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The thermal oxidation of Ge-implanted Si single crystals has been investigated for different Ge doses (3 × l0[sup 15] cm[sup -2] and 3 × 10[sup 16] cm[sup -2]) and different oxidation processes (in wet ambient at 920 °C for 30, 60, and 120 min, or dry ambient at ll00 °C for 30 min). The oxide roughness, the oxidation rate, the Ge diffusion, precipitation, and clustering, have been monitored by several experimental techniques: atomic force microscopy, transmission electron microscopy, Rutherford backscattering spectrometry, and x-ray absorption spectroscopy. We found that the surface roughness is related to the segregation of Ge at the oxide/substrate interface, occurring when the oxidation rate is faster than the Ge diffusion, in particular at the higher implanted dose (3 × 10[sup 16] cm[sup -2]) when processed in a wet ambient. For these conditions, we also observed an oxidation rate enhancement with respect to pure Si, and a strong indication that pure Ge clusters were formed. When a critical Ge concentration at the interface is reached, the oxidation mechanisms change and the oxidation rate is reduced, along with Ge diffusion into the substrate and a consequent reduction of the Ge fraction at the interface. Nevertheless, the oxide roughness still increases despite the Ge concentration reduction, resulting from the initial nucleation of precipitates. [ABSTRACT FROM AUTHOR]

The injection of Si self-interstitial atoms during dry oxidation at 815 °C of very shallow SiGe layers grown on Si (001) by molecular-beam epitaxy (MBE) has been investigated. We first quantified the oxidation enhanced diffusion (OED) of two boron deltas buried into the Si underlying the oxidized SiGe layers. Then, by simulating the interstitial diffusion in the MBE material with a code developed on purpose, we estimated the interstitial supersaturation (S) at the SiGe/Si interface. We found that S (a) is lower than that observed in pure Si, (b) is Ge-concentration dependent, and (c) has a very fast transient behavior. After such a short transient, the OED is completely suppressed, and the suppression lasts for long annealing times even after the complete oxidation of the SiGe layer. The above results have been related to the mechanism of oxidation of SiGe in which the Ge piles up at the SiO2/SiGe interface by producing a thin and defect-free layer with a very high concentration of Ge. [ABSTRACT FROM AUTHOR]

Abstract: Radio frequency magnetron sputtering has been used for the synthesis of aligned carbon nanotubes (CNTs) on SiO2/Si substrate. The results were obtained by depositing catalytic nano-particles in advance (ex situ) or simultaneously to the C deposition (in situ), which have been compared showing that the oxidation of the metal catalyst deposited in advance is detrimental for the good outcome of the CNTs growth. An in situ catalyst deposition allows to get rid of the contamination problem and to grow aligned CNTs on a substrate, as shown by scanning electron microscopy. Transmission electron microscopy shows that the so-achieved CNTs own a bamboo-like structure and the catalytic Ni nanoparticle is on the tip of the CNTs. Our method allows to perform catalyst deposition and growth of CNT on a SiO2/Si substrate simultaneously and its use can be extended to a variety of catalytic elements and substrates, in principle without many efforts. [Copyright &y& Elsevier]

The effect of thermal dry oxidation on an off-axis (111) 3C-SiC film have been studied in order to subsequently realize a metal-oxide-semiconductor structure. A morphological characterization of the SiO2 surface, grown at 1200 °C in an O2 flux, pointed out some defect-related effects as a consequence of the preferential oxidation of stacking faults over the (111) 3C-SiC surface. Scanning electron microscopy and atomic force microscopy confirmed such a hypothesis. Stacking faults are seen as promoters of a local polarity inversion in (111) 3C-SiC, from Si- to C-terminated surface, resulting in a higher oxidation rate as compared to defect-free zones. [ABSTRACT FROM AUTHOR]

The thermal oxidation of Ge or As implanted Si single crystals has been investigated for two different oxidation processes (in wet ambient at 920 °C and dry ambient at 1100 °C). Using the atomic force microscopy the oxide morphology and roughness has been determined as a function of the different oxidation processes. The X-ray absorption spectroscopy has been employed to determine the structural coordination around the dopant atoms.We found that the surface roughness is related to the segregation of Ge or As at the oxide/substrate interface, occurring when the oxidation rate is faster than the dopant diffusion, in particular at the higher implanted dose processed in wet ambient.The segregation of Ge at the interface gives rise to the formation of germanium rich alloy region, whereas the segregation of As induces the precipitation of SiAs monoclinic islands.The formation of islands is directly related to the dopant segregation, but their size is not. In fact, after a critical concentration of dopant at the interface is reached, a dissolution of the precipitates takes place. A memory effect causes the continuous growing of the islands, even once the diffusion of Ge or As takes place. [Copyright &y& Elsevier]

Abstract: In this paper we compare dry oxidation, at different temperatures and oxidation times, on epitaxial SiGe films and Si reference samples. Rapid and conventional furnaces and several analysis techniques, such as Rutherford backscattering spectrometry, transmission electron microscopy and secondary ion mass spectroscopy, have been used to process and characterize our samples. We focused the attention on the thin oxide regime (3–30nm), pointing out substantial differences between Si and SiGe in the oxidation kinetics and point defect injection. In fact, SiGe films show an oxidation rate enhancement with respect to Si, previously reported by other groups only for wet ambient. The enhancement, however, decreases with temperature and oxide thickness. From our data we estimated the activation energies for Si and SiGe oxidation in our range of thickness. We also show that Ge segregates behind the oxide forming a Ge-rich layer, free of extended defects. Finally, the study of the broadening of thin boron spikes, introduced in some of our samples, has allowed us to measure the interstitial injection during the oxidation and to demonstrate that it is strongly reduced in the case of SiGe samples. [Copyright &y& Elsevier]