Copper nanoparticles synthesized in sapphire by ion implantation

Sapphire-based composite layers implanted with 40-keV Cu⁺ ions to a total dose of 1.0×10¹⁷ cm⁻² at an ion beam current density varied from 2.5 to 10 μA/cm² were studied using Rutherford backscattering and optical reflectance methods. The appearance of optical plasma resonance lines in the reflectance spectra indicates that ion implantation allows copper nanoparticles to be synthesized in the subsurface region of the dielectric crystal studied.     

Si+ and N+ ion implantation for improving blood compatibility of medical poly(methyl methacrylate)

Si⁺ and N⁺ ion implantation into medical poly(methyl methacrylate) (PMMA) were performed at an energy of 80 keV with fluences ranging from 5×10¹² to 5×10¹⁵ ions/cm² at room temperature to improve blood compatibility. The results of the blood contacting measurementsin vitro showed that the anticoagulability and anticalcific behaviour on the surface morphology were enhanced after ion implantation. No appreciable change in the surface morphology was detected by scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) analysis indicated that ion implantation broke some original chemical bonds on the surface to form some new Si- and N-containing groups. These results were considered responsible for the enhancement in the blood compatibility of PMMA.     

Silicide formation by Ar+ ion bombardment of Pd/Si

Palladium films, 45 nm thick, evaporated on to Si(111) were irradiated to various doses with 78 keV Ar⁺ ions to promote silicide formation. Rutherford backscattering spectroscopy (RBS) shows that intermixing has occurred across the Pd/Si interface at room temperature. The mixing behaviour is increased with dose which coincides well with the theoretical model of cascade mixing. The absence of deep RBS tails for palladium and the small area of this for silicon spectra indicate that short-range mixing occurs. From the calculated damage profiles computed with TRIM code, the dominant diffusion species is found to be silicon atoms in the Pd/Si system. It is also found that the initial compound formed by Ar⁺ irradiation is Pd₂Si which increases with dose. At a dose of 1×10¹⁶ Ar⁺ cm^–2, a 48 nm thickness of Pd₂Si was formed by ion-beam mixing at room temperature.     

ZnO nanoparticles embedded in sapphire fabricated by ion implantation and annealing

ZnO nanoparticles were fabricated in sapphire (α-Al(2)O(3) single crystal) by Zn ion implantation (48?keV) at an ion fluence of 1 × 10(17)?cm(-2) and subsequent thermal annealing in a flowing oxygen atmosphere. Transmission electron microscopy (TEM) analysis revealed that metallic Zn nanoparticles of 3-10?nm in dimensions formed in the as-implanted sample and that ZnO nanoparticles of 10-12?nm in dimensions formed after annealing at 600?°C. A broad absorption band, peaked at 280?nm, appeared in the as-implanted crystal, due to surface plasma resonance (SPR) absorption of metallic Zn nanoparticles. After annealing at 600?°C, ZnO nanoparticles resulted in an exciton absorption peak at 360?nm. The photoluminescence (PL) of the as-implanted sample was very weak when using a He-Cd 325?nm line as the excitation source. However, two emission peaks appeared in the PL spectrum of ZnO nanopraticles, i.e., one ultraviolet (UV) peak at 370?nm and the other a green peak at 500?nm. The emission at 500?nm is stronger and has potential applications in green/blue light-emitting devices.     

Formation and thermal stability of aluminium nanoparticles synthesized via yttrium ion implantation into sapphire

Yttrium ion implantation of 1 1 2 3 alumina resulted in the formation of metallic aluminium–yttrium, face centred cubic (a0=0.41 nm) spherical nanocrystals ( 12 nm in diameter) embedded in an amorphous matrix. A fluence of 5×1016Y+/cm2 implanted at ambient temperature and accelerating energies of 150 or 170 keV yielded this result. Crystalline nanoparticles were not present in the amorphous matrix for implantations done with identical conditions but lower energy (100 keV). Substrates implanted at 150 keV were annealed in laboratory air for times ranging from 20 to 90 min and temperatures ranging from 1000 to 1400°C. A clear progression of morphologies resulted from these annealing treatments. A 1000°C, 90 min anneal produced 13% recrystallization of the amorphous region and induced the formation of crystallites of a metastable Y–Al alloy. An 1100°C, 90 min anneal demonstrated 40% recrystallization of the amorphous region, accompanied by the formation of partially aligned internal grains of Y2O3. Electron diffraction shows that the Y–Al alloy crystallites which formed in the 1000°C anneal are also present at 1100°C. A highest temperature anneal of 1400°C, 60 min induced essentially complete recrystallization of the amorphous phase, the dissolution of the metastable Y–Al alloy, the retention of the internal yttria grains, and the formation of partially oriented external grains of yttria resulting from the segregation of yttrium to the substrate surface.     

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.     

Cubic BN formation by ion implantation

Boron nitride was synthesized by nitrogen ion implantation. Boron films were prepared as implantation targets on single-crystal Si(100) substrates by 13.56-MHz radio frequency sputtering. The diatomic single 30-keV nitrogen ions were chosen for implantation. The implantation dose ranged from 1×10¹⁷ ions/cm² to 2×10¹⁸ ions/cm². The films were characterized using a transmission electron microscope. Several phases of boron nitride were found at the medium implantation dose. At the high dose of 2×10¹⁸ ions/cm², the pure c-BN phase was observed. It is believed that the transition from the low ordered phases to c-BN phase occurred during implantation. The films showed good adhesion to the Si substrate.     

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.     

Mechanical property changes in sapphire by nickel ion implantation and their dependence on implantation temperature

Sapphire plates, cut parallel to an {0001} plane, have been implanted with 300 keV nickel ions to doses ranging from 5×10¹² to 1×10¹⁷ Ni cm^–2 at specimen temperatures of 100, 300 and 523 K, in order to investigate the effect of implantation temperature on the mechanical property changes in sapphire caused by ion implantation. The measured changes in surface hardness, surface fracture toughness and bulk flexural strength were found to depend strongly on the implantation temperature, and were largely correlated with the residual surface compressive stress measured by using a cantilever beam technique. The surface amorphization that occurred only by the implantation at 100 K and at doses larger than 2×10s15 Ni cm^–2 reduced the hardness to 0.6 relative to the value of the unimplanted sapphire, and considerably increased the surface plasticity. Furthermore, the amorphization was found to involve a large volume expansion of 30% and to change drastically the apparent shape and size of a Knoop indentation flaw made prior to implantation. This effect was suggested to reduce stress concentrations at surface flaws and hence to increase the flexural strength.     

Structurally perfect silicon layers produced on sapphire by oxygen ion implantation

We demonstrate that the structural perfection of silicon layers on sapphire can be improved through high-temperature solid-state recrystallization after preamorphization of the most imperfect silicon layer near the silicon/sapphire interface by high-energy oxygen ions, followed by high-temperature recrystallization in an inert atmosphere.     

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.     

Nonlinear optical properties of gold nanoparticles synthesized by ion implantation in sapphire matrix

Single crystal Al₂O₃ substrates have been implanted with 160-keV Au⁺ to a dose of 0.6 × 10¹⁷ or 1.0 × 10¹⁷ cm⁻², with a postimplantation annealing for 1 h at 800°C in air. The obtained composite layers were studied by the method of linear optical reflection; the nonlinear optical characteristics were determined by the RZ-scan technique using picosecond radiation pulses of an Nd:YAG laser operating at 1064 nm. The appearance of a characteristic surface optical plasmon resonance band in the linear reflection spectra was indicative of the formation of gold nanoparticles in a subsurface layer of ion-irradiated Al₂O₃. It is shown that the synthesized particles are responsible for the observed manifestations of nonlinear refraction. The composite layers were characterized by the nonlinear refractive index (n ₂) and the real part of the third-order nonlinear susceptibility (Reϰ ⁽³⁾).     

The effects of N 2 + and B+ ion implantation on the hardness behaviour and near-surface structure of SiC

The effects of ion implantation on the near-surface deformation behaviour and structure of both single crystal (6H) silicon carbide and a reaction-bonded SiC composite (REFEL) have been studied using 80 keV N ₂ ⁺ and 40 keV B⁺ ions in the dose range 1 to 1 × 10¹⁷ ions cm^–2. The ion species were chosen to have different effects on the polytype stability of SiC but produce similar distributions of damage. Subsequent room temperature, load-variant, indentation hardness tests showed that N ₂ ⁺ implantations produced a marked near-surface softening above a critical dose of 4 × 10¹⁷ ions cm^–2 . The effect, which appeared specific to N ₂ ⁺ implanation is possibly attributable to the rapid thickening of the surface amorphized damage layer by nitrogen ges bubble formation. Implantation with both species suppressed the breakout of the lateral cracks produced by indentation fracture and this is presumed due to the production of a compressive surface stress. Scratch tests established that aven the lowest doses of both species suppressed chipping to the extent that scratch tracks appeared plastically deformed only Subsequent TEM examination showed that the microcrystalline or amorphous material produced by implantation with either species had transformed during deformation to the low-temperature-stable cubic (3C) polytype despite the differing expected influences of boron and nitrogen on polytype stability.     

Si nanocrystals formation in SiO2 by ion implantation: The effects of RTA and UV irradiation on photoluminescence

Si ion implantation was widely used to synthesize specimens of SiO₂ containing supersaturated Si and subsequent high temperature annealing induces the formation of embedded luminescent Si nanocrystals. In this work, the potentialities of excimer UV-light (172 nm, 7.2 eV) irradiation and rapid thermal annealing (RTA) to enhance the photoluminescence and to achieve low temperature formation of Si nanocrystals have been investigated. The Si ions were introduced at acceleration energy of 180 keV to fluence of 7.5 × 10¹⁶ ions/cm². The implanted samples were subsequently irradiated with an excimer-UV lamp. After the process, the samples were rapidly thermal annealed before furnace annealing (FA). Photoluminescence spectra were measured at various stages at the process. We found that the luminescence intensity is strongly enhanced with excimer-UV irradiation and RTA. Moreover, effective visible photoluminescence is found to be observed even after FA at 900 °C, only for specimens treated with excimer-UV lamp and RTA. Based on our experimental results, we discuss the effects of excimer-UV lamp irradiation and RTA process on Si nanocrystals related photoluminescence.     

The effects of ion implantation on the friction behaviour of sapphire

The friction behaviour of ion-implanted sapphire in contact with diamond cones and spheres of a range of materials has been investigated as a function of implantation dose and implant species. Generally, an increase in friction is observed at low doses followed by a decrease once amorphization takes place. For the sharp diamond cones this can be correlated with changes in ploughing behaviour controlled by near-surface plasticity, whereas, for the spheres, the increase in friction for low-dose implants is due to changes in adhesion between the spheres and the implanted layer. The implications of these observations for the creation of lubricating surface layers by high-dose ion implantation are discussed.     

N等离子体基注渗方法研究

等离子体基注渗技术在材料表面改性中具有极为重要的应用，本文报道了一种实现恒温条件的N等离子体基注渗的工艺方法，利用该方法可以根据工艺研究需要，实现注渗剂量、注渗能量(加速电压)和注渗温度单一参数调节，为等离子体体基注渗工艺的优化提供了一种切实可行的研究方法。利用本文提出的工艺方法，对纯铁进行了各种温度下的N离子注渗。结果表明，处理过程中，可依据工艺设计，单参数大范围改变注渗电压或注渗恒温温度，温度波动很小，离子注入层厚度得到明显提高。