Transmission electron microscopy of Li+ implanted Al films

Aluminium films implanted with 30 keV lithium ions of doses from 2.2 × 10¹⁶ to 1 × 10¹⁷ ions cm^?2 were studied by transmission electron microscopy. Samples implanted with 6 × 10¹⁶ and 1 × 10¹⁷ ions cm^?2 showed the presence of the Al-Li phase, while no change was observed in specimens implanted with 2.2 × 10¹⁶ ions cm^?. Microdiffraction patterns obtained from different areas of an aluminium film implanted with 2.0 × 10¹⁷ Li⁺ ions cm^?2 at 35 keV, revealed the presence of a stable Al-Li phase along with a metastable phase. Furthermore, on annealing the implanted samples at 200°C for 20 min an increase in ‘d’ values was noticed when compared with non-annealed specimens. However the annealed samples showed a very small lattice mismatch between the metastable phase and the Al matrix, thus indicating the presence of a metastable Al₃Li phase, responsible for hardening in binary Al-Li alloy.     

Structural and chemical characteristics and oxidation behaviour of chromium-implanted single crystal silicon carbide

High-dose chromium implantation resulted in complex changes in the structure, chemistry, and oxidation behaviour of beta-type single-crystal silicon carbide. Detailed analytical studies indicated that, in addition to the primary process of surface doping, chromium implantation of silicon carbide to 3.90×10¹⁷ ions cm⁻² at 200 keV was accompanied by many secondary processes such as surface sputtering, lattice damaging, and silicon depletion/carbon enrichment in the implanted region. These changes resulted in accelerated oxidation of the implanted samples by a factor of 1.14 as compared with the unimplanted crystals in 1 atm of flowing oxygen at 1100°C. The oxidation layer exhibited interesting structural and compositional inhomogeneity which could be explained based upon chromium mobility variation in the implanted region. The presence of densely populated chromium oxide precipitates in the outer region of the oxidation layer played a significant role in keeping the degree of oxidation acceleration low under the detrimental influence of lattice damages and silicon deletion/carbon enrichment. It was concluded that the potential of chromium implantation to improve the oxidation resistance of silicon carbide can be realized only when the implantation-induced secondary effects are suppressed.     

Rutherford backscattering analysis of oxide layers formed by ion implantation into single-crystal silicon

Single-crystal silicon was implanted with 40 keV and 60 keV oxygen ions. Rutherford backscattering (RBS) analysis was used to determine the oxygen profile, the ratio of oxygen to silicon in the implanted layer and the extent of radiation damage for doses up to 3 × 10¹⁸ ions cm^-2. The measured oxygen profiles appear to agree with theory at low doses. The radiation damage, as characterized by the damage peak and the yield _χmin behind the implanted layer, saturates at a dose of approximately 1 × 10¹⁶ ions cm^-2. The oxygen content of the layer is directly proportional to dose until the peak value of the oxygen:silicon ratio reaches 2.0. At higher doses the oxygen concentration only increases in the region between the peak and the surface, resulting in a uniform layer of thickness 2R_p (SiO₂). Infrared transmission measurements also indicate that stoichiometric SiO₂ is formed. Annealing at 900 °C has no effect on the RBS spectrum from the implanted layer but the area of the interfacial damage peak is reduced by 60%. Two interesting effects occur: (a) _χmin rises to a peak when the oxygen:silicon ratio is approximately unity; (b) the interfacial damage peak decreases with increasing dose once a uniform layer has been formed.     

Electrical and electron microscope observations on antimony-implanted silicon

Sheet resistivity and Hall effect measurements have been combined with controlled anodic oxidation and hydrofluoric acid stripping to determine donor distributions with depth and mobilities in antimony implanted silicon (50 and 100 keV, 10¹³ to 3×10¹⁵ ions/cm²). The mobilities were found to be similar to those in diffused junctions, but the peak of the donor profile was significantly deeper than expected theoretically. Electron microscopy has been used to investigate unusual effects occurring at the highest doses where the solid solubility (10²⁰ atoms/cm³) was exceeded, giving rise to antimony precipitation together with poor surface recrystallisation on annealing.     

Surface-hardening effect of B implantation in 6H-SiC ceramics

This study was conducted on the surfacehardening effect of boron ion implantation in 6H-SiC ceramics. The SiC samples prepared by pressureless sintering were carefully polished, and 500 keV B⁺ implanted in 6H-SiC ceramics at room temperature and four implantation doses, namely, 1×10¹⁵, 5×10¹⁵, 1×10¹⁶, and 5×10¹⁶ cm⁻², were chosen. The implanted samples were analyzed by scanning electron microscope and Raman spectra. The Vickers hardness of the samples was evidently increased. The thickness of the damage layer was about 1 μm, which is consistent with the simulated results. The structure of the damage layer was different from the internal part and severely damaged at high doses.     

Thermodynamic and kinetic properties of indium-implanted silicon II: High temperature diffusion in an inert atmosphere

Impurity depth profiles were obtained by differential sheet resistivity and Hall coefficient measurements on Si(100) implanted with indium to doses of 10¹³ and 10¹⁴ ions cm^-2 at an energy of 190 keV.After recovery of the implant damage the samples were diffused in an inert atmosphere at temperatures ranging from 1000 to 1200 °C.The data show that the carrier concentration is nearly independent of the implanted dose, while the indium diffusivity in silicon is higher for the samples implanted at 10¹⁴ ions cm^-2. The solid solubility of indium in silicon is around 10¹⁷ cm^-3. The hole mobility is about half that of boron-doped silicon and, in the range considered, the main contribution to the resistivity is from ionized impurity scattering.A model is proposed to account for the peculiar behaviour observed in indium-implanted silicon.     

SIMS analysis of ultrathin implanted arsenic layers in silicon

A new regime of secondary ion mass spectrometry (SIMS) is proposed, which allows a depth resolution of λ=1.4 nm to be achieved. The profiles of arsenic implanted into silicon, measured using this regime on a Cameca IMS-4f microprobe, were close to the true distributions. SIMS profiling of the samples of silicon implanted with 30-keV As⁺ ions to a total dose of (1.25–3.13)×10¹³ cm^?2 through a 20-nm-thick thermal oxide layer showed the presence of a sharp peak of arsenic accumulated at the oxide/silicon interface, which is explained by the diffusion of arsenic to this interface as a result of annealing.     

RBS,infrared and diffraction compared analysis of SiC synthesis in C implanted silicon

Monocrystalline (111) and (100) silicon substrates were implanted with singly charged carbon ions, and synthesis of silicon carbide through thermal processes was considered. Implantation energies from 10 to 40 keV were used with fluences ranging between 5×10¹⁶ and 5×10¹⁷ ions cm^?2. Analysis of the material obtained was performed using Rutherford backscattering, infrared spectra and electron diffraction. Correlations between corresponding data reported here give evidence of the respective influence of implantation energy, fluence, substrate orientation and annealing temperature.     

Diffusion of Pb in (100) Si under electron beam annealing following dual ion implantations of Pb/Ne, Pb/O and Pb/N

(100) Si was dual-implanted with the ions Pb⁺/²²Ne⁺ (7 and 30 keV), Pb⁺/¹⁶O⁺ (7 and 26 keV) and Pb⁺/¹⁴N⁺ (7 and 24 keV) to peak concentrations of typically 10 at.%. The implanted samples were then electron beam annealed at 900 °C for 30 s with a temperature gradient of 5 °C s⁻¹ under high vacuum conditions. Channelled RBS measurements performed with 1.5 MeV ⁴He⁺ ions showed that annealing of the Pb/Ne and Pb/O samples resulted in an almost complete recrystallisation of the amorphous layers caused by the ion implantations and a total loss of the implanted Pb. For the Pb/Ne samples the Ne diffused out to leave a rough surface sprinkled with deep craters; for the Pb/O samples some SiO₂ formed below the surface. In contrast, for the Pb/N samples most of the amorphous layer survives annealing and almost all the Pb is retained. A striking feature is that annealing causes the Pb to diffuse away from the surface to be trapped in a deep diffusion sink provided by the implanted N. XRD analyses exhibited Pb (111) and Pb (220) reflections suggesting that Pb nanoclusters have grown in the understoichiometric silicon nitride layer. These structures offer an interesting opportunity for controlled carbon nanotube (CNT) growth on silicon nitride.     

Effect of silicon ion implantation on the properties of a cast Co–Cr–Mo alloy

The effect of silicon ion implantation upon the corrosion resistance and structure of the cast Co–Cr–Mo alloy of the Vitalium type, was examined. The silicon fluences were 1.5, 3.0 and 4.5 × 10¹⁷Si⁺ cm^-2. The surface layer of the Vitalium samples implanted with these silicon doses was found to become amorphous. Further annealing of the samples at 200 °C resulted in the Cr₃Co₅Si₂ phase being formed, whereas the amorphous layer was preserved. The Vitalium samples submerged in the 0.9% NaCl solution underwent mainly uniform corrosion, irrespective of whether or not they had been implanted with Si⁺ ions. With increasing doses of implanted silicon and after annealing at 200 °C (samples implanted with 1.5 × 10¹⁷Si⁺ cm^-2), the corrosion resistance increased. The thickness of the oxide layer formed during the anodic polarization depended on the implanted silicon doses. This revised version was published online in November 2006 with corrections to the Cover Date.     

Structural modification of tantalum crystal induced by nitrogen ion implantation

This paper investigates the effect of nitrogen ion implantation on tantalum surface structure. In this experiment, nitrogen ions which had an energy of 30 keV and doses of 1 × 10¹⁷ to 10 × 10¹⁷ ions cm^?2 were used. X-ray diffraction analysis (XRD) was applied for both the metallic Ta substrate and the study of new structures that have been created through the nitrogen ion implantation. Atomic force microscopy (AFM) was also used to check the roughness variations prior to and also after the implantation phase. The experimental results show the formation of hexagonal tantalum nitride (TaN_0.43) in addition to the fact that by increasing the ion dose, the nitrogen atoms occupy more interstitial spaces in the target crystal. The nitride phase also seen for 3 × 10¹⁷ and 5 × 10¹⁷ ions cm^?2, while it disappeared for higher dose of 7 × 10¹⁷ and 1 × 10¹⁸ ions cm^?2. The FWHM of the dominant peak of tantalum nitride suggest the growth of the crystallite’s size, which is in agreement with the AFM results of the grains.     

Mixing induced by swift heavy ion irradiation at Fe/Si interface

The present work deals with the mixing of metal and silicon by swift heavy ions in high-energy range. Threshold value for the defect creation in metal Fe calculated was found to be ∼ 40 keV/nm. A thin film of Fe (10 nm) was deposited on Si (100) at a pressure of 4 × 10⁻⁸ Torr and was irradiated with 95 MeV Au ions. Irradiation was done at RT, to a dose of 10¹³ ions/cm² and 1 pna current. The electronic energy loss was found to be 29.23 keV/nm for 95 MeV Au ions in Fe using TRIM calculation. Compositional analysis of samples was done by Rutherford backscattering spectroscopy. Reflectivity studies were carried out on the pre-annealed and post-annealed samples to study irradiation effects. Grazing incidence X-ray diffraction was done to study the interface. It was observed that ion beam mixing reactions at RT lead to mixing as a result of high electronic excitations.     

Phase instabilities during Ti-nitride precipitation in nitrogen implanted Ti-6AI-4V alloy

Grazing incidence X-ray diffraction, performed on a 70 keV nitrogen implanted Ti-6Al-4V system, reveals phase instabilities, during the course of nitride formation. With the build up of unbound N atom concentration, for a dose of 1×10¹⁶ ions/cm², the surface region becomesα-rich, whereas, on precipitation of Ti-nitrides at a high dose of 1×10¹⁷ ions/cm², theβ-Ti phase reappears, at the surface and beyond the implanted zone. The low concentration of V and the strain in the nitrided zone, have led to radiation induced martensitic transformation of theβ-Ti phase.     

Interdiffusion and growth of chromium silicide at the interface of Cr/Si(As) system during rapid thermal annealing

In this work, the solid-state reaction between a thin film of chromium and silicon has been studied using Rutherford backscattering spectroscopy, X-ray diffraction and the sheet resistance measurements. The thickness of 100 nm chromium layer has been deposited by electronic bombardment on Si (100) substrates, part of them had previously been implanted with arsenic ions of 10¹⁵ at/cm² doses and an energy of 100 keV. The samples were heat treated under rapid thermal annealing at 500 °C for time intervals ranging from 15 to 60 s. The rapid thermal annealing leads to a reaction at the interface Cr/Si inducing the formation and the growth of the unique silicide CrSi₂, but no other phase can be detected. For samples implanted with arsenic, the saturation value of the sheet resistance is approximately 1.5 times higher than for the non-implanted case.     

Thermal effect of nitrogen implantation on high carbon steels

Quenched and annealed samples of a high carbon steel implanted with 105 keV nitrogen at a nominal dose of 3 × 10¹⁷ ions cm^-2 and current densities of 50, 100 and 200 μA cm^-2 were analysed by a nuclear technique to measure the retained dose. The dose thus measured depends on the beam current density as well as on the initial steel structure: it decreases with the beam current density and is systematically lower in quenched steel than that in the annealed steel. Microhardness measurements and conversion electron Mössbauer scattering were used to study the structural modifications induced by various implantation conditions. The mean implantation temperature of the samples, as evaluated on the basis of the microhardness values and checked by a thermocouple, lies in the tempering range of hardened structures at the above implantation current densities. The metallurgical transformations observed can account for the different amount of retained implanted ions in the first 200 nm below the surface.     

HI-ERDA, Micro-Raman and HRXRD studies of buried silicon oxynitride layers synthesized by dual ion implantation

Silicon oxynitride (Si_xO_yN_z) buried insulating layers were synthesized by dual implantation of nitrogen (¹⁴N⁺) and oxygen (¹⁶O⁺) ions sequentially into single crystal silicon in the ratio 1:1 at 150 keV to ion-fluences ranging from 1 × 10¹⁷ to 5 × 10¹⁷ cm⁻². Heavy ion elastic recoil analysis (HI-ERDA) studies of as implanted samples show Gaussian like distributions of nitrogen and oxygen. After annealing at 800 °C, both the nitrogen and oxygen distributions appear as flat plateau like regions near projected range showing the formation of a continuous buried oxynitride layer. Micro-Raman study of as implanted samples shows a broad peak at 480 cm⁻¹ for all fluences. It signifies a complete amorphization of silicon due to high fluence implantation. The annealing at 800 °C results in the reduction of the intensity of the broad peak observed at 480 cm⁻¹ and also gives rise to an additional peak at 517 cm⁻¹. It shows partial recrystallization of damaged silicon due to annealing. The X-ray rocking curves studies from high-resolution X-ray diffraction (HRXRD) of the samples implanted with different fluences have also further confirmed partial recrystallization of damaged silicon on annealing.     

Ion irradiation-induced modifications of diamond nanorods synthesised by microwave plasma chemical vapour deposition

Diamond nanorods (DNRs) synthesised by the high methane content in argon rich microwave plasma chemical vapour deposition (MPCVD) have been implanted with nitrogen ions. The nanorods were characterised by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. The DNRs consist of single-crystalline diamond cores of 3–5?nm in diameter and several tens of nanometres in length. For purification from non-diamond contents, hydrogen plasma etching of DNRs was performed. Structural modifications of etched DNRs were studied after irradiating with 50?keV nitrogen ions under the fluence of 5?×?10¹⁴, 1?×?10¹⁵, 5?×?10¹⁵ and 1?×?10¹⁶?ions?cm^?2. Nitrogen-ion implantation changes the carbon–carbon bonding and structural state of the nanocrystalline diamond (NCD). Raman spectroscopy was used to study the structure before and after ion irradiation, indicating the coexistence of diamond and graphite in the samples. The results indicated the increase in graphitic and sp²-related content, at the expense of decrease in diamond crystallinity, for ion implantation dose of 5?×?10^15?cm^?2 and higher. The method proves valuable for the formation of hybrid nanostructures with controlled fractions of sp³–sp² bonding.     

Effect of Hf ion implantation on grain growth in Ni nanocrystalline electrodeposits

Abstract

The microstructural stability of Ni nanocrystalline electrodeposits was investigated to verify general principles underlying the suppression of grain growth by microalloying with elements of very low solid solubility. Hf ions at 300 keV energy were implanted in Ni nanocrystalline foils at low (5·8 × 10¹⁵ ions cm^?2) and high (3·0 × 10¹⁶ ions cm^?2) doses. Their effects on grain growth at 550°C were studied in situ by transmission electron microscopy at 1·25 MeV and by selected area electron diffraction. Grains roughly doublled in size during implantation, but grain growth during subsequent heat treatment was dose dependent and significantly less than in specimens without implantation. Observation on implanted Ni single crystals revealed clustering and the formation of fine Ni₅Hf precipitates. A possible mechanism of grain growth suppression is discussed.     

Effect of implanted phosphorus ions on the crystallization of amorphous silicon films under the action of pulsed excimer laser radiation

We have studied the effect of implanted phosphorus ions on the crystallization of thin amorphous silicon films under the action of nanosecond radiation pulses of a XeCl excimer laser. The amorphous silicon films with a thickness of 90 nm, obtained by plasmachemical deposition on glass substrates, were implanted with phosphorus ions at a dose of 3 × 10¹⁴ and 3 × 10¹⁵ cm⁻². The subsequent laser treatments were performed using energies both above and below a threshold corresponding to the fusion of amorphous silicon. The structure of the silicon films was studied using Raman scattering spectroscopy. An analysis of the experimental data shows that implanted phosphorus stimulates nucleation, especially in the case of liquid phase crystallization. The results are of interest for the development of the technology of thin-film transistors on nonrefractory substrates.     

The effects of N+ implantation on the wear and friction of type 304 and 15-5 PH stainless steels

Ion implantation of N⁺ into mechanically polished type 304 and 15-5 PH stainless steels was studied to determine its effect on dry wear and friction behavior. Implantation of 4.0 × 10¹⁷ N⁺ cm^-2 at 50 keV yielded a depth profile with a peak concentration of about 45 at.% at a depth of 70 nm which dropped to about 10 at.% at 120 nm. Wear and friction were studied in an unlubricated pin-on-disc configuration using type 304 and 440C stainless steel pins. Both N⁺-implanted steels exhibited reduced wear at low loads but no significant reduction in the coefficient of friction was found. At the lowest normal load studied (12.3 gf), the average maximum wear depth of the implanted 15-5 PH stainless steel disc (about 0.1 μm) was reduced to approximately 10% of that for the corresponding unimplanted pin-on-disc pair after 1000 cycles. At normal loads of 50 gf or above (corresponding to hertzian stresses of 1160 MPa or higher) all beneficial effects were gone. Vacuum heat treatment at 923 K for 1.8 ks of an identically implanted type 304 stainless steel specimen eradicated the benificial effects of the nitrogen implantation. The N⁺-implanted discs show similar reductions in wear to discs implanted with titanium and carbon, but the N⁺-implanted discs do not exhibit the reductions in the coefficient of friction seen with the discs implanted with titanium and carbon.