Experimental Study On Thermal And Electrical Transport Properties Of Micronanowires

Metal nanowires have broad application prospects in engineering fields such as industrial aerospace,microelectronics systems,catalysis,sensing,and thermoelectric conversion systems.Due to the size effect,metal nanowires have very different thermal and electrical properties compared to bulk materials.The direct current heating method is used to measure the thermoelectric properties of metal nanowires.An experimental test system is designed to calibrate the ambient temperature when the sample is measured using a Pt line with a diameter of 19 μm as a resistance thermometer.The thermoelectric properties of silver and platinum nanowires are measured experimentally:the resistivity of silver nanowires is 1.87×10-8 Ω·m at 140 K,which is much higher than that of bulk silver at the same temperature.The thermal conductivity of silver nanowires at room temperature is about 180±40 Wm-1K-1,The Lorentz number is 2.5×10-8 WΩK-2,which is similar to that of bulk silver.The platinum nanowires have a resistivity of 8.4×10-7 Ω·m at 200 K.The thermal conductivity of platinum nanowires is in the range of 11 Wm-1K-1～20 Wm-1K-1,which is far lower than the thermal conductivity of the platinum material.After the silver nanowire sample is exposed to air for 24 hours,it is measured again.As a result,it is found that the resistivity and Lorentzian number of the silver nanowires are increased as compared with the values measured before being placed in air.Due to the contact resistance between the sample and the electrode,the measurement results obtained using different measurement methods are also different.A micro-structured chip is designed and the thermoelectric properties of the silver nanowires are measured using the two-wire method and the four-wire method to investigate the effect of contact thermal resistance and contact resistance on the measurement results.As a result,it is found that the contact resistance between the sample and the electrode is about 19 Ω,and do not substantially change with the temperature,indicating that electrons are mainly transported by ballistic transport at the contact position of the nanowire and the electrode.The measured thermal conductivity of the silver nanowires by the two-wire method is 100 Wm-1K-1 greater than that measured by the four-wire method,and the electrical conductivity is reduced by one-third,indicating that the contact resistance has a great influence on the measurement results.The introduction of contact thermal resistance increases the measured thermal conductivity of the sample.The four-wire measurement results confirm that the Wiedemann-Franz law applies to single-crystal silver nano wires.After successfully measuring the thermoelectric properties of a single metal nanowire,the thermoelectric properties of the metal nanowire bundle need to be further studied.Due to the relatively difficult characterization of nanowire bundles,the subjects are changed to carbon fibers.Experiments compared tube bundles and individual carbon fiber measurements.And experiments compared tube bundles and individual carbon fiber measurements.The steady-state"T" method is used to measure the carbon fiber tube bundle.The theoretical model of the ratio of the outer radius of the carbon fiber bundle to the cross-sectional area is given.The measurement results showed that the thermal conductivity of the carbon fiber bundle remained stable with the number of roots.With this method,it is possible to estimate the thermal properties of microwires and nanowires that are not easily prepared for a single sample.In summary,the experiment provides a reliable method for measuring the thermoelectric properties of metal nanowires.