Preparation Of ZnO Nanowire Arrays And Their Gas Sensing And Field Emission Properties

Due to their small tip scale effect and surface effect,one dimensional ZnO nanomaterials possess excellect electrical and optical properties and have been extensively concerned in recent years.In this work,firstly,Au film and ZnO seed-layer film have been deposited on the single-crystal silicon substrates by the resistive thermal evaporation method and the plused laser deposition(PLD)method respectively.Then,ZnO nanowire arrays have been grown on above substrates by the chemical vapor deposition(CVD)method and the effects of the different growth processes on the morphologies and the structures for ZnO nanowire arrays have been studied.At last,the applications of ZnO nanowire arrays in the areas of the gas sensor and the field electron emission(FEE)have been researched preliminarlily,and following results have been obtained.The growth of ZnO nanowire arrays on Au films.Au films with different thicknesses(0.5,1.0,2.5,5 nm)have been deposited on the single-crystal Si substrates by resistance thermal evaporation method,and then ZnO nanowire arrays were grown by CVD method on above substrates.The results show that ZnO nanowire as grown exhibits the hierarchy configuration structrue,in which ZnO nanowire has the bigger bottom size and the smaller top size.These nanowires have the average lengths of 14 ?m and the bottom diameters of 300~500 nm.With the rise of the Au film thicknesses,the sizes and quantities of Au catalyst droplets on the substrate surface during the nanowire growth process are all increase,which leads to the fromations of ZnO nanoplates on the substrate surface and finally results in the decrease of ZnO nanowires.The growth of vertical ZnO nanowire arrays on ZnO seed-layer films.ZnO films with the thicknesses of 250 nm have been deposited on the Si O2/Si substrates by PLD method,and then the large-area ZnO nanowires with the uniform diameters were vertically grown on the substrate surfaces by CVD method.The results show that with the increase of the growth temperatures,the diameters of ZnO nanowires increase from 100~200 nm to 400~600 nm,the lengths improve from 12 ?m to 51 ?m,and the areal densities reduce from 4.34×108 /cm2 to 2.60×107 /cm2.Following analysis is given to explain the above variation trend.The improvement of the growth temperature leads to the increase of the migration energy for Zn atom adsrobed on the substrate surface,and finally results in the diameter increase and quantity decrease of Zn/ZnO alloy droplets on the same surface area.The gas sensing property studies of ZnO nanowires surface-modificated by Pd nanoparticles.Pd nanoparticles have been modificated on ZnO nanowire surfaces and the gas sensing propertyies of ZnO nanowire arrays grown on ZnO seed-layer films have been characterized.The results show that the optimal working temperature of all sensors is 260 ?.When the sputtering time is 10 s,the Pd nanoparticles modificated on the nanowire surfaces have the little sizes and the more quantity,which leads to the best reponse of 5.12.For the ethanol gas,the sensor exhibits better gas selectivity.The error values of the response stabilities for all sensors are lesser than 2.1%,and the response-recovery times are 7 s and 95 s respectively.After the surface modification of Pd nanoparticles,the gas sensing properties of ZnO nanowire arrays promote,and following explanation is given.The existence of Pd nanoparticles on the nanowire surfaces increases the gas' adsorption area and produces more oxygen ions,which leads to the increase of the resistance values for ZnO nanowire arrays.The FEE property studies of ZnO nanowires coated with Mo films.CVD method has been used to grow ZnO nanowire arrays on Au films with different thidknesses of 0.5,1.0 and 2.5 nm and magnetron sputtering method has been used to deposite Mo films on ZnO nanowire surfaces.Nanowires coated with Mo films have the average diameters of 200 nm.Mo film exhibits the polycrystalline structrue and the thickness is about 50 nm.All ZnO nanowires coated with Mo films exhibit the better stability of the FEE current densities.The ture-on electrical fields and the threshold fields for three samples are 7.80?7.29?10.90 V/?m and 12.15?11.20?15.35 V/?m,respectively.The field enhancement factors are 959?807?461 in sequence.With the increase of the thicknesses for Au films,the central bright spots in FEE images decrease gradually.Following analysis is given to explain the above variation trend.The bend and fracture of ZnO nanowire from the coated Mo films leads to the increase of the electron emission area for nanowire and the decrease of the areal density for ZnO nanowire,and finally results in the above variations of the ture-on electrical field,the threshold fields and the field enhancement factors.