Ion mobility time of flight measurements: effect of experimental parameters on measurements in a non-hydrogen bonded system
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Time-of-Flight
Abstract Time‐of‐flight (TOF) systems are one of the most widely used mass analyzers in native mass spectrometry (nMS) for the analysis of non‐covalent multiply charged bio‐macromolecular assemblies (MMAs). Typically, microchannel plates (MCPs) are employed for high mass native ion detection in TOF MS. MCPs are well known for their reduced detection efficiency when impinged by large slow moving ions. Here, a position‐ and time‐sensitive Timepix (TPX) detector has been added to the back of a dual MCP stack to study the key factors that affect MCP performance for MMA ions generated by nMS. The footprint size of the secondary electron cloud generated by the MCP on the TPX for each individual ion event is analyzed as a measure of MCP performance at each mass‐to‐charge ( m/z ) value and resulted in a Poisson distribution. This allowed us to investigate the dependency of ion mass, ion charge, ion velocity, acceleration voltage, and MCP bias voltage on MCP response in the high mass low velocity regime. The study of measurement ranges; ion mass = 195 to 802,000 Da, ion velocity = 8.4 to 67.4 km/s, and ion charge = 1+ to 72+, extended the previously examined mass range and characterized MCP performance for multiply charged species. We derived a MCP performance equation based on two independent ion properties, ion mass and charge, from these results, which enables rapid MCP tuning for single MMA ion detection.
Microchannel plate detector
Time-of-Flight
Characterization
Microchannel
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Various combinations of B/sup +/, H/sup +/, and H/sub 2//sup +/ ions were implanted into Czochralski-grown 20 /spl Omega/-cm, phosphorus-doped, (100) silicon wafers at energies such that their respective projected ranges differ. The implanted silicon was annealed in Ar gas at 1000/spl deg/C for 30 min. The B and H atom distributions on the annealed samples were independent of the dose and energy of hydrogen ions. The carrier distributions, however, depended strongly on the dose and energy of hydrogen ions: they became shallower with increasing dose of hydrogen ions; when hydrogen ions were implanted at energies such that the projected range was smaller than that of B ions, the carrier distributions were strongly dependent on the dose of hydrogen ions, rather than that in silicon when hydrogen ions were implanted at the projected range smaller than B ions.
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Abstract It is shown that for type 304L stainless steel at room temperature and ion energies of 100 eV a large part of the recycling occurs with hydrogen residence times in the wall of about 100 ms. The use of wall temperatures from 80 to 500 K permits differentiation between thermally activated processes and ion bombardment-induced phenomena. For low energy ions (100 eV) onto 300 K stainless steel walls recycling increases to more than 90% in a few tenths of a second at; 3 × 10 16 ions cm −2 s −1 . For ions up to 300eV at this flux there is little energy dependence. Both thermally- and ion-induced processes can be important at room temperature, but under the conditions of this study thermal processes greatly enhance the recycle rates at 300 and 500 K. Preliminary results indicate that recombination of atomic hydrogen to molecular hydrogen can be rate controlling in some practical regimes.
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A new apparatus for kinetic energy measurements of fragment ions has been developed. This apparatus is based on a time-of-flight (TOF) mass spectrometer with a pulsed electron gun. We can distinguish between thermal ions and energetic ions on a TOF spectrum obtained from this apparatus, using the time-lag defined by the time between the ionization and the application of the extracting pulse. During this time-lag, since energetic ions are dispersed from the ionization region, we can't detect the energetic ions except ones that move in the direction of the detector. On the other hand, since the thermal ions move little, all of thermal ions can be detected. The kinetic energy distributions of fragment ions were calculated by considering the collection efficiency of ions. The performance of our new technique is evaluated by the comparison between our experimental data of kinetic energy distributions of the protons dissociated from a methane molecule and those of the previous works.
Time-of-Flight
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Time-of-Flight
Low-energy ion scattering
Charge exchange
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The yields of H -,H,H 2,H + 2 and H + 3 of Hydrogen ions H +,H + 2 and H + 3 ions passing through carbon foils have been measured, respectively. The results showed that the charge exchange process in the interaction of hydrogen ions with carbon foils played a key role in the formation of these products. The cluster effects and wake effect of H + 2 and H + 3 ions in carbon foils are also discussed.
Carbon fibers
Charge exchange
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Neutral molecules and especially positive ions and their energy
distributions were measured in low-pressure (ca 4 Pa) high
frequency (13,56 MHz) capacitively coupled discharge ignited in
the mixtures of hydrogen and nitrogen. Especially, the
hydrogen-rich mixtures were investigated. Firstly, the energy
dependence of the spectrometer was calculated and the ion
energy distributions were corrected. The dominant ions were H3+
and HN2+. Ions without hydrogen (N2+ and N+) were significant
only at low hydrogen concentration (less than 10%). Also a high
amount of ions NH4+ was detected. The nitrogen addition caused
a quite steep decrease of the dominant hydrogen ion H3+.
Further, an unusual behaviour of NH4+ and H+ was observed.
Concerning creation of neutral stable molecules, only a small
amount of ammonia was detected.
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Experimental data on generation of negative hydrogen ions on cesiated molybdenum surfaces are presented. The following processes are discussed: backscattering of protons and H2+ ions, sputtering of adsorbed hydrogen by cesium ion bombardment, and backscattering of a thermal or superthermal distribution of hydrogen atoms. The data are compared with theoretical calculations. Surface production is an important process in most negative hydrogen ion sources. An example of a negative hydrogen ion gun using hyperthermal hydrogen atoms incident on an external converter is presented.
Caesium
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The time-of-flight secondary ion mass spectrometry (TOF-SIMS) spectra of a metal cluster complex, Ir 4 (CO) 12 , evaporated on a Si wafer have been analyzed to clarify the origin of the mass deviation of the peaks from the true mass positions expected from the m / z values. Most of the peaks in the TOF-SIMS spectra are found to show shifts from the true positions due to the dissociation of secondary ions, i.e., release of a CO ligand, after the ionization. In conclusion, the ion peaks that can be used as mass markers of the TOF-SIMS system must be stable parent ions; such peaks are those assigned to Ir 4 (CO) 12 + ( m / z 1,100–1,108) and Ir 5 (CO) 14 + ( m / z 1,347–1,357) for positive ions, and Ir 4 (CO) 11 - ( m / z 1,072–1,080), Ir 5 (CO) 13 - ( m / z 1,319–1,329), and Ir 8 (CO) 22 - ( m / z 2,144–2,160) for negative ions with 10–50 ppm precision.
Time-of-Flight
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