Showing papers on "Time of flight published in 2014"

An Iodide-Adduct High-Resolution Time-of-Flight Chemical-Ionization Mass Spectrometer: Application to Atmospheric Inorganic and Organic Compounds

Abstract: A high-resolution time-of-flight chemical-ionization mass spectrometer (HR-ToF-CIMS) using Iodide-adducts has been characterized and deployed in several laboratory and field studies to measure a suite of organic and inorganic atmospheric species. The large negative mass defect of Iodide, combined with soft ionization and the high mass-accuracy ( 5500) of the time-of-flight mass spectrometer, provides an additional degree of separation and allows for the determination of elemental compositions for the vast majority of detected ions. Laboratory characterization reveals Iodide-adduct ionization generally exhibits increasing sensitivity toward more polar or acidic volatile organic compounds. Simultaneous retrieval of a wide range of mass-to-charge ratios (m/Q from 25 to 625 Th) at a high frequency (>1 Hz) provides a comprehensive view of atmospheric oxidative chemistry, particularly when sampling rapidly evolving plumes from fast moving platforms like an aircraft. We pres...

Optical phase noise from atmospheric fluctuations and its impact on optical time-frequency transfer

Abstract: The time of flight for a laser beam through the atmosphere will fluctuate as the path-averaged index of refraction varies with atmospheric turbulence, air temperature, and pressure. We measure these fluctuations by transmitting optical pulses from a frequency comb across a 2-km horizontal path and detecting variations in their time of flight through linear optical sampling. This technique is capable of continuous measurements, with femtosecond resolution, over time scales of many hours despite turbulence-induced signal fading. The power spectral density for the time of flight, or equivalently for the optical phase, follows a simple power-law response of $\ensuremath{\propto}$${f}^{\ensuremath{-}2.3}$ measured down to Fourier frequencies, $f$, of 100 \ensuremath{\mu}Hz. There is no evidence of a roll-off at low frequencies associated with an outer scale for turbulence. Both of these results depart from the predictions of turbulence theory, but are consistent with some other results in the literature. We discuss the implications for the stability and accuracy of one-way optical time-frequency transfer.

Time-of-flight - Energy spectrometer for elemental depth profiling - Jyväskylä design

Abstract: A new time-of-flight elastic recoil detection spectrometer has been built, and initially the main effort was focused in getting good timing resolution and high detection efficiency for light elements. With the ready system, a 154 ps timing resolution was recorded for scattered 4.8 MeV 4 He 2+ ions. The hydrogen detection efficiency was from 80% to 20% for energies from 100 keV to 1 MeV, respectively, and this was achieved by having an additional atomic layer deposited Al 2 O 3 coating on the first timing detector’s carbon foil. The data acquisition system utilizes an FPGA-card to time-stamp every time-of-flight and energy event with 25 ns resolution. The different origins of the background events in coincident time-of-flight-energy histograms have been studied and explained. The built system has proved to be able to routinely depth profile films thinner than 10 nm.

New perspectives in the surface analysis of energy materials by combined time-of-flight secondary ion mass spectrometry (ToF-SIMS) and high sensitivity low-energy ion scattering (HS-LEIS)

Abstract: Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and low-energy ion scattering (LEIS) are recently attracting great interest in energy materials research due to their capabilities in terms of surface sensitivity and specificity, spatial resolution and their ability to analyse the isotopic chemical composition. This work shows the synergy provided by this powerful combination to further our understanding of the surface chemistry and structure that ultimately determines the electrochemical performance in advanced electro-ceramic materials for energy storage and energy conversion applications. In particular, this novel approach has been applied to the analysis of (Li3xLa2/3−x□1/3−2x)TiO3 perovskite materials used as the electrolyte in lithium batteries and (La, Sr)2CoO4+δ epitaxial thin films used as oxygen electrodes in solid oxide fuel cells and solid oxide electrolysers. The analysis of these two promising materials requires the development and optimisation of new analytical approaches that take advantage of the recent instrumental developments in order to characterise the outermost and near-surfaces at the atomic scale.

Time-of-flight detectors with improved timing performance for isochronous mass measurements at the CSRe

Abstract: In isochronous mass spectrometry (IMS) established in heavy-ion storage rings the revolution times of the stored secondary ions should be independent of their velocity spread. However, this isochronous condition is fulfilled only in first order and in a small range of revolution times. To correct for the non-isochronicity an additional measure of the velocity or magnetic rigidity of each stored ion is required. For this purpose two new time-of-flight (TOF) detectors were installed in a straight section of the experimental Cooler Storage Ring CSRe in Lanzhou. The performance of the new time-of-flight (TOF) detectors, which is crucial for the achievable efficiencies and mass resolving power, was significantly improved. The time resolution of the TOF detector in offline tests was σ = 18.5 ± 2 ps . The detector setup was put into operation with a stable beam of 78Kr.

Development of mass spectrometry by high energy focused heavy ion beam: MeV SIMS with 8 MeV Cl7+ beam

Abstract: Particle induced X-ray emission (PIXE) at microprobe of Jožef Stefan Institute is used to measure two-dimensional quantitative elemental maps of biological tissue. To improve chemical and biological understanding of the processes in vivo, supplementary information about chemical bonding and/or molecular distributions could be obtained by heavy-ion induced molecular desorption and a corresponding mass spectroscopy with Time-Of-Flight (TOF) mass spectrometer. As the method combines the use of heavy focused ions in MeV energy range and TOF Secondary Ion Mass Spectrometry, it is denoted as MeV SIMS. At Jožef Stefan Institute, we constructed a linear TOF spectrometer and mount it to our multipurpose nuclear microprobe. A beam of 8 MeV 35Cl7+ could be focused to a diameter of better than 3 μm × 3 μm and pulsed by electrostatic deflection at the high-energy side of accelerator. TOF mass spectrometer incorporates an 1 m long drift tube and a double stack microchannel plate (MCP) as a stop detector positioned at the end of the drift path. Secondary ions are focused at MCP using electrostatic cylindrical einzel lens. Time of flight spectra are currently acquired with a single-hit time-to-digital converter. Pulsed ion beam produces a shower of secondary ions that are ejected from positively biased target and accelerated towards MCP. We start our time measurement simultaneously with the start of the beam pulse. Signal of the first ion hitting MCP is used to stop the time measurement. Standard pulses proportional to the time of flight are produced with time to analog converter (TAC) and fed into analog-to-digital converter to obtain a time histogram. To enable efficient detection of desorbed fragments with higher molecular masses, which are of particular interest, we recently implemented a state-of art Field Programmable Gate Array (FPGA)-based multi-hit TOF acquisition. To test the system we used focused 8 MeV 35Cl7+ ion beam with pulse length of 180 ns. Mass resolution of measured SIMS spectra, dominantly determined by the duration of the beam pulse, is in good agreement with resolution estimated from pulse length. With improved high-voltage switching ability that will enable beam pulses with duration of 50 ns, a mass resolution of better than 500 is anticipated.

Relationship between Mobilities from Time-of-Flight and Dark-Injection Space-Charge-Limited Current Measurements for Organic Semiconductors: A Monte Carlo Study

Abstract: The dark-injection space-charge-limited current (DI-SCLC) and the time-of-flight (TOF) measurements are both widely used methods to obtain the charge mobilities of organic materials. The current formula used to calculate the mobility in the DI-SCLC measurement is based on the relationship that the peak time equals 0.787 times the transit time in the TOF measurement. This conclusion, however, is reached by assuming a constant mobility and a negligible carrier diffusion, which is not valid for organic materials. Here, we perform Monte Carlo simulations of the multiparticle charge carrier movement in the TOF and DI-SCLC measurements. We found that the relationship between the peak time and the transit time depends on the disorder of the system. For organic semiconductors, the current formula used in the DI-SCLC measurement is only valid when the energetic disorder is small or when the temperature is high, and large deviation will occur otherwise, which is due to the enhanced charge transport induced by high ...

A simple electron time-of-flight spectrometer for ultrafast vacuum ultraviolet photoelectron spectroscopy of liquid solutions

Abstract: We present a simple electron time of flight spectrometer for time resolved photoelectron spectroscopy of liquid samples using a vacuum ultraviolet (VUV) source produced by high-harmonic generation. The field free spectrometer coupled with the time-preserving monochromator for the VUV at the Artemis facility of the Rutherford Appleton Laboratory achieves an energy resolution of 0.65 eV at 40 eV with a sub 100 fs temporal resolution. A key feature of the design is a differentially pumped drift tube allowing a microliquid jet to be aligned and started at ambient atmosphere while preserving a pressure of 10−1 mbar at the micro channel plate detector. The pumping requirements for photoelectron (PE) spectroscopy in vacuum are presented, while the instrument performance is demonstrated with PE spectra of salt solutions in water. The capability of the instrument for time resolved measurements is demonstrated by observing the ultrafast (50 fs) vibrational excitation of water leading to temporary proton transfer.

Time-of-flight spectra for mapping of charge density of ions produced by laser

Abstract: Aspace-resolvedchargedensityofionsisderivedfromatime-resolvedcurrentofionsemittedfromlaser-producedplasmaandexpandedintothevacuumalongcollision-freeandfield-freepaths.Thisderivationisbasedonasimilarityrelationshipforioncurrentswith “frozen”charges observedatdifferentdistancesfromthetarget. This relationship makes itpossibletodetermine a map of ion charge density at selected times after the laser plasma interaction from signals of time-of-flightdetectors positioned at a certain distance from the target around a target-surface normal. In this work, we present mapsof the charge density of ions emitted from Cu and polyethylene plasmas. The mapping demonstrates that bursts of ionsare emitted at various ejection angles f n with respect to the target-surface normal. There are two basic directions f 1 and f 2 , one belonging to the fastest ions, i.e., protons and carbon ions, and the other one to the slowest ions being apart of each plasma plume.Keywords: Angular distribution of slow and fast ions; Ion expansion; Laser ion sources; Map of ion charge density;Modeling

A simple electron time-of-flight spectrometer for ultrafast VUV photoelectron spectroscopy of liquid solutions

Abstract: We present a simple electron time of flight spectrometer for time resolved photoelectron spectroscopy of liquid samples using a vacuum ultraviolet (VUV) source produced by high-harmonic generation. The field free spectrometer coupled with the time-preserving monochromator for the VUV at the Artemis facility of the Rutherford Appleton Laboratory achieves an energy resolution of 0.65 eV at 40 eV with a sub 100 fs temporal resolution. A key feature of the design is a differentially pumped drift tube allowing a microliquid jet to be aligned and started at ambient atmosphere while preserving a pressure of 10(-1) mbar at the micro channel plate detector. The pumping requirements for photoelectron (PE) spectroscopy in vacuum are presented, while the instrument performance is demonstrated with PE spectra of salt solutions in water. The capability of the instrument for time resolved measurements is demonstrated by observing the ultrafast (50 fs) vibrational excitation of water leading to temporary proton transfer.

Signal processing for the measurement of the deuterium/hydrogen ratio in the local interstellar medium

Abstract: We report on a comprehensive signal processing procedure for very low signal levels for the measurement of neutral deuterium in the local interstellar medium from a spacecraft in Earth orbit. The deuterium measurements were performed with the IBEX-Lo camera on NASA’s Interstellar Boundary Explorer (IBEX) satellite. Our analysis technique for these data consists of creating a mass relation in three-dimensional time of flight space to accurately determine the position of the predicted D events, to precisely model the tail of the H events in the region where the H tail events are near the expected D events, and then to separate the H tail from the observations to extract the very faint D signal. This interstellar D signal, which is expected to be a few counts per year, is extracted from a strong terrestrial background signal, consisting of sputter products from the sensor’s conversion surface. As reference we accurately measure the terrestrial D/H ratio in these sputtered products and then discriminate this terrestrial background source. During the three years of the mission time when the deuterium signal was visible to IBEX, the observation geometry and orbit allowed for a total observation time of 115.3 days. Because of the spinning of the spacecraft and the stepping through eight energy channels the actual observing time of the interstellar wind was only 1.44 days. With the optimised data analysis we found three counts that could be attributed to interstellar deuterium. These results update our earlier work.

TNSA ion acceleration at 10 16 W/cm 2 sub-nanosecond laser intensity

Abstract: Micrometric thin targets have been irradiated in vacuum in TNSA (Target Normal Sheath Acceleration) configuration at PALS Laboratory in Prague by using 1016 W/cm2 laser intensity, 1315 nm wavelength, 300 ps pulse duration and different laser beam energies and focal positions. The plasmas produced were characterized by using ion collectors, semiconductor SiC detectors, X-ray streak camera and Thomson parabola spectrometer. Time of flight techniques, time resolved imaging and ion deflection spectrometry were used to characterize the laser-generated non-equilibrium plasma and the electric field driving ion acceleration developed at the rear side of the target. The maximum ion acceleration can be obtained for optimal film thickness depending on the laser energy and on the kind of irradiated targets. Special targets containing nanostructures, showing high absorption and low reflective coefficients, induce resonant absorption effects enhancing the electric acceleration field. The maximum kinetic energy measured for proton ions was above 5.0 MeV and the ion distributions can be fitted with Coulomb-Boltzmann shifted functions.

Information on the Aromatic Structure of Internal Diesel Injector Deposits From Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS)

Abstract: The nature of internal diesel injector deposits (IDID) continues to be of importance to the industry, with field problems such as injector sticking, loss of power, increased emissions and fuel consumption being found. The deposits have their origins in the changes in emission regulations that have seen increasingly severe conditions experienced by fuels because of high temperatures and high pressures of modern common rail systems and the introduction of low sulphur fuels. Furthermore, the effect of these deposits is amplified by the tight engineering tolerances of the moving parts of such systems. The nature and thus understanding of such deposits is necessary to both minimising their formation and the development of effective diesel deposit control additives (DCA). The focused ion beam technique coupled with time of flight secondary -ion mass spectrometry (ToF-SIMS) has the ability to provide information on diesel engine injector deposits as a function of depth for both organic and inorganic constituents. Our previous work with this novel technique is unique in that it has shown layering effects in deposits which may be due to the residual fuel either evaporating and leaving residues or being unable to keep insoluble residues in solution during the injection process. As part of our on-going work to understand the nature of field deposits, the aromatic compounds present have been investigated. To help interpret the results for the aromatic structures present, spectra of a model polycyclic aromatic hydrocarbon (PAH), coronene (C24H12), and coal tar pitch (CTP) have been used as a basis to determine the ring structure of internal diesel; deposits. This work confirms the presence of aromatic ring structures of greater than six rings in composition in injector needle carbonaceous deposits. Introduction The current industry interest in internal diesel injector deposits (IDID) shows no sign of decline. In fact, CRC (Central Research Council Diesel Performance Group-Deposit Panel Bench/Rig/Investigation sub panel), CEN (Committee European de NormalisationTC19/WG24Injector Deposit Task Force, engine test, and CEC (Coordinating European Council TDFG-110) in Europe have sub committees and panels investigating the production and characterization of these deposits. This interest continues because injector malfunction is manifested in: • Reduced fuel economy • Higher emissions • Misfiring

Depth-resolved grazing-incidence time-of-flight neutron scattering from a solid–liquid interface

Abstract: Small-angle scattering in grazing-incidence beam geometry has been applied on a time-of-flight neutron instrument to investigate a solid–liquid boundary. Owing to the broad wavelength distribution provided for a specific incident beam angle, the penetration depth of the neutron beam is varied over a wide range in a single measurement. The near surface structures of block copolymer micelles close to silicon substrates with distinct surface energies are resolved. It is observed that the very near surface structure strongly depends on the surface coating, whereas further away from the surface, bulk-like ordering is found.

Time of flight emission spectroscopy of laser produced nickel plasma: Short-pulse and ultrafast excitations

Abstract: We report the experimental investigation and comparison of the temporal features of short-pulse (7 ns) and ultrafast (100 fs) laser produced plasmas generated from a solid nickel target, expanding into a nitrogen background. When the ambient pressure is varied in a large range of 10−6 Torr to 102 Torr, the plume intensity is found to increase rapidly as the pressure crosses 1 Torr. Time of flight (TOF) spectroscopy of emission from neutral nickel (Ni I) at 361.9 nm (3d9(2D) 4p → 3d9(2D) 4s transition) reveals two peaks (fast and slow species) in short-pulse excitation and a single peak in ultrafast excitation. The fast and slow peaks represent recombined neutrals and un-ionized neutrals, respectively. TOF emission from singly ionized nickel (Ni II) studied using the 428.5 nm (3p63d8(3P) 4s→ 3p63d9 4s) transition shows only a single peak for either excitation. Velocities of the neutral and ionic species are determined from TOF measurements carried out at different positions (i.e., at distances of 2 mm and ...

Time-of-flight measurement of fast neutrons with Timepix detectors

Abstract: Timepix pixel detectors have been used to study the response of silicon hybrid pixel detectors to fast neutrons from a pulsed neutron beam at WNR FP30R, a 14 m long flight path, in the Los Alamos Neutron Science Center. Neutrons with kinetic energies up to 600 MeV were available. In order to enhance the conversion of neutrons to energetic charged particles, several converter foils and filters were attached to the 300 μm thick silicon sensor, i.e. polyethylene, polyethylene with aluminum, 6LiF, 6LiF with aluminum, aluminum. The Time-of-Arrival mode of the Timepix detectors has permitted the application of the Time-of-Flight (TOF) technique for the assignment of the detected interactions in the form of clusters (groups of adjacent pixels) in the pixel matrix, to the kinetic energies of the incident neutrons. It was found that, for lower neutron energies ( ~ MeV range) the cluster rates below the polyethylene and the polyethylene and aluminum region, produced by recoil protons, are a good measure for the mean kinetic energies of neutrons. For energies above 50 MeV nuclear reactions in the silicon dominate the detector response. In this energy range the shape of the clusters indicates the neutron kinetic energy.

Development of position-sensitive time-of-flight spectrometer for fission fragment research

Abstract: A position-sensitive, high-resolution time-of-flight detector for fission fragments has been developed. The SPectrometer for Ion DEtermination in fission Research (SPIDER) is a 2 E –2 v spectrometer designed to measure the mass of light fission fragments to a single mass unit. The time pick-off detector pairs to be used in SPIDER have been tested with α-particles from 229 Th and its decay chain and α-particles and spontaneous fission fragments from 252 Cf. Each detector module is comprised of thin electron conversion foil, electrostatic mirror, microchannel plates, and delay-line anodes. Particle trajectories on the order of 700 mm are determined accurately to within 0.7 mm. Flight times were measured with 250 ps resolution FWHM. Computed particle velocities are accurate to within 0.06 mm/ns corresponding to a precision of 0.5%. An ionization chamber capable of 400 keV energy resolution coupled with the velocity measurements described here will pave the way for modestly efficient measurements of light fission fragments with unit mass resolution.

Method for evaluating position and motion using time of flight detectors

Abstract: A method is for evaluating a coverage factor of a photon emission cone of a time of flight sensor. The method may include the steps of assigning a reference curve to the sensory providing a photon flux intensity as a function of time of flight; and acquiring a time of flight and a corresponding flux intensity with the sensor. The method may also include reading the intensity provided by the reference curve for the acquired time of flight, and providing an indication of the coverage factor based on the ratio between the acquired intensity and the read intensity.

A novel “correlated ion and neutral time of flight” method: Event-by-event detection of neutral and charged fragments in collision induced dissociation of mass selected ions

Abstract: A new tandem mass spectrometry (MS/MS) method based on time of flight measurements performed on an event-by-event detection technique is presented. This “correlated ion and neutral time of flight” method allows to explore Collision Induced Dissociation (CID) fragmentation processes by directly identifying not only all ions and neutral fragments produced but also their arrival time correlations within each single fragmentation event from a dissociating molecular ion. This constitutes a new step in the characterization of molecular ions. The method will be illustrated here for a prototypical case involving CID of protonated water clusters H+(H2O)n = 1–5 upon collisions with argon atoms.

Use of Natural Fluctuations of Flow Parameters for Measurement of Velocity Vector

Abstract: The main drawback of standard hot-wire anemometric methods consists of the difficulty in their employment and a considerable measurement uncertainty in the case of flows in which high-amplitude fluctuations of temperature or other physical quantities occur. It is caused by the interaction between these fluctuations and measurement signal. In this paper, we propose a method for the determination of 2- or 3-D velocity vector of fluids flow or gases based on the employment of several detectors of fluctuations of temperature, velocity, or other physical quantity propagating with the velocity equal to the velocity of flow of the medium or higher by a known value. By analyzing the signals obtained by the detectors, the times of flight required for flat isophase surface of fluctuation to travel between the detectors in the direction of velocity vector are determined. On their basis, the flow velocity vector is calculated using the system of equations of motion of flat isophase surface of fluctuation. In this paper, we present an idea of this measurement method, developed sensor and measurement system, algorithm for signal processing, examples of measurement signals, and we also show the potential area of applicability. Considering the fact that the proposed measurement method is based on measurement of the path and time of flight of a fluctuation, the system implements an absolute measurement of velocity vector and does not require any calibration to be carried out in the flow of known parameters. In addition, the measurement is insensitive to the change in the parameters of the flowing medium.

CHAPTER 5:Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS): Principles and Practice in the Biogeosciences

Abstract: Time-of-flight secondary ion mass spectrometry (TOF-SIMS) provides chemical information on the outermost molecular layers of sample surfaces without solvent extraction. In TOF-SIMS, a pulsed beam of high-energy ions (primary ions) is scanned over a selected analysis area on the sample. During the primary ion bombardment, neutral and charged particles (secondary ions) are released from the outermost molecular layers of the sample surface. Analysis of the secondary ions in a TOF analyser yields a mass spectral data set that allows the retrospective production of(1) ion images showing the spatial signal intensity distribution from selected ions over the analysis area; (2) mass spectra from the total analysis area; or (3) mass spectra from user-defined regions of interest inside the analysis area. In the so-called static SIMS regime, the primary ions are provided in very short pulses and the analysis is completed before the incoming primary ions damage a significant fraction of the surface. Static TOF-SIMS is therefore capable of providing molecularly specific secondary ions, and thus mass spectra with detailed organic information, which is not possible with other (‘dynamic’) SIMS techniques. In this chapter, we describe the principles of static TOF-SIMS instrumentation and data evaluation, review a number of relevant applications, and discuss the potential of this technique in the biogeosciences, with a focus on organic biomarker applications.

Spin-polarized hydrogen Rydberg time-of-flight: experimental measurement of the velocity-dependent H atom spin-polarization.

Abstract: We have developed a new experimental method allowing direct detection of the velocity dependent spin-polarization of hydrogen atoms produced in photodissociation. The technique, which is a variation on the H atom Rydberg time-of-flight method, employs a double-resonance excitation scheme and experimental geometry that yields the two coherent orientation parameters as a function of recoil speed for scattering perpendicular to the laser propagation direction. The approach, apparatus, and optical layout we employ are described here in detail and demonstrated in application to HBr and DBr photolysis at 213 nm. We also discuss the theoretical foundation for the approach, as well as the resolution and sensitivity we achieve.