An improved high intensity recycling helium-3 beam source

Hedgeland, Holly; Kole, P. R.; Allison, W.; Ellis, John; Jardine, A. P.

doi:10.1063/1.3186733

Cited by 8 publications

(5 citation statements)

References 6 publications

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“…The source was later upgraded to a dry system, using turbomolecular pumps and a scroll backing pump to avoid contamination of the helium-3 recycling system with pump oil [25]. The change to a pump of lower capacity may have resulted in a transition from the Fenn regime towards the Campargue regime, which would explain the discrepancies between simulations and experiments with the new source.…”

Section: Discussion and Future Workmentioning

confidence: 99%

“…After a prototype was presented by De Kieviet and coworkers [20,21], the Surface Physics group at Cambridge developed the first HeSE apparatus with su cient momentum transfer space resolution to map out adsorbate di↵usion, where accessible timescales range from 0.01 ps to 680 ps [13,23]. helium-3 gas which is then expanded into the source chamber through a cooled nozzle and recirculated back into the system after expansion [23][24][25]. The nominal beam energy for the spectrometer is 8 meV, for which energy the magnets provide optimal focussing.…”

Section: The Cambridge Helium-3 Spin-echo Spectrometermentioning

confidence: 99%

“…B) shows a schematic cross section of the new source. The nozzle itself is a Cambridge type nozzle design[66] with a 10 µm diameter aperture, connected to the helium-3 recycling system[25] by an 1/8 inch stainless steel tube. Two copper blocks are mounted onto the second cooling stage of the expander head which clamp the helium gas supply tube and the nozzle, providing the cold path between expander head and nozzle.…”

mentioning

confidence: 99%

“…All pressures are corrected for the gauge factor of helium and the background in the chamber. Data for the original source are shown in blue circles (measured by Pepijn Kole[25]), for the new source with the standard 0.5 mm skimmer in red triangles and for the new source with a 0.4 mm diameter skimmer in green crosses. The panel on the left is for low nozzle temperatures while the data in the right-hand side panel were recorded using a room temperature nozzle.…”

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confidence: 99%

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Studying Complex Surface Dynamical Systems Using Helium-3 Spin-Echo Spectroscopy

Lechner¹

2014

Springer Theses

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The aim of the present thesis is to extend the range of application of the helium-3 spin-echo (HeSE) technique to complex surface dynamical systems. A twofold approach is presented: the development of improved experimental equipment and the investigation of a series of prototypical aromatic adsorbate systems. Chapter 1 discusses the motivation for this work and compares HeSE with other techniques probing surface motion. Subsequently, an introduction to the HeSE method is given in Chapter 2, explaining the theoretical background and describing the main components of the Cambridge spectrometer as well as the principle data aquisition and interpretation methods. Chapters 3 and 4 describe the development and testing of two new pieces of equipment. MiniScat, a compact helium atom scattering apparatus, has been designed as a sample preparation facility to enable structural studies and increase the experimental throughput. A new supersonic helium beam source improves the resolution of the HeSE spectrometer by a factor of 5.5 and extends accessible timescales into the nanometre range. The dynamics of cyclopentadienyl (Cp) on Cu(111) are presented in Chapter 5. The ionically bound Cp is remarkably mobile, moving in single jumps between adjacent hollow sites over an energy barrier of 41 ± 1 meV. The data exhibit multicomponent lineshapes that allow the determination of the energy di↵erence between fcc and hcp sites of 12.3±0.3 meV in a Bayesian method probing the probability space of all data combined. Molecular dynamics (MD) simulations provide a friction coe cient of 2.5 ± 0.5 ps 1. Chapter 6 shows that a physisorbed pyrrole hops between bridge sites on Cu(111). Strong lateral interactions alter the lineshapes from a predicted double exponential towards an apparent single exponential decay. First principles density functional theory calculations by Sacchi and Jenkins reveal that a large contribution to the experimentally determined apparent activation energy of 53 ± 4 meV arises from a site-dependence in the zero point energies, primarily of the vibrational C-H and N-H out-of-plane bending and ring torsion modes which are not directly involved in the di↵usion process. The surface dynamics of thiophene/Cu(111) are investigated in Chapter 7. Thiophene adsorbs on top sites and forms a covalent S-Cu bond. Two competing activated processes manifest themselves in a kink in the Arrhenius plot: jump di↵usion between adjacent top sites over a barrier of 59 ± 4 meV and rotation around the S-Cu anchor point over a barrier of 22 ± 2 meV. In addition, vertical motion relative to the surface is observed. MD simulations of the di↵usive motion reveal an exceptionally high friction of 5 ± 2 ps 1 .

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Section: Discussion and Future Workmentioning

confidence: 99%

Section: The Cambridge Helium-3 Spin-echo Spectrometermentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Studying Complex Surface Dynamical Systems Using Helium-3 Spin-Echo Spectroscopy

Lechner¹

2014

Springer Theses

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“…In terms of a compact beam source for a prototype desktop helium microscope, the critical parameters are the centreline beam intensity and the source dimensions, which are tied closely to the pumping requirements. Modern HAS beam sources typically deliver intensities in the range of 10 19 -10 20 atoms s −1 sr −1 , which necessarily requires large and expensive pumps with speeds of the order 1500-18 000 L s −1 [17][18][19].…”

Section: Introductionmentioning

confidence: 99%

A desktop supersonic free-jet beam source for a scanning helium microscope (SHeM)

Barr

O’Donnell

Fahy

et al. 2012

Meas. Sci. Technol.

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A simple design for an inexpensive, compact, desktop-sized helium free-jet beam source is described. The apparatus, which is Campargue-like in design and utilizes mostly off-the-shelf parts, is capable of producing a centreline intensity of 1.2 × 1019 atoms per second per steradian. The beam performance was investigated using a conventional ion gauge and a stagnation detector, with the latter being used to produce beam flux profiles. The profile of the macroskimmed beam has been experimentally demonstrated to be strongly Gaussian.

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The Helium-3 Spin-Echo Experiment

Lechner

2014

Springer Theses

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An improved high intensity recycling helium-3 beam source

Cited by 8 publications

References 6 publications

Studying Complex Surface Dynamical Systems Using Helium-3 Spin-Echo Spectroscopy

Studying Complex Surface Dynamical Systems Using Helium-3 Spin-Echo Spectroscopy

A desktop supersonic free-jet beam source for a scanning helium microscope (SHeM)

The Helium-3 Spin-Echo Experiment

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