Low Energy Ne Research Articles

Determining the stopping power of low kinetic energy Ne+ projectiles in self-Assembled monolayers

Neutral impact collision ion scattering spectroscopy (NICISS) is used to measure the energy loss in organic self-assembled monolayers (SAMs) on Au using Ne+ with low kinetic energies from 3 to 5 keV. With increasing film thickness, the energy loss of the projectiles increases because the projectile experiences more collisions with target atoms.Through comparing Monte-Carlo simulations with the NICISS experiments, it was found that contributions from nuclear stopping for Ne+ were significantly larger than for He+ mainly due to the stronger contribution of small-angle scattering of Ne+ making Ne NICISS unsuitable for depth profiling at energies of 5 keV or lower. The measured Ne+ electronic stopping in SAMs is small despite the large atomic number of Ne. Comparing experiments and DFT calculations shows that the latter accurately reproduce stopping powers for Ne+, while SRIM overestimates the stopping power. This contrasts He+ ions, where DFT and SRIM align closely with experiments.

Deuterium retention in tungsten co-deposits with neon and argon inclusions

Deuterium (D) retention in tungsten (W) co-deposited layers, in the presence of neon (Ne) and argon (Ar), was investigated using the bipolar High Power Impulse Magnetron Sputtering (BP-HiPIMS) technique. The deposited layers have a polycrystalline structure, with a preferential growth of W(110) phase. The concentration of D and noble gases (Ne and Ar) is almost constant throughout the depth of the layers. In a D2-Ar discharge, the deposited layers exhibit compressive stress, indicating that Ar is mostly incorporated into the interstitial sites of the W crystal lattice. D retention increases when Ne is added in the discharge, especially when the deposited layer is bombarded with highly energetic ions. Low energy Ne ions (below the W damaging threshold) induce compressive stress, indicating that Ne atoms occupy interstitial sites in the W crystal lattice. High energy Ne ions induce tensile stress, a sign that Ne is trapped in the grain boundaries as inert-gas-vacancy defects, leading to a grain-boundary relaxation. In the presence of Ne, the ion acceleration towards the layer from 0 V to 300 V results in an increase of the D content of about three times, from 3.2 at.% to 8.6 at.%.

Scattering of low-energy Ne+ ions from the stepped surface of InGaP(001)<110> at the small angles of incidence

Scattering of Ne+ ions at small angles of incidence from a stepped InGaP(001) <110> surface by the E0=5 keV was simulated using computer simulation. The trajectories of dechanneled ions from defect surface, as well as their energies at the scattering and scattering angle, are studied. It is shown that before dechanneling, the frequency and amplitude of the trajectory of ions, which move the surface channel formed by the stepped atom, increase. The energy distributions of these ions are obtained and the part of the spectrum corresponding to these ions is determined. It has been established that the energetic dechanneled ions formed low intensity peaks on the low-energy part of the spectrum.

Charging Amorphous Solid Water Films by Ne+ Ions Characterized by Contact Potential Difference Measurements

The study of amorphous solid water (ASW) films on solid substrates has been instrumental in understanding the structure and morphology of water ices. In addition, they have the potential to help researchers understand how complex molecules are formed in regions of the interstellar medium (ISM) where many surfaces are coated with ASW. We have studied ASW films charged by low-energy Ne+ ions under ultrahigh vacuum conditions by measuring the contact potential difference of the charged films with a Kelvin probe. The film becomes positively charged when impinging Ne+ ions oxidize the surface water molecules and subsequently scatter back to the vacuum as neutral Ne atoms. The charged ASW film follows plate capacitor physics, displaying a linear dependence of voltage on ASW layer thickness. Electrical fields of 2 (± 1) × 108 V/m are generated within the films. The level of charging, charge stability, and thermal binding energy of the charges to the ASW film are all very sensitively dependent on the film growth temperature and the temperature of the film during Ne+ ion impingement. We propose that these properties are affected by the film’s porosity and the nature of the proton binding sites, which are dictated by the film growth temperature. The protons are trapped in undercoordinated water molecule defect sites and L-defect sites, with thermal binding energies ranging from 3.4 to 9.4 kcal/mol, as determined by differential contact potential difference (d(ΔCPD)/dT) measurements, obtained during sample annealing.

Neon ion beam induced pattern formation on amorphous carbon surfaces

We investigate the ripple pattern formation on amorphous carbon surfaces at room temperature during low energy Ne ion irradiation as a function of the ion incidence angle. Monte Carlo simulations of the curvature coefficients applied to the Bradley-Harper and Cater-Vishnyakov models, including the recent extensions by Harrison-Bradley and Hofsäss predict that pattern formation on amorphous carbon thin films should be possible for low energy Ne ions from 250 eV up to 1500 eV. Moreover, simulations are able to explain the absence of pattern formation in certain cases. Our experimental results are compared with prediction using current linear theoretical models and applying the crater function formalism, as well as Monte Carlo simulations to calculate curvature coefficients using the SDTrimSP program. Calculations indicate that no patterns should be generated up to 45° incidence angle if the dynamic behavior of the thickness of the ion irradiated layer introduced by Hofsäss is taken into account, while pattern formation most pronounced from 50° for ion energy between 250 eV and 1500 eV, which are in good agreement with our experimental data.

Low energy Ne ion beam induced-modifications of magnetic properties in MnAs thin films

Investigations of the complex behavior of the magnetization of manganese arsenide thin films due to defects induced by irradiation of slow heavy ions are presented. In addition to the thermal hysteresis suppression already highlighted in Trassinelli et al (2014 Appl. Phys. Lett. 104 081906), we report here on new local magnetic features recorded by a magnetic force microscope at different temperatures close to the characteristic sample phase transition. Complementary measurements of the global magnetization in different conditions (applied magnetic field and temperatures) enable the film characterization to be completed. The obtained results suggest that the ion bombardment produces regions where the local mechanical constraints are significantly different from the average, promoting the local presence of magneto-structural phases far from the equilibrium. These regions could be responsible for the thermal hysteresis suppression previously reported, irradiation-induced defects acting as seeds in the phase transition.

Defect states of transition metal-doped MgO for secondary electron emission of plasma display panel

High secondary electron emission (SEE) yield is one of the important properties of MgO for industrial applications such as alternating-current plasma display panel (AC-PDP), which reduces the firing voltage for discharge. SEE induced by low-energy Ne and Xe ions can be described by potential emission mechanism of Auger neutralization. Defect states in MgO can play an important role in enhancing the SEE. The electronic density of states of Ti-, Cr-, Fe-, Ni-, Zn-doped and undoped MgO was calculated using CASTEP. The occupied defect levels of the Ti-, Cr-, Fe-, Ni- and Zn-doped MgO are at 5.23, 3.90, 2.76, 1.22 and 0.06 eV above the valence band, respectively. Higher defect level appears to be advantageous for getting larger SEE yield. Considering the fact that Ti-doped MgO reveals n-type conductivity, Cr seems to be the proper dopant among the studied elements for the purpose of high SEE yield in AC-PDP.

Modification of Barium Cerate by Heavy Ion Irradiation

The effect of irradiation with heavy ions Ne, Ar, and Kr of various energies on the structure and properties of ceramic barium cerate doped with neodymium and annealed in air at 650°C for 7 hours is studied. It is noted that blistering was observed on cerate surface during its irradiation by low energy Ne ions, whereas it was not observed under low-energy Ar and Kr ions irradiation. Irradiation of the cerate with high energy ions caused partial amorphization of the irradiated surface of the material, while the structure of the non-irradiated surface did not change. In addition, the irradiated surface of the cerate endured solid-phase structural changes. Thus, upon high-energy ions irradiation in the range of Ne, Ar, Kr the cerate surface resembled the stages of spherulite formation - nucleation, growth (view of cauliflower), formation of spherulitic crust, respectively. The increase in water molecules release and reduction of molecular oxygen release from the barium cerate, irradiated by high-energy ions is found during vacuum constant rate heating. It is concluded that cerates undergo changes to the distances significantly exceeding the ion ranges in these materials. Features of high-energy ions influence on thermal desorption of carbon dioxide from cerates show, apparently, the formation of weakly bound carbonate compounds on the cerate surface in the irradiation process.

Relativistic calculations of inner-shell atomic processes in low-energy ion–atom collisions

Relativistic calculations of inner-shell atomic processes in low-energy Ne–F8+(1s) and Xe–Xe53+(1s) collisions are performed. The method of calculation exploits the active-electron approximation and is based on the coupled-channel approach with atomic-like Dirac–Sturm–Fock orbitals, localized at the ions (atoms). The screening density-functional theory is applied for description of the interaction with passive electrons. The role of relativistic effects is analyzed.

Channeling of low-energy ions on hydrogen-covered single-crystal surfaces

Low-energy ion beam techniques such as direct recoil spectroscopy (DRS) are well-suited for directly detecting adsorbed hydrogen. However, with this approach it has previously only been possible to detect the hydrogen configuration on single-crystal surfaces for a narrow range of conditions (e.g., when the adsorbate atoms reside close to the surface). In this study we investigate the experimental and modeling tools needed to extend DRS to a much wider range of adsorption geometries. At grazing incidence, we show how adsorbed hydrogen affects ion focusing along open surface channels, thereby revealing fine details about the binding geometry even for adsorbates residing high above the substrate. Under such conditions, the scattering process is characterized by ions interacting with many atoms simultaneously. Therefore interpreting these types of measurements properly requires realistic molecular dynamics (MD) simulations with accurate scattering potentials at large distances. As an illustration of the progress that can be made, we consider how hydrogen is recoiled from W(100)$+$H(ads) during exposure to a low-energy (1 keV) Ne${}^{+}$ analysis beam at grazing incidence. The closest approach distance of the ions is $>$1 $\AA{}$, making hydrogen located high above the substrate readily accessible. By mapping the hydrogen recoils over different crystallographic directions using DRS, we identify focusing mechanisms that provide information on the adsorbed hydrogen configuration. When W(100) is continuously dosed with H${}_{2}$(g) to maintain a saturation coverage, we observe enhanced recoil signals along the $\ensuremath{\langle}$100$\ensuremath{\rangle}$ and $\ensuremath{\langle}$110$\ensuremath{\rangle}$ azimuths consistent with hydrogen residing in bridge sites. The reproduction of the complex experimental scattering spectra by our MD modeling techniques offers a pathway to locate hydrogen well within its vibrational envelope.

Low Energy Ne Scattering Spectroscopy for Insulators, and Materials in the Electric/Magnetic Fields

ABSTRACTThis study describes a low-energy atom scattering system that was combined with a time-of-flight spectrometer for insulator surface structural analysis. We show one example. MgO(001) crystal was used to study the surface analysis technique and is illustrated here. Insulator surface structure is difficult to study because of the charging effects during electron or ion-beam bombardment. Nevertheless, structural analysis of insulator surfaces is very important in fundamental research as well as in technology fields.

The Systems of TOF-low Energy Ne Scattering Spectroscopy for Insulator

We have developed a home-made low-energy Ne scattering system combined with a time-of-flight spectrometer for insulator surface structural analysis. Insulator surface structure is difficult to study because of charging effects during electron or ion beam bombardment. To avoid the charging effects, low energy atom particle beams (2keV-20Ne0) were projected onto the sample surfaces. As an example of data measured by the developed system, a time of flight spectrum obtained from MgO (001) crystal is presented. [DOI: 10.1380/ejssnt.2010.194]

Oxygen interaction with single-walled carbon nanotubes

Oxygen interaction with single-walled carbon nanotubes (SWCNTs) has been studied with x-ray photoemission spectroscopy. We found that at low pressures, molecular oxygen does not interact with clean and pristine SWCNTs, or even with low energy Ne + bombarded SWCNTs, and that irradiation with 300 eV O 2 + ions results in oxygen chemisorption.

Low energy ion and atom scattering spectroscopy for surface structural analysis of single metal and insulator crystals

Applications of low energy ion scattering and low energy atom scattering spectroscopy have been described. Time of flight impact-collision ion scattering (TOF-ICISS) has been used to investigate the heteroepitaxial growth of 3ML of FCC elements on Ni(111) and Cu(111) over a wide temperature range from 300K through 700K. There were two different types of epitaxial growth; FCC(111)[112¯]//Sub(111)[112¯] and FCC(111)[1¯1¯2]//Sub(111)[112¯]. FCC represents Au, Ag, Pb, Pd and Sub represents Ni or Cu. Relative amounts of these two growth modes show oscillatory dependence on the substrate temperature during deposition. However, it is not understood the physics behind this behavior. TOF-ICISS is quite useful to know the surface structure of epitaxy. A low energy Ne atom scattering system combined with a time-of-flight spectrometer for insulator surface structural analysis. Insulator surface structure is difficult to study because of charging effects during electron or ion beam bombardment. It has a potential for insulator surface structural analysis.

Determination of deuterium adsorption site on palladium(1 0 0) using low energy ion recoil spectroscopy

Ion beam analysis has been recently applied to study the adsorption phenomena of some adsorbates on metal surfaces. In this paper, surface recoils created by low energy Ne + ions are employed to study the adsorption site of deuterium (D) atoms on Pd(1 0 0). This technique is extremely surface sensitive with the capacity for atomic layer depth resolution. From azimuthal angle observations of Pd(1 0 0) specimen, it was found that at room temperature, D was adsorbed in the fourfold hollow site of Pd(1 0 0) at a height of 0.25 ± 0.05 Å above the surface. The adsorbate remains in the hollow site at all temperatures to 383 K though the vertical height above the surface is found to depend on coverage and for the first time evidence is found of a transition to a p(2 × 2) structure for the adsorbate. There is no evidence of D sitting in the Pd(1 0 0) subsurface at room and higher temperatures.

Characteristic velocity for inner-shell charge exchange of low energy Ne ions scattered from a polycrystalline Ni surface

The threshold energy of charge exchange processes involving inner-shell electron promotion is investigated in the case of low collision energy Ne ions scattered from a polycrystalline nickel surface. Two distributions of charge fractions are measured from time-of-flight spectra at constant perpendicular velocity in the outgoing path. The energy distribution (energy=2–12keV, constant scattering angle=12°) and the angular distribution (scattering angle=7–50°, constant energy E=4keV) allow the crossing distance RC for electronic transitions during the close-encounter to be determined. Using the value of RC in statistical distributions of close collisions coupled with the Landau–Zener model, we obtain the characteristic velocity VC of the crossing point in the Ne/Ni system.

Neutralization of hyperthermal Ne + on metal surfaces

Relative ion yields of low energy (320 eV) Ne + ions scattered off a number of elemental surfaces are compared. Ion survival probabilities are seen to change significantly from one element to another depending on the surface work function, suggesting that resonant charge exchange between the metal conduction band and Ne 3s atomic level may be just as important as Auger neutralization processes. The observed yield dependence on work function is qualitatively explained using a description of resonant neutralization (RN) based on the Anderson model of an atomic level near a surface. Auger processes are found to be important in determining the final charge state of outgoing ions, while quasi-resonant interactions between the core atomic levels are seen to be nonexistent.

Development of a low energy Ne atom scattering system for insulator surface strctural analysis

AbstractWe have been developing a low energy Ne atom scattering system combined with a time-of-flight spectrometer for insulator surface structural analysis. Insulator surface structure is difficult to study because of charging effects during electron or ion beam bombardment. Structural analyses of insulator surfaces are very important in fundamental research as well as technology fields. In our system, charged ion beams of 2 keV-Ne+ are converted into neutral beams by charge exchange with the same element gas after the primary beam passes through a chopper. Other features of this system are pulsed beams, time-of-flight measurements, and a micochannel plate (MCP) detector is coaxially mounted along the primary beam. This is a home made equipment. We will show the detection systems, as well.

Calculation of elastic integral and differential collision cross-sections for low energy Ne +, Ar +, Kr + and Xe + ions with neutral He atoms

Calculation of elastic integral and differential collision cross-sections for low energy Ne +, Ar +, Kr + and Xe + ions with neutral He atoms

Quasi-single scattering of low-energy Ne + ions from the Fe 3O 4 surfaces

The energy spectra of positive and negative ions emitted from single-crystalline Fe 3O 4 (0 0 1) and (1 1 1) surfaces under low-energy Ne + ion bombardments were investigated in the temperature range from 85 to 300 K. The characteristics of the LEIS spectra of the two surfaces are very similar. The positive-charged-ion spectra have revealed the O +-recoil and the quasi-single scattering Ne +–Fe peak, while a large broad O −1 recoil signal was observed in the negative-charged-ion ones. No change of the peak shape and of the energy position have revealed for the (0 0 1) surface, whereas the (1 1 1) one implies an appearance of a small peak around 150 K attributed to recoil-oxygen ions from the double-collisions.