Table of contents

Rapid formation of electric field profiles has been observed directly for the first time in nanosecond narrow-gap parallel-plate discharges at near-atmospheric pressure. The plasmas examined here are of hydrogen, and the field measurement is based on coherent Raman scattering (CRS) by hydrogen molecules. Combined with the observation of spatio-temporal light emission profiles by a high speed camera, it has been found that the rapid formation of a high-voltage thin cathode sheath is accompanied by fast propagation of an ionization front from a region near the anode. Unlike well-known parallel-plate discharges at low pressure, the discharge formation process at high pressure is almost entirely driven by electron dynamics as ions and neutral species are nearly immobile during the rapid process.

A newly developed device, a hairpin resonator, is used to generate an atmospheric-pressure microplasma with a 1.8 GHz power supply in argon. The two-dimensional distributions of emission lines in such a microplasma are obtained by a spatially resolved optical system. For the first time, it is found that the distributions of high-energy and low-energy electrons have different patterns. The density distribution of the high-energy electrons (with energy higher than that of argon 2p levels) is obtained from the line intensity, while the density of the low-energy ones (approximately equal to the total electron density) is deduced from the emission line ratios. The difference in distribution between the two groups of electrons is related to the different energy-loss characteristic lengths.

Lateral force microscopy (LFM) is a variation of atomic/scanning force microscopy (AFM/SFM). It relies on the torsional deformation of the AFM cantilever that results from the lateral forces acting between tip and sample surface. LFM allows imaging of heterogeneities in materials, thin films or monolayers at high spatial resolution. Furthermore, LFM is increasingly used to study the frictional properties of nanostructures and nanoparticulates. An impediment for the quantification of lateral forces in AFM, however, is the lack of reliable and established calibration methods. A widespread acceptance of LFM requires quantification coupled with a solid understanding of the sources of uncertainty. This paper reviews the available experimental calibration methods and identifies particularly promising approaches.

Bi₄(Ti₁Fe₂)O_12−δ ceramics were prepared by the conventional solid state reaction method. The sample exhibited ferroelectricity and magnetism simultaneously at room temperature, which was demonstrated by the ferroelectric (2P_r = 4.1 µC cm⁻², 2E_c = 42 kV cm⁻¹ at applied electric field 31 kV cm⁻¹) and ferromagnetic (M_r = 3 × 10⁻³ emu g⁻¹, H_c = 218 Oe) hysteresis loops. Changes of 19.7% and 17.1% in, respectively, remanent polarization and magnetization after poling the sample in magnetic and dc electric for fields 10 min were evidence of magnetoelectric coupling between the electric dipoles and magnetic dipoles at room temperature.

Magnetite (Fe₃O₄) is predicted to be half metallic at room temperature (RT) and it shows the highest Curie temperature among oxides. The use of Fe₃O₄ thin films is therefore promising for spintronic devices such as magnetic tunnel junctions (MTJs) and magnetoresistive sensors. The structural, magnetic and magnetotransport properties of magnetite are reported to be strongly dependent on the growth conditions. We have developed a very simple deposition chamber for growing thin magnetite films via a chemical vapour deposition (CVD) process based on the Fe₃(CO)₁₂ carbonyl precursor. The structural, morphological, and magnetic properties of the as deposited Fe₃O₄ films have been investigated by means of time of flight secondary ion mass spectrometry, grazing incidence x-ray diffraction, x-ray reflectivity, atomic force microscopy, conversion electron Mössbauer spectroscopy and superconducting quantum interference device magnetometry. Magnetotransport measurements show magnetoresistance up to −2.4% at RT at the maximum applied field of 1.1 T. Resistivity measurements in the 100–300 K temperature range reveal that the magnetotransport properties of the Fe₃O₄ films are governed by inter-granular tunnelling of the spin-polarized electrons. The spin polarization is estimated to be around −16%. A possible route for increasing the spin-polarized performances of our magnetite films is proposed. We have also deposited Fe₃O₄/MgO/Co stacks by using a combined CVD and atomic layer-deposition process. The trilayer's hysteresis curve evidences the presence of two distinct switching fields making it promising for magnetite-based MTJ applications.

The results from an experimental measurement of the spark channel radius in a sliding multichannel discharge of opposite polarities in Ne, Ar and Xe are presented and discussed. The experiments were performed at submicrosecond discharge pulse duration (90–190 ns current pulse FWHM) and gas pressures of 30 and 100 kPa, with alumina ceramics as the dielectric substrate. The data showed the optical radius of the negative polarity spark channels to exceed 1.27–1.6 times those of the positive channels, depending on the gas type and its pressure. The earlier theoretical study by U Ebert, W van Saarloos and C Caroly on the propagation of opposite polarity ionization wave fronts was applied to the analysis of experimental results. From the two approaches of theory, only the 'non-localized initial conditions' one, which in addition to the gas impact ionization, drift and diffusion of electrons also takes into account the free initial electrons in the gas ahead of the ionization wave front, is capable of explaining concurrently the experimental observations on positive and negative channel radii, their ratios and the dependence on gas type and pressure. Numerical solutions of the channel expansion equation specified that the expansion speed is governed by both the drift electrons and free electrons generated by a short-range source in a narrow layer around the channel lateral surface. The depth of the latter layer was estimated to be comparable to the expansion wave front depth and, thus, much less than the channel radius.

This work reports results obtained from heat flux measurements performed during the deposition of metallic thin films by low-pressure plasma sputtering. It introduces a sensitive diagnostic, which allows us to perform such measurements directly during the process and to follow in real-time mechanisms involved in the plasma/surface interaction. Although quantitative results are provided and discussed, the main scope of this paper is a qualitative study of the sputter-deposition process via the energy flux transfers. The diagnostic developed for energy flux measurements is presented and the versatility of the experimental apparatus is described. Results on the study of the deposition of Pt (and Fe) thin films demonstrate a good reproducibility of the measurements and the ability to separate the energetic contribution of the main plasma (∼300 mW cm⁻²) from the deposition process contribution (2 to 23 mW cm⁻²). The influence of gas pressure, plasma power and target bias voltage on the energy transferred to the silicon substrate is also studied.

We developed a neutral-beam-enhanced method of chemical vapour deposition (NBECVD) to obtain a lower dielectric constant for the SiOCH interlayer dielectric film while maintaining a reasonable modulus. We achieved a higher deposition rate than that with the precursor of dimethyl-dimethoxy-silane (DMDMOS) we previously reported on by using Ar NBECVD with a precursor of dimethoxy-tetramethyl-disiloxine (DMOTMDS). This is because of the high absorption coefficient of DMOTMDS. Ar NBECVD with DMOTMDS also achieved a much lower dielectric constant than the conventional PECVD film, because this method avoids the precursor dissociation that causes low dielectric film with many linear Si–O structures. We obtained a k value of 1.9 for the super-low-k SiOCH film with an extremely water resistant, and very thermally stable and integration-possible modulus (>4 GPa) by controlling the bias power.

The dimensional analysis technique is used to formulate a correlation between ozone generation rate and various parameters that are important in the design and operation of positive wire-to-plate corona discharges in indoor air. The dimensionless relation is determined by linear regression analysis based on the results from 36 laboratory-scale experiments. The derived equation is validated by experimental data and a numerical model published in the literature. Applications of such derived equation are illustrated through an example selection of the appropriate set of operating conditions in the design/operation of a photocopier to follow the federal regulations of ozone emission. Finally, a new current–voltage characteristic equation is proposed for positive wire-to-plate corona discharges based on the derived dimensionless equation.

Surface dielectric barrier discharges (DBDs) used as plasma actuators can induce significant time-averaged forces in nearby neutral gases. For single-barrier actuators (one electrode insulated) these forces are dependent on the geometry of the exposed electrode. We demonstrate that using thin cylindrical exposed electrodes can increase the induced force by several hundred percent compared with an actuator with a rectangular exposed electrode of the same thickness. This difference is due almost exclusively to the extent of the exposed electrode in the same direction as the gap between the two electrodes, which tends to be much longer for actuators constructed with rectangular exposed electrodes. The exact shape of the electrode cross-section plays no role. In addition, using an intensified digital camera we observed a new filament-free plasma that occurred only in discharges with exposed electrodes smaller than approximately 0.15 mm in diameter. These discharges spent an increasing fraction of the applied voltage period in this mode as we reduced the exposed electrode diameter. The mode shared several characteristics with a positive corona, and was partially responsible for a decrease in the electrical power used by these discharges.

The deposition of films under normal and off-normal angles of incidence has been investigated in order to explore the relevance of non-sticking and self-sputtering of energetic ions. Non-sticking and self-sputtering lead to the formation of neutral atoms which return to the plasma and affect its properties. The flow of energetic ions was obtained using a filtered cathodic arc system in high vacuum. The range of materials included Cu, Ag, Au, Pt, Ti and Ni. Consistent with molecular dynamics simulations published in the literature, the experiments showed that the combined effects of non-sticking and self-sputtering appear to be significant, although the relatively large error range of the experimental method would not allow us to derive quantitative data. It was shown that modest heating of the substrate and intentional introduction of oxygen background gas considerably affected the results.

This paper details the electro-thermal study of the sublimation phase on a zinc oxide surface. This thermodynamic process occurs when a ZnO target is bombarded by a pulsed electron beam source composed of polyenergetic electrons. The source delivers short pulses of 180 ns of electrons with energies up to 16 keV. The beam total current reaches 800 A and is focused onto a spot area 2 mm in diameter. The Monte Carlo CASINO program is used to study the first stage of the interaction and to define the heat source space distribution inside the ZnO target. Simulation of the second stage of interaction is developed in a COMSOL multiphysics project. The simulated thermal field induced by space and time heat conduction is presented. Typically for a pulsed electron beam 2 mm in diameter of electrons having energies up to 16 keV, the surface temperature reaches a maximum of 7000 K. The calculations are supported by SEM pictures of the target irradiated by various beam energies and numbers of pulses.

Structural changes in multilayered AlN/TiN nanocomposites upon Ar⁺ ion irradiation were investigated. Reactive sputtering was used to deposit (AlN/TiN) × 5 multilayers on Si(1 0 0), to a total thickness of ∼270 nm. Argon was implanted at 200 keV, to 5 × 10¹⁵–4 × 10¹⁶ ions cm⁻². The as-deposited multilayers had a very fine columnar nanocrystalline structure, the width of individual grains was up to ∼10 nm. It was found that this immiscible system exhibits a high ion radiation stability, the AlN and TiN layers remaining well separated, with sharp interfaces. Ion irradiation induced small local density changes and only a slight increase in individual grains, in the region where most damage was deposited by the impact ions. For the highest irradiation fluence there was also some migration of Ti into AlN in this region, which was assigned to excess nitrogen within the AlN layers. Due to these small structural changes, ion irradiation enhanced the mechanical strength of the multilayered nanocomposites.

Nanocrystalline dielectric thin films of (Pb_1−xSr_x)TiO₃ were dip-coated on different substrates from highly stable precursor solutions derived from a unique metal organic system. Highly crystalline, fine-grained, uniform and crack-free thin films were obtained at temperatures as low as 450 °C. The structural and dielectric properties of the thin films have been investigated to study the suitability of the thin films for tunable dielectric applications.

We compare the characteristics of GaSb quantum dots (QDs) grown by molecular beam epitaxy on GaAs at temperatures from 400 to 490 °C. The dot morphology, in terms of size, shape and density, as determined by atomic force microscopy (AFM) on uncapped QDs, was found to be highly sensitive to the growth temperature. Photoluminescence (PL) spectra of capped QDs are also strongly dependent on growth temperature, but for samples with the highest dot density, where the QD luminescence would be expected to be the most intense, it is absent. We attribute this to dissolution of the dots by the capping layer. This explanation is confirmed by AFM of a sample that is thinly capped at 490 °C. Deposition of the capping layer at low temperature resolves this problem, resulting in strong QD PL from a sample with a high dot density.

We used a dedicated hemispherical energy analyzer to measure energetic and angular distributions of electrons emitted from molybdenum microtips integrated in a 1 cm² field emitter array designed by the CEA/LETI laboratory. Such cathodes typically deliver about 25 mA at an extraction voltage of 100 V, and are studied in order to replace heated wires as electron sources for space applications. We find that the energy distribution of the beam strongly depends on the extraction voltage, and is therefore expected to vary across the emission lifetime of the device, at a rate depending both on the alteration of the resistive structure with time and on the fate of adsorbed contaminants at the tip surface. A semi-empirical model of the emitters is proposed and used to determine parameters of energetic and angular distributions. The energy dispersion of the beam is found to increase from 2 eV ± 20% up to 9 eV ± 20% eV, for extraction voltages varying from 40 to 100 V. The mean angular dispersion of the beam is found to be 42° ± 20% when a null electric field is set at the grid extraction surface.

The extraction efficiency f for the photoelectrons emitted from a CsI photocathode into gaseous Xe–CH₄ and Ne–CH₄ mixtures is investigated by Monte Carlo simulation. The results are compared with earlier calculations in Ar–CH₄ mixtures and in the pure gases Xe, Ar, Ne and CH₄. The calculations examine the dependence of f on the density-reduced electric field E/N in the 0.1–40 Td range, on the incident photon energy E_ph in the 6.8–9.8 eV (183–127 nm) VUV range and on the mixture composition. Results calculated for irradiation of the photocathode with a Hg(Ar) lamp are compared with experimental measurements for this lamp. To test the electron scattering cross-sections used in the simulations, electron drift parameters in Xe, Ne and their mixtures with CH₄ are also presented and compared with available experimental data.