Atomic Beam Research Articles

Formation of molecular hydrogen in diamond-like carbon films during deposition: Molecular dynamics simulations

The existence states of the H atoms in hydrogenated diamond-like carbon (a-C:H) films were simulated using a modified REBO II potential function-based large-scale atomic/molecular parallel simulator (LAMMPS) and neutral C and H atom beam impingement. The fraction of the H atoms in the incident source (H-flux fraction) in the source must be considered when investigating the effects of the incident energy combination on the H content and mass density of the films. In simulations a-C:H film deposition using a 15 % H-flux fraction, films with densities of 2.6–2.8 g/cm3 could be obtained, and their H content varied with the incident energy. However, the H contents of films simulated using a 70 % H-flux fraction could be kept in the range of 40–50 at.%. The H atoms in the films preferentially reacted with the C atoms to form CH bonds. Regardless of the incident energy combination used, the total sp3C fraction in the film increased with the H-flux fraction of the source. An incident energy of >36 eV for the H atoms was necessary to form H2 during the film deposition. Instead of being formed in the surface growth zone, H2 molecules were synthesized in the stabilized zone, where a high density of sp3C—Hn was favorable.

Breit interaction overtaking Coulomb force at low energies: an unexpectedly efficient mechanism for ionization in slow collisions

Abstract It is generally assumed that ionization in slow collisions of light atomic particles, whose constituents (electrons and nuclei) move with velocities orders of magnitude smaller than the speed of light, is driven solely by the Coulomb force. Here we show, however, that the Breit interaction—a relativistic correction to the Coulomb interaction between electrons—can become the main actor when the colliding system couples resonantly to the quantum radiation field. Our results demonstrate that this ionization mechanism can be very efficient in various not too dense physical environments, including stellar plasmas and atomic beams propagating in gases.

Slowing Down a Coherent Superposition of Circular Rydberg States of Strontium.

Rydberg alkaline earth atoms are promising tools for quantum simulation and metrology. When one of the two valence electrons is promoted to long-lived circular states, the second valence electron can be optically manipulated without significant autoionization. We harness this feature to demonstrate laser slowing of a thermal atomic beam of circular strontium atoms. By driving the main ion core 422nm wavelength resonance, we observe a velocity reduction of 50 m/s without significant autoionization. We also show that a superposition of circular states undergoes very weak decoherence during the cooling process, up to the scattering of more than 1000 photons. This robustness opens new perspectives for quantum simulations over long timescales with circular atoms, while simultaneously cooling their motional state. It makes it possible to mitigate the harmful effects of unavoidable heating due to spin-motion coupling during a quantum simulation.

Absorption line broadening in atomic beams produced in a molecular beam epitaxy environment

Absorption line broadening in atomic beams produced in a molecular beam epitaxy environment

Amorphous carbon-coated storage cell tests for the polarized gas target at LHCb

The LHC beams cannot be polarized. Hence, the implementation of a dense polarized gas target at the LHCb experiment at CERN, to be operated simultaneously with beam–beam collisions, will enable high-energy fixed target interactions to explore a range of spin physics measurements. Using an atomic beam source at the Forschungszentrum Jülich to provide a polarized atomic hydrogen beam, we investigated the properties of a storage cell coated with amorphous carbon. A notable recombination rate, lying between 93 and 100%, and a preservation of polarization during recombination exceeding 74% was observed. We were able to generate H2 molecules with a nuclear polarization of −0.59. Remarkably, no water layer accumulated on the cooled storage cell surface, even over extended periods. Furthermore, we examined the influence of Lyman-α radiation on the recombination rate on carbon, addressing a prominent question in the field of astrophysics.

Spectroscopy of resonantly saturated selective reflection from high-density rubidium vapor using the pump-probe technique

We study the resonant saturation of selective reflection at the interface between a transparent dielectric and high-density rubidium vapor on the D2-line. Our estimates suggest that, within the selected atomic density range, the dipole–dipole self-broadening of the line can vary from 13.2 to 39.6 GHz. Two tunable lasers are used as sources of pump and probe beams with orthogonal linear polarizations. The selective reflection spectra of the probe laser beam are studied at different atomic densities and pump beam intensities ranging from 0 to 8.8 kW cm−2. At high pump intensities, narrow structures are observed around the pump beam frequency, which are associated with power broadening effects. Increasing the pump intensity reduces the spectral width and the magnitude of the selective reflection resonances. The intensity dependence of the width and the magnitude is measured. By adjusting the pump intensity, it is possible to control the spectral width and reflectivity.

Neutral beam microscopy with a reciprocal space approach using magnetic beam spin encoding

The emerging technique of neutral beam microscopy offers a non-perturbative way of imaging surfaces of various materials which cannot be studied using conventional microscopes. Current neutral beam microscopes use either diffractive focusing or pin-hole scanning to achieve spatial resolution, and are characterised by a strong dependence of the imaging time on the required resolution. In this work we introduce an alternative method for achieving spatial resolution with neutral atom beams which is based on manipulating the magnetic moments of the beam particles in a gradient field, and is characterised by a much weaker dependence of the imaging time on the image resolution. The validity of the imaging approach is demonstrated experimentally by reconstructing one dimensional profiles of the beam which are in good agreement with numerical simulation calculations. Numerical simulations are used to demonstrate the dependence of the signal to noise on the scan resolution and the topography of the sample, and assess the broadening effect due to the spread of velocities of the beam particles. The route towards implementing magnetic encoding in high resolution microscopes is discussed.

Realization of a single-beam, detachable, cascaded 2D magneto-optical trap based modular cesium source

We present a detachable, cascaded modular cesium loading source based on a 2D magneto-optical trap (MOT). Our design utilizes only a single beam of mixed cooling and repumping light that is split evenly into five discrete trapping regions, each with horizontal and vertical beams. The pre-aligned, single-beam design makes our module suitable for miniaturization. The generated cold atomic beam serves to load a 3D MOT, whose loading rate we use to characterize the efficiency of our design. The effect of individual trapping regions relative to the differential tube and to each other on the loading rate has also been examined. Experimental results were compared with a numerical simulation. We are able to obtain an experimental loading rate of nearly 8×107atoms/s and a vapor density of about 3×1015atoms/m3 in our 2D MOT module.

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In order to establish important reaction properties, such as rate coefficients, it is often necessary to know the number of reactants that are present in an interaction region. The absolute number densities of pulsed supersonic molecular (NH3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_3$$\\end{document}) and atomic (H) beams are reported using a laser-based detection method, under a range of experimental conditions including photolysis, Zeeman deceleration, and magnetic focusing. 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The average density of the undecelerated H atom beam is approximately an order of magnitude higher (2.9 ± 1.9) ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes $$\\end{document} 105\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^5$$\\end{document} cm-3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-3}$$\\end{document}, with the average density of the molecular ammonia beam over two orders of magnitude higher again (5.1 ± 2.9) ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes $$\\end{document} 107\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^7$$\\end{document} cm-3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-3}$$\\end{document}. The average number densities measured for the two different species of interest in this work span more than three orders of magnitude. These findings highlight the need for accurate and precise experimental measurements of number densities—for each species of interest, under the appropriate experimental conditions—before doing absolute rate coefficient calculations.Graphical abstract

Low-energy atomic and molecular hydrogen ion interaction with low-work function electride 12CaO · 7Al2O3

To efficiently generate H− ions from positive atomic or molecular hydrogen beams injected onto a solid surface, it has been suggested to use a material with a low-work function as the target material. However, it is not clear under what conditions the most efficient H− production is realized for incident beam parameters or reflection angles. Therefore, we studied the interaction between low-energy atomic and molecular hydrogen beams (less than 1 keV/nucleon) with a low-work function electride 12CaO⋅7Al2O3 (C12A7). The production ratio of H− to H+ ions from the C12A7 electride was much higher than Mo targets with higher work functions, especially at smaller incident and smaller reflection angles. The H− to H+ production ratio slightly increased as the incident energies were decreased, but there was no significant difference between the electride and Mo targets. These results indicate that smaller incident angles and lower beam energies of the incident hydrogen beam are favorable for the enhancement of the production ratio of H− to H+ ions in C12A7. The higher production ratio appeared at the vertical beam energies less than on the order of 100 eV, where quantum mechanical processes may become important.

The role of carbon segregation in the electrical activity of dislocations in carbon doped GaN

Dislocations have been proposed to affect the performance and reliability of GaN power semiconductors by being conductive pathways for leakage current. However, no direct evidence of a link between their electrical behavior and physical nature in carbon-doped semi-insulating GaN buffer layers has been obtained. Therefore, we investigate the electrical activity of dislocations by conductive atomic force microscopy and electron beam induced current to distinguish electrically active dislocations from non-active ones. We investigated six electrically active dislocations and discovered distinct carbon enrichment in the vicinity of all six dislocations, based on cross-sectional scanning transmission electron microscopy using electron energy loss spectrometry. Electrically non-active dislocations, which are the vast majority, sometimes also showed carbon enrichment, however, in only two out of seven cases. Consequently, carbon segregation seems to be a requirement for electrical activity, but a carbon surplus is not sufficient for electrical activity. We also performed first-principles total-energy calculations for mixed type threading dislocations, which validates carbon accumulation in the dislocation vicinity. The electrical and physical characterization results, complemented by density functional theory simulations, support the previously hypothesized existence of a carbon defect band and add new details.

Practical guides for x-ray photoelectron spectroscopy: Use of argon ion beams for sputter depth profiling and cleaning

Ion beams are used in x-ray photoelectron spectroscopy (XPS) to clean samples and perform compositional sputter depth profiles. The purpose of this article is to compile good practice, recommendations, and useful information related to the use of argon ion sources for inexperienced users of XPS instrumentation. The most used type of ion source generates monoatomic argon ions at a range of energies from a fixed direction relative to the instrument. The angle and direction of the ion beam with respect to the surface are normally altered by manipulating the sample, and this may involve tilting the sample to change the angle of incidence or rotating the sample to change the azimuthal incidence angle. Atomic argon ion beams cause damage to the structure of the material surface, which may exhibit itself as a change in stoichiometry or topography as well as the implantation of argon atoms. Therefore, caution is required in the interpretation of XPS depth profiles. Gas cluster ion sources offer new possibilities and choices to XPS users. Gas cluster sources enable the sputtering of organic materials with high yield in comparison to inorganic materials and offer the potential for nearly damage-free depth profiling of delicate organic materials as well as low damage cleaning of inorganic materials. It may be possible to use argon clusters to reduce damage during the depth profiling of inorganic materials, but there is currently insufficient evidence to make any general recommendations.

Searching for axion forces with spin precession in atoms and molecules

We propose to use atoms and molecules as quantum sensors of axion-mediated monopole-dipole forces. We show that electron spin precession experiments using atomic and molecular beams are well-suited for axion searches thanks to the presence of co-magnetometer states and single-shot temporal resolution. Experimental strategies to detect axion gradients from localised sources and the earth are presented, taking ACME III as a prototype example. Other possibilities including atomic beams, and laser-cooled atoms and molecules are discussed.

Mechanical Properties of Mouse Lung Cells and Their Effects on the Atomic Force Microscope Beam Vibrations.

In the present investigation, the mechanical properties of mouse normal and carcinomatous (LL/2) lung tissue cells were investigated using atomic force microscopy (AFM). The normal lung cells have been derived directly from C57BL mice. Initially, the elastic modulus of LL/2 cells was measured following chemotherapy with the anti-cancer drug Cisplatin and plasma treatment. MTT evaluation was used to determine the optimal dosages for 24- and 48-h incubations based on the IC50 cell viability concentration during chemotherapy treatment. After 24 and 48 h, the results demonstrated that Cisplatin-based chemotherapy increases the elastic modulus of LL/2 cells by 1.599 and 2.308 times compared to untreated cells. LL/2 cells were subsequently treated with plasma for 30 and 60 s for 24 and 48-h incubation. The plasma treatment decreased the LL/2 cell's elastic modulus, and the time duration of plasma treatment increased the reduction amount of elastic modulus. During the second section of the study, theoretical (finite element analysis [FEM]) and experimental techniques were used to examine the resonant frequencies and magnitude of the frequency response function (FRF) of the AFM cantilever's movements when applying normal and cancerous cells before and after chemo and plasma treatments as specimens. The results indicated that increasing the samples' elastic modulus raises the resonant frequency, so the resonant frequency of treated cells as a sample is greater than untreated cells. In conclusion, the FEM and experimental results were compared and found to be in good agreement.

Atomic layer molecular beam epitaxy of kagome magnet RMn6Sn6 (R = Er, Tb) thin films

Kagome lattices have garnered substantial interest because their band structure consists of topological flat bands and Dirac cones. The RMn6Sn6 (R = rare earth) compounds are particularly interesting because of the existence of the large intrinsic anomalous Hall effect (AHE), which originates from the gapped Dirac cones near the Fermi level. This makes RMn6Sn6 an outstanding candidate for realizing the high-temperature quantum AHE. The growth of RMn6Sn6 thin films is beneficial for both fundamental research and potential applications. However, most of the studies on RMn6Sn6 have focused on bulk crystals, and the synthesis of RMn6Sn6 thin films has not been reported so far. Here, we report the atomic layer molecular beam epitaxy growth, structural and magnetic characterizations, and transport properties of ErMn6Sn6 and TbMn6Sn6 thin films. It is especially noteworthy that TbMn6Sn6 thin films have out-of-plane magnetic anisotropy, which is important for realizing the quantum AHE. Our work paves the avenue toward the control of the AHE using devices patterned from RMn6Sn6 thin films.

A high resolution reaction microscope with universal two-region time-focusing method.

This paper presents a novel reaction microscope designed for ion-atom collision investigations, established at the Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou, China. Its time-of-flight (TOF) spectrometer employs an innovative flight-time focusing method consisting of two acceleration regions, providing optimal time focusing conditions for charged fragments with diverse initial velocities. The TOF spectrometer's axis intentionally tilts by 12° relative to the ion beam direction, preventing potential obstructions from the TOF grid electrodes. The introduced focusing method allows for a flexible time-focusing TOF spectrometer design without restricting the length ratio of the two regions. In addition, this configuration in our case significantly suppresses noise on the recoil ion detector produced by residual gas in the ion beam trajectory, which is a considerable challenge in longitudinal spectrometers. In a test experiment on the single electron capture reaction involving 62.5 keV/u He2+ ions and a helium atomic beam, the recoil longitudinal momentum resolution achieved 0.068 atomic units. This novel configuration and successful test run show excellent precision for ion-atom collision studies.

Closed-loop dual-atom-interferometer inertial sensor with continuous cold atomic beams

Closed-loop dual-atom-interferometer inertial sensor with continuous cold atomic beams

Mechanical properties of human kidney cells and their effects on the atomic force microscope beam vibrations.

In the present investigation, the mechanical properties of normal and carcinomatous cells of kidney tissue (HEK-293, ACHN, respectively) were investigated using atomic force microscopy (AFM). Initially, the elastic modulus of ACHN cells was measured following chemotherapy with the anti-cancer drug Cisplatin and plasma treatment. The MTT assay was employed to ascertain the most effective dosages for incubation periods of 12, 24, 48, 72, and 96 h, guided by the IC50 concentration for cell viability during chemotherapy treatment. Analysis at these specified time points revealed a progressive increase in the elastic modulus of ACHN cells when subjected to Cisplatin-based chemotherapy. Specifically, the elastic modulus increased by 1.847, 4.416, 6.035, 8.029, and 9.727 times in comparison to untreated cells at 12, 24, 48, 72, and 96 h, respectively. ACHN cells were subsequently treated with plasma for 30 and 60 s for 24 and 48-h incubation periods. The plasma treatment increased the ACHN cell's elastic modulus. In the subsequent phase of the research, a combination of theoretical (finite element method [FEM]) and experimental methodologies was employed to investigate the resonant frequencies and magnitude of the frequency response function (FRF) concerning the movement of the AFM cantilever. This examination was conducted using ACHN cells as specimens, both before and after exposure to chemotherapy and plasma treatments. The results showed that higher sample elastic modulus increased the resonant frequency, indicating that treated cells had a higher resonant frequency than untreated cells. In conclusion, the FEM and experimental results were compared and found to be in good agreement. HIGHLIGHTS: Using Cisplatin anti-cancer drug increases the elastic modulus of ACHN cell. Applying plasma treatment increases the elastic modulus of ACHN cell. For both of the chemo and plasma therapies, increasing the incubation time increases the influence of therapies oh the cell mechanics. Using finite element modeling (FEM) the real dynamic behavior of atomic force microscope cantilever by considering human kidney cells as the soft samples is possible.

Measuring scattering distributions in scanning helium microscopy

A scanning helium microscope typically utilises a thermal energy helium atom beam, with an energy and wavelength (¡100meV, ∼0.05 nm) particularly sensitive to surface structure. An angular detector stage for a scanning helium microscope is presented that facilitates the in-situ measurement of scattering distributions from a sample. We begin by demonstrating typical elastic and inelastic scattering from ordered surfaces. We then go on to show the role of topography in diffuse scattering from disordered surfaces, observing deviations from simple cosine scattering. In total, these studies demonstrate the wealth of information that is encoded into the scattering distributions obtained with the technique.

Continuous generation of an ultracold atomic beam using crossed moving optical lattices

Continuous generation of an ultracold atomic beam using crossed moving optical lattices