Microalloy layer formation by ion implantation

In this article we emphasize the new opportunities made available to crystal growers by the access to earth-orbiting spaceships for a fairly large duration. Spacelab capabilities are briefly described; there follows a survey of the benefits expected from vapour growth in space. It is also shown that material processing in space is associated with severe but inherent constraints which may compete with its attractiveness.     

Metastable alloy formation by ion implantation

Implantation into metals at room temperature and at lower temperatures can result in the formation of metastable phases. For low concentrations (not more than about 1 at.%) substitutional and interstitial solutions have been observed for implantation in beryllium, iron, nickel and copper. These results have been explained in terms of modified Hume-Rothery rules and also Miedema coordinates. At higher concentrations (not less than about 10 at.%) both metastable solid solutions and amorphous alloys have been formed in iron, nickel and copper.     

Refractory metal silicide formation by ion implantation

A systematic study of interface mixing of transition metal-Si structures by ion implantation was carried out. High resolution Auger analyses at the mixed region of the implanted samples showed an energy shift of the Auger Si LVV transition and a change in the spectrum relative to that of elemental silicon. The elemental depth distribution obtained using Auger electron spectroscopy combined with ion sputtering illustrated a composition plateau for the ion-implanted structures. The X-ray diffraction data show the presence of silicides. These results illustrated metal silicide formation and a reduction in the thermal reaction barrier for forming refractory metal silicides by ion implantation.     

ARE法制取立方氮化硼膜时提高膜基结合力方法的研究

采用活性反应离子镀装置,通过电子束蒸镀金属纯硼,在氮、氩混合气体等离子体中,合成了ｃ－ＢＮ膜。对沉积后的ｃ－ＢＮ膜,在充入高纯氮的条件下,原位进行消应力退火处理以提高膜与基体的结合力。用富立叶变换红外透射谱分析ｃ－ＢＮ膜的结构,用弯曲法测量膜的残余压应力,通过划痕试验测量膜与基体的结合力。沉积态的 ｃ－ＢＮ膜的残余压应力高达６．６ ＧＰａ,当退火温度不超过６００℃时,膜的残余压应力消减效果不大;但当经８００℃退火 １ｈ后,ｃ－ＢＮ膜的残余压应力大幅度下降,降到约 ２ ＧＰａ,膜与基体的结合力有很大提高,划痕试验时临界载荷高达 １４ Ｎ;而富立叶变换红外分析结果表明,高温退火不改变ｃ－ＢＮ膜的相结构。     

Void formation in silica glass induced by thermal oxidation after Zn ion implantation

Thermal annealing effects on Zn⁺ ion-implanted silica glass (a-SiO₂) have been studied in order to control void formation. Void formation in a-SiO₂ with Zn⁺ ion implantation and subsequent oxidation has been observed using transmission electron microscopy (TEM). Zn⁺ ions of 60 keV were implanted into a-SiO₂ to a fluence of 1.0 × 10¹⁷ ions/cm². After the implantation, thermal annealing at 600 or 700 °C for 1 h in oxygen gas was conducted. In as-implanted state, metal Zn nanoparticles (NPs) of 10-15 nm in diameter are formed in the depth region around the projected range. The size of the Zn nanoparticles increases after the annealing at 600 °C in oxygen gas. Annealing in oxygen gas at 700 °C for 1 h caused two processes: (1) the migration of Zn atoms which formed Zn NPs in as-implanted state to the surface of the a-SiO₂ substrate and (2) the transformation to the oxide phase on the substrate. The transportation of Zn NPs to the surface leaves voids of 10-25 nm in diameter inside the a-SiO₂. These results indicate that the oxidation at 700 °C for 1 h causes the migration of Zn atoms to the surface without diffusion and recombination of vacancies which form the voids.     

Peculiarities in the formation of gold nanoparticles by ion implantation in stabilized zirconia

The investigation of bulk single crystals and sputter-deposited films of yttria-stabilized zirconia (YSZ) upon irradiation by gold (Au) ions with an average energy of 160 keV followed by postimplantation annealing revealed peculiarities in the formation of nanocrystalline metal (nc-M) particles in this matrix. In the case of irradiation to small doses (∼5 × 10¹⁵ cm⁻²), the optical absorption spectra of samples showed evidence of the formation of nanoclusters of matrix cations (nc-Zr). In these samples, postimplantation annealing at temperatures ∼700°C and above leads to the formation of nc-Au particles. Local elemental analysis of individual nc-M particles in the YSZ matrix irradiated to a dose of 4 × 10¹⁶ cm⁻² and annealed at 800°C showed the presence of metal nanoparticles with complex compositions including both implanted Au and matrix Zr atoms.     

Graphene synthesis by ion implantation

We demonstrate an ion implantation method for large-scale synthesis of high quality graphene films with controllable thickness. Thermally annealing polycrystalline nickel substrates that have been ion implanted with carbon atoms results in the surface growth of graphene films whose average thickness is controlled by implantation dose. The graphene film quality, as probed with Raman and electrical measurements, is comparable to previously reported synthesis methods. The implantation synthesis method can be generalized to a variety of metallic substrates and growth temperatures, since it does not require a decomposition of chemical precursors or a solvation of carbon into the substrate.     

Sialon formation by Si+ and N2 + ion implantation into sapphire

Single-crystal alumina was implanted firstly with 400 keV Si⁺ and subsequently with N₂ ⁺ ions and then annealed at 1673 K in an No atmosphre. The implanted layers were characterized by means of X-ray diffraction, Rutherford backscattering-channelling of 2 MeV He⁺ ions, and the resonance nuclear reaction¹⁵N(p,)¹²C. The annealing of sapphire implanted at ambient temperature resulted in the formation of-sialon, a solid solution of-silicon nitride and alumina in the subsurface layer, while implantation at 100 K resulted in the formation of aluminium oxynitride in the surface layer. In the latter case, the implanted silicon atoms were believed not to react vxi1h the implanted nitrogen atoms but with the substrate oxygen atoms. These crystalline precipitates were found to have epitaxial relations with the sapphire substrate.     

Improvement of metal properties by ion implantation

Ion implantation is being investigated as a technique for the beneficial modification of surface-sensitive and life-limiting properties of metals including resistance to wear and fatigue. Ion implantation is a process of accelerating ions to high velocities and directing them into the near-surface regions of materials (e.g. alloys) to produce in essence a different material (alloy) in the near-surface region. Ion implantation can produce a graded alloy from the surface to the unchanged underlying bulk alloys so that both the surface and the bulk alloys can be independently optimized. The implanted layer is typically hundreds to thousands of ångströms deep with implanted atom concentrations of up to fifty atomic per cent or more. The sliding-wear rate between various steel alloys was significantly reduced by implanting one of the surfaces with selected elemental species such as nitrogen, carbon and titanium. Experiments were conducted on a number of materials including stainless steel, too steel, bearing alloys and silicon nitride. The implantation technique has also been reported to increase fatigue lifetimes in low-carbon steel by a factor of 50–100. Experimentation is now being directed towards other materials of major technological interest such as titanium alloys. The effect of ion implantation on (1) the wear and fatigue properties and (2) the microstructural characteristics of implanted materials with selected examples is discussed.     

Formation of AlN by nitrogen ion implantation

The phase composition of aluminium after bombardment with doses from 1 × 10¹⁶ to 1 × 10¹⁸ N⁺ ions cm^-2 is investigated by high voltage electron microscopy and selected area diffraction. This implantation always produced polycrystalline aluminium nitride (AlN). A thermal treatment to 600 °C did not yield new crystalline phases. At low temperatures the growth of AlN precipitations takes place mainly coherently as a result of a high vacancy density. Larger AlN precipitations grow similarly to the Ostwald ripening process. In this process incoherent precipitations are associated with a high dislocation density with an anisotropic distribution.     

Surface softening in silicon by ion implantation

Load-variant microhardness tests have been used to investigate the hardness behaviour of ion-implanted (1 1 1) silicon wafers. A variety of ion doses, energies and species, including n-type, p-type and isovalent ions, have been implanted. At the high doses used (1 to 8 x 10¹⁷ ions cm^2–), all implantations resulted in a surface amorphous layer being formed. The microhardness behaviour has been interpreted in terms of the presence of a surface layer of lower hardness than the substrate. The thickness of this layer has been investigated experimentally using Rutherford backscattering and the results correlated with simple theoretical predictions. Finally, the microhardness behaviour of a soft layer on a harder substrate has been modelled in order to try to predict the hardness variations arising from differing layer thicknesses and different indentation sizes. It is concluded that the amorphous layer produced by implantation appears to show no variation of microhardness with load and has a hardness typically between 400 and 700 Vickers (VHN). Further, the previously reported critical dose of 4 x 10¹⁷ ions cm^–2 necessary to observe significant surface softening seems to correspond to the regime in which the amorphous layer shows a rapid increase with dose.     

Surface hardening of beryllium by ion implantation

The effectiveness of ion implantation for the production of a hard wear-resistant surface on instrument grade beryllium of high strength (HP-40) was explored. Samples of beryllium were implanted with boron and were subjected to microhardness tests in both the as-implanted state and after annealing. The implanted region was examined using Rutherford backscattering to determine the depth distribution of the implanted boron. By using ion implantation to produce a buried layer containing boron, the limitations imposed by solubility and diffusivity are avoided and much greater boron concentrations than those attainable with conventional thermal treatments are generated.