Study On Ultrasonic Nanowelding Between Single-walled Carbon Nanotubes/Diamond And Metal

Field emission display(FED) is described as the most promising display in the 21 th century due to its fast response speed, clear resolution and long service life. Some nanomaterials(such as: carbon nanotubes, nano diamond and its composites material) has important applications in the field emission cold cathode because of their special structure, excellent electrical conductivity, thermal conductivity and chemical stability. However, during the fabrication of cold cathode, the performance of FED is heavily limited due to unreliable contact and high contact resistance between nanomaterials and metal substrate.Ultrasonic nanowelding method has received considerable attention for its low-cost, high efficiency and wide applicability. By using this simple and effective method, the contact between nanomaterial and metal substrate can be greatly improved, and the contact resistance can be effectively reduced.In this paper, experimental method is the main factor to be studied while molecular dynamics(MD) simulation is the supplement. The mechanism of ultrasonic nanowelding between single-walled carbon nanotubes(SWNTs) and metal substrate as well as carbon nanotubes-diamond composites was studied. The details are as follow:(1) SWNTs films were successfully prepared on Ni substrate by EPD method as well as the effects of EPD time on SWNTs films were studied. The results showed that the optimum SWNTs films could be formed at EPD voltage of 30 V and EPD time of 8-10 min, which laid a solid foundation for the next welding.(2) With MD simulation and experimental method, the nanowelding between SWNTs and Ni substrate was studied.The horizontal oriented nanowelding system which is similar to the nanowelding in experiments was established for simulation study. The nanowelding system was composed of Ni electrode and SWNT(5, 5) subsystem. The dynamic process of nanowelding was described completely at atomistic length scales, and the evolution of welding interface structure under different temperature and time was revealed by MD method. The simulation results was verified that the nanowelding process could be carried out(1500K) below the melting point of Ni(1726K). That is because high frequency ultrasonic energy makes Ni metal softening and plastic deformation occurs under the clamping force, resulting in the movement of Ni atoms in the atomic scale. Finally, the softening Ni wrap out SWNTs and in-situ welding is realized.Based on simulation results, with the method of electrophoretic deposition(EPD) and ultrasonic nanowelding, reliable and enhanced contact between SWNTs and Ni substrate was realized under proper parameters. Different ultrasonic nanowelding parameters including welding amplitude, welding pressure and welding time were used to study the nonaowelding process, which would result in the change of temperature in welding interface and had serious influence on the properties of emission. Optimal welding parameters are prerequisite for successful nanowelding and can be determined by carrying out many experiments. Scanning electron microscopy results further proved that SWNTs were embedded into Ni under proper parameters. In field emission measurements, the welded cathode also exhibited improved field emission properties. The turn-on field of welded cathode decreased from 5.2 to 2.1 V/μm as well as the emission current of welded cathode is greater and more stable than the non-welded one.(3) The SWNTs-nano diamond composite films were successfully deposited on Al substrate by two EPD. A layer of diamond film was deposited on SWNTs films(experiment 1). The influence of different alcohol on the quality of the films was studied and ultrasonic nanowelding technology was tried to improve the field emission of SWNTs-nano diamond composite films.