“…from the pseudo first order rate coefficients, it is possible, with knowledge of the pressure of No, the cell geometry 5 and ion gauge gas sensitivity 44 factors, to obtain absolute rate constants. the absolute rate coefficients for each reaction for all naked clusters n = 2-19 are shown in figure 2 and summarised in table 1. the overall rate constants are large, exceeding, in many cases, the collision rate as calculated using the surface charge capture (Scc) 45 model.…”
The reactions of niobium cluster cations, Nb(+)(n) (n = 2-19), with nitric oxide have been investigated using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR). The overall reaction rate constants are found to be in reasonable agreement with collision rates calculated using the surface charge capture model. The dominant reaction for small clusters (n <9) involves reaction-induced fragmentation resulting in the loss of either NbO or NbN. By contrast, the main reaction observed for the larger clusters (n> 11) is sequential NO chemisorption. Clusters n = 9, 10 exhibit both extremes of behaviour and are the only clusters upon which there is evidence of NO decomposition with N(2) loss observed whenever multiple NO molecules are co-adsorbed. The rate constants for each process have been determined as a function of cluster size.
“…from the pseudo first order rate coefficients, it is possible, with knowledge of the pressure of No, the cell geometry 5 and ion gauge gas sensitivity 44 factors, to obtain absolute rate constants. the absolute rate coefficients for each reaction for all naked clusters n = 2-19 are shown in figure 2 and summarised in table 1. the overall rate constants are large, exceeding, in many cases, the collision rate as calculated using the surface charge capture (Scc) 45 model.…”
The reactions of niobium cluster cations, Nb(+)(n) (n = 2-19), with nitric oxide have been investigated using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR). The overall reaction rate constants are found to be in reasonable agreement with collision rates calculated using the surface charge capture model. The dominant reaction for small clusters (n <9) involves reaction-induced fragmentation resulting in the loss of either NbO or NbN. By contrast, the main reaction observed for the larger clusters (n> 11) is sequential NO chemisorption. Clusters n = 9, 10 exhibit both extremes of behaviour and are the only clusters upon which there is evidence of NO decomposition with N(2) loss observed whenever multiple NO molecules are co-adsorbed. The rate constants for each process have been determined as a function of cluster size.
“…Due to lower ionization efficiency, the sensitivity factor with hydrogen is about one third of the value with nitrogen. The oxygen calibration curve is slightly lower than nitrogen curve owing to the similarity of the ionization efficiencies between two gas species [30–32]. Fig.…”
Section: Resultsmentioning
confidence: 99%
“…After balancing several key characteristic properties, including high ionization efficiency and low outgassing rates, the thermionic cathode ionization gauges are commonly designed to maintain the electron energies at around 150~200 V [3, 32, 35]. For the field emission based gauge, the electron energies are normally higher due to the existence of high electron extraction field [16, 18, 36].…”
The field emission properties and the vacuum measurement application are investigated from the multi-walled carbon nanotubes (MWNTs) grown directly on catalytic stainless steel substrates. The MWNT emitters present excellent emission properties after the acid treatment of the substrate. The MWNT gauge is able to work down to the extreme-high vacuum (XHV) range with linear measurement performance in wide range from 10−11 to 10−6 Torr. A modulating grid is attempted with improved gauge sensitivity. The extension of the lower pressure limit is attributed largely to low outgassing effect due to direct growth of MWNTs and justified design of the electron source.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-015-1207-6) contains supplementary material, which is available to authorized users.
“…Ionization gauges are widely used as pressure measuring devices in the low pressure range [1][2][3][4]. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) is a well suited tool to investigate bimolecular cluster ion-molecule reactions [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”
Section: Introductionmentioning
confidence: 99%
“…In the region of 10 -10 -10 -7 mbar, measuring absolute pressure is not a trivial task. Different ionization probabilities have an effect on the reading, but it also depends on the gauge voltage, geometry and several other instrumental effects [3,13,21,22]. Standard ionization gauges are calibrated against nitrogen [1,4,23].…”
A new method to determine the absolute pressure in an ultra-high vacuum apparatus is tested using ion molecule reactions with 6 CoAr + . In a collision with a neutral reactant, the complex between Co + and the collision partner is stabilized by evaporation of argon atoms. If 6 CoAr + reacts with collision rate, the absolute pressure can be determined by comparing the experimental collision rate with the collision rate calculated from average dipole orientation theory. The experimental results with N 2 O, NO and NO 2 indeed show that the collision complex is frozen out. Comparison of the rates of primary, secondary and tertiary reaction products, however, suggests that not all collisions of 6 CoAr + are reactive. PACS: 82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions.
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