Influence of thermal oxidation on the interfacial properties of ultrathin strained silicon layers

In this work we examine the influence of thermal oxidation on the electrical characteristics of ultra-thin strained silicon layers grown on relaxed Si_0.78Ge_0.22 substrates under moderate to high thermal budget conditions in N₂O ambient at 800 °C. The results reveal the presence of a large density of interfacial traps which depends on the oxidation process. As long as the strained silicon layer remains between the growing oxide and the underlying Si_0.78Ge_0.22 layer, the density of interface traps increases with increasing oxidation time. When the oxidation process consumes the s-Si layer the interface state density undergoes a significant reduction of the order of 40%. This experimental evidence signifies that the strained silicon-Si_0.78Ge_0.22 interface is a major source of the measured interfacial defects. This situation can be detected only when the front SiO₂-strained silicon interface and the rear strained silicon-Si_0.78Ge_0.22 interface are in close proximity, i.e. within a distance of 5 nm or less. Finally, the influence of the material quality deterioration—as a result of the thermal treatment—to the interfacial properties of the structure is discussed.     

Conductive atomic force microscope nanopatterning of hydrogen-passivated silicon in inert organic solvents

Ambient liquid phase atomic force microscope (AFM) techniques for nanopatterning organic molecules on silicon through direct Si-C bonds rely on reactions that are in direct competition with spurious oxidation. We study the effectiveness of an inert hydrophobic organic solvent at suppressing oxidation of hydrogen-passivated silicon under ambient conditions. Nanometer scale features were fabricated on an H:Si(111) substrate using a conductive AFM in hexadecane. The patterned features show chemical and kinetic behavior consistent with field induced oxidation (FIO) in air. The mechanism for FIO in hexadecane is discussed.     

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.     

Surface passivation of multicrystalline silicon wafers by porous silicon combined with an ultrathin nanoparticles aluminum coating film

In this paper, we demonstrate that we may efficiently improve surface passivation of multi-crystalline silicon (mc-Si) while combining formation of porous silicon (PS) and deposition of ultrathin aluminum (Al) film. Aluminum Nanoparticles were deposited by thermal evaporation onto PS formed on mc-Si wafers. Optoelectronic properties of Al/PS/mc-Si and Al/mc-Si treated samples were investigated before and after annealing in the 400–700 °C temperature range. The surface passivation effectiveness was pointed out based on minority carrier lifetime and photoluminescence measurements. It was found that, at a minority carrier density Δn = 10¹⁵ cm^?3, the effective minority carrier lifetime increases from 1.5 μs (for the bare mc-Si wafer) to about 6 and 14 μs before and after thermal annealing, respectively. FTIR analyses show strong correlation between the minority carrier lifetime values and hydrogen and Al passivation. Major beneficial effect of the co-presence of Al and Al–O on the optoelectronic properties is also demonstrated. The reflectivity of Al/PS treated mc-Si decrease significantly at 500 nm as compared to untreated mc-Si (from 31 % for untreated mc-Si wafers to 8 % for Al/PS treated ones), which is due to the roughly ordered structure and to the Al nanoparticles.     

Measurement of the bending strength of vapor-liquid-solid grown silicon nanowires

The fracture strength of silicon nanowires grown on a [111] silicon substrate by the vapor-liquid-solid process was measured. The nanowires, with diameters between 100 and 200 nm and a typical length of 2 microm, were subjected to bending tests using an atomic force microscopy setup inside a scanning electron microscope. The average strength calculated from the maximum nanowire deflection before fracture was around 12 GPa, which is 6% of the Young's modulus of silicon along the nanowire direction. This value is close to the theoretical fracture strength, which indicates that surface or volume defects, if present, play only a minor role in fracture initiation.     

Enhanced free exciton and direct band-edge emissions at room temperature in ultrathin ZnO films grown on Si nanopillars by atomic layer deposition

Room-temperature ultraviolet (UV) luminescence was investigated for the atomic layer deposited ZnO films grown on silicon nanopillars (Si-NPs) fabricated by self-masking dry etching in hydrogen-containing plasma. For films deposited at 200 °C, an intensive UV emission corresponding to free-exciton recombination (~3.31 eV) was observed with a nearly complete suppression of the defect-associated broad visible range emission peak. On the other hand, for ZnO films grown at 25 °C, albeit the appearance of the defect-associated visible emission, the UV emission peak was observed to shift by ~60 meV to near the direct band edge (3.37 eV) recombination emission. The high-resolution transmission electron microscopy (HRTEM) showed that the ZnO films obtained at 25 °C were consisting of ZnO nanocrystals with a mean radius of 2 nm embedded in a largely amorphous matrix. Because the Bohr radius of free-exictons in bulk ZnO is ~2.3 nm, the size confinement effect may have occurred and resulted in the observed direct band edge electron-hole recombination. Additionally, the results also demonstrate order of magnitude enhancement in emission efficiency for the ZnO/Si-NP structure, as compared to that of ZnO directly deposited on Si substrate under the same conditions.     

Observation of defects evolution in strained SiGe layers during strain relaxation

Misfit defects in strained-SiGe layers grown on (100) Si-substrates by reduced pressure chemical vapor deposition (RPCVD) were investigated by using high-resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM). While (004) omega rocking curve (ω-RC) is not sensitive to 60° misfit dislocations in a slightly strain-relaxed sample, they caused an asymmetrical shape to (113) ω-RC. On the other hand, it was found that the partial dislocations associated with stacking faults in highly strain-relaxed sample contributed to significant and symmetric peak broadening of both ω-RCs.     

Galvanisability of silicon free CMnAl TRIP steels

Abstract

Transformation induced plasticity (TRIP) steels are a promising solution for the production of cars with low body mass because of the combination of high strength and large uniform elongation that they offer. However, conventional CMnSi TRIP steels with more than 1 wt-%Si have the drawback of poor Zn coating quality after continuous galvanising. This problem is due to the presence of complex Si–Mn oxides on the strip surface. The present research work therefore focused on the full substitution of Si by Al in TRIP steels and the detailed analysis of the galvanising behaviours of these Si free CMnAl TRIP steels. If the hot dipping is done after a combination of intercritical annealing and isothermal bainitic transformation in a furnace atmosphere with a high dewpoint, the wetting of the strip by the liquid Zn is improved significantly. However, the improvement is limited and not enough to avoid bare spots and coating defects cannot be avoided on conventional CMnSi TRIP steel. In contrast, the Si free CMnAl TRIP steel has a much better wettability when annealed at a low dewpoint. The surface segregation of the elements, which have a high affinity for oxygen, i.e. Si, Al, and Mn, was studied in detail and this revealed that Si was much more readily enriched on the surface than Al during the annealing in the low dewpoint atmosphere. The difference in the surface segregation between Si and Al resulted in a clear difference in the galvanisability. The limited presence of Al on the strip surface is due to the fact that Al can be oxidised internally during hot rolling. As a result, an Al depleted surface region is formed owing to selective internal oxidation of Al before the continuous galvanising.     

Strengthening of silicon carbide by surface compressive layer

Silicon carbide ceramics containing 4.7 wt% WC and 0.3 wt% Co were fabricated by hot-pressing with various additives (B, AIN, and polycarbosilane). Addition of WC and Co liquid phase resulted in considerable increase in flexural strength up to 1085 MPa for the 1 wt% AIN, 0.5 wt% B, and 20 wt% polycarbosilane-added specimen. The improved flexural strength was a result of surface compressive layer. The surface compressive layer was introduced by the liquid flow phenomenon during hot pressing.     

Si-rich surface layer of photochemically deposited silicon nitride

The etching reaction of a photochemically deposited silicon nitride film with F₂ has been observed in situ using polarization-modulation infrared spectroscopy and quadruple mass spectrometry. The infrared spectrum of the silicon nitride film before etching exhibited two bands at 1030 and 975 cm^–1, arising from Si-N vibration. Exposure of the film at 423 K to F₂ led to an intensity decrease of the lower-frequency band, while the higher-frequency band increased. Simultaneous mass analysis revealed that the etching products evolved into the gas phase were SiF₄ and H₂. However, a further admission of F₂ resulted in a slight decrease in intensity of the 975 cm^–1 band as well as a slight evolution of SiF₄. These results strongly suggest the presence of a metastable Si-rich layer on the surface of the silicon nitride film prior to reaction with F₂. Infrared measurements have also been made in the Si-H stretching region, the results of which are described and discussed.     

Implantation of silicon ions into a surface layer of the Ti6A14V titanium alloy and its effect upon the corrosion resistance and structure of this layer

The effect of silicon ion implantation upon the corrosion resistance and structure of the surface layers formed during the implantation in the Ti6A14V titanium alloy was examined. The silicon doses were 0.5, 1.5, 3.0 and 4.5 × 10¹⁷Si⁺/cm², and the ion beam energy was 100 keV. The corrosion resistance of the samples exposed to a 0.9% NaCl solution at a temperature of 37 °C was measured using electrochemical methods. The structure of the surface layers formed during the implantation was examined by a transmission electron microscope (TEM). The results of the corrosion resistance examinations have shown that the unimplanted and 0.5 × 10¹⁷Si⁺/cm² implanted samples undergo uniform corrosion. At higher silicon doses, the samples show pitting corrosion. The highest corrosion resistance was shown by the alloy implanted with 0.5 × 10¹⁷Si⁺/cm². It has been found that, after a long-term (1200 h) exposure to a 0.9% NaCl solution, the corrosion resistance of the samples is greater than that observed after a short-term exposure. TEM examinations have shown that, beginning from a dose of 1.5 × 10¹⁷Si⁺/cm², the surface of the Ti6A14V alloy samples becomes amorphous. Heating of the 1.5 × 10¹⁷Si⁺/cm² implanted samples at 200 and 500 °C does not change their structure, whereas after heating at 650 °C, the amorphous phase vanishes.     

An analysis of the creep of hot pressed silicon nitride in bending

The creep behaviour of hot pressed silicon nitride is investigated in four-point-bend tests at temperatures of about 1200° C. By use of appropriate creep laws for the primary creep range as well as for the secondary range the experimental results can be well described analytically.     

Investigation of opto-electronic properties on gradient-porosity porous silicon layer

Electrochemical etching with step-gradient current was applied to form gradient-porosity porous silicon (PS) layer on n-Si substrate and Al/gradient-porosity. PS/n-Si structure was fabricated to extract its opto-electronic properties using reflectivity, spectral response, and scanning electron microscopy. A conventional single-layer PS etched with constant-current was also compared. Compared to the single-layer PS, the absorption wavelength of gradient-porosity PS is blue-shifted due to a smaller quantum size, hence a wider band-gap. Such a wider band-gap leads to a larger barrier-height in Al/gradient-porosity PS than that in Al/single-layer PS one. More dangling bonds are found on the surface of gradient-porosity PS owing to inhomogeneous etching, thus a poor electronic property, though it has a lower broadband antireflection than single-layer PS.     

Layer by layer deposition of zirconium oxide onto silicon

Zirconium oxide films have been produced by sequential adsorption of diluted zirconium alkoxide solutions onto a silicon wafer. After 100 deposition cycles, the film thickness increases quasi linearly with the alkoxide concentration. However, the film density decreases. Analysis of these results demonstrates that the amount of zirconium grafted at each cycle follows a Freundlich-type adsorption law, characterizing a disordered adsorption with condensation between adsorbates. Although an average monolayer can be adsorbed at each cycle, it is not dense. The resulting films are highly homogeneous and remain amorphous up to 600 °C. Despite of the low film density, the static dielectric constant measured at 1 kHz in capacitance-voltage geometry is around 15 for the films heat-treated at 300 °C in air as compared to 22 for the bulk ZrO₂.