Thermal Evaporation Of SiO Powders Research Articles

Diffraction Studies of the Formation of Silicon Nanocrystals in the SiOx/Si Compounds after Carbon Ion Implantation

The films have been deposited on the silicon subtracts with the (111) and (100) orientations by thermal evaporation of SiO powder and carbon implanted with doses of 6 · 1016 to 1,2 · 1017 cm−2 followed by annealing in nitrogen at 1100 oC. Diffraction studies of these structures confirm the occurrence of a preferred orientation in the nanocrystals during high temperature thermal annealing, controlled by the substrate orientation. It was possible to detect the existence of two arrays of silicon nanocrystals in the dielectric matrix, with one having a smaller average size of 5—10 nm and a lattice parameter close to that of crystalline silicon, and the other one having a large size of 50—100 nm and a greater lattice parameter. We have estimated the carbon implantation doses for which the large size nanocrystals (> 50 nm) do not form. This dose is 6 · 1016 cm−2 for the (111) substrates and 9 · 1016 cm−2 for the (100) ones.

Vibrational spectroscopy of SiO on Si(111)

The growth of ultrathin SiO layers on clean Si(111) was observed by in situ infrared spectroscopy under ultra-high vacuum conditions. SiO was deposited by thermal evaporation of SiO powder from a Knudsen cell. A large shift of the SiO main vibrational line, from about 864 cm−1 for sub-monolayer coverage up to the bulk value of SiO at about 982 cm−1 for thicknesses above 10 Å, was observed. The extraordinary low vibrational frequencies for species at the SiO–Si interface corroborate recently published theoretical results for SiO adsorption on Si and for the SiO2–Si interface.

Ag-modified silicon nanowires substrate for ultrasensitive surface-enhanced raman spectroscopy

We report a unique substrate for surface-enhanced raman spectroscopy (SERS) based on silver nanoparticles-embedded silicon nanowires (SiNWs). The SiNWs were prepared by thermal evaporation of SiO powder via oxide-assisted growth, oxide removed with HF, and then used to reduce silver ions to form a highly decorated Ag-embedded surface. Such modified SiNWs substrates yielded ultrahigh SERS sensitivity, which could detect 25μl of 1×10−16M Rhodamine 6G, 1×10−16M crystal violet, and 1×10−14M nicotine in methanol solutions. An Ag-modified SiNW strand could also enable SERS detection of 25μl of 1×10−8mg∕ml calf thymus DNA. The possible mechanisms for the ultrahigh SERS sensitivity were discussed.

Millimeter-Long and Uniform Silicon Nanocables

An ultralong Si nanocable has been prepared by simple thermal evaporation of SiO powder mixed with a small amount of Sn. The nanocable has a uniform diameter of about 680 nm and millimeters in length. The core of the nanocable is single-crystal Si with an average diameter of 160 nm, and the shell is composed of compact amorphous SiO x with a uniform thickness of 260 nm. The cladding SiO x emits strong light in a wide spectral range from UV to visible. In particular, each nanocable has a droplet head of Si-Sn eutectic and an uncovered Si core at the tail. The nanocables can be directly fabricated into metal-oxide-semiconductor field effect transistors (MOSFETs) via simple thermal deposition of Au electrodes. The performance of the MOSFETs reveals that the Si nanocables are p-type semiconductors with 1.1 x 10 17 cm -3 hole concentration and 3.69 cm 2 V -1 s -1 hole mobility.

Cathodoluminescence investigation of silicon nanowires fabricated by thermal evaporation of SiO

Silicon nanowire samples fabricated by thermal evaporation of SiO powder were investigated by Cathodoluminescence. Three main bands were found at low temperatures, namely, peak 1 at about 620–650 nm (2.0–1.91 eV), peak 2 at 920 nm (1.35 eV), and peak 3 at 1280 nm (0.97 eV). An additional broad band (peak 4) in the infrared region with its maximum at ∼1570 nm (0.79 eV) appears at room temperature. The origins of the emission bands are discussed.

Field emission from nonaligned SiC nanowires

β-SiC nanowires with an average diameter of 8–20nm were synthesized using a simple thermal evaporation of SiO powders onto activated carbon fibers. Field emission was investigated based on the SiC nanowires deposited on a platinum film. A low turn-on field of 3.1–3.5Vμm−1 was measured at an anode-sample separation of 100–140μm. This type of SiC nanowires can be applied as field emitters in displays as well as vacuum electronic devices.

Fabrication of Germanium‐Filled Silica Nanotubes and Aligned Silica Nanofibers

Germanium‐filled SiO2 nanotubes and aligned SiO2 nanofibers are synthesized via a two‐stage process: thermal evaporation of SiO powder, followed by laser ablation of a Ge target. The nanotubes are either partially filled with Ge nanoparticles/nanorods or completely filled with Ge nanowires, forming Ge/SiO2 nanocables (see Figure). The products were characterized using a variety of spectroscopic techniques.

Visible Photoluminescence from Evaporated SiOx Thin Films

SiOx thin films were prepared by thermal evaporation of SiO powder in vacuum onto Si substrates. The as-deposited samples exhibited blue emission under UV irradiation. Post-annealing was carried out in vacuum, and the photoluminescence (PL) spectra were redshifted from the visible to near-infrared range as the annealing temperature increases. It was also found that the main PL peak wavelength was affected by the deposition rate. The PL spectra of the films consisted of a red and a blue PL. Annealing treatments in oxygen atmosphere were also carried out to investigate the effect of oxidation. From the analysis of the results of infrared spectrometry, we attributed the blue emission to oxygen vacancies in SiOx. And the red PL could be explained by the quantum confinement effect in Si clusters embedded in the SiOx matrix.

Temperature dependence of morphology and diameter of silicon nanowires synthesized by laser ablation

The silicon nanowires (SiNWs) with different diameters and morphologies were synthesized by laser ablation of a target containing metals over a temperature range 910–1120 °C. The octopus-shaped wires of larger diameters were formed in lower temperature zone (910–960 °C), while SiNWs and silicon nanoparticle chains of smaller diameters in higher temperature zone (960–1120 °C). The distribution of the morphology and diameter of SiNWs as a function of growth temperature differs from that reported by thermal evaporation of SiO powders. The study shows that the morphology and diameter of SiNWs synthesized by laser ablation not only correlate closely with the growth temperature of SiNWs, but also with the nature of a catalyst. By change of nucleation temperature and critical nucleus size of nucleus droplets in vapor–liquid–solid (VLS) growth process, a catalyst can change relationships between the morphology, diameter, and growth temperature of SiNWs.

Characterization and light-emitting properties of Au/SiO x/p-Si and Au/Ni-implanted-SiO x/p-Si structures

SiO x layers were fabricated by thermal evaporation of SiO powders onto p-type Si(100) substrates at 200°C to investigate the electrical and light-emitting properties of the layers. After deposition, Ni ions of 70 keV were also implanted into SiO x layers at room temperature. Then both of the as-deposited and as-implanted samples were annealed in N 2 ambient for 2 h at 500°C. Violet photoluminescence (PL) due to radiative defects was observed from all the SiO x samples but annealed ones showed more intense PL than unannealed samples. Red electroluminescence (EL) was obtained from the SiO x in metal–insulator–semiconductor (MIS) structures and the annealed SiO x layers also exhibit more intense EL than unannealed layers. Particularly, the SiO x annealed after Ni-implantation showed the most intense EL which may be caused by highly concentrated radiative defects in the implanted SiO x .

Temperature-Controlled Growth of Silicon-Based Nanostructures by Thermal Evaporation of SiO Powders

Silicon-based nanostructures with different morphologies, sizes, compositions, and microstructures were grown on Si wafers by thermal evaporation of SiO powders at 1350 °C for 5 h under 300 Torr of a flowing gas mixture of 5% H2-Ar at a flow rate of 50 standard cubic centimeters per minute (sccm). The SiO powders and Si wafers were placed inside an alumina tube, which was heated by a tube furnace. The local temperature inside the tube was carefully calibrated by a thermal couple. After evaporation, Si-containing products with different colors and appearances were formed on the surfaces of the Si wafers over a wide temperature range of 890-1320 °C and a long distance of 85 mm. Basing on the colors and appearances of the products, five distinct zones, which corresponding to different temperature ranges, were clearly identified from the highest temperature of 1320 °C to the lowest temperature of 890 °C. They are zone I (1250-1320 °C), zone II (1230-1250 °C), zone III (1180-1230 °C), zone IV (930-1180 °C), and zone V (890-930 °C). The deposited products were systematically studied by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results show that, besides Si nanowires, many other kinds of Si-based nanostructures such as octopuslike, pinlike, tadpolelike, and chainlike structures were also formed. The temperature distribution inside the alumina tube was found to play a dominant role on the formation of these structures. It is demonstrated that a control over the growth temperature can precisely control the morphologies and intrinsic structures of the silicon-based nanomaterials. This is an important step toward design and control of nanostructures. The growth mechanisms of these products were briefly discussed.

Morphology and growth mechanism study of self-assembled silicon nanowires synthesized by thermal evaporation

Silicon nanowires (SiNWs) grown from `sunflower-seed'- and `mushroom'-shaped particles have been observed by electron microscopies. The SiNWs were synthesized by thermal evaporation of SiO powders without any metal catalysts. The SiNWs grown on the sunflower-seed-shaped particles had sub-branches of SiNWs terminated by Si bulbs. The SiNWs on the mushroom-shaped particles were densely and uniformly distributed on the surface of the mushroom cone. The growth history suggests that these SiNWs were formed by nucleation which originated from the surface of amorphous SiO particle matrixes via phase separation and precipitation followed by growth through oxide-assisted vapor–soild reaction.

Strong visible photoluminescence in amorphous SiO x and SiO x : H thin films prepared by thermal evaporation of SiO powder

Amorphous SiO x and SiO x : H films were prepared by thermal evaporation of SiO powder in ultrahigh vacuum or under a flow of hydrogen ions onto silicon substrates maintained at 100°C. Photoluminescence (PL) can be seen in the visible range with the naked eye on the as-deposited samples without post-treatments. Composition and structure investigations were performed by infrared and Raman spectrometry experiments on films annealed at different temperatures. Hydrogen and oxygen bonding was studied by infrared spectrometry. The PL is attributed to the quantum confinement of excitons in a-Si clusters embedded in the a-SiO x matrix. Our results demonstrate that oxygen creates an efficient potential barrier and no further passivation by hydrogen is necessary.