The Debye-Waller factor for the noble gas solids

The mean-square nuclear displacements u ², the Debye 's associated with the u ², and the Debye 's associated with the temperature derivatives of u ² at constant volume have been calculated for the noble gas solids Ne, Ar, Kr, and Xe as a function of temperature and volume using self-consistent phonon theory. Instead of using the equation of state which gives volumes which are consistently smaller than the experimental volumes, the experimental lattice parameters at the saturated vapor pressure were used. In the case of neon, the theoretical u ² were also obtained as a function of temperature and the experimental lattice volume atT=0K. The interaction forces are described by a nearest neighbor (12–6) Mie–Lennard-Jones potential.     

Microprobe analysis of noble gas encapsulates in zeolites

Electron microprobe analysis has been employed for the first time to investigate gases immobilized in zeolites. Two trapping procedures and two different molecular sieves were tested: on one hand Kr as well as one to one $\text{Xe}\text{Kr}$ and $\text{Xe}\text{Ar}$ mixtures were trapped hydrothermally in X-ray amorphous zeolite 5A, and on the other, Kr was immobilized in mordenites by a combination of physical sorption and chemical modification procedure. The results show that the noble gases Ar, Kr and Xe can be quickly and specifically identified in these inorganic matrices. Because in all samples the density of the noble gas follows exactly the density of the aluminosilicate framework it is concluded that the noble gas is homogeneously distributed in the zeolite material. Analysis of noble gas mixtures indicates that each of the noble gases Ar, Kr and Xe can be specifically monitored in the presence of the two others. In addition, an analysis of other elements present in the pellet can be simultaneously carried out. The variation of the concentration of these elements with structure can be followed with resolution of ≈ 1μm.     

On the Gruneisen parameter in the noble gas solids

The Gruneisen parameter atT=0 K in neon, argon, krypton, and xenon is calculated in first-order self-consistent phonon theory. The results are discussed in the context of existing calculations of the Gruneisen parameter at higher temperatures and are compared with the available experimental data.     

Atomic near-infrared noble gas scintillations I: Optical spectra

Particle beam excited emission spectra from Ne, Ar, Kr and Xe in the wavelength range 350–930 nm and in the pressure range 20–200 kPa are studied. Ar, Kr and Xe show dominant emission from neutral atoms in the near-infrared region. For Ne this emission extends from the visible to the near-infrared region.To study the emission spectra of electrostatic field enhanced scintillations a wire was inserted into the chamber and spectra from Ne, Ar, Kr and Xe were recorded with positive and negative wire potentials. The same dominant emission from neutral atoms is present in these spectra. Due to contamination of N₂ in the Ne gas strong emission of N₂ bands are seen in the electrostatic field enhanced scintillation Ne spectra.     

Implanted noble gas atoms as diffusion markers in silicide formation

Implanted noble gas atoms of Ar and Xe have been used as diffusion markers in growth studies of silicides formed by reacting metal films with silicon substrates. MeV ⁴He ion backscattering has been used to determine the displacement of the markers. Two approaches were used: either the silicon samples were implanted with Xe or Ar and then covered with a thin layer of metal, or the metal layer was implanted with the marker. When the sample was heated to form the silicide layer, the displacement of the marker relative to the surface determined the identity of the diffusing species.Diffusion markers have been used in growth studies of six silicides: Ni₂Si, Mg₂Si, FeSi, VSi₂, TiSi₂ and Pd₂Si. We found that Si atoms are the predominant moving species in diffusion in VSi₂, TiSi₂ and FeSi, while Ni atoms are the moving species in Ni₂Si and Mg in Mg₂Si. In Pd₂Si, both Pd and Si are diffusing species with Si the faster of the two.Chemical effects can play a role in marker studies. In the thermal oxidation of Si, the displacement of Xe markers is consistent with the fact that oxygen is the moving species. Implanted As, on the other hand, accumulates at the Si-SiO₂ interface. Therefore, it is necessary to choose markers which are chemically inert.     

A fence line noble gas monitoring system for nuclear power plants

A noble gas monitoring system has been installed at Ontario Power Generation's Pickering Nuclear Generating Station (PNGS) near Toronto, Canada. This monitoring system allows a direct measure of air kerma from external radiation instead of calculating this based on plant emission data and meteorological models. This has resulted in a reduction in the reported effective dose from external radiation by a factor of at least ten. The system consists of nine self-contained units, each with a 7.6 cm x 7.6 cm (3 inch x 3 inch) NaI(TI) detector that is calibrated for air kerma. The 512-channel gamma ray spectral information is downloaded daily from each unit to a central computer where the data are stored and processed. A spectral stripping procedure is used to remove natural background variations from the spectral windows used to monitor xenon-133 (133Xe), xenon-135 (135Xe), argon-41 (41Ar), and skyshine radiation from the use of radiography sources. Typical monthly minimum detection limits in air kerma are 0.3 nGy for 133Xe, 0.7 nGy for 35Xe, 3 nGy for 41Ar and 2 nGy for skyshine radiation. Based on 9 months of continuous operation, the annualised air kerma due to 133Xe, 135Xe and 41Ar and skyshine radiation were 7 nGy, 8 nGy, 26 nGy and 107 nGy respectively.     

The effect of noble gas bombarding on nitrogen diffusion in steel

The low energy (∼50–350 eV) noble gases ion bombardment of the steel surface shows that the pre-treatments increase nitrogen diffusion by modifying the outermost structure of the material. The surface microstructure and morphology of the studied samples were characterized by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The crystalline and chemical structures in the outermost layers of the surface were analyzed by grazing angle X-ray diffraction (GAXRD) and photoemission electron spectroscopy (XPS). Temperature effusion studies of the implanted ions are used to elucidate the noble gases site localization in the network. The local compressive stress induced by the nearby iron atoms on the core level electron wave functions of the trapped noble gases are studied by photoemission electron spectroscopy (XPS) and interpreted considering a simple mechanical model. Nano-hardness measurements show the dependence of the material elastic constant on the energy of the implanted noble gases. Although the ion implantation range is about few nanometers, the atomic attrition effect is larger enough to modify the material structure in the range of micrometers. Two material stress zones were detected where the outermost layers shows compressive stress and the underneath layers shows tensile stress. The implanted noble gases can be easily removed by heating. A diffusion model for polycrystalline-phase systems is used in order to discuss the influence of the atomic attrition on the N diffusion coefficient. The concomitant effect of grain refining, stress, and surface texture on the enhancing nitrogen diffusion effect is discussed.     

‘The crystal structure problem’ in noble gas nanoclusters

Calculations of the energetics of multiply twinned particles (MTPs) such as icosahedra and decahedra with fivefold symmetry as well as face-centered cubic (fcc) and hexagonal close-packed (hcp) particles in the size interval from 13 up to ∼ 45,000 atoms were made applying Lennard-Jones potentials. We essentially extended the size interval comparatively with previous studies and included shape-optimized hcp clusters in the global energy analysis that gives rise to the new insight into the basic fcc/hcp problem. For the cluster size N from minimal up to N ∼ 2000 atoms the binding energy is highest for icosahedra, in the size interval from 2000 up to ∼ 11,500 atoms decahedra prevail, above N ∼ 11,500 atoms decahedra and optimized fcc clusters were found to alternate. The hcp structure was revealed to become favorable above N ∼ 34,000 atoms. Thus, hcp clusters can attain their preference with respect to MTPs (comprising fcc fragments) and optimized fcc clusters only for very large sizes. The comparison with several other models is suggested and the opportunity of experimental observations is discussed.     

The desorption of condensed noble gases and gas mixtures from cryogenic surfaces

In accelerators, operating at liquid-helium temperature, cold surfaces are exposed to intense synchrotron radiation and bombardment by energetic electrons and ions. Molecular desorption yield and secondary electron yield can strongly influence the performance of the accelerator. In order to predict the gas density during the operation, the knowledge of electron-induced desorption yields of condensed gases and of its variation with the gas coverage is necessary. Desorption yields under electron impact of various noble gases and gas mixtures condensed on a copper surface cooled at 4.2 K have been measured.     

Atomic-scale electron-beam sculpting of near-defect-free graphene nanostructures

In order to harvest the many promising properties of graphene in (electronic) applications, a technique is required to cut, shape, or sculpt the material on the nanoscale without inducing damage to its atomic structure, as this drastically influences the electronic properties of the nanostructure. Here, we reveal a temperature-dependent self-repair mechanism that allows near-damage-free atomic-scale sculpting of graphene using a focused electron beam. We demonstrate that by sculpting at temperatures above 600 °C, an intrinsic self-repair mechanism keeps the graphene in a single-crystalline state during cutting, even though the electron beam induces considerable damage. Self-repair is mediated by mobile carbon ad-atoms that constantly repair the defects caused by the electron beam. Our technique allows reproducible fabrication and simultaneous imaging of single-crystalline free-standing nanoribbons, nanotubes, nanopores, and single carbon chains.     

Atomic near-infrared noble gas scintillations II: Application to particle beam intensity measurement

In line with previous work [1], results from a study using particle beam exited atomic emission scintillations for monitoring beam intensity are presented. A device suitable for intensity measurements during proton induced X-ray emission analyses was constructed. The light emission was measured with a light-sensitive silicon diode.     

DFT calculation of the stability and mobility of noble gas atoms in silicon

We have investigated the stability and the migration of single noble gas atoms (He, Ne, Ar, Kr) in bulk silicon, by performing first-principles calculations. Our results indicate that all noble gas interstitials were found to be preferentially located in a tetrahedral site. Other possible sites have been studied too, like the hexagonal one which becomes unstable for large noble gas atoms such as Ar and Kr. Using nudged elastic band technique, we have determined the minimum energy path, and the associated migration energies. Our results are discussed and compared to other works.     

Nanometer-thin solid-state nanopores by cold ion beam sculpting

Recent work on protein nanopores indicates that single molecule characterization (including DNA sequencing) is possible when the length of the nanopore constriction is about a nanometer. Solid-state nanopores offer advantages in stability and tunability, but a scalable method for creating nanometer-thin solid-state pores has yet to be demonstrated. Here we demonstrate that solid-state nanopores with nanometer-thin constrictions can be produced by "cold ion beam sculpting," an original method that is broadly applicable to many materials, is easily scalable, and requires only modest instrumentation.     

Thermal activation and saturation of ion beam sculpting

We report a material-dependent critical temperature for ion beam sculpting of nanopores in amorphous materials under keV ion irradiation. At temperatures below the critical temperature, irradiated pores open at a rate that soon saturates with decreasing temperature. At temperatures above the critical temperature, the pore closing rate rises rapidly and eventually saturates with increasing temperature. The observed behavior is well described by a model based on adatom diffusion, but is difficult to reconcile with an ion-stimulated viscous flow model.     

单纳米孔传感器分析研究进展

综述了单纳米孔传感器中的生物纳米孔和固态纳米孔的研究现状,重点介绍了α-HL溶血素孔、生物纳米孔及人工固态纳米孔传感器的制备,以及单纳米孔传感器在单分子检测和DNA测序方面的应用进展,并展望了该领域的发展趋势和应用前景.     

Sputtering of thin films of bariated molecules of arachidic acid by large noble gas clusters

Coarse-grained molecular dynamics computer simulations have been employed to investigate the sputtering process of a multilayer organic system composed of long, well-organized linear molecules induced by an impact of slow clusters composed of large number of noble gas atoms. The organic system is represented by Langmuir–Blodgett multilayers formed from bariated molecules of arachidic acid. The sputtering yield, surface modifications and the angular distributions of ejected species have been analyzed as a function of the kinetic energy of an Ar₈₇₂ cluster projectile and the thickness of the deposited multilayer. It has been shown that the physics of ejection by these large and slow clusters is distinct from the ejection events stimulated by the popular SIMS clusters: C₆₀, Au₃ and SF₅. The organic molecules are not ejected by interaction with the energized substrate but by direct interactions with the projectile atoms.     

Nanopore tomography of a laser focus

We demonstrate that the ionic current through a solid-state nanopore can be used to measure at single nanometer resolution the three-dimensional intensity profile of a laser directly in the focus of a microscope objective. We find a linear dependence of the ionic current on the incident laser power since the laser-induced heat increases the temperature locally in the solution. Our data show a temperature increase of up to 20 K in the center of the focus for a laser wavelength of 1064 nm. Measurements of the two-dimensional temperature profiles at different positions along the optical axis allow us to reconstruct the three-dimensional temperature profile of the laser focus, similar to tomography. Our new technique does not rely on the help of any optical elements and allows quantitative measurement of optical intensity or temperature distributions in aqueous environments with nanometer resolution.     

Nanopore sensors for nucleic acid analysis

Nanopore analysis is an emerging technique that involves using a voltage to drive molecules through a nanoscale pore in a membrane between two electrolytes, and monitoring how the ionic current through the nanopore changes as single molecules pass through it. This approach allows charged polymers (including single-stranded DNA, double-stranded DNA and RNA) to be analysed with subnanometre resolution and without the need for labels or amplification. Recent advances suggest that nanopore-based sensors could be competitive with other third-generation DNA sequencing technologies, and may be able to rapidly and reliably sequence the human genome for under $1,000. In this article we review the use of nanopore technology in DNA sequencing, genetics and medical diagnostics.