J.M. Williams

Ion implantation effects in silicon carbide

Abstract Results from a program, which has existed for some years, on ion implantation effects in α and β silicon carbide will be summarized. Silicon carbide is easily amorphized by ion implantation at room temperature. Amorphization as determined by Rutherford backscattering spectrometry (RBS) occurs for damage energies of about 20 eV/atom, corresponding to 0.2 to 0.3 displacements per atom (dpa), at room temperature. Implantation at higher temperatures (≈ 500°C or above) does not produce an amorphous region for damage levels as high as 17 dpa. Recovery of damage at the subamorphous damage level is fairly complete by 1000°C. Epitaxial regrowth after amorphization occurs over a very narrow temperature range at ≈ 15000°C in an almost “explosive” fashion. Damage and amorphization are accompanied by swelling of up to 15%. The hardness and elastic modulus values of amorphous SiC are 40 and 70%, respectively, of the unimplanted single crystalline values, but before amorphization, the hardness first increases during the early damage phase and then decreases upon amorphization. The oxidation and chemical rates of the amorphous state are higher than for crystalline material. Amorphization kinetics, annealing kinetics and properly changes are broadly compatible with the idea of a critical accumulation model for amorphization.

Ion implantation and thermal annealing of α‐Al2O3 single crystals

The effects of ion implantation and post‐implantation thermal annealing of α‐Al2O3 have been characterized using ion scattering‐channeling techniques, and correlated with electron paramagnetic resonance (EPR) and microhardness measurements. Although most of the work was done on 52Cr implanted specimens, preliminary results have been obtained also for implanted 90Zr and 48Ti. For Cr implantation, the Al2O3 lattice damage saturates at relatively low doses, but the near‐surface region never becomes amorphous. A preferential annealing behavior begins in the Al sublattice after ∼800 °C annealing, and in the oxygen sublattice, only after 1000 °C annealing. Lattice location measurements show that after annealing to 1500 °C, Cr is greater than 95% substitutional in the Al sublattice. Above 1500 °C, implanted Cr atoms redistribute by substitutional diffusion processes. EPR measurements show that part, if not all, of the implanted Cr is trivalent and substitutional after annealing to 1600 °C. Microhardness measurem...

Recrystallization of ion-implanted α-SiC

The annealing behavior of ion-implanted α-SiC single crystal was determined for samples implanted with 62 keV 14 N to doses of 5.5X10 14 /cm 2 and 8.0X10 16 /cm 2 and with 260 keV 52 Cr to doses of 1.5X10 14 /cm 2 and 1.0X10 16 /cm 2 . The high-dose samples formed amorphous surface layers to depths of 0.17 μm (N) and 0.28 μm (Cr), while for the low doses only highly damaged but not randomized regions were formed. The samples were isochronically annealed up to 1600°C, holding each temperature for 10 min. The remaining damage was analyzed by Rutherford backscattering of 2 MeV He + , Raman scattering, and electron channeling. About 15% of the width of the amorphous layers regrew cpitaxially from the underlying undamaged material up to 1500°C, above which the damage annealed rapidly in a narrow temperature interval. The damage in the crystalline samples annealed linearly with temperature and was unmeasurable above 1000°C.

Damage accumulation in ceramics during ion implantation

Abstract The damage structures of α-Al2O3 and α-SiC were examined as functions of ion implantation parameters using Rutherford backscattering-channeling, analytical electron microscopy, and Raman spectroscopy. Low temperatures or high fluences of cations favor formation of the amorphous state. At 300 K, the mass of the bombarding species has only a small effect on the residual damage state, but certain ion species appear to stabilize the damage microstructure and increase the rate of approach to the amorphous state. The type of chemical bonding present in the host lattice is an important factor in determining the residual damage state.

Ion implantation, ion beam mixing, and annealing studies of metals in Al2O3, SiC and Si3N4☆

Abstract Ion scattering/channeling, TEM, EPR and optical microscopy are utilized to determine the structural modifications of ion implanted and annealed Al2O3, SiC, and Si3N4, and to correlate these modifications to surface mechanical property measurements. Ion beam mixing is also studied for inducing increased adherence of metal films on these insulators.

Near surface modification of α-Al2O3 by ion implantation followed by thermal annealing☆

Abstract Structural changes in α-Al2O3 crystals implanted by 48Ti and 90Zr and subjected to thermal annealing have been investigated using ion scattering/channeling techniques. For the case of Ti implantation, the implanted species exhibits substitutionality in the as-implanted condition and undergoes anisotropic diffusion along the 〈0001〉 axis at a temperature of 1200°C which gives rise to the formation of needle-like precipitates partially coherent along the 〈0001〉 direction. For the case of Zr implantation, recovery of lattice damage begins in the Al sublattice at ∼ 800°C and in the O sublattice at ∼ 1300°C. Zr is not observed to be substitutional even after annealing to temperature of 1600°C. Results on the structural changes are correlated with measured mechanical property changes for the case of Cr, Ti, and Zr implanted into Al2O3 and thermally annealed to temperatures of 1600°C.

Properties of nitrogen-implanted alloys and comparison materials

Abstract The nanoindentation hardness technique and the atomic force microscopy technique have been combined in a study of surface and near-surface properties of nitrogen ion-implanted alloys versus ion fluence. The two alloys studied were Ti-6Al-4V and a CoCrMo alloy. Properties results have been compared with those of non-ion-implanted reference materials, such as electroplated hard chrome, rutile, and amorphous TiO2. Large areas of both alloys were polished to finish levels of approximately 1 nm, but for the CoCrMo, the finish level, by profilometer, over long traces is limited to about 30 nm. This results from the very different hardnesses of the carbide and matrix phases of the CoCrMo. In either case, nanoindentations of only 50 nm in depth still penetrate to about 50 times the local roughness values. The alloys were ion implanted to the same respective treatment depths (150 nm) by use of an energy grade suitable for each alloy. By 6 × 1017 cm−2, the hardness of the Ti-alloy had increased from a value of 4 to 12 GPa. A rutile crystal was amorphized by ion bombardment, so that a hardness value for amorphous TiO2 could be obtained. The results indicate that after only a small dose, the Ti alloy is harder than its own passive oxide. Ion implantation first softens and then rehardens the carbide phase of the CoCrMo. The matrix of that alloy is not quite as hardenable as the Ti-6Al-4V alloy. These results are relevant to orthopedics applications, tribological mechanisms, ion implantation process design, and substitute coatings for electroplated hard chrome.

Phase transformation of Ni2Al3 to NiAl. I. Ion irradiation induced

An ion‐irradiation‐induced phase transformation from Ni2Al3 to NiAl has been investigated by transmission electron diffraction. Compound samples of Ni2Al3 were irradiated at liquid nitrogen, room temperature, and 100 °C with 300‐keV Xe and 60‐keV Ne ions. Transformation to NiAl was observed in all cases. Detailed examination of the closely related equilibrium NiAl and Ni2Al3 structures permits explanation of this transformation based on the structural similarity of the two phases and using a model built around radiation disordering of vacancies.

Implantation of gases into sapphire

Ions of neon, argon, and bromine were implanted into single crystals of α-Al 2 O 3 . Implantation energies of 125 keV to 3 MeV and fluences of 1 10 16 to 3 × 10 17 ions/cm 2 were used. Some samples were subjected to post-implantation annealing. Scanning electron micrographs showed profuse (30–50% of surface area) blistering for implants of 1 × 10 17 Ar/cm 2 (230 keV) and 3 × 10 17 Ne/cm 2 (3 MeV). Specimens implanted with 4 × 10 16 Br/cm 2 (175 keV) contained a few ruptured blisters on the as-implanted surface. The implanted layer was severely embrittled and readily spalled from the substrate. Heating the specimens caused further blistering, cracking, and exfoliation in each case.

The reactivity of ion-implanted SiC

Abstract Implantation of chromium into single-crystal or polycrystalline α-SiC produces a surface amorphous layer for displacement damage greater than about 0.2 displacements per atom at room temperature. The enhanced chemical reactivity of such specimens was studied by two methods: chemical etching rate and oxidation rate. The chemical etching rates in a saturated solution of 50%K 3 Fe(CN) 6 plus 50% KOH were measured. The etching rate for the amorphous layer was 2.4−3.7 times that of the polycrystalline samples and 3.0–4.1 times that of the single-crystal samples. Polycrystalline specimens were exposed to flowing oxygen for 1 h at 1300 °C. Rutherford backscattering and the nuclear reaction 16 O(d,p) 17 O ∗ were used to determine the amount of oxygen on the surface. The amount of oxygen (and the thickness of oxide) over the amorphous region was 1.67 times that over the crystalline region. The relative thicknesses of the oxide on the amorphous and crystalline regions were confirmed by measuring the sputtering time required to remove the oxygen signal in an Auger spectrometer.