keV Ar Ions Research Articles

Probing Ar ion induced nanocavities/bubbles in silicon by small-angle x-ray scattering

Small-angle x-ray scattering (SAXS) measurements have been performed to investigate the nanocavities/bubbles and the amorphous silicon surrounding the cavities/bubbles generated after high fluence medium-energy (60 keV) Ar ion implantation in single crystalline Si as a function of incidence angle (with respect to the surface normal of the sample). The measurements were carried out using a high flux/high transmission laboratory scale SAXS set up with Mo-Kα radiation in transmission geometry. The scattering data have been used to calculate the average size (Dave), number density (dN), and volume fraction (Vf) of cavities/bubbles in ion induced amorphous layer of the crystalline Si substrate. The novelty of the SAXS technique applied in the present case lies on its ability to detect ultrafine defect features of size even less than 1 nm, which is otherwise impossible from the transmission electron microscopy measurements usually employed for inert gas ion induced cavities/bubbles in amorphous silicon.

Ion-beam irradiation effects on reactively sputtered CrN thin films

The present study deals with CrN/Si bilayers irradiated at room temperature (RT) with 120 keV Ar ions. The CrN layers were deposited by d.c. reactive sputtering on Si(1 0 0) wafers, at different nitrogen partial pressures (2 × 10 −4, 3.5 × 10 −4 and 5 × 10 −4 mbar), to a total thickness of 240–280 nm. The substrates were held at room temperature (RT) or 150 °C during deposition. After deposition the CrN/Si bilayers were irradiated up to fluences of 1 × 10 15 and 1 × 10 16 ions/cm 2. Structural characterization was performed with Rutherford backscattering spectroscopy (RBS), cross-sectional transmission electron microscopy (XTEM) and grazing angle X-ray diffraction (XRD). For the highest nitrogen pressure (5 × 10 −4 mbar) a pure stoichiometric CrN phase was achieved. The results showed that Ar ion irradiation resulted in the variation of the lattice constants, micro-strain and mean grain size of the CrN layers. The observed microstructural changes are due to the formation of the high density damage region in the CrN thin film structure.

Ion irradiation of multi‐walled boron nitride nanotubes

AbstractMulti‐walled boron nitride nanotubes were irradiated with low and medium energy argon and helium ions at room and elevated temperatures. The irradiated samples were characterized by transmission electron microscopy and Raman spectroscopy, and a comparison to the response of carbon nanotubes to irradiation was made. A dose of 2 × 1015 ions/cm2 was found to give rise to complete amorphization for irradiation with 40 keV Ar ions,while a comparable dose (in terms of displacement per atom) of 1.2 × 1018 ions/cm2 for 350 keV He caused significantly less damage. Elevated temperatures considerably reduce the amount of damage indicating that efficient annealing of defects occurs in BN nanotubes already at 3000 C. Our results provide evidence that multi‐walled BN nanotubes have similar or even better stability under ion irradiation than their carbon counterparts. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural and magnetic properties of Fe-Al2O3 films prepared by helicon plasma sputtering

Fe-Al2O3 films have been prepared by on-off deposition of Fe with continuous Al2O3 deposition, and also subsequently irradiated by 400 keV Ar ions for controlling of the structural and magnetic properties of the films. CEM spectra of the as-deposited films show the decrease in the average hyperfine fields (Hhfs) with decreasing Fe/ Fe-Al2O3 volume ratio with keeping the Hhfs orientation parallel to the film plane. The decrease in Hhfs indicates the decrease of the Fe particle size and the in-plane orientation of Hhfs implies the non spherical shape of Fe particles in the film. On the other hand, 400 keV Ar ion irradiation induces the change from the superparamagnetic characteristics to the ferromagnetic one; the ferromagnetic peaks showing the random orientation of Hhfs appear and indicate the spherical growth of Fe particles in Al2O3 matrix.

Nanosmoothing of single crystal diamond chips by 1 keV Ar+ ion bombardment

In this article the authors have studied the smoothing of diamond chips by irradiating them with 1 keV Ar ion beam at ion incident angles of 0°, 30°, 45°, 60°, and 80° with ion doses from 3.4×1018 to 6.8×1018 ions/cm2. They found that using ion dose of 6.8×1018 ions/cm2 at incident angles from 0° to 45°, the unprocessed surface (rms=0.14–1.2 nm) turned into ultrasmooth processed surface (rms=0.1 nm). Their results also confirmed the formation of ripples on diamond surface when the surface was irradiated with 1 keV Ar+ ion at incident angles of 60°–80°. They have also discussed the mechanism of smoothing and roughening of the surface by employing Bradley and Harper model and equations. These studies led to the understanding of the role of induced viscous flow in the smoothing process. Therefore, by choosing right conditions, 1.0 keV Ar+ ion beam machining can be employed to make diamond tools with nanofinished surface without any ripple effect.

Nanoscale metal-silicide films prepared by surfactant sputtering and analyzed by RBS

Surfactant sputtering has been applied to modify the surface structure of Si substrates and to produce ultrathin metal-silicide films with nickel and platinum surfactants, utilizing the steady state coverage of a Si-substrate surface with surfactant atoms simultaneously during sputter erosion by combined ion irradiation and surfactant atom deposition. Si (1 0 0) substrates were eroded using 5 keV Xe-ions and 10–30 keV Ar ions at incident angles of 65° and 70° with fluences of up to 2 × 10 18 /cm 2 under continuous sputter deposition of platinum and nickel from targets irradiated simultaneously by the same ion beam. These surfactant atoms form metal-silicides in the surface near region and strongly modify the substrate sputter yield and the surface nanostructure. Atomic force microscopy and scanning electron microscopy were carried out to observe a transition of surface topography from ripple to relief patterns, granular patterns or smooth surfaces. The Si and metal sputter yield as function of the steady state metal coverage were determined by combination of Rutherford-backscattering spectroscopy (RBS) and profilometry. The composition and the depth distributions of metal-silicide films were analyzed via high-resolution RBS and transmission electron microscopy. We show that RBS results in comparison with SRIM and TRIDYN sputter yield simulations allows us to identify the silicide surface structure on the nanometer scale.

Defect studies in ion irradiated AlGaN

Abstract Defects created in Al 0.4 Ga 0.6 N crystals by 320 keV Ar ion irradiation were studied using Rutherford Backscattering Spectroscopy/Channeling (RBS/C) and Transmission Electron Microscopy (TEM) techniques. One of the main aims of the work was to use a revised version of McChasy, a Monte-Carlo simulation code of backscattering spectra, for the analysis of experimental results obtained for a dislocation-containing crystal. TEM was used to get a better insight into dislocation and dislocation loop geometries in order to restrict the range of parameters used in simulations. RBS/C analysis was performed in a 1.5–3 MeV energy range to check if MC simulations correctly reproduce backscattering spectra at different energies.

MD simulation of ion implantation damage in AlGaAs: III. Defect accumulation and amorphization

The defect accumulation and amorphization in (0 0 1)Al x Ga 1− x As due to irradiation with 200 keV Ar ions at 20 K is investigated with the help of classical molecular dynamics computer simulation using a modified Tersoff potential. The amount of disorder as a function of the number of displacements per atom has been calculated for x = 0, 0.2, 0.5, 0.75, 0.9 and 1.0. The results reasonably agree with the corresponding RBS data from the literature for x ⩽ 0.9, however, they completely disagree in the case of x = 1. An artificial increase of thermally activated processes shows that thermal annealing during the irradiation may be responsible for the outstanding behavior of AlAs. In addition, the structure of the damage is investigated by visualizing the amorphous clusters and their evolution. It is shown that dynamic annealing does exist. It is negligible for x = 0 but it becomes more and more important with increasing Al content x. Furthermore, it is shown that the generation of damage is supported by pre-damage. This effect dominates the dynamic annealing for x ⩽ 0.5.

Characterization of defects introduced in Sb doped Ge by 3keV Ar sputtering using deep level transient spectroscopy (DLTS) and Laplace-DLTS (LDLTS)

Abstract We have used deep level transient spectroscopy (DLTS), and Laplace-DLTS to investigate the defects created in antimony doped germanium (Ge) by sputtering with 3 keV Ar ions. Hole traps at EV+0.09 eV and EV+0.31 eV and an electron trap at EC−0.38 eV (E-center) were observed soon after the sputtering process. Room temperature annealing of the irradiated samples over a period of a month revealed a hole trap at EV+0.26 eV. Above room temperature annealing studies revealed new hole traps at EV+0.27 eV, EV+0.30 eV and EV+0.40 eV.

Surface segregation of Ti atoms during NiTi alloy sputtering

The paper addresses NiTi alloy sputtering by 9 keV He and Ar ions and discusses the experiment performed by V.S. Chernysh et al. about 10 years ago. The binary collision simulation has been applied to extract the concentrations of surface Ni and Ti atoms from the experimental data. The results of simulations favor segregation of Ti for both He and Ar ion bombardment. The effect of non-symmetric surface collisions (Ti on Ni and Ni on Ti) was found to be negligible. A pronounced effect of the interatomic (target–target) potential is noted.

Structural characterization of TiN coatings on Si substrates irradiated with Ar ions

The present study deals with TiN/Si bilayers irradiated at room temperature (RT) with 120 keV Ar ions. The TiN layers were deposited by d.c. reactive sputtering on Si(100) wafers to a thickness of ∼ 240 nm. After deposition the TiN/Si bilayers were irradiated to the fluences of 1 × 10 15 ions/cm 2 and 1 × 10 16 ions/cm 2. Structural characterization was performed with Rutherford backscattering spectroscopy (RBS), cross-sectional transmission electron microscopy (XTEM), grazing angle X-ray diffraction (XRD) and atomic force microscopy (AFM). The results showed that the variation of the lattice constants, mean grain size and micro-strain can be attributed to the formation of the high density damage region in the TiN film structure. It has been found that this damage region is mainly distributed within ∼ 100 nm at surface of the TiN layers.

Competition of terrace and step-edge sputtering under oblique-incidence ion impact on a stepped Pt(1 1 1) surface

Using molecular-dynamics simulation, we study the sputtering of a Pt(1 1 1) surface under oblique and glancing incidence 5 keV Ar ions. For incidence angles larger than a critical angle ϑ c , the projectile is reflected off the surface and the sputter yield is zero. We discuss the azimuth dependence of the critical angle ϑ c with the help of the surface corrugation felt by the impinging ion. If a step exists on the surface, sputtering occurs also for glancing incidence ϑ > ϑ c . We demonstrate that for realistic step densities, the total sputtering of a stepped surface may be sizable even at glancing incidence.

Temperature-dependent surface modification of InSb(0 0 1) crystal by low-energy ion bombardment

Structural and compositional modification of InSb(0 0 1) single crystal surfaces induced by oblique incidence 2–5 keV Ar and Xe ion irradiation have been investigated by means of scanning tunneling and atomic force microscopies, and time-of-flight mass spectroscopy of secondary ion emission. In general, ion-induced patterns (networks of nanowires, or ripples) are angle of incidence- and fluence-dependent. Temperature dependences (from 300 to 600 K) of the RMS roughness and of the ripple wavelength have been determined for the samples bombarded with various fluences. Secondary ion emission from an InSb(0 0 1) surface exposed to 4.5 keV Ar + ions has been investigated with a linear TOF spectrometer working in a static mode. Mass spectra of the sputtered In +, Sb + and In 2 + secondary ions have been measured both for the non-bombarded (0 0 1) surface and for the surface previously exposed to a fluence of 10 16 ions/cm 2. In + and In 2 + intensities for the irradiated sample are much higher in comparison to the non-bombarded one, whereas Sb + ions show a reversed tendency. This behavior suggests a significant In-enrichment at the InSb(0 0 1) surface caused by the ion bombardment.

Radiation damage in ZnO ion implanted at 15 K

Commercial O-face (0 0 0 1) ZnO single crystals were implanted with 200 keV Ar ions. The ion fluences applied cover a wide range from 5 × 10 11 to 7 × 10 16 cm −2. The implantation and the subsequent damage analysis by Rutherford backscattering spectrometry (RBS) in channelling geometry were performed in a special target chamber at 15 K without changing the target temperature of the sample. To analyse the measured channelling spectra the computer code DICADA was used to calculate the relative concentration of displaced lattice atoms. Four stages of the damage evolution can be identified. At low ion fluences up to about 2 × 10 13 cm −2 the defect concentration increases nearly linearly with rising fluence (stage I). There are strong indications that only point defects are produced, the absolute concentration of which is reasonably given by SRIM calculations using displacement energies of E d(Zn) = 65 eV and E d(O) = 50 eV. In a second stage the defect concentration remains almost constant at a value of about 0.02, which can be interpreted by a balance between production and recombination of point defects. For ion fluences around 5 × 10 15 cm −2 a second significant increase of the defect concentration is observed (stage III). Within stage IV at fluences above 10 16 cm −2 the defect concentration tends again to saturate at a level of about 0.5 which is well below amorphisation. Within stages III and IV the damage formation is strongly governed by the implanted ions and it is appropriate to conclude that the damage consists of a mixture of point defects and dislocation loops.

The formation and evolution of vacancy-type defects in Ar-implanted silicon studied by slow-positron annihilation spectroscopy

The Doppler broadening spectrum of a silicon wafer was measured using a variable-energy positron beam to investigate the effects of vacancy-type defects induced by 180 keV Ar ion implantation. The S-parameter in the damaged layer decreases with annealing temperature up to 673 K, and then increases with annealing temperature from 673 to 1373 K. At low annealing temperatures ranging from room temperature to 673 K, argon-decorated vacancies are formed by argon atoms combining with open-volume defects at inactive positron sites. With further increase of annealing temperature, argon-decorated vacancies dissociate and subsequently migrate and coalesce, leading to an increase of S-parameter. Furthermore, the buried vacancy-layer becomes narrow with increasing annealing temperature. At 1373 K, the buried vacancy-layer moved towards the sample surface.

Formation, trapping, and ejection of radiolytic O2 from ion-irradiated water ice studied by sputter depth profiling

We report experimental studies of 100 keV Ar(+) ion irradiation of ice leading to the formation of molecular oxygen and its trapping and ejection from the surface, at temperatures between 80 and 150 K. The use of a mass spectrometer and a quartz-crystal microbalance and sputter depth profiling at 20 K with low energy Ar ions allowed us to obtain a consistent picture of the complex radiolytic mechanism. We show that the dependence of O(2) sputtering on ion fluence is mainly due to the buildup of trapped O(2) near the surface. A small proportion of the O(2) is ejected above 130 K immediately upon creation from a precursor such as OH or H(2)O(2). The distribution of trapped oxygen peaks at or near the surface and is shallower than the ion range. Measurements of sputtering of H(2) help to elucidate the role of this molecule in the process of O(2) formation: out-diffusion leading to oxygen enrichment near the surface. The competing phenomena of OH diffusion away from the ion track and hydrogen escape from the ice and their temperature dependence are used to explain the finding of opposite temperature dependencies of O(2) and H(2)O(2) synthesis. Based on the new data and understanding, we discuss the application of our findings to ices in the outer solar system and interstellar space.

Ion beam synthesis of germanium nanostructures

Si and Ge nanocrystals embedded in SiO 2 have attracted much attention due to their possible application in integrated optoelectronic devices. Ion beam mixing of Ge film into fused silica to form Ge nanoparticles is one of the possible methods to controllably produce embedded nanoclusters. In this work, Ge nanocrystals in fused silica were formed by defect induced nucleation and ion beam mixing. In our experiment, we have created defects in fused silica using 200 keV Ar ions with different fluences ranging from 1 × 10 15 to 2 × 10 16 ions/cm 2 (pre-mixing irradiation). Ge film (20 nm) was then deposited on it and ion beam mixed using 230 keV Ar ions at a fluence of 2 × 10 16 ions /cm 2. The Ge–SiO 2 composite films were characterized using UV–visible and Micro-Raman spectroscopy. UV–visible spectra showed variation in absorption band gap with ion beam fluence used for pre-mixing irradiation. Micro-Raman spectra showed formation of Ge nanoparticles in SiO 2.

Cell patterning on a glass surface by a mask-assisted ion implantation

A simple patterning method of cells on a glass has been developed by using ion implantation. The glass was implanted through a pattern mask with 150 keV Ar ions in the absence or presence of oxygen. Surface properties of the ion-implanted glass were investigated by means of X-ray photoelectron spectroscopy, contact angle measurement and cell culture test. The results showed that more hydrophilic groups were formed on the glass surface implanted in the presence of oxygen. Thus, the glass surface implanted in the presence of oxygen showed lower contact angle compared with the glass surface implanted in the absence of oxygen. The cells were strongly adhered to and proliferated on the ion-implanted regions of the glass. The cell population was found to be the highest on the glass implanted at a fluence of 1 × 10 16 ions/cm 2 in the presence of oxygen.

Optimization of parameters of the linear TOF-SIMS spectrometer by DOE method

Time of flight SIMS spectrometers are widely used in many industrial and scientific applications. Mass spectra of secondary ions ejected from a bombarded surface supply valuable data on its composition and give insights into physical and chemical processes at the surface. The data quality depends on several parameters, which control the spectrometer functioning. This contribution presents our work on an application of a so-called Design of Experiments (DOE) procedure to optimize working parameters of a home-assembled linear TOF-SIMS spectrometer. The efficiency of optimization procedures was tested for mass spectra of positive ions sputtered from Al surface under keV Ar ion bombardment. In particular, we show that use of the method leads to a large increase both of the mass resolution and of the signal/noise ratio ( S/ N), i.e. improves two quantities, which play a crucial role in mass spectrometry measurements. In addition, it is shown that DOE' method allows to reduce significantly the number of test measurements, and therefore to shorten the adjusting procedure to a minimum.

Compositional dependence of damage buildup in Ar-ion bombarded AlGaN

Results are presented for the RBS/channeling study of the structural defect behavior in ion bombarded Al x Ga 1 − x N (for x = 0; x = 0.44; x = 1) compounds at RT. Epitaxial layers of approximately 1 μm thickness were grown by the MOVPE technique on sapphire substrates. Experiments consisted of implantation with 320 keV Ar ions to fluences ranging from 5 × 10 12 to 1 × 10 17 at/cm 2 followed by RBS/channeling measurements using 1.7 MeV 4He ions. Damage distributions were evaluated using the McChasy Monte Carlo simulation code assuming that they consist of randomly displaced lattice atoms. Detailed dependence of damage buildup on the alloy composition was determined and evaluated in the frame of the Multi-step Damage Accumulation model.