Investigation of silicon doped by zinc ions with a large dose

The formation of nanoparticles in СZn-Si(100) implanted with ⁶⁴Zn⁺ ions using a dose of 5 × 10¹⁶ cm^–2 and an energy of 50 keV at room temperature with subsequent thermal processing in oxygen at temperatures ranging from 400 to 900°C is studied. The surface topology is investigated with scanning electron (in the secondary emission mode) and atomic force microscopes. The structure and composition of the near-surface silicon layer are examined using a high-resolution transmission electronic microscope fitted with a device for energy dispersive microanalysis. An amorphized near-surface Si layer up to 130 nm thick forms when zinc is implanted. Amorphous zinc nanoparticles with an average size of 4 nm are observed in this layer. A damaged silicon layer 50 nm thick also forms due to radiation defects. The metallic zinc phase is found in the sample after low-temperature annealing in the range of 400–600°C. When the annealing temperature is raised to 700°C, zinc oxide ZnO phase can form in the near-surface layer. The complex ZnO · Zn₂SiO₄ phase presumably emerges at temperatures of 800°C or higher, and zinc-containing nanoparticles with lateral sizes of 20–50 nm form on the sample’s surface.     

Formation of nanoparticles containing zinc in Si(001) by ion-beam implantation and subsequent annealing

The formation of nanoparticles containing zinc in Si(001) substrates by the implantation of ⁶⁴Zn⁺ ions and subsequent annealing in dry oxygen at 800 and 1000°C for 1 h is studied. The structure of the samples is studied by high-resolution transmission electron microscopy, X-ray diffraction, and photoluminescence spectroscopy. 20-nm zinc nanoparticles located at a depth of about 50 nm are revealed in the as-implanted sample. 10–20-nm pores are observed in the surface layer. Annealing leads to oxidation of the Zn nanoparticles to the Zn₂SiO₄ state. It is shown that the oxidation of Zn nanoparticles begins on their surface and at an annealing temperature of 800°C results in the formation of nanoparticles with the “соre–shell” structure. The X-ray diffraction technique shows simultaneously two Zn and Zn₂SiO₄ phases. ZnO nanoparticles are not formed under the given implantation and annealing conditions.     

Coarsening-resistant Ag nanoparticles stabilized on amorphous TiO<Subscript>x</Subscript> nanoparticles

Bare Ag nanoparticles (～10 nm) and Ag nanoparticles (1–20 nm) on the surfaces of larger TiO_x nanoparticles were prepared by laser ablation of microparticle aerosols (LAMA). The behaviors of the nanoparticles during high temperature annealing were then studied with ex situ and in situ transmission electron microscopy. For the ex situ heating experiments, Ag and Ag-on-TiO_x NPs were collected onto gold TEM grids and subjected to annealing treatments at 500 °C in argon, vacuum, and air. At this temperature, bare Ag NPs on carbon TEM supports coarsened rapidly in both air and argon atmospheres. In contrast, Ag-on-TiO_x NPs that were heated to 500 °C in flowing argon or in a vacuum did not coarsen significantly and were remarkably stable. Ag-on-TiO_x NPs that were heated to 500 °C in air, however, behaved quite differently. The TiO_x crystallized upon heating and a significant loss of Ag were observed from the surfaces of the TiO_x, likely due to sublimation. These results demonstrate that the surface defect structure and chemistry of the oxide support strongly influence the thermal stability of Ag NPs produced by LAMA.     

Annealing induced transformations in structural and optical properties of Ge30Se70−xBix thin films

ABSTRACT

Thin films of Ge₃₀Se_70?xBi_x (x?=?5, 15, 20) were prepared by thermal evaporation method on glass substrates with thickness 800?nm. The films were annealed at 250°C and 320°C for 2?h to study the annealing-induced structural and optical change. The X-ray diffraction characterization revealed the amorphous to crystalline phase transformation with annealing. The indirect optical band gap decreased with annealing which is explained on the basis of phase transformation and density of localized states. The formation of surface dangling bonds around the crystallites during crystallization process reduced the band gap. The Tauc parameter and Urbach energy change show the degree of chemical disorderness in the films. The transmitivity decreased while the absorption coefficient increased with the annealing process. The microstructural study done by Field emission scanning electron microscopy shows the formation of crystallites upon annealing. Atomic force microscopy investigation on these films shows the influence of annealing on surface topography.     

Controlled SnO2 nanocrystal growth in SiO2–SnO2 glass‐ceramic monoliths

Crack‐free (100–x) SiO₂–x SnO₂ glass‐ceramic monoliths have been prepared by the sol–gel method obtaining for the first time SnO₂ concentrations of 20% with annealing at 1100 °C. Heat‐treatment resulted in the formation and growth of SnO₂ nanocrystals within the silica matrices. Combined use of Fourier transform–Raman spectroscopy and in situ high‐temperature X‐Ray diffraction shows that SnO₂ particles begin to crystallize in the cassiterite‐type phase at 80 °C and that their average apparent size remains around 7 nm, even after annealing at 1100 °C. Nanocrystal sizes and size distributions determined by low‐wavenumber Raman are in good agreement with those obtained from transmission electron microscopy measurements. Results indicate that the formation and the growth of SnO₂ nanocrystals impose a residual porosity in the silica matrix. Copyright © 2011 John Wiley & Sons, Ltd.     

Anodic oxidation during electrostatic bonding

During electrostatic bonding, anodic oxidation of the anode material, for instance silicon, is thought to be the essential step in the bonding mechanism, leading to the formation of a permanent, strong and vacuum-tight bond. Despite the perceived importance of this step in the bonding mechanism of this well-established bonding technique, there is little experimental evidence for anodic oxidation during electrostatic bonding. One reason is that a thin (approximately 10–20?nm) amorphous anodic oxide layer is difficult to detect adjacent to an amorphous cation-depleted glass. Here, silicon–Pyrex and aluminium–Pyrex electrostatic bonds are made and the anodic oxidation process is studied directly using transmission electron microscopy. The consumption of silicon is demonstrated by the movement of the crystalline–amorphous interface compared with a marker under the original silicon–Pyrex interface. The formation of an anodic silica layer can also be demonstrated using electron-energy-loss spectrometry. An amorphous reaction layer 5–20?nm thick is formed during the bonding cycle. For aluminium anode materials bonded at 450°C a nanocrystalline γ-Al₂O₃ reaction layer is formed, which can be readily detected by transmission electron microscopy. At a bonding temperature of 350°C, no such crystalline reaction layer can be detected between Pyrex and aluminium.     

Thermal stability of second generation carbosilane dendrimers with peripheral ammonia groups

Spinel nickel zinc ferrite nanowires were successfully prepared in mesoporous silica SBA-15 as a host matrix. The powder was annealed at a range of temperatures (500–900 °C) with heating rate 0.5 °C/min. The required NiZnFe₂O₄ phase was obtained at 700 °C. The specific surface area S_BET data revealed that the surface area of the mesoporous silica after annealing was decreased from 821 to 90 m²/g which indicated that the spinal ferrite fills the channels of mesoporous materials. The one-dimensional spinel nanostructures were characterized by X-ray diffraction, infrared spectroscopy, vibrating sample magnetometer, and transmission electron microscopy before and after a selective removal of the silica template in aqueous solution of NaOH or HF. The presence of SBA-15 lowers the formation temperature of nickel zinc ferrite nanowires compared to the corresponding bulk material. The magnetic properties revealed a high saturation magnetization level (~43 emu/g) for the Ni–Zn nanowires at 900 °C.     

Synthesis,characterization, and thermal stability of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript>/CR-Ag multilayered nanostructures

The controllable synthesis and characterization of novel thermally stable silver-based particles are described. The experimental approach involves the design of thermally stable nanostructures by the deposition of an interfacial thick, active titania layer between the primary substrate (SiO₂ particles) and the metal nanoparticles (Ag NPs), as well as the doping of Ag nanoparticles with an organic molecule (Congo Red, CR). The nanostructured particles were composed of a 330-nm silica core capped by a granular titania layer (10 to 13 nm in thickness), along with monodisperse 5 to 30 nm CR-Ag NPs deposited on top. The titania-coated support (SiO₂/TiO₂ particles) was shown to be chemically and thermally stable and promoted the nucleation and anchoring of CR-Ag NPs, which prevented the sintering of CR-Ag NPs when the structure was exposed to high temperatures. The thermal stability of the silver composites was examined by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). Larger than 10 nm CR-Ag NPs were thermally stable up to 300 °C. Such temperature was high enough to destabilize the CR-Ag NPs due to the melting point of the CR. On the other hand, smaller than 10 nm Ag NPs were stable at temperatures up to 500 °C because of the strong metal-metal oxide binding energy. Energy dispersion X-ray spectroscopy (EDS) was carried out to qualitatively analyze the chemical stability of the structure at different temperatures which confirmed the stability of the structure and the existence of silver NPs at temperatures up to 500 °C.     

Formation of new structural states in compressed BaTiO<Subscript>3</Subscript> nanopowders

The structural changes in BaTiO₃ nanocrystal powder and tablets have been probed via X-ray diffraction, scanning electron and transmission microscopy, and differential calorimetry after successive hightemperature annealing in air. It is shown that, beginning with the annealing temperature of 1200°C, significant amount of the Ba₂TiO₄ phase forms in the tablets together with the BaTiO₃ phase. This phase is equilibrium one; it practically vanishes when the annealing temperature decreases to 700–600°C; and this phase practically restored to the initial state when the annealing temperature is again increased to 1200°C. Annealing the powders causes no formation of new phases, but an increase in their crystallite sizes. A probable reason of the emergence of Ba₂TiO₄ phase in tablets and its absence in free powder is discussed, as well.     

Morphological and optical properties of soft-landed supported nanoclusters: effect of rapid thermal annealing

We report the formation of large islands of bi-modal lateral size distributions having one peak at lateral size ～100 nm (height ～70 nm) and another at ～160 nm (height ～110 nm) by soft-landing of size-selected copper nanoclusters (3 nm in diameter) at room temperature (26 °C). Si(100) wafer containing native oxide is used as substrate. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) are employed to study the morphological aspects and for optical aspect cathodoluminescence measurement is used. Rapid thermal annealing (RTA) (200 °C, dry N₂, 120 s) induced effects on the morphology shows that individual islands are morphologically stable. A careful qualitative study of the optical property using cathodoluminescence in a SEM before and after the thermal treatment, using RTA, reveals very low diffusion of the cluster material into the substrate.     

Effect of the chromium layer thickness on the morphology and optical properties of heterostructures Si(111)/(CrSi<Subscript>2</Subscript> nanocrystallites)/Si(111)

Growth and the optical properties of epitaxial heterostructures Si(111)/(CrSi₂ nanocrystallites)/Si(111) based on nanosized islands of chromium disilicide (CrSi₂) on Si(111) were studied using low-energy electron diffraction, atomic-force microscopy, and optical reflection and transmission spectroscopy. The heterostructures with thicknesses of 0.1, 0.3, 0.6, 1.0, and 1.5 nm were formed by reactive epitaxy at a temperature of 500°C followed by the epitaxial growth of silicon at 750°C. The specific features of changes in the density and sizes of CrSi₂ islands on the silicon surface were determined at T = 750°C as the chromium layer thickness was increased. It was established that, in the heterostructures with chromium layer thicknesses exceeding 0.6 nm, a small part of faceted Cr₂Si₂ nanocrystallites (NCs) emerge into near-surface region of the silicon, which is confirmed by the data from optical reflectance spectroscopy and an analysis of the spectral dependence of the absorption coefficient. A critical size of NCs is shown to exist above which their shift to the silicon surface is hampered. The decreased density of emerging NCs at chromium layer thicknesses of 1.0–1.5 nm is associated with the formation of coarser NCs within a silicon layer, which is confirmed by the data from differential reflection spectroscopy.     

Luminescence and structure of nanosized inclusions formed in SiO2 layers under double implantation of silicon and carbon ions

Luminescent and structural characteristics of SiO₂ layers exposed to double implantation by Si⁺ and C⁺ ions in order to synthesize nanosized silicon carbide inclusions have been investigated by the photoluminescence, electron spin resonance, transmission electron microscopy, and electron spectroscopy methods. It is shown that the irradiation of SiO₂ layers containing preliminary synthesized silicon nanocrystals by carbon ions is accompanied by quenching the nanocrystal-related photoluminescence at 700–750 nm and by the enhancement of light emission from oxygen-deficient centers in oxide in the range of 350–700 nm. Subsequent annealing at 1000 or 1100°C results in the healing of defects and, correspondingly, in the weakening of the related photoluminescence peaks and also recovers in part the photoluminescence of silicon nanocrystals if the carbon dose is less than the silicon dose and results in the intensive white luminescence if the carbon and silicon doses are equal. This luminescence is characterized by three bands at ～400, ～500, and ～625 nm, which are related to the SiC, C, and Si phase inclusions, respectively. The presence of these phases has been confirmed by electron spectroscopy, the carbon precipitates have the sp ³ bond hybridization. The nanosized amorphous inclusions in the Si⁺ + C⁺ implanted and annealed SiO₂ layer have been revealed by high-resolution transmission electron microscopy.     

Synthesis of ceramic composites using three-dimensional nanostructuring (reinforcement) of alumina matrix with TiN and SiC nanostructures and study of their mechanical properties

The paper considers a new 3D nanostructuring technology of next-genergtion ceramic composites based on a ceramic matrix reinforced with titanium nitride (TiN) gnd silicon carbide (diC). Research data are reported on the formation of TiN and diC nanostructures on the surface of disperse alumina during successive gas chemisorption of organic Ti(N(CH₃)₂)₄ (tetrakis-dimethylamino-titanium, TDMAT) and ammonia NH₃ in the first case and Cl₂Si(CH₃)₂ and methane CH₄ in the second. Such chemisorption increases the number of surface-attached Ti-N groups crystallized on annealing at 1100°C with the formation of a TiN or a SiC nanoparticle layer. According to X-ray diffraction and electron microscopy, TiN nanoparticles with an average size of about 40 nm are formed on the surface of alumina particles after TDMAT and NH₃ treatment for 2 h and subsequent annealing at 1100°C. The mechanical properties of compacted α-A1₂O₃-based ceramics reinforced with TiN and SiC nanoparticles excel the properties of the best ceramic materials provided by different manufacturers.     

Facile synthesis of nanostructured CuO for low temperature NO2 sensing

Detection of environmental pollutant and health hazardous, nitrogen dioxide (NO₂) is reported using nanostructured CuO particulates (NPs). Powder X-ray diffraction and field emission scanning electron microscopy were used to probe crystalline phase and morphological details, respectively. Small crystallites of ∼10–12 nm and a strain of 4% were found in the leafy structure of CuO. Raman studies further supported the presence of nanosized CuO phase. This is the first instance of utilizing CuO NPs to detect 5 ppm of NO₂ even at a low operating temperature of 50 °C. The highest sensitivity for NO₂ was observed at 150 °C, for the first time, in CuO NPs. A low activation energy of 0.18 eV was found for sensing process. The CuO NPs sensor responded to NO₂ within a few seconds and recovered totally under a minute. The kinetics of the NO₂ gas adsorption on the CuO film surface was described following the Elovich model.     

Nanostructure materials for destruction of warfare agents and eco-toxins prepared by homogeneous hydrolysis with thioacetamide: Part 1—zinc oxide

Zinc sulphide (ZnS) nanoparticles were prepared by homogeneous hydrolysis of zinc sulphate and thioacetamide (TAA) at 80 °C. After annealing at temperature above 400 °C in oxygen atmosphere, zinc oxide (ZnO) nanoparticles were obtained. The ZnS and ZnO nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission microscopy (HRTEM), selected area electron diffraction (SAED), by BET and BJH methods used for surface area and porosity determination. The photocatalytic activity of the as-prepared ZnO samples was determined by the decomposition of Orange II in the aqueous solution under UV irradiation of 365 nm of wavelength.     

Preparation and electrochemical performances of nanoporous/cracked cobalt oxide layer for supercapacitors

Nanoporous/cracked structures of cobalt oxide (Co₃O₄) electrodes were successfully fabricated by electroplating of zinc–cobalt onto previously formed TiO₂ nanotubes by anodizing of titanium, leaching of zinc in a concentrated alkaline solution and followed by drying and annealing at 400 °C. The structure and morphology of the obtained Co₃O₄ electrodes were characterized by X-ray diffraction, EDX analysis and scanning electron microscopy. The results showed that the obtained Co₃O₄ electrodes were composed of the nanoporous/cracked structures with an average pore size of about 100 nm. The electrochemical capacitive behaviors of the nanoporous Co₃O₄ electrodes were investigated by cyclic voltammetry, galvanostatic charge–discharge studies and electrochemical impedance spectroscopy in 1 M NaOH solution. The electrochemical data demonstrated that the electrodes display good capacitive behavior with a specific capacitance of 430 F g^?1 at a current density of 1.0 A g^?1 and specific capacitance retention of ca. 80 % after 10 days of being used in electrochemical experiments, indicating to be promising electroactive materials for supercapacitors. Furthermore, in comparison with electrodes prepared by simple cathodic deposition of cobalt onto TiO₂ nanotubes(without dealloying procedure), the impedance studies showed improved performances likely due to nanoporous/cracked structures of electrodes fabricated by dealloying of zinc, which provide fast ion and electron transfer routes and large reaction surface area with the ensued fast reaction kinetics.     

Novel and low reflective silicon surface fabricated by Ni-assisted electroless etching and coated with atomic layer deposited Al2O3 film

In this paper, nickel nanoparticles (Ni NPs) were deposited on planar silicon and pyramidal silicon wafers by the magnetron sputtering method, and then these Ni NP-covered samples were etched in a hydrofluoric acid, hydrogen peroxide, and deionized water mixed solution at room temperature to fabricate a low reflective silicon surface. An alumina (Al₂O₃) film was then deposited on the surface of the as-etched pyramidal sample by atomic layer deposition to further reduce the reflectance. The morphologies and compositions of these samples were studied by using a field emission scanning electron microscope attached to an energy-dispersive X-ray spectrometer. The surface reflectance measurements were carried out with a UV-Vis-NIR spectrophotometer in a wavelength range of 200–1100 nm. The SEM images show that the as-etched planar and pyramidal silicon samples were covered with many rhombic nanostructures and that some nanostructures on the planar silicon surface were ready to exhibit a flower-like burst. The reflectances of the as-etched planar and pyramidal silicon samples were 5.22 % and 3.21 % in the wavelength range of 400–800 nm, respectively. After being coated with a 75-nm-thick Al₂O₃ film, the etched pyramidal silicon sample showed an even lower reflectance of 2.37 % from 400 nm to 800 nm.     

Infrared photoluminescence from GeSi nanocrystals embedded in a germanium–silicate matrix

We investigate the structural and optical properties of GeO/SiO₂ multilayers obtained by evaporation of GeO₂ and SiO₂ powders under ultrahigh vacuum conditions on Si(001) substrates. Both Raman and infrared absorption spectroscopy measurements indicate the formation of GeSi nanocrystals after postgrowth annealing at 800°C. High-resolution transmission electron microscopy characterizations show that the average size of the nanocrystals is about 5 nm. For samples containing GeSi nanocrystals, photoluminescence is observed at 14 K in the spectral range 1500–1600 nm. The temperature dependence of the photoluminescence is studied.     

Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> alloy nanoparticles embedded SiO<Subscript>2</Subscript> films: synthesis and structure

Cu–Ni fcc alloy nanoparticles (NPs) of tunable atomic ratios were generated in SiO₂ films. The films were prepared using the Cu(NO₃)₂ and Ni(NO₃)₂ co-doped inorganic–organic hybrid silica sols by single dipping. Transparent, crack-free, glassy SiO₂ films of 310 ± 10 nm in thickness embedded with high mol percent of Cu–Ni alloy NPs were yielded after annealing at 750 °C in 10% H₂-90% Ar atmosphere. Nominal compositions of the films were 20 mol% (Cu–Ni)-80 mol% SiO₂. Optical spectral study of the heat-treated films showed disappearance of Cu plasmon bands due to Cu–Ni alloy formation. Grazing incidence X-ray diffraction (GIXRD) studies revealed the formation of Cu–Ni alloy (2:1, 1:1 and 1:2) NPs inside the SiO₂ film. GIXRD showed a systematic shifting of the diffraction peaks with respect to the fcc Cu–Ni alloy composition, maintaining the nominal ratios. Transmission electron microscopy (TEM) studies of the representative Cu_0.5Ni_0.5-doped film showed existence of homogeneously dispersed Cu–Ni alloy NPs of average size 6.35 nm inside the SiO₂ matrix. The energy dispersive X-ray scattering (EDX) analysis of the individual NPs using the nano-probe (scanning TEM mode) confirmed the presence of both the Cu and Ni with the desired atomic ratio.     

Microdisperse Iron Silicide Structures Produced by Implantation of Iron Ions in Silicon

Iron implanted and subsequently annealed n-type Si(111) was studied by conversion electron Mössbauer spectroscopy for phase analysis and Auger electron spectroscopy for sputter depth profiling and element mapping. During implantation (200 keV, 3 × 10¹⁷ cm^?2, 350°C) a mixture of β- and α-FeSi₂ is firmed and after the subsequent annealing (900°C for 18 h and 1150°C for 1 h) a complete transition to the β- and the α-phase can be detected. The as-implanted profile has Gaussian shape and is broadening during annealing at 900°C to a plateau-like profile and shows only a slight broadening and depth depending fluctuations of the iron concentration after the 1150°C annealing. With scanning Auger electron spectroscopy the lateral iron and silicon distribution were investigated and show for the sample annealed at 900°C large separated β-FeSi₂ precipitates which grow due to the process of Ostwald ripening. At 1150°C additionally coalescence of the precipitates occur and a wide extended penetration α-FeSi₂ network structure is formed.