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Chemical and phase compositions of silicon oxide films with nanocrystals prepared by carbon ion implantation
Abstract
The chemical and phase compositions of silicon oxide films with self-assembled nanoclusters prepared by ion implantation of carbon into SiOx
(x < 2) suboxide films with subsequent annealing in a nitrogen atmosphere have been investigated using X-ray photoelectron spectroscopy in combination with depth profiling by ion sputtering. It has been found that the relative concentration of oxygen in the maximum of the distribution of implanted carbon atoms is decreased, whereas the relative concentration of silicon remains almost identical over the depth in the layer containing the implanted carbon. The in-depth distributions of carbon and silicon in different chemical states have been determined. In the regions adjacent to the layer with a maximum carbon content, the annealing results in the formation of silicon oxide layers, which are close in composition to SiO2 and contain silicon nanocrystals, whereas the implanted layer, in addition to the SiO2 phase, contains silicon oxide species Si2+ and Si3+ with stoichiometric formulas SiO and Si2O3, respectively. The film contains carbon in the form of SiC and elemental carbon phases. The lower limit of the average size of silicon nanoclusters has been estimated as ∼2 nm. The photoluminescence spectra of the films have been interpreted using the obtained results.
... The observed peaks at E bind ≈ 102.3 eV (Fig. 2a), which corresponds to the Si-О bond within silicon-oxygen tetrahedra and ring and chain-structured natural silicates [13,14], are shifted into E bind ≈ 103.3 eV position (Figs. 2b-2d) characteristic of the Si-O bond in the silicon dioxide (SiO 2 ) structure in the amorphous state, or silica gel SiO 2 ·nH 2 O [15][16][17]. ...
... Analysis of the fine structure of the Si 2p photoelectron spectra (Fig. 2) showed that a weakly expressed shoulder in the 100.5-103.1 eV binding energy region formed as a result of the contact between eudialyte particles and the leaching solution (Fig. 1b). As such, the change in the spectrum was probably caused by the formation of additional component with bind 101.5 101.7 E = − eV, corresponding assumingly to the amorphous silicon oxide (SiO y ), oxinitride (SiO x N y ) and nitride (Si 3 O 4 ) [14,16,18]. With respect to a sample given to a 3 min electromagnetic pulse treatment prior to leaching, the fraction of this component in the Si 2p spectrum was ~10% (Fig. 2b), while this fraction did not exceed 2% for other samples (Figs. ...
The mechanism of weakening and directional change in structural and chemical properties of eudialyte under nonthermal exposure to nanosecond high-voltage electromagnetic pulses and nitric-acid leaching is studied. The methods of X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy and microhardness measurement are used. The rational mode of high-energy pulsed treatment is determined. After such mode treatment, the acid leaching of eudialyte concentrate results in recovery of zirconium and total rare earth elements higher by 1.7 and 1.4 times as against reference standards.
... The luminescent band shift to short wavelengths, overlapping the whole visible range, can extend applications possibilities of silicon structures for different optoelectronics devices. It has been shown (see, for example, Zhao et al., 1998;Gonzalez-Varona et al., 2000;Perez-Rodriguez et al., 2003;Tetelbaum et al., 2009;Boryakov et al., 2012) that simultaneous implantation of silicon and carbon ions into SiO 2 films leads to photoluminescence in the range from near infra-red to ultraviolet wavelengths due to the formation of silicon nanocrystals as well as carbon and silicon carbide nanocrystals. The luminescence extension to the visible and ultraviolet spectral range was realised by carbon ion implantation into SiO x films on silicon substrates where the nanocrystalline silicon phase was formed as the non-stoichiometric oxide decomposition SiO x ! ...
... Si + SiO 2 under high-temperature annealing . By means of the X-ray photoelectron spectroscopy (XPS) technique it was found (Boryakov et al., 2012; that silicon atoms with Si 2p core-level bindingenergy values close to crystalline SiC (100.8 eV; Dufour & Rochet, 1997) were located over the 70-170 nm surface layers of investigated samples. However, the absence of a sharp SiC peak in the XPS data mentioned above as well as the presence of low oxidation degree oxides at the same depth with silicon binding energies of $ 100.5-101.2 ...
Substructure and phase composition of silicon suboxide films containing silicon nanocrystals and implanted with carbon have been investigated by means of the X-ray absorption near-edge structure technique with the use of synchrotron radiation. It is shown that formation of silicon nanocrystals in the films' depth (more than 60 nm) and their following transformation into silicon carbide nanocrystals leads to abnormal behaviour of the X-ray absorption spectra in the elementary silicon absorption-edge energy region (100-104 eV) or in the silicon oxide absorption-edge energy region (104-110 eV). This abnormal behaviour is connected to X-ray elastic backscattering on silicon or silicon carbide nanocrystals located in the silicon oxide films depth.
... When the spectrum was decomposed into Gaussians, four bands were revealed. Based on XPS analysis results and known literature data [81][82][83][84][85][86], PL spectra can be associated with specific phases. The allocation of bands is given in Table 4. ...
A mesoporous amorphous crystalline nanopowder (NP) Si–SiO2 with a specific surface area (SSA) of 35 m2/g was produced by pulsed electron beam evaporation (PEBE) of a compact of micron commercial SiO2 powder (0.9 m2/g). Si semimetal nanoparticles (NPles) reduced in for vacuum (≈4 Pa) had a marked effect on the
thermal and luminescent properties of the Si–SiO2 nanoparticles compared to the properties of amorphous SiO2 NPles produced earlier by PEBE evaporation of a target compound made from NP Aerosil 90 (Degussa). Photocatalytic capabilities of Si–SiO2 nanoparticles were evaluated. NPles Si–SiO2 showed high antioxidant activity on HELA cancer cells.
... Recently, the possibility of obtaining semiconductor structures with self-organized nanoclusters using methods of molecular-beam epitaxy [1,2], ion implantation [3,4] and under the action of laser irradiation [5,6], as well as the ability to control their physical properties, have become the subject of intense research. In particular, laser-induced periodic surface nanostructures can be generated practically on any material (metals, semiconductors, dielectrics) at linearly polarized irradiation and are formed in a wide range of intervals of impulses, ranging from continuous wave radiation to several femtoseconds [7][8][9][10]. ...
In the paper, the effect of the electric field on the conditions of formation and on the period of the surface superlattice of adatoms in n-GaAs semiconductor is investigated. It is established that in GaAs semiconductor, an increase in the electric field strength, depending on the direction, leads to an increase or decrease of the critical temperature (the critical concentration of adatoms), at which the formation of self-organized nanostructure is possible. It is shown that in strongly alloyed n-GaAs semiconductor, an increase of the electric field strength leads to a monotonous change (decrease or increase depending on the direction of the electric field) of the period of self-organized surface nanostructures of adatoms.
... It is seen that as the annealing time of the films increases, a lower binding energy shoulder arises in the spectra. According to the literature data, 18 The decomposition of the experimental spectra was carried out using Gauss symmetric functions. An example of decomposition is shown in Fig. 4. It was found that all the spectra can be represented as the sum of two peaks with maxima of 103.2 (Si 4+ ) and 101.3 (Si 2+ ). ...
A method for the growth of nanocomposite layers in stoichiometric amorphous silicon dioxide is proposed. It is shown that, after annealing at a temperature of 1150°C in nitrogen atmosphere, a layer containing silicon nanoclusters is formed. Silicon nanoclusters have a crystal structure and a size of 3–6 nm. In a film grown on a n-type substrate, a layer of silicon nanoclusters with a thickness of about 10 nm is observed. In the case of a film grown on a p-type substrate, a nanocomposite layer with a thickness of about 100 nm is observed. The difference in the formation of a nanocomposite layer in films on various substrates is associated with the doping of silicon dioxide with impurities from the substrate during the growth of the film. The formation of the nanocomposite layer was confirmed by transmission electron microscopy, XPS and local cathodoluminescence studies.
... The limiting detectable content of ele-ments was defined by the signal/noise ratio in the photoelectron spectra and corresponded to 0.1-0.5 at %. The content was determined and the chemical bonding was analyzed by a procedure described elsewhere [9]. To conduct layer-by-layer profiling, we etched the samples with Ar + (1 keV) ions using an ISE-10 source. ...
The composition and structure of silicon surface layers subjected to combined gallium and nitrogen ion implantation with subsequent annealing have been studied by the X-ray photoelectron spectroscopy, Rutherford backscattering, electron spin resonance, Raman spectroscopy, and transmission electron microscopy techniques. A slight redistribution of the implanted atoms before annealing and their substantial migration towards the surface during annealing depending on the sequence of implantations are observed. It is found that about 2% of atoms of the implanted layer are replaced with gallium bonded to nitrogen; however, it is impossible to detect the gallium-nitride phase. At the same time, gallium-enriched inclusions containing ∼25 at % of gallium are detected as candidates for the further synthesis of gallium-nitride inclusions.
... Recently, we have observed intensive researches into obtaining semiconductor structures with selfassembled nanoclusters by methods of molecular beam epitaxy [1,2], ion implantation [3,4] and under the action of laser irradiation [5][6][7], as well as the possibility of controlling their physical properties. ...
The theory of nucleation of nanoscale structures of the adsorbed atoms
(adatoms), which occurs as a result of the self-consistent interaction of
adatoms with the surface acoustic wave and electronic subsystem is developed.
Temperature regimes of formation of nanoclusters on ${n}$-GaAs surface under
the action of laser irradiation are investigated. The offered model permits to
choose optimal technological parameters (temperature, doping degree, intensity
of laser irradiation) for the formation of the surface periodic
defect-deformation structures under the action of laser irradiation.
Implantation of ions into amorphous silicon dioxide (a-SiO2) is widely used in microelectronics (mainly, using Si ions) and in the production of light-guiding components of optical fibers (Ge, P, B ions). All of these elements interact with the matrix oxygen, so the point defects that occur during implantation are not only the result of the displacement of the silicon–oxygen frame atoms from their equilibrium positions, but also reflect the specific chemical interaction in the material. In this study, inert argon ions were implanted into silicon dioxide plates, which excluded chemical reactions. It is demonstrated using photoluminescence (PL) that the highest concentration of point defects in the damaged silicate network belongs to neutral oxygen vacancies (NOVs). The concentration of these and some other induced defects increased with an increase in fluence up to 5 × 10¹⁵ Ar⁺/cm², and, with a further increase in dose, the concentration dropped due to annealing of defects in the layer heated by the introduction of ions. The NOV defects appeared in the photoluminescence spectrum in the form of doublets, that is, pairs of bands belonging to the same optical transition. The appearance of doublets is explained by the dependence of the optical transition energy on the localization of identical point defects in zones of different distortions of the matrix structure.
The theory of nucleation of nanometer structure of the adatoms under the action of comprehensive pressure taking into account acousto-electronic interaction is developed. Self-organization occurs as a result of defect-deformation instability caused by self-consistent interaction between the adsorbed atoms and the surface acoustic wave. Within this theory the influence of comprehensive pressure and doping degree of semiconductor on the conditions of formation and the period of nanometer structure of the adatoms is investigated. The period of nanometer structure of the adatoms depending on the value of comprehensive pressure, temperature, average concentration of the adatoms and conduction electrons is defined. It is established that the increase in pressure leads to expansion of temperature intervals within which nanometer structures of the adatoms are formed, and the decrease of their period.
The chemical and the phase compositions of multilayer nanoperiodic SiOx/ZrO2 structures prepared by vacuum evaporation from separated sources and subjected to high-temperature annealing have been studied by X-ray photoelectron spectroscopy with a layer-by-layer etching. It is found that, under deposition conditions used, the silicon suboxide layers had the stoichiometric coefficient x ~1.8 and the zirconium-containing layers were the stoichiometric zirconium dioxide. It was found, using X-ray photoelectron spectroscopy, that annealing of the multilayer structures at 1000C leads to mutual diffusion of the components and chemical interaction between ZrO2 and SiOx with predominant formation of zirconium silicate at heteroboundaries of the structures. The SiOx layers of the annealed nanostructures contained ~5 at % elemental silicon as a result of the phase separation and the formation of fine silicon nanocrystals.
The role of acoustoelectric effects in the formation of nanoscale structures of adatoms, resulting from the self-consistent interaction of adatoms with a surface acoustic wave and the electronic subsystem, is studied for the case of charged and uncharged adatoms. It is shown that an increase in the doping level of a semiconductor with donor impurities at a fixed average adatom concentration results in an increase in the critical temperature below which self-organization processes occur.
Thin films made up of arrays of amine-terminated silicon nanoparticles (NH2-SiNPs) synthesized by a new evaporation technique have been formed by employing TEM grids as nanostencils. FTIR imaging illustrates the feasibility of the method in nanoscale device fabrication applications. Micro-mapping over areas of the nanoparticle material allows the surface chemistry to be examined. FTIR imaging shows trace amounts of oxide confined to the NP surfaces. Thicker films formed by dropcasting allowed the nanoparticle behaviour to be studied under conditions of extended exposure to 150 eV photons radiation by X-ray photoelectron spectroscopy (XPS). The XPS spectrum was monitored over the Si2p region and the initial peak at 100.53 eV was observed to shift to higher binding energies as irradiation progressed which is indicative of charge trapping within the film. This result has potential consequences for applications where NH2-SiNPs are used in X-ray environments such as in bioimaging where the increasing charge buildup is related to enhanced cytotoxicity.
The formation of silicon nanocrystals in SiO2 layers implanted with Si ions was investigated by Raman scattering, X-ray photoelectron spectroscopy, and photoluminescence.
The excess Si concentration was varied between 3 and 14 at. %. It was found that Si clusters are formed immediately after
implantation. As the temperature of the subsequent annealing was raised, the segregation of Si accompanied by the formation
of Si-Si4 bonds was enhanced but the scattering by clusters was reduced. This effect is attributed to the transformation of loosely
packed clusters into compact, separate-phase nanoscale Si precipitates, with the Raman peak observed at 490 cm−1 being related to surface scattering. The process of Si segregation was completed at 1000°C. Nevertheless, characteristic
nanocrystal photoluminescence was observed only after annealing at 1100°C. Simultaneously, scattering in the range 495–520
cm−1, typical of nanocrystals, appeared; however, the “surface-related” peak at 490 cm−1 persisted. It is argued that nanocrystals are composed of an inside region and a surface layer, which is responsible for
their increased formation temperature.
Experimental data on ion synthesis of nanocomposite layers with carbon-rich clusters and silicon nanocrystals by irradiation
of nonstoichiometric silicon oxide (SiO
x
) films with carbon ions followed by high-temperature annealing are reported. It is shown that, at rather high doses of C+ ions, the resulting films exhibit photoluminescence with a spectrum that encompass the entire visible and near-infrared regions.
The formation of carbon-rich clusters and silicon nanocrystals is confirmed by X-ray photoelectron spectroscopy data. The
distribution of carbon practically reproduces the calculated profile of ion ranges, suggesting that there is no noticeable
diffusive redistribution of carbon. A qualitative model of the layered structure of ion-synthesized structures is suggested.
Nanostructured silicon carbide has unique properties that make it useful in microelectronics, optoelectronics, and biomedical engineering. In this paper, the fabrication methods as well as optical and electrical characteristics of silicon carbide nanocrystals, nanowires, nanotubes, and nanosized films are reviewed. Silicon carbide nanocrystals are generally produced using two techniques, electrochemical etching of bulk materials to form porous SiC or embedding SiC crystallites in a matrix such as Si. Luminescence from SiC crystallites prepared by these two methods is generally believed to stem from surface or defect states. Stable colloidal 3C-SiC nanocrystals which exhibit intense visible photoluminescence arising from the quantum confinement effects have recently be produced. The field electron emission and photoluminescence characteristics of silicon carbide nanostructures as well as theoretical studies of the structural and electronic properties of the materials are described.
Ion implantation is a convenient tool for synthesis of silicon nanocrystals in SiO2 matrix which exhibit strong red/near-IR luminescence at room temperature. Ion beams can be successfully used also for controllable modification of the nanostructures by introducing defects or changing their phase composition. In the present work, both possibilities are tested by implantation of carbon into thermal SiO2 films either containing pre-fabricated Si nanocrystals or as-implanted with Si. In the carbon-free SiO2 films, Si nanocrystals were synthesized at typical Si excess of about 10 at.% and annealing temperatures of 1000 and 1100 °C. It is shown that carbon ion irradiation of the Si-implanted and then annealed SiO2 films completely quenches a luminescence band at 650–850 nm related to Si nanocrystals and gives rise to emission in the range of 350–650 nm that originated from oxygen-deficient defects. The subsequent final thermal treatment reduces concentration of the matrix defects, but only partially recovers photoluminescence from Si nanocrystals depending on the C dose. The latter is explained by the hindering effect of implanted carbon on growth and crystallization of Si phase inclusions. Strong “white” emission in the spectral range of 350–800 nm is observed only for the equal Si and C concentrations, irrespective of the sequence of carbon introduction and Si nanocrystal formation. This broad spectral band consists of the three sub-bands at around 400, 500 and 620 nm attributed to inclusions of SiC, C and Si phases, respectively. Electron spectroscopy analysis of the annealed layers confirms the presence of silicon carbide phase and carbon precipitates showing the diamond-like sp3, not the graphitic sp2 hybridization. The Si- and C-rich nanoclusters with a size of 3–5 nm were identified in the co-implanted films by electron microscopy as amorphous nanoparticles.
Nucleation and growth process of nanocrystalline silicon (nc-Si) formed by radio frequency (RF) sputtering method and subsequently thermal treatment has been studied by using high resolution-transmission electron microscope (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) methods. Silicon (Si) atoms in amorphous sub-oxide (a-SiOx) film were coagulated to form nc-Si with diameter of approximately 1.5nm in the film after annealing at 900°C. The size and number of nc-Si increased with the increase of the annealing temperature. The average size of nc-Si observed at annealing temperature of 1100°C was 2.5nm. We also observed nc-Si with high pressure phase in the annealed sample.
Carbon nanoclusters formed using ion implantation and thermal annealing are shown to photoluminescence in the visible range. Silica samples were implanted with a fluence of 2×1017atoms/cm2, 70keV carbon ions and thermally annealed for 4h at 1100°C. Photoluminescence measurement made at select intervals during the anneal process show continued growth of the nanoclusters within the silica throughout the process. However, Rutherford backscattering showed a rapid loss of carbon during the initial 15min of annealing indicating a competition between the growth of the second-phase nanoparticles and the formation of CO, a volatile form of carbon.
High-resolution gold-valence-band photoemission spectra were obtained by the use of monochromatized Al Kα radiation and a single-crystal specimen. After background and scattering corrections were made, the results were compared directly with broadened theoretical density-of-states functions. The following conclusions were drawn: (i) Relativistic band-structure calculations are required to fit the spectrum. (ii) Both the Korringa-Kohn-Rostoker calculation of Connolly and Johnson and the relativistic-augmented-plane-wave calculation by Christensen and Seraphin give density-of-states results that (after broadening) follow the experimental curve closely. (iii) Of the theoretical functions available to date, those with full Slater exchange agree best with experiment (perhaps because of a cancellation of errors). Fractional (2/3 or 5/6) exchange gives d bands that are too wide. (iv) Eastman's 40.8-eV ultraviolet photoemission spectrum is similar to the x-ray spectrum, suggesting little dependence on photon energy above 40 eV. (v) Both (ii) and (iv) imply an absence of strong matrix-element modulation in the photoemission spectrum of gold.
The microstructural and optical analysis of SiO2 layers emitting white luminescence is reported. These structures have been synthesized by sequential Si+ and C+ ion implantation and high-temperature annealing. Their white emission results from the presence of up to three bands in the photoluminescence (PL) spectra, covering the whole visible spectral range. The microstructural characterization reveals the presence of a complex multilayer structure: Si nanocrystals are only observed outside the main C-implanted peak region, with a lower density closer to the surface, being also smaller in size. This lack of uniformity in their density has been related to the inhibiting role of C in their growth dynamics. These nanocrystals are responsible for the band appearing in the red region of the PL spectrum. The analysis of the thermal evolution of the red PL band and its behavior after hydrogenation shows that carbon implantation also prevents the formation of well passivated Si/SiO2 interfaces. On the other hand, the PL bands appearing at higher energies show the existence of two different characteristics as a function of the implanted dose. For excess atomic concentrations below or equal to 10%, the spectra show a PL band in the blue region. At higher doses, two bands dominate the green–blue spectral region. The evolution of these bands with the implanted dose and annealing time suggests that they are related to the formation of carbon-rich precipitates in the implanted region. Moreover, PL versus depth measurements provide a direct correlation of the green band with the carbon-implanted profile. These PL bands have been assigned to two distinct amorphous phases, with a composition close to elemental graphitic carbon or stoichiometric SiC. © 2003 American Institute of Physics.
Si-based β-SiC quantum dots (QDs) were fabricated for exploring efficient blue emission from β-SiC nanostructures. Microstructural observations and x-ray photoemission spectroscopy reveal that the β-SiC QDs with sizes of 5–7 nm are embedded in the SiO2 and graphite matrices, displaying a locally tetragonal symmetry. Photoluminescence spectral examinations show two narrow blue-emitting bands at 417 and 436 nm, which are determined by both quantum confinement and surface structure of the β-SiC QDs. Electron spin resonance investigation demonstrates that the photoexcited carriers partially come from the β-SiC QD core with a widened band gap, whereas the radiative recombination occurs in Si excess defect centers at the β-SiC QD surface. A theoretical calculation about electronic states caused by the vacancy defects in the gap of balls formed with excess Si atoms at the surfaces of the β-SiC QDs supports our assignment to the two blue-emitting origin. © 2003 American Institute of Physics.
The correlation between the structural (average size and density) and optoelectronic properties [band gap and photoluminescence (PL)] of Si nanocrystals embedded in SiO2 is among the essential factors in understanding their emission mechanism. This correlation has been difficult to establish in the past due to the lack of reliable methods for measuring the size distribution of nanocrystals from electron microscopy, mainly because of the insufficient contrast between Si and SiO2. With this aim, we have recently developed a successful method for imaging Si nanocrystals in SiO2 matrices. This is done by using high-resolution electron microscopy in conjunction with conventional electron microscopy in dark field conditions. Then, by varying the time of annealing in a large time scale we have been able to track the nucleation, pure growth, and ripening stages of the nanocrystal population. The nucleation and pure growth stages are almost completed after a few minutes of annealing time at 1100 °C in N2 and afterward the ensemble undergoes an asymptotic ripening process. In contrast, the PL intensity steadily increases and reaches saturation after 3–4 h of annealing at 1100 °C. Forming gas postannealing considerably enhances the PL intensity but only for samples annealed previously in less time than that needed for PL saturation. The effects of forming gas are reversible and do not modify the spectral shape of the PL emission. The PL intensity shows at all times an inverse correlation with the amount of Pb paramagnetic centers at the Si–SiO2 nanocrystal–matrix interfaces, which have been measured by electron spin resonance. Consequently, the Pb centers or other centers associated with them are interfacial nonradiative channels for recombination and the emission yield largely depends on the interface passivation. We have correlated as well the average size of the nanocrystals with their optical band gap and PL emission energy. The band gap and emission energy shift to the blue as the nanocrystal size shrinks, in agreement with models based on quantum confinement. As a main result, we have found that the Stokes shift is independent of the average size of nanocrystals and has a constant value of 0.26±0.03 eV, which is almost twice the energy of the Si–O vibration. This finding suggests that among the possible channels for radiative recombination, the dominant one for Si nanocrystals embedded in SiO2 is a fundamental transition spatially located at the Si–SiO2 interface with the assistance of a local Si–O vibration. © 2002 American Institute of Physics.
The methods of X-ray photoelectron and extended electron energy loss fine structure (EELFS) spectroscopy were used for the investigation of phase composition and structure of SiO2 layer implanted sequentially by Si+ (energy of 100 keV, dose of 7 × 1016 cm−2) and C+ (energy of 50 keV, dose of 7 × 1016 cm−2) ions and postannealed at 1000 or 1100 °C (2 h). The SiSi and SiC bonds in carbide (SiC) nanoinclusions and CC bonds of sp3 type in carbon inclusions are identified. The concentration of dangling bonds significantly decreases with elevation of annealing temperature. The distribution of SiC nanoinclusions at 1100 °C annealing corresponds to the distribution of implanted atoms, whereas sp3-C phase is distributed nearly homogeneously over the implanted layer. The ratio of SiC to sp3-C quantities is lower when intermediate annealing at 1100 °C is provided after Si+ implantation. The local atomic structure near the surface is determined from the EELFS. The experimental results demonstrate the physical basis of white photoluminescence, originating from the SiC nanocrystals, diamond-like carbon particles, matrix, and interfacial defects. Copyright © 2008 John Wiley & Sons, Ltd.
In this paper, the luminescence properties of thin, thermally grown SiO 2 layers implanted with silicon and carbon ions are explored. The doses and energies were chosen in such a way that the resulting peak concentration of excess Si and C amounts to 5–10% in a depth region of 60–180 nm below the surface. The microstructure was investigated by Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). Amorphous nanostructures with a size between 2 and 3.5 nm were found in depth region between 80 and 150 nm below the oxide surface. Strong photoluminescence (PL) around 2.1 and 2.7 eV has been observed after excitation at 4.77 eV. Si y C 1Ày O x complexes with x < 2 are assumed to cause the observed PL in the blue spectral region. # 2001 Elsevier Science B.V. All rights reserved.
The photoluminescence intensity (PLI) related to Si nanocrystals in a SiO2: nc-Si system synthesized by ion implantation is studied experimentally and theoretically as a function of the Si+ ion dose
at various annealing temperatures T
ann (1000–1200°C). The dose corresponding to the maximum PLI is found to decrease with increasing T
ann. These data are explained in terms of a model taking into account the coalescence of neighboring nanocrystals and the dependence
of the probability of radiative recombination of quantum dots on their size. It is found that, when silicon oxide is grown
in a wet atmosphere, the photoluminescence spectrum contains an additional band (near 850 nm), which is related to shells
around the nanocrystals. This band weakens abrupily after high-temperature annealing in an oxidizing atmosphere (air).
The surface oxidation process of Si(100), and the distribution of intermediary oxidation states at the SiO 2 /Si interface have been extensively studied by high resolution (ΔE≪0.3 eV) photoemission spectroscopy using synchrotron radiation. The results show that the ratio at the SiO 2 /Si interface for three intermediary states, Si<sup>3</sup><sup>+</sup>, Si<sup>2</sup><sup>+</sup>, and Si<sup>1</sup><sup>+</sup> (SiO x ), is strongly dependent on SiO 2 layer thickness. In particular, the proportion of Si<sup>3</sup><sup>+</sup> increases with the formation of the 0∼1 nm thick SiO 2 layer. However, the three intermediary components at the interface are distributed with ratios of Si<sup>3</sup><sup>+</sup>:Si<sup>2</sup><sup>+</sup>:Si<sup>1</sup><sup>+</sup>=7:2.5:1 in the oxidation stage where a SiO 2 layer is formed over 1 nm.
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