Low Energy Ion Bombardment Research Articles

Molecular dynamics simulation of bipartite bimetallic clusters under low-energy argon ion bombardment

The evolution of bipartite bimetallic atomic clusters within 5 ps under bombardment with monoenergetic argon ions at the initial energy ranging from 1 eV to 1.4 keV has been simulated by the classical molecular dynamics method with a target obtained from Ni‒Al and Cu‒Au clusters consisting of 78 and 390 atoms, equally divided between the corresponding monometallic parts, the simulated pairs of which have different heats of intermixing. The changes in the potential energy and temperature, the sputtering yields, and the intensity of the ion-stimulated movement of atoms at the interface of the monometallic parts of clusters of both sizes have been determined as functions of the energy of the bombardment.

Optical absorption enhancement of CdTe nanostructures by low-energy nitrogen ion bombardment

In this paper we present the fabrication of cadmium telluride (CdTe) nanostructures by means of RF magnetron sputtering followed by low-energy ion implantation and post-thermal treatment. We have thoroughly studied the structural, optical, and morphological properties of these nanostructures. The effects of nitrogen ion bombardment on the structural parameters of CdTe nanostructures such as crystal size, microstrain, and dislocation density have been examined. From x-ray diffractometer (XRD) analysis it could be deduced that N+ ion fluence and annealing treatment helps to form (3 0 0) orientation in the crystalline structure of cadmium-telluride films. Fluctuations in optical properties like the optical band gap and absorption coefficient as a function of N+ ion fluences have been observed. The annealing of the sample irradiated by a dose of 1018 ions cm−2 has led to great enhancement in the optical absorption over a wide range of wavelengths with a thickness of 250 nm. The enhanced absorption is significantly higher than the observed value in the original CdTe layer with a thickness of 3 μm. Surface properties such as structure, grain size and roughness are noticeably affected by varying the nitrogen fluences. It is speculated that nitrogen bombardment and post-annealing treatment results in a smaller optical band gap, which in turn leads to higher absorption. Nitrogen bombardment is found to be a promising method to increase efficiency of thin film solar cells.

A Sensitivity Enhanced MWCNT/PDMS Tactile Sensor Using Micropillars and Low Energy Ar⁺ Ion Beam Treatment.

High sensitive flexible and wearable devices which can detect delicate touches have attracted considerable attentions from researchers for various promising applications. This research was aimed at enhancing the sensitivity of a MWCNT/PDMS piezoresistive tactile sensor through modification of its surface texture in the form of micropillars on MWCNT/PDMS film and subsequent low energy Ar+ ion beam treatment of the micropillars. The introduction of straight micropillars on the MWCNT/PDMS surface increased the sensitivity under gentle touch. Low energy ion beam treatment was performed to induce a stiff layer on the exposed surface of the micropillar structured MWCNT/PDMS film. The low energy ion bombardment stabilized the electrical properties of the MWCNT/PDMS surface and tuned the curvature of micropillars according to the treatment conditions. The straight micropillars which were treated by Ar+ ion with an incident angle of 0° demonstrated the enhanced sensitivity under normal pressure and the curved micropillars which were treated with Ar+ ion with an incident angle of 60° differentiated the direction of an applied shear pressure. The ion beam treatment on micropillar structured MWCNT/PDMS tactile sensors can thus be applied to reliable sensing under gentle touch with directional discrimination.

Oxidation of nickel surfaces by low energy ion bombardment

We have studied formation of oxides on Ni surfaces by low energy oxygen bombardment using X-ray photoemission spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). Different oxidation states of Ni ions have been identified in XPS spectra measured around Ni 2p and O 1s core-levels. We have compared our results with thermal oxidation of Ni and shown that ion bombardment is more efficient in creating thin oxide films on Ni surfaces. The dominant Ni-oxide in both oxidation processes is NiO (Ni2+ oxidation state), while some Ni2O3 contributions (Ni3+ oxidation state) are still present in all oxidised samples. The oxide thickness of bombarded Ni samples, as determined by SIMS, was shown to be related to the penetration depth of oxygen ions in Ni.

Formation of nanometer-thick delaminated amorphous carbon layer by two-step plasma processing of methacrylate-based polymer

The authors show that extended He plasma pretreatment (PPT) of methacrylate-based 193 nm photoresist (PR) material in conjunction with a subsequent biased Ar plasma treatment can lead to blister formation at the polymer surface due to delamination of an ultrathin, ion-induced, dense, amorphous carbon (DAC) layer formed by low energy ion bombardment. For our experimental conditions, the delaminated layer is 1–2 nm thick and primarily composed of sp2-hybrized amorphous carbon. A He or Ar plasma process alone will not lead to this phenomenon, and so far the authors have only observed it for a methacrylate polymer. A possible mechanism of the formation of the ultrathin layer that is consistent with all observations is as follows: During He plasma pretreatment, volatile species are produced by ultraviolet/vacuum ultraviolet radiation-induced photolysis of the polymer pendant groups, e.g., adamantyl and chain-scissioning of the polymer backbone to a depth of greater than 100 nm. While volatile products formed close to the polymer surface can diffuse out during He PPT, those formed deep within the polymer bulk cannot and their concentration will become significant for extended He PPT. During the biased Ar plasma treatment step, a DAC surface layer is generated by Ar+ ion bombardment within the first seconds of plasma exposure. The thickness is dependent on ion energy and in the range of one to several nanometers. This layer appears to be impermeable to gaseous products formed in the PR material. Thus, volatile species diffusing to the surface can accumulate underneath the DAC layer, causing a loss of adhesion and subsequent delamination of this layer from the PR bulk film. The authors also report surface and electrical characterizations of the ultrathin DAC layer using optical microscopy, transmission electron microscopy, Raman and x-ray photoemission spectroscopy, and two-point probe techniques.

Molecular dynamics simulation on selective etching of α -quartz and amorphous quartz substrate using low-energy argon ion bombardment model in dry etching process

We investigated the physical sputtering of low-energy argon bombardment onto α-quartz and amorphous quartz substrate using dynamics simulations. We reported the effects of etching selectivity, the effect of surface temperature, Ts, and the effect of incident energy, Ei on sputtering yield. The second generation charge-optimized many body (COMB10) potential was utilized to model the interatomic potential of quartz substrates. Simulations were conducted at incident energies of Ei=50, 100, and 150 eV and substrate temperatures of Ts=300, 500, and 800 K. α-quartz shows higher sputtering yield compared to amorphous quartz at any given incident energy, Ei and substrate temperature, Ts. α-quartz has also produced more stoichiometric yield compared to amorphous quartz.

Computer simulation of the single crystal surface modification and analysis at grazing low-energy ion bombardment

The specific peculiarities of 0.5-10 keV Ne+, Ar+, Kr+, Be+ and Se+ ions scattering, sputtering and implantation processes at grazing ion bombardment of GaAs (001), Si(001), SiC(001) and Cu(100) surfaces and their possible application for the surface modification and analysis have been studied by computer simulation. Sputtering yields in the primary knock-on recoil atoms reghne versus the initial energy of incident ions (E0 = 0.5-5 keV) and angle of incidence (ψ = 0-30°) counted from a target surface have been calculated. The colliding particles mass ratio influence on the energy losses of scattering particles, sputtering yields and near-surface depth distributions of implanted particles is established, ft was shown that in the case of grazing ion bombardment the layer-by-layer sputtering is possible and its optimum are observed within the small angle range of the glancing angles near the threshold sputtering angle. Comparative studies of layer-by-layer sputtering for Si(001) and SiC(001) surfaces versus the initial energy of incident ions as well as an effective sputtering and sputtering threshold are discussed.

Formation of titanium monoxide (001) single-crystalline thin film induced by ion bombardment of titanium dioxide (110).

A plethora of technological applications justify why titanium dioxide is probably the most studied oxide, and an optimal exploitation of its properties quite frequently requires a controlled modification of the surface. Low-energy ion bombardment is one of the most extended techniques for this purpose and has been recently used in titanium oxides, among other applications, to favour resistive switching mechanisms or to form transparent conductive layers. Surfaces modified in this way are frequently described as reduced and defective, with a high density of oxygen vacancies. Here we show, at variance with this view, that high ion doses on rutile titanium dioxide (110) induce its transformation into a nanometric and single-crystalline titanium monoxide (001) thin film with rocksalt structure. The discovery of this ability may pave the way to new technical applications of ion bombardment not previously reported, which can be used to fabricate heterostructures and interfaces.

Ion damage overrides structural disorder in silicon surface nanopatterning by low-energy ion beam sputtering

We investigate the role of the initial structural condition in silicon surface nanopatterning by low-energy ion beam sputtering. Specifically, we address the influence of the target atomic structure in ripple formation under oblique irradiation by 500 eV ions. To this end, we compare results obtained on single-crystal, amorphous, and pre-implanted silicon targets. In spite of the differences in terms of structural order, and in contrast to previous results for medium energies, surface dynamics are found to be quantitatively similar in all these systems. We explain our results through molecular dynamics simulations of the initial irradiation stages, with the conclusion that the damage induced by low-energy ion bombardment overrides the initial atomic state of the silicon target, irrespectively of its preparation method and allows silicon re-using for nanostructuring.

Non-crystallization and enhancement of field emission of cupric oxide nanowires induced by low-energy Ar ion bombardment

The effect of low energy Ar ion bombardment on the structure and field emission properties of CuO nanowires was studied. The morphology and structure were characterized by scanning electron microscopy and high resolution transmission electron microscopy. Non-crystallization of the nanowire was found after bombardment, which was due to the diffusion of the defects induced by knock-on ions. The work function of nanowires decreased after bombardment which was attributed to the preferential sputtering of oxygen. Field emission measurements showed that after bombardment with different energy the turn-on field decreased first and then increased with increasing ion energy. The lowest turn-on field was obtained with the optimal ion energy of 215eV. The typical turn-on fields of the as-grown samples and samples after Ar ion bombardment with energy of 215eV were about 6.5V/μm and 5.25V/μm, respectively. The lowered field emission turn-on field was attributed to the increase of field enhancement factor and decrease of work function.

Evolution of isolated copper clusters under low-energy argon ion bombardment

The molecular dynamics simulation of the evolution of clusters of copper in a vacuum under low-energy argon ion bombardment has been performed. The clusters consisting of 26, 78, and 390 atoms have been studied at a bombarding particle energy ranging from 1 to 800 eV. The potential of the interaction between copper atoms has been simulated using the embedded atom method, whereas the interaction of copper atoms with argon atoms has been described using the Ziegler-Biersack-Littmark potential. As a result of the simulation, time dependences of the temperature and potential energy and the numerical values of the sputtering coefficients of free clusters under the ion bombardment have been obtained.

Stress evolution in Si during low-energy ion bombardment

Abstract

Short-range ordering of ion-implanted nitrogen atoms in SiC-graphene

We perform a structural analysis of nitrogen-doped graphene on SiC(0001) prepared by ultra low-energy ion bombardment. Using scanning tunneling microscopy, we show that nitrogen atoms are incorporated almost exclusively as graphitic substitution in the graphene honeycomb lattice. With an irradiation energy of 25 eV and a fluence of approximately 5 × 1014 cm−2, we achieve a nitrogen content of around 1%. By quantitatively comparing the position of the N-atoms in the topography measurements with simulated random distributions, we find statistically significant short-range correlations. Consequently, we are able to show that the dopants arrange preferably at lattice sites given by the 6 × 6-reconstruction of the underlying substrate. This selective incorporation is most likely triggered by adsorbate layers present during the ion bombardment. This study identifies low-energy ion irradiation as a promising method for controlled doping in epitaxial graphene.

Electronic structure of nitinol surfaces oxidized by low-energy ion bombardment

We have studied the electronic structure of nitinol exposed to low-energy oxygen-ion bombardment, using x-ray photoemission spectroscopy (XPS) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy. XPS spectra reveal a gradual transformation of nitinol surfaces into TiO2 with increased dose of implanted oxygen. No oxidation of Ni atoms has been detected. NEXAFS spectra around O K-edge and Ti L2,3-edge, reflecting the element-specific partial density of empty electronic states, exhibit features, which can be attributed to the creation of molecular orbitals, crystal field splitting, and the absence of long-range order, characteristic of the amorphous TiO2. Based on these results, we discuss the oxidation kinetics of nitinol under low-energy oxygen-ion bombardment.

Submonolayer films on a Si(111) surface under low-energy ion bombardment

The kinetics of deposition for monomolecular submonolayer films on a Si(111) surface is studied via low-energy electron diffraction with measurements of the intensities of diffraction reflection and the elastic background. The degree of structural perfection in growing films is estimated for alkali-metal silicides and silicon from low-energy beams. The optimum energy and dose intervals of silicide film formation are determined.

Structural and optical properties of magnetron-sputtered Er-doped AlN films grown under negative substrate bias

Abstract In seeking suitable host-microstructures enhancing photoluminescent (PL) efficiency of reactively sputtered Er-doped AlN films deposited under varying negative substrate bias, we observed that the films’ Er-emitted PL intensity at the wavelength of 1.54 μm builds up with bias up 50 V, before falling sharply and collapsing for U above 90 V. We studied for further insight the bias-induced effects on the film microstructural and optical properties. The transmission electron microscope images of these films biased up to ∼50 V showed improved film crystallographic quality with wide and long columnar microstructures. The columnar crystallized volumes therein are maximized around a particular bias value around 90 V, above which they have finely grained nano-granular microstructures. This film-microstructural evolution concurs well with the film refractive index n and extinction coefficient k obtained from ellipsometry. Both surge for films biased from ∼50 V to ∼90 V. These correlating evidences point out that adequate adatom mobility gained under low-energy ion bombardment with bias up to 50 V properly configures the AlN Wurzite planes while leaving behind fewer sites for PL-quenching defects. Meanwhile, Urbach tail states associated with other visible-light absorbing defects created by some material disorder in appropriate locations within the columns should have absorb the exciting photon energy and transfer it efficiently to the emitting Er3+ ions. These evidences further indicate that the newer defects created under bias above 100 V act as non-radiative centers in putting out the PL. We suggest that these latter defects would be located with a high density, at the numerous grain boundaries of the nano-crystallized volumes.

Nanostructuring of Iron Surfaces by Low-Energy Helium Ions

The behavior of iron surfaces under helium plasma exposure is investigated as a function of surface temperature, plasma exposure time, and He ion flux. Different surface morphologies are observed for a large process parameter range and discussed in terms of temperature-related surface mechanisms. Surface modification is observed under low-He ion flux (in the range of 10(20) m(-2) s(-1)) irradiation, whereas fiberlike iron nanostructures are formed by exposing the surface to a high flux (in the range of 10(23) m(-2) s(-1)) of low-energy He ions at surface temperatures of 450-700 °C. The effects of surface temperature and plasma exposure time on nanostructures are studied. The results show that surface processing by high-flux low-energy He ion bombardment provides a size-controlled nanostructuring on iron surfaces.

Band alignment and Schottky behaviour of InN/GaN heterostructure grown by low-temperature low-energy nitrogen ion bombardment

InN/GaN heterostructure based Schottky diodes are fabricated by low energetic nitrogen ions at 300 °C.

Oxidation of GaN(0001) by low-energy ion bombardment

Abstract Oxygen bombardment is used as the oxidation method to form an insulator on GaN substrate at room temperature. The surface of clean substrate and the Ga2O3/GaN interface are characterized in situ by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and low-energy electron diffraction (LEED). XPS spectra of the Ga 2p core level show a peak shift of ∼1 eV from Ga O to Ga N bonding, demonstrating an oxide formation of Ga2O3. Electron affinity of the clean GaN surface amounts to 3.65 eV; the electron affinity of the Ga2O3 on GaN(0001) surface is 3.7 eV. Valence band offset (VBO) of the Ga2O3/GaN interface measured using XPS and UPS is 1.15 eV. After annealing the system at 500 °C the electron affinity and the VBO decrease to the values 3.5 and 0.35 eV, respectively.

Controlled deposition of sulphur-containing semiconductor and dielectric nano-structured films on metals in SF6 ion-ion plasma

In the present paper, the deposition processes and formation of films in SF6 ion-ion plasma, with positive and negative ion flows accelerated to the surface, are investigated. The PEGASES (acronym for Plasma Propulsion with Electronegative GASES) source is used as an ion-ion plasma source capable of generating almost ideal ion-ion plasma with negative ion to electron density ratio more than 2500. It is shown that film deposition in SF6 ion-ion plasma is very sensitive to the polarity of the incoming ions. The effect is observed for Cu, W, and Pt materials. The films formed on Cu electrodes during negative and positive ion assisted deposition were analyzed. Scanning electron microscope analysis has shown that both positive and negative ion fluxes influence the copper surface and leads to film formation, but with different structures of the surface: the low-energy positive ion bombardment causes the formation of a nano-pored film transparent for ions, while the negative ion bombardment leads to a continuous smooth insulating film. The transversal size of the pores in the porous film varies in the range 50–500 nm, and further analysis of the film has shown that the film forms a diode together with the substrate preventing positive charge drain, and positive ions are neutralized by passing through the nano-pores. The film obtained with the negative ion bombardment has an insulating surface, but probably with a multi-layer structure: destroying the top surface layer allows to measure similar “diode” IV-characteristics as for the nano-pored film case. Basing on results, practical conclusions for the probes and electrodes cleaning in ion-ion SF6 plasmas have been made. Different applications are proposed for the discovered features of the controlled deposition from ion-ion plasmas, from Li-sulphur rechargeable batteries manufacturing and nanofluidics issues to the applications for microelectronics, including low-k materials formation.