A specialized torsion balance designed to measure the absolute flux density of hyperthermal molecular beams containing reactive species

Abstract

Articles you may be interested inThe influence of the ionizer geometry on the absolute density calibration of reactive neutral species in a molecular beam mass spectrometry Rev. Sci. Instrum. 83, 045114 (2012); 10.1063/1.3703305Understanding gas-surface interactions from direct force measurements using a specialized torsion balance J. Vac. Sci. Technol. A 15, 1553 (1997); 10.1116/1.580630Flux measurement of a hyperthermal atomic oxygen beam A torsion balance is described that has been used to measure the absolute flux density of seeded hyperthermal molecular beams containing reactive and/or condensable species with uncertainties of approximately Ϯ5%. The balance is ultrahigh-vacuum compatible and can be used in corrosive environments. A specially designed beam stop mounted on the torsion balance lever arm, traps the incoming beam and allows only completely thermalized molecules to exit. The thermalized molecules exit the beam stop in equal numbers per unit time in opposite directions, ensuring that the force exerted on the beam stop by the exiting molecules is zero. The balance was suspended from a 25-m-diam gold-coated tungsten wire that had a torsion constant of 6.04ϫ10 Ϫ8 N m/rad and a period of slightly larger than 400 s. Absolute molecular beam flux density measurements were made using both the torsion balance and the effusive method for a variety of pure and seeded molecular beams. The beams were composed of gases that could easily be measured by the effusive method. Measured fluxes ranged from 2.41ϫ10 15 mol/s cm 2 for a beam of CO seeded in H 2 to 1.25ϫ10 17 mol/s cm 2 for a beam of pure H 2 . A comparison of the two methods establishes the ability of the torsion balance to accurately measure the flux of molecular beams.

Optical emission studies and neutral stream characterization of a surface reflection materials processing source

“…The force applied on the particle catcher by the fast neutral flux can be calculated from 23 FϭA⌽m ϪN r m r , ͑5͒ The details of this calibration can be found in the papers of Cook and co-workers, 23,24 whose methods we used to calibrate the torsion constant.…”

Cold-cathode Penning discharge-based ionizer for detection of hyperthermal neutral beams

“…This is because detection and measurement of low-energy uncharged beams is not a simple matter. 1,[6][7][8] Mass spectrometric techniques involving postionization while difficult have, under special circumstances, been able to provide information on neutral energy distributions. 1,9,10 The main difficulty is a low ionization efficiency of cross-beam ionizers employed in mass spectrometers.…”

Approach to improve the angle sensitivity and resolution of the optical beam deflection method using a passive interferometer and a Ronchi grating

“…4,5 In the latter case, the OBDM is commonly referred to as the mirage detection technique. The OBDM may also be used to probe inhomogeneities in physical properties of a flat surface such as its conductivity, 6 to calibrate a small-displacement actuator, 7 to measure the rotation angle in very sensitive torsion balances, 8 or to measure the profile of smooth objects. 9 A detailed analysis of the most common configurations of the OBDM used in atomic force microscopy was published by Putman et al a few years ago.…”

“…[1][2][3][4][5][6][7][8][9][10] For example, in some atomic force microscopes [1][2][3] it is used to measure the vibration amplitude of a small cantilever as it interacts with the sample. Changes in the vibration amplitude on the order of angstroms must be accurately detected.…”