Target Gas Pressure Research Articles

Light emission processes in the context of optical beam profile monitors

Light emission from gas targets using heavy ion beam excitation is described. Typically 32S beams with ≈90 MeV (2.8 MeV/amu) particle energy were used. This study was performed in context of optical beam profile measurements. Optical transitions from neutral and singly ionized rare gases are suggested for this application. Emission spectra and their line intensities are presented for a wide range of target pressures from about 10–5 to 300 mbar. The effect of secondary electrons on the beam profiles is discussed. A comparison of ion beam and electron beam-induced spectra is shown and interpreted by a semi-quantitative model of the excitation mechanisms. Examples of beam profiles recorded with three different cameras through appropriate optical filters are presented. A comparison of projected profiles and radial profiles obtained by Abel inversion is given. Effective emission cross sections were measured for atomic and ionic lines at various target gas pressures and their pressure dependence interpreted by the excitation mechanisms. Examples of time-resolved measurements of light emission following pulsed excitation support the interpretation of the excitation mechanisms discussed in this overview of ion beam-induced light emission of gas targets.Graphical

Stable attosecond beamline equipped with high resolution electron and XUV spectrometer based on high-harmonics generation

We present a high-resolution and delay-stabilized setup for attosecond spectroscopy based on high-order harmonic generation from the intense laser passing through a differential gas cell. It shows the ability to generate the tunable photons from VUV to Soft X-ray (20–180 eV) at low backing pressure of target gas. This atto-beamline consists of an HHG source, electron and XUV spectrometers, and an active stabilization system. The measurements show it can be stabilized to sub-20 as in hours, together with a home-built XUV spectrometer with an energy resolution better than E/ΔE≥1200 in the wavelength range of 5–25 nm. We demonstrated its applications for producing the narrowband XUV source, extending the cutoff energy of HHG, and performing RABBITT measurements, particularly for investigating the excitation and ionization dynamics of atoms and molecules in a broad energy range by measuring the electrons and photons with attosecond temporal resolution.

Electron-impact ionization and ionic fragmentation of O2from threshold to 120 eV energy range

We study the electron-impact induced ionization of O2from threshold to 120 eV using the electron spectroscopy method. Our approach is simple in concept and embodies the ion source with a collision chamber and a mass spectrometer with a quadruple filter as a selector for the product ions. The combination of these two devices makes it possible to unequivocally collect all energetic fragment ions formed in ionization and dissociative processes and to detect them with known efficiency. The ion source allows varying and tuning the electron-impact ionization energy and the target-gas pressure. We demonstrate that for obtaining reliable results of cross-sections for inelastic processes and determining mechanisms for the formation of O[Formula: see text] ions, it is crucial to control the electron-impact energy for production of ion and the pressure in the ion source. A comparison of our results with other experimental and theoretical data shows good agreement and proves the validity of our approach.

Coherent two-photon emission from hydrogen molecules excited by counter-propagating laser pulses

We observed two-photon emission (TPE) signal from the first vibrationally excited state of parahydrogen gas coherently excited by counter-propagating laser pulses. A single narrow-linewidth laser source has roles in the excitation of the parahydrogen molecules and the induction of the TPE process. We measured dependences of the signal energy on the detuning, target gas pressure, and input pulse energies. These results are qualitatively consistent with those obtained by numerical simulations based on Maxwell–Bloch equations with one spatial dimension and one temporal dimension. This study of the TPE process in the counter-propagating injection scheme is an important step toward neutrino mass spectroscopy.

High Ferroelectricities and High Curie Temperature of BiInO3PbTiO3 Thin Films Deposited by RF Magnetron Sputtering Method☆☆Supported by the National Natural Science Foundation of China under Grant No 11304160, the Special Fund for Public Interest of China under Grant No 201510068, and the NUPTFC under Grant No NY215111.

Properties of ferroelectric xBiInO3-(1 − x)PbTiO3 (xBI-(1 − x)PT) thin films deposited on (101) SrRuO3/(200) Pt/(200) MgO substrates by rf magnetron sputtering method and effects of deposition conditions are investigated. The structures of the xBI-(1 − x)PT films are characterized by x-ray diffraction and scanning electron microscopy. The results indicate that the thin films are grown with mainly (001) orientation. The chemical compositions of the films are analyzed by scanning electron probe and the results indicate that the loss phenomena of Pb and Bi elements depend on the pressure and temperature during the sputtering process. The sputtering parameters including target composition, substrate temperature, and gas pressure are adjusted to obtain optimum sputtering conditions. To decrease leakage currents, 2 mol% La2O3 is doped in the targets. The P–E hysteresis loops show that the optimized xBI-(1 − x)PT (x = 0.24) film has high ferroelectricities with remnant polarization and coercive electric field . The Curie temperature is about 640 °C. The results show that the films have optimum performance and will have wide applications.

Distinguishing Bulk Conduction from Band Bending Transduction Mechanisms in Chemiresistive Metal Oxide Gas Sensors

Chemiresistive metal oxide gas sensors based on materials including SnO2, ZnO, TiO2, and WO3 have been investigated extensively for a wide range of applications. The band bending model, based on the surface chemistry of highly reactive ionosorbed species (O2– or O–) and the semiconducting material properties of SnO2, TiO2, and ZnO, adequately predicts the dependence of steady state response on target gas pressure and temperature for these materials. However, the assumptions associated with the band bending model are not valid for sensors based on reducible oxides such as WO3, MoO3, and V2O5, in which lattice oxygen reacts with adsorbed target gases creating oxygen vacancies which diffuse rapidly into the bulk and modulate the conductivity. Here, we develop a model that includes surface reactions and vacancy diffusion for the bulk conduction mechanism and describe characteristics of the sensor behavior that allow bulk conduction to be distinguished from the band bending transduction mechanism. We illustrate the predictions of the model regarding how the change in conductivity, Δσ, and response time, τ, depend on target gas pressure, temperature, and film thickness using well-characterized WO3 sensors, including epitaxially oriented polycrystalline thin films and nanorod structured glancing angle deposition (GLAD) films. The physical/chemical parameters of the model are determined in independent measurements. Expressions for the limiting cases in which τ is determined either by surface reactions or by bulk diffusion provide design criteria to predict the theoretical performance limits of sensors which operate via this transduction mechanism.

Broadening and shift of the spectral lines of hydrogen atoms and silicon ions in laser plasma

We report an experimental investigation of the broadening and shift of discrete lines in the plasma spectrum produced in the laser ablation of silicon in a broad pressure range of the ambient gas . The broadening and line shifts are measured in relation to the distance from the target and initial gas pressure. The threshold nature of the resulting dependences is found to be related to the formation of virtual percolation clusters proceeding in the hot dense plasma.

Measurement and calculation of absolute single- and double-charge-exchange cross sections forO6+ions at 1.17 and 2.33 keV/u impacting He andH2

Absolute single- and double-charge-exchange cross sections for the astrophysically prominent ${\mathrm{O}}^{6+}$ ion with the atomic and molecular targets He and ${\mathrm{H}}_{2}$ are reported. These collisions give rise to x-ray emissions in the interplanetary medium, planetary atmospheres, and comets as they approach the sun. Measurements have been carried out using the Caltech Jet Propulsion Laboratory electron cyclotron resonance ion source with ${\mathrm{O}}^{6+}$ at energies of 1.17 and 2.33 keV/u characteristic of the slow and fast components of the solar wind. Absolute charge-exchange (CE) data are derived from knowledge of the target gas pressure, target path length, incident ion current, and charge-exchanged ion currents. These data are compared with results obtained using the $n$-electron classical trajectory Monte Carlo method. The radiative and Auger evolution of ion populations following one- and two-electron transfers is calculated with the time-dependent collisional-radiative code nomad using atomic data from the flexible atomic code. Calculated CE emission spectra for $100\phantom{\rule{4pt}{0ex}}\AA{}l\ensuremath{\lambda}l1400\phantom{\rule{4pt}{0ex}}\AA{}$ are reported as well and compared with experimental sublevel spectra and cross sections.

Optical Emission Spectroscopic Analysis of Plasma Plume during Pulsed Laser Deposition of PZT

Spatial variation in intensity of spectral emission, electron temperature, number density, and the time of flight (TOF) of ions and neutrals at various oxygen ambiances has been investigated on ferroelectric lead zirconium titanate (PZT) plasma using optical emission spectroscopy. Plasma produced by ablating PZT ceramic target using Nd-YAG laser operating at the third harmonics (λ=355 nm, τ=10 ns, repetition frequency 10 Hz) was investigated at various oxygen partial pressures and at various distances from the target surface. Here energy density for laser fluence was fixed as 3.13 Jcm−2 and distance from the target and ambient gas pressure were varied. The electron number density Ne and electron temperature of the PZT plasma at the early stage of plume expansion were measured as 1.7×1017 Jcm−2 and 13200 K, respectively, and thus verified the existence of local thermodynamic equilibrium (LTE). Time of flight spectra (TOF) of neutral and singly ionized species in plasma were recorded. The result shows that plasma parameters and velocity of species are of same order for various oxygen partial pressures but have a decreasing tendency with distance. The energy of almost all species in the plume become more or less same at 0.1 mbar. These conditions favour the growth of perovskite PZT thin films.

EUV spectra of Xe xvii–Xe xxi produced in charge-exchange collisions

Charge-state-specific spectra produced from charge exchange collisions between xenon ions and helium target atoms using an ECR (electron cyclotron resonance) source have been recorded in extreme ultraviolet (EUV). At low target gas pressures, the spectra were produced after a single collision event involving electron capture by the projectile ion and in each case intense emission near 11 nm was observed. The spectra of Xe${}^{16+}$ to Xe${}^{20+}$ are compared with atomic structure calculations and the possible mechanisms for electron capture are discussed. There is some evidence that for lower charged ions the spectra in the 10--15 nm region result mainly from transfer excitation or ionization processes rather than direct single electron capture into high $nl$ states.

Investigation of Plasma Immersion Ion Implantation Process in Magnetic Mirror Geometry

Plasma immersion ion implantation (PIII) with low external magnetic field has been investigated both numerically and experimentally. The static magnetic field considered is essentially nonuniform and is generated by two magnetic coils installed outside the vacuum chamber. Experiments have been conducted to investigate the effect of two of the most important PIII parameters: target voltage and gas pressure. In that context, it was found that the current density increased when the external parameters were varied. Later, the PIII process was analyzed numerically using the 2.5-D computer code KARAT. The numerical results show that the system of crossed <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\bf E} \times {\bf B}$</tex></formula> fields enhances the PIII process. The simulation showed an increase of the plasma density around the target under the operating and design conditions considered. Consequently, an increase of the ion current density on the target was observed. All these results are explained through the mechanism of gas ionization by collisions with electrons drifting in crossed <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\bf E} \times {\bf B}$</tex></formula> fields.

Effect of transverse magnetic field on the laser-blow-off plasma plume emission in the presence of ambient gas

In the present paper we report the effect of variable magnetic field in the range of 0.04–0.2 T on the emission of two neutral Lithium lines Li I 670.8 nm and Li I 610.3 nm and one ionic line Li II 548.4 nm in the presence of ambient gas on the laser-blow-off plasma plume. Enhancement in the intensity associated with structures was observed in the temporal profile of neutrals, which is strongly dependent on the magnetic field intensity, distance from the target and background gas pressure. At 6 mm distance and 1.33 Pa argon pressure, apart from overall enhancement in the intensity of both the neutral lines, the results reveal some interesting features, e.g. disappearance of structures and narrowing of the temporal extent of 670.8 nm line at higher magnetic fields. On the other hand, the 610.3 nm line exhibits a significant enhancement in the intensity at the trailing part as the field is increased. At a shorter distance (2 mm) and for relatively higher pressures (133.3 Pa), the effect of field is not much prominent. Interestingly, the ionic spectral line does not exhibit any significant change with both, magnetic field and ambient gas. We explain the results by considering the role of various atomic processes viz. electron impact excitation, recombination and diffusion of ambient gas into plume in collisional and hydrodynamical regimes.

Explicit formulation for the response of neat oxide semiconductor gas sensor to reducing gas

The response of a neat semiconductor gas sensor to a reducing gas has successfully been formulated theoretically as a function of the partial pressure of target gas under the conditions of volume depletion and the presence of residual electrons inside the depletion region. This was achieved by considering the steady state of resistance instead of that of the surface density of adsorbed oxide ions. The derived equation, given as a combination of several physicochemical parameters, reproduces main features of practical response behavior well. It is exemplified that the equation provides the analysis or extension of response data with an important theoretical base.

Efficient growth of multi-walled carbon nanotubes by continuous-wave laser vaporization of graphite containing B 4C

Multi-walled carbon nanotubes (MWCNTs), 7–70 nm thick and up to 30 μm long, were efficiently grown by room-temperature continuous-wave laser vaporization of a graphite target containing B 4C in an ambient Ar gas. Adjusting the boron content in the target and Ar gas pressure resulted in a maximum fraction of ∼60% of MWCNTs in the deposits. The straightness of the MWCNTs and graphene layers with an interlayer spacing of ∼0.35 nm indicated that the degree of graphitization was fairly high in the grown MWCNTs. However, the features of D, G, and 2D bands in the Raman spectrum of a deposit suggested boron doping in the MWCNTs. An apparent Young’s modulus of a grown MWCNT was measured to be 0.68 TPa and comparable to those of heat-treated vapor grown carbon nanofibers. MWCNTs are thought to grow on molten boron carbide particles acting as seeds at high temperatures of up to ∼2400 °C.

MEASUREMENT AND CALCULATION OF ABSOLUTE SINGLE AND MULTIPLE CHARGE EXCHANGE CROSS SECTIONS FOR Feq+IONS IMPACTING H2O

Charge exchange (CE) plays a fundamental role in the collisions of solar- and stellar-wind ions with lunar and planetary exospheres, comets, and circumstellar clouds. Reported herein are absolute cross sections for single, double, triple, and quadruple CE of Fe q + (q = 5-13) ions with H2O at a collision energy of 7q keV. One measured value of the pentuple CE is also given for Fe 9 + ions. An electron cyclotron resonance ion source is used to provide currents of the highly charged Fe ions. Absolute data are derived from knowledge of the target gas pressure, target path length, and incident and charge-exchanged ion currents. Experimental cross sections are compared with new results of the n-electron classical trajectory Monte Carlo approximation. The radiative and non-radiative cascades following electron transfers are approximated using scaled hydrogenic transition probabilities and scaled Auger rates. Also given are estimates of cross sections for single capture, and multiple capture followed by autoionization, as derived from the extended overbarrier model. These estimates are based on new theoretical calculations of the vertical ionization potentials of H2O up to H2O10+.

Measurement and calculation of absolute single- and multiple-charge-exchange cross sections for Feq+ions impacting CO and CO2

Absolute cross sections are reported for single, double, and triple charge exchange of Fe${}^{q}$${}^{+}$ ($q=5--13$) ions with CO and CO${}_{2}$. The highly charged Fe ions are generated in an electron cyclotron resonance ion source. Absolute data are derived from knowledge of the target gas pressure, target path length, and incident and charge-exchanged ion currents. Experimental results are compared with new calculations of these cross sections in the $n$-electron classical trajectory Monte Carlo approximation in which the ensuing radiative and nonradiative cascades are approximated with scaled hydrogenic transition probabilities and scaled Auger rates. The present data are needed in astrophysical applications of solar- and stellar-wind charge exchange with comets, planetary atmospheres, and circumstellar clouds.

Collision induced dissociation in a flowing afterglow-tandem mass spectrometer for the selective detection of C 5 unsaturated alcohols and isoprene

A flowing afterglow-tandem mass spectrometer (FA-TMS) was used to study a series of C 5 unsaturated alcohols and isoprene. The analytical procedure was validated through collision induced dissociation (CID) experiments on proton hydrates. In the FA, reagent H 3O + ions were used to chemically ionize the alcohols under study and isoprene. Chemical ionization (CI) by H 3O + is widely used, especially in PTR-MS instruments, and produces a main peak at m/ z 69 for all studied compounds, implying the impossibility to distinguish them by a simple quadrupole mass filter. The CID of these ions at m/ z 69 resulted in daughter ions with the same masses but with different intensities depending on the organic compound, the collision energy and the Ar target gas pressure in the collision cell. From these observations, pentenols were easily distinguished from methylbutenols and 3-methyl-3-buten-1-ol from the other compounds. CID experiments were also performed on the protonated alcohol, which is only a stable ion for 1-penten-3-ol, 2-methyl-3-buten-2-ol and 3-methyl-3-buten-1-ol, showing different CID patterns as a function of the collision energy. The coupling between a FA reactor and a TMS has proven to be a valuable approach to identify C 5 unsaturated alcohols and isoprene.

Identification of 4d–5p transitions in the spectra of Sn XV–Sn XIX recorded from collisions between Sn ions and He

Charge-state-specific extreme ultraviolet (EUV) spectra produced from charge exchange collisions between tin ions in charge states from Sn15+ to Sn18+ and rare gas target atoms using an ECR (electron cyclotron resonance) source have been recorded at Tokyo Metropolitan University. At low target gas pressures, the spectra were produced by single collision and capture events, and in each case they were dominated by intense emission near 13 nm. In the spectra of Sn XV–Sn XIX this emission has been shown to arise from 4s24pm−14d–4s24pm−14f + 4s24pm−24d2 transitions. However, in addition, a distinct group of lines resulting from 4s24pm−14d–4s24pm−15p (2 ⩽ m ⩽ 6) transitions centred near 11.5 nm in Sn XV was seen to shift to shorter wavelength with increasing ionic charge, and the strongest lines were identified by comparison with atomic structure calculations. These identifications are the subject of the present work.

Transitions and the effects of configuration interaction in the spectra of Sn XV–Sn XVIII

Charge state specific euv spectra from a range of tin ions have been recorded at Tokyo Metropolitan University. The spectra were produced from charge-exchange collisions between tin ions and helium atoms using an electron cyclotron resonance source. At low target gas pressures, the spectra were dominated by single capture events. The spectra were, unexpectedly, found to be dominated by an intense unresolved transition array near 13 nm while the resonance lines, including the previously identified $4p\ensuremath{-}4d$ ${^{1}S}_{0}\ensuremath{\rightarrow}{^{1}P}_{1}$ resonance line of Sn XV, were relatively weak. From atomic structure calculations, it was found that the unresolved transition array arises from $4{s}^{2}4{p}^{m\ensuremath{-}1}4d\ensuremath{-}4{s}^{2}4{p}^{m\ensuremath{-}1}4f+4{s}^{2}4{p}^{m\ensuremath{-}2}4{d}^{2}$ transitions. In addition it proved necessary to include interaction with core excited $4s4{p}^{m}4d$ configurations to fully explain the observed spectra.

Influence of argon gas pressure and target power on magnetron plasma parameters

The use of thin film sensors for measuring pressure and temperature distribution in tribological contacts was limited to hydrodynamic and elasto-hydrodynic contacts. Under mixed lubrication conditions the sensors regularly failed in the past. Therefore a new sensor generation is to be developed, which withstands the conditions of boundary friction within certain limits. These are based on electrically isolating DLC thin films (diamond-like carbon) as protecting and insulating coatings, between which the sensors are embedded. DLC thin films were deposited by r.f. magnetron sputtering of a graphite target (75 mm in diameter) in a pure argon discharge at low substrate temperatures (60–150 °C). For optimization of film constitution and properties, the target power was changed in the range of 50 W and 500 W and the argon gas pressure between 0.4 Pa and 0.7 Pa. The film characteristics were studied and related to plasma parameters and particle fluxes onto substrate and target during deposition, including ion saturation current density, electron saturation current density, plasma density, electron temperature und plasma potential. These plasma parameters were systematically analyzed in dependence of target power and gas pressure by using electrical double probes.