Surface Chemistry Of Nanocrystals Research Articles

Nanocrystals as Very Active Interfaces: Ultrasensitive Room-Temperature Ozone Sensors with In2O3 Nanocrystals Prepared by a Low-Temperature Sol−Gel Process in a Coordinating Environment

In2O3 nanocrystals were prepared by injection of In2O3 sol in a hot (160 °C) solution of tetradecene and an amine. By properly controlling the amine chain length, the processing of the starting sol and the heat-treatment temperature, In2O3 nanocrystals with a size ranging from 4 to 10 nm were obtained. The nanocrystals suspensions could be easily processed by drop-coating onto alumina substrates to obtain gas-sensing devices. The devices displayed an enormous response to ozone gas, with a response of several orders of magnitude even to 60 ppb of ozone. In particular, the monitoring of low ozone concentrations was possible even by operating at room temperature, where the ozone concentration profile could be rapidly and reversibly monitored. The enhanced gas-sensing properties were explained as the cooperative effect of the nanocrystal size and surface chemistry, characterized by high densities of oxygen vacancies.

Colloidal blue and red luminescent silicon nanocrystals and their elaboration in pure and doped spin on glasses

Investigation of the surface chemistry of silicon nanocrystals (Si-ncs) in colloidal solutions is important to clarify factors involved in stability, luminescence efficiency and surface functionalization. We report on the photoluminescence (PL) properties of colloidal Si-ncs fabricated by two independent methods and elaborated in pure and phosphorous-doped spin on glasses (SOGs). Red luminescent Si-ncs were prepared by electrochemical etching and blue luminescent by nanosecond pulsed laser fragmentation of silicon micrograins. Our experimental results show that the PL maxima can be blue shifted within 40 nm with increase of phosphorous concentration in SOG matrix and a further blue shift (more than 250 nm) with efficient PL increase can be achieved by direct-nanosecond pulsed laser fragmentation of silicon micrograins in both pure and phosphorous-doped SOG colloidal solutions.

Effect of Ligand Exchange on the Stability and Optical Properties of CdSe Quantum Dots

ABSTRACTA new post-synthesis heat/ligand-exchange treatment on CdSe nanocrystal quantum dots that allows fine-tuning the quantum dots size without losing important properties (e.g. photoluminescence) is presented. The careful control of parameters such as the reaction temperature, the quantum dot to alkyl-amine ligand mole ratio and the solvent volume is shown to provide tunable size reduction of the nanocrystals. This size reduction phenomenon provides new insights into the surface chemistry and stability of nanocrystals and can serve as a platform for designing, controlling and processing nanomaterials with tailored properties.

Photoelectrochemical properties of hybrid junctions based on zinc phthalocyanine and semiconducting colloidal nanocrystals

In this paper, a photoelectrochemical study of hetero-junctions formed by zinc phthalocyanine (ZnPc) and semiconductor oxide nanocrystals (NCs), is reported. To this purpose, thin films composed of either size- and shape-controlled ZnO or TiO 2 NCs, synthesized by both hydrolytic and non-hydrolytic colloidal methods, were investigated as photo-anodes with ZnPc as the sensitizer. The effects of the oxide nature, of the nanocrystal shape and surface chemistry, and of the modality of photo-anode preparation on the resulting photoelectrochemical response were evaluated. In general, the photoactivity was found to be significantly enhanced when ZnO NCs were used as compared to TiO 2 NCs. In the latter case, the hetero-junctions based on non-hydrolytically prepared TiO 2 provided remarkably lower photocurrents with respect to those formed by its hydrolytically synthesized analogous. Moreover, a slight improvement of photoactivity was observed if spherical TiO 2 NCs were replaced by rod-like particles. Finally, as opposed to expectations, photo-anodes deposited from NC-ZnPc blended solutions exhibited a photoelectrochemical response comparable to that of sensitized films prepared by layer-by-layer procedure.

Photoelectrochemical properties of Zn(II) phthalocyanine/ZnO nanocrystals heterojunctions: nanocrystal surface chemistry effect

Hetero-junctions prepared by deposition of unsubstituted Zn(II) phthalocyanines (Zn(II)Pc) onto a film of colloidal ZnO nanocrystals, were studied. Photoelectrochemical measurements were performed on the sensitized nanocrystalline ZnO films deposited onto optically transparent electrodes, to characterize the photoactivity of the heterojunction. A comparison between ZnO nanocrystals prepared by using a hydrolytic and non-hydrolytic route was performed in order to investigate the effect of nanocrystal surface chemistry on the photoelectrical response. The photoactivity was found to be significantly enhanced when non-hydrolytically prepared nanocrystals were used to form the heterojunction.

Proximity Effects in Self-Organized Binary Particle–Block Copolymer Blends

Dependent on the surface chemistry of gold nanocrystals of equal metal core size, two morphological types of self-organized block copolymer-particle blends are observed: (1) the segregation of the nanocrystals to the interfacial areas or (2) the preferential uniform distribution within one of the respective polymer domains. The confinement of the nanocrystals to the narrow interfacial regions of the microstructure in type one blends results in high local particle filling fractions and gives rise to electromagnetic coupling upon light irradiation, accompanied by a pronounced increase in absorbance.