Showing papers in "Journal of Physics D in 2004"

Recent progress in nanoimprint technology and its applications

Abstract: Nanoimprint is an emerging lithographic technology that promises high-throughput patterning of nanostructures. Based on the mechanical embossing principle, nanoimprint technique can achieve pattern resolutions beyond the limitations set by the light diffractions or beam scatterings in other conventional techniques. This article reviews the basic principles of nanoimprint technology and some of the recent progress in this field. It also explores a few alternative approaches that are related to nanoimprint as well as additive approaches for patterning polymer structures. Nanoimprint technology can not only create resist patterns as in lithography but can also imprint functional device structures in polymers. This property is exploited in several non-traditional microelectronic applications in the areas of photonics and biotechnology.

Understanding plasma spraying

Abstract: This article intends to summarize our actual knowledge in plasma spraying with an emphasis on the points where work is still in progress. It presents successively: the plasma torches with the resulting plasma jets and their interactions with the surrounding environment; the powder injection with the heat, momentum and mass transfers between particles and first plasma jets and then plasma plume; the particles flattening and solidification, forming splats which then layer to form the coating; the latest developments related to the production of plasma sprayed finely structured coatings.

Overview of high performance fibre-optic sensing

Abstract: An overview of fibre-optic interferometry based sensing is given, particularly as it applies to high-performance sensing applications. The operation of a fibre-optic interferometer as a sensor is reviewed. The sensitivity limitations of a fibre-optic sensor are derived, and the system impact of multiplexing many sensors together is explored. A review of the development of the fibre-optic acoustic transducer is presented, as well as system applications and future trends in fibre-optic interferometric sensing.

Ablation of metals by ultrashort laser pulses

Abstract: Ablation of Fe by ultrashort laser pulses with durations 0.1, 1, and 5 ps were investigated experimentally. The laser fluence varied from the ablation threshold up to 100 J cm−2. Above 1 J cm−2, the ablation rate depended on the laser pulse duration, with the shortest pulse producing the highest value. A change in the ablation rate as the laser fluence increased was also observed. These results were analysed using molecular dynamics simulations. We show that the change in the ablation rate is connected to an overheating of the material above the critical point, which results in a steep rise of the pressure developed. Furthermore, due to the electron heat diffusion, the overheated volume increases and involves material located deeper than the skin depth. An increase in the pulse duration results in a decrease in the degree of overheating.

Tin oxide transparent thin-film transistors

Abstract: A SnO2 transparent thin-film transistor (TTFT) is demonstrated. The SnO2 channel layer is deposited by RF magnetron sputtering and then rapid thermal annealed in O2 at 600°C. The TTFT is highly transparent, and enhancement-mode behaviour is achieved by employing a very thin channel layer (10–20 nm). Maximum field-effect mobilities of 0.8 cm2 V−1 s−1 and 2.0 cm2 V−1 s−1 are obtained for enhancement- and depletion-mode devices, respectively. The transparent nature and the large drain current on-to-off ratio of 105 associated with the enhancement-mode behaviour of these devices may prove useful for novel gas-sensor applications.

Tailoring magnetism by light-ion irradiation

Abstract: Owing to their reduced dimensions, the magnetic properties of ultrathin magnetic films and multilayers, e.g. magnetic anisotropies and exchange coupling, often depend strongly on the surface and interface structure. In addition, chemical composition, crystallinity, grain sizes and their distribution govern the magnetic behaviour. All these structural properties can be modified by light-ion irradiation in an energy range of 5–150 keV due to the energy loss of the ions in the solid along their trajectory. Consequently the magnetic properties can be tailored by ion irradiation. Similar effects can also be observed using Ga+ ion irradiation, which is the common ion source in focused ion beam lithography.Examples of ion-induced modifications of magnetic anisotropies and exchange coupling are presented. This review is limited to radiation-induced structural changes giving rise to a modification of magnetic parameters. Ion implantation is discussed only in special cases.Due to the local nature of the interaction, magnetic patterning without affecting the surface topography becomes feasible, which may be of interest in applications. The main patterning technique is homogeneous ion irradiation through masks. Focused ion beam and ion projection lithography are usually only relevant for larger ion masses. The creation of magnetic feature sizes below 50 nm is shown. In contrast to topographic nanostructures the surrounding area of these nanostructures can be left ferromagnetic, leading to new phenomena at their mutual interface.Most of the material systems discussed here are important for technological applications. The main areas are magnetic data storage applications, such as hard magnetic media with a large perpendicular magnetic anisotropy or patterned media with an improved signal to noise ratio and magnetic sensor elements. It will be shown that light-ion irradiation has many advantages in the design of new material properties and in the fabrication technology of actual devices.

Pulsed terahertz tomography

Abstract: Terahertz time-domain spectroscopy (THz-TDS) is a coherent measurement technology. Using THz-TDS, the phase and amplitude of the THz pulse at each frequency can be determined. Like radar, THz-TDS also provides time information that allows us to develop various three-dimensional THz tomographic imaging modalities. The three-dimensional THz tomographic imagings we investigated are: terahertz diffraction tomography (THz DT), terahertz computed tomography (THz CT), THz binary lens tomography and THz digital holography. THz DT uses the THz wave as a probe beam to interact with a target, and then reconstructs the three-dimensional image of the target using the THz waves scattered by the target. THz CT is based on geometrical optics and inspired by x-ray CT. THz binary lens tomography uses the frequency dependent focal length property of binary lenses to obtain tomographic images of an object. THz three-dimensional holography combines radar and conventional holography technology. By separating the multiple scattered THz waves of different scattering orders, we used a digital holography method to reconstruct the sparsely distributed scattering centres. Three-dimensional THz imaging has potential in such applications as non-destructive inspection. The interaction between a coherent THz pulse and an object provides rich information about the object under study; therefore, three-dimensional THz imaging is a very useful tool to inspect or characterize dielectric and semiconductor objects. For example, three-dimensional THz imaging can be used to detect and identify the defects inside a space shuttle insulation tile.

Independent control of ion current and ion impact energy onto electrodes in dual frequency plasma devices

Abstract: Dual frequency capacitive discharges are designed to offer independent control of the flux and energy of ions impacting on an object immersed in a plasma. This is desirable in applications such as the processing of silicon wafers for microelectronics manufacturing. In such discharges, a low frequency component couples predominantly to the ions, while a high frequency component couples predominantly to electrons. Thus, the low frequency component controls the ion energy, while the high frequency component controls the plasma density. Clearly, this desired behaviour is not achieved for arbitrary configurations of the discharge, and in general one expects some unwanted coupling of ion flux and energy. In this paper we use computer simulations with the particle-in-cell method to show that the most important governing parameter is the ratio of the driving frequencies. If the ratio of the high and low frequencies is great enough, essentially independent control of the ion energy and flux is possible by manipulation of the high and low frequency power sources. Other operating parameters, such as pressure, discharge geometry, and absolute power, are of much less significance.

Plasma electron temperatures and electron energy distributions measured by trace rare gases optical emission spectroscopy

Abstract: This article reviews a spectroscopic method for extracting plasma electron temperatures and electron energy distributions: trace rare gases optical emission spectroscopy. Specifically, traces of Ne, Ar, Kr, and Xe are added to the plasma and the intensities of emissions from the Paschen 2p levels are recorded. Intensities are also computed from a model that includes direct excitation from the ground state, as well as two-step excitation through the 3P2, and 3P0 metastable levels. A Maxwellian electron energy distribution function (EEDF), described by an electron temperature (Te), is assumed, and Te is extracted from the best match between the observed and calculated relative emission intensities. By choosing emission from specific sets of levels, the range of electron energies effective in exciting emission can be selected and various portions of the EEDF can be investigated. Accurate measurement of Te depends critically on accurate cross sections for electron impact excitation, and hence a large portion of this article is devoted to a critical review of this subject. Improving on previous treatments, the model for computing emission intensities and electron temperatures includes a complete analysis of the complex excitation and de-excitation of the metastable levels. Previous measurements of Te and EEDFs in chlorine and oxygen inductively coupled plasmas are re-evaluated with the current model. In general, the current version of the model yields similar results; specific differences are discussed.

Description of bipolar charge transport in polyethylene using a fluid model with a constant mobility: model prediction

Abstract: We present a conduction model aimed at describing bipolar transport and space charge phenomena in low density polyethylene under dc stress. In the first part we recall the basic requirements for the description of charge transport and charge storage in disordered media with emphasis on the case of polyethylene. A quick review of available conduction models is presented and our approach is compared with these models. Then, the bases of the model are described and related assumptions are discussed. Finally, results on external current, trapped and free space charge distributions, field distribution and recombination rate are presented and discussed, considering a constant dc voltage, a step-increase of the voltage, and a polarization–depolarization protocol for the applied voltage. It is shown that the model is able to describe the general features reported for external current, electroluminescence and charge distribution in polyethylene.

Vertical-external-cavity semiconductor lasers

Abstract: Surface-emitting semiconductor lasers can make use of external cavities and optical pumping techniques to achieve a combination of high continuous-wave output power and near-diffraction-limited beam quality that is not matched by any other type of semiconductor source. The ready access to the laser mode that the external cavity provides has been exploited for applications such as intra-cavity frequency doubling and passive mode-locking. The purpose of this Topical Review is to outline the operating principles of these versatile lasers and summarize the capabilities of devices that have been demonstrated so far. Particular attention is paid to the generation of near-transform-limited sub-picosecond pulses in passively mode-locked surface-emitting lasers, which are potentially of interest as compact sources of ultrashort pulses at high average power that can be operated readily at repetition rates of many gigahertz.

A numerical modelling of an electric arc and its interaction with the anode: Part I. The two-dimensional model

Abstract: A two-dimensional numerical model of the interaction between an electric arc and a solid anode of different types is presented in this study. The CFD commercial code FLUENT is used to model the plasma flow and the solid anode domain. Quantities such as the velocities or the temperature are presented, and the energy transfer components between the plasma and the anode are quantified. Comparisons of the calculated results with the available experimental data in the literature show that the model predictions are in good agreement. In the case of argon gas and a copper anode, with the distance between the two electrodes 10 mm, the maximum temperature near the cathode tip is 21 000 K for a current of I = 200 A. For the same configuration, the maximum of the current density in the copper electrode is found to be −2.5 × 106 A m−2. The electrical flux is the main component of the transferred flux on the anode. Once validated, our model is applied to other theoretical and experimental configurations and allows us to study several parameters when attention is focused on the influence of metal vapour from the vaporization of the anode or the current-carrying path in the electrode on the arc behaviour. According to the current-carrying path in the anode, the current density distribution is affected in the material and its surface.

Modelling the geometry of a moving laser melt pool and deposition track via energy and mass balances

Abstract: The additive manufacturing technique of laser direct metal deposition allows multiple tracks of full density metallic material to be built to form complex parts for rapid tooling and manufacture. Practical results and theoretical models have shown that the geometries of the tracks are governed by multiple factors. Original work with single layer cladding identified three basic clad profiles but, so far, models of multiple layer, powder-feed deposition have been based on only two of them. At higher powder mass flow rates, experimental results have shown that a layer's width can become greater than the melt pool width at the substrate surface, but previous analytical models have not been able to accommodate this. In this paper, a model based on this third profile is established and experimentally verified. The model concentrates on mathematical analysis of the melt pool and establishes mass and energy balances based on one-dimensional heat conduction to the substrate. Deposition track limits are considered as arcs of circles rather than of ellipses, as used in most established models, reflecting the dominance of surface tension forces in the melt pool, and expressions for elongation of the melt pool with increasing traverse speed are incorporated. Trends in layer width and height with major process parameters are captured and predicted layer dimensions correspond well to the experimental values.

Application of excitation cross sections to optical plasma diagnostics

Abstract: Many optical-based plasma diagnostic techniques require electron-impact excitation cross sections. In recent years, a considerable number of new results have become available for excitation of rare-gas atoms from both the ground state and metastable states. Using relatively simple techniques these cross sections can be combined with plasma emission measurements to extract many useful plasma parameters such as the electron temperature. Many of the limitations of simple plasma emission models such as the corona model can be overcome by using cross section measurements to select what particular emission lines to use in the analysis.

Influence of interband electronic transitions on the optical absorption in metallic nanoparticles

Abstract: Electronic interband transitions influence the surface plasmon resonance in metallic nanoparticles significantly. We derive expressions for the resonance frequency, the bandwidth and the maximum of the light absorption cross section of noble metal nanoparticles, taking into account the interband transitions in the dielectric function. We propose a simple method for determining the width of the plasmon resonance based on an analysis of the dielectric permittivity of the constituent metal.

A unified model of transport phenomena in gas metal arc welding including electrode, arc plasma and molten pool

Abstract: This paper presents a theoretical model for describing globular transfer in gas metal arc welding. The heat and mass transfer in the electrode, arc plasma and molten pool are considered in one unified model. Using the volume of fluid method, the transport phenomena are dynamically studied in the following processes: droplet formation and detachment, droplet flight in arc plasma, impingement of droplets on the molten pool and solidification after the arc extinguishes. The simulation of heat and mass transfer in the arc plasma considers the developing surface profile of the electrode and molten pool and also the effect of the flying droplet inside the arc plasma. Furthermore, the heat inputs to the electrode and the molten pool result from the simulation of the arc plasma. In addition, a He–Ne laser in conjunction with the shadow-graphing technique is used to observe the metal-transfer process. The theoretical predictions and experimental results are shown to be in good agreement.

Magnetic semiconductors and half-metals

Abstract: Variants of fully spin-polarized electronic structures that may be found in ferromagnetic metals, semimetals and semiconductors are reviewed, with examples. A simple classification scheme is presented, with six broad categories. The attribution of a material to a particular category is based on chemical systematics, or density functional theory calculations. A simplified notation for the electronic structure of these ferromagnets is proposed.(Some figures in this article are in colour only in the electronic version)

Magnetic-dielectric properties of NiFe2O4/PZT particulate composites

Abstract: Particulate composites of lead–zirconate–titanate (PZT) and NiFe2O4 were prepared using conventional ceramic processing. The measured magnetoelectric (ME) response demonstrated strong dependence on the volume fraction of NiFe2O4, the magnetic field, and the angle between the magnetic field and polarization in the ceramics. A large ME voltage coefficient of about 80 mV cm−1 Oe−1 was observed for 0.32NiFe2O4/0.68PZT composite ceramic. In particular, at low magnetic fields, the ceramics were found to have a large ME response, linearly varying with both dc and ac magnetic fields.

Preparation and characterization of electrochemically deposited carbon nitride films on silicon substrate

Abstract: Carbon nitride films (CNx films) were deposited on Si(100) substrates by the electrolysis of methanol–urea solution at high voltage, atmospheric pressure, and low temperature. The microstructure and morphology of the resulting CNx films were analysed by means of Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectrometry (FTIR), x-ray diffraction (XRD), and atomic force microscopy. The tribological properties of the CNx films were examined on an UMT-2MT friction and wear test rig. The Raman spectrum showed two characteristic bands: a graphite G band and a disordered D band of carbon, which suggested the presence of an amorphous carbon matrix. XPS and FTIR measurements suggested the existence of both single and double carbon-nitride bonds in the film and the hydrogenation of the carbon nitride phase. The XRD spectrum showed various peaks of different d values, which could confirm the existence of the polycrystalline carbon nitride phase. The hydrogenated CNx films were compact and uniform, with a root mean square roughness of about 18 nm. The films showed excellent friction-reduction and wear-resistance, with the friction coefficient in the stable phase being about 0.08. In addition, the growth mechanism of the CNx films in liquid phase electro-deposition was discussed as well. It was assumed that the molecules of CH3OH and CO(NH2)2 were polarized under high electric field, and the CNx film was formed on the substrate through the reaction of the –CH3 and –NH2 groups on the cathode.

Preparation and characterization of copper oxide thin films deposited by filtered cathodic vacuum arc

Abstract: Copper oxide thin films deposited on Si (100) by a filtered cathodic vacuum arc with and without substrate bias have been studied by atomic force microscopy, x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The results show that the substrate bias significantly affects the surface morphology, crystalline phases and texture. In the film deposited without bias, two phases—cupric oxide (CuO) and cuprous oxide (Cu2O)—coexist as cross-evidenced by XRD, XPS and Raman analyses, whereas CuO is dominant concurrent with CuO (020) texture in the film deposited with bias. The film deposited with bias exhibits a more uniform and clearer surface morphology although both kinds of films are very smooth. Some explanations are given as well.

Effects of current limitation through the dielectric in atmospheric pressure glows in helium

Abstract: The influence of the dielectric barrier on the discharge regime of a uniform atmospheric pressure glow discharge is studied through fast, time-resolved imaging of the discharge optical emission and by a one-dimensional fluid model. The experiments show that the discharge regime can be adjusted over a wide range from a glow-like regime with a pronounced Faraday dark space and positive column to a Townsend-like discharge regime in which those features are absent. The determining factor for the discharge regime is the current limitation through the dielectric. Results of the one-dimensional fluid model confirm this observation. The fluid model also indicates that metastable helium atoms generated during a discharge pulse contribute significantly to the pre-ionization of the gas before the next breakdown through Penning ionization of nitrogen impurities.

Advances in low-voltage circuit breaker modelling

Abstract: This paper is devoted to the study of electric arc behaviour under the influence of an external magnetic field. This situation is close to that occurring in a low-voltage circuit breaker where an arc, after ignition, is submitted to the magnetic field of the circuit. After a discussion of the literature, we present our contribution. Two different methods are compared to take the magnetic effects into account. Arc displacement in the geometry studied is dealt within a specific development presented in this paper. We show the influence of the nature of the gas on the arc velocity and on possible re-strike using air and an air–PA6 mixture as the plasma gas.

An electronically tunable ultrafast laser source applied to fluorescence imaging and fluorescence lifetime imaging microscopy

Abstract: Fluorescence imaging is used widely in microscopy and macroscopic imaging applications for fields ranging from biomedicine to materials science. A critical component for any fluorescence imaging system is the excitation source. Traditionally, wide-field systems use filtered thermal or arc-generated white light sources, while point scanning confocal microscope systems require spatially coherent (point-like) laser sources. Unfortunately, the limited range of visible wavelengths available from conventional laser sources constrains the design and usefulness of fluorescent probes in confocal microscopy. A 'hands-off' laser-like source, electronically tunable across the visible spectrum, would be invaluable for fluorescence imaging and provide new opportunities, e.g. automated excitation fingerprinting and in situ measurement of excitation cross-sections. Yet more information can be obtained using fluorescence lifetime imaging (FLIM), which requires that the light source be pulsed or rapidly modulated. We show how a white light continuum, generated by injecting femtosecond optical radiation into a micro-structured optical fibre, coupled with a simple prism-based tunable filter arrangement, can fulfil all these roles as a continuously electronically tunable (435-1150 nm) visible ultrafast light source in confocal, wide-field and FLIM systems.

Modelling analysis of surface stress on a rectangular cantilever beam

Abstract: Three models of surface stress on a rectangular cantilever beam are presented. The surface stress is modelled as a corresponding concentrated moment at the beam free end, a corresponding concentrated moment plus a corresponding concentrated axial load at the beam free end, and a corresponding uniformly distributed axial stress plus bending moment per unit length along the beam span, respectively. The results of the three models are compared under three different loading scenarios. We also present an analysis of the error source, when using Stoney’s formula to predict the surface stress, by comparing the kinematic and loading assumptions of the three models. The surface stress effects on structure deflection are usually modelled as bending moments applied at structure free edge(s)/end(s). Modelling the surface stress effect along the beam neutral axis is presented and compared with modelling its effect at free edge(s)/end(s). The stiffening effect of tensile surface stress is also studied.

The metrics of surface adsorbed small molecules on the Young's fringe dual-slab waveguide interferometer

Abstract: A method for analysing thin films using a dual-waveguide interferometric technique is described. Alternate dual polarization addressing of the interferometer sensor using a ferroelectric liquid crystal polarization switch allowed the opto-geometrical properties (density and thickness) of adsorbed layers at a solid?liquid interface to be determined. Differences in the waveguide mode dispersion between the transverse electric and transverse magnetic modes allowed unique combinations of layer thickness and refractive index to be determined at all stages of the layer formation process. The technique has been verified by comparing the analysis of the surface adsorption of surfactants with data obtained using neutron scattering techniques, observing their behaviour on trimethylsilane coated silicon oxynitride surfaces. The data obtained were found to be in excellent agreement with analogous neutron scattering experiments and the precision of the measurements taken to be of the order of 40?pm with respect to adsorbed layer thicknesses. The study was extended to a series of surfactants whose layer morphology could be correlated with their hydrophilicity/lipophilicity balance. Those in the series with longer alkyl chains were observed to form thinner, denser layers at the hydrophobic solid/aqueous liquid interface and the degree of order attained at sub-critical micelle concentrations to be correlated with molecular fluidity.The technique is expected to find utility with those interested in thin film analysis. An important and growing area of application is within the life sciences, especially in the field of protein structure and function.

Extreme ultraviolet light sources for use in semiconductor lithography—state of the art and future development

Abstract: This paper gives an overview of the development status and plans of extreme ultraviolet (EUV) light sources at XTREME technologies, a joint venture of Lambda Physik AG, Gottingen and JENOPTIK LOS GmbH, Jena, Germany. Results for gas discharge-produced plasma (GDPP) and laser-produced plasma (LPP), the two major technologies in EUV sources, are presented.The GDPP EUV sources use the Z-pinch principle with efficient sliding-discharge pre-ionization. First prototypes of commercial gas discharge sources with an EUV power of 35 W in 2π sr have already been integrated into EUV microsteppers. These sources are equipped with a debris-filter which supports an optics lifetime exceeding 100 million pulses at 1 kHz repetition rate. The same lifetime was achieved for the components of the discharge system itself.The progress in the development of high-power discharge sources based on xenon resulted in an EUV power of 200 W into a 2π sr solid angle, in continuous operation, at 4.5 kHz repetition rate, by implementation of porous-metal cooling technology. The available intermediate focus (IF) power is 22 W taking into account experimentally verified losses in a 1.8 sr source collector module. The usable IF power depends on the etendue of the optical system of the EUV scanner. For the current size of the EUV emitting plasma the etendue acceptance factor may be below 0.5. The currently usable IF power with 1.8 sr collector mirror may therefore be about 10 W.Z-pinch discharge sources with Sn as the emitter have been developed as a more efficient alternative to xenon fuelled sources. Tin sources showed a conversion efficiency (CE) that was double that of xenon. EUV power of 400 W in 2π sr has been generated at only 4.5 kHz repetition rate. The available IF power is 44 W. Estimates evaluating the tin source performance reveal the potential for achieving high-volume manufacturing (HVM) power specification by using existing technology.Because of their small plasma size and the rather simple thermal management in the EUV generator the LPP EUV sources are investigated as alternatives to GDPP sources to achieve sufficient power for HVM with EUV lithography. These sources use xenon-jet target systems and high-power pulsed lasers as plasma excitation drivers developed at XTREME technologies. The maximum CE from laser power into EUV in-band power is 1.0% into a solid angle of 2π. Experimentally, 7 W EUV radiation is generated at 13.5 nm in a 2π sr solid angle with 0.7 kW laser power on the target. The small source volume of <0.5 mm diameter will allow large collection angles of 5 sr. The corresponding usable IF power is estimated to be 2.3 W. With the full power of the installed 1.2 kW laser driver 10 W EUV power in 2π sr is expected. LPP sources with tin targets are estimated to achieve nearly 10 W IF power with existing driver laser technology.GDPP and LPP sources still compete for the technology of HVM sources for EUV lithography. Each of these technologies has its challenges. The optimization potential of the etendue of the optical system of EUV scanners will certainly influence any decision for a HVM source technology.

The influence of Al doping on the electrical, optical and structural properties of SnO2 transparent conducting films deposited by the spray pyrolysis technique

Abstract: In this study, the influence of increasing the Al concentration on the electrical, optical and structural properties of spray-pyrolysis-deposited SnO2 films has been investigated. The SnO2 : Al films were deposited at a substrate temperature of 480°C using a hydro-alcoholic solution consisting of tin and aluminium chlorides with various Al-doping levels from 0 to 30 wt% in solution. The [Al]/[Sn] atomic ratios were from 0 to 12.1 in films. The results of x-ray diffraction have shown that the deposited films are polycrystalline without any second phases with preferential orientations along the (110), (211) and (301) planes and an average grain size of 28.7 nm. Also, the Hall effect and resistivity measurements of the films show that for a specific acceptor dopant (Al) concentration (8.0 at% in film), majority carriers convert from electrons to holes and p-conductivity dominates. The optical absorption edge for undoped SnO2 films lies at 4.105 eV, whereas for high acceptor-doped films it shifts towards lower energies (longer wavelengths) in the range of 4.105–3.604 eV.

N2+/N2 ratio and temperature measurements based on the first negative N2+ and second positive N2 overlapped molecular emission spectra

Abstract: The and molecular emission spectra are frequently observed simultaneously in plasmas containing nitrogen. Relative band intensities of these systems are very sensitive to a variation of the ratio and temperature. The spectrum, emitted between 3800 and 4000 A, has been used to measure rotational and vibrational temperatures, and to estimate the ratio when the electron temperature is known, in different plasma sources (Glidarc, ac discharge between tips). The proposed method is based on a point-to-point comparison of an experimentally measured spectrum with the computer-simulated one.

Improvement of piezoelectric activity of cellular polymers using a double-expansion process

Abstract: Expansion of cellular polypropylene films through an increase in gas pressure and subsequent pressure release at elevated temperatures prior to charging is known to enhance the piezoelectric d33-coefficient of the material. By means of a second pressure expansion the piezoelectric activity can be further increased by more than 40% in comparison with samples subjected to only a single expansion. The effectiveness of the double-expansion process must be attributed to the gain in thickness through the second expansion, following the charging and metallization processes. This thickness change causes a decrease in Young's modulus and thus an increase in d33. Typical d33-coefficients of 1400 pC N−1 at 0.01 Hz and about 500 pC N−1 at 25 kHz have been achieved.

Deposition of thin organosilicon polymer films in atmospheric pressure glow discharge

Abstract: The atmospheric pressure glow discharge burning in nitrogen with small admixture of organosilicon compounds such as hexamethyldisilazane or hexamethyldisiloxane was used for the deposition of thin organosilicon polymer films. The properties of the discharge were studied by means of optical emission spectroscopy and electrical measurements. The deposited films were characterized by atomic force microscopy, x-ray photoelectron spectroscopy, infrared transmission measurements, ellipsometry, depth sensing indentation technique and contact angle measurements. The films were polymer-like, transparent in the visible range, with uniform thickness and without pinholes. The film hardness varied from 0.3 to 0.6 GPa depending on deposition conditions, the elastic modulus was in the range 15-28 GPa and the surface free energy was in the range 26-45 mJ m-2. The studied films exhibited good adhesion to the substrate.