Sinc Research Articles

Density functional theory study on the B doping and B/P codoping of Si nanocrystals embedded in SiO2

Doping silicon nanocrystals (Si NCs) embedded in silicon dioxide ($\mathrm{Si}{\mathrm{O}}_{2}$) with boron (B) and phosphorus (P) is a promising way of tuning the properties of Si NCs. Here we take advantage of density functional theory to investigate the dependence of the structural and electronic properties of Si NCs embedded in $\mathrm{Si}{\mathrm{O}}_{2}$ on the doping of B and P. The locations and energy-level schemes are examined for singularly B-doped or B/P-codoped Si NCs embedded in $\mathrm{Si}{\mathrm{O}}_{2}$ with a perfect or defective Si/$\mathrm{Si}{\mathrm{O}}_{2}$ interface at which a Si dangling bond exists. A dangling bond plays an important role in the doping of Si NCs with B or B/P. The doping behavior of B in Si NCs embedded in $\mathrm{Si}{\mathrm{O}}_{2}$ vastly differs from that of P. The electronic structure of a B/P-codoped Si NC largely depends on the distribution of the dopants in the NC.

SPRY4-IT1 contributes to increased cell proliferation by activating zinc finger protein 703 expression in non-small cell lung cancer

Objective To observe the long non-coding RNA SPRY4-IT1 expression level in non-small cell lung cancer and its biological funciton in aspects of cell proliferation. Methods Real-time quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR) was used to measure the expression of SPRY4-IT1 in 32 non-small cell lung cancer (NSCLC) patients. Loss of function approach was then applied to confirm the biological function, especially cell prolifieration in cultured human lung cancer cells A5549, by cell counting kit-8 (CCK-8) and clonogenic assay. We further used western blot to reveal the activation of zinc finger protein 703 (ZNF703) by SPRY4-IT1. Results The SPRY4-IT1 relative expression level were 1.12±0.78 and 3.24±2.01 respectively for tumor tissue and norma tissue of NSCLC patients with statistical difference (t=5.56, P=0.001); SPRY4-IT1 expression level were significant decreased by transinfection of si-SPRY4-IT1 in A549 cells. A549 cell clone formation ability was significantly reduced by traninfection of si-SPRY4-IT1. The mRNA expression of ZNF703 were 0.61±0.07 and 0.96±0.08 for si-SPRY4-IT1 and si-nc A549 cells with statistical difference (P=0.001); The protein expression of ZNF703 were 0.08±0.02 and 0.12±0.03 for si-SPRY4-IT1 and si-nc A549 cells with statistical difference (P=0.001). Conclusion SPRY4-IT1 expression is up-regulated in tumor tissue of non-small cell lung cancer patients and the SPRY4-IT1/ZNF703 axis might contribute to increased proliferation ability of lung cancer cells. Key words: SPRY4-IT1; Non-small cell lung cancer; Long chain of non encoding RNA; Proliferation ability

Alternative investigation into “Surprising sinc sums and integrals”

Alternative investigation into “Surprising sinc sums and integrals”

Down-regulation of microRNA-146b-5p repress proliferation of thyroid carcinoma cells by enhancing autophagy activity

Objective To investigate the influence of autophagy on proliferation of human papillary thyroid carcinoma cells (TPC-1) repressed by down-regulation of microRNA (miRNA, miR)-146b-5p. Methods TPC-1 cells were transient transfected by Lipofectmine 2000, and then cells were devided into four groups: as-miR, as-NC, co-transfection (as-miR-146b-5p+ siBeclin1) and co-transfection for control (as-miR-146b-5p+ siNC). Then the transfection efficiency was determined by invert fluorescence microscope and real-time quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR). Western blotting and RT-qPCR were used to analyzed the protein and mRNA levels of Beclin1 of the transfected cells, respectively. Transmission electron microscopy was used to evaluated the expression of autophagsome of the transfected cells. And cell counting kit-8 and colony formation assay were used to detected the proliferation of the transfected cells. Results Compared with those treated with as-NC, miR-146b-5p expression was decreased to (0.380±0.021), and the protein and mRNA levels of Beclin1 were increased to (0.612±0.014), (0.413±0.005) respectively, and the absorbance at 72 h and amount of colony foci was decreased to (1.470±0.062, P=0.007), (29.000±3.610)% (P=0.031) respectively, and the autophagsome expression was significantly increased in TPC-1 cells treated with as-miR-146b-5p after 24 h. Compared with those co-transfected with as-miR-146b-5p+ siNC, the protein and mRNA levels of Beclin1 were decreased to (0.286±0.027), (0.265±0.025, P=0.006) respectively, and the absorbance at 72 h and amount of colony foci was increased to (2.564±0.050), (49.000±2.821)% respectively (P=0.027), and autophagsome expression was significantly decreased in TPC-1 cells co-transfected with as-miR-146b-5p+ siBeclin1 after 36 h. Conclusion Down-regulation of miR-146b-5p inhibit the viability of TPC-1 cells via strengthening autophagy activity. Key words: MicroRNA-146b-5p; Papillary thyroid carcinoma; Atophagy; Beclin1

Formation of silicon nanocrystals in silicon carbide using flash lamp annealing

During the formation of Si nanocrystals (Si NC) in SixC1−x layers via solid-phase crystallization, the unintended formation of nanocrystalline SiC reduces the minority carrier lifetime and therefore the performance of SixC1−x as an absorber layer in solar cells. A significant reduction in the annealing time may suppress the crystallization of the SiC matrix while maintaining the formation of Si NC. In this study, we investigated the crystallization of stoichiometric SiC and Si-rich SiC using conventional rapid thermal annealing (RTA) and nonequilibrium millisecond range flash lamp annealing (FLA). The investigated SixC1−x films were prepared by plasma-enhanced chemical vapor deposition and annealed at temperatures from 700 °C to 1100 °C for RTA and at flash energies between 34 J/cm2 and 62 J/cm2 for FLA. Grazing incidence X-ray diffraction and Fourier transformed infrared spectroscopy were conducted to investigate hydrogen effusion, Si and SiC NC growth, and SiC crystallinity. Both the Si content and the choice of the annealing process affect the crystallization behavior. It is shown that under certain conditions, FLA can be successfully utilized for the formation of Si NC in a SiC matrix, which closely resembles Si NC in a SiC matrix achieved by RTA. The samples must have excess Si, and the flash energy should not exceed 40 J/cm2 and 47 J/cm2 for Si0.63C0.37 and Si0.77C0.23 samples, respectively. Under these conditions, FLA succeeds in producing Si NC of a given size in less crystalline SiC than RTA does. This result is discussed in terms of nucleation and crystal growth using classical crystallization theory. For FLA and RTA samples, an opposite relationship between NC size and Si content was observed and attributed either to the dependence of H effusion on Si content or to the optical absorption properties of the materials, which also depend on the Si content.

All-silicon tandem solar cells: Practical limits for energy conversion and possible routes for improvement

Silicon nanocrystals (Si NCs) embedded in a dielectric matrix is regarded as one of the most promising materials for the third generation photovoltaics, owing to their tunable bandgap that allows fabrication of optimized tandem devices. Previous work has demonstrated fabrication of Si NCs based tandem solar cells by sputter-annealing of thin multi-layers of silicon rich oxide and SiO2. However, these device efficiencies were much lower than expected given that their theoretical values are much higher. Thus, it is necessary to understand the practical conversion efficiency limits for these devices. In this article, practical efficiency limits of Si NC based double junction tandem cells determined by fundamental material properties such as minority carrier, mobility, and lifetime are investigated. The practical conversion efficiency limits for these devices are significantly different from the reported efficiency limits which use Shockley-Queisser assumptions. Results show that the practical efficiency limit of a double junction cell (1.6 eV Si NC top cell and a 25% efficient c-Si PERL cell as the bottom cell) is 32%. Based on these results suggestions for improvement to the performance of Si nanocrystal based tandem solar cells in terms of the different parameters that were simulated are presented.

Stimulated degenerate four-wave mixing in Si nanocrystal waveguides

Parametric frequency conversion via four-wave mixing (FWM) in silicon nanocrystal (Si NC) waveguides is observed at 1550 nm. To investigate the role of Si NC, different types of waveguides containing Si NC in a SiO2 matrix were fabricated. Owing to the increase of the dipole oscillator strength mediated by the quantum confinement effect, the non-linear refractive index () of Si NCs is found to be more than one order of magnitude larger than the one of bulk Si. Coupled differential equations for the degenerate FWM process taking into account the role of Si NC were numerically solved to model the experimental data. The modeling yields an effective for Si NCs in SiO2 waveguides which is similar to the one of Si waveguides. We also measured a large signal to idler conversion bandwidth of ∼22 nm. The large non-linear refractive index is joined with a large two photon absorption coefficient which makes the use of Si NC in non-linear optical devices mostly suitable for mid-infrared applications.

Organo‐Functionalization of Silicon Nanocrystals Synthesized by Inductively Coupled Plasma Chemical Vapor Deposition

Octadecyl‐terminated silicon nanocrystals (ODE‐Si NCs) are obtained via a surface‐initiated thermal hydrosilylation reaction on hydride‐terminated Si NCs (HSi NCs). Pristine Si NCs were synthesized at the gram scale by using inductively coupled plasma chemical vapor deposition (ICP‐CVD). The HSi NCs were produced through a chemical etching process with hydrofluoric acid (HF), ethanol (EtOH), and distilled water (d‐H2O). The results obtained from X‐ray diffraction (XRD) and field emission scanning electron microscopy (FE‐SEM) indicate that the synthesized Si NCs obtained via ICP‐CVD have diamond cubic‐structured silicon with a grain size of 10 nm and a densely packed Si NC array consisting of individual NCs. Organo‐functionalized Si NCs, i.e., ODE‐Si NCs, are well soluble in organic solvent whereas pristine Si NCs synthesized through ICP‐CVD are not. The surface chemistry of the ODE‐Si NCs was confirmed via Fourier transform infrared spectroscopy (FT‐IR), proton nuclear magnetic resonance spectroscopy ( 1H‐NMR), and field emission transmission electron microscopy (FE‐TEM). Thereby, these newly synthesized and scalable organo‐functionalized Si NCs are applicable as raw materials for practical use in devices by tuning the surface chemistry with various capping molecules.

Monolithic Si nanocrystal/crystalline Si tandem cells involving Si nanocrystals in SiC

AbstractMonolithic tandem cells involving a top cell with Si nanocrystals embedded in SiC (Si NC/SiC) and a c‐Si bottom cell have been prepared. Scanning electron microscopy shows that the intended cell architecture is achieved and that it survives the 1100 °C anneal required to form Si NCs. The cells exhibit mean open‐circuit voltages Voc of 900–950 mV, demonstrating tandem cell functionality, with ≤580 mV arising from the c‐Si bottom cell and ≥320 mV arising from the Si NC/SiC top cell. The cells are successfully connected using a SiC/Si tunnelling recombination junction that results in very little voltage loss. The short‐circuit current densities jsc are, at 0.8–0.9 mAcm−2, rather low and found to be limited by current collection in the top cell. However, equivalent circuit simulations demonstrate that in current‐mismatched tandem cells such as the ones studied here, higher jsc, when accompanied by decreased Voc, can arise from shunts or breakdown in the limiting cell rather than improved current collection from the limiting cell. This indicates that Voc is a better optimisation parameter than jsc for tandem cells where the limiting cell exhibits poor junction characteristics. The high‐temperature‐stable cell architecture developed in this work, coupled with simulations highlighting potential pitfalls in tandem cell analysis, provides a suitable route for optimisation of Si NC layers for photovoltaics on a tandem cell device level. Copyright © 2016 John Wiley & Sons, Ltd.

Research on an Equal Wavelength Spectrum Reconstruction Method of Interference Imaging Spectrometer

Interference imaging spectrometer is one of the most important equipments of Chang'E 1 satellite, which is applied to analysis the material composition and its distribution of the surface on the moon. At present, the spectral resolution of level 2B scientific data obtained by existing methods is 325 cm(-1). If we use the description way of wavelength resolution, various spectrum is different: the first band is 7.6 nm, the last band is 29 nm, which introduces two questions: (1) the spectral resolution description way mismatch with the way of ground spectral library used for calibration and comparison; (2) The signal-to-noise ratio of the spectra in the shortwave band is low due to the signal entering narrow band is little. This paper discussed the relationship between wavelength resolution and cut-off function based on the reconstruction model of CE-1 interference imaging spectrometer. It proposed an adjustable cut-off function changing with wavelength or wavelength resolution, while selected the appropriate Sinc function as apodization to realize the reconstruction of arbitrary specified wavelength resolution in the band coverage. Then we used this method to CE-1 on orbit 0B data to get a spectral image of 29 nm wavelength resolution. Finally, by using the signal-to-noise ratio, principal component analysis and unsupervised classification method on the reconstruction results with 2 grade science data from ground application system for comparison, the results showed that: signal-to-noise ratio of the shortwave band increased about 4 times, and the average increased about 2.4 times, the classification based on the spectrum was consistent, and the quality of the data was greatly improved. So, EWSR method has the advantages that: (1) in the case of keeping spectral information steadiness, it can improve the signal-to-noise ratio of shortwave band spectrum though sacrificed part of spectral resolution; (2) it can achieve the spectral data reconstruction which can set arbitrary band position or specify any wavelength resolution within the band range.

Ligand-Free, Colloidal, and Plasmonic Silicon Nanocrystals Heavily Doped with Boron

Colloidal heavily doped silicon nanocrystals (Si NCs) exhibiting tunable localized surface plasmon resonance (LSPR) are of great interest in cost-effective, solution-processed optoelectronic devices given the abundance and nontoxicity of Si. In this work we show that tunable plasmonic properties and colloidal stability without the use of ligands can be simultaneously obtained for Si NCs heavily doped with boron (B). The heavily B-doped Si NC colloids are found to be stable in air for months, opening up the possibility of device processing in ambient atmosphere. The optical absorption of heavily B-doped Si NCs reveals that the heavy B doping not only changes the concentration of free carriers that are confined in Si NCs but also modifies the band structure of Si NCs. After heavy B doping both indirect and direct electronic transition energies remarkably decrease in Si NCs because the heavy B doping induced movement of the conduction band toward the band gap could be more significant than that of the Fermi ...

Temperature dependent electroluminescence from all-Si-nanocrystal p-i-n diodes grown on dielectric substrates

In this work, we demonstrate for the first time the electroluminescence (EL) from a mesa isolated p-i-n diode based on silicon nanocrystals (Si NCs) embedded in a SiO2 matrix fabricated on a dielectric substrate. The structure fabricated on a dielectric substrate ensures that the EL signal originates entirely from the Si NC material. A small offset between the EL (1.28 eV) and photoluminescence (PL) (1.33 eV) peak energies has been observed at room temperature. We attribute this discrepancy to the different subset of light-emitting Si NCs in EL and PL. A model classifying Si NCs into connected NCs and isolated NCs is proposed. Atom probe tomography is employed to visualize the existence of isolated NCs and connected NCs. This model has been further studied using temperature dependent EL and PL, where a blue-shift of peak energy is observed as the temperature is increased. The blue-shift is attributed to the temperature dependent transport between the two subsets of NCs and the quenching of the PL emission from the connected NCs at higher temperatures.

Silicon nanocrystal-noble metal hybrid nanoparticles.

We report a novel and facile self-limiting synthesis route of silicon nanocrystal (Si NC)-based colloidally stable semiconductor-metal (gold, silver and platinum) hybrid nanoparticles (NPs). For the formation of hybrid NPs, we employ ligand-free colloidal Si NCs with heavily boron (B) and phosphorus (P) doped shells. By simply mixing B and P codoped colloidal Si NCs with metal salts, hybrid NPs consisting of metal cores and Si NC shells are spontaneously formed. We demonstrate the synthesis of highly uniform and size controllable hybrid NPs. It is shown that codoped Si NCs act as a reducing agent for metal salts and also as a protecting layer to stop metal NP growth. The process is thus self-limiting. The development of a variety of Si NC-based hybrid NPs is a promising first step for the design of biocompatible multifunctional NPs with broad material choices for biosensing, bioimaging and solar energy conversion.

Effects of chemical stoichiometry on the structural properties of Si-rich oxide thin films

In this work, the various chemical stoichiometry (O/Si ratios) of silicon-rich SiO2 (SRO) thin films were deposited and then annealed by rapid thermal annealing (RTA) to form SiO2-matrix silicon nanocrystals (Si–NCs). The effects of the O/Si ratios on the structural properties of SRO thin films were investigated systematically using Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Results showed that the micro-structure of as-deposited SRO thin films with higher O/Si ratios hindered formation of Si–Si4 clusters, Si clusters and Si rings, then hindered the phase separation and the crystallization of annealed thin films. When the O/Si ratios was increased from 0.7 to 1.5, the crystalline temperature was increased from 900°C to 1000°C, the crystalline fraction of the 1000°C-annealed thin films was reduced from 39.4% to 22.7%, the average Si–NC size was reduced from 3.8nm to 3nm, and the residual stress was increased from 1.9GPa to 2.8GPa, respectively. The changes in micro-structure were most possibly due to the fact that the different amount of Si-O bonds in the as-deposited thin films with various O/Si ratios.

Silyl Radical Abstraction in the Functionalization of Plasma-Synthesized Silicon Nanocrystals

Many silicon nanostructures have exhibited favorable optical properties following surface functionalization with molecular groups through a silicon–carbon bond. Here, we show the mechanism of functionalization of silicon nanocrystals synthesized in a nonthermal radiofrequency plasma is fundamentally different than in other silicon systems. In contrast to hydrosilylation, where homolytic cleavage of Si–H surface bonds is typically a prerequisite to functionalization, we demonstrate the dominant initiation step for plasma-synthesized silicon nanocrystals is abstraction of a silyl radical, ·SiH3, and generation of radical at the silicon nanocrystal surface. We experimentally trap the abstracted silyl radical and show this initiation mechanism occurs for both radical- and thermally-initiated reactions of alkenes using complementary FTIR and 1H NMR spectroscopies. These data additionally indicate that silylsilylation, addition of a Si–SiH3 group across an unsaturated hydrocarbon, competes with hydrosilylation. We also present a new empirical sizing curve as a convenient method to determine Si NC size from photoluminescence peak energy.

Tunability Limit of Photoluminescence in Colloidal Silicon Nanocrystals.

Luminescent silicon nanocrystals (Si NCs) have attracted tremendous research interest. Their size dependent photoluminescence (PL) shows great promise in various optoelectronic and biomedical applications and devices. However, it remains unclear why the exciton emission is limited to energy below 2.1 eV, no matter how small the nanocrystal is. Here we interpret a nanosecond transient yellow emission band at 590 nm (2.1 eV) as a critical limit of the wavelength tunability in colloidal silicon nanocrystals. In the “large size” regime (d > ~3 nm), quantum confinement dominantly determines the PL wavelength and thus the PL peak blue shifts upon decreasing the Si NC size. In the “small size” regime (d < ~2 nm) the effect of the yellow band overwhelms the effect of quantum confinement with distinctly increased nonradiative trapping. As a consequence, the photoluminescence peak does not exhibit any additional blue shift and the quantum yield drops abruptly with further decreasing the size of the Si NCs. This finding confirms that the PL originating from the quantum confined core states can only exist in the red/near infrared with energy below 2.1 eV; while the blue/green PL originates from surface related states and exhibits nanosecond transition.

ENHANCED FORMATION OF Si NANOCRYSTALS IN SiO2 BY LIGHT-FILTERING RAPID THERMAL ANNEALING

In this work, silicon-rich oxide (SRO) films with designed thickness of ~100 nm were deposited by a bipolar pulse and radio frequency magnetron co-sputtering. For comparison, the samples were then treated in a nitrogen atmosphere by conventional rapid thermal annealing (CRTA) or light-filtering rapid thermal annealing (LRTA) at 900–1100°C for 2 min. Raman spectra, grazing incident X-ray diffraction (XRD), transmission electron microscopy (TEM), Hall measurements, and current density–voltage measurements were carried out to analyze the microstructural and electrical properties of samples. Compared with the control sample using CRTA method, the crystalline volume fraction and number density of Si nanocrystals ( Si NCs ) in silicon oxide prepared by LRTA were greatly increased. The quantum effects of the short wave-length light (less than 800 nm) of these tungsten halogen lamps during the rapid thermal annealing process have negative effects on the formation of Si NCs in SiO 2 films. Si NCs with crystal volume fraction of 73%, average size of 2.53 nm, and number density of ~1.1 × 1012 cm-2 embedded in the amorphous SiO 2 matrix can be formed by LRTA at 1100°C. Enhancement of more than one order of magnitude in conductivity and higher current density were obtained from the LRTA annealed sample compared to the CRTA annealed sample. The improvements in conductivity and current density were attributed to the high density Si NCs . Our results show that the LRTA method is a suitable annealing tool for the formation of Si NC in thin SiO x films.

Structural and optical properties of silicon nanocrystals embedded in silicon carbide: Comparison of single layers and multilayer structures

The outstanding demonstration of quantum confinement in Si nanocrystals (Si NC) in a SiC matrix requires the fabrication of Si NC with a narrow size distribution. It is understood without controversy that this fabrication is a difficult exercise and that a multilayer (ML) structure is suitable for such fabrication only in a narrow parameter range. This parameter range is sought by varying both the stoichiometric SiC barrier thickness and the Si-rich SiC well thickness between 3 and 9nm and comparing them to single layers (SL). The samples processed for this investigation were deposited by plasma-enhanced chemical vapor deposition (PECVD) and subsequently subjected to thermal annealing at 1000–1100°C for crystal formation. Bulk information about the entire sample area and depth were obtained by structural and optical characterization methods: information about the mean Si NC size was determined from grazing incidence X-ray diffraction (GIXRD) measurements. Fourier-transform infrared spectroscopy (FTIR) was applied to gain insight into the structure of the Si–C network, and spectrophotometry measurements were performed to investigate the absorption coefficient and to estimate the bandgap E04. All measurements showed that the influence of the ML structure on the Si NC size, on the Si–C network and on the absorption properties is subordinate to the influence of the overall Si content in the samples, which we identified as the key parameter for the structural and optical properties. We attribute this behavior to interdiffusion of the barrier and well layers. Because the produced Si NC are within the target size range of 2–4nm for all layer thickness variations, we propose to use the Si content to adjust the Si NC size in future experiments.

Self-assembled silicon nanocrystal arrays for photovoltaics

Silicon nanocrystals (Si NCs) are a promising candidate for the top cell of Si tandem solar cells since their bandgap exceeds that of bulk silicon and can be tuned by adjusting nanocrystal size. Due to this effect, size control is required to maintain a uniform bandgap throughout a Si NC film. This can be achieved by annealing superlattices of Si-rich and stoichiometric dielectrics. This paper reviews the progress that has been made using host matrices SiO2, Si3N4, and SiC. Si NCs in SiO2 show excellent NC size and shape control and strong quantum-confinement-related photoluminescence, however electrical conductivity is poor. Ordering and size control is also obtained in Si3N4, but conclusive evidence of quantum confinement is lacking. Preparing ordered but separated Si NCs in SiC is difficult, but the narrow parameter space in which this is possible has been elucidated, good electrical conductivity was obtained, and functioning single-junction and tandem cells have been produced. Si NC formation can now be well-controlled in all three materials, and the key weaknesses for photovoltaics have been identified to be the electrical conductivity of SiO2, and defect density for Si3N4 and SiC. Addressing these is expected to lead to competitive Si tandem solar cells.

Oxygen passivation of silicon nanocrystals: Influences on trap states, electron mobility, and hybrid solar cell performance

Surface quality of nanostructures has a significant influence on related device performance. In this study, a large number of dangling bonds are detected on the silicon nanocrystal (Si NC) surface after surface modification. These dangling bonds work as carrier traps and degrade particle electrical properties. Therefore, controlled particle oxidization is proposed as a substitution method for surface passivation, which can reduce carrier traps easily and effectively. Electron mobility is improved dramatically after a 12-hour controlled oxidation, and as a result, Si NC/PTB7 hybrid solar cells (HSC) achieves an efficiency of 3.6%; this is more than twice the efficiency of devices fabricated with fresh Si NCs (without passivation), and the highest efficiency for Si NC-based HSCs reported to date. However, excessive oxidation should be avoided because it introduces an oxygen rich layer on the particle surface, which blocks carrier transport and deteriorates electrical properties inversely.