On the production and annealing of bombardment induced surface damage on a nickel (110) surface

The production and annealing of damage on a nickel (110) surface has been studied with low energy ion scattering (LEIS) and the results are discussed and compared with previously reported LEED, LEIS and TEM results. It is concluded that the production of damage on crystal surfaces which remain crystalline under ion bombardment may be explained in terms of the nucleation and growth of vacancy clusters. It is found that the damage, as observed by ion scattering, saturates at a level which does not depend on such bombardment conditions as temperature or ion species. The experiments indicate that at saturation, the surface is in a state of dynamic equilibrium in which the rates of creation and loss of surface pits are equal. Expressions are derived to explain both the present and previously reported ion scattering results. The annealing measurements show that two different anneal processes can be distinguished.     

Low sputter damage of metal single crystalline surfaces investigated with medium energy ion scattering spectroscopy

It was observed clearly that the sputter damage due to Ar⁺ ion bombardment on metal single crystalline surfaces is extremely low and the local surface atomic structure is preserved, which is totally different from semiconductor single crystalline surfaces. Medium energy ion scattering spectroscopy (MEIS) shows that there is little irradiation damage on the metal single crystalline surfaces such as Pt(111), Pt(100), and Cu(111), in contrast to the semiconductor Si(100) surfaces, for the ion energy of 3–7 keV even above 10¹⁶–10¹⁷ ions/cm² ion doses at room temperature. However, low energy electron diffraction (LEED) spots became blurred after bombardment. Transmission Electron Microscopy (TEM) studies of a Pt polycrystalline thin film showed formation of dislocations after sputtering. Complementary MEIS, LEED and TEM data show that on sputtered single-crystal metal surfaces, metal atoms recrystallize at room temperature after each ion impact. After repeated ion impacts, local defects accumulate to degrade long range orders.     

Ripening of subsurface amorphous C clusters formed by low energy He ion bombardment of graphite

Surfaces of highly oriented pyrolytic graphite (HOPG) were bombarded with 100 eV and 500 eV He ions at ion doses of a few 10¹⁵ cm² and temperatures ranging from 300 K to 800 K. AFM images were recorded to investigate the topography of the surfaces after ion bombardment. Supplementary electron energy loss (EEL) and thermal desorption (TD) spectra were measured to determine the C sp² fraction of the bombarded surfaces and the amount of trapped He. The temperature at which He ion bombardment was performed had a drastic effect on the surface structure and topography of the targets on the angstrom-scale and micrometer-scale as well. At 300 K, limited defect atom transport revealed an amorphous but relatively flat HOPG surface. Bombardment at 400 K leads to a granular structure of small protrusions in micrometer-scale AFM images, however, without crystalline order on the surface. The protrusions are due to the formation of subsurface clusters of carbon formed by atoms displaced by ion irradiation. Towards higher temperatures during bombardment the clusters agglomerate and cause the surface layers to bend upwards in dome-like shapes. Simultaneously, the microscopic order of the graphite lattice recovers. At 800 K large areas of the top layer retain their order during bombardment, however, a small number of domes indicate that there still exist some subsurface C clusters. The cluster–cluster distance deduced from the dome distribution indicates that the clusters grow through a ripening process. Annealing of graphite at high temperatures subsequent to ion bombardment at low temperatures is much less effective for recovering the surface crystallinity than ion bombardment at high temperature.     

Mechanisms of oxidation-reduction processes on metal and oxide surfaces under ion bombardment

Surface oxidation occurs if metals are bombarded with low-energy (1–5 keV) ions of a chemically active gas (oxygen) in vacuum. It is ascertained that ion bombardment leads to the generation of lower, intermediate, and higher oxides. The composition and thickness of an oxidized layer depend on the metal reactivity and the dose and energy of oxygen ions. The mechanism underlying the ion-beam oxidation of metal surfaces is proposed. Surface reduction is observed if higher oxides are bombarded with low-energy (1–5 keV) ions of inert gases (argon and helium) in vacuum. It is revealed that ion bombardment not only generates intermediate and higher oxides but sometimes gives rise to surface metallization. The composition and thickness of the reduced layer are determined by the oxide type, the kind of inert gases, and the dose and energy of bombardment. The mechanism describing the ion-beam reduction of higher metal oxide surfaces is proposed.     

Determination of the thickness and density of the ion bombardment induced altered layer in SiC by means of reflection electron energy loss study

The steady state surfaces of ion bombarded 3C-, 4H- and 6H-SiC samples were studied by means of reflected electron energy loss spectroscopy (REELS). The REELS exhibit a well-defined loss peak in the region of about 20 eV. The position of the maximum of the loss peak depends on the bombarding ion energy (decreasing with increasing ion energy), and on the primary electron beam energy (increasing with increasing primary energy). This behavior can be explained if we suppose that the plasmon energy in the altered layer (produced by ion bombardment) is different from that of the unaltered bulk. In this case the measured loss peak is the sum of two overlapping plasmon peaks. With modeling the system as a homogeneous altered layer and a homogeneous unaltered substrate the plasmon energy in the altered layer was derived to be 19.8 eV. The large change of the plasmon energy with respect to the bulk value of 23 eV is explained by a thin low density overlayer on the surface of the sample produced by the ion bombardment.     

Interplay of parallel electric field and trapped electrons in kappa-Maxwellian auroral plasma for EMEC instability

In this paper, propagation characteristics of electromagnetic electron cyclotron(EMEC) waves based on kappa-Maxwellian distribution have been investigated to invoke the interplay of the electric field parallel to the Earth's magnetic field and auroral trapped electrons. The dispersion relation for EMEC waves in kappa-Maxwellian distributed plasma has been derived using the contribution of the parallel electric field and trapped electron speed. Numerical results show that the presence of the electric field has a stimulating effect on growth rate, which is more pronounced at low values of wave number. It is also observed that as the threshold value of trapped electron speed is surpassed, it dominates the effect of the parallel electric field and EMEC instability is enhanced significantly. The electric field acts as another source of free energy, and growth can be obtained even in the absence of trapped electron drift speed and for very small values of temperature anisotropy. Thus the present study reveals the interplay of the parallel electric field and trapped electron speed on the excitation of EMEC waves in the auroral region.     

Sputtering of ordered nickel-aluminium alloys: II. Preferential sputtering of NiAl single crystals and discussion

Atom-probe field-ion microscopy together with X-ray photoelectron spectroscopy and secondary ion mass spectrometry have been applied to the microanalysis of fully ordered NiAl single crystals subjected to 3 keV inert gas ion bombardment. As with the studies of Ni₃Al (the companion paper) aluminium was found to be preferentially sputtered by both argon and xenon bombardment. Comparisons between depth profiles through Ni₃Al and NiAl targets have provided information about the role of binding energies in the selective sputtering process. These data have also permitted conclusions to be drawn about the correct choice of bombarding species for sample cleaning and depth-profiling applications in surface analysis. Examination of field-ion images from specimens after bombardment suggests that the surface is microroughened and this has been confirmed using transmission electron microscopy.     

Incident-energy dependence of crystalline structures of ion beam deposited Au thin films

The energy dependence of crystalline structures in Au thin-film deposition processes was investigated with the use of a low-energy mass-selected ion beam system. Au films deposited on Si(100) untreated wafer surfaces by the beam system at different ion energies in the range of 20–200?eV were analyzed by atomic force microscopy (AFM), X-ray diffraction (XRD) and in-situ reflection high-energy electron diffraction (RHEED). The XRD results show that the kinetic energy provided by ion bombardment can facilitate crystal growth with specific orientations such as (100) or (110), the surfaces of which have relatively high surface energies. Our observations also suggest that each crystalline orientation appears only in a specific energy range of ion bombardment. These results indicate that Au crystalline orientations may be controlled by the ion irradiation energy during deposition processes.     

The influence of argon ion bombardment on the electrical and optical properties of clean silicon surfaces

The effect of low energy noble gas ion bombardment on the electrical and optical properties of Si(211) surfaces has been investigated by surface conductivity and field effect measurements, ellipsometry and AES. With this combination of techniques, information is obtained concerning the electrical properties, the chemical composition and the damage of the surface layer. Upon ion bombardment in the energy range of 500–2000 eV, ellipsometry shows the formation of a damaged surface layer with optical properties close to those of an evaporated amorphous silicon film. In order to measure the conductivity changes as sensitive as possible, nearly intrinsic silicon crystals were used. For the clean, 5200 Ω cm Si(211) surface, bombarded only with a mass-analyzed argon ion beam, a small increase in conductivity is found to occur after a small ion dose (saturation after 5 × 10¹⁴ ions cm^?2 while after 5 × 10¹³ ions cm^?2 already half of the increase has occurred). The effect was found to be independent of ion energy between 500 and 2000 eV. As the field effect signal did not change after this treatment, it is concluded that the surface state density in the neighbourhood of the Fermi level shows a slight decrease.     

ESCA studies on changes in surface composition under ion bombardment

The influence of ion bombardment on the composition of surfaces was investigated by means of ESCA. The bombardment of metal oxides with inert gas ions results, not only in sputtering of the surface, but also in reduction of the oxides. The rate of reduction is particularly high when the oxide/metal interface is within the range of the bombarding ions. Ion induced reduction was found in oxide layers, thinner than the escape depth of the photoelectrons, on Mo, W, Nb, Ta, Ti, Zr, Si, and Bi. The relationship between reduction phenomena, on the one hand, and the ion energy, angle of incidence, mass of the gas used for bombardment, and ion current density, on the other hand, was investigated in the case of the Mo/Mo-oxide system. Ion bombardment of surfaces may also result in the formation of new compounds. Two examples of this are the formation of carbides through the bombardment of contaminated surfaces and the ion induced formation of C-F compounds from a mixture of K₂SiF₆ and carbon.     

Influence of surface topography on the secondary electron yield of clean copper samples

Secondary electron yield (SEY) due to electron impact depends strongly on surface topography. The SEY of copper samples after Ar-ion bombardment is measured in situ in a multifunctional ultrahigh vacuum system. Increasing the ion energy or duration of ion bombardment can even enlarge the SEY, though it is relatively low under moderate bombardment intensity. The results obtained with scanning electron microscopy and atomic force microscopy images demonstrate that many valley structures of original sample surfaces can be smoothed due to ion bombardment, but more hill structures are generated with stronger bombardment intensity. With increasing the surface roughness in the observed range, the maximum SEY decreases from 1.2 to 1.07 at a surface characterized by valleys, while it again increases to 1.33 at a surface spread with hills. This phenomenon indicates that hill and valley structures are respectively effective in increasing and decreasing the SEY. These obtained results thus provide a comprehensive insight into the surface topography influence on the secondary electron emission characteristics in scanning electron microscopy.     

在低温等离子体及低能离子作用下PET表面氮的XPS研究

经X射线光电子能谱(XPS)分析,在空气等离子体和氩等离子体作用下,(PET)表面上结合了不同的氮化合物。特别是在氩等离子体作用5min以后,N₁₅出现双峰,表明PET表面上结合了氮的氧化官能团。通过低能氮离子和氩离子轰击PET表面的实验,证明这种N₁₅双峰结构不是低能离子单独作用引起的。 关键词：     

Stability of ZnO{0 0 0 1} against low energy ion bombardment

The steady-state surface compositions of the polar (O and Zn terminated) faces of ZnO{0 0 0 1} produced by low energy (0.3-2 keV) Ar⁺ ion bombardment were studied by Auger electron spectroscopy and electron energy loss spectroscopy. The alterations produced by the ion bombardment using different ion energies were monitored by calculating the intensity ratios of the low and high energy Zn Auger peaks (59 eV and 994 eV, respectively); Zn and O Auger peaks (59 eV and 510 eV, respectively). Based on the dependence of these ratios on the ion energy and termination of the surface, we could conclude that the stability of the Zn face is higher against the low energy argon ion bombardment-induced compositional changes than that of the O face.     

Structural and electrical analysis of S ion bombarded p-InP(1 0 0)

The chemical state of sulfur and surface structure on low-energy S⁺ ion-treated p-InP(1 0 0) surface have been investigated by high-resolution X-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED). S⁺ ion energy over the range of 10-100 eV was used to study the effect of ion energy on surface damage and the process of sulfur passivation on p-InP(1 0 0) by S⁺ ion beam bombardment. It was found that sulfur species formed on the S⁺ ion-treated surface. The S⁺ ions with energy above 50 eV were more effective in formation of In-S species, which assisted the InP surface in reconstruction into an ordered (1 × 1) structure upon annealing. After taking into account physical damage due to the process of ion bombardment, we found that 50 eV was the optimal ion energy to form In-S species in the sulfur passivation of p-InP(1 0 0). The subsequent annealing process removed donor states that were introduced during the ion bombardment of p-InP(1 0 0). Results of theoretical simulations by Transport of Ions in Materials (TRIM) are in accordance with those of experiments.     

Steady state shapes of periodic profiles on (110), (100), and (111) surfaces of nickel

Periodic surface profiles with amplitudes of ≦0.4 μm and periodicities of 4–20 μm were prepared on Ni(110), (100), and (111) single crystal surfaces. These crystals were annealed in ultra-high vacuum (UHV) at 1073–1327 K after they had been cleaned by Ar ion bombardment and investigated by Auger electron spectroscopy. The geometry of the profiles was studied in UHV by laser diffraction and outside the vacuum by interference microscopy. The profiles have sinusoidal shapes on Ni(110) but trapezoidal shapes on both the (100) and (111) surfaces. This type of faceting can be understood on the basis of the anisotropic surface energy of Ni, with cusps at the (100) and (111) orientations. Model calculations show in the case of anisotropic surface energy that periodic profiles develop facets which correspond to the low surface energy orientations (close-packed surfaces).     

Selective X-ray generation by heavy ions (Part 1) the use of energetic heavy ions to generate characteristic X-rays from elements in a selective manner

The selective generation of characteristic X-rays during heavy ion bombardment of solids is briefly described. The principles can be understood in terms of the Fano-Lichten model, which postulates that during heavy ion collisions, interactions occur between the electronic systems of the target and projectile atoms, leading to electron promotions and consequent inner shell vacancies. The resultant X-rays have the advantage of being essentially free from the continuous background radiation which accompanies X-rays produced by electron bombardment. It is shown how the characteristic X-rays of certain elements may be generated in a selective manner by bombardment with an appropriate heavy ion of optimum energy. The resultant technique is particularly applicable to the analysis of elements located on or near to surfaces, and may therefore be used for the elucidation of distribution profiles of ion-implanted elements.     

质量分离低能离子束沉积碳膜及离子轰击效应

用质量分离的低能离子束沉积技术得到了非晶碳薄膜,X射线衍射、Raman谱以及俄歇深度谱的线形表明,此种非晶碳膜中镶嵌着金刚石颗粒.碳离子的浅注入是该碳膜SP³形成的主要机理.从一个侧面说明了化学气相沉积法中偏压预处理增加金刚石成核的主要原因是因为离子轰击效应. 关键词： 非晶碳 离子轰击 质量分离低能离子束     

Surface energy and hybridization studies of amorphous carbon surfaces

Surface properties of a large number of amorphous carbon (a-C) films have been investigated using contact angle measurements and X-ray photoelectron spectroscopy (XPS). Dense a-C surfaces with variable sp³/(sp² + sp³) average hybridization were grown using sputtering or pulsed laser deposition (PLD) and were further chemically modified by thermal annealing, ion bombardment or covalent grafting of organic monolayers. The average carbon hybridization, impurity level and mass density, were deduced from XPS and photoelectron energy loss spectroscopy (PEELS). The depth sensitivity of the dispersive (Lifshitz–van der Waals) interaction, estimated at 1–2 nm from the dependence of γ^LW on the grafted perflorodecene molecule coverage, is much better than XPS which probes a 3–5 nm depth. The observation of a non-monotonic behavior in the correlation between surface hybridization and electron donor component of surface energy reveals that the average carbon hybridization alone does not describe the entire surface energy physics. The role of π bond clustering in the polar interactions is thus considered and some implications on surface reactivity and mutual interactions with molecular or biomolecular species are discussed.     

Early stage in low energy ion-induced damage on InP(110) surface

The change in the short-range order created by ion milling in the near surface region of InP single crystals was investigated by primary beam diffraction modulated electron emission (PDMEE). The very early stage of the damage creation by low energy (0.6–1 keV) Ar ions in normal and oblique incidence was studied. A simple model based on the weighted combination of perfectly crystalline and completely amorphous regions was used to model the experimental results. Evidence of a subsurface nucleation of the amorphization process was found. We also found that the total sputtering yield is markedly dependent on the ion dose, being on the undamaged surface much larger than its steady state value. Low energy electron diffraction (LEED) measurements were also performed to correlate long-range and short-range order removal by ion bombardment. Finally, the ion damage on the GaAs and InP surfaces was comparatively discussed.     

Low energy ion assisted atomic assembly of metallic superlattices

Metallic superlattices with planar, unalloyed (unmixed) interfacial structures are difficult to fabricate by all conventional vapor deposition methods. Molecular dynamics simulations have been used to explore the ways in which inert gas ions can be used to control the atomic assembly of a model Cu/Co metallic super lattice system. High energy, high atomic weight ions are shown to smooth rough interfaces but introduce undesirable intermixing at interfaces. Light ions with very low energies fail to flatten the rough surfaces that are naturally created during deposition at ambient temperature where surface atom mobility is kinetically constrained. The optimum energies for achieving the lowest combination of interfacial roughness and interlayer mixing have been found for each inert gas ion species and the key mechanisms of surface structure reorganization activated by ion impacts have been identified over the range of ion masses and energies studied. Optimum ion energies that maximize the interface structural perfection have been identified.