Helium Ion Channeling Research Articles

Quantitative investigation of surface structure and interatomic potential with impact-collision ion scattering spectroscopy

Helium ion beam interactions with materials have important implications for magnetic confinement fusion, material modification, and helium ion microscopy. These interactions depend on the precise physics of how helium ions channel into the materials, which can vary greatly based on the local crystalline orientation. In this work, we performed a dedicated experiment to investigate helium ion channeling in a well-characterized tungsten single crystal. Time-of-flight impact-collision ion scattering spectroscopy was used to obtain multi-angle maps of the backscattering intensity for 3 keV He+ → W(111). We found that the backscattering intensity profile arising from helium ion channeling could be well described by a shadow cone analysis. This analysis revealed that subsurface W atoms as deep as the ninth monolayer contributed to the backscattering intensity profile. Binary collision approximation simulations were performed with MARLOWE to model the experimental maps with sufficient accuracy to allow for quantitative comparisons using reliability factors. These quantitative comparisons were applied to investigate how the W lattice structure and He–W interatomic potential affect the multi-angle maps.

Channeling of charged particles in crystals as an effective tool for studying Mo-Re alloys

The crystal structure of Mo-Re alloys is investigated by channeling of helium ions at an energy of 1.8 MeV in the concentration range in which the electronic topological transition was previously revealed from an analysis of the superconducting and normal properties. It is found that, for Mo-Re alloys containing 11 and 32 at. % Re, the dependences of the yield Y of backscattered particles on the angle θ between the particle beam and the 〈110〉 crystallographic direction exhibit a specific feature in the form of an additional maximum at the half-width (θ = 0.8°). It is assumed that the observed feature is associated with the formation of a superstructure due to the electronic topological transition in Mo-Re alloys.

Experimental evidence for intrinsic ferroelastic nanodomains and their effect on the physical properties of HTSC cuprates

The experimental evidence for ferroelasticity and ferroelastic nanodomains in HTSC perovskite cuprates is reviewed. The evidence for ferroelastic transitions in cuprates has been provided by stress–strain experiments, helium-ion channeling, EXAFS and Raman measurements. Diffuse electron diffraction contrast measured in YBCO with a high resolution electron microscope has shown that due to a ferroelastic misfit between copper–oxygen and barium–oxygen planes, the CuO planes are partitioned into ferroelastic nanodomains. Because of the short coherence length of HTSC, the ferroelastic nanodomains govern the transport properties of cuprates such as the temperature dependence of the critical current density and that of the superfluid density, and their magnetic properties such as the magnetic flux pinning, which determines dependence of the energy barrier against magnetic flux motion on current density and the corresponding magnetic relaxation rates. Ferroelastic nanodomains could be responsible for nanoscopic inhomogeneous charge distribution in YBCO as revealed by inelastic neutron scattering measurements and for nanoscopic regions of high density of states and nanoscopic inhomogeneities (variation of the energy gap) in BSCCO as revealed by the STM experiments.

Transfer of n-type GaSb onto GaAs substrate by hydrogen implantation and wafer bonding

Many GaSb devices would greatly benefit from the availability of a semi-insulating substrate. Since semi-insulating GaSb is not currently available, the formation of thin GaSb layers through wafer bonding and tranfer onto a semi-insulating GaAs substrate was investigated. GaSb-on-insulator structures, formed on GaAs substrates, were realized by the ion-cut process using H+ ions. Blistering, bonding and layer splitting phenomena were studied to optimize the ion dose and the process window. Bonded structures of thin layers of GaSb bonded to GaAs wafers were formed using a borosilicate glass (BSG) layer. The transferred GaSb layers were characterized by atomic force microscopy, MeV helium ion channeling and high-resolution x-ray diffractometry. The transferred film possessed a narrow x-ray linewidth of about 140 arcsec indicating improved crystalline quality over the direct growth of GaSb on GaAs.

Ion-Channeling Studies of Interfaces and Defect Properties in Silicon Carbide

Helium ion channeling has been used in a detailed study of 3C-SiC films on a Si/SiO2/Si (SIMOX) substrate. The strain-induced angular shift was determined to be 0.16?? 0.05?, indicating a kink between the SiC and Si layers along the axis. Single crystals of 6H-SiC have been irradiated with a variety of ions over a range of fluences. The relative disorder on Si sublattice shows a sigmoidal dependence on dose for all ions. In isochronal and isothermal annealing studies, two distinct recovery stages are identified with activation energies of 0.25? 0.1 eV and 1.5? 0.3 eV, respectively. Deuterium ion channeling is also applied to simultaneously study accumulated disorder on Si and C sublattices in 6H-SiC crystals irradiated at 100 and 300 K.

Ion scattering studies of strained Si/Si 1−xGe x superlattices

Helium ion channeling and backscattering experiments have been performed on MBE-grown Si/Si 1−xGe x superlattices to investigate interdiffusion, defect densities and tetragonal lattice distortion. Rapid Thermal Annealing (RTA) of these structures leads to substantial interdiffusion and strain relaxation. In some cases also relaxation by dislocation formation is observed after RTA, depending on the alloy composition x. Grazing incidence Rutherford backscattering spectroscopy was employed to observe the modulation of the backscattering yield of the superlattices. The modulation decreases due to interdiffusion after RTA. Interdiffusion coefficients were deduced for Ge concentrations between x=0.20 and x=0.70 in the temperature range between 900°C and 1125°C. The diffusivity increases with larger Ge concentrations. The activation energy for interdiffusion is 3.8 ± 0.2 eV.

Surface structure of VN0.89(100) determined by low-energy electron diffraction.

The structure of the (100) surface of substoichiometric vanadium nitride was studied by low-energy electron diffraction on a ${\mathrm{VN}}_{0.89}$(100) sample. A simple 1\ifmmode\times\else\texttimes\fi{}1 (100) diffractogram was observed. To describe the electron scattering in substoichiometric VN we apply the averaged t-matrix approximation to the nitrogen atoms. We find that the best structural model is one having no nitrogen vacancies in the surface region. It turns out that the first layer is rippled with the N atoms displaced 0.17 \AA{} above the subplane of V atoms, that the spacing between this subplane and the second layer is 1.92 \AA{}, and that the spacing between the second and the third layer is 2.08 \AA{}. In relation to the (100) spacing of the bulk, 2.06 \AA{}, these spacings are 6.8% contracted and 1% expanded, respectively. The Debye temperature of VN is found to be 660 K in good agreement with a prediction from entropy data and from neutron diffraction and helium-ion channeling experiments.

Formation of silicon carbide in silicon substrates during CF 4/H 2 dry etching

Silicon specimens which had been reactive ion etched in CF 4/ X%H 2 (0≤ X ≤40) and subsequently air exposed have been characterised by X-ray photoelectron emission spectroscopy. Angular rotation was used to study films deposited by the plasma process onto the Si surface. In agreement with previous studies it is found that plasma exposure of Si specimens leads to the deposition of a fluorocarbon film. An intriguing new finding was the discovery of subsurface silicon carbide. The existence of this carbide layer was found to be independent of gas composition from 0–40% H 2 for a one-minute plasma exposure. Helium ion channeling studies of the same specimens show Si near-surface disorder. A silicon-carbide formation mechanism is suggested according to which carbon is deposited below the Si surface by the bombardment of carbon containing ions, thus enabling silicon-carbon bonding.

Ion channeling studies of low energy ion bombardment induced crystal damage in silicon

Helium ion channeling has been used to measure the amount of crystalline damage produced by low energy(⩽ 1 keV) argon, neon and hydrogen ion bombardment of single crystal Si as a function of dose and energy. Using a glancing exit geometry, with a scattering angle of 98°, has allowed an estimate of the damage depth profile particularly for hydrogen ion bombardment. The total damage expressed as an equivalent amorphous silicon thickness was found to be 65 Å for argon, 80 Å for neon and 275 Å for hydrogen for 1 keV ions after a dose of 2–3 × 10 17 cm −2. Under these conditions, crystalline damage produced by hydrogen ions is detected by ion channeling down to a depth of ⪢475 Å. For argon and neon, the total damage scaled with the square root of the ion energy and reaches a near saturation level after an ion dose of 2–3 × 10 15 cm −2. For hydrogen ion bombardment, damage is still clearly increasing even after a dose of 5 × 10 17 cm −2. These results are compared to the predictions of a model based on a calculation of energy deposition per unit volume using the low energy nuclear stopping power of Wilson, Haggmark and Biersack.

Ion channeling study of radiation induced defects in a bent silicon crystal

High energy proton channeling (12–120 GeV) and low energy helium ion channeling (1.5–4 MeV) have been used to study the effects of radiation damage induced in silicon by high energy (400 GeV) proton irradiation. It is shown that radiation fluence up to 10 17/cm 2 does not preclude deflection of high energy charged particle beams in elastically bent silicon crystals. Evidence of macroscopic segregation of residual defects in the strain field of a deformed crystal is demonstrated.

Lattice-Location Experiment of the Ni-Si Interface by Thin-Crystal Channeling of Helium Ions

A thin-crystal channeling experiment has been devised to locate preferential sites of monolayers of Ni atoms deposited onto Si crystalline substrates. The Ni scattering yield shows dips or peaks in the angular scan measurements when channeled along the major crystallographic axes and planes of Si. The results can be explained by a dispersed Ni-Si interface with 2.1\ifmmode\times\else\texttimes\fi{}${10}^{15}$ Ni atoms/${\mathrm{cm}}^{2}$ occupying the tetrahedral interstitial voids of Si.

Ion beam annealing of semiconductors

The first use of an intense pulsed ion beam to anneal ion-implanted semiconductors is reported. Helium ion channeling shows that a single 80-ns pulse 200-keV H+ ions at ∼100 A/cm2 produced good crystallinity in silicon implanted with 1014 As/cm2 at 100 keV.

Channeling of helium ions in lead titanate

Channeling of helium ions in lead titanate

Planar channeling of helium ions along (100), (110) and (111) MgO

Planar channelling of 1, 1.5 and 2 MeV 4He + ions along (100), (110) and (111) MgO have been studied experimentally using Rutherford backscattering. Values of the half angle ψ P 1 2 , shoulder half angle ψ s 1 2 and surface minimum yield x P min have been determined for channelling with respect to the two sublattices. Agreements and discrepancies with existing theories are discussed.