Showing papers on "Buffer gas published in 2008"

Gas management system for a laser-produced-plasma euv light source

Abstract: Devices and corresponding methods of use are described herein which may comprise an enclosing structure defining a closed loop flow path and a system generating a plasma at a plasma site, e.g. laser produced plasma system, where the plasma site may be in fluid communication with the flow path. For the device, a gas may be disposed in the enclosing structure which may include an ion-stopping buffer gas and/or an etchant. A pump may be provided to force the gas through the closed loop flow path. One or more heat exchangers removing heat from gas flowing in the flow path may be provided. In some arrangements, a filter may be used to remove at least a portion of a target species from gas flowing in the flow path.

Photocatalytic activity of pulsed laser deposited TiO2 thin films

Abstract: Nanostructured TiO 2 thin films were prepared by pulsed laser deposition (PLD) on indium-doped tin oxide (ITO) substrates. Results from X-ray photoelectron spectroscopy (XPS) show that Ti 2p core level peaks shift toward the lower binding energy with decrease in the buffer gas pressure (O 2 :Ar = 1:1). This suggests that oxygen vacancies are created under insufficient oxygen conditions. Anatase-to-rutile ratio is also found to be system pressure dependent. Under deposition pressure of 100 Pa, only anatase phase was observed even at 1073 K substrate temperature which is much higher that the bulk anatase-to-rutile phase transformation temperature. The deposited TiO 2 thin films were fabricated as photoanodes for photoelectrochemical (PEC) studies. PEC measurements on TiO 2 photoanodes show that the flatband potential ( V fb ) increases by 0.088 eV on absolute vacuum energy scale (AVS) with decrease in the deposition pressure from 100 to 33 Pa at 873 K. The highest incident photon to current conversion efficiency [IPCE( λ )] of 2.5 to 6% at λ = 320 nm was obtained from the thin films prepared at substrate temperature of 873 K. Combining the results from XPS and PEC studies, we conclude that the deposition pressure affects the concentration of the oxygen vacancies which changes the electronic structure of the TiO 2 . With reference to photoelectrochemical catalytic performance, our results suggest that it is possible to adjust the Fermi energy level and structure of TiO 2 thin films by controlling the buffer gas pressure and temperature to align the energy of the flatband potential ( V fb ) with respect to specific redox species in the electrolyte.

Cryogenic Ion Trapping Systems with Surface-Electrode Traps

Abstract: We present two simple cryogenic RF ion trap systems in which cryogenic temperatures and ultra high vacuum pressures can be reached in as little as 12 hours. The ion traps are operated either in a liquid helium bath cryostat or in a low vibration closed cycle cryostat. The fast turn around time and availability of buffer gas cooling made the systems ideal for testing surface-electrode ion traps. The vibration amplitude of the closed cycled cryostat was found to be below 106 nm. We evaluated the systems by loading surface-electrode ion traps with $^{88}$Sr$^+$ ions using laser ablation, which is compatible with the cryogenic environment. Using Doppler cooling we observed small ion crystals in which optically resolved ions have a trapped lifetime over 2500 minutes.

Chemical probing spectroscopy of H3+ above the barrier to linearity

Abstract: We have performed chemical probing spectroscopy of H3+ ions trapped in a cryogenic 22-pole ion trap. The ions were buffer gas cooled to ∼55 K by collisions with helium and argon. Excitation to states above the barrier to linearity was achieved by a Ti:sapphire laser operated between 11 300 and 13 300 cm−1. Subsequent collisions of the excited H3+ ions with argon lead to the formation of ArH+ ions that were detected by a quadrupole mass spectrometer with high sensitivity. We report the observation of 17 previously unobserved transitions to states above the barrier to linearity. Comparison to theoretical calculations suggests that the transition strengths of some of these lines are more than five orders of magnitude smaller than those of the fundamental band, which renders them—to the best of our knowledge—the weakest H3+ transitions observed to date.

Pressure shifts and broadening of the Cs D1 and D2 lines by He, N2, and Xe at densities used for optical pumping and spin exchange polarization

Abstract: The production of hyperpolarized gases by spin-exchange optical pumping (SEOP) requires exact knowledge of the alkali metal’s D1 absorption profile and the degree to which it is broadened and shifted by varying buffer gas composition and pressure. We have measured these parameters for cesium (Cs) in the presence of Xe, N2, and H4e perturber gases at densities up to 10 amagats. The effects of these gases are important as Cs is attracting increasing interest for SEOP applications. Our measurements were made using simple white-light illumination of the Cs vapor while characterizing the D1 (6S1/2 to 6P1/2) and D2 (6S1/2 to 6P3/2) resonances using a high-resolution optical spectrometer. For the Cs D1 resonance at T=120 °C, we report shifts from the 894.59 nm vacuum wavelength caused by H3e, H4e, N2, and Xe of −0.017±0.003, −0.013±0.002, 0.026±0.002, and 0.029±0.002 nm/amagat. We also report the shifts for the D2 resonance as well as pressure broadening coefficients for both resonances.

Cluster growth in an ablation plume propagating through a buffer gas

Abstract: A phenomenological mixed-propagation model that describes the expansion of an ablation plume through a buffer gas is introduced. Selected experiments including LaMnO3 and tin ablation in oxygen, as well as tungsten ablation in argon, are analysed. For given ablation conditions the expansion parameters required to model the growth of clusters in the expanding plasma plume are deduced and the average asymptotic size of the clusters is calculated and compared (for tungsten) with the size of clusters measured by transmission electron microscopy.

Effect of buffer gas ratios on the relationship between cell temperature and frequency shifts of the coherent population trapping resonance

Abstract: We studied the relationship between pressure ratio of the buffer gases (argon and neon) and the rate of coherent population trapping resonance frequency shift with cell temperature in Rb85. We found that when the total pressure of the buffer gases varies within the range of 5–15kPa, the frequency shift rate varies along a bell shaped curve. Every curve crossed the horizontal axis at two points that are roughly symmetrical with respect to the midpoint at 1:1. This allows us to minimize the rate of frequency shift by adjusting the pressure ratio of the buffer gases to these two points.

Nanoscale ferromagnetic chromium oxide film from gas-phase nanocluster deposition

Abstract: Ferromagnetic film of densely packing chromium oxide nanoparticles has been fabricated by vacuum deposition of chromium oxide clusters at room temperature. The clusters were generated with a magnetron plasma gas aggregation source by introducing a mixture of argon and oxygen as buffer gas. A magnetic hysteresis loop similar to that of bulk CrO2 was observed in a wide temperature range. The rise in the ferromagnetic property of the film was attributed to the nanoscale CrO2 composition. The work demonstrates a simple way to fabricate ferromagnetic films of chromium oxide nanoparticles under high-vacuum compatible low temperature condition.

Magnetic trapping of silver and copper, and anomalous spin relaxation in the ag-he system.

Abstract: We have trapped large numbers of copper (Cu) and silver (Ag) atoms using buffer-gas cooling. Up to 3 x 10{12} Cu atoms and 4 x 10{13} Ag atoms are trapped. Lifetimes are as long as 5 s, limited by collisions with the buffer gas. Ratios of elastic to inelastic collision rates with He are >or=10{6}, suggesting Cu and Ag are favorable for use in ultracold applications. The temperature dependence of the Ag-3He collision rate varies as T;{5.8+/-0.4}. We find that this temperature dependence is inconsistent with the behavior predicted for relaxation arising from the spin-rotation interaction, and conclude that the Ag-3He system displays anomalous collisional behavior in the multiple-partial wave regime. Gold (Au) was ablated into 3He buffer gas, however, atomic Au lifetimes were observed to be too short to permit trapping.

Nonlinear effects in pulse propagation through Doppler-broadened closed-loop atomic media

Abstract: Nonlinear effects in pulse propagation through a medium consisting of four-level double-$\ensuremath{\Lambda}$-type systems are studied theoretically. We apply three continuous-wave driving fields and a pulsed probe field such that they form a closed interaction loop. Due to the closed loop and the finite frequency width of the probe pulses, the multiphoton resonance condition cannot be fulfilled, such that a time-dependent analysis is required. By identifying the different underlying physical processes we determine the parts of the solution relevant to calculate the linear and nonlinear response of the system. We find that the system can exhibit a strong intensity-dependent refractive index with small absorption over a range of several natural linewidths. For a realistic example we include Doppler and pressure broadening and calculate the nonlinear self-phase modulation in a gas cell with sodium vapor and argon buffer gas. We find that a self-phase modulation of $\ensuremath{\pi}$ is achieved after the propagation of a few centimeters through the medium while the absorption and pulse shape distortion in the corresponding spectral range is small.

Spectroscopy of atomic rubidium at 500 − bar buffer gas pressure: Approaching the thermal equilibrium of dressed atom-light states

Abstract: We have recorded fluorescence spectra of the atomic rubidium D-lines in the presence of several hundreds of bars of buffer gas pressure. The large collisional broadening of this system interpolates between usual atomic physics gas phase and solid-liquid phase conditions. In our buffer gas cell, with additional saturation broadening, a spectral linewidth comparable to the thermal energy of the atoms in the cell is achieved. An observed intensity-dependent blue asymmetry of the spectra is interpreted as evidence for the onset of thermal equilibrium of dressed atom-light states.

New concepts for the ion guide technique

Abstract: The technique of using noble gases to cool energetic beams offers fast extraction times, very little sensitivity to chemical properties of the ions and very low-energy spreads. A variant of this method is based on the selective laser ionization of radioactive species after they have been thermalized in gas as neutral atoms. The laser ion source in Jyvaskyla is used to highlight the importance of buffer gas purity using yttrium, a particularly chemically reactive element. The time distribution profiles obtained on-line illustrate the competing factors that create and destroy the ion of interest during evacuation from the ion guide. A review of the extraction efficiencies of gas catchers of different volumes, buffer gases, projectile energies and electric fields all show a common decrease as a function of ionization-rate density. The reasons for this decline and possible solutions to tolerate higher primary beam intensities are discussed.

Production of long-lived atomic vapor inside high-density buffer gas

Abstract: (Dated: February 1, 2008)Atomic vapor of four different paramagnetic species: gold, silver, lithium, and rubidium, is pro-duced and studied inside several buffer gases: helium, nitrogen, neon, and argon. The paramagneticatoms are injected into the buffer gas using laser ablation. Wires with diameters 25 µm, 50 µm,and 100 µm are used as ablation targets for gold and silver, bulk targets are used for lithium andrubidium. The buffer gas cools and confines the ablated atoms, slowing down their transport to thecell walls. Buffer gas temperatures between 20 K and 295 K, and densities between 10

Conformal filling of silicon micropillar platform with b10oron

Abstract: A recently proposed micropillar semiconductor platform filled with a high volume of isotopic b10oron (B10) has great potential to yield efficient thermal neutron detectors because B10 has a high thermal neutron cross section Here, the authors report the development of conformal filling of high aspect ratio silicon micropillar platforms with B10 by low pressure chemical vapor deposition (LPCVD) using B10-enriched decaborane (B10H14) The relationships between the pillar structure and the key process parameters including reaction temperature, process pressure, and buffer gas flow rates were investigated to optimize the conformal filling on these structures Reaction temperature of 420–530 °C, process pressure of 50–450 mTorr, 03 SCCM (SCCM denotes cubic centimeter per minute at STP) B10H14 flow rate, and argon buffer gas flow rate of 0–200 SCCM were used to deposit B10 materials into the micropillar structures with aspect ratios of 3:1, 6:1, and 10:1 All three mentioned pillar structures were found to be

Two-step formation of hydrocarbon-based polymer film

Abstract: A method of forming a surface-treated hydrocarbon-based polymer film includes: supplying a hydrocarbon gas as a source gas, and an inert gas, and applying RF power to generate a plasma and form a hydrocarbon-based principal film on a substrate; and without extinguishing a plasma, changing flow of the hydrocarbon gas and the inert gas by continuously decreasing a flow ratio of the hydrocarbon gas to the inert gas with time to treat a surface of the principal film on the substrate

Simulations for Ion Traps Buffer Gas Cooling

Abstract: Buffer gas cooling of ions in traps and radiofrequency ion guides has become the method of choice to improve the quality of continuous ion beams and to provide cooled ion bunches with low emittance and small energy spread. The method is chemically unselective and has consequently been applied to manipulate ion beams ranging from He to the heaviest elements. Depending on the buffer gas type and pressure, cooling times can be as low as a few milliseconds. The transmission efficiency of today’s buffer gas coolers is approaching unity. These features make buffer gas coolers particularly useful at rare-isotope facilities, where speed, applicability, efficiency and good beam properties are essential to perform precision experiments with nuclei far from the valley of beta stability. Two types of gas-filled coolers/bunchers are currently in use at rare-isotope facilities. They are based on linear Paul traps and on Penning traps: First the externally produced ions are electrostatically slowed down to a few electron-volt energy and injected into the gas-filled ion trap. For deceleration, the central trap electrodes are typically operated at a pedestal voltage close to beam potential. Inside the trap the ions are slowed down by collisions with buffer gas molecules and accumulate in the effective potential well provided by the ion trap. Finally, the cooled ion cloud is ejected out of the trap by a strong electric field and the ion pulse is then reaccelerated to a desired beam energy. A radiofrequency (RF) multipole ion guide uses RF electric fields for the transverse confinement of ions and employs DC electric fields in the axial direction to

Photodissociation and collisional cooling of rhodamine 575 cations in a quadrupole ion trap.

Abstract: The photodissociation of rhodamine 575 cations held in a quadrupole ion trap is studied using 514 nm light as a function of buffer gas pressure, irradiation time, and laser fluence. The laser-induced photodissociation decays of rhodamine ions have lifetimes on the order of seconds for the range of pressures and powers investigated and exhibit strong nonlinear pressure dependence. Dissociation mechanisms are considered that involve the sequential absorption of multiple photons and several collisional deactivation steps.

Characterization of the LISOL laser ion source using spontaneous fission of 252Cf

Abstract: A spontaneous fission Californium-252 source was placed inside a gas cell in order to characterize the LISOL laser ion source. The fission products from 252Cf are thermalized and neutralized in the plasma created by energetic particles. Two-step selective laser ionization is applied to produce purified beams of radioactive isotopes. The survival of fission products in a single charge state has been studied in argon as a buffer gas for different elements.

Pulsed extraction of ionization from helium buffer gas

Abstract: The migration of intense ionization created in helium buffer gas under the influence of applied electric fields is considered. First the chemical evolution of the ionization created by fast heavy-ion beams is described. Straight forward estimates of the lifetimes for charge exchange indicate a clear suppression of charge exchange during ion migration in low pressure helium. Then self-consistent calculations of the migration of the ions in the electric field of a gas-filled cell at the National Superconducting Cyclotron Laboratory (NSCL) using a particle-in-cell computer code are presented. The results of the calculations are compared to measurements of the extracted ion current caused by beam pulses injected into the NSCL gas cell.

Ultralong aligned multi-walled carbon nanotube for electrochemical sensing.

Abstract: We have investigated electrochemical sensing properties of electrodes fabricated with ultralong aligned multi-walled carbon nanotube (MWNT) bundles synthesized using water-assisted chemical vapor deposition on aluminum (Al) and iron (Fe) coated silicon wafer with ethylene and argon/hydrogen gas as carbon source and buffer gas respectively. Cyclic voltammograms performed on these electrodes show diffusion-controlled-reversible reaction. The dominance of radial diffusion mass transport at these electrodes was also indicated by sigmoidal-shaped voltammograms obtained at various scan rates. These electrodes were able to sense very low concentration of ascorbic acid (approximately 0.7 microM) and dopamine (approximately 1.87 microM), two model species often used in electro-analysis. The excellent electrochemical properties along with good single species detection ability suggest that these MWNTs are promising electrode materials for developing very sensitive chemical and/or biological sensors.

Distant dipolar fields in laser-polarized gases on macroscopic scales

Abstract: Distant dipolar fields among nuclear spins on macroscopic scales in the gas phase are reported for the first time. Their observation via interatomic multiple quantum coherences requires high nuclear spin polarization corresponding to spin temperatures of a few mK, which is generated in laser-polarized 3He, and proper control of the gas diffusion through a heavier buffer gas. This combination of physics at low and ambient temperatures opens up new ways of studying the relative translational diffusion of atoms and of gas diffusion in structures with a large range of length scales.

Spectroscopy and dissociative recombination of the lowest rotational states of H3

Abstract: The dissociative recombination of the lowest rotational states of H3+ has been investigated at the storage ring TSR using a cryogenic 22-pole radiofrequency ion trap as injector. The H3+ was cooled with buffer gas at ~15 K to the lowest rotational levels, (J,G)=(1,0) and (1,1), which belong to the ortho and para proton-spin symmetry, respectively. The rate coefficients and dissociation dynamics of H3+(J,G) populations produced with normal- and para-H2 were measured and compared to the rate and dynamics of a hot H3+ beam from a Penning source. The production of cold H3+ rotational populations was separately studied by rovibrational laser spectroscopy using chemical probing with argon around 55 K. First results indicate a ~20% relative increase of the para contribution when using para-H2 as parent gas. The H3+ rate coefficient observed for the para-H2 source gas, however, is quite similar to the H3+ rate for the normal-H2 source gas. The recombination dynamics confirm that for both source gases, only small populations of rotationally excited levels are present. The distribution of 3-body fragmentation geometries displays a broad part of various triangular shapes with an enhancement of ~12% for events with symmetric near-linear configurations. No large dependences on internal state or collision energy are found.

Competition between convection and diffusion in a metal halide lamp, investigated by numerical simulations and imaging laser absorption spectroscopy

Abstract: The effect of the competition between convection and diffusion on the distribution of metal halide additives in a high pressure mercury lamp has been examined by placing COST reference lamps with mercury fillings of 5 and 10 mg in a centrifuge. By subjecting them to different accelerational conditions the convection speed of the mercury buffer gas is affected. The resulting distribution of the additives, in this case dysprosium iodide, has been studied by numerical simulations and measurements of the density of dysprosium atoms in the ground state using imaging laser spectroscopy. The competition between axial convection and radial diffusion determines the degree of axial segregation of the dysprosium additives.

Numerical simulations of space charge effects and plasma dynamics for FEBIAD ion sources

Abstract: The FEBIAD (“forced electron beam induced arc discharge”) ion sources are used for the production of radioactive ion beams for a wide range of chemical elements. Their small volume and high operating temperature provide good confinement times and ionization efficiencies. The extracted ion current from a FEBIAD ion source depends on the parameters of the plasma created inside (density, temperature, potential), parameters which are themselves dependent on the input gas pressure and composition. Within the framework of the HIGHINT Marie Curie and the EURISOL DS programs, investigations are ongoing for high power direct targets, which can accommodate up to 100 kW incoming proton beam power. For such systems, the quantity of impurities entering the ion source will increase, thus leading to a change of the plasma characteristics. The gas flow coming from the target will exceed the buffer gas flow, and the ionization of the trace elements will be controlled by the gas composition released from the target. An insight on the complex phenomena taking place in the ion source can be achieved using a Particle-In-Cell code (VORPAL, “versatile, object-oriented, relativistic, plasma analysis code with lasers”), which can simulate the dynamics of neutral and charged particles inside the plasma: ionization, recombination and charge exchange phenomena, secondary emissions and sputtering.

Depolarizing collision anisotropy and collision echo in ytterbium vapor

Abstract: A photon echo induced exclusively by collisions of ytterbium atoms with buffer gas atoms has been observed at a 0 ⟷ 1-type1S0(6s2)-3P1(6s6p) 174Yb transition. The polarization properties of a collision echo and the buffer gas density dependence of its intensity agree with theoretical predictions of a model of depolarizing collisions that takes into account the dependence of a relaxation matrix on the velocity of active particles. Thus, direct experimental evidence of the relaxation anisotropy due to depolarizing collisions has been obtained.

Resonance transition 795-nm rubidium laser using He buffer gas

Abstract: Resonance transition rubidium laser (5 2 P 1/2 →5 2 S 1/2 ) is demonstrated with a hydrocarbon-free buffer gas. Prior demonstrations of alkali resonance transition lasers have used ethane as either the buffer gas or a buffer gas component to promote rapid fine-structure mixing. However, our experience suggests that the alkali vapor reacts with the ethane producing carbon as one of the reaction products. This degrades long term laser reliability. Our recent experimental results with a "clean" helium-only buffer gas system pumped by a Ti:sapphire laser demonstrate all the advantages of the original alkali laser system, but without the reliability issues associated with the use of ethane. We further report a demonstration of a rubidium laser using a buffer gas consisting of pure 3 He. Using isotopically enriched 3 He gas yields enhanced mixing of the Rb fine-structure levels. This enables efficient lasing at reduced He buffer gas pressure, improved thermal management in high average power Rb lasers and enhanced power scaling potential of such systems.

Hydrocarbon-free resonance transition 795-nm rubidium laser

Abstract: An optical resonance transition rubidium laser (52P1/2 → 52S1/2) is demonstrated with a hydrocarbon-free buffer gas. Prior demonstrations of alkali resonance transition lasers have used ethane as either the buffer gas or a buffer gas component to promote rapid fine-structure mixing. However, our experience suggests that the alkali vapor reacts with the ethane producing carbon as one of the reaction products. This degrades long term laser reliability. Our recent experimental results with a "clean" helium-only buffer gas system pumped by a Ti:sapphire laser demonstrate all the advantages of the original alkali laser system, but without the reliability issues associated with the use of ethane.

Chemical Oxygen-Iodine Laser Diluted by CO2/N2 Buffer Gases with a Cryosorption Vacuum Pump

Abstract: Experiments were carried out on a verti-chemical oxygen-iodine laser (COIL), which was designed for N-2 and energized by a square-pipe jet singlet oxygen generator (JSOG). A cryosorption vacuum pump was used as the pressure recovery system for CO2 and N-2 buffer gases. The output power with CO2 was 27.3% lower than that with N-2, but the zeolite bed showed an adsorption capacity threefold higher for CO2 than for N-2 in the continuous operation with a Cl-2 flow rate of 155 mmol/s and a total flow rate of 430 +/- 3 mmol/s. [DOI: 10.1143/JJAP.47.8446]