Noble Gas Ion Bombardment Research Articles

Monte Carlo simulations of MgO and Mg(OH) 2 thin films sputtering yields by noble-gas ion bombardment in plasma display panel PDP

Abstract MgO is known to be a material suitable for barrier coating of commercial plasma display panel (PDP) cells owing to its excellent electrical insulating property, good resistance to sputtering, large secondary-electron emission coefficient and high transmittance. It is also a valuable information for improving the efficiency and the lifespan of the PDP. However, the effect of moisture emitted from the wall and phosphor materials of the PDP cells, an Mg(OH)2 is formed on the top surface of an MgO protective layer. In this work, the Monte Carlo simulation program SRIM-2013 was applied to calculate the sputtering yields of magnesium hydroxide Mg(OH)2 by low-energy noble-gas ion bombardment. The comparison between results obtained by Monte Carlo simulation and those obtained by experiments is elucidated in this paper. Furthermore, the surface binding energies for MgO and Mg(OH)2 layers on sputtering yield are discussed. It is found that the sputtering yield of Mg(OH)2 is generally lower than that of MgO at each incident energy. On the other hand, the sputtering yield depends on the properties of both the incident particle and the target.

Sputtering yields of magnesium hydroxide [Mg(OH)2] by noble-gas ion bombardment

Magnesium oxide (MgO) is widely used for barrier coating of plasma display panel (PDP) cells and its resistance against ion sputtering is a critical issue for the prolongation of lifetime of PDPs. The top surface of an MgO barrier coat may be hydrated to form a thin layer of magnesium hydroxide [Mg(OH)2] due to moisture inadvertently contained in the gas of the PDP cell. In this study, sputtering yields of Mg(OH)2 by low-energy noble-gas ion bombardment have been evaluated experimentally with the use of a mass-selected ion beam system and compared with those of MgO. It has been found that the etched depths of Mg(OH)2 and MgO are nearly equal when they are subject to the same noble-gas ion bombardment conditions.

Sputtering Yields of CaO, SrO, and BaO by Monochromatic Noble Gas Ion Bombardment

Sputtering Yields of CaO, SrO, and BaO by Monochromatic Noble Gas Ion Bombardment

Sputtering Yields of CaO, SrO, and BaO by Monochromatic Noble Gas Ion Bombardment

Although MgO is widely used for barrier coating in the current generation of commercial plasma display panel (PDP) cells, other alkaline earth oxides have been studied as alternatives to MgO because some of them have lower discharge breakdown voltages for PDP cells, which would increase energy efficiency of the cells. On the other hand, the resistance against physical sputtering is another critical parameter for barrier coating. In this work, sputtering yields of CaO, SrO, and BaO by monochromatic He+, Ar+, or Kr+ ion beams of normal incidence have been obtained experimentally at relatively low incident energies by a mass-selected ion beam system. Despite the large differences in mass among the target materials, sputtering yields are found to be similar in magnitude among them for a given incident energy. It has been also found that sputtering yields depend weekly on the mass of incident species among Ne+, Ar+, Kr+, and Xe+ ions.

Sputtering yields of Au by low-energy noble gas ion bombardment

Sputtering yields of gold (Au) by noble gas (He, Ne, Ar, Kr or Xe) ions have been measured in the low injection energy range 25–200 eV. The yield data presented here were obtained from mass-selected ion beam sputtering experiments, in which the ion beam has a very narrow energy spread and contains no impurity ions. The newly obtained yield data set, together with the fitting functions for the yield dependence on the injection energy, provide an accurate and reliable database for the study of fundamental physical mechanisms of sputtering phenomena at low energies, where experimental data had been scarce.

Ion fluence dependence of the Si sputtering yield by noble gas ion bombardment

The effect of sputtering yield enhancement by implantation of noble gases into solid silicon is investigated with the Monte Carlo program SDTrimSP. The process of diffusion is incorporated into the program to describe the outgassing of noble gases. The bombardment of Si with He, Ne, Ar, Xe at normal incidence is studied in the energy range from 1 to 500keV. Good agreement of the calculated results with experimental data is found.

Ion energy dependence of nanodot formation by nitrogen-bombarded InP

Abstract When InP is bombarded with noble gas ions or nitrogen ions, nano-scaled sputter cones appear on the surface. In this study, we report on the ion energy dependence of the surface topography due to nitrogen ion bombardment. InP(1 0 0) substrates were bombarded with 1–5 keV N 2 + ions at an angle of incidence of 41° with respect to the normal. The fluence was fixed at 5 × 10 16 N 2 + cm - 2 . The topographies of the virgin and bombarded samples were investigated by AFM (atomic force microscopy) and high-resolution SEM (scanning electron microscopy). There are similarities between the topographies of the nitrogen-bombarded surfaces to those reported for noble gas ion bombardment. The AFM-measured topographies were quantified in terms of the root mean square (rms) roughness. The rms of 12 roughness initially decreases from a high value at 0.5 keV per nitrogen atom to reach a minimum somewhere between 1.5 and 2 keV per nitrogen atom. The results are compared to the results reported for noble gas ion-bombarded InP and to the standard theories in this field. In general, the rms roughness as a function of ion energy is ion mass dependent, in agreement with results reported for ripples on Si and GaAs. However, there seems to be only a slight dependence on the chemical reactivity of the bombarding ions with the InP substrate. No ripples were observed on the samples.

Fluence dependence of the surface roughness of InP after [formula omitted] bombardment

InP(100) surfaces were sputtered under ultrahigh vacuum conditions by 5keV N2+ ions at an angle of incidence of 41° to the sample normal. The fluence, ϕ, used in this study, varied from 1×1014 to 5×1018N2+cm−2. The surface topography was investigated using field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). At the lower fluences (ϕ⩽5×1016N2+cm−2) only conelike features appeared, similar in shape as was found for noble gas ion bombardment of InP. At the higher fluences, ripples also appeared on the surface. The bombardment-induced topography was quantified using the rms roughness. This parameter showed a linear relationship with the logarithm of the fluence. A model is presented to explain this relationship. The ripple wavelength was also determined using a Fourier transform method. These measurements as a function of fluence do not agree with the predictions of the Bradley–Harper theory.

Production of Nanowires on Semiconductor Surfaces by Ion Bombardment

Low energy (typically in the keV regime) ion bombardment of some semiconductor materials can lead to the development of regularly spaced ripples on the surfaces, which with suitable doping procedures, can be employed as nanowires. Although these ripples are reminiscent of those induced by the action of wind on sand dunes or by water currents on the seabed, the mechanisms are different. The formation of the bombardment-induced ripples depends primarily on the material sub-strate. The average distance between the ripples, i.e. ripple wavelength is also a function of ion spe-cies, ion energy, angle of incidence, ion areic dose and substrate temperature. In this paper, some of the reported results on the effect of areic dose on ripples produced by noble gas, oxygen and nitrogen ion bombardment on selected semiconductor materials will be tested against Bradley-Harper theory. Some of the ripple properties can be explained by this analytic theory. The analysis suggests that room temperature bombardment of silicon might be transition regime between those of a low ion areic dose rate at high temperature and a high areic dose rate at low temperature bombardment. For a full understanding of bombardment-induced topography on semiconductor surfaces at room temperature, one will have to resort to the more advances theories, which can only be solved numerically, with all it associated difficulties.

Bombardment-induced ripple topography on GaAs and InP

Bombardment-induced ripples have possible application in nano-technology as nano-wires. This paper reviews some of the published experimental data of ripple formation on GaAs and InP resulting from noble gas, oxygen, nitrogen and cesium ion bombardment. The dependences of the ripples and their corresponding wavelengths on substrate temperature, areic dose and (to a lesser extent) angle of incidence were considered. The experimental results were tested against the predictions of the Bradley–Harper theory [J. Vac. Sci. Technol. A 6 (1988) 2390]. Surprisingly good agreement was obtained between the experimental data and this theory. This is probably due to the amorphisation of the substrates under ion bombardment and, thereby, minimising the effect of crystallographic-orientated self-diffusion on metals, and of energy barriers (Ehrlich–Schwoebel barriers) to interlayer surface diffusion. From the data of MacLaren et al. [J. Vac. Sci. Technol. A 10 (1992) 469], the activation energy for surface self-diffusion of GaAs in the temperature range 60–100 °C was determined as 0.26 eV.

Resonant ion stimulated desorption of protons from cerium oxide

The emission of protons from the polycrystalline CeOx surface was investigated during noble-gas ion bombardment (E0<2 keV), in comparison with low-energy proton scattering (E0=100 eV). At the reduced CeOx surface, the proton survives neutralization with a higher probability when scattered from oxygen than from cerium. The surface hydrogens are sputtered as protons by ion irradiation via the non-collisional electronic transition. The probability for H+ desorption decreases in order of He+, Ne+ and Ar+. This is because hydrogen desorbs from the antibonding OH group with an O 2s core hole which is created via the quasi-resonant charge exchange with the primary ions. The ionization of hydrogen occurs during the O–H bond breakage via the interatomic Auger decay of the O 2s hole. The resulting H+ ion survives neutralization preferentially from O of CeO2 as confirmed from the H+ scattering experiment. On the basis of these findings, we propose resonant ion stimulated desorption (RISD) as a tool for quite sensitive detection of surface hydroxyl group and apply it to in situ observations of hydrogen segregation to the surface.

Effects of potential energy on sputtering ofF+from theCaF2(111)surface by noble-gas ion bombardment

The mechanism of ion- and electron-stimulated desorption of ${\mathrm{F}}^{+}$ from the ${\mathrm{CaF}}_{2}(111)$ surface has been investigated. By ${\mathrm{He}}^{+}$ bombardment, a considerable amount of the ${\mathrm{F}}^{+}$ ions are sputtered due to the potential energy of ${\mathrm{He}}^{+}.$ The yield of ${\mathrm{F}}^{+}$ via the potential sputtering from the polycrystalline ${\mathrm{CaF}}_{2}$ film is three times as large as that from the ${\mathrm{CaF}}_{2}(111)$ surface, suggesting that the fluorine at the lower coordination sites or the defect sites preferentially desorbs as ${\mathrm{F}}^{+}.$ The probability for the potential sputtering increases relative to that for the kinetic sputtering with increase of the primary energy of ${\mathrm{He}}^{+},$ whereas most of the ${\mathrm{F}}^{+}$ ions by ${\mathrm{Ar}}^{+}$ are kinetically sputtered. On the basis of these experiments as well as ab initio molecular-orbital calculations, it is concluded that desorption of fluorine is initiated by creation of the F $2s$ hole as a result of the nonadiabatic charge exchange with the primary ion. The ionization of the core-excited fluorine occurs on the way out from the surface due to the intra-atomic Auger decay. The fluorine can be ionized positively during collision with He backscattered from the solid due to the electron promotion mechanism, that is responsible for the kinetic sputtering of ${\mathrm{F}}^{+}.$

Resonant ion-stimulated desorption and low-energy proton-scattering study of interactions of hydrogen and oxygen with theSrTiO3(100)surface

The mechanism of proton desorption by low-energy noble-gas ion bombardment of the ${\mathrm{SrTiO}}_{3}(100)$ surface was investigated, in comparison with scattering of hyperthermal energy ${\mathrm{H}}^{+}$ ions. The ionization of sputtered hydrogen occurs via both collisional and noncollisional electronic transitions as revealed from the energy distribution of the sputtered proton. The noncollisional sputtering is very efficient for ${\mathrm{He}}^{+}$ bombardment and decreases in order of ${\mathrm{He}}^{+},$ ${\mathrm{Ne}}^{+},$ and ${\mathrm{Ar}}^{+}.$ The initiating event for the noncollisional sputtering of proton is found to be the formation of the $\mathrm{O}2s$ core hole via the quasiresonant charge exchange with the primary ion. The core-excited hydroxyl species have the antibonding character with a long lifetime from which the hydrogen desorbs. The ionization of hydrogen occurs due to the interatomic Auger decay of the $\mathrm{O}2s$ hole in the course of the O-H bond breaking. On the basis of these findings, we propose resonant ion stimulated desorption as a technique quite sensitive to the surface hydroxyl group and apply it to an analysis of interactions of oxygen and hydrogen with the ${\mathrm{SrTiO}}_{3}(100)$ surface. It is found that oxygen is adsorbed preferentially on the reduced ${\mathrm{Ti}}^{3+}$ site and that hydrogen or deuterium incorporated in the bulk tends to be segregated to the surface in the form of the hydroxyl group to occupy the oxygen vacancy of the reduced surface.

Characterization of optically active defects created by noble gas ion bombardment of silicon

The modification in the G-line (969.5 meV) and the C-line (789.4 meV) photoluminescence (PL) intensities were studied as a function of the fluence, energy, and mass of the bombarding ions (He, Ne, Ar, and Kr). The intensities of the luminescent lines induced by 1 keV Ne bombardment were found to decrease with increasing dose after reaching a maximum at about 1×1012 ions/cm2. Considerable reductions in the intensities of the G- and C-lines were also recorded during bombardment using heavier noble gas ions and they have been attributed to the higher rates of nuclear energy deposition with increasing bombarding ion mass. The incident ion energy at which the PL intensities of the spectral lines reached their maximum values was found to be dependent on the ion mass and fluence. We have explained the decrease in PL intensities of the G-line and C-line to be due to the introduction of increased amounts of nonradiative recombination centers with increasing incident ion dose and mass. Further, the integral sum of defects induced during bombardment as a function of projected ion range and excitation depth of the Ar-ion laser has been used to qualitatively describe the decrease in the intensities of the two lines.

Electrical and Optical Characterisation of Defects Induced in Epitaxially Grown n-Si During 1 keV Noble Gas Ion Bombardment

Electrical and Optical Characterisation of Defects Induced in Epitaxially Grown n-Si During 1 keV Noble Gas Ion Bombardment

Atomic Force Microscopy Investigation of Noble Gas Ion Bombardment on InP: Effect of Ion Energy

Mirror-polished InP(100) samples, n-doped with S atoms to 4×1018 cm−3, were bombarded with neon, argon and krypton ions. The energy of the ions was varied from 0.5–5 keV at a constant angle of incidence at 41° with respect to the sample normal. The ion dose density for Ne+ was 1.8×1016 ions cm−2 and for Ar+ and Kr+ was 5×1016 ions cm−2. A low ion current density of 5×1013 ions cm−2 s−1 was used to minimize sample heating. The resulting topography development was investigated by atomic force microscopy (AFM). The topography development was quantified in terms of RMS (root-mean-square) roughness using the software of the AFM and analysed as a function of the energy of the bombarded ions. Atomic force micrographs showing various types of topography for some specific ion energies are presented. For each ion species there is a critical energy for which the surface roughness attains a maximum value.

Atomic Force Microscopy Investigation of Noble Gas Ion Bombardment on InP: Effect of Ion Energy

Atomic Force Microscopy Investigation of Noble Gas Ion Bombardment on InP: Effect of Ion Energy

A study of the compositional changes in chemically etched, Ar ion bombarded and reactive ion etched GaAs(100) surfaces by means of ARXPS and LEISS

The effects of chemical etching, noble gas ion bombardment and reactive ion etching on GaAs(100) surfaces was investigated by angle resolved X-ray photoelectron spectroscopy (ARXPS) and low energy ion scattering spectroscopy (LEISS). The results show that at the “as received” GaAs surface, Ga oxide is the major component, resulting in a Ga concentration slightly higher than As. Chemical cleaning by hydrochloric acid (at a HCl(conc.) to H 2O ratio of 1:1) followed by solvent washing efficiently removed the oxide layer, however, ARXPS showed that strong As enrichment occurs at the cleaned GaAs surface. Ion bombardment was carried out using 3 keV Ar ions with a beam current density of 1 μA cm −2 for a period of 50 min. XPS results show that at steady state the ion bombarded GaAs surface is depleted in As ( As Ga ≈ 0.8 ), but ARXPS indicates an As increase at the very surface. This is further confirmed by Ne + LEISS analysis, which shows in the top layer the As concentration is increased by 50% after ion bombardment. The results indicate that bombardment induced compositional changes in this surface are due to Gibssian segregation. The results of reactive ion etching in a 200 W Freon 12 plasma for a period of 5 min at 60 mTorr, showed that this apparently low damage process also produces significant compositional changes in the surface. The report illustrates the benefits of using complementary surface analytical techniques in such studies.

ARXPS and LEISS characterizations for chemically etched and ion‐bombarded GaAs(100) surfaces

AbstractThe effects of chemical etching and noble gas ion bombardment on GaAs(100) surfaces were investigated by angular resolved x‐ray photoelectron spectroscopy (ARXPS) and low energy ion scattering spectroscopy (LEISS). The results show that at the As received GaAs surface, Ga oxide is the major component, resulting in a Ga concentration slightly higher than As. Chemical cleaning by hydrochloride acid (HCl(conc.) to H2O1:1) followed by solvent washing efficiently removed the oxide layer, but ARXPS showed a strong As enrichment occurs at the cleaned GaAs surface. Ion bombardment was carried out using 3 keV Ar ions with a beam current of 1 mA for 50 min. XPS results show that at steady state the ion‐bombarded GaAs surface is depleted in As (As/Ga ∼ 0.8), but ARXPS indicates an As increase at the very surface. This is further confirmed by Ne+ LEISS analysis, which shows the top layer As concentration is increased by 40% after ion bombardment. The results indicate that bombardment‐induced compositional changes are due to Gibbsian segregation.

Ion-assisted modification of the condensation of thermal carbon atoms

The condensation of thermal carbon atoms under simultaneous noble gas ion bombardment was investigated as functions of ion energy, angle of ion incidence, ion mass, and ion-to-atom arrival ratio. The effects of the different growth conditions are discussed in terms of changing the ion-atom interaction processes and the effective area of energetically activated carbon matrix with respect to the protective film behaviour. Thus, the intrinsic film stress, the corrosion protection potential and the microhardness of the films were investigated, using the bending-beam method, cyclic voltammetry and dynamic Vickers indentation respectively. Especially at ion angles of about 60° with respect to the target normal, it is possible to obtain very adherent, hard, protective carbon films under bombardment by argon ions of energy 6 keV. Under normal low energy neon ion bombardment, the film hardness behaviour was observed to change abruptly with the ion/atom ratio. The experiments show the strong dependence of the film properties on the ion bombardment parameters and the possibility to control precisely the protection behaviour.