Experimental Study On Thermoelectric Properties Of Metal Nano Contact

With the development of science and technology,nanotechnology research has become a hot spot in current scientific research.The special structure of nanomaterials determines its special properties that different from conventional materials.Therefore,the application prospects of nanomaterials in various fields are extremely broad,especially in the application in aerospace,microelectronic systems,thermoelectric conversion systems and other engineering fields.Studying the contact thermal resistance at the micro-nano scale can help solve the heat dissipation problem of microelectronic devices,reduce the size of micro devices,improve the reliability of micro devices,and is extremely important for the development of microelectronic device heat dissipation and micro/nano technology research.In this paper,the thermoelectric properties of nano-contacts between metal micro-wires are measured,and the contact and separation of the crossed metal micro-wire nodes are realized by adjusting the magnetic field strength.An experimental system for measuring the thermal resistance of two microwire or nanowire contact resistance contacts was established.The system mainly includes a temperature control system,a vacuum system,a preamplifier circuit,a magnetic field system,and a data acquisition and storage system.A copper base device for cross-contact of two micro-wires was designed and fabricated,and the sample preparation and cleaning process was detailed.In order to effectively measure the weak current signal,this experiment specially designed and manually fabricated a preamplifier circuit for amplifying the weak current signal,which realized an effective measurement of the nA level current.With the help of data acquisition card and labview software,the data acquisition and storage can be completed,and the simultaneous measurement of the contact resistance and contact thermal resistance of the two cross-structure micro-wires under vacuum environment is realized.The contact resistance and contact thermal resistance of platinum-platinum and gold-gold at normal temperature(300K)and low temperature(100K)were measuredrespectively.The effective surface decontamination method mainly includes ultrasonic cleaning and ohmic of organic solvent.The current heating method effectively avoids the influence of dust,oxide layer,etc.on surface contact.Both the later AFM and SEM images show that the microwire surface has a good degree of cleanliness.The experimental results show that the ratio of contact resistance and contact thermal resistance of the effectively treated microwires satisfies Wiedemann-Franz's law well.In addition,the experiment also measured the temperature resistance coefficient of the contact resistance with a small range of temperature changes.As the contact resistance increases,the temperature resistance coefficient gradually decreases to a small value and remains stable,indicating that the electrons at the node are diffused to the ballistics transport.For more in-depth research to understand the relevant properties of atomic/molecular contacts,the experiment also measured the electrical properties of Ag nanowire contacts.It is generally accepted that the low-energy electron beam(e-beam)irradiation has a negligible effect on the physical properties of metallic nanostructures during the in-situ imaging and welding inside the scanning electron microscope.Here,a pronounced decrease in the electrical conductivity of Ag nanowires is obtained after contacting the ends by using the e-beam induced deposition nanolithography.A vivid crystal defect mi-gration inside nanowire is observed under the transmission electron microscope,revealing that the e-beam induced internal stress provides an explanation for the remarkable conductivity decrease.These observations indicate that e-beam exposure can cause anomalous morphology change inside Ag nanowire.In addition,the electrical conductivity provides an effective strategy to monitor the related nanostructure change.In summary,a reliable method for measuring the thermoelectric properties of metal nanocontacts is provided.