Ion Bombardment Of Solids Research Articles

Calculation of Self-Sputtering Yield under Ion Bombardment of Solids: Computer Simulation and Theory

We developed a computer simulation program for investigation of solid self-sputtering under ion bombardment. The program is based on binary collision approximation, truncated Coulomb potential, and the model of local inelastic losses proportional to energy. As a result of simulation, the self-sputtering yield is calculated as a function of atomic number and ion energy. To verify the cascade simulation code, we created a self-sputtering theory for the case of hard sphere potential. Simulation results show good agreement with both experimental data and theory.

Hydrodynamic model of wave-ordered structures formed by ion bombardment of solids

The model of a wave-ordered structures (WOS) formed by ion-bombardment on a surfaces of amorphous materials is put forward. The model is based on the assumption that amorphous layer under ion-bombardment may be considered as Newtonian fluid on a hard substrate in the field of external force. Within this approach the mathematical model of an amorphous layer is formulated as a boundary value problem for Navier–Stokes and continuity equations for incompressible liquid. Analysis of the problem results in two quasi-stationary spatial-periodic solutions governed by two control parameters: one of them a⊥ is a capillary constant under a vertical ion beam incidence, normalized to layer thickness, another is an angle of incidence Θ. In the general case a capillary constant a⊥(L,Θ) is a convex function of both variables viz. normalized spatial-period L and an angle of incidence Θ. With energy E0=9 keV this function exhibits a local maximum at L=1.77,Θ=50.4∘ which is already global a⊥c=0.375 when E0=5 keV and (as judged by indirect measurements) becomes more convex with further energy reduction. Collation of a⊥(L,Θ) with experimental data reveals that the observed maximum value of capillary constant a⊥ob=0.367, which due to an inherent supercriticality is a little bit lower than a⊥c, falls at Θ=55∘, i.e., with energy diminution angular range should contract to this point. This outcome is consistent with our experimental results on N2+–Si system, manifesting that angular range reduces to a small vicinity of Θcin=55∘ when ion energy tends to minimum energy of WOS formation E0=1.5 keV.

Ion beam modification of ceramics

Abstract Ion-solid interactions that occur during ion bombardment of solids are nonequilibrium in nature; however, the response of a specific material may be governed by thermochemical and thermodynamic factors. Defects are created during irradiation by the elastic and inelastic collisions of the bombarding ions with the target atoms (ions). The types of defects that exist after the cascade cool-down period may be determined by chemical factors. In many cases, the introduction of a defect or an impurity ion must be done in a manner that maintains electrical neutrality; consequently, charged point defects or impurity-point defect complexes are often produced. This paper reviews the structural features of implanted ceramics using sapphire (single crystal α -Al 2 O 3 ) as an example of a ceramic with largely ionic bonding and silicon carbide (6H α -SiC) as one with covalent bonding.

The effects of model parameter variations on high-fluence ion implantation

A general form of the balance equation, to describe the variation of concentration of atomic species during ion bombardment of solids, is employed to reveal the influence of model parameters (atomic volumes and target relaxation) in determining atomic redistribution during high-fluence ion implantation. The study, firstly, of a simple case, ion implantation without mixing, allows us to obtain analytic solutions of the balance equation and to perform an analysis of parametric dependences due to atomic volume mismatch. We also show the effects of atomic mixing and relaxation on the target density, obtained via full numerical solution of the balance equation. The importance of specifying appropriate atomic volumes for the different species involved in the description of mixing is stressed.

The structure of small clusters ejected by ion bombardment of solids

The structure of small clusters predicted by the many-body potentials used in Molecular Dynamics (MD) simulations of semiconductor processes is investigated. The potential minima are determined by using global optimisation algorithms which also find the local minima. It is shown that there are many such local minima for the Tersoff type potentials. If an MD simulation requires an accurate description of the small cluster geometries and energetics, then the potential can describe them provided they are included in the fitting process.

Summary Abstract: Scattered ion yields from 0.2 to 2 keV helium neutral or ion bombardment of solids

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Scattered ion yields from 0.2 to 2 keV helium neutral or ion bombardment of solids

The scattered ion yield from polycrystalline Ag, Al, Au, Cd, Co, Cr, Cu, Fe, In, Mo, Ni, Pd, Si, Sn, Ta, and W foils has been measured for 0.2, 0.5, 1.0, 1.5, and 2.0 keV incident helium neutrals (NSS) or ions (ISS). Measurable scattered helium ion spectra in NSS, which were obtained for all sixteen elements from 1, 1.5, and 2 keV incident neutral helium, consisted of two peaks, I s and I B from surface and subsurface scattering, respectively. In all cases, E E 0 for I s is 25 eV (the ionization energy for He), below that for a single binary elastic collision (SBEC). The intensity of I B depends strongly on the element bombarded; it is smallest for Ag, Au, and In and largest for Cr, Mo, Ta, and W. The ISS spectra yielded peak positions that varied from 0 to 30 eV below that for a SBEC. The low energy tails of the spectra consist of ion yields from scattered ions and reionized neutrals. The energy dependence of the shape of these low energy tails results from the relative fractions of scattered ions and reionized neutrals, where the relative fractions are strongly material dependent.

Scattered ion yields from 0.2 to 2 keV helium neutral or ion bombardment of solids

The scattered ion yield from polycrystalline Ag, Al, Au, Cd, Co, Cr, Cu, Fe, In, Mo, Ni, Pd, Si, Sn, Ta, and W foils has been measured for 0.2, 0.5, 1.0, 1.5, and 2.0 keV incident helium neutrals (NSS) or ions (ISS). Measurable scattered helium ion spectra in NSS, which were obtained for all sixteen elements from 1, 1.5, and 2 keV incident neutral helium, consisted of two peaks, I S and I B, from surface and subsurface scattering, respectively. In all cases, E/ E 0 for I S is 25 eV (the ionization energy for He), below that for a single binary elastic collision (SBEC). The intensity of I B depends strongly on the element bombarded; it is smallest for Ag, Au, and In and largest for Cr, Mo, Ta, and W. The ISS spectra yielded peak positions that varied from 0 to 30 eV below that for a SBEC. The low energy tails of the spectra consist of ion yields from scattered ions and reionized neutrals. The energy dependence of the shape of these low energy tails results from the relative fractions of scattered ions and reionized neutrals, where the relative fractions are strongly material dependent.

Development of microcones induced by contamination lithography

The method of contamination lithography was applied for the generation and investigation of microcones and related topographies which occur during the ion bombardment of solids. One of the mechanisms for the development of microstructures under ion bombardment is the initial shadowing of the sample surface by micro particles. In contrast to the generally unintended deposition of such impurities, the proposed method allows the definite production of 3-dimensional carbonaceous contamination shields with adjustable height and extension, so that systematical studies of the development of the ion beam induced microcones and the behaviour of the surface topography under further ion beam exposure are possible. For deposition of the desired contamination shields a standard commercial scanning electron microscope was used. Pb single crystals have been prepared with contamination shields of 0.4 μ m height. Subsequent Ar +-ion bombardment was performed for different erosion depths and for ion incidence angles of 0°, 25° and 45° relative to the target normal. During oblique ion bombardment the target rotated around the normal. Cones, cylinders and double cones of micron size were produced under the different exposure conditions and investigated for different stages of development with respect to size and flank elevation angles.

4973. A first order diffusion approximation to atomic redistribution during ion bombardment of solids, II. Finite range approximation: G Carter et al, Rad Effects, 55 (1/2), 1981, 99–110

4973. A first order diffusion approximation to atomic redistribution during ion bombardment of solids, II. Finite range approximation: G Carter et al, Rad Effects, 55 (1/2), 1981, 99–110

A first order diffusion approximation to atomic redistribution during ion bombardment of solids, II. finite range approximation

Abstract An improved diffusion approximation, in which diffusion enhancement operates only over a finite depth, to model atomic redistribution resulting from recoil and cascade mixing during ion bombardment of solids is described, it is shown that this model correctly simulates the main results of the more complex linear cascade atomic collision calculations of positive mean depth shifts, negative peak shifts, broadenings and exponential tails in surface concentration of diffusant marker species during sputter erosion. The analytic method of generalisation to any arbitrary and more realistic diffusivity-depth profiles is also outlined.

A first order diffusion approximation to atomic redistribution during ion bombardment of solids: I. Infinite range approximation

Abstract A diffusion approximation to the ion bombardment induced ‘mixing’ of tracer atoms, initially located as a delta function of depth, in a host matrix of like atoms, with congruent erosion of the surface is considered. A depth and ion fluence diffusivity independence is assumed. It is shown that both “shifts” and “broadenings” in the surface concentration of marker as a function of depth eroded relative to the no diffusion case occur. These shifts and broadenings follow similar directional but dissimilar parametric dependence upon the initial marker depth to linear cascade treatments. Suggestions for improved depth truncated and depth dependent diffusivities and additional drift terms are explored.

Threshold studies of secondary electron emission induced by macro-ion impact on solid surfaces

Incident ion velocity thresholds for secondary electron emission induced by ion bombardment of solids have been determined in the range 1 × 10 6 cm/s−1 × 10 7 cm/s using positive water molecule cluster ions with m/e up to ∼6 × 10 4. With the relatively high molecular weight species, shifts in values of incident ion velocity thresholds down to approximately 1.5 × 10 6 cm/s were observed. This is a factor of three lower than previously determined values using molecule or cluster ions which were more than an order of magnitude smaller in mass. These observations are taken as evidence for multiple collisions between electrons and displaced energetic lattice atoms in the collision spike and collisions of more than one atom in the projectile clusters with an electron in the solid surface. A kinetic secondary electron emission mechanism involving energy equilibration between lattice atoms and electrons in the collision spike is suggested.

Influence of the radiationless transitions on an intensity of the optical radiation emitted by excited atoms ejected from solids by an ion beam

The excited atoms of the target material are ejected during an ion bombardment of solids. These atoms belong to one of two velocity groups — fast or slow. The fast atoms arise in binary collisions of bombarding ions with target atoms and the slow ones are knocked out as a result of a sputtering process. Excited atoms flying off the surface intersect the solid-vacuum boundary and can transfer their excitation energy in the radiationless transitions mainly of the resonance ionization type. The probability of this process depends strongly on the electronic energy level structure of solids and a velocity of ejected atoms. On this statement our method of the electronic energy level structure of solids study is based by means of investigation of excited atoms velocity spectrum.

Combined UHV ion-scattering and secondary-ion mass spectrometer using magnetic analysis

A combined ion-scattering and secondary-ion mass spectrometer, for use in studies of low-energy ion bombardment of solids, is described. The secondary ions from the target (both sputtered and scattered) are analysed by a momentum analyser having a 14 cm radius and 90 degrees magnetic sector which provides their positive identification in mass and energy. It is an ultrahigh-vacuum instrument; inert-gas primary ions of energies in the range 15-2000 eV are used. The principle of operation, constructional details and capabilities are presented. The use of the instrument in secondary-ion mass spectrometry and ion-scattering studies is discussed. The magnetic analysis used allows the sputtered and scattered ions to be distinguished even at very low primary-ion energies (below 100 eV).

Sputtering during ion implantation into gallium arsenide

The surface erosion caused by ion bombardment of solids and its effect on the number of ions retained in the solid was studied experimentally for a variety of ions implanted into GaAs with various fluences and energies. Experimental methods were interferometry and semi quantitative X-ray analysis by means of an electron microprobe. By an easy-to-use computer calculation the change in the implantation profiles was determined and the number of retained ions were related to the surface shift caused by sputtering. Comparison of this shift with the real erosion found before and after annealing was made. From the results, we conclude that the collapse of the crystal lattice contributes to the sinking of the bombarded surface. Sputtering data necessary to estimate the technical consequences of sputtering, range data of 100 keV Fe ions, and data indicating the sensitivity of X-ray analysis are presented.

Dose regularities under ion bombardment of solids

Abstract Among other parameters which influence various processes associated with ion bombardment of solids (such as sputtering, secondary electron emission, ion scattering and so on) there is “ion dose”. As the ion dose the product of ion current density (or total ion current) and time of irradiation is usually accepted. However, this definition is valid in such cases only when the time interval required for the actual experiment (or for the actual measurement) is small as compared with a certain time interval (relaxation time) which may be approximately determined as the bombarded ion penetration depth divided by the velocity of the irradiated surface motion due to target sputtering. The examination of the situations which take place in typical ion bombardment experiments (ion current densities of about 0.01–1.00 ma/cm2, sputtering ratios of about 1–10 at/ion) shows that the relaxation time turns out to be of the order of some minutes to some seconds depending strongly, in particular, on the crystalline...

Ion Bombardment of Solids

Ion Bombardment of Solids

EXCITATION OF ELECTRONS IN SOLIDS BY RELATIVELY SLOW ATOMIC PARTICLES

I. Introduction 332 II. Excitation of Electrons Due to the Internal Energy of the Atomic Particle-plus-solid System and Potential Ejection of Electrons 332 III. Kinetic Ejection of Electrons in Vacuum 342 IV. Radiative (Induced) Conductivity of Semiconductors Bombarded with Ions 353 V. Excitation of Luminescence by Ion Bombardment of Solids, and Ionoluminescence 358 VI. Conclusion 362 Cited Literature 364

The effects produced by positive ion bombardment of solids: metallic ions

The following is a preliminary account of experiments made in an attempt to obtain information about the relation between the energy of a positive ion and the effect produced on a surface which it bombards. The energy relations which hold in collisions between rapidly moving positive ions and the molecules of a gas or of a solid are of extreme importance in the theory of gaseous discharges at low pressures, in particular of the initiation of the self-sustained discharge.