Low-energy Ion Fluxes Research Articles

Deuterium retention in sintered boron carbide exposed to a deuterium plasma

Depth profiles of deuterium up to a depth of 10 μm have been measured using the D( 3He,p) 4He nuclear reaction in a resonance-like technique after exposure of sintered boron carbide, B 4C, at elevated temperatures to a low energy (≈200 eV/D) and high ion flux (≈10 21 m −2 s −1) D plasma. The proton yield was measured as a function of incident 3He energy and the D depth profile was obtained by deconvolution of the measured proton yields using the program SIMNRA. D atoms diffuse into the bulk at temperatures above 553 K, and accumulate up to a maximum concentration of about 0.2 at.%. At high fluences (⩾10 24 D/m 2), the accumulation in the bulk plays a major role in the D retention. With increasing exposure temperature, the amount of D retained in B 4C increases and exceeds a value of 2 × 10 21 D/m 2 at 923 K. The deuterium diffusivity in the sintered boron carbide is estimated to be D = 2.6 × 10 −6exp{−(107 ± 10) kJ mol −1/ RT} m 2 s −1.

Preparation of Super-Hard Nanocomposite Films by ICP Assisted Magnetron Sputtering

Super-hard nanocomposite films were deposited on Si(100) substrates with irradiation of a high-density (~2.0 mA/cm2) low-energy (~22 eV) ion flux by an inductively coupled plasma (ICP) assistance to magnetron sputtering process. Low-stress, super-hard nanocomposite Ti-Cu-N and Ti-Si-N films could be synthesized at low deposition temperatures below 300 oC. Prepared films exhibited a pronounced TiN(200) texture and the film hardness was significantly enhanced by the addition of Cu and Si, where a maximum value of 42 GPa at approximately 2 at% Cu addition and 48 GPa at approximately 5.8 at.% Si. Ti-Cu-N films were consisting of nanocolumns of TiN crystallites with dispersion of Cu crystallites around the columnar boundaries. While Ti-Si-N films were characterized as having a nanocolumns of TiN crystallites with amorphous Si3N4 inside the columnar boundaries. The residual compressive stresses of these films were lower than 1.5 GPa and no refinement of crystallite size by the addition of Cu and /or Si was observed, from which the hardness enhancement was attributed to a nanocomposite effect.

Real-time spectroscopic ellipsometry study of Ta–Si–N ultrathin diffusion barriers

This article reports on the use of real-time spectroscopic ellipsometry (RTSE) to (1) understand the growth process of ultrathin (10 nm thick) Ta–Si–N diffusion barriers and to (2) monitor their thermal stability up to a temperature of 800 °C. Thin films of Ta–Si–N diffusion barriers and Cu overlayers were deposited on Si(111) substrates using reactive unbalanced magnetron sputtering. In order to reduce roughness and interdiffusion between consecutive surfaces, a modulated low energy and high flux ion assistance was utilized. The initial part of the films (2 nm) of each layer was deposited with a high flux of low energy ions (<10eV) to reduce intermixing, while higher energies (between 40 and 130 eV) were utilized for the remainder of the layer to decrease the percolation thickness. RTSE data were simulated using the Drude-Lorentz model to obtain information about the growth mechanism and the conduction electron transport properties for these structures. The films were annealed at 800 °C and the diffusion of copper into silicon was evaluated by monitoring changes in the optical properties of the bilayers. The pseudodielectric function of the films was found to be altered whenever diffusion proceeded. Thermal stability at 800 °C was achieved for samples produced using the ion-assistance technique. The results deduced from RTSE were verified by characterizing the elemental composition of the as-deposited and heat-treated films using Rutherford backscattering and time-of-flight secondary ion mass spectrometry.

Structure and properties of Ti–Si–N films prepared by ICP assisted magnetron sputtering

Inductively coupled plasmas (ICPs) were generated to assist magnetron sputtering. By bombarding the growing film with a high-density (∼2.0 mA/cm 2) low-energy (∼22 eV) ion flux, Ti–Si–N films containing 0–12 at.% Si were deposited on Si(100) substrates at low deposition temperature (<150 °C). The residual compressive stresses of these films were measured to be lower than 1.5 GPa. Film hardness was significantly enhanced by the addition of a small amount of Si and attained a maximum value of 48 GPa at approximately 5.8 at.% Si. From X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results, the superhard Ti–Si–N films were characterized as having a nanocomposite structure, consisting of nanocolumns of TiN crystallites with amorphous Si 3N 4 inside the column boundaries. The hardest Ti–Si–N film exhibited a pronounced TiN(200) texture. No refinement of crystallite size by the addition of Si was observed in the present series of Ti–Si–N films. Thus, the hardness enhancement was attributed to nanocomposite effect.

FAST and IMAGE‐FUV observations of a substorm onset

On 6 February 2002 the NASA FAST satellite transited a substorm break up arc approximately 1 min after substorm onset as identified by the NASA IMAGE satellite far ultraviolet (FUV) instrument complement. These IMAGE data show that both the intense electron and proton precipitation features seen by FAST were not present prior to substorm onset. The most intense onset poleward surge was produced by superthermal electrons, and their energy spectrum and field‐aligned angular distribution were consistent with wave accelerated electrons. The low energy ion fluxes in the E × B direction and magnetometer measurements confirmed the presence of waves in this feature. Thus the leading edge of the auroral surge was not produced by quasi‐static field‐aligned currents and related “inverted V” electric fields. The onset arc was also the poleward boundary of intense energetic protons. The FUV proton auroral images indicate that substantial part of the ion energy was carried by protons of energy &gt;25 keV. Equatorward of the surge, there was a broader region of electron precipitation with embedded quasi‐static “inverted V” electric fields. The FAST particle and magnetometer measurements are consistent with a field‐aligned current structure in which the bulk of the upward current was carried by the “inverted V” precipitation region. The region of the superthermal electrons carried very little net current. The high‐density upward field‐aligned current carried by the superthermal electrons was presumably balanced by oppositely directed downward currents carried by cold electrons. The ground onset location was separated from the closed/open field line boundary by an extended region of closed field lines. In this region there was some weak plasma sheet electron and proton precipitation, but there was no clear signature of any distant, prebreakup substorm onset activity.

Blister formation on tungsten surface under low energy and high flux hydrogen plasma irradiation in NAGDIS-I

This study presents experimental results on hydrogen blister formation on powder metallurgy tungsten (PM-W) surface under low energy (<100 eV) and high ion flux (>10 21 m −2 s −1) hydrogen plasma irradiation in a divertor plasma simulator-NAGDIS-I. The tungsten samples were exposed to steady-state hydrogen plasma at various sample temperatures and fluences. Hydrogen blister formations are clearly observed on tungsten surface at the surface temperature below 950 K. The blister size is from a few 10 μm to a few 100 μm. It was found that the blister formations obviously depend on the surface temperature and the incident hydrogen ion fluence. No blisters are observed on tungsten surface at the surface temperature above 950 K even if the fluence is high enough.

On the Possible Detection of Evidence for the Approach of Voyager 1 to the Heliospheric Boundaries

Quite an unusual behavior of the low-energy ion fluxes measured with the LECP and CRS instruments onboard Voyager 1, which is located in the outer heliosphere at a distance of about 90 AU, has been observed since July 2002 until recently (February 2003). This behavior can be interpreted as a possible manifestation of a combination of the global heliospheric disturbance produced by solar activity and the precursor of the outer heliosphere with its termination shock. The extremely large variability of the enhanced ion fluxes since the second half of 2002 in several energy channels from 0.5 to several MeV/nucleon is presumed to be associated with the sources of their acceleration near the termination shock. The simultaneous increase in the flux of protons with energies above 70 MeV may result from the easier penetration of Galactic cosmic rays because of the reduction in modulation at the declining phase in the current solar cycle 23 after the maximum in 2000 and from an admixture of the anomalous component accelerated at the termination shock.

609 超硬ナロコンポジット薄膜の低温合成

An inductively coupled plasma (ICP) was sustained by an internal antenna with insulting covering to assist dc magnetron sputtering. This incorporated a high-density low-energy ion flux to bombard the growing film on grounded Si (100) substrate. Thus, superhard nanocomposite Ti-Si-N and Ti-Cu-N thin films with low residual stress were synthesized at low deposition temperature. Form XRD, TEM and XPS, it was assumed that nc-TiN/a-Si_3N_4 and nc-TiN/nc-Cu nanocomposites were formed, respectively. TiN was composed of nanocrystallite of approximately 20-30 nm. Film hardness strongly depended on the content of Si or Cu, and reached a value higher than 40 GPa in both cases. Hardness enhancement by the addition of Si or Cu could be attributed to nanocomposite effect.

Nucleation and initial growth of platinum islands by plasma sputter deposition

The nucleation and islands growth of platinum have been followed from an early stage through to complete substrate coverage. Thus, this study of initial stages of thin film growth has allowed to improve the understanding of growth mechanisms and to control the final nanomaterials structure. In the presented deposition method, the metal atom source is a negatively biased metal wire submitted to the bombardment of ions created in HF plasma. The originality of this plasma sputtering technique is that in addition to the metal atom flux, the substrate surface is submitted to a high flux of low energy ions, inducing a high atomic surface mobility and modifying the growth mode with respect to conventional deposition techniques (magnetron sputtering or evaporation). Platinum deposits have been investigated by ex situ characterisation techniques: grazing incidence-small angle X-ray scattering (GISAXS) and X-ray diffraction (GIXD) in conjunction with transmission electron microscopy (TEM). Using morphological parameters as coverage rate, islands number density and islands size, different mechanisms (scale laws, islands mobility, coalescence, etc.) governing the growth are described vs. Ar ion and Pt atom energies and fluxes.

Highlight Results from Ulysses

Launched in October 1990, the ESA-NASA Ulysses mission has conducted the very first survey of the heliosphere within 5 AU of the Sun over the full range of heliolatitudes. The first polar passes took place in 1994 and 1995, enabling Ulysses to characterise the global structure of the heliosphere at solar minimum, when the corona adopts its simplest configuration. The most important findings to date include a confirmation of the uniform nature of the high-speed (~ 750 km s−1) solar wind flow from the polar coronal holes, filling two-thirds of the volume of the inner heliosphere; the sharp boundary, existing from the chromosphere through the corona, between fast and slow solar wind streams; the latitude independence of the radial component of the heliospheric magnetic field; the lower-than-expected latitude gradient of galactic and anomalous cosmic rays; the continued existence of recurrent increases in the flux of low-energy ions and electrons up to the highest latitudes.

An investigation of the electron irradiation of carbon blacks in various gas atmospheres using a modified electron microscope

The behaviour of carbon black particles immersed in a variety of gases and simultaneously irradiated with an electron beam has been investigated. Because this treatment was performed in a modified high‐resolution transmission electron microscope, the remarkable morphological and microstructural changes that occurred could be observed directly. In addition to the physical damage to the specimens, believed to be caused by a high flux of low energy ions generated by the electron beam, the use of reactive gases in this study exposed additional chemical sputtering effects that will be of importance for future controlled‐environment microscopy.

Field‐line resonances triggered by a northward IMF turning

A sudden northward rotation of the IMF observed by IMP 8 near the bow shock at 21:22 UT on January 10, 1997, triggered surface waves and fast mode waves at the flanks of the duskside magnetosphere, as observed by GEOTAIL instruments. The power spectral density of these waves peaked in the frequency range where field‐line resonances were observed by the POLAR satellite in the region L = 6.6–10.2. The oscillation periods of the observed field‐line resonances were L‐dependent with two distinct peaks which may be explained by increased heavy ion content at those field lines. The ULF waves also caused enhanced low‐energy ion fluxes from the ionosphere.

Surface nitridation of silicon dioxide with a high density nitrogen plasma

A high density nitrogen plasma generated with a helicon plasma source has been used to incorporate approximately 15 at. % nitrogen into the top 0.5 nm of a silicon dioxide layer. The surface nitridation was accomplished in 10 s with a high flux of low energy ions which were extracted from the high density nitrogen plasma and accelerated in the plasma sheath towards the surface an electrically floating silicon dioxide surface. A rf compensated Langmuir probe was used to measure the nitrogen ion energy and ion current density as a function of the nitrogen pressure and source power. The nitrogen ion energy, ion current density, and exposure time determine the nitrogen range and dose into the silicon dioxide surface. This process may be advantageous for nitriding the gate oxide in advanced complementary metal–oxide semiconductor process flows.

Low energy (E

Low energy (<400 eV) ion fluxes measured by the hyperbolic retarding potential analyser (HARP), during the first two elliptic orbits of the Phobos 2 spacecraft, are presented. Combining these results with the overlapping higher energy observations of the TAUS instrument, carried on the same spacecraft, we show the presence of flowing and shocked/thermalized solar wind ions inside the magnetosheath and antisunward flowing heavy ion population below the upper boundary of the magnetic barrier. Our results are not consistent with the presence of a dense, stagnated planetary ion population there, in the region explored by Phobos-2. Our results do not indicate the existence of additional sharp plasma boundaries, such as the proposed ion composition (mass loading) boundary. The observed characteristics of the outer regions of the Venus mantle and the combined HARP and TAUS measurements close to and inside of the magnetic barrier at Mars do not indicate the presence of significant differences.

Etching 0.35 μm polysilicon gates on a high-density helicon etcher

This article describes an evaluation of a helicon high-density plasma etch tool for etching 0.35 μm polysilicon gates. The objective of the evaluation was to establish whether it is possible to etch 0.35 μm lines of both doped and undoped polysilicon (simultaneously) while maintaining straight profiles across the wafer and a very high polysilicon-to-oxide selectivity. Several high-density plasma (HDP) polysilicon etch tools for 0.35 μm technology have been tested at Texas Instruments. It is known that HDP tools operating at low pressures can obtain high polysilicon etch rates and anisotropic etch profiles. Most of the HDP sources utilize two separate radio-frequency (rf) power supplies; one to generate the high-density plasma and a second to bias the chuck. This allows relatively independent control of the ion density and the ion energy. It is possible to attain high polysilicon-to-oxide selectivity in the overetch step by using a high flux (high rf power to the plasma) of low energy (low rf power to the chuck) ions. This high selectivity is particularly important when long overetches are required with thin gate oxides.

On the minimum fluxes of low-energy ions (0.5 MeV/nuc – 8 MeV/nuc) at high heliospheric latitudes

The quiet-time fluxes of ions from 0.5 MeV/nuc to 7 MeV/nuc (for oxygen) have been studied for the time period between mid-1993 through the first 104 days of 1994. During this time period Ulysses was below the heliographic current sheet. We find that at the quietest times, the ion population is dominated by the ACR component. For more active times, but still avoiding the most active time periods, the population below 3 MeV/nuc contains a CIR component as well as ACR ions.

Over the southern solar pole: low-energy interplanetary charged particles.

The heliosphere instrument for spectrum, composition, and anisotropy (HISCALE) recorded the fluxes of low-energy ions and electrons (> 50 kiloelectron volts) when Ulysses crossed the southern solar polar region and revealed that the large-scale structure of the heliosphere to at least approximately -75 degrees was significantly influenced by the near-equatorial heliospheric current sheet. Electrons in particular were accelerated by the current sheet-produced and poleward-propagating interplanetary reverse shock at helioradii far from the Ulysses location. At heliolatitudes higher than approximately -75 degrees on the Ulysses ascent to the pole and approximately -50 degrees on the descent, small, less regular enhancements of the lowest energy electron fluxes were measured whose relations to the current sheet were less clear. The anomalous component of low-energy (approximately 2 to 5 megaelectron volts per nucleon) oxygen flux at the highest heliolatitudes was found to be approximately 10(-8) [per square centimeter per second per steradian (per kiloelectronvolt per nucleon)]; the anomalous Ne/O ratio was approximately 0.25.

Ion populations in the tail of Venus

Plasma measurements in the tails of Venus showed the existence of several ion populations. Measurements performed on Venera and Pioneer Venus spacecraft at different planetocentric distances showed the evolution of the plasma parameters along the tail. Low-energy ion fluxes measured in the tail at close downstream distances, are also observed farther downstream, and show low acceleration from 0.5 R(sub V) to 12 R(sub V). High energy ions (energetic O(+) ions) reported from Pioneer Venus Orbiter (PVO) observations in the tail at 10-12 R(sub V) seem to be the same ion component that was observed as energetic ions at the tail boundary close to the planet on Venera spacecraft. We give evidence that these ions are accelerated in the narrow shear layer near the tail boundary.

Helicon ion source for plasma processing

The results of theoretical and experimental investigations of dense plasma source resonantly excited by helicon wave are presented. Driven by a single-loop low-voltage (≂300 V) antenna, a source generates a plasma of density up to 5×1011 cm−3 at gas pressures 0.5–20 mTorr, operates at magnetic fields &amp;lt;100 Gs, and produces low-energy ion fluxes (&amp;lt;60 eV) with current densities up to 7 mA/cm2 and 3.5% nonuniformity within a diameter 10 cm. A high-efficiency helicon source originates in a special kind of ‘‘resonance’’ wave discharge, where a sharp increase of plasma resistance occurs near the helicon wave dispersion branches.

In situ investigation of silicon surface cleaning and damage by argon electron cyclotron resonance plasmas

An argon electron cyclotron resonance (ECR) plasma process has been optimized to successfully remove oxide films from a silicon surface at elevated temperatures leaving smooth Si surfaces devoid of an amorphized silicon damage layer. Etch rates of over 10 nm/min have been achieved at ion energies below 100 eV. The low ion energy (−50 V dc bias) and high ion fluxes (1×1016 ions/cm2 s) represent a significant improvement from conventional Ar ion sputter cleaning processes. In situ spectroscopic ellipsometry and ex situ atomic force microscopy were used to characterize the surface condition during and after cleaning to establish a 700 °C argon plasma cleaning process for silicon. Real-time single wavelength ellipsometry was used to study the cleaning kinetics, determine the optimal end point, and elucidate a controversy about the level of damage in the argon ECR plasma cleaning process.