Synthesis and size control of Si nanocrystals by SiO/SiO2 superlattices and Er doping

ABSTRACTThe synthesis of nc-Si by reactive evaporation of SiO and subsequent thermal induced phase separation is reported. The size control of nc-Si is realized by evaporation of SiO/SiO2 superlattices. By this method an independent control of crystal size and density is possible. The phase separation of SiO into SiO2 and nc-Si in the limit of ultrathin layers is investigated. Different steps of this phase separation are characterized by photoluminescence, infrared absorption and transmission electron microscopy measurements. The strong room temperature luminescence of nc-Si shows a strong blueshift of the photoluminescence signal from 850 to 750 nm with decreasing crystal size. Several size dependent properties of this luminescence signal, like decreasing radiative lifetime and increasing no-phonon transition properties with decreasing crystal size are in good agreement with the quantum confinement model. Er doping of the nc-Si shows an enhancement of the Er luminescence at 1.54 μm by a factor of 5000 compared to doped SiO2 layers. The decreasing transfer time for the nc-Si to Er transition with decreasing crystal size can be understood as additional proof of increasing recombination probability within the nc-Si for decreasing crystal size.

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Size-Controlled Synthesis of CoFe2O4Nanoparticles Potential Contrast Agent for MRI and Investigation on Their Size-Dependent Magnetic Properties

Journal of Nanomaterials ◽

10.1155/2013/462540 ◽

2013 ◽

Vol 2013 ◽

pp. 1-9 ◽

Cited By ~ 8

Author(s):

Fujun Liu ◽

Sophie Laurent ◽

Alain Roch ◽

Luce Vander Elst ◽

Robert N. Muller

Keyword(s):

Magnetic Layer ◽

Size Control ◽

Correlation Spectroscopy ◽

Local Concentration ◽

Long Term Stability ◽

Size Dependent ◽

Transmission Electron ◽

Size Controlled ◽

Size Of Nuclei

Cobalt ferrite nanoparticles (CoFe2O4NPs) were synthesized by coprecipitation followed by treatments with diluted nitric acid and sodium citrate. Transmission electron microscope (TEM) and photon correlation spectroscopy (PCS) characterization showed that the size distributions of these nanoparticles were monodisperse and that no aggregation occurred. This colloid showed a long-term stability. Through adjustment of the concentrations of reactants and reaction temperature, the size of the NPs can be tuned from 6 to 80 nm. The size-control mechanism is explained by a nucleation-growth model, where the local concentration of monomers is assumed to decide the size of nuclei, and reaction temperatures influence the growth of nuclei. Magnetization and relaxivityr1,2measurements showed that the NPs revealed size-dependent magnetization and relaxivity properties, which are explained via a “dead magnetic layer” theory where reductions of saturation magnetization (Ms) andr1,2are assumed to be caused by the demagnetization of surface spins.

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Stability of Nanometer-Size Si Crystals in Amorphous Si Thin Films under Ion Irradiation

MRS Proceedings ◽

10.1557/proc-311-185 ◽

1993 ◽

Vol 311 ◽

Cited By ~ 1

Author(s):

Chih M. Yang ◽

Harry A. Atwater

Keyword(s):

Electron Microscopy ◽

Thin Films ◽

Transmission Electron Microscopy ◽

Crystal Size ◽

Ion Irradiation ◽

Shrinkage Rate ◽

Nanometer Size ◽

Size Dependent ◽

Transmission Electron ◽

Amorphous Si

ABSTRACTIn this paper we discuss the size-dependent shrinkage rate of nanometer-size Si crystals in amorphous Si thin films during ion irradiation. We obtain shrinkage rate of nanometersize crystals at low temperature under ion irradiation by studying the evolution of the crystal size distribution using transmission electron microscopy. Our results indicate that crystals less than 10 nm in diameter decrease in size faster than larger crystals under ion irradiation. In addition, we fit our data to a capillary model for growth of Si crystals in amorphous Si under ion irradiation.

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Formation of Luminescent Si Nanocrystals by High-Temperature Annealing of Ion-Beam-Sputtered Si/SiO2 Multilayers

MRS Proceedings ◽

10.1557/proc-775-p9.57 ◽

2003 ◽

Vol 775 ◽

Author(s):

Suk-Ho Choi ◽

Jun Sung Bae ◽

Kyung Jung Kim ◽

Dae Won Moon

Keyword(s):

Quantum Confinement ◽

Radiative Recombination ◽

Ion Beam ◽

Quantum Confinement Effect ◽

Visible Range ◽

Ion Beam Sputtering ◽

Transmission Electron ◽

Si Nanocrystals ◽

Beam Sputtering ◽

Microscopy Images

AbstractSi/SiO2 multilayers (MLs) have been prepared under different deposition temperatures (TS) by ion beam sputtering. The annealing at 1200°C leads to the formation of Si nanocrystals in the Si layer of MLs. The high resolution transmission electron microscopy images clearly demonstrate the existence of Si nanocrystals, which exhibit photoluminescence (PL) in the visible range when TS is ≥ 300°C. This is attributed to well-separation of nanocrystals in the higher-TS samples, which is thought to be a major cause for reducing non-radiative recombination in the interface between Si nanocrystal and surface oxide. The visible PL spectra are enhanced in its intensity and are shifted to higher energy by increasing TS. These PL behaviours are consistent with the quantum confinement effect of Si nanocrystals.

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A Cross-Method Comparison of Sub-10 nm Nanoparticle Size Distribution

10.26434/chemrxiv.9891992.v1 ◽

2019 ◽

Cited By ~ 1

Author(s):

Ye Yang ◽

Suiyang Liao ◽

Zhi Luo ◽

Runzhang Qi ◽

Niamh Mac Fhionnlaoich ◽

...

Keyword(s):

Size Distribution ◽

Analytical Ultracentrifugation ◽

Statistical Significance ◽

Method Comparison ◽

Size Determination ◽

Size Dependent ◽

X Ray Scattering ◽

Transmission Electron ◽

Gold Nps ◽

Reliable Representation

Accurate nanoparticle (NP) size determination is essential across research domains, with many functions in nanoscience and biomedical research being size-dependent. Although transmission electron microscopy (TEM) is capable of resolving a single NP down to the sub-nm scale, the reliable representation of entire populations is plagued by challenges in providing statistical significance, predominantly due to limited sample counts, suboptimal preparation procedures and operator bias during image acquisition and analysis. Meanwhile alternative techniques exist, but reliable implementation requires a detailed understanding of appendant limitations. Herein, conventional TEM is compared to the size determination of sub-10 nm gold NPs in solution by small-angle X-ray scattering and analytical ultracentrifugation. Form-free Monte Carlo fitting of scattering profiles offers access to a direct representation of the core size distribution while ultracentrifugation sedimentation velocity analysis provides information of the hydrodynamic size distribution. We report a comparison of these three methods in determining the size of quasi-monodisperse, polydisperse and bimodal gold nanoparticles of 2 – 7 nm and discuss advantages and limitations of each technique.

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Size Control of Synthesized Silver Nanoparticles by Simultaneous Chemical Reduction and Laser Fragmentation in Origanum majorana Extract: Antibacterial Application

Materials ◽

10.3390/ma14092326 ◽

2021 ◽

Vol 14 (9) ◽

pp. 2326

Author(s):

Entesar Ali Ganash ◽

Reem Mohammad Altuwirqi

Keyword(s):

Silver Nanoparticles ◽

Irradiation Time ◽

Chemical Reduction ◽

Size Control ◽

Reduction Process ◽

Laser Wavelength ◽

X Ray Diffraction ◽

Ag Nps ◽

Transmission Electron ◽

Origanum Majorana

In this work, silver nanoparticles (Ag NPs) were synthesized using a chemical reduction approach and a pulsed laser fragmentation in liquid (PLFL) technique, simultaneously. A laser wavelength of 532 nm was focused on the as produced Ag NPs, suspended in an Origanum majorana extract solution, with the aim of controlling their size. The effect of liquid medium concentration and irradiation time on the properties of the fabricated NPs was studied. While the X-ray diffraction (XRD) pattern confirmed the existence of Ag NPs, the UV–Vis spectrophotometry showed a significant absorption peak at about 420 nm, which is attributed to the characteristic surface plasmon resonance (SPR) peak of the obtained Ag NPs. By increasing the irradiation time and the Origanum majora extract concentration, the SPR peak shifted toward a shorter wavelength. This shift indicates a reduction in the NPs’ size. The effect of PLFL on size reduction was clearly revealed from the transmission electron microscopy images. The PLFL technique, depending on experimental parameters, reduced the size of the obtained Ag NPs to less than 10 nm. The mean zeta potential of the fabricated Ag NPs was found to be greater than −30 mV, signifying their stability. The Ag NPs were also found to effectively inhibit bacterial activity. The PLFL technique has proved to be a powerful method for controlling the size of NPs when it is simultaneously associated with a chemical reduction process.

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Structural changes in titanium dioxide nanocrystals during plastic deformation

Journal of Applied Crystallography ◽

10.1107/s0021889805020418 ◽

2005 ◽

Vol 38 (5) ◽

pp. 749-756 ◽

Cited By ~ 5

Author(s):

Ulrich Gesenhues

Keyword(s):

Structural Changes ◽

Crystal Size ◽

Lower Layer ◽

High Energy ◽

Primary Crystal ◽

X Ray Diffraction ◽

X Ray ◽

Transmission Electron ◽

Hall Method ◽

Means Of Transmission

The polygonization of 200 nm rutile crystals during dry ball-milling at 10gwas monitored in detail by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD). The TEM results showed how to modify the Williamson–Hall method for a successful evaluation of crystal size and microstrain from XRD profiles. Macrostrain development was determined from the minute shift of the most intense reflection. In addition, changes in pycnometrical density were monitored. Accordingly, the primary crystal is disintegrated during milling into a mosaic of 12–35 nm pieces where the grain boundaries induce up to 1.2% microstrain in a lower layer of 6 nm thickness. Macrostrain in the interior of the crystals rises to 0.03%. The pycnometrical density, reflecting the packing density of atoms in the grain boundary, decreases steadily by 1.1%. The results bear relevance to our understanding of plastic flow and the mechanism of phase transitions of metal oxides during high-energy milling.

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Carbon-coated titania nanostructured particles: Continuous, one-step flame-synthesis

Journal of Materials Research ◽

10.1557/jmr.2003.0373 ◽

2003 ◽

Vol 18 (11) ◽

pp. 2670-2676 ◽

Cited By ~ 23

Author(s):

Hendrik K. Kammler ◽

Sotiris E. Pratsinis

Keyword(s):

Crystal Size ◽

Nitrogen Adsorption ◽

Titanium Tetraisopropoxide ◽

X Ray Diffraction ◽

Composite Powders ◽

Nanostructured Particles ◽

Carbon Particles ◽

Transmission Electron ◽

Carbon Coated ◽

One Step

Concurrent synthesis of titania-carbon nanoparticles (up to 52 wt.% in C) was studied in a diffusion flame aerosol reactor by combustion of titanium tetraisopropoxide and acetylene. These graphitically layered carbon-coated titania particles were characterized by high-resolution transmission electron microscopy (HRTEM), with elemental mapping of C and Ti, x-ray diffraction (XRD), and nitrogen adsorption [Brunauer-Emmett-Teller (BET)]. The specific surface area of the powder was controlled by the acetylene flow rate from 29 to 62 m2/g as the rutile content decreased from 68 to 17 wt.%. Light blue titania suboxides formed at low acetylene flow rates. The average XRD crystal size of TiO2 decreased steadily with increasing carbon content of the composite powders, while the average BET primary particle size calculated from nitrogen adsorption decreased first and then approached a constant value. The latter is attributed to the formation of individual carbon particles next to carbon-coated titania particles as observed by HRTEM and electron spectroscopic imaging.

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