Qianmin Dong

Design of a silver nanoparticle for sensitive surface enhanced Raman spectroscopy detection of carmine dye

Flower-shaped silver nanoparticles have been successfully synthesized by a simple aqueous phase silver nitrate reduction by ascorbic acid in the presence of polyvinylpyrrolidone (PVP) surfactant. The nanoparticles diameters were adjusted from 450 to 1000nm with surface protrusions up to 10-25nm. The growth direction of silver nuclei is controlled by their degree of coating by PVP. The flower-shaped silver nanostructures obtained were used as stable Surface Enhanced Raman Scattering (SERS) substrates with high SERS activity for detecting Rhodamine 6G (R6G), at a concentration of only 10-9M, where the SERS signal is still clear. SERS spectra of the dye carmine was analysed and the characteristic bands were identified. An improved principle component analysis (PCA) was used for carmine detection, at concentrations down to 10-8M. The characteristic peaks of the carmine (1019, 1360, and 1573cm-1) remained at 10-8M. This indicated that the minimum detection limit of AgNP-based substrate for carmine is about 10-8M.

Rapid qualitative and quantitative determination of food colorants by both Raman spectra and Surface-enhanced Raman Scattering (SERS)

Surface Enhanced Raman Scattering (SERS) spectroscopy technology is widely used in materials analysis, environmental monitoring, biomedical, food security and other fields. Flower-shaped silver nanoparticles have been successfully synthesized by a simple aqueous phase silver nitrate reduction by ascorbic acid in the presence of polyvinylpyrrolidone (PVP) surfactant. The nanoparticles diameters were adjusted from 450 to 1000nm with surface protrusions up to 10-25nm. The flower-shaped silver nanostructures obtained were used as stable SERS substrates with high SERS activity for detecting Rhodamine 6G (R6G), at a concentration of only 10-9mol/L, where the SERS signal is still clear. SERS spectroscopy of four different food colorants (e.g. food blue, tartrazine, sunset yellow, acid red) were analysed and the characteristic bands were identified. An improved principle component analysis (PCA) was used for four different food colorants detection, at concentrations down to about 10-8mol/L. Thus, the LOD of food blue, tartrazine, sunset yellow and acid red are 79.285μg/L, 5.3436μg/L, 45.238μg/L and 50.244μg/L, respectively.

Enhancement of the accuracy of the simplified modal method for designing a subwavelength triangular grooves grating

The validity and accuracy of the simplified modal method for a highly efficient transmission subwavelength triangular grating are fully and quantitatively evaluated by a comparison of diffraction efficiencies predicted from the modal method to exact results calculated by a rigorous coupled wave analysis. The larger errors are revealed in smaller periods and in lower groove depths. More importantly, with the consideration of the reflection loss of the two propagating modes, the accuracy of the simplified modal method is significantly enhanced. The calculated diffraction efficiencies are in good agreement with the results of the vector method. This enhanced simplified modal method can be effectively used in the design of a shallower subwavelength grating. It is important to note that the consideration of the modal reflection loss can be applicable to any dielectric diffraction structure, e.g., the rectangular grating, in which the accuracy of the simplified modal method could be excellently improved to more exactly design a grating.

Analysis of the transmission characteristics of an internal reflection microstructure grating

The transmission characteristics of an internal reflection grating primarily integrated into light-emitting diodes are numerically calculated and optimized by using rigorous coupled-wave analysis (RCWA). The obvious polarization effect of the near field distribution is demonstrated. To easily analyze the transmittance performance of the internal reflection grating, simple methods involving scalar diffraction theory and effective medium theory are used. The validity of both methods is quantitatively evaluated by comparing the transmittance results obtained using the simple methods and RCWA. The limitation of both simple methods mainly depends on the grating structure parameters, such as the normalized period and normalized groove depth. Generally, when the dimensions of the normalized period is more than twofold wavelengths of incident light, the scalar treatment can be used to calculate precisely the transmittance of the optical element within 5% error. Also, the validity of the scalar theory is slightly influenced by the change in incident angle. The effective medium theory is accurate for evaluating the transmittance within 1% error when higher-order diffraction waves other than zeroth-order waves do not propagate.

Effect of surface passivation on optical and electronic properties of ultrathin silicon nanosheets

The binding energy, electronic structure and optical properties of H-, H3C-, and HS-cluster-passivated ultrathin silicon (single-layer and double-layer) nanosheets were calculated using density functional theory based on the plane-wave ultra-soft pseudopotential. Firstly, the most stable configuration was selected from passivated configurations according to the principle of lowest energy after calculating their total energies. Then the density of state and the band structure of the different passivated systems were calculated. It was found that different passivation clusters could affect the forbidden band, theremore the passivated cluster with sulfur could greatly decrease the width of the forbidden band through electron transfer. Lastly, the light absorption and reflection properties were also investigated. All results were conducive to the development of silicon-based optoelectronic devices.

Innovative research on the group teaching mode based on the LabVIEW virtual environment

This paper discusses the widely existing problems of increasing demand of professional engineer in electronic science major and the backward of the teaching mode at present. From one specialized course “Virtual Instrument technique and LABVIEW programming”, we explore the new group-teaching mode based on the Virtual Instrument technique, and then the Specific measures and implementation procedures and effect of this teaching mode summarized in the end.

Numerical calculation of the accuracy of approximate analysis methods for binary rectangular groove diffraction phase grating

Abstract. The range of the accuracy of scalar diffraction theory and effective medium theory for binary rectangular groove phase grating is evaluated by the comparison of diffraction efficiencies predicted from scalar theory and effective medium theory, respectively, to exact vector results calculated by Fourier modal method. The effect of element parameters (depth, period, index of refraction, angle of incidence, and fill factor) on the accuracy of scalar treatment and effective medium theory is quantitatively determined. Generally, it is found that the scalar method is valid when the normalized period is more than fourfold wavelength of incident light at normal incidence. The error of transmittances between vector method and scalar method increases as the incident angle and refractive index increase. Furthermore, when the higher diffraction orders other than zero-th order are not to propagate, the effective medium theory is accurate to evaluate the transmittance of grating at normal incidence. The error of transmittances between effective medium method and rigorous vector theory increases as the incident angle and refractive index increase. Also, the error of diffraction efficiencies between the simple methods and the vector method on the polarization state of incident light is clearly demonstrated.