of the original pollutant must be recycled and reused. This work proposes a vacuum stripping process to strip the volatile pollutant from the coacervate, leaving the concentrated surfactant solution to be recycled to the CPE process. An acrylic column was packed with glass Raschig rings and operated under rough vacuum in co-current mode to remove toluene from the coacervate phase containing the t-octylphenolpolyethoxylate (OP(EO 7)) nonionic surfactant. Co-current operation is necessary to avoid excessive foaming. In this study, although the apparent Henry's law constant of toluene was drastically reduced due to toluene solubilization in surfactant micelles, up to 90% of toluene was removed from 300 mM OP(EO) 7 surfactant solution using a 30.5-cm long column. The packed column can be operated without flooding and plugging, despite the viscous nature of the coacervate. The toluene removal increases with decreasing liquid loading rate, and column pressure, but with increasing number of distributor holes. The overall liquid phase volumetric mass transfer coefficient is reported for this system.

Determination of an optimal pressure under field emission from diamondlike films

A model accounting for anomalously high field emission of electrons from diamondlike films in a rough vacuum is suggested. This effect is shown to be associated with a positive ion charge forming on the film. The ions arise because of residual gas ionization in the electrode gap. The pressure maximizing the emission current is determined.

Effect of ion beam irradiation on the structure of ZnO films deposited by a dc arc plasmatron

The deposition of polycrystalline ZnO film on a cold substrate was performed by using a plasmatron in rough vacuum condition. Low energy oxygen ion beam generated by a cold cathode ion source was introduced during the deposition process. The change of film property on the ion beam energy was checked. It is shown that irradiation by 200 eV ions improves crystalline structure of the film. Increasing of ion beam energy up to 400 eV leads to the degradation of a crystalline structure and decreases the deposition rate.

Evacuated aerogel glazings

This paper describes the main characteristics of monolithic silica aerogel and its application in evacuated superinsulating aerogel glazing including the evacuation and assembling process. Furthermore, the energetic benefit of aerogel glazing is quantified. In evacuated aerogel glazing the space between the glass panes is filled with monolithic silica aerogel evacuated to a rough vacuum of approximately 1–10 hPa. The aerogel glazing does not depend on use of low emissive coatings that have the drawback of absorbing a relatively large part of the solar radiation that otherwise could reduce the space heating demand in residential buildings. The U-value of the glazing can be designed to meet the required value by increasing the monolithic silica aerogel thickness without the need for additional layers of glass. An aerogel glazing with 20 mm glass distance can reach a U-value below 0.5 W/(m 2 K) combined with a solar energy transmittance above 0.75.

Photoluminescence of amorphous niobium oxide films synthesized by solid-state reaction

Niobium oxide amorphous films were deposited on silicon substrates at a temperature range of 300–400 °C by heating a pure niobium foil in a rough vacuum. The films were amorphous in structure and with morphology of vertically aligned nano-columns. This feature resulted in interesting photoluminescence (PL) property in the visible light range. The intensity of the photoluminescence spectrum of the as-deposited amorphous film is small. However, the PL intensity of the same sample after annealing below 500 °C increases greatly and consists of two peaks centered at ~ 630 nm (1.97 eV) and ~ 715 nm (1.74 eV). The mechanism for the PL behavior of the amorphous niobium oxide films was also investigated and discussed.

Spectral Analysis of Pulsed Volume Breakdown in $ \hbox{SF}_{6}$ at High Pressures

The Z-machine, which is located at Sandia National Laboratories, is currently undergoing refurbishment to increase the output drive current. Due to increased switching voltage requirements, some switch failure modes have been identified with the laser-triggered gas switch design, including envelope surface flashover. In order to improve the performance and lifetime of these switches, a basic understanding of the underlying physics of the failure mechanisms is required. A small-scale experimental setup has been constructed to approximate conditions within the switch. The possible impact of the SF6 volume spark between the switch electrodes on the envelope surface flashover is investigated. Measured optical spectra of the SF6 volume spark over a wide pressure range, from rough vacuum to 40 psig overpressure, are analyzed regarding their potential to contribute to switch failure.

Synthesis and optical properties of V2O5 nanorods

A two-step method was proposed in synthesizing V2O5 nanorods on planar substrates, i.e., depositing a V2O3 thin film at approximately 220 degrees C (by heating a pure sheet of vanadium in a rough vacuum) and then heating it in air at approximately 400 degrees C. The V2O5 nanorods produced by this technique are single crystalline and could emit intense visible light at room temperature, possibly due to some defects such as oxygen vacancies which got involved during growth. This study provides a simple and low-substrate-temperature route in fabricating V2O5 nanorods on planar substrates, which might be also applicable to other metal oxides.

Cover Picture: Background coverpicture: Refining process of aluminium in a vertical zone meltining furnace. Inlet: Casting of a special steel melt in a vaccum induction furnace under rough vacuum beyond a heated font in a watercooled copper ingot (Adv. Eng. Mater. 4/2007)

Cover Picture: Background coverpicture: Refining process of aluminium in a vertical zone meltining furnace. Inlet: Casting of a special steel melt in a vaccum induction furnace under rough vacuum beyond a heated font in a watercooled copper ingot (Adv. Eng. Mater. 4/2007)

Intense photoluminescence from amorphous tantalum oxide films

Tantalum oxide films were deposited on silicon substrates at a temperature of ∼450°C by heating a pure tantalum foil in a rough vacuum. The films were amorphous in structure and consisted of fully oxidized Ta2O5 and (TaOx, x<2.5) suboxides. This feature resulted in strong visible light emission from the films further oxidized in the air at temperatures of 200–300°C. The mechanism for this photoluminescence behavior of the amorphous tantalum oxide films was also investigated and discussed. This study suggests that wide-band-gap materials could act as effective visible light emitters and provides a simple route to synthesize such materials.

Free-space optical link by microelectromechanical system array and corner cube reflector

We show here a laboratory demonstration of a free-space optical retrocommunication link using a laser at a wavelength of 1.064 μm. The link consists of a transmissive mechanically active antireflection switch array and a corner cube reflector. This link is 3 m long and the beam diameter at the chip is 1.5 mm. A 40% modulation has been achieved at 30-V peak-to-peak bias for a data rate of 2.5 kb/s in atmosphere. We have previously shown that the small etchant hole in the membrane causes a slower data rate, which can be fixed by operating the device in a rough vacuum.

New roughing pump: Fast Evacuation thanks to Diaphragm Stabilization System

Diaphragm pumps are used in turbomolecular pumps to generate a rough vacuum. They are characterized by high suction speed, which however deteriorates when the working pressure decreases. This is caused by the difference between the working pressure of the pump and the ambient pressure. The larger the pressure difference, the more the elastic diaphragm bulges, lowering the effective input volume of the pump. This problem is alleviated by a newly developed diaphragm stabilization system. Diaphragm roughing pumps equipped with this system pump down faster than pumps without the system. Due to the enhanced suction speed, they also ensure greater process reliability. The first application of the diaphragm stabilization system (patent applied for) is in a newly developed diaphragm roughing pump. This pump is driven by a compact, brushless DC motor with very high efficiency. The pump is available in 24 volt DC and 90- to 264 volt, 50/60 Hz AC versions. OEM and portable versions are available.

A new total reflection X-ray fluorescence vacuum chamber with sample changer analysis using a silicon drift detector for chemical analysis

There are several TXRF spectrometers commercially available for chemical analysis as well as for wafer surface analysis, but there is up to now no spectrometer for chemical analysis available that allows to measure samples under vacuum conditions. Simply a rough vacuum of 10 −2 mbar for the sample environment reduces the background due to scattering from air, thus to improve the detection limits. The absorption of low energy fluorescence radiation from low Z elements is reduced and therefore extends the elemental range to be measured down to Na. Finally evacuation of the chamber removes the Ar K-lines from the spectrum. The new vacuum chamber for TXRF named WOBISTRAX is equipped with a 12-position sample changer, a 10-mm 2 silicon drift detector (SDD) with an 8-μm Be entrance window and electrical cooling by Peltier effect, so no LN 2 is required. The chamber was designed to be attached to a diffraction tube housing. WOBISTRAX can be operated with a 3 kW long fine focus Mo-X-ray tube and uses a Mo/Si multilayer for monochromatization. The modified software is performing the motion control between sample changer and MCA features. The performance is expressed in terms of detection limits which are 700 fg Rb for Mo Kα excitation with 50 kV, 40 mA excitation conditions, 1000 s livetime. Using a Cr-X-ray tube for excitation of Al the achieved detection limits are 52 pg. So it could be shown that with the same measuring chamber and using an SDD with 8 μm Be window and a Cr-tube for excitation, low Z elements can be also measured with good detection limits.

Electric strength of the accelerating gap of a plasma electron source at rough vacuum

Conditions for the electric breakdown of the accelerating gap of a plasma electron source are determined. It is shown that, depending on the gas pressure and the size of openings in the emission electrode, two types of breakdown can occur. One of them is due to the ignition of a low-voltage discharge between the electrodes of the accelerating system, and the other one is caused by switching of the main discharge from the anode to the accelerating electrode.

A far-infrared beamline for ultrahigh vacuum surface vibrational spectroscopy at Aladdin

A far-infrared beamline has been implemented on port 031 of the Aladdin Storage Ring. Port 031 has been designed to capture the edge radiation produced by the fringe field of a bending magnet rather than normal bending magnet radiation. Calculations indicate that in cases where the aperture is limited edge radiation provides higher flux than bending magnets, particularly at the longer wavelengths. The far-infrared (IR) beamline shares this port with a mid-IR microscope beamline and uses the same optics to collect and collimate the light. To install the far-IR beamline, a special mirror was designed to deflect light to the purged bench and microscopes or to move out of the light path and allow the light to continue to the far-IR beamline. The vacuum bench employs a Thermo Nicolet interferometer with a solid substrate beamsplitter modified for use under rough vacuum. The light from the interferometer is focused through CsI windows on a sample in an ultrahigh vacuum chamber. The specular reflected light from the sample is collected by an elliptical mirror and focused onto a bolometer detector. The details of the beamline will be discussed as well as the first experimental results.

Device for calibration of low pressure gauges development

Vacuum system set-up is presented and used for calibration of pressure gauges in the region of rough vacuum, from 103 mbar to 10-1 mbar, with dry air. The capacitance manometer is used for the calibration of piezoresistant manometer, oil, mercury and mercury micrometers U manometers. The applicability of the experimental set-up and obtained results for the low pressure gauges calibration in the medium and high vacuum region is approved. It was shown how calibration of some cheaper pressure gauges might be performed and reliable measurements of the pressure may be made in the region that is of interest for atomic and molecular collision physics and low-pressure gas discharges. It was also shown that mentioned calibration procedure could be used for calibration of different U manometer types in order to renormalize older atomic and molecular collision data.

The influence of vacuum conditions on the microwave generation in a vircator

The effect of residual gases on the lifetime of a virtual cathode (VC) was studied. Dependence of the output pulse energy of a high-power vircator on the vacuum conditions was studied. It is demonstrated that a rough vacuum of 5×10−4 Torr achieved with a mechanical pump is sufficient for a vircator operation without significant loss of the output radiation energy. The experimental data agree with a model of the mechanism of VC degradation as a result of the gas ionization.

Contact discharges as a source of sub-nanosecond high voltagepulses

This paper describes a novel method for generating electricaltransients. A small charged metal sphere coming into contact with the centreconductor of a coaxial transmission line is used to produce pulses with arisetime below 60 ps and amplitude of 500 V or more. The phenomenon isinvestigated experimentally to determine whether the gaseous medium in whichthe discharge takes place affects the pulse shape. Measurements in sulphurhexafluoride, argon and rough vacuum indicate that the breakdown mechanism isnot a gas discharge, but the gas does affect the amplitude range, shape andvariability of the current pulses. Results are interpreted in the light ofprevious investigations into arcs between electrodes separated by gaps of lessthan 100 µm, in which field emission of electrons from the cathode wasrecognized as the principal source of charge carriers. Potential applicationsfor the contact discharge pulse generator are proposed and aspects of itsoperation that could be refined to reduce pulse shape variability are identified.

The reactivity of a Fe–Ti–O mixed oxide under different atmospheres: study of the interaction with simple alcohol molecules

In this paper, the interaction between simple alcohols (methanol to 1-butanol) and a Fe–Ti mixed oxide was investigated. The reactivity of the mixed system was studied both at atmospheric pressure and in vacuum conditions and compared with that of the pure oxides (TiO 2 and Fe 2O 3). To understand the influence of the oxygen presence in the reaction mixture, the reactivity was investigated both in inert gas as well as in oxygen atmosphere. X-ray photoelectron spectroscopy (XPS) and quadrupole mass spectrometry (QMS) have been used for the experiment in high vacuum (HV), while Fourier transform infrared spectroscopy (FTIR) and QMS have been used for the experiment in rough vacuum and under atmospheric pressure conditions. The characterisation of the sample by means of XPS, X-ray diffraction and IR spectroscopy preceded the reactivity study. When compared with Fe 2O 3, the Fe–Ti–O mixed oxide seems to be less reactive with respect to the alcohols; the interaction between alcohol and surface is mainly molecular, as in the case of TiO 2. Moreover, the oxidising power of the mixed oxide is lower than that of Fe 2O 3 (only traces of carbonic compounds are evident).

Laser generation of acoustic waves in the ablative regime

A practical model of acoustic wave generation by a pulsed laser source in the ablative regime is presented. The pressure exerted on the surface during Q-switched laser heating is calculated through a finite difference solution of the vaporization problem. The epicentral displacement is found through summation of the displacement field induced by the vaporization process with that caused by thermoelastic expansion. The model is restricted to the weakly ablative regime in the absence of a backing gas. The results are compared to the epicentral displacements generated in aluminum samples under rough vacuum conditions at generating wavelengths of 532 and 1064 nm. The waveforms compare well over a limited irradiance range. The effects of rough vacuum conditions on the generated acoustic signals are also examined and compared to signals generated in the presence of a backing gas. The divergence in the shape and amplitude of these signals observed under highly ablative conditions is discussed.