The Probe-type Ultrasonic Transducer Based Devices for Nano Fabrication

Author:Wang Xu

Supervisor:hu jun hui


Degree Year:2018





At present,researchers have made some progress on nano-processing technology in the following aspects:(1)ultrasonic tweezers for nano trapping have non-contact trapping and contact trapping mode.In the non-contact trapping mode,the captured nano-object is not in contact with the micro-manipulation probe,while in the contact mode,the captured nano-object is in contact with the micro-manipulation probe;(2)ultrasonic tools have been used to cut micron objects;(3)silver nanosheets are prepared mainly by chemical methods,including induced chemical reduction,rapid reduction and precipitation,soft template,pyrolysis deposition and so on;(4)syringe-type pipette can produce micro/sub-micro liquid droplets.However,there are still some shortcomings in the above technologies:(1)the existing ultrasonic nano trapping devices can only achieve a single function,i.e.non-contact trapping or contact trapping;(2)the ultrasonic cutting method has not been applied to the processing of an individual nano-object;(3)when chemical methods are used to produce silver nanosheets,some harmful chemicals will be used or produced,or high temperature and high pressure working conditions are required,thus greener and more convenient fabrication methods of silver nanosheets are needed to accelerate the application of silver nanosheets;(4)the volume of pipette pipetting is difficult to minimize to nano litre.To overcome the shortcomings of the above nano fabrication,the following works have been carried out:The non-contact and contact modes of trapping nanowires are integrated into one device through ultrasonic vibration with linear and elliptical trajectories of the micro manipulation probe at appropriate operating frequencies,which generates different acoustic flow patterns around the micro manipulation probe.The non-contact trapping mode enables the device to deal with viscous nano-samples,and the contact trapping mode facilitates the transfer of samples.A silver nanowire cutting method is also presented in this paper.In this method,the cutting of an individual silver nanowire on the substrate is realized by utilizing the ultrasonic vibration with the linear and elliptical trajectories at the tip of the micro cutting tool and the adhesion force between the silver nanowire and the substrate.The quality of the cut depends on the vibration speed and the nanowire diameter.For cutting based on vibration with linear and elliptical trajectories,the vibration speed must be greater than the critical value in order to achieve a flat incision.For nano-cutting based on vibration with elliptical trajectory,fin-shaped patterns with gradually decreased thickness appear at both ends of the incision of silver nanowires.In addition,in this work,a flexible ultrasound micro-tool is proposed and developed to roll silver nanowires and silver microparticles on solid substrates in the air to fabricate silver nanosheets.The thickness of silver nanosheets can be as thin as tens of nanometers,and the rolling effect is insensitive to pre-pressure when the vibration is large enough.The method can also be used to weld a single silver nanowire onto a gold interdigital electrode on a substrate,and welding strength of this structure is good.Finally,the device with micro ring-shaped head proposed in this paper has effectively and conveniently realized the transfer and release of individual water droplets in micro/nano litre.The transfer of nanomaterials can be achieved by adding a certain number of nanomaterials in deionized water.The device can realize on-line observation and complete the separation of micro-nanoliter droplets at the initial stage of transferring droplet,so that there would be no convection between micro-nanoliter droplets in the final release of micro-nanoliter droplets containing nano-solid materials.When using conventional syringe pipette to produce micro-litre droplets,the droplets are obtained by pressing the syringe to squeeze the liquid in the syringe.The method in this paper uses the surface tension of the liquid at the interface to realize the transfer of droplets.The innovation of the paper is as follows:1.By adjusting the vibration modes of micro-manipulation probe in acoustic tweezers for nano trapping,the contact and non-contact dual-function trapping modes of nanowires at the water film-substrate interface were realized.2.A new method of cutting silver nanowires is proposed,which has the advantages of non-gasification and real-time cutting with observation under optical microscope.3.A flexible fabrication method is proposed to mechanically convert silver nanowires or silver microparticles into silver nanosheets with controllable thickness and width,and flexible design can avoid the damage of hard materials to the nanosheets.4.Based on the interfacial surface tension characteristics of liquids,a simple and reliable design method of device with ring-shaped head for transferring nano litre droplet is proposed.By adding nano-particles into droplets,the transferring of nano solid materials can be realized.Compared with the substrate-driven structure,the probe-driven micro/nanofabrication device in this paper has the inherent advantage of easy selection of an individual object.It can be applied in the manufacturing of nanoelectronic devices,the detection of medical samples,the preparation of flexible conductive display screen and other industries.