Carbon Clusters And Carbon-based Composite Nanostructures: Their Fabrications And Applications In Electrochemical Sensors

Carbon has abundant allotropes due to the diversity of its hybridization methods.During the past few decades,a variety of carbon nanostructures based on these allotropes have been synthesized and studied.It is highly valued in application fields such as biomedicine,information industry,industry and environmental monitoring.The structure and properties of carbon nanomaterials are largely dependent on their bonding components and configuration.By changing the ratio of Sp²C and Sp³C in the material,their properties can be tailored to meet the corresponding application.Nanomaterials directly assembled by carbon nanoclusters have many advantages:1)The ratio of Sp²C and Sp³C in the material can be adjusted on the nanoscale;2)The carbon cluster beams energy is relatively low when they reach the substrate surface.Therefore,the clusters can maintain their structure and characteristics in free state;3)The large surface composition and special properties of carbon clusters make the materials directly assembled by carbon clusters show special properties.In this paper,the cluster beam technology based on the gas aggregation method is used to prepare carbon clusters,which are combined with metal clusters to assemble ultra-thin composite nanofilms and three-dimensional porous composite nanostructures to study their regulation and optimization of catalytic properties.Through the selection of the operating parameters of the cluster source such as the condensation distance and the buffer pressure,quantitative or semi-quantitative control of the size and aggregation state of the clusters prepared by the plasma gas aggregation method was achieved.Our experiment finds that the size,structure and aggregation state of the carbon clusters prepared by the magnetron plasma gas aggregation method highly depend on the magnetron sputtering method of the cluster source.Spherical carbon clusters with smooth surface,uniform shape and diameter of about 3-6 nm are prepared by direct current?DC?magnetron sputtering cluster source,while carbon clusters with irregular surface and size of about 50 nm are obtained by the radio frequency?RF?magnetron sputtering cluster source.The carbon clusters prepared by DC sputtering show a highly discrete and uniform spatial distribution on the substrate,and all clusters remain independent spherical without fusion and growth.However,the carbon clusters prepared by RF sputtering have a high degree of aggregation.With the increase of condensation distance,the dense aggregates with ballistic cluste-cluster aggregation characteristics of about 500 nm in size turn into the dendritic fractal aggregates with diffusion-limited cluster aggregation characteristics of several?m or even 10?m in size.The Sp²C composition and crystallinity of the carbon clusters prepared by RF sputtering are much higher than those prepared by DC sputtering.The former is mall graphite crystal grain whose surface has not been sufficiently relaxed,while the latter has a severe distortion of the graphite lattice to form a spherical surface.Pd and C clusters are alternately deposited in situ by a dual-target plasma gas clustering source,and Pd clusters with an average size of 4.5 nm are overlaid on the C cluster layer with an average size of 5 nm to form C-Pd cluster composite nanofilm,which is used to modify glassy carbon electrode to construct the H₂O₂ electrochemical sensor.The test of H₂O₂ electrochemical catalytic by cluster composite film modified electrode shows that the introduction of C cluster intermediate layer can enhance the reduction reaction of H₂O₂ catalyzed by Pd cluster.When the deposition amount of C clusters is a single layer?the coverage rate is about 90%?,the enhancement effect is most obvious,which is shown as the reduction peak current and sensitivity of the composite film modified electrode is twice that of the electrode modified with Pd clusters only.Using the"self-masking"effect during the glancing angle deposition of directional collimated gas-phase cluster beam deposition,three-dimensional porous carbon nanofilms with pore size of 10 nm to 20 nm can be prepared by controlling the incident angle of the clusters,which are stacked by slanted columnar carbon clusters.The combination of glancing angle deposition technology and dual-target magnetron plasma gas aggregation method is used to alternately deposit carbon and palladium clusters to prepare C-Pd cluster composite porous nanofilms.These films consist of clearly identifiable cluster columns,which are formed by densely stacking discrete carbon clusters and palladium clusters alternately.In such composite porous nanofilms with controllable porosity and compositions,the metal clusters embedded in the pores of the carbon clusters greatly improves the load of unit area of the metal clusters as well as maintains extremely high effective reaction area,also the columnar nanopores can provide special restricted reaction environment for the catalytic process of metal clusters,thus such nanofilms are expected to show unique and excellent catalytic performance.