Research On Chemical Modification Of Properties Of Nano-optoelectronic Materials

Because of the special characteristics of the nano-materials, such as the small sizeeffect, surface effect, quantum confinement effect, quantum tunneling effect, dielectricconfinement effect et al., the optical properties, optoelectronic properties, chemicalreactivity, melting point, superconductivity, plastic deformation, and many otherphysical and chemical properties of the nano-materials will change significantlycompared with the bulk material. This makes the nano-materials get significantimportance in the optoelectronics, microelectronics, catalysis, sensing, bionic,chemistry and many other fields. A simple photoelectronic system mainly include thefunctions of photoluminescence, absorption, interconnection, photodetection, etc. Thesystem consist of functional devices, whose properties mainly regulated by physicalmethods, such as bandgap engineering, doping and photonic bandgap. But for thechallenges of indirect bandgap lighting, wide spectrum absorption, nano-interconnection, and high efficiencyspectral detection, it’s hard to be efficientlysolvedonly by physical regulating. We start from the point of chemical method to regulate theproperties of the photoelectronic nanomaterials. Specific results obtained are as follows:1. In the light emission, we researched on the improvement mechanism of thephotoluminescence efficiency in indirect bandgap semiconductor like siliconnanocrystal. As the property of indirect bandgap, crystalline silicon has a lowluminescence efficiency, which limits its application in the field of photoelectronics.We studied the silicon nanocrystal passivated by a series of N-linking organic ligandsand got ultrabright photoluminescence. This phenomenon is not the first time wediscovered, but the physical mechanism is not yet clear. We combined femtosecondtransient absorption (TA) spectroscopy with time-resolved fluorescence spectroscopyto systemically investigate the excited-state dynamics in the surface modification ofsilicon quantum dots (Si QDs), and proposed two types of interaction mode for the SiQDs: weak coupling and strong coupling. In weak coupling mode, there is a fastspectral evolution in transient absorption spectra accompanied with no special absorption structure in steady-state absorption spectra. For strong coupling mode, thereis strong stimulated emission signal in transient absorption spectra and no spectralevolution can be observed. In the steady-state absorption spectra, it also can formspecial absorption structures in the band edge. The strong coupling model waseventually attributed to a certain integrated direct transition energy structure caused bythe communization of the N-linking organic ligand and the silicon core. Following thisessential understanding, Si QDs with orange emission and blue emission aresuccessfully prepared by surface-modified.2. Corresponding to the photoluminescence, absorption decides the energy efficiencyof the system. We choose the problem of limited absorption spectral width in thephotocatalytic reaction of TiO2nanoparticles. As a UV catalytic materials, TiO2canonly absorb the ultraviolet light which account for7%of the total energy in the solarspectrum (wavelength less than400nm), as a result of which the catalytic efficiency ofTiO2remains low. In this paper, we combined the graphene quantum dots (GQDs) withTiO2nanoparticles (P25) and effectively improved its photocatalytic activity in visiblespectral by the luminescence upversion of the GQDs. We prepared the GQDs bychemical peel of the multi-walled carbon nanotubes, and then supported them on P25.The absorption of the GQDs/P25in visible spectral (400~800nm) was greatlyenhanced. The property of conductivity of the GQDs could suppress the recombinationof the photon-generated carrier and improve the photocatalytic activity effectively.Sensitized by quenching in200℃could reduce the defects states of the GQDs andenhance the transport capability of the carrier, thus to further improve their catalyticefficiency. Using the photocatalytic decomposition of methyl orange and rhodamine Bas examples, we further demonstrated the significant improvement of the catalyticefficiency of the GQDs/P25-R in visible spectral.3. For the photoelectronic integration devices, only photoluminescence andabsorption are not enough. The interconnection of the photoelectronic signal becomesmore important. Usually the interconnection of light is accomplished by fibers andwaveguides and the interconnection the electronic is directed by metal wiring. Fornanophotonic and nanophotonic devices, above mentioned methods are both hard to carry out, especially for the interconnection of arbitrary nanodevices. We proposed theself-assembly of nanoparticles induced by laser fabrication. We used metalnanoparticles and semiconductor nanoparticles as precursor, and achieved theinterconnection of micro-nano-device at random location under the interaction of thephoton momentum (optical tweezers force) and energy (micro-fusion) in the focusedfemtosecond laser.4. In the photoelectric detection, we focused the problem of expensive device andcomplicated process of the traditional surface-enhanced Raman scattering (SERS)substrates, and gave a new approach to prepare SERS strips with natural substrates.Surface-enhanced Raman scattering (SERS) has been widely studied as an ultra-sensitive molecular vibrational spectroscopy technique. But the research mostlyarrested in the laboratory scale due to the complicated process. In this paper, weprepared SERS test strips with the natural substrate of the fiber in paper as templatesand a layer of silver deposited by physical vapor deposition. The intrinsic wrinkle andnanofiber on the paper would produce tremendous enhancement in surface plasmonpolartions which contributed greatly to SERS. In addition, the SERS test strips alsoshowed unique advantages of flexibility and hydrophobicity which could concentratethe probe molecule and further improve the sensitivity. This approach has theadvantages of high sensitivity, good homogeneity, low cost and simple preparation. Thestrips were easy to store and carry and could be prepared in large quantities, whichmade this method exhibit broad commercial prospect in the near future.