Electrical transients in the ion-beam-induced nitridation of silicon

We have studied the dynamics of the initial stages of silicon nitride formation on siliconsurfaces under nitrogen beam bombardment in the secondary ion mass spectrometry apparatus. We have shown that the secondary ion signal exhibits damped oscillations below the critical impact angle for nitride formation. We have described this oscillatory response by a second-order differential equation and argued that it is initiated by some fluctuations in film thickness followed by the fluctuations in surface charging

Mechanically activated catalyst mixing for high-yield boron nitride nanotube growth

Boron nitride nanotubes (BNNTs) have many fascinating properties and a wide range of applications. An improved ball milling method has been developed for high-yield BNNT synthesis, in which metal nitrate, such as Fe(NO(3))(3), and amorphous boron powder are milled together to prepare a more effective precursor. The heating of the precursor in nitrogen-containing gas produces a high density of BNNTs with controlled structures. The chemical bonding and structure of the synthesized BNNTs are precisely probed by near-edge X-ray absorption fine structure spectroscopy. The higher efficiency of the precursor containing milling-activated catalyst is revealed by thermogravimetric analyses. Detailed X-ray diffraction and X-ray photoelectron spectroscopy investigations disclose that during ball milling the Fe(NO(3))(3) decomposes to Fe which greatly accelerates the nitriding reaction and therefore increases the yield of BNNTs. This improved synthesis method brings the large-scale production and application of BNNTs one step closer

Segregation Effects of Li, K and F in Si During Depth Profiling by Oxygen Ions

The migration behavior of Li, K, and F during secondary ion mass spectrometry (SIMS) depth profiling was investigated in both n-and p-type Si using different oxygen bombardment conditions. The presence of an electric field across the surface oxide is shown to be the major driving force for both the segregation of Li and K at the SiO2/Si interface and the antisegregation of F into the oxide. Room temperature SIMS measurements revealed that K segregates at the oxide side of the SiO2/Si interface, whereas Li segregates at the silicon side of the interface. We have also found that the field-induced segregation of Li and antisegregation of F are less pronounced in high resistivity (11 000-16000 Ωcm) p-type Si than in low resistivity (∼0.011 Ωcm) n-type Si. Although Li segregates at the Si side of the interface in both types of Si, some Li, however, remains at the oxide side in the high resistivity p-type Si. The high solid solubility of Li in amorphous Si is also considered as a driving force for its segregation

On the Migration Behaviour of Metal Impurities in Si During Secondary Ion Mass Spectrometry Profiling Using Low-Energy Oxygen Ions

Secondary ion mass spectrometry (SIMS) was used to investigate the segregation of several metal impurities in Si under low-energy oxygen ion bombardment. Our results suggested that both the segregation of Ca, Cr, and Ta at the SiO2/Si interface, and the antisegregation of Ti, Hf, and Zr into the oxide were thermodynamically driven. The migration behavior of Ca indicates that CaO, having a higher heat of formation than Si, was most probably formed under oxygen bombardment. Sharper in-depth profiles were obtained for Ti, Zr, and Hf (metals with lower heat of oxide formation than Si) by bombarding at angles of incidence for which a stoichiometric surface oxide is formed. The effect of impurity diffusivity is demonstrated through SIMS measurements at elevated temperatures (∼350-380°C) for Cr, Zr, Ta, and Ti

Angular and Energy Dependence of the Ion Beam Oxidation of Si Using Oxygen Ions from a Duoplasmatron Source

Oxygen ions with energy in the range 4-15 keV O+ were used to synthesize surface oxide layers by bombarding Si samples at different angles of incidence with respect to the surface normal. High-resolution Rutherford backscattering spectroscopy and channelling were used to determine both the stoichiometry and thickness of the surface oxides. In particular, the effect of energy on the critical angle for the formation of SiO2 was determined. The thickness of the oxide layers were also simulated using the PROFILE and TRIM codes. A stoichiometric oxide was obtained for angles of incidence of <25°, irrespective of the ion energy used. The critical angle for oxide formation was found to be largest for the highest ion energy. The thickness of SiO2 varies linearly with the ion energy, and correlates very well with PROFILE and TRIM code simulations

Oxidation of Cobalt by Oxygen Bombardment at Room Temperature

Most experiments on thermal oxidation of cobalt have shown the parabolic growth rate consistent with the diffusion of cations through neutral cation vacancies. Here, we present experimental results on the oxidation of Co metal by low-energy oxygen bombardment at room temperature, which scales with the dose of implanted oxygen, Φ, as Φ^1/6. This type of oxide growth, predicted theoretically for diffusion of cobalt cations by doubly charged cation vacancies, has not been observed previously in thermal oxidation of Co. Our results demonstrate that oxidation of Co, which involves formation of both monoxide, CoO, and spinel, Co₃O₄, oxide structures, can be indeed driven by doubly charged vacancies, as predicted theoretically, when oxidation conditions enhance both the production of point defects and the mobilities of cobalt cations and oxygen anions within cobalt oxide